Structuring porous adsorbents and composites for gas separation and odor removal

Neda Keshavarzi

Structuring porous adsorbents and composites for gas separation and odor removal

Neda Keshavarzi

Doctoral Thesis 2014

Department of Materials and Environmental Chemistry

Stockholm University

SE-10691 Stockholm, Sweden

Cover:

The cover shows the SEM cross section of zeolite-cellulose nanofibrils film

and its flexibility. The photograph of smoke on the right side of the cover is

printed with permission from ©Michiel Van Lun, 2014.

Faculty Opponent:

Prof. Kurosch Rezwan,

Advanced Ceramics Group,

Faculty of Production Engineering

University of Bremen, Germany

Evaluation committee:

Prof. Mark Rutland, School of Chemical Science and Engineering, division

of Surface and corrosion Science, Royal Institute of Technology (KTH)

Docent Daniel Söderberg, School of Engineering Sciences, Department of

Mechanics, Royal Institute of Technology (KTH)

Docent Aji Mathew, Department of Engineering Science and Mathematics,

Luleå University of Technology

Substitute:

Associate Prof. Lars Eriksson, Department of Materials and Environmental

Chemistry, Stockholm University

©Neda Keshavarzi, Stockholm University 2014

ISBN 978-91-7649-005-1

Printed in Sweden by US-AB, Stockholm 2014

Distributor: Department of Materials and Environmental chemistry

دبندی هن کنی یی گشا د هنر آموز زک هنرمندی سنگ از لعل و زآب آرد ب د ره هک ز آموختن ندارد ننگ

آموزی دانش ز دارد ننگ رههک دانش نباشدش روزی رفوش سفال کاهلی از شد هک ای بسا تیز طبع کاهل کوش

اقلیم هفت القضات اقضی گشت وای بسا کور دل هک از تعلیم ) نظامی گنجوی، هفت پیکر،رقن ششم هجری(

Seek knowledge, for through knowledge you effect that doors to you be opened and not

closed.

He who shames not at learning can draw forth pearls from the water, rubies from the

rock.

Whilst he to whom no knowledge is assigned—that person (you will find) ashamed to

learn.

How many, keen of mind, in effort slack, sell pottery from lack of pearls (to sell)!

How many a dullard, through his being taught, becomes the chief judge of the Seven

Climes!

(Nizami Ganjavi, the Seven Beauties 1197, English translation by Charles Edward

Wilson 1924)

Dedicated to the sake of being...

Abstract

Porous zeolite, carbon and aluminophosphate powders have been colloidally

assembled and post-processed in the form of monoliths, flexible free stand-

ing films and coatings for gas separation and odor removal. Zeolite 13X

monoliths with macroporosites up to 50 vol% and a high CO2 uptake were

prepared by colloidal processing and sacrificial templating. The durability of

silicalite-I supports produced in a binder-free form by pulsed current pro-

cessing (PCP) were compared with silicalite-I supports produced using clay-

binders and conventional thermal treatment. Long-term acid and alkali

treatment of the silicalite-I substrates resulted in removal of the clay binder

and broadened the size-distribution of the interparticle macropores. Further-

more, strong discs of hydrothermally treated beer waste (HTC-BW) were

produced by PCP and the discs were activated by physical activation in CO2

at high temperatures. The activated carbon discs showed high strength up to

7.2 MPa while containing large volume of porosities at all length scales.

PCP was further used to structure aluminomphosphate powders (AlPO4-17

and AlPO4-53) into strong functional monoliths. The aluminophosphate

monoliths had strengths of 1 MPa, high CO2 uptake and were easy to regen-

erate. Zeolite Y, silicalite and ZSM5 were selected as potential zeolite ad-

sorbents for removal of sulfur containing compounds, e.g. ethyl mercaptan

(EM) and propyl mercaptan (PM). A novel processing procedure was used to

fabricate free-standing films and coatings of cellulose nanofibrils (CNF)

with a high content of nanoporous zeolite; 89 w/w% and 96 w/w%, respec-

tively. Thin flexible free-standing films and coatings of zeolite-CNF on pa-

perboards with thickness around 100 µm and 40 µm, respectively, were pro-

duced. Headspace solid phase microextraction (SPME) followed by gas

chromatography- mass spectroscopy (GC/MS) analysis showed that the zeo-

lite-CNF films can efficiently remove considerable amount of odors below

concentration levels that can be sensed by the human olfactory system.

Keywords: Structure, pulsed current processing, zeolite, aluminophosphate,

activated carbon, CO2 separation, adsorption, durability, cellulose, film,

coating.

List of publications

1. F. Akhtar, L. Andersson, N. Keshavarzi, and L. Bergström. Colloidal

processing and CO2 capture performance of sacrificially

templated zeolite monoliths. Applied Energy. 97, SI, 289–296 (

2012).

I contributed in the processing and characterization of zeolite 13X

monoliths.

2. F. Akhtar, N. Keshavarzi, D. Shakarova, O. Cheung, N. Hedin, L.

Bergström. Aluminophosphate monoliths with high CO2-over-N2

selectivity and CO2 capture capacity. RSC Advances. 4, 99, 55877-

55883 (2014).

I characterized the monoliths by XRD and CO2 adsorption and con-

tributed to the data analysis and writing.

3. N. Keshavarzi, F. Akhtar, L. Bergström. Chemical durability of hi-

erarchically porous silicalite-I membrane substrates in aqueous

media. J. Materials Research. 28, 17, 2253-2259 (2013).

I planned the study and performed most of the experiments, charac-

terization and data analysis as well as outlining and writing the arti-

cle.

4. W. Hao, N. Keshavarzi, A. Branger, L. Bergström, N. Hedin. Strong

discs of activated carbons from hydrothermally carbonized beer

waste. Carbon. 78, 521–531 (2014).

I performed the PCP, thermal analysis, and mechanical characteriza-

tion of the carbon discs. I contributed to the data analysis and writing.

5. N. Keshavarzi, F. Mashayekhy Rad, A. Mace, F. Ansari, F.Akhtar, U.

Nilsson, L.Berglund, L.Bergström. Nanocellulose-zeolite composite

films for odor elimination. To be submitted.

I planned all the experiments and performed the majority of the char-

acterization. I did the major part of data analysis and writing.

Table of Contents

Structuring porous adsorbents and composites for gas separation

and odor removal ......................................................................................... i

1. Introduction ......................................................................................... 1 1.1 Carbon dioxide capture and odor removal ................................................. 2 1.2 Microporous adsorbents................................................................................. 4 1.3 Structuring and colloidal processing of adsorbents .................................. 6

Aim of the thesis .......................................................................................... 9

2. Experimental.......................................................................................... 10 2.1 Materials and processing................................................................................. 10 2.2 Characterization methods ............................................................................... 12

2.2.1 Scanning electron microscopy (SEM) .................................................. 12 2.2.2 Thermal analysis ...................................................................................... 12 2.2.3 N2 and CO2 adsorption, textural analysis ............................................ 12 2.2.4 Porosity and density determination ..................................................... 13 2.2.5 Mercury porosimetry ............................................................................... 13 2.2.6 X-ray diffraction analysis ....................................................................... 14 2.2.7 Analysis of mechanical properties ........................................................ 14 2.2.8 Inductively coupled plasma-atomic emission spectroscopy (ICP-

AES) ...................................................................................................................... 15 2.2.9 Solid-phase microextraction (SPME) headspace gas

chromatography-mass spectroscopy (GC/MS) ............................................. 15 2.2.10 Fourier transform infrared spectroscopy (FT-IR) ............................ 16

3. Results and discussion ........................................................................ 17 3.1 Hierarchically porous monoliths of zeolites and aluminophosphates

(Papers I, II, III) ..................................................................................................... 17 3.1.1 Sacrificially templated Zeolite 13X monoliths (Paper I) ................... 17 3.1.2 Binder-free aluminophosphate monoliths (Paper II) ........................ 21 3.1.3 Strong silicalite-I substrates with high chemical durability (Paper

III) ........................................................................................................................ 26 3.2 Shaping hydrothermally carbonized beer waste (HTC-BW) into activated

carbon monoliths by PCP (Paper IV) .................................................................... 31 3.2.1 Structural and mechanical properties .................................................. 32 3.2.2 Pore formation during consolidation and after activation ................ 34

3.3 Flexible composites of zeolite-cellulose nanofibrils (CNF) for odor

removal (Paper V) ................................................................................................... 38 3.3.1 Thiols uptake capacity of zeolites by thermogravimetry analysis

and infrared spectroscopy ..................................................................................... 39

3.3.2 Structural features and mechanical properties of free- standing

films ...................................................................................................................... 41 3.3.3 Odor removal efficiency ......................................................................... 43 3.3.4 Composite coatings on paper board .................................................... 45

4. Conclusions ............................................................................................ 47

5. Future outlook ....................................................................................... 49

Acknowledgement ..................................................................................... 50

References .................................................................................................. 52

1

1. Introduction

The application of tailored porous materials in economically important areas

such as catalysis, separation and energy storage have over the last decade

generated an increasing demand for production of structured materials where

a low pressure drop, high exchange rate and efficient heat transfer is com-

bined with a high mechanical strength and good chemical durability.1–5

Hier-

archically porous materials such as free standing films, coating, spheres,

fibers, foams and monoliths containing porous adsorbents e.g. zeolites, acti-

vated carbons and aluminophosphates can be fabricated through colloidal

processing routes or dry powder processing.6–13

Structured porous adsorbent

have the potential to improve the energy and production costs in gas separa-

tion and catalysis applications by providing a more compact configurations

and higher production rates. 14–16

Adsorbent laminates of zeolites produced

to be used in high frequency pressure swing adsorption cycles, composite

membranes of ALPO4 with improved H2/CO selectivity and monoliths of

activated carbon fibers prepared for adsorption of volatile organic com-

pounds are examples of adsorbents structured for gas separation applica-

tions.17–19

In the following chapters, hierarchically porous monolithic and composite

structures based on zeolites, activated carbons and aluminophosphates as the

active adsorbent in particulate form will be introduced. First of all, a back-

ground about the use of hierarchically ordered monoliths in the separation of

CO2 is given. Release of CO2 from anthropogenic sources has been identified

as a major cause of the continuous temperature rise on the surface of the

earth. The application of structured zeolites in membrane technology will be

described and followed by discussing the problems and solutions regarding

the chemical and mechanical durability. Finally, the use of zeolites as adsor-

bents in novel areas, e.g. for odor removal, is presented and discussed.

2

1.1 Carbon dioxide capture and odor removal

The anthropogenic emission of carbon dioxide, mainly by combustion of

fossil fuels, 20,21

has been shown to contribute to global warming. The report

of the intergovernmental panel on climate change (IPCC) in 2013 shows that

the increase of the atmospheric CO2 concentration from 234.3 ppm in 1750

to 390.5 ppm in 2011 is strongly connected to the increase of the average

surface temperature on Earth.22

The CO2 concentration continues to increase

and there is a need to mitigate the CO2 emission not only by using renewable

energy sources instead of fossil fuels and improving the fuel efficiency, but

perhaps also by implementing carbon dioxide capture and storage processes

(CCS). 23–27

The currently available methodologies for CO2 capture are pre-

combustion, oxy-fuel combustion and post-combustion capture (Fig. 1).28,29

The different methods have reached different stages of maturity and one of

the most promising technologies is post-combustion capture where CO2 is

separated by a cyclic adsorption process. Pressure swing adsorption (PSA)

and temperature swing adsorption (TSA) are already used in several cost-

and energy-efficient industrial processes e.g. oxygen production and CO2

removal from natural gas.30–33

Furthermore, gas removal and separation by

adsorption is also used for removal of volatile organic compounds (VOCs) at

low concentrations. Volatile sulfur-containing organic compounds (VSOCs)

are the origin of the fetid smell emitted from some industrial and natural

sources.34–36

VSOCs include sulfides, thioethers, thioesters and mercaptans

(thiols) that are present in e.g. fruits, fermented food products and vegeta-

bles.37,38

Garlic, onion and durian fruit are some examples of natural sources

of VSOC.39–41

3

Fig 1. The three conventional CO2 capture technologies; post combustion,

oxy-fuel combustion and pre combustion that can remove CO2 emitted from

fossil fuel combustion.

4

1.2 Microporous adsorbents

The choice of sorbent material is critical for the efficiency of adsorption

processes. Solid adsorbents with high surface area and long term stability are

good candidates for cyclic adsorption processes. Zeolites, activated carbons,

aluminophosphates, metal organic frameworks, hydrotalcites, and mesopo-

rous silica are examples of solid adsorbents (Fig. 2).42

Zeolites are mi-

croporous crystalline aluminosilicates with a well-defined micropore size

distribution, typically ranging from 0.2-1.5 nm that can selectively adsorb

specific molecular species. Zeolites structures carry a negative charge on

their framework balanced with exchangeable cations that creates an electric

field gradient interacting with adsorbate species. Compared with many other

molecular sieves, zeolites are easily regenerated by heating or vacuum

treatment. Zeolites are used as adsorbents for desulfurization of natural gas,

transportation fuels and in the process of synthesis and recovery of sulfur

compounds.43,44

The high surface area, thermal stability and acidity of zeo-

lites gives them the possibility to interact with polar species e.g. sulfur con-

taining compounds. Studies have shown that zeolites used for removal of

VSOCs should have a high silica to alumina ratio in order to exhibit suffi-

cient hydrophobicity to reduce the water content, medium to large pore di-

ameter (larger than 0.55-0.60 nm), and of course, an adsorption affinity for

polar molecules.45

Zeolite 13X is a well-studied material that has a three-dimensional channel

system with a pore diameter of 0.74 nm. The large pore volume and high

density of exchangeable cations in zeolite 13X contributes to the high CO2

adsorption capacity of 4.5 mmol/g at 1 bar and 295 K .46,47,48

Crystalline

aluminophosphates (AlPO4) are zeolite-like molecular sieve adsorbents that

differ from zeolites in that the tetrahedral silicon atoms are alternately re-

placed by aluminum and phosphor atoms.49

These zeolite-like materials have

no negative framework charge and are thus less water sensitive compared

with zeolites. Some aluminophosphates e.g. ALPO4-14 (AFN framework)

have a CO2 uptake of 2.0-2.7 mmol/g at 1 bar and 273-300 K.50

.

Carbon adsorbents are produced from wide range of natural carbon rich

sources e.g. coals, industrial byproducts and biomasses. 51

5

Fig 2. Schematic illustration of the important classes of solid adsorbents with

their porous structures. The Faujasite structure of zeolite is taken from the

international zeolite database.52

The MOF example is taken from Furukawa

et al.53

Activated carbon obtains its high surface area and adsorption capacity in two

steps; carbonization (removal of all other non-carbonaceous components)

and activation (physical or chemical).54–57

The source of carbon and the pro-

cessing steps defines a large range of textural properties for activated car-

bons. Despite the often lower CO2 adsorption capacity of activated

carbons58,59

compared to zeolites, they offer benefits over zeolites because

of lower sensitivity to moisture, a reduced energy demanding regeneration

process and lower production cost.59,60

6

Efficient CO2 or gas removal using any of the aforementioned methods and

adsorbent materials requires development of structured adsorbents with su-

perior performance. Tackling issues regarding mass transfer, pressure drop,

and content of adsorbent per unit volume through structuring can result in

higher gas uptake and working capacity, reduced adsorption cycle time and

decreases the energy cost of the whole system.61

Various approaches for

production of structured adsorbents will be discussed in the next section.

1.3 Structuring and colloidal processing of adsorbents

Operating cyclic adsorption processes e.g. PSA, TSA on fine particulate

adsorbents is inefficient due to excessive pressure drop and kinetic con-

straints of gas flow. Structuring the adsorbent into monoliths, laminates and

foams is an approach to overcome the problem with the pressure drop and

can improve the efficiency of the entire gas separation process. It was shown

by Rezaei et al. that structured adsorbents containing multiscale pore sys-

tems decrease the pressure drop by 3-5 times compared to packed beds in

pressure swing adsorption process.61

High uptake capacity and kinetics must

be combined with high selectivity, good thermal stability and mechanical

strength of the adsorbent for energy and cost-effective CO2 separation.

Structured adsorbents can be fabricated by mixing colloidal dispersion of

adsorbent powder with additives. The colloidal mixture is either shaped in

wet form, or is dried first and then subsequently formed into the desired

shape, e.g. by pressing or extrusion. Finally, the powder bodies are thermally

treated to obtain structures with sufficient strength.

7

Fig 3. Schematic illustration of colloidal processing and shaping routes for

the production of hierarchically porous adsorbents. Picture of PCP consoli-

dated silicalite-I monoliths is reprinted with permission from Akhtar et.al.62

Colloidal processing routes utilize stable dispersions of e.g. zeolite, alumi-

nophosphate, carbon together with suitable additives e.g. binder, dispersant,

and plasticizers dispersed in a liquid or polymer matrix with desired rheolog-

ical properties (Fig.3). 63,64

The final material, often of complex shape and

internal structure, can then be formed from the dispersion by different meth-

ods such as tape casting, slip casting, gel casting, filtration, or can be applied

as coatings by e.g. spin coating or using a film applicator. The dispersions

are often highly concentrated to minimize the solvent removal step and allow

near-net shaping. Sacrificial templating can also be used to introduce mul-

tiscale interparticle porosities in the structured adsorbents in addition to the

intrinsic porosity of the microporous adsorbent. Introducing macroporosities

within the structured adsorbent improves the performance of the adsorbent

e.g. by reducing pressure drop and increasing mass transfer. The fabrication

of structured adsorbents with sufficient mechanical strength for handling and

performance is commonly performed by utilizing inorganic or organic bind-

ers. However, the use of binders can impede the adsorption efficiency of the

structured adsorbents. Binder-free structured adsorbents can be produced by

pressing the dry powder particles in a die and can be further consolidated by

pulsed current processing (PCP) method. In the following chapters, we will

show how a combination of colloidal processing routes and shaping ap-

proaches together with conventional and advanced sintering (PCP) methods

can be used to produce structured adsorbents. It will be shown that these

8

methods can be used to produce highly advanced structured adsorbents in the

form of strong monoliths, flexible films and coatings in binder-free or bind-

er-assisted state. Moreover, the properties of the structured adsorbents will

be evaluated and discussed with respect to their application.

9

Aim of the thesis

In this work, porous materials and methods for structuring them into hierar-

chical macroscopic shapes is studied. The properties of macroscopic hierar-

chically porous materials of different shapes e.g. monoliths, discs and com-

posites have been investigated with regard to their gas separation perfor-

mance. In the first part of the work, the objective was to use sacrificial tem-

plating and colloidal processing as an approach to structure and control the

pore morphology and porosity of zeolite 13X monoliths with potential appli-

cations for CO2 capture. Pulsed current processing (PCP) has also been in-

vestigated as a binder-less method to structure aluminophosphates into mon-

oliths with high CO2 capture capacity, CO2 over-N2 selectivity and good

mechanical stability. Furthermore, another target was to attempt the produc-

tion of strong structured monoliths of carbon rich materials (hydrothermally

carbonized beer waste) with multiscale porosity by the PCP method. The

aim was to consolidate carbonaceous material into dense discs that has the

ability to withstand the post treatment processes like physical activation.

Zeolite substrates in catalysis applications are exposed to chemically corro-

sive environments, sometimes at extreme pH values. Therefore, another ob-

jective was to evaluate the chemical and mechanical durability of a typical

zeolite substrate (silicalite-I) in acidic and alkaline solutions. Specifically,

the intent was to understand the role of the clay binder in the degradation

process at chemically harsh conditions. Finally, the last objective was to use

cellulose nanofibrils (CNF) together with zeolites to produce flexible and

mechanically stable odor-removing composite films and coatings through a

colloidal processing route. We wanted to demonstrate how such low-cost

adsorbents and coatings can be used in packages of foul-smelling fruits and

vegetables.

10

2. Experimental

2.1 Materials and processing

In paper I, monoliths of zeolite 13X (Si/Al = 1.4, Luoyang Jianlong Chemi-

cal Industrial Co., Ltd., Yanshi, Henan, China) with hierarchical porosity are

produced by using kaolin as binder. Glassy carbon spheres (SPI-CHEM,

West Chester, PA, USA) and carbon fibers (SIGRI GmbH, Meitingen, Ger-

many) are coated with polyacrylic acid (PAA, Polysciences Europe GmbH,

Germany, sodium salt, 25 wt.% in water, Mw = 50.000) and polyethylene-

imine (PEI, Polysciences, Inc., USA, ammonium salt, 99% purity,

Mw = 10.000). Subsequently, polyelectrolyte-coated carbon particles are

coated with zeolite powders in aqueous suspension. The composite powder

is uniaxially dry-pressed into a 10 mm diameter die at 10 MPa. Carbon con-

stituents are removed by thermal treatment in Nabertherm muffle furnace

(Nabertherm GmbH, Lilienthal, Germany) at 550 °C and further consolidat-

ed at temperatures between 700–850 °C with no holding time.

In paper II, AlPO4-17 and AlPO4-53 are produced by hydrothermal synthe-

sis. The powders are consolidated by pulsed current processing (PCP) in a

spark plasma sintering machine (Dr Sinter 2050, Sumitomo Coal Mining

Co., Ltd., Japan) into hierarchically porous cylindrical monoliths of with a

diameter of 12 mm. Commercial zeolite 13X (Pingxiang Xintao Chemical

Packaging Co. Ltd., China) beads of 1.5-2.5 mm in diameter are used for

comparison of adsorption properties with our PCP-consolidated AlPO4 mon-

oliths.

In paper III, binder-free silicalite-I (Si/Al: 1200, Sud-Chemie AG,

Bruckmühl, Germany) substrates with a diameter of 25 mm are consolidated

at 1250 °C and 1300 °C by PCP. Binder-containing silicalite-I substrates are

synthesized by mixing 25 wt.% kaolin/colloidal silica (Sigma-Aldrich

Chemie GmbH, Germany) with deionized water in a stirrer. The dispersion

of silicalite-I /kaolin is dried at 60 °C and silicalite-I /colloidal silica disper-

sion is heated under stirring until is dried. The dry powders are then consoli-

dated by conventional thermal treatment at 1150 °C and 1400 °C to obtain

cylindrical substrates with a diameter of 13 mm containing silicalite-I pow-

der with kaolin and colloidal silica, respectively. Silicalite-I substrates are

then exposed to aqueous solutions, where the pH is adjusted to 2.0, 10.6 and

11

13.0 using NaOH (Sigma Aldrich Chemie GmbH, Germany) and HCl

(Mallinckrodt Baker, Inc. Netherlands and Analar Normapur, France, 37% ),

at 90 °C for 168 hours to measure their durability in such conditions. Fur-

thermore, the binder-free silicalite-I substrates PCP consolidated at 1300 °C

is exposed to an aqueous solution with pH 10.6 at 90 °C for time period of

2, 4, 8, 14, 16 and 24 days. After the treatment the substrates are washed

once with an aqueous solution of the identical pH, and then rinsed by deion-

ized water and finally dried at 80 °C.

In paper IV, carbon discs of a diameter of 12 mm were prepared by PCP

consolidation of hydrothermally treated carbon powder from beer waste

(HTC-BW, Biokol KB, Sweden) with and without tar at 25, 100 and 150

°C.65

Thereafter, the HTC-BW discs were physically activated in a CO2 flow

at 800 °C at different activation times in a home-built vertical reactor.

In paper V, zeolites of silicalite-I, ZSM-5 (cation: ammonium, Si/Al: 140,

Zeolyst Int. USA), zeolite beta (cation: hydrogen, Si/Al: 180, Zeolyst Int.,

USA), zeolite Y (cation: hydrogen, Si/Al: 15 Zeolyst Int., USA) and mor-

denite (cation: hydrogen, Si/Al: 45, Zeolyst Int., USA) powders are charac-

terized for ethanethiol and propanethiol (Sigma-Aldrich Chemie GmbH,

Germany) adsorption capacity. Free-standing films and coatings consisting

of silicalite, ZSM-5 and zeolite Y, cellulose nanofibrils (1 wt.% aqueous

solution of TEMPO-CNF from wood, ρ=1.5 g/cm3,Wallenberg wood sci-

ence center at Royal Institute of Technology prepared according to proce-

dure explained by Saito et al.66

), CaCl2 (Merck, ρ= 2,15 g/cm3 Darmstad,

Germany) and polyethylene glycol (PEG, Sigma-Aldrich Chemie GmbH,

Germany, Mw= 8000, ρ= 1.128 g/cm3) are prepared by colloidal processing

in water. The dispersion of zeolite-CNF is formed into free-standing films by

vacuum filtration and dried in a climate chamber (KBF 115, Binder, Germa-

ny) at 30 °C and 50% R.H. Thin coatings of zeolite-CNF composite are ap-

plied using a film applicator (universal applicator, ZUA 2000, Switzerland)

with the gap size adjusted to 1 mm on paper board (white paper, Lessebo

Paper AB, Sweden), which is pre-treated with 0.01 M solution of CaCl2.

12

2.2 Characterization methods

2.2.1 Scanning electron microscopy (SEM)

SEM micrographs were obtained by a field emission gun scanning electron

microscope (FEG-SEM) JSM-7000F (JEOL, Tokyo, JAPAN). The SEM

pictures of zeolite 13X monoliths, carbon templates (paper I) and alumino-

phosphate monoliths (paper II) are taken at accelerating voltage of 5 KV and

working distance of 10 mm with no surface treatment of the specimens. The

morphology of uncoated silicalite-I substrates (paper III) and uncoated com-

posites of zeolite-cellulose nanofibrils (paper V) is observed at accelerating

voltage of 1.5 KV and working distance of 6 mm.

2.2.2 Thermal analysis

Thermogravimetric analysis (TGA7, Perkin Elmer, USA) was used to meas-

ure the amount of mass loss within temperature range of 20 to 900 °C under

the flow of dry air. A heating rate of 20 °C/min was applied to zeolite pow-

ders (20 mg) before and after adsorption of thiols. The total mass losses at

900 °C for the as-received zeolite powders compared to the moisture-

containing zeolites which were exposed to thiols are reported as the amount

of thiols adsorbed on each respective zeolite powder. The hydrothermally

treated beer waste was heated at 10 °C/min.

2.2.3 N2 and CO2 adsorption, textural analysis

Nitrogen adsorption-desorption experiments are performed at -196 °C on a

Micrometrics ASAP2020 volumetric analyzer (Micromeritics, Norcross GA,

USA). The surface areas are calculated using the Brunauer, Emmet and

Teller (BET) model using N2 uptake within 0.01-0.2 P/P0 relative pressure.

The PCP consolidated adsorbent monoliths are degassed under dynamic

vacuum condition at 300 °C during treatment time of 5-6 and 10 hrs for

HTC-BW/ AlPO4 and zeolite 13X monoliths, respectively. CO2 and N2 ad-

sorption measurements on AlPO4 are performed on Micrometrics Gemini V

2390 apparatus (Micromeritics, Norcross GA, USA) at 0 and 20 °C within a

pressure range from 0 to 101 kPa. The CO2 adsorption on zeolite 13X mono-

liths is measured on Micrometrics Gemini 2375 at 0 °C within a relative

pressure region of 0.001-0.998 P/P0. Prior to CO2 adsorption measurements,

13

the powders and monoliths are pre-treated under a flow of dry N2 gas at a

temperature of 300-350 °C for 8–10 hrs. The zeolite 13X monoliths are re-

generated at 350 °C for 6 hrs in cycle 1 and regenerated by being evacuated

to near-vacuum condition in cycles 2 and 3. The cyclic performance of the

AlPO4 monoliths is tested by recording the CO2 uptake of the samples after

regeneration by vacuum only at room temperature.

2.2.4 Porosity and density determination

The experimental densities of zeolite-CNF films are determined by measur-

ing the mass and volume of oven dried specimens. The volume is measured

by determining the thickness (Mitutoyo micrometer, Japan, accuracy of

0.001 mm) and area (Mitutoyo caliper, Japan, accuracy of 0.01 mm) of a

square piece cut from the zeolite-CNF film. The experimental density is then

compared with the theoretical density ρc,t of the zeolite-CNF films, calculat-

ed from equation 1.

𝜌𝑐,𝑡 = (𝑤𝑐

𝜌𝑐+

𝑤𝑧

𝜌𝑧+

𝑤𝑝

𝜌𝑝+

𝑤𝐶𝑎

𝜌𝐶𝑎)

−1

(eq. 1)

where ρc is the density of CNF , ρz is the density of zeolite particles, ρp is

density of PEG, ρCa is density of CaCl2 , and wc, wz, wp and wCa are the mass

fractions of CNF, zeolite, PEG and CaCl2, respectively. This comparison

allows us to calculate the porosity of the zeolite-CNF according to equation

2.

𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 = 𝜌𝑐,𝑡−𝜌𝑐,𝑚

𝜌𝑐,𝑡∗ 100 (eq. 2)

Where ρc,m is the measured density of the composite. The densities of HTC-

BW discs both before and after activation were evaluated by Archimedes’

principles using water as the immersion fluid.

2.2.5 Mercury porosimetry

Mercury intrusion porosimetry on Autopore III (Micromeritics, Norcross,

GA, USA) is used to determine the pore size distribution and to estimate the

porosity of the specimens within the intrusion pressure range from 0.03 MPa

to 420 MPa, which corresponds to pores above 5 nm in diameter. Pores with

diameter of 500 µm to 3.0 nm can be characterized by mercury intrusion

porosimetry according to Washburn equation ( eq. 3) that expresses the in-

14

verse relation between the pore diameter and the pressure required to force a

non-wetting liquid to enter a pore:

PL-PG = PD

cos4 (eq. 3)

Where PL is pressure of the liquid, PG is pressure of gas, γ is the surface

tension of the liquid, Ɵ is the contact angle between the liquid and solid and

Dp is the pore diameter. In this work the surface tension and the contact angle

of mercury are set to 0.485 N/m and 130°, respectively.

2.2.6 X-ray diffraction analysis

The structural analysis was performed by X-ray diffraction (XRD) on a

PANalytical X’Pert PRO powder diffractometer (PANalytical, Almelo,

Netherlands) with CuKα radiation λ=1.540598 Å, operating at 45 kV and 40

mA.

2.2.7 Analysis of mechanical properties

The strengths of the porous solids are determined by various mechanical

tests. The strength of monoliths and discs of zeolite 13X, binder-containing

silicalite-I, activated carbon, and aluminophosphates, are determined by a

diametral compression test (Fig.4a) by applying a displacement rate of 0.5

mm/min on a Zwick Z050 (Zwick GmBH Co & KG, Ulm, Germany) in-

strument. Biaxial flexural strength test (Fig.4b, ASTM standard F394-78) is

performed on binder-free PCP consolidated silicalite-I substrates. Uniaxial

tensile tests (Fig.4c) is carried out on an Instron 5944 with a 50 N load cell

to measure the tensile strength of zeolite-CNF free standing films. The films

are conditioned at 23 °C and relative humidity of 50% for at least two days

prior to the testing, then rectangular samples (35 mm by 5 mm) are tested at

10% strain/min. Strain is calculated using digital image correlation (Vic 2D

and LIMESS) and Young’s modulus is calculated from the rate of linear

increase in stress, typically between 0.1% and 0.3% strain.

15

Fig 4. Schematic of (a) diametral compression test; (b) biaxial flexural

strength test; (c) uniaxial tensile test.

2.2.8 Inductively coupled plasma-atomic emission spectroscopy

(ICP-AES)

The concentrations of silicon and aluminum in water solution are quantified

using inductively coupled plasma-Atomic emission spectroscopy (ICP-AES,

Vista AX, Varian, Agilent technology Inc., USA) with sample preparation

system SPS-5 equipped with simultaneous CCD solid-state detector (Fig 5).

The method has a detection limit of 3 ppb for both silicon and aluminum.

2.2.9 Solid-phase microextraction (SPME) headspace gas

chromatography-mass spectroscopy (GC/MS)

Gas chromatography-mass spectrometry (Varian GC/MS/MS ion trap series

4000, USA) with headspace solid-phase micro extraction (SPME) technique

is used for measurement of the thiol in the headspace of the sampling con-

tainer. The SPME used in this work is a metallic fiber coated with 85 μm of

carboxen/polydimethylsiloxane (CAR/PDMS) that has a high affinity for

highly volatile polar organic compounds with small molecular weights.67

16

Fig 5. The schematic presentation of an ICP-AES instrument.

2.2.10 Fourier transform infrared spectroscopy (FT-IR)

An infrared (IR) spectrometer (Varian 670, Varian, Inc. USA) equipped with

an attenuated total reflection (ATR, single reflection diamond element) and

detection device (Goldengate by Specac) is used to measure the adsorption

bands of the thiols in liquid phase and adsorbed phase on the zeolites. a

droplet of thiols or small amounts of zeolite powders is put on the diamond

substrate and one hundred scans are accumulated in the spectral region of

390-4000 cm-1

.

17

3. Results and discussion

3.1 Hierarchically porous monoliths of zeolites and

aluminophosphates (Papers I, II, III)

Microporous zeolites and aluminophosphates in particular form have been

structured into macroscopic shapes suitable for gas separation applications,

e.g. carbon capture. In the next section, the structural features and CO2 ad-

sorption properties of hierarchically porous monoliths of zeolite 13X pre-

pared by sacrificial templating method is presented. This is followed by a

presentation and discussion of binder-free structured adsorbents of AlPO4-17

and AlPO4-53 with respect to the PCP processing condition and their CO2

uptake. Finally, structuring of zeolites of silicalite-I into monolithic sub-

strates is presented and the resistance of such substrates to chemically corro-

sive environments is discussed.

3.1.1 Sacrificially templated Zeolite 13X monoliths (Paper I)

Hierarchically porous monoliths of zeolite 13X have been produced by col-

loidal processing of a 13X powder together with different amounts of a kao-

lin binder (2-45 wt.%) and carbon fibers/spheres (Fig. 6a and 6c), followed

by thermal treatments. The glassy carbon spheres/fibers are pretreated

through polyelectrolyte deposition (PAA and PEI, respectively) in order to

obtain a positive surface charged. Electrostatic interactions between the neg-

atively charged 13X particles and the positively charged polyelectrolyte-

coated carbon fibers/spheres result in the attachment of zeolite particles onto

the carbon surface. The mixture is dry pressed into tablets and is thermally

treated to remove the carbon phase. In the last step, the composite powder

bodies are thermally treated at temperatures in the range of 750 -850 °C to

remove the sacrificial carbon phase. Zeolite 13X monoliths with large chan-

nels (Ø= 8 μm, Fig. 6b) or spherical pores (Ø = 0.5–5 μm, Fig. 6d) with uni-

form size distribution are formed. The monoliths display a hierarchical struc-

ture with pores on three length scales: imprinted large pores created by sacri-

ficial templating, interparticle pores and the characteristic micropores inher-

ent to zeolite 13X (Table 1).

18

Fig 6. Scanning electron micrographs of (a) as-received carbon fibers (Ø = 8

μm); (b) thermally treated zeolite 13X monoliths templated with carbon fi-

bers ; (c) as-received glassy carbon spheres (Ø = 0.5–5 μm); (d) thermally

treated zeolite 13X monoliths templated with glassy carbon spheres ( Taken

from paper I).

The CO2 adsorption capacities of the 13X monoliths and the as-received

powder have been measured. 13X monoliths containing 2-3 wt.% kaolin

consolidated at 800 °C are very fragile but they show CO2 uptake capacities

close to the as received 13X powder (Fig. 7a). The CO2 adsorption capacity

of zeolite 13X monoliths that contain a very high binder content of 45 wt.%

of kaolin is reduced to only 2 mmol/g that is only about one third of the CO2

uptake of the as received 13X powder (Fig. 7a). Large amounts of binder in

13X monoliths decrease the volume efficiency of the adsorbent monolith and

block the pores thus reduce the accessibility of the microporous adsorbent.

19

Fig 7. CO2 adsorption isotherms of zeolite 13X monoliths; (a) consolidated

at 800 °C with varying kaolin content; (b) with 5 wt.% kaolin at different

consolidation temperature; (c) with 5 wt.% kaolin and consolidated at 800

°C containing different volumes of macroporosity; and (d) cyclic CO2 up-

take capacity and regeneration conditions after of zeolite 13X monoliths

consolidated at 800 °C with 5 wt.% kaolin . The monoliths were regenerated

at 350 °C for 6 hrs in cycle 1 and regenerated by evacuation in cycle 2 and 3

(Figures a, b and c taken from paper I).

However, the CO2 adsorption capacity of monoliths of 13X with only 5

wt.% kaolin treated at 800 °C is ca. 5.5 mmol/g; and these monoliths display

a mechanical strength (diametral compression test) between 0.1 and 0.2

MPa (Table 1),which is comparable to the previously reported binder-less

13X monolith.68

Increasing the thermal treatment temperature above 800 °C

significantly reduces the CO2 adsorption capacity, which can be related to a

deterioration of the microporous structure (Fig. 7b).68

The addition of large

pores and channels (up to 49 vol%), in the zeolite 13X monoliths does not

significantly reduce the CO2 adsorption capacity of the monoliths (Fig. 7C

and Table 1). Monoliths processed at the optimum temperature of 800 °C

20

with 5 wt.% kaolin retain their high adsorption capacity and keep more than

85% of the surface area compared to the unprocessed 13X powder (Table 1).

Table 1. Specific surface area (BET), macro-porosity measured by mercury

porosimetry, total macro-pore area and mechanical strength (diametral com-

pression test) of hierarchically porous zeolite 13X monoliths prepared with 5

wt.% of kaolin consolidated at 800 °C (Taken from paper I).

From the CO2 uptake capacity for zeolite 13 X monoliths (macroporosity 40

%) it is estimated that a total volume of structured monoliths of 4.33 m3 is

required to capture one ton of CO2. The feasibility for cyclic adsorption us-

ing the 13X monoliths containing 5 wt% kaolin and consolidated at 800 °C

is studied by repeated uptake measurements (Fig. 7d). The monoliths were

first regenerated at 350 °C for 6 hrs, after which the CO2 uptake was 5.70

mmol/g. A repetition of the measurement with regeneration only by vacuum

decreases the CO2 uptake to 4.91 mmol/g, and a third repetition under the

same conditions corroborated this value. The cyclic performance shows that

structured zeolite 13X monolithic adsorbents are robust and promising ad-

sorbents with long lifetimes.

21

3.1.2 Binder-free aluminophosphate monoliths (Paper II)

Microporous adsorbent powders of AlPO4-17 and AlPO4-53 have been syn-

thesized by a hydrothermal synthesis route and then calcined and assembled

into binder-free structured monoliths by PCP processing (PCP). Alumino-

phosphates have micropores with 8-ring pore windows that permit some

light gas molecules, e.g. CO2, CH4 and N2 to penetrate into them. For this

reason they are recognized as potential adsorbents for gas separation applica-

tions. AlPO4-17 has similar structure to zeolite erionite with window size of

3.6 x 5.1 Å2 along the [001] direction and AlPO4-53 has AEN framework

type with window size of 4.3 x 3.1 Å2 along the [100] direction.

52

Fig 8. X-ray diffractograms of synthesized powders and PCP treated mono-

liths of AlPO4-17 (a) and AlPO4-53 (b). The temperatures given in the figure

represent the maximum temperature applied during PCP (Taken from paper

II).

The processing temperature has a significant effect on the structure of the

AlPO4 powders. Structural analysis by XRD (Fig. 8) shows that at high PCP

treatment temperatures (950 °C), the AlPO4-17 undergoes a phase transfor-

mation into a crystalline porous sodalite structure (Fig. 8a), and the AlPO4-

53 powder transforms into a dense tridymite structure (Fig.8b).We have

found that PCP processing at a temperature of 650 °C and a compressive

pressure of 20 MPa is optimal for PCP processing of AlPO4-17 powder and

the monoliths prepared under these conditions are named as AlPO4-

17mPCP650. For the AlPO4-53, a combination of 400 °C and an applied

pressure of 50 MPa is suitable to produce mechanically stable monoliths by

PCP, which are named as AlPO4-53mPCP400 throughout the text. TheAl-

PO4-17mPCP650 and AlPO4-53mPCP400 monoliths have a relatively high

strength of ca. 1.0 MPa ( Diametral compression test) that is comparable to

22

zeolite 13X monoliths prepared by colloidal processing.68–70

Moreover, SEM

micrographs (Fig. 9) show that PCP processing does not affect the morphol-

ogy of the rod-like AlPO4-17 and polyhedral AlPO4-53 crystals.

Fig 9. Scanning electron micrographs from fractured surfaces of; (a) AlPO4-

17mPCP650; and (b) AlPO4-53mPCP400. The insets show photographs of

the monoliths (Taken from paper II).

The PCP processing also significantly influences the CO2 and N2 uptake

capacities at high temperatures above 650 °C (Fig 10). However, there is

only a 12% reduction in CO2 and N2 adsorption capacity after PCP pro-

cessing at 650 °C as compared to the synthesized powder (Fig.10a and 10b).

This small reduction can be related to the surface amorphization or phase

transformation to a non-adsorbing phase at the contact points of AlPO4-17

crystals during PCP treatment .62,71

PCP treatment of AlPO4-17 powder at

750 °C reduces the CO2 adsorption capacity of the monoliths significantly to

1.2 mmol/g (Fig. 10a). AlPO4-53 monoliths prepared by PCP at 400 °C and

50 MPa pressure also have only a slight decrease in the CO2 and N2 uptake

capacities compared to the capacity of the synthesized powders (Fig.10c and

10d). The N2 uptake on AlPO4-17 and AlPO4-53 powders and monoliths is

generally small, which can be explained by the electric quadrupole moment

that controls the affinity of the adsorbate molecule to the electric field gradi-

ent in the micropores. The quadrupole moment of N2 (-4.6 x 10-40

Cm-2

) is

almost three times smaller compared to CO2 (-14 x 10-40

Cm-2

).72

23

Fig 10. Adsorption isotherms of CO2 and N2 at 0 °C on powders and mono-

liths of AlPO4-17mPCP650 and AlPO4-53mPCP400 consolidated at com-

pressive pressure of 20 and 50 MPa, respectively; (a) CO2 uptake on AlPO4-

17: powder (□), monoliths prepared at 650 °C (○),750 °C ( ), and 950 °C

(Δ); (b) N2 uptake on AlPO4-17: powder (□), monoliths prepared at 650 °C

(○),750 °C ( ), and 950 °C (Δ); (c) CO2 uptake on AlPO4-53: powder (■),

monoliths prepared at 400 °C (●),500 °C (▼),and 950 °C (▲); (d) N2 uptake

on AlPO4-53: powder (■), monoliths prepared at 400 °C (●), 500 °C (▼),

and 950 °C (▲); (e) CO2 uptake at 20 °C on monoliths: AlPO4-17-based

prepared at 650 °C (○) and AlPO4-53-based prepared at 400 °C (●); (f) N2

uptake at 20 °C on monoliths: AlPO4-17-based prepared at 650 °C (○) and

AlPO4-53-based prepared at 400 °C (●) (Taken from paper II).

24

The CO2 adsorption data (Fig 10) show that AlPO4-17mPCP650 has a higher

CO2 adsorption capacity, 2.5 mmolg-1

, compared to AlPO4-53mPCP400 with

1.65 mmolg-1

uptake at 100 KPa. On the other hand, the nitrogen adsorption

is lower on AlPO4-53mPCP400, 0.05 mmol/g than that of AlPO4-

17mPCP650 with 0.24 mmolg-1

uptake at 100 KPa. These data suggest that

AlPO4-17mPCP650 has a high CO2 adsorption capacity but AlPO4-

53mPCP400 possess a higher adsorption selectivity of CO2 over N2. The

CO2 and N2 adsorption capacities of AlPO4-17mPCP650 monoliths are also

higher than monoliths of AlPO4-53mPCP400 at 20 °C (Fig 10e and 10f). In

summary, structured monoliths of AlPO4-17 and AlPO4-53 PCP consolidat-

ed at optimal conditions are suitable adsorbents for carbon capture with a

high CO2 capture capacity and relatively high mechanical strength.

In swing adsorption carbon capture processes (pressure or temperature swing

adsorption, PSA or TSA), the amount of CO2 that can be removed per kilo-

gram of structured AlPO4 monoliths needs to be determined. The CO2 cap-

ture capacities in an idealized PSA process have been estimated using the

CO2 adsorption isotherms of AlPO4-17mPCP650 (Fig. 10e, open circles) and

AlPO4-53mPCP400 (Fig. 10e, filed circles). The estimation in this work is

based on a flue gas containing 15 mol% CO2 and 85 mol% N2 at 20 °C. The

total pressure of the process is allowed to swing from 1 bar to 6 bar, which

corresponds to CO2 partial pressures of 0.15 bar (15 kPa) and 0.90 bar (90

kPa), respectively in a simple and hypothetical PSA process. For these con-

ditions, the CO2 capture capacity is defined as the difference between the

CO2 uptake at 0.9 bar and 0.15 bar and represent the amounts of CO2 gas

that can be removed in a PSA cycle per kilogram of the adsorbent. We esti-

mate a CO2 capture capacity of 0.8 mmol/g for AlPO4-53mPCP400, which is

somewhat lower than the capacity of AlPO4-17mPCP650, 1.4 mmol/g at 20

°C, by applying boundary conditions of an idealized PSA process. Typically,

zeolite 13X is a benchmark material for CO2 capture.47,68,70,73

However, the

capture capacity of commercial granules of zeolite 13X is lower than that of

AlPO4-17mPCP650 and AlPO4-53mPCP400 monoliths. In the first and sec-

ond adsorption cycle, the CO2 capture capacity of 13X granules is 0.7

mmol/g and 0.67 mmol/g, respectively (Fig. 11). As is true for many zeo-

lites, the total CO2 adsorption capacity of 13X granules is reduced after the

first cycle from 2.9 to 2.5 mmol/g. This phenomena can be related to chemi-

sorption of CO2 on 13X granules where chemisorbed molecules are tightly

attached and the adsorbent cannot be completely regenerated without apply-

ing high temperature.47,73

25

The unprocessed flue gas also contains water vapor that reduces the CO2

capture capacity of AlPO4 monoliths and 13X granules due to high affinity

of water for the adsorbents. However, at low partial pressure of water vapors

the aluminophosphates are less hydrophilic.74,75

The water adsorption capaci-

ty of AlPO4-17, AlPO4-53 and 13X powders have been previously measured

by Liu et al. and were found to be 0.17, 0.15 and 0.37 g/g, respectively.49

Fig 11. CO2 adsorption isotherm of 13X granules, first CO2 adsorption cycle

(○) and second CO2 adsorption cycle (●), The 13X granules were regenerat-

ed by lowering the pressure (near vacuum conditions) without application of

heat after first CO2 adsorption cycle. The shaded areas show the pressure

swing cycle between 0.15 to 0.9 bar (corresponding to 1 bar and 6 bar pres-

sure of flue gas containing 15 mol % CO2 and 85 mol % N2) and the parallel

horizontal lines show the CO2 working capacity of 13X beads (Taken from

paper II).

It is known that zeolite 13X has a type-I water adsorption isotherm and the

AlPO4-ns have type-V water adsorption isotherms, which shows that AlPO4-

17 and AlPO4-53 adsorb less water than 13X zeolite and are less hydro-

philic.74,76

Therefore, there will be a significantly smaller reduction of the

CO2 adsorption capacities from (wet) flue gas of AlPO4s as compared with

zeolites. Granules of zeolite 13X are probably more useful in low-pressure

PSA processes where the pressure is between 0.01 to 0.3 bar for CO2 capture

from dry flue gas.77

In summary, we have shown how aluminophosphates

can be successfully consolidated by PCP into structured AlPO4-17mPCP650

and AlPO4-53mPCP400 monoliths with high mechanical stability and CO2

26

capture capacity. The combination of these properties suggest that these

monoliths are very promising candidates for efficient CO2 removal process-

es.

3.1.3 Strong silicalite-I substrates with high chemical durability

(Paper III)

Substrates of silicalite-I in binder-free and binder-containing (25 wt.%) form

are consolidated by pulsed current processing and conventional thermal

treatment respectively. These substrates are listed in Table 2 and a short

name is given to them which will be used trough the text. The chemical du-

rability of silicalite-I substrates is studied in aqueous solution at different pH

values. The pH adjustments is performed using a sevenMulti instrument

(Mettler-Toledo AB, Stockholm, Sweden) equipped with an Inlab expert

NTC 30 electrode (Mettler-Toledo AB, Stockholm, Sweden).

Table 2. Silicalite-I substrates consolidated with different compositions and

heat treatment methods (Taken from paper III).

After the given exposure time the aqueous solution is analyzed by ICP-AES

to determine the elemental composition of the solution. The data (Table 3)

show that the amount of dissolved aluminum from all the silicalite-I sub-

strates is between 0.1 to 10 ppm, and is always significantly lower than the

amount of dissolved silicon. Silicon is detected in large quantities (between

1300 and 2000 ppm) in solutions with pH 13.0 compared to moderate

amounts detected in solutions at pH 2.0 (Table 3). The higher ratio of the

dissolved silicon to aluminum for colloidal silica-containing substrates

(SCC, Table 2) suggests that colloidal silica dissolves more readily than the

silicalite-I material. It is reported by Iler that the solubility of colloidal silica

particles is higher than that of crystalline siliceous materials.78

Kaolin with

low crystallinity dissolves from silicalite-I substrates containing kaolin

(SKC) at pH 2.0 and pH 13.0 which is indicated by higher aluminum con-

27

centration in solution at pH 2.0 and 13 compared with other silicalite-I sub-

strates (Table 3).79,80

Table 3. The concentration of silicon and aluminum dissolved in the solution

(in ppm) after treatment of silicalite-I substrates at pH 2.0, 10.6 and 13.0 at

90 °C for 168 hrs (Taken from paper III).

The SEM micrographs of the untreated SP substrate (Fig. 12a) and the SP

substrate treated at pH 13.0 (Fig. 12d) shows that the silicalite-I crystals are

etched and that the distinct particle morphology is partially lost. The untreat-

ed binder-containing substrates, SKC (Fig. 12b) and SCC (Fig. 12c) display

larger silicalite-I crystals fused together by the binder which occurred during

thermal treatment. The silicalite-I crystals of the binder-containing substrates

are also leached after treatment at pH 13.0 (Fig. 12e and 12f) but they are

less affected than the binder-free material (Fig. 12d). The presence of large

holes and channels on the surface of the silicalite-I particles after the treat-

ment at high pH (Fig. 12e and 12f) suggests that the silicalite-I particles are

partially dissolved in the presence of binder.

28

Fig 12. HRSEM micrographs taken from the uncoated surface of the sili-

calite-I substrates before and after treatment at pH 13.0 for 168 hrs; (a) un-

treated PCP consolidated substrate, SP; (b) untreated kaolin containing sub-

strate, SKC; (c) untreated colloidal silica containing substrates, SCC and (d)

treated SP, (e) treated SKC, (f) treated SCC substrates (Taken from paper

III).

Mercury intrusion measurements of the silicalite-I substrates shows that

additional pores are created (Fig. 13d) when the SP substrates are treated at

pH 13.0 (Fig. 12d), and therefore a significant amount of material is re-

moved. Treatment at pH 13.0 results in the formation of intra-crystalline

mesopores and broadening of the size distribution of the interparticle

macropores.

29

Fig 13. The pore size and pore size distribution of SP substrates; (a) untreat-

ed substrate and after treatment for 168 hrs at 90 °C in an aqueous solution

at; (b) pH 2.0; (c) pH 10.6; and (d) pH 13.0 (Taken from paper III).

Acid leaching at pH 2.0 and base treatment at pH 10.6 does not induce any

significant changes in the pore size distribution of silicalite-I crystals (Figs.

13b-c) and similar trends are also observed for SKC and SCC substrates.

Previous studies have shown that kaolin and silica are less soluble in acidic

and mild alkali solutions, but both are significantly degraded if treated in

strong alkaline solutions.80,81

It is therefore shown by this experiment that

silicalite-I crystals degrade to a lower degree when binder is present in the

substrates. The mechanical strength of binder-free silicalite-I substrates, SP

(biaxial flexural strength test) and binder-containing silicalite-I substrates,

SKC/SCC (diametral compression test) show that the strength of SP sub-

strates is not affected after exposure to acidic and alkaline conditions (Table

4). This is due to the presence of necks between silicalite-I particles after

treatment, visible in the high-resolution SEM micrographs in Fig. 12d.

30

Table 4. Mechanical strength of the silicalite-I substrates treated at pH 2.0,

10.6 and 13.0 at 90 °C for 168 hrs (Taken from paper III).

The mechanical strength of SP substrates is twenty times higher than SKC

and SCC substrates and our results show that it is not deteriorated after

treatment in chemically corrosive environment during an exposure of 168

hrs. This higher and more stable mechanical stability of SP substrates high-

light the advantages of using substrates consolidated by pulsed current pro-

cessing.

The effect of longer exposure times on the mechanical strength is investigat-

ed by treating silicalite-I substrates in mild alkaline conditions at pH 10.6

and 90 °C. Binder-free silicalite-I substrates that have been consolidated by

PCP at 1300 °C display a mechanical strength (biaxial flexural strength test)

of 15 MPa before treatment. It is found that the mechanical strength increas-

es from 15 MPa to 23 MPa after exposure to pH 10.6 for a period of 8 days,

(Table 5). Longer exposure times at pH 10.6 up to 16 days further increases

the strength to 32 MPA. However, the mechanical strength of silicalite-I

substrates is reduced to 7 MPa after 24 days of exposure at pH 10.6 (Table

5). The significant increase in the mechanical strength of silicalite-I sub-

strates by a factor of two after 16 days can be attributed to the deposition of

the dissolved silica particles on the surfaces with negative curvature particu-

larly at the necks between two fused silicalite particles.82,83

31

Table 5. The changes in the mechanical strength of the silicalite-I substrates

PCP consolidated at 1300 °C treated at pH 10.6 at 90 °C and pH of solution

after 8, 16 and 24 days.

It is known that the deposition of dissolved silica species will minimize the

surfaces with negative curvatures (necks and particle contact points).82

Pre-

cipitation of the dissolved silica species at the contact points that are formed

during consolidation, strengthens the existing bonds and thus the overall

strength of the substrate. Moreover, the pH of aqueous solution dropped to

7.16 after 8 days and remained almost constant after 24 days (Table 5).

Large amounts of silicon are initially dissolved in the form of silicic acid in

water, which lowers the pH of the solution. Further analysis is required to

characterize the presence of such precipitate at particles contact point, and is

the subject of future works.

3.2 Shaping hydrothermally carbonized beer waste

(HTC-BW) into activated carbon monoliths by PCP

(Paper IV)

Structuring activated carbon into the form of robust monoliths has several

advantages in gas adsorption processes. Volumetric efficiency, resistance to

attrition and longer lifetime of the adsorbent are benefits of using dense

monoliths of activated carbon in e.g. pressure swing adsorption and natural

gas upgrading. Monoliths of activated carbon are usually produced using

binders e.g. polytetrafluoroethylene and polyvinyl alcohol (PVA).4 However,

the presence of binder reduces the performance of activated carbon mono-

liths due to pore blockage. Pulsed current processing (PCP) of hydrothermal-

ly carbonized beer waste (HTC-BW) without addition of binder is employed

32

in this work to produce robust carbon based structures that can be success-

fully activated by physical activation in CO2 flow.

3.2.1 Structural and mechanical properties

The HTC beer waste (HTC-BW) powder used in this work has similar com-

position to peat and contains water and large amount of tar. Both tar contain-

ing (HTC-BW) and tar extracted powders (HTC-BW-E) are consolidated by

PCP processing at 100 and 150 °C (Fig.14a and 14b) and at 25 °C (no heat-

ing) with an applied pressure of 50 MPa. The HTC discs remain in their

cylindrical form after activation at 800 °C in CO2 (Fig.14c and 14d). The low

consolidation temperature not higher than 150 °C ensured that the HTC-BW

and HTC-BW-E are not degraded. TG analysis of the HTC-BW powders

(Fig.14e) show that the significant mass loss at temperatures above 150 °C is

related to decomposition of the HTC-BW and HTC-BW-E. It is known that

HTC-BW and HTC-BW-E contain some unreacted biopolymers such as

hemicellulose, cellulose and lignin that decompose at temperatures higher

than 150 °C.84,85

For both HTC-BW and HTC-BW-E, the mass loss at tem-

peratures < 150 °C is related to evaporation of water.

Fig 14. Photos of discs of hydrothermally carbonized beer waste without

extraction, prepared by pulsed current processing at 150 °C; (a) and (b) are

HTC discs PCP treated at 150 before activation; (c) and (d) are HTC discs

PCP treated at 150 °C and activated in a flow of CO2 at a temperature of 800

°C for 2hrs; (e) TG curves of tar-extracted (HTC-BW-E) and tar-containing

(HTC-BW) hydrothermally carbonized beer waste powder measured in an

atmosphere of N2 (Taken from paper IV).

33

Table 6 shows that the PCP processing temperature has a strong effect on the

densities of the discs. The densities increase from 0.69 to1.08 g/cm3 for discs

prepared at 100 C, and from 1.36 to1.42 g/cm3 when the PCP temperature is

150 C (Table 6). It is assumed that tar acts more efficiently as binder when

the PCP temperature is 150 C. The tar compounds melts at 150 C and fill

the voids, thus the density observed for both tar extracted and tar containing

discs prepared at this temperature are higher compared with the densities of

the discs after processing at 100 C (Table 6). After the activation process,

the densities of HTC discs both with and without tar treated by PCP at 150

C remain unchanged and are reduced for HTC discs treated by PCP at 100

C (Table 6). This is due to the fact that CO2 permeation through the discs

prepared at 150 C is hindered due to closely packed arrangement of carbon

particles. Gas diffusion is an important factor in the pore formation during

activation of carbons.86

The thickness and diameter of HTC discs prepared at

150 C (Fig.14a-d) are around 4 and 12 mm, but reduce to around 2.5 and 9

mm, respectively, after activation.

Table 6. The densities and mechanical strength of discs of the hydrothermal-

ly carbonized beer waste (acetone extracted and without extraction), pressed

at 100 and 150 °C, and the corresponding discs of activated carbon prepared

by activation at 800C for 2h (Taken from paper IV)

The mechanical strength (diametral compression) of HTC discs PCP treated

at 100 and 150 C after activation is measured on four identical discs (Table

6). Loosely packed HTC discs pressed at 25 C collapsed after the activa-

tion. The High mechanical strength of ca.7 MPa that is observed for HTC

discs that are prepared at 150 C (Table 6) can be correlated with the highly

dense structure. The XRD pattern of the HTC discs before activation (Fig.

15a) and after activation (Fig. 15b) at 800 C shows that the discs have a

high amorphous content before and after activation. However, two broad

peaks appear at 2Ɵ= 26 and 44 (Fig. 15b) after activation (ACD) and are

representative of activated carbons.87

These peaks are attributed to the for-

34

mation of a small graphitic phase after activation.88,89

The peak at 2Ɵ= 44

is formed due to decomposition of carbon and formation of pores along the

[100] direction of the graphite structure during activation.90

The HTC discs

before activation (Fig. 15a) had no such lines. The sharp diffractions at 2Ɵ=

22.5 (Fig. 15a) is assigned to disordered cristobalite in the ash.91

Fig 15. X-ray diffraction patterns of the discs of hydrothermally carbonized

(HTC) beer waste with (HTC-D) and without tar (HTC-D-E) pressed at

100°C and 150°C; (a) before activation; (b) after activation at 800°C for 2

hrs and CO2 flow of 48 dm3/h, designated with ACD and ACD-E (Taken

from paper IV).

3.2.2 Pore formation during consolidation and after activation

The specific surface areas of activated carbon discs (ACDs) in Table 7 are

not as high as usually is reported for activated carbons being activated in a

flow of CO2.92

For each of the ACDs prepared from HTC-BW powder

pressed at 25, 100, and 150 °C and 50 MPa there is a certain activation time

that results in the highest surface area, e.g. after 2 hrs. The maximum surface

area of ACD prepared from HTC-BW powder pressed at 100°C is 567 m2/g

and is achieved after 2 hrs of activation (Table 7). The optimal activation

time increases with the increase of the HTC-BW pressing temperature from

25 to 150 °C. The highest surface area of 533 m2/g is obtained for ACD pre-

pared after 5 hrs activation of a HTC-BW powder pressed at 150°C. The

high surface area of the ACD prepared from HTC-BW pressed at 100°C

only after 2 hrs of activation is an indication of a better CO2 permeation in a

less dense discs of carbon (Table 6 and 7).

35

Table 7. Specific surface area of activated carbon discs. Activated carbon

discs prepared from hydrothermally carbonized beer waste with or without

tar and were activated at 800 °C for 2 hrs in flow of CO2 (Taken from paper

IV).

Mercury intrusion porosimetry (MIP) and nitrogen adsorption data (Table 8)

show that activation of carbon discs at 800 °C for 2 hrs (ACDs) results in

development of pores at various length scales. The micropore volume is a a

measure of pores below 2 nm, the external pore volume is determined as the

difference of total pore volume and the micropore volume and the

macroporosity is estimated by MIP (Table 8). CO2 permeation and subse-

quent carbon decomposition created additional macropores in HTC discs

during activation. ACDs prepared from tar extracted and tar containing

HTC-BW pressed at 100 °C has a macroporosity of around 40% of the vol-

ume of the disc (Table 8). However, activated carbon discs of tar extracted

and tar containing carbon consolidated at 150 °C have a significantly smaller

macroporosity of ca. 21 % and 28 %, respectively, compared with activated

carbon discs consolidated at 100 °C (Table 8) This is due to denser packing

of the carbon discs consolidated at 150 °C which hinders CO2 permeation

and pore creation during activation (Table 6).

36

Table 8. Pore properties of the activated carbon discs. Activated carbon discs

prepared from hydrothermally carbonized beer waste with or without tar and

were activated at 800 °C for 2 hrs in flow of CO2 (Taken from paper IV).

The pore size distributions (Fig.16) show that all the activated carbon discs

have micro-meso porosities. The micropore size distributions determined by

DFT analysis (Fig.16a and 16 b) of N2 adsorption isotherms of the activated

carbon discs show a multimodal pore size distributions in the range of 0.8

nm to 2 nm for the tar-containing activated carbon discs (Fig.16a). However,

a narrow micropore size distribution around 0.9 nm is observed for tar ex-

tracted activated carbon discs (Fig.16b). The presence of hierarchical porosi-

ties (micro-meso) in activated carbon discs is especially suitable for gas sep-

aration applications. The mesopore size distributions are modeled by the

BJH method using both the N2 adsorption and desorption isotherms (Fig.16c

and 16d). A sharp peak at pore size of ca. 4 nm appears for all the desorption

branches but does not exist in adsorption branches. This may be explained

by the size of the cavitation droplet of liquid N2 during desorption, which

predicts that a measurable fraction of the mesopores had ink bottle shapes

with openings of < 4 nm (Fig.16c and 16d).93–95

37

Fig 16. Pore size distributions; (a and b) using DFT model; (c and d) using

BJH model. The data is collected by N2-adsorption and desorption on acti-

vated carbon discs with tar (ACD) or without tar (ACD-E) pressed at 25,

100, and 150 °C and activated in a flow of CO2 at 800 °C for 2 hrs. Indicated

as ACD/ACD-E-temperature-activation time, in the graphs (Taken from

paper IV).

38

3.3 Flexible composites of zeolite-cellulose nanofibrils

(CNF) for odor removal (Paper V)

The postharvest storage of fruits and vegetables results in accumulation of

high concentration of odors within the packaging. Volatile sulfur containing

compounds are one of the key components of such odors from some fruits

and vegetables e.g. durian, onion and lettuce. The use of active packaging

material and barrier coatings can provide an efficient way of reducing odors

originated from volatile organic compounds. Problems related to the waste

management of fossil fuel based packaging materials have spurred a great

interest in the development of renewable packaging materials. Renewable

materials such as e.g. cellulose and proteins can be employed to produce

composite packaging and coatings made of organic-inorganic materials. The

inorganic particulates e.g. Zeolite and activated carbons are the active

sorbent for applications where odor removal from the packaging environ-

ment is desired. Lately, The German division of SCA Company (SCA Pack-

aging Deutschland Stiftung & Co. KG), together with the Fraunhofer Insti-

tute, incorporated zeolites into the corrugated cardboard to remove ethylene

produced by fruits and vegetables (Fig.17a).

Fig 17. (a) The prototype of the active packaging from SCA96

; (b) The single

cellulose chain with (C6H10O5)n repeating unit, the β 1- 4 glucosidal bond

connecting C1 and C4 is indicated.

Nanofibrillated cellulose (CNF) of 5-20 nm in diameter and 2 microns in

length can be obtained by acid hydrolysis or mechanical disintegration of

wood or plant cellulose fibers.97,98

Cellulose fibrils have been used as rein-

forcement material for adhesives, electronic devices, biomaterial, foams,

aerogels and textiles.99–102

We will show how suitable zeolite thiol adsor-

bents are identified and a colloidal processing approach can be introduced to

fabricate free-standing zeolite-CNF films and coatings for thiol removal.

39

Cellulose is an abundant biodegradable polysaccharide that can be used as a

minor organic binder in organic-inorganic systems. Cellulose has a linear

chain of glucose molecules that are connected to each other through the

shared covalently bonded oxygen between the C1 of one glucose ring to C4

of the neighboring ring (Fig.17b).

3.3.1 Thiols uptake capacity of zeolites by

thermogravimetry analysis and infrared spectroscopy

The thiol uptake on five different, commercially available microporous zeo-

lites: ZSM5, zeolite Y, silicalite, zeolite beta, and mordenite has been stud-

ied. The mass loss due to desorption of water and thiols from zeolite surface

are measured by TGA (Fig. 18a). The significant mass desorbed from ZSM5

powder after exposure to thiols (Fig. 18a, dashed and dotted lines) compared

with the unexposed ZSM5 powder (Fig. 18a, solid line) is attributed to the

thiols that were strongly adsorbed on ZSM5 surface during the exposure

time with thiols.

The TGA data shows that zeolite Y, ZSM5 and silicalite display the highest

uptake of propanethiol; about 87 mg/g of adsorbents, while zeolite Y display

the highest uptake of ethanethiol; about 63 mg/g (Table 9). The adsorption of

thiols on zeolite beta and mordenite is insignificant, which can be related to

their high water uptake. Hence, zeolites of the MFI (ZSM5, silicalite) and

Faujasite (zeolite Y) type are able to adsorb relatively large amounts of thi-

ols even in the presence of moisture, and were thus chosen as the prime can-

didates for the preparation of odor-removing zeolite-CNF composites. The

adsorption of thiols on zeolites is confirmed by infrared analysis (Fig.18b). It

is found that IR bands characteristic for thiols at 2875, 2930 and 2965 cm-1

,

and C-H stretching and C-H bending vibrations at 1375 and 1455 cm-1

ap-

pear after exposure of ZSM5 to thiols (Fig.18b). The data from TGA and IR

confirm that stable and yet reversible thiol-zeolite surface complexes are

formed when zeolites are in contact with thiols.103,104

40

Fig 18. (a) TG curves of ZSM5 powder as received (solid line), exposed to

ethanethiol (dotted line) and exposed to propanethiol (dashed line). The

powders were not degassed before exposure to thiols and were exposed to

thiols for 1 hr at the boiling point of thiols, then were exposed to air for 1 hr

before measurements; (b) Infrared spectra of as received ZSM5 powder

(dashed line), liquid propanethiol (dotted line) and ZSM5 powder after 1h

exposure to propanethiol (solid line). The C-H stretching vibrations at 2875,

2930 and 2965 cm-1 and C-H deformation vibrations at 1375 and 1455 cm-1

are indicated with vertical lines. The same bands appeared after exposure to

ethanethiol and when silicalite and zeolite Y were exposed to thiols (Taken

from paper V).

Table 9. Water content and thiol uptake capacity of zeolite powders after 1

hr exposure to thiols at their boiling temperature measured by TGA and the

corresponding adsorption values in parenthesis are obtained from simulated

adsorption isotherms (Taken from paper V).

41

3.3.2 Structural features and mechanical properties of free-

standing films

Free-standing films of zeolite powders; ZSM5 and zeolite Y together with

cellulose nanofibrils (CNF) have been prepared by colloidal processing (Fig.

19a).105,106

Free-standing films of Zeolite-CNF with high flexibility (Fig.

19b) and a thickness of about 115 µm (Fig. 20 d) have been fabricated by

vacuum filtration of the colloidal dispersion and drying. SEM micrographs

of the ZSM5-CNF (Fig. 19c) show that the ZSM5 zeolite particles are ho-

mogeneously distributed in the CNF network, although the presence of some

holes (Fig. 19c) is related to defects due to air bubbles.

Fig 19. Free-standing zeolite-CNF films: (a) Photograph of zeolite-CNF

free-standing films with ratio of 89/9 wt.% after drying; (b) demonstration of

the flexibility of zeolite-CNF films; (c) SEM micrograph of ZSM5-CNF top

surface zeolite particles entrapped and connected by cellulose network; (d)

SEM cross sectional view of ZSM5-CNF film with a relatively uniform

thickness of 115 µm (Taken from paper V).

42

The mechanical strength of the zeolite-CNF films is relatively unaffected

within a wide compositional range (Fig. 20a). However, when the CNF con-

tent is reduced to ca. 3 vol%, the mechanical integrity is substantially lost

(Fig. 20a). It is possible that at extremely low concentrations, CNF cannot

form a percolating network.107

It is shown that the strength of zeolite-CNF

films prepared with 10 vol% of CNF decreases with the following order:

ZSM5-CNF ˃ Silicalite-CNF ˃ Zeolite Y-CNF (Fig. 20a). The density of the

film (Table 10) is strongly related to the tensile strength of the films; the

denser ZSM5-CNF film displays a tensile strength of 10 MPa while the most

porous films of zeolite Y-CNF has a tensile strength of only 6 MPa. The

porosity of the zeolite-CNF films is estimated from the weight and dimen-

sions of the films (Table 10, experimental section). The least porous films

with 63% porosity contain the spherical ZSM particles which display the

highest modulus and strength (Table 10). However, the silicalite-CNF and

zeolite Y-CNF films consisting of irregularly shaped zeolite powders have

higher porosities of 65% and 70%, respectively and show similar yield

strengths. The characteristic features of a neat CNF film (nanopaper) where

the initial elastic response is followed by yielding and strain hardening is

clearly demonstrated in the stress-strain curves of the zeolite-CNF films

(Fig. 20b).108

Table 10. BET surface area, zeolite particle size, theoretical porosity,

Youngs modulus and mechanical strength of the zeolite-CNF films. The data

in brackets are the standard deviations. The powders were degased at 80 °C

for 5 hrs before BET measurement (Taken from paper V).

43

Fig 20. Mechanical properties of zeolite-CNF films: (a) Tensile strength of

ZSM5-CNF films at different CNF concentrations (●) and comparison of

strength variations in films prepared with 10 vol.% of CNF containing sili-

calite-CNF (■) and zeolite Y-CNF (▲); (b) Tensile stress as function of

tensile strain for zeolite-CNF films with 10 wt.% of CNF prepared with dif-

ferent zeolite types; ZSM5-CNF film (▲),silicalite-CNF films (■)and zeolite

Y-CNF films (●) (Taken from paper V).

3.3.3 Odor removal efficiency

The propanethiol removal capacity of zeolite-CNF films at vapor concentra-

tions of ca. 1 ppm and below has been evaluated using SPME/GC/MS.

Standard vapor concentration at ca. 2 ppmv is made by drawing a volume of

0.02 μl of propanethiol into the tip of the pipet, the tip is then inserted into a

30-L container, sealed with a Teflon septum and allowed to equilibrate.

SPME and GC/MS analysis at different time intervals show an unchanged

thiol concentration with no detectable losses up to 24 hrs after the first

measurement (longer periods of time were not investigated). Inserting a

small CNF-zeolite film (0.35 g) into the container results in a decrease of the

thiol concentration to a level as low as ca. 0.009 (±0.005) ppmv, (Fig. 21a).

Exposure times beyond 20 hrs did not yield any further significant reduction

in thiol levels (Fig. 21a).

44

Fig 21. Thiol elimination from the head space of a container: (a) Decrease of

the propanethiol vapor concentration with time after adding 0.35 g of a

ZSM5-CNF film to the sampling container; (b) Schematic presentation of

the test measuring the propanethiol outflow through 1-mm ZSM5-CNF films

(Taken from paper V).

A simple sniff test for thiol vapor performed after 22 hrs of exposure by four

non-trained individuals in the lab indicates that the ZSM5-CNF film is able

to reduce the propanethiol concentration down to levels where it is not clear-

ly detected by the human olfactory system, and thus of little or no discom-

fort. However, this should be further investigated by sensory analysis (test

panel evaluation) with qualified and trained assessors in odorless rooms.

The ability of a 1 mm thick ZSM5-CNF film (10 compressed layers) to serve

as a membrane for propanethiol vapor at high concentration (ca.3x10^3

ppmv) is investigated by the set-up shown in figure 21b. Sampling of the gas

outside the propanethiol-filled cylinder with SPME and GC/MS analysis

show no detectable propanethiol (Fig. 22) and thus a complete elimination

by the ZSM5-CNF film.

45

Fig 22. Headspace SPME/GC/MS analyses after 30-min sampling of (a) a

reference 22ml vial containing ca.200 ppmv (0.02 μl) of proranethiol vapor

representing full propanethiol release and (b) headspace of a sealed 22ml

vial enclosing a propanethiol-filled cylinder (1.7 ml vial sealed with 10

compressed layers of 1-mm zeolite-CNF film) containing ca.3x10^3 ppmv

propanethiol (0.02 μl) (Taken from paper V).

3.3.4 Composite coatings on paper board

Dispersions of ZSM5, silicalite and zeolite Y with CNF at a zeolite solid

loading of 96 w/w % have been prepared. The zeolite-CNF dispersion is

applied onto the surface of a white paper board (white paper, Lessebo Paper

AB, Sweden) that has been pre-treated with a 0.01 M calcium chloride solu-

tion. The calcium modified surface of paperboard ensures a strong surface

attachment of the zeolite-CNF to the substrate due to physical crosslinking

of the CNF during application. A film applicator (universal applicator, ZUA

2000-100, Switzerland) with the gap size adjusted at 1 mm is used to apply

zeolite-CNF dispersion on the paperboard (Fig. 23a).

46

Fig 23. (a) Universal film applicator with adjustable gap height; (b) The

white coating of zeolite-CNF on paperboard after drying, the arrow shows

the direction of the coating; SEM cross section of coatings of (c) ZSM5-

CNF; (d) silicalite-CNF; (e) zeolite Y-CNF.

At this gap size (1mm), a homogenous thin coating of zeolite-CNF with

thickness of ca. 40 or 100 μm was formed on paperboards after drying (Fig.

23b). Cross sectional electron microscopy images show that the densest and

thinnest coating with thickness ca. 40 μm are produced with ZSM5-CNF

dispersions (Fig. 23c). However, large holes and channels up to 10 μm paral-

lel to the coating surface are present in the coatings prepared with silicalite-

CNF (Fig. 23d) and zeolite Y-CNF (Fig.23e). The thick and less dense coat-

ings of silicalite-CNF and zeolite Y-CNF with thickness of ca.100 μm are

result of inefficient packing of zeolite particles with irregular shapes com-

pared with the spherical ZSM5 particles.

47

4. Conclusions

In this work, porous and strong monoliths and substrates of adsorbent zeo-

lites, aluminophosphates and carbon materials have been structured by col-

loidal processing and pulsed current processing (PCP). The processing con-

ditions have been optimized and adjusted with the material in use, and the

properties of porous monolithic structures have been studied with respect to

CO2 adsorption capacity, mechanical stability, and chemical durability.

A novel colloidal processing route was developed to synthesis free-standing

films and coating composites of adsorbent zeolite with small content of cel-

lulose nanofibrils as binder or matrix phase. Hierarchical porosities at vari-

ous length scales including large macropores was incorporated in zeolite

13X monolith that contained only 5 wt.% of binder by a sacrificial templat-

ing method. High CO2 uptake of 5.5 mmol/g combined with high mechanical

strength of 0.1 MPa sufficient for handling and use in a PSA process was

obtained with such highly porous 13X monoliths.

Strong binder-free monoliths of AlPO4-17 and AlPO4-53 with mechanical

strength of 7 MPa and CO2 uptake up to 2.5 mmol/g were consolidated by

pulsed current processing. It was shown that AlPO4-17 and AlPO4-53 mono-

liths have CO2 adsorption capacities that exceed those of the standard zeolite

13X in particulate form, in a hypothetical PSA process. Monoliths of AlPO4-

17 and AlPO4-53 are expected to be less hydrophilic than zeolite 13X and

thus using them in a real implementation of CO2 adsorption process reduces

the cost for drying the flue gas.

Binder-free silicalite-I substrates consolidated by PCP showed superior

chemical and mechanical stabilities in comparison with binder-containing

silicalite-I substrates after treatment in aqueous solution at different pH val-

ues for 168 hrs and 90 °C. The mechanical strength of silicalite-I substrates

was degraded when binder was present due to selective removal of binder in

chemically corrosive environments. It was found that longer exposure of the

binder-free silicalite-I substrates at pH 10.6 for 16 days, improved the me-

chanical strength by a factor of two due to re-precipitation of dissolved silica

at contact points. Binder-free PCP treatment is found a practical approach

for producing chemically and mechanically durable substrates for chemically

demanding applications.

PCP processing of hydrothermally treated beer waste biomass (HTC-BW)

produced strong carbon discs that remained mechanically strong and highly

48

porous after the physical activation process. It was shown that the PCP pro-

cessing temperature significantly affects the density of the carbon disc and

the properties of the disc after activation. Activated carbon discs that com-

bined high density, 1.42 g/cm3, high mechanical strength, ca. 7 MPa and

high surface area of 458 m2/g were obtained by physical activation of carbon

discs that were consolidated by pulsed current processing at 150 °C. Activat-

ed carbon discs with high porosities larger than 40 vol% and multimodal

pore size distributions are potential candidates for gas separation applica-

tions, e.g. CO2 adsorption.

It was shown by a combination of experimental studies and simulations that

zeolites of MFI (ZSM5 and silicalite) and FAU (Y) type are highly efficient

adsorbents for uptake and removal of light thiols e.g. ethanethiol and pro-

panethiol, that are common odors in fruit and vegetables. Functional and

flexible free standing zeolite-cellulose nanofibrils composite films and coat-

ings with zeolite solid loadings of 89 w/w% and 96 w/w%, respectively have

been produced by a colloidal processing route. Free-standing zeolite-

cellulose nanofibrils films showed high mechanical strength of 10 MPa and

could efficiently remove low concentrations of thiols to levels below the

human olfactory threshold. These composites are promising alternatives as

packaging materials where considerable concentrations of malodors are ac-

cumulated within the packaging environment.

49

5. Future outlook

This work identified some methods for development of hierarchically struc-

tured adsorbent by different colloidal processing route. The adsorbent were

structured to satisfy the demands enforced by the applications e.g. high vol-

ume efficiency, low pressure drop and improved heat and mass transfer in

CO2 separation processes. It is important to develop adsorbent structures that

can withstand rapid cycling in CO2 separation systems e.g. PSA processes.

Cost efficient new processing methods still need to be investigated to fabri-

cate adsorbents into shapes with pre-defined structures that ensure compati-

ble properties for gas adsorption processes. Novel structuring techniques

such as 3D printing can be used for quick and reliable production of struc-

tured laminate sheets, coatings and multilayered adsorbents. It would be

interesting to measure and compare the adsorption behavior and efficiency

of different structured shapes. More advanced characterization techniques

e.g. X-ray micro-computed tomography (µ-CT) can also be used to visualize

the porous network formed in the structured monoliths. The structured ad-

sorbent must also be designed to provide durable substrates where the selec-

tive adsorbent layer is a thin film deposited on the substrate. Such structures

can be used in separation processes that use membrane systems. Studies with

focus on pore tuning, mechanical stability and chemical durability of struc-

tured monoliths and substrates must be performed to adopt and enhance the

performance of adsorbents for demanding applications. Furthermore, it is of

interest to optimize and determine the feasibility and processing conditions

of the existing structuring techniques e.g. extrusion, PCP and casting for

binder-free structuring of carbon materials derived from bio-mass. Moreo-

ver, cheap, easy and environmentally friendly material and processing meth-

ods must be studied for large scale structuring of active sorbents that can be

incorporated into packaging materials. Novel adsorbent materials that can be

easily processed in complex shapes and geometries must be identified. It

must be noted that porous strong discs, monoliths or substrates with struc-

tures that are finely tuned and designed have potential applications for elec-

tronic applications. Therefore, the capabilities of existing shaping techniques

for production of structured devices with well-defined geometries need to be

explored.

50

Acknowledgement

Here I like to mention some people who supported me during important

times of my education.

First of all I want to thank my supervisor Prof. Lennart Bergström and ap-

preciate all his constructive advices, valuable critiques and encouragement

that he dedicated to my research work and for the learning opportunities that

he provided to me. I would like to appreciate that you let me work with great

level of independence! I am also very grateful for all the help with planning

and the effort that you put into my work to keep my progress on schedule. I

also wish to offer my special thanks and gratitude to Dr. Farid Akhtar with-

out whose useful suggestions and patience the completion of my tasks would

not have been accomplished. I am thankful that you were willing to gener-

ously dedicate your time for listening and discussing enthusiastic ideas.

I like to thank Prof. Niklas Hedin, Prof. Ulrika Nilsson and Prof. Lars Ber-

glund for nice collaboration and discussions. I appreciate all the technical

and scientific knowledge that I learned from Dr. Kjell Jansson and Dr. Lars

Eriksson in electron microscopy and X-ray diffraction. My thanks are also

extended to Dr. Zoltan Bacsik for his technical support with IR and adsorp-

tion analysis. I owe special gratitude to Andreas, Andy and Arto for spend-

ing their time to read and give suggestions to improve my thesis. I would

like to express my gratitude to the staff at MMK working in the administra-

tion office, computer support, library and workshop. Hanna, Daniel, Anna-

Karin, Ann-Brit, Roffe, Hillevi, Anita, Pelle and Hans Erik, are thanked for

efficient and skilled help and for being supportive during my 5 years of stud-

ies at MMK. I also like to thank Ann, Tatiana, Camila and Pia for their help

with the administrative issues. I enjoyed quite a lot of my time at MMK and

will carry the pleasure of knowing all of you. I thank Prof. Gunnar Svensson

for his understanding and guidance since the beginning of my studies at

MMK. I want to appreciate kind supports of Prof. Sven Lidin at the start of

my studies. I wish to give my gratitude to all the academic stuff at MMK

who are not mentioned here but helped to add up to my knowledge at any

level.

51

My deep and enormous appreciation goes to my dear friend Barozh whose

intellectual inputs created another dimension in my life. There are no words

that can express how fortunate I am since and ever for such encounter! I am

delighted to thank my dear friend Linnea as well for all the moments that we

shared and for her kind but even distant care. I like to thank Ehsan for being

a supportive friend. Farshid whose generous help always astonished me is

specially thanked for the nice collaboration, supportive friendship and read-

ing the test print of my thesis; I wish all the best for you! Jovic, thanks for

the nice and relaxing times we spend together specially the massage ses-

sion. I wish to thank my friends Sophie, Miia, Alexandra, Amber and Eva

for sharing thoughts, open inspiring discussions and all the cheerful time we

had together! My friends Shadi, Sachli, Farrokh, Sepideh, Iman, Saied,

Narges, Diletta, Michiel, Utsa, Nizar, and Shakiba, thousands thanks for all

the empathy and happy time that we shared in my free times sometimes even

in different countries.

I am glad that I had the pleasure to have the companionship of nice room-

mates and colleagues even for a short while sometimes; Yuan, Andreas,

Bernd, Konrad, Leo, German, Erik, Wenming, Samrand, Bertrand, Henrik

(Fahlquist), Henrik (Svengren), Jon, Arto, Christina, Duan, Mehdi, Kamran,

Darius, Masoud, Asieh, Saina, Sumit, Nicolas, Mohsen, Verina, Kristina,

Tom, Ken, Fabian, Cecilia, Fredrik, Mikaela, Arnaud, Julian, Valentina,

Kornelya, Reji, Michael, Dilshod, Mukta, Marta, Ocean, Dickson and Julia.

Daniel, thanks for all the information and wonders that you shared about

different stones! I also like to thank Farhan for our fruitful collaboration.

Claude Philogène, Astrid, Ingela, Andreas and Inhee, I like to thank you for

the nice birthday dinner. Special thanks to Michal for the beautiful flowers,

you are great!

And to this end I would like to express my profound appreciation to my par-

ents who did not have the chance to continue their support throughout my

research, but they left unutterable print of love, confidence and hope that

gave me the strength and ambition to reach my goals. My lovely sister

Hoda, my little curious niece Kiana and my dear brothers Mohammad and

Reza are mostly appreciated for their patience in difficult times without my

presence; their never-failing sympathy was always a source of inspiration.

Mohammad my lovely unique brother, I would like to specifically thank you,

you provided me with the strongest support that a sister could ever get!

Stockholm, November 13, 2014

Neda Keshavarzi

52

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