Lignins: from plants to applications

In biopolymers course - CHEM-E2155

15.03.2021Chamseddine Guizani

Lignin in few lines

• Most abundant aromatic biopolymer in Nature.

• Main component of plant biomass (15-35 wt.%).

• Amorphous and polydisperse mixture of methoxylated polyphenols.

• Light to dark brown color.

• Dissolved from wood chips during pulping processes (black liquor).

• Black liquor combusted for materials and energy recovery.

• Lignin is under valorized as a material.

• A victim of prejudices: “You can make anything out of lignin – except money”

O

HO O

HO

OMe

Lecture content

Lignin in plant

Availability of lignins and

isolation processes

Lignin characterization

Lignin applications and

engineering

1. Lignin in plants

Component Woody feedstock,wt.% d.b

Nonwoody feedstock,wt.% d.b

Cellulose 40-45 30-45Hemicelluloses 25-35 20-35

Lignin 20-30 10-25Extractives 2-5 5-15

Proteins < 0.5 5-10Inorganics 0.1-1 0.5-10

SiO2 <0.1 0.5-7

Typical composition of woody and non-woody feedstocks [1]

[1] : Stenius, P. et al., 2000, Papermaking Science and Technology, Book 3.Forest Products Chemistry. Fapet Oy, Jyväskylä.

Lignin content in lignocellulosic biomass

Average chemical composition of Scots pine and Silver birch [1]

40 40

27,5 32,5

27,5 22,55 5

Pine Birch

Cellulose Hemicelluloces Lignin Extractives

Pine (softwood)

Birch (hardwood)

[1] : Stenius, P. et al., 2000, Papermaking Science and Technology, Book 3.Forest Products Chemistry. Fapet Oy, Jyväskylä.

• Lignins fills the space between plant cell-walls (Glue).• Covers microfibrils and has strong interactions with the carbohydrates in the plant cell walls.• Has several functions in the plant: strength, barrier, water transport.

Lignin in plant cell walls

Ultrastructure of wood cell wall: middle lamella (ML), primary wall

(P), secondary wall (S1, S2, S3 layers). Coté, (1967).

Transverse section TEM image of earlywood tracheids in tamarack

wood. Sjostrom, E (1993).Distribution of lignin, cellulose, and

hemicellulose in a softwood. Meier H (1964)

Lignin biosynthesisLignin is synthesized in cell walls through an enzyme initiated radical polymerization of three monolignols.

Phenylalanine Monolignols Lignin

Enzyme initiated dehydrogenation and radical

Polymerization of monolignols

OHO

NH2

Shikimic acidGlucose

Metabolic routes producing monolignols

from glucose

Photosynthesis of glucose

There are structural differences in lignins according to their botanical origin

Softwoods(Pine)

Hardwoods (Birch)

Grasses(Esparto)

G-lignin GS-lignin HGS-lignin

O

OOMe

OOMeMeO

OOMe

OOMeMeO

OOMe

GG

G

S HS

Major structural units

6

54

3

21

C

C

C

O

O C

α

β

γ

C

C

C

O

O C C

C

C

O

O C

C

C

C

OOC

C

C

C

O

O C

O

COC

C

C

Ethers

β-O-4(40-60 %)

α-O-4(5-10 %)

γ-O-4(< 5 %)

5-O-4(5-10 %)

γ-O- α(< 5 %)

Glycerldehyde or glycerol 2-aryl ether

(< 5 %)

C

C

C

O

C

O

C

C

C

O

C

O

5-5 (and 5-6)(5-20 %)

β -5 (both ring and open structure)(5-20 %)

C

C

C

O

C

C

C

O

β - β(< 5 %)

C

C

C

O

O

β - 1(< 5 %)

C

C

C

O

O

C

β – 6 (and β – 2) (< 5 %)

C-C bonds

Esters

C

C

C

O

O C C

O

α-ester(< 5 %)

C

C

C

O

O C C

O

γ-ester(< 5 %)

Source: Stenius, P. et al., 2000, Papermaking Science and Technology,Book 3.Forest Products Chemistry. Fapet Oy, Jyväskylä.

Functional groups

[1] Stenius, P. et al., 2000, Papermaking Science and Technology, Book3.Forest Products Chemistry. Fapet Oy, Jyväskylä.

Functional group Softwood lignin Hardwood lignin

Phenolic hydroxyl 20-30 10-20

Aliphatic hydroxyl 115-120 110-115

Methoxyl 90-95 140-160

Carbonyl 20 15

Functional groups of native lignin (per 100 C6C3 units) [1]

Elemental ratio: C:H:O=64:6:30 C:H:O=59:6:35

OH

OMe

HO

O

O

OMe

OMe

OMe

HO

HO

HOHO

O

OMe

OH

O

OH

O

OMe

OH

OMe

HO

O

HO

OH

O

OMe

O

HO

OMe

OH

OH OH

MeO

O

HO

MeO

OH

O

OHOMeHO

HO

O

OMeO

OH

O OMe

O

HO

OMeHO

O

HO

OMe

OH

HO

O

OMe

O

OH

HO

O

O

OMe

OMe

O

OOH

O

O

HO

HOOMe

OHMeO

OMe

A β O 4, β

ether

B β-5, phenylcoumaran

C β−β, resinol

D 5-5/β-O-4, dibenzodioxocin

E 5-O-4, biphenyl etherF spirodienoneX1 cinnamyl alcohol endgroupX7 glycerol endgroup

Models of lignin structure

Lignin polymer model for a softwood based on the ligninfication theory

Source: Ralph, J. et al. Handbook of Plant Science, 2, 1123-1132, 2007

More on lignin structure using NMR

Models of lignin structure

Aalto lignin modelBalakshin M, et al (2020) Green Chem 22:3985–4001.

Lignin polymer model for spruce milled woodlignin based on the state of the art analytical data

2. Lignin availability and isolation methods

Sources of lignin

Pulp

mill

s

Kraft(Kraft lignin, potential market 3.5-14 Mt/year)

Sulfite(Lignosulfonates, commercial product, 1 Mt/year)

Soda(Soda lignin, 5-10 kt/year)

Organosolv(Organosolv lignin)

Bior

efin

erie

sHydrothermal treatment

Acid hydrolysis

Steam explosion

Supercritical water hydrolysis

Pulping lignins

Biorefineries lignins(high production

potential)

How much lignin is available ?

• 50 million tons of extracted lignin inPulp and & Paper industry (2004).

• Limited markets and focus on low valueproducts: dispersing or binding agents.

• ~ 2% used commercially with theremainder burned as a low value fuel.

Source: Gosselink RJA et al (2004). Ind Crops Prod 20:121–129

1 0,1

49

~ 50 M TONS/YEAR

Lignosulfonates products

Kraft lignins products

Burned as fuel

Sources of lignin

Lignin source

Potential production,

Mt/y

Purity Feedstock range

Process flexibility

Cost Application value

Additional revenue,

%

Pulping 5-20 Med-high narrow narrow Med-high Med-high 5-20**

Biorefinery >200 Low wide wide Low Low-high* ~50-100

*According to the current research**For Kraft lignins

[1] Balakshin MY et al (2020). ChemSusChem 1016–1036.

Comparison of pulping and biorefinery lignins [1].

Isolation of lignin from spent pulping liquors

[1] Sewring, T. et al. (2019). J. Wood Chem. Tech., 39, 1-13. [2] Beisl, S. et al (2020). Molecules 2020, 25, 1388. [3] Sumerskii, Iet al. (2015) Rsc Advances, 5(112), 92732-92742.

Acid precipitation from alkaline solutions (e.g., from Kraft process black liquor) [1].

Antisolvent precipitation: adding water to an organic solvent containing dissolved lignin (e.g., in Organosolv processes) [2].

Ultrafiltration and adsorption [3].

https://boku.ac.at

Beisl, S. et al (2020).

Commercial lignin isolation processes

[1] Tomani P (2010). Cellul Chem Technol 44:53–58[2] Kouisni, L et al (2012). J. Sc. & Tech. For. Prod. Proc. 2, 6-10.

Based on pH reduction using CO2 inducing lignin precipitation at pH 10.

The Lignoboost technology invented by Innventia and acquired by Valmet [1].

The Lignoforce technology oxidizes the lignin before CO2 precipitation [2].

3. Lignin characterization

0,00

0,20

0,40

0,60

0,80

1,00

0,0 2,0 4,0 6,0

Diff

eren

tiaal

wei

ght

frac

tion

Log(MM)

012345678

0,01 1 100

Volu

me

frac

tion,

%

Particle Size, µm

Lignin properties• Molecular structure: functional groups, molecular weight distribution,

structural units and interunit linkages.

• Elemental composition: C, H, O, N, S and minerals.

• Purity: presence of carbohydrates and proteins.

• Physical properties: particle size, morphology, thermal and otherspecific material properties.

Analytical tools for lignin characterization• Numerous analytical methods for characterizing lignin properties.

• An exhaustive characterization is too time consuming and often not necessary.

• Be pragmatic: keep in mind your application and the key lignin properties in relation to it.

Key lignin propertiesto measure

Performance in applications

Examples of analytical tools for lignin characterizationNuclear Magnetic Resonance spectroscopy

[1] Balakshin MY, Capanema EA (2015). RSC Adv 5:87187–87199.

• NMR spectroscopy applies a magnetic field to a specific atomicnucleus in the lignin sample (e.g., the most common stableisotopes 1H, 13C, 31P…) and radio frequency pulses tocharacterize the resonant frequency of that atomic nucleus.

• The environment around the specific nuclei in the ligninmolecule changes the nuclei resonance frequency.

• The “shifts” in the resonance frequency give details on theelectronic structure and the functional groups in the lignin.

• 13C NMR delivers a wealth of quantitative structuralinformation [1].

Source: Wikipedia

Examples of analytical tools for lignin characterization

[1] Trogen M et al (2021). Carbohydr Polym 252:117133. [2] Balakshin MY, Capanema EA (2015). RSC Adv 5:87187–87199.

Quantification of various structural features in spruce and beech lignin by 13C NMR [1] [2]

SL BLper 100Ar mmol/g per 100Ar mmol/g

CO nonconjugated 9 0.51 9 0.48CO conjugated 5 0.28 10 0.54

total CO 14 0.79 19 1.02COOR nonconjugated 6 0.34 6 0.32

COOR conjugated 1 0.06 1 0.05total COOR 7 0.40 7 0.38

OMe 85 4.80 115 6.18G2 90 5.08 35 1.88

S2,6 90 4.84H (apprx.) 4 0.23 1 0.05

S+G+H 94 5.31 81 4.35S/G ratio na na 1.29

ArH 200 11.30 189 10.16DC, % 96 39

90-78 ppm 19 1.07 27 1.4578-67 ppm 17 0.96 28 1.5167-58 ppm 42 2.37 64 3.44

Oxygeneted Aliphatic 78 4.41 119 6.40Saturated Aliphatic 105 5.93 97 5.22

side chain 204 11.53 242 13.01b-O-4 5 0.28 7 0.38

Carbohydrates <1 <1EtO-ether 8 0.45 9 0.48EtO-ester 4 0.23 3 0.16EtO-total 12 0.68 12 0.65

M-Ar, g/mole 177 186

Examples of analytical tools for lignin characterizationChemical degradations of lignin

• Reductive treatments: thioacidolysis…

• Oxidative treatments: nitrobenzene oxidation,cupric oxide oxidation…

• Gas or liquid chromatography coupled to a specificdetector for the quantification of the degradationproducts.

[1] Lin SY, Dence CW (1992) Methods in Lignin Chemistry.

Nitrobenzene and cupric oxide oxidation products of lignins (a) and (b) analysis of Nitrobenzene degradation products using GC-MS [1]

(a)

(b)

Size exclusion chromatography

• Chromatographic method in which ligninmolecules in solution are separated by their size.

• SEC possible in aqueous or organic eluant.• Lignin must be fully dissolved and have low

interactions with the SEC columns material• Indirect (using calibrants and UV or RI) and direct

(using light scattering detection) molecular weightmeasurements.

Examples of analytical tools for lignin characterization

Aqueous phase SEC of lignosulfonate. Sulfonated polystyrene calibrants. UV

detection at 280 nm [1].

Time

[1] Guizani C, Lachenal D (2017). Int J Mol Sci 18.

Examples of analytical tools for lignin characterizationMorphology and size

012345678

0,01 0,1 1 10 100

Volu

me

frac

tion,

%

Particle Size, µm

Particle size distribution of a softwood Kraft lignin using laser diffraction

Scanning electron microscopy image of a softwood Kraft lignin

4. Commercial applications of lignin

Sources of lignins, types and products from lignin (LigniMatch project)

product routes in commercial markets today

routes of most interest to develop further

Lignin and lignin-based solid biofuel

Lignin as a solid biofuel

Source: Per Tomani et al (2011) LignoBoost Kraft Lignin, a New Renewable Fuel and a Valuable Fuel Additive. International bioenergy and bioproducts confrence, 11-14 March 2011, Atlanta GA USA.

Fuel properties Lignin Coal Wood chips Bark pelletsMoisture, wt.% 30-40 9 50 10.3

Ash, wt.% 0.02-1 11.7 2-3 3-6HHV, MJ/kg d.b 26-27 29.8 20 21LHV, MJ/kg d.b 17-19 25.9 7.7 17.7

Sulphur, wt.% d.b 2-3 0.4 0.05 0.04Chloride, wt.% 0.01 0.04 0.03 0.02

Bulk density, kg/m3 630-720 d.b 800 200-300 550-700

Lignoboost® Kraft lignin fuel characteristicswith comparison to other solid fuels

More on lignoboost process anduse of lignin as a biofuel

Lignin as a solid biofuel

Kraft lignin pellets (100%) or asadditive (1-10%) in wood pellets [2].

[1] Kuparinen K, et al (2017). BioResources 12:4031–4048.[2] Berghel J et al (2013). Fuel Process Technol 112:64–69.

Lime kiln fuel in P&P mill [1]CaCO3+→CaO+CO2

Co-firing with coal in power plants

Lignin in adhesive applications

The phenol-formaldehyde (PF) resins • Phenol-Formaldehyde (PF) resins production ~ 3.0 Mt in 2009• Market ~ $2.3 billion.• Average annual growth ~ 3.9% from 2009 to 2013.• PF obtained by the catalyzed polycondensation of phenol and formaldehyde

More on PF resins synthesis

The phenol-formaldehyde (PF) resins

PF resins

High adhesive strength

Moisture resistance

Good thermal stability

High mechanical

strengthWood particle board

Plywood

Lignin as substitute to phenol in PF resinsQuestion: could lignin be a good substitute to phenol in the synthesis of

lignin-phenol-formaldehyde resins ?

Phenol Lignin

Lignin as substitute to phenol in PF resins• Part of the phenol is substituted by lignin

during the synthesis of LPF resins (10-50wt.%)

• Lignin performance in adhesive applicationis evaluated using the standardized ABESsystem (ASTM standard test method D7998-5)

Automated Bonding Evaluation System (ABES) for evaluating lignin performance in adhesives applications

(https://www.adhesiveevaluationsystems.com/)

LPF resins

Lignin

PhenolCH2O

Lignin as substitute to phenol in PF resinsNo significant correlation between the shear strength (ABES test) and the number of reactivecenters, and thus no real disadvantage for hardwood lignins.

Balakshin and Capanema, 14th EWLP, V.I, 63 (2016)

0

1

2

3

4

5

6

7

110 120 130 140 150

Shea

r st

reng

th, M

Pa

Press temperature, °C

PFSHR-50SW KraftD.Fir OSAlcellAspen SodaBirch KraftBagasse Soda

ABES test, 30% plywood PF substitution, Press time 90 sec.

Reactive centers mmol/g

Control0.652.362.611.221.111.042.26

OH

12

345

6

OCH3

OH

12

345

6

OCH3

OH

H3CO

12

345

6

H

S

G

Lignin as substitute to phenol in PF resins• Problems related to lignin reactivity:

• Lignin reactivity <<< phenol reactivity : larger molecular structure and less reactive sites.• Higher reaction temperatures and longer reaction time in the LPF synthesis.

• Solutions to make lignin more reactive:• Chemical modification: methylolation and phenolation of lignin [1].• Thermochemical treatment: depolymerization [2].

[1] Vázquez G, et al. (1997). Bioresour Technol 60:191–198.[2] Solt P, et al. (2018). Polymers 10:1162.

Base catalyzed depolymerization of KL resulted in high adhesive performance of the lignin oligomeric fraction [2]

Lignin in thermoplastic applications

Lignin in thermoplasticsArboform® bioplastic (liquid wood)

•A lignin-based thermoplastic.

•Pelletized mixture of lignin (up to 50%), fine fibers of wood, hemp or flax, and wax.

•Liquifies at 170°C (PP ~160°C, PE~105-120°C, PS~240°C).

•Thermally stable up to 105°C.

•Can be used in injection molding like conventional plastic.Illustration of the molding process

Commercial uses of lignosulfonates

Lignosulfonates• Lignosulfonates, or sulfonated lignin

produced during sulfite pulping. Lignin isextracted using various salts of sulfurousacid.

• Sulfonate groups are introduced in thelignin structure during pulping.

• 330-540 kg of LS/1000 kg of wood• Lignosulfonate is a lypohydrophilic

molecule: hydrophobic aromatic structureand hydrophilic sulfonate groups. Theyare water-soluble anionic polyelectrolytepolymers

Several hundred applications:• flow modifier in cement

and concrete,• dispersing agent, emulsion

stabilizer….

World revenue generatedfrom lignosulfonatesestimated at 490-550 M $

Properties of lignosulfonatesAverage molecular weight: 20-80 kDaPolydispersity: 8-6

0 2 4 6 8

log10

(M [Da])

0.5

1

1.5

2

2.5

Diff

eren

tial w

eigh

t fra

ctio

n [-]

10 -3 =280nm

LS-Rep1LS-Rep2

Sulfonate groups: 0.6-1.2 per monomerOrganic sulfur: 4-8 wt.%

Highly soluble in water at all pH, insoluble in most organic solvents

Color: very light to very brown

Nontoxic: LD50> 5g/kg

Use of lignosulfonates as dispersants

Adding LS disperses the coal particles and decreases the viscosity of CWS [2]

Adding LS disperses the cement particles, ↑ the cement flowability and workability [1]

Flow modifier in cement and concrete formulation

• Concrete = water + cement+ sand + stone• Strength ↓ when H2O wt.% ↑

Coal–water slurry (CWS) dispersant

[1] Ouyang X et al. (2006). Colloids Surfaces A 282–283:489–497.[2] Yang D, et al. (2007). Energy Convers Manag 48:2433–2438.

• Combustible mixture of fine coal particles suspended in water

Vanillin from lignosulfonates

[1] https://www.bioref-integ.eu/fileadmin/bioref-integ/user/documents/Martin_Lersch__Borregaard_-_Creating_value_from_wood_-_The_Borregaard_biorefinery.pdf[2] Bjørsvik H-R, Minisci F (1999). Org Process Res Dev 3:330–340.

• Alkaline catalytic oxidative depolymerization of LS • Temperature: 170-200 °C, pH>7, Cu catalyst,

pressurized O2 [2].• Cu catalyst is recycled

https://www.vanillin.com/Products/eurovanillin-natural

Yield: 3 kg of vanillin /1000 kg of wood [1]. Higheryields are reported in the literature [2].

~20 % of vanillin is produced from lignin and ~80% from crude oil using the guaiacol route

Applications under R&D

Emerging applications

Emerging applications

BTX

Natural dyeing agent

Pyrolysis oil

Biobased Carbon fibers

Activated carbons

Lignin nanoparticles

Adsorption of pollutants from water

Electrodes in energy storage devices

5. Lignin engineering

Lignin engineering: concept, methodology and tools

Botanical origin and processing

steps

Lignin properties

Performance in a target

application

How to engineer the best lignin candidate for your application?

Reading assignment

You will have to read certain chapters of three peer-reviewedpublications and answer to the questions given in theassignment document available in MyCourses platform.