33

2 Nano-catalysis and valorization of glycerol

34

2.1 Introduction

As stated in the previous chapter, the central theme of the current research is

valorization of glycerol using catalysis under the ambit of Green Chemistry.

Heterogeneous catalysis by nanoparticles of metal oxides, semiconductor, oxides and

other compounds is the oldest industrial practice. Due to their large surface-to-volume

ratio compared to bulk materials, they are attractive candidates for use as catalysts.

The key feature of nanocatalyst is to intensify reaction rates due to extremely high

activity, low energy consumption and long life time.

Heterogeneous catalysis, in particular, addresses the goals of green chemistry by

providing the ease of separation of product and catalyst, thereby eliminating the need

for separation through distillation or extraction. In addition, environmentally benign

catalysts such as clays and zeolites may replace more hazardous catalysts currently in

use (Barrault et al., 2002; Blaser et. al., 1999). To achieve maximum selectivity, the

catalyst should be tailored by precisely controlling the size, shape, spatial distribution,

surface composition and electronic structure, and thermal and chemical stability of the

individual nanocomponents. Bio-glycerol is sol co-product formed during the

biodiesel production. It is formed in 10% by weight of biodiesel produced.

Considering economic practicability of biodiesel production, this glut of crude

glycerol needs to be utilized to produce industrially significant chemicals which

ultimately add value to biodiesel process economy; hence it is necessary to explore

new applications for transformation of glycerol to industrially important chemicals.

The current work deals with the use of nanocatalysts in valorization of glycerol to

industrially important chemicals, the relevant literature is briefly discussed here. In

particular, nano acid/base catalysis, bioglycerol based chemicals are considered.

2.2 History of Nano catalysis

Catalysis research and catalyst-based technologies have been at the heart of

nanotechnology for many years. Nanoparticles of metals, oxides and sulfides have

been developed and used as catalysts for hydrocarbon conversion, partial oxidation

and combustion reactions since the 1920’s; as such they represent the oldest

commercial application of nanotechnology (Somorjai et al., 2001). The development

of supported noble metal catalysts in the 1950’s aimed at reducing costs for large

commercial applications resulted in catalysts with noble metal particle of sizes less

35

than 10 nm, which by today’s standard are nanomaterials. Zeolite catalysts,

discovered in the late 1960s, are another example of nanomaterials (Zhou et al.,

2004). By deliberate design and preparation of the catalyst structure at the atomic and

molecular level, researchers at Mobil Oil Co. were able to synthesize zeolites such as

ZSM-5, a nanostructured crystalline material with a 10 atom ring and pore size of

0.45-0.6 nm, enabling the control of selectivity for petrochemical processes at a

molecular level. Such nanocatalysts revolutionized the petrochemical industry. Today,

zeolite catalysts are used in processing over 7 billion barrels of petroleum and also

many chemicals annually. In 1992, researchers at Mobil Corporation discovered the

M41S family of silicate/aluminosilicate mesoporous molecular sieves with

exceptionally large uniform pore structures. Due to the higher accessibility of

reactants in mesoporous MCM-41 as compared to zeolite (microporous material), it is

suitable for catalytic reactions dealing with large size molecules such as heavy gas oil

cracking (Ciesla et al., 1999).

2.3 Methods for synthesizing of nano catalyst

There are different methods to prepare nanocatalyst some of them are discussed here.

2.3.1 Sol gel method

The sol-gel process, developed in 1960’s, is a wet-chemical technique widely used in

material science and ceramic engineering. The process is described as “formation of

an oxide network through polycondensation reactions of a molecular precursor in a

liquid.”

A sol is a stable dispersion of colloidal particles or polymers in a solvent. The

particles may be amorphous or crystalline. An aerosol is particles in a gas phase,

while a sol is particles in a liquid. A gel consists of a three dimensional continuous

network, which encloses a liquid phase, in a colloidal gel, the network is built from

agglomeration of colloidal particles. In a polymer gel the particles have a polymeric

sub-structure made by aggregates of sub-colloidal particles. The typical sol-gel

method is as shown in Figure 2.1.

Sol-gel processing refers to the hydrolysis and condensation of alkoxide-based

precursors such as Si (OEt) 4 (tetraethyl orthosilicate, or TEOS). The reactions

36

involved in the sol-gel chemistry based on the hydrolysis and condensation of metal

alkoxides M(OR)z can be described as follows:

MOR + H2O → MOH + ROH (hydrolysis) (1)

MOH+ROM→M-O-M+ROH (condensation) (2)

Figure 2.1: Sol-gel method (Suneel, 2012)

The sol-gel method is very efficient in producing various nano metal oxides in which

particle size, porosity can be controlled and successful application can be achieved

(Dimitriev et. al., 2008; Eastoe et al., 2006).

2.3.2 Micro emulsion

Nanoparticle synthesis in microemulsions has been topic of interest since the early

1980s, when the first colloidal solutions of platinum, palladium and rhodium metal

nanoparticles were prepared. Microemulsions are thermodynamically stable system

composed of water, oil and surfactant. (Lo´pez-Quintela, 2003) Droplets of water in

oil or oil in water are stabilized by surfactants when small amount of water or oil are

used, respectively. The size of droplets can be controlled by changing the ratio of

water or oil and surfactant in nanometer range. These nanodrops can serve as

nanoreactor to produce nanoparticle.

The microemulsion method is a versatile technique which allows the preparation of a

wide range of nanomaterials just alone or in combination with other techniques.

37

Particle growth has shown to be strongly dependent on intermicellar exchange rates.

The resultant particle size appears to be dependent on parameters such as solvent type,

surfactant and co-surfactant, concentration of reagents, ionic additives, etc.

2.3.3 High energy milling

High energy milling is an effective and simple technique without involving high

temperature treatment for the production of nanocrystalline powders, with the

possibility of obtaining large quantities of materials with modified properties. In this

technique, starting powder particles are trapped between highly kinetic colliding balls

and the inner surface of the vial, which causes repeated deformation, rewelding, and

fragmentation of premixed powders resulting in the formation of fine, dispersed

particles in the grain-refined matrix.

2.3.4 Hydrothermal/solvothermal processes

Hydrothermal or solvothermal synthesis is generally defined as synthesis of

nanomaterials or crystal growth under high temperature and pressure solvent

conditions from substances which are insoluble in ordinary temperature and pressure

(Figure 2.3). When the water is used as media the process is called hydrothermal and

when any other solvent is used then it is called as solvothermal process. The

production of various nano metal oxide particles such as TiO2, ZrO2, AlOOH, Al2O3,

SnO2 has been demonstrated by hydrothermal batch and flow reaction system

(Hayashi et al., 2010). Solvothermal method is also extensively used in the

preparation of structured nanomaterials, e.g. Zeolites (Merzhanov et al., 2005).

2.3.5 Combustion synthesis

Combustion synthesis (CS) or self-propagating high-temperature synthesis (SHS) is

an effective, emerging low-cost method for production of ceramics (structural and

functional), catalysts composites, alloys, intermetallics and various nanomaterials

materials (Merzhanov et al., 1969). Today preparation of nanomaterials by CS method

has become a very popular approach. Recently, a number of important breakthroughs

in this field have been made, notably for development of new catalysts and

nanocarriers with properties better than those for similar materials prepared by

traditional processes. The combustion synthesis method explores an exothermic,

generally very fast and self-sustaining chemical reaction between the desired metal

38

salts and a suitable organic fuel, which is ignited at a temperature much lower than the

actual phase formation temperature. Its key feature is that the heat required to drive

the chemical reaction and accomplish the compound synthesis is supplied by the

reaction itself and not by an external source.

On the basis of physical nature of the initial reaction medium, CS of nanomaterials is

differentiated in three types.

1. Conventional SHS -initial reactants are in solid state (condensed phase

combustion).

2. Solution-combustion synthesis (SCS) - initial reaction medium is aqueous

solution.

3. Synthesis of nanoparticles in flame, - gas-phase combustion.

Combustion synthesis processes are characterized by high-temperatures, fast heating

rates and short reaction times. These features make CS an attractive method for the

manufacture of technologically useful materials at lower costs compared to

conventional ceramic processes.

2.3.5.1 Conventional SHS

In conventional SHS solid reactants are subjected to high temperature to combust

(Figure 2.2). In this process the solid reactant used are in the range of 10-100 µm and

at high temperatures (> 2000 K), which makes difficult to synthesize nanomaterials

with high surface area. Hence to achieve the nano crystals with high surface area it

can be coupled with various techniques such as

(i) SHS synthesis, followed by intensive milling

(ii) SHS + mechanical activation (MA)

(iii) SHS synthesis followed by chemical dispersion

(iv) SHS with additives

(v) carbon combustion synthesis (CCS)

Solid state combustion synthesis has been extensively used to prepare a variety of

catalyst such as oxynitrides (honeycomb support for nobel metal), Complex cuprates

LnMCu, Ln=Y or La, M= Ca, Ba or Sr (ethylene synthesis). This method produces

well crystalline powders. The only disadvantages of this method is, the initial

precursor being solid state do not offer perfect homogeneity. It results into partially

unburnt material and impuritites. To overcome theses disadvantages, solution

combustion approach is often preferred (Aruna et al., 2008).

39

Figure 2.2: Solid state combustion (Aruna et al., 2008)

2.3.5.2 Solution-combustion synthesis (SCS)

SCS is an emerging technique with many recent developments in nano material

synthesis. It is versatile, simple and rapid, which allows effective synthesis of a

variety of nanosize materials. It is self-propagating reaction in homogeneous solution

of different oxidizers (e.g., metal nitrates) and fuels (e.g. urea, glycine, hydrazides)

(Figure 2.3). Depending on the type of the precursors, as well as on conditions used

for the process organization, SCS may occur as either volume or layer-by-layer

propagating combustion modes. This process not only yields nanosize oxide materials

but also allows uniform doping of trace amounts of rare-earth impurity ions in a single

step. Various procedures have been reported to achieve combustion: continuous

heating of reactant mixture (Erri et al., 2006) and instantaneous heating (Patil et al.,

1998). In the latter case, the combustible gel is kept into a preheated (at 400 oC)

furnace. In both the cases, the phase composition of product is not affected to larger

extent. The instant heating method is preferred over continuous heating method, as the

chances of presence of unvaporized water molecule at the time of combustion. A wide

range of useful nano metal oxides were prepared with interesting magnetic,

dielecmagnetic tric, electrical, mechanical, catalytic, luminescent and optical

properties. It is most preferred technique to prepare oxide materials with desired

composition, structure (spinel, perovskite, garnets, etc.) by SC. Table 2.1 summarizes

various metal oxides produced by solution combustion synthesis (Patil et al., 1998).

40

Figure 2.3: Solution combustion synthesis

Table 2.1: Metal oxides prepared by solution combustion synthesis (Patil et al., 1998)

Material Fuel Particle size (nm)

Application

TiO2 GLY 4-17 Photocatalyst

La0.8Sr0.2CrO3 GLY 100 nm Pervoskite membranes

Al2O3 U 40 Abrasive

Al2O3 U 19 Catalyst support

Al2O3-ZrO2 U 20-45 Cutting tool

M-Al2O4 (M= Zn, Mn) MA+

U/GLY/C

H/ODH

15-28 Catalytic support

MgAl2O4 U 13-20 Structural material

MMgAl2O4, M=Fe, Co,

Ni

U 10 Catalyst

Co2+/ Al2O3 U 20-30 Pigment

Eu3+/Y3Al5O12 U 60-90 Red phosphor

Ce1-xTbxMgAl11O19 CH 10-20 Green phosphor

41

M/Al2O3, M= Pt, Pd,

Ag, Au

U 7-10 Catalyst

Pd/Al2O3 U 10-18 Catalyst

CeO2-ZrO2 ODH 10-18 Oxygen storage

capacitor

M-CeO2, M=Pt, Pd, Ag ODH 1-2 Catalyst

Ce1-xPtxO2 CH 4-6 H –O combination

catalyst

Ce1-xPrxO2 CH 3-40 Red pigment

Ni-YSZ U 40 SOFC anode materials

Ln(Sr)MO3, M=Fe, Mn CH/ODH 20-30 SOFC cathode material

LaCrO3 U 20 Interconnect for SOFC

Y2O3-ZrO2 CH 59-65 SOFC electrolyte

LiCo0.5M0.5O2, M=Ni,

Mg,Zn

U 5-12 Cathode material for

lithium barriers

MFe2O4 ODH 60-100 Magnetic oxide

BaTiO3 GLY/CA 18-25 Dielectric material

Pb(Zr,Ti)O3 CA 60 Piezoelectric material

ZrO2 GLY 23 Oxygen sensor

ZnO U 100 Variastor

ZrW2O8 GLY 38 Negative thermal

expansion

Eu3+/Y2O3 GLY 20-30 Red phosphor

LiMn2O4 PAA 30-60 Lithium battery

InxGa1-xO3 HY 54-160 Optical coating for

sensors

Y2SiO5/Ce HA 20-80 Detection of ionizing

radiation and dense

scintillators

LaBO3 B = Cr, Mn, Fe

and Co

U 55-75 Catalyst in

decomposition of N2O

to N2 and O2

Cu/CeO U --------- de-NOx catalyst;

42

Ce 0.98 Pd 0.02 O 2-ρ

ODH 30-40 Catalyst for Selective

CO oxidation

Cu/ZnO/ZrO2/Pd

GLY 7-14 Catalyst in oxidative

hydrogen production

from methanol

Ni

GLY 24 Catalyst for Partial

oxidation of methane

to syn-gas

WO3–ZrO2

U 10-25 Catalyst in Solvent-

free synthesis of

coumarins

WO3

GLY 12-59 Removal of organic

dye from water

TiO2

GLY 8-12 Catalyst for

carcinogenic

hexavalent chromium

reduction

MgO

GLY 12-23 Catalyst in Fluoride

removal from drinking

water

U: urea, CH: carbohydrazide, ODH: oxalyldihydrazide, GLY: glycine, CA: citric acid, PAA:

poly acrylic acid, HY: hydrazine, MA: metal acetate,

HA: hexamine, SUC: sucrose

2.4 Suppoted Nanocatalysts

Nanoporous and nanocrystalline systems have a wealth of potential applications.

Nanoporous materials possess an ultra-high surface-to-volume ratio, which would

offer a greatly increased number of active sites for carrying out catalytic reactions

(Ying et al., 2000).

2.4.1 Supports for nano-catalyst

There are numerous inorganic supports available for preparing supported

nanocatalyst, such as silica, alumina, carbon (notably charcoal), montmorillonite

43

clays, zeolites, and other aluminosilicates, as well as more complex materials such as

partially substituted aluminosilicates (e.g. aluminophosphates or ALPOs) and more

complex materials such as heteropolyacids. All of these materials can exist in high

surface area forms (100 - 1000 m2g-1) and are normally porous, with average pore

diameter ranging from the microporous zeolite (from 0.3nm) to some macroporous

silicas (upto 100 nm at least). The particle sizes of such materials can range from

coarse (in the case of formed materials) to very fine (<1�m). The materials can be sub

classified in terms of their being: crystalline with regular pore structure and a very

narrow pore size distribution (e.g. zeolites); amorphous with a possible wide range of

pore structures and a broad pore size distribution that can range over several tens of

nanometers (e.g. conventional silica gels); and flexible layered structures (e.g.

montmorillonite clays). The range of suitable materials available has been greatly

enhanced through the discovery of the hexagonal mesoporous silicas (HMSs), notably

the MCM materials developed by Mobil (Smith et al., 1992). These offer the

intriguing possibility of being able to grow silicas, alumino-silicates and potentially

many other materials to almost any pore size. Such materials commonly have very

high surface areas (>1000m2g-1 is not uncommon). Several important factors of

inorganic support materials are summarized as follows.

A) Silica gels (commercial) – Silica gels are widely available and inexpensive.

They have high surface area, mesoporous and normally broad pore size

distribution. Their surfaces are heavily hydroxylated and easily functionalized.

B) Structured silica (synthetic) – Structured silica like MCMs and HMS

materials are mesoporous, usually prepared using sol-gel methods using onium

or amine templates. They posses very high surface areas (>1000 m2g-1) and

narrow pore size distribution but little long-range order and are often less

hydrophilic than normal.

C) Montmorillonites (natural and synthetic) – Natural clays can have swelling

structure giving microporosity, while pillared clay have large pores. Acid

treated clay are partially mesoporous (and may change with ageing)

D) Alumina – They have moderate surface area; available in acidic, basic and

neutral forms.

E) Zeolites – Zeolites are microporous and with tight pore size distribution. They

have high surface areas, highly structured, small pores can give high degree of

44

shape selectivity but may cause diffusional problems, especially in liquid

phase systems.

F) Other materials - Charcoal can have very high surface areas (> 1000 m2/g)

but complex surface functionalities; minerals such as calcium fluoride have

low surface areas but can be useful as highly inert surfaces.

2.4.2 Methods of synthesizing of supported nanocatalyst

There are several methods to prepare supported reagents. They can be elaborated as

follows

1) Sol-gel synthesis- It is direct method and can be used to introduce functional

group like NH3, SO3H e.g. via (MeO)Si-R and resulting materials can have

high surface areas.

2) Post-modification of support material – It is most commonly using silane,

but may be less stable than analogous sol-gel materials due to only partial

surface reaction; alternative methods include via chlorination (e.g. Si-Cl (Si-

R).

3) Impregnation (pore filling followed by evaporation of solvent) -

Impregnation is an extremely versatile technique which can be controlled to

give good dispersion and a known loading of reagent. It has been successfully

applied to many of the catalysts including supported zinc halides (used in

reactions including Friedel-Crafts alkylations and bromination reactions) and

supported fluorides (used as solid bases). It is also used extensively in the

industrial scale manufacture of solid catalysts (Clark et al., 1994).

4) Ion exchange -Ion exchange is the most important technique for the

preparation of clay and zeolite catalysts from the preformed supports. It is

used to make montmorillonite-Fe3+, which is a useful Diels-Alder catalyst that

can function in water and zeolite-Na+, H+ (i.e. partially proton-exchanged

zeolite), which can catalyze some aromatic chlorination with shape selectivity

(Clark et al., 1992).

5) Absorption from solution- It is the simplest technique but the highest

loadings could not be achieved.

6) Mixing/grinding - Easy and avoids other chemicals, but unlikely to give good

dispersion

45

2.4.3 Novelties of Clays as Nanocatalyst Support

Clays are nothing but naturally occurring alumino-silicates resulted from erosion of

rocks for millions of years. Clays are widely used due to wide ranging properties, high

resistance to atmospheric conditions, geochemical purity, and easy access to their

deposits near the earth’s surface and low price. The application of clay minerals in the

various process industries, engineering, petroleum discovery, recovery and refining,

and others, are closely related to their structure and composition. Important

characteristic relating to application of clay minerals are particle size, surface

chemistry, particle shape, surface area, and other physical and chemical properties

specific to a particular application such as viscosity; colour; plasticity; dry and fired

strength; absorption and adsorption; abrasion; and others. Clays are widely used as

catalysts in synthetic organic chemistry. Some of the clay catalyzed reactions include

alkylation and acylation of aromatics, esterification, etherification, isomerization,

cracking, hydration and dehydration, nitration and in petrochemical reactions

including NOx reduction and hydrodesulphurization. One of the major advantages of

clay catalysts is their higher thermal stability compared to ion-exchange resins; the

resins can be operated upto 120 oC, whereas clays can be safely used upto 200 oC.

Also clays are inexpensive compared to other new generation solid acid

heterogeneous catalysts.

2.4.4 Supported Heteropoly Acids and their Salts

2.4.4.1 Introduction

Heteropoly acids have gained a lot of attention as environmentally benign catalysts

for acid catalyzed reactions, which are among the most important reactions in the

chemical industry. Heteropoly acids (HPA) are strong Brønsted acids composed of

heteropoly anions and protons as the countercations. HPA are known as a condensate

of different kinds of oxoacids. A typical HPA of 12-tungstophosphoric acid is formed

when a phosphate ion is condensed with tungstate ion as shown below-

PO43- + 12 WO4

3- + 27 H+ → H3PW12O40 + 12 H2O (3)

The structure is composed of one heteroatom surrounded by four oxygen to form a

tetrahedron. The heteroatom is located centrally and caged by 12 octahedral MO6-

units linked to one another by the neighboring oxygen atoms. There are a total of 24

bridging oxygen atoms that link the 12 addenda atoms. The metal centres in the 12

octahedra are arranged on a sphere almost equidistant from each other, in four M3O13

46

units, giving the complete structure an overall tetrahedral symmetry. The bond length

between atoms varies depending on the heteroatom (X) and the addenda atoms (M)

(Mizuno et al., 1998). Figure. 2.4 shows the structural model of a Keggin anion

(PW12O403-) in which four oxygen atoms form a central tetrahedron of heteroatom P,

and 12 terminal and 24 bridged oxygen atoms form twelve octahedral of addenda

atoms W.

HPAs in the solid state are thermally stable and suitable to conduct vapour reactions

up to 400°C. The thermal stability of hydrogen forms of HPAs changes with

heteroatom, polyatom and polyanion structure (Misono et al., 1990) as follows:

H3PW12O40 > H3PMo12O40 > H4SiMo12O40.They are highly soluble in water, alcohol,

ether and ketone. It has been found that HPA anion is stable at lower pH during

hydrolysis in aqueous media. Typical HPAs having the Keggin structure, such as DTP

are strong acids; protons are dissociated completely from the structures in aqueous

solution (Kozhevnikov et al., 1987).

Figure 2.4: The structure of the Keggin heteropoly anion (_α-XM12O40)n−

2.4.4.2 Heteropoly Acids Supported on Porous Oxides

As described above heteropoly acids (HPA) possess strong acidity. Among all HPA’s

dodecatungstophosphoric acid (DTP) is the most extensively studied (Baba et al.,

1992; Pope et al.1983) since it possesses the highest Bronsted acidity (Corma et al.,

2000). However, low surface area, rapid deactivation and relatively poor stability are

some of the major problems associated with HPAs in bulk form. These problems were

solved by many research’s across the globe to convert HPAs into their heterogeneous

forms either by converting them into their alkali metal salts (Group A and B) or by

immobilizing them on high surface area inorganic support. Attempts to improve the

efficiency and stability of HPAs have been made by supporting them on various

47

supports including montmorillonite K10 clay, mesoporous silica, mesoporous

aluminosilicates, alumina, carbon, and zirconia (Misono et al., 1990; Okhura et al.,

1996; Mukai et al., 2001; Rao et al., 1989; Yadav and Kirthivasan, 1993). Recently

HPAs have been successfully impregnated onto MCM-41 (Kozhevnikov et al., 1996)

and HMS (Yadav and Manyar, 2003).

2.4.4.3 Supported Cesium Ion Exchanged Heteropoly Acid Salts

Hetrogenisation of HPA’s has been extensively explored by converting them into

their alkali metal salts. The salts of small cations (Na, K, etc. Group A) are highly

soluble in water while salts of large cations (NH4, Cs, etc. Group B) are completely

insoluble in aqueous and any organic solvents, making them useful for heterogeneous

reactions. Among all these various prepared salts of HPAs Cs2.5 salt of DTP

(Cs2.5H0.5PW12O40) has attracted a lot of attention due to its high catalytic activity,

surface area and stability in aqueous and organic solvents. The acidity of

Cs2.5H0.5PW12O40 is a superacid. Cs2.5H0.5PW12O40 is a homogeneous mixture of Cs3

salt of DTP (Cs3PW12O40) and H3PW12O40, and during the calcination, the protons

move to the surface of the catalysts rendering it very high activity. Cs2.5H0.5PW12O40

is also termed as water-tolerant catalyst, due to its superior stability than other solid

acids such as zeolites, in hydrolysis of 2-methylphenyl acetate (Kimura et al., 1997).

Although Cs2.5H0.5PW12O40 shows very high activity and stability for liquid phase

reactions as well as gas phase reactions, in liquid phase reactions, they form a

colloidal solution with the reaction media as they have a very fine particle size, which

makes recovery of the catalyst difficult from the reaction mixture after completion of

reaction. The catalyst has to be either filtered through celite pad or by centrifugation

method. However, its small particle size limits its catalytic applications in commercial

fixed bed or slurry reactors.

Unfortunately, direct impregnation of Cs2.5H0.5PW12O40 is not possible due to its

insolubility in any kind of solvent and is a quite challenging. To overcome this

problem, efforts have been made to immobilize Cs2.5H0.5PW12O40 on established

inorganic supports so as to easily separate the catalyst from reaction mixture. Our

laboratory has developed a novel protocol to create nanoparticles of Cs2.5H0.5PW12O40

in the pore space of K-10 clay (Yadav et al., 2003a). Efforts also have been made to

use different support such as SiO2 gel, dealuminated USY zeolite, SBA-15,

48

aminopropyl functionalized silica, (Izumi et al., 1995, Zhang et al., 2006, Rao et al.

2005, Misono et al., 2005). Supported Cs2.5H0.5PW12O40 was found to be highly active

and selective for industrially relevant liquid phase alkylation, acylation, esterification,

oxidation, dehydration and isomerization and acetal formation reactions.

2.5 VALORIZATION OF GLYCEROL

2.5.1 Introduction

Due to limited quantity of fossil fuels, several alternate energy sources are being

pursued vigorously. Biodiesel has proved its value as a fuel for diesel engines and is

renewable and clean. Biodiesel is produced through transesterification reaction in

which fatty acids present in vegetable or animal oil are reacted with alcohols.

Glycerol is produced as the sole co-product in this reaction and is about 10 wt %. As

the biodiesel production is increasing exponentially, enormous amounts of crude

glycerol is generated. Despite of the wide applications of pure glycerol in food,

pharmaceutical, cosmetics, and many other industries, it is too costly to refine the

crude glycerol to high purity, especially for medium and small biodiesel producers. If

this surplus of glycerol is utilized to produce industrially important chemicals, the

process economics of biodiesel production will improve and consequently lower its

cost.

Glycerol can be converted to various industrially important chemicals. Scheme 2.1

shows the possible value added chemicals from glycerol, which was subsequently

described in succeeding sections.

2.5.1.1 Oxidation

Glycerol on oxidation gives wide range of products such as dihydroxyacetone,

glyceraldehyde,

glyceric acid, glycolic acid, hydroxypyruvic acid, mesoxalic acid, oxalic acid, and

tartronic acid, They are widely applicable in industry as potential chemical

intermediate. Some of uses of every component is listed below

A) Dihydroxyacetone – Tanning agent in cosmetics, synthon in organic

chemistry, Starting material in D,L- serin synthesis.

B) Hydroxypyruvic acid- Starting material in D,L- serin synthesis, flavor

component.

49

C) Mesoxallic acid - as a complexing agent and as a precursor in organic

synthesis and recently was found to show activity as an anti-HIV agent.

D) Oxalic acid- Cleaning or bleaching, especially for the removal of rust,

mordant in dyeing processes, in backing powder.

E) Tartronic acid- Oxygen scavenger

F) Glycolic acid- chemical peel performed by a dermatologist, skin care products.

As large number of products formed in oxidation process, it is needed to develop

selective oxidation process for desired product. Numerous research groups have

investigated processes for selective oxidation using mono and bimetallic catalyst

based on noble metal like Au, Pd and Pt. Reaction temperature, pH and particle size

of metal catalyst play important role in selective oxidation.

Monometallic nano-catalysts like 1% Au/charcoal or 1% Au/graphite gave 100%

selectivity to glyceric acid under mild reaction conditions of 60 °C, 3 h, water as

solvent (Carrettin et al., 2002). Bimetallic catalyst composition consisting of Au, Pt,

Pd supported on carbon showed a higher activity with respect to monometallic

catalysts, which indicates a synergetic effect between the two metals (Nikolaos et al.,

50

Scheme 2.1: Valorization of glycerol

2006, William et al., 2007, Abbadi et al., 1996). Selective liquid-phase oxidation

route to produce of hydroxypyruvic acid over a bismuth-modified platinum catalyst is

reported using air as terminal oxidant. Metalllosilicates also were found to give

selective oxidation to glyceraldehydes, dihydroxyacetone, and glyceric acid, with

change in pore size (McMorn et al., 1999). Electrochemical oxidation methods have

been also reported using monometallic Pt and Au electrodes as well as electrodes

modified with bimetallic Pt-Pd and Ru nanoparticle (Enancio et al., 2002). There are

also reports on biocatalytic methods using enzymes and microorganisms and the

common chemical product is dihydroxyacetone (Wei et al., 2007)

51

2.5.1.2 Reduction

The main products formed in the reduction of glycerol are 1,3-propanediol and 1,2-

propanediol. 1,3-Propanediol is copolymerized with terephthalic acid to produce

polyester used in the manufacture of carpet and textile fibers exhibiting unique

properties in terms of chemical resistance, light stability, elastic recovery, and

dyeability. These diols can be produced by an alternative route involving selective

dehydroxylation of glycerol through chemical hydrogenolysis or biocatalytic

reduction. Several supported mono and bi-metallic transition metal catalysts

comprising of Pt (D’Hondt et al., 2008), Cu (Huang et al., 2008), Au-Ru (Maris et al.,

2007), Ni (Perosa et al., 2005), Ru-Re (Ma et al., 2009), and Cu-ZnO (Balaraju et al.,

2008) have been reported for the hydrogenolysis of glycerol. Activity of different

metal supported catalysts for glycerol hydrogenolysis follows the order Ru ≈ Cu ≈ Ni

> Pt > Pd (Chheda et al., 2007). Effect of various catalytic supports (ZnO, C and

Al2O3), solvents (H2O, Sulfolane and dioxane) and acidic or basic additives (H2WO4)

was studied to improve the glycerol conversion and selectivity of the product

(Chaminand et al., 2004). Many liquid phase catalysts were also reported for the

hydrogenolysis reaction, however, in liquid phase, special solvents are such as 1-

methyl-2-pyrrolidinone for Rh(CO)2(acac) + H2WO4 (Che et al., 1987), sulfolane for

Rh/C + H2WO4 (Shinmi et al., 2010) and 1,3-dimethyl-2-imidazolidinone for

Pt/WO3/ZrO2 (Kurosaka et al., 2008), were used in the reaction. Our laboratory has

reported a novel process for selective hydrogenolysis of glycerol to 1,2-propanediol

over silver incorporated octahedral molecular sieve (OMS-2) catalyst using different

loadings of silver in which the use of silver as the catalyst for the first time for

hydrogenolysis of glycerol. Both batch and continuous mode of operations have been

studied to determine the stability of the catalyst. 30 % w/w Ag-OMS-2 was the best

catalyst. It is a nano fibrous crystalline material (Yadav et al., 2012 b).

2.5.1.3 Carboxylaion

Glycerol on carboxylation different types of carbonates such as linear, cyclic,

linear/cyclic as shown in Scheme 2.2 (glycerol carbonate family).Glycerol carbonate

is a stable, colorless liquid. It is a useful solvent for plastics and resins, such as

cellulose acetate, nylon, nitrocellulose, and polyacrylonitrile. It reacts readily with

phenols, alcohols, and carboxylic acids when heated to form the glycerol ethers or

52

esters of these materials, for example, polyesters, polycarbonates, polyurethanes, and

polyamides.

Scheme 2.2: Glycerol carbonate family

Cyclic glycerol carbonate may be industrially obtained by reacting glycerol and

ethylene carbonate or dialkyl carbonates by transesterification using several basic

condensation catalysts (Ochoa-Go´mez et al., 2009). Dimethyl carbonate can be used

as carbonate source, because dimethyl carbonate can be manufactured by

environmentally safe industrial process from CO2 (La et al., 2007). Glycerol

carbonate has been also obtained from glycerol and dimethyl carbonate by a

transesterification catalyzed by lipases (Kim et al., 2007). Although this is a very

promising route for production of glycerol carbonate, its main drawbacks are the long

reaction times (higher than 25 h) and the use of solvents, such as tetrahydrofuran,

required for obtaining high yields. Recently, Aresta et al. (2006) reported the

carboxylation of glycerol carbonate with carbon dioxide in the presence of Sn

catalysts, such as n-Bu2Sn(OMe)2, n-Bu2SnO, and Sn(OMe)2, using either glycerol or

tetraethylene glycerol dimethyl ether as the reaction medium. Our laboratory has also

reported a novel process for making glycerol carbonate (Yadav and Chandan,

submitted to Biores. Tech. 2012).

2.5.1.4 Glycerol carbonate to glycidol

Glycerol cyclic carbonate can be converted to glycidol on decarboxylation. Glycidol

has wide applications. Glycidol is also used as an additive for oil and synthetic

53

hydraulic fluids, and as a diluent in some epoxy resins. The glycidol structure is

present in two commercially important groups of derivatives, glycidyl ethers and

glycidyl esters, neither of which is prepared directly from glycidol. The end product is

mixed ether, one component of which is the glycidyl group. Glycidyl esters are

prepared by reacting sodium salt of the appropriate carboxylic acid with

epichlorohydrin. Both types of derivatives are used almost exclusively as diluents in

epoxy resins. Glycidol also falls into the generalized category of chiral epoxides.

These chiral epoxides or glycidols can be used as reagents in a number of

pharmaceutical and fine chemical applications. They include pesticides and

herbicides, flavors and fragrances, chiral polymers, and liquid crystals. Glycidol is

used as a stabilizer for natural oils and vinyl polymers, demulsifier, dye-leveling

agent. It is used in surface coatings, sanitary chemicals and sterilizing milk of

magnesia, as a gelatin agent in solid propellants. Our laboratory has also reported a

novel process for making glycidol (Yadav and Chandan, submitted to Appl Cat A

2012)

Scheme 2.3: Glycerol to glycidol

OH OH

OHO

O

OH

O

+CH3

O OCH3

O

solid base catalyst

- MeOH

O

OH

- CO2Glycerol

Dimethyl Carbonate

Glycerol Carbonate Glycidol

54

Scheme 2.4: Applications of Glycidol

2.5.1.5 Etherification

Glycerol can form mono-, di-, and triethers. They may be either ethers of glycerol

with itself (polyglycerols), inner ether (glycidol), or mixed ethers of glycerol with

other alcohols. Glycerol ethers are outstanding oxygen additives for diesel fuel.

(Gupta et al., 1995) Vegetable oil or animal fat methyl esters cannot be used as fuel

for diesel engines because the limitation is the cloud point, which is -16 °C for

petroleum diesel fuels and around 0 °C for biodiesel. The addition of ethers such as

glycerol ethers decreases the cloud point of diesel fuels. Oxygenated diesel fuels are

of importance for both environmental compliance and efficiency of diesel engines.

Mixtures of mono-, di-, and trialkyl glycerols are suitable for use as oxygenates in

diesel fuels. Methyl-tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) are

currently used fuel additives. It was found that di-tertbutylglycerols (DTBG) and tri-

tert-butylglycerol (TTBG) derivates are also valuable fuel additives leading to a

decrease in the emission of particulate matter, hydrocarbons, carbon monoxide and

unregulated aldehydes.

Glycerol alkyl ethers can be produced by etherification (O-alkylation) by alkenes,

particularly isobutylene or the C4 fraction obtained from pyrolysis and FCC.

55

Etherification of bio-glycerol with isobutylene have been extensively investigated

over sulfonic mesostructured silicas (Melero et al., 2008), strong acid ion-exchange

resins, zeolite (Mravec et al., 2005) and complete conversion of glycerol with

selectivity of more than 90% was achieved.

Mono alkyl glyceryl ethers (MAGEs) find wide applications in cosmetics and

pharmaceuticals, since they exhibit a wide spectrum of biological activities such as

anti-inflammatory, antibacterial, antifungal, inmmunological stimulation and

antitumor properties. They are used as an important intermediate in synthesis of 1,3-

dioxolan-2-ones and bis(sodium sulfonate ester) type cleavable surfactants (Ono et al.,

1998).

2.5.1.6 Esterification

Glycerol on esterification with carboxylic acid gives monoglycerides and

diacylglycerol and triglycerides. They have been widely used in surfactants, food

additives, cosmetics, and plasticizers.

Monoglyceryl esters have amphiphilic propreties and can be used as nonionic

surfactants and emulsifiers. They are widely used as additives in bakery products,

margarines, dairy products, and sauces. In the cosmetic industry, they are added as

texturing agents for improving the consistency of creams and lotions. In addition,

because of their excellent lubricant and plasticizing properties, Monoglyceryl esters

are used in textile processing and formulation of oils for various types of machinery.

Monoglyceryl esters are industrially manufactured by at high temperature by

continuous chemical glycerolysis of fats and oils employing alkaline catalysts under a

nitrogen atmosphere (Sonntang et al., 1979) or aluminum- and zirconium-containing

mesoporous molecular sieves in supercritical carbon dioxide medium. (Sakthivel et

al.,2007) although the process suffers from several drawbacks low yield, burnt

product, distillation is required to get high purity food additive grade products.

Several bio-catalytic approaches have been also reported with excellent results for

glycerolysis in non continuous mode yielding 70-99% monoglycerides. (McNeill et

al., 1991) Ghamgui et al., 2006) achieved 70.6% yield for monoglycerides in

continuous mode with immobilized Staphylococcus simulans lipase on CaCO3 in a

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solvent-free system. Morever, high yields of monoglycerides can been achieved by

esterification of protected glycerol derivatives like 1,2-O-isopropylidene glycerol.

1,3 /1,2 -Diglyceryl ethers are naturally present as a minor components of edible fats

and oils from various sources. Nutritional properties and dietary effects suggest that

oil containing diglyceryl ethers in which 1,3- diglyceryl ethers is the major

component which plays a role in reducing serum triacylglycerol levels and, as a

result, decreases both body weight and visceral fat mass and hence useful in the

prevention of obesity and other lifestyle-related diseases. Both ethers have been

employed as a cocoa butter blooming agent and also an intermediate in the synthesis

of structural lipids. 1,3- Diglycerides can be prepared by various methods includes,

hydrolysis of triolein, glycerolysis of triglycerides and esterification of glycerol with

fatty acids (Berger et al., 1992). Most of the system use biocatalyst for the said

transformation, and reaction time is high. (Watanabe et al., 2005) reported

immobilized lipase catalyzed continuous process in a packed bed bioreactor for

regioselective synthesis of 1,3-diglycerides.

2.5.1.7 Dehydration

Dehydration of glycerol gives valuable chemicals like acrolein, and 3-

hydroxypropionaldehyde. Some of the important processes are discussed below.

A) Acrolein

Acrolein is a commercially important product which is having a key role as an

intermediate in various value added chemicals in industry. Acrolein is used in the

synthesis of various chemicals and compounds like polyester resin, L-methionine,

polyurethane, propylene glycol, glycerine, acrylic acid. The principal use of acrolein

is an intermediate in the synthesis of numerous chemicals, in particular acrylic acid

and its lower alkyl esters and DL-methionine, an essential amino acid used as feed

supplement for poultry and cattle. In the USA, in 1983, 91 to 93% of the total quantity

of acrolein produced was converted to acrylic acid and its derivatives (esters), and 5%

to methionine (Beauchamp et al., 1985). Other derivatives of acrolein are: 2-

hydroxyadipaldehyde, 1,2,6-hexanetriol, lysine, glutaraldehyde, tetrahydro-

benzaldehyde, pentanediols, 1,4-butanediol, tetrahydro-benzaldehyde, pentanediols,

allyl alcohol, quinoline, homopolymers, and copolymers (Hess et al., 1978). Among

the direct use of acrolein, its application as a biocide is the most singnificant one.

57

Acrolein at a concentration of 6-10 mg/litre in the water is used as an algicide,

molluscicide, and herbicide in recirculating process water system, irrigation channels,

cooling water towers, and water treatment ponds (Hess et al., 1978). About 66 tons of

acrolein is reported to be used annually in Australia to control submersed plants in

about 4000 km of irrigation channels (Bowmer and Sainty, 1977; Bower and Smith,

1984). Acrolein can also be used as a tissue fixative, warming agent in the methyl

chloride refigerants, lether tanning agent, and for immobilization of enzyme via

polymerization, ethrification of food starch, and the production perfumes and

colloidal metals (Hess et al., 1978; IARC, 1985).

Acrolein is commercially produced by gas phase oxidation of propylene in the

presence of Bi-Mo mixed oxide catalyst. The second root is the oxidation of propane

to acrolein/acrylic acid. This is also gas phase oxidation reaction used molybdenum

and vanadium based catalysts (Ning et al., 2008, Atia et al., 2008). There is no

commercial process operating for the production of acrolein based on glycerol.

Some of the important papers and patents based on glycerol are discussed below.

Gas-phase dehydration of glycerol to produce acrolein includes Nb2O5 catalyst (Chai

et al., 2007), silicotungustic acid supported on silica,(Satoshi Sato et al.), Activated

carbon supported silicotungstic acid, (Ning et al., 2008), different silica, alumina and,

aluminosilicate supported heteropolyacid, (Atia et al., 2008). A process for the

production of acrolein by dehydration of glycerol in the liquid phase or in the gaseous

phase, in each case solid acid catalyst, is described. The process uses glycerol-water

mixture with 10 to 40 wt. % of glycerol content. Reaction phase was liquid as well

gaseous. Reaction temperature ranged from 180 – 340 °C for liquid phase and 250-

340 °C for gaseous phase. The solid catalysts consist of H3PO4/Al2O3 or H3PO4/TiO2

for liquid phase and H-ZSM5 or H-Y Catalyst, mordenite, montmorillonite or acidic

zeolite, oxide, mixed oxide or heteropolyacids for liquid phase. According to the

authors of the said patent, the gas phase process is preferable since it enables a degree

of conversion of the glycerol of close to the 100% to be obtained, which leads to an

aqueous acrolein solution containing side products. A portion of about 10% of the

glycerol is converted into hydroxypropanone, which present as the major by-product

in the acrolein solution. The acrolein was recovered and purified by fraction

58

condensation or distillation (Neher et al., 1995). Our laboratory has obtained a few

patents on glycerol conversion to acrolein. (Yadav et al., 2010)

B) 3-Hydroxypropionaldehyde

3-Hydroxypropionaldehyde is an important intermediate for many chemicals such as

acrolein, acrylic acid, and 1,3-propanediol and is also used in polymer production.

Industrial catalytic processes by Degussa to produce 3-hydroxypropionaldehyde start

with propylene to give acrolein, which is followed by hydration to give 3-

hydroxypropionaldehyde (Haas et al., 1993). The Shell process begins with ethylene

to ethylene oxide, which on hydroformylation reaction under high pressure (150 atm)

with syngas yields 3-hydroxypropionaldehyde (Knifton et al., 2004). Both the existing

processes suffer from the separation problems, harsh reaction conditions, lower

yields, and toxic intermediate like acrolein is formed in the process.

Glycerol can be converted to 3-hydroxypropionaldehyde. Various enzymatic routs

have been reported with the yields (85-87% mol 3-hydroxypropionaldehyde/mol

glycerol) higher than those achieved by chemical synthesis (Toraya et al., 2000,

Vollenweider et al., 2004).

2.5.1.8 Chlorination

A) Introduction

Chlorination of glycerol lead to mono- and dichloropropanols which are valuable

intermediates to produce a variety of products.

Dicloropropanol is further used to produce epichlorohydrin. Epichlorohydrin is

extremely versatile chemical intermediate used in a wide variety of applications.

Approximately 76% of the world’s consumption of epichlorohydrin is used to make

epoxy resins.

It has also been used to cure propylene-based rubbers, as a solvent for cellulose esters

and ethers and in resins with high wet-strength for the paper industry (IARC 1999).

Epichlorohydrin is also used in the production of Zeospan, a specialty polyether

rubber used for automobile parts (Chem. Week 1986). There is widespread use of

epichlorohydrin as a stabilizer.

B) Commercial Applications of epichorohydrin

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a) Epoxy resins

Approximately 76% of the world’s consumption epichlorohydrin is used to make

epoxy resins which were used for corrosion resistance, solvent and chemical

resistance, hardness and adhesion.

b) Textiles

To improve wools resistance to moths, prepare fibers for dyeing, impart wrinkle

resistance and prepare anti static agent resistance and textile sizing.

c) Papers inks and dyes

To produce wet-strength paper sizing, special printing inks, textile print pastes, and

ultimately paper and paperboard products that have improved printability, pigment

retention, folding endurance and gloss.

d) Ion exchange resins

To produce anion exchangers used to clean polluted air and water.

e) Other applications

It is also used as raw material for surface active agents used in cosmetics and

shampoos; rubber exhibiting resistance to extreme temperatures, fuel oil and ozone,

for automotive and aircraft parts, seals gaskets, and agricultural products such as

incectsides, bactericides and fungicides.

Epichlorohydrin rubber is also called chlorohydrin rubber. It has excellent

comprehensive properties such as oil resistance, high and low-temperature resistance,

chemical stability, abrasion and tear resistance and small air permeability. It has

already been used in sealing parts for refrigerating compressors, expansion joints and

sealing parts for large oil transmission pipelines and sealing materials for

automobiles, planes and ships.

C) Commercial Analysis

Major ECH export countries in the world are the United States and Japan. Asia and

Eastern Europe are major import regions.

60

The current market price for epichlorohydrin is ~1 $/lb. Based on the estimated

production economics it appears that the bio-derived glycerin-to-epichlorohydrin

process is formidable competition to existing production.

Aser SRL, Dow Global Technologies, and Solvay Society are key players in the

production of epichlorohydrin. Their recently published world and U.S. patent

applications disclose technologies that claim improvements to the old art for

producing epichlorohydrin from glycerol.

Dow Epoxy announced Shanghai Chemical Industry Park (SCIP) as the selected site

for its world-scale 150,000-MTPA glycerin-to-epichlorohydrin (GTE) plant and

100,000-MPTA liquid epoxy resins plant both plants was slated to start up in the

2009-2010 timeframe (Chemical Business, 2006).

D) Various Routes and their Significance

Epichlorohydrin is prepared industrially by the various processes which involves high

temperature chlorination of propylene to allyl chloride and byproduct HCl followed

by hypo-chlorination of allyl chloride to give dichloropropanols followed by

dehydrochlorination using caustic affords epichlorohydrin. This process was first

introduced in the mid-1930s by Shell.

Another known process involves insertion of oxygen in allylic position of allyl

chloride using hydrogen peroxide over titano-silicate catalyst (Solvey process). This

process is also described in the Chinese journal Shiyou Huagong (Zugui et al., 2008).

The process starting from allyl chloride involves considerable drawbacks which

includes sacrificial use of chlorine and complication associated with the industrial use

and generation of hypochlorous acid. This process also involves formation of

unwanted chlorinated hydrocarbons involve trichloropropane, chlorinated ethers and

oligomers.

US Patent 4788351 describes process for preparation of dichloropropanols in high

yield by chlorinating allyl alcohol with chlorine gas with optionally hydrogen chloride

gas in to reaction containing aqueous hydrochloric acid (Takakuwa et al.,1998).

Showa Denko in 1980s commercialized a process in which propylene is converted to

allyl alcohol by oxidative acetoxylation to allyl acetate followed by hydrolysis. Allyl

61

alcohol is then chlorinated in aqueous HCl to give glycerol dichlorohydrin, followed

by dehydrochlorination using base to give epichlorohydrin.

In US patent 4634784 epichlorohydrin is prepared by reacting H2C:CHCH2OH (I)

with Cl at -30° to +20° and 0-10 atm in an aqueous solution. contg. 40-70% HCl,

forming HOCH2CHClCH2Cl (II), separating at least part of the HCl by heating the

reaction mixture, recycling the gas back to the first step, separating the reaction

mixture into aqueous and oil phases by cooling the liquid mixture to 40°, recycling at

least part of the aqueous phase back to the first step, and reacting the separated. oil

phase with an alkaline aqueous suspension at 40-110°, forming epichlorohydrin

(Nagato et. al., 1987). US 2860146 follows the acrolein route in which acrolein is

treated with Cl2 followed by treating the product with secondary alcohol and

aluminium tert.butoxide to give dichlorohydrin and finally dehydrochlorinating the

glycerol 1,2-dichlorohydrin with base to give epichlorohydrin (Furman et al., 1958).

One of the Dow’s patents goes through acrolein as an intermediate. In which

propylene is oxidized to acrolein in first step followed by chlorination to 2,3-

dihloropropanal in second step. 2,3- dichloropropanal is further hydrogenated to give

2,3- dichloropropanol which is dehydrochlorinated with base to epichlorohydrin.

According to an Asahi patent, acetone produced as coproduct from propylene via

Hock process for phenol, can be chlorinated to give dichloroacetone. Upon

hydrogenation, as per a Mitsubishi patent, dichloropropanol is formed.

Dehydrochlorinationwith base affords epichlorohydrin.

Glycerin is found to be low cost renewable feedstock which is obtained as byproduct

in biodiesel production. Thus, the glycerin derived from renewable resources can be

readily and effectively used in the reactions producing valuable organic compounds

for e.g. acrolein, 1, 3 propanediol, glycerol carbonate, etc.

The traditional process for conversion of glycerol to dichloropropanol involves

reacting glycerol with hydrochloric acid in presence of organic acid as the catalyst to

give dichlorohydrins as an intermediate followed by dehydrochlorination of

dichlorohydrin with base to give epichlorohydrin (Carra et al. 1979) (Scheme 5). The

process for dicloropropanol reported by Conant et al. includes purging large excess of

anhydrous HCl (up to 7 equivalents) through a stirred solution of glycerol and an

62

organic acid catalyst with atmosphere pressure of HCl. A large excess of HCl is

recommended to promote the azeotropic removal of water formed during the course

of reaction (Conant et. al., 1941).

Scheme 2.5: Glycerol chlorination

US Patent No. US 2,144,612 has used various kinds of inert water immiscible

solvents such as di-n-butyl ether, ethylene chloride, propylene chloride or

chlorobenzol for azeotropic removal of water at the suitable reaction temperature

(Britton et al., 1939).

U.S. Pat. No. 2,198,600 has tried to solve the problem of the purification and the

recovery of dichloropropanol from acid distillate by extraction using a suitable

organic solvent for dichloropropanol, preferably di-n-butyl ether (Pavel et al., 2011).

Canadian patent CA2546683A1 (Solvay process) describes the use of a catalyst based

on carboxylic acid or carboxylic acid derivatives, such as carboxylic acid anhydride a

carboxylic acid salt or a carboxylic acid ester is advantageously used (Krafft et al.,

2004).

A method described in WO2005/021476, consists of preparing dichloropropanol with

gaseous hydrogen chloride and carboxylic acid as the catalyst and continuous removal

of water of the reaction (Krafft et al., 2007).

According to patent WO2006/020234 (Dow global technology) describes process for

converting a multihydroxylated-aliphatic hydrocarbon or ester to a chlorohydrin, by

63

contacting the multihydroxylated-aliphatic hydrocarbon or ester with hydrogen

chloride at superatmospheric, atm. and subatmospheric pressure conditions for a

sufficient time and at a sufficient temp., preferably wherein such contracting step is

carried out without substantial removal of water, to produce the desired chlorohydrin

product using a catalyst that facilitates the conversion of multihydroxylated-aliphtic

hydrocarbon to a chlorohydrin for example a carboxylic acid, an ester, a lactone, an

amide or a lactam; and mixture thereof (Kruper et. al., 2006).

Patent WO2006/111810 describes semi-cotinuous process with continuous

elimination of water and dichlorohydrins. This process also involves use of organic

acid such as monocarboxylic acid with 3-10 carbon atoms or a dicarboxylic or

polycaboxylic acid with 2-10 carbon atoms (Siano et al., 2006). Conversion and

selectivity profile in convention processes is available in above patent and is shown in

Figure 2.4 and 2.5.

Figure 2.5: Composition profile of the reaction mixture over the time for the reaction

under reflux using malonic acid as catalyst

German patent No.197308 describes a method of preparing 1,3-dichloro-2-propanol

and 2,3-dichloro-1-propanol comprising hydrochlorinating glyceol and/or

monochloropropanediols with gaseous hydrogen chloride with catalysis of a

carboxylic acid, wherein said hydrochlorination is carried out solvent-free in at least

one continuous reaction zone at reaction temperatures in the range of 70-140° C and

with continuous removing of the water of reaction by distillation at reduced pressure,

64

the liquid feed containing at least 50% by weight of glycerin and/or

monochloropropanediols (Boehringer et al., 1906).

Figure 2.6: Composition profile of the reaction mixture over the time for the reaction

with stripping at 100oC using malonic acid as catalyst

US Patent 2008/0045728 (Dow global technology) describes use of a

superatmospheric partial pressure of hydrogen chloride for a sufficient time and at a

sufficient temperature, and wherein such contracting step is carried out without

substantial removal of water, to produce the desired chlorohydrin product; wherein

the desired product or products can be made in high yield without substantial

formation of undesired over chlorinated byproducts. This process also uses catalyst

such as carboxylic acid and its derivatives, an anhydride, an acid chloride, an ester, a

lactone, a lactam, an amide, a metal organic compound, a metal salt, any compound

convertible to a carboxylic acid under the reaction conditions of the process, or a

combination thereof (Kruper et al., 2005).

According to patent by Solvay WO2008/107468A1 describe the continuous processes

for the production of dichloropropanols from glycerol and /or monochloropropandiol

using aqueous or anhydrous hydrochloric acid as chlorinating agent and carboxylic

acid and its derivatives as the catalyst. The process claims manufacture of

dichloropropanol in reactor which is supplied with one or more liquid streams sum of

65

which contains glycerol and monochloropropanediol. Out of all streams at least one of

all is liquid recycling stream which comprises one of the following components

glycerol monochloropropanediol, chlorinating agent, salt, glycerol ester,

monochloropropanediol ester, water catalyst solvent, dichloropropanol ester, and

glycerol oligomer, chlorinated or esterified chlorinated oligomer (Krafft et al., 2008).

Korean patent KR/2008/038284 describes a continuous method comprising of the

chlorination of glycerol in hydrogen chloride atmosphere in the absence of catalyst to

provide dichloropropanol followed by the dehydrochlorination of dichloropropanol in

presence of catalyst to give epichlorohydrin (Cheol et al., 2008).

Chinese patent CN101195607 describes process in which glycerol is reacted with

hydrogen chloride at 120 oC for 20h in presence of glacial acetic acid to give

dichloropropanols with 60% selectivity. The second step i.e. dehydrochlorination of

dichloropropanols to epichlorohydrin catalyzed by 10% NaOH solution (Li et al.,

2008).

WO 2005054167 a patent by Solvay describes feeding HCl in a program of 5.2 mol/h

for 2 h, 3.8 mol/h for 100 min, and 1.3 mol/h for 317 min into 453 g glycerol and 29.5

g HOAc at 110 °C gave a product contg. glycerol 4.6,1-chloro-2,3-dihydroxypropane

166, 2-chloro-1,3-dihydroxypropane 40, 1,3-dichloropropan-2-ol 475, 2,3-

dichloropropan-1-ol 11,diglycerol 1, monochlorinated diglycerol 3, HOAc 21, org.

acetates 43, water 178, and HCl 58.8 g/kg (Krafft et al., 2005).

DE1075103 explains the continuous process in which anhydrous HCl was introduced

into a vessel containing. glycerol at 110-20°/460-560 mm., causing the azeotrope of

H2O (35%) and dichlorohydrin (50%) to distil with excess HCl (15%). The distillate

and 10-20% lime water were heated at 60°/100 mm. to give epichlorohydrin which

distilled at 50-60° as an azeotrope with H2O (Andreas et al., 1960).

I) Analysis of patents

The patented literature shows the following:

� Reaction mechanism zero order kinetics

� Use of HCl gas, pressure (1-10 atm)

66

� Presence of carboxylic acid as the catalyst

� Azeotropic distillation, reactive distillation

� Multiple rectors and seperators

� Separation of dichloropropanol least bioling

� Selectivity of 1,3-dichloropropan-2-ol most desirable; more reactive(100 times)

Also, homogeneous catalysts like carboxylic acids were widely used in conventional

processes are reported in literature.

II) Why Carboxylic acid used as the catalyst?

• The mechanism of the formation of glycerol-dichlorohydrin involves

formation of acetate followed by substitution reaction with halogen acid to

give chlorohydrins (Ref:-Oct.5, 1956)

• The presence of carboxylic acid in the reaction enhances the rate of the

reaction.

• Solvay uses carboxylic acid & their derivatives such as anhydride, carboxylic

acid chloride, salts having higher boiling point.( Ref.:- CA 2 546 683)

• A Dow chemical uses acetic acid as the catalyst with high pressure of

hydrogen chloride. (Ref. :- WO2006/020234)

F) Value added chemicals from chlorinated analogues of glycerol

Glycerol on chlorination gives Monochloropropanediols and dichloropropanol. These

chlorinated analogues can be converted into industrially valuable chemicals. Scheme

5 and 6 shows various possible products form mono and dichloropropanols

respectively. These products find wide applications in pharmaceuticals, paints,

polymers, foods, pestiside etc.

67

Scheme 2.6: Valorization of Monochloropropanediol

68

Scheme 2.7: Valorization of Dichloropropanol

SUMMARY

Current research work is focused on synthesis on novel nano catalyst by combustion

synthesis method, which offers efficient method with high catalytic activity and

69

selectiveity towards desired product. Their applications in industrially important

chemicals starting with glycerol, which were not reported elsewhere. Conversion of

glycerol to epichlorohydrin has been patented by many which are in public domain.

The all of the above patents demonstrate the epichlorohydrin production by using

organic acids. In the current work, all the catalyst systems which are prepared and

screened for conversion of glycerol to dichloropropanol are the original contributions

and most of them are patented. Hence the catalyst systems used are non-infringing,

even if the reaction conditions fall in the range of patented claims. Further,

derivatization is done to produce new processes.