chapter 3 synthesis of acrolein by dehydration of glycerol...

Synthesis of acrolein by dehydration of glycerol

45

© Suraj Onkar Katole, Institute of Chemical Technology (ICT), Mumbai, India

CHAPTER 3

SYNTHESIS OF ACROLEIN BY DEHYDRATION OF GLYCEROL IN FIXED

BED CATALYTIC REACTOR


46


3.1. INTRODUCTION

As stated in previous chapter, fossil fuel based economy has many drawbacks

with regard to sustainability and global warming and thus it becomes necessary to shift

from the non renewable to the renewable feedstock based chemical and allied industries.

In the 21st century, utilization of renewable biomass into the conversion of industrially

important chemical substances has been intensely pursued by using principles of green

chemistry. Plant derived sugars and other compounds should be used to synthesize the

necessary compounds for the production of pharmaceuticals, agricultural chemicals,

plastics, and transportation fuels. The biorefinery concept is analogous to today’s

petroleum refinery, which produce multiple fuels and product from petroleum.

Biorefinery is a facility that integrates biomass conversion process and equipment to

produce fuels, power and chemicals from biomass (Dubois et al. 2006).

Glycerol, one of the potential renewable resources, is obtained as a by-product/co-

product in hydrolysis of fat, soap-manufacturing process and production of biodiesel. In

the biodiesel production processes the ratio of biodiesel to crude glycerol produced are

about 9:1. It is predicted that as the biodiesel production increases, supply of the glycerol

will be excess than the market demand and glycerol cost will further decrease. Therefore,

a new application of glycerol needs to be found. Dehydration of glycerol produces two

important commodity chemicals, 3-hydroxypropionaldehyde and acrolein. Acrolein is an

important bulk chemical used as a feedstock for acrylic acid production, pharmaceuticals

intermediates, fibre treatments, and methionine (used in animal feed) (Hess et al. 1978).

The most significant application of acrolein is an herbicide to control the growth of

aquatic plants. It kills the plant cells by reaction with biological molecules and

destruction of the cell membrane integrity, as well as by its affinity for sulfydryl groups,

causing the denaturation of vital enzymes (Corma et al. 2007).

Acrolein is the simplest unsaturated aldehyde. The primary characteristic of

acrolein is its high reactivity due to conjugation of the carbonyl group with a vinyl group.

Acrolein is a highly toxic material with extreme lacrimatic properties. At room

temperature, acrolein is highly volatile, respiration inhibitor and flammable liquid.

Special care in handling is required because of the flammability, extraordinary high

reactivity, pungent order and high toxicity of acrolein (Mcketta et al. 2006).


47


3.1.1 Commercial value of acrolein

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

intermediate in various value added chemicals in a chemical industry. Acrolein is used in

the synthesis of following chemicals and compounds:

Polyester resin

L-methionine

Polyurethane

Propylene glycol

Glycerin (when biodiesel concept was not practiced; now it is exactly opposite as

will be discussed in this chapter)

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 past, ~91 to

93% of the total quantity of acrolein produced was converted to acrylic acid and its

derivatives (esters), and 5% to methionine. However, more than 80% of the refined

acrolein that is produced goes into synthesis of methionine (Liu et al. 2012). Other

derivatives of acrolein including are: 2-hydroxyadipaldehyde, 1, 2, 6-hexanetriol, lysine,

glutaraldehyde, tetrahydro-benzaldehyde, pentanediols, 1, 4-butanediol, allyl alcohol,

quinoline, homopolymers, and copolymers. Among the direct use of acrolein, its

application as a biocide is the most important one. Acrolein at a concentration of 6-10

ppm in the water is used as an algaecide, molluscicide, and herbicide in re-circulating

process water system, irrigation channels, cooling water towers, and water treatment

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

chloride refrigerants, leather tanning agent, and for immobilization of enzyme via

polymerization (Gerhartz et al. 2008).

3.1.2 Various routes for the synthesis of acrolein

There are two major routes to produce acrolein, one is based on a non-renewable

resource like petroleum feedstock and, another one is on a renewable resource like


48


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

presence of Bi-Mo mixed oxide catalyst (Beauchamp et al. 1985, Bowmer and Sainty

1977, Carrazan et al. 2006). The second route is the oxidation of propane to

acrolein/acrylic acid. This is also gas phase oxidation reaction using molybdenum and

vanadium based catalysts (Zhao and Wachs 2008, Wu et al. 2007).

Production of acrolein by dehydration of glycerol is not yet commercialized. Some of the

important papers and patents based on glycerol are discussed below. Bo-Qing Xu et al.

(2007) reported gas-phase dehydration of glycerol to produce acrolein at 315 °C over

Nb2O5 catalyst. They achieved 51 mol% acrolein selectivity; also observed deactivation

after using this catalyst. Tsukuda et al. (2007) found that silicotungustic acid supported

on silica with mesopores of 10 nm showed stable catalytic activity with the highest

acrolein selectivity of greater than 85 mol%. The catalyst showed gradual deactivation

after 5 h. Ning et al. (2008) reported activated carbon supported silicotungustic acid

catalysts to produce acrolein from glycerol dehydration. They found that 10%

silicotungustic acid exhibited the space time yield of acrolein 68.5 mmol/ (g.h). Reaction

was carried out at 330 °C under atmospheric pressure for 5 h. Watanabe et al. (2005) have

reported glycerol dehydration reaction at high temperature and high pressure water (573

to 673 K, saturated pressure or 34.5 MPa) using a batch and flow apparatus. Glycerol

conversion was 90% and acrolein selectivity was 80% with H2SO4 in supercritical

condition (673 K and 34.5 MPa).

Ott et al. (2006) conducted the reaction in a high pressure plug flow reactor from

300-390 °C, 25-34 MPa, 10-60 s residence time and varying amount of zinc sulfate. They

have reported that near sub-critical temperature, increase in the amount of salt enhances

the glycerol conversion. The maximum acrolein selectivity was 75 mol% at 360 °C, 25

MPa, 470 ppm zinc sulfate and a conversion of 50%. Neher et al. (1995) describe the

process for the production of acrolein by dehydration of glycerol in the liquid phase or in

the gaseous phase with solid acid catalysts. They used glycerol-water mixture with 10 to

40 wt. % of glycerol content. Reaction phase was liquid as well gaseous. Reaction

temperature was in the range from 180 – 340 °C for liquid phase and 250- 340 °C for

gaseous phase. The solid catalysts consisted of H3PO4/Al2O3 or H3PO4/TiO2 for liquid


49


phase and H-ZSM5 or H-Y Catalyst, mordenite, montmorillonite or acidic zeolite, oxide,

mixed oxide or heteropolyacids for gaseous phase. According to this 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.

Heteropolyacids are less harmful to the environment than mineral sulfuric acid. It

was reported that supported heteropolyacid effectively work in the dehydration reaction

(Izumi et al. 1983).

Since it was reported that heteropolyacids give better selectivity to acrolein (Atia

et al. 2008, Tsukuda et al. 2007, Ning et al. 2007), dodeca-tungustophoric acid (DTP) as

heteropolyacid was targeted in this work for dehydration of glycerol to acrolein process.

The present work deals with use of DTP/HMS (dodeca-tungustophoric acid (DTP)

supported on hexagonal mesoporous silica (HMS)) for dehydration of glycerol to acrolein

in vapour phase fix bed catalytic reactor (Yadav et al. 2009). Scheme.3.1 shows the

dehydration of glycerol with acrolein as major product.

Scheme 3.1: Dehydration of glycerol to acrolein


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3.2. EXPERIMENTAL

3.2.1 Chemicals

The following chemicals were procured from reputed firms and used without any

further purification: Glycerol (LR), ethanol, dodeca-tungustophoric acid (DTP) (AR),

methanol (M/s. s.d. Fine Chemicals ltd, Mumbai, India), tetraethyl orthosilicate (TEOS)

(Fluka, Germany), hexadecyl amine (Spectrochem Ltd., Mumbai, India).

3.2.2 Catalyst preparation

Hexagonal mesoporous silica (HMS): The ordered hexagonal mesoporous silica

(HMS) was prepared using the following procedure. 5 g Dodecyl amine was dissolved in

41.8 g of ethanol and 29.6 g of distilled water. 20.8 g of tetraethyl orthosilicate (TEOS)

was added under vigorous stirring. The addition of ethanol improved the solubility of the

template. The reaction mixture was aged for 18 h at 30 °C. The clear liquid above the

white colored precipitate was decanted and the precipitate HMS was dried on a glass

plate. The template was removed by calcination by keeping the resultant material at 650

°C in air for 3 h.

20% w/w DTP/HMS: It was prepared by incipient wetness technique for which

2 g of dry dodecatungstophosphoric acid was weighed accurately. This was dissolved in 8

ml of methanol. The solution was added in small amount of 1 ml each time to the silica

molecular sieve with constant stirring using a glass rod. The solution was added at time

intervals of 2 min. At the outset of addition of DTP solution on HMS was in powdery

form but on complete addition it formed a paste. The paste on further kneading for 10

minutes resulted in a free flowing powder. The performed catalyst was dried at 120 °C

for removal of water and other occluded volatiles materials. Then it was subsequently

calcined at 300 °C temperature for 3 h. to get active catalyst (Yadav and Manyar 2003,

Yadav and Lande 2006). 20% w/w DTP/K-10 (Yadav and Kirthivasan 1995; Yadav and

Krishnan 1998; Bokade and Yadav 2012), 20% Cs-DTP/K-10 (Yadav et al. 2003; Yadav

and Asthana 2003) and 20% w/w DTP/OMS (octahedral molecular sieves) were prepared

as the method reported in literature (Yadav and Mewada 2012; Yadav and Mewada

2013). 20% w/w NiO/HMS, 20% w/w CoO/HMS, 20% w/w CuO/HMS, and 20% w/w


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Fe2O3/HMS were prepared by adding nitrate solution of respective metal precursor to

HMS by wet incipient technique and further calcination was done at 650 0C for 3 h.

3.2.3 Experimental set up and analytical method

Dehydration of glycerol was carried out at atmospheric pressure in a fixed bed

catalytic reactor, with a down flow fixed bed equipped with as upstream vaporizer and

downstream condenser. The liquid feed was fed by double piston pump (Well Chrom

HPLC-pump K-120) to the vaporizer by using N2 as a carrier gas. The catalyst was

loaded in the form of powder to form catalytic bed. Inert glass bead were used as packing

material and placed above and below the catalyst bed. The temperature of the bed was

maintained with the help of PID controller. Flow rate of the gas was measured and

controlled by mass flow controllers (MFC). Reaction samples were collected in liquid

form, from the bottom of the condenser. Catalyst was activated under nitrogen flow for 2

h prior to use at the reaction temperature. The schematic diagram of the fixed bed

catalytic reactor was shown in Figure 3.1. The analysis of reaction products was carried

out using GC (Chemito 1000) equipped with a BPX-50 capillary column (length: 30m,

ID: 0.25mm) and with FID detector. Confirmation of products was done by GC-MS

using same capillary column.


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Figure 3.1 Schematic diagram of fixed bed catalytic reactor

Notations: 1. Pump, 2. Vaporizer, 3. Reactor, 4. Condenser, 5. Phase Separator, 6.

Receiver.

3.3 RESULTS AND DISCUSSION

3.3.1 Catalyst characterizations of 20 %( w/w) DTP supported on K10, HMS and OMS.

The three different supports K10, HMS and OMS were used to incorporate

dodecatungstophosphoric acid. The total acidity measurement of K10 and HMS were

carried using NH3-TPD were found to 0.139 mmol/g and 0.021 mmol/g, respectively

while basicity measurement of OMS was carried out by CO2-TPD was measured to be

4.76 mmol/g. 20% (w/w) DTP/K10 and 20% (w/w) DTP/HMS are completely

characterized again during this work for both virgin and used catalysts by NH3-TPD,

FTIR, XRD, SEM, and BET surface area, and the some characterization was published

by our group (Yadav and Kirthivasan 1995; Yadav and Krishnan 1998; Yadav and

Asthana 2003). 20% (w/w) DTP/OMS was characterized similarly. Only a few salient

features are reported here. The acidity of 20% w/w DTP/K-10 catalyst was measured by

NH3-TPD and found to be 0.423 mmol/g. The IR spectrum of 20% (w/w) DTP/K10, 20%

(w/w) DTP/HMS and 20% (w/w) DTP/OMS catalyst exhibits bands at 3450, 1652, 1092,

990.7, 893, 817, and 466 cm-1. The XRD analysis confirmed that 20% w/w DTP/K-10 is

crystalline in nature. The BET surface area of 20% w/w DTP/K-10 was found to be 135

m2/g. The preparation of 20% w/w DTP/HMS and its application is also reported by our

group (Yadav and Manyar 2003). The acidity of 20% w/w DTP/HMS was measured by

NH3-TPD and found to be 0.130 mmole/g. 20% w/w DTP/HMS characterized by XRD

and no crystalline phase was detected which indicates, the uniform distribution of DTP in

HMS. Hence, these materials are completely amorphous in nature. The BET surface area

of 20% w/w DTP/HMS was found to be 299.7 m2/g and is a type-IV isotherm, indicates

mesoporosity is retained after DTP loading. The OMS-2 catalyst has a one-dimensional

tunnel structure formed by 2 ×2 edge shared MnO6 octahedral chains. X-ray diffraction

patterns show d-spacing values which match with the reported data of OMS-2 and the

corresponding (h k l) values are (1 0 1), (0 0 2), (3 0 1), (2 1 1), (3 1 0), (1 1 4) and (6 0


53


0) at 2 theta values of 12.7, 18.0, 28.7, 37.4, 41.8, 50.0, 55.3. When DTP is dispersed in

OMS-2, there is a linear decrease in surface area from 69.4 to 42.4 m2/g.

Keggin type heteropoly acid (HPA) catalysts are strong Bronsted acids. HMS is neutral.

The active species in DTP/HMS are Bronsted acids arising from the

doedcatungstophosphoric acid was reported by us earlier (Yadav and Manyar 2003) and

(Bardin et al. 1998). There are abundant silanol groups (#Si-OH) on the surface of

mesoporous silica owing to its amorphous wall structure. With these reactive silanol

groups, one can effectively immobilize organic functional groups onto a silica surface

through either covalent bonding or hydrogen bonding (Rouxhet and Sempels 1974). On

silica, only H-bond formation occurs indicating a rather weak acidity of the silanol

groups, quantitatively characterized by pKa = 7. (Tsyganenko et al. 2000) Hexagonal

mesoporous silica is neutral and does not create acidity by steam generated in situ during

dehydration, particularly at the reaction temperature of 225 oC.

3.3.2 Catalysts characterization (20% DTP-HMS)

3.3.2.1 Surface area analysis

The specific surface area, pore volume and pore diameter were determined by N2

adsorption-desorption isotherm at low temperature (77 K) using a Micromeritics ASAP

2010 instrument of fresh and used 20% (w/w) DTP/HMS. The catalyst samples were

degassed under vacuum at 200ºC for 3 h. The measurements were made using N2 gas as

the adsorbent and with a multipoint method. Isotherms were measured at liquid nitrogen

temperature. Surface area, pore volume and pore diameter were calculated from N2

adsorption-desorption isotherm using conventional BET method. Figures 3.2 and 3.3

show the isotherm of fresh and used catalyst. According to results it can be concluded

that surface area of the fresh catalyst was decreased because of the coke deposition

occurred inside the pore of the catalyst. In support of these results elemental analysis was

carried out and it was found that 3.87% carbon was deposited on the catalyst. Results

were shown in Table. 3.1.


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Table 3.1 Surface areas, pore volume and pore diameter of fresh and used catalyst

Catalyst (20% DTP-HMS) Fresh Used

BET Surface Area 299.7 m2/g 1.32 m2/g

Pore Volume 0.204 cm3/g 0.002 cm3/g

Pore Diameter 27.16 A0 ----

Figure 3.2 Adsorption desorption isotherm of fresh 20%DTP-HMS catalyst


55


Figure 3.3 Adsorption desorption isotherm of used 20%DTP-HMS catalyst

3.3.2.2 Temperature programmed desorption (NH3-TPD)

Acidic sites of the catalyst were determined with temperature programmed

desorption (TPD) analysis using Autochem II 2910 (Micromeritics, USA) with ammonia

as probe molecules. A quantity of 30 mg of the catalyst was taken in a quartz tube and

degassed up to 300 0C under the flow of nitrogen. Then ammonia was passed for 30 min

to adsorb the ammonia over the surface of the catalysts at room temperature. Physisorbed

gas was removed by passing inert nitrogen at room temperature. Chemisorbed ammonia

was desorbed by using temperature programmed desorption and detected by TCD. NH3-

TPD data of fresh and used 20% DTP-HMS catalyst are shown in Figures 3.4 and 3.5.

NH3-TPD data of used catalyst indicate that acidity of the used catalyst has completely

decreased. This is because of deposition of the coke during reaction and also leaching of

DTP during the process of washing of the used catalyst.


56


Fig.3.4. NH3-TPD of fresh 20% (w/w) DTP/HMS catalyst

Figure 3.5 NH3-TPD of used 20% (w/w) DTP/HMS catalyst

3.3.2.

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58


3.3.2.4 Elemental analysis by EDX

Elemental analysis of fresh and used catalyst was also done by EDX and it was

found that the used catalyst contain 3.87% carbon present on the catalyst. These carbons

are due to coke deposition inside the catalyst during reaction, results were shown in Table

3.2.

Table 3.2 Elemental analysis by EDX

3.3.3 Efficacies of different support and catalyst screening

20% w/w DTP was loaded on different support like K-10 (acidic), HMS (neutral)

and OMS (basic) to evaluate the effect of support on glycerol conversion and acrolein

selectivity. Although, all the catalysts have the same 20% w/w DTP loading, it was

observed that neutral support (HMS) showed better selectivity for acrolein as compared

with other support (Table 3.3). The increase in selectivity also can be due the presence of

free hydroxyl group which make the catalyst more hydrophilic in nature. Therefore,

various HMS supported catalysts such as 20% w/w CoO/HMS, 20% w/w CuO/HMS,

20% w/w NiO/HMS, 20% w/w Fe2O3/HMS, 20% w/w CsDTP/HMS and 20% w/w

DTP/HMS were prepared and screened for vapor phase glycerol dehydration reaction.

Recently, the redox active metals such as copper, iron and nickel were used in the

catalyst composition for dehydration of glycerol to acrolein (Miranda et al. 2014; Lei et

Elements % Mass of fresh

20%(w/w) DTP/HMS

% Mass of used

20%(w/w) DTP/HMS

C ---- 3.87

O 41.53 40.97

Si 29.90 30.25

W 28.57 24.91

Total 100 100


59


al. 2013). Therefore, copper, iron, nickel and cobalt were supported on HMS and their

activity for acrolein preparation was evaluated. However, it was observed that HMS

supported copper, iron, nickel and cobalt catalysts showed poor acrolein selectivity as

compared to heteropoly acid based catalysts such as 20% w/w CsDTP/HMS and 20%

w/w DTP/HMS, which can be due to redox properties of these metals (Figure 3.8).

Typical reaction conditions were: 1.0 g of catalyst loading, 225 0C of reactor bed

temperature, 225 0C of preheator temperature, 20% (w/w) glycerol solution, 10.2 ml/h of

feed flow rate (glycerol solution), 1.5 lit/h of N2 flow rate, 4 h reaction duration and

10.74 h-1 of WHSV. 20% w/w DTP/HMS was found to be the best catalyst as compared

to other catalysts. The increase in activity can be due to the synergistic effect of DTP and

hydrophilic nature of HMS support which has high surface area and mesoporosity.

Hence, further, experiments were carried out by using 20% w/w DTP/HMS catalyst.

Table 3.3 Efficacy of different support

Catalyst % Conversion

(glycerol)

% Selectivity

Acrolein Hydroxyacetone Others*

20% w/w DTP/K-10 89 50 10 40

20% w/w DTP/HMS 94 80 9 11

20% w/w DTP/OMS 62 45 14 41

*acetaldehyde, propionaldehyde, acetone, allyl alcohol

Reaction conditions: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 225 0C, 1.5

L/h of N2 flow rate, 10.2 ml/h of glycerol flow rate, 10.74 h-1 of WHSV, 4 h.


60


Figure 3.8 Catalysts screening

Reaction conditions: 20% (w/w) glycerol solution, 1.0 g catalyst weight, 225 °C

temperature, 1.5 lit/h N2 flow rate, 10.2 ml/h feed flow rate (glycerol solution), 10.74 h-

1WHSV, 4 h.

3.3.4 Effect of temperature

The glycerol conversion as a function of temperature was studied in the range of

200 to 325°C under similar reaction conditions over 20% w/w DTP-HMS catalyst. It was

observed that conversion of glycerol increased with increasing temperature from 200 to

325°C. At 200°C conversion was 61% which increased up to 96% at 325°C. It was found

that after 225°C there is a marginal increase in conversion up to 325°C from 94 to 96.0%

respectively. But selectivity of acrolein was highest at 225°C and found that 80%. Above

225°C, selectivity of acrolein decreased up to 325°C; which can be attributed to carbon

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62


after 10, 13, 15 and 19 h (Figure 3.10). 50% w/w DTP/HMS has more catalyst active

sites and hence it takes longer time to deactivate as compared to 20% w/w DTP/HMS.

The deactivation of 20% w/w DTP/HMS catalyst was further studied by NH3-TPD, BET-

surface area, SEM and EDX analysis.

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63


Figure 3.10 Effect of DTP loading on HMS

Reaction conditions: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 225 0C, 1.5

L/h N2 of flow rate, 10.2 ml/h of feed flow rate, 10.74 h-1 of WHSV.

3.3.6 Effect of glycerol concentration

Different concentrations of glycerol such as 10%, 20% and 50% (w/w) were used

to evaluate the activity of the catalyst. It was observed that 10% and 20% (w/w) of

glycerol solution gave almost similar results. However, 50% (w/w) of glycerol solution

resulted into a decrease in glycerol conversion as well as acrolein selectivity. This is due

to the fact that as concentration of glycerol increases on sites; it leads to cracking and

coking of the catalyst. Hence there is decrease in selectivity and conversion. Hence, 20%

w/w of glycerol solution was used for further optimization (Figure 3.11).

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Effect of

eaction. It wa

tivity of acr

ed away by N

rate was fou

0

20

40

60

80

100

Per

cen

tage

(%

)

Onkar Katole

Fig

onditions: 20

tem

N2 Flow rate

N2 flow rate

as observed

rolein decre

N2 gas, and

und to be opt

5.1

e, Institute of

gure 3.12 E

0% (w/w) gly

mperature, 1.

es 0.72, 1.5,

that with in

ased. This i

did not get

timized and

10.2

Con

Synthesis o

65

Chemical Tec

ffect of feed

ycerol soluti

5 L/h N2 flo

, and 3.0 L/h

ncrease in N

is because a

enough time

used for furt

20

version S

of acrolein b

chnology (ICT

d flow rate

on, 1.0 g cat

ow rate, 4 h.

h were selec

2 flow rate f

at higher N2

e to get cond

ther study (F

0.4

Selectivity

y dehydratio

T), Mumbai, In

talyst weight

cted to estab

from 0.72 L

2 flow rate,

densing. Hen

Figure 3.13)

40.8

on of glycero

ndia

t, 225°C

blish its effec

/h to 3.0 L/h

acrolein wa

nce 1.5 l/h N

.

ol

ct

h,

as

N2

Reac

3.3.9

loadin

expec

due t

found

© Suraj

tion conditio

Effect of ca

Effect of

ng the reac

cted that wit

to proportion

d optimum a

0

20

40

60

80

100

Per

cen

tage

(%

)

Onkar Katole

Fi

ons: 20% (w

atalyst loadin

f catalyst lo

tor with 0.2

th increase i

nal increase

and used furt

0.72

e, Institute of

igure 3.13 E

w/w) glycerol

weight, 225

ng

oading with

25, 0.5, 1.0

in catalyst lo

in catalyst a

ther for reusa

Conv

Synthesis o

66

Chemical Tec

Effect of N2

l solution, fe

°C temperat

the conver

, and 2.0 g

oading, the

active sites.

ability study

1.5

version Se

of acrolein b

chnology (ICT

Flow rate

eed flow rate

ture, 4 h.

rsion of gly

g of 20%DT

life of cataly

Hence 1.0 g

y (Figure 3.1

3

electivity

y dehydratio

T), Mumbai, In

e 10.2 ml/h,

ycerol was

TP-HMS cat

yst can also

g of catalyst

4).

3

on of glycero

ndia

1.0 g catalys

evaluated b

talyst. It wa

be increase

t loading wa

ol

st

by

as

ed

as

Rea

3.3.1

After

with

surfa

befor

filtrat

than

found

© Suraj

action condit

0 Reusabilit

Catalyst r

r the comple

water and m

ce of the ca

re using in t

tion. Hence,

the previou

d that after

0

20

40

60

80

100

Per

cen

tage

(%

)

Onkar Katole

Fig

ions: 20% (w

fl

ty study of c

reusability s

etion of react

methanol tw

atalyst. Then

he next batc

, actual amo

us batch. Th

completion

2

e, Institute of

ure 3.14 Eff

w/w) glycero

flow rate, 225

atalyst

study was c

tion, the cata

wo three tim

n it was filt

ch of reactio

ount of catal

he loss of ca

n the reactio

1

Conv

Synthesis o

67

Chemical Tec

fect of catal

ol solution, f

5°C tempera

arried out u

alyst was co

mes to remov

ered and dr

on. There wa

lyst used in

atalyst was

on catalysts

0

version S

of acrolein b

chnology (ICT

lyst loading

feed flow rat

ature, 4 h.

using optimi

ollected from

ve adsorbed

ried at 120 °

as predictab

the next ba

made-up wi

s undergo d

0.5

Selectivity

y dehydratio

T), Mumbai, In

te 10.2 ml/h

ized reaction

m the reactor

d material pr

°C for 2 h,

le loss of ca

atch, was alm

ith fresh cat

deactivation

0.25

on of glycero

ndia

, 1.5 lit/h N2

n parameter

r, and washe

resent on th

and weighe

atalyst durin

most 5% les

talyst. It wa

due to cok

ol

2

s.

ed

he

ed

ng

ss

as

ke

depos

leach

reuse

Reac

© Suraj

sition. In reu

hing of DTP

e this catalys

tion conditio

0

20

40

60

80

100

Per

sen

tage

(%

)

Onkar Katole

use study co

at the time

st (Figure 3.

Figu

ons: 20% (w

weight, 1.5

e, Institute of

onversion an

of catalyst

15).

ure 3.15 Cat

w/w) glycerol

5 lit/h N2 flo

Fresh

Conv

Synthesis o

68

Chemical Tec

nd selectivity

washing aft

talyst reusa

l solution, fe

w rate, 225°

version S

of acrolein b

chnology (ICT

y is drastica

er first use.

ability study

eed flow rate

°C temperatu

Used

Selectivity

y dehydratio

T), Mumbai, In

ally decrease

Hence it wa

y

e 10.2 ml/h,

ure, 4 h.

on of glycero

ndia

ed because o

as planned t

1.0 g catalys

ol

of

to

st


69


3.4 CONCLUSION

Continuous synthesis of acrolein by dehydration of glycerol was investigated in a

fixed bed catalytic reactor using several solid acid catalysts. Out of them 20% w/w DTP-

HMS catalyst gives high glycerol conversion and selectivity towards acrolein. 98%

conversion of glycerol and 80% selectivity towards acrolein were obtained at optimized

reaction conditions. The various process parameters, such as effects of temperature,

glycerol concentration, feed flow rate, N2 flow rate and catalyst loading were studied and

optimized. This catalyst shows extremely good result at lower temperature at 225 °C as

compared to other published literature so far. Catalyst was well characterized before and

after use using NH3-TPD, BET-surface area, SEM image and EDX analysis, to find out

exact reason for catalyst deactivation. Deposition of carbon on the surface of the catalyst

is major concern of this reaction, so development of reusable catalyst for this process was

the emphasis for further study. In next chapter, a new catalyst development is presented

to overcome these entire problems.

chapter 3 synthesis of acrolein by dehydration of glycerol...

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