Selective Dehydration of Glycerol to Acrolein: Development of Efficient

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Selective Dehydration of Glycerol to Acrolein: Development of Efficient and Robust Solid Acid Catalyst MUICaT-5 Ganapati D. Yadav, Rajesh V Sharma, and Suraj O Katole Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie401098n • Publication Date (Web): 28 Jun 2013 Downloaded from http://pubs.acs.org on July 7, 2013

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Industrial & Engineering Chemistry Research

22 23

Abstract:

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Valorization of bioglycerol to industrially relevant products has been targeted worldwide

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to make biodiesel production cost competitive. Among several bulk chemicals derived

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from glycerol, synthesis of acrolein/acrylic acid is one route which is favoured for which

27

several catalysts and processes have been proposed in literature. The present work reports

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gas phase dehydration of glycerol to acrolein by using several catalysts and supports.

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Dodecatungstophosphoric acid supported (DTP) on hexagonal mesoporous silica (HMS)

30

showed promise.

31

selectivity as compared to K-10 clay, and octahedral molecular sieves (OMS). 20% w/w

32

DTP/HMS catalyst resulted in 94% of glycerol conversion and 80% of acrolein

33

selectivity at 225 0C. However, it suffered with severe deactivation due to coke

34

deposition. Various techniques such as NH3-TPD, BET-surface area, SEM image and

35

EDX analysis were used for catalyst deactivation study. Then a new robust catalyst,

36

MUICaT-5, was then synthesized by using deactivation data of 20% w/w DTP/HMS

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catalyst. MUICaT-5 catalyst gave 86% of glycerol conversion and 60% of acrolein

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selectivity. The stability and activity of the MUICaT-5 catalyst were evaluated by time on

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stream (TOS) studies up to 100 h at 275 oC. After regeneration, reusability of MUICaT-5

40

catalyst was carried out up to six times, without affecting acrolein selectivity and glycerol

41

conversion. Catalyst reusability was also supported by characterization using NH3-TPD,

42

BET-surface area measurements, SEM and EDX techniques.

It was observed that HMS acted as better support for acrolein

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Keywords: Biomass, Bioglycerol, Acrolein, Heteropoly acid, HMS, Solid acid catalyst,

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MUICaT-5, Dehydration.

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1. INTRODUCTION

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The spectacular rise in demand for clean fuels and chemicals from renewable resources

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has led to intensive research to develop industrial applications of biomass of all sorts. A

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lot of emphasis on biodiesel production is a result of such demand.1 Glycerol is a main

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co-product of biodiesel production with 10% w/w mass. Glycerol is a very promising

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low-cost feedstock for producing a range of value-added specialty and fine chemicals.1-3

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The chemistry of glycerol shows that with its three hydroxyl groups it can undergo

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dehydration, reforming, oxidation, hydrogenolysis, etherification, and esterification

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reactions to produce several commodity chemicals.4-6 Use of catalysis in these processes

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will be helpful in developing sustainable chemical production processes. Dehydration of

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glycerol produces two important bulk chemicals, namely, 3-hydroxypropionaldehyde and

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acrolein. Catalytic conversion of glycerol could offer a cost effective and sustainable

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alternative route for the present acrolein production technology which based on

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petroleum-derived propylene. Acrolein is an important and versatile chemical. It finds

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direct applications in a spectrum of areas ranging from medicine, water treatment,

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petroleum industry and formulations industry as biocide. For instance, acrolein is used for

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the synthesis of agrochemicals like methionine, fragrances and dyes. It also acts act as a

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precursor for the production of acrylic acid, acrylic acid esters, super absorber polymers

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and detergents.2,7-9

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

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

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acrolein/acrylic acid.10-12 It is a vapor phase oxidation reaction using molybdenum and

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vanadium based catalysts.13 The production of acrolein by dehydration of glycerol is not

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yet commercialized. Various reports are available for glycerol dehydration reaction.

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Solid acid catalysts such as sulfates, phosphates and zeolites have been used

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either in gaseous or liquid phase reactions.14-17 Acidic ZSM-5 or HY zeolites give 75% of

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acrolein yield with complete conversion of glycerol at 250-340 0C, but they suffer from a

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sharp deactivation. Dehydration of glycerol is also reported in supercritical water (T >

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374 0C, P >221 atm) with liquid acid H2SO4 to get acrolein selectivity of 84% at 40% of

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glycerol conversion or with zinc sulfate salt as catalyst with 75% of acrolein selectivity at

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50% of glycerol conversion.17 Acrolein selectivity up to 80% at 90% of conversion was 3 ACS Paragon Plus Environment

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reported with H2SO4 as a catalyst at 400 0C,18 which is polluting. Sulfated zirconia19 and

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Nb2O520 were also used, but these catalysts also gave poor results.

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Keggin type heteropoly acid (HPA) catalysts are strong Bronsted acids.21

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Supported HPAs have excellent superacidic prpoerties.22,23 Clays and hexagonal

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mesporous silica (HMS) are some of the most widely used supports for a variety of

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catalysts including HPAs.23,24 HMS possesses high surface area vis-à-vis clays and

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regular hexagonal porous structure and has been used in a number of processes.25 Our lab

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demonstrated that clay supported HPAs such as H3PW12O40 (dodecatungstophoshoric

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acids,DTP)23 and its partially substituted nano-form Cs2.5H0.5PW12O40 (Cs-DTP)24 are

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superior catalysts in several acid catalysed reactions including dehydration, alkylation,

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acylation, etc. DTP supported on HMS is a very good catalyst.26 A few researchers have

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reported that supported HPAs are effective for the glycerol dehydration reaction27 and

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gives better selectivity to acrolein and these catalysts included silica-supported

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silicotungstic acid,28,29 activated carbon-supported silicotungstic acids,30 modified

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molecular sieve zeolite (HY>Hß> Mordenite > SBA-15 >ZSM-23),31 and zirconium and

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niobium mixed oxides.32 Different silica-, alumina-, and aluminosilicate-supported

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heteropolyacid catalysts were prepared by Atia et al.33 using phosphomolybdic acid,

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phosphotungstic acid, silicotungstic acid, and ammonium phosphomolybdate as

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precursors. Alumina was found to be superior to silica as support with regard to catalyst

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activity and selectivity. In their studies, tungsten based heteropolyacids showed

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outstanding performance and stability whereas molybdenum-containing HPAs tend to

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decompose partly close to 400 oC into molybdates and MoO3 whereas tungsten-

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containing catalysts were stable. This suggested that tungsten-based materials interesting

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acid catalysts for the dehydration of glycerol in the gas phase.33 Metal oxide supported

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HPAs are stable up to 400 oC without any decomposition33,34 and in certain metal oxide

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supported heteropolyacids are shown to be stable even at higher temperature; for

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instance, zirconia supported HPAs are stable at 600oC and beyond.35 The most of the

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heteropoly acid based glycerol dehydration reactions were reported at 270-325 oC.27-35

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HMS has more silanol (Si-OH) groups on surface which makes the support more

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hydrophilic, which can increase the interaction between glycerol hydroxyl group and

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support hydroxyl group and may increase the selectivity of the acrolein. Hence, the 4 ACS Paragon Plus Environment


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principal objectives of the present work was based on preparation of HMS based catalysts

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and evaluation of their effects on glycerol dehydration reaction. The two different set of

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catalysts were prepared: (i) heteropoly acid supported on HMS, and (ii) other solid acids

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supported on HMS. The sencondary objective of the present work was to screen a large

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number of catalysts (heteropoly acid and solid acid supported on HMS) and arrive at

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optimum conditions for dehydration of glycerol to acrolein. If catalyst deactivated, either

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due to use of severe conditions or due to any other process parameter was observed, then

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it could be the basis for developing a new catalyst. This work also discusses a systematic

118

evaluation of the various catalysts including the characterization of the most active, used

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and reused catalyst to understand the process parameters which will help in further

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research. In the current investigation, a new catalytic material (MUICaT-5) based on

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HMS as support has been prepared, and used as solid acid for the dehydration of glycerol

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to acrolein in vapor phase. This catalyst has good recyclability and delineates the

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novelties of the process. MUICaT is an acronym for Mumbai University Institute of

124

Chemical Technology by which this institute was formerly known (now it is a separate

125

deemed university called ICT). The catalyst activity was evaluated using 20% w/w

126

glycerol solutions. The purpose was to reduce reactor size and possible scale-up for

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commercial use of the process to improve economics.

128 129

2. EXPERIMENTS

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2.1. Materials

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The following chemicals were procured from firms of repute and used without

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further purification: glycerol (LR), dodecatungstophosphoric acid (AR), methanol (s.d.

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Fine Chem., Mumbai, India), aluminum nitrate (s.d. Fine Chem., Mumbai, India),

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tungstic acid (s.d. Fine Chem., Mumbai, India), ethanol (s.d. Fine Chem., Mumbai,

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India), zirconium oxychloride (LR) (s.d. Fine Chem., Mumbai, India), tetraethyl

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orthosilicate (TEOS) (Fluka, Germany), hexadecyl amine (Spectrochem Ltd., Mumbai,

137

India).

138 139

2.2. Catalyst Preparation


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Hexagonal mesoporous silica (HMS) was synthesized by neutral SoIo templating

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route.25a,26a The process is briefly described here. The synthesis mechanism is based on

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hydrogen bonding and self-assembly between neutral primary amine surfactants (So) and

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neutral inorganic precursor (Io). In a typical preparation, tetraethyl orthosilicate (TEOS)

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was added under vigorous stirring to a solution of dodecyl amine (DDA) in ethanol and

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de-ionised water to obtain a gel of composition 1.0 TEOS : 0.27 DDA : 9.09 EtOH : 50.8

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H2O. After ageing for 18 h at ambient temperature, template silica with short range

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hexagonal morphology was recovered. Template removal was achieved by calcination at

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550 0C in the air. 20% w/w dodecatnugstophosphoric acid (DTP)/HMS was prepared by

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incipient wetness technique, as descried earlier by us,27

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dodecatungsto phosphoric acid was weighed accurately. It was dissolved in 8 ml of

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

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molecular sieve with constant stirring with a glass rod or kneading it properly. The

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solution was added at time intervals of 2 min. Initially on the addition of the DTP

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solution, HMS was in powdery form but in complete addition it formed a paste. The paste

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on further kneading for 10 minutes resulted in a free flowing powder. The performed

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catalyst was dried at 120 0C for removal of water and other occluded volatiles and

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subsequently calcined at 300 0C temperature for 3 h. 20% w/w DTP/HMS,26 20% w/w

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DTP/K-1023, 20% Cs-DTP/K-1024 and 20% w/w DTP/OMS (octahedral molecular

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sieves) were prepared as the method reported in literature36. 20% w/w NiO/HMS, 20%

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w/w CoO/HMS, 20% w/w CuO/HMS, and 20% w/w Fe2O3/HMS were prepared by

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adding nitrate solution of respective metal precursor to HMS by wet incipient technique

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and further calcination was done at 650 0C for 3 h.

for which 2 g of dry

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MUICaT-5 was synthesized as follows: 2.39 g of zirconium oxychloride and 0.11

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g of aluminum nitrate were dissolved in aqueous solution, and added to 5 g of precalcined

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HMS by incipient wetness technique. After addition, the solid was dried in an oven at

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110 0C for 3 h. The ammonia gas was passed through dried material for 2h, and then

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material was washed with deionized water until a neutral filtrate which was detected by

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phenolphthalein, and the absence of chlorine ion is detected by silver nitrate tests. A

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material balance on chlorine before and after precipitation was done, and the washing

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showed no retention of chlorine on the solid. It was then dried in an oven for 24 h at 110 6 ACS Paragon Plus Environment


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0

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tungstic acid (0.1078 g) with 0.9 g of zirconium hydroxide and aluminum hydroxide on

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HMS followed by hydrothermal treatment and then it was calcined at 750 0C for 3 h.37

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The various HMS based solid acid catalysts such as UDCaT-138, UDCaT-439 and

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UDCaT-640 were prepared by the reported methods from our laboratory.

C. The generation of acidic centers into this material was made possible by grinding

176 177

2.3. Characterization of Catalyst

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2.3.1. NH3-TPD

179

Acidic sites of the catalyst were determined with temperature programmed

180

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

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ammonia as probe molecule. A quantity of 30 mg of the catalyst was taken in a quartz

182

tube and degassed up to 300 0C under the flow of nitrogen. Then, ammonia gas was

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passed for 30 min to adsorb the ammonia over the surface of the catalysts at room

184

temperature. Physisorbed gas was removed by passing inert nitrogen at room

185

temperature. Chemisorbed ammonia was desorbed by using temperature programmed

186

desorption and detected by TCD.

187 188

2.3.2. Surface Area, Pore Volume and Pore Diameter Analysis

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The surface properties of fresh and used catalysts were measured by the

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Brunauer–Emmett–Teller (BET) method using ASAP 2010 (Micromeritics, USA)

191

instrument. The catalyst samples were degassed under vacuum at 200 0C for 4 h. The

192

measurements were made using N2 gas as the adsorbent and with a multipoint method.

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Isotherms were measured at liquid nitrogen temperature.

194 195

2.3.3. SEM and EDX Analysis

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External surface morphology of the catalyst sample was captured by scanning electron

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microscope (SEM) (Camera SU 30 microscope, JEOL, Japan). The dried samples were

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mounted on specimen studs and sputter coated with a thin film of gold to prevent

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charring. The gold coated surface was then scanned at various magnifications by using

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scanning electron microscope. Elemental analysis of fresh, used and regenerated catalysts

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was determined by energy dispersive X-ray spectroscopy (EDXS) (KEVEX X-ray 7 ACS Paragon Plus Environment

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spectrometer JED-2300, JEOL, Japan). However, to avoid the error in quantification of

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bulk composition, X-ray beam was focused at three spot in the catalyst, and average

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value of each metal is presented.

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2.4. Apparatus and Reaction Procedure

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Vapor phase dehydration of glycerol was carried out in a fixed bed stainless steel

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reactor (17.2 mm diameter (ID) and 250 mm height) (Chemito). The bed was packed with

209

a known quantity of dry catalyst. Inert glass bead packing was placed above the catalyst

210

bed. The stainless steel reactor was equipped with liquid feed pump (HPLC grade,

211

Knauer, USA), preheater, gas flow arrangement with mass flow controller and condenser.

212

The role of N2 in the feed is to carry out the reaction in inert atmosphere, and also to

213

avoid the further decomposition of acrolein to other by-products by decreasing the

214

residence time of acrolein in the catalyst. Under standard reaction condition: the

215

temperature of the bed was maintained with 225±1 0C of accuracy. The flow rate of the

216

nitrogen gas was measured and controlled by mass flow controllers at 10.2 ml/h. WHSV

217

was kept at 10.74 h-1 with the residence time of 35 s. Reaction samples were collected

218

from the bottom of the condenser. The catalyst was activated under the flow of nitrogen

219

for 2 h at the reaction temperature.

220 221

2.5. Method of Analysis

222

Analysis of reaction mixture was performed by GC on a Chemito 1000 model. A

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30 m × 0.15 mm internal diameter capillary column (BPX-50) was used for analysis in

224

conjunction with a flame ionization detector. The quantification of collected data was

225

done through a calibration procedure by using synthetic mixtures. Dodecane was used as

226

an internal standard to correct the volumetric changes during the reaction by taking the

227

ratio of glycerol and dodecane concentrations. The amount of acrolein and

228

hydroxyacetone obtained was calculated through calibration curve and product yields

229

were calculated. Product selectivity was calculated by the equation 3 as reported by Gu et

230

al.41 The gaseous by-product and coke deposited on the catalyst were not analyzed

231

quantitatively and its percentage was mentioned as others by keeping an account of the

232

material balance. The products were confirmed by GC-MS and authentic samples. 8 ACS Paragon Plus Environment


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Commonly used terms for calculation of conversion, product yield, product selectivity

234

and weight hourly space velocity (WHSV) are as follows: Glycerol conversion, % = Product yield, mol % =

235

Glycerol conc. in feed − Glycerol conc. in product x100 Glycerol conc. in feed

Mol of carbon in defined product x100 mol of carbon in glycerol in feed

Product selectivity, mol % =

WHSV =

Product yield x100 Glycerol conversion

F

(1) (2) (3) (4)

W

236 237

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Where WHSV = Weight hourly space velocity, h-1

238

F = Total mass flow of liquid feed (glycerol solution), g/h

239

W = Weight of catalyst, g

240 241

3. RESULTS AND DISCUSSION

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Scheme 1 shows the mechanism for the glycerol dehydration reaction. Glycerol

243

dehydration over a heterogeneous catalyst follows two parallel paths a and b leading to

244

three products which are all interesting, which are temperature dependent reactions. By

245

dehydration path a it produces 3-hydroxypropanal (A1) which is further dehydrated to

246

give acrolein (A2) which is the desired product. There could be break-up of A1 by path aa

247

to acetaldehyde (A11) and formaldehyde (A12). On the contrary, path b leads

248

hydroxyacetone (B2), which is also industrially important. It has been reported that

249

hydroxyacetone is obtained at high temperature, and also acrolein undergoes cracking

250

and produces acetaldehyde and formaldehyde at higher temperature.42 Preliminary

251

analysis had suggested that type of acidity, its distribution and temperature would play

252

dominant roles in selectivity to acrolein.

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H3C

H

H

H

O

O

(A11)

(A12) Formaldehyde

Acetaldehyde

Path aa

H2C

Path a

HO HO

O

O

OH

-H2O HO

-H2O

(A1)

(A2)

3-Hydroxypropanal

OH

Acrolein

desired path OH

Glycerol

-H2O

H2C

H3C OH

Path b

OH

OH

O

(B1)

(B2)

254 255 256

Hydroxyacetone

Scheme 1. Dehydration of glycerol over solid acid

257 258

3.1 Catalyst charecterizations of 20%(w/w) DTP supported on K10, HMS and OMS

259

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

260

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

261

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

262

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

263

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

264

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

265

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

266

by our group.23,24,39 20% (w/w) DTP/OMS was characterized similarly. Only a few

267

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

268

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

269

DTP/K10, 20% (w/w) DTP/HMS and 20% (w/w) DTP/OMS catalyst exhibits bands at

270

3450, 1652, 1092, 990.7, 893, 817, and 466 cm-1. The XRD analysis confirmed that 20%

271

w/w DTP/K-10 is crystalline in nature. The BET surface area of 20% w/w DTP/K-10 was

272

found to be 135 m2/g. The preparation of 20% w/w DTP/HMS and its application is also 10 ACS Paragon Plus Environment


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reported by our group.26 The acidity of 20% w/w DTP/HMS was measured by NH3-TPD

274

and found to be 0.130 mmole/g. 20% w/w DTP/HMS characterized by XRD and no

275

crystalline phase was detected which indicates, the uniform distribution of DTP in HMS.

276

Hence,these materials are completely amorphous in nature. The BET surface area of 20%

277

w/w DTP/HMS was found to be 299.6 m2/g and is a type-IV isotherm, indicates

278

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

279

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

280

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

281

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

282

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

283

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

284

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

285

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

286

doedcatungstophosphoric acid was reported by us earlier26 and Bardin et al.43

287

are abundant silanol groups (#Si-OH) on the surface of mesoporous silica owing to its

288

amorphous wall structure. With these reactive silanol groups, one can effectively

289

immobilize organic functional groups onto a silica surface through either covalent

290

bonding or hydrogen bonding.44 On silica, only H-bond formation occurs indicating a

291

rather weak acidity of the silanol groups, quantitatively characterized by pKa = 7.

292

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

293

situ during dehydration. particularly at the reaction temperature of 225 oC.

There

45

294 295

3.2. Efficacies of Different Support and Catalyst screening

296

20% w/w DTP was loaded on different support like K-10 (acidic), HMS (neutral)8

297

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

298

selectivity. Although, all the catalyst has same 20%w/w DTP loading, it was observed

299

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

300

support (Table 1). The increase in selectivity also can be due the presence of free hydoxy

301

group which make the catalyst more hydrophilic in nature. Therefore, various HMS

302

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


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303

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

304

were prepared and screened for vapor phase glycerol dehydration reaction (see Figure 1).

305

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

306

catalyst composition for dehydration of glycerol to acrolein.16,41,

307

iron, nickel and cobalt were supported on HMS and their activity for acrolein preparation

308

was evaluated. However, it was observed that HMS suppored copper, iron, nickel and

309

cobalt catalysts showed poor acrolein selectivity as compared to heteropoly acid based

310

catalysts such as 20% w/w CsDTP/HMS and 20% w/w DTP/HMS, which can be due to

311

redox properties of these metals.

312

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

313

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

314

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

315

10.74 h-1 of WHSV. 20% w/w DTP/HMS was found a better catalyst as compared to

316

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

317

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

318

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

46

Therefore, copper,

319 320

3.3. Effect of Temperature (20% w/w DTP/HMS)

321

Since most of the literature on HPA catalyzed glycerol dehydration reaction were

322

reported at 270-325 0C. Thermogravimetric analysis of 20% w/w DTP/HMS revealed that

323

catalyst is stable at 325 0C.23d,26 Hence, catalytic activity of 20% w/w DTP/HMS was

324

tested at 325 0C. In all the cases, catalyst was preheated for 2 h at a desired reaction

325

temperature to activate the catalyst which also insures the stability of the catalyst. a

326

series of experiments were performed at 200, 225, 275 and 325 0C to investigate the

327

effects of temperature on glycerol conversion and acrolein selectivity by using 20%w/w

328

DTP/HMS catalyst (see Figure 2). 20% w/w DTP/HMS showed 94% of glycerol

329

conversion and 80% of acrolein selectivity at 225 0C. Temperature below 225 0C is not

330

sufficient to vaporize glycerol and hence conversion of glycerol and selectivity of

331

acrolein was decreased. It was also observed that beyond 225 0C of temperature the

332

conversion of glycerol was almost the same but selectivity of acrolein decreased.



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Page 12 of 36

333

It was also observed that beyond 225 0C, the conversion of glycerol was almost the same

334

whereas selectivity of acrolein was decreased. This anomalous result indicates that 225

335

0

336

effect of the hydrophilic of HMS and Bronsted acidic of DTP. However, selectivity of

337

acrolein was decreased with increased in the temperature from 225 to 325

338

could be due to the cracking of acrolein occurs at higher temperature and also due to

339

deposition of coking on the support.42 Therefore, we can conclude that the synergistic

340

effect of DTP and HMS favors the acrolein selectivity at low temperature i.e. 225 0C as

341

compared to 275-300 0C. Hence, further experiments were performed at 225 0C.

C is sufficient for complete conversion of glycerol which could be due the synergistic 0

C which

342 343

3.4. Effect of DTP Loading on HMS

344

Time on stream data for DTP loading on HMS was recorded for 25 h. It was

345

found that increase in DTP loading from 20% to 50% leads to increase in life of the

346

catalyst without affecting acrolein selectivity. This increased in the life of catalyst with

347

increase in DTP loading may be due to proportional increase in catalyst active sites. It

348

was also found that 20%, 30% 40% and 50% DTP/HMS catalyst undergoes deactivation

349

after 10, 13, 15 and 19 h (see Figure 3). Though, 50% w/w DTP/HMS has more catalyst

350

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

351

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

352

surface area, SEM and EDX analysis for better understanding and design of new catalyst.

353 354

3.5. Regeneration and Reusability of 20% w/w DTP/HMS Catalyst

355

The spent catalyst was collected from the reactor and washed with methanol to

356

remove adsorbed polymeric material from pore of the catalyst. Then, catalyst was

357

subjected to calcination at 300 0C for 3 h in flowing air. A 10% loss of catalyst during

358

regeneration process was made up with the fresh catalyst, and catalyst reusability study

359

was carried out at standard reaction conditions. It was observed that catalyst undergoes

360

severe deactivation after first run (see Table 2). The cause of catalyst deactivation was

361

investigated by NH3-TPD analysis, BET surface area, BJH pore volume, SEM image and

362

EDX elemental analysis.

363 13 ACS Paragon Plus Environment

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364


3.6. Activity and Selectivity of Virgin and Used 20% w/w DTP/HMS Catalysts

365

NH3-TPD profile of fresh and used 20% DTP/HMS are shown in Figures 4a and

366

4b. The acidity of the used catalyst was found completely decreased. This was because of

367

deposition of the coke during the reaction which is in agreement with the literature.40,41

368

Also, DTP was leached out during washing of the used catalyst which was confirmed by

369

EDX data by tugsten content in the regenerated catalyst (see Table 3). The surface

370

properties of fresh and used and regenerated 20% DTP/HMS are given in Table 4. BET

371

surface area of regenerated catalyst had decreased from 299.7 to 119.21 m2/g, pore

372

volume from 0.203 to 0.082 cm3, and pore diameter from 27.16 nm to 13.01 nm. The

373

decrease in BET surface area, pore volume and pore diameter is due to the coke

374

deposition inside the pore of the catalyst which is confirmed by EDX data of regenerated

375

catalyst, and also responsible for the decrease in the activity of the catalyst. Figures S1

376

show SEM image of fresh and regenerated 20% w/w DTP/HMS catalyst. It was observed

377

that both the catalyst has marginal difference in the SEM image because deposited coke

378

is present in the pore of the catalyst. Elemental analysis of fresh, used and regenerated

379

catalyst was done by EDX (see Table 3). It was found that the regenerated catalyst

380

contained 5.01 mass% of carbon which was due to coke deposition inside the catalyst

381

during the reaction. Also, the tungsten (W) mass percentage of regenerated catalyst

382

decreased from 11.42 to 1.04 mass %, which was due to leaching of DTP from the

383

catalyst during washing step. Hence, it can be concluded that 20% w/w DTP/HMS which

384

is Bronsted acid catalyst gave the good results for first run and after that it undergoes

385

severe deactivation due to coke deposition and leaching of DTP form HMS support.

386

Thus, part (II) of this work is devoted to preparation of HMS supported moderate Lewis

387

acid site based catalyst because strong Lewis acid also leads to severe deactivation as

388

mentioned in the literature report.32

389 390

3.7. Selection of Lewis acid based catalyst supported on HMS

391

In our laboratory, we have been working in the preparation on supported solid

392

acid catalyst. In part (I) study we observed that hexagonal mesoporous silica (HMS) act

393

as better support for acrolein selectivity. In part (II) investigation, a new MUICaT-5

394

catalyst based on HMS as support was prepared, and used as moderate Lewis acid 14 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

395

catalyst for the dehydration of glycerol to acrolein in vapor phase under milder conditions

396

in comparison with other reported catalysts. The moderate acid strength was confirmed

397

by NH3-TPD profile. MUICaT-5 catalyst has W-Zr-Al/HMS catalyst composition and the

398

elemental composition is mentioned in Table 8. It was reported that zirconium and

399

tungsten based catalyst has more Lewis acid character.47-49 The exact catalytic reaction

400

mechanism of MUICaT-5 to convert glycerol to acrolein is not known, however some

401

report mentioned that tungsten oxide is converted into tungsten hydroxide at elevated

402

temperature in presence of steam, which could provide Bronsted acidity.49 Typical

403

reaction conditions were: 1.0 g of catalyst loading, 275 0C of reactor bed temperature,

404

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

405

rate (glycerol solution), 1.5 L/h of N2 flow rate, 4 h, and 10.74 h-1 of WHSV. The various

406

solid acid catalysts such as UDCaT-1, UDCaT-4, UDCaT-6, and MUICaT-5 were

407

screened for glycerol dehydration reaction.

408

conversion of glycerol and acrolein selectivity was mention in Table 5. It was observed

409

that MUICaT-5 catalyst showed the highest glycerol conversion and highest acrolein

410

selectivity as compared to other studied HMS based catalysts. It can be due the presence

411

of moderate acid site on MUICaT-5 catalyst which is confirmed by NH3-TPD profile.

412

Hence, further studies have been carried out by using MUICaT-5 catalyst. This enhanced

413

activity of MUCaT-5 catalyst was further co-related to NH3-TPD profile, BET surface

414

area, pore volume, and EDX elemental analysis for better understanding.

The catalyst composition, percentage

415 416

3.8. Time on Stream Data (MUICaT-5 Catalyst)

417

The stability and activity of the MUICaT-5 catalyst were evaluated by time on

418

stream (TOS) data up to 100 h. Figure 5 shows that catalyst MUICaT-5 was stable and

419

active up to 15 h without any appreciable loss in activity, and selectivity of acrolein.

420

After that it undergoes gradual deactivation which is also in accordance with the

421

literature report that the solid acid catalyst undergoes deactivation due to coke formation

422

during the reaction.19,32 The coke deposition on the active site of the catalyst was

423

confirmed by BET and EDX analysis data.

424 425 15 ACS Paragon Plus Environment

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426


3.9. Regeneration and Reusability of MUICaT-5 Catalyst

427

The spent catalyst was removed from the reactor and washed with methanol to

428

remove the adsorbed polymerized material from the catalyst. Then, catalyst was

429

subjected to calcination at 750 0C for 3 h in the flowing air to burn off coke present on

430

the catalyst. There was an inevitable loss of catalyst particles during these operations.

431

Hence, the actual amount of catalyst used in the next batch was almost 10% less than the

432

previous batch. The loss of the catalyst was made up with fresh catalyst. Catalyst

433

reusability was verified by performing the reaction under standard condition for 10 h. The

434

catalyst was activated under the flow of N2 at 275 0C for 2 h. Table 6 shows that there

435

was no appreciable decrease in the activity of the catalyst even after 6th run of the

436

catalyst. MUICaT-5 catalyst shows the good reusability without affecting acrolein

437

selectivity hence ex-situ regeneration of the catalyst process can be a cost effective

438

process. The fresh and regenerated catalysts were subjected to characterization to

439

correlate the activity and reusability of the catalyst for glycerol dehydration reaction.

440 441

4. MUICaT-5 CATALYST CHARACTERIZATION

442

Acidic sites of the catalyst were determined by temperature programmed

443

desorption (TPD) analysis with ammonia as probe molecules. Figure 6a and Figure 6b

444

show NH3-TPD data of fresh and regenerated MUICaT-5 which confirmed that

445

MUICaT-5 catalyst has moderate acid strength, and the acidity of the used catalyst was

446

regained after calcination at 750 0C in flowing air. At 750 0C of temperature the coke

447

which was deposited on active site of used catalyst is burn off and makes the catalyst

448

active for further reaction.

449

Surface area and pore volume of fresh, used and regenerated catalyst were

450

calculated from N2-adsorption–desorption isotherms using conventional BET and BJH

451

methods and represented in Table 7. The surface area of the fresh and regenerated

452

catalyst was decreased from 143.93 m2/g to 138.01 m2/g, pore volume from 0.144 cm2/g

453

to 0.140 cm2/g, and pore diameter 40.13 nm to 40.09 nm were observed. Hence it can

454

conclude that coke was completely removed from pore of the used catalyst and make the

455

catalyst active. It is also in accordance with the reusability data of MUICaT-5 catalyst.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

456

Figure S2 (a), (b) and (c) represent the external morphology of the fresh, used and

457

regenerated MUICaT-5 catalyst. The external morphology of fresh and regenerated

458

catalyst were quite similar however, used catalyst shows some agglomerated particles on

459

the catalyst surface which could be due to coke deposition. The elemental analysis of

460

fresh, used and regenerated catalyst was represented in the Table 8. It was observed that

461

used catalyst has carbon elemental mass percentage is 4.19%, however, regenerated

462

catalyst has no carbon elemental mass percentage hence we can conclude that calcination

463

at 750 0C for 3 h, removed the coke deposited in the pore of used catalyst. Therefore,

464

NH3-TPD data, BET surface area, BJH pore volume, SEM image and EDX elemental

465

analysis provides evidence for reusability of MUICaT-5 catalyst.

466 467

5. PROCESS OTIMIZATION

468

5.1. Effect of Temperature (MUICaT-5 Catalyst)

469

The glycerol dehydration reaction was carried out at four different temperatures

470

325, 300, 275 and 250 0C under otherwise similar reaction conditions. Figure 7 shows

471

that with increasing the temperature from 275 to 325 0C, the selectivity of the acrolein

472

was decreased, however glycerol conversion is increased from 86 to 98%. The decresed

473

in acrolein selectivity can be due to the side reaction occurs at higher temperature in the

474

presence of solid acid catalyst.19 However, at 250 0C of temperature gives the poor

475

glycerol conversion and acrolein selectivity. At 275 0C, MUICaT-5 catalyst gave 86%

476

glycerol conversion and 60% of acrolein selectivity. Hence, 275 0C was chosen for

477

further reaction parameter optimization.

478 479

5.2. Effect of Glycerol Concentration

480

Glycerol is a by-product of biodiesel process and is obtained in different

481

concentration depending on the workup procedure used. Hence, different concentrations

482

of glycerol such as 10%, 20% and 50% (w/w) were used to evaluate the activity of the

483

catalyst. It was observed that 10% and 20% (w/w) of glycerol solution gave almost

484

similar results. However, 50% (w/w) of glycerol solution resulted into a decrease in

485

glycerol conversion as well as acrolein selectivity (see Figure S3). This is a complex

486

reaction network strongly depedent on reaction temperature and concentration (partial 17 ACS Paragon Plus Environment

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487

pressure). As the concentration of glycerol increases on sites, it leads to cracking and

488

coking. Some pore channels become inaccessible due to deposition of carboneous

489

(viscous) material. Even if a few junctions are blocked , the number networks become

490

less

491

conversion. Hence, 20% w/w of glycerol solution was used for further optimization.

492

4.1. Nature of active sites

493 494

reducing the number of active sites.

Hence there is decrease in selectivity and

Since HMS is the support in MUICaT-5 catalyst, it is important to throw light on nature of acidity.

495 496

5.3. Effect of Glycerol Flow Rate

497

Glycerol flow rate was optimized by conducting the reaction at four different

498

glycerol flow rate 5.1, 10.2, 20.4 and 40.8 ml/h with WHSV of 5.37, 10.74, 21.48 and

499

42.96 h-1 respectively. It was observed that with increasing glycerol flow rate from 10.2

500

to 40.8 ml/h, the conversion and selectivity both decreased (see Figure S4). The decrease

501

in catalyst activity is due to increase in WHSV values hence; the residence time of

502

glycerol is decreased. Also, the catalyst to substrate weight ratio is decreases with the

503

increase in feed flow rate so the less number of catalyst active sites is available to convert

504

glycerol to acrolein. Therefore, 10.2 ml/h of glycerol flow rate was chosen for further

505

reaction parameter optimization.

506 507

5.4. Effect of N2 Flow Rate

508

The different N2 flow rates 0.72, 1.5, and 3.0 L/h were selected to establish its effect on

509

reaction. It was observed that with increase in N2 flow rate from 0.72 L/h to 3.0 L/h,

510

selectivity of acrolein has decreased. This is because at higher N2 flow rate, acrolein was

511

carried away by N2 gas, and did not get enough time to get condense (see Figure S5). The

512

escaped gases was collected by bubbling it through 250 ml distilled water and confirms

513

presence of acrolein by injecting in GC. The total carbon balance was obtained in the

514

range of 89-93% for all liquid products by on line GC analysis. The remaining was

515

gaseous phase and carbon deposited on the catalyst pores.

516 517

5.5. Effect of Catalyst Loading (MUICaT-5 Catalyst) 18 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

518

It was anticipated that with increase in catalyst loading, the life of catalyst can also be

519

increased due to propotional increase in catalyst active sites. Hence, the effect of catalyst

520

loading with the conversion of glycerol was evaluated by loading the reactor with 0.5,

521

1.0, and 2.0 g of MUICaT-5 catalyst with WHSV value 5.37, 10.74 and 21.48

522

respectively by using 20% w/w of glycerol solution. Figure 8 shows that with increase in

523

catalyst loading from 0.5 to 2.0 g, catalyst life increased from 6 to 15 h without affecting

524

the selectivity of acrolein.

525 526

CONCLUSIONS

527

Three different supports (acidic, neutral and basic) were used for catalyst

528

development for selective dehydration of glycerol to acrolein in a continuous fixed bed

529

catalytic reactor using various catalysts. The work was divided in two parts. In part I,

530

heteropoly acids were used initially as suitable catalysts. Among hexagonal mesoporous

531

silica (HMS) as a netural support, two different sets of catalysts were prepared: (i)

532

heteropoly acids supported on HMS, and (ii) different metal oxides supported on HMS.

533

It can be concluded that HMS as support increased the selectivity of acrolein due to

534

presence of free hydroxyl group, hydrophilicity, and neutral nature. With 20% w/w

535

dodecatungstophopshoric acid (DTP)/HMS as catalyst, which has Bronsted acidic

536

characteristics, good results were obtained at low temperature (225 0C). However, the

537

catalyst underwent severe deactivation due to coke deposition in the pore space of the

538

catalyst which was confirmed by BET-surface area, and EDX elemental analysis. It was

539

also observed that the regenerated DTP/HMS catalyst has very low activity for glycerol

540

conversion, which was due to leaching of DTP from catalyst support. Although 20% w/w

541

DTP/HMS showed promise for glycerol conversion and acrolein selectivity, it is not a

542

reusable catalyst. Thus, more rigourous studies were done in Part II work which dealt

543

with selection and preparation of moderate Lewis acid based catalysts supported on

544

HMS, and its effects on glycerol dehydration and acrolein selectivity. It was found that

545

MUICaT-5 catalyst also undergo deactivation due to coke deposition inside the pore of

546

the catalyst. However, the used catalyst regains its activity after calcination at 750 0C.

547

The catalytic activity of regenerated catalyst was confirmed by NH3-TPD data, BET

548

surface area, BJH pore volume, SEM image and EDX elemental analysis. Hence, 19 ACS Paragon Plus Environment

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549

MUCaT-5 catalyst which has moderate acid site, confirmed by NH3-TPD analysis, has

550

good activity and reusability for glycerol dehydration reaction to get acrolein in good

551

yield. At optimized reaction conditions it gave 86% of glycerol conversion, and 60% of

552

acrolein selectivity at 225 oC, which is lower than temperatures used by others. The

553

catalyst was recycled up to 6 times without affecting the activity of catalyst and

554

selectivity of acrolein.

555

The global market for biodiesel is estimated to reach 180 million tons by 2016

556

and to grow at the rate of 42% per year.6 which will make huge amount of glycerol

557

available as a cheap feedfstock to produce several chemicals. Glycerol can also be

558

chemically converted to acrylic acid by dehydration to acrolein followed by oxidation to

559

acrylic acid which is an important chemical building block, and used in production of

560

polyacrylates and commodity acrylates. The global market for acrylic acid was worth

561

US$8 billion in 2011 and growing at 3 to 4 percentage per year. Hence, the proposed

562

route can also be useful to meet the acylic acid market demand.50

563 564

Overall this work has added useful new knowledge to dehydration of glycerol to acrolein.

565 566

ACKNOWLEDGMENT: This research was supported by CSIR-NMITLI program

567

under the project on “Bioglycerol based chemicals”. G.D.Y. received support from R.T.

568

Mody Distinguished Professor Endowment, and J.C. Bose National Fellowship of DST,

569

Govt of India. R.V.S. and S.O.K. received JRF under this project.

570 571

SUPPORTING INFORMATION AVAILABLE: Figures S1-S5 are available free of

572

charge via the Internet at http://pubs.acs.org.

573 574 575 576 577 578

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

762 763 764 765

Table 1. Efficacy of different support: 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. % Conversion Acrolein (glycerol) 20% w/w DTP/K-10 89 50 20% w/w DTP/HMS 94 80 20% w/w DTP/OMS 62 45 *acetaldehyde, propionaldehyde, acetone, allyl alcohol Catalyst

766 767 768 769 770 771 772

773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790

Page 26 of 36

% Selectivity Hydroxyacetone Others* 10 40 9 11 14 41

Table 2. Catalyst reusability study (20% w/w DTP/HMS): 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 feed flow rate 10.74 h-1 WHSV, 4 h. % Selectivity % Conversion Hydroxyacetone No. (glycerol) Acrolein 9 1st run 94 80 13 2nd run 35 73 14 3rd run 20 65 *acetaldehyde, propionaldehyde, acetone, allyl alcohol

Others* 11 14 21

Table 3. Energy dispersive X-ray spectroscopy (EDXS) analysis of 20% w/w DTP/HMS (fresh, used and regenerated catalyst). Fresh catalyst Used catalyst Regenerated Element Catalyst (%Mass) (% Mass) C 6.87 5.01 O 50.14 49.76 52.20 Si 38.44 36.25 41.75 W 11.42 7.12 1.04 Total 100 100 100 Table 4. Surface area, pore volume and pore diameter analysis of 20% w/w DTP/HMS (fresh, used and regenerated catalyst). Catalyst Fresh 20% w/w DTP/HMS Used 20% w/w DTP/HMS Regenerated 20% w/w DTP/HMS

BET surface area (m2/g) 299.6 13.1 119.2

Pore Volume (cm2/g) 0.203 0.019 0.082

791 27 ACS Paragon Plus Environment

Pore diameter (nm) 27.16 2.11 13.01

Page 27 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

792 793 794 795 796 797


Table 5. The Lewis acid based catalyst screening (catalyst composition, percentage conversion of glycerol, and acrolein selectivity): 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 275 0C, 1.5 L/h of N2 flow rate, 10.2 ml/h of feed flow rate 10.74 h-1 WHSV, 10 h. Catalyst % Conv. composition (glycerol) Acrolein UDCaT-1 Sulfuric acid 60 28 treated - Zr/HMS UDCaT-4 Persulfated Zr68 38 Al/HMS UDCaT-6 Chlorosulfonic acid 71 29 treated- Zr/HMS 86 60 MUICaT-5 W-Zr-Al/HMS *acetaldehyde, propionaldehyde, acetone, allyl alcohol Catalyst

798 799 800 801 802 803 804 805

% Selectivity Hydroxyacetone 15

Others* 57

16

46

14

57

10

30

Table 6. MUICaT-5 catalyst reusability study: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 275 0C, 1.5 L/h of N2 flow rate, 10.2 ml/h of feed flow rate 10.74 h-1 WHSV, 10 h.

% Selectivity % Conversion (glycerol) Hydroxyacetone Others* Acrolein 11 30 1st run 86 59 10 32 2nd run 84 58 12 31 3rd run 83 57 11 33 4th run 81 56 10 34 5th run 78 56 12 33 6th run 76 55 *acetaldehyde, propionaldehyde, acetone, allyl alcohol Catalyst run

806 807 808 809 810 811

Table 7. Surface Area, Pore Volume and Pore Diameter Analysis of MUICaT-5 catalsyt (fresh, Used and regenerated). Catalyst Fresh MUICaT-5 Used MUICaT-5 Regenerated MUICaT-5

BET surface area (m2/g) 143.9 25.2 138.0

Pore Volume (cm2/g) 0.144 0.055 0.140

812 813 814 28 ACS Paragon Plus Environment

Pore diameter (nm) 40.13 85.72 40.09


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

815 816 817 818 819 820 821 822 823

Table 8. Energy dispersive X-ray spectroscopy (EDXS) analysis of MUICaT-5 catalyst (fresh, used and regenerated catalyst). Element

% Mass (Fresh) ----

% Mass (Used) 4.19

% Mass (regenerated) ----

824

C

825

O Al

45.26

43.51

44.67

0.20

0.20

0.19

Si

34.12

32.68

33.08

Zr W

9.79

11.43

11.73

10.63

7.98

10.32

Total

100

100

100

826 827 828 829 830 831 832


Page 28 of 36

Page 29 of 36

833

Figures

834 100 Percentage (%)

80 60 40 20 0

% Conversion of Glycerol

835 836 837 838 839

% Selectivity of Acrolein

Figure 1. Efficacy of Various Catalysts: 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 feed flow rate, 10.74 h-1 of WHSV, 4 h.

100 80 Percentage (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60 40 20 0 325 C

840 841 842 843 844

275 C

% Conversion of Glycerol

225 C

200 C

% Selectivity of Acrolein

Figure 2. Effect of temperature: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 325-200 0C, 1.5 L/h of N2 flow rate, 10.2 ml/h of feed flow rate, 10.74 h-1 of WHSV,4 h.

845



Conversion of glycerol (%)

120 100 80 60 40 20 0 0

5

10

15

20

25

30

Time (h)

20%(w/w) DTP/HMS

30%(w/w) DTP/HMS

40%(w/w) DTP/HMS

50%(w/w) DTP/HMS

846 100

80

Selectivity of acrolein (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 36

60

40

20

0 0

5

10

15

Time (h)

20

25

20%(w/w) DTP/HMS

30%(w/w) DTP/HMS

40%(w/w) DTP/HMS

50%(w/w) DTP/HMS

30

847 848 849 850 851

Figure 3. Effect of DTP loading on HMS: 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.


Page 31 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


852 853

Figure 4a. NH3-TPD result of fresh 20%w/w DTP/HMS

854

855 856

Figure 4b. NH3-TPD of used 20%w/w DTP/HMS

857 858 32 ACS Paragon Plus Environment


859 100 90 80 Percentage (%)

70 60 50 40 30 20 10 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Time (h) % Conversion of glycerol % Selectivity of acrolein

860 861 862 863 864

Figure 5. Time on stream data: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 275 0C, 1.5 L/h of N2 flow rate, 10.2 ml/h of feed flow rate (glycerol solution), 10.74 h-1 WHSV, 100 h.

0.0035 0.003 TCD Signal (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 36

0.0025 0.002 0.0015 0.001 0.0005 0 50

100

150

200

250

300

350

400

450

500

Tem perature 0C

865 866

Figure 6a. NH3-TPD of fresh MUICaT-5 catalyst


550

Page 33 of 36

0.0035

TCD Signal (a. u.)

0.003 0.0025 0.002 0.0015 0.001 0.0005 0 50

100

150

200

250

300

350

400

450

500

550

0

Tem perature C

867 868

Figure 6b. NH3-TPD of regenerated MUICaT-5 catalyst 100

80

Percentage (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

40

20

0

250 C

275 C

300 C

%Conversion of glycerol

869 870 871 872

325 C

% Selectivity of acrolein

Figure 7. Effect of temperature: 20% (w/w) glycerol solution, 1.0 g of catalyst weight, 250-325 0C, 1.5 L/h of N2 flow rate, 10.2 ml/h feed flow rate 10.74 h-1WHSV, 10 h.



Conversion of glycerol (%)

100 80 60 40 20 0 0

5

10

15 Time (h) 0.5 g 1.0 g 2.0 g

20

25

873 874

Figure 8 (a). Plot of conversion of glycerol (%) vs. Time (h) 70 Selectivity of acrolein (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 36

60 50 40 30 20 10 0 0

5

10

15

20

25

Time (h) 0.5 g

1.0 g

2.0 g

875 876

Figure 8 (b). Plot of selectivity of acrolein (%) vs. Time (min)

877 878 879 880

Figure 8. Effect of catalyst loading: 20% (w/w) glycerol solution, 0.5-2.0 g of catalyst weight, 275 0C, 1.5 L/h N2 of flow rate, 10.2 ml/h feed flow rate, 20 h.


Page 35 of 36

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Graphical abstract: Selective Dehydration of Glycerol to Acrolein: Development of Efficient and Robust Solid Acid Catalyst MUICaT-5

Ganapati D. Yadav,* Rajesh V. Sharma and Suraj O. Katole

MUICaT-5 HO

O

OH OH

Glycerol

86% conversion, 60% selectivity, 275 oC

Acrolein

ACS Paragon Plus Environment

Selective Dehydration of Glycerol to Acrolein: Development of Efficient

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