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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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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
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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)
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showed promise.
31
selectivity as compared to K-10 clay, and octahedral molecular sieves (OMS). 20% w/w
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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
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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
43 44
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
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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
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Chemical Technology by which this institute was formerly known (now it is a separate
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deemed university called ICT). The catalyst activity was evaluated using 20% w/w
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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.
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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,
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India).
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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
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2.3. Characterization of Catalyst
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2.3.1. NH3-TPD
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Acidic sites of the catalyst were determined with temperature programmed
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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
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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
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temperature. Physisorbed gas was removed by passing inert nitrogen at room
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temperature. Chemisorbed ammonia was desorbed by using temperature programmed
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desorption and detected by TCD.
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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)
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instrument. The catalyst samples were degassed under vacuum at 200 0C for 4 h. The
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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
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a known quantity of dry catalyst. Inert glass bead packing was placed above the catalyst
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bed. The stainless steel reactor was equipped with liquid feed pump (HPLC grade,
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Knauer, USA), preheater, gas flow arrangement with mass flow controller and condenser.
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The role of N2 in the feed is to carry out the reaction in inert atmosphere, and also to
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avoid the further decomposition of acrolein to other by-products by decreasing the
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residence time of acrolein in the catalyst. Under standard reaction condition: the
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temperature of the bed was maintained with 225±1 0C of accuracy. The flow rate of the
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nitrogen gas was measured and controlled by mass flow controllers at 10.2 ml/h. WHSV
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was kept at 10.74 h-1 with the residence time of 35 s. Reaction samples were collected
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from the bottom of the condenser. The catalyst was activated under the flow of nitrogen
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for 2 h at the reaction temperature.
220 221
2.5. Method of Analysis
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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
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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
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ratio of glycerol and dodecane concentrations. The amount of acrolein and
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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
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al.41 The gaseous by-product and coke deposited on the catalyst were not analyzed
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quantitatively and its percentage was mentioned as others by keeping an account of the
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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
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and weight hourly space velocity (WHSV) are as follows: Glycerol conversion, % = Product yield, mol % =
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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
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F = Total mass flow of liquid feed (glycerol solution), g/h
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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
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dehydration over a heterogeneous catalyst follows two parallel paths a and b leading to
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three products which are all interesting, which are temperature dependent reactions. By
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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
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hydroxyacetone (B2), which is also industrially important. It has been reported that
249
hydroxyacetone is obtained at high temperature, and also acrolein undergoes cracking
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and produces acetaldehyde and formaldehyde at higher temperature.42 Preliminary
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analysis had suggested that type of acidity, its distribution and temperature would play
252
dominant roles in selectivity to acrolein.
253
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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
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The three different support K10, HMS and OMS were used to incorporate
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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
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4.76 mmol/g. 20% (w/w) DTP/K10 and 20% (w/w) DTP/HMS are completely
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characterized again during this work for both virgin and used catalysts by NH3-TPD,
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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
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measured by NH3-TPD and found to be 0.423 mmol/g. The IR spectrum of 20% (w/w)
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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
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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
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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.
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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.
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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.
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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
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20% w/w DTP was loaded on different support like K-10 (acidic), HMS (neutral)8
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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
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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
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group which make the catalyst more hydrophilic in nature. Therefore, various HMS
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supported catalysts such as 20% w/w CoO/HMS, 20% w/w CuO/HMS, 20% w/w
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NiO/HMS, 20% w/w Fe2O3/HMS, 20% w/w CsDTP/HMS and 20% w/w DTP/HMS
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were prepared and screened for vapor phase glycerol dehydration reaction (see Figure 1).
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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.
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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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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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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
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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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Industrial & Engineering Chemistry Research
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.
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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
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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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Industrial & Engineering Chemistry Research
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
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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
792 793 794 795 796 797
Industrial & Engineering Chemistry Research
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
Industrial & Engineering Chemistry Research
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
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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
Industrial & Engineering Chemistry Research
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
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Industrial & Engineering Chemistry Research
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
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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.
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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
Industrial & Engineering Chemistry Research
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
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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
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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
Industrial & Engineering Chemistry Research
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.
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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
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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.
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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
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