Dueto long-term sustainability issues of fossil fuel resources it has been necessitatesfor the application of renewable biomass source to the energy, chemicals andalternative fuels.
1,2 InIndian context, as per TIFAC(Technology InformationForecasting & Assessment Council ) 2014 report of Government of India, almost623.4 Million Metric Ton per yearbiomass waste is generated in which 70% contributions is from agriculturalwaste such as Rice husk; Wheat and Rice straw; Sugarcane baggasse etc. Ingeneral such type of biomass contained mainly C6 sugar and its contribution isin the domain of 33-51% based on the biomass source.
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1 Thus,converting this major compound of C6 sugar such as cellulose, glucose, fructoseto valuable chemicals is an industrially and academically attractive option.3Cellulose and glucose can be easily converted to fructose by acidhydrolysis and isomerization, respectively.4,5 Further efficientconversion of fructose to desired chemicals using right choice of heterogeneouscatalyst is challenging and need more research and development activity to makethe catalytic process benign and industrially relevant. Among various reactionsof fructose conversion, efficient transformation of fructose to 5-hydroxymentylfurfural (5-HMF) is an important reaction to explore to identify new, stable,economical, reusable, easily available heterogeneous catalyst. This type ofcatalyst offer several advantages over liquid acid catalyst like easyseparation of product, reusability of catalyst and no corrosion of equipment,which makes them more suitable for an industrial application.6,7 As per the updated evaluation of the U.S.
Department of Energy (DOE) top 10 list of biobased chemicals, where furanmolecules such as 5-hydroxymethyl-furfural (HMF), furfural, and2,5-furandicarboxylic acid are mentioned in the “Top 10 +4” as additions to theoriginal DOE list. HMF stands out amongthe platform chemicals for a number of reasons: a) It has retained all sixcarbon atoms that were present in the hexoses, b) high selectivity have beenreported for its preparation, in particular from fructose, c) which compares favourablywith other platform chemicals, such as levulinic acid or bioethanol, d) numberof important C-6 compounds can be formed through HMF includesAlkoxymethylfurfurals, 2,5 furandicarboxylic acid,5-hydroxymethylfuroic acid,hydroxymethylfuran, 2,5-dimethylfuran, and e) the diether of HMF are furanderivatives with a high potential in fuel or polymer applications. Some otherimportant non furanic compounds can also be produced from HMF, namely,levulinic acid, adipic acid, 1,6-hexanediol, caprolactam and caprolactone etc.
8The di?cultyof achieving a highly selective process with a highly isolated yield has thus sofar resulted in a relatively high cost of HMF, restricting its potential as akey platform chemical. The stability of 5-HMF can be improved in reaction byusing suitable extracting solvents like dimethyl sulfoxide (DMSO), methylisobutyl ketone (MIBK) and MIBK-water biphasicsystem. Amongst these solvents, MIBK-Water biphasic system was reported to bethe best solvent system which improves activity especially for fructosedehydration to 5-HMF.6,7,9 Various acidic heterogeneous catalystssuch as Al, Al-Si, Zr phosphate10, niobic acid 11,ion-exchange resins12,13 zeolites14 like Mordinite, H-?,H-ZSM-5, H-Y are reported.
Among these catalysts, zeolites seems to be thepotential option due to its thermal stability, porous structure, adjustableacidity, commercially available and reusability associated with catalyticperformance. Based on the available reported literature, H-USY zeolite and itsmodified versions having additional features of mesoporosity as a catalyst is not explored for fructose dehydration to5-HMF so far. H-USY zeolite is usedin petroleum processes and is a ultrastable form of Y zeolite and was prepared by steaming treatment ofY zeolite.15,16 Activity performance of H-USY can betuned by altering its acidity. To modifythe acidity of H-USY, it is necessary to modify the catalyst during synthesisor by post treatment. A dealumination of zeolite, in which the Al atom isexpelled from the zeolite lattice, is one of the best post-synthesis treatmentsto ulter the acidity. Dealumination by thermal or hydrothermal or chemicaltreatments and acids leaching.
17 The modifed H- USY zeolites, makechanges in the Si/Al ratio of framework, its structure, acidity and porosityusually exhibit improved reactivity, selectivity and coking behaviour for acatalytic reaction, which is of great interest to the petroleum and chemicalindustry.18 Ithas been suggested that the amount of extra-framework Al species formed during the process of dealumination,is one of the key factors that significantly influence catalytic activity.19,20 Theacid treatment in H-USY helps in further dealumination by removing Al fromframework or extraframework and creating mesoporosity which is one of thecriteria for transformation of bulky molecules like fructose. Different acidslike oxalic and nitric acid are reported for this treatment.
21 In this work H-USY was treated withphosphoric (H3PO4) and sulfuric (H2SO4)acid and application of these acidtreated H-USY for 5-HMF synthesis by fructose dehydration, which probably not reported sofar. Inthe present study, H-USY zeolite was modified by treating with 10-30%phosphoric (H3PO4) acid and sulphuric (H2SO4)acid in aqueous medium. The prepared and well characterized catalysts were usedfor its application in fructose dehydration to 5-hydroxymethyl furfuralreaction in biphasic (MIBK-Water) system. The optimization of processparameters and catalyst reusability study was also done. 2.
Experimental2.1. Chemicals& ReagentsH-USY(CBV 760) was procured from Zeolyst International (USA), D-Fructose , Isobutylmethyl ketone (99 % ) was obtained fromM/s Loba Chemie, Mumbai (India), Isopropyl alcohol and toluene were procured from Thomas Baker, Mumbai(India), Ethanol (99%) was supplied by M/s E Merck, Mumbai (India),Phosphoricacid (93%), Sulfuric acid (98%) were taken from Thomas Baker ,Mumbai (India).HPLC grade Acetonitrile and formic acid were procured from M/s Loba Chemie,Mumbai (India). All analytical gradereagents were used as such without any purification. 2.
2. CatalystSynthesis H-USY zeolite was modified by treating withsulphuric and phosphoric acid as follows: 1g of H-USY was added to 50 ml aqueoussolution of 10 wt % phosphoric acid. Resultant mixture was aged at 100oCwith constant stirring for 2 h. After 100oC, 2h ageing, the mixturewas stirred for one more hour. Finally, mixture was filtered and then washedwith 1 L of distilled water, followed by drying (120°C) in air for 6 h and thencalcined at 500oC for 5h. The final sample was designated as 10P-Y.
Similarly, 20P-Y and 30P-Y samples were prepared using aqueous solution of 20and 30 wt % phosphoric acid Similar procedure was followed to preparecatalysts by acid treatment with different percent of sulphuric acid on H-USYand was designated as 10, 20 and 30S-Y, respectively. 2.3 Catalyst characterizationXRD plots of synthesized catalysts were recorded on X-raydiffractometer P Analytical PXRD system, Model X-Pert PRO-1712 using Cu K?(?=1.
5404 Å) radiation for the phase identification at a scanning rate of0.0671°/s in the 2? range from 5 to 50°. Relative crystallinity was calculatedby considering the peak intensities of 10-30P-Y and 10-30S-Y zeolite samples ascompared to parent H-USY sample. The crystallinity of H- USY is considered as100%. The total integrated intensities of five peaks at 2q =6.33o, 10.36o,12.
14o, 15.97o, 24.03o were considered for thecomparison.The% relative crystallinity = ( Ai/AR)*100 (1)Where Ai : Total integratedintensities of the five peaks of 10-30P-Y and 10-30S-YAR: Total integratedintensities of the five peaks of H-USY. The total acidity andacid strength associated with sites were measured by NH3 TPD using aMicromeritics AutoChem (2910, USA) equipped with thermal conductivity detector.
For each experiment, prior to the measurements, 100 (± 2) mgsample was dehydrated at 400 ?C in He (30 cm? min?1)for 1 h. The temperature was then decreased to 50 ?Cand then NH3 was allowed to adsorb by exposing sample to a gasstream containing 10% NH3 in He for 1 h. It was then flushed with Hefor another 1 h. The NH3 desorption was carried out in He flow (30cm? min?1) by increasing the temperature up to 600 ?Cwith a heating rate of 10 ?C min?1. FTIR spectra & Pyridine-IR of the sampleswere scanned on a Perkin Elmer spectrum in the domain of 450-4000 cm-1.Energy dispersive analysis X-ray (EDAX) was done formicro structural and compositional analysis. The samples were recorded onAMETEK (EDAX) of detector type Octane Elite Plus and detector is SIN-C2.
Foranalysis, the powder samples were stick on the copper grids, that grids weresubjected to analysis. The solid state 31P and 27Al MAS NMRspectra were generated on a JEOL- 400 MHz spectrometer, operated at 9.39 tesla.A fine powder of sample was placed in 4 mm zirconia rotor and spun at 8 KHz for31P and 27Al.2.
4 Catalytic evaluation Fructose transformation to 5-HMF over H-USY and acid modifiedH-USY zeolite was evaluated in a 150 ml SS316 pressure autoclave. Thetemperature was monitored with an accuracy of ± 0.5 K with PID controller. In astandard run, fructose (1g), catalyst(1g) and 50 cc of MIBK & water mixture (MIBK:Water volumeratio of 10:1 i.e. 45.
5 cc of MIBK &4.5 cc of water) was placed in the autoclave. The reaction was conducted in thetemperature of 100-140oC for 5h at 600 rpm. As per the open literature 11,33,34the external diffusion does not interfere the overall rate of reaction unlessstirrer speed is very low (<250rpm) or the viscosity of reactant mixture isvery high. Thus, speed of agitation of 600rpm was maintained for all studiedexperiments. Increasing of the stirring speed did not show any change incatalytic activity (not shown). It is also documented that there is no externalor internal mass transfer resistance below 82µm average particle size.
In thepresent work, average particle size of 0.7µm was maintained for all theexperiments. 22-25 After 5h of reaction,the reactor was cooled down by rapid quenching under tap water and then wholemixture was centrifuged for catalyst separation.
The decanted reaction mixturewas then analyzed using HPLC (Dionex Ultimate 3000 system with a binarygradient pump, an auto sampler, a UV/vis detector and chromelon software). The analysis of product was carried out on aThermo make C18 column (5µm × 4.6 mm × 250 mm) using 1:9 v/v acetonitrile:water, formic acid (0.1%) as mobile phase with a 1 ml/min flow rate.
Anexternal standard calibration was used for quantification of various products. Activityvalues were calculated as:Fructose Conversion (%) = (Fructose inFeed – Fructose in Product)/Fructose in Feed) * 100 (2)5-HMF Selectivity (%) = 5-HMF inProduct/Total product formed * 100 (3)5-HMF Yield (%) = % Fructose conversion x % 5-HMF Selectivity/ 100 (4)