CATALYTIC CONVERSION OF GLUCOSE TO VALUE ADDED CHEMICALS

Abstract

In very recent the production of fuels, fuel additives and valuable chemicals from the renewable sources such as biomass has gained significant attention globally due to the faster depletion of conventional fossil sources and environmental issues. Glucose is the most abundant and environmentally friendly hexose present in nature and can be obtained from the hydrolysis of lignocellulose biomass. Glucose can be a promising alternative for the production of value-added chemicals such as 5-hydroxymethylfurfural (HMF), levunilic acid (LA), formic acid (FA), lactic acid, acetic acid, gluconic acid etc. Among all these chemicals, HMF has significant commercial value and most importantly this compound has been recognized as a top ten building block chemical globally. HMF can also be converted into many others valuable compounds such as dimethylfuran (DMF), furandicarboxylic acid (FDCA), caprolactum etc. This study focused on the development of catalyst and catalytic process for the conversion of glucose to HMF. Sulphated zinc oxide catalysts were prepared by precipitation and wetness impregnation method. The catalysts were characterised by different techniques such powdered- X-ray diffraction (XRD), field emission scan electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), specific surface area (BET), thermogravimetric analysis (TGA) and ammonia-temperature programmed desorption (NH3-TPD). Catalytic activity was evaluated in a three neck flat bottom glass reactor equipped with a reflux condenser and temperature controlled magnetic stirrer. To maximize glucose conversion and HMF yield, various reaction parameter such as temperature (180-280oC), time (1-12 h), sulfuric acid concentration (1- 4.5 M) in the catalyst, glucose to catalyst weight ratio (0.5 - 3) were varied. The reaction products were analysed in an offline high-performance liquid chromatograph (HPLC) equipped with BIORAD Aminex 87H ion exclusion column and refractive index (RI) detector. Results demonstrated that, 2.5 M-SO42-/ZnO catalyst showed 15.8% yield of HMF with complete conversion of glucose at 220 °C after 6 h of reaction in presence of dimethylsulphoxide (DMSO) as a solvent. The formation of other unidentified side reaction products restricted the higher yield of HMF. Reaction parameter study suggested that, higher reaction temperature (> 220oC), higher substrate to catalyst ratio (> 0.5) was not beneficial for higher yield of HMF. Longer reaction time did not at all affect the yield of HMF. The results obtained also suggested that the acidic nature of catalyst was responsible for the high conversion of glucose.