Effect of type and concentration of acid on characteristics of functionalized biochar and its performance in converting fructose to 5-HMF

Abstract

Biomass, with its high cellulosic content, represented renewable source capable of being converted into essential platform chemicals like 5-hydroxymethylfurfural, levulinic acid, formic acid, and furfural. Currently, conversion of fructose to 5-HMF was achievable through various acid homogeneous catalysts. Although these catalysts yield higher outputs, they might pose challenges in recycling and corrosion issues. This thesis's novel approach involved preparing heterogeneous catalysts through pyrolysis and hydrothermal treatment of watermelon rind to create watermelon rind biochar (WB). Subsequently, WB underwent functionalization using HCl, H2SO4, and H3PO4 at concentrations of 1.6, 3.2, and 4.8N, respectively, at temperatures of 150 °C. These treated WB samples, identified as xWBy (where x denoted acid used and y indicated concentration), served as acidic heterogeneous catalysts. To observe catalytic performance, 0.2 g of biochar catalyst and fructose 40 w/v% were mixed with 30 mL of DI water in autoclave reactor, maintaining temperature of 160 °C for 90 mins. Characterization of pristine and functionalized biochar samples was conducted using Field emission scanning electron microscopic (FESEM), N2 adsorption/desorption, elemental analysis, Fourier transform infrared spectroscopy (FTIR), and Ammonia-temperature programmed desorption (NH3 – TPD). Findings revealed that pristine biochar treated with 4.8N sulfuric acid displayed a combination of microstructural and mesoporous properties, processing specific surface area of 464 m2/g and pore volume of 0.33 cm3/g. Additionally, successful incorporation of acidic functional groups, particularly sulfonic groups, was observed, enabling them to act as acids and facilitate proton transfer to fructose molecules, producing 5-HMF. Quantity of acidity, confirmed via NH3-TPD analysis, measured at 4.31 mmol/g. These catalysts provided fructose conversion of 72.3% along with the highest 5-HMF yield and selectivity of 46% and 63%, respectively. Functionalized biochar showed significant potential in utilizing a cost-effective and efficient catalyst derived from agricultural sources for 5-HMF production.