Improved Microwave-Assisted Ethyl Levulinate Production Using Rice Husk-Derived Biobased Mesoporous Silica as Catalyst

This study presents the synthesis and characterization of mesoporous silica using biobased silica recovered from rice husks (RHs) as an excellent example of the circular economy. Distinct hydrothermal methods were used, namely, the autoclave hydrothermal method and microwave irradiation. Furthermore, the microwave-synthesized SBA-15 material was subjected to post-functionalization with -SO3H groups using the organosilane 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS). The structural and chemical properties of the prepared materials were rigorously characterized through several techniques, thereby confirming the successful preparation of this functionalized material. Subsequently, the functionalized SBA-15 (CSPTMS@SBA-15) was employed as a catalyst in the synthesis of ethyl levulinate (EL) from 5-hydroxymethylfurfural (5-HMF) using different methodologies: typical high-pressure batch reactor, conventional heating, and microwave irradiation. This investigation aimed to elucidate the influence of microwave and non-microwave heating methods on the efficient conversion of 5-HMF into EL. The findings revealed that the microwave reactor exhibited superior conversion rates and selectivity when compared to the non-microwave heating methods. The study also explored the effects of temperature and utilization of various alcohols as both solvents and reagents. The results demonstrated that higher temperatures favored the production of alkyl levulinate and that complete conversion of 5-HMF was attainable for all the alcohols employed. Specifically, for methanol and ethanol a 100% yield of alkyl levulinates was achieved, while for 1-propanol and butanol a reduction in the yield of alkyl levulinates was observed. These outcomes underscore the feasibility of achieving significant yields of various alkyl levulinates through the utilization of CSPTMS@SBA-15 as a catalyst.