Production of biofuels additives from lignocellulosic biomass by heterogeneous acid catalysis

Lignocellulosic biomass represents the most abundant renewable resource with great potential for a sustainable production of energy products and platform chemicals. Among these 5-hydroxymethyl-2-furfural (HMF), obtained by its acid-catalyzed conversion, has attracted considerable attention because it can be converted in high performing biodiesel additives. In this work we studied the acid-catalyzed etherification of HMF with ethanol to biodiesel additives on heterogeneous solid acid catalysts that allow to overcome the drawback connected with the traditional homogeneous acid systems. We selected catalysts with both microporous and mesoporous structure, respectively based on MOR, MFI and BEA zeolites in H+ and NH4+ form, and on zirconia and sulfated zirconia supported on SBA-15 (Z-SBA-15 and SZ-SBA-15). The catalytic reaction of HMF with ethanol was carried out in an autoclave (Teflon lined) at 140 °C under autogeneous pressure . The reaction system was stirred for 5 h at about 1500 rpm and the reaction products were analyzed by a Finnigan GC –Mass Spectrometer. We obtained valuable biodiesel additives and intermediates such as 5-(ethoxymethyl)furan-2-carbaldehyde (EMF), 1,1-dietoxyethane (DE) and ethyl 4-oxopentanoate (EOP). The data of conversion and selectivity evidenced that all forms of zeolite are able to convert HMF: with respect to MOR and MFI, BEA gives the highest conversion of HMF. Moreover, the tridimensional channel system of BEA in ammonium form showed the best selectivity in EMF, whereas the formation of EOP was favored by using the corresponding H+ form. As regards mesoporous catalysts, we observed that the selectivity to the products is closely related to the nature of acidic sites. In fact when a high Brnsted acidity is present on the catalysts, like in the case of SZ-SBA-15, the yield in EOP is increased, whereas EMF formation is favored by Lewis acidity. For mesoporous catalysts the structure - activity relationship was derived by FT -IR pyridine adsorption characterization.