Conventional and microwave assisted hydrolysis of urban biowastes to added value lignin-like products

The hydrolysis of fermented urban wastes at alkaline pH in the 60-200 °C range has been carried by microwave and/or by conventional heating. It is shown that the recalcitrant lignin fraction of these materials may be converted to added values soluble lignin-like products in high yields. The hydrolysate products are mixture of complex polymeric molecules which maintain the memory of the proximates of the pristine materials. The reaction heating mode does not to affect the product nature. Microwave heating allows to obtain the same product yields as conventional heating in 1-2 order magnitude lower time. The kinetics of the reaction carried out by microwave heating is however strongly dependent upon the reactor configuration and applied power. It is possible to achieve 50-60 % yields of soluble lignin-like products at relatively low temperature 100 °C. The obtained yield vs. temperature trend in the 22-100 °C range indicates that even higher yields may be obtained at higher temperature. The results offer worthwhile research scope in order to assess the optimum microwave system configuration, operation frequency, and power level and pulsing mode applied, to be compared with conventionally heated reactors at temperature above 100 °C.