Microwave pyrolysis of polymeric materials: lignocellulosic biomasses as case of study

This research project was focused on the use of microwaves (MWs) as an alternative energy source, microwave (MW), for pyrolytic treatments of waste polymeric materials. Particularly it was focused on processing waste biomasses using a multimode microwave oven in a batch process using different reaction conditions and correlating the products obtained with the biomass tested and the conditions adopted. The liquid fraction, also known as bio-oil, has been obtained with very interesting yields (from 20 to 40 %) and showed very promising performances (i.e. low viscosity and limited water content). A large set of analysis was run to characterize the very complex nature of bio-oil: gas chromatographic analysis (GC-MS, GC-FID; spectroscopic analysis (UV-Vis, FT-IR ATR); NMR (1H-NMR); rheological and proximate analysis. Solids, also known as biochar, have been characterized by FT-IR ATR, ultimate and proximate analysis to assess its possible uses and proving to be suitable as a solid fuel for carbon sequestration processes. Furthermore the samples did not contain any extractable materials. -cellulose was studied in order to evaluate the behaviour of the main component of lignocellulosic biomasses during microwave assisted pyrolysis (MAP). With the same aim MAP of Kraft lignin at different pressure was tested to correlate the residual pressure on the yield of aromatics compounds generated from the most abundant aromatic containing polymer. Finally MAP of common wastes coming from different lignocellulosic sources such as Arundo donax, Oliva europea, Vitis vinifera, and different poplar clones, were tested under different pyrolysis conditions in order to evidence their behaviour during MAP experiments. Various degradation mechanisms of cellulose and Kraft lignin were deeply investigated and some reaction pathways proposed. The interaction between microwave absorbers and feedstocks was also object of this study.