Thermochemical Conversion and Valorization of Woody Lignocellulosic Biomass in Hydrothermal Media

Abstract

Biomass conversion can provide the sustainable and promising alternative solution for the future energy demands and fuel supply. It can also be a major contributor to the chemical demand by acting as primary source for biofuel and value added chemicals. Thermochemical conversion can be a faster solution for this problem. Lignocellulosic biomass is the more preferred to other biomasses as it has uniform composition and well established models for degradation of its constituents such as Cellulose, Hemicellulose and Lignin. This process of thermochemical conversion of biomass is usually performed in the presence of hydrothermal media like water or acetone at high temperature and high pressure. The woody lignocellulosic biomass has a complex sterochemical structure compared to agricultural residues and energy crops. It is depolymerised into small compounds in sub critical and supercritical conditions to form three distinct phases such as: bio-oil, bio-gas and bio-carbon, which has their own significant role in the biorefinery. Based on the process conditions (temperature, pressure, media) the yield of the phases varies accordingly. According to the physicochemical properties of media, the process can be classified as hydrothermal carbonization, hydrothermal liquefaction and hydrothermal gasification. For the past two decades, significant researches is being reported for thermochemical conversion of various lignocellulosic biomass (hardwood/softwood), agricultural residues, fruit shells, cellulose wastes, industrial co-products, etc. in both wet and dry conditions. Also it was found that the wet biomass conversion results in high yield of various chemicals like alkanes, alkenes ketones, aldehydes, acids, alcohols, phenols, esters, ethers and other aromatic compounds with some amount of polymeric impurities. In this chapter more emphasis is given on the thermochemical conversion of woody biomass, its pre-treatment, hydro processing and refining of the products synthesised. It also focuses on the valorization of the end products obtained from the hydrothermal processing into value added chemicals in the presence of homogeneous and heterogeneous catalysts.