Yuanhui Zhang

Abstract

All fossil fuels found in nature—petroleum, natural gas, and coal, based on biogenic hypothesis—are formed through processes of thermochemical conversion (TCC) from biomass buried beneath the ground and subjected to millions of years of high temperature and pressure. In particular, existing theories attribute that petroleum is from diatoms (algae) and deceased creatures and coal is from deposited plants.

TCC is a chemical reforming process of biomass in a heated and usually pressurized, oxygen deprived enclosure, where long-chain organic compounds (solid biomass) break into short — chain hydrocarbons such as syngas or oil. TCC is a broad term that includes gasification, including the Fisher-Tropsch process, direct liquefaction, hydrothermal liquefaction, and pyrolysis. Gasification of biomass produces a mixture of hydrogen and carbon monoxide, commonly called syngas. The syngas is then reformed into liquid oil with the presence of a catalyst. Pyrolysis is a heating process of dried biomass to directly produce syngas and oil. Both gasification and pyrolysis require dried biomass as feed­stock, and the processes occur in an environment higher than 600°C. The hydrothermal liquefaction (HTL) involves direct liquefaction of biomass, with the presence of water and perhaps some catalysts, to directly convert biomass into liquid oil, with a reacting temperature of lower than 400-C.

This chapter only covers the topic of HTL of biomass. Biomass feedstocks include biowaste (manure and food processing waste), lignocellulose (crop residue), and algae. The chapter is in two parts. The first part covers HTL fundamentals based on the current knowledge, and the second part is a summary of state-of-the-art knowledge of HTL for various feedstocks. The author has attempted to organize this chapter for a variety of readers who are interested in the topic of HTL, including students and professionals.

Biofuels from Agricultural Wastes and Byproducts Edited by Hans P. Blaschek, Thaddeus C. Ezeji and Ju rgen Scheffran 201 © 2010 Blackwell Publishing. ISBN: 978-0-813-80252-7