Hydrothermal Processing of Biomass

Abstract

Biomass can be reformed into higher-value fuels using hydrothermal processes that employ high-temperature and high-pressure water as a reaction medium. Hydrothermal processing obviates feedstock drying and can achieve high energy efficiencies through heat integration. Hydrothermal liquefaction occurs under mild conditions (250–350 °C) in which biomass hydrolyzes rapidly and reacts to form a viscous bio-crude oil. At higher temperatures (350–500 °C), catalysts may be employed to promote the formation of CH4-rich gas in the process of catalytic hydrothermal gasification. Supercritical conditions (500–800 °C) may be used to achieve a H2-rich gas through supercritical water gasification (SCWG). The reaction chemistry underlying these hydrothermal processes is complex and not fully understood, but the influence of temperature, pressure, feedstock concentration, and the presence of catalysts on this chemistry has been extensively studied. In this chapter, we review hydrothermal processing of biomass, with a focus on the chemistry that describes biomass conversion under various hydrothermal conditions. Special attention is given to the relatively recent interest in processing aquatic feedstocks, such as algae, in a hydrothermal environment.

Advances in Bioprocess Technology

“…However, it is important to note that beyond the temperature range explored in this study (above 390 C), further increase in temperature from a particular optimum temperature may cause the bio-oil yield to decrease, as commonly observed in several works Akhtar and Amin 2011;Qian et al 2007). This is due to the occurrence of competing reactions such as gasification, condensation, cyclization and repolymerization at higher temperatures that convert bio-oil components formed in the initial stages of the liquefaction process to char, water-soluble and gaseous products which cannot be extracted as bio-oil (Valdez et al 2012;Savage et al 2010).…”

“…Liquefaction of biomass is a process whereby biomass is treated with a solvent at high temperature and pressure. The heated and pressurized solvent acts as a good medium and reactant to break down the complex structure of biomass, thereby producing liquid products (Savage et al 2010). Bio-oil produced is then extracted from the liquid products using organic solvents.…”

Characterization and pyrolysis behaviors of sunflower stalk and its hydrolysis residue

“…[14,15] Biomass structure also has a significant impact on product yields and products during thermal processing. [16] During hydrolysis by aqueous ammonia and/or aqueous alkali, lignin was first degraded into oligomers, and then was degraded into soluble substances. Lignin can be removed from the original biomass to varying degrees through alkaline hydrolysis, while hemicellulose and cellulose have only a small loss.…”

Development of torre-briquetting process to convert mixed MSW into high energy density solid fuel

“…At higher temperature, the process was also reported to be able to produce chlorinefree solid fuel from plastic waste [7]. Since the process uses water as reaction medium, waste with high moisture content can be directly processed without the need of pre-drying, and the hot water can act as solvent, reactant, and catalyst for the processed materials [8].…”