Hydrothermal carbonization of biomass: A summary and discussion of chemical mechanisms for process engineering

TLDR

Hydrothermal carbonization, a century‑old process that dehydrates and decarboxylates biomass to increase its carbon content and calorific value, has received limited attention in recent biomass conversion research. This review aims to summarize the chemical nature of hydrothermal carbonization for process design. The process operates at 180–220 °C in water under saturated pressure, employing hydrolysis, dehydration, decarboxylation, aromatization, and condensation polymerization to transform biomass. The review shows that hydrothermal carbonization produces a lignite‑like fuel from moist biomass residues, enabling broader energetic applications and informing fundamental process‑design improvements. © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd.

Abstract

Abstract Hydrothermal carbonization can be defined as combined dehydration and decarboxy lation of a fuel to raise its carbon content with the aim of achieving a higher calorific value. It is realized by applying elevated temperatures (180–220°C) to biomass in a suspension with water under saturated pressure for several hours. With this conversion process, a lignite‐like, easy to handle fuel with well‐defined properties can be created from biomass residues, even with high moisture content. Thus it may contribute to a wider application of biomass for energetic purposes. Although hydrothermal carbonization has been known for nearly a century, it has received little attention in current biomass conversion research. This review summarizes knowledge about the chemical nature of this process from a process design point of view. Reaction mechanisms of hydrolysis, dehydration, decarboxylation, aromatization, and condensation polymerization are discussed and evaluated to describe important operational parameters qualitatively. The results are used to derive fundamental process design improvements. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd