Hydrothermal Reduction of Carbon Dioxide to Low-Carbon Fuels

Fangming Jin, Fangming Jin

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351262828
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Combustibles fossiles

The book covers advances in hydrothermal reduction of CO2 into low-carbon fuels. It offers perspectives from chemical engineering, environmental chemicals, organic chemistry, inorganic chemistry, physical chemistry, geology and materials science. It addresses fundamentals and applications of hydrothermal chemical processes, associated materials, and technologies. It describes reduction with biomass and dissociation of water by solar energy-driven two-step process. Challenges and strategies are discussed to facilitate research and development.

1Water under High-Temperature and High-Pressure Conditions and Some Special Reactions under Hydrothermal Conditions

Zheng Shen, Wei Zhang, Xu Zeng, Fangming Jin, Guodong Yao, and Yuanqing Wang

1.1Introduction

1.2Ion Product

1.3Water Density

1.4Dielectric Constant

1.4.1Dielectric Constant of HTW

1.5Hydrogen Bonding

1.6Hydrolysis

1.7Isomerization

1.8Dehydration

1.9Retro Aldol Reaction

1.10Decarboxylation and Decarbonylation

References

1.1Introduction

For water under high-temperature and high-pressure conditions, there are diverse terminologies that have been used in the literature. For example, high-temperature water (HTW) is defined as liquid water above 200°C [1]. Hot compressed water can also be used to denote water above 200°C and at sufficiently high pressure [2]. Water can be divided into subcritical water (below its critical point) and supercritical water (above its critical point) based on its critical point (Tc = 373°C, Pc = 22.1 MPa). The lower limit of temperature of subcritical water can be 100°C in the liquid state [3]. The terminology “near-critical water” is also often employed [4]. Aqueous phase processing is employed in the liquid water at temperatures of 200–260°C and at pressures of 10–50 bar to produce H2, CO, and light alkanes from sugar-derived feedstocks [5]. The terminology “hydrothermal,” which is originally from geology, has been more broadly and popularly used in literatures to refer to the reaction medium of high-temperature and high-pressure water. According to the different main products, it can be divided into hydrothermal carbonization (usually conducted at 100–200°C) [6], hydrothermal liquefaction (often at 200–350°C) [7], and hydrothermal gasification (often at 350–750°C) [8]. Therefore, in this chapter, the terminology “hydrothermal” will be mostly adopted to denote water above 100°C and 0.1 MPa, including subcritical and supercritical water.

The products distribution from hydrothermal biomass conversion, including gas, liquid, and solid, mainly depends on the properties of water at different states. Two competing reaction mechanisms are present: an ionic or polar reaction mechanism typical of liquid-phase chemistry at low temperature and a free radical reaction mechanism typical of gas-phase reactions at high temperature [9,10]. The latter radical reactions are preferred, leading to gas formation [11]. In addition, molecular reaction, which is different from ionic and radical reactions, is molecular rearrangement enhanced by coordination with water and proceeds around the critical region of water [12].

Herein, in the following sections, the representative properties of water under high-temperature and high-pressure conditions will be introduced, such as ion product, density, dielectric constant, and hydrogen bonding, and some special re...