Production of Chemicals in Supercritical Water

Abstract

Supercritical water (SCW) is expected to be a green solvent for dissolving substances, for chemical synthesis, or for chemical reactions, and thus various study has been carried out. Production of chemicals has been found possible in SCW. This chapter reviews the chemical production in terms of feedstocks and reactions. The feedstocks can include biomass (cellulose, hemicellulose and lignin), plastics, other wastes (e.g., tire, rubber), inorganics and waste water. The reactions include SCW gasification (where hydrolysis and pyrolysis take important roles), SCW oxidation, depolymerization, precipitation, hydrothermal synthesis, other organic reactions for synthesis of chemicals. In these reactions, roles of H 2 O are: (1) Reactant/product (hydrolysis, hydration, hydrogen source and freeradical chemistry) or catalyst (Acid/base catalyst precursor and catalyst in the transition state); (2) Intermolecular interactions in high temperature water: Solvation effects (effects of preferential solvation, hydrophobicity and solvent dynamics) and density inhomogeneity effects (ions, organic compounds, noble gases and radicals); (3) Medium: Energy transfer, diffusion and solvent cages and phase behavior. However, low selectivity and yield and high production cost are barriers for the commercialization of production of chemicals in SCW.