An overview of recent advances in research on selective conversion of carbohydrates into products with hydrothermal chemistry is given. Conversion methods tend to use acid- or base-catalysed reactions and oxidation reactions. Conversion products that can be selectively produced include acetic acid, formic acid, lactic acid, levulinic acid, 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (2-FA). Future conversion paths and possible new products that can be formed with hydrothermal chemistry include aldol/reverse condensation, dehydration, benzilic acid rearrangement, keto-enol tautomerization, Lobry de Bruyn–Alberda van Ekenstein transformation and oxidation reactions.

Rapid and highly selective conversion of biomass into value-added products in hydrothermal conditions: chemistry of acid/base-catalysed and oxidation reactions

Subcritical water, that is, water above the boiling and below critical point, is a unique and sustainable reaction medium. Based on its solvent properties, in combination with the often considerable intrinsic water content of natural biomass, it is often considered as a potential solvent for biomass processing. Current knowledge on biomass transformation in subcritical water is, however, still rather scattered without providing a consistent picture. Concentrating on fundamental physical and chemical aspects, this review summarizes the current state of knowledge of hydrothermal biomass conversion in subcritical water. After briefly introducing subcritical water as a reaction medium, its advantages for biomass processing compared to other thermal processes are highlighted. Subsequently, the physical-chemical properties of subcritical water are discussed in the light of their impact on the occurring chemical reactions. The influence of major operational parameters, including temperature, pressure, and reactant concentration on hydrothermal biomass transformation processes are illustrated for selected carbohydrates. Major emphasis is put on the nature of the carbohydrate monomers, since the conversion of the respective polymers is analogous with the additional prior step of hydrolytic depolymerization.

Subcritical Water as Reaction Environment: Fundamentals of Hydrothermal Biomass Transformation

Conversion of glucose and cellulose into value-added products in water and ionic liquids

This study highlights the recent advances in the treatment and value addition of lignocellulosic wastes (LCW) with main focus on domestic and agro-industrial residues. Mechanical, physical and biological treatment systems are brought into perspective. The main value-added products from lignocellulosic wastes are summarized in a manner that pinpoints the most recent trends and the future directions. Physicochemical and biological treatment systems seem to be the most favored options while biofuels, biodegradable composites and biosorbents production paints a bright picture of the current and future bio-based products. Engineered microbes seem to tackle the problem of bioconversion of substrates that are otherwise non convertible by conventional wild strains. Although the main challenge facing LCW utilization is the high costs involved in treatment and production processes, some recent affordable processes with promising results have been proposed. Future trends are being directed to nanobiotechnology and genetic engineering for improved processes and products. The paper presents state of the art review of the dual advantage of handling LCW for cleaner environment and production of renewable bio-products.

https://www.ajol.info/index.php/ajb/article/download/60134/48385

Recent advances in pretreatment of lignocellulosic wastes and production of value added products

Hydrothermal conversion of carbohydrate biomass into formic acid at mild temperatures.

To increase the acetic acid yield in a wet oxidation of lignocellulosic wastes, a new two-step reaction process is proposed. The first step produces 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (2-FA) by dehydration of monosaccharides which are formed by hydrolysis of polysaccharides under the condition of non-supply of oxygen. In the second step, HMF and 2-FA are oxidized to acetic acid with oxygen newly added. The yield increased about twofold.

Hydrothermal process for increasing acetic acid yield from lignocellulosic wastes

A new process for producing calcium magnesium acetate (CMA) deicer with acetic acid, produced by wet oxidation of organic wastes, and Ca/Mg wastes is proposed. Four kinds of representative organic waste were used as low-cost raw materials, for production of acetic acid, which was then converted to CMA by mixing with a Ca/Mg source such as oyster shells and industrial Mg wastes. The conversion efficiencies to acetic acid and from acetic acid to CMA achieved 14–16% and higher than 99%, respectively.

A New Process for Producing Ca/Mg Acetate Deicer with Ca/Mg Waste and Acetic Acid Produced by Wet Oxidation of Organic Waste

Supercritical water oxidation (SCWO) is an attractive alternative mean for treatment of organic wastes of high water contents. However, for most of organic compounds, acetic acid is a stable intermediate product, and a high reaction temperature or catalyst is required for its complete decomposition. In this study, a new method of utilization, rather than decomposition, of residual acetic acid produced by supercritical water oxidation of beef suet was investigated. That is, the residual acetic acid was converted into (CH3COO)2Ca, which can be used as a deicer to reduce environmental pollution problems caused by the road deicing salts (NaCl and CaCl2) presently available. Results showed that acetic acid of high concentration (6,000 mg / l) and relatively high purity was obtained under the condition of 400 °C of reaction temperature, 30 seconds of reaction time and 150 % of H2O2 supply, and 97 % of residual acetic acid was covered to (CH3COO) 2Ca by adding Ca(OH)2 or CaCO3 in the both cases of its addition before and after the oxidation reaction. However, in the former case, when excess Ca(OH)2 or CaCO 3 was added, some products by thermal decomposition and hydrolysis appeared, and production of acetic acid decreased.

Production of Calcium Acetate from Acetic Acid Formed by SCWO of Beef Suet. Utilization of acetic acid formed by supercritical water oxidation of garbage. 1 st Report.

The production of acetate for use as a roadway deicer by wet oxidation of organic waste

PROBLEM TO BE SOLVED: To provide a treatment method for an organic waste for almost perfectly decomposing garbage in a short time while acetic acid of an intermediate product is effectively utilized to obtain valued resources SOLUTION: Calcium carbonate or calcium hydroxide is added to an organic waste or its decomposed material before or after supercritical water wet oxidation reaction, and the organic waste is oxidation decomposed by the supercritical water wet oxidation reaction

Naohiro Sato

Papers

Hydrothermal process for increasing acetic acid yield from lignocellulosic wastes

A New Process for Producing Ca/Mg Acetate Deicer with Ca/Mg Waste and Acetic Acid Produced by Wet Oxidation of Organic Waste

Production of Calcium Acetate from Acetic Acid Formed by SCWO of Beef Suet. Utilization of acetic acid formed by supercritical water oxidation of garbage. 1 st Report.

The production of acetate for use as a roadway deicer by wet oxidation of organic waste

Treatment method for organic waste