Abstract
The production of carboxylic acids by partial wet oxidation of alkali lignin at elevated temperatures and pressures was studied experimentally. Two different heteropoly acids, phosphotungstic acid (H3PW12O40) and phosphomolybdic acid (H3PMo12O40), were used to catalyze the oxidation of lignin under hydrothermal conditions. Factors influencing the total yield of carboxylic acids formed during the partial oxidation of lignin were investigated. Formic, acetic and succinic acids were the major products identified. Of the two catalysts used, phosphomolybdic acid gave the most promising results, with carboxylic acid yields and lignin conversions of up to 45% and 95%, respectively.
Highlights
IntroductionIndustrial production of a wide range of chemicals and fuels relies greatly on fossil resources
Industrial production of a wide range of chemicals and fuels relies greatly on fossil resources.uncertainty surrounding oil prices and dwindling reserves of extractable fossil fuels, along with growing environmental concerns, have resulted in increased attention being given to the possible replacement of existing fossil-based feedstocks with renewable resources [1]
Acetic, and succinic acids were the main carboxylic acid compounds identified by high-performance liquid chromatography (HPLC), and glutaconic and malonic acids were among the compounds identified in trace amounts
Summary
Industrial production of a wide range of chemicals and fuels relies greatly on fossil resources. Non-catalytic partial wet oxidation of lignin in an alkaline condition to produce carboxylic acids has been previously studied in [10], where formic acid, acetic acid, succinic acid, oxalic acid and glutaconic acid were the main products identified These compounds are important commodity chemicals in themselves, but are intermediates in the production of various fuels and chemicals through further transformations. It can be expected that in the treatment of solid biomass, they are prone to low catalytic activity, due to poor access for solids on the catalyst surface It is, important to find suitable homogenous catalysts that are readily separable and reusable after partial wet oxidation and that have the lowest possible environmental impact. The influence of different operational conditions is investigated, to determine the optimal conditions to achieve the maximum yield of products and lignin conversion
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