Production of acetic acid from lignocellulosic biomass in the presence of mineral acid and oxygen under hydrothermal condition

Abstract

Nowadays, lignocellulosic biomass is considered as renewable source for the substitute of traditional fossil energy resources. The production of biofuel intermediates such as 5-hydroxymethylfurfural (5-HMF), levulinic acid and γ-valerolactone (GVL), and commercially interesting compounds such as lactic acid and ethylene glycol from biomass has become an important issue for world-wide researchers. In this work, we focused on the conversion of lignocellulosic biomass into acetic acid through a "one-pot two-step" method over inorganic acids in aqueous media. The first step was the hydrolysis of the raw biomass with sulfuric acid at 190℃, 1.0 MPa N2 for 1 h. After that, the reaction was changed to 2.0 MPa O2 and allowed to react for another 9 h. HPLC analysis of the result mixture showed that mass yield of acetic acid from corn stover was up to 21.3%, and the selectivity of acetic acid was as high as 84.6% of the total liquid products. Besides, the other lignocellulosic biomass feedstocks such as corn cob, bagasse, bamboo, poplar and pine were also successfully converted into acetic acid in good yields under the optimized reaction condition. In addition, the stability of the catalyst acid was examined, and the recovery of the catalyst acid is about 95%. Thus, to achieve the reuse of the catalyst acid, the addition of extra 10% catalyst acid after each catalytic cycle was needed. Finally, the reaction pathway was explored by using the components of the lignocellulosic biomass feedstocks as the starting materials (sugars etc.). The results showed that the carbohydrates especially hexoses were the main source of acetic acid. It was dehydrated and hydrolyzed into the intermediate levulinic acid, which was then oxidized into acetic acid by C-C bond oxidative cleavage. The current method provided a new access to the bulk acetic acid from sustainable raw biomass.