Production of levulinic acid from cellulose by hydrothermal decomposition combined with aqueous phase dehydration with a solid acid catalyst

Abstract

In this paper we introduce a process to produce levulinic acid from cellulose without the use of a homogeneous acid catalyst. The process consists of 2 reaction steps: (1) non-catalytic hydrothermal decomposition of cellulose at moderate temperatures (190–270 °C) to produce organic water-soluble compounds including glucose and HMF; (2) water-soluble compounds are further reacted with a solid acid catalyst at relatively low temperatures (160 °C) to produce levulinic acid and formic acid. Unreacted cellulose can be recycled back to the first reactor for further decomposition. The cellulose hydrothermally decomposes at high initial cellulose concentrations of 29 wt% while maintaining high selectivity towards water-soluble compounds, which are levulinic acid precursors. The maximum amounts of usable water soluble organics are produced at relatively higher temperatures and shorter residence times (220 °C and 30 min). Amberlyst 70 was used as a solid acid catalyst for conversion of the water soluble organics into HMF, levulinic acid and formic acid. Amberlyst 70 has comparable activity to HCl, with a slightly lower selectivity towards levulinic acid. The maximum obtainable yield of levulinic acid we obtained was 28% of the theoretical. This study lays the grounds for further optimization to produce levulinic acid from cellulose without using homogeneous acid catalysts.