Less severe reaction conditions to produce levulinic acid with reduced humins formation at the expense of lower biomass conversion: Is it economically feasible?

Abstract

Esters of levulinic acid constitute a promising class of renewable fuel additives that improve the cold properties of diesel and reduce soot emissions. However, the production of levulinic acid via thermolysis of biomass has low selectivity, a problem that compromises both yield and reactor operability, with impacts on cost. The main undesirable byproducts of this process are called humins, a dark insoluble residue. This work proposes and simulates an alternative reactor arrangement based on experimental results and analyzes reaction conditions via design of experiments to determine the factors that influence humins formation in the production of levulinic acid from sugarcane bagasse. Results indicate that a high residence time in hydrolysis increases humins formation, and a high temperature was found to deteriorate selectivity even further. Therefore, a high catalyst loading combined with low residence time and temperature is required to decrease losses. Considering the limitations of the simulated model, the conditions that minimize humins formation led to yields of 109 kg of furfural (from hemicelluloses) and 74 kg of levulinic acid (from cellulose) per dry tonne of sugarcane bagasse, with the production of 58 kg of humins. Results of economic analysis demonstrated that if humins disposal is associated with a high cost, low biomass conversion is required to yield a promising economic result, even though this might compromise the yield of levulinic acid and furfural. On the other hand, if value-added applications for humins become available, a similar conclusion applies if their production compromises reactor operability.