Kinetics and Deactivation Mechanisms of a Solid Bronsted Acid Catalyst in Catalytic Conversion of Sucrose into Levulinic Acid

Abstract

Levulinic acid (LA) is identified by the US Department of Energy as a platform chemical that can be derived from renewable carbohydrates with acid catalysts. It serves as a building block for a range of bio-based chemicals, materials and fuels. Compared to the traditional mineral acid catalysts, solid Bronsted acids can provide economical and environmental benefits because the solid catalysts can be conveniently recovered for repeated use. However, the solid catalysts may be quickly deactivated in repeated use, a universal technical challenge to various solid catalysts in refining of carbohydrates, which limits industrial application of the heterogeneous acid catalysis. In order to understand the deactivation mechanisms, a typical solid Bronsted acid, Amberlyst-36, was investigated in this research. Kinetic models were used as a tool to quantitatively analyze the catalyst deactivation, including the changes of catalyst's activity and selectivity in different reaction conditions. Hydrochloric acid was used as a benchmark to compare the performance of the solid Bronsted acid. Two major catalyst deactivation mechanisms were identified: (a) the proton loss due to ion exchange with common ions in reaction solution, and (b) the blocked catalyst surface by reaction byproducts or humins. In addition to variations in the reaction rate and the yield of levulinic acid, the deactivation was also examined in detail via an array of characterization techniques. It was found that the catalyst activity could be maintained very well in the presence of both heterogeneous acid and homogeneous acid at appropriate dosages for a high yield of levulinic acid (80%-90%). The deactivated catalyst, after long time use, can also be re-activated after appropriate treatments. According to the author's knowledge, this is the first time systematical study on the combined deactivation effects of ion exchange and humins deposition on a heterogeneous acid catalyst in conversion of carbohydrates into levulinic acid.