Recovery approaches for sulfuric acid from the concentrated acid hydrolysis of lignocellulosic feedstocks: A mini-review

Abstract

The two-step concentrated acid hydrolysis approach is a very efficient method for the generation of monomeric sugars from lignocellulosic biomass, due to its ability to generate near-theoretical sugar yields, at moderate processing times. Sulfuric acid is the most frequently employed acid due to its combination of low cost, high efficiency, and low toxicity and corrosivity compared to other acids. A challenge with this approach is the ability to recover and re-use the acid catalyst in order to make the process economical and reduce waste streams. This paper reviews different acid recovery techniques found in literature and compare them based on performance. The three most investigated and best performing approaches are ion exclusion chromatography, solvent extraction and electrodialysis. Of these, ion exclusion chromatography is the most investigated, and also applied at bigger scale for recovering acid from the final sugar hydrolysate stream. Solvent extraction is a popular option when acid recovery is performed on the intermediate product stream in the two-step process. The studied techniques achieve high acid recovery performance and acid-sugar separation efficiencies, with acid recoveries of 90–99% reported, with low loss of sugars (higher than 90% glucose yields). More research is required into the impact on process performance of re-using the acid catalyst after recovery.