Hydrolysis of Golenkinia sp. biomass using Amberlyst 36 and nitric acid as catalysts

Abstract

Golenkinia sp. is a microalga with potential commercial value because of its high carbohydrate content (more than 40%). The major challenge is to find hydrolytic processes that can efficiently convert these carbohydrates into fermentable sugars. Hydrolysis of microalgal biomass generally uses a dilute liquid acid catalyst, such as hydrochloric acid, sulfuric acid, or nitric acid. However, neutralization and desalting processes are needed after this procedure for production of a hydrolysate that is suitable for use as a fermentable broth. These processes require large amounts of energy and are, therefore, very expensive. In this work, we hydrolyzed 10g/L of Golenkinia sp. using 9.2g/L of Amberlyst 36 with 0.01N of nitric acid at 150°C for 160min, a process that required no desalting. 88% of total sugar yield mainly glucose and galactose was obtained after a 120min reaction. Our results also showed that these 2 catalysts had a prominent synergistic effect, in that the yield when both catalysts were used together was much greater than the sum of the yields of the individual catalysts. The small amount of nitric acid reduced the particle size of the Golenkinia substrate, and this led to a greater total surface area and 135% increase in the hydrolysis efficiency of Amberlyst 36. The Golenkinia sp. hydrolysate (3.7g/L sugars) was used as a carbon source for 2,3-butanediol fermentation by Klebsiella oxytoca, with no need for further detoxification or deionization processes. The yield was 0.19g of 2,3-butanediol per g of sugar.