Hydrolysis of microalgal biomass by using solid acid catalyst

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 10 g/L of Golenkinia sp. using 9.2 g/L of Amberlyst 36 with 0.01 N of nitric acid at 150℃ for 160 min, a process that required no desalting. 88% of total sugar yield mainly glucose and galactose was obtained after a 120 min 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. Futhermore, rotating packed bed reactor was suggested for recycle of Ambelryst 36. The structure of Amberlyst 36 was destroyed due to physical forces. Rotating packed bed prevented that damage and enhanced recyclability of Amberlyst 36. When the Amberlyst 36 was packed in the column, it could be used infinitely without significant destruction. Also, cell debris coated on surface of Ambelryst 36 was eliminated by sonication to maintain more than 70%(g/g) of total sugar yield until 6th recycle run. After 11th recycle run, the sulfonic groups of Amberlyst 36 was totally neutralized or missed. These dead Amberlyst 36 was reactivated with sulfuric acid and it recovered to initial state. Those developed process was optimized to hydrolysis 10g/L of microalgal biomass, but that was not suitable for concentrated biomass. Therefore newly Amberlyst 45 was introduced, and 71.9 % of total sugar yield was obtained at 180℃ when 30g/L of biomass was loaded. Unfortunately, in case of over the 50g/L biomass, 31.3% of total sugar was obtained, therefore these system was not acceptable for hydrolysis concentrated biomass effectively.