Strategic adsorption/desorption of cellulases NS 50013 onto/from AVICEL PH 101 and protobind 1000

Abstract

Desorption of active cellulases from lignocellulosic substrates is a potential technique to reuse cellulases for the production of bioethanol. For desorption studies, adsorption of cellulases had to be performed first. Adsorption of cellulases NS 50013 onto microcrystalline cellulose (Avicel PH 101) and wheat straw lignin (Protobind 1000) was studied. It was found that Protobind adsorbed twice the amount of cellulases than Avicel did. An adsorption strategy developed was to work at pH 5 and a temperature less than 323 K to get maximum adsorption on the cellulose component, less adsorption on the lignin component of lignocellulosic materials, and to harmonize adsorption temperature with the industrial hydrolysis situation. Desorption of cellulases from Avicel and Protobind over a range of 298 K to 343 K and a pH of 6 to 9 was studied. Desorption obtained at pH 9 and 333K was optimum for both Avicel and Protobind. Hence, desorption was enhanced by 21 % and 11% for Avicel and Protobind respectively. The cellulases activity for Avicel was 48 FPU mL-1 at pH 9, 333 K, 5% glycerol, representing 91 % of the initial activity and for Protobind, the activity was 33 FPU mL-1 which represents about 66 % of the initial activity. All of these values were higher than ever reported in literature. At pH 5 and 298 K the amount of cellulases desorbed from untreated wheat straw (WS) was 33 % of those initially used for the adsorption step. It was increased to 42 % when 30 % delignified WS was used, and was further increased to 48 % for 60 % delignified WS. Desorption obtained for 60 % delignified WS was 75 % at pH 9, 333K and 5% glycerol. The desorption strategy recommended for bioethanol producing industries, is: 1) removal of lignin; 2) adsorption of cellulases at pH 5 and lower than 323K; 3) hydrolysis of lignocellulosic material; and 4) desorption of cellulases from non-hydrolyzed material at 333 K, pH 9, with 5-10 % glycerol. The proposed strategic desorption of cellulases may reduce the cost of Canadian bioethanol production by 26.5 % due to 75 % recyclability of active cellulases.