Proteína de soja como aditivo na sacarificação enzimática da biomassa vegetal: desenvolvimento e análise tecno-econômica do processo

Abstract

The implementation of the biochemical conversion process of lignocellulosic biomass into biofuels and other bioproducts still have some technological challenges to be overcome, such as low yield of the enzymatic hydrolysis step and the high cost of cellulolytic enzymes. Among the strategies to increase efficiency of biomass enzymatic saccharification, the use of additives has shown positive effects, since they decrease unproductive adsorption of cellulases in the lignin, reducing loss of enzymes in the process. However, the use of low-cost additives is necessary to make the process economically feasible. Thus, the present study evaluated the use of soy protein as an additive to reduce unproductive adsorption of enzymes during the enzymatic hydrolysis of sugarcane bagasse. In order to achieve this objective, initially, a statistical experimental design methodology was used as a tool to optimize the solids loading and soy protein concentration, setting these variables for subsequent steps of this study at 15% (w/v) and 12% (w/w), respectively. The time profile for glucose release using different enzyme loads allowed to stablish a loading of 10 FPU/g of bagasse and it also showed that it was for the hydrolysis time of 24 hours that soy protein was more effective in relation to the control (hydrolysis without additive). The saccharification of the liquid hot water pretreated sugarcane bagasse at these conditions allowed to increase the amount of glucose released in the process by up to 26%. This condition was validated during the hydrolysis in a 0.5 L reactor, which represents conditions more similar to the industrial reality. Assays performed with the soluble fraction of soy protein and its association with the surfactant Tween 80 showed that it was possible to reduce considerably the additive concentration used in the hydrolysis and still have similar or higher gains than those obtained by 12% (w/w) of soy protein. The physicochemical characterization of the biomass-additive interaction performed by FTIR and by the elemental nitrogen analysis, as well as the verification of the effect of soy protein on the activity and stability of the enzymatic cocktail indicated that the additive, besides reducing the non-productive adsorption between enzymes and lignin, also has a positive effect on the stability of the enzymes. Transversally to these experimental activities, a methodology developed by the LaDABio/UFSCar was used to analyze the reverse techno-economic feasibility of the process, allowing the definition of performance targets within the context of an integrated biorefinery of 1G-2G ethanol, in order to make it economically feasible. This analysis showed that, in order to allow techno-economic feasibility of the use of soy protein in the context of 1G-2G biorefinery, the conversion provided by the additive should be increased and the enzymatic load reduced. In addition, working with 12% (w/w) of protein in the hydrolysis reactor had an interesting result. It led to an increase in the NPV (Net Present Value) of the process, due to the increase in the amount of electric energy generated by the plant due to the burning of the protein in the boilers.