Energy assessment of biofuels production from fast pyrolysis of sugarcane straw, and upgrading of the bio-oil produced through hydrotreatment

Abstract

Second-generation biofuels are produced from non-food biomass such as the lignocellulosic residues of sugarcane processing, namely, bagasse and straw. Sugarcane processing is one of the most important economic activities in Brazil, producing ethanol and sugar for domestic and international markets. The use of these lignocellulosic residues would increase the second-generation biofuel production without increasing the sugarcane planted area. Among the second-generation technologies available nowadays, the fast pyrolysis is a thermochemical process that produces mainly bio-oil, which is a liquid that has several advantages in transportation, pumping, storage and handling, in comparison to solid biomass. Moreover, the bio-oil can be upgraded in order to obtain biofuels of higher added-value. Among feasible upgrading technologies for bio-oil, the hydrotreatment is one of the most promising for eliminating the reactive functionalities of the bio-oil by removing oxygen or cracking large molecules in the presence of hydrogen; however, the hydrogen consumption is significant. In this way, the aim of this study is to evaluate the biofuel production by means of fast pyrolysis of sugarcane straw, followed by a hydrotreatment to upgrade the produced bio-oil. The evaluation is performed through an energy assessment. The energy and mass balances of the processes were performed using the software Aspen Plus. Furthermore, the possibilities of the integration of the bio-oil production and upgrading into the conventional ethanol and sugar production process will also be evaluated. The final products of bio-oil upgrading plant showed a yield of 0.086 kg/kg of dry straw and 0.080 kg/kg of dry straw for renewable gasoline and diesel respectively. The heat integration of pyrolysis process, hydrotreating and hydrogen production process presented a significant potential for steam production. This could be integrated into the conventional sugar and ethanol production process, which could save 28.6% of steam and increase the surplus electricity in 6%.