Assessment of Pre-Treatment Methods for Bio-ethanol Production from Sugarcane Bagasse

Abstract

Lignocellulosic biomass such as sugarcane bagasse is non-food biomass that can be used to produce ethanol. Lignocellulose is a complex network of cellulose, hemicellulose and lignin, which requires pre- treatment to improve access to cellulose for hydrolysis which produces glucose for fermentation. Lignin prevents access to cellulose thus delignification using alkaline is often included before hydrolysis. A variety of pre-treatment methods exist requiring different raw materials and operating conditions thus having different economics and environmental impacts. This paper aims to use computer modelling in an optimisation environment called GAMS (General Algebraic Modelling System) to screen a host of pre- treatment options of sugarcane bagasse for bio-ethanol production. The criteria to determine the best pre- treatment option evaluates both economic and environmental objectives. Pre-treatment options included steam explosion, with and without acid catalysis, and acid pre-treatment. Methane was produced from xylose formed in pre-treatment in all options. Delignification using NaOH was included in some investigated pre-treatment flowsheets. The delignification was included in these flowsheets prior to the hydrolysis stage which used either acid or enzymes. The solution space was used to evaluate possible flowsheets in terms of the two aforementioned objectives. For a scenario where methane is the only desired product, steam explosion would be recommended. Adding acid hydrolysis to steam explosion (SA) to produce bio-ethanol increases profitability and reduces environmental impact however the glucose flowrate from this flowsheet is low. For a scenario where higher glucose flowrate is desired, steam explosion with enzymatic hydrolysis pre-treatment flowsheet is recommended however the environmental impact of this flowsheet may be large depending on the energy efficiency of enzyme production.