Towards Bioethanol production in Kenya – Enhanced pretreatment of Prosopis Juliflora using ionic liquids

Abstract

Lignocellulosic biomass especially from nonfood crops is widely regarded as a sustainable second-generation bioethanol raw material. However, production of bioethanol from the abundant and inexpensive sources of lignocellulosic biomass such as Prosopis Juliflora requires that the latter undergo pretreatment processes. A new pretreatment method by use of Ionic Liquids has shown to be promising. This research work analyzed pretreatment of Prosopis Juliflora stem using 1-butyl-3-methylimidazolium chloride ([BMIM]Cl),1-butyl-4-methylpyridinium chloride ([4MBP]Cl) and trihexyltetradecylphosphonium chloride ([P66614]Cl). Regeneration of cellulose from the Ionic Liquids was carried out and the performance of the Ionic Liquids established through analysis of glucose concentrations upon hydrolysis. Pretreatment of Prosopis Juliflora was carried out at varied temperatures (80°C–140°C), pretreatment periods (40min– 160min) and a biomass loading of 6%wt. Simple acid hydrolysis was then performed at a temperature of 130°C for a duration of 10 minutes. Finally glucose measurement was done using a Shimadzu UV–Vis Spectrophotometer at a wavelength of 520nm. Pretreatment of the biomass with the ionic liquids resulted in an increase in glucose yield of 1.78 times with phosphonium IL, 18.1 times with imidazolium IL and 15.21 times with pyridinium IL as compared to the unpretreated biomass. Ionic liquid pretreatment is therefore an effective and viable process that can be applied towards unlocking lignocelluloses recalcitrance. However [BMIM]Cl and [4MBP]Cl showed better performance generally as compared to P66614]Cl with respect to maximum glucose yield obtained with each of the ILs (7.19% in the P66614]Cl pretreated case, 73.27% in the [BMIM]Cl pretreated case and 61.63% in the [4MBP]Cl pretreated case. Prosopis Juliflora yielded a substantial amount of glucose hence qualifying as a potential non food-based biomass substitute suitable for bioethanol production.