Study of selected Ionic Liquids in the Pretreatment of Prosopis Juliflora and Gadam Sorghum stalks for Bioethanol Production

Abstract

Production of bioethanol as an alternative energy source, from the abundant sources of lignocellulosic biomass requires that the latter undergo pretreatment processes. Conventional pretreatment methods tend to be harmful to the environment. A new pretreatment method by use of Ionic Liquids (ILs) has shown to be promising. This research work analyzed pretreatment of Prosopis Juliflora and Gadam Sorghum stalks using three different types of ILs (Imidazolium, Phosphonium and Pyridinium based). Regeneration of cellulose from the ILs was carried out and the performance of the ILs established through analysis of glucose concentrations upon hydrolysis. Inhibitor (furfural) production was also investigated. Finally recyclability of ionic liquids (IL) was established. Pretreatment was carried out on both biomasses at varied temperatures (80°C–140°C), pretreatment periods (40min – 160min) and a biomass loading of 6%wt using 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-butyl-4-methylpyridinium chloride ([4MBP]Cl) and trihexyltetradecylphosphonium chloride ([P66614]Cl). Simple acid hydrolysis was then done at a temperature of 130°C for a duration of 10 minutes. Finally glucose measurement was done using a UV – Vis Spectrophotometer at a wavelength of 520nm. Furans in the hydrolysate were also monitored at a wavelength of 284nm. The glucose yields varied according to the pretreatment time, temperature, type of IL and biomass. [P66614]Cl gave the least glucose yield overally (maximum of 7.19% ) as compared to [4MBP]Cl (maximum of 61.63%) and [BMIM]Cl (maximum of 73.27%). Higher overall glucose yields were also observed with Prosopis Juliflora (73.27%) as compared to Gadam Sorghum (60.42%). This can be attributed to the higher cellulose content in its structure. The investigation on furfural inhibitor production showed a decrease of between 46.2% and 64% in furfural concentration when ILs were used for pretreatment as compared to dilute alkaline pretreatment. It was also established that using the Imidazolium based IL, it is possible to recycle the IL about six times without any deleterious effect on generation of fermentable sugars. The use of prosopis juliflora and gadam sorghum as biomass will go a long way in supplementing the dwindling petroleum oil reserves while easing food versus fuel competition. Recycling of the IL will facilitate cost effective use of ionic liquids for pretreatment hence reducing pretreatment cost.