A biorefinery concept for simultaneous recovery of cellulosic ethanol and phenolic compounds from oil palm fronds: Process optimization

Abstract

In this study, process optimization of an ultrasonic-assisted organosolv/liquid oxidative pretreatment (SOP) of oil palm fronds (OPFs) for the simultaneous recovery of cellulose, bioethanol and biochemicals (i.e. phenolic compounds) in a biorefinery concept was carried out. The effects of time (30–60min.), temperature (40–80°C), NaOH concentration (1–5%) and sample:solvent ratio (1:10–1:50g/ml) on cellulose content, bioethanol yield and total phenolics contents (TPC) after SOP were investigated. At optimum conditions of pretreatment (i.e. 60°C, 40min, 3% w/v aq. NaOH and 1:20g/ml sample to solvent ratio), the recovered cellulose (55.30%) which served as substrate for enzymatic hydrolysis and subsequent fermentation yielded about 20.1g/l glucose, 11.3g/l xylose and 9.3g/l bioethanol (yield of 0.769g/g). The pretreatment liquor (mostly regarded as wastes) obtained at the optimum pretreatment conditions contained about 4.691mg gallic acid equivalent (GAE)/g OPFs of TPC, 0.297mg vanillic acid (VA)/g OPFs, 1.591mg gallic acid (GA)/g OPFs and 0.331mg quercetin (QU)/g OPFs. The pretreatment liquor was again analyzed to possess high antiradical scavenging activity (about 97.2%) compared to the synthetic antioxidant, 3,5-di-tert-butyl-4-hydroxytoluene (BHT) (80.7%) at 100ppm. Thus one sustainable way of managing wastes in biorefinery is the recovery of multi-bioproducts (e.g. bioethanol and biochemicals) during the pretreatment process.