Recovery of kraft lignin from pulping wastewater using emulsion liquid membrane process

Abstract

Lignin represents a key sustainable source of biomass for transformation into biofuels and high-value specialty chemicals. Excess of lignin that imparts brownish dark coloration in pulping wastewater causes adverse pollution problems, hence affecting human. Therefore, there is a necessity for removal and recovery of lignin from wastewater. In this research, emulsion liquid membrane (ELM) technology has been applied. This study involved studies on liquid membrane formulation, stability of emulsion and extraction of lignin from simulated kraft lignin solution. An optimization of kraft lignin recovery from real pulping wastewater was performed using the response surface methodology (RSM). An ELM extraction model was developed to predict the extraction performance. The liquid membrane formulation was investigated on the choice of carrier, diluent and stripping agent using liquid-liquid extraction. ELM stability was determined at different surfactant concentrations, homogenizer speed, emulsifying time and agitation speed. Several important parameters governing the extraction process of lignin including concentration of carrier and stripping agents, treat ratio and extraction time were investigated. The liquid membrane formulation contains kerosene as a diluent, tricaprylmethylammonium chloride (Aliquat 336) as a carrier, sorbitan monooleate (Span 80) as a surfactant, 2- ethyl-1-hexanol as a modifer and sodium bicarbonate (NaHCO3) as a stripping agent. The results depicted that the most stable emulsion was observed at 3 % (w/v) of Span 80, 12000 rpm of homogenizer speed, 5 min of emulsification time and 250 rpm of agitation speed. At the optimum condition of 10 min of extraction time, 0.007 M of Aliquat 336, 0.1 M of NaHCO3 and 1:5 of treat ratio, the performance of extraction, stripping and recovery was 95%, 100% and 98% respectively in a one step process. The optimization by RSM showed that 97% of lignin was recovered at 0.012 M of Aliquat 336, 0.32 M of NaHCO3 and 1:4.8 of treat ratio. In addition, the developed model was accepted to predict the kraft lignin extraction as the simulation results were consistent with the experimental result at the optimum condition. Therefore, ELM process is a promising technology to recover lignin from pulping wastewater while solving environmental problems simultaneously.