Assessment of aqueous biphasic systems (ABS) as an alternative delignification process

The environmental problems associated with traditional pulping processes are addressed in this study which deals with the technical feasibility of an alternative pulping method using polymer based aqueous biphasic systems (ABSs). The alternative systems are nontoxic and nonflammable, and show reasonable phase separation characteristics that improve delignification performance.; Evidence is reported that a catalytic, extractive, and reactive process based on ABS (metal salt/PEG) is effective in separating wood into its constituent parts. Pulping results of such a system show an improvement in delignification selectivity over selected “Control” systems (simulating traditional pulping). Li₂SO₄/PEG system gives improvements in selectivity of nearly 18%, and 10%, respectively, for hardwood and softwood. In these metal salt/PEG ABSs, pH adjustment in batch reaction processes is needed to prevent lignin precipitation.; Four commercially available polymers were studied: PEG, PEI, EOPO and Sunbright (phase diagram studies shows that they are good potential candidates for ABS pulping), and results are presented showing an improved extractive and reactive process based on ABS (Kraft-like chemicals/polymer). For both hardwood and softwood, ABS gives an improvement in selectivity of nearly 30% compared with the “Control” system. Other polymers show improvement over the traditional solution, but at lower levels than that shown for PEG.; The ability of different polymers to swell wood is directly correlated with the selectivity of delignification: PEG > Sunbright > EOPO > PEI > water. At a temperature of 85°C, the volumetric swelling wood from of PEG, Sunbright, EOPO, PEI, and water, are 17.86% ± 0.18%, 15.41% ± 0.17%, 14.76% ± 0.13%, 14.02% ± 0.13%, and 13.19% ± 0.22%, respectively. This experiment provided evidence that the existence of the physical interactions between polymer and wood constituents is a controlling factor, especially during the initial phase of delignification that is controlled by diffusion of treating solution into the wood matrix.; Evidence shows that the presence of polymer lowers the apparent activation energy (E) in the Arrhenius expression describing the initial phase of delignification. Typical results for hardwood and softwood delignification show improvements of E nearly 30% and 20%, respectively.