Recovery of acetic acid from prehydrolysis liquor of kraft based hardwood dissolving pulp process
University of New Brunswick
The utilization of dissolved organics in the pre-hydrolysis liquor (PHL) for the production of value-added chemicals can open a biorefinery platform for kraft-based dissolving pulp mills. In this dissertation, it was focused on the recovery of acetic acid which is the second major component in the PHL. Three different chemical processes were studied to separate acetic acid from sugars and lignin: 1) Adsorption, 2) Reactive extraction and 3) Membrane filtration. The adsorption of acetic acid by activated carbon and tertiary amine based resin led to 98% of acetic acid recovery from Model solution (MAA) and 46% from carbon treated PHL (TPHL). For the reactive extraction, the Trioctyl amine (TOA)/octanol system had 80.48%, 61.84% and 63.53% of acetic acid recovery from MAA, PHL and TPHL respectively. Subsequently, acetic acid in the organic phase (TOA-octanol) was back extracted using a sodium hydroxide solution, while the solvent (TOA- octanol) was regenerated and recycled successfully. The third separation concept was applied using the strategy combined with activated carbon, nanofiltration (NF) and reverse osmosis (RO) processes. To reduce the fouling due to the lignin present, PHL was firstly subjected to activated carbon adsorption, then the treated PHL (TPHL) was passed through a nanofiltration (NF DK) membrane to retain and concentrate the sugars, and the permeate of acetic acid rich solution was passed through multistage reverse osmosis (RO SG) units. It showed a significant increase in the final concentration of dissolved organics: total sugar from 48 g/L to 227g/L and acetic acid from 10 g/L to 55 g/L. Therefore, it was concluded that the membrane process could be a better option than reactive extraction and adsorption process in terms of product quality, yield, cost, feasibility of operation and environment.