Separation of Acetic Acid and Water Using Reverse Osmosis Membranes

Reverse osmosis can potentially be used for separation of acetic acid from waste stream. However, the investigation on the separation of this binary mixture utilizing reverse osmosis is scarce. Thus, this study aims to evaluate the feasibility of lab-synthesized and commercially available reverse osmosis membranes to separate low acetic acid concentration from aqueous mixture. A commercially available AG membrane and three laboratory synthesized polysulfone (PSf) membranes were used in this work. Initial test for water permeation using dead end filtration found that 17.5 wt% PSf has the highest water permeability. As the polymer concentration decreases, the membrane porosity increases which decreases the resistance which enables the penetration of the permeant more easily through the membrane matrix resulting in higher water permeation when 17.5wt% PSf was used. Further modification by interfacial polymerization to form a thin polyamide layer on the porous support was seen to have had improved the membrane affinity towards water resulted in increased of permeation through the membrane matrix. However, the rejection was lower than that of the AG membrane. This indicates that, the increase in water permeation when 17.5wt%PSf was used is due to the high membrane porosity. This is evidence since 17.5wt%PSf has the highest water flux but lower acetic acid rejection compared to the commercial AG membrane. Low rejection of acetic acid when reverse osmosis membrane was applied indicates that other factor such as Donnan effect has to be further considered when synthesizing the membrane.