Pervaporation membranes show promise for alkaline wastewater reclamation

Industrial processes often generate a large amount of alkaline waste solutions. The existing alkali treatment processes require high investment, and are complicated and have a low rate of efficiency. Membrane technology has the advantages of high efficiency and energy savings. However, current polymeric membrane materials are not strong enough in harsh alkaline environments. To solve this problem, Prof. Li Pei from Beijing University of Chemical Technology and Dr. Jianzhong Xia from Shenzhen University have developed an alkali-resistance pervaporation membrane. The relevant work was published in Frontiers of Chemical Science and Engineering on March 28, 2022.

In this work, they synthesized a super alkali-resistant polymer-sodium carboxymethyl cellulose, and coated it on top of a chemical stable polyethylene porous substrate. They also created a spray-coating technology to solve the incompatible problem between the hydrophobic polyethylene layer and the sodium carboxymethyl cellulose layer. Pervaporation flux of the composite membrane reached 35 ± 2 kg·m⁻²·h⁻¹ with a sodium chloride rejection of 99.9% ± 0.1% when separating a 3.5 wt-% sodium chloride solution at 70 °C. The desalination performance was stable after soaking the membrane in a 20 wt-% NaOH solution at room temperature for 9 days and in a 10 wt-% NaOH solution at 60 °C for 80 h. Moreover, the membrane was stable in 4 wt-% sulfuric acid and a 500 mg·L⁻¹ sodium hypochlorite solution. In a process of concentrating a NaOH solution from 5 to 10 wt-% at 60 °C, an average water flux of 23 kg·m⁻²·h⁻¹ with a NaOH rejection over 99.98% was obtained.

Because the composite membrane has excellent alkali resistance, the membrane material shows good application prospects in alkali concentration in papermaking, the electroplating industry, water resource recovery in the coal chemical industry, and in the alumina production industry.