An integrated system for CO2 capture and water treatment by forward osmosis driven by an amine-based draw solution

Abstract

In this study, a new forward osmosis (FO)-based system designed to integrate CO2 capture and water treatment has been proposed as an innovative green technology for fossil-fuel power stations. Monoethanolamine (MEA), the most commonly used solvent for chemical absorption of CO2 from flue gas, plays a key role in the suggested system, acting as both a chemical absorbent for CO2 separation and a draw solution for water treatment and/or production; CO2-lean and CO2-rich MEA solutions were evaluated as water extraction agent. Higher FO performance (in particular noticeably less reverse solute flux) was observed with the rich MEA liquid, mainly due to the effect of CO2 dissolution. From a series of FO experiments conducted with saline feed solutions, it was confirmed that the rich MEA absorbent can extract water molecules efficiently from various water sources including highly saline streams (1.5 M NaCl or more) with decent performance. Because of the high osmotic potential of the rich MEA draw solution, treatment of flue gas desulfurization (FGD) wastewater, which is typically difficult to treat owing to its high ion concentration and scaling potential, was also accomplished successfully, presenting a concentration rate of more than 75%. Membrane distillation (MD) was adopted as an intermediate process between the FO-water extraction and CO2 desorption steps, and the test results indicated that the production of purified water from the diluted rich MEA absorbent can be achieved by the MD process. The proposed hybrid FO system is expected to address environmental concerns related to fossil fuel combustion power plants carbon emission and water stress – by allowing CO2 capture and water treatment simultaneously.