Advanced reverse osmosis membranes for desalination and inorganic/polymer composite membranes for CO2 capture

摘要

Desalination of brackish water or seawater to produce clean water has been developed as one of the most promising solutions to meet the exponential growth of water demand caused by the fast growths of global population and economy. Among all the approaches, reverse osmosis is the most widely applied technology for water desalination due to its low capital cost, high energy efficiency, and simple operation. However, the further application of reverse osmosis desalination process by using the conventional polyamide thin film composite membrane is limited by its inherently low water flux and high vulnerability to foulants.;In the present work, advanced reverse osmosis membranes were synthesized by incorporating a hydrophilic additive during the interfacial polymerization to increase the overall hydrophilicity. Different kinds of hydrophilic additives were first investigated to enhance the membrane water flux for brackish water desalination (2000 ppm NaCl solution and 225 psi) to demonstrate this novel concept. The effects of different concentration for each hydrophilic additive were evaluated for optimization. In addition, a post-treatment was developed and employed to further improve the membrane desalination performance. As a result, the advanced reverse osmosis membrane showed a water flux of 52.6 gallons/ft2/day and a salt rejection of 98.8%, as well as good stability during a 30-day continuous test. After optimizing the reactant concentrations and interfacial polymerization time for membrane synthesis, cross-linked polyethylene glycol was synthesized and applied on the resulting membrane for brackish water desalination, which not only further increased membrane water flux but also improved membrane fouling resistances to dodecyltrimethylammonium bromide and tannic acid, respectively. Scanning electron microscopy and atomic force microscopy analyses showed the membrane surface became smoother after coating the cross-linked polyethylene glycol layer.;The novel concept of hydrophilic additive was also extended to seawater desalination (3.28 wt% NaCl solution and 800 psi). The effects of additive concentration, isopropanol concentration, additional amine drying time, and hydrocarbon removal time on membrane desalination performance were investigated. The synthesized membrane showed a very high flux of 44.4 gallons/ft2/day and a salt rejection of 99.4%. Contact angle measurement confirmed the improvement of membrane surface hydrophilicity with the incorporation of the hydrophilic additive. Moreover, the advanced membrane showed very good and stable desalination performances for 30 days using seawater from Port Hueneme, CA. The incorporation of the hydrophilic additive also resulted in a smoother membrane surface and improved membrane fouling resistance to sodium alginate.;CO2 produced from coal-fired plants contributes to 40% of the total CO2 emission. Therefore, post-combustion CO2 capture from flue gas is crucial to reduce the anthropogenic impact on global climate change. Absorption, adsorption and membrane technology have been developed and investigated for this application. Membrane technology shows great potential for CO2 capture due to its low energy consumption, simple operation and maintenance, and compact configuration.;As part of the present work, a novel concept of multi-layer inorganic/polymer composite membrane was developed and applied to CO2 capture from flue gas. The zeolite Y nanoparticles were successfully deposited onto two commercial polymer supports with uniform coverage by the vacuum-assisted dip coating approach. Scanning electron microscopy (SEM) analysis indicated that the thickness of the zeolite Y layer on the flexible polymer support was only around 500 nm. Atomic force microscopy (AFM) analysis showed that the surface roughness of the polymer support was reduced by the deposition of zeolite Y nanoparticles. In comparison with the bare Biomax PES support, the Pebax®/PEG-200 membrane prepared on the zeolite Y/Biomax PES substrate with the same procedure exhibited higher CO2 permeance, because the penetration of PEG-200 was minimized by the smaller interparticle pore size on the zeolite Y layer. This multi-layer composite membrane showed a CO2 permeance of 745 GPU and a CO2/N2 selectivity of 25.4 under flue gas operating conditions (feed gas containing 20% CO2 and 80% N2).