Shuaifei Zhao

Innovative Use of Membrane Contactor as Condenser for Heat Recovery in Carbon Capture

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.

Osmotic pressure versus swelling pressure: comment on "bifunctional polymer hydrogel layers as forward osmosis draw agents for continuous production of fresh water using solar energy".

The authors thought that the principle ofabsorbing water of the hydrogels was based on forwardosmosis, that is, the hydrogel particles (2−25 μm) provided theosmotic pressure. The authors may misunderstand the swellingpressure of hydrogels as the osmotic pressure. The followingdiscussion aims to clarify two confused concepts (i.e., osmoticpressure and swelling pressure) and to differentiate theprinciples of forward osmosis and of hydrogel absorbingwater for both readers and the authors. It is believed that theclarification is very necessary because a number of publishedpapers

Pd-doped organosilica membrane with enhanced gas permeability and hydrothermal stability for gas separation

Abstract A Pd-doped organosilica membrane based on bis(triethoxysilyl)ethane is successfully developed by the polymeric sol–gel method. Its microstructure, chemical composition, and separation performance are compared with those of the undoped organosilica membrane. Gas adsorption analysis indicates that the Pd-doped organosilica membrane has larger micropores compared with the undoped organosilica membrane. The gas permeation results show that the Pd-doped organosilica membrane has much higher gas permeances than the undoped organosilica membrane due to the enlarged micropores after Pd-doping. The Pd-doped organosilica membrane also exhibits a significantly improved hydrothermal stability. The enhanced hydrothermal stability can be explained by the mechanism that Pd particles act as inhibitors and prevent the formation of mobile silica groups (e.g., Si–OH) under steam condition. Metal-doping (e.g., Pd-doping in this work) may offer a new approach to develop high performance membranes with enhanced gas permeances and hydrothermal stabilities in gas separation applications.

Closing CO2 Loop in Biogas Production: Recycling Ammonia As Fertilizer

We propose and demonstrate a novel system for simultaneous ammonia recovery, carbon capture, biogas upgrading, and fertilizer production in biogas production. Biogas slurry pretreatment (adjusting the solution pH, turbidity, and chemical oxygen demand) plays an important role in the system as it significantly affects the performance of ammonia recovery. Vacuum membrane distillation is used to recover ammonia from biogas slurry at various conditions. The ammonia removal efficiency in vacuum membrane distillation is around 75% regardless of the ammonia concentration of the biogas slurry. The recovered ammonia is used for CO2 absorption to realize simultaneous biogas upgrading and fertilizer generation. CO2 absorption performance of the recovered ammonia (absorption capacity and rate) is compared with a conventional model absorbent. Theoretical results on biogas upgrading are also provided. After ammonia recovery, the treated biogas slurry has significantly reduced phytotoxicity, improving the applicability for agricultural irrigation. The novel concept demonstrated in this study shows great potential in closing the CO2 loop in biogas production by recycling ammonia as an absorbent for CO2 absorption associated with producing fertilizers.

Developing new adsorptive membrane by modification of support layer with iron oxide microspheres for arsenic removal

Arsenic-contaminated water has significant adverse impacts on human health and ecosystems. We developed a new adsorptive membrane by modifying the porous support layer of a phase inversion formed membrane for arsenic removal. Iron oxide (Fe3O4) microspheres were immobilized in the support layer of the membrane by reverse filtration, followed by dopamine polymerization. The prepared adsorptive membrane was compared with a virgin membrane without Fe3O4 microspheres and a Fe3O4 blended membrane in terms of membrane structures and separation performance. The adsorptive membrane prepared by our new method had comparable water permeability and rejection performance with the virgin membrane without Fe3O4 microspheres, but higher rejection performance and dynamic adsorption capacity than the membrane prepared by the conventional blending method. Both static and dynamic adsorption modes were used to evaluate the adsorption performance of the membranes. Our new adsorptive membrane also had excellent regeneration performance. After three regeneration cycles, the membrane was still capable of treating more than 2 tons of As-contaminated water/m2. The adsorptive membrane of 1 m2 could treat over 7 tons of water to the drinking water standard in terms of arsenic concentration during three regeneration cycles. Therefore, our adsorptive membrane may pave a new way for arsenic removal from water and ensuring drinking water security.

Conventional ultrafiltration as effective strategy for dye/salt fractionation in textile wastewater treatment

Use of tight ultrafiltration (UF) membranes has created a new pathway in fractionation of dye/salt mixtures from textile wastewater for sustainable resource recovery. Unexpectedly, a consistently high rejection for the dyes with smaller sizes related to the pore sizes of tight UF membranes is yielded. The potential mechanism involved in this puzzle remains unclear. In this study, seven tailored UF membranes with molecular weight cut-offs (MWCOs) from 6050 to 17530 Da were applied to separate dye/salt mixtures. These UF membranes allowed a complete transfer for NaCl and Na2SO4, due to large pore sizes. Additionally, these UF membranes had acceptably high rejections for direct and reactive dyes, due to the aggregation of dyes as clusters for enhanced sizes and low diffusivity. Specifically, the membrane with an MWCO of 7310 Da showed a complete rejection for reactive blue 2 and direct dyes. An integrated UF-diafiltration process was subsequently designed for fractionation of reactive blue 2/Na2SO4 mixture, achieving 99.84% desalination efficiency and 97.47% dye recovery. Furthermore, reactive blue 2 can be concentrated from 2.01 to 31.80 g·L-1. These results indicate that UF membranes even with porous structures are promising for effective fractionation of dyes and salts in sustainable textile wastewater treatment.