Selective water vapor permeation from steam/non-condensable gas mixtures via organosilica membranes at moderate-to-high temperatures

Bis(triethoxysilyl)ethane (BTESE)-Organosilica Membranes for H2O/DMF Separation in Reverse Osmosis (RO): Evaluation and Correlation of Subnanopores via Nanopermporometry (NPP), Modified Gas Translation (mGT) and RO Performance

A 40 cm length Bis(triethoxysilyl)ethane (BTESE) membrane having different pore sizes was successfully prepared by changing the number of coating times for gas permeation (GP) and organic solvent reverse osmosis (OSRO) separation study. It was found that BTESE-6 membranes prepared through six-time coating consisted of small-sized pores in the range 0.56 to 0.64 nm estimated using modified Gas Translation (mGT) method and 0.59 to 0.67 nm estimated by nanopermporometry (NPP) method, respectively. These membranes demonstrated a high DMF rejection, RDMF > 95% with total flux, Jv total > 5 kg m-2 h-1 at operating condition feed pressure, Pf: 8 MPa; feed temperature, Tf : 50 °C; and feed flowrate, Qf : 30 mL/min; and they exhibited a high degree selectivity of He/SF6 in the range of ~ 260-3400 at a permeation temperature 200 °C. On the other hand, the larger pore sizes of the BTESE-4 membranes (pore size estimates > 0.76 nm to 1.02 nm) exhibited low DMF rejection and a low degree selectivity of He/SF6 around ~30% and 25, respectively, at the same operating condition as BTESE-6. Both GT and NPP methods can be considered as an indicator of the measurement membrane pore size. From this study, it was found that He and SF6 gases can be some of the potential predictors for water and DMF permeance. Furthermore, by comparing our OSRO membrane with other PV membranes for DMF/H2O separation, our BTESE-6 membranes still exhibited high flux in the range of 3-6 kg m-2 h-1 with a separation factor H2O/DMF in the range of 80-120.

Steam recovery from flue gas by organosilica membranes for simultaneous harvesting of water and energy

Steam recovery from the spent gases from flues could be a key step in addressing the water shortage issue while additionally benefiting energy saving. Herein, we propose a system that uses organosilica membranes consisting of a developed layered structure to recover steam and latent heat from waste. Proof-of-concept testing is conducted in a running incinerator plant. The proposed system eliminates the need for a water supply while simultaneously recovering latent heat from the waste stream. First, the long-term stability of an organosilica membrane is confirmed over the course of six months on a laboratory-scale under a simulated waste stream. Second, steam recovery is demonstrated in a running waste incinerator plant (bench-scale), which confirms the steady operation of this steam recovery system with a steam recovery rate comparable to that recorded in the laboratory-scale test. Third, process simulation reveals that this system enables water-self-reliance with energy recovery that approximates 70% of waste combustion energy.

Network tailoring of organosilica membranes via aluminum doping to improve the humid-gas separation performance

Organosilica membranes have recently attracted much attention due to excellent hydrothermal stability which enables their use in the presence of water. In particular, during humid-gas separations at moderate-to-high temperatures, these membranes have shown excellent water permeance and moderate water selectivity, which has been a breakthrough in separation performance. In the present work, we found that aluminum doping into the bis(triethoxysilyl)ethane (BTESE)-derived organosilica structure further improves water selectivity (H₂O/N₂, H₂O/H₂) while maintaining a level of water permeance that reaches as high as several 10⁻⁶ mol (m⁻² s⁻¹ Pa⁻¹). Single-gas permeation and nitrogen adsorption experiments have revealed that aluminum doping promotes densification of the pore structure and improves molecular sieving. In addition, water adsorption and desorption experiments have revealed that aluminum doping enhances water adsorption onto the pore walls, which blocks permeation by other gasses and significantly improves water permeation selectivity during the separation of humid gases. Our results provide a strategy for the fabrication of a membrane that provides both a high level of water permeance and enhanced water selectivity.

Al doping densified and hydrophilized the pore structure of organosilica membranes, which resulted in improved permselectivity in humid-gas separation at moderate-to-high temperature.

Ultrafast Synthesis of Silica-Based Molecular Sieve Membranes in Dielectric Barrier Discharge at Low Temperature and Atmospheric Pressure

Microporous silica membranes have shown promise as potential candidates for energy-efficient chemical separation. Herein, we report the ultrafast synthesis of silica membranes, on the order of minutes, in atmospheric-pressure, low-temperature plasma. Direct deposition in the discharge region of atmospheric-pressure plasma enables the immediate formation of a thin silica layer on a porous substrate. The plasma-deposited layer had a thickness of ∼13 nm and was confined to the immediate surface of the substrate. With an increase in deposition temperature, we observed an increase in the inorganic nature of the plasma-deposited layer and simultaneous improvement in the membrane performance. Consequently, the resulting membranes exhibited outstanding permeance for small-sized gas molecules, such as H₂ (>10^-6 mol m^-2 s^-1 Pa^-1), with a high H₂/SF₆ permeance ratio of ∼6300, providing a nonthermal alternative for the fabrication of silica-based membranes.