HCl modification and pervaporation performance of BTESE membrane for the dehydration of acetic acid/water mixture

Application of MIL-101(Cr) for biofuel dehydration and process optimization using the central composite design method

Nowadays, researchers from various fields are aiming to replace petro-based and other fossil fuels with green and renewable alternatives. One of the potential candidates, requiring a highly pure reactant, is biofuel. The use of alcohol-containing water as a reactant can lead to different types of problems including the generation of side reactions, hydrolysis, equilibrium shifts, catalyst deactivation and process complexity. A metal-organic framework, MIL-101(Cr), was successfully synthesized using the hydrothermal method and subsequently employed for the dehydration of a standard biofuel. With this goal in mind, we aimed to optimize the effects of operational parameters-specifically, initial water concentration, adsorbent dosage, and temperature-using the central composite design (CCD) method, while also analyzing their behaviors by applying variance analysis. To predict the process behavior, we propose a refined quadratic equation under various conditions, achieving an R 2 value of 95.26. The results showed that the process was more influenced by temperature variations than the other two parameters. The optimal conditions were predicted with an initial concentration of 1.41, catalyst dosage of 0.14, and a temperature of 302.5 K, resulting in a capacity of 1349.72 and a desirability value of 0.95. Additionally, the synthesized MIL-101(Cr) was characterized using XRD, SEM, DSC/TGA, and N2 physisorption techniques. The results indicated that the particles possessed microporous windows and mesoporous cages, exhibiting a uniform octahedral shape with an average size ranging between 200 and 500 nm.

Hydrogen (H2)/Toluene (TOL) Separation via One and Two Stages of the Bis(triethoxysily)ethane (BTESE) Membranes

The separation ability of bis(triethoxysilyl)ethane (BTESE) membranes for hydrogen (H2) purification from hydrogen (H2)/toluene (TOL) gas mixtures after a methylcyclohexane (MCH) dehydrogenation process was investigated via one-stage and two-stage membrane processes. This study revealed that BTESE membranes of varied pore sizes (0.4, 0.5, and 0.7 nm) in a one-stage configuration can manage to achieve a H2 purity ~99.9%. However, the TOL concentrations fell within a wide range, ranging from 280 to 5441 ppm. A primary goal of this research was to lower the TOL concentration in the permeate stream below 200 ppm. Hence, by applying the two-stage membrane, it was demonstrated that the TOL concentration in the permeate stream could be lowered below 200 ppm.

Synthesis optimization and separation mechanism of ZSM-5 zeolite membranes for pervaporation dehydration of organic solvents

Pervaporation (PV), as an energy-efficient mixture separation technology, plays an important role in the chemical industry. In this work, no organic templates were needed to produce high-performance ZSM-5 membranes with an extremely low Si/Al ratio of 3.3 on α-Al2O3 tubular supports using 100 nm nanoseeds. The effects of preparation parameters on the crystalline phase structures, micromorphologies, and PV separation performance of ZSM-5 membranes were comprehensively investigated. The results revealed that the Si/Al ratio of gels significantly affected both the Si/Al ratio and the crystal orientation of the final ZSM-5 membrane. The optimized ZSM-5 membrane with a thickness of 1.8 μm was utilized to dehydrate various organic solvents via PV, and the influence of the operating parameters on PV dehydration performance was evaluated and is described herein. Furthermore, the permeation behaviors of single gases and PV were examined using permeate molecules within a similar size range to reveal the PV mechanism of the ZSM-5 membrane. The results demonstrated that gas permeation followed Knudsen diffusion, while PV permeation was decreased with decreases in the affinity of molecules, revealing an adsorption-diffusion mechanism that dominated PV dehydration through the ZSM-5 membrane. Moreover, the as-synthesized ZSM-5 membrane had good water permselectivity for water/acetone (e.g., total flux = 1.03 kg/(m2 h), α = 307) and for water/isopropanol (e.g., total flux = 1.49 kg/(m2 h), α = 1070) mixtures compared with other membranes reviewed in the literature. The synthesized ZSM-5 membrane also exhibited excellent reproducibility, high stability, and attractive PV separation performance, demonstrating its significant potential application in the PV dehydration of organic solvents.

Micro and Nanoporous Membrane Platforms for Carbon Neutrality: Membrane Gas Separation Prospects

Recently, carbon neutrality has been promoted as a potentially practical solution to global CO2 emissions and increasing energy-consumption challenges. Many attempts have been made to remove CO2 from the environment to address climate change and rising sea levels owing to anthropogenic CO2 emissions. Herein, membrane technology is proposed as a suitable solution for carbon neutrality. This review aims to comprehensively evaluate the currently available scientific research on membranes for carbon capture, focusing on innovative microporous material membranes used for CO2 separation and considering their material, chemical, and physical characteristics and permeability factors. Membranes from such materials comprise metal-organic frameworks, zeolites, silica, porous organic frameworks, and microporous polymers. The critical obstacles related to membrane design, growth, and CO2 capture and usage processes are summarized to establish novel membranes and strategies and accelerate their scaleup.

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.

Fabrication of isomorphously substituted W-MFI membrane with high performance for ethanol separation from water

Isomorphous substitution of heteroatoms is an effective platform for finely tuning the pore chemistry, pore structure, and surface properties of the zeolite framework as catalysts or separation membranes. A continuous and compact isomorphously substituted tungsten (W)-MFI membrane was firstly developed on coarse α-Al 2 O 3 tubes dip-coated with W-MFI seeds using hydrothermal secondary growth using pretreated synthesis solution. The synthesized W-MFI membrane is found to be ethanol permselective having a pervaporation based separation factor and flux of 69 and 2.50 kg/m 2 .h, respectively while exhibiting the highest separation index of 170 kg/m 2 .h for the separation of 5 wt. % ethanol-water mixture among the reported tubular MFI membranes. The isomorphous substitution of W improves the hydrophobicity and also plays a significant role for the enhanced separation performance.

Progress on Silica Pervaporation Membranes in Solvent Dehydration and Solvent Recovery Processes

Separation processes aimed at recovering the solvent from effluent streams offer a means for establishing a circular economy. Conventional technologies such as distillation are energy-intensive, inefficient and suffer from high operating and maintenance costs. Pervaporation based membrane separation overcomes these challenges and in conjunction with the utilization of inorganic membranes derived from non-toxic, sufficiently abundant and hence expendable, silica, allows for high operating temperatures and enhanced chemical and structural integrity. Membrane-based separation is predicted to dominate the industry in the coming decades, as the process is being understood at a deeper level, leading to the fabrication of tailored membranes for niche applications. The current review aims to compile and present the extensive and often dispersive scientific investigations to the reader and highlight the current scenario as well as the limitations suffered by this mature field. In addition, viable alternative to the conventional methodologies, as well as other rival materials in existence to achieve membrane-based pervaporation are highlighted.