Task-specific polymeric membranes to achieve high gas-liquid mass transfer.

In the current study, Polyimide (P84)-based polymeric membranes were fabricated and used as spargers in the bubble column reactor (BCR) to get a high gas-liquid mass transfer (GL-MT) rate of oxygen in water. Different polymeric membranes were fabricated by incorporating polyvinyl pyrrolidone (PVP) as a porogen and a Zeolitic Imidazolate Framework (ZIF-8) to induce high porosity and hydrophobicity in the membranes. The GL-MT efficiency of membranes was evaluated by measuring the overall volumetric mass transfer coefficient (kLa) of oxygen in air. The kLa of O2 (in air) was measured by supplying the gas through a fixed membrane surface area of 11.94 cm2 at a fixed gas flow rate of 3L/min under atmospheric pressure. The results revealed that adding porogen and ZIF-8 increased the porosity of the membranes compared to the pure polymeric membranes. In comparison, the ZIF-8 (3 wt%) based membrane showed the highest porosity (80%), hydrophobicity (95° contact angle) and kLa of oxygen in air (241.2 h-1) with 78% saturation in only 60 s. ZIF-8 based membranes showed the potential to increase the amount of dissolved oxygen in BCR by reducing the bubble size, increasing the number of bubbles, and improving the hydrophobicity. The study showed that ZIF-8 based membrane diffusers are expected to produce high GL-MT in microbial syngas fermentation. To the best of our knowledge, this is the first study on the fabrication and application of polymeric membranes for GL-MT applications. Further research should be conducted under real fermentation conditions to assess the practicality of the system to support substrate utilization, microbial growth, and product formation.

Controlled Covalent Functionalization of ZIF-90 for Selective CO2 Capture & Separation.

Mixed Matrix Membranes (MMM) with enhanced selectivity and permeability are preferred for gas separations. The porous metal-organic frameworks (MOFs) materials incorporated in them play a crucial part in improving the performance of MMM. In this study, Zeolitic imidazolate frameworks (ZIF-90) are selected to fabricate Polyetherimide (PEI) MMMs owing to their lucrative structural and chemical properties. This work reports new controlled post-synthetic modifications of ZIF-90 (50-PSM-ZIF-90) with ethanolamine to control the diffusion and uptake of CO2. Physical and chemical properties of ZIF-90, such as stability and presence of aldehyde functionality in the imidazolate linker, allow for easy modulation of the ZIF-90 pores and window size to tune the gas transport properties across ZIF-90-based membranes. Effects of these materials were investigated on the performance of MMMs and compared with pure PEI membranes. Performance of the MMMs was evaluated in terms of permeability of different gases and selective separation of CO2 and H2 gas. Results presented that the permeability of all membranes was in the following order, i.e., P(H2) > P(CO2) > P(O2) > P(CH4) > P(C2H6) > P(C3H8) > P(N2), demonstrating that kinetic gas diffusion is the predominant gas transport mode in these membranes. Among all the membranes, permeability of pure PEI membrane was highest for all gases due to the uniform porous morphology. The pure PEI membrane showed highest permeability of H2, which is 486.5 Barrer, followed by 49 Barrer for O2, 29 Barrer for N2, 142 Barrer for CO2, 41 Barrer for CH4, 40 Barrer for C2H6 and 39.6 Barrer for C3H8. Results also confirm the superiority of controlled PSM-ZIF-90-PEI membrane over the pure PEI and ZIF-90-PEI membranes in CO2 and H2 separation performance. The 50-PSM-ZIF-90 PEI membrane exhibited a 20% increase in CO2 separation from methane and a 26% increase over nitrogen compared to the ZIF-90-PEI membrane. The 50-PSM-ZIF-90 PEI membrane showed 15% more H2/O2 separation and 9% more H2/CH4 separation than ZIF-90 PEI membrane. Overall, this study represents the role of controlled PSM in enhancing the property of new materials like ZIF and its application in MMMs fabrication to develop a promising approach for the CO2 capture and separation.

Development of highly permselective Mixed Matrix Membranes comprising of polyimide and Ln-MOF for CO2 capture.

Mixed Matrix Membranes (MMMs) with hybrid organic-inorganic characteristics offer a strong alternative to traditional polymer-based membranes to reduce the trade-off between gas permeability and selectivity. This work incorporated lanthanum-Metal Organic Frameworks in the Matrimid to fabricate MMMs. To understand the effects of nano-filler on membranes' morphology, porosity, thermal stability, and chemical composition, MMMs were fabricated with three different loadings of nano-filler, i.e., 10, 20 and 30 wt%. The selectivity and permeability of CH4, CO2, and N2 gases through MMMs were investigated at 10 bar pressure and temperatures ranging from 25 to 55 °C. All MMMs exhibited enhanced CO2 permeation with increased nano-filler loading because the porous nano-filler provided additional channels and fractional free volume in the polymer matrix. The 30 wt% loaded membrane showed a 183% increase in permeability of CO2 than neat membrane. With increasing nano-filler loading, the selectivity of MMMs increased from 34.1 to 48.45 for CO2/N2 and from 36.2 to 54.67 for CO2/CH4, confirming the absence of membrane defects, improved filler/polymer interface, and excellent dispersion of nano-filler in the polymer matrix. The results proved that these membranes could be further used for gas separation industrial applications.

Exploring the potential of highly selective deep eutectic solvents (DES) based membranes for dehydration of butanol via pervaporation.

N-butanol has unique physicochemical and combustion properties, similar to gasoline, which makes it an environmentally friendly alternative to conventional fuels. To improve the efficiency, the dehydration of butanol is necessary. This paper aims to investigate the performance of Deep Eutectic Solvents (DESs) based membranes for the dehydration of n-butanol by the pervaporation process. Three DES with different combinations of hydrogen bond donors and acceptors, i.e., DL-menthol: Lauric acid (DES), DL-menthol-Palmitic acid (DES), and [TETA] Cl: Thymol (DES), were used. We hypothesized that (i) incorporation of hydrophobic DES would increase the hydrophobicity of the membranes; (ii) specific functional groups (phenolic group, amine group) in DESs would enhance the butanol-philic character of membranes, and (iii) hydrophobic DESs would increase the butanol separation efficiency and permeability of membranes. FTIR analysis and physicochemical parameters of the resultant liquid mixture validated the DESs' production. The DESs were then filled into the permeable support, resulting in supported liquid membranes (SLMs). An additional layer of polydimethylsiloxane (PDMS) was coated directly on the DES-PSf layer to prevent leaching out of DES. A feed containing a 6 wt % aqueous solution of butanol under varying temperatures was studied. The results showed that among all membranes, [TETA] Cl: Thymol DES-based membrane showed the highest sorption of 36% at room temperature. The introduction of DES in membranes resulted in a remarkable increase in the separation factor while sustaining a reasonable flux. Among all the membranes, the DL-menthol: Lauric acid (DES) based membrane exhibited the highest separation factor of 57 with a total flux of 0.11 kg/m2. h. Significantly high butanol-water separation was attributed to the low viscosity and high butanol solubility of the chosen DES, which makes it a suitable substitute to conventional ILs.

Mixed-Matrix Membranes Comprising of Polysulfone and Porous UiO-66, Zeolite 4A, and Their Combination: Preparation, Removal of Humic Acid, and Antifouling Properties.

High-performance Mixed-Matrix Membranes (MMMs) comprising of two kinds of porous fillers UiO-66 and Zeolite 4Aand their combination were fabricated with polysulfone (PSf) polymer matrix. For the very first time, UiO-66 and Zeolite 4A were jointly used as nanofillers in MMMs with the objective of complimenting synergistic effects. The individual and complimentary effects of nanofillers were investigated on membrane morphology and performance, pure water flux, humic acid rejection, static humic acid adsorption, and antifouling properties of membranes. Scanning Electron Microscopy (SEM) analysis of membranes confirmed that all MMMs possessed wider macrovoids with higher nanofiller loadings than neat PSf membranes and the MMMs (PSf/UiO-66 and PSf/Zeolite 4A-UiO-66) showed tendency of agglomeration with high nanofiller loadings (1 wt% and 2 wt%). All MMMs exhibited better hydrophilicity and lower static humic acid adsorption than neat PSf membranes. Pure water flux of MMMs was higher than neat PSf membranes but the tradeoff between permeability and selectivity was witnessed in the MMMs with single nanofiller. However, MMMs with combined nanofillers (PSf/Zeolite 4A-UiO-66) showed no such tradeoff, and an increase in both permeability and selectivity was achieved. All MMMs with lower nanofiller loadings (0.5 wt% and 1 wt%) showed improved flux recovery. PSf/Zeolite 4A-UiO-66 (0.5 wt%) membranes showed the superior antifouling properties without sacrificing permeability and selectivity.