Journal of Membrane Science最新文献

The recovery of valuable chemicals, such as sinapic acid, from enzymatic hydrolysates is essential to enabling a sustainable biorefinery. In this study, we designed a system to recover sinapic acid produced chemo-enzymatically from waste mustard bran. The process involves sequential separation, beginning with size partitioning using ultrafiltration for enzyme removal and recovery, followed by charge-mediated size partitioning via nanofiltration to isolate sinapic acid from other extracts. Four polyethersulfone (PES) ultrafiltration membranes with molecular weight cut-offs (MWCOs) of 5000 and 10 000 Da and maximum allowable working pressures (MAWPs) of 3 and 10 bar were screened for their effectiveness in removing Bovine Serum Albumin (BSA) as a model compound. Subsequently, these membranes were applied to recover the feruloyl esterase enzyme. The membrane with an MWCO of 5000 Da and an MAWP of 10 bar achieved 97.93 % enzyme recovery with a permeate flow rate of 31.4 L/h/m² at 6 bar. Next, we evaluated the effects of zeta potential interactions on the preferential rejection of sinapic acid using various nanofiltration membranes with potentially charged surfaces, including polyimide, silicon-based thin film composite, and polypiperazine amide membranes with MWCOs ranging from 150 to 600 Da. The polypiperazine amide membrane demonstrated the highest recovery of sinapic acid, achieving 86 % recovery from a model solution and 64 % recovery from mustard bran hydrolysate. Compositional analysis of the permeate confirmed that the rejection rate (R) is influenced primarily by the pKa rather than molecular size, following the trend: sinapic acid (pKa = 4.58; 224.2 Da; R = 64.0 %), acetic acid (pKa = 4.76; 60.1 Da; R = 23.8 %), xylose (pKa = 12.15; 150.1 Da; R = 13.7 %), glucose (pKa = 12.28; 180.2 Da; R = 8.7 %), and arabinose (pKa = 12.34; 150.1 Da; R = 8.5 %). The zeta potential interactions across nanofiltration membranes enhanced sinapic acid recovery from the mustard bran hydrolysate, hence, charge mediation significantly influenced the membrane separation of these complex mixtures with varying pKa values.

We present a systematic theoretical investigation of gas permeability through single-layer nanoporous graphene membranes with N-terminated (pyridinic and mixed pyridinic/pyrrolic) pores for He, H${}_2$, N${}_2$, O${}_2$, CO, CO${}_2$, H${}_2$O, and CH${}_4$. Our study is based on density functional theory transition-state calculations and the kinetic theory of gasses. We systematically evaluate pores of varying sizes and shapes up to 5.7 Å in diameter. According to our findings, membranes with pores in the size regime (4.5 Å - 5.0 Å) may exhibit industrially acceptable permeance to several gas molecules and advanced selectivity. Notably, we found that, among a few others, a pore with the same topological features at the pore boundary as those of the characteristic pore of g-C${}_3$N${}_4$ carbon nitride, is particularly promising. In addition, membranes with larger pores, $\sim$5.5 Å - 5.7 Å, can effectively separate CH${}_4$ from the other molecules. Our findings support the advanced potential of single-layer graphene membranes with nitrogen-terminated sub-nanometer pores, for gas separation applications.

Developing composite separator membranes with low area resistance, high bubble point pressure, and long-term safety and stability is crucial for alkaline water electrolysis for hydrogen production as a key component of electrolyzer systems. In this study, PPS mesh fabric reinforced PSF@ZrO₂ composite separator membranes were successfully prepared using the immersion-drawing phase inversion method, with PSF as the alkali-resistant polymer matrix and porous irregular ZrO₂ nanoparticles as the hydrophilic additive. The experimental results showed that replacing commercial ZrO₂ with porous irregular ZrO₂ nanoparticles at an 85 wt% ZrO₂ nanoparticle loading improved both bubble point pressure and current transmission efficiency, attributed to the change in the morphological structure of the ZrO₂ nanoparticles. The P-Z85 composite separator membrane exhibited highly promising characteristics, with a high bubble point pressure of 3.76 bar and a low area resistance of 0.20 Ω cm². Stability tests conducted in 30 wt% KOH electrolyte at 80 °C and a current density of 0.65 A cm⁻² demonstrated excellent continuous electrolysis stability for the P-Z85 composite separator membrane. These results indicate that the PSF@ZrO₂/PPS composite separator membrane prepared in this study exhibits excellent performance in 30 wt% KOH electrolyte, significantly extending its service life.

Separation of the xylene isomers has always been of great challenge and interest to the industry. Here, separation factors of 51 and 9 for p-/o-xylene and p-/m-xylene with a p-xylene permeance of 1.2 × 10⁻⁷ and 2.2 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹, respectively, are achieved on the simple tandem fluorinated MXene lamellar membranes with 11%F and 1%F content through insight into the inversion behavior of the adsorption configuration enabled by the difference in dipole moments of xylenes under the combined interaction of xylene–CH₃ ^… F attraction and xylene–π–bond ^… F repulsion. The favorable configuration of p-xylene maintains the flat adsorption, while that of m- and o-xylene undergoes a transition from upright to tilted and flat adsorption. DFT calculations confirm the weak flat adsorption of p-xylene on MXene-11%F repelled by the π–bond ^… F repulsion and the strong upright adsorption of m- and o-xylene via the regulation of the repulsion, which contributes to a high throughput of p-xylene. As the F content decreases to 1 %, the low π–bond ^… F repulsion results in strong flat configuration of p-xylene and weak flat configuration of m- and o-xylene. This work provides ideas for separating isomers by controlling the adsorption configuration through understanding their interaction forces in the membrane channel.

In this study, by connecting the amino ligand in ZIF-8-NH₂ with an alkyl side chain containing sulfonic acid groups in a one-step method, a novel nanofiller (ZIF-8-NS) with bifunctional amino and sulfonic acid groups was formed. Sulfonated poly (aryl ether ketone sulfone) containing fluorene group (F-SPAEKS) was chosen as the polymer matrix. The nanofiller not only had good hydrophilicity but also had electrostatic interaction with the polymer matrix, which effectively promoted the compatibility problem among the polymer matrix and the filler. The nanofillers were characterized by XRD, FT-IR, SEM and XPS. The composite membranes were prepared by the NIPs method. The antifouling and separation properties of the prepared mixed matrix membranes (MMMs) were investigated using positively charged dye (RHB) and negative charge bovine serum albumin (BSA) as model contaminants. The water flux of the pure membrane achieved 529.16 L/m² h. When the addition amount of ZIF-8-NS was 0.1 %, the water flux of M4 (F-SPAEKS/ZIF-8-NS-0.1 %) could reach 838.84 L/m² h. The retention rate of the BSA solution could reach 99.06 %, and the FRR value was kept at a high level (81.45 %). Meanwhile, the dynamic retention of M4 on the primary adsorption of the dye RHB could even reach 99.89 %. Therefore, the innovative design of the novel MMMs not only improved the flux, retention, and other separation properties but also enhanced their excellent adsorption capacity for RHB dyes. This result indicated that the nanofiller ZIF-8-NS provided an interesting reference for the study of ultrafiltration membranes.

Applying a transport membrane condenser (TMC) based on the hydrophilic ceramic membrane to recover the waste heat from the hot stripped gas could effectively reduce the heat consumption of CO₂ regeneration in the carbon capture process. However, the high cost of ceramic membrane hindered the development of this technology. So in this study, a novel mixed matrix membrane (MMM) was proposed to replace the conventional ceramic membrane. MMMs were prepared by mixing carbon nanotube (CNT) into polyvinylidene fluoride (PVDF) casting solution through non-solvent phase separation method, and then were adopted for the waste heat recovery from the stripped gas featured with the molar ratio of CO₂ to H₂O(g) of 1:1∼1:2. Furthermore, the heat transfer resistance between the stripped gas and bypassed CO₂-rich solvent when adopting MMMs was also analyzed through computational fluid dynamics (CFD). Results indicated that the addition of CNT or hydroxylated CNT (CNT-OH) effectively enhanced the heat recovery performance of MMMs. Moreover, MMMs prepared by mixing CNT-OH and hydroxylated boron nitride (BN–OH) further boosted the heat flux, achieving a maximum value of 23.72 MJ/(m²·h), representing an increase of up to 8.41 % compared to the original PVDF membrane without adding any additives. At the experimental conditions in this study, the gas-side individual thermal resistance dominated the overall thermal resistance and consequently the heat transfer performance. With an increase in the stripped gas flow rate, the ratio of individual heat transfer resistance of membrane to the overall resistance increased. Notably, the installation of baffles on the gas side of TMC reduced the gas-side thermal resistance. In this study, the optimum thermal conductivity of the organic membrane increased with the waste heat recovery scale from stripped gas. In addition, when the thermal conductivity of membrane exceeded 4 W/(m·°C), the increase in thermal conductivity on the waste heat recovery was not significant. This study confirmed the application potential of MMMs in the waste heat recovery.

Ionic liquids (ILs) have excellent ability to capture CO₂ due to their unique properties. The observation on the evolution process of solid-supported IL nanomembranes at the nanoscale benefits understanding the interaction between IL nanomembranes and CO₂. In this work, we have investigated the CO₂-induced evolution process of solid-supported nanomembranes formed by the imidazolium-based ILs with alkyl chains of different lengths but with a common anion by in-situ atomic force microscopy (AFM). The morphology evolution and mechanical properties of the IL nanomembranes have been quantitatively analyzed. The results show that similar phenomena were observed for the three IL nanomembranes, i.e., the absorption of CO₂ presents a maximal impact on the innermost layer of the solid-supported IL nanomembranes. The innermost layer of IL nanomembranes becomes fragmented and tends to re-assemble into a multi-layer structure, while the area of the multi-layer IL nanomembranes expands due to the incorporation of some small regions. In addition, the morphology changes of IL nanomembranes are dependent on the length of cation alkyl side chain. For the [BMI][TFSI] nanomembrane, the morphology change is faster than the other two IL nanomembranes in the preliminary stage of CO₂ absorption and reaches a stable state in a shorter time. AFM quantitative nanomechanical measurements show that Young's moduli of the three IL nanomembranes significantly decrease after CO₂ absorption, which supports that CO₂ molecules could weaken the interaction among IL anions, cations and mica, and thus lead to the morphology changes of the three solid-supported IL nanomembranes. Our work provides microscopic insights into the process of CO₂ absorption by ILs, which lays a foundation for further studying the interaction between CO₂ and solid-supported IL nanomembranes.

Membrane separation for 2,3-butanediol (2,3-BDO) recovery from fermentation broth is highly valued for sustainable and renewable processes, but it requires efficient membrane materials. This work evaluates the sulfonated polybenzimidazole (sPBI) and its graphene oxide (GO) doped composite membrane for separating 2,3-BDO and water via atomistic simulations. Density functional theory calculations are applied to identify various forms of sPBI structures and quantify their binding interactions with 2,3-BDO and water. Classical molecular dynamic simulations are used to evaluate the structural changes, diffusivity, and selectivity of 2,3-BDO and water in different sPBI models, GO surfaces, and GO-doped sPBI composite models. Our results suggest that sPBI slightly increases the crystallinity of the membrane structures, enhances the adsorption strength for both 2,3-BDO and water, and improves the water/2,3-BDO selectivity by 2–3 times. The GO surfaces display a maximum selectivity at a surface coverage of 0.1–0.15 for both hydroxyl and epoxy surface groups. The addition of GO flakes to sPBI creates new interaction sites for 2,3-BDO and water at the interface of sPBI and GO, and the water/2,3-BDO selectivity of GO-doped sPBI models is further increased up to 3 times. This work illustrates how the integrated addition of sPBI and GO flakes offers a promising approach to selective separation of 2,3-BDO and water, providing theoretical guidance for polybenzimidazole-based membranes in the potential application of 2,3-BDO recovery.