High free volume polymers for pervaporation

Mixed matrix membrane of poly(4-methyl-1-pentyne) and ZIF-8 for enhanced CO2 separation over H2 and CH4

Carbon dioxide (CO2) generally exists as the main impurity in natural gas, whose main component is methane. The presence of CO2 reduces the energy content of natural gas and also causes the corrosion of pipelines. To prevent such problems, natural gas must contain a small concentration of CO2 (less than 2% by weight). Membrane technology is an attractive separation method that has been widely studied due to its advantages such as high efficiency, low operating costs, and low energy requirements. However, in the last decade, Mixed Matrix Membranes (MMMs) have attracted the attention of many researchers due to their suitable capabilities in separating polar from non-polar gases. In this research, a new MMMs was obtained by adding imidazole zeolite nanoparticle (ZIF-8) to the poly methyl pentene (PMP) polymer matrix. The polymer part of this membrane can provide high permeability and suitable mechanical and thermal stability. In addition, ZIF-8 particles enhance CO2 separation by offering high CO2 adsorption capacity and molecular sieving, improving selectivity. The gas permeability test was performed on pure and mixed matrix membranes at 30 ℃ and pressures of 2, 6 and 10 bar. In addition, the fabricated membranes were evaluated by FESEM, FTIR-ATR, BET, DMA and TGA tests. The results indicated that in the MMMs containing 30 wt% of nanoparticles in the polymer, the permeability of CO2 gas improved by more than 180% and reached about 278.95 barrer, compared to the pure polymer membrane at a pressure of 10 bar. Moreover, the selectivity of CO₂/CH₄ and CO₂/H₂ increased by 142% and 155%, respectively, primarily due to the preferential sorption of CO₂ over H₂ and CH₄ facilitated by ZIF-8 particles.

Polyacrylonitrile Ultrafiltration Membrane for Separation of Used Engine Oil

The separation of used engine oil (UEO) with an ultrafiltration (UF) membrane made of commercial copolymer of poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA)) has been investigated. The P(AN-co-MA) sample was characterized by using FTIR spectroscopy, 13C NMR spectroscopy, and XRD. The UF membrane with a mean pore size of 23 nm was fabricated by using of non-solvent-induced phase separation method-the casting solution of 13 wt.% P(AN-co-MA) in dimethylsulfoxide (DMSO) was precipitated in the water bath. Before the experiment, the used engine oil was diluted with toluene, and the resulting UEO solution in toluene (100 g/L) was filtered through the UF membrane in the dead-end filtration mode. Special attention was given to the evaluation of membrane fouling; for instance, the permeability of UEO solution was dropped from its initial value of 2.90 L/(m2·h·bar) and then leveled off at 0.75 L/(m2·h·bar). However, the membrane cleaning (washing with toluene) allowed a recovery of 79% of the initial pure toluene flux (flux recovery ratio), indicating quite attractive membrane resistance toward irreversible fouling with engine oil components. The analysis of the feed, retentate, and permeate by various analytical methods showed that the filtration through the UF membrane made of P(AN-co-MA) provided the removal of major contaminants of used engine oil including polymerization products and metals (rejection-96.3%).

Cooperative Adsorption and Diffusion of Small Alcohols in Metal-Organic Framework ZIF-8 and Intrinsically Microporous Polymer PTMSP

Fundamental understanding of molecular interactions and transport within microporous materials displaying cooperative Type V adsorption is challenged by the unique features of this isotherm type. In order to capture a broad understanding of this uncommon, yet industrially relevant, behavior in microporous materials, this investigation examines the adsorption equilibria and kinetics of methanol and ethanol in both a metal-organic framework (MOF) material, ZIF-8, and a high free volume polymer of intrinsic microporosity, poly[1-(trimethylsilyl)-1-propyne] (PTMSP). A novel formulation that can capture the cooperative effects of small alcohols in its description of adsorption equilibria and kinetics is proposed. It is subsequently applied to successfully capture some previously uncharacterized or semiempirically characterized data for equilibria and the loading dependence of the diffusivity in both ZIF-8 and PTMSP, which are materials chosen for their industrial relevance. Finally, it is anticipated that the results of this study can fill the current void that exists in meaningful mechanistic and analytical descriptions of cooperative equilibrium and diffusion phenomena in microporous materials.

Pervaporation and Gas Separation Properties of High-Molecular Ladder-like Polyphenylsilsesquioxanes

This paper presents the results of studies on the pervaporation properties (for benzene/hexane mixtures) and gas permeability (for He, H2, N2, O2, CO2, CH4, C2H6, and C4H10) of ladder-like polyphenylsesquioxanes (L-PPSQ) with improved physical and chemical properties. These polymers were obtained by condensation of cis-tetraphenylcyclotetrasiloxanetetraol in ammonia medium. The structure of L-PPSQ was fully confirmed by a combination of physicochemical analysis methods: 1H, 29Si NMR, IR spectroscopy, HPLC, powder XRD, and viscometry in solution. For the first time, a high molecular weight of the polymer (Mn = 238 kDa, Mw = 540 kDa) was achieved, which determines its improved mechanical properties and high potential for use in membrane separation. Using TGA and mechanical analysis methods, it was found that this polymer has high thermal (Td5% = 537 °C) and thermal-oxidative stability (Td5% = 587 °C) and good mechanical properties (Young's module (E) = 1700 MPa, ultimate tensile stress (σ) = 44 MPa, elongation at break (ε) = 6%), which is important for making membranes workable under various conditions. The polymer showed a high separation factor for a mixture of 10% wt. benzene in n-hexane (126) at a benzene flow of 33 g/(m2h).

Ultramicroporous Polyphenylenes via Diels-Alder Polycondensation Approach

Development of new microporous organic polymers attracts significant attention due to a wide scope of promising applications. In addition, the synthesis of soluble, non-crosslinking polymers of high surface area and uniform microporosity is very challenging, and the methods for soluble microporous polymers formation are rather limited. In this work, we report a new approach to construct porous polyphenylenes which employs the Diels-Alder polycondensation of multifunctional ethynyl-containing monomers of different spatial architecture with bis(cyclopentadienone)s. The resulting polymers were soluble in common organic solvents, and their structure and properties were assessed by NMR, TGA, DSC, and SEC studies. The polymers demonstrated a specific surface area up to 751 m2·g-1 and ultramicroporous (pore size ≤ 0.6 nm) structure. N2 and CO2 adsorption-desorption data revealed that porosity parameters, e.g., specific surface area and pore sizes, can be tuned selectively by varying the type of monomers and reaction conditions.

High Efficiency Membranes Based on PTMSP and Hyper-Crosslinked Polystyrene for Toxic Volatile Compounds Removal from Wastewater

For the first time, membranes based on poly(1-trimethylsilyl-1-propyne) (PTMSP) with 5–50 wt% loading of hyper-crosslinked polystyrene sorbent particles (HCPS) were obtained; the membranes were investigated for the problem of effective removal of volatile organic compounds from aqueous solutions using vacuum pervaporation. The industrial HCPS sorbent Purolite Macronet™ MN200 was chosen due to its high sorption capacity for organic solvents. It has been found that the membranes are asymmetric when HCPS content is higher than 30 wt%; scanning electron microscopy of the cross-sections the membranes demonstrate that they have a clearly defined thin layer, consisting mainly of PTMSP, and a thick porous layer, consisting mainly of HCPS. The transport and separation characteristics of PTMSP membranes with different HCPS loading were studied during the pervaporation separation of binary and multicomponent mixtures of water with benzene, toluene and xylene. It was shown that the addition of HCPS up to 30 wt% not only increases the permeate fluxes by 4–7 times, but at the same time leads to 1.5–2 fold increase in the separation factor. It was possible to obtain separation factors exceeding 1000 for all studied mixtures at high permeate fluxes (0.5–1 kg/m²∙h) in pervaporation separation of binary solutions.