Analysis of hollow fibre membrane systems for multicomponent gas separation

This paper analysed the performance of a membrane system over key design/operation parameters. A computation methodology is developed to solve the model of hollow fibre membrane systems for multicomponent gas feeds. The model represented by a nonlinear differential algebraic equation system is solved via a combination of backward differentiation and Gauss–Seidel methods. Natural gas sweetening problem is investigated as a case study. Model parametric analyses of variables, namely feed gas quality, pressure, area, selectivity and permeance, resulted in better understanding of operating and design optima. Particularly, high selectivities and/or permeabilities are shown not to be necessary targets for optimal operation. Rather, a medium selectivity (<60 in the given example) combined with medium permeance (∼300–500 × 10⁻¹⁰ mol/s m² Pa in the given case study) is more advantageous. This model-based membrane systems engineering approach is proposed for the synthesis of efficient and cost-effective multi-stage membrane networks.     

The study of elongation and shear rates in spinning process and its effect on gas separation performance of Poly(ether sulfone) (PES) hollow fiber membranes

The influence of elongation and shear rates induced by the geometry of spinnerets on gas performance of PES hollow fiber membranes has been studied. Different elongation and shear rates were introduced in various spinnerets with flow angles of 60°, 75° and 90° by changing the flow rate of dope solution. The PES hollow fiber membranes were fabricated under the wet-spun condition without extra drawing force and their gas performances were tested by using O₂ and N₂. The flow profiles of dope solution and the elongation and shear rates at the outermost point of the outlet of spinnerets were simulated by the computational fluid dynamics model. A hypothetic mechanism is assumed to explain the effects of elongation and shear rates on the changes of conformation of polymer chain. While trying to correlate the elongation and shear rates with the gas performance of hollow fibers, we have come to some preliminary conclusions that the elongation rate has more contribution portion in permselectivity than in permeance and the shear rate has more contribution portion in permeance than in permselectivity.     

Simulation of binary gas separation with asymmetric hollow fibre membranes and case studies of air separation

A mathematical model for high‐flux asymmetric hollow fibre membrane was developed considering the effect of permeate pressure build‐up inside the fibre bore. A new solution technique was developed to solve the model equations, which constitute a boundary value problem. The ordinary differential equations were solved as an initial value problem in two successive steps using the Gear's BDF method. The technique is advantageous since it requires minimum computational time and effort with improved solution stability, and the computational complexity does not multiply as the number of components increases. The model predictions and the robustness of the numerical technique were validated with experimental data for several membrane systems with different flow configurations. The model and the solution technique were applied to evaluate the separation characteristics of air using representative membranes with different configurations, including single‐stage, single‐stage with permeate recycle, single‐stage with retentate recycle, air blending, and two stages in series. The study demonstrates that the new solution technique can conveniently handle the high‐flux hollow fibre membrane problems with different module configurations. © 2011 Canadian Society for Chemical Engineering     

Novel composite hollow fibre gas separation membranes with high selectivity and improved solvent resistance

Composite gas separation membranes with a 0.1–3 μm thick film of Hyflon AD 60X on a porous hollow fibre ultrafiltration membrane support of amorphous poly(ether ether ketone), were prepared. The influence of the coating conditions on the film thickness and on the pure gas transport properties was studied. The gas transport properties were related to the film thickness and to the morphology of the supporting UF membrane.     

聚氨酯丙烯酸酯紫外光固化PVC涂料的研制

通过对涂料不同组分的种类及配比进行调节,制备不同配方的PVC清漆。在测试附着力、硬度、耐温、耐水性能的基础上,优化涂料配方,并配制出性能优异的PVC清漆涂料。     

Graphene oxide membranes supported on the ceramic hollow fibre for efficient H2 recovery

The special channels and intrinsic defects within GO laminates make it a very potential candidate for gas separation in recent years. Herein, the gas separation performance of GO membranes prepared on the surface of ceramicα-Al_2O_3 hollow fibre was investigated systematically. The microstructures of ceramic hollow fibre supported GO membranes were optimized by adjusting operation conditions. And, the GO membrane fabricated at 30 min exhibited great promising H_2 recovery ability from H_2/CO_2 mixture. At room temperature, the H_2 permeance was over 1.00 × 10~(-7)mol·m~(-2)·s~(-1)·Pa~(-1)for both single gas and binary mixture. The corresponding ideal selectivity and mixture separation factor reached around 15 and 10, respectively. In addition, humility, operation temperature, H_2 concentration in the feed and the reproducibility were also studied in this work.     

Poly(vinyl chloride) hollow‐fiber membranes for ultrafiltration applications: Effects of the internal coagulant composition

Poly(vinyl chloride) (PVC) hollow‐fiber membranes were spun by a dry/wet phase‐inversion technique from dopes containing 15 wt % PVC to achieve membranes with different pore sizes for ultrafiltration (UF) applications. The effects of the N,N‐dimethylacetamide (DMAc) concentration in the internal coagulant on the structural morphology, separation performance, and mechanical properties of the produced PVC hollow fibers were investigated. The PVC membranes were characterized by scanning electron microscopy, average pore size, pore size distribution, void volume fraction measurements, and solubility parameter difference. Moreover, the UF experiments were conducted with pure water and aqueous solutions of poly(vinyl pyrrolidone) as feeds. The mechanical properties of the PVC hollow‐fiber membranes were discussed in terms of the tensile strength and Young's modulus. It was found that the PVC membrane morphology changed from thin, fingerlike macrovoids at the inner edge to fully spongelike structure with DMAc concentration in the internal coagulant. The effective pores showed a wide distribution, between 0.2 and 1.1 μm, for the membranes prepared with H₂O as the internal coagulant and a narrow distribution, between 0.114 and 0.135 μm, with 50 wt % DMAc. The results illustrate that the difference in the membrane performances was dependent on the DMAc concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication of hollow fibre gas separation membranes

Over a century ago, researchers discovered that membranes could separate gases. However, this technology has been commercialized only recently, mainly because the early membranes had low permeance and permselectivity, making them uneconomical. With the discovery of thin barrier membranes, either in dense, asymmetric, or thin-film composite form, gas separation by membranes has become commercially viable. Furthermore, the discovery of hollow fibre technology has permitted low-cost membrane fabrication and high-efficiency module design. Homogeneous dense hollow fibre membranes are fabricated from polymer melts using a special die. Asymmetric membranes with integral dense skins, however, are made by controlled coagulation of polymer solutions. Finally, thin-film composite membranes, where a thin dense barrier layer is made separately on a microporous substrate, are made either by simple dip coating or by complex interfacial processes. The latter concept is versatile because it permits formation of thin barrier layers by a variety of methods. The apparatus used to fabricate various membrane types and the critical factors influencing the membrane properties are discussed.     

Poly(vinyl chloride) and its fire properties

This work provides an up‐to‐date review of the fire properties of poly(vinyl chloride) (PVC) materials, both rigid (unplasticized) and flexible (plasticized). The fire properties addressed include ignitability, ease of extinction (oxygen index), flame spread (small scale and intermediate scale), heat release, smoke obscuration, smoke toxicity, hydrogen chloride emission and decay, and performance in real‐scale fires. This comprehensive review includes a wide selection of references and tables illustrating the properties of PVC materials in comparison with those of other polymeric materials, including, in many instances, wood materials. The work puts these fire properties in perspective, showing that the heat release rate (the key fire property) of rigid PVC (and that of properly flame‐retarded flexible PVC) are among the lower values found for combustible materials. This work also shows that the smoke toxicity and smoke obscuration resulting from burning PVC materials in real‐scale fires is in the same range as those of other materials.     

PVC辅助热稳定剂己二酸季戊四醇酯催化合成研究及应用

以己二酸、季戊四醇为原料,对甲苯磺酸作催化剂,采用直接酯化反应合成了己二酸季戊四醇酯,考查了温度、催化剂用量、原料配比和带水剂用量对己二酸季戊四醇酯收率的影响,确定了最佳工艺条件:醇酸物质的量比为3.4:1,带水剂用最为体系总质量的20%,催化剂用量为酸质量的2.2%,反应时间为1.5 h,己二酸季戊四醇酯收率可达99...     

马来酸酐接枝改性氯化聚氯乙烯的制备及其在PVC中的应用

采用固相法制备马来酸酐接枝氯化聚氯乙烯(CPVC-g-MAH),得到了接枝率达2.91 %的CPVC-g-MAH,并对其进行了性能测试,探讨了聚氯乙烯(PVC)/CPVC-g-MAH共混物的冲击性能和加工性能,与PVC/氯化聚氯乙烯(CPVC)共混物进行对比以观察改性效果。结果表明,CPVC-g-MAH的热性能较CPVC有较大提高;PVC/CPVC-g-MAH共混物的冲击性能比PVC/CPVC共混物有所提高,而平衡转矩有所降低,说明CPVC-g-MAH相比于CPVC对PVC共混物加工性能改善效果更加明显。     

Highly selective polymeric membranes for gas separation

Polymeric membranes have gained an important place in chemical technology and are used in a broad range of applications. The key property that is exploited is the ability of a membrane to control the permeation rate of a chemical species through the membrane. The goal is to allow one component of a mixture to permeate the membrane freely, while hindering permeation of other component. To accomplish this, we proposed a novel concept of a (universal) ‘organic molecular sieve’ and experimentally proved its possibility by showing that organic polymer molecules at the interface between the permeable phase and the impermeable phase play the role of molecular sieves. This resulted in a significantly improved selectivity in gas separation, in fact going over the so-called ‘upper-bound’ sought for the past 30 years by many researchers but without much success. Since, this is not size selective like an inorganic molecular sieve but diffusion selective (the compatibilizer works like a molecular sieve to separate one gas molecules from the other), it can be used for the preparation of polymeric membranes for separation of any gas molecules pair. Because of polymer processability, this method is quite promising for the continuous mass production of polymeric membranes for real applications, especially when the polymers are insoluble to common solvents so that solution based techniques are hard to apply. This strategy can be applicable to various separation processes of many chemicals and gases.     

Preparation,structure, and transport properties of ultrafiltration membranes of poly(vinyl chloride) (PVC), carboxylated poly(vinyl chloride) (CPVC), and PVC/CPVC blends

Ultrafiltration (UF) membranes were prepared from poly(vinyl chloride) (PVC), carboxylated poly(vinyl chloride) (CPVC), and PVC/CPVC blends by the phase-inversion method. The physical structure of the membranes was characterized by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The fouling characteristics of all the three membranes and acrylamide (AA)-grafted PVC membranes were characterized by ultrafiltration of bovine serum albumin (BSA) solution over a range of pH and of salt concentrations. Maximum adsorption of the protein on the membrane occurred near the isoelectric point of BSA and in the presence of the salts. The charge on BSA appears to be a dominant factor in determining the fouling. The UF results are explained in terms of nature of the membrane polymer, and effect of different ionic environments on the conformational changes of the protein. The ultrafiltration fluxes are correlated by a model based on the membrane resistance and the time-dependent resistance of the concentration polarization layer of the protein. The values of a mass transfer coefficient and concentration polarization were determined. Zeta potential of the membranes were also determined before and after the UF. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1117–1130, 1999     

聚氯乙烯结皮发泡棒材生产技术

较详细地讨论了单螺杆挤出机生产聚氯乙烯结皮发泡棒材的有关技术问题,包括挤出机和模具的结构参数、最佳配方设计和关键工艺条件控制,认为采用长径比大于２５的普通单螺杆挤出机,在合理配方和工艺条件下,可生产高质量聚氯乙烯结皮发泡棒材,φ１０￣３８ｍｍ的棒材的生产可采用φ６５ｍｍ螺杆的挤出机。     

医用PVC注塑料的研究与应用

研究以混合稳定剂体系来改善ＰＶＣ塑料的热稳定性,用注塑方法成型血袋配件,取得了良好效果。     

Stability of PVDF hollow fibre membranes in sodium hydroxide aqueous solution

The stability of PVDF hollow fibre membranes in sodium hydroxide (NaOH) aqueous solutions were investigated in this study. PVDF hollow fibre membranes were prepared from each of the three commercial raw PVDF materials (Kynar 761, Solef 1015 and Solef 6010) from two major suppliers (Atofina Chemicals Inc., USA and Solvay, Belgium) for comparison purposes. The effect of NaOH concentration, treatment time and temperature on mechanical properties, thermal properties and crystalline structure of the PVDF hollow fibre membranes were investigated through mechanical strength measurement, surface area analysis, XRD, FTIR and DSC analyses. The obtained results indicate that the reaction between PVDF and NaOH was initiated even at low concentrations of NaOH and was aggravated with the extended treatment time, resulting in the decrease in mechanical strength and crystallinity of PVDF hollow fibre membranes. The reaction was accelerated and intensified by increasing the concentration of NaOH and/or treatment temperature. At 70 °C, the mechanical integrity of the PVDF membranes was completely destroyed in 4 wt% NaOH solution within 24 h or in 10 wt% NaOH solution within 8 h. The deterioration of stability in NaOH solutions is considered universal for all PVDF employed in this study, irrespective of the raw materials or the corresponding hollow fibre membranes.     

Preparation of poly(vinyl chloride) (PVC) ultrafiltration membranes from PVC/additive/solvent and application of UF membranes as substrate for fabrication of reverse osmosis membranes

Ultrafiltration (UF) membranes were prepared from poly(vinyl chloride) (PVC) as main polymer, poly(vinyl pyrrolidone) (PVP) as additive, and 1‐methyl‐2‐pyrrolidone (NMP) as solvent using Design Expert software for designing the experiments. The membranes were characterized by SEM, contact angle measurement, and atomic force microscopy. The performance of UF membranes was evaluated by pure water flux (PWF) and blue indigo dye particle rejection. In addition, the molecular weight cutoff of UF membranes was determined by poly(ethylene glycol) (PEG) rejection. The UF membranes were used as substrates for fabrication of polyamide thin film composite (TFC) reverse osmosis (RO) membranes. The results showed that the model had high reliability for prediction of PWF of UF membranes. Also, increment in PVC concentration caused reduction of PWF. Moreover, at constant PVC concentration and if the concentrations of PVC was lower than 10 wt %, the PWF reduced by increasing the concentration of PVP. However, at PVC concentration higher than 11 wt %, increment in PVP concentration showed increment and reduction of PWF. The PEG rejection results showed that the prepared membranes had UF membranes properties. Finally, the NaCl rejection tests of RO membranes by PVC as substrates indicated that the performance of RO membranes were lower than commercial membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46267.     

羟基锡酸锌包覆纳米氢氧化镁在PVC中的应用

通过均匀沉淀法制备了羟基锡酸锌包覆纳米氢氧化镁并将其应用到聚氯乙烯(PVC)中。利用XRD、TG、DTA对羟基锡酸锌包覆纳米氢氧化镁的性能进行了研究,并通过氧指数、烟密度研究了羟基锡酸锌包覆纳米氢氧化镁对PVC的阻燃和抑烟性能的影响,同时对其力学性能也进行了研究。结果表明:纳米氢氧化镁表面均匀地包覆了羟基锡酸锌;羟基锡酸锌包覆纳米氢氧化镁对PVC的阻燃和抑烟性能明显优于单独添加羟基锡酸锌、纳米氢氧化镁以及羟基锡酸锌包覆微米氢氧化镁和羟基锡酸锌与纳米氢氧化镁混和物时的阻燃、抑烟性能;纳米材料的加入对PVC的力学性能也产生了有利的影响。     

化学微交联聚氯乙烯的结构和性能

通过氯乙烯/邻苯二甲酸二烯丙酯(VC/DAP)悬浮共聚,合成了含部分凝胶结构的化学微交联PVC树脂,对微交联PVC的玻璃化转变行为、加工性能、消光性能、加热-形变行为和力学性能进行了研究。当DAP用量在0.25%mol以下时,PVC的玻璃化温度变动不大。凝胶含量的增加将导致交联PVC_d~T的光泽度下降,消光性能提高;塑化时间和加工扭矩均增加,加工性能急剧变差;加热变形值下降,最高使用温度提高。凝胶对PVC拉伸性能的影响较为复杂,但压缩永久变形则随凝胶含量的增加而下降,材料的弹性性能逐渐提高。     

Modelling of multicomponent gas separation with asymmetric hollow fibre membranes—methane enrichment from biogas

A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fibre membranes was developed considering the permeate pressure build‐up inside the fibre bore and cross flow pattern with respect to the membrane skin. The solution technique provides reliable examination of pressure and concentration profiles along the permeator length (both residue/permeate streams) with minimal effort. The proposed simulation model and scheme were validated with experimental data of gas separation from literature. The model and solution technique were applied to investigate dynamic performance of several membrane module configurations for methane recovery from biogas (landfill gas or digester gas), considering biogas as a mixture of CO₂, N₂ and CH₄. Recycle ratio plays a crucial role, and optimum recycle ratio vital for the retentate recycle to permeate and permeate recycle to feed operation was found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane‐selective or nitrogen‐selective membranes was calculated. © 2012 Canadian Society for Chemical Engineering