Identification of optimum synthesis conditions for a novel anion exchange membrane by response surface methodology

The Response Surface Methodology (RSM) was employed for the optimization of the synthesis conditions of an anion exchange membrane. A novel chlorinated‐polypropylene heterogeneous anion exchange membrane was made via phase inversion. A nonionic surfactant was incorporated into the composition as an additive to enhance the membrane properties. The membrane performance was measured in terms of ion exchange capacity (IEC) and permselectivity. An experimental design was used to quantify the effects of variables including the ratio of resin/polymer, the ratio of additive/total solid, and the ratio of solvent/polymer, on IEC and permselectivity. For each function, a quadratic model was developed to correlate the relationship between variables and the response. The results demonstrated the accuracy of the two models. The anion exchange membrane with the best combination of a high IEC and high permselectivity was synthesized with a solvent/polymer ratio of 18.63 (v/w), resin/polymer ratio of 1 (w/w), and additive/total solid ratio of 0.02 (w/w). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39888.     

Novel Composite Membranes for Gas Separation: Preparation and Performance

High performance composite membranes based on molecular sieving silica (MSS) were synthesized using sols containing silicon co-polymers (methyltriethoxysilane and tetraethylorthosilicate). Alpha alumina supports were treated with hydrochloric acid prior to sol deposition. Permselectivity of CO2 over CH4 as high as 16.68 was achieved whilst permeability of CO2 up to 36.7 GPU (10–6 cm3 (STP) cm–2 · s–1 · cm Hg–1) was measured. The best membrane's permeability was finger printed during various stages of the synthesis process showing an increase in CO2/CH4 permselectivity by over 25 times from initial support condition (no membrane film) to the completion of pore structure tailoring. Transport measurement results indicate that the membrane pretreated with HCl has highest permselectivity and permeation rate. In particular, there is a definite cut-off pore size between 3.3 and 3.4 angstroms which is just below the kinetic diameters of Ar and CH4. This demonstrates that the mechanism for the separation in the prepared composite membrane is molecular sieving (activated diffusion), rather than Knudsen diffusion.     

Chiral separation with polyurea membrane consisting of L‐lysinyl residue: Proposal of facile method for prediction of permselectivity

Novel chiral polyureas were prepared from L ‐lysine‐4‐nitroanilide and 2,4‐toluene diisocyanate. The polyurea thus prepared gave a durable self‐standing membrane that can be directly converted into molecular recognition membranes by applying an alternative molecular imprinting. The Z‐D ‐glutamic acid (D ‐Glu) molecularly imprinted membrane adsorbed D ‐Glu in preference to L ‐glutamic acid (L ‐Glu) from racemic mixture of Glu and vice versa. Those two types of molecularly imprinted membrane showed optical resolution ability, adopting a concentration gradient as a driving force for membrane transport. A facile method to predict permselectivity of racemic mixture of charged permeant was proposed. From the observed membrane resistance, the permselectivity was predicted. The predicted permselectivity coincided with the observed one. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Permselectivity of nonporous polyurethane membranes for immunoisolation. I. The influence of hydrogen bonding

Nonporous polyurethane membranes were synthesized using toluene 2,4-diisocyanate (TDI), polypropylene glycol (PPG), or polytetramethylene glycol (PTMG) as polyols and 1,4-butanediol as chain extender. The percentage of hard segments was varied keeping the NCO/OH ratio constant as 1. 1. The permeation of glucose, albumin, and insulin through these membranes was studied using spectrophotometric assays. The permeation of glucose was found to be dependent on the hard segment content and hydrophobicity of the polyols, whereas insulin permeation was found to vary with the hydrogen bonding and hard segment content. The permeation of albumin was almost negligible in both systems. As the synthesized nonporous polyurethanes allow the transport of the nutrients' glucose and insulin and prevent the transport of albumin with a molecular weight of 60,000 and immunoglobulins with a molecular weight of 150,000, the membranes are proposed as potential encapsulation matrices for the immunoisolation of islet cells. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1949–1954, 1999     

Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al₂O₃ catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a Ni–Co/Al₂O₃ catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 °C, +22% at 500 °C and +18% at 550 °C) and hydrogen production (+42% at 450 °C, +32% at 500 °C and +22% at 550 °C) compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 °C, maintained with constant separation factors (7 for H₂/CH₄, 8 for H₂/CO and 10 for H₂/CO₂), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane.     

面向工程应用的果蔬气调包装设计理论与方法

为提高果蔬气调包装的工程化应用水平,根据相关理论公式,提取8个关键参数组成4对参数比例;以此为基础,开发了面向工程应用的"5+1"设计流程。以番石榴为例,设计了气调包装规格参数,分别采用实验和计算机数值模拟技术对包装内气体浓度变化进行了研究分析。结果表明,番石榴气调包装内能够形成并保持所设计的目标气体氛围,证明了所提方法的有效性。     

基于聚乳酸的草莓自发气调包装薄膜设计

目的研究材料气体透过性及选择透过性对草莓自发气调包装效果的影响。方法以密闭系统法测定草莓的呼吸速率,结合米氏方程推导呼吸速率与包装膜渗透性的关系式。采用已知渗透性的薄膜结合渗透系统法测定实际贮藏中达到动态平衡时草莓的呼吸速率,根据米氏和动态平衡方程推导适宜草莓自发气调材料的气体选择比。在此基础上,选用对CO_2具有较强选择溶解性的聚乙二醇(PEG)对聚(L-乳酸)(PLLA)进行改性,调整其透气性和CO_2/O_2选择透过性。结果在一定使用面积下,经PEG改性后的PLGL35G20膜包装内的气氛组成可以达到较理想的草莓的AMAP气调浓度。结论PEG起到了良好的调节PLLA薄膜气调包装性能的效果,推测通过调节PEG嵌段和PLLA嵌段的长度及PEG在共聚物薄膜中的含量,可调控薄膜的气体渗透性和选择性,最终使其满足不同果实自发气调包装的最佳要求。     

Study on the permselectivity of ion exchange membrane

Ion exchange membranes with high permselectivity (the character of separating cations from anions or anions from cations)and high selectivity(the character of separating cations or anions of different valencies)are important for electrodialysis process.The Donnan equilibrium theory,based on the equilibrium of ions and no electric field,can not exactly explain the permselectivity of ion exchange membrane for ED process,since it is impossible to set up a ion exchange equilibrium between membrane and solution and to neglect the influence of electrical driving force on ions during ED process.A novel model named “anti-electric potential”is established to interpret the permselectivity of ion exchange membrane according to the determination of electric potential between membranes and the variation of elements content in solutions and membranes,The results of experiment prove that the “anti-electric potential”really exists within membranes.As for the selectivity,the results reveal that electric potential and hydration energy have great influence on the concentration and mobility of ions in membranes.     

刚性二酐改性HQDEA-ODA型聚醚酰亚胺的透气性能

本文合成了一系列刚性二胺改性HQDEA-ODA型聚醚酰亚胺,研究了它们对H_2、O_2和N_2三种气体的透过性能与分子结构之间的关系。结果表明,第二种二酐单体的结构对共聚醚酰亚胺的透气性能有很大的影响。当第二种二酐单体的含量占二酐单体总量的20%时,其聚醚酰亚胺的透氢系数和H_2/N_2分离系数均比均聚物HQDPA-ODA的高。     

Preparation,Characterization and H<Subscript>2</Subscript>O<Subscript>2</Subscript> Selectivity of Hyperbranched Polyimides Containing Triazine

Novel polyimides based on aromatic dianhyride and various hexahydrotriazine monomers were synthesized via two-stage solution polycondensation method. The resulting polyimides were characterized by solubility, viscosity, density, spectroscopic and thermal analysis methods. The results showed that polyimides soluble in polar solvents and had inherent viscosities ranging from 1.92 to 2.32 dL/g. The glass transition temperatures were 315 and 344 ^○C, and the 10% weight loss temperatures were above 604 and 628 ^○C. Then, polyimide-modified electrodes were prepared for the selective determination of hydrogen peroxide. The electrochemical behavior of the resulting polyimide film electrodes to the electroactive and non-electroactive species such as ascorbic acid, oxalic acid, hydrogen peroxide, lactose, sucrose and urea was examined by CV, DPV and TB techniques. From the obtained findings, it was shown that polyimide-coated electrode (PI-2) was only permitted to hydrogen peroxide among the species examined. As a result, it is claimed that polyimide electrode could be used as a selective membrane for hydrogen peroxide.