Zhongqi Ren

The Study on Pervaporation Behaviors of Dilute Organic Solution Through PDMS/PTFE Composite Membrane

As an energy-efficient alternative to distillation, pervaporation has been widely combined with fermentation to remove organic compounds from their dilute solutions in a fermentation broth. In this work, the organic permselective composite membrane is prepared by coating polydimethylsiloxane (PDMS) cross-linked with n-heptane on the substrate of polytetrafluoroethylene(PTFE) membrane. The separation behavior is studied in different dilute organic solutions, which include acetone dilute solution, butanone dilute solution, cyclohexanone dilute solution, ethanol dilute solution, isopropanol dilute solution, n-butyl alcohol dilute solution, acetic acid dilute solution, and ethyl acetate dilute solution. Most of these solutions are main reaction products or by-products from fermentation process. The effects of solubility of organics in the membrane, molecular weight, and polarity of the organics on the pervaporation performance are investigated. The effects of operating temperature and organic concentration in the feed solutions on the performance of composite membrane are studied as well. The experimental results show that molecular volume has less influence than solubility and molecular polarity for these organic solvent. The selectivity of PDMS membrane to ethyl acetate is relative high due to good solubility and diffusion of ethyl acetate molecules in polymer.

Preparation and adsorption characteristics of an ion-imprinted polymer for fast removal of Ni(II) ions from aqueous solution

A novel Ni(II) ion-imprinted polymer (IIP) was synthesized by bulk polymerization for fast removal of Ni(II) ions from aqueous solution. Effects of preparation conditions on adsorption performance were investigated. Diphenylcarbazide (DPC) and N,N-azobisisobutyronitrile (AIBN) were used as ligand and initiator, respectively. Various monomers, solvents, cross-linking agents and molar ratios of template, monomer and cross-linking agent for polymerization were studied to obtain the largest adsorption capacity. The prepared Ni(II)-IIPs were characterized using Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX) and thermogravimetric analysis (TGA). The elution process has no influence on the three-dimension network structure observed on the surfaces of Ni(II)-IIPs. Ni(II) ions could be eluted from IIPs successfully with HCl solution. Effects of operating time, pH and initial concentration of Ni(II) in aqueous solution on adsorption performance were investigated too. The adsorption equilibrium was reached within 30min. The maximum adsorption capacity of Ni(II)-IIPs was 86.3mgg-1 at pH 7.0 with initial Ni(II) concentration of 500mgL-1. The adsorption by Ni(II)-IIPs followed a pseudo-second-order kinetic and Freundlich isotherm models. The selectivity coefficients for all Ni(II)/interfering ions are larger than one because of the imprinting effect. The Ni(II)-IIPs also showed high reusability and stability.

The Transport of Copper(II) through Hollow Fiber Renewal Liquid Membrane and Hollow Fiber Supported Liquid Membrane

Abstract In this paper, hollow fiber renewal liquid membrane (HFRLM) and hollow fiber supported liquid membrane (HFSLM) were used to simultaneously remove and recover copper(II) from aqueous solutions, and the transport performance of these two techniques were compared under the similar conditions for the system of CuSO4 +D2EHPA in kerosene +HCl. The results showed that the HFRLM process was more stable than the HFSLM process. The HFRLM process had a higher overall mass transfer coefficient than that of HFSLM process in single-pass experiments. These were because the renewal effect of the liquid membrane layer could reduce the mass transfer resistance of the lumen side and replenish the loss of the membrane liquid in the HFRLM process. The transport results were better in the HFRLM process than that in the HFSLM process with recycling experiments. Therefore, HFRLM technique is a promising method for simultaneous removal and recovery of heavy metal from aqueous solutions.

Immobilization of lipase on porous monodisperse chitosan microspheres

Porous monodisperse chitosan microspheres were synthesized for enzyme immobilization. The microspheres were prepared using microchannels and modified with glutaraldehyde. The microspheres had a mean diameter of 495 µm; the polydispersity indices were less than 0.08, and the specific surface area was between 121 and 173 m2/g. Candida sp. 1619 lipase was selected as a model lipase. Immobilization conditions such as enzyme loading, glutaraldehyde concentration, and immobilization time were optimized. The temperature, pH, and storage stability of the free and immobilized enzymes were also investigated. The immobilized enzyme had broad‐ranging pH and temperature optima as compared with free enzyme. The storage stability of the immobilized enzyme was higher than that of the free enzyme.

Experimental Study of the Effect of Membrane Porosity on Membrane Absorption Process

Abstract Five kinds of expanded polytetrafluoroethylene (ePTFE) flat membranes with different porosity and micro‐pore size were chosen to carry out the unsteady state gas absorption experiments. The influence of the membrane porosity and micro‐pore size on the membrane absorption process was investigated. Experimental results showed that the membrane porosity had an impact on the membrane absorption process, and the degree of this impact depended on the absorption system and the membrane pore size. For a rapid mass transfer process, the porosity affected the mass transfer more significantly, while for the slow mass transfer process the porosity almost did not affect the mass transfer. The modeling analysis showed that the porosity affected the concentration profile of the solute near the membrane surface on the liquid side, which led to the reduction of the mass transfer area of the membrane. Hence, the apparent effect on the mass transfer of the membrane absorption process.

Chiral liquid membrane for enantioselective separation of racemic ibuprofen by L-tartaric acid derivatives

The chirality of drugs plays a significant role in most chemical and biochemical process. In this paper, a chiral liquid membrane using L-tartaric ester dissolved in n-octane as liquid membrane phase and polyvinylidene fluoride hollow fibers as membrane support was investigated to separate racemic ibuprofen. For L-dipentyl tartaric ester, the separation factor was 1.18. The favorable L-dipentyl tartaric ester concentration was 0.20 mol L−1. With an increase of flow rates on two sides, a flux change of mass transfer in stripping phase was not observed. The same trend is obtained in feed phase. The concentration of both R-ibuprofen and S-ibuprofen in stripping phase increased with an increase of pH value. The best pH in stripping phase was 2.5 and the separation factor was about 1.2. The best separation factor was up to 1.38 after a six-level experiment.

Treatment of azo dye (Acid Orange II) wastewater by pulsed high-voltage hybrid gas–liquid discharge

Pulsed high-voltage electrical discharge was used in treating azo dye (Acid Orange II, AO7) wastewater. The effects of initial pH, Fe2+ concentration, discharge mode, conductivity of initial aqueous solution and the type of bubbling gas (air, O2, N2) on AO7 degradation were studied. A new gas–liquid discharge (NGL) mode, by which a plate was exposed to air and needles were immersed in liquid, displayed a remarkably better AO7 degradation than the gas–liquid discharge (GL) mode and the liquid discharge (L) mode. The lower conductivity of aqueous solution and the higher oxygen concentration in bubbled gas were of benefit to the degradation process. In addition, owing to the multi-point structure and self-provided Fe2+, the electrode with iron mesh-plate discharge showed a more competitive degradation performance than that with multi-needle-plate discharge. The oxidant of ˙OH and H2O2 induced by the discharge process were also studied to explore the degradation processes. By NGL mode with iron mesh electrode and bubbled air in reactor, the degradation efficiency of AO7 was up to 85.8% when the initial pH, conductivity and Fe2+ concentration were 2.28, 200 μS·cm−1 and 1.635 mmol L−1, respectively.

Preparation and application of a novel ethanol permselective poly(vinyltriethoxysilane) membrane

A novel thin poly(vinyltriethoxysilane) membrane with hydrophobic Si–O–Si backbone and vinyl groups is proposed to recover ethanol by pervaporation. It exhibits high flux (>10000 g m−2 h−1), which is about ten times higher than that of PDMS, demonstrating that this membrane would facilitate the ethanol industrial production by pervaporation–fermentation process.

Modeling Study of the Influence of Porosity on Membrane Absorption Process

Abstract A theoretical model based on the advancing front model was developed to analyze the influence of porosity on membrane absorption process. Perturbation solutions were obtained and a nonlinear transformation was applied to increase the accuracy of the solutions. The concentration profile of the solute in the liquid side near the membrane surface was simulated for different operation conditions. The influencing factors on the diffusing rate of the solute concentration profile were analyzed qualitatively. In the case of the rapid mass transfer system, the time of reaction front to reach the midpoint of two proximate pores is relatively long, which means that the concentration layer of solute overcasts the whole surface of membrane slowly, there is a “dead” area for mass transfer, so the influence of porosity should be taken into account. In the case of slow mass transfer system, the time can be ignored compared with the overall experiment time, and the influence of porosity is negligible. The absorption rates were calculated based on the developed model and the calculated results agreed well with the literature results.

Extraction of aniline from wastewater: equilibria, model, and fitting of apparent extraction equilibrium constants

The physical and reactive extraction equilibria of aniline at 298.2 ± 0.5 K were studied. n-Butylacetate (BA), n-decanol, n-heptane and methyl tert-butyl ether (MTBE) were used for physical extraction. The distribution coefficient (D) of aniline follows the sequence BA > MTBE > n-decanol > n-heptane. The largest distribution coefficient (D = 22.58) can be obtained with BA owing to its strong polarity. The equilibrium temperature almost has no effect on the distribution coefficient except for MTBE. Tributyl phosphate (TBP), acetamide (N503), trialkylamine (N235), di-(2-ethylhexyl) phosphoric acid (D2EHPA) and (2-ethylhexyl) 2-ethylhexylphosphanate (P507) were used as extractants with BA, kerosene and n-heptane as diluents for the reactive extraction. TBP, N503 and N235 show weak removal abilities because of their neutral and basic characteristics. For the acidic phosphorus-containing extractants, namely, D2EHPA and P507, equilibrium models are presented that employ the mass action law and used to determine model parameters and apparent extraction equilibrium constants (K11, K12, and K21). The reactive extraction complexes are considered as 1:1 and 1:2 aniline to D2EHPA complexes with BA as diluent, 1:2 aniline to D2EHPA complexes with kerosene and n-heptane as diluents, and 1:1 and 1:2 aniline to P507 complexes with kerosene and n-heptane as diluents. The distribution coefficients and loadings of D2EHPA and P507 calculated using the equilibrium model parameters and apparent extraction equilibrium constants efficiently agree with the experimental data, which indicates that the models are valid in representing the equilibrium behavior of aniline with the selected extractants in reactive extraction. The effects of temperature on extraction abilities were investigated and the enthalpy change of the extraction process with D2EHPA in kerosene was obtained.