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Li X.,Tsinghua University | Cai W.,Tsinghua University | Wang T.,Tsinghua University | Wu Z.,Ordos Redbud Innovation Institute | And 3 more authors.
Separation and Purification Technology | Year: 2017

The use of OSN in the production of edible oil conserves energy making it extremely attractive, however, it should be noted that a physically and chemically stable membrane for this is required. Considering this, we selected the AF2400/PTFE composite membrane to recover hexane from the crude mixture of soybean oil and hexane via the OSN process. We carried out pure solvent permeation and rejection experiments, which verified the effectiveness of the membrane in separating and recovering hexane or other aliphatic solvents. We also conducted a comprehensive study on the effect of operational parameters, including long-term operation, transmembrane pressure, oil concentration and operational temperature. Permeate flux value varied in the range of 0.8–1.1 l m−2 h−1 bar−1 with oil rejection above 98% before or after physical aging for 1440 h in pure hexane. Experimental results confirmed the effectiveness of the AF2400/PTFE composite membrane in hexane recovery, showing high oil rejection and excellent long-term operational stability. We attributed the excellent performance of the AF2400/PTFE composite membrane to its unique surface properties, confirmed by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The study presented herein indicates that fluoropolymer based membranes are promising candidates in aliphatic solvent separation via the OSN process. © 2017 Elsevier B.V.

Sun T.,Tsinghua University | Fang M.,Tsinghua University | Wu Z.,Ordos Redbud Innovation Institute | Yu L.,Tsinghua University | Li J.,Tsinghua University
Modelling and Simulation in Materials Science and Engineering | Year: 2017

Molecular dynamics (MD) simulation was used to study the structural and diffusive properties of zeolitic imidazolate framework-8 (ZIF-8)/polydimethylsiloxane (PDMS), a novel alcohol-permselective mixed matrix membrane (MMM). Simulation models of one pure PDMS membrane and three ZIF-8/PDMS MMMs with increasing loadings were successfully constructed. Non-bond energy turned out to be a strong attractive interaction between the PDMS matrix and ZIF-8 cells. The morphology and mobility of PDMS chains were characterized by mean square displacement (MSD). The fraction of free volume (FFV) of the pure membrane and MMMs was calculated and showed declining trends with increasing ZIF-8 loadings. The diffusion coefficients of n-butanol and water molecules were calculated by the Einstein relation Dn-butanol. first increased then decreased, while decreased with the increasing loadings. The mechanism of selective diffusion behaviour was investigated and it was found that the inner channels of ZIF-8 provided selective pathways for n-butanol. Diffusion coefficients were correlated with FFV and the results showed that the logarithm of Dwater demonstrated a good linear relation with the inverse FFV and was in agreement with the free volume theory, while Dn-butanol showed a significant deviation in the case of MMM-1 due to the selective diffusion channels provided by ZIF-8. © 2017 IOP Publishing Ltd.

Wang J.,Tsinghua University | Zhao C.,CAS Research Center for Eco Environmental Sciences | Wang T.,Tsinghua University | Wu Z.,Ordos Redbud Innovation Institute | And 2 more authors.
RSC Advances | Year: 2016

In this study, a facile polypiperazine-amide (PPA) composite nanofiltration (NF) membrane with nanomaterial graphene oxide (GO) incorporated into a polyamide (PA) layer for high water flux and anti-fouling was fabricated by interfacial polymerization (IP). The chemical composition, structure and surface properties of the fabricated PPA/GO and PPA composite NF membranes were characterized by FTIR, XPS, FE-SEM, AFM, zeta-potential and contact angle measurements. The separation properties and anti-fouling ability of the PPA/GO NF membrane were investigated and discussed. The experimental results indicated that the water flux of the PPA/GO (300 mg L-1 GO) membrane increased from 66 (L m-2 h-1) to 87.6 (L m-2 h-1) under the operating pressure of 0.6 MPa, almost 1.4 times that of the PPA (without GO) membrane. However, the high salt rejection was still retained in the order of Na2SO4 (98.2%) > MgSO4 (96.5%) > NaCl (56.8%) > MgCl2 (50.5%). An anti-fouling test revealed that the PPA/GO membrane had excellent anti-fouling properties due to the enhanced hydrophilicity and decreased roughness induced by the GO nanosheets. Thus, the PPA/GO membrane can be efficiently and endurably applied in water purification. © 2016 The Royal Society of Chemistry.

Xia Y.,Tsinghua University | Xia Y.,Shenzhen Capital Group | Wu Z.,Ordos Redbud Innovation Institute | Lu B.,Tsinghua University | And 2 more authors.
RSC Advances | Year: 2016

The UNIFAC model and its various modified models on behalf of the group contribution methods offer reliable knowledge of phase equilibrium data, which are making great contributions for separation processes. The application of the UNIFAC-ZM model for the silicone polymer system is not only restricted by the poor accuracy under a large temperature range, but also limited by the lack of SiO group related group interaction parameters. In this work, first, modification of the model was made with consideration of the temperature effect on group interactions. Then inverse gas chromatography (IGC), a simple method to determine the infinite dilution activity coefficient, was applied to determine the interaction parameters between the common groups CH3, OH, H2O, CH3CO and SiO contained in polydimethylsiloxane (PDMS) based on the equilibrium chromatography theory. The achieved model was further proved to agree with the experimental results well. The new model was also applied in the calculation of the partition equilibrium between acetone/butanol/ethanol water solutions of different concentrations and PDMS of different polymerization degrees and side chain length. All these results would not only help the improvement of UNIFAC model, but also instruct the separation processes of silicone polymer compounds. © 2016 The Royal Society of Chemistry.

Xia Y.,Tsinghua University | Chen J.,Tsinghua University | Wu Z.,Ordos Redbud Innovation Institute | Wang T.,Tsinghua University | Li J.,Tsinghua University
European Polymer Journal | Year: 2015

Inverse gas chromatography is a versatile and effective method for the characterization of the solubility thermodynamics and diffusion kinetic of solvent-polymer system with the advantages of fast, low dosage of samples and large range of temperature. Polydimethylsiloxane (PDMS) is well known as an excellent polymer membrane material for its high permeability to gases and liquids and widely used in the separation and purification of bio-fermentation broth which was mainly consisted by acetone, butanol, ethanol and water. In this paper, the inverse gas chromatography method was applied to measure solubility thermodynamics parameters like the infinite dilution activity coefficient and Flory-Huggins interaction parameter between those small molecules and PDMS. The infinite dilution diffusion coefficients were calculated by Van Deemter model over a temperature range of 373.2-413.2 K. The diffusion coefficient was fitted with the temperature according to the Arrhenius correlation. The data could help the selection of membrane material in pervaporation or gas separation and the analysis of mass transfer process. © 2015 Elsevier Ltd.

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