Jiangnan Shen

The use of BMED for glyphosate recovery from glyphosate neutralization liquor in view of zero discharge.

Alkaline glyphosate neutralization liquors containing a high salinity pose a severe environmental pollution problem by the pesticide industry. However, there is a high potential for glyphosate recovery due to the high concentration of glyphosate in the neutralization liquors. In the study, a three-compartment bipolar membrane electrodialysis (BMED) process was applied on pilot scale for the recovery of glyphosate and the production of base/acid with high concentration in view of zero discharge of wastewater. The experimental results demonstrate that BMED can remove 99.0% of NaCl from the feed solution and transform this fraction into HCl and NaOH with high concentration and purity. This is recycled for the hydrolysis reaction of the intermediate product generated by the means of the Mannich reaction of paraformaldehyde, glycine and dimethylphosphite catalyzed by triethylamine in the presence of HCl and reclamation of the triethylamine catalyst during the production process of glyphosate. The recovery of glyphosate in the feed solution was over 96%, which is acceptable for industrial production. The current efficiency for producing NaOH with a concentration of 2.0 mol L(-1) is above 67% and the corresponding energy consumption is 2.97 kWh kg(-1) at a current density of 60 mA cm(-2). The current efficiency increases and energy consumption decreases as the current density decreases, to 87.13% and 2.37 kWh kg(-1), respectively, at a current density of 30 mA cm(-2). Thus, BMED has a high potential for desalination of glyphosate neutralization liquor and glyphosate recovery, aiming at zero discharge and resource recycling in industrial application.

Mixed matrix membranes containing MIL-53(Al) for potential application in organic solvent nanofiltration

Aromatic poly(m-phenyleneisophthalamide) (PMIA) and the metal-organic framework (MOF) MIL-53(Al) were employed as the polymer matrix and additive, respectively, to develop mixed matrix membranes (MMMs) via non-solvent induced phase separation for potential application in organic solvent nanofiltration. The prepared membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and water contact angle measurements. The membrane water permeance enhanced when MIL-53(Al) was incorporated into the membrane structure while the rejection had no significant change. The optimum MMM (with 0.5 wt% MOF concentration) passes mono and bivalent inorganic salts but rejects larger charged organic molecules and has a mean effective pore size of 0.7 nm. The influence of organic solvents on MMM performance was also investigated and the result shows that the performance shifts towards a lower pure water permeance and a higher rejection after exposure to organic solvents (ethyl acetate or methanol). The membrane performance in organic solvent nanofiltration was evaluated on the basis of the permeance and rejection of brilliant blue G in ethanol, and the result showed that the permeance of MMMs significantly increased (by 289%) while the rejection slightly reduced by 4% in contrast to the pure membrane.

Preparation of a Facilitated Transport Membrane Composed of Carboxymethyl Chitosan and Polyethylenimine for CO2/N2 Separation

The miscibility of carboxymethyl chitosan/polyethylenimine (CMCS/PEI) blends was analyzed by FT-IR, TGA and SEM. Defect-free CMCS/PEI blend membranes were prepared with polysulfone (PSf) ultrafiltration membranes as support layer for the separation of CO2/N2 mixtures. The results demonstrate that the CMCS/PEI blend is miscible, due to the hydrogen bonding interaction between the two targeted polymers. For the blended membrane without water, the permeability of CO2 gas is 3.6 × 10−7 cm3 cm−2 s−1 cmHg−1 and the corresponding separation factor for CO2 and N2 gas is about 33 at the pressure of 15.2 cmHg. Meanwhile, the blended membrane with water has the better permselectivity. The blended membrane containing water with PEI content of 30 wt% has the permeance of 6.3 × 10−4 cm3 cm−2 s−1 cmHg−1 for CO2 gas and a separation factor of 325 for CO2/N2 mixtures at the same feed pressure. This indicates that the CO2 separation performance of the CMCS/PEI blend membrane is higher than that of other facilitated transport membranes reported for CO2/N2 mixture separation.

Enhanced Performance of Polyurethane Hybrid Membranes for CO2 Separation by Incorporating Graphene Oxide: The Relationship between Membrane Performance and Morphology of Graphene Oxide

Polyurethane hybrid membranes containing graphene oxide (GO) with different morphologies were prepared by in situ polymerization. The separation of CO2/N2 gas mixtures was studied using these novel membranes. The results from the morphology characterization of GO samples indicated that the oxidation process in the improved Hummers method introduced oxygenated functional groups into graphite, making graphite powder exfoliate into GO nanosheets. The surface defects on the GO sheets increased when oxidation increased due to the introduction of more oxygenated functional groups. Both the increase in oxygenated functional groups on the GO surface and the decrease in the number of GO layers leads to a better distribution of GO in the polymer matrix, increasing thermal stability and gas separation performance of membranes. The addition of excess oxidant destroyed the structure of GO sheets and forms structural defects, which depressed the separation performance of membranes. The hybrid membranes containing well-distributed GO showed higher permeability and permeability selectivity for the CO2. The formation of GO aggregates in the hybrid membranes depressed the membrane performance at a high content of GO.

Enhanced conductivity of monovalent cation exchange membranes with chitosan/PANI composite modification

The application of electrodialysis (ED) for desalination requires the use of natural seawater or river water, in which the presence of multivalent ions is inevitable. This currently limits the process performance. Membranes with selectivity for monovalent ions may overcome this limitation. This study used the method of electro-deposition with chitosan/aniline polymer as a modification material to coat a commercial anion exchange membrane in view of obtaining selectivity for monovalent ions. Chitosan was grafted with polyaniline through copolymerization using ammonium persulfate as an initiator. FTIR spectra of the composites revealed that there was a strong interaction between substituted polyanilines and chitosan. The method was used to prepare a series of membranes by varying the aniline ratio and polymerization time. The chemical composition and surface properties of the membranes were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Current–voltage curves and resistance were measured to characterize the transport properties of the membranes and the membrane conductivity. The results show that the membrane conductivity increases with the aniline ratio; the selectivity initially increases with the aniline ratio, and then decreases again. The optimum modification condition was an electrodeposition time of 4 h with an aniline ratio of 0.4. Using the modified membrane in concentrated sea water, it was demonstrated that the modified membrane has an excellent selectivity towards monovalent cations.

Recovery of chemically degraded polyethyleneimine by a re-modification method: prolonging the lifetime of cation exchange membranes

Selectivity for monovalent cations is an important property of cation exchange membranes (CEMs). The cation exchange membranes of the CSO modified with polyethyleneimine type have a higher selectivity for monovalent cations than the multivalent cations. Unfortunately, the loss of selectivity for these kinds of CSO seems to be unavoidable due to fouling and degradation of polyethyleneimine groups. In this situation, a “re-modification” technique was developed for recovery of fouled CSO, activating the fouled CSO by methanol and a sulfuric acid solution with ultrasonic vibration, followed by a layered surfacial electro-deposition method to prolong the lifetime of cation exchange membranes. A series of electrodialysis experiments for Na+/Ca2+ separation was performed for evaluating and comparing the monovalent cation selectivity of the samples. The restoration of the surface and cross section morphology after “re-modification” was demonstrated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As a result of the re-modification method the membranes with chemically degraded polyethyleneimine were again made functional. The ion exchange groups of the CSO modified with polyethyleneimine were successfully recovered, giving the membrane a high permselectivity again.

Potential applications of abandoned aromatic polyamide reverse osmosis membrane by hypochlorite degradation

Reverse osmosis (RO) membranes might experience significant changes in surface structure and performance after disinfection has been applied, or after membrane cleaning, because of hydrolysis and oxidation processes. This study reports potential applications of aromatic polyamide RO membrane exposed to a sodium hypochlorite solution for desalination of dye solutions. Changes in the chemical composition, morphology and performance of such membrane were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), contact angle measurements, scanning electron microscope (SEM), atomic force microscopy (AFM) and streaming potential measurements. After chlorination, the water flux of RO membrane doubled, and the NaCl and Na2SO4 rejection of the RO membrane decreased to 46.2% and 86.2%, respectively. However, the rejection of congo red, methyl blue and direct red 80 were 99.4%, 98.0% and 100%, respectively. This indicates that abandoned RO membranes can be recovered as “nanofiltration functional membranes” after sodium hypochlorite exposure, and be suitable for fractionation purposes.

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl−/SO42− separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl−/SO42− permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm2 30 minutes later.

Fabrication of Polyimide Membrane Incorporated with Functional Graphene Oxide for CO2 Separation: The Effects of GO Surface Modification on Membrane Performance

Two kinds of isocyanate were used to modify graphene oxide (GO) samples. Then, polyimide (PI) hybrid membranes containing GO and modified GO were prepared by in situ polymerization. The permeation of CO2 and N2 was studied using these novel membranes. The morphology experiments showed that the isocyanate groups were successfully grafted on the surface of GO by replacement of the oxygen-containing functional groups. After modification, the surface polarity of the GO increased, and more defect structures were introduced into the GO surface. This resulted in a good distribution of more modified GO samples in the PI polymer matrix. Thus, the PI hybrid membranes incorporated by modified GO samples showed a high gas permeability and ideal selectivity of membranes. In addition, enhancement of the selectivity due to the solubility of CO2 played a major role in the increase in the separation performance of the hybrid membranes for CO2, although the diffusion coefficients for CO2 also increased. Both the higher condensability and the strong affinity between CO2 molecules and GO in the polymer matrix caused an enhancement of the solubility selectivity higher than the diffusion selectivity after GO surface modification.

Preparation and characterization of an amphiphilic polyamide nanofiltration membrane with improved antifouling properties by two-step surface modification method

Membrane fouling is an urgent problem needing to be solved for practical application of nanofiltration membranes. In this study, an amphiphilic nanofiltration membrane with hydrophilic domains as well as low surface energy domains was developed, to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism. A simple and effective two-step surface modification of a polyamide NF membrane was applied. Firstly, triethanolamine (TEOA) with abundant hydrophilic functional groups was grafted to the membrane surface via reacting with the residual acyl chloride group of the nanofiltration membrane, making the nanofiltration membranes more hydrophilic; secondly, the 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), well-known as a low surface energy material, was covalently grafted on the hydroxyl functional groups through hydrogen bonding. Filtration experiments with model foulants (bovine serum albumin (BSA) protein solution, humic acid solution (HA) and sodium alginate solution (SA)) were performed to estimate the antifouling properties of the newly developed nanofiltration membranes. As a result of surface modification proposed in this study the antifouling properties of an amphiphilic modified F-PA/PSF membrane were enhanced more than 10% compared to the PA/PSF specimen in terms of flux recovery ratio.