Xueli Gao

O-(carboxymethyl)-chitosan nanofiltration membrane surface functionalized with graphene oxide nanosheets for enhanced desalting properties.

A novel O-(carboxymethyl)-chitosan (OCMC) nanofiltration (NF) membrane is developed via surface functionalization with graphene oxide (GO) nanosheets to enhance desalting properties. Using ring-opening polymerization between epoxy groups of GO nanosheets and amino groups of OCMC active layer, GO nanosheets are irreversibly bound to the membrane. The OCMC NF membranes surface-functionalized with GO nanosheets are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle analyzer, and zeta potential analyzer. The membranes exhibit not only higher permeability but also better salt rejections than the pristine membranes and the commercial NF membranes; besides, the desalting properties are enhanced with the concentration of GO nanosheets increasing. Furthermore, the transport mechanism of GO-OCMC NF membranes reveals that the nanoporous structure of GO-OCMC functional layer and size exclusion and electrostatic repulsion of water nanochannels formed by GO nanosheets lead to the membranes possessing enhanced desalting properties.

Highly and Stably Water Permeable Thin Film Nanocomposite Membranes Doped with MIL-101 (Cr) Nanoparticles for Reverse Osmosis Application

A hydrophilic, hydrostable porous metal organic framework (MOF) material-MIL-101 (Cr) was successfully doped into the dense selective polyamide (PA) layer on the polysulfone (PS) ultrafiltration (UF) support to prepare a new thin film nanocomposite (TFN) membrane for water desalination. The TFN-MIL-101 (Cr) membranes were characterized by SEM, AFM, XPS, wettability measurement and reverse osmosis (RO) test. The porous structures of MIL-101 (Cr) can establish direct water channels in the dense selective PA layer for water molecules to transport through quickly, leading to the increasing water permeance of membranes. With good compatibility between MIL-101 (Cr) nanoparticles and the PA layer, the lab made TFN-MIL-101 (Cr) membranes integrated tightly and showed a high NaCl salt rejection. MIL-101 (Cr) nanoparticles increased water permeance to 2.2 L/m2·h·bar at 0.05 w/v % concentration, 44% higher than the undoped PA membranes; meanwhile, the NaCl rejection remained higher than 99%. This study experimentally verified the potential use of MIL-101 (Cr) in advanced TFN RO membranes, which can be used in the diversified water purification field.

Study on seawater nanofiltration softening technology for offshore oilfield polymer solution preparation

Abstract Nanofiltration (NF) is suitable for softening seawater and providing permeates with excellent quality for oilfield water injection. However, the industrial application of aqueous polymer solution prepared by NF softened seawater for oilfield polymer flooding has not been reported yet. In this work, a pilot-scale ultrafiltration (UF)–NF integrated membrane system (IMS) has been investigated as a method of removing divalent ions from seawater and providing softened water for oilfield polymer flooding. The performance of the selected NF 4040 spiral membrane module was investigated under different operating conditions. In addition, the performance of the NF membrane module at high system recovery was also investigated to simulate the practical situation. Finally, NF permeation waters were used to prepare HPAM polymer solutions to evaluate the possibility of preparing polymer solution with NF permeation water for polymer flooding in offshore oilfield. The results showed that, with the properly selecte...

Investigation of synchronous arsenic and salinity rejection via nanofiltration system and membrane cleaning

AbstractThe coexistence of arsenic (As) and other salts in high concentrations in groundwater in northwest China restricts its use as a drinking water supply source. The behavior of negatively charged membrane of nanofiltration (NF) at pilot-scale was investigated over the simultaneous removal of As and salinity from a synthetic solution. The parameters that affected the rejection of As(V) and salinity were studied; that include pH and temperature of the feed, applied pressure, natural organic matter (NOM), and the presence of different salts in the feed. Meanwhile, membrane fouling and cleaning while using this application were also investigated. The study shows the removal efficiency of the membranes increased in the sequence of NF-6u2009<u2009NF-2Au2009<u2009NF-3A. Among those parameters, the pH of the feed greatly affected As(V) rejection; temperature and applied pressure influenced it slightly; and the existence of NOM was of great benefit to As and salinity removal. Meanwhile, with the concentration of background s...

Developing homogeneous ion exchange membranes derived from sulfonated polyethersulfone/N-phthaloyl-chitosan for improved hydrophilic and controllable porosity

Ion exchange membranes (IEMs) composed of sulfonated poly (ether sulfone) (SPES) and N-phthaloyl chitosan (NPHCs) were synthesized. NPHCs was employed in membrane fabrication to improve the porosity and hydrophilicity of membranes. The effect of blend ratio of sulfonation (DS) and NPHCs content on physico-chemical characteristics of home-made membranes was investigated. The morphology of prepared membranes was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and scanning electron microscopy (SEM). SEM images revealed the formation of a more porous membrane structure and smoother surface. The electrochemical and physical properties of CEMs were characterized comprising water content, contact angle, ion exchange capacity (IEC) and thermal stability. Membrane water content, surface hydrophilicity and IEC were enhanced with increase of DS and NPHCs blend ratios in casting solution. Furthermore, the diffusion coefficient was also improved slightly with increase of DS and NPHCs blend ratios in prepared membranes. Membrane potential, permselectivity, transport number and areal membrane resistance all showed decreasing trends by the increase in NPHCs blend ratio in casting solution. These results indicated that the prepared membrane has good prospective and great potential for desalination in electrodialysis applications.

Separation and purification of L-phenylalanine from the fermentation broth by electrodialysis

AbstractElectrodialysis (ED) is an electrochemical separation process during which ion exchange membranes use an electric potential as the driving force to separate and purify ionic species. In the experiment, the limiting current is firstly determined to avoid the polarization phenomenon. Then, the effects of the feed pH, feed concentration, and the glucose concentration on the performance of separation and purification are studied to determine the optimal operating conditions in terms of L-phenylalanine recovery and salt removal. The optimal operating conditions in this study are the limiting current of 0.75 A, feed pH of 5.91, feed concentration of 10xa0g/L, and the glucose concentration of 5xa0g/L, respectively. Under the optimal operating conditions, the L-phenylalanine recovery and salt removal can reach up to 84.3 and 98.5%, respectively.

CaCO3 scaling of oilfield produced water in “electrochemical pre-oxidation–coagulation sedimentation–filtration” process: reason, mechanism, and countermeasure

AbstractChemical stability of oilfield injection water is a critical factor to avoid corrosion and scaling of water treatment devices and pipelines. Especially, Guangli oilfield (a branch of Shengli Oilfield) has achieved remarkable success in anti-corrosion by applying an electrochemical pre-oxidation process into strong corrosive wastewater treatment, while scaling was aggravated therefore. XRD, SEM, EDS, and chemical analysis demonstrated the major component of the scale deposit was calcite. Succeedingly, chemical analysis of produced water along the process showed that pH, concentration of calcium ions, bicarbonate ions, and suspended solids changed remarkably before and after the mixing reactor. Further studies revealed that the addition of water treatment chemicals (Na2CO3) in the mixing reactors induced the precipitates of CaCO3, which could serve as crystal seeds and resulted in the continuous precipitation of calcium ions. Moreover, calcite saturation ratio increased from 0.97 to 3.94 could contr...