Xuehua Ruan

Bis-ammonium immobilized polystyrenes with co-catalyzing functional end groups as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate from CO2 and epoxides

A series of novel bis-ammonium ionic liquid immobilized polystyrene (BisAm-i-PS) heterogeneous catalysts with co-catalyzing functional end groups of –CH2COOH, –CH2CH2OH, and –CH2CH2NH2 were synthesized for the cycloaddition reaction of CO2 and epoxides without any additional co-catalyst and organic solvent. All the ammonium immobilized catalysts showed high selectivity. Bis-ammonium immobilized catalysts were more efficient than single-ammonium ones. The yield was further increased by introducing the functional end groups. Both –CH2COOH and –CH2CH2OH terminated BisAm-i-PS catalysts achieved high activities (yield: >99%), while the –NH2 terminated one had a slightly lower activity (yield: 97.3%) under the same reaction conditions. The effects of different parameters, such as the halide anions of the catalysts, reaction temperature, initial pressure and reaction time were also investigated with –CH2CH2OH terminated BisAm-i-PS (BisAm-OH-i-PS) as the catalyst. Under optimal reaction conditions (1.2 MPa, 130 °C and 2.5 h), BisAm-OH-i-PSs with 2Br− and 2I− showed very high efficiencies. For each of them, propylene carbonate selectivity and yield were more than 99% and 99%, respectively. In addition, the catalyst possessed good stability, and both catalytic activity and selectivity were always more than 99% for 5 times of recycle tests.

Pressure swing adsorption/membrane hybrid processes for hydrogen purification with a high recovery

Hydrogen was recovered and purified from coal gasification-produced syngas using two kinds of hybrid processes: a pressure swing adsorption (PSA)-membrane system (a PSA unit followed by a membrane separation unit) and a membrane-PSA system (a membrane separation unit followed by a PSA unit). The PSA operational parameters were adjusted to control the product purity and the membrane operational parameters were adjusted to control the hydrogen recovery so that both a pure hydrogen product (>99.9%) and a high recovery (>90%) were obtained simultaneously. The hybrid hydrogen purification processes were simulated using HYSYS and the processes were evaluated in terms of hydrogen product purity and hydrogen recovery. For comparison, a PSA process and a membrane separation process were also used individually for hydrogen purification. Neither process alone produced high purity hydrogen with a high recovery. The PSA-membrane hybrid process produced hydrogen that was 99.98% pure with a recovery of 91.71%, whereas the membrane-PSA hybrid process produced hydrogen that was 99.99% pure with a recovery of 91.71%. The PSA-membrane hybrid process achieved higher total H2 recoveries than the membrane-PSA hybrid process under the same H2 recovery of membrane separation unit. Meanwhile, the membrane-PSA hybrid process achieved a higher total H2 recovery (97.06%) than PSA-membrane hybrid process (94.35%) at the same H2 concentration of PSA feed gas (62.57%).

Effect of Hydrogen-Bonding Interaction on the Arrangement and Dynamics of Water Confined in a Polyamide Membrane: A Molecular Dynamics Simulation

An increasing demand for freshwater inspires further understanding of the mechanism of water diffusion in reverse-osmosis membranes for the development of high-performance membranes for desalination. Water diffusion has a close relationship with the structural and dynamical characteristics of hydrogen bonds, which is not well-understood for the confining environment inside the polyamide membrane at the molecular level. In this work, an atomistic model of a highly cross-linked polyamide membrane was built with an equilibrated mixture of m-phenylenediamine and trimesoyl chloride monomers. The structure and dynamics of water in the regions from the bulk phase to the membrane interior were investigated by molecular dynamics simulations. Explicit hydrogen bond criteria were determined for hydrogen-bonding analysis. The local distribution and orientation of water reveal that the hydrogen-bonding affinity of the hydrophilic functional groups of polymers inhibits water diffusion inside the membrane. The affinity helps to produce percolated water channels across the membrane. The hydrogen-bonding structures of water in different regions indicate dehydration is required for the entry of water into the polyamide membrane, which dominates water flux across the membrane. This paper not only deepens the understanding of the structure and dynamics of water confined in the polyamide membrane but also stimulates the future work on high-performance reverse-osmosis membranes.

Integration of molecular dynamic simulation and free volume theory for modeling membrane VOC/gas separation

Gas membrane separation process is highly unpredictable due to interacting non-ideal factors, such as composition/pressure-dependent permeabilities and real gas behavior. Although molecular dynamic (MD) simulation can mimic those complex effects, it cannot precisely predict bulk properties due to scale limitations of calculation algorithm. This work proposes a method for modeling a membrane separation process for volatile organic compounds by combining the MD simulation with the free volume theory. This method can avoid the scale-up problems of the MD method and accurately simulate the performance of membranes. Small scale MD simulation and pure gas permeation data are employed to correlate pressure-irrelevant parameters for the free volume theory; by this approach, the microscopic effects can be directly linked to bulk properties (non-ideal permeability), instead of being fitted by a statistical approach. A lab-scale hollow fiber membrane module was prepared for the model validation and evaluation. The comparison of model predictions with experimental results shows that the deviations of product purity are reduced from 10% to less than 1%, and the deviations of the permeate and residue flow rates are significantly reduced from 40% to 4%, indicating the reliability of the model. The proposed method provides an efficient tool for process engineering to simulate the membrane recovery process.

Tailored Robust Hydrogel Composite Membranes for Continuous Protein Crystallization with Ultrahigh Morphology Selectivity

The tailored and robust hydrogel composite membranes (HCMs) with diverse ion adsorption and interfacial nucleation property are prepared and successfully used in the continuous lysozyme crystallization. Beyond the heterogeneous supporter, the HCMs functioning as an interface ion concentration controller and nucleation generator are demonstrated. By constructing accurately controlled nucleation and growth circumstances in the HCM-equipped membrane crystallizer, the target desired morphology (hexagon cube) and brand-new morphology (multiple flower shape) that differ from the ones created in the conventional crystallizer are continuously and repetitively generated with ultrahigh morphology selectivity. These tailored robust HCMs show great potential for improving current approaches to continuous protein crystallization with specific crystal targets from laboratorial research to actual engineering applications.

Parameters optimisation of isopropanol purification by hybrid distillation-vapour permeation process using response surface methodology

A hybrid distillation-vapour permeation (D-VP) system was selected to get Isopropanol (IPA) with high purity. In this study, a technical and economic analysis was performed comparing the hybrid D-VP systems with polymeric (PVA/PVDF) and ceramic (NaA type zeolite) membranes. Response surface methodology (RSM) was used to optimise the hybrid process parameters. First of all, the simulation of hybrid D-VP process for IPA purification was conducted with UniSim Design. Then Plackett-Burman design was employed to screen the significant parameters affecting total annual cost (TAC) from 11 variables. After that, steepest ascent method was undertaken to determine the optimal regions of the selected significant parameters. Finally, Box-Behnken design was adopted to further analyse the mutual interactions between these parameters and to identify their optimal values that would generate a minimum TAC. Optimal parameters were the vapour flow-rate to VP of 580 kg/h, VP operating temperature of 140 °C, permeate pressure of 1.5 kPa. And the TAC of optimal HDCM system is 49.06 €/t, about 19.80 % less than that of pri-optimised system.