中空纤维式渗透汽化膜内流动的CFD模拟

采用计算流体动力学(CFD)数值模拟软件研究了入口速度和管径对中空纤维式渗透汽化膜内流动特征及分离性能的影响.结果表明,膜通道内压降和壁面剪切应力与入口速度呈正相关,与管径呈反相关;分离性能随着入口速度的增大,呈现先增大后减小的趋势;管径越小,分离性能越高.     

Three‐dimensional simulation of the time‐dependent fluid flow and fouling behavior in an industrial hollow fiber membrane module

A novel three‐dimensional CFD model has been developed on the basis of fluid flow in the shell and lumen sides, and permeation and fouling behavior in the porous membrane zone. The simulated 25‐min dead‐end outside‐in filtration process showed that the energy consumed by the inlet manifold decreases during the constant pressure filtration. The velocity and pressure distributions in the module change with time. Flux distribution both in the axial and radial directions becomes increasingly more uniform, so does the cake distribution. Flux distribution and cake distribution inter‐adjust each other in different modes. A correlation equation has been developed to describe the relationship between the volumetric flow rate and accumulated water production. The correlation equation with simple experiment enables the dynamic evolution of energy consumed by shell inlet manifold to be presented, which can be the criterion of how well the shell inlet manifold or module has been designed. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2655–2669, 2018     

Enhancing CO2 absorption efficiency using a novel PTFE hollow fiber membrane contactor at elevated pressure

The internal structure design of membrane module is very important for gas removal performance using membrane contactor via physical absorption. In this study, a novel membrane contactor developed by weaving polytetrafluoroethylene (PTFE) hollow fibers was applied to remove CO₂ from 60% N₂ + 40% CO₂ mixture (with CO₂ concentration similar to that of biogas) at elevated pressure (0.8 MPa) using water as absorbent. Compared with the conventional module with randomly packed straight fibers, the module with woven PTFE fibers exhibited much better CO₂ absorption performance. The weaving configuration facilitated the meandering flow or Dean vortices and renewing speed of water around hollow fibers. Meanwhile, the undesired influences such as channeling and bypassing were also eliminated. Consequently, the mass transfer of liquid phase was greatly improved and the CO₂ removal efficiency was significantly enhanced. The effects of operation pressure, module arrangement, feed gas, and water flow rate on CO₂ removal were systematically investigated as well. The overall mass‐transfer coefficient (K_OV) varied from 1.96 × 10^?5 to 4.39 × 10^?5 m/s (the volumetric mass‐transfer coefficient K_La = 0.034–0.075 s^?1) under the experimental conditions. The CO₂ removal performance of novel woven fiber membrane contactor matched well with the simulation results. © 2017 American Institute of Chemical Engineers AIChE J, 64: 2135–2145, 2018     

Simulation of gas separation using partial element stage cut modeling of hollow fiber membrane modules

A mathematical model is developed to simulate a gas separation process using a hollow fiber membrane module. In particular, a new numerical technique is introduced based on flash calculation. Such analysis allows identifying the required membrane properties needed to reach module performance of interest. This model is validated for six different gas separation cases taken from literature. Then, the validated model is used to investigate the effect of O₂ and N₂ permeances on O₂ recovery and O₂ mole fraction in the permeate stream. A realistic two‐stage air enrichment process is also proposed for O₂ production using an industrial module with different fibers numbers. Moreover, this model is used to simulate a natural gas purification process using a single unit to determine the required membrane separation area and CH₄ loss. Finally, a two‐stage process is proposed to equally enhance CH₄ retentate mole fraction and decrease CH₄ loss. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1766–1777, 2018     

膜反应器包衣酶法水解橄榄油的研究

在聚丙烯腈中空纤维膜反应器油-水两相体系中,使用表面活性剂包衣酶催化水解橄榄油。含有橄榄油和包衣酶的油相(有机相)在中空纤维膜管束内循环流动,而在纤维膜管束外则是水相循环。实验表明橄榄油和油酸的截留率分别为91％和82％,包衣酶全部截留在管束内。在30℃、橄榄油浓度为0.62 mol/L时,包衣酶催化底物转化率为60％,是相应脂肪酶催化转化率的2倍。     

Preparation and performance evaluation of composite hollow fiber membrane for SO2 separation

Emission of sulfur dioxide (SO₂) from coal power plants has to be controlled and minimized to reduce environmental risk. This study aimed to investigate the hollow fiber composite membrane was used for the removal of SO₂ from a SO₂/CO₂/N₂ mixed gas. Moreover, for the improvement of SO₂ removal efficiency, the polyetherimide (PEI) membrane was coated with poly(vinyl chloride)‐graft‐poly(oxyethylene methacrylate) (PVC‐g‐POEM). The PVC‐g‐POEM/PEI composite hollow fiber membrane was extensively characterized by various techniques including scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. Experiments with permeation of SO₂, CO₂, N₂, and a ternary gas mixture were carried out to observe membrane behavior in response to different operating conditions. As a result, permeance of SO₂ was 105–2705 GPU and selectivity of SO₂/CO₂ was 3.9–175.6. From the mixed gas separation experiment, the maximum SO₂ removal efficiency reached up to 84.5%. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2298–2306, 2014     

Investigation of CO2 removal by immobilized carbonic anhydrase enzyme in a hollow‐fiber membrane bioreactor

Gas–liquid membrane contactors are compelling candidate bioreactors for implementing CO₂ capture because of large mass transfer rates and liquid–solid interfaces, low pressure drop, low axial dispersion and mixing, modularity, simple scale‐up or scale‐down, and operational suppleness. Binding the carbonic anhydrase (CA) enzyme on the membrane surface adds extra advantages due to the impressive large hydration turnover number and offers an attractive way for CO₂ capture. This novel approach to CO₂ removal by immobilized CA in a hollow‐fiber membrane bioreactor (HFMB) was investigated via a multiscale steady‐state model, under gas‐filled and partially liquid‐filled membrane pores conditions. The impact of CA loading, buffer acid‐base constant and concentration, membrane wetting, uncatalyzed/catalyzed CO₂ hydration in the wetted membrane zone, operating conditions, and cocurrent/countercurrent flow orientation on the HFMB performance was analyzed. The results showed that this low‐cost, green, and environmentally friendly technology could be an appealing alternative to CO₂ capture from stationary emissions sources. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2996–3007, 2017     

CO2 removal by single and mixed amines in a hollow‐fiber membrane module—investigation of contactor performance

This work investigates CO₂ removal by single and blended amines in a hollow‐fiber membrane contactor (HFMC) under gas‐filled and partially liquid‐filled membrane pores conditions via a two‐scale, nonisothermal, steady‐state model accounting for CO₂ diffusion in gas‐filled pores, CO₂ and amines diffusion/reaction within liquid‐filled pores and CO₂ and amines diffusion/reaction in liquid boundary layer. Model predictions were compared with CO₂ absorption data under various experimental conditions. The model was used to analyze the effects of liquid and gas velocity, CO₂ partial pressure, single (primary, secondary, tertiary, and sterically hindered alkanolamines) and mixed amines solution type, membrane wetting, and cocurrent/countercurrent flow orientation on the HFMC performance. An insignificant difference between the absorption in cocurrent and countercurrent flow was observed in this study. The membrane wetting decreases significantly the performance of hollow‐fiber membrane module. The nonisothermal simulations reveal that the hollow‐fiber membrane module operation can be considered as nearly isothermal. © 2014 American Institute of Chemical Engineers AIChE J, 61: 955–971, 2015     

Hybrid FSC membrane for CO2 removal from natural gas: Experimental,process simulation,and economic feasibility analysis

The novel fixed‐site‐carrier (FSC) membranes were prepared by coating carbon nanotubes reinforced polyvinylamine/polyvinyl alcohol selective layer on top of ultrafiltration polysulfone support. Small pilot‐scale modules with membrane area of 110–330 cm² were tested with high pressure permeation rig. The prepared hybrid FSC membranes show high CO₂ permeance of 0.084–0.218 m³ (STP)/(m² h bar) with CO₂/CH₄ selectivity of 17.9–34.7 at different feed pressures up to 40 bar for a 10% CO₂ feed gas. Operating parameters of feed pressure, flow rate, and CO₂ concentration were found to significantly influence membrane performance. HYSYS simulation integrated with ChemBrane and cost estimation was conducted to evaluate techno‐economic feasibility of a membrane process for natural gas (NG) sweetening. Simulation results indicated that the developed FSC membranes could be a promising candidate for CO₂ removal from low CO₂ concentration (10%) NGs with a low NG sweetening cost of 5.73E?3 $/Nm³ sweet NG produced. © 2014 American Institute of Chemical Engineers AIChE J 60: 4174–4184, 2014     

Effect of hypochlorite treatment on performance of hollow fiber membrane prepared from polyethersulfone/N‐methyl‐2‐pyrrolidone/tetronic 1307 solution

Polyethersulfone (PES) hollow fiber membrane was prepared by blending with nonionic surfactant Tetronic 1307 to improve its hydrophilicity. The membranes were posttreated by hypochlorite solution of 10, 100, 500, and 2000 ppm. The effect of hypochlorite treatment on the performance of PES membrane was investigated. Experimental results showed that the water permeability of treated membrane was two to three times higher than that of untreated membrane in case of blend membrane prepared from PES/N‐methyl‐2‐pyrrolidone (NMP)/Tetronic 1307 solution. On the other hand, hypochlorite treatment has no effect on water permeability of the membrane prepared from PES/NMP solution. Elemental analysis and ATR–FTIR measurement results indicated that hypochlorite treatment led to decomposition and leaching out of Tetronic 1307 component from the membrane. The change of membrane surface structure by the hypochlorite treatment was confirmed by atomic force microscopy measurement. The hypochlorite treatment brought about no significant impact on the mechanical property of the membranes. This indicated that the hypochlorite treatment of PES membrane prepared with surfactant was a useful way to improve the water permeability without the decrease of membrane strength. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

La0.6Sr0.4Co0.8Ga0.2O3‐δ (LSCG) hollow fiber membrane reactor: Partial oxidation of methane at medium temperature

In this study, La_0.6Sr_0.4Co_0.8Ga_0.2O_3‐δ (LSCG) hollow fiber membrane reactor was integrated with Ni/LaAlO₃‐Al₂O₃ catalyst for the catalytic partial oxidation of methane (POM) reaction. The process was successfully carried out in the medium temperature range (600–800°C) for reaction of blank POM with bare membrane, catalytic POM reaction and swept with H₂:CO gas mixture. For the catalytic POM reaction, enhancement in selectivity to H₂ and CO is obtained between 650–750°C when O₂:CH₄ <1. High CH₄ conversion of 97% is achieved at 750°C with corresponding H₂ and CO selectivity of about 74 and 91%. The oxygen flux of the membranes also increased with the increase in oxygen partial pressure gradient across the membrane. The postreacted membranes were tested via XRD and FESEM‐EDX for their crystallinity and surface morphology. XPS analysis was further used to investigate the O1s, Co 2p and Sr 3d binding energies of the segregated elements from the reducing reaction environment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3874–3885, 2013     

Partial oxidation of methane in hollow‐fiber membrane reactors based on alkaline‐earth metal‐free CO2‐tolerant oxide

The U‐shaped alkaline‐earth metal‐free CO₂‐stable oxide hollow‐fiber membranes based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) are prepared by a phase‐inversion spinning process and applied successfully in the partial oxidation of methane (POM) to syngas. The effects of temperature, CH₄ concentration and flow rate of the feed air on CH₄ conversion, CO selectivity, H₂/CO ratio, and oxygen permeation flux through the PLNCG hollow‐fiber membrane are investigated in detail. The oxygen permeation flux arrives at approximately 10.5 mL/min cm² and the CO selectivity is higher than 99.5% with a CH₄ conversion of 97.0% and a H₂/CO ratio of 1.8 during 140 h steady operation. The spent hollow‐fiber membrane still maintains a dense microstructure and the Ruddlesden‐Popper K₂NiF₄‐type structure, which indicates that the U‐shaped alkaline‐earth metal‐free CO₂‐tolerant PLNCG hollow‐fiber membrane reactor can be steadily operated for POM to syngas with good performance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3587–3595, 2014