PVDF中空纤维膜接触器分离烟气CO2

以水（H2O）、氢氧化钠（NaOH）、氨基乙酸钾（GLY）、氨基乙酸钾-哌嗪（GLY-PZ）水溶液为吸收剂,研究了疏水性聚偏氟乙烯（PVDF）中空纤维膜接触器分离CO2/N2模拟烟气中CO2的技术,具体考察了流动方式、气液流率、吸收液浓度和温度、原料气CO2浓度、填充密度等对膜接触器吸收效率的影响。结果表明,气液逆流的腔流程模式具有较高的分离效率。不同吸收剂的分离性能为：NaOH > GLY-PZ > GLY > H2O。温度对各种吸收剂的影响随其种类不同而有所差异。膜接触器对烟气CO2的分离效率随填充密度、吸收液浓度和流率的提高而增大,随气体流率及其中CO2浓度的增大而减小。     

Removal of Benzene/Toluene from Water by Vacuum Membrane Distillation in a PVDF Hollow Fiber Membrane Module

Abstract

Asymmetric polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by a phase inversion method using dimethylacetamide (DMAc) and a mixture of water/LiCl as solvent and a nonsolvent additive, respectively. The prepared membranes were characterized by scanning electron microscopy (SEM) for observing its microstructures and by a gas permeation method for measuring its surface porosity, pore size, and pore size distribution. Wetting pressures of the dry hollow fiber membranes were also measured. Using the prepared PVDF hollow fiber membranes, a membrane module was fabricated for removal of benzene/toluene from water. Effects of various operating parameters such as downstream vacuum levels, feed temperatures, and feed flow rates on performances of the module were investigated experimentally. The benzene/toluene removal was achieved over 99% under an optimal operating condition. Mass transfer of benzene or toluene removal is controlled not only by the liquid phase resistance but also by the membrane and gas phase resistances. Benzene and toluene can be removed from water simultaneously with no adverse coupling effects.     

Designing Asymmetric PVDF Hollow Fibres for Soluble Gas Removal

Tailor‐made polyvinylidene fluoride (PVDF) asymmetric hollow fibre membranes are employed for the removal of soluble gases, such as H₂S or SO₂, from waste gas streams. This study focuses on techniques of fabricating and characterizing the PVDF asymmetric hollow fibre membrane used as a stable interface for absorption of H₂S or SO₂ using an alkaline solution. The effects of operating conditions and the morphological structures of the membranes on the membrane's coefficient, k̄_AM are examined. Capabilities of the hollow fibre membranes developed for the removal of H₂S and SO₂ from waste gas streams are evaluated.     

Experimental study of CO2 absorption/stripping via PVDF hollow fiber membrane contactor

Gas–liquid hollow fiber membrane contactor can be a promising alternative for the CO₂ absorption/stripping due to the advantages over traditional contacting devices. In this study, the structurally developed hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared via a wet spinning method. The membranes were characterized in terms of morphology, permeability, wetting resistance, overall porosity and mass transfer resistance. From the morphology analysis, the membranes demonstrated a thin outer finger-like layer with ultra thin skin and a thick inner sponge-like layer without skin. The characterization results indicated that the membranes possess a mean pore size of 9.6 nm with high permeability and wetting resistance and low mass transfer resistance (1.2 × 10⁴ s/m). Physical CO₂ absorption/stripping were conducted through the fabricated gas–liquid membrane contactor modules, where distilled water was used as the liquid absorbent. The liquid phase resistance was dominant due to significant change in the absorption/stripping flux with the liquid velocity. The CO₂ absorption flux was approximately 10 times higher than the CO₂ stripping flux at the same operating condition due to high solubility of CO₂ in water as confirmed with the effect of liquid phase pressure and temperature on the absorption/stripping flux.     

Theoretical and Experimental Studies on Acetylene Absorption in a Polytetrafluoroethylene Hollow‐Fiber Membrane Contactor

The separation of acetylene from a gas mixture was investigated using a polytetrafluoroethylene hollow‐fiber membrane contactor and 1‐methyl‐2‐pyrrolidinone as absorbent. The effects of the gas velocity, the liquid velocity, the feed gas concentration, and the module length on the acetylene mass transfer were investigated. The results showed that the acetylene mass transfer flux increased with increasing liquid velocity, gas velocity, and feed gas concentration, but decreased with increasing membrane module length. A mathematical model was used to predict the wetting extent of the membrane and the mass transfer resistance in the acetylene mass transfer process. The wetting extent of the membrane was found to increase with increasing liquid velocity and to be effectively restrained with increasing gas velocity. The liquid phase resistance and the wetted‐membrane phase resistance controlled the acetylene mass transfer in the acetylene absorption process. The acetylene absorption efficiency was maintained at 90 % for 114 h of the C₂H₂ membrane absorption–thermal desorption cycle process.     

Removal of Gas Pollutants of a Thermal Oxidizer with a Dynamic Scrubber

The absorption of gas pollutants including CO₂, CO, NO, NO₂, SO₂, and H₂S from the exhaust of a paint recuperative oxidizer into NaOH solution has been studied using an industrial scale dynamic scrubber. Experimental results show the influence of the absorbent concentration on the pollutant removal efficiency. The best removal efficiencies of CO₂, CO, NO, NO₂, SO₂, and H₂S were 79, 80, 80, 100, 75 and 88 %, respectively, with 2 % NaOH as the absorbent. A comparison of these results with previous studies shows that the liquid‐to‐gas flow rate ratio (F_L/F_G) in this dynamic scrubber is much smaller than for traditional NaOH scrubbers and spray dryers.     

Simultaneous removal of gaseous pollutants with a novel swirl wet scrubber

In recent years, researchers have put a considerable effort to decrease the emission of harmful gaseous pollutants to the atmosphere. Although conventional wet scrubbers are being widely used to remove harmful gases, they have low removal efficiencies. This study reports the effect of some operating conditions on simultaneous removal of NO, NO₂, SO₂, and CO₂, using a novel swirl wet scrubber system. The gaseous pollutants were absorbed into NaOH solution. As the absorbent media was circulated continuously for removal purpose, therefore the production of chemical wastes were minimized. The effect of absorbent concentration, gas flow rate, and liquid flow rate were investigated. The best efficiencies of NO, NO₂, SO₂, and CO₂ simultaneous removal were 77, 88, 100 and 80%, respectively, with 2%, w/v NaOH as the scrubber medium. A comparison between this study and literature data shows that the liquid-gas flow rate ratio (F_L/F_G) in the novel scrubber of this work is much smaller than other gaseous pollutant removal systems. Therefore higher removal efficiency is obtained based on the same liquid flow rates.     

Preparation,characterization, and performance evaluation of coated PES polymer materials fabricated via dry/wet phase inversion technique

Sulfur dioxide (SO₂) is the major air pollutant which is emitted from the power plant. In this study, hollow fiber membrane (HFM) separation process is applied for the improvement of SO₂ removal efficiency in the post‐combustion gas. HFM was produced by dry/wet phase inversion method and then coated with Polydimethylsiloxane (PDMS). The membrane morphology and characterization were examined with help of scanning electron microscope (SEM), energy dispersion of X‐ray spectroscopy (EDX), Fourier transform infrared (FT‐IR) and atomic force microscopy (AFM). Polyethersulfone (PES) hollow fiber membranes were tested for the SO₂/N₂ binary mixed gas separation. Single gas permeance of SO₂, N₂, and binary mixture gas (200 ppm of SO₂) separation experiment was initiated to observe membrane behavior according to temperature and pressure difference and retentate flow rate. As a result, permeance of SO₂ was 24.9–47.4 GPU and selectivity of SO₂/N₂ was 1.6–4.2. From the mixture gas separation experiment, SO₂ removal efficiency increased according to stage cut and operating pressure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39711.     

Removal of CO2 and/or SO2 from gas streams by a membrane absorption method

Studies were made on the membrane absorption of CO₂ and/or SO₂ using hydrophobic microporous hollow-fibre (HF) membrane modules. The absorbent liquids used were aqueous solutions of NaOH, K₂CO₃, alkanolamines and Na₂SO₃, flowing on the lumen side of the HF in laminar flow. A semi-empirical correlation was derived for the gas-phase mass-transfer coefficient on the shell side, by including geometrical factors of the HFs and the shell tube in the general correlation for mass transfer. It was found that the CO₂ absorption rate in various aqueous solutions of alkalis and alkanolamines is successfully described by a model based on gas diffusion through the membrane pores subsequent to gas absorption accompanied by chemical reaction. The simultaneous membrane absorption of SO₂ and CO₂ was also studied using aqueous Na₂SO₃ solution, the selective removal of SO₂ to CO₂ being successfully achieved when both the liquid flow rate and solute concentration are low. This suggests that this membrane absorption method provides an energy saving process for SO₂ removal from flue gases.     

Absorption of carbon dioxide by the absorbent composed of piperazine and 2-amino-2-methyl-1-propanol in PVDF membrane contactor

This paper tests the performance of microporous polyvinylidinefluoride (PVDF) hollow fiber in a gas absorption membrane process (GAM) using the aqueous solutions of piperazine (PZ) and 2-amino-2-methyl-1-propanol (AMP). Experiments were conducted at various gas flow rates, liquid flow rates and absorbent concentrations. Experimental results showed that wetting ratio was about 0.036% when used with the aqueous alkanolamine solutions, while that was 0.39% with aqueous piperazine solutions. The CO₂ absorption rates increased with increasing both liquid and gas flow rates at N_Re < 20. The increase of the PZ concentration showed an increase of absorption rate of CO₂. The CO₂ absorption rate was much enhanced by the addition of PZ promoter. The resistance of membrane was predominated as using a low reactivity absorbent and can be neglected as using absorbent of AMP aqueous solution. The resistance of gas-film diffusion was dominated as using the mixed absorbents of AMP and PZ. An increase of PZ concentration, the resistance of liquid-film diffusion decreased but resistance of gas-film increased. Overall, GAM systems were shown to be an effective technology for absorbing CO₂ from simulated flue gas streams, but the viscosity and solvent-membrane relationship were critical factors that can significantly affect system performance.     

中空纤维膜接触器中N,N-二甲基乙醇胺吸收CO2的特性

N,N-二甲基乙醇胺（DMEA）是一种很有前途的吸收剂,具有较快的反应速率和较高的CO₂捕集能力。在本研究中,DMEA作为一种新型吸收剂被应用于中空纤维膜接触器,用于从CO₂/CH₄气体混合物中分离CO₂。通过建立二维稳态数学模型,模拟了MEA、DEA、MDEA和DMEA四种吸收剂在不同操作条件下对CO₂吸收性能的影响。结果表明,脱碳性能大小为MEA>DMEA>DEA>MDEA;气相参数对脱碳率的影响比液相参数更显著;提高气体流速和CO₂浓度,脱碳率均会下降;提高液速和吸收剂浓度,脱碳率均增大,适当提高吸收剂流速和吸收剂浓度可以提高CO₂去除效率。此外,CO₂吸收通量将随着气体速度的增加而增加,随着液相中CO₂负荷的增加而减少。最后,通过两种影响因素共同作用确定了膜接触器分离酸性气体的最佳操作条件。因此,膜吸收法在天然气脱碳方面有良好的潜力。     

Mass Transfer and Liquid‐Film Formation in a Spray Tower for SO2 Removal in Sodium Hydroxide Solution

Spray towers allow for controlling air pollution in which a liquid is sprayed in small droplets to produce a large interfacial area for mass transfer between a gas and a liquid phase. An experimental study of a spray tower for removing SO₂ is described. The experiments were carried out under different operating conditions by varying the gas velocity, liquid flow rate, and SO₂ concentration. SO₂ removal efficiency, volumetric mass transfer coefficient, and liquid‐film formation as a result of the collision of droplets against the tower wall are investigated. Removal efficiency and volumetric mass transfer coefficient are analyzed as a function of gas velocity, liquid flow rate, and SO₂ concentration, while liquid‐film formation is evaluated as a function of tower height. The results indicate high removal efficiency. Correlations to predict the volumetric mass transfer coefficient are also proposed.     

Investigations on the ability of di‐isopropanol amine solution for removal of CO2 from natural gas in porous polymeric membranes

In this study, capture of CO₂ and H₂S from natural gas mixture using porous polymeric membranes has been investigated numerically to assess the capacity of a novel absorbent, di‐isopropanol amine (DIPA), in CO₂ removal. Diffusion of acid gases through porous polymeric membranes was simulated by employing CFD techniques and considering a gas feed stream, a porous membrane and a reaction medium. For solving conservation equations, finite element method was applied to calculate the rate of CO₂ and H₂S absorption in the membrane. The type of membrane in this work is a hollow‐fiber module. According to the modeling results, a high H₂S removal can be achieved by DIPA absorber. Moreover, CO₂ was captured from natural gas in an efficient manner in low gas/liquid flow rates. POLYM. ENG. SCI., 55:598–603, 2015. © 2014 Society of Plastics Engineers     

Determination of mass transfer resistance during absorption of carbon dioxide by mixed absorbents in PVDF and PP membrane contactor

In this study, the absorption of carbon dioxide by the absorbent which was composed of 2-amino-2-methyl-l-propanol (AMP) + piperazine (PZ) or methyldiethanolamine (MDEA) + piperazine (PZ) in polyvinylidinefluoride (PVDF) and polypropylene (PP) membrane contactors werewas examined. Three resistances were considered in each hollow fiber, i.e., liquid-film diffusion, membrane diffusion, and gas-film diffusion. The mass transfer resistance of membrane k_m was influenced by the wetting ratio using an absorbent with higher reaction rate. The wetting ratio was affected by contact angle between the membrane and absorbent and the viscosity of absorbent. The calculated absorption rates considering wetting ratio of membrane and using the modified correlation equation of gas-phase mass transfer coefficient were reasonably agreeable to those of measured ones (standard deviation, 4%). The fractional resistance of each transport step during the experiments was then determined. The rate-controlling step was dominated by the resistance of gas-film diffusion with mixed absorbents. The absorption rates of CO₂ increase with the increasing of gas flow rates in the most experimental cases. The resistance of liquid-film diffusion was only important using an absorbent with lower reaction rate. The rate-controlling step was the membrane diffusion only at higher gas flow rate with the absorbent composed of AMP and PZ in PVDF hollow fiber membrane contactor.     

Carbon dioxide absorption in a cross-flow rotating packed bed

This work investigates the feasibility of applying the cross-flow rotating packed bed (RPB) to the removal of carbon dioxide (CO₂) by absorption from gaseous streams. Monoethanolamine (MEA) aqueous solution was used as the model absorbent. Also, other absorbents such as the NaOH and 2-amino-2-methyl-1-propanol (AMP) aqueous solutions were compared with the MEA aqueous solution. The CO₂ removal efficiency was observed as functions of rotor speed, gas flow rate, liquid flow rate, MEA concentration, and CO₂ concentration. Experimental results indicated that the rotor speed positively affects the CO₂ removal efficiency. Our results further demonstrated that the CO₂ removal efficiency increased with the liquid flow rate and the MEA concentration; however, decreased with the gas flow rate and the CO₂ concentration. Additionally, the CO₂ removal efficiency for the MEA aqueous solution was superior to that for the NaOH and AMP aqueous solutions. Based on the performance comparison with the conventional packed bed and the countercurrent-flow RPB, the cross-flow RPB is an effective absorber for CO₂ absorption process.     

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     

Gas absorption of carbon dioxide in a hollow fiber contained liquid membrane absorber

Experiments on the absorption of CO₂ into a hollow fiber contained liquid membrane absorber were performed. The feed gas was a mixture of CO₂ and N₂, absorbent liquid was 2-amino-2-methyl-l-propanol and the hollow fiber was a microporous hydrophobic polytetrafluoroethylene membrane. Outlet concentration of CO₂ from the absorber decreased as absorbent concentration increased, gas flow rate increased and were held constant for speed of agitation, but had a maximum value in the range of inlet concentration of CO₂ from 5 to 40 mole%. The reaction rate constant obtained for CO₂-amine system was 231 I/mol · s at 25 °C using a flat stirred vessel, and the membrane-side-mass-transfer coefficient was 1.217 × 10⁻⁵ mol/cm² · s · atm in CO2/N2-amine system. A diffusion model based on mass transfer with fast-reaction was proposed to predict the performance of the absorber.     

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     

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     

陶瓷膜接触器化学吸收氮氧化物的传质过程与阻力分析

针对选择性催化还原技术(SCR)存在装置大、运行费用高、催化剂中毒失活等问题,将平均孔径为100 nm的Al₂O₃陶瓷膜进行疏水改性并组装成膜接触器,以NaClO₂水溶液为吸收液,开展陶瓷膜接触器在烟气脱硝领域的应用研究。考察了陶瓷膜接触器在化学吸收脱硝中的稳定性,以及气体流量、吸收液浓度、吸收液流量、吸收液pH等因素对NO脱除率和传质通量的影响,基于阻力串联模型,建立总传质系数方程。研究表明,陶瓷膜接触器在连续600 min运行过程中,NO的脱除效率及传质通量分别稳定在99%和0.038 mol·m^-2·h^-1左右。进气流量的增加会促进NO的吸收,吸收液pH=3时具有最高的氧化吸收性能,同时提高吸收液的浓度会增强NO的脱除效果。NO的传质过程同时受气、液、膜三相阻力控制,传质阻力分析结果表明,可以通过增加气体流速减小气相阻力,增加吸收液浓度同时降低pH减小液相阻力。本研究在烟气脱硝领域具有良好的应用前景。