聚酰亚胺中空纤维膜分离二氧化碳实验研究

采用实验室自制小型聚酰亚胺中空纤维膜组件,在实验室建立膜分离天然气脱CO_2实验装置,系统考察高压侧放空气流量、压力、温度、长期运行稳定性等参数对膜组件性能的影响并进行实际工况模拟分析。试验分析表明,随着尾气放空量的增加,混合气渗透速率不断变大,而无论在渗透气还是尾气中,CO_2的体积分数都随着尾气放空量的增加而增加,且CO_2的脱除率不断下降;具体到不同压力之间的比较,可以看到更高的压力可以有更大的处理量;随着混合气温度的升高,渗透速率都明显上升,符合阿累尼乌斯公式;在长期测试过程中,聚酰亚胺膜组件的混合气渗透速率略有下降,整体而言渗透速率维持比较平稳,且CO_2对N2的分离系数也表现得较为稳定。     

多孔石墨烯气体分离膜分子渗透机理

通过分子动力学方法模拟了4种不同气体分子(He,H2,N2和CH4)在多孔石墨烯气体分离膜中的穿透过程,揭示了气体分子穿透石墨烯纳米孔的渗透机理,指出分子的渗透不仅与其动力学参数有关,如分子直径和质量,还与分子在石墨烯表面的吸附有关。石墨烯表面的吸附层给气体分子的渗透提供了一个额外的路径,因此分子在石墨烯表面的吸附越强,分子的渗透通量越大。同时,不同大小的纳米孔下H2分子的渗透通量都随着压力的增加而线性增加。     

两级喷射式环流反应器流体力学与传质特性研究

为改善气体分布,提高传质性能,文中开发出一种两级喷射式环流反应器,研究了液体喷射速度、空塔气速和下级进气比对该反应器流体力学和传质特性的影响。分别采用压差法、电导电极法和动态溶氧法对反应器气含率、环流液速和体积传质系数进行了测量。实验结果表明:液体喷射速度和空塔气速的增加,环流反应器可以得到理想的流体力学和传质特性;分段进气比的变化显著影响了反应器体积传质系数,且存在最佳进气比;最佳进气比随着液体喷射速度的增加而增大,而基本不受空塔气速的影响;与单级喷射环流反应器相比,采用最佳进气比的两级喷射式环流反应器的传质效率有了显著的提升。     

氨氢氮在含氟聚合物膜上的渗透

以国产含氟树脂制得的选择性透氨膜,当ΔP=0.6～0.8MPa、室温,渗透系数P_(NH3)=700～1000cm~3·cm~2/cm~2pa·s,P_(NH3)/P_(H2)和P_(NH3)/P_(N2)分别可达100和300,高于一般气体膜分离过程。含氟膜经化学改性后,P_(NH3)可提高到改性前的2～3倍,P_(H2)和P_(N2)基本不变,氨通量和氨氮、氨氢渗透比均成倍提高。含氨31～46％的氨氢氮混合气经一级膜渗透可得含氨90％以上的透过气,含氨7％的混合气经两级渗透可使透过气中氨增浓至90％以上。     

真空膜蒸馏海水淡化过程的强化研究

采用气液两相流技术对管状炭膜真空膜蒸馏模拟海水淡化过程进行强化研究。纯水物系和NaC l水溶液的气液两相流强化实验中,相比未通气体时通量分别增加了29%~35%和16%~66%。气体流量、渗透侧真空度和膜组件放置方式对两相流膜蒸馏过程通量的影响结果表明:气液体积流量之比在(1~2)∶1时两相流强化效果最佳;通量随着渗透侧真空度的增大而增大,且气液两相流操作在较小真空度时通量增加的幅度大于较大真空度时;膜组件的放置方式对通量影响较大,相对于水平放置时,膜管竖直放置时的通量较大,最大可达水平放置时的131%左右。     

MFI型分子筛膜的制备及表征

采用无模板剂的二次生长合成方法,在-αA l2O3基膜上合成了MFI型分子筛膜,用XRD,SEM和气体渗透实验等方法进行表征,表明合成在-αA l2O3基膜的物质为MFI型分子筛。二次生长分子筛膜的正/异丁烷理想分离系数在298 K和473 K时分别为77和70,气体分离数据表明,2种分子筛膜对气体分离是由分子筛分占主导,同时分子筛膜完整无裂缺。不同温度,通过MFI分子筛膜渗透汽化分离质量分数分别为5%、50%和95%的乙醇/水的渗透通量和分离因子,结果表明渗透通量随温度的升高而升高,而分离因子随温度的升高却降低;渗透通量随乙醇质量分数的升高而降低,分离因子却随质量分数的升高而升高。     

内压式中空纤维膜气体脱CO2应用研究

针对天然气、沼气、烟道气等脱CO_2应用需求,探究了内压式中空纤维膜的气体分离性能,考察了压力、温度、处理量等对膜分离性能的影响。结果显示,与外压式膜不同,随着压力的增加内压式中空纤维膜的气体渗透通量显著增加。压力越高对混合气的处理能力越大,且膜组件存在最优处理能力。随着温度的增加,渗透通量增加、分离系数下降。     

气体分离用管状炭分子筛膜

以无机陶瓷管为支撑体、热塑性酚醛树脂为原料,经高温炭化制备了炭分子筛膜。用低温N2吸附的方法测定了炭分子筛膜的比表面积,用扫描电子显微镜对膜的形貌和厚度进行了表征。考察了膜的气体透过率以及气体的理想选择性随温度的变化关系:H2、CO2、O2、N2和CH4的透过率随温度的升高而增大;理想选择性α(H2/N2)、α(CO2/N2)、α(CO2/CH4)随温度的升高而减小,而α(O2/N2)随温度的升高先增大后减小,在90℃左右气体选择性达到最大。最后由阿累尼乌斯公式计算了气体透过炭分子筛膜的活化能,进一步说明气体透过机理为活化扩散。     

大尺度浆态床内气含率和气液传质特征

测定了中试规模的浆态床反应器装置(内径0.29 m,高为3 m)内气含率和气液体积传质系数,其中,采用费托合成蜡和铁系催化剂且N2和He的混合气代替合成气CO和H2来模拟费托合成条件,费托合成蜡的黏度、密度、表面张力和扩散系数以及亨利系数等由实验或ABC混合模型研究得到。研究结果表明:气含率和体积传质系数随压力(0.5—3.5 MPa)、温度(380—500 K)、气体表观气速(0.1—0.3 m/s)增加而增加,但随固体体积分数(0—10%)和气体体积比(He/N2)增加而减小,基于实验数据提出了新的体积传质系数经验关联式。     

Beta/碳纳米复合分子筛膜的制备

利用浸渍提拉方法,在平均孔径500 nm的管状a-Al2O3陶瓷管载体上成功制备了无缺陷的Beta/碳纳米复合分子筛膜. 通过室温下单组分气体渗透实验,发现当Beta分子筛在聚糠醇/丙酮溶液中的含量逐渐加大时,复合膜的气体分离因数略有增加,同时气体渗透通量明显加大. 经优化后氢气渗透通量比纯碳膜增加了一个数量级,说明Beta分子筛起到了加快气体渗透通量的作用. 由SEM照片可以发现,随着Beta分子筛含量的增加,制备的纳米复合膜的厚度由平均14 mm减少到7 mm左右,从而减少了气体渗透的阻力.结合实验数据,探讨了沸石分子筛/碳复合膜气体渗透路径.     

Gas permeation performance of cellulose hollow fiber membranes made from the cellulose/N‐methylmorpholine‐N‐oxide/H2O system

Cellulose hollow fiber membranes (CHFM) were prepared using a spinning solution containing N‐methylmorpholine‐N‐oxide as solvent and water as a nonsolvent additive. Water was also used as both the internal and external coagulant. It was demonstrated that the phase separation mechanism of this system was delayed demixing. The CHFM was revealed to be homogeneously dense structure after desiccation. The gas permeation properties of CO₂, N₂, CH₄, and H₂ through CHFM were investigated as a function of membrane water content and operation pressure. The water content of CHFM had crucial influence on gas permeation performance, and the permeation rates of all gases increased sharply with the increase of membrane water content. The permeation rate of CO₂ increased with the increase of operation pressure, which has no significant effect on N₂, H₂, and CH₄. At the end of this article a detailed comparison of gas permeation performance and mechanism between the CHFM and cellulose acetate flat membrane was given. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1873–1880, 2004     

Upgrading of a syngas mixture for pure hydrogen production in a Pd-Ag membrane reactor

Water gas shift (WGS) is a thermodynamics limited reaction and CO equilibrium conversion of a traditional reactor is furthermore reduced owing to the presence of H₂ (ca. 50%) in the feed stream coming from a reformer.The upgrading of a simulated reformate stream was experimentally investigated as a function of temperature (280-320 °C), feed pressure (up to 600 kPa), gas hourly space velocity (GHSV), etc. using a Pd-alloy membrane reactor (MR) packed with a commercial catalyst CuO/CeO₂/Al₂O₃; no sweep gas was used. The MR performance was also evaluated using new parameters such as conversion index, H₂ recovery and extraction index, etc., which evidence the advantages with respect to a traditional reactor.A Pd-based MR operated successfully overcoming the thermodynamic constraints of a traditional reactor and, specifically, the drawback introduced by the hydrogen presence. In fact, a CO conversion of 90% significantly exceeded (three times) the thermodynamics upper limit (<36%) of a traditional reactor owing to ca. 80% of hydrogen permeated through the membrane.The overall process performance was significantly improved by the presence of the Pd-based membrane and, thus, by the high reaction pressure which allowed and drove the hydrogen permeation.     

Transport and Permeation Properties of a Ternary Gas Mixture in a Medium-Size Polysulfone Hollow Fiber Permeator

Abstract

Permeation properties were analyzed for a mixture of CO₂, O₂, and N₂ in a medium-size polysulfone hollow fiber permeator with a net permeation area of 4.22 m². Measurements were conducted as a function of feed composition, reject flow rate, and feed pressure. Results included variations in species permeability, separation factor, permeate enrichment, reject depletion, and stage cut as a function of system parameters. Variations in permeation properties show strong dependence on feed composition, reject flow rate, and feed pressure. Permeability of carbon dioxide was higher at larger feed pressures and higher carbon dioxide content in the feed stream. Effect of increasing the reject flow rates on the permeability of carbon dioxide was affected by the system pressure and the carbon dioxide content in the feed stream. At low pressures, increase of the reject flow rate resulted in a decrease of carbon dioxide permeability. The opposite behavior was obtained at higher feed pressures. Increase of the reject flow rate reduced the gas residence time within the permeator. Increase of reject flow rate reduced species residence within the permeator and in turn increased resistance to species transport within the permeator. However, higher system pressures and carbon dioxide content in the feed stream resulted in larger levels of membrane plasticization, which increased the permeation rates of all species. The combined efféct of reducing the species residence time within the permeator and the level of membrane plasticization favored the permeation of carbon dioxide versus the other two species. Variations in other permeation properties, which include oxygen and nitrogen permeabilities, stage cut, permeate enrichment in carbon dioxide, and reject depletion in carbon dioxide, were also explained in terms of resistances encountered within the permeator and the membrane.     

Characterization of the permeation properties of CO2N2 gas mixtures in silicone rubber membranes

The separation characteristics of silicone rubber membranes are determined for CO₂N₂ gas mixtures. The analysis is performed as a function of composition, flow rate and pressure of the feed gas. Results are presented in terms of the variation in component permeability and separation factor as a function of the above parameters. Component permeabilities are calculated using the complete mixing model. Data analysis over the studied pressure range shows that the permeability coefficient of pure CO₂ gas in silicone rubber is 15 times higher than that of pure N₂ gas. This behaviour is completely altered for a mixture of the gases, where the calculated separation factors at low feed pressures and low CO₂ mole fractions in the feed stream are two- to three-fold lower than the separation factors for the pure gases. At higher feed pressures and high CO₂ mole fractions in the feed stream, the above behaviour is reversed; the separation factors for the gas mixture are now higher than those for the pure gases. Comparison of the permeation characteristics of silicone rubber and cellulose acetate membranes for CO₂N₂ gas mixtures shows similar ranges and values for the gas permeabilities and separation factors. However, much higher separation factors are obtained for the cellulose acetate membrane in the case of pure gas permeation.     

Enrichment of helium by asymmetric hollow-fiber membrane of cellulose triacetate

The permeation behavior of pure He and separation characteristics of He–air mixtures were examined using asymmetric hollow-fiber-type membrane modules of cellulose triacetate. The module was operated in a feed-outside mode. In permeation of pure He, the permeation rate coefficients slightly increased with increasing upstream pressure, and they agreed fairly well with those calculated on the basis of the assumption that the permeate flow inside the fiber is governed by the Hagen-Poiseuille equation. In the single-stage hollow-fiber module used, the molar fraction of He in the permeate stream was increased to 0.99 and 0.999 at the stage cuts of lower than 0.3 when the molar fraction in the feed stream was 0.90 and 0.99, respectively. The molar fractions of He in the permeate stream were numerically evaluated for various combinations of operating conditions in terms of a countercurrent plug flow model. © 1994 John Wiley & Sons, Inc.     

Characteristics of permeation and separation of aqueous alcoholic solutions through a poly[bis(2,2,2-trifluoroethoxy)phosphazene] membrane by evapomeation and pervaporation

The characteristics of permeation and separation for aqueous solutions of methanol and ethanol through a poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PBTFP) membrane were studied by pervaporation and evapomeation. In pervaporation technique, methanol was preferentially permeated in all of the feed solution compositions and ethanol was permeated in lower ethanol concentrations of the feed solution. Water was predominantly permeated from the feed solutions with higher ethanol concentration. In evapomeation technique, water was selectively permeated in both all of the feed vapor compositions for aqueous methanol and ethanol solutions. These different permselectivities depended on the feed composition and the membrane permeation technique and could be discussed by a difference in the mechanisms of permeation and separation. It was found that the permeation rate was influenced remarkably by the degree of swelling of the PBTFP membrane and the permselectivity for water of aqueous alcoholic solutions was enhanced by an increasing degree of swelling of the membrane. When the degree of swelling of the membrane with rising permeation temperature was small, both the permeation rate and permselectivity for alcohol in pervaporation and evapomeation increased with the permeation temperature. The above results are discussed considering the PBTFP membrane structure in evapomeation and pervaporation.     

Effect of pressure drop on performance of hollow-fiber membrane module for gas permeation

The pressure drop mainly due to viscous friction inside hollow fibers is taken into consideration by nondimensionalization and numerical simulation of governing equations. For pure gas, the permeation pressure and velocity of actual situations with a viscous fluid deviate significantly from those of the corresponding inviscid or no-pressure-drop cases. The apparent permeability estimated from the relation of permeate flow rate and pressure difference is considerably underestimated in actual situations, and more severely for the region of small pressure difference and large module length. Numerical simulation shows that the estimated permeability behaves as if it were an increasing function of pressure difference for a constant permeability and roughly a constant for a dual-sorption-type permeability, respectively. For binary-mixture permeation the cut ratio and purity of permeate stream are mainly governed by two dimensionless parameters standing for pressure drop and permeability, respectively. The cut ratio and corresponding product composition are predictable without the rigorous simulation of the governing equations.     

Separation of binary mixtures by dense membrane processes: influence of inert gas entrance under variable downstream pressure conditions

The influence of an inert gas on the separation performances of a dense polymeric membrane module working under partial vacuum on the downstream side, such as possibly encountered in gas permeation, vapor permeation or pervaporation, has been investigated through an experimental and theoretical study. A whole range of situations on the downstream side, covering ideal vacuum pumping (i.e. zero downstream pressure under leak free conditions) to inert gas sweeping under atmospheric pressure has been tested. A theoretical framework, previously developed for single permeant situation has been extended to the multicomponent case. The separation of methanol and 2-propanol by a dense silicone rubber membrane confirms the ability of this simple modelling strategy to offer quantitative predictions of the permeate composition under variable downstream pressure and inert gas flowrate conditions. Based on this observation, the implications of an inert gas contribution on pervaporation or gas separation operation are discussed, particularly in relationship to the global energy consumption of the system or to analytical devices making use of a gas sweep.     

合成氨贮罐气膜法氢回收的设计和操作

采用膜分离技术回收合成氨贮罐气中的氢组分,返回合成氨系统作为加氢脱硫单元的氢源。设计膜分离器时,膜面积增加使渗透气氢浓度降低而经济效益上升。当贮罐气流量1300Nm3/h、渗透气绝压为0.8MPa,氢产品浓度为85%-90%时,可以获得约287.7×104Yuan/a以上的经济效益,投资回收期在17个月内。在膜分离器操作时,氢氮选择性系数降低以及贮罐气压力降低都会引起氢回收率降低,导致经济效益下降,二者对氢浓度的影响不明显。     

二氧化硫和二氧化碳在离子液体支撑液膜中的渗透率和选择性

Permeabilities and selectivities of gases such as carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen (N2) and methane (CH4) in six imidazolium-based ionic liquids ([emim][BF4], [bmim][BF4], [bmim][PF6], [hmim][BF4], [bmim][Tf2N] and [emim][CF3SO3]) supported on polyethersulfone microfiltration membranes are investigated in a single gas feed system using nitrogen as the environment and reference component at temperature from 25 to 45ºC and pressure of N2 from 100 to 400 kPa. It is found that SO2 has the highest permeability in the tested supported ionic liquid membranes, being an order of magnitude higher than that of CO2, and about 2 to 3 orders of magnitude larger than those of N2 and CH4. The observed selectivity of SO2 over the two ordinary gas components is also striking. It is shown experimentally that the dissolution and transport of gas components in the supported ionic liq-uid membranes, as well as the nature of ionic liquids play important roles in the gas permeation. A nonlinear in-crease of permeation rate with temperature and operation pressure is also observed for all sample gases. By considering the factors that influence the permeabilities and selectivities of CO2 and SO2, it is expected to develop an optimal supported ionic liquid membrane technology for the isolation of acidic gases in the near future.