疏水性聚丙烯中空纤维膜中n-甲酰吗啉膜吸收含苯废气过程模拟

以疏水性聚丙烯中空纤维膜为气液膜接触器,n-甲酰吗啉水溶液为吸收剂,研究了膜气体吸收工艺分离C6H6/N2的传质过程. 在非润湿条件下,建立了膜气体吸收C6H6传质微分模型,模拟了C6H6在疏水性聚丙烯中空纤维膜管程及膜孔内的传质过程,并对C6H6的吸收速率进行预测. 结果表明,在实验条件下,膜气体吸收C6H6的速率为(0.89~6.13)′10-2 mg/(m2×s),微分模型对吸收速率预测的平均误差为1.9%,能准确描述中空纤维膜吸收C6H6的过程.     

气体在高分子膜中的溶解行为

对气体在高分子膜中的溶解行为进行了研究,建立了通用的单组分气体-膜体系,以及多组分混合气体-膜体系的溶解行为模型。经采用在不同温度及压力下的不同的气体-膜体系的浓度实验数据验证,理论值与实验值吻合。对前人提出的单组分气体-膜-框架模型,给出了简洁的寻常热力学论证方法。     

浆料反应增强气液传质

针对液膜区存在复杂反应的浆料吸收体系,通过气体吸收对分散相颗粒溶解增强作用的研究,建立了反应浆料增强气体吸收的三区域模型.采用搅拌槽间歇吸收实验测定了不同搅拌强度和Mg(OH)₂浆料固含率时SO₂吸收速率增强.研究发现,颗粒粒径、浆料浓度、“惰性区”厚度以及待吸收气体分压等参数是影响吸收增强作用的主要参数.考虑气液近界面“惰性区”和浆料表观黏度影响后的三区域模型结果与实验结果具有良好的一致性.     

膜吸收法回收烟气CO_2传质过程研究

在0.1~2 m~3/h模拟烟气膜吸收处理装置上,进行了膜吸收法捕集CO_2传质过程研究。在其他条件不变的情况下,考察了气体流量、吸收液流量和吸收液浓度对传质过程的影响;结合吸收溶剂的化学反应增强因子及中空膜本身的参数,建立了膜吸收过程的传质计算模型。试验结果表明:在有化学吸收推动的膜吸收传质过程中,膜吸收的传质阻力集中在气相和膜的界面,而反应发生在液膜界面,所建立的计算模型也很好地反映了这一现象。通过建立传质模型,可以推算出膜表面吸收传质过程,从而为膜吸收过程的工业放大提供支撑。     

浆料反应增强SO2吸收的间歇过程研究

采用搅拌槽间歇吸收实验测定了298K下Mg(OH)2浆料对SO2的吸收增强作用。通过液膜内待吸收气体与溶解分散相颗粒间反应的研究，建立Mg(OH)2浆料增强SO2吸收的三区域模型，模拟了间歇吸收过程中分散相颗粒粒径、待吸收气体分压和增强因子等随时问的变化。考虑了气液近界面“惰性区”影响和分散相颗粒粒径与浆料表观粘度变化后的间歇吸收过程的模拟结果与实验结果具有良好的一致性。     

聚四氟乙烯膜气体吸收数学模型和孔隙率的影响

膜吸收是将膜分离与传统的吸收技术相结合的一种新型分离技术。在这些过程中经常使用多孔膜,多孔膜对过程的传质性能有一定的影响。对不同孔隙率的微孔聚四氟乙烯(PTFE)疏水性平板膜的膜气体吸收过程中液相传质性能进行了实验研究。当采用去离子水-CO2吸收体系时,多孔膜的孔隙率对液相传质性能没有影响;当采用NaOH水溶液-CO2吸收体系时,多孔膜的孔隙率对液相传质性能有明显的影响。在相同流速下,孔隙率大的膜液相传质系数高于孔隙率小的膜。以双膜理论为指导,建立了多孔膜气体吸收过程中液相传质模型。用该模型描述多孔膜孔隙率对液相传质系数的影响,其结果与实验数据具有良好的一致性。     

中空纤维膜气体溶剂的吸收分离过程

测定了不同条件下聚丙烯疏水性中空纤维膜组件中ＣＯ２－ＮａＯＨ体系气体溶剂吸收过程的总传质系数．建立了溶剂吸收过程总传质系数的计算模型．以此模型为基础,结合实验结果对气体溶剂吸收过程进行了分析,提出了提高总传质系数的有效方法．     

混合溶剂在高分子膜中的传递模型

以单溶剂在高分子膜中的蠕变传递模型为基础,通过考虑溶剂间的耦合作用对溶剂在高分子膜中传递过程的影响,建立了混合溶剂在高分子膜中传递的蠕变模型.对模型参数进行了数值模拟研究,并使用该模型关联了吸收实验曲线.计算结果显示模型具有一定的预测功能.     

炭分子筛膜气体分离传递机理研究的新进展

炭分子筛膜由于其本身具备的独特优势以及其在气体分离方面的应用潜力,已引起了世人的关注.但对炭分子筛膜分离机理特别是传递过程机理研究的不足限制了其发展.本文介绍炭分子筛膜气体分离机理特别是传递过程机理研究的最新进展,包括针对制备方法不同所建立的气体传递机理模型,如Maxwell模型和Bruggeman模型;详细介绍了两种孔结构模型平行阻力模型和阻力串联模型.在此基础上,分析了各模型中存在的问题和不足,认为需要对炭分子筛膜进行进一步的完善并建立合理的传递机理模型,才能推动炭分子筛膜用于气体分离的进程.     

尾气排放中氟含量超标的原因分析及处理方法

气体与液体接触后,都会产生溶解。吸收过程就是在一定条件下,溶质(即气体)在某种溶剂中溶解的过程。利用这一原理在生产过磷酸钙的氟吸收系统中,使用初期,性能良好,尾气中氟含量可以维持在国家标准以下。但运行一段时间以后,效果就达不到要求。为了达到标准,在生产过程中,找到了一些原因并采取相应处理方法。     

Transport phenomena in gas permeation through glassy polymer membranes with concentration-dependent sorption and diffusion parameters

The modified dual-mode mobility model for permeation of a gas in glassy polymer membranes was combined with the extended dual-mode sorption model to take account of the plasticization effect of sorbed gas molecules on both sorption and diffusion processes. The combined model was further simplified by the introduction of a concentration of the mobile gas species. However, the observed pressure dependence of mean permeability coefficients of carbon dioxide in methylmethacrylate-n-butyl acrylate copolymer and polymethylmethacrylate films at 30°c and also that of oxygen in a polycarbonate film at 50°C and 60°C showed that a plasticization action of sorbed gas species has an influence on the diffusion process rather than on the sorption process, that is, were simulated by the modified dual-mode mobility model combined with the conventional dual-mode sorption model.     

Sorption and permeation behavior for a gas in glassy polymer membrane near the glass transition temperature

The deviation from the conventional dual-mode sorption and mobility model for a gas in glassy polymer membranes has separately been studied thus far, and to simulate sorption and diffusion behavior, an extended dual-mode sorption model and a modified dual-mode mobility model, respectively, have been proposed independently. However, simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in cases of CO₂in poly-4-methyl-1-pentene membrane at 20°C and in polystyrene membrane at 60 and 70°C. The plasticization effect of sorbed CO₂ on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules exists. © 1996 John Wiley & Sons, Inc.     

Evidence of dual mobility in sulfur dioxide-polyarylate system: An integral sorption analysis

Integral sorption/desorption measurements were carried out for the sulfur dioxide-glassy polyarylate polymer system at 25°C, 40°C, 55°C, and 63°C. The transport of sulfur dioxide in the glassy polyarylate polymer was governed by Fickian diffusion. The effective diffusion coefficient of sulfur dioxide increased with increasing penetrant concentration. The concentration dependence of the effective diffusion coefficient is explained on the basis of the partial-immobilization model developed by Paul and Koros. The mobility of the molecules sorbed in the Langmuir mode is shown to be significantly lower than the mobility of the molecules in Henry's law dissolution mode. The predictions of permeability values as a function of upstream gas pressure are presented. The equilibrium sorption isotherms for this system are well represented by the dualmode sorption model. The eltergetics and the temperature dependence of the dual-mode parameters are also discussed.     

Gravimetric and volumetric study of the sorption of gases and vapors in poly(vinyl chloride) powders

The sorption of a variety of gases and organic vapors in poly(vinyl chloride) (PVC) powders has been studied gravimetrically with a recording microbalance and volumetrically with a gas pycnometer and an automatic surface area analyzer. For nitrogen, carbondioxide, vinyl chloride, methanol, acetone, n-butane, and benzene at low penetrant activities and temperatures below T_g, sorption isotherms exhibit the downward curvature characteristic of dual-mode sorption. The solubility of each of these penetrants is lower in heat-treated PVC samples than in samples recovered from the polymerization without additional heating. It has been possible to estimate the parameters of the dual-mode sorption model for carbondioxide, vinyl chloride, and methanol. The results indicate that the history-dependence of gas or vapor solubility is associated only with the “hole-filling” term of the dual-mode model; the normal dissolution or Henry's Law term is essentially unaffected by the prior heat treatment of the PVC.     

Gas permeation through glassy polymer membranes with relatively low glass-transition temperature

When the glass-transition temperature of the polymer is not so much higher than the experimental temperature, the pressure dependence of the mean permeability coefficient of the poly-mer membrane to a gas is apt to deviate from the prediction by the conventional dual-mode mobility model, and to obey a similar model with concentration-dependent diffusivities because of the plasticization action of sorbed gas in the polymer membrane. In this work, sorption and permeation for oxygen and carbon dioxide in a membrane of polystyrene whose glass-transition temperature is 95°C, were measured to discuss the mechanism of gas diffusion in glassy polymer membranes with relatively low glass-transition temperature at 30, 40 and 50°C respectively.     

Diffusion of an acid dye in nylon—in relation to sorption and diffusion of a gas in glassy polymers

The steady-state permeation rate data of an acid dye in a nylon film were analyzed via dual-mode sorption and mobility model based on gradients of concentration. The model used incorporates diffusion in a porelike region, unlike diffusion of a gas in a glassy polymer. There was some possibilities of the Nernst to the Langmuir mode diffusion jump, and the diffusivity was estimated.     

Residual porosity in polymeric latex films

Solubility and diffusivity measurements of a probe gas (CO₂), which has an inherently low solubility in the polymer, have been used to characterize residual porosity in polymeric latex films. Sorption isotherms resembling those of a glassy polymer were obtained, even though the glass transition temperature of the polymer was 1°C, about 30°C below the experimental temperature. Solvent cast films of the same polymer exhibited much lower solubilities, and followed the expected Henry's law behavior. CO₂ solubility and diffusivity were found to decrease with aging time for the latex films, but did not quite reach the values of the solvent cast films, even after 75 days at room temperature. The sorption data could be described by the dual-mode sorption model, which is commonly employed in the analysis of glassy polymer sorption isotherms. Estimates of the amount of porosity were made from the sorption data, and values ranging from 0.6–0.03% were obtained for latex films aged from 62 h to 75 days, respectively. Our results suggest that permeability differences noted by others for latex and solvent cast films of the same polymer are due to the substantial solubility differences for low-solubility penetrants in these two types of films.     

Gas sorption in poly(butylene terephthalate). I. Influence of gas molecules

The sorption of CO₂ and the noble gases Ne and Ar in semicrystalline glassy poly(butylene terephthalate) (PBTP) films was measured by the gravimetric method with a recording microbalance at 298 K. The sorption of CO₂ was found to be significantly higher than that of Ne and Ar. This is attributed to a specific interaction between CO₂ and PBTP. The sorption isotherm for CO₂ was analyzed by the dual-mode sorption model, while the sorption behaviors for Ne and Ar did not follow this model. Their sorption isotherms can be described by the sorption model developed here for the noble gases in PBTP. A critical adsorption pressure p^* that is dependent mainly on the relative size of the frozen microvoids and the noble gas atoms is defined in this model. The Langmuir adsorption for describing the sorption in this gas/polymer system in addition to Henry's solubility happens just above this p^*, whereas only Henry's solubility takes place below p^*. © 1993 John Wiley & Sons, Inc.     

Low-pressure CO2 sorption in poly(vinyl benzoate) conditioned to high-pressure CO2

Sorption of CO₂ in poly(vinyl benzoate) was gravimetrically measured at pressures up to 1 atm. Sorption isotherms were determined above and below the glass transition temperature T_g from 5 to 85°C. The isotherms were analyzed by the dual-mode sorption model assuming that the plasticizing effect of sorbed CO₂ is negligible at this pressure range. The solubilities and Henry's law dissolution parameters were compared with those obtained by the high-pressure sorption and permeation measurements. Henry's law dissolution parameters were in good agreement with one another. However, the solubilities first determined here were smaller than those determined by the high-pressure sorption experiment at the same temperature. It was clear that the Langmuir capacity of the present specimen was smaller in spite of similar high-pressure CO₂ exposure. Relaxation of the polymer was expected to be one of the reasons. This expectation was confirmed from the observation and analysis of sorption isotherms after two kinds of treatments. After annealing above T_g, the Langmuir capacity was shown to be decreased to 1/2 or even to 1/3 from the sorption isotherms below 45°C. This means that the conditioning to the high-pressure CO₂ surely has a large effect on the nature of glassy polymer. Just after high-pressure CO₂ exposure at 25°C, increased solubility was observed. Furthermore, the slow decrease of solubility, that is, the decrease of conditioning effect, was also followed from the continual measurements at 25°C. This result reflects not only the characteristic of sorption capacity after high-pressure CO₂ exposure, but also the relaxation of polymer in glassy state.     

Numerical examination of the dual-mode model for permeation,sorption, and desorption rate curves

Numerical solutions were applied to the dual-mode sorption and transport model for gas permeation, sorption, and desorption rate curves allowing for mobility of the Langmuir component. Satisfactory agreement is obtained between integral diffusion coefficient from sorption and desorption rate curves and apparent diffusion coefficient from permeation rate curves (time lag method). These rate curves were also compared to the curves predicted by Fickian-type diffusion equations. © 1992 John Wiley & Sons, Inc.