膜结构填料的物化特性对精馏分离异丙醇/水体系的影响

选用了三种不同材料的中空纤维膜(PP,PS和PES)构建新型膜接触器结构填料,并对异丙醇/水体系进行了精馏分离过程研究.在新型膜接触器中,液相和气相分别在管程和壳程进行逆向流动.实验结果表明:三种结构填料对异丙醇/水体系的分离效果依序为PES>PP>PS.不同材料的中空纤维膜作为结构填料对异丙醇/水溶液体系的分离效率均...     

新型中空纤维膜接触器用于乙醇/水体系分离的探索

引言 醇/水体系分离一直是化工生产中的重要环节,高效的醇/水分离技术能够使醇的产量大大提高,满足日益增长的工业生产需求.传统的分离方法如精馏、萃取等已经相当成熟,但是这些方法在工业生产过程中能耗巨大,越来越受到面临能源资源匮乏的当代社会的关注和制约.在此背景下,面向高效、节能的新型膜接触分离器应运而生,如Alan等[1]指出,工业化或半工业化的过程已经包括膜吸收、膜萃取以及渗透蒸馏等多个耦合分离单元[2-6].     

中空纤维PVA/PAN复合膜填料的乙醇水溶液精馏性能

以乙醇/水溶液为分离对象,中空纤维PVA/PAN复合膜作为精馏填料,考察了不同膜组件的传质分离效率。实验结果表明:各种组件的分离效率均随塔釜加热功率的增加而减小;和大多数中空纤维膜接触器一样,其总传质系数Ky随中空纤维膜组件填充密度φ的增加而减少;相比于传统精馏填料而言,用中空纤维膜做精馏填料分离乙醇水溶液的分离效果更好,可以在常规填料不能操作的液泛线以上进行操作。当塔釜加热功率为120 W,45根中空纤维膜封装在内径为1.6 cm玻璃管中的传质单元高度(HTU)为5.64 cm。     

填充密度对中空纤维膜接触器精馏过程壳程传质的影响

探讨了填充密度对新型聚丙烯中空纤维膜接触器精馏过程中壳程传质的影响。中空纤维膜接触器在填充密度为4.7%、9.5%、19%时均可在远离常规填料液泛线以上的气速范围操作。低填充密度下,壳程的Sherwood数理论值大于实验值,但填充密度较高时,实验值大于理论值。高Reynolds数有利于壳程传质,低填充密度时的Sherwood数高于高填充密度时。随着F因子逐步增大,壳程气相传质阻力随之变小,且膜接触器的填充密度越高,气相传质阻力越大。3种不同填充密度膜接触器的气相总传质系数随着接触器填充密度的增大而迅速减小,由391.84×10^-5 m·s^-1降低为83.28×10^-5 m·s^-1。     

Vergleich der Effektivität von bewehrten und unbewehrten Rührsystemen in der chemischen Verfahrenstechnik

In spite of the fact that vortex formation, in unbaffled agitated vessels, is in most cases an undesirable phenomenon, many cases exist in chemical engineering where unbaffled systems can be used with greater effectivness than systems with baffles, at the same or even smaller energy consumption levels. Satisfactory results can also be obtained in unbaffled agitatated vessels without an air-liquid interface. These facts, viewed in the light of energy problems in the chemical industry, show the current importance of comparative studies of baffled and unbaffled systems. In the present review article some characteristic cases from the fields of fluid dynamics, homogeneous distribution processes, suspensions, as well as mass-transfer and heat-transfer operations in baffled and unbaffled agitated vessels are presented and comparatively discussed in relation to their effectivness.     

膜接触器及其相关过程在废水处理中的应用

膜接触器是一种通过膜作为两相之间的分离界面而实现相间传质的新型杂化膜过程,具体应用形式包括膜蒸馏、膜萃取、膜吸收、膜结构填料等.膜接触器使用微孔中空纤维膜将两流体分隔开,膜孔为两流体之间提供传质的场所.与传统接触分离器相比,新兴的膜接触器拥有分离效率高、工作范围宽、两相流速可单独控制以及结构紧凑等诸多独特的优点.文章着重于膜接触器及其相关过程在废水处理领域的最新研究成果和进展,具体分析比较了上述几种膜接触器的结构、工作原理和操作特点,充分展示了膜接触器在废水处理以及化工、医药、食品等领域特种分离中的广阔应用前景.     

膜结构填料涂覆改性对精馏分离异丙醇/水体系的影响

采用聚二甲基硅氧烷(PDMS)对聚砜(PSf)、聚偏氟乙烯(PVDF)两种不同材料中空纤维膜结构填料进行了疏水涂覆改性,并研究了改性前后膜结构填料在异丙醇/水体系精馏分离中的材料性能变化。实验结果表明:PDMS涂覆使PVDF膜的分离效果提高了约20%,但使PSf膜的分离效果下降3%~10%。经涂覆后,膜结构填料的传质单元高度均在20 cm以下,最小可达5 cm左右;所有膜结构填料均可突破传统精馏操作弹性限制,其传质时间小于10 s,水力学特性和传质效率更优。     

环境化工中的气/液膜接触分离过程及其特性

阐述了新型膜接触器由于避免了传统分离设备的一系列缺点和不足,具有操作范围宽,分离效率高,气液两相的流速可独立控制,可直接线性放大和结构紧凑等众多优点,日益成为分离科学研究的热点。并着眼于3种气/液界面膜接触分离过程(膜吸收、膜蒸馏、膜结构填料替代)在废气、废水等环境治理与化工分离方面的研究,从膜接触器结构、膜材料、传质、分离效率等方面详细分析和探讨了三种膜过程的分离特点,并对其作用原理、操作参数及分离性能进行了综合比较。     

Particle suspension in top-covered unbaffled tanks

Unbaffled stirred tanks are seldom employed in the process industry as they are considered poorer mixers than baffled vessels. However, they may be expected to provide significant advantages in a wide range of applications (e.g. crystallization, food and pharmaceutical processes, etc.), where the presence of baffles is often undesirable. In the present work solid–liquid suspension in an unbaffled stirred tank is investigated. The tank was equipped with a top-cover in order to avoid vortex formation. A novel experimental method (the “steady cone radius method”, SCRM) is proposed to determine experimentally the minimum impeller speed at which solids are completely suspended. Experimental N_js and power consumption data are provided over fairly wide ranges for particle size, density and concentration. Dependence of N_js on particle density and concentration is similar to that observed in baffled tank. Conversely, a negligible dependence of particle diameter on N_js is observed in the unbaffled tank, a difference from baffled vessels with important practical implications.Finally, the mechanical power required to achieve complete suspension in unbaffled tanks is shown to be much smaller than in baffled vessels. This, in conjunction with the previously ascertained excellent particle-fluid mass-transfer promotion, could make unbaffled tanks a best choice for many solid–liquid operations, where mass transfer is the main limiting factor.     

Hollow fiber membrane contactor as a gas-liquid model contactor

Microporous hollow fiber gas-liquid membrane contactors have a fixed and well-defined gas-liquid interfacial area. The liquid flow through the hollow fiber is laminar, thus the liquid side hydrodynamics are well known. This allows the accurate calculation of the fiber side physical mass transfer coefficient from first principles. Moreover, in the case of gas-liquid membrane contactor, the gas-liquid exposure time can be varied easily and independently without disturbing the gas-liquid interfacial area. These features of the hollow fiber membrane contactor make it very suitable as a gas-liquid model contactor and offer numerous advantages over the conventional model contactors. The applicability and the limitations of this novel model contactor for the determination of physico-chemical properties of non-reactive and reactive gas-liquid systems are investigated in the present work. Absorption of CO₂ into water and into aqueous NaOH solutions are chosen as model systems to determine the physico-chemical properties for non-reactive and reactive conditions, respectively. The experimental findings for these systems show that a hollow fiber membrane contactor can be used successfully as a model contactor for the determination of various gas-liquid physico-chemical properties. Moreover, since the membrane contactor facilitates indirect contact between the two phases, the application of hollow fiber model contactor can possibly be extended to liquid-liquid systems and/or heterogeneous catalyzed gas-liquid systems.     

Mechanism of mixing enhancement with baffles in impeller-agitated vessel, part I: A case study based on cross-sections of streak sheet

Enhancement mechanism of mixing with baffle in agitated vessel using rotated two-bladed paddle impeller was investigated under a laminar condition. In mixing pattern, the toroidal isolated mixing region in the baffled vessel becomes distortive and much smaller than that of unbaffled vessel. From the visualization of streak cross-sections in the baffled vessel, interestingly, the renewed streak folds (streak lobes) are generated at the vicinity of baffles in both the vertical and horizontal cross-sections. These behaviors of streak are unlike the unbaffled case that the streak stretches straightforwardly. The streak lobe is known as the mixing template that its number and size are key factor for laminar mixing in agitated vessel. The results suggest that baffles can effectively transform the circumferential flow to vertical and/or radial flows. Consequently, in the baffled vessels, not only the vicinity of vessel wall but also the tip of baffles can become the origination of streak lobe formation, and folds of streak in the vertical and circumferential directions are further enhanced with baffles.     

Transferts de chaleur a la paroi d'une cuve mecaniquement agitee

Local heat transfer coefficient between the agitated liquid contained in a tank and the wall of the tank has been determined for baffled and unbaffled tanks. The diameter of the six blade-turbine used was one third of the tank diameter. The overall coefficient has been calculated by integration of the local values. Results show the influence of the position of the turbine and of the baffles.     

气/液膜接触分离过程及其膜材料研究

新型气液膜接触器是很多具有共同特点膜过程的总称,它使用高分子膜将两流体分隔开,膜孔为两流体提供有效传质的场所,与传统分离器相比具有许多独特的优点,日益成为分离科学研究的热点。简述膜接触器在不同气/液分离体系中的应用,针对膜吸收、膜蒸馏、膜结构填料等三种典型的气/液界面膜接触分离过程,从结构、膜材料、传质、分离效率等方面详细进行了分析和比较。着重介绍了近年来相关领域膜材料学的研究进展,如高分子膜材料、成膜方法以及膜材料的改性方法(等离子体改性法、紫外辐照法和表面涂覆改性法等)等。     

聚丙烯中空纤维膜组件分离烟气中的CO2

膜吸收法在大型工业燃煤电厂二氧化碳（CO2）捕集方面具有很好的应用前景,但烟气组分对该技术效果影响还有待进一步研究。本文以单乙醇胺（MEA）为吸收剂,开展了疏水性聚丙烯（PP）中空纤维膜组件分离模拟烟气中的CO2的实验研究,考察了吸收操作条件以及燃煤烟气中水汽和SO2对膜组件吸收效率的影响。结果表明,试验的最佳液气比为24 L/m3;MEA的浓度为0.6 mol/L;膜组件进口的温度变化对吸收效率基本没有影响;CO2的浓度在10%～20%内变动对吸收效率影响不大。与CO2相比,SO2会优先发生吸收作用,而水汽则会吸附在聚丙烯中空纤维膜组件的孔壁上,产生毛细管凝聚现象,阻塞CO2的渗透吸收。     

Membrane Gas-Solvent Contactor Pilot Plant Trials of CO2 Absorption from Flue Gas

Membrane gas-solvent contactors have received much attention for CO₂ absorption, as the approach incorporates advantages from both solvent absorption and membrane gas separation. This study reports on pilot plant trials of three membrane contactors for the separation of CO₂ from flue gas. The contactors were porous polypropylene (PP), porous polytetrafluoroethylene (PTFE), and non-porous polydimethylsiloxane (PDMS), with the solvent PuraTreatTM F^TM. To enable performance comparison, laboratory measurements based on a gas mixture of 10% CO₂ in N₂ were also undertaken on the same contactor–solvent systems. It was found that the PP contactor experienced significant pore wetting in both laboratory and pilot plant studies. In contrast, the PTFE contactor experienced only minor pore wetting in the laboratory. However, in the pilot plant trial of the PTFE contactor extensive pore wetting was observed, and the overall mass transfer coefficient measured was comparable with the PP contactor. The non-porous PDMS contactor had an overall mass transfer coefficient two orders of magnitude less than the PP contactor, due to the greater mass transfer resistance of the polymeric film. However, the non-porous membrane does not experience pore wetting, which resulted in the overall mass transfer coefficient being similar for both laboratory and pilot plant measurements.     

Experimental investigation on a membrane distillation based micro-separator

In this work a novel micro-separator combining the sweep gas membrane distillation principle with micro-fluidic channels was designed and tested for the separation of a mixture of methanol and water with a low to high methanol concentration. The performance of the new separation device was studied with different liquid–vapor/gas membrane contactors with respect to the separation factor and the distillate flux rate by varying the relevant operating parameters of the process like the methanol concentration in the feed (5–70 wt.%), the feed temperature (40–65 °C), the feed flow rate (up to 30 ml/min), and the flow rate of the inert carrier gas nitrogen (up to 600 ml/min at standard conditions). For all performed experiments, the feasibility of the separation has been proved and the possibility to separate mixtures with high methanol concentration by using a membrane distillation based micro-separator has been for the first time reported. The inert gas flow rate was identified as the crucial operating parameter influencing the separation performance of the micro-separator. In addition, the selection of an appropriate membrane liquid–vapor/gas contactor was found to be an important design parameter for the reduction of temperature polarization effects.     

A PRELIMINARY STUDY ON LIQUID MEMBRANE SEPARATION IN ROTATING DISK CONTACTORS WITH PERFORATED DISKS

A rotating disk contactor (RDC) with perforated disks was employed for liquid membrane separation. Hydrodynamic characteristics and rate of mass transfer in the contactor were studied. Experimental results indicated that the rotating perforated disks contributed tremendously to liquid-liquid dispersion as well as to the rate of mass transfer. It is claimed, therefore, that contactors equiped with perforated disks is well adaptable to the continuous processing of liquid membrane separations     

HOLLOW FIBER AND SPIRAL WOUND CONTACTORS FOR FLUID/PARTICLE CONTACT AND INTERACTION

The unit operations of fluid/particle contact and interaction are the basis of many chemical processing operations. The mass transfer rate and pressure drop in the contactor are critical to the process performance. Hollow fiber and spiral wound contactors, which are derived frommodule development in membrane separation technology, have been recently developed as an alternative to the conventional design of fluid/particle contactors. These novel contactors allow the use of minute particles to enhance mass transfer without giving rise to a high pressure drop and can be used to carry out adsorption separation or catalytic reaction. In this paper, therecent developments in this area are reviewed, and some outstanding issues yet to be solved are highlighted. Though there are some preliminary proof-of-concept studies, further investigations are required to establish the relationships between the contactor design parameters, the process variables, and the process performance. Continued efforts are needed to identify the specific niche applications for the new contactor technology.     

Hollow fiber and spiral wound contactors for fluid/particle contact and interaction

The unit operations of fluid/particle contact and interaction are the basis of many chemical processing operations. The mass transfer rate and pressure drop in the contactor are critical to the process performance. Hollow fiber and spiral wound contactors, which are derived frommodule development in membrane separation technology, have been recently developed as an alternative to the conventional design of fluid/particle contactors. These novel contactors allow the use of minute particles to enhance mass transfer without giving rise to a high pressure drop and can be used to carry out adsorption separation or catalytic reaction. In this paper, therecent developments in this area are reviewed, and some outstanding issues yet to be solved are highlighted. Though there are some preliminary proof-of-concept studies, further investigations are required to establish the relationships between the contactor design parameters, the process variables, and the process performance. Continued efforts are needed to identify the specific niche applications for the new contactor technology.