精馏分离中的新型中空纤维膜结构填料及其传递现象

以异丙醇/水体系为研究对象,采用有挡板的新型聚醚砜中空纤维膜接触器作为精馏结构填料,进行了精馏分离过程和现象的研究。通过不同流动方式的比较,在新型膜接触器中设计了液体管内流动、蒸气壳层沿挡板逆向流动的改进型平行流方式。实验结果表明：无论有无挡板,中空纤维膜结构填料对异丙醇/水溶液的分离效率均较常规结构填料要高得多,且操作气速可以在常规填料液泛线以上,表明其不易受常规填料的操作弹性限制。有挡板膜接触器的性能和分离效率较无挡板时更优,运行参数更为稳定,其最小传质单元高度HTU值可达5.4cm。与其它中空纤维膜分离器类似,其总传质系数K随中空纤维膜的填充密度φ加大而变小,但新型膜接触器精馏过程的总传质系数值较液液萃取要高出约5～10倍。     

填充密度对新型中空纤维膜接触器分离性能和传质的影响

采用聚丙烯中空纤维膜接触器作为新型精馏结构填料对甲醇水溶液体系进行了精馏分离过程的实验研究,探讨了填充密度对中空纤维膜接触器分离性能和过程传质的影响.结果表明,填充密度为4.7%时,接触器塔顶甲醇浓度比填充密度为9.5%时的高,且两种填充密度的膜接触器组件均可在远离常规填料液泛线以上的气速范围操作.随着气速逐步增大,传质单元高度变大,壳程气相传质系数随之变大,填充密度高的组件的气相传质系数较小.     

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。     

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...     

基于Aspen仿真的乙醇水溶液精馏方案优化

为了实现对乙醇水溶液精馏方案进行优化设计,本文首先基于物料平衡、相平衡、物流各组分摩尔分率归一化以及热量平衡,针对整个填料塔精馏过程建立了稳态和动态模型,并利用数学模型对每部分精馏操作时的关键参数以及能耗进行了理论计算。为了检验数学模型和理论计算的合理性,同时鉴于Aspen Plus和Aspen Dynamics中已经建立了完善的精馏塔模型,本文以乙醇水溶液精馏方案为例,以达到浓度和回收率要求为约束条件,过程中最小能耗为目标函数,对回流比、馏出液流量、进料流量、进料温度、塔釜加热功率等几个输入变量分别进行了灵敏度分析,对理论计算的操作变量进行校正,确定出实际操作中的操作变量,优化乙醇水溶液精馏过程,从而得到最优的精馏操作序列。     

超重力减压间歇精馏的传质性能

以不锈钢波纹丝网为填料,应用超重力减压精馏间歇全回流操作分离乙醇/水共沸物系。考察了进料乙醇质量分数x_f为50%~95%、操作压力P为101.33~11.33kPa和超重力因子β为20.90~130.64时乙醇-水体系的传质性能。实验中设备运行稳定并且单级旋转精馏床传质性能随着超重力因子β的增大先增强后减弱,随着压力P的减小和进料浓度x_f的增加而增强,并在P=11.33kPa时分离高浓度原料时打破共沸点。与相同条件下传统填料塔相比,分离效果明显高于传统塔,且HETP为7.94~14.20mm,仅为传统塔的1/6~1/4,传质性能显著增强。并对能耗进行分析,超重力装置由于自身体积小等优点便于达到所需真空度,能耗降低明显。     

多级超重力精馏过程的传质性能

超重力精馏设备因具有体积小、能耗低且传质效率高的优势已引起人们广泛关注。文中以不锈钢波纹丝网为填料,以甲醇/水溶液为物系,在超重力因子β为21—131、回流比R为1.5—4.0、原料流量q为1.24—2.50kmol/h、原料摩尔分数xf为0.09—0.32、常压操作和室温进料条件下,考察多级超重力精馏过程的传质性能研究,并与其他超重力精馏填料的传质性能进行比较。研究表明:装有不锈钢波纹丝网填料的多级超重机在精馏实验过程中运行平稳;实验最佳操作条件为q=1.248 3 kmol/h,R=4,β=83.609 4,xf=0.090 3,精馏段、提馏段和整个系统的理论塔板数NTP分别为5.1,5.5和10.6;设备的理论塔板高度为37.6—58.4mm;塔顶、塔底分离效果可达97.6%以上和1%以下(质量分数),其传质效率优于常规塔设备及实验室设备。     

新型气隙式膜蒸馏组件脱盐过程

利用基于聚丙烯中空纤维膜和聚丙烯中空纤维换热管的新型能量回收式膜组件(AGMD-HF),以70 g·L^-1的氯化钠溶液为研究对象,考察了膜组件长度和膜孔径大小对膜组件脱盐性能的影响。为直接衡量操作条件、组件参数以及温差、浓差极化现象对传质系数的影响,引入总传质系数,并研究进料温度和膜孔径对总传质系数的影响。实验结果表明,总传质系数随着温度的升高、膜孔径的增大而增大,提高膜孔径可有效提高总传质系数,同时可有效提高通量和造水比。通量随组件长度的增大而减小,而造水比增大,因此在应用过程中可综合考虑通量和造水比以便选择合适的组件长度。     

带塔底储罐的间歇萃取精馏的实验研究

提出了带塔底储罐的间歇萃取精馏操作方式.新操作方式使精馏过程中加入的溶剂及塔内回流液直接流入塔底储罐,不再返回塔釜.以乙二醇为溶剂分离乙醇–水共沸物的实验研究表明,新操作方式克服了普通间歇萃取精馏塔釜体积庞大的缺陷,同时具有塔釜温度稳定、加热容易控制、收率提高等优点.     

旋转填料床精馏性能研究

以乙醇-水溶液为物系,对转子内径为60mm,外径为180mm,高40mm的旋转填料床进行精馏试验。结果表明,在低转速区旋转填料床的理论塔板数随气相动能因子F和超重力因子β的增大而增大,传质单元高度为1．09～1．76cm;并建立了传质模型。     

Effects of baffles on separation of aqueous ethanol solution with hollow fibers

The effects of baffles on the operation and mass-transfer characteristics in novel hollow fiber membrane contactor used in distillation were investigated. Hollow fiber membranes, coated with a 7 μm polydimethyl-siloxane, were operated as structural packing in the separation of ethanol-water solutions. The parallel flow mode was chosen for separation due to the stronger driving force of the concentration difference, in which liquid flows through the lumens of the fibers and vapor flows countercurrent-wise outside the fibers. Two baffles were installed on the shell side of the membrane contactors to enhance separation, which had a round shape with a semi-lunar hole. The results show that both baffled and unbaffled membrane contactors gave better, more productive separations than traditional packing in distillation, such as the excellent Sulzer Gauze BX structured packing. The baffled membrane contactors performed better than unbaffled ones, especially at high vapor velocities. The minimal HTU of membrane contactor with baffles could reach as low as 4.5 cm, and almost all the contactors could work well above the limit where flooding normally occurs in conventional cases. Theoretical analysis predicted that baffles helped membrane module to obtain a higher masstransfer coefficient and a smaller mass-transfer resistance. Finally, theoretical mass-transfer coefficient and experimental value were compared as well as the contribution of each individual mass-transfer coefficients among liquid, gas and membrane.     

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concen-tration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle. Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.     

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.     

Fabrication of highly permeable PDMS@ZIF-8/PVDF hollow fiber composite membrane in module for ethanol-water separation

The construction of high-performance MOF-based hollow fiber composite membrane (HFCM) modules is a significant, yet challenging task for the biofuel production industry. In this study, a novel approach was taken to fabricate PDMS@ZIF-8/PVDF HFCMs in modules through a facile ZIF-8 self-crystallization synthesis followed by pressure-assisted PDMS infusion for pervaporation ethanol-water separation. The as-prepared HFCMs exhibited an ultrathin separation layer (thickness, 370 ± 35 nm), which was achieved through precise regulation of the ZIF-8 membrane and defect repair by PDMS infusion. Moreover, the strategy utilized in this study resolved the defect issues arising from MOF agglomeration in conventional composite membranes. Impressively, at the optimal packing density, the prepared membrane demonstrated a remarkable ethanol flux (1.11 kg m⁻² h⁻¹) with an PSI value (26.59 kg m⁻² h⁻¹) and showed promising long-term stability for the pervaporation of 5 wt% ethanol aqueous solution at 40°C.     

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].     

巡视中空纤维膜的研发和产业进展

介绍了国内外用于人工肾的中空纤维透析膜、用于废水处理的微滤、超滤中空纤维及膜生物反应器（MBR）、用于海水淡化的中空纤维反渗透膜、用于气体分离及有机物代精馏的中空纤维膜、用于双亲和性吸附蛋白质的固定双配合剂多微孔中空纤维膜、用于回收海水资源的微滤和纳滤膜、用于脱氧核糖核酸链（DNA）切片的内含亲水性聚合物的中空纤维膜以及新型电池隔膜.     

烧结温度对TiO2/不锈钢中空纤维复合膜结构和性能的影响

不锈钢中空纤维膜基膜孔径大,直接涂覆分离层容易产生表面缺陷。在二氧化钛悬浮液中加入聚乙烯醇作为黏结剂,通过真空辅助抽滤法在不锈钢中空纤维基膜表面形成一层均匀的分离层。通过高温烧结得到了TiO₂/不锈钢中空纤维复合膜,考察了烧结温度对于TiO₂/不锈钢中空纤维复合膜表面分离层形貌和结构的影响。不同烧结温度时,TiO₂/不锈钢中空纤维复合膜的表面形貌有所差异;随着烧结温度的升高,不锈钢复合膜的孔径和纯水通量均先升高再下降。当烧结温度为500℃时,表面涂层均匀,孔径分布集中,水通量较高。最后,以SPT-500膜测试了水包油乳液分离效果,分离效率达到99%以上,且具有良好的抗污染性能。     

中空纤维膜萃取苯酚的传质及流动特性

以体积分数为30％的磷酸三丁酯＋煤油－水为实验体系，研究了中、高装填密度的中空纤维膜萃取处理苯酚衡溶液的传质效果和传质特性以及膜器壳程流动状况。实验结果表明，中空纤维膜萃取可以高效去除水中的苯酚，萃取率最高可达到99．9％。比较了总传质系数的实验值与多个传质系数关联式的预测值之间的偏差，发现从中、高装填密度膜器得到的传质关联式偏差较小，而从低装填密度膜器得到的传质关联式偏差较大。通过测量膜器壳程流动的停留时间分布曲线，证实了偏差是由于中、高装填密度的膜器壳程流动的复杂性造成的。     

A continuous‐effect membrane distillation process based on hollow fiber AGMD module with internal latent‐heat recovery

A continuous‐effect membrane distillation (CEMD) process was developed by equipping air gap membrane distillation (AGMD)‐based and strictly‐parallel hollow fiber module with internal heat recovery. Its performance was indicated by flux, performance ratio and evaporation efficiency. Two kinds of CEMD modules made from different membrane fibers were tested. A face‐centered central composite experimental design was conducted to investigate the influences of operating variables including cold‐feed temperature, hot‐feed temperature, and feed‐in flow rate on the performance. Within the studied experimental range, the maximum PR of 13.8 was obtained. A theoretical model based on governing transport equations was established to predict the process performance, and the model described the experimental data fairly well. In light of the model, possible ways to further increase PR were predicted. The dilute aqueous sugar solution was successfully concentrated 12‐fold to a final concentration of about 20 wt % by using CEMD process with a final PR of 8.2. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1278–1297, 2013