【作者】 白跃华；

【导师】 刘家祺；

【作者基本信息】 天津大学 ， 化学工艺， 2005， 博士

【摘要】 催化裂化干气中含氢量非常可观,利用气体膜分离技术回收干气中的氢气的研究已成为关于能源和环境的重要课题之一。对于高渗透速率和高渗透选择性的PDMS/PS中空纤维复合膜的研制开发和氢气膜分离过程传质机理的研究都是非常重要的研究内容。本论文以从催化裂化干气中回收氢气分离过程为研究内容,采用PDMS/PS中空纤维复合膜对回收氢气分离过程进行了研究。选择聚砜(PS)中空纤维膜作为复合膜的基膜,为了弥补基膜致密层上的缺陷孔,选择透气性能优异的硅橡胶(PDMS)作为涂层材料。硅橡胶仅起到堵孔弥补缺陷的作用,起主导分离作用的是聚砜基膜的致密层。采用浸渍涂敷法制备了PDMS/PS中空纤维复合膜,用扫描电镜、红外光谱和TG/DTA等表征方法对硅橡胶涂层、聚砜基膜以及中空纤维复合膜的结构和性能等进行了剖析。其次,考察了基膜结构、基膜热处理温度、基膜热处理时间、PDMS浓度、催化剂用量、交联剂用量、交联时间和浸渍时间以及涂敷次数等因素对复合膜气体分离性能的影响。通过分析得到了最佳制膜配方和制膜条件,截留分子量为20000的聚砜基膜分离效果较好。还考察了不同原料气压力、原料气流速、透过气中氢气分压和操作温度等工艺操作条件下PDMS/PS中空纤维复合膜的气体分离性能,氢气渗透速率可以达到16.12GPU,分离因子在40以上。还研究了气体在复合膜中的传质机理,首次将原料侧和透过侧边界层阻力引入到Henis’阻力模型中建立了基于Henis’阻力模型和边界层理论的串联阻力模型。利用串联阻力模型对气体通过PDMS/PS中空纤维复合膜的传递过程进行了研究,估算得到PDMS/PS中空纤维复合膜的结构参数,揭示了边界层阻力对气体分离性能的影响,分析和考察了原料气流速、原料气压力和透过气中氢气分压等操作条件对阻力分布的影响,还分析了复合膜结构参数聚砜基膜致密层孔隙率、致密层厚度、致密层缺陷孔孔径和涂层厚度等对氢气渗透性能的影响,对PDMS/PS氢气分离膜的进一步改进具有理论指导作用。最后,建立了描述氢气膜分离过程的设计型数学模型,该模型是基于气体混合物的线性流速建立的,通用性优于文献中基于气体流量所建立的数学模型,可以广泛用于气体膜分离过程的模拟。采用四阶龙格-库塔法求解数学模型,研究了中空纤维丝长度、原料气处理量和透过气压力等对分离过程的影响。对采用PDMS/PS中空纤维复合膜从催化裂化干气中回收氢气的气体膜分离中试装置进行了初步设计,提出了中试装置设想和实验流程。更多还原

【Abstract】 The hydrogen of catalytic cracking dry gas is in very vast scale. Separation andrecovery of hydrogen using membrane technology is one of the most importantsubjects about energy and environment. PDMS/PS hollow fiber compositemembranes, which are the “resistance type” membranes, are the very suitable forrecovery of hydrogen from catalytic cracking dry gas. The preparation andapplication of PDMS/PS composite membranes and the mass transfer mechanism ofhydrogen membrane separation process are both very important. In this study,hydrogen recovery process from the catalytic cracking dry gas was investigated.Firstly, the polysulfone membrane is chose as the substrate layer, and PDMS is asthe coating layer material in order to cover the shortage in the dense layer of PS. Thedense layer of PS plays an important role in hydrogen separation process, but thePDMS layer only cover the shortage in PS dense layer. The PDMS/PS hollow fibercomposite membranes were prepared by dip-coating method. Some penetratingbehaviors of hydrogen through the composite membranes were discussed. Thestructure and properties of silicone rubber, polysulfone membrane and hollow fibercomposite membranes was analyzed by SEM, IR and TG/DTA methods.Secondly, the effects of polysulfone substrate layer and the silicone rubber coatinglayer on preparation process of composite membranes were investigated. The effectsof some factors, which are different structures of polysulfone substrate layer, thetemperature of heat treatment, the time of heat treatment, the number of coating andthe PDMS, catalyst and cross-linker concentration, on gas separation performance ofcomposite membranes also were discussed. The suitable formula and operationconditions for preparing the composite membrane were found, and the separationresult of the PS membrane whose cut molecular weight is 20000 was better. Theeffects of feed pressure, feed flow rate, the partial pressure of hydrogen in permeateand operating temperature on the gas separation performance also investigated, andthe hydrogen permeance and the separation factor could be to 16.12GPU and morethan 40, respectively.Then, a resistances-in-series model based on the Henis-Tripodi’s model and thetheory of the boundary layer for gas separation in composite membranes waspresented, in which the resistance of the boundary layer and the resistance ofmembrane have been taken into account at the first time. The composite membranestructure parameters were calculated according to the resistance-in-series model. Theeffect of boundary layer resistance on gas separation properties is investigated. Thenthe influences of feed flow rate, feed pressure, and the partial pressure of hydrogen inpermeate gas on gas permeability and selectivity of hollow fiber compositemembranes have been considered and analyzed. In our study, the effect of thecomposite membrane structure parameters such as the dense layer porosity of PSsubstrate, the thickness of dense layer, the average pore size of defects in dense layerand the coating layer thickness on gas separation properties are also discussed.Lastly, for PDMS/PS hollow fiber membrane, a countercurrent-flow design modelwas established which can describe hydrogen separation process. This mathematicalmodel was based on the gas linear flow rate and could be applied in more gasseparation processes, which was better than the model in most references. Thesimulation using the model is performed by changing the operating conditions and theoptimum operating factors and the required membrane area are investigated. Then thedesign proposal of this technique for industrial application was brought forward.更多还原