【作者】 黄秀辉；

【导师】 钱锋；

【作者基本信息】 华东理工大学 ， 过程系统工程， 2014， 博士

【摘要】 本文以工业精对苯二甲酸装置中以醋酸正丙酯为共沸剂的非均相共沸精馏醋酸脱水过程为研究对象,考虑溶剂醋酸中未反应的前体对二甲苯以及反应的副产物醋酸甲酯的影响及回收利用,从体系中所含五元混合物的相平衡及精馏特性入手,通过实验室相平衡实验,结合文献数据,关联获得了该体系中五元混合物系相平衡热力学参数,分析预测其多元相平衡行为及精馏特性,在此基础上建立了能正确描述实际超负荷工况的非均相共沸精馏醋酸脱水塔过程操作特性的工艺机理稳态模型,并在此模型基础上对关键操作参数进行了灵敏度分析,确定影响该醋酸脱水过程能耗的关键操作参数,分别对各单元设备及全流程进行了操作优化,确定了最佳操作条件,为提高现有生产装置的分离效率,降低能耗提供了严格的理论指导。主要研究内容如下：(1)选用循环法,利用Ellis平衡蒸馏器,通过测定对二甲苯+醋酸体系的相平衡数据与文献值对比验证了实验仪器和实验方法的可靠性,再在此基础上测定了文献中没有报道二甲苯+醋酸甲酯和对二甲苯+醋酸正丙酯以及文献数据不准确的醋酸甲酯+醋酸正丙酯三组二元体系等压汽液平衡数据,采用Herington的积分检验法对实验所得四组等压汽液相平衡数据的热力学一致性进行了检验,检验结果显示四组等压汽液平衡实验数据均满足热力学的一致性。(2)根据醋酸脱水过程中的醋酸+水+醋酸正丙酯+对二甲苯+醋酸甲酯五元体系的物系性质及特点分析,分别选择了HOC方程和UNIQUAC方程来修正体系汽液相非理想性。结合实验室测得的相平衡数据与文献数据,采用极大似然法关联了UNIQUAC模型中的二元交互作用参数,所得参数预测的汽液相平衡结果与测量数据吻合良好。在所得参数的基础上,通过三角相图及剩余曲线图讨论分析了本研究非均相共沸精馏醋酸脱水过程中五元体系的相平衡关系及其在各精馏塔中的精馏特性,为后面的模拟计算研究提供严格的理论指导及模型的初值预测参考。(3)建立了适用于非均相共沸精馏塔模拟计算的平衡级稳态机理模型,借助流程模拟计算软件Aspen Plus搭建了包括醋酸脱水塔、对二甲苯回收塔、倾析器和共沸剂回收塔在内醋酸脱水系统的流程模型,结合标准设计工况工艺数据,实现对该非均相共沸精馏醋酸脱水过程基于机理模型的流程模拟仿真。得到与流程数据吻合良好的模拟计算结果,关键流股的温度与流量误差大部分均在±3%以内,最大误差不超过±6%,验证了模拟计算该非均相共沸精馏醋酸脱水过程三塔体系所选用的热力学模型、关联拟合所得的二元交互作用参数、各单元模块模型及模拟方法的正确性。在标准设计工况流程模型的基础上,结合实际工况采集分析数据对模型进行修正,得到了能够正确描述该实际超负荷工况醋酸脱水过程的工艺机理及操作特性的流程模型,关键温度点以及关键组分的相对误差基本小于±0.5%,各流股流量误差小于士8%。在所得模型基础上,对该实际工况醋酸脱水过程影响能耗及分离效果的关键操作参数进行了灵敏度分析,灵敏度分析结果显示对醋酸脱水塔能耗影响最大的是回流(包括回流量、回流温度和回流中的醋酸甲酯含量)和塔釜水含量,低压饱合蒸汽进料直接影响对二甲苯回收塔的分离效果,共沸剂回收塔的分离效果也直接决定于其塔釜蒸汽量和侧线采出流量。(4)基于严格的机理模型计算,结合剩余曲线图、灵敏度分析及软件优化计算模块对工业醋酸脱水过程包括醋酸脱水塔、倾析器、共沸剂回收塔在内的三个单元设备分别进行了操作优化分析,在确保各单元设备的最优分离效果的前提下,以全流程总再沸加热量最小为优化目标,对该醋酸脱水过程进行了全流程操作优化,确定了以醋酸脱水塔釜水含量、醋酸脱水塔顶回流、倾析器操作温度、共沸剂回收塔塔顶采出量和中部侧线采出组成为关键操作变量。最后得到在最优操作条件下的醋酸脱水塔所需回流量大幅减少,釜水含量增加,醋酸甲酯回收率大幅提高,醋酸甲酯在流程内的累积量明显降低；醋酸脱水塔单塔每小时可以节约3.27吨低压饱合蒸汽,约合353万元每年,全流程每小时可节约2.56吨低压饱合蒸汽,约合276万元每年。可见本研究的优化策略使得工业醋酸脱水过程的分离效果得到了有效改善,能耗得到了明显降低,对工业实际过程的优化运行有良好的指导意义。更多还原

【Abstract】 In the production of pure terephthalic acid, tiny amount of reactant p-xylene (PX) and by-product methyl acetate (MA) may enter into the acetic acid (HAc) dehydration system through the feed stream. In this work, considering PX and MA as feed impurities in the industrial HAc dehydration process via heterogeneous azeotropic distillation using n-propyl acetate (NPA) as entrainer, the binary parameters for the thermodynamic model of the quinary mixture were obtained by correlating the phase equilibrium data from experiment and literature. The phase equilibrium behavior and distillation character of the quinary system in the process were predicted and analyzed. Based upon the phase equilibrium thermodynamics, the models of the actual overloaded HAc dehydration process were developed and the process simulation was conducted. Then the sensitivity analyses of key operation parameters were conducted, and the operation optimization of each plant and the whole process was carried out. All these provide a new technical guidance for the operation optimization in HAc dehydration process. The main contents of this paper are summarized as follows:(1) The vapor-liquid equilibrium (VLE) of four bianry systems of PX+HAc, PX+MA、 PX+NPA and MA+NPA were measured under atmospheric pressure using cycle method with Ellis ebulliometer, in which the system of PX+HAc was employed to verify the reliability of our experimental approach, and the other three systems are not credible or can’t be found in literature. To confirm the quality of experimental data, the thermodynamic consistency tests of the VLE data of these four systems were conducted with Herington’s area test method, and the results shows all the four systems pass the tests.(2) According to the physical property of the quinary mixture of HAc+Water+NPA+PX+MA, HOC and UNIQUAC models were chose respectively to compute the strong nonideality of vapor and liquid phase caused by the association of HAc. The binary parameters of the quinary mixture in the UNIQUAC model were regressed with the equilibrium data from experiment and literature using Maximum Likelihood Method, and the estimated results of phase equilibrium agree well with the measured data. Based on these regressed parameters, the distillation characters of the quinary mixture in the industrial HAc dehydration columns were analyzed by triangle phase diagrams and residuce curve maps (RCM), which provides rigorous theory guidance and initial value prediction reference for the further modeling research.(3) The equilibrium stage steady-state mechanism model of heterogeneous azeotropic distillation was developed, and the simulation of the industrial HAc dehydration system including HAc dehydration column, PX pure column, decanter and NPA recovered column under standard design condintion was carried out with Aspen Plus. The simulation results agree well with the process data with the error being in±6%, which indicates the correctness of the thermodynamic model, the regressed binary parameters, the mechanism model and the simulated method used in the reseach. Then the simulated process model of the HAc dehydration process under actual overloaded condition was was conducted by amending the model of standard condition using the process data collected from acutual prodution, and the model can accurately describe process mechanism and operating characteristics of the actual overloaded process with the error of simulation results within±8%. Based on the model, the influences of key operation parameters to the energy consumption and separation effect were analysed. The results show that the greatest impact to the energy consumption of HAc desydration column are the reflux and the bottom water content; feed flow of saturated steam direcly influencs the separation effect of PX pure column; and the separation effect of NPA recycle column directly depends on the flow rate of saturated steam and side-draw.(4) Based on the strict calculation of mechanism model, the operation optimization analysis of each plant (HAc dehydration column, decanter and NPA recycle column) was conducted using RCMs, sensitivity analysis and software optimization module. Then the operation optimization of the whole dehytration process was carried out with the minimum total reboiler duty on the basis of best separating effect as optimal object, and the bottom water content and reflux of HAc dehydration column, temperature of decanter, component of side-draw and flowrate of top distillate of NPA recycle column were choosen to be the key operating variables. Under the optimized conditions, there is3.27t/hr saturated steam (about3.53million Yuan) can be saved for the single HAc dehytration column and2.56t/hr saturated steam (about2.76million Yuan) can be saved for the whole HAc dehytration process. Operating under the optimal conditions will enhance separating effect and reduce the energy consumption and thereby increase profit, which provids effective theoretical guidance for the optimizing operation of actual process.更多还原