【作者】 陈礼科；

【导师】 赵玲； 袁渭康；

【作者基本信息】 华东理工大学 ， 化学工程， 2013， 博士

【摘要】 聚酯多元醇是生产聚酯型聚氨酯主要原料之一,现有的聚酯多元醇工业生产均为间歇搅拌釜合成工艺,虽然其生产产品种类灵活,但产品质量不稳定,影响了后续聚氨酯产品的生产加工,同时由于传质传热受限,反应时间长,如合成己二酸系列聚酯多元醇产品需要20多小时。采用连续工艺合成聚酯多元醇,特别是聚己二酸乙二醇酯(Poly ethylene adipate, PEA)等产能较大的聚酯多元醇品种,一方面可使生产过程和产品质量更加稳定,另一方面通过匹配高效的传质传热设备可以显著提高过程能效。为此本研究构建了新型的连续塔式反应器-6级串联鼓泡反应精馏塔(Bubble Reaction Distillation Tower, BRDT),成功实现了制备分子量2000左右PEA的连续酯化过程和连续缩聚过程,总反应时间只需6小时。本文从PEA制备过程的反应动力学、新型反应器BRDT的构建及其流体力学性能、BRDT中PEA酯化和缩聚过程的连续化模试实验研究、连续酯化过程和连续缩聚过程的建模及优化、连续反应过程全流程模拟等方面开展了较系统的实验和模拟计算研究,为PEA连续化制备提供了关键技术和系统数据：1、采用间歇实验考察分析了反应温度、醇酸摩尔配比、反应压力、催化剂种类及添加量等对PEA酯化过程和缩聚过程影响,在乙二醇(EG)和己二酸(AA)醇酸配比1.2、常压、160～230℃温度范围研究了不外加催化剂的PEA酯化过程反应动力学,综合考虑了酯化反应和缩聚反应及其逆反应水解反应和醇解反应,基于AA和EG酯化过程中酯化反应催化机理的不同,分别建立了二级、变级数、三级等3个酯化过程反应动力学模型。在真空、160～230℃温度范围研究了25ppm钛酸异丙酯(TPT)催化的PEA缩聚过程反应动力学,基于有外加催化剂存在下酯化和缩聚反应均为二级反应建立了动力学模型。同时通过动力学模型检验和辨识,发现无论是酯化过程还是缩聚过程,二级反应动力学模型均可很好地表征PEA反应过程。2、基于PEA制备过程反应特征和物系特性认识,构建了新型的连续塔式反应器-6级串联鼓泡塔,耦合了酯化／缩聚反应和移走可逆反应生成的小分子水的精馏过程。通过特殊设计的塔盘结构,实现反应器内气液流动、停留时间、压降等可控。流体力学实验验证了常压和真空条件下液体于塔式反应器中可以由上级塔盘溢流经降液管流至下一级塔盘,气体通过气管由下而上,与向下流动的液态物料逆向流动鼓泡向上,各个塔盘由于气体的剧烈鼓泡而达到充分混合,单个塔盘接近于全混,多个塔盘串联的整个反应器趋向平推流：气管的直径大小是反应器稳定操作的关键。3、实施了BRDT中制备低分子量PEA的连续酯化过程和连续缩聚过程模试,成功得到羧基浓度小于1mo·kg-1的酯化过程齐聚物和分子量2000左右、羧基浓度小于0.02mol·kg-1的缩聚过程PEA产品。建立了BRTD中PEA连续酯化过程和连续缩聚过程数学模型,实验值与模拟计算值平均相对偏差分别小于14%和19%。在模拟考察反应温度、反应压力、停留时间、醇酸摩尔配比、氮气流量等操作因素影响的基础上,结合模试实验确定了连续酯化和连续缩聚的最优工艺条件：对于连续酯化过程,常压且6个塔盘反应温度分布160℃、180℃、200℃、220℃、230℃、230℃,EG和AA摩尔配比1.2,塔底N2流量100ml·min-1,各塔盘停留时间35min；对于真空连续缩聚过程,塔顶压力2000Pa,6个塔盘反应温度分布220℃、230℃、230℃、230℃、230℃、230℃,塔底N2流量100ml·min-1,各塔盘停留时间30min。4、进行了聚酯多元醇PEA连续反应过程全流程模拟分析。考察了缩聚过程塔顶气相EG和水的循环对整个反应过程的影响,相比EG和水不循环及EG循环、水不循环过程,缩聚阶段EG和水同时循环过程最优,连续酯化阶段进料的醇酸配比可由1.2降低至1.095,酯化过程各塔盘停留时间由35min降低至30min,最终PEA缩聚产物分子量Mn为1960,羧基浓度为0.0181mol·kg-1,整个连续工艺流程更为简易和经济。更多还原

【Abstract】 Polyester polyols are macroglycols prepared by the condensation of a glycol and a dicarboxylic acid or acid derivative, which can further react with isocyanates to produce polyurethane. Nowadays industrial technologies for the manufacture of polyester polyols all use batch stirred tanks, which are benefit to the flexibility of products, but reduce the stability of product quality. Moreover, due to the limited heat and mass transfer, the batch industrial reaction time of adpic acid series polyester polyols need more than20hours. A continuous process for the preparation of polyester polyols has been developed in this thesis. An innovational six-stage bubbling reactive distillation tower (BRDT) reactor has been constructed to perform both esterification process and polycondensation process, and the total residence time for the preparation of poly (ethylene adipate)(PEA) with average molecular weight (Mn)2000is significantly shortened to about6hours.Many aspects including the reaction kinetics of PEA esterification process and polycondensation process, the principle for the construction of BRDT and the hydrodynamics of BRDT, hot model experiments for PEA continuous esterification and polycondensation process in BRDT, the modelling and simulation optimization for polyester polyols continuous synthetic process in BRDT have been studied, which provide the key technologies and basic data as well as strategies for the development and optimization of PEA continuous process.First, the effects of different parameters (including reaction temperature, feed ratio of alcohol and acid, reaction pressure, different kinds of catalyst, the catalyst dosage, et al.) on PEA esterification and polycondensation process were investigated. Under the conditions of temperature range160～230℃and feed ratio of1.2at atmospheric pressure, the second-order, shift-order and third-order reaction kinetic models for the direct esterification process between AA and EG without additional catalyst had been developed on the basis of different catalytic mechanisms of esterification reactions. Under the conditions of temperature range160-230℃, pressure2kPa and in the present of additional25ppm catalyst of tetraisopropyl titanate (TPT), the second-order kinetic model for PEA polycondensation process had been developed. Model identification results showed that the second-order model could well express the kinetic feature of both esterification and polycondensation process.Second, an innovational six-stage BRDT was constructed to perform PEA esterification and polycondensation process, which coupled reaction with distillation to remove by-products efficiently. In this tower reactor, the liquid/gas flow, residence time and pressure drop could be manipulated using special tray structure with liquid downflow and gas upflow pipes. The visual cold model experiments showed that the liquid flowed through each tray from the top to the bottom, and was discharged from the bottom of the column, while gas passed the trays from the bottom to the top. The flowing fluid on the column trays had little dead zone due to the intensive bubbling effect of the gas, ensuring there optimum intermixing. Each column tray acted as a CSTR, and the fluid through multi-stages tended to be plug flow. The diameter of gas pipe in column tray was the key factor for stable operation of this kind reactor.Third, a bench scale BRDT was built to carry out the continuous esterification and polycondensation process respectively to prepare low-molecular-weight PEA. The esterification oligomers with carboxyl groups less than1mol·kg-1and polycondensation products with Mn about2000as well as carboxyl groups less than0.02mol·kg-1had been obtained successfully. A comprehensive mathematical model for PEA continuous esterification and continuous polycondensation process in BRDT was developed; the calculated results were in good agreement with experimental data. The influence of the major operating conditions on reactor performance was further simulated, it was found that the optimal operating conditions as following:the temperature distribution was160,180,200,220,230,230℃, residence time for each column tray35min, feed ratio1.2, reaction pressure1atm, nitrogen flow rate100ml min-1for continuous esterification process; and the temperature distribution was220,230,230,230,230,230℃, residence time for each column tray30min, reaction pressure2kPa, nitrogen flow rate100ml min-1for continuous polycondensation process; these optimal conditions were also verified experimentally.Fourth, the whole flow sheet of PEA continuous process was simulated. The influence of the circulation of water and EG from polycondensation process was calculated, compared with no water and EG circulation and only EG circulation, after both water and EG generated in polycondensation process were recycled to the esterification process, the feed ratio could be decreased from1.2to1.095and the residence time of each column tray could be decreased from35min to30min in esterification process, therefore the whole process became more simple and economical.更多还原