【作者】 李奕川；

【导师】 沈本贤；

【作者基本信息】 华东理工大学 ， 化学工艺， 2014， 博士

【摘要】 丙烯双氧水直接环氧化制环氧丙烷绿色工艺是环氧丙烷产业转型升级、可持续发展的方向之一。论文在1500t/a丙烯直接环氧化中试试验基础上,开展丙烯直接环氧化制环氧丙烷节能降耗工艺技术研究,基于反应与分离工艺技术的进一步优化,实现系统能量的集成,节能降耗,增强丙烯直接环氧化工艺的核心竞争力。论文首先分析了1500t/a丙烯直接环氧化中试试验结果。结果表明,双氧水转化率达到90%～96%,环氧丙烷选择性达到90%～92%,催化剂累积运行4000h性能未见明显下降,环氧丙烷产品达到了国家标准GB/T14491-2001中一级品的技术要求；环氧丙烷生产的实际丙烯物耗为0.893t/tPO,而理论物耗为0.724t/tPO。其中丙烯转化为副产物的物耗为0.089t/tPO,占丙烯总物耗的9.97%；在产品精制过程中,反应精馏损失的环氧丙烷物耗为0.111t/tPO,即反应精馏除醛损耗的丙烯物耗为0.08t/tPO,占丙烯总物耗的8.96%。总计在消耗的丙烯原料中有18.93%的丙烯未转化为环氧丙烷产品。整个中试装置的750kPa蒸汽消耗量为12t/tPO,在溶剂回收塔中9.6t/tPO的甲醇蒸汽未得到有效利用。整个工艺在提高产物环氧丙烷选择性、优化产品精制流程和系统能量集成等方面存在技术进步的需求。在此基础上,论文采用催速试验考察了丙烯直接环氧化反应副产物及其杂质的形成因素。结果表明：以甲醇为溶剂的丙烯环氧化无法避免副反应的发生。减少反应生成的环氧丙烷与催化剂床层以及剩余双氧水的接触时间、控制催化剂床层的温度可减缓副产物生成。产物中的杂质乙醛是由工业用丙烯原料中带入的微量乙烯氧化生成的。考察的乙腈溶剂并不适合作为丙烯直接环氧化工艺的反应溶剂。同时建立了丙二醇单甲醚醚化副反应动力学方程：相关系数R=0.967。采用二维拟均相模型建立了中试单管固定床反应器的主反应动力学模型：相关系数R=0.990,采用Crank-Nicholson隐式差分格式法求解,定量模拟了中试单管固定床反应器床层温度分布与产物浓度分布。结果表明在床层入口处温升较大；当1500t/a丙烯直接环氧化中试反应器的进料质量空速为20h-1时,反应器出口的环氧丙烷选择性为89.9%。根据模拟结果优选液相进料质量空速为33h-1,产物环氧丙烷选择性可提高至93.1%。验证试验表明,当反应液相进料的质量空速从24h-1提高为32h-1时,环氧丙烷选择性可由90.6%提高至93.2%。其次,筛选了5A分子筛为吸附分离去除环氧丙烷产物中微量杂质乙醛的吸附剂,优化了吸附操作条件：液相进料质量空速1h-1,吸附温度15～20℃。得到了吸附分离杂质乙醛的脱附条件,循环脱吸附试验的结果表明,8次循环脱吸附后的环氧丙烷收率在92%以上,得到的环氧丙烷产品中乙醛浓度为0.0187%,乙醛脱除率达到了96.3%,达到了国家标准工业用环氧内烷GB/T14491-2001中级品对醛质量分数的技术要求。吸附剂可循环多次使用。在吸附分离杂质乙醛的过程中,环氧丙烷的物耗为0.085t/tPO。与反应精馏去除杂质乙醛工艺相比,吸附分离法有利于降低环氧内烷在产品精制过程中的物耗。再次,利用化工流程模拟软件优化了溶剂回收塔的模拟操作参数：溶剂回收塔的最优塔板数为13,最优进料位置为第8块板,再沸器最小负荷为0.7046MW。溶剂回收塔再沸器的蒸汽(750kPa)消耗量由10.5t/tPO下降至10.0t/tPO,节能率为4.8%a根据多效精馏原理设计并模拟优化了溶剂回收的双塔精馏流程。在优化的双塔精馏塔的操作条件下,溶剂回收高压塔再沸器的负荷为0.43MW,即溶剂回收区的750kPa蒸汽消耗量为6.016t/tPO,模拟能耗较单塔粘馏减少了39.01%。溶剂回收过程中单塔和双塔精馏的组分动态控制模拟试验结果表明,即使进料流量发生±10%波动时,单塔分离中甲醇产品的纯度能在10h内回到稳态值,双塔分离中甲醇产品的纯度能在15h内回到稳态值,且产品甲醇浓度波动幅度在±0.15%以内,控制效果好。接着,为了进步考察催化剂制备的放大效应,同时为了满足万吨级环氧内烷反应器对催化剂用量的需求,采用10m3晶化釜合成了TS-1分子筛,并通过成型等步骤制各了TS-1分子筛催化剂。从SEM、BET、XRD和FT-IR等的表征结果来看,10m3晶化釜合成的TS-1分子筛与2m3晶化釜合成的TS-1分子筛具有相同的物化性质。丙烯环氧化间歇和连续反应结果表明,10m3晶化釜与2m3晶化釜合成的催化剂的催化性能基本相当。综合催化剂物化性质表征以及催化性能评价结果,表明完全掌握了TS-1分子筛催化剂的放大技术,10m3规模制备的TS-1分子筛催化剂能够满足万吨级环氧丙烷反应器对催化剂量的需求。最后,在1500t/a丙烯直接环氧化中试成果以及研究结果基础上,对万吨级内烯直接环氧化工业装置的列管式固定床反应器、吸附分离塔以及溶剂回收双塔进行了初步设计,并在天津大沽化工股份有限公司建成了万吨级丙烯直接环氧化工业试验装置。但由于受时间与场地等条件的限制,在万吨级内烯直接环氧化工业试验装置中仍采用加添加剂反应精馏脱除环氧丙烷产物中的乙醛。万吨级内烯直接环氧化工业装置的开车试验结果表明,万吨级内烯直接环氧化工业装置能够为聚醚的生产提供合格的环氧内烷。与1500t/a内烯直接环氧化中试相比,万吨级内烯直接环氧化工业装置的环氧化反应产物选择性从90%～92%提高至92%～95%,双氧水转化率维持在90%～94%：生产每吨环氧内烷的内烯物耗从0.893t/tPO卜降至0.856t/tPO,降幅为4.14%;生产每吨环氧丙烷的750kPa蒸汽消耗量从12t/tPO降至7.72t/tPO,降幅达35.7%。有效增强了丙烯直接环氧化工艺的综合竞争力,为丙烯直接环氧化法制环氧内烷的进一步工业应用提供了基础数据和设计依据。更多还原

【Abstract】 The green technology that hydrogen peroxide to propylene oxide (HPPO) is one of the direction of propylene oxide (PO) industry transformation and sustainable development. In this paper, based on the results of1500t/a HPPO pilot-scale experiment, the technology of consumption reducing and energy saving in HPPO process was carried out. Upon the further optimizing of reaction and separation technology, with the aiming to integrate the energy system and reduce the material and energy consumption, it would pave the way to enhance the core competitiveness of the HPPO process.The results of1500t/a HPPO pilot-scale experiment were analyzed. It was showed that H2O2conversion was90%～96%, PO selectivity was90%～92%, and the catalytic performance of catalyst was no significant decline in the long run test of4000h. The PO products met the first grade technical requirements of industrial PO according to GB/T14491-2001. The actual consumption of propylene for one ton PO was0.893t, while the theoretical consumption is0.724t. The propylene consumption to byproduct was0.089t/tPO and, accounting for9.97%of total propylene consumption. In the process of product purification, the PO consumption was0.111t/tPO. That meant the propylene consumption was0.08t/tPO during the reactive distillation in order to remove the impurities of acetaldehyde, accounting for8.96%of total propylene consumption. There was accounting for18.93%propylene of total propylene consumption was not converted to PO product. Steam (750kPa) consumption of the pilot-plant was12t/tPO, and9.6t/tPO methanol vapor was not been effectively utilized in the solvent recycle process. Therefore, the selectivity of PO. the product refining technology and energy system integration in1500t/a HPPO pilot-scale process can be further improved.Firstly, the formation factors of by-products and impurities were investigated in propylene epoxidation by accelerated tests. It was showed that the byproducts were inevitable in propylene epoxidation reaction with methanol as solvent. The reaction of PO open-ring was promote with the existence of the catalyst and the rising of temperature, the etherification reaction of PO was accelerated by the existence of H2O2. Therefore, it would decelerate the formation of byproduct by reducing the contact time between PO and residual H2O2. and controlling the temperature of catalyst bed. The impurity of acetaldehyde was produced by the oxidation of trace ethylene which was in the raw material in the industrial propylene.. The acetonitrile solvent was not suitable for propylene epoxidation. At the same time, the kinetic equation of propylene glycol monomethyl ether (PGME) in etherification side reaction was established: its correlation coefficient was reached to0.967. The main reaction kinetic equation of PO in the single pipe fixed bed reactor of pilot-plant was then established according to quasi-homogeneous two-dimensional model: its correlation coefficient was0.990. The distribution of temperature and concentration in the catalyst bed were quantitative simulated by solving the model with Crank-Nicholson method. The results showed that temperature rise was considerable at the entrance of bed. When the WHSV of feed in the pilot-plant was20h-1, the selectivity of PO at reactor outlet was89.9%, but if the WHSV of feed was33h-1, the selective of PO could increase to93.1%. Verification tests revealed that when the WHSV of feed was from24h-1to32h-1, the selective of PO would be improved from90.6%to93.2%.Secondly,5A molecular sieve was selected as the adsorbent to remove the micro-impurity in PO product solution. The adsorption operating conditions were optimized: the WHSV of feed was1h-1and the adsorption temperature was15”20℃. The operating conditions of desorption were also investigated. Cyclic desorption and adsorption tests showed that the yield of PO was above92%, the concentration of acetaldehyde in the PO product solution was0.0187%, the removal rate of acetaldehyde was96.3%, the first grade technical requirements of industrial PO according to GB/T14491-2001was achieved. The PO consumption was0.085t/tPO during the adsorption of acetaldehyde removal. Compared with the method of reaction distillation, removing acetaldehyde by adsorption was better to decreasing the material consumption of PO in the process of product purification.Thirdly, the simulation operating parameters of solvent recycle distillation were optimized by chemical process simulation software of ASPEN PLUS:the tray number was13, the feed tray was the8th, and the minimum load of reboiler was0.7046MW. The steam (750kPa) consumption of reboiler was decreased from10.5t/tPO to10.Ot/tPO, the ratio of energy saving was4.8%. The double-column distillation of solvent recycle process were designed and simulated also by ASPEN PLUS. Under the optimized operation conditions of double-column distillation, the load of high pressure column reboiler was0.43MW, it meant the steam (750kPa) consumption of solvent recycle is6.016t/tPO, energy saving by39.01%compared with single-column distillation. The results of simulation dynamic control tests showed that even if the flow rate of feed fluctuated±10%. the methanol product purity of single-column distillation could return to steady-state value within10h, and double-column distillation could return to steady-state value within15h. The methanol product concentration fluctuated within±0.15%, it indicated that the control was fairly well.In order to further investigate the amplification effect of catalyst preparation, and meet the amount demand of catalyst for the10000t/a HPPO industrial trial,, TS-1molecular sieve was synthesized in10m3autoclave, and TS-1catalyst was prepared by extruding. TS-1molecular sieves synthesized in10m3autoclave and2m3autoclave had the similar physicochemical properties according to the characterization of SEM, BET, XRD and FT-IR, et al.. There was no obviously difference in the propylene epoxidation catalytic performances for the TS-1catalyst synthesized between10m3autoclave and2m3autoclave from the batch reactor and continuous fixed bed reactor It indicated that the amplification technology of TS-1catalyst preparation has been completely mastered, and the amount demand of catalyst for the10000t/a HPPO industrial trial can be achieved.Finally, the fixed tube array reactor, adsorption tower of removing impurity and two-rectification towers of solvent recycle for10000t/a HPPO industrial trial process was preliminary designed, respectively, and the10000t/a HPPO industrial device was built at Tianjin Dagu Chemical Co., Ltd. Removing the acetaldehyde impurity by reaction distillation was still used in this device due to the time and place. The running test results of10000t/a HPPO industrial device showed that qualified PO for producing PPG could be provided by the device. Compared with the1500t/a HPPO pilot-scale test, the selectivity of PO increased from90%～92%to92%～95%, the conversion of H2O2maintained at90%～94%, the material consumption of propylene decreased from0.893t/tPO to0.856t/tPO, the reducing rate was4.14%, and the steam (750kPa) consumption for HPPO plant decreased from12t/tP0to7.72t/tPO, saving by35.7%. The comprehensive competitiveness of HPPO process was effectively improved, and the basic data as well as design consideration for further industrial application of HPPO process were provided.更多还原