| 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. |
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