Energy Integration And Optimization Of A Reactive Distillation System For Ethylene Glycol Production

Reactive distillation (RD) is a typical intensification technology of chemicalprocess, involving the reaction and separation within a reactive distillation column.Also, it is one of the most important issues in academic research and technologydevelopment of chemical engineering. In the study of reactive distillation, it has beenpaid much attention to synthesize ethylene glycol through the hydration of ethyleneoxide, because the selectivity of ethylene glycol has been significantly improved andthe heat of reaction can be fully used. In this paper, the reactive distillation processof synthesizing ethylene glycol through the hydration of ethylene oxide is studied,which focuses on the energy integration and optimization with the aid of ASPENPLUS simulation. In order to provide theoretical guidance and model for theoptimization of reactive distillation system, the engineering method of energyintegration and optimization is also studied.1.The conventional ethylene glycol reactive distillation process is simulated,with theoptimization of key parametersFirst, the relation between H2O/EO ratio and conversion of ethylene oxide aswell as selectivity of ethylene glycol is analyzed to obtain a proper H2O/EO ratio.The ratio is optimized with the target of minimizing the total heat duty of reactivedistillation column and water recovery column. It turns out that H2O/EO ratio is2:1,not1:1written in other papers. Second, the distribution of liquid holdup in reactivesection, the feed tray locations of ethylene oxide and the number of stages areoptimized in order to minimize the heat duty of the reboiler. The results indicate thatthe heat duty is minimal when the total number of stages is11and the feed traylocation is6. Third, the reaction heat effects and the influence are analyzed.Theresults obtained shows that, in the convenional design of RD column, in which thereactive section is superimposed onto the stripping section, the heat of reaction isfinally removed from the condenser by the cooling medium, i.e., the heat of reaction has not been directly utilized in the RD column for improving separation operationor reducing the heat duty of reboiler.2. Thqe reaction, separation and integration of the ethylene glycol reactive distillationsystem are studied, and a systematic methodology is built in order to make full useof the energy in the system.According to the features of ethylene glycol reactive distillation system, thetechnologies of heat pump and internal heat integration are applied into theprocess.Six process schemes are proposed, with detailed analysis and comparisonson energy savings. First, one of the most important approaches of reducing theenergy consumption in the ethylene glycol reactive distillation column is to decreasethe operation in the ethylene glycol reactive distillation column to decrease theoperating temperature of thr rebolier as much as possible. In order to achieve this,the reactive section and stripping section should be separated with the reactivesection operated in high temperature and high pressure, which the stripping sectionin low temperature and low pressure. Second,66%of energy and above can be savedby simultaneously adopting the external heat integration (to match the heat duties ofthe condenser and rebolier) and internal heat integration (to remove the heat ofreaction from the reactive section into the stripping section). Third, by exploiting theheat of the ethylene oxide hydration reaction, the rebolier in the reactive distillationsystem can be removed, with a small amount of electricity power required by thecompressor. Not only can the energy consumption be reduced, but also the capitalinvestment.The proposed methodology provides theoretical guidance and model for theoptimization of ethylene glycol reactive distillation column. Furthermore, it can beextended to the optimization of other internally heat-integrated reactive distillationcolumns, especially those with heat integration of reaction.