Process Simulation Of Producing Propylene Glycol By Hydration Of Propylene Oxide By Reactive Distillation

At present, the hydration process of producing Propylene Glycol with Propylene Oxide and excessive Water were adopted by many producers home and abroad .The mole rate of Propylene Oxide to water is 15~20:l.The reaction occurred under the temperature of 180? to 235 ? and the pressure of 1~3 Mpa .Under this condition .the selectivity of the reaction is only 85% or so .And multi-evaporator must be used in the process, as a result, the process is not only complicated but also with high raw material consumption and low selectivity .New process of reactive distillation method which designed by Hunan Academy of Chemical Design of producing Propylene Glycol was adopted by Yunnan Yuxi Tianshan Chemical Corporation Limited .The process is with five columns continuos operation. The mole rate of Propylene Oxide to water is 1.5~3:1. The selectivity raised from 85%of the old process to over 95% of the new process. The consumption of Propylene Oxide dropped from 970Kg to 853Kg.In this article new design and optimization of the process of reactive distillation method was carried out by using ASPEN Process Simulation software.The process of producing Propylene Glycol was improved from five columns operation to three columns operation through simulation calculation method. The reactivity raised from 80.26% to 94.5% and the consumption of raw material reduced from 853 Kg of Propylene Oxide and 300Kg of Water to 736Kg of Propylene Oxide and 248Kg of water.The column of reactive distillation was improved from compound tower to sieve tray tower which is famous for its lower cost of equipment and simpler operation and cleaning .The optimized producing conditions of the reactive distillation column were found as follows :Top stage pressure of the column was 11 bar. Rate of raw material water to Propylene Oxide was 1.2:1.Residence time was 16 second. The locations of feed stages were 2 of Water and 8 of Propylene Oxide. The number of stage was 13.Special rules of reactive distillation were verified that more than one reactive zones existed in the column. Detailed analysis of the phenomena was carried out and thought that the concentration difference of reactant was the main reason which caused the difference of objective product on the stage.The high rate of water on the stage was verified that mixture of raw material was not the main reason related to reaction.