Design and Control of Trans-esterification Reaction Process for the Production of Diethyl Carbonate

• Main Authors: Yin-Chi Wang, 王銀吉
• Other Authors: I-Lung Chien
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/u87z23

碩士 === 國立臺灣大學 === 化學工程學研究所 === 107 === Break the azeotropes limits, increased conversion and reduced capital cost are well-known features of reactive distillation processes. An intensification design configuration of reactive dividing-wall column (RDWC) may be proposed to reduce equipment costs and energy consumption in conventional reactive distillation process. RDWC has both the advantages of reactive distillation column and dividing wall column and can avoid unnecessary energy consumption. In general, it is expected that the total annual cost will be lower by RDWC design compared with that of the conventional process. This research focuses on two topics about the production of diethyl carbonate (DEC). The first topic is that the thermodynamic parameters from previous paper are modified and redo the conventional process design for the production of DEC. Afterwards, RDWC design is proposed to not only reduce capital cost but also operating cost by eliminating remixing effect. As a result, the result shows that the TAC with RDWC design can be reduced by about 13% compared with that of the conventional process. Besides, further study finds that when the feed ratio of reactant is exactly at stoichiometric ratio instead of excess ratio, the reaction and separation task can be achieved by using only one RD column if the rectifying stages are increased. Hence, capital cost and operation cost can be dramatically decreased. The result shows that the TAC can be reduced by about 34% compared with that of the conventional process. Dynamic structure and control strategy are also discussed on one RD column design. Closed-loop disturbance tests are performed to confirm that when the ±20% flowrate disturbance or -10%、-20% feed composition disturbance enter the process, the distillation column can still hold the high-purity specifications of the two products. The results show that the feed flowrate and feed composition disturbance can be effectively eliminated with dual temperature control and feed forward control. The second topic concentrates on different design flowsheets for the production of DEC from the azeotrope composed of DMC and methanol. The azeotrope feed composition is from previous paper, and it contains 17.86mol% DMC and 82.14mol% methanol. There are four different design flowsheets in this topic. The first one is the conventional process which has four distillation columns. The second one is that RDWC design is applied to the conventional process. The third one is that the feed ratio of reactant for the production of DEC is exactly at stoichiometry ratio. All the above three design flowsheets separate the azeotrope firstly by extractive distillation, and then take excess ethanol to react with dimethyl carbonate. The fourth one is that ethanol is taken to react with this azeotrope directly to produce product DEC and methanol. Only one reactive distillation column is needed to accomplish the reaction and separation task. Although this proposed design method can decrease the complexity of the conventional process, it doesn’t have economic benefit because of its higher operating cost. The results show that the third design flowsheet has the lowest TAC and its TAC can be reduced by about 26% compared with that of conventional process. The third design flowsheet also has the highest earnings per year. This illustrates that the design flowsheet for the production of DEC from the azeotrope has more economic benefit when the azeotrope is separated firstly and then react with ethanol by stoichiometry ratio.