Study Of The Catalyst And Process For The Direct Synthesis Of Dimethyl Ehter

With the appearance of global tense situation about energy utilization and thedeterioration of the environmental problem in recent years, dimethyl ether (DME), which iscalled the"clean energy for 21st century", has gained more and more attention. The process ofdirect DME synthesis from syngas has great economical and social effect.In this paper, for the high conversion of syngas to DME, the catalyst for the direct DMEsynthesis is investigated. The catalyst research includes: (1) the effect of Li ofCu-Zn-Al-Li/HZSM-5 on the direct DME synthesis; (2) the effect of different methods for thecatalyst preparation on the DME direct synthesis; (3) the effect of reaction conditions on theDME direct synthesis. The results show that Cu-Zn-Al-Li/HZSM-5 has higher performance inthe DME direct synthesis, compared to Cu-Zn-Al/HZSM-5. The conversion of CO is 57.3%,the selectivity of DME is 65.68%, and the STY of DME is 0.228g-DME/g-cat/h, which isincreased by 137%, 2.2% and 22%, respectively. Compared to mechnical mixing,Cu-Zn-Al-Li/HZSM-5 prepared by precipitation sedimentation shows higher activity. Underthe condition of 533K,4.0MPa,3000h-1 , the CO conversion is up to 88.9%, and the STYofDME is up to 0.404g-DME/g-cat/h. With the increasing of temperature, the catalystperformance increases but then decreases. There is an optimal temperature for the direct DMEsynthesis. Among the range of 1 to 4 MPa, with the increasing of pressure, the catalystperformance increases. From 2500h-1, with the increasing of GHSV, the CO conversion, theselectivity of DME and the STYof DME decrease. Through XRD spectra, the main reason ofdeactiviation is the acticitydecrease of methanol synthesis catalyst.After the research of catalyst, with the help of data from experiment, the technologicalprocess for the DME direct synthesis is studied by Aspen Plus. Through the simulation andcalculation of technological process for 100 kt/a DME production, the conclusion is got asfollows: (1) The product of DME and methanol is got respectively. The mole flow of DMEproduct is 262.700kmol/h, the mass percentage purity is 99.8% and the percent recovery is96.4%. The mole folw of methanol product is 10.800kmol/h, the mass percentage purity is99.6% and the percent recovery is 96.3%. (2) By the results of Aspen Plus, the total energy iscalculated. In order to reach the seperation requirement, 83314.88MJ/h of heat energy,36544.98MJ/h of cold energy and 56.94t/h of cooling water are needed. (3) The calculation ofenergy is optimized. Through the optimization, no additional heat energy is needed, whichdecreases energy supply largely. (4) The top product of absorber, which contains a largeamount of combustible gas, is fed into the gas turbine.The generated electricityis 43kW.