Study On Single-Step Synthsis Dimethyl Ether (DME) By Phosphorus Modified Bi-Function Catalyst

The scale method for synthesis dimethyl ether (DME) is two-step method, ie. First, methanol is synthesized from the syngas, then the methanol dehydrate to DME. The process of two-step method for synthesis DME is not economic in kinetics and thermodynamics. The results from process by single-step synthesis DME in single reactor indicated:a double function catalyst had been increnced the conversion rate of CO and H2, but there is a problem that the activity temperature of synthesis methanol from syngas and methanol dehydration to DME is different in the catalyst system, and the activation of catalyst can not exert its catalysis maximum. Secondly, the basic material to synthesize cleanliness energy sources, DME, is from coal or nature gas, and it will consume the fossil energy sources in the Earth. But there are a large of tail gas contained high concentration CO to be discharge to air from the plant, which produce metal and nonmetallic with coal/coke or nature gas for reducer agent in the metallurgy and chemical industry, for example, yellow phosphorus tail gas, airproof calcium carbide tail gas, steel-making converter tail gas, oil refining tail gas, tail gas from portion oxidation of nature gas, copper wash relax gas of synthesis ammonia and so on. The usual treatment method about this kind tail gas is burning them and using portion heat, or burning by torch, which result is conversion the CO to CO2 to vent into air. How to using the invaluablener resource gas contained CO, reducing discharge, ease off the conflict of scarce energy sources and aggravating environment worsening, realizing saving energy and reducing pollution is very important in China.There are summarized about the synthesis technique and reaction mechanism of DME at home and abroad to be discussed and the research harvest about technological progress and basic theory of single-step synthesis DME from syngas was presented emphatically in this paper. This thesis discuss the single-step process for synthesis DME by modified bifunctional the catalysis in a slurry reactor, using the simulation syngas with high rate of CO/H2 contained CO2 from the yellow phosphorus tail gas via portion water-shift. The research included the phosphorus modified of catalysis, optimization of the technology condition in a slurry reactor, and study of the process dynamics and thermodynamics. A new modified bifunctional catalyst (C301/P-γ-Al2O3) is preparation with basic Cu (C301) catalyst for synthesis Methanol and modified dehydrate catalyst (P-γ-Al2O3) with H3PO4 dipping and calcinations. There are new O=P—O bond to be found in the modifiedγ-Al2O3 by analyse with FT-IR and X-ray diffraction, and it increase the pair acid-alkali in dehydrate catalyzer. And the modified bifunctional catalyst(C301/P-γ-Al2O3) enhance the capability of methanol conversion to DME, and increas the conversion rate of total Carbon and selectivity of DME, and restrain the by-reaction from CO to CO2.A optimum technology reaction conditions are obtained after study the transfer and reaction condition with the modified bifunctional catalyst (C301/P-γ-Al2O3) in slurry bed, namely,250-270℃of system temperature,4.3MPa of the system pressure,600mL/h·gcat of space time, H2/(CO+CO2)≈1.5,150ml of the inert solvent,7.3% of the catalyst to the solvent,750r/min of the stirrer rotate speed. When the modified catalyst was used for synthesis DME in slurry bed reactor from the rich carbon syngas cantained CO2, the conversion rate of CO achieved 95.90% and selectivity of DME is 60%., which is outclass the 34.61% of the selectivity in using the non-modified catalyst system. And it is ture that the production ratio of CO2 is reduced evidently, the methanol is little or none in production system.The relation equations about reaction heat and reaction balance constant with the system temperature were built by process thermodynamics analysis. The all reactions are exothermic reaction, and their balance constant will reduce when the reaction temperature increase, and the balance constant for methanol synthesis is most sensitivity, the CO/H2O shift reaction is secondly. The calculated value of total carbon and selectivity of DME are 72% and 95.4% by Matlab software from optimum equation about rich carbon syngas contained CO2 at 250℃, which closed to the experiment value. The calculate results prove single-step synthesis DME technology by P modified bifunctional catalyst (C301/P-y-Al2O3) from syngas contained CO2 will overcome the problem of the restriction of chemistry reaction balance.The kinetics modeling basic rich carbon syngas contained CO2 synthesis DME with the modified bifunctional catalyst(C301/P-y-Al2O3) in slurry bed reactor can be express with the combination of reaction rate equations about:1)syngas to methanol,2) methanol dehydrate to DME, and 3) CO-H2O shift to CO2. The reaction process mechanism is that CO and CO2 all are the Carbon resource to synthesis Methanol, the middle process include: 1) adsorbed CO/CO2 convert to intermediate, formate, and it continuous add H with adsorbed OH/H to methanol; 2) adsorbed methanol and isolate adsorbed methanol convert to DME; 3) the by-reaction are form by formate deoxidized to CO2 and adsorbed H convert to H2.The calculation data with kinetics model have a good inosculated with check-up by experimentation. It is be found that the CO2 in syngas can restrain the CO-H2O shift reaction, and increase the selectivity of DME. But excessive CO2 will be competed adsorption on the face of catlyzer with CO, and it will result the reaction rate decrease.A new analysis system with GC for analyzing complexity production gas in the single-step synthesis DME system was built, which change the side-by-side double column to tandem Prorapak Q and molecule sieve filled column, and the sample pass though the TCD detector twice. The analysis system and method have solved the problem which need sampling and insert sample time after time in experiment, and the trouble for conversion data, and it is make the analyzing reaction gas quickly and easy on-line.Anyway, using the resource for the tail gas contained high concentration CO to synthesis DME is an excellent path, which achieve saving energy, lowering energy consumption and reducing pollutants discharge. The modified of bifunctional catalyst by P can improved the matching temperature of the function group; and has a application worth practicality for synthesis DME from rich carbon syngas cantained CO2 in slurry bed; And the theorys about kinetics and thermodynamics have a guidance significance for scale in the industry.