Controllable Preparation Of Sulfur-tolerant Pd Catalysts Under Microwave Irradiation And Application Of These Catalysts In One-step Synthesis Of Dimethyl Ether

Dimethyl ether (DMA) is an important chemical, used in many areas, therefore, production of DME have attracted ever-increasing attentions. Direct syngas to DME (STD) is especially suitable for industrial production of large-scale coal-hased syngas conversion, which can break the limit of thermodynamic equilibrium in themethanol synthesis, greatly improve the conversion rate of raw materials, reactivity under very mild reaction condition. Today the integrated gasification combined cycle (IGCC) is a new process schemes for the synthesis of DME from coal. However, IGCC syngas still contains at least 40 ppm sulfur if desulfurized by acid gas removal technologies, while commonly used Cu/ZnO/Al₂O₃ catalysts for CH3OH synthesis do not tolerate more than 0.1 ppm H2S, thus developed sulfur-resistance catalyst to shorten the production process are significant to develop DME poductions industry. At the same time, utilizing modern microwave technology to shorten the catalyst preparation process, and realize the controllable preparation of catalyst, which has a very high theory value for the application of microwave to catalysts preparation technology. According to the development of the STD technology, in this work, the hybrid catalyst preparation of Palladiuman (Pd) metal-support for DME synthesis by microwave technology has been studied and developed, which has a good effect of sulfur tolerance. All research is divided into following three sections.Firstly, Pd metal-support catalyst for STD reaction has been researched. Three series of Palladiuman catalysts supported on different carriers,γ-Al₂O₃, HZSM-5 and Al-MCM-41 respectively, were prepared by impregnation. The properties of catalysts, such as surface phase structure and adsorption, reduction properties, surface acidity have been controlled by changing calcination condition, Pd loading, or single and binary promoters and its added amount. The relationship between STD reactivity and the intrinsic characteristics of the catalyst had been investigated. The results show that there are different optimum preparation conditions and promoters for the Pd catalysts with different carriers. The suitable microwave power of Pd/γ-Al₂O₃, Pd/HZSM-5 and Pd/Al-MCM-41 catalysts is 420 W, 560 W and 560 W respectively. And the best preparation conditions for Pd/γ-Al₂O₃ series catalysts is 2%CeO₂ -1%ZrO₂-2%Pd, Pd/HZSM-5 series catalysts is silicon-aluminum ratio 50 and 2%CeO₂-1%CaO-2%Pd and Pd/Al-MCM-41 series catalysts is 0.4molSO42-1%ZrO₂-2%Pd. By coMParison, 2%CeO₂^-1%CaO-2%Pd/HZSM-5 has higher stability and better catalysis ability, over which the DME space-time yield could reach 34.75 mmol·g^-1·h^-1.Secondly, the sulfur-tolerant mechanism of Pd catalysts has been researched. The STD activity of catalysts after the process of sulfur poisoning with H2S or thiophene and regeneration with syngas has been investigated, the influence of carriers type and promoters type on the catalysts'sulfur tolerance has been analysis, the catalysts'structure and the reactants'chemical structures were characterized based on various characterizations, and then the adsorption patterns and characteristics of sulfide on Pd metal active sides and acid active sides were revealed. It was found that the stronger of Bronsted acid on the carrier, the weaker reaction ability between palladium and sulfide, and the less formation of combinable sulfur, ultimately, the sulfur-tolerant performance of Pd metal was improved. Adding CeO₂ or CeO₂-CaO promoters can reduce Pd metal sulfide of CeO₂-CaO-Pd/HZSM-5 catalyst, improve the acid sides retention rate of regeneration catalyst and thus effectively improve sulfur-tolerant performance of CeO₂-CaO-Pd/HZSM-5 catalyst.Finally, adsorption position of organic sulfur poisons and inorganic sulfur poisons on in CeO₂-CaO-Pd/HZSM-5 catalyst was determined based on GC-MS, and the possible transformation mechanism of sulfides on catalyst were suggested.Finally, the kinetics of STD reaction over CeO₂-CaO- Pd/HZSM-5 catalyst has been researched. Because owing to good STD reactivity and sulfur tolerant, STD process conditions over CeO₂-CaO- Pd/HZSM-5 catalyst was further studied. The results show that the best process conditions are: reaction temperature 240³00 oC, reaction pressure 3⁴ MPa, weight hourly space velocit 2000³000 L·kg^-1·h^-1 and n(H₂)/n(CO)=2:1. The kinetic equations for STD reaction over CeO₂-CaO- Pd/HZSM-5 catalyst in a fixed-bed reactor within the process conditions above were established. Statistical test shows the data calculated by the mechanism models are consistent with the experiments, so these models are reliable. 73 figs., 42 tabs. , 167 refs.