Preparation And Catalytic Performance Of Chlorine-free Copper Catalyst In Vapor Oxidative Carbonylation Of Methanol

As an environment benign green-chemical, dimethyl carbonate (DMC) is regarded as"new building block"in organic synthesis. It can served as green and safe substitute for phosgene and dimethyl sulfate, which are highly toxic and corrosive used in commercial chemical processes of methylatiion and carbonylation. In addition, DMC is also good solvent and additive in gasoline. In the all routs of DMC synthsis, vapor phase oxidative carbonylation of methanol to DMC has been considered as the most promising way because of its simple process, friendly environment and low cost.In the process of oxidative carbonylation of methanol in vapor phase, metal chloride supported catalysts have good activity but suffer from the quick deactivation and equipment corrison due to the loss of chlorine during the reaction running. Prepared by solid-state ion-exchange reaction of CuCl and acidic zeolite, the CuI/zeolite with low chlorine exhibited good activity and stability,but still suffer from the loss of chlorine. In this thesis, CuCl₂·2H₂O was used as substitute of CuCl to produce CuI/Y catalyst by solid-state ion-exchange reaction, and the preparation process and morphological structure of the CuI/Y catalyst were characterized. The supported Cu₂(OH)₃Cl catalyst were also studied. By aqueous ion-exchange reaction of Cu²⁺ and NaY zeolite or heat treatment of Cu₂(OH)₃NO₃/AC precursor, the chlorine-free copper catalysts were made and studied. The micro-structure, active species of catalysts were analyzed by CO-TPD, XRD, TG-DTG, XPS, SEM and EA technics. The obtained main conclusions are listed as following.(1) Under inert atmosphere, CuCl₂·2H₂O lost its crystal water below 200oC, and decomposed into CuCl and Cl₂ gas between 300°C and 550°C, then the formed CuCl sublimated above 550°C. The temperature of CuCl₂ decomposition to CuCl is in the range of of solid-state ion-exchange temperature between CuCl and HY zeolite.(2) CuCl₂·2H₂O can substitute CuCl to prepared CuI/Y catalyst by solid-state ion-exchange reaction. Under inert atmosphere, the CuCl₂ by dehydration of CuCl₂·2H₂O decomposed into CuCl and Cl₂ from 300℃to 550℃, the produced CuCl ion-exchanged with HY zeolite to form Cu/Y catalyst; the extra CuCl in the surface of catalyst sublimed above 550℃.(3) In the Cu/Y catalyst prepared by heat treatment of CuCl₂·2H₂O and HY zeolite, the Cu existed in the form of CuCl or CuCl₂ in the zeolite surface, while ion- exchanged Cu+ and little adsorbed CuCl in the zeolite cages. Comparing to the catalysts from CuCl and HY zeolite, the catalysts from CuCl₂·2H₂O and HY zeolite have lower Cu and Cl amount, but higher catalytic activity in the oxidative carbonylation of methanol in vapour phase, the space-time yield of DMC was 110mg(g·h), selectivity of DMC was 72.56%.(4) The catalytic activity and stability of Cu₂(OH)₃Cl supported catalysts were higher than that of CuCl₂ supported catalyst, activated carbon was the best support. The methanol conversion, selectivity and space time yield of DMC on the Cu₂(OH)₃Cl/AC of 18.71% Cu were 6.93 %, 67.3 % and 139.13 mg/(g·h) respectivly.(5) The dispersion property of Cu₂(OH)₃Cl in Cu₂(OH)₃Cl/AC catalyst was getting worse and the Cu₂(OH)₃Cl was transformed to CuCl₂ and CuO during the reaction, resulting in the decrease of catalytic activity. The unique Cuâ…¡ species in the fresh catalyst transferred into CuI species partially during the reaction.(6) The chlorine-free CuNaY catalysts prepared by ion-exchange reaction of NaY zeolite and Cu²⁺ aqueous solution were poor in catalytic activity. When the pH value of Cu²⁺ aqueous solution was adjusted to 12 by adding of ammonia, the copper ammonia complex was formed, and the catalytic activity and selectivity of DMC increased greatly.(7) With the adding of ammonia, the pH value of copper nitrate solution increased, the ion-exchanged Cuâ…¡and catalytic activity of the produced CuNaY catalyst increased consequently. The increase of catalytic activity was obvious when the pH value was between 3 to 10, and unconspicuous when the pH value was above 10.(8) Under inert atmosphere, the chlorine free CuO/AC, Cu₂O/AC or Cu/AC catalyst can be obtained by heat treatment of Cu₂(NO₃)(OH)3/AC precursor sample. When heated under 200°C, the main product on AC support was CuO. With heating temperature rising, the CuO turned to Cu₂O gradually. The Cu₂O/AC was obtained under 300°C to 400°C, and Cu0/AC was under 450°C.(9) In oxidative carbonylation of methanol in vapor phase, the catalytic activity of the catalyst by heat treatment of Cu₂(NO₃)(OH)3 /AC increased in the sequences of CuO/AC 2O/AC