Catalytic Hydrocarboxylation Of Acetyent To Acrylic Acid Over Nickel-base Catalysts

Acrylic acid, as one of the most important polymer monomers and basic organic chemical raw materials, is present synthesized mainly by partial oxidation of propene from petroleum route in the industry. To expand the application field of coal and acetylene chemical and to dissolve the fact that the commercial production of bulk chemicals in China excessively depends on oil and foreign technology, it is urgen to speed up the diversification of raws and products. Reconsidering acetylene as a feedstock for the production of acrylate provides at least a useful complement to now petroleum route. The hydrocarboxylation of acetylene is deemed as an ideal "atomic economic reaction" and conforms to the principles of "Greeen Chemistry". Currently, the traditional homogeneous catalytic processes encounter many problems such as the seperation of product and catalysts, the volatilization of highly toxic nickel carbonyl, the corrosion of strong acid additives and the environmental pollution caused by acid emission, it is vital to develop heterogeneous catalysts to avoid these issues. Because of the lack of fundamental research for this process, we firstly focused on the study of homogeneous catalysts, the factors for casusing sediments and its structure properties were investigated, and next a series of metal-modified zeolites and metal oxides were prepared, their catalytic performance were evaluated after characterization by PSD,SEM,XRD,Raman, BET,ICP-AES,XRF,TG,FTIR,NH3-TPD,H2-TPR and XPS. The catalytic mechanism was proposed after the detailed exploring the structure-activity relationship of catalysts. The mainly research contents are as follows:Firstly, the homogeneous catalyst systems were investigated in this thesis. The results showed that the nickel salts constituted the active site, while the copper salts only worked as additive, and the latter was the mainly factors for causing the production of acetaldehyde and sediments. The 120h of steady test in a tubular reactor showed that 80% of acrylic acid yield and only 6% of acetaldehyde yield could be obtained under the following optimized conditions:temperature between 240 and 250℃;total pressure of 8MPa; residence time of 0.5h; the volume ration of THF/H2O and CO/C2H2 is 6 and 1.3, respectively; the mass fraction of Ni2+ and Cu2+ is 0.1% and 0.05%, respectively. Characterization of sediments indicated that different kinds of sediments with different morphologies were found, which belong to different carbon types. Most of them could be assigned to "soft coke", while these few "hard coke" should be removed at higher temperature.Base on the previous studies, NaY zeolite was chosen as support, and NiY, CoY, FeY and CuY zeolites were prepared by liquid phase ion exchange method. The performance of modified zeolits showed the following order:NiY>CoY>FeY(≈CuY≈NaY≈0). A large amount of polymers were found when using CuY as catalyst. The characterization resutls showed no obvious structure changes, while the total amount of acid and acid types were greatly affected after the introduction of metal, and the types of metal played a decisive role in the performance. To further investigate the effect of preparation methods, NiO/NaYand NiY were prepared by wetness impregnation and ion-exchange, respectively. It was found that the catalytic performance of NiY was much higher than that of NiO/NaY, and the nickel state on the zeolite had great influence on the catalytic reaction. The catalytic reaction rate increased as the increase in the exchange degree of zeolites and initial total pressure, the optimal reaction temperature was 235 ℃, and a certain of acidity favored the carbonylation. Characterization indicated two different types of coke, mainly locating outside the zeolite crystals and thus makes NiY maintain a higher reusability.Next, the MCM41 with higher surface area and pore volume was synthesized by hydro-thermal method in an autoclave. Catalysts such as Ni-MCM41, Ni-β, Ni-ZSM-5 and Ni-IM-5 were prepared by ion-exchange. Their catalytic performance decreased in the order of Ni-MCM41(2.1%)>Ni-β(4.1%)>Ni-IM-5(1.3%)>Ni-ZSM-5(1.5%). Characterization confirmed that the catalytic activity increased as the increase in the molar ratio of Ni2+/acid sites, and both metal center and acid center constituted the active sites. The catalytic path includes the activity of gas molecules and its adsorption to metal center, and then the migration and insertion of carbonyl into nickel-acetylene bond and lastly the attack of nucleophilic reagents.Subsequently, the Ni2O3/CuBr2 combined catalysts were detailed investigated. The comparison of activity among Ni2O3 and other various catalysts followed the sequence of Ni2O3>Ni(OAc)2>NiCl2≈NiBr2>NiO>Ni(NO3)2>Ni(OAc)2/PPh3/MSA> Ni(=0). The activity as high as 764.6molAA/(molNi·h) was obtained when reacting 0.1g Ni2O3,0.8～1.0mM/L CuBr2,15ml water,150ml acetone,235℃.1.5 moral ratio of CO/C2H2,4MPa of initial total pressure, and 15min reaction time. The Ni2O3 catalyst could be reused at least five times without obvious loss in activity, and the characterization of reacted catalysts revealed that the state of nickel remains unchanged during the reaction, and the coke belongs to "soft coke"Lasty, nano-NiO with different morphologies and particles sizes and Bi2O3-modified NiO were prepared by precipitation. It was found the the NiO with flower-like, plate-like and sphere-like structures was respectively obtained by using urea, ammonium hydroxide and sodium carbonate as precipitator. The reduction temperature depends on the morphology and grain size, while the catalytic performance of NiO only increases with the decrease in the grain size. The introduction of bismuth oxide would change the physical and chemical properties of NiO. Specifically, it will disperse, stabilize and reduce the NiO grain size, the morphology of NiO becomes regular sphere shapes from irregular structure, and the decrease in the particle size makes it easy to be reduced. The catalytic performance of Bi2O3/NiO depends on the content of Bi2O3, and a composite oxide catalyst with 11.1wt% of Bi2O3 showed significantly higher activity of 788.5 molAA/(molNi·h). The "synergistic effect" of copper salts and Bi2O3 would lead acetylene to adsorp to the metal center with the best activation state, and thus promote the carbonylation reaction.