Preparation Of Raney-Ni/Al₂O₃ And Reasearch Of Its Application On Coking C₉ Hydrogenation

Coking C₉,as the main fraction of coking benzene?30%wt?,contained large amount of unsaturated compounds such as alkenl aromatics and indene etc.Therefore,most of coking C₉ was burned directly since unsaturated compounds could be oxidated and polymerized automatically in room temperature,which generated large amount of gum and lowered its oxidation stability.Hydrogenation was a proper method to enhance the utilization efficiency of coking C₉ since the unsaturated compounds were converted into alkylbenzene and indane during this process.Generally speaking,Ni catalysts were applied to hydrogenation process whereas few reports emphasized application of Raney-Ni/Al₂O₃on hydrogenation of coking C₉.Therefore,in this paper,preparation of Raney-Ni/Al₂O₃ catalyst and its application on hydrogenation of coking C₉ were studied in order to prepare a kind of catalyst which could be applied on fixed-bed reactor.Ni-Al alloy powder and pseudo-boehmie powder,as raw materials,were peptized and extruded to little strips initially and then,a series of supported Raney-Ni/Al₂O₃ catalysts with certain compressive strength could be achieved by means of calcinating those strips and activating calcinated precursors in sodium hydroxide solution?leaching process?.XRD?SEM?TG-DTA?BET?H₂-TPR?XPS as well as strength tester were applied to characterize the catalysts and hydrogenation of indene was served as probe reaction so as to evaluate the catalytic performance of catalysts.As a result,calcination atmosphere had significant influence on catalytic performance of Raney-Ni/Al₂O₃ catalyst.The precursor calcinated in argon exhibited better hydrogenation activity than the one calcinated in air since NiAl₃ could not transform to Ni₂Al₃ under anaerobic conditions.Leaching process gave higher surface area and pore volume with 113.2m²·g^-11 and 0.245cm³·g^-1,reapectively.Indene conversion reached the highest point at 91%during 30-hour reaction period and the compressive strength of catalyts was as high as33.9N·mm^-11 when the mass ratio of Ni-Al alloy powder and pseudo-boehmie powder was 6:4.Furthemore,since phase transition from NiAl₃ to Ni₂Al₃ is difficult when the precursor calcinated at 800?,the catalyst exhibited high surface area(123.2m²·g^-1)and low crystalline aggregation and thus indene conversion arrived at 90%during 30-hour reaction period.Nevertheless,the catalyst showed lower compressive strength of mere 28.4N·mm^-1 since lower Ni₂Al₃ content decreased the compressive strength.Besides,effect of leaching temperature on physicochemical properties of catalyst was also taken into consideration.Higher leaching temperature promoted the reaction between Ni₂Al₃ and sodium hydroxide solution,which gave more skeletal Ni and resulted in higher indene conversion.Nevertheless,excessive high leaching temperature always resulted in low Ni₂Al₃ content and as a result,the inferior compressive strength.Thus,the optimal leaching condition was summerized as follows:Temperature=50?,Time=4 h,Concentration=20%.The conversion of indene remained stablie at just over 95%during30-hour period under such leaching condition and the compressive of catalyst reached 35.0N·mm^-1.Technological conditions of coking C₉ hydrogenation,which was catalyzed by Raney-Ni/Al₂O₃ catalyst obtained by the method mentioned above,were investigated.As a result,reaction temperature was of significant inportance to catalytic activity.Indene conversion was as high as 95%when the reaction eas carried out at the optimal operation conditions:T=220?,P?H₂?=2.5MPa,LSHV=3.0h^-1and hydrogen-oil ratio=200:1.