The investigation of solid-liquid reaction during preparation of raney-cobalt type catalysis

Raney metal type catalysts are prepared by leaching a reactive material out from alloys of catalytically active transition metals such as Ni, Co, Fe, Cu and reactive materials such as Al and Si with a concentrated alkaline solution. Raney metal catalysts are widely used for hydrogenation and dehydrogenation reactions. In this study, metal type Co-Al alloy consisting of 36 wt% Co and 64 wt% Al was prepared by melting cobalt and aluminum mixing then uniformally fallowed by quenching. The alloy prepared was powdered by using attritor, and then was sieved to obtain different particle sizes. Raney Co catalyst was prepared by leaching out aluminum from Co-Al alloy with sodium hydroxide solution. The structural properties of the alloy and the catalyst were determined by SEM, XRD and BET analysis. The leaching out aluminum from Co-Al alloy with an aqueous sodium hydroxide was studied in a 1000 mL stirred-batch reactor placed in a temperature controlled water bath. The effects of reaction temperatures of 10, 25 and 40°C), concentration of sodium hydroxide (2, 4 and 6 M), solid to liquid ratio (2, 3 and 4 g/L) and particle size (10-38, 45-53 and 53-100 ?m) on leaching were investigated by following the increase of the amount of aluminum in the reaction mixture. The amount of leached aluminum from the alloy was determined from the samples withdrawn from the reaction mixture at certain time intervals. Based on the central composite design method, the effects of temperature, concentration of sodium hydroxide and solid to liquid ratio on the leaching rate were also evaluated statistically, and a model with interaction terms was developed between the aluminum amount leached from the alloy and relevant parameters. Also, various model equations were tested against the experimental data, and the kinetic model best fitting the experimental results was determined.