Study On Fixed-bed Sweetening Catalyst For Heavy Mercaptans Oxidation

Recently there arouse a problem that some heavy mercaptans (mercaptans with large molecular weight) which regenerated after FCC gasoline hydro-refined cannot be easily removed in some Chinese refineries. Aimed to solve this problem a study on improving the catalytic activity and other using performances of fixed-bed sweetening catalyst was made.The technique of“components impregnating in sync with surface activating”was firstly used to prepare the fixed bed sweetening catalyst. Following the schemed catalyst-making process, preparing conditions such as absorption capabilities of different active carbon carriers, the stabilities of different immersion liquid and adding methods of cocatalyst were investigated carefully. And it was confirmed that the newly prepared catalyst being made in the optimized conditions had a comparatively higher catalytic activity towards iso-thiols and heavy mercaptans.Using performaces of the catalyst including catalytic activity were investigated. It was indicated that newly prepared catalyst had higher catalytic activity than the three industrial fixed-bed sweetening catalyst. It also showed that newly prepared catalyst had higher mechanical strength, better bleeding-resistant performance and reserve stability. SEM results showed that CoPcS and alkali dispersed evenly on the surface of the carrier, formed a single layer on the surface and combined with the carrier surface firmly.The effect of factors such as mercaptan structure, mercaptan concentration, reaction temperature, cocatalyst content, water content and reserve atmosphere on catalytic activity had been studied respectively. Results showed that iso-thiols and heavy mercaptans could be harder to remove than that of normal and light ones. The higher the initial mercaptan concentration was the faster the catalytic oxidation rate would be. Within certain range, mercaptan catalytic convertions could be increased by elevating temperature. Catalytic activity of catalyst was different with changes of cocatalyst content and water content. Cocatalyst content of 0.002g/gcarrier and water content of 10%~20% were the optimize contents respectively. And catalyst would be much more stable in N2 atmosphere.The UV spectrum methods to detect the active component on fixed-bed catalyst carrier and in alkali solutions were established respectively. Effects of alkali concentrations and storage time of solutions on the determination of active component were investigated. Results showed that alkali concentration has little effect on the determination but the sample quantity did affect the accuracy of the determination. With the storage time of active component solutions prolonged, the active component could not distribute evenly in the solution because of the coagulation of some of the component, thus the accurate content of active component in the solution could not be determined. Calcination condition, sample quantity and catalyst type were investigated respectively. It was found that the optimize calcination condition was that catalyst must be under the temperature of 650℃for 6 hours, and the type of catalyst carrier did affect the determination of CoPcS and this method mentioned above can be only applied to analyzing catalysts with their carriers being easily to deal with.