Study On Preparation Of Solid Base Catalyst And Its Capabilities Of Mercaptan Oxidaion

At present,Merox sweetening craft is adopted by most processing plants around the world. In this kind of sweetening craft, liquid alkali is used as the catalyst. As a result, great deal of spent alkali as a hazardous material to environment is produced. Under this situation, people turn to solid base catalyst as the most effective way to replace the liquid alkali to solve the problem of environment pollution. Through study on LPG (liquid petroleum gas) sweetening, the author of this paper discussed preparation methods of the solid base catalyst, its capabilities of removing mercaptan and its industry application feasibility.Mercaptan oxidation catalyst of different Mg/Al mole ratios was prepared by coprecipitation method and mixed method. Moreover, influence of sour gases as impurities in LPG, diffusion resistance of the oxidation reaction, pretreatment temperature of the catalyst, and addition of NiO as cocatalyst into the catalyst were discussed. It was proved out that: (1) Compared to coprecipitation method, the solid base catalyst prepared by mixed method had higher activity and stability. And furthermore, it was not ready to adsorb carbon CO₂ and H₂O in air and lose its activity. (2) Although increase of Mg/Al mole ratios of the catalyst could strengthen the basicity of the catalyst and speed up the oxidation reaction, the catalyst of higher Mg/Al mole ratio was more ready to adsorb CO₂ and H₂O in air and lose its activity. (3) Addition of NiO to the catalyst could not only increase its activity but also improve its stability. Results of CO₂-TPD experiments showed that the kinds of basic site increased when NiO was added into the catalyst. XRD technique was also used. And the result showed that the diffraction peaks of the catalyst were broadened. Accordingly, we could conclude that Ni^{2+} in the catalyst occupied the position of Mg^{2+}, which led to crystal disfiguration of the catalyst so as to change its surface properties.(4) The deactivation mechanism of the catalyst was as following. Firstly, Sour impurities such as H₂S and CO₂ in LPG led to deactivation of the catalyst. Secondly, the catalyst adsorbed the reaction product RSSR and lost its activity. And at last, the residua of heavy oils in LPG walled up the tiny bores in the catalyst.(5) In addition, the author of this paper explored the regeneration of the deactivatedcatalyst and its capabilities of mercaptan oxidation. It was turned out that the regenerative catalyst had fairly high activity and stability.To sum up, the solid base mercaptan oxidation catalyst had high initial activity and high stability. And in air, it was not ready to adsorb CO₂ and H₂O and lose its activity. Furthermore, the catalyst was easy to regenerate and the regeneration was very effective. So the catalyst was promising and maybe found widely in use in the near future.