Preparation Of Solid Base Catalyst And Its Application To The Sweetening Of Liquefied Petroleum Gas

A series of Mg-Al mixed oxide solid bases were prepared in this paper. After supported sulfonated cobalt phthalocyanine (CoPcS) the catalytic performance of these catalysts was evaluated in the mercaptan oxidation reaction. The samples were characterized by X-ray diffraction (XRD), CO₂ temperature-programmed desorption (CO₂-TPD), FTIR, surface area measurement (BET), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The effect of preparation method, Mg/Al mole ratios, loading content of CoPcS, impregnation solutions and co-catalyst NiO, Fe₂O₃, CuO was discussed. The MgO/Al₂O₃-CoPcS catalyst was applied to the sweetening of liquefied petroleum gas (LPG) instead of the alkali and water washing process to observe the lifetime of the catalyst. On the base of the above research the deactivation mechanism of MgO/Al₂O₃-CoPcS catalyst during the sweetening of LPG was discussed which made preparations for the regeneration and industrial application of the catalyst. The experimental results show that: 1. MgO/Al₂O₃-CoPcS catalyst (prepared by mixing method) not only shows a better catalytic activity and lifetime in mercaptan oxidation reaction but has a better stability in air than Mg(Al)O-CoPcS catalyst (prepared by precipitation method). Mg/Al mole ratio has a great effect on the activity. The catalytic activity is improved with the increase of Mg/Al mole ratio. However, the catalyst with high Mg/Al ratios is easier to adsorb CO₂ and H₂O in air, which results into the declining of the activity. 2. The loading content of CoPcS has an obvious effect on the catalytic activity of MgO/Al₂O₃-CoPcS catalyst. With the increase of CoPcS content the oxidation rate is accelerated. But the activity decreases as CoPcS content is overfull. In this paper the appropriate loading content of CoPcS is 1%. 3. MgO/Al₂O₃-CoPcS catalyst impregnated in methanol solution shows better catalytic activity than the catalysts impregnated in ethanol or water. MgO content in the catalyst has changed into Mg(OH)2 when the impregnation solution is water, which results into the great loss of the amount of basic sites. 4. MgO/Al2O3-CoPcS catalyst shows high initial activity and good stability in the application of sweetening of LPG. XRD,CO2-TPD,SEM and BET results reveal that the deactivation mechanism of catalyst is as follows: firstly the basic sites on the catalyst surface are poisoned by the acidic materials such as hydrogen sulfide in LPG. Secondly, the catalyst is poisoned by reaction product dithio-ether and reactant mercaptan. Thirdly, heavy oil and residual blocks the micropores of the catalyst, which results into the loss of surface area and speeds up the deactivation rate of catalyst. 5. Addition of NiO, CuO or Fe2O3 contributes to the improvement of the catalytic activity of MgO/Al2O3-CoPcS. The proper addition amount of the co-catalyst is 5～15 wt% (NiO), 4～8 wt%(CuO) and 4～14 wt%(Fe2O3). NiO or CuO increases the activity of the catalyst by increasing the basicity of the catalyst surface. However, the amount of basic sites and oxidation ability both increase as Fe2O3 is added in.