Preparation, Characterization And Performance Of Pd-based Catalysts For Selective Hydrogenation Of Reformate

To produce qualified aromatics and solvent products, a small amount olefins must be removed which are contained in reformate processed from catalytic reform. It was a valid means to take selective hydrogenation to remove olefins deeply; accordingly, it was key method to develop a new hydrogenation catalyst with high activity and selectivity. In this paper, preparation rules and influencing factors of noble Pd-based catalysts used to deeply removed olefin were researched and a Pd-based double metal catalyst with high activity, selectivity and stabilization was developed. This catalyst possesses some characteristics of good hydrogenation performance, low cost and wide feeds adaptability, which especially can be used for hydrogenation of whole fraction.At the first, study on preparation and application of single Pd catalysts was performed. A series of Pd-based catalysts which were supported on Al2O3 with egg-shell distribution of Pd in the catalyst had been prepared by dry impregnation and the catalytic performances of these catalysts had been studied on a high-pressure microreactor utilizing model oil and reformate oil as reactants. The research results of catalyst preparation showed that the optimal calcination temperature of pseudo-boehmite should be 700°C; the addition of alkali-metal could decrease the surface acidity of support; the egg-shell distribution single Pd catalyst could be obtained under pH value bigger than 4 of impregnation resolution; the content of Pd should be lower than 0.2m%.This Pd/Al2O3 catalyst exhibited good activity and selectivity in the selective hydrogenation reaction of BTX fraction.It was found that the catalysts were temporarily deactived when the single Pd catalysts were used to process whole fraction of reformate oil. By means of micro-reaction tests and analysis of catalysts before and after using, the results indicated that due to thermo sensitive high-boiling heavy component which was produced from catalytic reform process adsorbed or partially polymerized to the catalyst surface under relatively severe operation condition.The method of adding promoter to modify the single Pd catalyst was applied and with the function of the second metal Pt the double metal catalyst can be used to hold good stabilization to selective hydrogenation of refomate at the aim that the result products can meet the industrial requirement. The best preparation conditions of this modified double metal were shown as follow: the pseudo-boehmite can be taken as the material, the optimal calcination temperature of support should be 700°C, and alkali promoter can be used to modify the support; the solution of PdCl2 and H4PtCl6 was used to co-impregnate the support by dry impregnation, the impregnate time was 30min; the best atomic ratio of Pd/Pt was 2 and total metal content was 0.2m%.Considering the activity and selectivity of catalyst, it was suitable that the distribution of Pd and Pt in support existed in egg-shell state and the thickness of egg-shell was about 150μm in the research of heterogeneous distribution of active component .In the discussion of hydrogenation mechanism to double metal catalysts, it was found that the interactions of two metals led to the increase the degree of metal dispersion. As a result, due to the (Pd+Pt)/Al2O3 catalysts had higher hydrogenation activity; it was easy that the heavy component adsorbed changed to relatively light component which had minor endangering and the stabilization of catalyst was increased greatly. The results of pulse micro-reactor and in-situ IR showed that hydrogenation of C=C double bond and hydrogenation of benzene cycle occurred on the same active site of double metal catalyst. The competitive adsorption existed between two reactions and relatively strong interaction took place in each other.The double metal catalyst UDO-01 could fulfill the requirement of selective hydrogenation of benzene fraction, BTX fraction and whole fraction. It was concluded that the in the running process, feeding in low temperature and temperature-programmed procedure were employed to avoid the excess conversion of aromatics after the catalysts were reduced without presulfurization process. The results of hydrogenation tests to whole fraction of reformate on a 100ml-scale pilot unit indicated that the double metal had higher stabilization, selectivity and major temperature interval. In the hydrogenation process, the bromine number of products was less than 200mgBr/100g oil and aromatics loss was lower than 0.5m%.