Studies On Deactivation And Regeneration Of Coal Tar Hydrogenation Catalyst

Coal tar is an important by-product of coal pyrolysis poly-generation technology.Catalytic hydrogenation of coal tar to produce fuel oil can improve its utilization value and reduce environmental pollution.For the rapid decrease of the hydrogenation catalyst activity at the initial stage of the reaction,we studied the reasons of catalyst deactivation and the regeneration of deactivated catalyst in this paper,which aimed to lay a basis for retarding the deactivation rate of the catalyst,ensuring the stability of the catalyst,as well as extending its service life and reducing costs.Firstly,eight representative materials highly contained in medium and low temperature coal tar were used as hydrogenation feedstock,which were catalyzed by NiWP/Al₂O₃ to simulate the hydrogenation reaction process of coal tar,and the properties of the catalyst before and after the reaction were analyzed.The results showed that there was material accumulation on the surface of the catalyst after reaction,the specific surface area,pore volume,pore size decreased,and the crystal phase did not change obviously.Carbon was detected in the catalyst,and its content increased with the increasing of reaction time;the surface of the catalyst was detected to have aromatized C=C bond,C-C bond,C-H bond,C-N bond,C-S bond functional groups.The main reason for the rapid decrease for the activity of the catalyst in the reaction is the formation of carbon deposits on the surface,which consists of hydrocarbons containing heteroatoms.Then,the reactants were changed to coal tar distillate and single polycyclic aromatic hydrocarbon,heterocyclic compound,and the catalytic hydrogenation experiments were carried out under the same reaction conditions,and the composition of the carbon deposited in the catalysts in different reaction times and different reactants was analyzed by GC-MS.The carbon on catalyst surface was mainly aromatic hydrocarbons and alkanes,which was composed of reactant component,hydrogenation intermediate product,polymerization product,and the like.As time increased,the alkane backbone grew significantly.Both polycyclic aromatics and heterocyclic compounds formed carbon deposits,but in mixtures,the effect of polycyclic aromatics was more obvious.Finally,the deactivated catalyst was oxidized and regenerated at different temperatures to investigate the catalyst regeneration effect and the influence of temperature.The research showed that under the same conditions used as the previous experiment,the oxidation treatment at 400°C was not enough to achieve the purpose of regeneration;the oxidation regeneration at 500°C could make the physicochemical properties of the catalyst very similar to that before the reaction,and the hydrodenitrogenation and hydrodesulfurization activities reached 99%of the fresh catalyst;the oxidative regeneration treatment at 600°C produced a NiWO₄ crystal phase which is difficult to be reduced in the catalyst,the catalyst activity decreased,and the regeneration effect is not good.