Studies On Catalyst And Technique For Hydrodearomatization Of Coal Tar

Coal tar is a by-product of coal gasification and pyrolysis,which is mainly composed of aromatic hydrocarbons,phenols and heterocyclic compounds containing sulfur and nitrogen.Preparation of clean fuel oil by hydrogenation of coal tar can increase the added value of coal tar,realize the clean and efficient use of coal,and provide a new supply route for China’s growing energy demand.However,the development level of China’s coal tar processing enterprises is low,and the processing depth is not enough.This leads to a low diesel cetane number and still high aromatics content.In this paper,the diesel oil fraction of coal tarthat has been hydrogenated oncewas selected as theraw material.In order to prepare low-cost clean fuel oil for diesel engine in the premise of mild hydrogenation condition,we focused on the optimization of coal tar hydrogenation process conditions and the development of hydrodearomatization（HDA）catalyst.The effects of technological conditions on the HDA activity of coal tar were investigated in a fixed bed by a self-developed catalyst,and the optimum technological conditions for the HDA activity were determined as follows: temperature 340 ℃,hydrogen pressure 8.0 MPa,space velocity 0.3 h-1,volume ratio of hydrogen to oil 1500.A series of NiW-P/Al₂O₃ catalysts were prepared by adding different amounts of ammonium phosphide,and the effects of phosphide amount on the structure and physicochemical properties were investigated with XRD,NH₃-TPD,H₂-TPR,N₂ adsorption and HRTEM techniques.The HDA activity of catalysts were evaluated in a fix-bed reactor.Studies have shown that a proper amount of P loading can effectively improve the acid properties,pore structure and dispersion of the catalysts,and the excess P will react with the carrier,resulting in the collapse of the carrier framework.When the content of P is 2.0%,the HDA activity of the catalyst is the best.A series of NiMo/Al₂O₃ catalysts were prepared by adding ammonium phosphide with different methods,and the effects of P-adding methods on the structure and physicochemical properties were investigated with XRD,NH₃-TPD,Py-IR,H₂-TPR and N₂ adsorption techniques.The HDA activity of catalysts were evaluated in a fix-bed reactor.Studies have shown that P-adding methods have a great influence on the structure and properties of catalysts.The metal active phases of the catalyst prepared with Ni P-Mo method are reduced most easily and disperse evenly.The pore structure of the catalyst is suitable,and HDA activity is the best.