Synthesis Of Intermediates And HDS Of DBT Over Ni₂P Catalysts

Polyaromatic sulfur compounds and their substituted derivatives are present in oil fractions such as diesel fuels.Dibenzothiophene(DBT) and4,6-dimethyldibenzothiophene(DMDBT) are the most refractory sulfur-containing molecules in gasoil..Consequently,they are often used as model molecules,and their HDS has been studied in depth.Better understanding of the reaction mechanisms and network of these sulfur compounds is critical for deep hydrodesulfurization.The network of the HDS of DBT is complex.Except for the products such as biphenyl(BP),cyclohexylbenzene(CHB) and bicyclohexyl(BCH),Hydrogenated intermediates such as tetrahydro-(TH-),hexahydro-(HH-) intermediates were also formed during the HDS of DBT.To gain further insight into the HDS mechanism,we studied the HDS of the hydrogenated intermediates of DBT.The Tetrahydrodibenzothiophene(THDBT) was synthesized by a Tilak reaction and a following cyclization reaction using 2-bromocyclohexanone and thiophenol as the starting materials.Hexahydrodibenzothiophene was obtained by the reduction of TH-DBT at ambient temperature using trifluoroacetic acid and Zn.The hydrodesulfurization(HDS) mechanism of DBT and the two intermediates was investigated over Ni₂P Catalysts in the absence and presence of piperidine.The HDS of DBT occurred mainly through the DDS pathway.The hydrogenation of THDBT and dehydrogenation of HHDBT was fast.THDBT underwent desulfurization by hydrogenolysis to 1-phenylcyclohexene,followed by hydrogenation to phenylcyclohexane.The desulfurization of HHDBT occurred by hydrogenolysis of the aryl C-S bond and then cleavage of the cycloalkyl C-S bond of the resulting thiol byβ-elimination to 2-phenylcyclohexene.2-phenylcyclohexene was isomerized to 1-phenylcyclohexene and 3-phenylcyclohexene,followed by hydrogenation to phenylcyclohexane.Piperidine also had a strong inhibitory effect,especially on(de)hydrogenation and,to a lesser extent,on desulfurization.The order of the inhibition of DBT,THDBT,and HHDBT was explained by the adsorption constants of these three molecules.Synthesis of 4,6-DM-THDBT were attempted.O-thiocresol(2-methylthiophenol) could reacted with 2-halo-3-methylcyclohexanone and TH-DMDBT were obtained.However, synthesis of 2-Bromo-3-methylcyclohexanone was still a problem,which should be investigated further.