Study On The Catalytic Transformation Reaction Of Organic Sulfur Compounds Over HZSM-5 Zeolites In The Presence Of Methanol

Light oil products mainly contain some organic sulfur compounds such as mercaptan-type, sulfides-type and thiophenes-type. It is the basis of developing new desulfurization method to discuss the reaction of these organic sulfides. At present, there are far from enough to investigate the catalytic reaction especially catalytic reaction course of organic sulfides at the point of molecular level.The thermal conversion and catalytic desulfurization conversion and mechanism of iso-butyl mercaptan, di-n-butyl sulfide, di-n-butyl disulfide and thiophene as probe molecules over neutral Al2O3, acidic HZSM-5 and La or Ce modified HZSM-5 zeolites have been studied in a fixed-bed micro-reactor.The course of thermal reaction for iso-butyl mercaptan, di-n-butyl sulfide and di-n-butyl disulfide is free radical mechanism. Iso-butyl mercaptan was easily thermally transformed to yield hydrogen sulfide, the thermal inversion was perfect under the condition of more than 400℃. Di-n-butyl sulfide began to conduct obvious thermal inversion reaction at temperature of more than 400℃, there was little hydrogen sulfide and tetrahydrothiophene (THT) and certain n-butyl mercaptan, the thermal inversion was almost all fulfilled while the reaction temperature was more than 500℃. Di-n-butyl disulfide was comparatively easy to cracking to yield corresponding thiol and hydrogen sulfide.The transformation mechanism of mercaptan, sulfide, disulfide and thiophene over acidic catalysts were all carbenium ion mechanism. Mercaptan and disulfide over HZSM-5 zeolite catalysts were comparatively easily to transforming to yield hydrogen sulfide. The transformation of organic sulfur compounds were more easily with more strong acidity of catalysts. Isobutyl mercaptan may full be transformed while the reaction temperature got up to 300℃; Di-n-butyl sulfide is easily cracked and basically converted into H2S over HZSM-5 zeolite catalyst while the reaction temperature exceeds 350℃. As a main product, THT is formed in the course of the cracking-desulfurization of di-n-butyl sulfide; The cracking reaction of thiophene could be carried out only at high temperature over HZSM-5 zeolite, and coke was formed with a small part hydrogen sulfide in the absence of hydride donor.Alcohol-type substances especially methanol have not only certain polarity, but also better reaction activity, they are usually as reaction assist to accelerate the reaction. The transformation reaction of organic sulfur compounds in the presence of methanol have been discussed in the paper. It is found that their thermal conversion pathway of mercaptan, sulfides and disulfides can change after the addition of few methanol. The catalytic transformation pathway can change to decrease the yield of hydrogen and yield methyl-contained sulfides such as methyl mercaptan, dimethyl sulfide and dimethyl disulfide, but overlarge concentration of methanol would holdback the transformation of isobutyl mercaptan. The transformation of isobutyl mercaptan was favorable if the volume ratio of methanol and benzene was 0.2.The addition of methanol assume certain effect on the catalytic cracking of di-n-butyl sulfide in solvent benzene but without changing the cracking reaction mechanism of di-n-butyl sulfide. The reaction mechanism of di-n-butyl sulfide is investigated, and the key step of cracking reaction is the rupture of C-S bond to yield thiol-like intermediate in the cracking course of alkyl-sulfide compounds. Formation mechanism of THT can be that n-butyl carbenism ion attack primary carbon hydrogen and cyclize in the cooperation course of primary carbon and sulfur.Thiophene conversion is increased and the cracking temperature of thiophene is remarkably decreased when methanol is added to the feed. At the same time, thiophene converted into main product of hydrogen sulfide other than evolving alkyl-benzothiophenes in the presence of hydrogen donor methanol. The yield of hydrogen sulfide is favored at high temperature and in the presence of much methanol and low space velocity. In addition, the conversion of thiophene increases while sulfur content in stocks decreases, but the thiophene is more inclined to form alkyl-benzothiophenes to give large amounts of coke.There were facilitation for the catalytic transformation of isobutyl mercaptan over La or Ce modified HZSM-5 zeolites catalysts and there was better effect while the content of 1.0% La2O3 or 1.5% CeO2 was dipped. The La or Ce modified HZSM-5 zeolites catalysts by impregnant show higher cracking conversion of sulfide than parent HZSM-5 zeolite, and the yield of THT increases. La-modified HZSM-5 zeolites catalysts have comparatively better facilitation on the catalytic transformation of thiophene, but Ce-modified HZSM-5 zeolites catalysts have hardly any facilitation.