Because of the unique three-dimensional 10-MR cross-channel and adjustable acidity, ZSM-5 zeolite has special shape-selective catalytic properties and become an excellent catalyst for methanol to propylene (MTP). Domestic and foreign scholars have carried out extensive researches about the influence of acid properties and pore structure of ZSM-5 zeolite on the MTP reaction and its reaction mechanism. In 2006, Shenhua Coal Industry Group in Energy and Chemical Engineering Base of Ningxia introduce the Lurgi’s technology of Germany and built two sets of 470 kilotons/a MTP plant, which are running well. However, the catalyst used still dependent on the Sud-Chemie Co. of Germany so far which is monopolize in technology and has an expensive price causes an very low economic benefit. Therefore, the development of domestic catalysts for MTP is hot in recent years. But none of domestic catalyst has been industrialized, the key issue of which is that the effects of surface acidity of ZSM-5, including acid type, acid strength and acid amount on the reaction mechanism, or on the product distribution and coking behavior in MTP have not been clearly known. In this paper, citric acid, ammonium hexafluorosilicate and various combinations of dealumination agents was used to adjust the surface acid property of HZSM-5. The reaction mechanism of MTP reaction will be deeply known and the nature that the effect of surface acidity of ZSM-5 on the product distribution and coking will be revealed by studying the relationship between the surface acidity of ZSM-5 and its catalytic performance or coking amount, which will provide a theoretical guide for developing the catalyst for the conversion of methanol to propylene (MTP) and other hydrocarbons (MTO/MTG/MTA).In the present thesis, the effect of citric acid, ammonium hexafluorosilicate and various combinations of dealumination agents on the surface acidity of HZSM-5 was investigated in detailed. The acid amount and silica-alumina ratio of ZSM-5 varied in different degree after it was treated and the order of removing aluminium is:citric acid< ammonium hexafluorosilicate< various combinations of dealumination agents. The influences of three treatment ways on total acid amount, B or L acid amount and acid strength are basically same. With the increase of dosage (liquid-solid ratio and concentration), treatment time and treatment temperature, the crystallinity is not significantly damaged, the total acid amount, B or L acid amount all reduced, and the acid strength of strong acid showed decreasing. The decrease of acid strength and B acid amount inhibited the hydrogen transfer reaction between light olefins and aromatics and the cracking reaction of higher olefins in dual cycle mechanism of MTP, which helped improving the selectivity to light olefins, especially propylene, by citric acid, ammonium fluosilicate, composite processing propylene selectivity from powder 9.68% to 16.39%,19.24% and 21.90%, respectively. Also reduced the selectivity to alkanes and aromatics, simultaneously inhibiting further dehydrogenation of alkanes and aromatics into polycyclic aromatics to reduce the coking amount on the catalyst surface, from 6.46% down to 3.02%,3.02% and 2.36% respectively. It is worth mentioning that the acid strength, especially in the distribution of strong B acid influenced the MTP product distribution and coking a lot.Even though the total acid amount decreaed, the increase of acid strength still reduced the selectivity to propylene. If the amount of strong B acid became more after treatment, it would result in the decrease in selectivity to light olefins, especially propylene, the increase in the selectivity to alkanes, aromatics and as well as coke amount. |