| Gasoline is the lifeblood of the transportation, and its raw materials is fossil oil for the traditional preparation method. But fossil oil is drying up with the human’s continue exploitation. Therefore, it has become one most important subject of current society to look for some suitable fossil oil alternatives. Among them, natural gas, coal and biomass with relatively abundant reserves have been seen as primary choices of oil alternatives. As the key step of the conversion processes of these oil alternatives, methanol to gasoline causes everyone’s wide focus.MTG reaction can conduct on many kinds of catalysts, such as Y-type, MOR-type and ZSM-5 zeolite catalysts. Among them, ZSM-5 zeolite catalyst has attracted much attention for its better activity, more highly selectivity, and stronger aromatization ability etc. in MTG reaction. However, by now, there are two main problems for ZSM-5 zeolites catalyst. One is the short life and the other is the low liquid hydrocarbon selectivity.In order to achieve the purpose that catalysts possessing long life and high liquid hydrocarbon selectivity simultaneously, this paper prepared nano hierarchical ZSM-5 zeolite catalysts in supersaturated solution with single template method. In this part, for the first time, the pore structure and acid nature of the catalyst were control simply by regulating the crystallization time. Based on the procedure mentioned above, nano hierarchical ZSM-5 zeolite catalyst with higher mesoporous volume and more uniform pore size was prepared by introducing the soft template into the synthesis solution during the preparation of the catalyst for methanol to gasoline (MTG). Then, nano hierarchical Zn/ZSM-5 catalyst was prepared by impregnation method with zeolite catalysts prepared by soft template method as the matrix. The main contents and conclusions of this paper are as follows:By single template method, nano hierarchical ZSM-5 zeolites catalyst with high mesoporous volume and micro-meso composite channels was prepared. The effect of parameters on the performance of the catalyst were investigated, including the influences of the condition for hydrolysing the aluminum source, the time for removing alcohol and water, crystallization temperature and crystallization time. It has been concluded that it was favor to the formation of the mesoporous structure and the increasing of acid site of the catalyst that the dissolution of crystals after their complete crystallization. The optimal conditions for preparation of nano hierarchical ZSM-5 zeolites by single template method were:hydrolysing isopropanol aluminum (AIP) in ice-water bath, the time of 14 min for removing alcohol and water, the crystallization temperature of 170℃. The catalysts with crystallization time of 48 h (s-48) and 72 h (s-72) performed better in MTG reaction. For s-48, the catalytic stability was 45 h and the liquid hydrocarbon selectivity was 30.52%. For s-72, the catalytic stability was 35 h and the liquid hydrocarbon selectivity was 34.65%.By soft template method, with the procedure similar to that of s-72, nano hierarchical ZSM-5 zeolite with higher mesoporous volume was prepared. In this part, poly dimethyl diallyl ammonium chloride (PDDA) was used as the soft template. The effect of PDDA/Si (mole ratio) on the catalyst was investigated. The conclusion was that, by introducing the soft template PDDA into the synthesis solution, the mesoporous volume of the catalyst became higher and the pore size became more uniform. When PDDA/Si (mole ratio)≤ 0.070, the catalyst possessed good physical and chemical properties. For the catalyst d(1) with PDDA/Si(mole ratio) of 0.047, the catalytic stability was 52 h and the liquid hydrocarbon selectivity was 33.09%. As to another catalyst d(m)with PDDA/Si(mole ratio) of 0.070, the catalytic stability was 70 h and the liquid hydrocarbon selectivity was 29.80% in MTG reaction.In order to improve the liquid hydrocarbon selectivity, nano hierarchical Zn/ZSM-5 zeolite catalyst was prepared by introducing Zn into the catalyts d(m) by impregnation method. The effect of Zn load on the physical and chemical properties of Zn/ZSM-5 zeolite catalyst was investigated. The results were that, the optimal Zn load of the matrix d(m) was 0.07 wt% and the performance of the catalyst Zn (0.07) with Zn load of 0.07 wt% improved greatly in MTG reaction. The catalytic stability of Zn(0.07) was more than 100 h, and the liquid hydrocarbon selectivity was improved to 62.50%. But it was a pity that the liquid hydrocarbon selectivity reduced to about 15% rapidly during the time on the steam of 15 h. |
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