| As an oil-free route, methanol to hydrocarbons (MTH) attract great interest since it was discovered in1970s. To satisfy different demand in chemical industry, MTH reaction is applied as methanol to olefins (MTO, methanol to gasoline (MTG) and methanol to aromatics (MTA), respectively. In the present study, three types of molecular sieves were used as methanol to olefins, methanol to gasoline and methanol to aromatics catalyst respectively in fixed-bed reactor, and kinds of characterization techniques were applied to investigate the mechanism.The phosphorous modified HMCM-22was applied in MTH reaction, and the mechanism was investigated in detail. HMCM-22prepared by hydrothermal method showed good activity and stability. As nSi/nAl of HMCM-22increased, the selectivity of olefins rose and selectivity of aromatics decreased. Olefin polymerization is catalyzed by weak acid site while aromatization is a strong acid site catalyzed reaction. As the nSi/nAl rose, the amount of both weak and strong acid sites decreased, so the process of olefin polymerization and aromatization slowed down. HMCM-22with low nsi/nAl was impregnated with phosphorous and applied in MTH reaction, reaction result showed that phosphorous modified catalyst achieved higher selectivity of olefins especially selectivity of propene. NH3-TPD, NMR, in-situ UV/Vis and GC-MS were applied to characterize the acidity, intermediates species and organics occluded in the channel after reaction, the results showed that phosphorous impregnation covered some Bronsted acid sites and caused dealumination to some extent, hence the amount of available Bronsted acid sites decreased. Change of acidity influenced the amount of intermediates so as to affect the selectivity of olefins. Therefore a conclusion was drawn that phosphorous impregnation is an effective method to tune the acidity and future to tune the olefins selectivity.SAPO-41was applied as a model to certify the dual cycle mechanism in MTH reaction for the first time. Reaction result showed that high temperature facilitate olefins production and prolong the lifetime of SAPO-41. The intermediates detected by in-situ UV/Vis, in-situ FTIR and1H NMR MAS comprised olefins and aromatics, then co-feed was carried out and proved that both olefins and aromatics acted as intermediates in the reaction, in other words, the reaction ran according to the dual cycle mechanism. In the in-situ UV/Vis and in-situ FTIR patterns the aromatics signal was very weak, and1H NMR MAS reault contained no benzene-based carbenium ions, however, abundant olefin signal was detected in all the three patterns. Considering the high selectivity of C5～C8at400℃, the olefin-based cycle played a key role in MTH reaction over SAPO-41, while aromatic-based cycle contributed only a little. At400℃selectivity of C5伍C8kept stable between50%and60%, which means that SAPO-41could be used as an ideal catalyst to produce non-aromatic gasoline.Ga impregnated nano ZSM-5was used as catalyst to convert mixed alcohol (methanol and1-butanol mixed at certain ratio in mole) to aromatics. Reaction result showed that Ga modified nano ZSM-5showed excellent reactivity while the stability needed improving. ICP result revealed that continuous Ga loss caused the decreased aromatics selectivity. Adding1-butanol to methanol improved the stability greatly, no deactivation was observed even after40h, which is due to the slower loss of Ga and the lower activation energy requirements for the oligomerization of the dehydration products from1-butanol compared with dehydration products from methanol. N2adsorption result showed that coke accumulated during the mixed alcohol conversion was more than during methanol conversion, considering the better stability in the mixed alcohol conversion, we concluded that coke had nothing to do with the activity decrease of catalyst. |
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