The Conversion Of Methanol To Propylene Over Modified BZSM-5Catalysts

In recent years, propylene and its derivatives are in great need both at home and abroad. The traditional propylene production methods have not already met this demand. Methanol to propylene technology (MTP) has got great attention of researchers and has wide development space owing to its cheap reactants, moderate reaction conditions, relatively higher light olefins selectivity. At present, ZSM-5is the most common used catalyst for MTP reaction. Considering the acidity of BZSM-5itself is weaker than that of ZSM-5, we took BZSM-5as catalyst, fixed bed as reactor and investigated the effect of TEOS modification and acid treatment over BZSM-5for MTP reaction, compared the performance of different catalysts and also determined the optimum process conditions.The impact of TEOS modification over BZSM-5for MTP reaction was studied. It was found that acid centers were reduced with the increasing amount of TEOS. As a result, the activity and stability of the catalyst were improved. Given that continuously increasing the content of TEOS is likely to block the catalyst’s pore structure, we adopted acid treatment to further modify the acidity of catalyst.The effect of acid treatment temperature on the catalytic performance of BZSM-5zeolite in methanol to propylene (MTP) reaction was investigated. Acid content and intensity decreased with the increasing acid treatment temperature, and propylene selectivity and catalytic life were improved. Acid treatment could remove impurities in the channels, expose more effective acid centers and reach complete methanol conversion.80℃is determined as the optimal acid treatment temperature. In the experiment of amplification (the amount of loaded catalyst was increased from1g to5g), propylene selectivity could reach to40%with methanol conversion above99%within1000h.BZSM-5, ZSM-5(high Si/Al ratio), B-β, B-MCM-22were treated by HC1under80℃respectively and examined their performance for MTP reaction. The results indicated that BZSM-5showed the highest propylene selectivity and the best stability.The influences of reaction temperature, feed space velocity, material composition and other factors for MTP reaction were researched based on BZSM-5treated by HC1under80℃. The results showed that the selectivity of ethylene and propylene increased when raising the reaction temperature and kept constant when the temperature rose to a certain degree. Increasing space velocity was harmful to the methanol conversion and the selectivity of propylene and ethylene but beneficial to the selectivity of C5and C6+species. Increasing the proportion of water in methanol led to increase of propylene selectivity but decrease of ethylene and butylene. Optimized reaction condition for MTP reaction was as follows: reaction temperature450℃; WHSV (MeOH)1h-1, the molar ratio of water and methanol5, and the optimal acid type was hydrochloric acid.