Research On The Co-feeding Of Methanol To Propylene Reaction And Coke Behavior

Low-carbon olefins can be obtained not only from traditional petroleum processes,including steam cracking of naphtha,but also from methanol to propylene(MTP).The MTP reaction is in line with our country's energy structure of rich coal and meager oil,and will play an important role in the chemical industry of China in the future.The methanol-to-propylene(MTP)reaction catalyzed by ZSM-5 molecular sieves industrially refining(recycling by-products)to increase the yield of ethene and propylene.Correspondingly,the academic community studied refining by means of co-feeding of hydrocarbons and methanol.Scholars may focus more on the reaction pathways of the hydrocarbons in co-feeding,and their effects on the MTP reaction mechanism and product selectivity.The impact of co-feeding on reactivity and stability hasn't been explored.ZSM-5 molecular sieve is inevitably deactivated during the MTP reaction,resulting in the activity decreasing,and its single-life isn't high.Therefore,the paper mainly studies the effects of hydrocarbons co-feeding on the activity and catalyst deactivation.The paper focuses on the effect of hydrocarbons co-feeding on the MTP reaction and carbon deposition behavior.Firstly,three kinds of representative substances with different methylation and cracking rates were selected.One is butene that to olefins reaction rate is relatively inert,the methylation rate is rapid,but the butene sepcies is hardly cracked.In actual reaction,butene is gas,which is difficult to control the feeding concentration,so the butanol was used instead of the butene for co-feeding on MTP reaction.The second is hexene that to olefins reaction is relatively active,the methylation rate is quickly,and the ?-crack is easy to happen.The last is an aromatic hydrocarbon,which doesn't undergo that to olefins reaction itself,but co-feeding with methanol,the toluene can quickly undergo the methylation and dealkylation reactions.The effects of the three sepecies co-feeding on the reaction behavior,which including the reaction activity and product selectivity were investigated.At the same time,through the TG?C/H?BET?NH3-TPD,the influence of co-feeding to the behavior of carbon deposition was studied.In addition,the differences of carbon deposits in catalysts for differenet industrial long-term and laboratory reaction end-points were compared.The main research contents of this paper are as follows:1.The effects of butanol,hexene and toluenen co-feeding on the reaction behavior,which including the reaction activity and product selectivity,of MTP reaction catalyzed by ZSM-5 catalyst(Si/Al=860)were studied.The butanol co-feeding was compared with the butenen co-feeding on MTP reaction,the performance showed that the butanol enters the reaction and rapidly dehydrates water to form the corresponding olefin,so the butanol co-feeding can be used instead of the butenen co-feeding.Through the three sepcies co-feeding with different feed ratios,it was found that the three feeds could increase the methanol conversion and the ethene and propylene yield.The difference was that the higher the concentration of butanol co-feeing,the promotiong effects were better.Moreover,the methylene rate of butanol was fast,so the C5 and C6 yield increased;but the butanol co-feeding will inhibit the aromatic cycle,then reduced the C6+yields.2.The hexene co-feeding experiment was investigated.With the increasing of hexene feeding,the methanol conversion and the ethene and propylene yields increased first and then decreased.When the co-feeding ratio was 1:50,the methanol conversion and the ethene and propylene yields were the best.This is due to some hexene feed can promote methylation reactions.When the hexene was more,the probablitily of the form C6+increased.Then the probablitily of hydrogen transfer reaction increased.So the more aromatic component deposited in the catalysts.Finally the activity was reduced.At the same time,hexene co-feeding caused the C4-C6 yields increasing,indicating that the hexene was susceptible to cracking to form low-chain olefins.3.The toluene co-feeding experiment was investigated.With toluenen increasing,the methanol conversion and the ethene and propylene yields increased first and then decreased.When the co-feeding ratio was 1:25,the methanol conversion and the ethene and propylene yields were the best.This due to the feed a small amount toluene,could promote the circulation of aromatic hydrocarbons,and the reactivity was improved.Then methylation and other reactions were continuously formly to form macromolecular aromatic hydrocarbons,such as polymethylbenzene or polymethylnapthalene,which weren't easily diffused in ZSM-5.The coke deposited,so the activity was reduced.Toluene co-feeding causes the ethene yield increasing,shows that ethene come out from the aromatic cycle.Finding the best co-feeding ratio can make some guidance for industrial MTP reaction.4.The effects of butanol,exene and toluene co-feeding on the MTP reaction coke behavior were studied using the catalyst(Si/Al=200).It was found that the best co-feeding concentrations of butanol and hexene were the same as that of the SKY-8 catalyzed,but the toluene co-feeding was optimal as 1:75.It may be because the increase on the ratio of silicon to aluminum of the catalysts,an increase in the acid sites,and a corresponding decrease in the toluene concentration required to reduce the carbon deposition.Through the results of TG,C/H,founding that the results were corresponding to the reaction performance.When the yields of ethene and propylene were high,the amount of coke and the C/H were low;when the yields were low,the amount of coke and the C/H were high.In addition,through the BET,the specific surface and mesoporous volume of the catalyst were larger at the best co-feeding concentration point,the difference from the fresh catalyst was the samller,the reaction·performance was better.It also can be used to explain that after co-feeding hexene and toluene reactions,the acidity of the catalyst didn't change.What's more,the weak acid strength of the catalyst through the co-feeding butanol reaction was increasing.5.Comparing the coke depositing of industrial long-term(5th,8th,9th,12th cycles)catalysts and the laboratory(12 h)catalyst,results showed that polymethylbenzene and polymethylnapthalene carbonaceous precursors were found in the out-pores of industrial catalysts,and the size of the detected substances increased with the increasing of the reaction term.However,nothing founds in the inter-pores of industrial catalysts.In laboratory catalyst,the results were opposite.