Study On Methanol To Olefins Catalyzed Over Phosphorus-Modified And Alkali Metals-modified SAPO-34

The increasing need of light olefins,such as ethylene and propylene,have greatly stimulated the development of the alternative non-oil routes for light olefins production.However,research and development of the catalyst for MTO is still a challenge.SAPO-34 catalyst is regarded as a promising catalyst for the MTO reaction,due to its with moderate acid strength and pore structure,thermal stability and hydrothermal stability,and high selectivity to olefins.However,SAPO-34 catalyst is easily coked,and lead to shorten the lifetime.So how to improve the ability of resistance to carbon deposition and prolong the lifetime is a important subject.This thesis aimed to prolong the lifetime of the MTO catalyst and improve selectivity of the light olefins with phosphorus-modified and alkali metals-modified SAPO-34.FT-IR,XRD,NH3-TPD,BET,TG,etc.were employed for the catalyst characterization.Firstly,the catalysts prepared by different loading of phosphorus were evaluated using methanol-to-olefins(MTO)in the normal pressure continuous flowing fixed bed reactor.Compared with unmodified catalyst,the yield of the light olefins were reduced and the lifetime was shortened by P-SAPO-34 catalysts.Secondly,the SAPO-34 modified by different alkalimetals were investigated for the reaction of MTO and it was found that light olefins selectivity and lifetime were improved,compared with unmodified SAPO-34,except Cs-modified SAPO-34.Ethylene and propylene selectivities of Li-modified SAPO-34 catalyst was about 77% and its lifetime was 500 min,prolonged by 2.5 times.After regeneration for three times,the selectivity of ethylene and propylene remains almost the same.Thirdly,it was investigated that the relationship between the selectivity or lifetime and the loading of Li.It was found that the selectivity and lifetime were increased at first and then descend with the loading of Li increasing.So the best loading of Li was 2%.The process conditions were firstly investigated for optimal catalyst of 2Li-SAPO-34,and the optimum reaction conditions proposed in this paper were as follows: the pressure was normal pressure,the reaction temperature was 450?,the methanol weight hourly space velocity was 1h-1,the mass ratio of methanol to water was 1:1 and gas atmosphere was water gas.