Technical Research And Development Of Methanol To Gasoline

Methanol to gasoline?MTG?process is a process of converting methanol into gasoline product,mainly catalyzed by ZSM-5,undergoing a series of reactions such as dehydration,oligomerization,alkylation and aromatic structure reaction.MTG technology can combine coal based energy chemical industry and petrochemical industry.The MTG technology will have a great potential for development due to china's energy structure,that is rich in coal,deficient oil and lean gas.Methanol to gasoline technology can ease the excess of methanol production and excessive dependence on oil resources to a large extent.At present,many domestic research institutes and enterprises are carrying out research,such as Exxon Mobile of the United States and the Chinese Academy of Sciences,Shanxi Institute of coal chemical technology,which are in a leading position in technology.At present,one of the main technical problems in MTG gasoline is the higher content of the sym-tetramethylbenzene more than 5.5%wt%,so the MTG catalyst and process conditions should be further optimized and developed.In this paper,the catalytic MTG process performance of ZSM-5 catalysts with different Si/Al ratio was evaluated in a kind of self designed fixed bed reactor.It was found that the ZSM-5 catalyst with Si/Al ratio 150 was relatively higher catalytic activity and selectivity for the methanol to gasoline process.The MTG reaction conditions were optimized as following:reaction temperature 380?,reaction pressure 1.0MPa,air speed 1.0h^-1,alcohol water to methanol ratio?mass ratio?ratio of 7:3.In order to obtain higher liquid yield,higher aromatic hydrocarbon content,lower sym-tetramethylbenzene content and higher octane number gasoline,the ZSM-5 catalyst with Si/Al ratio 150 was modified with phosphorus,zinc,gallium elements respectively by equal volume impregnation method.The catalysts were characterized by XRD,BET,NH₃-TPD and FT-IR before and after modification.XRD results showed that after the modification by P,Zn,Ga elements,ZSM-5 molecular sieve remained the skeleton of the crystal structure unchanged,there was no other diffraction peaks;the BET analysis results showed that the surface area of the modified ZSM-5 catalysts decreases slightly,and the micropore size changed slightly,maintaining the shape selective catalytic ability of micro-porous molecular sieve.The catalytic MTG performance evaluation of P modified ZSM-5 catalyst showed that methanol conversion rate was nearly 100%,and the liquid yield was 26.09wt%,in which containing 42.54⁴6.42wt%aromatics,and much higher content of by-product 5.90⁶.85wt%sym-tetramethylbenzene,the liquid gasoline product's octane number was 92.0.The catalytic MTG performance evaluation of Zn modified ZSM-5 catalyst indicated that methanol conversion rate was nearly 100%,and liquid yield was 28.73%,in which containing about 39.98⁴1.39%aromatics,and merely 4.01wt%sym-tetramethylbenzene.The liquid gasoline product's octane number was about 89.0⁹1.7.The catalytic MTG performance evaluation of Ga modified ZSM-5 catalyst showed that methanol conversion rate was nearly 100%,the liquid yield was about 25.26wt%in which contained much higher 52.63⁵9.3wt%aromatic hydrocarbons,and the octane number of gasoline product was 92.0⁹2.3.The obvious advantage of the catalytic performance was low selectivity to sym-tetramethylbenzene resulting in the relatively low content of 3.64⁴.21wt%sym-tetramethylbenzene by-product.It can be concluded that 2.5%Zn modified ZSM-5 catalyst was of high activity for MTG and low selectivity to sym-tetramethylbenzene by-product.The optimal reaction conditions were obtained:airspeed 2.0h^-1,alcohol to water ratio 8:2,reaction pressure 1.5MPa,reaction temperature 380?.Under the optimal conditions,the methanol conversion rate was nearly100%,the liquid yield can reach about 36%,the sym-tetramethylbenzene by-product content lower than 4.01wt%,and the aromatic content about 56.80wt%.The catalyst has high activity,good stability,good selectivity,high gasoline yield,and can meet the catalytic performance need of domestic industrial catalysts.