Study On Catalyst Modification And Operation Conditions Effects For Methanol To Aromatics Process

Aromatics are important raw materials in the chemical industry.The traditional production route uses petroleum as raw material.However,due to the depletion of petroleum and increasing demand for aromatics,its market supply in China is seriously insufficient.Therefore,developing the non-petroleum production technology has great significance.Methanol to aromatics process（MTA）uses coal,natural gas,biomass as raw materials and thus has a promising future.However,there are still some issues worthy further studies such as short catalytic lifetime and low aromatics yield.Moreover,the previous researches were limited to the low WHSV and low pressure conditions,which were not favorable for the commercial application.In this work,the modification of HZSM-5 zeolite and effect of operation conditions were studied,in order to improve the catalytic performance of the HZSM-5 catalyst.The main results are as follows:（1）Alkali treatment of the HZSM-5 catalysts.The catalysts were treated with strong base,weak base and organic base respectively.Their properties were characterized and catalytic performance of MTA were tested.It was found that the pore volume and specific surface area of the zeolites treated by NaOH,Na₂CO₃ and NH₃·H₂O were increased,and their catalytic lifetime were prolonged.The 0.2 M NaOH solution was most effective which increased total pore volume by 25%and prolonged catalytic lifetime for 70%.（2）Metal modification of the HZSM-5 catalysts.The catalysts were modified by transition metals Zn,Cu,Fe,Ni,Ag and their catalytic performance were tested.The results showed that Zn was most effective.The effect of Zn loading on the properties of the catalyst was studied.The results indicated that the optimal Zn weight fraction was 1%.The incorporation of Zinc species modified the acidity of the catalyst,suppressed the hydrogen trasfer and improved the cyclizaion and dehydrogenation reaction,so that improved the aromatics selectivity.（3）Effects of operation conditions.The effects of reaction temperature,WHSV and reaction pressure over 1%Zn/HZ catalyst were studied.It was found that the higher the temperature,the higher the aromatics yield and shorter the lifetime;the higher the space velocity,the lower the aromatics yield and shorter the lifetime;increasing the reaction pressure could delay the decline of aromatics yield and prolong the catalytic lifetime.Under the optimal conditions of 420℃,WHSV=4 h^-1,0.5 MPa,the initial aromatics yield over 1%Zn/HZ was 58.6%and kept above 50%in 28 h,the catalytic lifetime reached 48 h.