Study On The Catalytic Conversion Of Methanol To Aromatics

Shortage of oil resources will limit the supply of aromatic hydrocarbons. Preparation of aromatic hydrocarbons from coal has caused domestic and international widespread attention of scientific researchers.The catalytic conversion of methanol to aromatics (MTA) is studied. First, the qualitative and quantitative analysis of products obtained from MTA is discussed. The gas product which contains C1 to C5 hydrocarbons, CO and CO2 is analyzed on-line by a gas chromatograph equipped with a Porapak-Q and a TCD, and is quantified by area normalization. A gas chromatograph equipped with a FID and a HP-5 is employed to analyze the oil phase which contains mostly aromatics and the water phase which contains unconverted methanol. Heptane and isopropanol as internal standard are employed to quantitative analysis of the oil phase and water phase, respectively. The relative standard deviations of repeatedly detecting the components in oil and water phases are all lower than 4.0%, the recoveries of standard components in both oil and water phases are 95.0% ~ 976%.Through calculating enthalpies of the main reactions and major side reactions, it is confirmed that the MTA is a strong exothermic reaction which contains 30-60 KJ/molmethanol reaction heat. Through examining the impact of water/methanol ratio, diluted catalyst, hydrogen on the MTA reaction, the results show that the catalyst's lifetime will be prolonged by removing some of the reaction heat.The preparation of hierarchical porous Zn/ZSM-5 zeolite by NaOH treatment and its application in the conversion of methanol to aromatics are studied. The conversion of methanol, the yield of liquid hydrocarbons and aromatic hydrocarbons over Zn(0.8)/HZSM-5/0.3AT catalyst, which was made by Zn impregnation after 0.3 M NaOH treatment for 2 h at 353 K, slightly changed from 100% to 80.5%, 57.9% to 38.7% and 34.9% to 10.4% respectively, at 710 K and weight hourly space velocity of 3.2 h-1 with the TOS (time on stream) increased from 3 to 44 h. The values for HZSM-5 catalyst (commercial ZSM-5 zeolites with no treatment) sharply decreased from 100% to 34.7%, 48.8% to 19.9% and 38.8% to 14.3%, respectively, with the TOS increased from 3 to 6 h. The Zn(0.8)/HZSM-5/0.3AT exhibited a longer catalytic lifetime and a higher yield of liquid hydrocarbons than HZSM-5. N2 adsorption–desorption results show the mesopores with sizes of 2–20 nm in HZSM-5/0.3AT was formed by alkali-treatment. TG/DTA results confirm that the hierarchical porous Zn(0.8)/HZSM-5/0.3AT is more resistant to cokes than HZSM-5. The catalysts before or after modification are also characterized by XRF, XRD, SEM and NH3-TPD.