Study On Methanol Aromatization Performance Of Levulinic Acid Modified HZSM-5 Molecular Sieve

Acid treatment is an important method to modify ZSM-5.Levulinic acid as a weak organic acid,can widen the pores and introduce mesoporous structure to increase the average pore size without destroying the framework structure of the molecular sieve;while reducing the amount of acid reduce the acid strength and improve the catalytic life and BTX selectivity of ZSM-5 in the MTA reaction.In this paper,HZSM-5 was modified with different levulinic acid concentration,acid treatment time and acid treatment temperature,and characterized by XRD,XRF,N₂adsorption-desorption,NH₃-TPD and Py-FTIR analysis techniques.Evaluation of methanol aromatization performance of modified catalyst.Investigate the influence of acid treatment temperature,concentration,and time on the catalyst pore composition and acidity of the catalys,the relationship between catalyst organization and catalytic performance were explored.（1）The HZSM-5 was modified by levulinic acid with concentration of 0.5%at acid treatment temperature of 100 ℃,160 ℃ and 180 ℃,and it was found that the catalysts under different temperature treatments all appeared mesoporous structure.As the acid treatment temperature increases,the average pore diameter first increases and then decreases.The introduction of mesopores is beneficial to the diffusion of macromolecular aromatic products and increases the catalytic life;the acid content and acid strength decrease with increasing temperature,the decrease of acid content is beneficial to slow down the rate of heavy aromatics generation;B/L with the increase of acid concentration first increases and then decreases.A higher B/L is beneficial to increase the selectivity of BTX.Compare the catalytic performance of several catalyst samples,the catalyst with an acid treatment temperature of 160 ℃ has the longest catalyst longetive in the MTA reaction,can reach 164 h,the BTX selectivity is the highest,can reach 55.51%,and the oil phase is recovered the highest rate,can reach13.20%.（2）The HZSM-5 was modified by levulinic acid with concentration of 0.5%,1%and 3%at acid treatment temperature of 160 ℃.It was found that different concentrations caused the catalyst to introduce a mesoporous structure.With the increase of acid concentration,the average pore diameter first increased and then decrease,the larger the pore size is beneficial to inhibit the formation of carbon deposit precursors and prolong the catalytic life;the acid content and acid strength decrease with the increase of acid concentration,and the smaller acid content is beneficial to slow down the coking rate;With the increase of acid concentration,B/L first increases and then decrease.Higher B/L is beneficial to the enhancement of the acid synergistic effect to increase the selectivity of BTX.Compare the catalytic performance of several catalyst samples,the levulinic acid concentration is 1%has the longest life in the MTA reaction,can reach 188 hours,the BTX selectivity is the highest,can reach 57.66%,and the oil phase yield is the highest,can reach 19.31%.（3）HZSM-5 was modified by levulinic acid with a concentration of 1%under the conditions of acid treatment time of 12 h,24 h and 36 h,and it was found that HZSM-5 produced mesoporous structure under different acid time modification.The average pore size,acid amount,acid strength and B/L value decreased with the increase of acid treatment time.Combining the pore structure and acid properties,and comparing the catalytic performance of several catalyst samples,the catalyst with an acid treatment time of 12 h has the longest life in the MTA reaction,up to 238 h,and the BTX selectivity is the highest,up to 59.55%.The highest rate,up to 26.46%.