Enhanced selectivity of benzene-toluene-ethyl benzene and xylene (BTEX) in direct conversion of n-butanol to aromatics over Zn modified HZSM5 catalysts

Abstract

The sustainable aromatics production from renewable source is indispensable to circumvallate the dependence on fossil fuel for commodity chemicals. Direct conversion of n-butanol to aromatics using xZn-HZSM5 (0–10 wt%, SiO 2 /Al 2 O 3 = 23, 55 and 280) catalysts was proposed in the present investigation. Characterization studies revealed the formation of different Zn species depending on the Zn loading. Furthermore, XPS analysis confirmed strong interaction of Zn species with the electronegative oxygen atom of zeolite framework. Zn deposition enhanced the selectivities of aromatics and BTEX. The presence of Zn species suppressed the hydride transfer reaction and promoted the dehydrogenation reaction resulting in higher selectivities of aromatics and BTEX. The rising temperature and declining in WHSV enhanced the selectivities of aromatics and BTEX. The high pressure had adverse effect on the selectivities of aromatics. The maximum selectivity of total aromatics (74.83%) and BTEX (68.75%) were achieved at 723 K, 1 bar pressure and 0.75 h −1 of WHSV. The coke analysis revealed the formation of polynuclear aromatic coke at high pressure. The alkyl substitute aromatics and polynuclear aromatics were formed predominately on pure HZSM5 (55) than 5Zn-HZSM5 (55). A plausible reaction mechanism was suggested considering the products distribution. • Direct conversion of n-butanol to aromatics and BTEX using Zn-HZSM5. • Characterization results revealed formation of different Zn species, ZnOH + and ZnO. • Zn species suppress hydride transfer reaction and promotes dehydrogenation reaction. • The maximum selectivity of aromatics (74.83%) and BTEX (68.75%) were achieved. • High reaction pressure results in the formation of polynuclear aromatic type coke.