Production of Aromatics from n‑Butanol over HZSM-5, H‑β, and γ‑Al2O3: Role of Silica/Alumina Mole Ratio and Effect of Pressure

The production of aromatics from biomass is very much essential to address the sustainability issue of human civilization. The present work proposed a novel process for aromatics production from n-butanol (BTA) using various solid acid catalysts (HZSM-5, H-β, and γ-Al2O3) in a high-pressure fixed-bed reactor. γ-Al2O3 is associated with Lewis acid sites only and hence selective toward butylenes. H-β showed lower selectivity toward aromatics and benzene–toluene–ethylbenzene–xylene (BTEX) compared to HZSM-5 because of rapid catalyst deactivation. The selectivity to aromatics was strongly dependent on the silica/alumina (Si/Al) mole ratio of HZSM-5. The highest selectivity to aromatics was observed over HZSM-5 (Si/Al = 55) because of the presence of an optimum quantity of Brønsted acid sites and organic radicals. The aromatics and BTEX selectivity improved with increasing operating pressure up to 20 bar and reduced slightly at higher pressure. The aromatics and BTEX selectivity, however, declined with increasing weight hourly space velocity (WHSV) and enhanced with increasing temperature up to 623 K. The maximum aromatics selectivity was 49.2% with 29.4% BTEX over HZSM-5 (Si/Al = 55) under optimum reaction conditions: 20 bar, 623 K, and 0.75 h–1 WHSV. A comprehensive reaction mechanism was further delineated correlating variation of product distribution obtained over a broad range of process conditions.