Valorization of rice husk to aromatics via thermocatalytic conversion in the presence of decomposed methane

Herein, the thermocatalytic conversion of rice husk is studied as a valorization method for the production of benzene, toluene, ethylbenzene, and xylene (BTEX). The reaction environment, the type of zeolite, the SiO₂/Al₂O₃ ratio of the zeolite, and the Ga loading on the zeolite are considered in order to maximize the BTEX yield. Five distinct reaction media are tested, including N₂, CH₄, and gas streams evolved from the ex-situ decomposition of CH₄ at 650, 725, and 800 °C (designated as CH₄-D(650), CH₄-D(725), and CH₄-D(800), respectively). The thermocatalytic conversion of rice husk in CH₄-D(650) with a H₂/CH₄ molar ratio of 0.88 is shown to provide the highest BTEX yield. In addition, the use of the HZSM-5 zeolite, with its relatively low SiO₂/Al₂O₃ ratio, is shown to provide a further increase in the BTEX yield due to the higher density of Brønsted acid sites. The highest yield of BTEX (18.3 wt%) is achieved in the presence of Ga/HZSM-5 (Ga loading: 1 wt%) under the CH₄-D(650) atmosphere. The further addition of Ga to the HZSM-5 (2 and 5 wt% Ga) is shown to decrease the BTEX yield because excess Ga loading on the zeolite decreases the number of available Brønsted acid sites. The present study provides useful information on the effects of various factors upon the thermocatalytic conversion of waste biomass such as rice husk to achieve high yields of value-added chemicals such as BTEX.