The influence of dual-catalyst bed system of zeolitic and metal oxide catalysts on the production of valuable hydrocarbons during co-pyrolysis of rice straw and waste tire

The influences of acidic (HZSM-5) and basic oxide (CaO/MgO) catalysts and their combinations on yield and quality of pyrolytic oil, derived from co-pyrolysis of rice straw (RS) and waste tire (WT), were investigated. The pyrolytic oil from non-catalytic co-pyrolysis of RS/WT was found to have 31, 27, and 36 peak area% of monocyclic aromatic hydrocarbons (MAHs), aliphatic hydrocarbons, and oxygenates, respectively. The yield of MAHs was increased by 43.63% for RS/WT/HZSM-5 while that of oxygenates was decreased by 55.56%. Superior surface area, abundant acidic sites, and selectivity of HZSM-5 towards aromatics render it more efficient than either of metal oxides catalyst (CaO/MgO) alone. Dual-catalyst bed of HZSM-5/CaO at mass ratio of 1:1 was superior to all other combinations with MAH yield of 59 peak area% while the selectivity of benzene, toluene, and xylenes (BTX) at the same ratio was 18.79%, 33.81%, and 41.85%, respectively. Similarly, the optimum combination of HZSM-5/MgO was also 1:1 which was as equally efficient in deoxygenation as HZSM-5 alone. Moreover, all combinations of HZSM-5/CaO were superior in the terms of HC production and deoxygenation compared to their respective mass ratios of HZSM-5/MgO. Additionally, the application of a dual catalytic bed significantly upgraded the calorific value (HHV) and other physico-chemical characteristics of pyrolytic oil.