Valorization of Lubrication Oil and Cooking Oil via Catalytic Copyrolysis with Ni Doped on Activated Carbon

The aim of the copyrolysis of used lubricant oil (ULO) and used cooking oil (UCO) was to investigate the effects of operating parameters on the thermal stability of ULO and UCO, which significantly improves the quality of fuel-like products. This process was carried out in a 3000 cm³ semibatch pyrolysis reactor; the systematic experimental design involved catalytic copyrolysis by varying the operating parameters of the pyrolysis temperature (400–500 °C), the inert nitrogen flow rate (25–150 mL/min), and the ratio of blended ULO/UCO from 0.9:0.1 to 0.2:0.8. The advantage of Ni modified to activated carbon is that it is considered a stronger acid solid catalyst with an extraordinary pore structure, which undergoes catalytic copyrolysis; the concentration of the Ni metal doped into the AC catalyst was 3–10 wt %, and the catalyst loading on the feedstocks (5–20 wt % of Ni/AC catalyst) was performed. The effects of the conversion of ULO/UCO on the yield and physicochemical properties of copyrolysis oil and the product distribution according to ASTM D86 were investigated. The 5 wt % Ni doped into the AC catalyst is related to the strength of the acid activity that accelerated the conversion of large hydrocarbon compounds to obtain a straight aliphatic hydrocarbon compound, and the Ni/AC catalyst also plays a role in facilitated C–C bond cleavage and bond scission to smaller hydrocarbon compounds. The highest yield of naphtha-like fraction of 25.34 wt % was obtained at the optimal condition of 425 °C, the N₂ carrier flow rate was 50 mL/min, the ULO/UCO ratio was 0.5:0.5, 5 wt % Ni was modified into the AC catalyst, and 5% catalyst was loaded into the feedstock. The synergistic effects of UCO and ULO during copyrolysis also revealed that the H-donor and hydrocarbon radicals of UCO decrease the thermal stability of ULO, whereas the addition of 5 wt % Ni to the AC catalyst, which is relevant to acid activity, is mainly responsible for bond scission, hydrogenation, isomerization, and oligomerization, resulting in the formulation of condensable volatile vapors to maximize the production of straight aliphatic and olefinic hydrocarbon compounds, which can be used as sustainable fuels from the conversion of waste to alternative energy.