Hydrotreating a waste engine oil and scrap tire oil blend for production of liquid fuel

In this contribution, the oil derived from hydrothermal liquefaction of scrap tires (STs) was hydrotreated with waste engine oil (WEO) for the production of liquid fuels. Five activated carbon-supported noble metal catalysts, namely, Pd/C, Pt/C, Ru/C, Ir/C, and Rh/C, were screened at 380 °C for 60 min with 10 wt% catalyst added under 6 MPa H₂. The mass ratio of scrap tire oil (STO) to WEO was 1:1. Among the catalysts, Rh/C showed the highest performance for sulfur removal from the resulting upgraded oil (UPO). With Rh/C, the effects of other reaction parameters, such as temperature (350–450 °C), catalyst loading (1–20 wt%), reaction time (30–150 min), STO/WEO mass ratio (0:5–5:0), and initial H₂ pressure (0.1–9 MPa), on the yield and property characteristics of the UPO were optimized. The STO/WEO mass ratio and initial H₂ pressure were the two main parameters that markedly affected the yield and property characteristics of the UPO. Using WEO as the reaction medium not only made the recovery of the UPO easier but also converted WEO into a major component of the UPO. WEO also suppressed coke formation and thus prolonged the lifetime of the catalyst. Compared with the initial STO and WEO blend, the UPO exhibited increased C and H contents but significantly decreased N, O, and S contents. N was more difficult to remove than S. Under optimal conditions, the N and S contents of the UPO were reduced to 0.04 and 0.03 wt%, respectively; the UPO had a higher heating value (HHV) of 48.08 MJ/kg. The UPO dominantly consisted of hydrocarbons (saturated and unsaturated) and aromatics whose contents were predominantly affected by the STO/WEO mass ratio and were very close to the mixture proportions of jet fuel and light diesel.