The increasing global population and the rapid industrial development associated therewith have increased the demand for fossil-derived fuel oils. The sources of fossil fuels are limited, and many studies have been being conducted to find alternative fuel sources. Waste tire pyrolysis oil (WTPO) attracts considerable attention as an alternative fuel because its properties are similar to those of diesel oil. However, WTPO has a high sulfur content of >1.0 wt%, which is above the environmental standard limit of 0.1 wt%; therefore, it cannot be used in engines directly. It is thus highly necessary to remove sulfur compounds from tire-derived oils. However, finding an appropriate and environmentally friendly process is proving difficult. This review article presents the various desulfurization methods used to removal sulfur from WTPO, such as hydrodesulfurization (HDS), oxidative desulfurization (ODS), ultrasound-assisted oxidative desulfurization (UAOD), and acid treatment. Of these, HDS is the most expensive as it involves high consumption of hydrogen, high temperature (~450 °C), and high pressure (~200 bar), whereas UAOD is an efficient and economic method of reducing the sulfur content of WTPO.

Heavy fuel oils contain a high amount of sulfur. In this work, an extent amount of sulfur content waste tire pyrolysis oil (WTPO) was used as a fuel feedstock. A promising alternative oxidative desulfurization (ODS) method was applied in sulfur removal from WTPO using a S-ZrO₂/SBA-15 solid acid catalyst, hydrogen peroxide (H₂O₂) as an oxidant and acetonitrile as an extracting solvent at varied conditions. The prepared catalyst was characterized by X-ray diffraction (XRD), Bruanuer-Emmet-Teller (BET) method and Fourier transform infrared spectroscopy (FTIR) analysis. The influence of reaction parameters such as reaction time (30-60 min), catalyst loading (0.5–1.5 wt.%), oxidant to oil mole ratio (5–15) at fixed reaction temperature 70 °C on desulfurization of WTPO were investigated. Taguchi method was selected to design the experiment for optimizing the reaction parameters by maximizing the sulfur removal efficiency. The maximum desulfurization efficiency 59.49% was obtained under optimum conditions reaction time (60 min), catalyst loading (1.0 wt.%) and oxidant to sulfur mole ratio (10:1). A catalytic S-ZrO₂/SBA-15 -H₂O₂ oxidation system for oxidative desulfurization of waste tire pyrolysis oil using at mild reaction conditions was developed.

The co-gasification of bio-oil produced via fast pyrolysis and black liquor from the pulp industry may yield a valuable feedstock for renewable gasification. This study investigated the synergistic potential of this co-gasification process. Experiments were conducted in a miniature conical spouted-bed reactor at 800 °C using bio-oil/black liquor mixing ratios ranging from 1:9 to 9:1 under equivalence ratios (ER) of 0.1, 0.3, and 0.5. Syngas characteristics and gasification performance were assessed using the lower heating value (LHV), H₂/CO ratio, cold gas efficiency (CGE), and carbon conversion ratio (CCR). Increasing the bio-oil fraction increased CO and CH₄ concentrations due to its higher carbon content and lower moisture content, whereas black liquor promoted H₂ formation through moisture-driven water–gas shift reactions. Higher ER values intensified combustion, increasing CO₂ while reducing combustible gases. The most energy-rich syngas, with the highest LHV and CGE, was obtained using a 9:1 mixture at ER = 0.1. The CCR was greatest for pure bio-oil and the 5:5 ratio among mixtures, reflecting the catalytic effects of alkali species in black liquor. These results demonstrate that co-gasification can improve syngas quality and carbon utilization, with optimal performance depending on the intended application.