Researchers at Henan Polytechnic University in China have hydrotreated the oil derived from hydrothermal liquefaction of scrap tires (STO) with waste engine oil (WEO) using five different activated carbon-supported noble metal catalysts—Pd/C, Pt/C, Ru/C, Ir/C, and Rh/C—for the production of liquid fuels.

In a paper in the journal Fuel, they report that 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.

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.

With the vigorous rise of the transportation industry, scrap tires (STs), which were once called “black pollution”, have become a critical threat to the human environment. Approximately 5 × 10⁶ tons of STs are discarded each year. Unfortunately, approximately 65–70% of those STs are dumped legally or illegally in landfills or suffer from direct exposure to air. Eventually, this disposal causes severe environmental contamination and high value-added material loss. One alternative way to address these issues of ST management is to transform STs into fuels and other useful chemicals via thermochemical techniques such as combustion, pyrolysis, gasification, and liquefaction.

In general, the thermochemical conversion of STs is a thermal decomposition process that produces recyclable solid, liquid and gaseous products. The liquid-state product, generally called oil, is one of the most promising feedstocks for use in fuels or chemicals. However, this kind of oil is usually characterized by high viscosity and high contents of N and S atoms. Therefore, additional processing is necessary to further decrease the N and S contents and viscosity of this oil prior to its utilization.

Currently, hydrotreatment is one of the most popular methods for the upgrading of bio-oil. This method simultaneously involves hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO) to eliminate S, N, and O heteroatoms in the forms of H₂S, NH₃, and H₂O, respectively, from bio-oil.

… Recently, considerable and increasing attention has been paid to the management or reuse of waste lubricating oil, particularly engine oil. According to statistics from the Chinese transportation industry, 25–30 million tons of waste engine oil (WEO) are produced every year, which can cause serious environmental contamination if the WEO is improperly disposed of. WEO, which has been suggested to be a promising medium for bio-oil upgrading, can not only enhance the mutual solubility of bio-oil and WEO but also reduce the generation of carbon deposits. In addition, WEO can be converted into the final product oil.

Therefore, in the present study, WEO was used as a medium for scrap tire oil (STO) upgrading.

—Liu et al.

The researchers concluded that co-hydrotreatment of STO and WEO blends is an effective way to obtain liquid fuel that can be used directly for combustion or act as a cofeeder for a petrochemical refinery. They found that the WEO could also be recovered as a major fraction of the UPO and used to adjust the relative proportions of the UPO components by varying the initial STO/WEO mass ratio.

The UPO mainly consisted of saturated hydrocarbons and aromatics, and its naphtha, jet fuel, light diesel, and heavy diesel fractions could be adjusted by varying the reaction parameters. Given these encouraging results, we suggest that the co-hydrotreatment of STO produced from hydrothermal liquefaction of STs and WEO is a promising way to reutilize two kinds of solid and liquid wastes at the same time.

—Lou et al.

Resources

• Xiao-Jie Liu, Feng Wang, Lu-Lu Zhai, Yu-Ping Xu, Long-Fei Xie, Pei-Gao Duan (2019) “Hydrotreating a waste engine oil and scrap tire oil blend for production of liquid fuel,” Fuel, Volume 249, Pages 418-426 doi: 10.1016/j.fuel.2019.03.129