A recent article titled “Co-Pyrolysis of Pinewood Biomass and Used Engine Oil Waste: A Sustainable Approach to Diesel-like Biofuel Production” by Mokhtar A. Babatabar and Ahmad Tavasoli in the Current Research in Green and Sustainable Chemistry journal details a sustainable approach to producing a diesel-like biofuel by co-pyrolyzing acid-washed pinewood biomass (APW) with used engine oil (UEO). The escalating global energy demand and the environmental toll of fossil fuels have intensified the search for efficient ways to convert waste into valuable energy. This research presents an innovative solution to this dual challenge by effectively valorizing two abundant waste streams: forestry residue (pinewood) and used engine oil, a significant environmental contaminant generated in massive quantities from automotive engines. Globally, an estimated 40 million metric tons of UEO enter the waste stream annually, with over half improperly landfilled or released into ecosystems, causing severe soil and water contamination.

The core of the study is the co-pyrolysis process, where the oxygen-rich pinewood and the hydrocarbon-rich UEO are thermally decomposed simultaneously. The key finding is the distinct synergistic interaction between the two feedstocks. This synergy is critical because co-pyrolysis yielded a higher liquid product (71.33%) than the theoretical additive yield (69.67%), an enhancement of 1.66%. This unexpected boost stems from a non-linear transfer of hydrogen from the UEO fragments, which effectively stabilizes oxygenated intermediates derived from the biomass. The initial pinewood was pre-treated with acid to eliminate mineral contaminants that otherwise promote unwanted reactions and diminish bio-oil quality. The acid-washed pinewood (APW) was selected due to its regional abundance as forestry residue and its complementary oxygenated structure, which facilitates the synergistic interaction with the hydrogen-rich UEO.

Using Response Surface Methodology (RSM), the researchers systematically optimized four key operating parameters to maximize the bio-oil output: reaction temperature, reaction time, carrier gas flow rate, and the UEO/feedstock ratio. The optimal conditions identified were a temperature of 520∘C, a reaction time of 25 minutes, a UEO/Feed ratio of 50 wt.%, and an inert gas flow rate of 20 mL/min. This recipe resulted in a maximum bio-oil yield of 71.33 wt.%. The UEO ratio was the most influential factor, and the total yield was highly sensitive to temperature, increasing up to 520∘C before dropping due to volatile product cracking at higher temperatures. The liquid product yield was significantly aided by the relatively high volatile matterVolatile matter refers to the organic compounds that are released as gases during the pyrolysis process. These compounds can include methane, hydrogen, and carbon monoxide, which can be captured and used as fuel or further processed into other valuable products.   More content of UEO (98.34 wt.%) compared to APW (80.88 wt.%). Faster carrier gas flow also helped by quickly flushing volatile components out of the reactor to minimize secondary cracking.

The quality of the bio-oil improved substantially, indicating successful conversion into a usable fuel. Co-pyrolysis with UEO drastically reduced the overall oxygenated compounds in the bio-oil to 29.77%, representing a reduction of approximately 64.6% from the 84.03% found in pinewood oil alone. The corresponding total hydrocarbon content was elevated to 70.23%. This deoxygenation is essential because oxygenates reduce a fuel’s energy content and increase its corrosiveness. The compositional analysis showed that the largest fraction of the hydrocarbons fell within the diesel range (C14​-C20​), accounting for 35.03% of the total hydrocarbons, underscoring its alignment with conventional diesel fuels. The produced biofuel had an effective hydrogen-to-carbon ratio of and a high heating value (HHV). Its properties, including viscosity, density, and low sulfur content, compare favorably with commercial diesel standards. The energy content of the liquid bio-oil fraction contained the majority of the feed energy (82.0%), demonstrating high energy recovery in the desired product. This process provides a promising, economically attractive pathway for integrated waste-to-energy conversion, contributing directly to Sustainable Development Goals (SDG) 7 (Affordable and Clean Energy) and SDG 12 (Responsible Consumption and Production).

In summary, the co-pyrolysis of acid-washed pinewood and used engine oil under optimized conditions is a viable and sustainable technology. The synergistic effects of the two waste streams maximize bio-oil yield and significantly improve the fuel quality by reducing oxygenates and enriching hydrocarbons in the diesel range. While further upgrading steps like catalytic hydrodeoxygenation (HDO) are necessary to meet all commercial diesel standards, this research establishes a strong foundation for producing renewable, high-energy liquid fuels from mixed waste.

Source: Babatabar, M. A., & Tavasoli, A. (2025). Co-pyrolysis of pinewood biomass and used engine oil waste: A sustainable approach to diesel-like biofuel production. Current Research in Green and Sustainable Chemistry.