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A significant portion of fuel energy in internal combustion engines is lost as waste heat, yet limited efforts have been made to recover it effectively. This research explores the utilization of exhaust heat from a diesel engine to produce H2-rich syngas through the methanol-steam reforming (MSR) process. The engine operates at varying loads (15, 30, 45, and 60 Nm) while maintaining a constant speed of 2000 rpm. Exhaust heat is redirected to an MSR reactor, where the methanol-to-water (MtW) molar ratio is adjusted (0.5, 1, 1.5, and 2). Results reveal that the highest hydrogen content in syngas (70.3 %) is achieved at an engine load of 30 Nm and an MtW ratio of 1. To further optimize hydrogen production, three novel algorithms (DSC-MOPSO, MOSPO, and MOGWO) are applied to key operation parameters. Optimization increases hydrogen content to 72.5 % with DSC-MOPSO, 72.4 % with MOSPO, and 72.1 % with MOGWO, with error margins below 0.7 %. 

Determination of olefins in pyrolysis oils from waste plastics and tires is crucial for optimizing the pyrolysis process and especially for the further advanced valorization of these oils in terms of the circular economy. Identifying olefins, even using high-resolution techniques like GC×GC, is challenging without TOF-MS, which allows modification of the ionization step. Currently, the only method for determining olefins in plastic pyrolysis oils is GC-VUV, recently standardized as ASTM D8519. However, TOF-MS and VUV are not affordable instruments for many research teams working on plastics recycling. This paper introduces a simple method for the selective micro-scale adsorption of olefins over AgNO3/SiO2, followed by the GC×GC-FID analysis. Olefins are determined indirectly from the loss of chromatographic area in respective hydrocarbon groups before and after removal. Only 50 μL sample and 15 min of sample separation are needed. Our method was extensively validated and provides a reliable determination of olefin content in a wide range of pyrolysis oils from plastics and tires and their products after mild hydrotreatment. It is affordable to all researchers and industrial companies working on plastics recycling by thermochemical processes as it does not require an MS detector. 

Global polystyrene (PS) waste accumulates at a rate of 28 million tons annually, while recycling rates stay at 1.3 %. PS degrades into microplastics, releasing various chemicals that affect ecosystems and human health. Conventional waste treatment methods are ineffective in reducing PS waste accumulation. This study developed batch low-pressure hydrothermal processing (LP-HTP) methods to convert PS to oils. Oil yields of 96–99 % were obtained with 1–2 % char and up to 2 % gas at average temperatures of 341–424°C for 19–75 minutes. Reversible reactions between monomers (C6-C9) and poly-aromatics (C10-C20+) were found to limit monomer yields. A two-step kinetic model accounting for the reversible reactions was developed. Temperature histories of the batch experiments were considered such that the estimated kinetic parameters were independent of reactor heating or cooling rates. The predicted yields of monomers and poly-aromatics agreed with experimental yields to within 6 %. The model predicted increasing monomer yields with decreasing PS loadings. This predictive model can aid future process optimization and scale-up. PS and polyolefins were co-processed to produce oils with 87 % yields and higher aromatic contents than oils produced from polyolefins alone. LP-HTP methods required no catalyst, had higher oil yields and less char formation than pyrolysis, and used much lower operating pressures and energy than supercritical water liquefaction. The methods also potentially have lower environmental impacts and 4.7 times higher energy recovery than incineration. The oils from LP-HTP, if separated into pure monomers, can be used as chemical feedstocks to achieve a circular use of hydrocarbons. 

The conversion of waste plastics and tires via pyrolysis to pyrolysis oil represents one of the most promising ways of chemical recycling. Determining aromatics in pyrolysis oils from these feedstocks is crucial for their utilization as both petrochemicals and fuels. In this study, we compared three standard methods commonly available in refinery laboratories (ASTM D1319 − FIA, EN12916 − HPLC-RI, ASTM D8396 − GC × GC-FID) for analyzing aromatic content across a wide range of waste plastic pyrolysis oils, their middle distillate fractions, and hydrotreated products. Using model compounds, we explained most of the observed differences in aromatic content determined by these methods. HPLC-RI and FIA resulted in significant errors. For instance, the FIA reports some dienes and heterocompounds as aromatics. The results from HPLC-RI showed that monoaromatics are overestimated, while polyaromatics are underestimated. Among the tested methods, GC × GC-FID provided the most reliable results. 

A total of 5.4 million tons of face masks were generated worldwide annually in 2021. Most of these used masks went to landfills or entered the environment, posing serious risks to wildlife, humans, and ecosystems. In this study, batch low-pressure hydrothermal processing (LP-HTP) methods are developed to convert disposable face masks into oils. Three different materials from face masks were studied to find optimal processing conditions for converting full face masks into oil. The oil and gas yields, as well as oil compositions, depend on the feedstock composition, particle size, and reaction conditions. Yields of 82 wt.% oil, 17 wt.% gas, and minimal char (~1 wt.%) were obtained from full masks. LP-HTP methods for converting face masks have higher oil yields than pyrolysis methods in the literature and have lower operating pressures than supercritical water liquefaction. LP-HTP methods for face masks can increase net energy returns by 3.4 times and reduce GHG emissions by 95% compared to incineration. LP-HTP has the potential to divert 5.4 million tons of waste masks annually from landfills and the environment, producing approximately 4.4 million tons of oil.