Toward Hydrogen Production via Catalytic and Non-Catalytic Hydrothermal Conversion of Heavy Oil in the Presence of Water as a Green Hydrogen Donor and PdO/Al2O3 Catalyst at Sub-Critical, Near-Critical and Supercritical Conditions

Abstract Sustainable hydrogen generation is undoubtedly a crucial goal in creating alternative energy systems for the future, aiming to offer a clean and cost-effective energy solution. Currently, the limited availability of readily accessible hydrogen sources compels exploration of various alternative methods for its production. This study presents a new approach and systematic study to evaluate the hydrogen production from heavy-oil in the presence of water as a green agent at sub-critical, near-critical and supercritical conditions. In this work, heavy-crude oil Ashal’cha heavy oilfield (Russia) was used as a feedstock for hydrothermal conversion (HTC) process in the presence of PdO/Al2O3 as a Platinum-Group Metal Catalyst-based (PGMC). The HTC experiments (with and without catalyst) were carried out using high/temperature & pressure-reactor under temperatures of 300°C, 350°C, and 400°C, and reaction times of 1, 3, and 6 hours. Obtained products (using material-balance), including gases, liquid, and coke (if formed), were analyzed to understand the dehydrogenation, and conversion performance at different conditions using different advance techniques including GC, elemental analysis, and dynamic viscosity. Moreover, the role of water as an additional hydrogen source was evaluated at 300°C and 6h of the reaction time using different deuterium tracing techniques including FTIR spectroscopy, gas chromatography–mass spectrometry (GC-MS) and isotope analysis for both gases and liquid (upgraded) products. According to the results of the catalytic and non-catalytic HTC process, the presence of the proposed PdO/Al2O3 is a favorable for improving the generation rate of H2 and hydrogen-rich evolved gases such as CH4 as well as upgrading performance in general. Heavy crude oil conversion under HTC with water only yields varying hydrogen concentrations from minimum value 0.1009 vol.% (6.57085×10-5 gr.) at 300 ºC and 1h, to the maximum value of 9.0754 vol.% (0.0357 g.) at 400ºC and 6h. Introducing PdO/Al2O3 into the HTC system improved the hydrogen generation performance from heavy crude oil and achieved a maximum concentration of hydrogen 18.8605 vol% (0.0995 g.) at 400ºC and 6h of the reaction time. In addition, the concentration of CH4 as a hydrogen-rich evolved gas ranging from 0.4099 vol.% (0.0043 g.) at 300 ºC and 1h, to 38.6471 vol.% (3.2719 g.) at 400ºC and 6h. The maximum hydrogen and hydrogen-rich gases (like CH4) generation was evaluated at 400°C and 6 h in the presence of water and PdO/Al2O3. It was found that even at 300°C hydrogen generation was possible. According to material balance, the presence of water and proposed catalyst increases the yield of converted oil (from 58.64 wt.% to 66.15 wt.%) while decreasing the amount of condensed coke (from 19.45 wt.% to 11.28 wt.%) and increasing of the amount of the evolved gases including hydrogen and hydrogen rich gas (CH4) in general. The increased gas yield is particularly advantageous for hydrogen production as it directly correlates with higher hydrogen availability. The experiments outlined that higher temperatures and extended reaction times lead to increased gas yields and decreased coke formation. Specifically, at 400°C for 6 hours, the catalytic process achieved maximum hydrogen and methane generation, illustrating the temperature's critical role in maximizing hydrocarbon conversion to lighter gases. The results of deuterium tracing techniques including FTIR, isotone analysis as well as changes in the GC-MS spectra, proved the role of water as a green hydrogen donor. This paper introduces an innovative approach to hydrogen production from heavy oil using hydrothermal upgrading in the presence of water as a green agent with PdO/Al2O3 as a catalyst. The findings can assist practicing engineers in developing efficient, green hydrogen production systems, especially in scenarios where traditional fossil fuels are the primary source. This research contributes to the growing body of knowledge in sustainable energy solutions within the oil and gas industry.