The desulfurization of natural oil feedstock for fuel purposes is crucial for environmental protection and sustainable development. Methane is the main component of natural gas resources with low added value. Distinctive characteristics are demonstrated if methane can be directly used for oil desulfurization, instead of being converted into hydrogen via methane stream reforming for hydrodesulfurization. Here, the methane-assisted catalytic desulfurization process is specifically developed for light oils such as marine diesel oil. First, different catalyst supports are selected and compared, among which Al2O3 is confirmed to provide the most favorable reaction performances. Then, the reaction is operated under different gas atmospheres including CH4, N2, and H2, to reveal the uniqueness of methane for a desulfurization process. Next, model compound oils are selected with thiophene as the sulfur-containing oil component. Heptane and toluene are used as solvents to represent paraffin-rich and aromatic-rich oil, respectively. It is found that the structural characteristic of the oil significantly influences the desulfurization performance and product distribution, based on which the respective reaction mechanism networks are proposed. It is concluded that despite the unparalleled desulfurization performance under hydrogen, the methane-assisted desulfurization process demonstrates distinctive characteristics to prevent light end loss and oversaturation as well as the formation of H2S as the primary desulfurization product, which can be better utilized under certain circumstances.

Methane is the main component of naturally abundant natural gas resources and is under-utilized. Bio-oil is a promising energy source with lower economic and environmental costs compared to fossil fuels. However, pyrolysis-derived bio-oil obtained from lipid sources is hindered by high oxygen content and unsaturated species. In this work, an Ir-Ga-Ce/TiO2-A catalyst is theorized and subsequently tailored to optimize deoxygenation product oil quality. After synthesis, 2-hexyl-1-decanol is employed as a model compound to understand the mechanism of deoxygenation under different atmospheres and rationalize the assistance of methane compared to inerts. It is found that methane significantly facilitates the deoxygenation and chain growth reactions by direct incorporation into the paraffinic and naphthenic liquid-phase products. In the gas-phase products, isotopic la-beling studies reveal that methane is directly involved with deoxygenation as a major contributor to CO2, and potentially CO. The role of each catalyst component (Ir, Ga, Ce, and TiO2-A) is elucidated, resulting in a so-phisticated network tailored for deoxygenation of alcohols with the assistance of methane. The Ir-Ga-Ce/TiO2-A catalyst is then subject to testing on a real pyrolysis-derived bio-oil and shows 84.7% deoxygenation, 0.07% water content by weight, 0.2 (mg KOH g-1) TAN and greater than 1.5% methane conversion, while maintaining the product oil's structural integrity as a renewable fuel. This work illustrates the potential of a methane-assisted deoxygenation process and explains multiple roles methane can play in achieving better reaction performance and product quality. The effective utilization of methane for bio-oil deoxygenation demonstrates unique benefits for the natural gas and fatty waste industries.

Methane is the main component of natural gas, and the latter is a clean natural resource with an abundant reserve and wide distribution. Elemental sulfur is both naturally available on the earth and being artificially generated as a recalcitrant solid waste in chemical processes. The co-utilization of elemental sulfur and methane is thus of economic and environmental benefits. Here, a new catalytic route for elemental sulfur-assisted methane activation is demonstrated over metal-loaded zeolite catalysts at a low temperature of 400 degrees C. Over 10% methane conversion can be achieved even after the catalyst is recycled five times, and the selectivity is well controlled, generating over 90% C-2-C-4 hydrocarbons as the main products. Control experiments are employed to demonstrate the strategy developed for catalyst design, and a series of verification experiments accompanied by various catalyst characterizations are also performed to elucidate the involved reaction mechanism. The results are further substantiated by theoretical calculations for proposing the possible reaction network. It is suggested that the Langmuir-Hinshelwood surface reaction mechanism might be followed, in which elemental sulfur and methane are both adsorbed over the catalyst surface in a competitive way. When methane activation is triggered and significantly enhanced in the presence of sulfur, both surface reaction and gas-phase reaction can proceed, generating sulfides as complete oxidation products and light hydrocarbons as partial oxidation products, respectively. As a result, the product distribution can be well modulated by the adsorption properties of the charged catalyst. This process provides a transformative cost- and energy-effective way for the co-utilization of two low value-added feedstocks with unique advantages in the natural gas and petroleum industry.

Vegetable oil is one of the most commonly used feedstocks for the production of biodiesel, while the first-generation biodiesel suffers from the disadvantages of considerable instability and corrosivity. Developing second-generation biodiesel is momentous for the sustainable development of global energy, which overcomes the shortcomings of first-generation biodiesel. The methanotreating of vegetable oil is a potential new route for the production of second-generation biodiesel, which is comprehensively investigated in this study. Throughout the screening of the catalysts, Ga-Ce/TS-1 demonstrates the best overall performances in this methane-incorporated process, leading to 84.23 % of liquid yield, 0.95 % of methane conversion, 72.8 % of oxygen content reduction, and 71% of light hydrocarbon distillates yield. The participation of methane promotes deoxygenation performance, optimizes the composition of paraffinic and olefinic hydrocarbons, as well as suppresses coke formation. The catalytic methanotreating of vegetable oil is confirmed to be a promising pathway to second-generation biodiesel.

Hydrodesulfurization is well established in the industry while costly and environmentally unfriendly due to CO2 emissions and H2S production. An alternative, cost-effective desulfurization process remains unreported. Here, we demonstrate a desulfurization process for dibenzothiophene, one of the most well-known and recalcitrant sulfur-containing model compounds against catalytic desulfurization, under the regulation of methane instead of hydrogen over a combination of two catalysts, generating a new sulfur-containing product, CS2, as an important intermediate in organic chemistry and non-polar solvent with lower environmental impact than H2S. A catalytic mechanism is proposed and supported by extensive experimental and computational evidence. It is discovered that methane acts as a critical initiator and intensifies the direct desulfurization pathway, where two catalysts must work cooperatively and a surface sulfur transfer process is indispensable. This study explores an alternative desulfurization route with unique reaction pathways towards CS2 formation, whose practical potential is also supported by the desulfurization performance over a series of real-world crude samples.

Developing novel, renewable and environmentally friendly fuel resources is a critical and urgent need for realizing a sustainable energy supply. Waste cooking oil (WCO), which was previously inappropriately treated or discarded, is a prominent biomass source with unique advantages for fuel production. Methane is another naturally abundant and cost-effective resource if it can be directly used in various chemical processes. The studies regarding WCO-based biodiesel production and methane-assisted biomass upgrading processes have been already established. Inspired by the concepts, a WCO valorization process under a methane environment can be expected to be promising both economically and environmentally. In this work, a 30-day long-term waste cooking oil valorization process under methane over a specifically designed catalyst was performed. The feed and product oils were comprehensively analyzed, in terms of viscosity, density, flash point, cloud point, freezing point, pour point, free fatty acid content, iodine number, total acid number, water content, ash content, organochlorine content, cetane number, heating value, oxidative stability, residual carbon, as well as distillation and elemental analyses. It was confirmed that the WCO valorization process under methane is successfully achieved with greatly improved oil qualities, overcoming the disadvantages of WCO-derived biodiesel for practical use and complying well with the corresponding renewable diesel standards, and thus demonstrating strong feasibility for further industrialization.

Asphaltenes are widely existing in crude oils, which are generally the heaviest and most intractable components with low value. However, it has been proved in our previous study that catalytic heavy oil upgrading process under methane environment can effectively convert asphaltenes into light fractions, leading to remarkable improvement of oil qualities such as decreased TAN, sulfur content and higher yield of light fractions. In this work, asphaltenes were extracted and upgraded under methane environment using several typical paraffinic and aromatic oil components as the solvents. It was found that the presence of solvent facilitates the mixing of catalyst and asphaltenes, reducing coke formation and enhancing the yields of light products. Specifically, paraffins such as heptane and eicosane lead to slightly decreased asphaltene conversion but much higher light fraction yield, which can be attributed to the formation of small hydrocarbon radicals through cracking of the paraffinic chain. Although aromatic solvents such as toluene and 1-methylnaphthalene have little interaction with asphaltenes in terms of chemical reactions during the upgrading process, heavier aromatic components such as 1-methylnaphthalene demonstrate noticeable solvent effect, which successfully prevent the excessive polymerization of asphaltenes towards coke formation by improving the dispersion of asphaltenes. It is suggested that this solvent effect is closely related to phase behavior, which is determined by whether the solvent remains in liquid phase under given reaction conditions. On the other side, the presence of asphaltenes generally lowers the conversions of methane and solvents by partially covering the catalytic surface. For paraffinic solvents, asphaltenes also reduce the selectivity of converted solvent molecules towards aromatics by blocking internal pores of catalysts. In summary, the interaction between solvent molecules and asphaltenes is essential for successful asphaltene conversion to desirable products in heavy oil upgrading processes.

Crude oil upgrading under methane has been reported to be an economically and environmentally promising process, while the advantageous effect of methane beyond a reactant is not fully explained. In this work, the catalytic performances, physicochemical properties and regenerability of used catalysts after crude oil upgrading under methane and nitrogen are investigated by n-butylbenzene model compound studies, catalyst characterizations and density functional theory calculations. Comparing to nitrogen, methane exhibits a protective effect on the charged catalyst despite the limited conversion, leading to better product quality and catalyst stability. This protective effect is attributed to the interaction between methane and catalytic active sites, which mainly occurs in the internal pores of the zeolitic catalyst support, resulting in unique coke distribution and inhibition of metal deposition. The interactive role of methane beyond a reactant, which is previously underestimated, is suggested to be critical for better performances of catalysts in relevant reaction processes.

Petroleum is one of the most important natural resources for human beings, while the contained sulfur heteroatoms lead to a series of problems1. Therefore, a desulfurization process to reduce sulfur content is mandatory for clean petroleum utilization. Hydrodesulfurization is currently mature in industry, while this process is costly, energy intensive and environmentally unfriendly due to CO2 emission and H2S production2,3. Alternative cost-effective desulfurization process with environmentally benign sulfur-containing products remains unreported. Here we demonstrate that the desulfurization of a heavy oil model compound dibenzothiophene can be successfully achieved under methane environment over creatively designed dual catalyst system, generating a new sulfur-containing product CS2. Control experiments indicate that the presence of methane as well as catalyst components for direct desulfurization and methane activation are all required. The reaction process is better understood by extensive evidences from isotope labeling experiments, catalyst and product characterizations, density functional theory calculations and verification experiments, based on which a reasonable catalytic mechanism is proposed. It is found that methane-assisted desulfurization requires more stringent conditions, where sulfur vacancy abundance, methane activation capability and surface sulfur transfer are all indispensable. This study pioneers a transformational desulfurization route, which is more economically and environmentally attractive for petroleum processing industry.

In this work, several heavy crudes with wide viscosity range from 1200 to 120,000 cP at 15.6 degrees C were partially upgraded with a specially designed catalyst under CH4 atmosphere. All these reactions were conducted using a batch mode high temperature and high-pressure Parr reactor. This technique was proved to be suitable for the heavy oil feeds with varied properties, confirming its generality for industrial practice. Upgrading under CH4 demonstrated much better performance than that under N-2 when the reaction conditions kept the same, confirming the role played by methane on facilitating heavy ends conversion during heavy oil partial upgrading. Furthermore, the effect of methane presence was further investigated through comparing with its N-2 counterpart at the similar asphaltene conversion by tuning the reaction time and temperature. Although it is well expected that coke yield and gas yield increased yet liquid yield decreased along with upgrading reaction proceeding, the reaction under CH4 showed noticeably lower coke and gas yield while higher liquid yield than its counterpart under N-2 at comparable asphaltene conversion, strongly indicating the methane's effect on effective suppression of thermal over-cracking of heavy crude, which is beneficial for achieving more high value-added liquid products. Moreover, the properties of the oil products derived from different atmospheres including viscosity, density, TAN (total acidic number), AMW (average molecular weight) and sulfur content were studied and compared. All these indexes showed a decreasing trend with increasing asphaltene conversion. The values for viscosity, density and AMW were higher under CH4 than those under N-2, while the TAN and sulfur content were lower when methane was present, implying the possible methane incorporation and its role played on promoting deoxygenation and desulfurization reactions. The research outcomes derived from this study further evidence the technical advantages of heavy crude partial upgrading under methane, thus providing a more cost-effective and environmentally friendly alternative to hydrotreating for processing heavy oil.

The desulfurization of marine gas oil (MGO) and marine diesel oil (MDO) is crucial for the bunker fuel industry due to the new regulation on SOx emission imposed by the International Maritime Organization. The catalytic desulfurization of such feedstock is conducted under methane environment in this study. Using a ZSM-5 with uniform cylindrical morphology (UZSM-5) as the catalyst support material, the over-cracking of oil molecules is inhibited. The incorporation of Ga and Mo enhances the activation of methane, aromatization of the feedstock and conversion of sulfur containing groups, particularly when marine diesel oil with a higher sulfur content is charged as the feed. Under CH4 environment, 58.8% sulfur content in the feedstock is converted comparing with that of 42.8% under N2 environment when Ga-Mo/UZSM-5 is employed as the catalyst. The participation of methane not only improves the desulfurization performance, but also suppresses coking and over-cracking of the feedstock as well as increasing the liquid product yield probably through methane incorporation to the product molecules.

Naphtha reforming processes are widely used for high-octane gasoline production. These processes require high reaction temperature and high pressure of expensive hydrogen. Also, olefins and aromatics are produced for achieving high octane number, which could cause severe environmental issues. Here, we report a novel method of non-thermal plasma assisted catalytic reforming of naphtha at near ambient conditions. Conventionally used hydrogen has been replaced by cheaper methane in this study. Non-thermal plasma could effectively convert methane and naphtha to high-quality fuel at near room temperature and atmospheric pressure. A high-quality fuel with high content of iso-paraffin and low content of olefin and aromatic is produced over optimized Ga/ mix-ZSM-5 with non-thermal plasma applied. The produced liquid product has a notably higher iso-paraffin content (increased from 21.5%-40.5%) than raw naphtha while the coke deposition (17.4 %) and the content of olefins (decreased from 13.5%-7.8%) and aromatics (dropped from 18.1%-5.9%) are well controlled. The partial desulfurization of fed coker naphtha by close to 60 % is also successfully achieved. A systematic model compounds study is conducted to investigate the involved mechanism of non-thermal plasma assisted catalytic naphtha reforming and coke deposition. Based on the studies of C6-C16 model compounds (including paraffins, olefins, dienes, cyclo-paraffins, cyclo-olefins and aromatics), a hypothetic reaction mechanism is proposed. A series of control experiments is also carried out to reveal the synergistic effect between non-thermal plasma, catalyst, and methane participation. This research thus pioneers a cost-effective and environmental-friendly route for naphtha reforming at mild conditions.

A catalytic asphaltene upgrading process was performed in the presence of methane. Through C-13 isotope labelling, methane was proven to be successfully incorporated into the liquid product, preferably in aliphatic structures. Control experiments suggested that the presence of both catalyst and methane is indispensable for improving product quality.