Vol 63, No 5 (2023)

This review provides an analysis of prior research on liquid-media methane pyrolysis for hydrogen production. It discusses the experimental studies and reported data on methane pyrolysis in molten metals, molten binary alloys, molten salts, and molten metal–salt media. The experimental data suggest that binary metal alloys are superior to pure metals in terms of catalytic performance. A comparative assessment of catalytic activity showed that the highest performance (methane conversion above 95% at temperatures below 1200°C) has been achieved by molten Ni–Bi and Cu–Bi alloys. Besides the thermobaric conditions and characteristics of the bubbling systems, the media’s reactivity plays a key role in pyrolysis efficiency. The combined use of molten metals and salts as a reaction medium noticeably enhances the methane conversion (due to the catalytic activity of molten metals) and appreciably reduces the content of metal impurities in the carbon product.

The paraffin–naphthenic fractions (with boiling points below 310°C) prepared from three high-viscosity naphthenic crude oils, classified as types B1 and B2 (according to Petrov’s classification), were subjected to thiocarbamide complexation. The molecular composition of polycyclic hydrocarbon biomarkers and C11–C13 adamantanes in the oil samples suggested a predominantly marine genotype of the precursor organic matter (OM). The molecular composition also suggested source rocks of a clayey type. Nonetheless, the biomarkers detected in one sample indicated some contribution of terrigenous components to the precursor OM. All the oils were generated under the conditions of the main oil generation zone and, presumably, underwent microbial transformations in the deposits. The compositions of C10–C14 adamantanes in the initial paraffin–naphthenic fraction, in the thiocarbamide adduct, and in the filtrate that remained after the adduction were comparatively characterized for each oil sample. The test conditions allowed us to have adamantane more than 100-fold concentrated (in the adduct), to quantify it in the oils, and to evaluate the concentrations of C11–C14 alkyladamantanes in the oils using adamantane as an internal standard. C10–C14 adamantanes exhibited selective adduction ability, with the extraction ratios of individual components being different. Taking into account these extraction ratios, the component concentrations were evaluated on crude oil basis: 2.7 to 7.6×10–3 wt % for adamantane and 87 to 267×10–3 wt % for total C10–C14 adamantanes. The identification of adamantanes in the initial paraffin–naphthenic fractions, adducts, and filtrates revealed the presence of some other tricyclanes (probable precursors of alkyladamantanes) as well as decaline homologues. Like adamantanes, these compounds exhibited selective ability to complex with thiocarbamide.

The study investigates the activity of in situ synthesized suspensions of nickel-promoted molybdenum disulfide particles in the hydroconversion of crude oil vacuum residues. The catalyst suspensions were prepared in situ from water-in-oil emulsions of aqueous solutions of precursors, specifically ammonium paramolybdate and nickel nitrate. The catalytic tests were carried out in a flow-type reactor at 430°C, WHSV 1 h–1, and 7 MPa hydrogen, with the Mo:Ni atomic ratio in the catalyst particles ranging from 1:0.022 to 1:1.43. The XRD of the toluene-insoluble solids (TIS) extracted from the hydrogenates identified sulfides such as MoS2, Ni3S4, and Ni3S2 in the dispersed catalyst. Increasing the nickel content in the catalyst favored its hydrogenation activity, which was indicated by an enhancement in the feed conversion, an increase in the content of paraffins and naphthenes, and a decrease in the sulfur content in the distillates and TIS derived from the hydrogenates. The conversion of high-molecular-weight feed components (resins, asphaltenes, and heavy aromatics) was enhanced as a result of the nickel promotion of the dispersed MoS2.

The study investigates the hydrodecyclization of decalin over zeolite catalysts. The synthesized catalysts were characterized using a combination of physicochemical methods, such as TEM, SEM, low-temperature nitrogen adsorption/desorption, and XPS. The zeolite structure was found to have a major effect on the hydrodecyclization process. This process involves the isomerization of one ring followed by the opening of that ring. Incorporating iridium into the catalysts promoted the production of branched hydrocarbons. When testing the process in the temperature range of 300–400°C and at an initial hydrogen pressure of 50 atm, the Ir/BEA catalyst exhibited the highest activity: at 350°C the decyclization of decalin exceeded 50%.

A series of CeO2–MgO catalysts with different molar ratio was prepared for the plasma-activated CO2 decomposition to CO and O2. The catalysts were synthesized by the sol-gel method and characterized by physicochemical methods (XRD, SEM, XPS, low-temperature N2 adsorption, CO2-TPD). The highest CO2 conversion (31%) was achieved in the presence of the catalyst with the highest CeO2 content. The addition of H2 into a CO2 decomposition system was also studied. No CO2 methanation occurred in the presence of synthesized catalysts, though an increase in the CO2-to-CO conversion was observed due to an increase of a discharge power in the presence of molecular hydrogen.

This paper reviews the research background and significance of foam drainage agents, foaming and foam stability mechanisms, and analyzes the advantages and drawbacks of conventional foam drainage agents. With the development of natural gas applications, the exploitation of gas fields becomes more stringent. A new type of foam drainage agent characterized by a wide applicability should be developed based on the particular needs of gas wells. A new foam drainage agent not only resolves the deficiency of conventional foam drainage agents, but also deals with the problem of high costs. It has a higher foam stability and provides a standard for the further design of special conventional and unconventional foam drainage agents for gas fields. Moreover, the polymer addition dramatically improves the performance of foam drainage agents. A Gemini surfactant opens up a new possibility for foam drainage agents. The use of nanoparticles provides the further enhancement of the foam stability for different types of gas reservoirs. The future application trends for foam drainage agents are also discussed. A low-cost and environmentally friendly natural gas promoting a low-carbon green energy, should be developed and used. Highly efficient, environmentally-friendly and recyclable low-cost foam drainage agents would become a hotly debated research point.