The regularities of the formation of carbon nanostructures from hydrocarbons based on the composition of the reaction mixture

Abstract

This paper presents the results of research on the regularities of the formation of carbon nanofibrous materials, as well as the influence of the composition of the model mixture of hydrocarbons S1–S4 on the morphological features and textural characteristics of the resulting carbon nanofibres (CNF).One of the most urgent issues faced by the oil and gas industry is how to increase the processing depth of associated petroleum gas (APG). In the Russian Federation alone, the annual economic losses from unutilisedAPG during processing are estimated at 2 billion dollars. It is known that the composition of APG can vary greatly, depending on the oil and gas field. In particular, the methane concentration, the main component of natural gas and associated gas, varies from 25 to 95 vol.%. In this study, we sought to identify the main factors that determine the morphology and structure of CNF, and to develop approaches in processing actual hydrocarbon mixtures to produce a carbon product with the desired or predictable characteristics. Such an approach can serve as a basis for resource-saving catalytic technology utilizing C1–C4 hydrocarbons that are currently disposed of as post-combustion flare gas. The research results clearly demonstrate that the morphology and texture of the carbon materials obtained by the decomposition of hydrocarbon mixtures depend on the composition of the reaction gas. The key components in this case are methane and the resultant hydrogen: their relationship at a specific temperature determines the direction of the reversible reaction of carbon hydrogenation: S + 2H2 = SH4. The decisive factor in the decomposition of hydrocarbons yielding carbon materials is the degree of deviation of the methanation reaction from equilibrium which can be influenced in two ways. The addition of hydrogen to the reaction gas promotes the driving force of the carbon hydrogenation reaction, resulting in defective high-surface carbon fibres. Increasing the concentration of methane in the reaction gas composition, in contrast, reduces the driving force of methanation until the process is suppressed, which promotes a more structured form of the CNF, without defects.