Review on the Usage of Small-Chain Hydrocarbons (C2-C4) as Aid Gases for Improving the Efficiency of Hydrate-Based Technologies

This review article aims to describe the main applications of gas hydrates in industrial processes and the related advantages and limitations. In particular, gas storage, energy storage, gas transportation, final disposal of greenhouse gases, desalination, wastewater treatments, food concentration, and other technologies are described in detail. Similarly, the benefits and disadvantages of the solutions, currently adopted to improve the process efficiency, are discussed in the text. A particular focus on the use of additives and their capability to intervene during the formation of hydrates and on the replacement process is provided. The second part of the article deals with the use of small-chain hydrocarbons as aid gases during formation, to improve the efficiency and the competitivity of hydrate-based processes. First, the thermodynamic properties of hydrates, containing only these compounds, are described. Then, based on a collection of experimental data available elsewhere in the literature, their effect on the hydrate formation process, when present in the mixture, is shown and detailed. Finally, direct and experimental applications of these gases during hydrate-based processes are described to definitively prove the possibility of solving, partially or completely, most of the main limiting problems for the diffusion of hydrate-based technologies.