Research progress on bio-additives in hydrate-based energy technologies: Application scenarios, classification, functions and mechanisms

Gas hydrate technology has broad application prospects in fields of natural gas storage & transportation and gas separation. However, the slow formation kinetics restrict the industrial applications of gas hydrate technology in these scenarios, which need to be improved. At the same time, hydrates can cause blockage in offshore oil-gas exploitation & transportation, which need to be avoided to guarantee security. Accordingly, proper additives, possessing with promoting or inhibiting effects on hydrate formation, have been employed for regulating hydrate formation kinetics in different hydrate-based energy technologies, for achieving the promotion or inhibition purpose. Currently, the majority of additives are non-renewable and non-biodegradable petrochemical derivatives, which cause severe pollutions on environment and pose threats on ecosystem. Comparatively, bio-additives are derived from biomass, and thereby are easily available, renewable, nontoxic and easily biodegradable, which are more eco-friendly and reasonably hold great potentials for serving as green regulators for gas hydrate formation process. This review aims at bio-additives for regulating gas hydrate formation kinetics, lists the types of bio-additives for four different application scenarios, evaluates their effects on hydrate formation kinetics, analyzes their function mechanisms, assesses their application potentials, and furthermore, discusses and prospects the future research directions.