Hydrophobic Effect on Gas Hydrate Formation in the Presence of Additives

Abstract

Additives such as surfactants, polymers, salts, and hydrophobic particles are well-known (and used) to influence gas hydrate formation (GHF). This paper reviews and discusses the mechanisms of their effects. The effects of additives on GHF appear to vary greatly from one additive to another. Even a given additive can change from a promoter to an inhibitor and vice versa when the working conditions are changed. The available literature cannot explain the diverse effects of additives. We argue that the hydrophobic effect plays a critical role in gas hydrate formation. A dissolved hydrophobe organizes the surrounding water into a clathrate-like structure and thereby promotes hydrate formation. A hydrophile, however, disrupts the surrounding water structure and inhibits hydrate formation. Moreover, cooperative hydrophobic interactions create an increased gas concentration around a hydrophobe, which also favors the hydrate formation. In contrast, a hydrophile competes with the gas for water and thereby hinders hydrate formation. In particular, when the additive is an amphiphile, the observed effect is the result of the competition between the hydrophobic moiety (a promoter) and hydrophilic moiety (an inhibitor). This hypothesis provides a universal explanation for the various effects of hydrate additives.

Experimental and modeling studies on enhancing the thermodynamic hydrate inhibition performance of monoethylene glycol via synergistic green material

“…Thus, by analyzing the enthalpy of carbon dioxide hydrate dissociation in the absence and presence of different chemical additives, it is found that maximum energy is used to destruct the hydrogen bonds between the water molecules in the hydrate structure. A thermodynamic hydrate inhibitor prevents the formation of hydrates by destroying water activity through hydrogen bonding 38 . The inhibition mechanism of combined inhibitors reduces molecule activity, thus increase the competition for water molecules.…”

Hydrate‐Based CO2 Capture through Nano Dry Gels + Tetrahydrofuran – A Kinetic and Thermodynamic Study

“…Dry water, a free-flowing powder prepared by mixing water and hydrophobic silica nanoparticles, has been recently introduced as kinetics and thermodynamic promoter [2,7,8,14,15,[32][33][34][35][36][37]. Dry water as a special encapsulated product has been resembled to reverse micelle and microemulsion systems that are formed by hydrophobic nanoparticles surrounding an aqueous core suspended in a nonpolar medium such as air [33,38].…”

Thermodynamic modeling of gas solubility in aqueous solutions of quaternary ammonium salts with the e-CPA equation of state

“…Nguyen and Nguyen [89] explained that the hydrophobic part of QAS (organic cation) acts as a hydrate promoter, while the hydrophilic part (anion) acts as a hydrate inhibitor. It creates two competitive effects on gas hydrate formation, the effects of salt depend on which effect is dominant in the working condition.…”