# Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review
###### Abstract  
Gas hydrates (GHs) are known to pose serious flow assurance challenges for the oil and gas industry. Neverthless, over the last few decades, gas hydrates-based technology has been explored for various energy- and environmentally related applications. For both applications, a controlled formation of GHs is desired. Management of hydrate formation by allowing them to form within the pipelines in a controlled form over their complete mitigation is preferred. Moreover, environmental, benign, non-chemical methods to accelerate the rate of hydrate formation are in demand. This review focused on the progress made in the last decade on the use of various surface coatings and treatments to control the hydrate formation at atmospheric pressure and in realistic conditions of high pressure. It can be inferred that both surface chemistry (hydrophobicity/hydrophilicity) and surface morphology play a significant role in deciding the hydrate adhesion on a given surface. gas hydrates; flow assurance; hydrate adhesion; hydrate-phobic surfaces; wettability; coatings +
Footnote †: journal: Physchem  
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J.M.S.S. ; [PERSON] Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review. _PhysChem_**2021**, \(1\), 272-287. [[https://doi.org/10.3390/physchem1030021](https://doi.org/10.3390/physchem1030021)]([https://doi.org/10.3390/physchem1030021](https://doi.org/10.3390/physchem1030021))  
Academic Editor:  
[PERSON]  
Received: 29 October 2021  
Accepted: 30 November 2021  
Published: 4 December 2021  
The formation of GHs is a crystallization step, where, first, the gas is dissolved in the aqueous phase at adequate temperature and pressure conditions. Once the aqueous phase is supersaturated, the nucleation occurs depending on the driving force (mainly subcooling or the initial pressure) followed by the hydrate crystals' growth until the system attains a steady state (when the maximum conversion of water to hydrates is reached) [13,14]. Homogeneous nucleation of hydrates is rarely observed, whereas nucleation that occurs in the presence of a foreign surface, known as heterogeneous nucleation, is more widespread since it is energetically favored [1]. Generally, gas hydrates grow at the gas/liquid interface and the importance of several aspects of the surface and interfacial phenomena involved in hydrate formation are documented in detail. For instance, [PERSON] et al. [15] identified that, in the case of a hydrate-forming system in a closed vessel or a pipeline, many interfaces exist that are prone to hydrate formation and agglomeration: vapor/liquid, vapor/solid, liquid/solid, solid/solid, and liquid/liquid, where the vapor indicates the hydrate-forming gas, solid is pipeline, reactor wall, or hydrate surface, and liquid can be either water, oil, or condensate. On one hand, GHs are a nuisance for the oil/gas industry, while, on the other, they can form/dissociate with ease and can accommodate a large quantity of gas, which opens many avenues for their usage in processes such as gas capture and storage, gas transportation, separation, refrigeration, and in desalination to name just a few [16, 17, 18, 19, 20, 21, 22]. Such applications require a rapid formation of hydrates. To accelerate the kinetics of formation, chemical or physical methods are generally used. [PERSON] et al. [23] reviewed the area of surfactants and concluded that the presence of a surfactant in the system reduces the interfacial tension between the vapor/liquid interface, which enhanced the mass transfer, resulting in more hydrate production. [PERSON] and [PERSON] [24] summarized the role of reactor designs and physical methods such as sand packs, silica gels, dry water, foams, nano particles, and hydrogels, which may help to enhance the surface area that ultimately leads to enhanced rates of hydrate formation.