Hydrate Nucleation in Water Nanodroplets: Key Factors and Molecular Mechanisms

Abstract

Clathrate hydrate nucleation in heterogeneous systems, such as the water-in-oil emulsions found in pipeline environments, is of considerable technological importance and scientific interest. While there has been a number of experimental studies investigating hydrate nucleation in water-in-oil emulsions, there have been essentially no molecular simulations to provide important molecular insights into the hydrate nucleation process. Here, we report extensive molecular dynamics simulations of gas hydrate nucleation to examine nucleation behavior in water nanodroplets immersed in a non-aqueous liquid, probing key factors impacting nucleation, including guest species, guest compositions, size of the nanodroplets, and temperature. The nucleation behavior with pure-guest (i.e., H2S, C3H8, and CO2) and H2S-containing mixtures, where the second guest species is one of C3H8, CH4, C2H6, and CO2, has been studied. For the various systems examined in this study, we find that H2S always tends to initiate hydrate formation, with the only exception being the H2S/CO2 mixture, where the relatively high solubility of H2S compared to the other guest species is identified as an important factor for the current systems. Three different sizes of water nanodroplets at different temperatures are used to examine hydrate nucleation with pure-H2S guest systems, where the observed mechanism of hydrate nucleation within nanodroplets exhibits behavior similar to that found in bulk counterparts. Within water nanodroplets, the hydrate nucleation process features the initial formation of amorphous solids, which can then be annealed into more recognizable hydrate-like structures. Detailed cage analyses provide insights into the impacts of temperature and the size of the water nanodroplet on the initial location and the induction time of hydrate nucleation. Our simulations improve the understanding of the molecular mechanism of clathrate hydrate nucleation in water-in-oil emulsions, thus helping the development of hydrate-related applications and exploitation.

Environmentally Sustainable Large-Scale CO2 Sequestration through Hydrates in Offshore Basins: Ab Initio Comprehensive Analysis of Subsea Parameters and Economic Perspective

“…Researchers have been working extensively to solve these mass transfer and thermodynamics barriers in the past few years using different additives. − Environmentally friendly additives such as biodegradable surfactants, amino acids, ionic liquids and natural nanoparticles now open up newer avenues among the research community. The in situ Raman spectroscopy, X-ray imaging, and molecular simulations help researchers to fundamentally understand CO 2 hydrates in sequestration conditions. − The long-term stability of hydrate, mechanical characteristics of hydrate-bearing sediments, and effect of sequestration conditions on hydrate formation and dissociation can be analyzed using the aforesaid techniques. Economic challenges such as carbon pricing, capital expenditure, unpredictable environmental policies and lack of transition will make large-scale storage in oceans difficult for both industries and government.…”

Expanding the horizons of covalent organic frameworks: sub-stoichiometric synthesis as an emerging toolkit for functional COFs

“…78,79 One of the most investigated classes of COFs is imine-linked, which involves the reaction between aldehydes and amines. [80][81][82][83] Several synthetic approaches, 44,[84][85][86] processing methodologies, 47,87,88 studies in terms of imparting structural stability 30,[89][90][91] and mechanistic understanding of the formation under different conditions 81,85,[92][93][94][95][96][97] have emerged over time. Postsynthetic introduction of primary amine groups or the presence of unreacted amino or carbonyl groups in imine-linked COFs have been shown to result in functional properties that are otherwise difficult to attain in fully formed networks.…”

Research Progress of β-Ketoenamine-Linked Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution

“…Thus, it is necessary to summarize the researches of Tp-COFs in photocatalytic hydrogen evolution based on molecular engineering strategy. Previous reviews of Tp-COFs focused on synthesis 15 and photocatalytic hydrogen evolution with a preference for composite engineering strategies 16 . Different from these reviews, this paper is dedicated to concentrating on Tp-COF photocatalysts from the perspective of molecular engineering, including the construction of planarization, optimization of ordered structure, precise organic functionalization and effect of morphology.…”

“…Previous reviews of Tp-COFs focused on synthesis 15 and photocatalytic hydrogen evolution with a preference for composite engineering strategies. 16 Different from these reviews, this paper is dedicated to concentrating on Tp-COF photocatalysts from the perspective of molecular engineering, including the construction of planarization, optimization of ordered structure, precise organic functionalization and effect of morphology. Finally, we also provide an outlook of the challenges and some enlightenments for the subsequent construction of high-efficiency Tp-COF photocatalysts.…”