Fig 2 - uploaded by Elena Brodskaya
Content may be subject to copyright.
Radial distribution functions (a) methane-methane (C-C) and (b) methane-water (C-O) under isochoric conditions at different temperatures: (1) 200, (2) 250, and (3) 260 K.

Radial distribution functions (a) methane-methane (C-C) and (b) methane-water (C-O) under isochoric conditions at different temperatures: (1) 200, (2) 250, and (3) 260 K.

Contexts in source publication

Context 1
... hydrate decomposition upon heating is evident from changes in the RDFs obtained by molecular dynamics simulation. Figure 2a shows the methane-methane two-particle distribution functions calculated in the NVT ensemble. At 200 K, distinctly resolved high peaks are observed, which indicate the existence of an ordered structure of methane located in hydrate cavities. ...
Context 2
... of methane located in hydrate cavities. The distance between adjacent methane molecules is about 6.5 Å, while the number of such neighbors is 9.4. Analogous structural characteristics were obtained at temperatures of 180, 210, 220, and 230 K. At 240 K, the intensities of the maxima are decreased, and the peaks are smoothed. It follows from Fig. 2 that the hydrate is completely decomposed upon the passage from 250 to 260 K. At the same time, the amount of the adjacent neighbors in the system decreases to 5.2 at 250 K and becomes almost zero (0.2) at 260 ...
Context 3
... to the C-O (methane-water) radial distribution functions (Fig. 2b), the crystalline structure is completely destroyed at 260 K. However, it should be noted that the intensity of the maxima begins to decrease at a lower temperature (230 K). This indicates that hydrate melting begins from the destroying of the water matrix, thereby promoting subsequent escape of the gas from the cavities. The number of ...
Context 4
... values of diffusion coefficients. Therewith, the diffusion coefficient of water begins to grow at a lower temperature and turns out to be higher than that of methane. For example, under the isochoric conditions, a noticeable increase in the diffusion coefficient of H 2 O takes place already at 230-240 K, while for methane, it is observed at 250 K (Fig. 4, curves 2, 4). When simulating the system at a constant pressure of 50 atm, the mobility of molecules begins to increase at higher temperatures: 240-250 K for water and 260 K for methane (Fig. 4, curves 1, 3). Judging by the data obtained, it may be assumed that methane hydrate begins to melt at 250 and 260 K under the isochoric and isobaric ...
Context 5
... molecules increases at temperatures of 220 and 230 K at constant volume and pressure, respectively (Fig. 5, curves 1, 3). For carbon dioxide hydrate at a constant pressure, additional calculations of melting were performed for a structure with incomplete filling, when only 86% of the cavities in the hydrate were initially occupied with the gas (Fig. 5, curve 2). It is seen that, below 230 K, the mobility of carbon dioxide molecules in the hydrate is independent of the degree of filling of the cavities; however, at 240 K, the gas diffusion coefficient in the partly filled hydrate becomes noticeably higher than that in the case complete filling. Probably, the temperature of 240 K corresponds to ...
Context 6
... in the diffusion coefficient with an increase in the temperature takes place in the same temperature range for both distributions of molecules over the cavities (a random filling or the filling of only large cavities). Thus, it can be seen that the melting of the partly and completely filled hydrates begins at the same temperature of nearly 230 K (Fig. 5, curves 2, ...
Context 7
... change in the external conditions has a noticeable effect only on the energy of carbon dioxide hydrate (Fig. 6, curves 2, 4). In the temperature dependence of the energy, the temperature range that corresponds to melting appears to be markedly narrower than that for methane, as was noted above when analyzing the RDFs. Under the isochoric conditions, carbon dioxide hydrate begins to melt at 210 K (Fig. 6, curve 4), while the potential energy of the CO 2 -CO ...

Similar publications

Article
Full-text available
Background Production of [¹¹C]CH4 from gas targets is notorious for weak performance with respect to yield, especially when using high beam currents. Post-target conversion of [¹¹C]CO2 to [¹¹C]CH4 is a widely used roundabout method in ¹¹C-radiochemistry, but the added complexity increase the challenge to control carrier carbon. Thus in-target-produ...
Thesis
Full-text available
Kinetic analysis of methane and methane-propane hydrate formation by the use of different impellers and flows with the use of different baffles together with the examination of different amino acids and their function as promoter or inhibitors.

Citations

... Also, between different ensembles, the sequence of accurate clathrate nucleation was found to be NPT > NVT > NVE; however, the crystallinity sequence is exactly reversed [116]. According to the dissociation of CO 2 and CH 4 hydrates at 180-280 K, it was concluded that hydrate stability using isochoric conditions is lower than that in isobaric conditions [117]. Although remarkable advances in macroscopic measurements have been accomplished, MD simulations as a powerful technique can provide insights into the fundamental mechanisms of gas hydrates at molecular and atomistic levels. ...
Article
Clathrate hydrates or gas hydrates have received worldwide attention due to their potential to be utilized in various sustainable technologies. The hydrate-based industrial applications as well as developing green technologies or safely extracting natural gases stored in the nature require profound comprehension of the phenomena associated with gas hydrates. On the flip side, identifying the characteristics of different hydrate formers and the effects of a wide range of introduced additives to these technologies is the critical objective, so that needs to be deeply investigated at both macroscopic and microscopic scales. The expensive experiments and limited availability of facilities at the nanoscale encourage researchers to apply novel computational methods and simulation approaches. For three decades, molecular dynamics (MD) simulations in the field of gas hydrates have been widely used to mathematically analyse the physical movements of molecules and the evolution of atomic positions in time. In this work, the mechanisms involved in the pure, binary, and mixed gas hydrates, and the impressions of promoters / inhibitors / minerals on gas hydrates were briefly reviewed. Also, the phenomena and properties associated with gas hydrates such as nucleation, growth, stability, dissociation, cage occupancy, storage capacity, morphology analysis, guest role, thermophysical and mechanical properties, dynamical and vibrational behaviours of gas hydrates were reviewed. This work aims to provide readers with an extensive overview of MD simulations of gas hydrates to stimulate further research on this riveting field.
... Interfacial properties of brine water and CO 2 +CH 4 mixture showed that the interfacial tension (IFT) of CH 4 +brine aqueous system in the existence of CO 2 decreases but consistent with experimental evidence, the degree of decline is directly dependent on the CO 2 concentration [453]. The properties of spherical nanoclusters of CO 2 /CH 4 hydrates and the effects of surrounded water/gas/porous environment can also be analysed by MD [454,455]. Recent MD research manifested that CO 2 +CH 4 molecules in the existence of THF+DMSO can diffuse into the hydrate structure more easily which brings about a greater amount of enclathrated gas molecules than using a single THF [456]. Also, due to the very strong distortion of SDS in the interaction with CO 2 , SDS+CH 4 and SDS+CO 2 behaviours consistent with experiments are entirely different [457]. ...
... Although CH 4 hydrate can dissociate somewhat above the bulk melting temperature, this is not the case for CO 2 hydrate which confirms that at the grain boundaries, the guest types and grain boundary structures (both) may affect the thermal stability of polycrystalline hydrates [487]. Decomposition analysis of CO 2 and CH 4 hydrates at 180-280 K and 0.1-10 MPa determined that hydrate stability using isochoric conditions is lower than that in isobaric conditions [454]. A faster layer-by-layer decomposition rate in the gas-solid interface than in the liquid-solid interface during the CO 2 decomposition cab also be observed. ...
Article
Global warming is one of the most pressing environmental concerns which correlates strongly with anthropogenic CO2 emissions so that the CO2 decreasing strategies have been meaningful worldwide attention. As an option, natural gas hydrate reservoirs have steadily emerged as a potent source of energy which would simultaneously be the proper places for CO2 sequestration if the method of CO2/CH4 replacement could be developed. On the flip side, CO2 hydrates as safe and non-flammable solid compounds without an irreversible chemical reaction would contribute to different industrial processes if their approaches could be improved. Toward developing substantial applications of CO2 hydrates, laboratory experiments, process modelling, and molecular dynamics (MD) simulations can aid to understand their characteristics and mechanisms involved. Therefore, the current review has been organized in form of four distinct sections. The first part reviews the studies on sequestering CO2 into the natural gas hydrate reservoirs. The next section gives an overview of process flow diagrams of CO2 hydrate-based techniques in favour of CO2 Capture and Sequestration & Utilization (CCS&U). The third section summarizes the merits, flaws, and different effects of hydrate promoters as well as porous media on CO2 hydrate systems at macroscopic and mesoscopic levels, and also how these components can improve CO2 hydrate properties, progressing toward the more feasibility of CO2 hydrate industrial applications. The final sector recapitulates the MD frameworks of CO2 clathrate and semiclathrate hydrates in terms of new insights and research findings to elucidate the fundamental properties of CO2 hydrates at the molecular level.
Preprint
Full-text available
This investigation aims to elucidate the dissociation of CO 2 gas from gas hydrates (GH) over a 60-minute duration at varying temperatures, with the objective of understanding the entrapment of CO 2 gas within GH with the use of GH promoters. The study examines four food-grade amino acids possessing surfactant capabilities—cysteine, leucine, methionine, and valine—as well as lecithin, to discern their potential as food-grade GH promoters. Dissociation of GH from its promoters is investigated at temperatures of -18°C, 10°C, 20°C, and 23°C. 0.1% and 1% of the weight of the water utilized in the GH reactor is comprised of amino acids and lecithin respectively. The study explores the individual and combined effect of promoters, with a specific attention on leucine and methionine, identified as the most effective amino acid promoters. These two promoters exhibit synergistic effects when combined with lecithin. The CO 2 content within normal GH is found to be 9.7% and 15.6% when employing methionine, leucine, and lecithin. Analysis of the GH dissociation graph at different temperatures, considering various promoters, indicates that the use of efficient promoters in combination enhances gas containment. Notably, enhanced stability is observed at higher temperatures, such as 20°C, extending over a prolonged duration of 20 minutes. This increased stability may prove advantageous for CO 2 GH applications in the food industry.
Article
Understanding and controlling the growth of CO2 hydrates is critical for a variety of industrial applications, such as sequestration of greenhouse gases. Due to the excellent physical and chemical properties, metal nanoclusters are widely used as additives in hydrate experiments. However, little is known about the molecular mechanism of this process. In this study, molecular dynamics (MD) simulation was performed at 260 K and 30 MPa by adding different types of metal particles (Cu, Fe and Ag) and different mass fractions (0.2 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt% and 1.3 wt%) to study the growth kinetics of the CO2 hydrate system containing pre-placed hydrate crystal cells. Simulation results showed that the presence of these metal particles has a mixed effect on the growth kinetics, and the extent of the effect seems to varies with different additives and also with the concentration of the metal particles used. It was observed that Cu particles had the most obvious promoting effect on hydrate growth. When the mass fraction of Cu particles was between 0.2 wt% and 1.0 wt%, the rate of hydrate formation increased, especially at the mass fraction of 1.0 wt%. The growth rate of CO2 hydrate was almost 50% higher than that of pure water system at this concentration. In addition, Fe particles had a medium effect on promoting CO2 hydrate growth. Ag particles had no obvious effect on CO2 hydrate growth. Results show that the addition of metal particles with high specific surface areas greatly increases the mass and heat transfer among the gas, liquid and hydrate phases, which is conducive to the growth of CO2 hydrate.