00640nas a2200157 4500008004100000245014500041210006900186260000800255300001200263490000800275100002200283700001800305700001500323700001900338856012500357 2016 eng d00aEffect of polyvinylpyrrolidone at methane hydrate-liquid water interface. application in flow assurance and natural gas hydrate exploitation0 aEffect of polyvinylpyrrolidone at methane hydrateliquid water in cDEC a613-6220 v1861 aChoudhary, Nilesh1 aDas, Subhadip1 aRoy, Sudip1 aKumar, Rajnish uhttps://library.ncl.res.in/content/effect-polyvinylpyrrolidone-methane-hydrate-liquid-water-interface-application-flow-102099nas a2200253 4500008004100000022001400041245007600055210006900131260000800200300001400208490000700222520131000229653001501539653001901554653001601573653001301589653003301602100002601635700002201661700001901683700002301702700001901725856010101744 2016 eng d a1875-510000aEffect of the amino acid L-histidine on methane hydrate growth kinetics0 aEffect of the amino acid Lhistidine on methane hydrate growth ki cSEP a1453-14620 v353 a

In the present study, the effect of a polar amino acid, L-histidine on methane hydrate growth kinetics has been investigated. Methane hydrate formation experiments were carried out in a stirred tank reactor setup at pressure and temperature conditions of 274.15 K and 5.0 MPa respectively. Two different concentrations (0.1 and 1 wt %) of L-histidine were studied. Hydrate growth through molecular dynamic (MD) simulation was also studied; pressure and temperature conditions for the simulations were set at 10.0 MPa and 270.0 K, while the concentration of L-histidine was kept fixed at 0.94 wt %. Hydrate formation runs using MD simulation were carried out with optimal concentration of methane in water. The presence of L-histidine in the system was found to significantly enhance methane hydrate growth kinetics as compared to pure water for both experimental and MD simulation runs. Final gas consumption with 1 wt % L-histidine was found to be comparable to that with 1 wt % SDS, the most commonly used additive for hydrate promotion studies. L-histidine is a benign additive which offers considerable enhancement in methane hydrate formation kinetics and can be utilized for various hydrate based technologies such as methane storage and transport. (C) 2016 Elsevier B.V. All rights reserved.

10aAmino acid10aCrystal growth10aGas hydrate10akinetics10aMolecular dynamic simulation1 aBhattacharjee, Gaurav1 aChoudhary, Nilesh1 aKumar, Asheesh1 aChakrabarty, Suman1 aKumar, Rajnish uhttps://library.ncl.res.in/content/effect-amino-acid-l-histidine-methane-hydrate-growth-kinetics01694nas a2200181 4500008004100000245013400041210006900175260000800244300001400252490000800266520099700274100002201271700002701293700002601320700002301346700001901369856012401388 2017 eng d00aMolecular dynamics simulation and experimental study on the growth of methane hydrate in presence of methanol and sodium chloride0 aMolecular dynamics simulation and experimental study on the grow cMAY a5026-50330 v1053 aThe plugging of processing and transportation lines by gas hydrate formation is a challenging problem for safe exploitation of oil and gas. The existence of water soluble third component (like methanol and sodium chloride) in the aqueous phase influence the gas hydrate formation thermodynamically also possibly affects the kinetics of hydrate growth. Inorganic salt and organic molecule (alcohols) at high concentration in the aqueous phase have been used as thermodynamic inhibitors to effectively prevent the hydrate formation. This study utilizes molecular dynamics as well as an experimental method to investigate the mechanism of the hydrate formation and the effect of additives. The MD simulation showed that at moderate temperature and pressure, a low concentration (1 wt %) of methanol and NaCl enhances methane hydrate growth kinetics. Significant numbers of methanol molecules were observed inside the gas hydrate cages whereas Na⁺/Cl⁻ ions leach out during hydrate formation.1 aChoudhary, Nilesh1 aKushwaha, Omkar, Singh1 aBhattacharjee, Gaurav1 aChakrabarty, Suman1 aKumar, Rajnish uhttps://library.ncl.res.in/content/molecular-dynamics-simulation-and-experimental-study-growth-methane-hydrate-presence01514nas a2200193 4500008004100000022001400041245010500055210006900160260000800229300001400237490000800251520082700259100002201086700002401108700001501132700002301147700001901170856013101189 2018 eng d a1520-610600aEffect of sodium dodecyl sulfate surfactant on methane hydrate formation: a molecular dynamics study0 aEffect of sodium dodecyl sulfate surfactant on methane hydrate f cJUN a6536-65420 v1223 a

In experimental studies, it has been observed that the presence of sodium dodecyl sulfate (SDS) significantly increases the kinetics of hydrate formation and the final water-to-hydrate conversion ratio. In this study, we intend to understand the molecular mechanism behind the effect of SDS on the formation of methane hydrate through molecular dynamics simulation. Hydrate formation conditions similar to that of laboratory experiments were chosen to study hydrate growth kinetics in 1 wt % SDS solution. We also investigate the effect of interactions with isolated SDS molecules on methane hydrate growth. It was observed that the hydrophobic tail part of the SDS molecule favorably interacts with the growing hydrate surface and may occupy the partial hydrate cages while the head groups remain exposed to water.

1 aChoudhary, Nilesh1 aHande, Vrushali, R.1 aRoy, Sudip1 aChakrabarty, Suman1 aKumar, Rajnish uhttps://library.ncl.res.in/content/effect-sodium-dodecyl-sulfate-surfactant-methane-hydrate-formation-molecular-dynamics-study01803nas a2200229 4500008004100000022001400041245012700055210006900182260000900251300000900260490000800269520100900277653001801286653001701304653002501321653001701346100002201363700002301385700001501408700001901423856013101442 2019 eng d a0301-010400aComparison of different water models for melting point calculation of methane hydrate using molecular dynamics simulations0 aComparison of different water models for melting point calculati cJAN  a6-140 v5163 a

Molecular dynamics simulation is a powerful tool to understand the gas hydrate nucleation, growth, and dissociation at molecular level. Prerequisite of super-cooling during gas hydrate formation and a certain degree of super-healing during melting shows significant hysteresis in the transition between solid and liquid state due to large nucleation barrier. Different water models quantitatively differ in their prediction of thermodynamic and kinetic properties of bulk water, including phase behaviour. The present work carries out a systematic investigation of the effect of the chosen water model on the phase behaviour, in particular, the decomposition of methane hydrate. Void-induced melting has been used to predict the melting point of methane hydrate using TIP4P/Ice, TIP4P/2005, TIP4P, and SPC/E water models. This method avoids the need for a predetermined interface for melting point calculations and thus may have its importance in identifying dissociation kinetics of bulk hydrate.

10adecomposition10aGas hydrates10aVoid-induced melting10aWater models1 aChoudhary, Nilesh1 aChakrabarty, Suman1 aRoy, Sudip1 aKumar, Rajnish uhttps://library.ncl.res.in/content/comparison-different-water-models-melting-point-calculation-methane-hydrate-using-molecular02708nas a2200313 4500008004100000022001400041245011000055210006900165260000900234300001100243490000800254520170900262653001601971653001301987653001902000653002002019653002102039653002402060653001202084100002602096700002202122700002002144700002402164700002102188700002002209700001502229700001902244856013102263 2019 eng d a0306-261900aMethane recovery from marine gas hydrates: a bench scale study in presence of low dosage benign additives0 aMethane recovery from marine gas hydrates a bench scale study in cNOV  a1135660 v2533 a

De-pressurization is one approach which has been found to be economically feasible for methane recovery from marine hydrates. Hydrate dissociation being an endothermic process suggests that de-pressurization alone would not be sufficient and some additional stimulation would be required for sustained production from one such reservoir. Thermal stimulation may overcome the challenge posed by the endothermic dissociation process; however, economically it may not be ideal. A possible way out is to use thermal stimulation, but at relatively low temperatures as compared to conventional practice. This would be economical and can be accomplished in the presence of small doses of additives mixed in with the water stream used for thermal stimulation. In the present study, a number of benign additives were identified which when used in low concentrations enhance the kinetics of methane hydrate dissociation compared to pure water. Additives were first shortlisted from a wide potential pool using quantum mechanical calculations. These additives were later tested for their efficacy in stirred tank reactor to quickly identify the best additives for the job and few selected additives were then studied in a larger bench scale setup (fixed bed configuration) where they were injected in the form of an additive-water stream to dissociate already formed hydrates. Factors such as toxicity of the additive, fluidity of additive-water stream, foam formation on mixing of additive with water, etc. were also taken into account. An energy and efficiency analysis revealed that reported additives enhance the energy ratio and thermal efficiency of the process as compared to pure water stimulation.

10aBench scale10akinetics10aMarine hydrate10amethane hydrate10aMethane recovery10aNatural gas hydrate10aProcess1 aBhattacharjee, Gaurav1 aChoudhary, Nilesh1 aBarmecha, Vivek1 aKushwaha, Omkar, S.1 aPande, Nawal, K.1 aChugh, Parivesh1 aRoy, Sudip1 aKumar, Rajnish uhttps://library.ncl.res.in/content/methane-recovery-marine-gas-hydrates-bench-scale-study-presence-low-dosage-benign-additives02139nas a2200193 4500008004100000022001400041245009700055210006900152260000900221300001600230490000700246520145600253100002201709700002701731700002601758700002301784700001901807856011901826 2020 eng d a0888-588500aMacro and molecular level insights on gas hydrate growth in the presence of hofmeister salts0 aMacro and molecular level insights on gas hydrate growth in the  cNOV  a20591-206000 v593 a

The effect of few monovalent salts (NaCl, NH4Cl, and GdmCl) as additives, according to the Hofrneister series on the growth of methane gas hydrates, has been studied using experiments as well as molecular dynamics (MD) simulation. Further, the Hofmeister effects on hydrate crystallization have been correlated with the methanol as an additive, which is a known thermodynamic hydrate inhibitor for hydrate growth. One of the previous studies (discussed later in this article) available in the literature concludes that methane hydrate formation from ice might show enhanced kinetics in the presence of salts; this behavior is contrary to the general usage of such salts as hydrate inhibitors. This conclusion may not necessarily be true for experiments done with liquid water, and therefore, this work explores the behavior of these salts in a lab-scale setup. In addition, current work reports detailed MD simulation studies to gain insight into the mechanism of hydrate formation in the presence of Hofmeister series salts at two different concentrations of 1 and 10 wt % in water and compare the results with hydrate formation in the methanol-water system. Our study suggests that the presence of these additives at low concentrations (1 wt %) does enhance the hydrate growth kinetics. However, at higher concentrations (10 wt %), inhibition by these additives persisted, and prolonged nucleation, as well as retarded growth, was observed.

1 aChoudhary, Nilesh1 aKushwaha, Omkar, Singh1 aBhattacharjee, Gaurav1 aChakrabarty, Suman1 aKumar, Rajnish uhttps://library.ncl.res.in/content/macro-and-molecular-level-insights-gas-hydrate-growth-presence-hofmeister-salts02321nas a2200181 4500008004100000022001400041245014200055210006900197260000900266300001100275490000800286520163300294100002001927700002201947700002301969700001901992856012802011 2020 eng d a0167-732200aMorphology and dynamics of self-assembled structures in mixed surfactant systems (SDS plus CAPB) in the context of methane hydrate growth0 aMorphology and dynamics of selfassembled structures in mixed sur cDEC  a1142960 v3193 a

Presence of small dosages of surfactants in the aqueous phase has been reported to enhance the rate of gas hydrate (clathrate) formation. In this work, using extensive atomistic molecular dynamics (MD) simulations, we have investigated how SDS (surfactant) aggregates in the presence/absence of CAPB (co-surfactant) at ambient conditions (temperature 298 K and pressure 1 bar) and at hydrate forming conditions (temperature 275 K and pressure 50 bar) resulting in altered growth kinetics of methane hydrate. We observe that SDS forms aggregates of different sizes and shapes depending on the thermodynamic condition starting from random distributions of the surfactants. In the presence of the CAPB co-surfactant, tightly packed mixed aggregates are formed. Using various structural order parameters, we demonstrate that shape of the aggregates deviates from spherical as well as cylindrical symmetry. During the aggregation process in presence of methane, the methane molecules get absorbed into the aggregates, enhance the aggregation kinetics and provide structural flexibility to the aggregates. This result is partly in agreement with previous experimental observations that SDS (with or without a co-surfactant) may form micelle-like structures under hydrate forming conditions and that methane gets absorbed by these aggregates leading to enhanced solubility of methane in the aqueous phase. Further, we have investigated the dynamics of shape fluctuations of the aggregates and observed that several distinct relaxation timescales exist in these heterogenous systems. (C) 2020 Elsevier B.V. All rights reserved.

1 aHande, Vrushali1 aChoudhary, Nilesh1 aChakrabarty, Suman1 aKumar, Rajnish uhttps://library.ncl.res.in/content/morphology-and-dynamics-self-assembled-structures-mixed-surfactant-systems-sds-plus-capb