Surfactants such as sodium dodecyl sulfate (SDS), which are used as kinetic hydrate promoters in various hydrate based technological applications, are facing a serious roadblock toward their commercial utilization as a result of the excessive amount of foam generation, particularly during hydrate dissociation. One of the approaches to alleviate this foam formation is the use of various antifoaming agents which may be employed in combination with surfactants. The possibility of using one such antifoaming agent, a silicone based polymeric surfactant, for hydrate based methane storage, has been explored in the current work through a detailed morphological study. Investigations on the morphology of hydrate formation and dissociation reveal the strong antifoaming activity of the silicone based compound and the optimal ratio in which it should be mixed with a surfactant, specifically SDS, in order to effectively alleviate unwanted foam formation. Further, kinetic data reveal that the generally observed kinetic promotion of methane hydrate formation in the presence of SDS is not affected by the addition of antifoam thus underlining the cause for the antifoam's free and possible use in various hydrate based technological applications. © 2018 American Chemical Society.

Rajnish Kumar

Department Of Chemical Engineering

Jitendra Shital Sangwai

Gaurav Pandey

Gaurav Bhattacharjee

Hari Prakash Veluswamy

Praveen Linga

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

ACS Applied Energy Materials

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. © 2019 Elsevier Ltd

Applied Energy

Methane recovery from marine gas hydrates: A bench scale study in presence of low dosage benign additives

Storing natural gas (NG) in the form of clathrate hydrates (solidified natural gas, SNG) is a promising technology for its long-term, large-scale storage because it is safe and economically feasible compared to liquefied natural gas and compressed natural gas. Recently, we reported rapid mixed methane hydrate formation kinetics in the presence of saline water and seawater for the SNG technology. In this study, we investigate in detail the morphology of mixed CH4/tetrahydrofuran hydrate formation and dissociation with and without the presence of salt (3 wt % NaCl). Knowledge about hydrate crystal morphology is a key aspect of SNG technology development. This study reports the morphology difference of mixed hydrates in the presence of saline and nonsaline water to shed light on the observed kinetic performance. Morphology changes observed during the nucleation, hydrate growth, and dissociation of mixed hydrates at two different formation pressures of 5 and 3 MPa at 283.15 K are presented. Subtle differences were observed with significant upward growth (above the gas-liquid interface) during the initial hydrate formation (until 5 min) for the saline system in comparison to significant downward growth (below the gas-liquid interface) in the bulk solution for the nonsaline system despite the similar operating conditions. Further, from morphology observations, it could be seen that the hydrate dissociation of mixed hydrates formed using saline water took less time (about 20 min) than that observed in nonsaline water (about 30 min). This can be attributed to the spread of hydrates along crystallizer walls in the case of the saline water system, resulting in better heat transfer during dissociation. © 2019 American Chemical Society.

Energy and Fuels

Morphology study of mixed methane-tetrahydrofuran hydrates with and without the presence of salt

Natural gas hydrate is a potential source of methane which needs to be extracted from under the sea bed. For the economic recovery of methane from natural gas hydrates, production approaches such as depressurization, thermal stimulation, and inhibitor injection are being investigated. However, studies involving hydrate-bearing clayey sediments and recovery of methane from such reservoirs are rare. This work investigates in detail the potency of hydrate dissociation methods such as depressurization by constant rate gas release, thermal stimulation and the combination of two for energy recovery from hydrate bearing clayey sediments underlying a free gas zone. Pure water and two different mud samples containing 3 and 5 wt% of bentonite were used for methane hydrate formation and dissociation studies. Thermodynamic study of methane hydrate in the presence of bentonite clay was also conducted for the above two concentrations. No considerable effect of clay on the inhibition or promotion of methane hydrate formation was observed. Initially, methane hydrate formation has been investigated using pure water, 3 and 5 wt% bentonite mud at an initial hydrate formation pressure of 8 MPa and at a temperature of 278.15 K. Subsequently, methane hydrate dissociation experiments were carried out using depressurization, thermal stimulation and their combination. The effect of the rate of gas release on hydrate dissociation by depressurization was investigated using two different rates of 10 mL/min and 20 mL/min. Thermal stimulation experiments were carried out for ΔT = 15 K at the rate of 7.5 K/hr and the results on methane recovery were recorded. The detailed investigation shows that the combination of the two methods is more efficient for methane production than the standalone method in clayey hydrate reservoir. This study provides important insights into the hydrate production methodology from clayey hydrate reservoirs. © 2018 Elsevier Ltd

Energy recovery from simulated clayey gas hydrate reservoir using depressurization by constant rate gas release, thermal stimulation and their combinations

Microorganisms play an important role in the formation of methane hydrate in subsea environment. Studies involving the effect of biosurfactants produced by microorganisms on methane hydrate formation kinetics are not well understood. The present work investigates the influence of cell free solution containing biosurfactant obtained during the cultivation of microorganisms on the formation kinetics of methane gas hydrate. Two microorganisms, viz., Pseudomonas aeruginosa CPCL and Bacillus subtilis YB7 have been used to produce biosurfactants namely, rhamnolipid and surfactin, respectively. The performance of the cell free solution containing various concentrations (200, 400, 600, 800 and 1000&nbsp;ppm) of biosurfactant to form the methane gas hydrate was analyzed by adding it into the pure water system and compared with synthetic surfactant, sodium dodecyl sulfate (SDS). It has been observed that the introduction of biosurfactant into pure water system improves the formation kinetics of methane hydrate and reduced the induction time. Addition of 200&nbsp;ppm of rhamnolipid solution in pure water system has resulted in 47.3% of methane gas to hydrate conversion with an induction time of about 0.23&nbsp;h, whereas pure water showed 45.1% conversion with an induction time of about 5.77&nbsp;h. The same concentration of surfactin and SDS have resulted in 42.7 and 33.3% of methane gas to hydrate conversion, respectively. Biosurfactants studied here shows efficient and better performance than their chemical counterpart, namely SDS. This study also provides information on the optimum biosurfactant concentration for the improved formation kinetics of methane hydrate. The results suggest that the utilization of environment friendly biosurfactant can be used as an effective kinetic promoter for the methane hydrate formation suitable for optimum storage and transportation of natural gases. © 2017 Elsevier B.V.

Journal of Natural Gas Science and Engineering

Effect of biosurfactants produced by Bacillus subtilis and Pseudomonas aeruginosa on the formation kinetics of methane hydrates

Kinetic studies concerning the combination of thermodynamic promoters (tetra-n-butyl ammonium bromide, TBAB and tetrahydrofuran, THF) and kinetic promoters (sodium dodecyl sulphate, SDS) have not yet been investigated in detail for methane hydrate system suitable for natural gas storage and transportation. In this work, experiments were conducted at an initial pressure conditions of 7.5&nbsp;MPa and 276.15&nbsp;K for pure water, SDS, TBAB, (TBAB&nbsp;+&nbsp;SDS), THF, (THF&nbsp;+&nbsp;SDS) and (THF&nbsp;+&nbsp;TBAB) aqueous systems for various concentrations. Similarly, at 5.5&nbsp;MPa and 276.15&nbsp;K, experiments were conducted for pure water, TBAB, (TBAB&nbsp;+&nbsp;SDS), THF and (THF&nbsp;+&nbsp;SDS) aqueous systems for various concentrations. In addition, at 3.0&nbsp;MPa and 276.15&nbsp;K, 0.05 and 0.1 mass fraction of TBAB, 0.005 and 0.01 mass fraction of THF and (0.01&nbsp;+ 0.1) mass fraction of (THF&nbsp;+ TBAB) aqueous systems have been considered for the experiments. It has been observed that the methane hydrate formed from pure water with SDS shows higher moles of gas consumption per mole of water as compared to other aqueous systems at higher pressure. Also, the use of SDS with THF shows drastic increase in methane consumption as against semiclathrate hydrate/hydrate formed using TBAB aqueous system and pure water. At lower pressure, of about 3&nbsp;MPa, gas consumption per mole of water in hydrate has found to enhance for a mixed promoter system containing (THF&nbsp;+ TBAB) as compared with the other aqueous systems. Theoretical and actual gas storage capacity calculations has also been performed for various concentrations of THF and TBAB aqueous systems. This study essentially helps to understand the behaviour of TBAB and THF aqueous solution with and without SDS and mixed promoter system of (THF&nbsp;+&nbsp;TBAB) for methane hydrate formation desirable for applications like gas storage, transportation and gas recovery using hydrate-based gas separation method. © 2016 Elsevier B.V.

Kinetics of methane hydrate formation in an aqueous solution of thermodynamic promoters (THF and TBAB) with and without kinetic promoter (SDS)

New kinetic promoters must be researched for hydrate formation suitable for natural gas storage and transportation to push this technology towards economic feasibility. In this study, the kinetics of the methane hydrate formation have been investigated in the presence of activated carbon and nano-silica (0.5, 1.0 and 2.0wt%) suspensions in an aqueous solution. Experiments were conducted at 8MPa and 275.15K using methane gas as the hydrate former. Particles (activated carbon and nano-silica) were analyzed using scanning electron microscope (SEM) and X-ray diffraction before use. Information on the number of moles of gas consumed during hydrate formation, induction time, rate of hydrate formation, water-to-hydrate and gas-to-hydrate conversion were investigated. It was seen that the kinetics of hydrate formation were more favorable at higher concentrations of particles of activated carbon and nano-silica in the suspension. The effect of the deactivation of activated carbon was also studied and has shown a reversed trend when compared to other particles, behaving as an inhibitor for methane hydrate formation. The rate of hydrate formation was enhanced in the presence of activated carbon and was on the higher side when compared to suspensions of nano-silica. The water-to-hydrate and gas-hydrate conversions observed were in-line with the trends seen in the moles of gas consumed, with activated carbon being more effective than the rest of the particles. The induction time was observed to be reduced in the presence of suspensions of activated carbon when compared to the other hydrate forming systems studied in this work. In general, the results show that both activated carbon and nano-silica have promoting effects on methane hydrate formation kinetics, however, the effect of activated carbon is significantly more pronounced. This study provides a precursor for an improved understanding on the role of particle suspensions for methane hydrate formation suitable for gas storage applications. © 2015 Elsevier B.V.

Journal	Data powered by TypesetACS Applied Energy Materials
Publisher	Data powered by TypesetAmerican Chemical Society
Open Access	No