Gas hydrate, a solid transformed from an ensemble of water and gaseous molecules under suitable thermodynamic conditions, is present in marine and permafrost strata. The ability of methane hydrates ...to exist outside of its standard stability zone is vital in many aspects, such as its utility in gas storage and transportation, hydrate-related climate changes and gas reservoirs on the planet. A systematic study on the stability of methane hydrates divulges that the gas uptake decreased by about 10% by increasing the NaCl content to 5.0 wt%. The hydrate formation kinetic is relatively slower in a system with higher NaCl. The self-preservation temperature window for hydrate systems with NaCl 1.5, 3.0 and 5.0 wt% dramatically shifted to a lower temperature (252 K), while it remained around 270 K for NaCl 0.0 and 0.5 wt%. Based on powder x-ray diffraction and micro-Raman spectroscopic studies, the presence of hydrohalite (NaCl·2H
O) phase was identified along with the usual hydrate and ice phases. The eutectic melting of this mixture is responsible for shifting the hydrate stability to 252 K. A systematic lattice expansion of cubic phase infers the interaction between NaCl and water molecules of hydrate cages.
Storage of greenhouse gases in the form of gas hydrates is attractive and is being pursued rigorously in recent times. However, slow formation rate and inefficient water to hydrate conversion are the ...main hindering factors. In this report, we examine the role of two amino acids (0.5 wt%), l-methionine (l-met) and l-phenylalanine (l-phe) on the formation of gas hydrates using methane (CH
), carbon dioxide (CO
) and their mixtures as guest molecules. Experiments are conducted under non-stirred and isochoric configurations. The hydrate conversion efficiency of both amino acids is identical for hydrates formed with CH
and mixture of (CO
+CH
). However, the hydrate conversion is significantly less in CO
hydrates in l-phe system. Addition of amino acids to the water dramatically improved the kinetics of hydrate formation and 90% of maximum gas uptake in hydrate phase occurred in less than an hour. The water to hydrate conversion is also very efficient (>85%) in the presence of amino acids. Therefore, the amino acids containing systems are suitable for storing both CH
and CO
gases. The gas hydrates were characterised using powder x-ray diffraction (XRD) and Raman spectroscopic measurements. These measurements indicate the formation of sI hydrates and encasing of gas molecules as guests.
Natural gas (NG) is considered a modern source of energy. Gas hydrates are anticipated to be an alternative method for gas storage and transportation applications. The process must be handy, rapid, ...and proficient for scale-up. In the present study, methane (CH
4
) and carbon dioxide (CO
2
) hydrates are synthesized by varying the guest (gas) to host (water) volume. The experiments are performed in a non-stirred system. The results specify that the maximum storage capacity is achieved when the molar liquid water-gas ratio is about 4.08 and 8.25 for CH
4
and CO
2
hydrates. At the optimal water-gas ratios, the total CH
4
and CO
2
gas uptake capacity is about 14.3 ± 0.4 and 9.1 ± 0.4 liters at standard temperature and pressure (STP) conditions. The gas uptake gradually increases with the solution volume and abruptly falls after a threshold point. The hydrate grows across the reactor's metal surface; when the process fully covers the surface, the growth continues horizontally (increase in thickness). With varying the liquid water-gas ratio (low to high), the formation kinetics (
t
90
) is delayed. The hydrate growth rate gradually decreases and does not significantly influence the hydrate formation temperatures. Optimizing the molar liquid water-gas ratio yields a high gas storage capacity and faster process kinetics.
Methane and carbon dioxide storage in hydrate form.
Methane emissions increase day by day into the atmosphere and influence global temperatures. The necessity to capture these emissions at the source point is a primary concern. Several ...methods/techniques are being adopted to capture these emissions. The methane hydrates could be a viable method among them. The present study exposes various amino acids' effects in methane hydrate formation. The formation temperatures are around ∼268 to 273 K except for l-cys, which is about ∼277 K. The required subcooling for hydrates to trigger is high and is increasing in the order l-thr > l-met > l-phe > l-val > l-cys. The methane hydrate conversion is high in the presence of nearly all the amino acids with methane uptake capacity of ∼80-85%, except l-thr, for which it is only 30% of the total uptake capacity. The side chain of l-thr comprises the hydroxyl group, making it a polar and uncharged amino acid. It is ascertained that hydroxyl groups alone can form hydrogen bonds with water, increasing the hydrophilicity and solubility of molecules, causing lesser conversion in the l-thr system. The gas uptake kinetics is faster in l-met and l-phe systems (
t
90
∼ 40 min), and sluggish kinetics is observed in l-cys, l-val, and l-thr systems. The investigations positively indicate using amino acids, l-met, l-phe, l-cys, and l-val as efficient materials for methane gas capture and storage in hydrate form, although not l-thr. Amino acids are readily dissolvable in water and could be easily pelletized for methane gas storage and transportation.
Methane gas storage in the hydrate form using amino acids.
Methane hydrates are promising materials for storage and transportation of natural gas; however, the slow kinetics and inefficient water to hydrate conversions impede its broad scale utilisation. The ...purpose of the present study is to demonstrate rapid (2-3 h) and efficient methane hydrate conversions by utilising the water molecules confined in the intra- and inter-granular space of silica powders. All the experiments were conducted with amorphous silica (10 g) powders of 2-30 μm; 10-20 nm grain size, to mimic the hydrate formations in fine sand and clay dominated environments under moderate methane pressure (7-8 MPa). Encasing of methane molecules in hydrate cages was confirmed by Raman spectroscopic (
ex situ
) and thermodynamic phase boundary measurements. The present studies reveal that the water to hydrate conversion is relatively slower in 10-20 nm grain size silica, although the nucleation event is rapid in both silicas. The process of hydrate conversion is vastly diffusion-controlled, and this was distinctly observed during the hydrate growth in nanosize silica.
Rapid and efficient methane hydrate conversions by utilising the water molecules confined in intra- and inter-granular space of silica powders.
A large number of natural gas hydrate deposits have been discovered worldwide so far, and the paramount interest is to evaluate them as an alternate source of energy. Further, the architecture of ...clathrate compounds finds many applications in gas separation, storage, and transportation processes. We examined methane hydrate (MH) formation/dissociation behavior in the presence of hollow silica grains in stirred and nonstirred reactor vessels and have observed an identical value for hydrate conversion. Thus, the stirring is avoidable in the process. Further, the results also show that the overall methane conversion in SiO2–H2O–CH4 has steadily increased, and the mole fraction of methane varies from 0.010 to 0.092 by varying the mole fraction of methane in the vapor phase in the range 0.017 to 0.283. Thereafter, the hydrate conversion is much slower even when the mole fraction in the vapor phase reached 0.647. The gas intake capacity in MH has not improved significantly at higher pressures (≥4 MPa to 5 MPa) in the water-saturated silica system. The effect of the load factor (varying CH4 vapor phase mole fraction with the addition of CH4 gas at a fixed amount of water) is significant on MH, and the CH4 mole fraction in hydrates was 0.142.
Gas hydrate based methodology plays a pivotal role in separation/storage. Some associated crucial issues are optimization of gas content and operational pressure and temperature and developing means ...of controlled gas liberation upon command and means of converting larger volumes of hydrates rapidly in a lighter (cheaper) medium. Accordingly, we carried out systematic studies, aiming to enhance the methane gas storage capacity in methane hydrates. We used hollow silica to improve the hydrate formation kinetics and efficiency. We observed over 90% hydrate conversion in a silica–water–methane system at moderately high pressure (5.0 MPa) and 278 K. Methane hydrate conversion in such a system is extremely fast, and this material is apt for multiple freezing–thawing cycles without noticeable reduction in the storage capacity. The volume storage capacity increased from 128 to 206 v (STP)/v by decreasing the combined mass of water and silica from 100 and 18 g in a fixed volume nonstirred reactor at pressures higher than 5.0 MPa.
Clathrate hydrates are attractive materials for storing greenhouse gases such as methane (CH4) and carbon dioxide (CO2). Inefficient water-to-hydrate conversion and sluggishness in kinetics are ...significant impeding factors. Some additives in lower dosages help accelerate the hydrate conversion process. The aqueous solution with amino acids (0.5 wt %), l-phenylalanine (l-phe), and l-threonine (l-thr) inhibits the CO2 hydrate formation in static (0 rpm) conditions. However, l-methionine (l-met) and l-valine (l-val) are promoters under these conditions. A mild stirring (≥100 rpm) of the aqueous solution favored the hydrate conversion. The overall gas uptake, under continuous stirring, progressively increased by about 15–20%. Another way to improve the storage capacity in l-phe and l-thr aqueous systems in the static reactor is by adding a small quantity of aqueous solutions of l-met or l-val (20% by volume). The overall gas uptake and kinetics under static conditions significantly improved in the l-thr dominant system. However, the gas uptake synergistically improved in mixed solutions with l-phe and l-met, while the gas uptake was insignificant in solution with l-phe and l-val.
Prevention of hydrate plugs during transportation of oil and natural gas in the pipeline network is challenging. Certain additives are often introduced into the process to eliminate/delay plug ...formation. Dominantly synthetic inhibitors are deployed in large volumes (∼20 to 30% by volume) to counter the problem and are highly expensive and, in some circumstances, toxic. The search for novel additives that are eco-friendly and act as inhibitors is in demand. The present study reports the thermodynamic inhibition (THI) capacity of some vastly available natural biopowders, such as Azadirachta indica (neem), Piper betel (betel), and Nelumbo nucifera (Indian lotus) in low dosage (0.5 wt %), on methane hydrate (MH) formation. Since the gas flow is dynamic, experiments are conducted in stirred geometry by varying the speed range from 0 to 1000 rotations per minute (rpm). All of the studies are performed in the isochoric method procedure. The biopowders act as efficient thermodynamic hydrate inhibitors. Once the nucleation triggers, they act as kinetic hydrate promoters. Since sodium dodecyl sulfate (SDS) is an excellent kinetic hydrate promoter in both stirred and nonstirred geometries, the obtained results are compared with the SDS system. Hydrate nucleation is triggered at higher subcooling (∼8 to 10 K) in the presence of water-soluble bioextracts. The neem leaf extracts showed a ∼30% lower hydrate conversion than SDS in identical experimental conditions. Two-stage hydrate nucleation occurred at higher stirring speeds, and the hydrate conversion is inferior (∼6%) between the primary and secondary stages. The addition of biopowder extracts is useful in controlling hydrate formation. A small quantity of biopowders provides higher inhibition and reduces synthetic chemicals used in real-time applications.
Hydrogen hydrates with tetrahydrofuran (THF) as a promoter molecule are investigated to probe critical unresolved observations regarding cage occupancy and storage capacity. We adopted a new ...preparation method, mixing solid powdered THF with ice and pressurizing with hydrogen at 70 MPa and 255 ± 2 K (these formation conditions are insufficient to form pure hydrogen hydrates). All results from Raman microprobe spectroscopy, powder X-ray diffraction, and gas volumetric analysis show a strong dependence of hydrogen storage capacity on THF composition. Contrary to numerous recent reports that claim it is impossible to store H2 in large cages with promoters, this work shows that, below a THF mole fraction of 0.01, H2 molecules can occupy the large cages of the THF+H2 structure II hydrate. As a result, by manipulating the promoter THF content, the hydrogen storage capacity was increased to ∼3.4 wt % in the THF+H2 hydrate system. This study shows the tuning effect may be used and developed for future science and practical applications.
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