Stability of Methane Clathrate Hydrates under Pressure - Report Example

Introduction Many scientists are of the opinion that methane could be found in large amounts with respectto the interior of the Titan and a number of icy moons such as those of Jupiter and Saturn. Other sources of the gases could also be found in exoplanets that have an abundant supply of water which many perceive as being likely stored clathrate hydrate form. The report aims to give insight and analysis on the investigation of the stability of methane clathrate hydrates under high pressure conditions by making use of Raman Spectroscopy, an x-ray diffraction and a diamond anvil cell in combination. Ammonia has for many years been viewed as an extra-terrestrial space in both the moons and comets, outer and interstellar planets and the network of ammonia, water and methane has been studied by many scientists. Ammonia’s main role has been that of being an anti-freeze agent for the formation of clathrate hydrate and ice and for been a modifier in the process of stabilizing the solid ice and the phases of methane clathrate as a thermodynamic inhibitor (Barbieri 57). It should be noted that even though ammonia is molecule made of methane meaning that it is suitable for housing the clathrate hydrate cages. There are however issues that may bar ammonia from being used as an ideal guest for the clathrate hydrate cages such as the assumption that guests need to hydrophobic for them to be combined into the clathrate and it has been previously observed that many stoichiometric non-clathrate stages of water and ammonia are obtained when it cools in the aqueous solution of ammonia. Initial experimental work regarding the linkage of water and ammonia and water. Ammonia and methane showed evidence of enclathration of ammonia but when keenly analyzed again, the high pressure of the ammonia monohydrate and low pressure of the ammonia dehydrate show the presence of common structural features with semi-clathrate structures and canonical clathrate (Heriot-Watt 113). In recent years, there have been molecular simulations and structural analysis conducted and they have indicated that few guest molecules that are responsible for creating very strong hydrogen bonds with the water compound contained in the clathrate hydrate lattice can produce phases that are stable. It has led to a section of scientists considering ammonia as a potential guest molecule for a clathrate. Additionally, research that was conducted earlier coupled with computational studies are of the opinion that in the gaseous state, water creates dodecahedral cages surrounding ammonia ions and ammonia and these structures may be used to point to a tendency that is geometrical in nature of the clathrate hydrate structures being attracted to the ammonium and ammonia molecules. Methodology The Raman Spectroscopy coupled with the x-ray diffraction was used to determine the phase changes experienced as a result of increased pressure and temperature (Herri 45). The Raman Spectroscopy moves in the v1 mode which symmetric stretch mode signature of the C-H for the solid methane and MHs which were experienced when the pressures ranged between 0.2 and 5 GPa. The dissociation temperatures relating to the MHs when the pressure ranged between 1.5 and 5 GPa were determined by observing the varying results in the diffraction peaks of the x-ray and the fluctuations from the Raman Spectroscopy. The results concluded that in the specified pressure range, the methane hydrates change into liquid water and solid methane when the temperatures are near the water ice’s melting curve. The Raman spectroscopy is measured by using an instrument called the Raman microscope which is used to place focus on the line of the Ar-ion laser at the point 514.5nm in order to facilitate excitation. On the other hand, the scattered light is dispersed by using a single grating spectrometer that has a 1200 grating measurement and is detectable by using a CCD detector which is maintained at the -90 degrees Celsius level assisted by the cooling properties of nitrogen. The sample used should be stored in liquid nitrogen and placed on top of a brass sample holder that is cooled down to an estimated level of 100K atmospherically and then measured when the temperature is increased. The sample holder should be covered by a glass made of quartz where dry nitrogen gas is blown on top of the surface when measurements are being taken so that the ice is inhibited from condensing in order to mimic the properties experienced in the icy moons of Saturn and Jupiter. The computational methods used should be conducted by using the DL POLY version 2.2 coupled with a time step calibrated to one fs and a leapfrog algorithm. The molecular water oxygen position structure and the structure of the clathrate should be obtained from the x-ray crystallography together with the assignment of water hydrogen atoms in the unit cell. The arrangement should be in such a way that it satisfies the ice rules and reduce the unit cell dipole period at the same time. Objectives The key objective of the experiments coupled with the numerical modelling include determining the stability of the chemical compounds that are contained in the interior satellite, to simulate the interactions experienced between the icy crust and the internal ocean into a model and to further understand the dynamics associated with the icy crust and conditions prevailing when cryomagma is produced is produced in the crust and outputted to the surface. The third objective should be attained by way of simulating an almost identical scenario to the actual one. The first objective is to determine the stability of methane clathrate hydrates when it is under pressure from within the interior of the Titan which was achieved by performing experiments in the H20-CH4-NH3 and H20-CH4 systems under very high pressure (Ramya 97).The experiment was conducted by using an optical anvil cell together with a Raman spectrometer in order to characterize the sample collected. The results from the experiment indicated that there were three factors that influenced the stability of the hydrates of methane clathrate and they were as follows:- a. Ammonia concentration in an aqueous solution b. The quantity of methane in the sample used in the experiment. c. The presence of other gases such as nitrogen The other objective was designed to discover the relationship between the icy crust and the internal ocean. It is widely held that the exchanges between the icy crust and the ocean have a very high likelihood of occurring at the interface between the icy shell and the ocean. Factors such as melting, crystallization are reliant on the energy budget which might allow exchanges of chemical compounds in the transition phase. Additionally, the melting and crystallization process may be affected by the instabilities in the convection currents of either the icy shell or the ocean water and even at times both of them which may result to an evolution of the water/ice interface that is not uniform (Tang 126). Results The experiment indicated that ammonia, in its aqueous solution form had a high correlation on the stability of hydrates of methane clathrate. For instance, when the sample was (10 wt. %) it was found that the ammonia solution was responsible for reducing the dissociation temperature pertaining to the methane clathrate by close to 25 K when the pressure used was 5MPa.The results clearly show outgassing and dissociation of the hydrates of methane clathrate can only be evidenced in the icy crust of Titan only if there is presence of a high concentration of ammonia coupled with warm temperatures (Thermodynamic Stability of Structure H Hydrates Based on the Molecular Properties of Large Guest Molecules 117). For the purpose of replicating these conditions especially regarding the interactions observed between the icy crust and the internal ocean in the simulation, a numerical code is currently being developed. The new numerical code is founded on element discretization that is finite which will allow for the description of the non-uniform evolution of the ice/water interface. When the crust becomes thicker, it becomes small in comparison to the diameter of the planet and the effect on its curvature can be ignored. In this instance, it is recommended that one uses a 2 dimensional Cartesian geometry for more accurate analysis and recording. In its preliminary version, the only factor considered is conduction via the icy crust (Atmospheric Conditions and Variability of Methane Trapping 88). The initial stage allows one to earn and investigate a stagnant liquid as it solidifies and the test cases chosen were the Stefan conundrum that are classical in nature. The Stefan problem refers to a situation where a solid layer thickens while simultaneously it is created at the liquid’s surface originally cooled from above at the melting temperature. In the two instances, the thickening of the crust and the analytical solution is well established which is parallel to the theory of Stefan. Additionally, the interface phase change and the adaptive mesh evolve together and in such instances, the interface is flat due to the presence of the underlying liquid. The aim of the developments in future is for the purpose of characterizing the icy crust dynamics coupled with the phase transition that is experienced within the convective layer and at the interface. It is therefore necessary to remember to include the mass transfers associated with the solid phase in your calculations and be keen on the fact that the icy crust is actively dynamic. The extraction of a variety of conceptual models coupled with the generation of cryomagma and crystal dynamics and structure have been put forward as solutions for the extraction and creation of cryomagma found on the icy moons (Harland 189). Discussion A number of missions have been commissioned to investigate the impact of the surface exchange processes on icy moons and on the Titan. Significant missions have been the Cassini-Huygens which took place between 2004 to 2010 and the Galileo Mission that was commissioned between 1995 to 2003.The Galileo mission was the initial one and it was responsible for orbiting Jupiter while Cassini-Huygens was responsible for orbiting Saturn since the two planets have in recent years been discovered to host a variety a number of active moons (Choukroun 97). The missions uncovered that icy moons are indeed very active as evidenced by the observations made by the satellites regarding the activity of jets of icy particles water vapor seen above the Enceladus’ South Pole. Other sites such as Europa were of significant value because hydrate salts were discovered on its surface which gave credence to the widely held belief in the scientific community that the exchanges occurring between icy crust and the internal ocean have been occurring on Europa’s surface for a long time and was still active up to date (Fischer 16). Measurements were also undertaken on Titan by using the Huygens mass spectrometer. The findings from the device were however inconclusive since the evidence provided was circumstantial regarding the recycling of atmospheric methane via the internal outgassing processes that are associated with activity that is cryovolcanic in nature. The processes were found to have a high probability of being operational at the time the discovery expedition took place (Makuch 201). It is worth noting that despite the overwhelming piling evidence regarding the exchanges between the surface of the icy moons and internal ocean via the cryovolcanic processes, the specific mechanism regarding the processes is unconstrained. An innovative approach coupled with intensive experimental investigations has to be devised in order to understand in depth how the exchanges occurring on the icy moons operate. In addition the experiments should be assessed through numerical modelling so that the objectives of the investigation can be achieved accurately and efficiently. When there is methane and ammonia in the clathrate produced it is more stable than a pure ammonium hydrate whose stability can be measured up to 150K in comparison to the mixed clathrate that records 180k.However.ammonia’s presence is very vital in the formation of a clathrate in temperature ranges that methane on its own cannot be able to form a clathrate hydrate. Scientists know of the activation of ice surfaces by ammonia in very low temperatures, therefore it may be concluded that ammonia’s synergistic behavior coupled with methane and its effect on ice surface that is known to be amorphous can produce a clathrate that is relatively stable. Ammonia is therefore used to kick start the process by incorporating methane and other defects in order to make clathrate lattice more stable which is achieved by reducing the guest host hydrogen bonding (Hughes 245). There have been other experiments conducted by using ammonia and ethane and they have yielded similar results and it’s clear from the experiments the ammonia plays an integral role in the phase of formation of a solid clathrate that is characterized by low temperatures which are experienced in the other planets except Earth. However, it may prove a bit difficult to sum up the effects of the ammonia in an environment where clathrate hydrates are formed and it begins to be clearer that in come stages of ammonia its existence is limited by time and temperature (Natural Gas Hydrates on the North Slope of Alaska 178). Recent experiments have indicated that there are variations in the reflective surface on Titan that have been pegged down to the episodes of cryovolcanic emissions which cause the eruption of ammonia from the Titan’s interior to its surface. The emitted ammonia is released in the form of frost or fog. Most experiments focusing their work on presence of ammonia on Titan stress ammonia has to be aqueous form in the magma which results in decomposition of the aforementioned region and the inhibition of the methane clathrate hydrate. From the experiments conducted it is seen that when the temperatures and pressure levels are simulated to replicate the ones available on Titan and a consideration on the presence of methane in the atmosphere and the presence of ice on its surface one can begin to see a pattern where the ammonia vapor is responsible for the creation of binary clathrate hydrate stages coupled with methane (Demirbas 145). This has led to the conclusion that if clathrate hydrate is formed after depositing ammonia vapor which is surrounded by the presence of methane gas coupled to annealing values of 100K then a mechanism can be developed that will assist in the removal of methane and ammonia from the atmosphere of Titan. Additionally, the mechanism can be used to catalyze the formation of ethane clathrate hydrate in the presence of ammonia. Saturn’s moon known as Enceladus also exhibits the same cryovolcanic activity where plumes of ammonia, water vapor and methane are emitted from the South Pole and the sources of the methane extrusions in the two moons have been attributed to the dissociation of the clathrate hydrate. Recommendations A study was conducted recently and it was proposed that the appearance of the hydrate of ammonia on the icy crust together with the clathrate hydrate in its gaseous form would be favorable in the extraction and generation of highly volatile cryolavas. The mechanism of producing the cryolavas is typically associated with thermal plumes that are both at depth and have very high temperatures and a deformation of the upper crust through crust which rupture. For the purposes of investigating the above phenomenon, a 2 dimensional series of Cartesian Codes is currently being developed which are thermo-compositional and convectional in nature. Additionally, there will be included a number of compounds such as ammonia hydrate, ice water and the CH4-C02 clathrate. Besides the presence of ice water in the icy crust, a complex rheology is incorporated for the purpose of allowing the description of the probable deformation of the upper crust through rupturing coupled with the possibility of exposing oneself to the high volatile and rich cryomagma (Oleson 77). This approach adopted of using numeric will allow investigators to figure out the prevailing conditions that must be met for there to be an occurrence of cryovolcanic series of activities that can be present on the Titan and Enceladus coupled with the effects of the emissions and the cryovolcanic activity on the evolution of the atmosphere in the long run. Conclusion The wider purpose for ammonia’s catalyzing effect on the formation of methane hydrate when exposed to conditions of vapor depositions is to simulate the conditions present in the models of the solar system formation comets and the ices in planets. Therefore, ammonia can be used to catalyze the creation of a hydrate of a non-stoichiometric gas that is frequently trapped in planetary objects and icy grains. Water miscible and polar molecules such as ammonia are classically termed as inhibitors of clathrate hydrate formation (Elsevier 34). The extensive research and computation used suggests that the inhibition effect attributed to ammonia is not because of the inherent instability associated with the solid phase of clathrate hydrate when it is in guest-host formation but is due to the stabilizing effect of ammonia and water in its aqueous form where the formation of the clathrate hydrate takes place. Work Cited Atmospheric Conditions and Variability of Methane Trapping." Planetary and Space Science (2007): 376-86. Print. Barbieri, Cesare. Galileos Medicean Moons: Their Impact on 400 Years of Discovery Proceedings of the 269th Symposium of the International Astronomical Union Held in Padova, Italy, January 6-9, 2010. Cambridge: Cambridge UP, 2010. Print. Choukroun, Mathieu, Olivier Grasset, Gabriel Tobie, and Christophe Sotin. "Stability of Methane Clathrate Hydrates under Pressure: Influence on Outgassing Processes of Methane on Titan." Icarus (2010): 581-93. Print. Demirbas, Ayhan. Methane Gas Hydrate. 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