Experimental determination of dissociation temperatures and enthalpies of methane, ethane and carbon dioxide hydrates up to 90 MPa by using a multicycle calorimetric procedure (original) (raw)
Related papers
Consistent Enthalpies of the Hydrate Formation and Dissociation Using Residual Thermodynamics
Journal of Chemical & Engineering Data, 2019
Kinetics of the hydrate phase transition is implicit functions of the free-energy change of the phase transition and the related dynamics of associated mass and heat transport. The enthalpy change of any phase transition is trivially coupled to the free-energy change of the phase transition. We propose a consistent scheme for calculating the free-energy change, as well as the associated enthalpy change, using residual thermodynamics for every component in all phases, this includes the hydrate phase. The proposed method does not have any limitations to pure components, although we focus on pure CH 4 and pure CO 2 hydrates in this work. One reason is that there are some experimental data for these components. But the main reason is that the work presented here is a part of a project related to the use of CO 2 for simultaneous production of CH 4 from natural gas hydrates and safe long-term storage of CO 2 in the form of hydrate. A fast mechanism for this exchange entails the formation of a new carbon dioxide (CO 2) hydrate from the injected CO 2 gas. The exothermic heat of formation released from this phase transition will help to dissociate the in situ methane (CH 4) hydrate. A brief review of the available experimental data from the open literature reveals the lack of important information in the reported data. Typical missing information are hydrate composition, pressure and/or temperature, as well as details on how the experiments have been conducted. Indirect methods that utilize measured or calculated hydrate pressure−temperature equilibrium curves are frequently oversimplified and of limited accuracy. Yet another advantage of the proposed method is that it is not limited to heterogeneous hydrate formation from water and a separate hydrate phase. Enthalpy change related to homogeneous hydrate formation from dissolved hydrate formers in water can also be calculated from the proposed approach.
Enthalpies of Hydrate Formation and Dissociation from Residual Thermodynamics
Energies
We have proposed a consistent thermodynamic scheme for evaluation of enthalpy changes of hydrate phase transitions based on residual thermodynamics. This entails obtaining every hydrate property such as gas hydrate pressure-temperature equilibrium curves, change in free energy which is the thermodynamic driving force in kinetic theories, and of course, enthalpy changes of hydrate dissociation and formation. Enthalpy change of a hydrate phase transition is a vital property of gas hydrate. However, experimental data in literature lacks vital information required for proper understanding and interpretation, and indirect methods of obtaining this important hydrate property based on the Clapeyron and Clausius-Clapeyron equations also have some limitations. The Clausius-Clapeyron approach for example involves oversimplifications that make results obtained from it to be inconsistent and unreliable. We have used our proposed approach to evaluate consistent enthalpy changes of hydrate phase ...
The Journal of Chemical Thermodynamics, 2018
Statistical Thermodynamics was used to derive an expression for hydrate enthalpy of dissociation. From this expression, a parameter regression methodology was proposed in which calorimetric experiments were included along with cage occupancies, guest mole fraction and equilibrium condition experiments. Since not all the experiments depend on the whole set of hydrate parameters, we developed a stepwise methodology that reduces hydrate estimation problem to three simple sub problems, being two of them analytically solvable. The solution of the stepwise methodology is then the initial guess of the hydrate global parameter estimation that can be solved using a deterministic algorithm. From the parameter estimation, we observed that the hard-core sphere parameter of the Kihara potential was not statistically significant in the case studied here. It was rejected with a significance degree of 5%, which lead to the use of the Lennard-Jones potential. After estimating hydrate parameters for carbon dioxide and methane sI hydrates, we could relate hydrate enthalpy of dissociation to equilibrium conditions for this binary mixture. We found that the empirical law that states that enthalpy of dissociation of mixed hydrates increases with the increase of occupancy of the largest guest in the large cavity was verified only when the waterpoor fluid phase is a vapor. This means that fluid phases also have an important role in hydrate enthalpy of dissociation. Highlights 1-Expression for hydrate enthalpy of dissociation from Statistical Thermodynamics. 2-Parameter estimation using calorimetric experimental data for hydrate formation. 3-A new stepwise and non-exhaustive parameter estimation methodology. 4-Enthalpy of dissociation and its relations to hydrate properties.
Modelling of Methane Hydrate Formation and Dissociation using Residual Thermodynamics
SNE Simulation Notes Europe
The available experimental data in literature for enthalpies of hydrate formation and dissociation are limited and often lacks relevant information required for interpretation. Commonly missing information include hydrate composition, hydration number, temperature and/or pressure data, and degree of super heating during dissociation of hydrate. Clausius-Clapeyron equations used with measured or calculated hydrate formation pressure-temperature equilibrium data is the simplest indirect methods used for evaluating enthalpy change involved in phase transition during hydrate formation or dissociation. However, this approach involves oversimplifications. These over simplifications make all the data based on Clausius-Clapeyron to be unreliable. And old data using Clapeyron do not have appropriate volume corrections. We therefore propose a thermodynamic scheme (residual thermodynamics approach) without these limitations. This method is based on residual thermodynamics for all properties like equilibrium (pressure-temperature) curves, free energy change as thermodynamic driving force in kinetic theories and enthalpies of hydrate formation and dissociation.
Enthalpies of Dissociation of Pure Methane and Carbon Dioxide Gas Hydrate
2014
In this study the enthalpies of dissociation for pure methane and pure carbon dioxide was calculated using a hydrate equilibrium data obtained in this study. The enthalpy of dissociation was determined using Clausius-Clapeyron equation. The results were compared with the values reported in literature obtained using various techniques. Keywords—Enthalpies of dissociation, methane, carbon dioxide, gas hydrate, natural gas.
The Role of Water in Gas Hydrate Dissociation
The Journal of Physical Chemistry B, 2004
When raised to temperatures above the ice melting point, gas hydrates release their gas in well-defined, reproducible events that occur within self-maintained temperature ranges slightly below the ice point. This behavior is observed for structure I (carbon dioxide, methane) and structure II gas hydrates (methane-ethane, and propane), including those formed with either H 2 O-or D 2 O-host frameworks, and dissociated at either ambient or elevated pressure conditions. We hypothesize that at temperatures above the H 2 O (or D 2 O) melting point: (1) hydrate dissociation produces water + gas instead of ice + gas, (2) the endothermic dissociation reaction lowers the temperature of the sample, causing the water product to freeze, (3) this phase transition buffers the sample temperatures within a narrow temperature range just below the ice point until dissociation goes to completion, and (4) the temperature depression below the pure ice melting point correlates with the average rate of dissociation and arises from solution of the hydrate-forming gas, released by dissociation, in the water phase at elevated concentrations. In addition, for hydrate that is partially dissociated to ice + gas at lower temperatures and then heated to temperatures above the ice point, all remaining hydrate dissociates to gas + liquid water as existing barriers to dissociation disappear. The enhanced dissociation rates at warmer temperatures are probably associated with faster gas transport pathways arising from the formation of water product.
Heat capacity and heat of dissociation of methane hydrates
AIChE Journal, 1988
The objective of this study was to determine the heat capacity and heat of dissociation of methane hydrates. A technique has been devised which circumvents the two major problems encountered in measuring gas hydrate heat capacity: the need to impose a mechanical pressure during the measurement and the need to have an absolutely pure hydrate sample. The technique was shown to be successful utilizing high-pressure, constant-volume cells in a differential scanning calorimeter.
University of Tehran, 2022
Due to high storage capacity, high dissociation enthalpy, and the appropriate melting point of gas hydrates, these compounds have the potential for many industrial applications. Tetra-n-butylammonium halides are molecules that can form semiclathrate hydrates. This manuscript employed the Clausius Clapeyron equation to evaluate the dissociation enthalpy of methane/nitrogen/carbon dioxide + tetra-n-butylammonium chloride (TBAC) semiclathrate hydrates (SCHs). Phase equilibrium data are measured in a batch reactor with an effective volume of 460 cc. The data of dissociation enthalpy were evaluated in the temperatures of (275.15 to 304.75) K and the pressures of (0.36 to 10.57) MPa at (0-0.36) mass fraction of TBAC. The results showed that the utilization of TBAC increases the amount of dissociation enthalpy of semiclathrate hydrates per mole of the hydrated gas. By increasing the amount of TBAC in the system, the quantity of dissociation enthalpy per mole of hydrated gas increased.