Heat Of Dissociation Research Articles

Evaluation of thermal stimulation on gas production from depressurized methane hydrate deposits☆

Natural gas hydrates have gained worldwide attention asan important potential non-conventional fossil fuel resource. Understanding the gas production behavior from hydrate deposits is critical to the utilization of the gas hydrate resource. In this study, the hydrate dissociation reaction was induced by depressurization in conjunction with thermal stimulation. Profiles of temperature, pressure, gas production rate, and cumulative gas production during the gas production processes were analyzed. The results show that the gas production process upon ice generation can be divided into five main stages: (1) a free gas release, (2) hydrate dissociation along the equilibrium curve driven by the reservoir sensible heat, (3) hydrate dissociation driven by the exothermic ice generation reaction, (4) ice melting and hydrate dissociation under ambient heat transfer, and (5) hydrate dissociation under ambient heat transfer. During the gas production process, two thermal stimulation methods—ambient heat transfer and warm water injection—were employed to supply heat for hydrate dissociation. The larger the heat flux supplied by ambient heat transfer, the greater the gas production. During the warm water injection process, the gas production time decreased as the temperature of the injected water increased. These two methods can effectively promote gas production from gas hydrate deposits. The findings of this study can provide some insight for designing and implementing optimal production techniques for use of hydrate resources.

Phase equilibria for Kr hydrate formed with 2,2-dimethylbutane, methylcyclohexane and 1-methylpiperidine

This paper reports the thermophysical properties of hydrates in the (krypton+1-methylpiperidine, 2,2-dimethylbutane or methylcyclohexane+water) system. Phase equilibrium conditions were measured in the temperature ranges from 274.6K to 297.3K at the corresponding equilibrium pressures between 0.532MPa and 6.246MPa in the (krypton+1-methylpiperidine+water) system. In the temperature ranges from 291.2K to 297.0K and 290.6K to 296.8K, the equilibrium pressure was between 4.035MPa to 8.936MPa and 3.993MPa to 9.128MPa, in the (krypton+2,2-dimethylbutane+water) system and (krypton+methylcyclohexane+water) system, respectively. These results indicate that hydrates can be formed under the condition of lower temperature and pressure in the (krypton+1-methylpiperidine+water) system than in the other two systems. The crystallographic structure of (krypton+1-methylpiperidine) hydrate was thereby identified to be structure H at 183K based on the Powder X-ray diffraction (PXRD) measurements. Dissociation heat of (krypton+1-methylpiperidine) hydrate was estimated to be 73.5kJ/mol, that is smaller than that of structure II hydrates containing krypton. These results support the potential for (krypton+1-methylpiperidine) structure H hydrate to be utilized in hydrate-based technologies.

Thermodynamic Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylammonium Propionate

AbstractThe phase equilibrium temperature and dissociation heat of tetrabutylammonium propionate (TBAPr) hydrate are reported. TBAPr hydrate is a type of ionic semiclathrate hydrates and also could potentially be used as thermal energy storage material. The temperature‐composition phase diagram of the TBAPr hydrate was determined in a defined range of mass fractions. Considering the dissociation heat of differential scanning calorimetry (DSC) measurements, multiple peaks of heat flow were observed in the TBAPr‐water system at the TBAPr mass fraction lower than 0.35, and there was a single peak at the mass fraction higher than 0.37.

Experimental Evaluation of Temperature and Concentration Effects on Heat of Dissociation of CO2-loaded MEA Solution in Strippers

Regeneration heat in strippers of CCS system is affected by operating temperature and concentration of amine solutions and accurate measurement, modelling and prediction of it are necessary to design the strippers with selecting new or blend amine solutions. This paper reports the heat of dissociation of CO2-loaded 30wt% monoethanolamine (MEA) solution quantified experimentally by a small-scale apparatus circulating the solution through absorber and stripper. This method can quantify total regeneration heat as well as breakdown of regeneration heat consisted of the heat of CO2 dissociation, the sensible heat of solution and the latent heat of condensed water simultaneously. The heat of CO2 dissociation agreed well with the heat of CO2 absorption at 120 degrees C in literatures. Aspen Plus offers an example file of rate-based CCS system using MEA, and the process flow diagram (PFD) was developed to simulate the apparatus by using it. The developed PFD with the original electrolyte NRTL model underestimated heat duty of the stripper. We modified temperature dependency of the specific heat capacity of protonated MEA. The modified model could predict accurately the heat of CO2 dissociation as well as mole fraction of chemical species, while effect of solution concentration on the heat of CO2 absorption was still not sufficiently simulated.

2-6.ガスハイドレートの分解熱測定((2)メタンハイドレートI,Session 2 天然ガス・メタンハイドレート等)

2-6.ガスハイドレートの分解熱測定((2)メタンハイドレートI,Session 2 天然ガス・メタンハイドレート等)

Phase equilibrium temperature and dissociation heat of ionic semiclathrate hydrate formed with tetrabutylammonium butyrate

This paper reports the phase equilibrium temperature and dissociation heat of ionic semiclathrate hydrate formed with tetrabutylammonium butyrate (TBABu). The temperature – composition phase diagram of the TBABu hydrate was determined in the mass fraction from 0.10 to 0.44. The highest equilibrium temperature of TBABu hydrate was 15.4 °C in the mass fraction range from 0.35 to 0.37. On the dissociation heat of DSC measurements, a single heat flow peak of TBABu hydrate excluding ice melting peak was observed at all the mass fraction systems. The largest dissociation heat was 184.9 ± 3.1 kJ/kg at the mass fraction 0.36. TBABu hydrate could potentially be used as a thermal energy storage material.

Numerical Investigation of the Production Behavior of Methane Hydrates under Depressurization Conditions Combined with Well-Wall Heating

In this study, a 2D hydrate dissociation simulator has been improved and verified to be valid in numerical simulations of the gas production behavior using depressurization combined with a well-wall heating method. A series of numerical simulations were performed and the results showed that well-wall heating had an influence enhancing the depressurization-induced gas production, but the influence was limited, and it was even gradually weakened with the increase of well-wall heating temperature. Meanwhile, the results of the sensitivity analysis demonstrated the gas production depended on the initial hydrate saturation, initial pressure and the thermal boundary conditions. The supply of heat for hydrate dissociation mainly originates from the thermal boundaries,whichcontrolthehydratedissociationandgasproductionbydepressurizationcombined with well-wall heating. However, the effect of initial temperature on the gas production could be nearly negligible under depressurization conditions combined with well-wall heating.

Thermodynamic characteristics of protolytic equilibria in aqueous solutions of glycyl peptides

Protolytic equilibria in aqueous solutions of glycyl-DL-serine, glycyl-DL-threonine, and glycyl-DL-valine are investigated by means of potentiometry and calorimetry. Dissociation constants and heat effects of the above dipeptides are determined. Standard thermodynamic characteristics (pK°, ΔdisG°, ΔdisH°, ΔdisS°) of the investigated equilibria are calculated. The obtained results are compared to corresponding data on relative compounds.

Phase Equilibrium of the Methane Hydrate System in the Presence of Mixed Promoters (THF + TBAB) and the Effect of Inhibitors (NaCl, Methanol, and Ethylene Glycol)

Tetra-n-butyl ammonium bromide (TBAB) and tetrahydrofuran (THF) are being widely used in gas hydrate research for their potential to store natural gas. The mixed promoter system of THF and TBAB has not yet been investigated for the phase stability conditions of methane hydrate. In this work, the phase stability of methane hydrate has been investigated in the presence of a mixed promoter (THF + TBAB) in the absence and presence of various inhibitors, viz., sodium chloride (NaCl), methanol (MeOH), and ethylene glycol (EG), at various concentrations. The phase equilibrium data has been reported in the temperature and pressure ranges of (282.25–289.65) K and (2.25–6.43) MPa, respectively. The heat of dissociation has been determined using the Clausius–Clapeyron equation for various methane hydrate systems. MeOH is observed to be an effective inhibitor as compared to EG and NaCl on the methane hydrate system formed from the mixed promoter system of THF + TBAB. With an increase in the concentration of MeOH, the...

Properties of equilibrium carbon dioxide hydrate in porous medium

Specific heat capacity, dissociation heat and hydration number of carbon dioxide hydrate in porous medium are determined by adiabatic calorimetry method. The measurements were carried out in the temperature range 250–290K and in pressure range 1–5MPa. The measured specific heat of the hydrate is approximately 2.7J/(g K), which is significantly larger than the specific heat of methane hydrate. In particular, at heating, larger value of the specific heat of carbon dioxide hydrate is a result of gas emission from the hydrate. The hydration number at the hydrate-gas coexistence changes from 6.2 to 6.9. The dissociation heat of carbon dioxide hydrate varies from the 55kJ/mol near the upper quadruple point to the 57kJ/mol near the lower quadruple point.

Factors influencing clathrate hydrate stability in equilibrium with liquid water: Insights from information-based statistical analysis

Screening of potential hydrate promoter/inhibitor species is essential in the investigation of clathrate hydrates in many areas of industrial interest. However, experimental analyses do not yield sufficient information to determine whether molecular size, dipole moment, molecular mass, or any other parameters influence the thermodynamic stability of clathrate hydrates in general. The present contribution employs a mutual information-based nonparametric statistical analysis to identify trends in a multivariate data set for 21 clathrate hydrate formers. It is showed through the introduction of a simple correlation that prediction of the heat of dissociation of a clathrate hydrate may be sufficient to predict the entire phase equilibrium curve above the ice point. The dipole moment and molecular volume of hydrate forming species influence the dissociation pressure curve, and distinctive behaviours may be observed for cyclic gas species as compared to non-cyclic species.

Simulation of gas hydrate dissociation caused by repeated tectonic uplift events

AbstractGas hydrate dissociation by tectonic uplift is often used to explain geologic and geophysical phenomena, such as hydrate accumulation probably caused by hydrate recycling and the occurrence of double bottom‐simulating reflectors in tectonically active areas. However, little is known of gas hydrate dissociation resulting from tectonic uplift. This study investigates gas hydrate dissociation in marine sediments caused by repeated tectonic uplift events using a numerical model incorporating the latent heat of gas hydrate dissociation. The simulations showed that tectonic uplift causes upward movement of some depth interval of hydrate‐bearing sediment immediately above the base of gas hydrate stability (BGHS) to the gas hydrate instability zone because the sediment initially maintains its temperature: in that interval, gas hydrate dissociates while absorbing heat; consequently, the temperature of the interval decreases to that of the hydrate stability boundary at that depth. Until the next uplift event, endothermic gas hydrate dissociation proceeds at the BGHS using heat mainly supplied from the sediment around the BGHS, lowering the temperature of that sediment. The cumulative effects of these two endothermic gas hydrate dissociations caused by repeated uplift events lower the sediment temperature around the BGHS, suggesting that in a marine area in which sediment with a highly concentrated hydrate‐bearing layer just above the BGHS has been frequently uplifted, the endothermic gas hydrate dissociation produces a gradual decrease in thermal gradient from the seafloor to the BGHS. Sensitivity analysis for model parameters showed that water depth, amount of uplift, gas hydrate saturation, and basal heat flow strongly influence the gas hydrate dissociation rate and sediment temperature around the BGHS.

Theoretical performance analysis of hydrate-based heat engine system suitable for low-temperature driven power generation

We analyzed a heat engine using clathrate hydrate as its working media and evaluate the performance of this system operated with high and low temperature reservoirs of 295 K and 280 K “OTEC (Ocean Thermal Energy Conversion)” may be a prospective example of the technologies utilizing the small-temperature difference for power generation. This heat engine generates mechanical power through the cycle of following processes: hydrate formation at low temperature, pumping of hydrate, isobaric heating of hydrate, hydrate dissociation and adiabatic expansions of dissociated gas and water. The thermal efficiency for Kr, Xe, CH3F, CH2F2 and CH4 hydrates were evaluated. The analysis showed the dominant properties were the enthalpy difference of the working media in the adiabatic expansions, the pressure range in the whole process and the dissociation heat. The thermal efficiency is 2.20% for Kr hydrate and 2.89% for Xe hydrate. While these are slightly inferior to those of Rankine cycle: 3.30% for C2H3F3 and 3.34% for C3H8, Kr and Xe hydrates are greatly favorable in terms of environmental friendliness. These results indicate the prospects of the hydrate heat engine for the power generation utilizing a small temperature difference as an environment-friendly technology.

Tetrabutylammonium butyrate ハイドレートの熱物性測定

This paper reports the phase equilibrium temperature and dissociation heat of tetrabutylammonium butyrate (TBABu) hydrate. TBABu hydrate is a type of ionic semiclathrate hydrates. This hydrate could potentially be used as thermal energy storage materials. The phase equilibrium temperature was measured by stepwise temperature increasing procedure. The temperature – composition phase diagram of the TBABu hydrate was determined in the mass fractions from 0.20 to 0.40. The highest equilibrium temperature of TBABu hydrate was 15.3 °C at the mass fraction 0.40. On the dissociation heat of DSC measurements, the largest dissociation heat was 172 kJ/kg at the mass fraction 0.40.

The Measurement of Dissociation Heat and Equilibrium Temperature of Tetrabutylammonium Propionate Hydrate

This paper reports the results of an experimental study conducted to measure the thermodynamics properties of ionic semiclathrate hydrate formed with tetrabutylammonium propionate (TBAPr). The thermodynamic measurements were performed on the equilibrium temperature and on the dissociation heat of the hydrate in the range of the mass fraction of tetrabutylammonium propionate wTBAPr from 0.10 to 0.43. The highest equilibrium temperature of the TBAPr system was 17.5 ̊C at wTBAPr = 0.37. The largest dissociation heat of TBAPr system was 193 kJ/kg at wTBAPr = 0.37. These findings indicate that TBAPr hydrate is promising for application in cool energy storage material.

Experimental study on combustion of a methane hydrate sphere

The combustion behavior of a methane hydrate sphere under normal gravity is experimentally investigated. The initial diameter of the sphere is 20 mm. Variation in temperature at the center of the sphere (T c) is measured with a K-type thermocouple at ignition temperatures (T c,i) from 193 to 253 K at 20 K intervals. Variation in the near-surface temperature of the sphere (T s) is measured at ignition temperatures (T s,i) from 233 to 263 K at 10 K intervals. Two combustion phases are observed. When the hydrate is ignited, a stable flame envelope is formed around the sphere (phase 1). In phase 1, the surface of the sphere is dry. After a few seconds, water formed by dissociation of the methane hydrate appears on the surface and methane bubbles are formed by methane ejected from inside the sphere (phase 2), thus destabilizing the flame and causing local extinction. Methane bubbles move down along the surface and merge into a large methane bubble at the bottom of the sphere. This bubble bursts, releasing methane to form a temporary flame, and the water drops from the hydrate sphere. Water on the surface is cooled by the hydrate inside, and an ice shell confines the methane gas that dissociated inside the sphere. Because the dissociation occurs continuously inside the hydrate, the inner pressure gradually increases and at some instant, the ice cracks and methane gas is ejected from the cracks, which results in a micro-explosion with a flame. In phase 1, the surface temperature is below the freezing point of water, and so the surface remains dry and a stable flame envelope is formed; in phase 2, the surface temperature is above the freezing point, and so water appears on the surface. When the temperature at the center of the sphere is lower (193, 213, or 233 K), some methane hydrate remains even after flame extinction because heat transfer from the flame decreases in phase 2 as a result of local extinction. The diameter of the sphere decreases during combustion in accordance with the d-square law, which indicates that the heat of dissociation is supplied by the flame and methane is supplied by the dissociation of methane hydrate in the sphere, as in single-droplet combustion.

Fervent: chemistry-coupled, ionizing and non-ionizing radiative feedback in hydrodynamical simulations

We introduce a radiative transfer code module for the magnetohydrodynamical adaptive mesh refinement code FLASH 4. It is coupled to an efficient chemical network which explicitly tracks the three hydrogen species H, H_2, H+ as well as C+ and CO. The module is geared towards modeling all relevant thermal feedback processes of massive stars, and is able to follow the non-equilibrium time-dependent thermal and chemical state of the present-day interstellar medium as well as that of dense molecular clouds. We describe in detail the implementation of all relevant thermal stellar feedback mechanisms, i.e. photoelectric, photoionization and H_2 dissociation heating as well as pumping of molecular hydrogen by UV photons. All included radiative feedback processes are extensively tested. We also compare our module to dedicated photon-dominated region (PDR) codes and find good agreement in our modeled hydrogen species once our radiative transfer solution reaches equilibrium. In addition, we show that the implemented radiative feedback physics is insensitive to the spatial resolution of the code and show under which conditions it is possible to obtain well-converged evolution in time. Finally, we briefly explore the robustness of our scheme for treating combined ionizing and non-ionizing radiation.

Effect of NaCl, methanol and ethylene glycol on the phase equilibrium of methane hydrate in aqueous solutions of tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB)

Hydrate or semiclathrate hydrate systems formed using tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB) show potential use for natural gas storage and transportation. Information on the effect of various inhibitors on their phase stability is necessary to effectively dissociate these hydrate systems for the end use application. In this work, the experimental data for the phase equilibrium of methane (CH4) hydrate system have been obtained in the presence of THF (0.005 and 0.01 mass fraction) and TBAB (0.1 and 0.2 mass fraction) with various inhibitors. Various inhibitors used in the study include sodium chloride (NaCl), methanol (MeOH) and ethylene glycol (EG) with mass fraction (0.03 and 0.1) of each inhibitors in aqueous solutions of THF and TBAB. The reported data lie in the temperature and pressure range of (277.56–290.43)K and (2.20–6.16)MPa, respectively. Comparative effects of NaCl, MeOH and EG on hydrate/semiclathrate hydrates of CH4+H2O+THF/TBAB have been studied. The inhibition effect of NaCl on hydrate of CH4+H2O+THF is observed to be higher as compared to MeOH and EG, whereas for semiclathrate hydrate of CH4+H2O+TBAB, MeOH is observed to be an effective inhibitor than NaCl and EG. In addition, as the concentration of promoters (THF and TBAB) increases, the effect of inhibitors is found to decrease. This indicates that lower concentrations of promoters along with inhibitors may be suitable for efficient formation and dissociation of natural gas storage and transportation. The heat of dissociation (Hdiss) determined using Clausius–Clapeyron equation is reported for various hydrate/semiclathrate hydrate system. The values of heat of dissociation are observed to be in good agreement with literature trend. Hdiss is observed to decrease with increase in concentration of NaCl, MeOH and EG for hydrate/semiclathrate hydrate of CH4+H2O+THF/TBAB.

Thermochemical study of acid-base interactions in aqueous solution of L-leucine

The heats of reactions of L-leucine solution with HNO3 and KOH solutions were measured calorimetrically in different pH ranges at 298.15 K and ionic strengths of 0.50, 0.75, and 1.00 (KNO3). The heats of stepwise dissociation of the amino acid were determined. The standard thermodynamic characteristics (ΔrH°, ΔrG°, and ΔrS°) of acid-base reactions in aqueous solutions of L-leucine were calculated. The relationship between the thermodynamic characteristics of dissociation of the amino acid and the structure of this compound was discussed.

Effect of Hydrate Saturation on the Methane Hydrate Dissociation by Depressurization in Sediments in a Cubic Hydrate Simulator

This study presents the three-dimensional (3D) cubic hydrate simulator (CHS) to analyze the methane dissociation phenomena from hydrate-bearing sediment with different hydrate saturation. The experiments by depressurization have been carried out at the environmental temperature of 281.15 K, the dissociation pressure of 5.0 MPa, and in the hydrate saturation range of 17.0-43.2%. The hydrate dissociation process consists of two periods: the depressurizing period and the steady-pressure period: In the depressurizing period, the hydrate dissociation occurs in the whole reactor. The cumulative gas production is similar, and the gas production rate is affected by the depressurization rate and the water production in this period. The cumulative water production increases With the decrease of the hydrate saturation in the whole depressurization process. In the steady-pressure period, the cumulative gas production increases with the increase of the hydrate saturation. The average gas production rate first increases with the increase of the hydrate saturation and then decreases at hydrate saturation of 43.2%. The water production during the steady-pressure period only occurs in the experiments with the high hydrate saturation. The temperatures in different regions in the reactor change with similar degrees in the depressurizing period and have the similar lowest values for different experiments. In the steady-pressure period, the temperatures increase gradually from the inner-wall region to the center region. On the basis of the calculation of the energy balance, it was found that the ratio of the sensible heat of the reservoir to the latent heat of the hydrate dissociation decreases with the increases of the hydrate saturation and the dissociation pressure.