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1.
Natural gas industry encounters systems that consist of gases like CO2 and H2S, and aqueous solutions of methanol and mixed electrolytes. A knowledge of the phase behavior of such systems, including hydrate formation, is essential in gas production and the design of facilities for gas transportation and processing. Recently, Dholabhai et al. (1997, 1996) and Bishnoi and Dholabhai (1998) described equilibrium conditions for CO2 and gas mixtures containing CO2 in the presence of methanol, electrolytes and ethylene glycol. In the present work aqueous three phase (aqueous liquid solution, vapor and incipient hydrate) equilibrium conditions of H2S hydrate formation in aqueous solutions of electrolytes and methanol are measured in the temperature range of 272 to 294 K and pressure range of 0.3 to 1.0 MPa. A ‘full view’ sapphire variable volume cell with a movable piston is used to obtain the experimental data. 相似文献
2.
Hyung Joon Shin Jun-Hyuck Im Jon-Won Lee Ju Dong Lee Ji-Ho Yoon 《Chemical engineering science》2009,64(24):5125-5130
The hydrate phase behavior of CO2/3-methyl-1-butanol (3M1B)/water, CO2/tetrahydrofuran (THF)/water and CO2/1,4-dioxane (DXN)/water was investigated using both a high-pressure equilibrium viewing cell and a kinetic pressure-temperature measurement system with a constant volume. The dissociation pressures of CO2/3M1B/water were identical to those of pure CO2 hydrate, indicating that CO2 is not acting as a help gas for structure H hydrate formation with 3M1B, thus the formed hydrate is pure CO2 structure I hydrate. The CO2 molecules could be encaged in small cages of the structure II hydrate framework formed with both of THF and DXN. For a stoichiometric ratio of 5.56 mol% THF, we found a large shift of dissociation boundary to lower pressures and higher temperatures from the dissociation conditions of pure CO2 hydrate. From the measurements using the kinetic pressure-temperature system, it was found that the solid binary hydrate samples formed from off-stoichiometric THF and DXN aqueous solutions are composed of pure CO2 hydrate with a hydrate number n=7.0 and THF/CO2 and DXN/CO2 binary hydrates with a molar ratio of xCO2·THF·17H2O and xCO2·DXN·17H2O, respectively. The X-ray diffraction was used to identify the binary hydrate structure and Raman spectroscopy was measured to support the phase equilibrium results and to investigate the occupation of CO2 molecules in the cages of the hydrate framework. 相似文献
3.
Jia-nan Zheng Lei Yang Shihui Ma Yuechao Zhao Mingjun Yang 《American Institute of Chemical Engineers》2020,66(2):e16820
Gas hydrate is a nonstoichiometric crystal compound formed from water and gas. Most nonvisual studies on gas hydrate are unable to detect how much water is converted to hydrates, and thus, the hydrate stoichiometry calculations are inaccurate. This study investigated the CO2 hydrate formation process in porous media directly and quantitatively. The characteristics of the time-variable consumption of hydrate formation indicated a two-stage formation, hydrate enclathration and continuous occupancy. The enclathration stage occurred in the first 20 min of the formation when considerable heat is released. The continuous occupancy stage lasted longer than the hydrate enclathration because the empty cages in previously formed hydrates would also be occupied. The higher formation pressures can accelerate water consumption and increase cage occupancy. The compositions of completely formed CO2 hydrates at 2.7, 3.0, and 3.3 MPa and 275.15 K were determined as CO2·6.90H2O, CO2·6.70H2O, and CO2·6.49H2O, respectively. 相似文献
4.
V.P. Melnikov A.N. Nesterov A.M. Reshetnikov V.A. Istomin 《Chemical engineering science》2011,66(1):73
In this study, the dissociation of isolated carbon dioxide hydrate particles of sizes in the range 0.25–2.5 mm was investigated. It was found that below the ice melting point, the hydrates dissociated into supercooled water (metastable liquid) and gas. The formation of the liquid phase during CO2 hydrate dissociation was visually observed, and the pressures of the hydrate dissociation into supercooled water and gas were measured in the temperature range 249–273 K. These pressures agreed well with the calculated data for the supercooled water–hydrate–gas metastable equilibrium (Istomin et al., 2006). In the P–T area on the phase diagram bounded by the ice–hydrate–gas equilibrium curve and the supercooled water–hydrate–gas metastable equilibrium curve, hydrates could exist for a long time because the metastable phase and their stability are not connected to the self-preservation effect. The growth of the metastable CO2 hydrate film on the surface of supercooled water droplets formed during the hydrate dissociation was observed at pressure above the three-phase supercooled water–hydrate–gas metastable equilibrium pressure but still below the three-phase ice–hydrate–gas equilibrium pressure. It was found that the growth rate of the metastable CO2 hydrate film was higher by a factor of 25 and 50 than that for methane hydrate and propane hydrate, respectively. 相似文献
5.
《Chemical Engineering Research and Design》2014,92(12):2977-2991
A new, rigorous framework centered around the multi-scale GHC equation of state is presented for predicting bulk density and phase equilibrium for light gas–water mixtures at conditions where hexagonal ice and structure I hydrate phases can exist. The novel aspects of this new framework include (1) the use of internal energies of departure for ice and empty hydrate respectively to determine densities, (2) contributions to the standard state fugacity of water in ice and empty hydrate from lattice structure, (3) computation of these structural contributions to standard state fugacity from compressibility factors and EOS parameters alone, and (4) the direct calculation of gas occupancy from phase equilibrium. Numerical results for densities and equilibrium for systems involving ice and/or gas hydrates predicted by this GHC-based framework are compared to predictions of other equations of state, density correlations, and experimental data where available. Results show that this new GHC-based EOS framework accurately predicts the densities of hexagonal water ice and structure I gas hydrates as well as phase equilibrium for methane–water and CO2–water mixtures. 相似文献
6.
7.
The paper takes into consideration a new approach for CO2 capture and transport, based on the formation of solid CO2 hydrates.Carbon dioxide sequestration from power plants can take advantage of the properties of gas hydrates. The formation and decomposition of hydrates from various N2-CO2 mixtures has been studied experimentally in a 2 l reactor, to determine the CO2 separation in terms of hydrate composition and residual CO2 content in the reacted gas.Carbon dioxide acts as a co-former for the production of hydrates containing nitrogen, besides CO2. The mixed hydrates that are obtained are less stable than simple CO2 hydrates. When CO2 content in the flue gas is higher than 30% by volume, the hydrates formed at 5 MPa are sufficiently concentrated (about 70% CO2) and carbon dioxide reduction in the reacted gas is acceptable.The application of a process based on hydrate formation could be especially interesting (for CO2 capture and transport) when connected to an oxy-coal combustion process; in this case the CO2 content in the flue gas is very high and the hydrate formation is greatly facilitated. 相似文献
8.
Gas hydrate formation from hydrogen/carbon dioxide and nitrogen/carbon dioxide gas mixtures 总被引:1,自引:0,他引:1
Praveen Linga 《Chemical engineering science》2007,62(16):4268-4276
Gas hydrates from CO2/N2 and CO2/H2 gas mixtures were formed in a semi-batch stirred vessel at constant pressure and temperature of 273.7 K. These mixtures are of interest to CO2 separation and recovery from flue gas and fuel gas, respectively. During hydrate formation the gas uptake was determined and the composition changes in the gas phase were obtained by gas chromatography. The rate of hydrate growth from CO2/H2 mixtures was found to be the fastest. In both mixtures CO2 was found to be preferentially incorporated into the hydrate phase. The observed fractionation effect is desirable and provides the basis for CO2 capture from flue gas or fuel gas mixtures. The separation from fuel gas is also a source of H2. The impact of tetrahydrofuran (THF) on hydrate formation from the CO2/N2 mixture was also observed. THF is known to substantially reduce the equilibrium formation conditions enabling hydrate formation at much lower pressures. THF was found to reduce the induction time and the rate of hydrate growth. 相似文献
9.
In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO2. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO2/CH4 molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO2 molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO2 concentration in the aqueous phase may not result in faster growth of CO2 hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO2, the growth for carbon dioxide hydrate was very slow in the beginning. 相似文献
10.
An investigation into the laboratory method for the evaluation of the performance of kinetic hydrate inhibitors using superheated gas hydrates 总被引:1,自引:0,他引:1
Kinetic hydrate inhibitors (KHIs) are used to prevent gas hydrate formation in gas and oilfield operations. Recently, a new KHI test method was reported in which hydrates are formed and re-melted just above the equilibrium temperature, before the fluids are re-cooled and the performance of the chemical as a KHI is determined. The method, which we have called the superheated hydrate test method, is claimed to be more reliable for KHI ranking in small equipment, giving less scattering in the hold time data due to avoiding the stochastic nature of the first hydrate formation. We have independently investigated this superheated hydrate test method in steel and sapphire autoclave tests using a gas mixture forming Structure II hydrates and a liquid hydrocarbon phase, which was necessary for satisfactory results. Our results indicate that hold times are shorter than using non-superheated hydrate test methods, but they are more reproducible with less scattering. The reduced scattering occurs in isothermal or slow ramping experiments even when the hydrates are melted at more than 10 °C above the equilibrium temperature (Teq). However, if a rapid cooling method is used, the improved reproducibility is retained when melting hydrate at 2.4 °C above Teq but lost when warming to 8.4 °C above Teq. Using the ramping test method, most, but not all the KHIs tested agreed with the same performance ranking obtained using traditional non-superheated hydrate test methods. This may be related to the variation in the dissociation temperature of gas hydrates with different KHIs and different KHI inhibition mechanisms. Results also varied between different size autoclave equipments. 相似文献
11.
Parisa Doubra Paramespri Naidoo Wayne Michael Nelson Deresh Ramjugernath 《American Institute of Chemical Engineers》2020,66(9):e16281
A new 750 cm3 pilot test rig based on the “isochoric pressure method” was designed and commissioned for the hydrate measurements to concentrate sucrose solutions. The reactor included an improved agitation system and enabled sampling of the sucrose solutions. The experimental method was validated be performing dissociation measurements for the CO2 + water system. Gas hydrate kinetic and sampling data were measured for the CO2 + sucrose solutions at sucrose concentrations between (12–60) oBrix, within the temperature range of (274.65–276.15) K and at pressures up to 3.70 MPa. Results showed that sucrose is a kinetic inhibitor. The data were modeled to obtain hydrate formation rate, storage capacity, gas consumption and apparent rate constant. Stage-wise concentration measurements were performed with reactor conditions at 274.65 K, 3.70 MPa and 130 rpm mixer speed with liquid sample withdrawal. A final sucrose product of approximately 60 oBrix was obtained. 相似文献
12.
《分离科学与技术》2012,47(1):144-154
ABSTRACTFor efficient xenon (Xe) recovery from natural gas (NG), multiple gas hydrate crystallization was considered. The optimal stages’ number for effective Xe recovery from model gas mixtures with close composition to NG one was determined. Gas hydrate distribution’s coefficients are defined for these gases at each stage, and each iterations of the multiple gas hydrate crystallization. In CH4+ H2S+CO2+ Xe gas mixture that is closest to NG composition, the maximum average Xe concentration in the gas hydrate phase was observed at the second stage of the multiple gas hydrate crystallization. 相似文献
13.
An elementary model for the dissolution of pure hydrate in undersaturated water is proposed that combines intrinsic decomposition within a desorption film and the subsequent diffusion of the released hydrate guest species into bulk water. Applying the proposed approach to recently published measurements of the decomposition rates of methane (CH4) and carbon dioxide (CO2) hydrates in deep seawater suggests that the concentration of the hydrate guest species at the interface between desorption film and diffusive boundary layer may be much lower than ambient solubility. Calculations, however, fail to account for the observed proportionality of decomposition rate with solubility for both CH4 and CO2 hydrates. This may indicate a limitation in the range of applicability of published formulas for intrinsic hydrate decomposition rates. 相似文献
14.
A calibration protocol to quantify the compositional information of gas hydrates using Raman spectroscopy is proposed. Structure I pure CH4‐, CO2‐ and C2H6‐hydrates in their deuterated and hydrogenated forms with known cage occupancies were investigated by Raman spectroscopy. Raman scattering cross sections of CH4 in the large and small cages were found to be very similar, but not identical. Some C2H6 bands of C2H6‐hydrate were tentatively reassigned or newly reported and assigned. Our results show that the relative cross sections of guest vibrational modes in the deuterated hydrate are in agreement with those in the hydrogenated hydrate, whereas they are considerably different from those in fluid phase. Using our Raman quantification factors, the relative cage occupancies can now be determined more reliably in CH4‐hydrates. Moreover, with additional assumptions, the absolute cage occupancies, the bulk guest composition and hydration number of pure or mixed gas hydrates become accessible by Raman spectroscopy. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2155–2167, 2013 相似文献
15.
《Chemical Engineering Communications》2012,199(2):185-193
AbstractIn this study, CF4 hydrate dissociation conditions in the presence of different TBAB aqueous solutions with the concentrations of 0.05, 0.10, 0.20, and 0.3 mass fractions were experimentally measured. Measurements were performed using a high pressure equilibrium cell with an approximate inner volume of 40?cm3. Hydrate measurements were performed in the temperature and pressure ranges of (273.8–285.6) K and (1.03–11.57) MPa, respectively. The results show that TBAB aqueous solutions with the concentration of 0.05, 0.10, and 0.20 (mass fractions) do not have a major promotion effect on the CF4 hydrate phase equilibrium. However, the aqueous solution with 0.30 mass fraction TBAB exhibited a significant promotion effect on CF4 hydrate formation. The model of Chen and Guo (1998) and Joshi et al. (2012) were used to estimate the hydrate dissociation conditions. The errors between the experimental and calculated data resulted in acceptable absolute relative deviations (ARD%) below 0.1%. 相似文献
16.
Daria Surovtseva 《Chemical Engineering Research and Design》2011,89(9):1752-1757
This project is a trial conducted under contract with CO2CRC, Australia of a new CO2 capture technology that can be applied to integrated gasification combined cycle power plants and other industrial gasification facilities. The technology is based on combination of two low temperature processes, namely cryogenic condensation and the formation of hydrates, to remove CO2 from the gas stream. The first stage of this technology is condensation at −55 °C where CO2 concentration is expected to be reduced by up to 75 mol%. Remaining CO2 is captured in the form of solid hydrate at about 1 °C reducing CO2 concentration down to 7 mol% using hydrate promoters. This integrated cryogenic condensation and CO2 hydrate capture technology hold promise for greater reduction of CO2 emissions at lower cost and energy demand. Overall, the process produced gas with a hydrogen content better than 90 mol%. The concentrated CO2 stream was produced with 95-97 mol% purity in liquid form at high pressure and is available for re-use or sequestration. The enhancement of carbon dioxide hydrate formation and separation in the presence of new hydrate promoter is also discussed. A laboratory scale flow system for the continuous production of condensed CO2 and carbon dioxide hydrates is also described and operational details are identified. 相似文献
17.
1 INTRODUCTION Gas hydrates are serious problems in the petroleum and petrochemical industries since it may cause the plugging of production facilities and trans- portation pipelines during gas and oil production. It is known to all that gas hydrates have three poten- tial hydrate formation structures: structure- structure- and structure-H (SH). The two for- mer structures have been studied extensively and their phase equilibrium conditions are well characterized. For a long time, molecu… 相似文献
18.
Wenxiang Zhang Shuanshi Fan Yanhong Wang Xuemei Lang Kai Guo Jianbiao Chen 《中国化学工程学报》2019,27(9):2081-2088
To provide an evidence of natural gas hydrate occurrence state, a series of experiments on multiple growth and dissociation of 90.0% methane/10.0% propane hydrates at 1.3 MPa and 270.15 K were carried out in two sediments for morphology observation via a visible jacketed-reactor. The gas hydrate crystals were observed to form and grow on the surface of sediments at the initial growth. During the thermal decomposition, gas and liquid products had an unceasingly impact on the sediments, then gas/liquid–solid migration occurred, and a large number of cavitation appeared. In the later growth and dissociation experiments, the gas hydrate particles were in suspension or supporting states in the interstitial pore space between the sediment particles, indicating that the gas hydrate displayed a pore-filling characteristics. Through analyzing the distribution of gas hydrates and bubbles, it was found that the amount of gas hydrates distributed in the sediments was improved with multiple growth-dissociation cycle proceedings. Gas migration enhanced the sediment movement, which led to the appearance of the increasing quantity of gas bubbles in the sediments during cycles. Salts affected the growth of the gas hydrates and the migration of sediment grains, which also restricted the accumulation of gas bubbles in the sediments. According to the Raman analysis, the results showed that sII hydrates were formed for CH4 and C3H8 gas mixtures in different sediments and solutions with hydration number of 5.84–6.53. The Salt restricted the access of gas into the hydrate cages. 相似文献
19.
Extraction of methane hydrate energy by carbon dioxide injection-key challenges and a paradigm shift
Peter Englezos 《中国化学工程学报》2019,27(9):2044-2048
Significant effort including field work has been devoted to develop a natural gas extraction technology from natural gas hydrate reservoirs through the injection of carbon dioxide. Natural gas hydrate is practically methane hydrate. The hypothesis is that carbon dioxide will be stored as hydrate owing to its favorable stability conditions compared to methane hydrate. Although the dynamics of the CO2/CH4 exchange process are not entirely understood it is established that the exchange process is feasible. The extent is limited but even if the CH4 recovery is optimized there is a need for a CH4/CO2 separation plant to enable a complete cyclic sequence of CO2 capture, injection and CH4 recovery. In this paper we propose an alternative paradigm to the Inject (CO2)/Exchange with (CH4)/Recover (CH4) one namely Recover (CH4) first and then Inject (CO2) for Storage. 相似文献
20.
Impact of water film thickness on kinetic rate of mixed hydrate formation during injection of CO2 into CH4 hydrate
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Khuram Baig Bjørn Kvamme Tatiana Kuznetsova Jordan Bauman 《American Institute of Chemical Engineers》2015,61(11):3944-3957
In this work, nonequilibrium thermodynamics and phase field theory (PFT) has been applied to study the kinetics of phase transitions associated with CO2 injection into systems containing CH4 hydrate, free CH4 gas, and varying amounts of liquid water. The CH4 hydrate was converted into either pure CO2 or mixed CO2?CH4 hydrate to investigate the impact of two primary mechanisms governing the relevant phase transitions: solid‐state mass transport through hydrate and heat transfer away from the newly formed CO2 hydrate. Experimentally proven dependence of kinetic conversion rate on the amount of available free pore water was investigated and successfully reproduced in our model systems. It was found that rate of conversion was directly proportional to the amount of liquid water initially surrounding the hydrate. When all of the liquid has been converted into either CO2 or mixed CO2?CH4 hydrate, a much slower solid‐state mass transport becomes the dominant mechanism. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3944–3957, 2015 相似文献