Hydrate Phase Equilibrium Data Research Articles

Determination of hydrate phase equilibrium (H-L-V) data for the binary CO2–CH4 gas mixture in the presence of 1,3 dioxolane

Present work details the determination of three phase hydrate equilibrium data (H-L-V) using temperature search method for the binary CO2/CH4 gas mixture (50:50 molar ratio) in presence of 1,3 dioxolane (DIOX). DIOX concentration used for phase equilibrium determination were 1,3 and 5.56 mol% respectively. In the presence of DIOX, it was observed that phase equilibrium curve was shifted right with respect to the curve using same gas mixture with no additive (pure water). This indicates that the presence of DIOX moderates the hydrate formation equilibrium conditions. Also, as DIOX concentration increases from 1 mol% to 5.56 mol%, a decrement in phase equilibrium pressure at same temperatures was observed, confirming the potential of DIOX as an effective thermodynamic promoter. Enthalpy of hydrate dissociation was calculated for CO2/CH4 gas mixture in presence of DIOX using Clausius- Clapeyron plot and it was found to be 90.81±6.55 KJ/mol which confirms the sII structure of CO2-CH4-DIOX mixed hydrate. Besides providing the phase equilibrium data of formed hydrates with CO2/CH4 gas mixture using different concentration of DIOX, the present study will aid in determining suitable experimental conditions for examining kinetics and performing separation studies of CO2/CH4 gas mixture through hydrate formation.

Low-temperature gel breaking fracturing fluid for marine hydrate reservoir fracturing and its effect on phase equilibrium of methane hydrates

Hydraulic fracturing has been proven useful for improving the gas production efficiency of low-permeability hydrate reservoirs. However, no specific fracturing fluid system exists for marine hydrate reservoirs. Applying conventional water-based fracturing fluids in low-temperature (<293.2 K) marine hydrate reservoirs can lead to difficulties in gel-breaking and hydrate instability caused by external additives. In this study, we developed two water-based fracturing fluid systems that exhibited good gel-breaking performance at low temperatures (278.2–288.2 K), one comprising ammonium persulfate (APS), ferrous sulfate (FeSO4), and citric acid (CA), the other APS and triethanolamine (TEA). In addition, we investigated the influence of crosslinking and gel-breaking reactions of the fracturing fluids on the methane hydrate phase equilibrium. The breaking time of the APS-FeSO4-CA system at 278.2K, 283.2K, and 288.2K was 30 min, 75 min, and 120 min respectively. On the other hand, the APS-TEA system accomplished the same task in 3 h, 6 h, and 10 h respectively. Furthermore, methane hydrate phase-equilibrium data showed that the fracturing fluid's three states, base fluid (BF), fracturing fluid gel (FFG), and gel-breaking liquid (GBL), all exerted an inhibitory effect on the phase equilibrium, with the hydrate suppression temperature (ΔT) ranging from 0.4 to 1.0 K. The differences in their inhibitory effect were primarily related to the micromorphology of the hydroxypropyl guar gum (HPG) molecules and the number of active hydroxyl (-OH) groups in the solution. Cryo-scanning electron microscopy (SEM) measurements revealed that the micromorphology of HPG in BF, FFG, and GBL transformed from regular ribbon-like structures to 3-D network structures and then to hole-containing, short ribbon-like structures. FFG formed a regular 3-D network structure after adding crosslinking agents to the BF. The ΔT values reversed from FFG < BF to FFG > BF when the HPG concentration increased from 0.3 wt% to 0.5 wt%, possibly due to the difference in the HPG molecules' water adsorption capacity before and after crosslinking. The broken HPG molecules with OH− groups in the solution were transformed into residues after gel-breaking, decreasing the GBL's inhibitory effect. Therefore, our results indicated that micromorphology variations could cause differences in the HPG molecules' water adsorption capacity, ultimately leading to ΔT differences. Based on our findings, the gel-breaking fracturing fluid systems we developed demonstrated potential for optimizing hydraulic fracturing in marine hydrate reservoirs.

Hydrate phase equilibrium determination and thermodynamic modeling of CO2 + epoxy heterocycle + water systems

Ethylene oxide (EO), 1,3-propylene oxide (PO), tetrahydrofuran (THF), 1,3-dioxolane (1.3-DX), 1,4-dioxane (1,4-DX) and 1,3,5-trioxane (s-TO) were selected to investigate their thermodynamic promotion effects on CO2 hydrate formation. New hydrate phase equilibrium data of carbon dioxide + epoxy heterocycles + water systems were determined employing an isochoric temperature-search method in the temperature range of (273.15 to 295.35) K and the pressure range of (0.4 to 4.5) MPa. Results showed that the presence of epoxy heterocycles significantly increased the hydrate formation temperature substantially compared with that of pure CO2 hydrate. Under the same conditions, the phase equilibrium temperature of CO2 hydrate under the action of the additive was from low to high: PO < 1,4-DX < 1,3-DX < s-TO < EO < THF. CO2 hydrate dissociation enthalpies with different epoxy heterocycles were also calculated from Clausius–Clapeyron equation to infer their stabilities and the structures formed. It was found that the estimated enthalpy of dissociation was consistent with the superiority sequence obtained from the phase equilibrium data, illustrating that the water-soluble sII clathrate former of THF had the highest hydrate promoting effect. Moreover, Chen-Guo model, associated with a modified Joshi empirical activity model and PR equation of state was proposed further to predict hydrate phase equilibrium. Satisfactory agreement was observed between predictions and experimental data. Analysis of the results confirmed that the proposed thermodynamic model worked well in describing phase behavior of complex hydrates and the maximum relative error of the pressure was less than 8.5%.

Midstream on a chip: ensuring safe carbon dioxide transportation for carbon capture and storage.

Emerging technologies like enhanced oil recovery and carbon sequestration rely on carbon dioxide water content data to ensure that pipelines remain sub-saturated to avoid corrosion and hydrate flow assurance issues. To improve throughput and confidence in the hydrate phase equilibria data to avoid pipeline blockages, further research into the carbon dioxide water content must be conducted. However, the liquid carbon dioxide regime is experimentally difficult to study and the available data disagree between studies. This work aims to provide the critical and accurate data for liquid carbon dioxide for a high pressure range (13.8 to 103.4 bar) and temperature range (20 and -30 °C) utilizing a small volume microfluidic reactor (<20 microliter) coupled with Raman spectroscopy, which can reveal any phase metastability in the system. The small volume of the microfluidic system (<20 microliter) allowed experiments to be run in a few hours, compared to a whole week for prior larger scale measurements. The carbon dioxide water content results from this work agree well with both model predictions and available literature data in the gas region; however, once carbon dioxide was converted to liquid, the data showed a weak function of pressure, similar to model predictions and some previous data sets. The discrepancies between literature data are attributed to metastable phases present in the equilibrium cells, as the data is usually taken in the carbon dioxide near critical region, close to carbon dioxide's dew point, and near the hydrate phase transition. For these reasons, it is important to observe and qualify all phases in the cell, as was done in this novel study with in situ Raman spectroscopy coupled to Midstream on a chip, to ensure accurate water content of the carbon dioxide fluid phase is being measured.

A robust and highly efficient phase boundary method for determining the thermodynamic equilibrium conditions of bulk gas hydrate systems

The phase equilibrium conditions of gas hydrate systems play a fundamental and essential role in establishing the feasibility of the various hydrate based technological applications. Although the classical isochoric and isothermal pressure search methods can provide accurate and reliable gas hydrate phase equilibrium data, these methods require researchers to devote tremendous time towards achieving each data point. Herein, we extend the phase boundary (PB) method for bulk hydrate systems and demonstrate it to be robust and highly efficient. The PB method involves a controlled pressure drop of the hydrate system to initiate the automatic trace of the pressure and temperature region upon dissociation of the hydrates. Three-phase equilibrium data for four different gas hydrate systems, namely pure methane (CH4), mixed CH4/1,3-dioxolane (DIOX), mixed hydrogen (H2)/DIOX, and mixed carbon dioxide (CO2)/DIOX, have been obtained using the PB method. Independent measurements made using the isochoric pressure search method have been obtained to validate the accuracy and reliability of the data obtained using the PB method.

Thermodynamic phase equilibrium of single-guest hydrate and formation data of hydrate in presence of chemical additives: a review

The present work deals with a review of single-guest hydrate phase equilibrium data and also hydrate equilibrium in presence of chemical additives, which operate as inhibitors, promoters, or both together. In the recent years, a very limited number of data collections on hydrate equilibrium has been produced; moreover, these data have not been fully reported in these works, making further research necessary to obtain complete information. We provide a detailed collection of the equilibrium data of hydrate containing single guest as CH4, C2H6, C3H8, C4H10, CO2, N2, Xe, Ar and Kr and a brief review of las-scale reactors nowadays used for making research on gas hydrate. These two kinds of information, will be extremely helpful for researchers which are planning to realize a new experimental apparatus for studying gas hydrate. It is well known how, rather than process parameters (i.e. pressure, temperature, presence of a porous medium and its permeability and porosity, presence of impurities, and so on), also specifics of each reactor may strongly intervene on formation results. The second part of this work consists in a collection of the thermodynamic equilibrium data of hydrate in the presence of additives. Some substances are known to be selective inhibitors (promoters); other compounds have greater efficiency when coupled to further chemicals while, in some cases, such coupling can cancel the inhibitory (or promoter) effect. Finally, a state of the art of hydrate equilibrium experiments carried out with methane and carbon dioxide, with a simultaneous presence of inhibitors and promoters, was provided.

Thermodynamic investigation of hydrate-based CO2 capture from simulated flue gas with new mixed promoters

Abstract CO2 hydrate-based desalination (CHBD) has been developing for decades to meet the global demands of decreasing carbon dioxide (CO2) emissions. In this work, the CO2 was captured from the simulated flue gas which consists of 18.30 mol% carbon dioxide and 81.70 mol% nitrogen in the presence of tetra-n-butyl ammonium bromide (TBAB) + cyclopentane (CP) + glucoamylase. Then the phase equilibrium data of CO2 hydrate were measured by the method of isochoric pressure-search. Among the seven cases with same concentration of TBAB (0.29 mol%) and CP (5.00 vol%) and different glucoamylase proportions (ranging from 0.00 to 20.00 wt%), the optimum concentration of glucoamylase in the mixed promoters was 3.00 wt%. The phase equilibrium data was calculated by the modified van der Waals–Platteeuw (vdW–P) model with a modification of vapor pressure of water in the empty hydrate lattice. The Peng–Robinson equation of state was used to calculate the fugacity of gas. The maximum average absolute deviation was 4.09% between the calculated results and the experimental results. It revealed that the calculated results were in good agreement with the experimental results.

A novel stirred microcalorimetric cell for DSC measurements applied to the study of ice slurries and clathrate hydrates

A novel prototype of a microcalorimetric cell with in-situ stirring has been developed to perform DSC measurements under atmospheric or pressure conditions. After a brief technical description of the apparatus, preliminary tests are presented which analyzed the influence of the stirrer rotation on the heat-flow signal. Experiments were then performed with complex fluids such as ice slurries and clathrate hydrates formed with cyclopentane and with carbon dioxide. They took place in stirred and non-stirred conditions and the results obtained were then compared. It was proven that the rotation of the microstirrer in the measuring cell does not disrupt the heat-flow signal during the analysis. As regards the practical applications tested, the in-situ stirrer efficiently reduces crystallization metastability, increases the water-to-hydrate conversion, and reduces the amount of time needed for analysis. The dissociation enthalpy of cyclopentane (CP) hydrates was measured at atmospheric pressure; it is effectively very difficult to analyze this system with non-stirred calorimetry techniques because the two liquid phases are immiscible. The experimental results, in good agreement with other data found in the literature, showed complete water-to-CP hydrate conversion within a short period of time using a simple protocol. Experiments were also performed under pressure to demonstrate that CO2 hydrate phase equilibrium data could be obtained rapidly and easily. It is therefore our opinion that the potential of this novel technology has been thoroughly demonstrated.

Clathrate hydrates at temperatures below the freezing point of water: A review

This paper provides the review focusing on the clathrate hydrates at the temperatures below the freezing point of water. The three main topics of the review are the chemical thermodynamics, naturally-occurring hydrates and novel industrial applications utilizing hydrates. Fundamental phase equilibria in the hydrate forming systems at the temperatures below the freezing point of water are first reviewed. The effects of water-soluble compound on the hydrate phase equilibria are extensively discussed based on the experimental data reported in the literature and the newly obtained experimental data on the solid ice + sodium chloride aqueous solution + carbon dioxide hydrate + carbon dioxide gas four-phase equilibria that were measured in the present study. Natural occurrence of hydrates is discussed by comparing the thermodynamic conditions in the planets and satellites with the relevant hydrate phase equilibrium data. The naturally-occurring hydrates would exist in the following planets and satellites; Mars and Titan. The storage of natural gas in the form of the hydrate has been well investigated in the past two decades. CO2 hydrate can be used as the fire-fighting agent and the solid carbonated foods. The refrigeration and engine utilizing hydrates as the working media may be the challenging technologies having the prospects in terms of the efficiency, environment friendliness and the safety.

Evaluation of clayed silt properties on the behavior of hydrate production in South China Sea

ABSTRACT Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas. The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China Geological Survey (CGS). During this test, there were many unique characteristics different from the sand reservoir, which was believed to be related to the clayed silt physical properties. In this paper, simulation experiments, facilities analysis, and theoretical calculation were used to confirm the hydrate structure, reservoir thermo-physical property, and bond water movement rule. And the behavior of how they affected production efficiency was analyzed. The results showed that: It was reasonable to use the structure I rather than structure II methane hydrate phase equilibrium data to make the production plan; the dissociation heat absorbed by hydrate was large enough to cause hydrate self-protection or reformation depend on the reservoir thermal transfer and gas supply; clayed silt got better thermal conductivity compared to coarse grain, but poor thermal convection especially with hydrate; clayed silt sediment was easy to bond water, but the irreducible water can be exchanged to free water under high production pressure, and the most obvious pressure range of water increment was 1.9–4.9 MPa.

Modification of a model for mixed hydrates to represent double cage occupancy

Gas hydrates are subject of current research work and are also important for several industrial applications. When transporting natural gases or oil through pipelines, the formation of gas hydrates and thus a blockage of the pipeline must be avoided. There is also a great interest to understand the thermophysical properties and the phase change behavior of hydrates during liquefaction processes of natural gases, for CO2 capture and sequestration (CCS) processes, and for CH4 and C2H6 hydrates, which can be found on the seabed or in permafrost soils as a potential energy source. In this work, the model for mixed gas hydrates (mixtures of water with more than one hydrate former), which has been introduced in a previous work [Fluid Phase Equilib. 459 (2018) 170–185] and is intended for the use in CCS relevant applications, is modified to take double cage occupancy into account. The three-phase equilibrium data can be reproduced up to high pressures at which N2, O2, and Ar are known to double occupy the hydrate cavities. The influence of double occupied hydrate cages and the improved reproduction of experimental phase equilibrium data at pressures at which double cage occupancy occurs are shown for pure hydrate and for mixed hydrate phase equilibrium and composition data. In case of mixed hydrates, comparisons are shown for synthetic air (N2+O2).

Phase Equilibrium Data of CO2–MCP Hydrates and CO2 Gas Uptake Comparisons with CO2–CP Hydrates and CO2–C3H8 Hydrates

Carbon dioxide (CO2) emission and fresh water scarcity have become two huge global issues over the last decades, and CO2 hydrate-based technology was promoted and developed to address them. This study investigated the effects of methylcyclopentane (MCP) on the hydrate formation condition and CO2 capture efficiency. Five cases and 31 cycles experiments of different MCP/water molar ratios (ranging from 0 to 0.03) in salt solution and porous media were conducted using the isochoric method. The hydrate phase equilibrium data of CO2–MCP hydrates were measured, and meanwhile the CO2 capture efficiencies were calculated. The results indicated that the rising MCP concentrations increase both the hydrate equilibrium temperature and the gas uptake. After the comparisons of the interpolated hydrate gas uptakes at uniform hydrate phase equilibrium pressure of 3 MPa among CO2–MCP, CO2–CP (cyclopentane), and CO2–C3H8 (propane) hydrates, CO2-MCP hydrates are especially suitable for CO2 capture. It should be noted that MCP is likely to form s-H hydrate with CO2 gas, but further confirmation is needed. Anyway, MCP can be thought as a potential coguest for integrated hydrate-based CO2 capture and desalination process.

A phase equilibrium model for hydrate in sediment accounting for pore capillary effect

The hydrate phase equilibrium relationship is the one of the most fundamental issues in the hydrate related research area. In the procedure for developing a phase equilibrium model, it is critical to address the influence of pore capillary effect of sediment. This paper firstly compares the influence mechanisms of pore size distribution on water-gas suction in unsaturated soil and on hydrate-water capillary suction during hydrate phase transition, and finds that both influence mechanisms are similar to each other. With reference to the existing formula used for describing the relationship of water-gas suction and water saturation, such as V-G model, an expression for relating hydrate-water capillary suction to hydrate saturation is presented. Combined with the van der Waals-Platteeuw thermodynamic model, a modified phase equilibrium model for hydrate in sediment accounting for pore capillary effect is proposed. Furthermore, an approach for quantifying model parameters is developed. Compared to the existing models, the micro model parameters, such as pore diameter, are not involved in the proposed model. Instead, the model parameters are macro variables, and can be calculated from the measured phase equilibrium data of hydrate in sediment. Finally, part of experimental data is used to determine the model parameters, and the other part of experimental data is employed to verify the proposed phase equilibrium model. Through the comparison of the model predicated results and experimental data, it have been demonstrated that the proposed model is able to effectively predicate the phase equilibrium condition for hydrate in sediment. Note that, the proposed phase equilibrium model is needed to be verified in the following work because of shortage of relative experimental data.

Implementing Cyclopentane Hydrates Phase Equilibrium Data and Simulations in Brine Solutions

Cyclopentane hydrate-based salt removal is considered to be a possible promising technology for desalination. In order to optimize such processes, phase equilibrium data of cyclopentane hydrates (C...

Hydrate Phase Equilibria for Methyldiethanolamine and Empirical Modeling for Prediction

The issue of gas hydrates in gas pipelines is commonly addressed by injecting hydrate inhibitors at the well heads. Alongside these inhibitors, other chemical additives are also injected to address various concerns such as to reduce the risk of corrosion and scaling. However, it is not clear how the combined chemical cocktail affects gas hydrate formation over a wide pressure range. Monoethylene glycol (MEG) and methyldiethanolamine (MDEA) are common chemicals that are usually used as part of hydrate inhibition and corrosion control programs respectively. Thus, in this study, the methane hydrate inhibition performance of MDEA in the presence and absence of MEG was assessed. The study produced new hydrate phase equilibria data at a high pressure range, suggesting MDEA performs as a thermodynamic hydrate inhibitor and thus enhances the hydrate inhibitory performance of MEG. Furthermore, because there does not appear to be any flow assurance prediction software that has the capability to simulate the effect of MDEA on hydrate formation, an algorithm that can accurately predict the equilibrium temperature of aqueous MDEA solutions with and without MEG was developed. The algorithm is based on the empirical modeling of the experimental data obtained in this study. This work will thus aid in the industrial application of hydrate inhibitors and improve gas hydrate prevention in production pipelines.

Assessing thermodynamic consistency of gas hydrates phase equilibrium data for inhibited systems

Phase equilibrium properties of gas hydrates in the presence of thermodynamic hydrate inhibitors (THIs) like alcohols, glycols, and salts are essential in developing thermodynamic prediction models to identify their physicochemical features and phase behavior for gas production from hydrates and operation of oil/gas production systems. Though a significant amount of experimental data are available in the literature and models have been developed based on those data, a reliable method to assess the thermodynamic consistency of the data has not been established. Here, we provide a rigorous method to assess the thermodynamic consistency of hydrate phase equilibrium data in inhibited systems. Fundamental thermodynamic relations are used to derive the assessment criteria for thermodynamic consistency, including the heat of dissociation for solid hydrate phase and the activity for liquid water. The quantitative assessment of CH4 hydrate + THIs, including salts, glycols, methanol, and amino acids are performed for demonstration, and guidelines on how to assess the thermodynamic consistency are provided.

An experimental and modeling study on incipient hydrate-forming conditions for ternary guests of carbon dioxide, nitrogen and sulfur dioxide

In carbon dioxide capture and sequestration (CCS) processes, captured CO2 may encounter conditions of hydrate formation due to the presence of water. For stable, long-term operation of CCS processes, hydrate-phase equilibrium data are essential. Captured CO2 from combustion of fossil fuel may include other impurities such as N2 and SO2. Phase equilibria including a single impurity (N2 or SO2) have been reported by other researchers, but no experimental observations have been obtained for ternary guest systems. In this work, the incipient hydrate-forming temperatures for a binary guest of CO2 and N2 and a ternary guest of CO2, N2 and SO2 were experimentally measured at 2.0–3.5 MPa. An effect of the ratio between guest components and water was observed. The experimental results were compared with calculations using an equation of state based on a hydrogen-bonding nonrandom lattice fluid (NLF-HB) combined with the van der Waals-Platteeuw model. The model predictions were in good agreement with experimental data with an overall average deviation of 2.6%.

Phase Equilibrium Data for the Hydrates of Synthesized Ternary CH4/CO2/N2 Biogas Mixtures

To enhance the energy efficiency of biogas and reduce environmental pollution, impurities such as CO2 and N2 must be removed. In this context, hydrate-based gas separation (HBGS) is a novel technology that has been utilized in gas purification. As such, the hydrate phase equilibrium data of the CH4/CO2/N2 gas mixture are crucial for application of the HBGS process in biogas separation. This study presents our investigation into the phase equilibrium conditions for the hydrates of synthesized ternary CH4/CO2/N2 biogas mixtures. All experiments were conducted at 276.2–286.3 K and 2.59–8.84 MPa using an isochoric method with different ternary CH4/CO2/N2 gas concentrations. The results obtained herein indicated that the hydrate phase equilibrium conditions shifted to lower pressures and higher temperatures with increasing CO2 contents. In addition, with a N2 content of about 10%, the hydrate phase equilibrium data of the ternary gas mixtures approached that of pure CH4.

Systematic evaluation of semiclathrate-based pre-combustion CO2 capture in presence of tetra-n-butylammonium fluoride (TBAF): effect of TBAF concentration and kinetic additives

In this study, tetra-n-butylammonium fluoride (TBAF) is investigated as a promoter for pre-combustion CO2 capture via hydrate formation process. Hydrate phase equilibrium data for fuel gas mixture at 6.0 MPa with TBAF of various concentrations (0.80, 1.50, 2.00, 2.50, 2.96 and 3.38 mol%) were first determined. The kinetic performance with different TBAF concentrations was studied at 6.0 MPa given the same temperature driving force (ΔT = 4.1 K) in a stirred tank reactor. 3.38 mol% TBAF performed the best in terms of normalized gas uptake based on unit amount of water, while 1.50 mol% TBAF solution could capture the most amount of gas in terms of unit volume of solution. Solution with a higher TBAF concentration resulted in a higher CO2 composition in the non-gaseous phase after hydrate formation, and 97.7 mol% CO2 composition was achieved by 0.80 mol% TBAF solution. The effect of three kinetic additives, namely sodium dodecyl sulfate (SDS), leucine and tryptophan, were also evaluated. All kinetic additives studied were able to significantly reduce the induction time. However, the short induction time and block of stirring caused by drastic hydrate formation leaded to low gas uptakes.

New insight into prediction of phase behavior of natural gas hydrate by different cubic equations of state coupled with various mixing rules

Progress in hydrate thermodynamic study necessitates robust and fast models to be incorporated in reservoir simulation softwares. However, numerous models presented in the literature makes selection of the best, proper predictive model a cumbersome task. It is of industrial interest to make use of cubic equations of state (EOS) for modeling hydrate equilibria. In this regard, this study focuses on evaluation of three common EOSs including Peng–Robinson, Soave–Redlich–Kwong and Valderrama–Patel–Teja coupled with van der Waals and Platteeuw theory to predict hydrate P–T equilibrium of a real natural gas sample. Each EOS was accompanied with three mixing rules, including van der Waals (vdW), Avlonitis non-density dependent (ANDD) and general non-quadratic (GNQ). The prediction of cubic EOSs was in sufficient agreement with experimental data and with overall AARD% of less than unity. In addition, PR plus ANDD proved to be the most accurate model in this study for prediction of hydrate equilibria with AARD% of 0.166. It was observed that the accuracy of cubic EOSs studied in this paper depends on mixing rule coupled with them, especially at high-pressure conditions. Lastly, the present study does not include any adjustable parameter to be correlated with hydrate phase equilibrium data.