Induction Time Of Hydrate Formation Research Articles

Experimental and modeling investigation of kinetics of methane gas hydrate formation in water-in-oil emulsion

Experimental data on hydrate formation kinetics for methane in water-in-oil emulsions are presented using a stirred batch reactor in the pressure range of 6.48–8.76MPa and temperature range of 274.2–278.2K. The influences of system temperature, initial pressure, and water cut of water-in-oil emulsion on the induction time of hydrate formation and hydrate growth rate were investigated, respectively. Experimental results show that the induction time varies inversely with initial pressure, and directly with temperature. The hydrate growth rate increases with increase of initial pressure and decrease of temperature. In the water-in-oil dispersed systems, the increase of water cut increases the hydrate growth rate. A mathematical model was developed for describing the formation kinetic behavior of methane hydrates in the dispersed system. The parameters of the model were determined by correlating the formation rate data, and the activation energies were further determined. The model was found to be able to calculate the formation kinetic behavior of methane hydrate in the dispersed system.

CO2 (carbon dioxide) separation from CO2–H2 (hydrogen) gas mixtures by gas hydrates in TBAB (tetra-n-butyl ammonium bromide) solution and Raman spectroscopic analysis

The hydrate-based CO2 (carbon dioxide) separation and capture from CO2/H2 (hydrogen) gas mixtures with the different CO2 concentrations is investigated in 0.29 mol% TBAB (tetra-n-butyl ammonium bromide) solution. Raman spectroscopic analysis is employed to determine the compositions of the mixed hydrates containing CO2, H2, TBAB and H2O (water). The phase equilibrium conditions shift to extreme conditions as decreasing CO2 from 40.0% to 10.0% in the gas mixtures. At the temperature of 274.15 K and under driving force of 3.0 MPa, the hydrate formation induction time increases while the CO2 recovery (or separation fraction) decreases with the decrease of CO2. Raman peaks for CO2 gas shift to higher frequency side of 6–10 cm−1 as the CO2 concentration turns from 40.0% to the range of 10.0–18.0%. Meanwhile, no Raman spectral signal is detected for H–H stretching vibration in the mixed hydrates.

Impact of Different Surfactants and their Mixtures on Methane‐Hydrate Formation

AbstractGas hydrates can be used as a potential means for natural gas storage. Design of a gas‐hydrate‐based unit requires accurate knowledge of hydrate‐formation kinetics especially in the presence of promoters. In this study, the effects of sodium dodecyl sulfate (SDS), hexa decyl trimethyl ammonium bromide (HTABr), polyoxy ethylene(20) cetyl ether (Brij‐58) and mixtures of SDS with HTABr and Brij‐58 have been investigated to determine their influence on the methane‐hydrate‐formation kinetics and thermodynamics. The study on the kinetics of hydrate formation is focused on the induction time and hydrate‐formation rate. It is found that induction time of hydrate formation in the presence of a promoter is reduced considerably for each test compared with a pure water test. The minimum value of the induction time is found for a mixture of SDS (500 ppm) with HTABr (700 ppm). All of the surfactants and their mixtures can be designated as hydrate‐formation promoters in the concentration ranges studied in the present work and can increase the hydrate‐formation rate. SDS at a concentration of 500 ppm is determined to be the best hydrate‐formation promoter among the surfactants tested. The percent conversion of methane to hydrate is increased in the presence of these surfactants at the end of hydrate formation. The maximum value of the conversion is observed for the 500 ppm concentration of SDS. The results demonstrate that these surfactants and their corresponding mixtures have no significant effect on the thermodynamics of methane hydrate formation.

Experimental investigation of gas consumption for simple gas hydrate formation in a recirculation flow mini-loop apparatus in the presence of modified starch as a kinetic inhibitor

The main objective of the present work is to investigate experimentally the formation of simple gas hydrate with or without the presence of kinetic inhibitors such as modified starch in a recirculation flow loop. For this purpose, a laboratory recirculation flow mini-loop apparatus was set up to measure the induction time for hydrate formation and gas consumption rate when a hydrate forming substance (such as C1, C3, CO2 and i-C4) is contacted with water in the absence or presence of dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with pure gas is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of the required gas make-up. The effect of pressure on gas consumption during hydrate formation is investigated with or without the presence of polyvinylpyrrolidone (PVP) and modified starch as kinetic inhibitors at various concentrations. Our results show that the modified starch can be applied as an inhibitor in prevention of simple gas hydrate formation.

Methane Hydrate Formation and Dissociation in the presence of Bentonite Clay Suspension

AbstractThe present work reports the effect of bentonite clay on methane hydrate formation and dissociation in synthetic seawater of salinity 3.55 % of total dissolved salts. Extensive observations of pressure‐temperature equilibrium during formation and decomposition of methane hydrate under different conditions have been made. It is observed that phase equilibrium conditions of hydrate are affected on changing the concentration of bentonite clay in synthetic seawater. Induction time for hydrate nucleation has been measured under different concentrations of clay and subcooling conditions. The presence of bentonite clay in synthetic seawater reduces the induction time of hydrate formation. Enthalpy of hydrate dissociation is calculated by Clausius‐Clapeyron equation using measured phase equilibrium data. The amount of gas consumed during hydrate formation has been calculated using real gas equation. It is found that a larger amount of gas is consumed upon addition of bentonite clay in synthetic seawater.

Effect of Surface Energy on Carbon Dioxide Hydrate Formation

In this work, the effect of the surface energy between the hydrate clusters and the aqueous phase on the hydrate formation of carbon dioxide was thoroughly investigated. Our results show that the threshold pressure for hydrate formation is less sensitive to the temperatures if the surface energy is not larger than 7 mJ/m(2). However, the threshold pressure is very sensitive to the temperatures and increases significantly with the surface energy if it is over 7, 9, and 10 mJ/m(2) for the temperatures of 279, 277.45, and 276 K, respectively. The value of the surface energy for the CO(2) hydrate/water system was determined as 9.3 mJ/m(2) by comparing our results with the experimental data for stable CO(2) hydrate formation at the temperature range of 277.45-278.85 K and at pressures of 55-165 bar. This value is very close to the recently reported value of 7.5 ± 1.4 mJ/m(2) from molecular simulation. A theoretical method was proposed for computing the induction time of hydrate formation adopting a composite of the time required for critical nuclei formation and their growth to a detectable size. By using this method, the surface energy was avoided in the induction time calculation and an average crystallite volume of 0.238 mm(3) at the induction time was derived based on the experimental data. It provides an approach for predicting the induction time for gas hydrate formation.

Accelerated nucleation of tetrahydrofuran (THF) hydrate in presence of ZIF-61

Clathrate hydrate can be used in energy gas storage and transportation, CO2 capture and cool storage etc. However, these technologies are difficult to be used due to the low formation rate and long induction time of hydrate formation. In this paper, ZIF-61 (zeolite imidazolate framework, ZIF) was first used in hydrate formation to stimulate hydrate nucleation. As an additive of clathrate hydrate, ZIF-61 promoted obviously the acceleration of tetrahydrofuran (THF) hydrate nucleation. It shortened the induction time of THF hydrate formation from 2–5 h to 0.3–1 h mainly due to the template function of ZIF-61 by which the nucleation of THF hydrate has been promoted.

Experimental investigation of double gas hydrate formation in the presence of modified starch as a kinetic inhibitor in a flow mini‐loop apparatus

AbstractThe main objective of the present work is experimental investigation of double gas hydrate formation with or without presence of modified starch as kinetic inhibitors in a flow mini‐loop apparatus. To this object, a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the rate uptake when a gaseous mixture (such as 75% C1–25% C3, 25% C1–75% C3, 75% C1–25% i‐C4 and 25% C1–75% i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, water blend saturated with gas mixture is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation is investigated with or without presence of polyvinylpyrrolidone and modified starch as kinetic inhibitors at various concentrations. Our results were shown that the modified starch can be applied as inhibitors in prevention of double gas hydrate formation in mini‐loop apparatus. © 2011 Canadian Society for Chemical Engineering

Induction time of hydrate formation in a flow loop

A set of experiments were developed to study the effect of the supersaturation on the induction time of the hydrate formation in a flow loop. Propane, carbon dioxide and a mixture of methane and propane were used to form hydrate in the loop. Induction time was measured with varying temperature and pressure which gave rise to change in the supersaturation. It was found that induction time was indirectly dependent on the supersaturation in all experiments. Measured values of induction time were in the range of 9–12 minutes for carbon dioxide, 82–103 minutes for propane and 7–22 minutes for 0.73C1+0.27C3 at the given operating conditions. Hydrate nucleation were carried out at 5°C and 3–5 MPa for carbon dioxide, 2–5°C and 1MPa for propane and 4°C and 2–4 MPa for 0.73C1+ 0.27C3. In order to calculate the induction time, a semiempirical correlation as a function of supersaturation was used. The equation parameters I were determined based on the experimental data via nonlinear regression.

Experimental and Theoretical Investigation of Double Gas Hydrate Formation in the Presence or Absence of Kinetic Inhibitors in a Flow Mini‐Loop Apparatus

AbstractDouble gas hydrate formation in the presence or absence of kinetic inhibitors in a flow mini‐loop apparatus was investigated. For the prediction of the gas consumption rate during hydrate formation in this system, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in a batch system was developed for double gas hydrate formation in a flow mini‐loop apparatus. To complete the theoretical evaluation of gas hydrate formation through the mini‐loop apparatus in the presence or absence of kinetic hydrate inhibitors (KHI), a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the uptake rate when a gaseous mixture (such as 75 % C1/25 % C3, 25 % C1/75 % C3, 75 % C1/25 % i‐C4, and 25 % C1/75 % i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with gas mixture was circulated up to the required pressure. The pressure was maintained at a constant value during the experimental runs by means of a required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation was investigated in the presence or absence of polyvinylpyrrolidone (PVP) and L‐tyrosine as kinetic inhibitors at various concentrations. A good agreement was found between the predicted and experimental data in the presence or absence of KHI. The total average absolute deviation percents between the experimental and predicted values of gas consumption were found to be 16.4 and 17.5 % for the double gas hydrate formation in the presence or absence of the kinetic inhibitors, respectively.

Experimental and theoretical investigation of simple gas hydrate formation with or without presence of kinetic inhibitors in a flow mini-loop apparatus

Gas hydrates are ice-like crystalline compounds, which form through a combination of water and suitably sized guest molecules under low temperature and elevated pressure conditions. These solid compounds give rise to problems in the natural gas oil industry because they can plug pipelines and process equipment. Low dosage hydrate inhibitors are a recently developed hydrate control technology, which can be more cost-effective than traditional practices such as methanol and glycols. The kinetics of hydrate growth has been modeled by numerous authors who have measured the gas consumption rate during hydrate formation in batch agitator reactors. The main objective of the present work is to investigate experimentally of simple gas hydrate formation with or without the presence of kinetic inhibitors in a flow mini-loop apparatus. To predict the gas consumption rate during hydrate formation in this system, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in a batch system was developed for this objective. To complete the theoretical evaluation of gas hydrate formation through the pipeline with or without the presence of kinetic hydrate inhibitors (KHIs), a laboratory flow mini-loop apparatus was set up to measure the induction time for hydrate formation and the uptake rate when a hydrate forming substance (such as C1, C3, CO 2 and i-C4) is contacted with water in the absence or presence of dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with pure gas is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of the required gas make-up. The effect of pressure on gas consumption during hydrate formation is investigated with or without the presence of polyvinylpyrrolidone (PVP) and l-tyrosine as kinetic inhibitors at various concentrations. A good agreement is found between the predicted and experimental data with or without the presence of KHIs. The total average absolute deviation percent between the experimental and predicted gas consumption is found to be 15.8% and 14.9% for simple gas hydrate formation with or without presence of kinetic inhibitors, respectively.

Dual function inhibitors for methane hydrate

The performance of five imidazolium-based ionic liquids as a new class of gas hydrate inhibitors has been investigated. Their effects on the equilibrium hydrate dissociation curve in a pressure range of 30–110 bar and the induction time of hydrate formation at 114 bar and a high degree of supercooling, i.e., about 25 °C, are measured in a high-pressure micro differential scanning calorimeter. It is found that these ionic liquids, due to their strong electrostatic charges and hydrogen bond with water, could shift the equilibrium hydrate dissociation/stability curve to a lower temperature and, at the same time, retard the hydrate formation by slowing down the hydrate nucleation rate, thus are able to act as both thermodynamic and kinetic inhibitors. This dual function is expected to make this type of inhibitors perform more effectively than the existing inhibitors.

Predicting the Induction Time of Hydrate Formation on a Water Droplet

Despite the importance of the induction time in hydrate formation studies, the scientists have not yet developed a generalized model due to its stochastic property. In this work, the induction time of hydrate formation of multicomponent gas mixtures on a water droplet has been modeled. Mass transfer through the droplet surface was modeled based on a diffusion equation where the rate of reaction was expressed based on the nucleation theory. Driving force for the hydrate formation was calculated based on the change in the Gibbs free energies of the gas, water and the hydrate. The model was validated by comparison of the predicted results with the experimental data from the literature. The induction time was calculated for hydrate formation from a mixture of 89.4% methane + 10.6% ethane on 1.5-7 mm in diameter of water droplets at 273.85 K and 3.6-5.1 MPa. It was found that, induction time is highly sensitive to the value of the driving force. Moreover, the induction times were not dependent on the size of the droplets and the induction time for the water droplets with hydrate memory was shorter than the droplets without hydrate memory.

Effect of pressure vessel size on the formation of gas hydrates

A Seafloor Process Simulator (SPS) has been used for mesoscale experiments investigating the nature of hydrate nucleation and dissociation. The SPS is a 72 L vessel which establishes the pressures and temperatures required for methane and carbon dioxide hydrate stability. This paper describes the experiments that have been performed in the SPS and have been duplicated in the smaller Parr vessel (450 mL). It was found that experiments in the SPS resulted in hydrates consistently forming at lower overpressures and in shorter induction times than equivalent experiments in the Parr vessel. The variability of pressure and/or induction time for hydrate formation was not eliminated by using the SPS, but it appeared to be less dramatic (small coefficients of variation) when compared with a 450 mL Parr vessel. Based on the experiments performed using the SPS this reduction in overpressure and/or induction time required for the accumulation of hydrates may be attributed to increased bubble surface area, increased gas concentration, increased lifetime of bubbles, increased total volume of the SPS, or a combination of the above. Mesoscale experiments, such as those in the SPS, may perhaps be more representative of hydrate accumulation in the natural environment.

Natural Gas Hydrate Formation in an Ejector Loop Reactor: Preliminary Study

A natural gas hydrate formation system based on the ejector-type loop reactor (ELR) has been built. Three types of flow patterns in the reactor are observed with variation of the gas entrainment rate, i.e., single-bubble regime, intermediate regime, and jet regime. The flow pattern under the free suction state of the ejector is in the jet regime. The microbubble generated from ELR with a static mixer can shorten the induction time for hydrate formation significantly. However, it cannot improve the hydrate formation rate as the gas entrainment rate decreased with the static mixer on. The hydrate formation rate of the ELR system is dependent on the subcooling, gas entrainment rate, and pressure and is fairly comparable with the formation rate of both water spraying and stirring reactor in the literature.

Effect of Cyclodextrins on Hydrate Formation Rates

Effects of cyclodextrins (CD) on hydrate formation kinetics were investigated. Several kinds of cyclodextrins, such as α-CD, β-CD, β-CD polymers, and β-CD modified with methyl and triacetyl groups were tested as additives for hydrate formation of xenon, with a concentration range of 0−5 wt %. Induction time for hydrate formation was reduced by the addition of any of the CDs; however, no clear relationship between the structure of CDs and the reduction effect was observed. The three-phase equilibrium pressure (H−V−Lw) was unaffected by the addition of the CDs, except for β-CDs modified with methyl or triacetyl groups. The hydrate formation rate, which was expressed as a rate constant based on the chemical potential, increased with the addition of α-CD, β-CD, and β-CD polymers. β-CD polymer showed the highest acceleration effect on the xenon hydrate at about 1 wt %; the rate constant was about three times larger than that for pure water. Contrastingly, modified β-CD and dextrin with a straight chain structu...

Surface Tensions of Aqueous Solutions of Sodium Alkyl Sulfates in Contact with Methane under Hydrate-Forming Conditions

This paper presents experimental data on the surface tensions of aqueous solutions of sodium alkyl sulfates (ionic surfactants) in contact with methane at a pressure of 3.90 MPa and a temperature of 275 K (i.e., a condition in which a clathrate hydrate of methane is thermodynamically stable). These data were obtained in the metastable absence of any hydrate in the experimental system (i.e., every measurement was accomplished during the induction time for hydrate formation). Three sodium alkyl sulfates appreciably different in length of the hydrophobic radicals were usedthey were sodium dodecyl sulfate (SDS), sodium tetradecyl sulfate (STS), and sodium hexadecyl sulfate (SHS). The concentration of each of these surfactants was varied over a range including the critical concentration above which the surface tension levels off. On the basis of visual observations of pendant drops of SDS solutions, we identified the critical concentration for SDS as the solubility above which a hydrated solid of SDS forms instead of the critical micelle concentration (CMC) above which micelles of SDS would form. The SDS solubility was thus determined to be (2.2 to 2.3) g·kg-1, which agrees, within mutual uncertainties, with the CMC determined at a higher temperature, 293 K, either in the same pressurized methane ambience or in the air under atmospheric pressure. These results completely conflict with those reported by Sun et al. in their recent paper published in this Journal (J. Chem. Eng. Data 2004, 49, 1023−1025).

Natural gas storage in hydrates with the presence of promoters

Hydrate technology is being developed for the storage and transport of natural gas. Micellar surfectant solutions were found to increase the gas hydrate formation rate and storage capacity. An anionic surfactant, a nonionic surfactant, their mixtures and cyclopentane were used to improve the hydrate formation of a synthetic natural gas (methane=92.05 mol%, ethane=4.96 mol%, propane=2.99 mol%) in a quiescent system in this work. The effect of an anionic surfactant (sodium dodecyl sulfate) on natural gas storage in hydrates is more pronounced compared to the effect of a nonionic surfactant (dodecyl polysaccharide glycoside). Cyclopentane could reduce hydrate formation induction time but could not improve the hydrate formation rate and storage capacity.

Effect of surfactants and liquid hydrocarbons on gas hydrate formation rate and storage capacity

Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non-ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non-ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd.