Study of Methane Hydrate Inhibition Mechanisms Using Copolymers (original) (raw)
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Energy & Fuels, 2011
A newly fabricated, stirred reactor was used to investigate hydrate inhibition and decomposition in the presence of two commercial, chemical kinetic inhibitors, polyvinylpyrrolidone (PVP) and H1W85281, as well as two antifreeze proteins (AFPs), type I and type III. The longest induction times and the slowest growth rates were observed with HIW8581, with the fastest growth recorded for PVP. Type I AFP (AFP-I) was a more effective inhibitor, with respect to induction time and growth, than either PVP or type III AFP (AFP-III). Complete hydrate decomposition occurred earlier in the presence of any of the inhibitors compared to water controls. However, depending on the type of inhibitor present during crystallization, hydrate decomposition profiles were distinct, with a longer, two-stage decomposition profile in the presence of the chemical kinetic inhibitors (PVP and H1W85281). The fastest, single-stage decompositions were characteristic of hydrates in experiments with either of the AFPs. These results argue that thought must be given to inhibitor-mediated decomposition kinetics in screens and designs of potential kinetic inhibitors. This is a necessary, practical consideration for industry in cases when, because of long shut in periods, hydrate formation may be unavoidable, even when inhibitors are utilized.
Use of Hydrophobic Particles as Kinetic Promoters for Gas Hydrate Formation
Journal of Chemical & Engineering Data, 2015
Hydrophobic particles have been tested as kinetic promoters for gas hydrate formation. The experimental results obtained with stationary beds of sands show that methane (CH 4) hydrate is more readily formed when the sand particles are hydrophobized by coating the surfaces with octadecyltrichlorosilane (OTS). The induction times decreased steadily with increasing water contact angles (θ) possibly due to the increased propensity of the water molecules in the vicinity of hydrophobic surfaces to form partial clathrates. The kinetics of CO 2 hydrate formation has been studied using Teflon and hydrophobic silica particles to disperse either water in gas phase to obtain "dry water" or to disperse gas in water phase to obtain foam. The results show that hydrates are formed instantaneously due to the increased mass transfer rates at the gas/water interface and the formation of partial clathrates in the vicinity of hydrophobic surfaces.
Energy & Fuels, 2019
Gas hydrate formation usually occurs with a certain delay after a system composed of water and a hydrate-forming gas is put under suitable thermodynamic conditions of pressure and temperature. This delay period is called the "induction time", and due to its large variability within a single experimental setting, hydrate formation is often referred to as a stochastic process. The evaluation of induction times, together with other measurements, are taken as an indication for the efficiency of hydrate inhibitors, and they are usually carried out by simply putting the experimental system under Page 1 of 19 ACS Paragon Plus Environment Energy & Fuels chosen P/T conditions, then waiting for the hydrate to form and measuring the time elapsed. In this paper, we present an improved procedure by which the variability of hydrate induction times can be remarkably reduced, while keeping a good correlation of measured induction times with the respective temperatures as obtained by a constant-cooling method. In this procedure, temperatures are lowered by 0.5°C after each time span of 3 hrs with no hydrate formation. Induction times obtained in this way show a remarkably lower coefficient of variation as compared to a standard induction time measurement.
Chemical Engineering Science, 2005
Methane hydrate equilibrium has been studied upon continuous heating of the water-hydrate-gas system within the temperature range of 275-300 K. This temperature range corresponds to equilibrium pressures of 3.15-55 MPa. The hydrate formation/dissociation experiments were carried out in a high-pressure reactor under isochoric conditions and with no agitation. A small amount of surfactant (0.02 wt% sodium dodecyl sulfate, SDS) was added to water to promote hydrate formation. It was demonstrated that SDS did not have any influence on the gas hydrate equilibrium, but increased drastically both the hydrate formation rate and the amount of water converted into hydrate, when compared with the experiments without surfactant. To understand and clarify the influence of SDS on hydrate formation, macroscopic observations of hydrate growth were carried out using gas propane as hydrate former in a fully transparent reactor. We observed that 10 −3 wt% SDS (230 times less than the Critical Micellar Concentration of SDS) were sufficient to prevent hydrate particles from agglomerating and forming a rigid hydrate film at the liquid-gas interface. In the presence of SDS, hydrates grew mainly on the reactor walls as a porous structure, which sucked the solution due to capillary forces. Hydrates grew with a high rate until about 97 wt% of the water present in the reactor was transformed into hydrate.
Annals of the New York Academy of Sciences, 2006
A BSTRACT : In a previous paper, 1 we proposed a complete model for methane hydrate crystallization from pure water and methane gas in a semibatch reactor. This model takes into account the crucial importance of the ratedetermining mass transfer at the gas/liquid interface, coupled with primary nucleation and growth. The validity of this model has been proved on a large number of experimental results. However, due to the complexity of the equations, only a numerical solution is possible, so that comparison between theory and experiment is not straightforward. In this paper, we consider a simple model of primary nucleation/growth and we propose an analytical solution for the time evolution of the total number of particles, mean diameter, and methane gas consumption rate during the first time of the crystallization. This model is used to analyze experimental results obtained in the presence of a kinetic additive: polyvinylpyrrolidone (PVP), in order to understand the origin of its effect.
Journal of Chemical & Engineering Data, 2015
Kinetic hydrate inhibitors (KHIs) or low dosage hydrate inhibitors (LDHIs) are known as additives employed to delay the onset of gas hydrate nucleation time in hydrocarbon pipelines. It has been observed, however, that in laboratory experiments accelerated hydrate growth called catastrophic growth can occur. This may be a serious problem if it occurs in a field application of kinetic inhibitors. The mechanism of such accelerated hydrate growth in the presence of KHIs is still not understood. A highpressure microdifferential scanning calorimeter was employed to study the accelerated hydrate growth in the presence of chemical and biological inhibitors. It is hypothesized that capillary action facilitates the transport of water molecules across the formed hydrate layer from the bulk of the liquid water phase to the gas−liquid interface. This in turn might be the governing mechanism for catastrophic hydrate growth in the presence of KHIs. In addition, the hydrate catastrophic index is introduced in this work as a parameter to quantify the phenomenon based on the laboratory data and the type of experiment conducted. The HCI may then serve as a measure of the pipeline hydrate plugging potential.
Chemical Engineering Science, 1999
In this paper we describe a new experimental set-up which makes possible the in situ determination of the particle size distribution of methane hydrate during its formation in a pressurized reactor. It has been installed on two research sites: one at the Institut Franiais du Pe´trole (IFP) and the other at the Ecole des Mines de Saint-Etienne (EMSE). Thanks to this apparatus, new data can be obtained, in particular concerning the granular aspects of the crystallization processes and the reproducibility of the results. Particularly, we propose a new experimental procedure which allows us two important improvements: -a better reproducibility of the induction time, -the possibility of doing a large number of experiments in a day (around fifteen). Using this protocol, the effect of some kinetic inhibitors of the crystallization processes are shown: increase of the induction time and/or decrease of the quantity of hydrate formed.
Journal of Crystal Growth, 2008
The influence of the kinetic inhibitor poly(N-vinylpyrrolidone) or PVP on hydrate methane/propane hydrate formation was studied in pre-saturated liquid water with and without the presence of heptane under different undercooling conditions. It was found that when the inhibitor concentration was 0.1 wt%, hydrate formation started as a film at the gas/water interface similar to the crystal behavior without inhibitor. When the inhibitor concentration was 0.5 wt% hydrate formation started at the wall above the gas/water interface and the hydrate film at the gas/water interface was observed as well. However, for inhibitor concentration 1.0 wt%, the hydrate started forming from water droplets attached to the wall above the gas/liquid interface and grew catastrophically.
Unusual kinetic inhibitor effects on gas hydrate formation
Chemical Engineering Science, 2006
Gas hydrate formation experiments were conducted with a methane-ethane mixture at 273.7 or 273.9 K and 5100 kPa and using water droplets or water contained in cylindrical glass columns. The effect of kinetic inhibitors and the water/solid interface on the induction time for hydrate crystallization and on the hydrate growth and decomposition characteristics was studied. It was found that inhibitors GHI 101 and Luvicap EG delayed the onset of hydrate nucleation. While this inhibition effects has been reported previously some unusual behaviour was observed and reported for the first time. In particular, the water droplet containing GHI 101 or Luvicap EG was found to collapse prior to nucleation and spread out on the Teflon surface. Subsequently, hydrate was formed as a layer on the surface. Catastrophic growth and spreading of the hydrate crystals was also observed during hydrate formation in the glass columns in the presence of the kinetic inhibitor. Finally, when polyethylene oxide (PEO) was added into the kinetic inhibitor solution the memory effect on the induction time decreased dramatically. ᭧