Presence Of Kinetic Inhibitors Research Articles

Insights into behaviors of guest and host molecules in methane hydrate formation process in the presence of kinetic inhibitors via in-situ micro-Raman spectroscopy

In-situ microscopic observation on methane hydrate formation in the presence of kinetic hydrate inhibitor, poly (vinyl caprolactam) (PVCap) or poly (N-isopropyl acrylamide) (PNIPAM), is conducted with a confocal Raman imaging microscope, and the behaviors of CH4 molecules and water molecules in hydrate formation process are studied to understand the inhibition mechanism. It is found that both PVCap and PNIPAM have influences on hydrate formation, but their interactions with host and guest molecules are different. PVCap with cyclic pendant groups works better on preventing hydrate formation from the gas–liquid interface into the bulk solution, while PNIPAM with acyclic pendant groups is more effectively on inhibiting hydrate growth to well-ordered clathrate structures. Those are caused by the difference in the prominent inhibition mechanism of the two types of kinetic hydrate inhibitors, lactam-based PVCap mainly limiting the diffusion of CH4 molecules from the gaseous phase to the liquid phase, while non-lactam PNIPAM undermining hydrate growth by retarding the rearrangement of water molecules to form clathrate structures.

Effects of ethanol on the performance of kinetic hydrate inhibitors

The main types of hydrate inhibitors are thermodynamic (THI), kinetics (KHI) and anti-agglomerants (AA) inhibitors. Kinetic inhibitors are used in low dosages but do not have satisfactory efficiency in large subcoolings. On the other hand, thermodynamic inhibitors are widely used in the industry and require high dosages. In order to study a combined inhibition, the behavior of three different commercial kinetic inhibitors combined with ethanol (THI) was tested under subcooling conditions in cases which unique kinetic inhibition did not yield satisfactory results. With 3% concentrations of kinetic inhibitors and a 10% by mass ratio of ethanol, it was possible to identify a significant increase in induction time for two of the inhibitors tested. Once the growth of the hydrate crystals began to appear, the presence of inhibitors did not result in significant gain in delaying the crystallization process. Some physical characteristics of the formed hydrates were altered in the presence of kinetic inhibitors and ethanol, evidencing a lower capacity of the crystals to adhere. With the same concentration of kinetic inhibitor and a 30% by mass ratio of ethanol the KHI presented low effectiveness.

Modeling of Gas Hydrate Formation in the Presence of Inhibitors by Intelligent Systems

Gas hydrate formation in production and transmission pipelines and consequent plugging of these lines have been a major flow-assurance concern of the oil and gas industry for the last 75 years. Gas hydrate formation rate is one of the most important topics related to the kinetics of the process of gas hydrate crystallization. The main purpose of this study is investigating phenomenon of gas hydrate formation with the Presence of kinetic Inhibitors in operation gas transmission, and prediction of gas hydrate formation rate in the pipeline. In this regard, by using experimental data and Intelligent Systems (Artificial neural networks and adaptive neural-fuzzy system), two different high efficient and accurate models were designed to predict hydrate formation rate of CO2, C1, C3, and i-C4. It was found that such models can be used as powerful tools, for prediction of gas hydrate formation rate with total average of absolute deviation less than 6%.

Evaluation of various types' equations of state for prediction of rate of double gas hydrate formation based on Kashchiev model in flow loop apparatus

This paper compares the effects of using various types of equations of state such as Peng Robinson (PR), Soave Redlich Kwong (SRK), Esmaeilzadeh – Roshanfeker (ER), Patel Teja (PT) and Valderrama–Patel–Teja (VPT) on the rate of hydrate formation based on the Kashchiev model for gaseous mixtures with experimental data points obtained in a mini flow loop apparatus in presence of the kinetic inhibitors (such as modified starch and l-tyrosine) at various pressures (1–4 MPa) and specified temperature (277.15 K). For this purpose, a laboratory mini flow loop apparatus was set up to measure the rate of gas hydrate formation when a hydrate forming mixture is contacted with water in the presence or absence 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 total average absolute deviation was found to be 18.7%, 19.8%, 19.2%, 20.2% and 20.7% of the PR, ER, SRK, VPT and PT equations of state for calculating of gas consumption for gaseous mixtures during gas hydrate formation (in the presence and absence of kinetic gas hydrate inhibitor), respectively. Comparison results between the calculated and experimental data points of gas consumption were obtained in a flow loop indicate that the PR and ER equations of state have lower errors than the SRK, VPT and PT equations of state for this model.

Synergistic kinetic inhibition of natural gas hydrate formation

Rocking cells were used to investigate the natural gas hydrate formation and decomposition in the presence of kinetic inhibitor, Luvicap. In addition, the influence of poly ethylene oxide (PEO) and NaCl on the performance of Luvicap was investigated using temperature ramping and isothermal experiments. Luvicap decreased the hydrate nucleation temperature in ramping and increased the hydrate nucleation time at fixed temperatures. The presence of PEO and NaCl enhanced the nucleation inhibition strength of Luvicap. However the addition of Luvicap promoted the hydrate growth after nucleation. PEO does not affect hydrate growth whereas NaCl reduced the hydrate growth both in the presence and absence of Luvicap. In addition complex two-stage hydrate growth was observed in the presence of Luvicap. Moreover, the hydrate formed in the presence of inhibitor took longer time/higher temperature to decompose completely. One should consider this complex inhibitor-mediated hydrate formation and decomposition kinetics when screening and designing kinetic inhibitors for field applications.

Assessing the performance of commercial and biological gas hydrate inhibitors using nuclear magnetic resonance microscopy and a stirred autoclave

The formation kinetics of methane/ethane/propane hydrate in the presence of kinetic inhibitors was investigated using 1H nuclear magnetic resonance imaging (MRI) as well as a more-traditional method using a stirred autoclave. These studies were facilitated by fabricating a multi-drop insert for 1H NMR micro-imaging, which allowed the comparison of the performance of microliter quantities of several inhibitors simultaneously and under the same conditions. Both methods showed that hydrate nucleation and growth were delayed significantly in the presence of inhibitors, which included two biological inhibitors (antifreeze proteins) and a commercial inhibitor. The results demonstrate that MRI is a useful tool for the visualization and evaluation of the performance of kinetic inhibitors on mixed gas hydrate formation. The MRI technique should prove especially valuable in the case of analysis of potential inhibitors, pre-commercialization, which are available in only limited quantities, such as biological inhibitors. This technique may also find utility in the exploration of differences in inhibitor performance, which may suggest distinct mechanisms of inhibitor action.

Experimental Investigation of Natural Gas Components During Gas Hydrate Formation in Presence or Absence of the L-Tyrosine as a Kinetic Inhibitor in a Flow Mini-loop Apparatus

Hydrates are crystalline compounds similar to ice, with guest molecules like methane and ethane trapped inside cavities or cages formed by the hydrogen bounded framework of water molecules. These solid compounds give rise to problems in the natural gas oil industry because they can plug pipelines and process equipments. 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 main objective of the present work is to experimentally investigate simple gas hydrate formation with or without the presence of kinetic inhibitors in a flow mini-loop apparatus. For this purpose, a laboratory flow mini-loop apparatus was set up to measure the induction time and gas consumption rate during gas hydrate formation when a hydrate forming substance such as methane, ethane, propane, carbon dioxide and iso- butane is contacted with water in the absence or presence of dissolved inhibitor at various concentration 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 PVP (polyvinylpyrrolidone) and L-tyrosine as kinetic inhibitors at various concentrations. The experimental results show that increasing the pressure of the system, causes to increase the experimental gas consumption and decrease the induction time. Also, the extent of gas hydrate formation at a given time is clearly less in the presence of the inhibitors. Moreover, when comparing the gas consumption during the hydrate formation for simple gas hydrate formation in presence of PVP and L-tyrosine inhibitors, it is seen that the gas consumption in presence of L-tyrosine is lower than that of PVP for all experiments.

Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 2. Stirred Reactor Experiments

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 ...

Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 1. High Pressure Calorimetry

The effect of kinetic inhibitors, both chemical (PVP and H1W85281) and biological (type III antifreeze protein), on natural gas hydrate formation was investigated using high pressure differential scanning calorimetry (HP-DSC). The presence of inhibitors decreased the overall formation of methane/ethane/propane hydrate compared to systems without added inhibitors. As well, all of the inhibitors significantly delayed hydrate nucleation as compared to water controls. However, the two classes of inhibitors were distinguished by the formation of hydrates with different stabilities. A single hydrate melting peak was seen with the antifreeze protein (AFP), and this was consistent after recrystallization. In contrast, multiple hydrate melting events, some indicating the formation of hydrate structures with high stability, were observed in the presence of the chemical inhibitors, and these varied depending on the crystallization cycle. This heterogeneity suggests that the use of these chemical inhibitors (PVP and ...

Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 3. Structural and Compositional Changes

A synthetic natural gas mixture composed of methane, ethane, and propane in a batch reactor was used to form gas hydrates in the presence of two commercial, chemical kinetic inhibitors, polyvinylpyrrolidone (PVP) and H1W85281, and one biological inhibitor, antifreeze protein type III (AFP-III). Powder X-ray diffraction and nuclear magnetic resonance spectroscopy showed that structure II hydrates dominated, as expected, but in the presence of the chemical inhibitors, structure I was also present. Raman spectroscopy confirmed the complexity and the heterogeneity of the guest composition within these hydrates, which was also consistent with the gas analysis obtained using gas chromatography. However, in the presence of AFP-III, hydrates appeared to be relatively homogeneous structure II hydrates, with weaker evidence of structure I. When individual gas cage occupancies were calculated, both classes of inhibitors reduced large cage methane occupancy by ∼25%. With the chemical inhibitors, these large cage meth...

THE EFFECT OF VARIOUS TYPES OF EQUATIONS OF STATE ON DRIVING FORCE CALCULATION AND GAS CONSUMPTION PREDICTION IN SIMPLE AND DOUBLE HYDRATE FORMATION WITH OR WITHOUT THE PRESENCE OF KINETIC INHIBITORS IN BATCH SYSTEMS

This article compares the effects of using various types of equations of state (Peng-Robinson, PR; Soave-Redlich-Kwong, SRK; Esmaeilzadeh-Roshanfekr, ER; Patel-Teja, PT; and Valderrama-Patel-Teja, VPT) on the calculated driving force and rate of gas consumption based on the Kashchiev model in simple and double-gas hydrate formation for methane, ethane, and their mixtures with 1130 experimental published data points with or without the presence of kinetic inhibitors at various pressures and temperatures. For the prediction of gas consumption rate in double-gas hydrate formation, the rate equation based on the Kashchiev model for simple gas hydrate formation was developed using the calculation of gas mole fraction in hydrate phase and then prediction of gas hydrate formation rate for each component in gaseous mixture. The total average absolute deviation was found to be 8.72%, 10.34%, 8.84%, 11.04%, and 14.16% for the PR, ER, SRK, VPT, and PT equations of state for calculating gas consumption in simple and double hydrate formation, respectively.

Effect of various types of equations of state for prediction of simple gas hydrate formation with or without the presence of kinetic inhibitors in a flow mini-loop apparatus

This paper compares the effects of using various types of equations of state (PR, 1 1 Peng–Robinson. SRK, 2 2 Soave–Redlich–Kwong. ER, 3 3 Esmaeilzadeh–Roshanfekr. PT 4 4 Patel–Teja. and VPT 5 5 Valderrama–Patel–Teja. ) on the calculated driving force and rate of gas consumption based on the Kashchiev and Firoozabadi model for simple gas hydrate formation for methane, carbon dioxide, propane and iso-butane with experimental data points obtained in a flow mini-loop apparatus with or without the presence of kinetic inhibitors at various pressures and specified temperatures. For this purpose, a laboratory flow mini-loop apparatus was set up to measure gas consumption rate when a hydrate forming substance (such as C 1, C 3, CO 2 and i-C 4) is contacted with water in the presence or absence 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 total average absolute deviation was found to be 15.4%, 16.3%, 15.8%, 17.8% and 17.4% for the PR, ER, SRK, PT and VPT equations of state for calculating gas consumption in simple gas hydrate formation with or without the presence of kinetic hydrate inhibitors, respectively. Comparison results between the calculated and experimental data points of gas consumption were obtained in flow loop indicate that the PR and ER equations of state have lower errors than the SRK, VPT and PT equations of state for this model.

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.

Continuum model for mesh crystallization

The front propagation of a single crystallizing domain has been well studied for more than a century. In many important crystallization processes, however, multiple domains grow simultaneously, resulting in a multicrystalline, meshlike aggregate. This is the typical case for organic compounds, including polymers and alkanes. We have studied such growth in the case of a normal alkane precipitating from solution in the presence of kinetic inhibitors--additives which, when present in trace amounts, have a dramatic effect on growth kinetics and morphology. In this case, we observe a distinct banded growth with a typical length scale of 300 microm superimposed on the finer mesh structure. We present a simple continuum model that demonstrates the essential behavior of this growth.

Banded crystallization of tricosane in the presence of kinetic inhibitors during directional solidification

Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphology. While the utility of such additives has been proven at the operational level, few studies have directly monitored their effect at microscopic scales. Here, we present a study of such additives in model n-alkane systems. We find a dramatic effect on the growth morphology: rather than the usual plate-like growth exhibited by pure wax, we see highly branched microcrystalline meshes. Under certain conditions, these meshes form well-defined bands with spacings larger than 200 μm. We suggest that successive bands form by nucleation via a metastable phase ahead of the inhibited growth front.