Author’s Accepted Manuscript

Experimental investigation of the effect of poly-N-vinyl pyrrolidone (PVP) on methane/propane clath-rates using a new contact mode

Nagu Daraboina, Praveen Linga

PII: S0009-2509(13)00103-6DOI: http://dx.doi.org/10.1016/j.ces.2013.02.011Reference: CES10870

To appear in: Chemical Engineering Science

Received date: 14 October 2012Revised date: 26 January 2013Accepted date: 4 February 2013

Cite this article as: Nagu Daraboina and Praveen Linga, Experimental investigation of theeffect of poly-N-vinyl pyrrolidone (PVP) on methane/propane clathrates using a newcontact mode, Chemical Engineering Science, http://dx.doi.org/10.1016/j.ces.2013.02.011

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Experimental investigation of the effect of poly­N­vinyl pyrrolidone (PVP) on methane/propane clathrates using a new contact mode 

 Nagu Daraboina1 and Praveen Linga2*

1Clean Energy Research Centre,

Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3.

2Department of Chemical and Biomolecular Engineering, National University of Singapore,

Singapore 117576  

ABSTRACT

Hydrate formation experiments were conducted for a methane/propane (90.5/9.5 mol%)

gas mixture in a new contact mode by dispersing water between silica sand to evaluate the

performance of poly-N-vinyl pyrrolidone (PVP) as a kinetic hydrate inhibitor. Experiments were

performed in the presence of water and different concentrations of PVP solutions (0.1, 0.5 and 1.0

wt% respectively). Induction time before heterogeneous nucleation and subsequent hydrate growth

was assessed by dispersing the water in the interstitial pores of the silica sand. The experiments

were studied at a starting pressure of 4.25 MPa and at a constant temperature of 4.0 0C. It was

found that the induction times for 0.1 % PVP solutions were about the same of pure water. For the

0.5wt% PVP solutions, induction times were ten times higher and for 1.0wt% PVP it was five

times higher than pure water. Hydrate formation reached plateau in one hour for the experiments

conducted with pure water while it took longer time (� 3h or more) for the experiments conducted

in the presence of 1 wt% PVP solutions. This was due to the fact that hydrate growth rate was

found to decrease with the increase in the concentration of the PVP solutions.

 Keywords: Gas hydrates, kinetics, silica sand, hydrate inhibition, hydrate growth, kinetic hydrate inhibitor *Corresponding author, Tel: (65) 6601-1487; e-mail: chepl@nus.edu.sg; Fax: (65) 6779-1936.

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1. INTRODUCTION

Due to environmental and economic factors, the oil and gas industry shifted from

thermodynamic inhibitors to low dosage hydrate inhibitors (LDHI’s) to manage the risk associated

from hydrate formation in pipelines (flow assurance) (Daraboina et al., 2011c; Englezos, 1996; Fu,

2002; Huo et al., 2001; Kvamme et al., 2005; Lovell, 2003; Mehta et al., 2003; Walker et al.,

2008). A large number of synthetic chemicals have been explored as kinetic hydrate inhibitors

(KHIs). In general, the successful KHIs are water soluble polymers (Freer and Sloan, 2000).

Kelland (2006) and recently Perrin et al. (2013) reviewed the history and development of low

dosage hydrate inhibitors (both KHIs and anti-agglomerates) and the successful and unsuccessful

attempts to commercialize these inhibitors.

The need to understand how inhibitors influence hydrate crystal nucleation and growth has led

to focus on the design of different apparatus such as: ball-stop rigs, high-pressure stirred cells,

spray columns, autoclave, flow loops, NMR micro imaging and morphology cells etc. (Daraboina

et al., 2011a; Daraboina et al., 2011b; Kobayashi et al., 2007; Kumar et al., 2008a; Lederhos et al.,

1996; Lee and Englezos, 2005; Lee et al., 2006; Moudrakovski et al., 2004; Ohno et al., 2010;

Talaghat, 2009; Talaghat et al., 2010; Urdahl et al., 1995). In the bulk system, hydrate conversion

appears to be a homogeneous process. However, micro imaging measurements (Lee et al., 2003;

Moudrakovski et al., 2004) showed that conversion of hydrate in dispersed water droplets is quiet

inhomogeneous. They observed that in the hydrate growth process that is strictly diffusion limited,

increased reaction rates in larger droplets of dispersed system are likely by reducing the surface-to-

volume ratio of the particles (Lee et al., 2003; Moudrakovski et al., 2004). Recently, Ohno et al.

(2010) quantified the induction period before heterogeneous nucleation and subsequent hydrate

crystal growth by dispersing the aqueous KHI solutions in silica gel pores using a high pressure

differential scanning calorimeter (DSC). Ohno et al. (2010) used silica gel and studied hydrate

formation in a high pressure DSC at a micro-scale ( �12 µL of liquid sample) and suggested that

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the performance of these inhibitors on nucleation inhibition and growth inhibition are different and

could not be correlated. Linga et al. (2009a) and Haligva et al. (2010) studied methane hydrate

formation and monitored hydrate nucleation at different locations using multiple thermocouples

inside the silica sand bed. The occurrence of multiple nucleation events and the spatial

heterogeneity of hydrate formation were observed and reported. It is evident from the literature

that hydrate formation in a dispersed system provides localized information about the hydrate

nucleation and it may be possible to monitor the entire system with various thermocouples

(Haligva et al., 2010; Linga et al., 2009a; Loh et al., 2012). Linga et al. (2009a) and Haligva et al.

(2010) reported water to hydrate conversions between 74 and 98% for the all the methane hydrate

formation experiments conducted in porous media. Recently, rate hydrate formation and extent of

hydrate formation in a dispersed system (water dispersed in silica sand) was found to be higher

than a mechanically agitated system for several gas/gas mixtures (Linga et al., 2012). This

enhancement of rate of hydrate formation and spatial heterogeneity in nucleation provides a

suitable environment that can be employed to evaluate the performance of inhibitors and assess

their strength. As reported by Ohno et al. (2010), the quantification of induction time and

subsequent hydrate growth by dispersing KHI solutions in silica gel provides a vigorous

environment to test and quantify the performance of kinetic inhibitors. Recently, Babu et al. (2012)

evaluated the kinetic performance of silica gel and silica sand as a medium for hydrate formation

and reported that silica sand performs better than silica gel as a medium for dispersing the aqueous

liquid phase for hydrate formation. Hence, in this work we have chosen silica sand has a medium

to test the performance of a kinetic hydrate inhibitor for both hydrate nucleation and hydrate

growth.

The performance of an inhibitor is a strong function of its concentration in the solution (Al-

Adel et al., 2008; 2008a; Lachance et al., 2009; Lederhos et al., 1996; Sloan and Koh, 2008).

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Kumar et al. (2008a) found that induction time increases with the decrease in sub cooling and

increase in PVP concentration. They also reported that in the presence of PVP (0.1 wt% and at

13.7 and 8.1 K sub cooling) whiskery or fiber type crystals were observed within the liquid pool,

which was not observed in absence of PVP. With higher concentrations of PVP (0.5 and 1 wt% )

there was no crystal growth in the liquid pool at a sub cooling of 3.2 K but hydrate started forming

from water droplets attached to the wall. The growth after nucleation was catastrophic at higher

concentrations of PVP (1.0 wt %). While the mechanism of action of PVP on hydrate crystal

morphology was not presented it was evident that PVP concentration altered the morphology of

the hydrate formed (Kumar et al., 2008a). Al-Adel et al. (2008) investigated the effect of the

kinetic inhibitor poly (N-vinyl pyrrolidone–co-N-vinyl caprolactam) (poly (VP/VC)) concentration

on methane hydrate growth inhibition. They found that 0.1 wt % inhibitor has a significant effect

on growth inhibition compared to other concentrations. However, the other concentrations were

lower than 0.1 wt %. Lachance et al. (2009) also reported that melting behavior of methane

hydrate formed in the presence of PVCap varied with inhibitor concentration. It is evident from the

literature that inhibitor concentration plays a vital role in hydrate nucleation and hydrate growth.

In this work the effect of PVP on methane (90.5%)/propane (9.5%) hydrate formation was

studied at various PVP concentrations in a new contact mode by dispersing water in the interstitial

spaces of silica sand particles.

2. EXPERIMENTAL SECTION

2.1. MATERIALS

Methane (90.5%)/Propane (9.5%) gas mixture was obtained from Praxair Technology Inc.

The sand particles (average diameter: 329 μm) and Poly vinyl pyrrolidone (PVP: Average

molecular mass: 10 kDa) were supplied from Sigma Aldrich. It is noted that additional details

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about the pore size, particle size distribution, surface area and porosity of the sand is available in

the literature (Linga et al., 2009a; 2009b).

2.2. APPARATUS

The apparatus (Figure 1) consists of a crystallizer (CR) immersed in a temperature-

controlled water bath. Pressure was monitored and measured with Rosemount smart pressure

transmitters supplied from Norpac controls. The hydrate phase and the gas phase temperatures

were measured using Omega copper-constantan thermocouples with an uncertainty of 0.1 K. The

detailed description of this experimental set up is available in the literature (Haligva et al., 2010;

Linga et al., 2009a).

2.3. PROCEDURE

The silica sand bed was created by placing 520 g of sand in the crystallizer. The volume of

solution required to fill the void space (100% saturation) was 113 mL, was calculated from

interstitial volume (0.217cm3/g) of sand particles. To achieve the uniform silica sand bed, sand and

water was split into three equal parts and placed in the batch order. This approach also helps to

minimize the presence of air pockets inside the bed. The procedure for setting up the sand/water

bed was similar to the one reported by Linga et al. (2009a). The crystallizer was pressurized with

the hydrate forming gas up to 500 KPa and then depressurized to atmospheric pressure three times

to remove the presence of air in the system. The temperature of the crystallizer was controlled by

the water bath and maintained at the experimental temperature. The pressure in the crystallizer was

then set to the experimental value. The pressure and temperature in the crystallizer was monitored

continuously. The temperatures at six locations of the silica sand bed (two at the bottom, two in

the middle and two at the top of the bed) were monitored using thermocouples. Figure 2 shows the

position of six thermocouples inside the silica sand bed. The experiment was stopped when there

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was no further drop in the crystallizer pressure. The number of moles consumed was calculated as

reported by Linga et al. (2007).

3. RESULTS AND DISCUSSION

The effect of Poly vinyl pyrrolidone (PVP) concentration on induction time and hydrate

growth of methane/propane hydrate formation was investigated at 0, 0.1, 0.5 and 1 wt %

respectively. It is noted that the equilibrium pressure for hydrate formation for C1/C3 gas mixture

used in our study at 277.15 K is 813 KPa and was calculated using CSMGem software (Sloan and

Koh, 2008). It is also noted that the C1/C3 gas mixture used in this study forms structure sII for

the experimental conditions employed in this study (Kumar et al., 2008b). Table 1 summarizes the

experimental conditions, measured induction times, gas consumption after 10 h of hydrate growth

from induction point and conversion of water to hydrates at the end of the experiment.

Figure 3 shows a typical gas uptake measurement curve obtained when water is present in

the interstitial spaces of the silica sand. Thermocouple locations inside the bed are given as an

inset in the figure. Hydrate formation is a crystallization and exothermic process. The nucleation

point or induction time is the time when the onset of nucleation occurs, which can be identified by

the increase in temperature of the reactor and sudden decrease in pressure (reflected in the increase

in the gas consumption). It is noted that all the thermocouples show an increase in the temperature

at the nucleation point and then follow different trajectories. This could be due to the

heterogeneous nature of hydrate formation in the dispersed phase. Several spikes can be observed

for thermocouples T1 and T2 (see extended graph in Figure 3) which are present at the bottom of

the crystallizer which we believe is due to the occurrence of new hydrate formation events. It is

also noted that hydrate formation was found to occur at a drastic rate as can be seen from the gas

uptake due to rapid hydrate growth. The formation reaction was completed for these (water)

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experiments at about 100 min beyond which the pressure in the crystallizer remained constant. It is

noted that the other repeat experiments (2&3) also exhibited the same hydrate growth behavior

(Figure S1, given in the supporting information). It is also seen in Figure 3 that, there is only one

period of temperature spike and for the remaining period the temperatures are constant and equal

to the desired experimental temperature and also the gas uptake reaches a plateau (no further

hydrate formation).

Figures 4, 5 & 6 represent the gas uptake measurement curves obtained by dispersing water

and PVP solutions (0.1, 0.5 & 1 wt%) in the interstitial spaces of the silica sand particles. Gas

uptake curve for 0.1 %PVP was found to mirror the experiment with water only indicating that the

presence of 0.1wt% PVP does not have a significant effect. This is consistent with the observed

induction times reported in Table 1 for 0.1wt% PVP. It is noted from the figures (3, 4, 5 & 6) that

the increase in the PVP concentration decreases the extent of heat released due to hydrate

formation. For instance, the T6 scales a peak of 9, 8.9, 7.8 and 7 °C corresponding to PVP

solutions of 0, 0.1, 0.5 and 1.0 wt% respectively. We believe this is due to the fact that less

hydrates were formed at any given time with the increase in the PVP concentration (can also be

seen in Figure 11 and is discussed in detail later in this section). In contrast to 0.0 and 0.1% PVP

(Figures 3 & 4), hydrate formation was found to occur at a slower rate and hydrate formation

continued mildly even after 100 min for 0.5 and 1 wt % PVP (Figures 5 & 6). This observation is

strengthened by the fact that a slight temperature increase can be observed in Figure 5 (at about

300 min) and a more prominent temperature increase in Figure 6 (at about 220 min). We believe

this is likely due to the occurrence of a new hydrate formation event (nucleation event) also

indicated by the increase in gas uptake for hydrate formation in the same experimental time in the

figures (Figures 5 and 6).

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The individual temperature rise at each thermocouple for water and PVP systems are

shown in Figure 7. The temperature rise was higher at thermocouples T5 and T6 suggesting that

hydrate formation was greater at the top portion of the bed in the presence/absence of PVP. This

may be due to the availability of the gas phase at the top of the bed. In addition, this temperature

peak broadens in the presence of PVP and this broadness increases with PVP concentration.

Figure 8 shows the effect of nucleation time or induction time on the PVP concentration.

The average and standard deviation of the experimental data is presented in Figure 8. As seen in

the figure, 0.1 wt % PVP has similar induction times compared to experiments conducted with

water and the inhibition effect of nucleation time at this concentration is negligible. However, the

induction time was delayed 10 times more with 0.5 wt% and 4.8 times more with 1 wt % PVP

compared to experiments conducted with water. It can be concluded that 0.5 wt % PVP has more

delay on the onset of hydrate nucleation compared to other concentrations and hence can be the

optimum required to obtain the maximum delay of the induction time for the concentration range

experimented in this study. It is noted that based on our study it is not possible to postulate why

the induction time is delayed further at 0.5 wt% compared to 1.0 wt%. Further detailed studies at

the molecular level employing 1H nuclear magnetic resonance imaging (MRI) can provide some

insights into this observation (Bagherzadeh et al., 2011; Daraboina et al., 2013). Recently,

Daraboina et al. (2013) found excellent correlations between macroscopic observations (gas

uptake) and MRI observations. They reported that both MRI (1 µL) and gas uptake (batch, 10 mL)

experiments showed the same trend for the hydrate nucleation times and hydrate growth

assessment. Induction time is a stochastic phenomenon and hence there will be a variation in the

experimental results at the same experimental conditions. However, in this work, the variation in

induction time is reasonable at the given experimental conditions (as can be seen in Figure 8)

when a dispersed contact mode with silica sand as a medium is employed. Kumar et al. (2008a)

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studied the C1/C3 system in the presence of PVP (0.1, 0.5 & 1.0 wt%) in a pre-gas saturated (gas

saturation done by stirring) quiescent system and reported that the induction times increased with

the increase in PVP concentration. This is definitely not the case in the dispersed system, where

there is an optimum PVP concentration of 0.5 wt % which gives the longest induction times.

Moudrakovski et al. (2004) reported based on magnetic resonance micro imaging that there will be

advantages to increasing nucleation events by adding suitable hydrate nucleators. Dispersing the

water provides a spatial heterogeneity in nucleation for the gas/liquid phase compared to the bulk

liquid/gas contact mode that uses a stirred system. In addition the presence of the water in

dispersed phase provides a large surface area of contact between the liquid and the gas phase.

Figure 9 shows the hydrate crystal growth (after induction point or nucleation time) for

water and PVP (0.1, 0.5 and 1 wt%) solutions. The hydrate growth for water and C1/C3 system

stayed above the other PVP solutions indicating that the hydrate growth was slowed down by the

presence of the PVP. The extent of slowdown of hydrate growth generally seems to increase with

the increase in the PVP concentration. The hydrate growth in the presence of 1 wt % PVP is

significantly less compared to pure water. The total number of moles consumed after 10 h is less in

the presence of 0.5 and 1 wt % PVP compared to pure water and 0.1 wt% PVP. This is also

reflected in the conversion of water to hydrate after 10 hours of hydrate formation given in Table

1. The effect of PVP concentration on the rate of hydrate formation is shown in Figure 10. The

average and standard deviation for all the experiments conducted is presented in the Figure. The

rate was calculated based on averaging the data points over 30 min (Linga et al., 2009a). As seen

in the figure, the rate of hydrate formation for pure water (no PVP) is the highest (0.101 mol of

gas/mol of water/hr) during first 30 min and gradually slows down and reaches a minimum after 2

hr. In the presence of 0.1 and 0.5 wt % PVP, the average rate (~0.068 mol of gas/mol of water/hr)

for 30 min is lower than pure water (no PVP) and also reaches a minimum after 2 h. However, in

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the presence of 1 wt % PVP the average rate was 0.026 mol of gas/mol of water/h, almost 3.9

times less than pure water and 2.6 times less than 0.1 and 0.5wt% concentrations of PVP and the

rate gradually decreased and reached a minimum after 5 h. Clearly, the influence of the increase in

the PVP concentration on the inhibition of the rate of hydrate formation can be seen in Figure 10

(shown in the inset). The hydrate formation completed in 5 h for the case of 1 wt % PVP where as

for the other concentrations and for pure water, the hydrate formation almost completed in about 2

hours.

Figure 11 shows the gas consumption for the different PVP concentrations at two different

experimental times (120 min after induction point and 600 min after induction point). At 120 min

after induction point, there was a clear trend that the gas consumption and conversion of water to

hydrates decreased with the increase in the PVP concentration. This means that the presence of

PVP decreases the extent of hydrate formation. This trend was also true for gas consumption for

hydrate formation and water conversion to hydrates at the end of the experiment (10 h from

induction point). It is also noted in Figure 11 that the hydrate formation completed in 120 min for

the experiments conducted without the presence of inhibitor indicating the hydrate formation was

rapid and fast when the water is dispersed between the interstitial spaces of the silica sand

particles. Whereas for the experiments conducted in presence of the inhibitor this difference

between gas consumption at 120 min and 600 min from induction time widens, as can be seen in

the figure. This significant deviation in the first two hours of hydrate growth could be due to a

combination of slower rate of hydrate growth and less extent of hydrate formation due to the

inhibiting effect of PVP and is found to be more prominent with the increase in the PVP

concentration investigated in this study. As can also be seen in Figure 11, after 10 h of hydrate

growth, there is still a decreasing trend in the gas consumption with the increase in PVP

concentration. Gaillard et al. (1999) also showed strong nucleation and growth inhibition for

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hydrate formation with high concentrations (20 vol%) of PVP in a flow loop. However, there is

evidence in literature for bulk liquid/gas contact system that catastrophic growth occurs after

nucleation even in the presence of inhibitor, in some cases this growth even greater than compared

to the absence of the inhibitor (Khokhar et al., 1998; Kumar et al., 2008a; Lederhos et al., 1996).

Kumar et al. observed catastrophic hydrate growth for 1.0 wt% PVP solution with the same

composition of C1/C3 gas mixture in pre-gas saturated (gas saturation done by stirring) quiescent

system. Khokhar et al., (1998) also reported that PVP promotes sH (methane+dimethyl butane)

hydrate formation and suggested that it was likely due to the lack of a hydrate cap formation.

Lederhos et al. (1996) suggested that small natural gas hydrate crystals formed in the presence of

PVP solution allow more water available to hydrate growth than crystals formed with ASTM sea

water. The reason for this catastrophic growth is still unresolved. Wathen et al., (2010) suggested

that the inhibition or promotion effect of PVP may depend on the orientation of the PVP molecule

in the Monte Carlo simulations. Moon et al. (2007) tested PVP with MD simulation and showed

that PVP interacts with nucleating clusters but not with hydrates crystals double the critical size.

However, it is noted that the critical size of a hydrate nucleus is still unresolved. There is no

concrete mechanism of PVP molecules on hydrate inhibition.

It is evident from the literature that polymers either inhibit hydrate nucleation, growth, or

together nucleation and growth (Kelland, 2006; Ohno et al., 2010; Sloan and Koh, 2008). From

our results it is clear that nucleation and hydrate growth inhibition also depends on the inhibitor

concentration and the performance of inhibition towards nucleation and growth need not be the

same at a given concentration. The PVP acts as a strong nucleation inhibitor at 0.5 wt % and as a

strong hydrate growth inhibitor at 1 wt %. However it is difficult to isolate these two phenomena.

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4. CONCLUSION

The performance of poly vinyl pyrrolidone (PVP) on methane/propane (90.5/9.5)

hydrate nucleation and growth was investigated in a new dispersed contact mode. The presence of

0.1 wt % PVP did not show nucleation inhibition but there was a significant delay in hydrate

nucleation in the presence of 0.5 (ten times) and 1 wt % PVP (five times). 0.1 and 0.5 wt % PVP

solutions showed significant reduction in hydrate growth. However the reduction in growth was

even higher in the presence of 1 wt % PVP. The average hydrate growth rates were determined

and the 1.0 wt% PVP solutions were found to be the lowest among hydrate growth rates during the

first one hour of hydrate growth. Based on our experiments it was found that 0.5 wt % PVP acts as

strongest nucleation inhibitor. Based on the gas consumption rates, it was found out that 1.0 wt %

PVP showed highest inhibition (lower hydrate growth rate). These results are evident that

nucleation and hydrate growth are found to independently depend on concentration of inhibitor.

5. ACKNOWLEDGEMENTS

The authors acknowledge Professor Peter Englezos for access to the lab facilities at the University

of British Columbia (UBC). Praveen Linga would like to thank the Ministry of Education’s AcRF

Tier 1 (R-279-000-317-133) for its financial support. Nagu Daraboina would like to thank UBC

for the Four Year Fellowship.

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Figure Captions Figure 1. Schematic of the experimental apparatus (adapted from Linga et al. (2009a)) Figure 2. Location of thermocouples inside the silica sand bed Figure 3. Typical gas uptake measurement curve obtained for hydrate formation with C1/C3 gas mixture and water (experiment 1) Figure 4: Gas uptake measurement curve obtained for hydrate formation with C1/C3 gas mixture and 0.1% PVP (experiment 4) Figure 5. Gas uptake measurement curve obtained for hydrate formation with C1/C3 gas mixture and 0.5% PVP (experiment 7) Figure 6: Gas uptake measurement curve obtained for hydrate formation with C1/C3 gas mixture and 1.0wt% PVP (experiment 10) Figure 7. Temperature rise at individual thermocouple for hydrate formation with C1/C3 gas mixture and (a) water (b) 0.1 wt% PVP (c) 0.5 wt% PVP (d) 1 wt% PVP solutions dispersed in silica sand particles Figure 8. Effect of PVP concentration on the induction time for hydrate formation. Figure 9. Gas uptake (hydrate growth) and water conversion to hydrates for hydrate formation in the presence of PVP. Time zero in the x-axis corresponds to the induction time for the experiment Figure 10. Average rate of hydrate formation as a function of PVP concentration in silica sand bed. Time zero corresponds to the induction time for the experiment Figure 11. Effect of PVP concentration on the gas consumption for hydrate formation and water conversion to hydrates

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Table 1 Experimental conditions and measured induction times of methane (91.5%)/propane (9.5%) hydrate formation at 277.15 K and at different PVP concentrations. It is noted that all the experiments were conducted in a batch manner starting with an experimental pressure of 4.25 MPa

Exp. No.

PVP

Concentration

(wt%)

Solution

Status

Induction Time

(IT)

(min)

Gas

consumption, 10

h from IT

(mol)

Water

conversion to

hydrates*, 10 h

from IP

(mol%)

1 0 Fresh 15.0 0.5376 68.4

2 0 Fresh 12.0 0.5225 66.5

3 0 Fresh 16.7 0.5384 68.5

4 0.1 Fresh 14.3 0.5195 66.2

5 0.1 Fresh 9.7 0.5382 68.5

6 0.1 Fresh 17.3 0.4999 63.7

7 0.5 Fresh 123.0 0.4792 61.3

8 0.5 Fresh 166.7 0.4790 61.2

9 0.5 Fresh 148.0 0.4709 60.2

10 1.0 Fresh 77.3 0.4760 61.2

11 1.0 Fresh 51.7 0.4348 55.9

12 1.0 Fresh 83.0 0.4840 62.2

*Hydration number of 8.01 was used for the calculation and was estimated at equilibrium conditions using CSMGem (Sloan and Koh, 2008).

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Highlights

• A new contact mode is proposed to test the strength of the kinetic inhibitors • Different concentrations of poly-N-vinyl pyrrolidone (PVP) solutions (0.1, 0.5 and 1.0 wt%

respectively) were tested • For 0.5wt% PVP solutions, induction time was ten times higher than water and was found

to be the optimum • Hydrate growth rate was found to decrease with the increase in the concentration of the

PVP solutions

Figure 1

Figure 2

Figure 3

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