- Email: [email protected]
Synergistic effect of Polyvinylpyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4 + C2H4 + C3H8 hydrate formation
Accepted Manuscript Synergistic effect of Polyvinyl Pyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4 + C2H4 + C3H8 hydrate formation Himangshu Kakati, Ajay Mandal, Sukumar Laik PII:
S1875-5100(16)30574-1
DOI:
10.1016/j.jngse.2016.08.027
Reference:
JNGSE 1724
To appear in:
Journal of Natural Gas Science and Engineering
Received Date: 11 May 2016 Revised Date:
8 August 2016
Accepted Date: 8 August 2016
Please cite this article as: Kakati, H., Mandal, A., Laik, S., Synergistic effect of Polyvinyl Pyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4 + C2H4 + C3H8 hydrate formation, Journal of Natural Gas Science & Engineering (2016), doi: 10.1016/j.jngse.2016.08.027. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Synergistic effect of Polyvinyl Pyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4+C2H4+C3H8 hydrate formation
RI PT
Himangshu Kakati, Ajay Mandal*, Sukumar Laik
Gas Hydrate Laboratory, Department of Petroleum Engineering, Indian School of Mines, Dhanbad 826004, India
SC
*Corresponding Author: E-Mail: [email protected], Fax: 91-326-229663
ABSTRACT
M AN U
Production and transportation of natural gas through pipeline is often hampered by formation of gas hydrates, which can be mitigated by using efficient inhibitors. In this work, the effect of Ltyrosine and NaCl on Polyvinylpyrrolidone (PVP) as kinetic inhibitor on formation of hydrate from methane/ethane/propane (89.93/7.04/3.03 mol %) gas mixture was studied. The effect of L-
TE D
tyrosine, NaCl and PVP on the nucleation and growth of hydrates was investigated by measuring the hydrate nucleation time and gas consumption profile. The addition of inhibitors was found to prolong the hydrate nucleation time and decrease the amount of gas consumption. The results
EP
showed that the presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP. Addition of 1.0% (wt.) PVP increased the induction time to 45 minutes compared to pure water
AC C
system where induction time was only 27 minutes. Again addition of 0.25% (wt.) NaCl, 0.25% (wt.) L-Tyrosine and 0.5% (wt.) PVP to the system increased the hydrate nucleation time further to 65 minutes and decreased the gas consumption 27% compared to pure water system. Keywords: Gas hydrate, Induction time, Synergist, Kinetic inhibitor, PVP, L-tyrosine, Gas consumption.
1
ACCEPTED MANUSCRIPT
1. Introduction Gas hydrates are solid, crystalline, non-stoichiometric compound formed when water and low
RI PT
molecular weight gas/gases (CH4, C2H6, C3H8, CO2, N2, H2S etc.) are kept at thermodynamically favorable pressure and temperature environment. Depending on the type and size of guest molecule(s) all known gas hydrate forms three types of structures, namely cubic structure I (sI),
SC
cubic structure II (sII) and hexagonal structure H (sH) (Sloan, 1998). Recently gas hydrate caught attention of many as it is a source of methane gas deposited in the sediment of ocean and
M AN U
permafrost region (Koh et al., 2012). Besides this, much research has also been going on to store gas in hydrate (Kakati et al., 2016, Veluswamy et al., 2016) as well as separation of gas using selective enclathration of gas molecules under specific pressure and temperature conditions (Seo and Kang, 2010, Kumar and Kumar, 2015, Kumar et al., 2014). But at the same time it is a concern for the oil and gas industry as it forms inside the offshore flowlines due to the favorable
TE D
pressure-temperature conditions resulting in blockage of the transmission lines (Sloan et al., 2009; Villano et al., 2010). This results in huge financial losses for oil and gas companies along with risk of pipeline explosions.
EP
There are a lot of measures that have been used by the petroleum industry to prevent the
AC C
problems associated with the formation of hydrate inside the oil and gas transmission lines. Some of these techniques are heating, lowering the pressure, insulation, water removal or the use of thermodynamic hydrate inhibitors (Talaghat, 2012). Thermodynamic hydrate inhibitors (THIs) include a variety of chemicals such as methanol, monoethylene glycol (MEG) etc. that are injected into the pipelines. These chemicals shift the hydrate equilibrium conditions outside the operating conditions of the transmission lines. This THI method is effective, but there are significant economic drawbacks. The volumes of inhibitors required for the inhibition are large 2
ACCEPTED MANUSCRIPT
(generally between 20 and 60% by weight). The cost of use and its recovery in such large volumes is very high (Lou et al., 2012). There is also concern for the not so environmentally friendly chemicals used as thermodynamic hydrate inhibitors (Phillips and Kelland, 1999). So
RI PT
industry is now moving toward risk management rather than complete prevention of hydrate formation inside the flowlines. This involves letting the formation of hydrate inside the flowlines but postponing nucleation of hydrate crystal or preventing agglomeration of hydrate particles
SC
using kinetic hydrate inhibitors (KHIs) or anti agglomerants (AAs), commonly called as lowdosage hydrate inhibitors (LDHIs) (Kim et al., 2014, Kumar et al., 2015).
M AN U
KHIs do not modify the thermodynamic conditions of hydrate formation, but delay the nucleation and/or retard growth of hydrates at low concentrations, typically less than 1% (wt.) of aqueous phase. Various types of KHIs include polymers (Larsen et al., 1998), antifreeze proteins (Zeng et al., 2006, Walker et al., 2015), ionic liquids (Kim et al., 2011), and quaternary
TE D
ammonium zwitterions (Storr et al., 2004). Though KHIs are gaining importance as a hydrate inhibitor, it is still unclear the mechanism of inhibition. Different authors propose different mechanism of hydrate inhibition. According to one mechanism based on simulation studies,
EP
perturbation of liquid water structure by KHIs prevents the growth of hydrate crystals to the critical cluster size or destabilizing partially formed hydrate clusters (Storr et al., 2004; Anderson
AC C
et al., 2005). In another study, Zeng et al. (2008) proposes that KHIs adsorb to the surfaces of “foreign” particles that would otherwise act as a site for heterogeneous hydrate nucleation. A third mechanism proposes that KHIs adsorb on the surfaces of growing hydrate crystal (subcritical or super-critical size), thus inhibiting further growth (King et al., 2000). Figure 1 shows the schematic diagram of hydrate inhibition by different proposed mechanism.
3
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 1. A schematic diagram of hydrate inhibition by different proposed mechanism
EP
For an effective design of KHI structure, it is important to study thoroughly all aspects of inhibition by KHI. Many different chemicals have been explored in the search for new LDHIs.
AC C
Generally, the effective KHIs are polymer with small cyclic amide groups such as pyrrolidone or capralactam as the active unit (Storr et al., 2004). Studies were also going on to improve the performance of exiting KHIs by using synergist materials. Cohen et al. (1998) reported that adding 2-butoxyethanol to VC- 713 in seawater increased the induction time from 40 min to over 1200 min. Kim et al. (2014) studied the hydrate inhibition performance of monoethylene glycol (MEG) and poly-(vinylcaprolactam) (PVCap) and found that mixing of a small amount of PVCap with MEG delayed the hydrate onset time. It also prevented the agglomeration of the 4
ACCEPTED MANUSCRIPT
hydrate particles. It is also found that polyethylene oxide (PEO) enhanced the performance of KHI, though PEO itself cannot inhibit the hydrate formation (Lee and Englezos, 2005). Yang and Tohidi (2011) studied the synergism of ether glycol for improving the performance of
RI PT
PVCap polymer and found that glycol ether compounds noticeably extend the hydrate nucleation time, and significantly prolong the delay of catastrophic growth. Khodaverdiloo et al. (2016) studied the synergistic effects of nonylphenol ethoxylates (NPEs) and polyethylene glycols
SC
(PEGs) on performance of PVP as hydrate inhibitor. They reported that presence of NPEs and PEGs increases the induction time and initial growth rate of ethane hydrate formation. The
M AN U
performance of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap) as kinetic hydrate inhibitors in saline solutions and n-heptane was studied by Sharif and his coworkers. They found that in presence of n-heptane, addition of kinetic inhibitor like PVP and PVCap decreased the induction time, but catastrophic growth did not occur. They also reported that in
TE D
presence of NaCl the above two KHIs significantly prolong the induction time (Sharif et al., 2014). Jokandan et al. (2016) studied the effect of polyethylene glycol (PEG), polyacrylamide (PAM) and hydroxyethyl cellulose (HEC) on hydrate inhibiting characteristics of PVP. They
EP
found that addition of PEG, PAM and HEC to PVP solution prolonged the hydrate nucleation and reduced the hydrate growth, thus enhanced the inhibition efficiency. Talaghat (2014) studied
AC C
the combined effect of PVP and L-Tyrosine on CH4+C3H8 and CH4+iso-C4H10 hydrate formation in a mini flow loop apparatus. Zhao et al. (2013) reported that NaCl showed strong synergetic effect on the performance of PVP. Therefore it is important to study the effect of synergist on inhibitors.
In this study the effect of L-tyrosine and NaCl on hydrate inhibition characteristics of Polyvinylpyrrolidone (PVP) have been studied with a mixture of gases having (mole) 89.93%
5
ACCEPTED MANUSCRIPT
CH4, 7.04% C2H6 and 3.03% C3H8. The formation of hydrate in presence of gas mixture is more complex than those formed from single gases or liquid hydrate formers (THF). Thus addition of inhibitors to such system complicate the process even more. So for a proper understanding of
RI PT
hydrate inhibition in actual oilfield conditions, it is important to study the hydrate formation in mixed gases system. In this work, the performance of the inhibitors is evaluated in terms of induction time. Induction time has been measured to analyze how much these inhibitors delaying
SC
the nucleation process. Growth of hydrate has also been studied by analyzing the gas
2. Experimental Section
AC C
EP
TE D
2.1 Experimental Apparatus
M AN U
consumption profile at various concentrations of different inhibitors.
Fig. 2. Schematic diagram of the experimental setup.
The schematic diagram of the experimental setup is shown in Figure 2. Our previous works (Kakati et al., 2014; 2015) describe the experimental setup in detail. Briefly, the setup consists of a stainless steel cell, a thermostatic bath, gas booster and data acquisition system. The bath contains a mixture of 85% water and 15% glycol to control the temperature inside the cell. The 6
ACCEPTED MANUSCRIPT
size of the bath is about 225 × 370 × 429 mm. The operating temperature range for the thermostatic bath is −10 to 60 °C with a maximum allowable pressure 20.68 MPa. The total capacity of the cell is 250 cm3. The temperature inside the cell is measured by a thermocouple
RI PT
(PT 100) through a port at the top of the cell. The uncertainty of the measurement is ±0.05 K. The accuracy of the pressure transducer, which measures the pressure inside the cell is 0.1% (Full scale). The fluid (water + additives) inside the cell is agitated with a magnetic stirrer with
SC
adjustable rotation speed (upto 1000 rpm) for proper mixing of the gas and the solution. The gas booster as seen in the Figure 2 is used to increase the gas pressure inside the cell. The data are
M AN U
recorded by a computer running an AppliLab (v6.0) software program.
2.2 Materials
The gas mixture used in the present study were supplied by Ultra Pure Gases (I) Pvt. Ltd. Gujrat, India. The composition of the gas mixture is given in the Table 1. NaCl and
TE D
Polyvinylpyrrolidone (PVP) were supplied by Merck Specialties Pvt. Ltd., Mumbai, India. While L-tyrosine were supplied by Central Drug House (P) Ltd (CDH), New delhi, India. Table 2 shows the structure molecular mass and supplier of the used chemicals. Distilled water produced
AC C
Table 1
EP
by a laboratory purification system was used in all experiments.
Composition of gas mixture
Component
Concentration (mole %)
Accuracy (%)
Propane
3.03
±1
Ethane
7.04
±1
Methane
Balance
-
7
ACCEPTED MANUSCRIPT
Table 2 The structure, molecular mass and supplier of the used chemicals. Structure
Purity
>99.0%
L Tyrosine
>99.0%
Merck Specialties Pvt. Ltd., Mumbai, India
M AN U
SC
PVP
Supplier
RI PT
Chemicals
2.3 Procedure
Central Drug House (P) Ltd (CDH), New delhi, India
TE D
Our previous work describes the experimental procedure in detail (Kakati et al., 2015). Briefly, initially the hydrate formers (i.e., gas and liquid) were kept at a pressure-temperature outside the hydrate phase stability region. Then the temperature of the cell was decreased to the nucleation
EP
temperature. Formation of hydrate was detected by an increase in cell temperature with a
AC C
simultaneous decrease in pressure. During the experiments induction time was measured and pressure decrease was recorded with time. The experiment was supposed to be completed when no further noticeable pressure drop was noticed.
3. Results & Discussion It is known that kinetic hydrate inhibitors (KHIs) could affect both the nucleation and growth of gas hydrate. In this study, experiments were performed to know the synergistic effect of NaCl, L-
8
ACCEPTED MANUSCRIPT
tyrosine and Polyvinylpyrrolidone (PVP) as hydrate inhibitor during CH4+C2H6+C3H8 hydrate formation. The performance of the kinetic hydrate inhibitors can be evaluated in terms of induction time. During growth stage, the effect of the inhibitors on the formation process can be
RI PT
assessed by the gas consumption pattern.
3.1 Hydrate Nucleation
SC
11.6 11.4
M AN U
11.2
Pressure (MPa)
11.0 10.8 10.6 10.4
10.0 9.8 9.6
TE D
10.2
Pure Water Water+1% (wt)Tyrosine Water+1% (wt)NaCl Water+1% (wt)PVP Water+0.5% (wt)PVP+0.5% (wt)NaCl Water+0.5% (wt)PVP+0.5% (wt)Tyrosine Water+0.5% (wt)PVP+0.25% (wt)NaCl +0.25% (wt)Tyrosine
EP
285
290
295
Temperature (K)
AC C
Fig. 3. Pressure-temperature plot during hydrate formation.
The onset of hydrate nucleation temperature was determined to know the effect of inhibitors on the hydrate formation temperature. To determine the nucleation temperature, the temperature of the cell that contains the samples (water + inhibitors) and the gas mixture was decreased stepwise. The initial pressure and temperature was 11.72 MPa and 20°C respectively. At each temperature the system was kept for one hour. So at start of the experiment the sample and the
9
ACCEPTED MANUSCRIPT
gas mixture were kept at 20°C for one hour. After one hour the temperature decreased to 19°C and kept the system at that temperature for the next hour. Similarly the temperature of the reactor decreased until the formation of hydrate. Hydrate formation was detected by the sudden decrease
RI PT
in pressure with simultaneous increase in temperature profile. Figure 3 shows the pressuretemperature plot during hydrate formation. The hydrate nucleation temperature in presence of various inhibitors is shown in Figure 4. As seen from the Figure 4 addition of inhibitors
SC
decreases the nucleation temperature. Initially in pure water the nucleation temperature for CH4+C2H6+C3H8 hydrate formation was around 14°C. But addition of the inhibitors decreases
M AN U
the nucleation temperature to around 9°C.
Water+0.5%(wt)PVP+0.25% (wt)NaCl+0.25%(wt)Tyrosine Water+0.5%(wt)PVP+ 0.5%(wt)Tyrosine
TE D
Water+0.5%(wt)PVP+ 0.5%(wt)NaCl Water+1%(wt)PVP
EP
Water+1%(wt)NaCl
AC C
Water+1%(wt)Tyrosine
Pure Water 0
2
4
6
8
10
12
14
Nucleation temperature (°C)
Fig. 4. The hydrate nucleation temperature in presence of inhibitors
3.2 Induction time
10
ACCEPTED MANUSCRIPT
When gas and water are kept within the appropriate pressure-temperature regime for natural gas hydrate to be stable, hydrate will not formed immediately. Gas hydrate formation initiates with a nucleation process, and the crystal growth process begins when the water-gas clusters reaches a
RI PT
critical nucleus size. A certain time is required for the first supernucleus sized hydrate cluster to appear (Kashchiev and Firoozabadi, 2003). This time lapse is known as induction time. There are many definitions of induction time as suggested by different authors. Sloan defined induction
SC
time as the time elapsed until ether the appearance of a detectable volume of hydrate phase or the consumption of a noticeable amount (moles) of hydrate forming gas (Sloan, 1998). It is basically
M AN U
the ability of the supersaturated system (gas in water) to remain in the state of metastability. Figure 5 shows the pressure-temperature response during hydrate formation in 1% (wt.) PVP in water. In this study induction time is measured from the time when the gas mixture (CH4+C2H6+C3H8) and the water are bought in contact (ts) to the time when the nucleation of
TE D
hydrate inside the reactor is detected by the sudden drop in pressure with simultaneous increase in temperature (t0). As seen from the Figure 5, initially there was gradual pressure drop due to gas dissolves in the solution. During nucleation the sudden pressure drop is due to gas goes into
EP
the cavities of the formed hydrate crystal. Prior to nucleation, gas molecules are in a state of disorder. During crystallization, these disorderly gas molecules arrange themselves into the
AC C
orderly hydrate crystal. During this process heat is evolved, which raises the temperature of the reactor.
11
ACCEPTED MANUSCRIPT
11.4
295
Temperature Pressure
11.2
RI PT
11.0 10.8 10.6
Induction Time
10.4 10.2
ts
280
t0 -50
0
50
M AN U
SC
285
100
150
200
250
300
10.0
Pressure (MPa)
Temperature (K)
290
9.8 9.6 9.4
350
400
Time (min)
TE D
Fig. 5. Temperature-Pressure response during hydrate formation in presence of 1.0% (wt.) PVP The induction time is an important characteristic in evaluating the inhibition effect of kinetic
EP
hydrate inhibitors (KHIs). Figure 6 shows induction time in presence of different inhibitors during CH4+C2H6+C3H8 hydrate formation. The induction time for CH4+C2H6+C3H8 hydrate
AC C
formation in pure water is 27 minutes. Addition of NaCl, L-tyrosine and PVP to water increases the induction time of hydrate formation. As seen from the Figure 6, in presence of 1% (wt.) NaCl and 1% (wt.) L-tyrosine in water, the induction time is 32 minutes and 36 minutes respectively, while addition of 1%(wt.) PVP increases the induction time to 45 minutes. So from the result obtained here, it is evident that PVP is effective in prolonging the hydrate nucleation. The increase in induction time in presence of PVP has also been reported by Salamat et al. (2013). They measured the induction time of H2S hydrate formation in presence of PVP and L-Tyrosine 12
ACCEPTED MANUSCRIPT
and found that PVP is more suitable than L-Tyrosine in prolonging the H2S hydrate nucleation. As expected the presence of NaCl slightly increases the induction time due to ions dissolved in water forming electrostatic bonds with dipoles of water molecules to form clusters (Sloan, 1998).
RI PT
This ionization allows fewer water molecules to form hydrate clusters and delays the hydrate nucleation. While as discussed earlier, PVP and L-tyrosine either adsorbed on the hydrate crystal through hydrogen bond or it may disturb the local water structure, thus increasing the barrier to
SC
nucleation (Zeng et al., 2007; Anderson et al., 2005).
(w t)T
P V
l
(w t)N aC
W at er +1 %
EP
Pu re W at er
0
TE D
10
(w t)P
20
W at er +1 %
30
W at er +1 %
Induction Time (min)
40
yr os in e
M AN U
50
AC C
Fig. 6. Induction time of hydrate formation in presence of NaCl, L-tyrosine and PVP
13
ACCEPTED MANUSCRIPT
70
50 40
RI PT
Induction Time (min)
60
30 20 10
W 0. ater 5% + (w 0.5% t)N ( aC wt) PV l P+ W a t 0. 5% er+ (w 0.5% t)T ( yr wt) os P W in VP (w ater e + t)N +0 aC .5% l+ ( 0. wt) 25 P % VP (w + t)T 0.2 yr 5% os in e
M AN U
SC
+1 % (w t )P V P W at er
Pu re
W
at er
0
Fig. 7. Induction time in presence of synergistic effect of NaCl and L-tyrosine on PVP as inhibitor during CH4+C2H6+C3H8 hydrate formation.
TE D
Figure 7 shows the synergistic effect of NaCl and L-tyrosine on PVP as inhibitor during CH4+C2H6+C3H8 hydrate formation. As seen from the figure, presence of both NaCl and Ltyrosine enhance the performance of PVP as inhibitor. The presence of NaCl+PVP and L-
EP
tyrosine+PVP in water increases the induction time to 59 minutes and 62 minutes respectively. Thus, the presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP, thus
AC C
prolonging the induction time and delaying hydrate formation (Talaghat, 2014; Zhao et al., 2015). The synergistic effect of NaCl on the performance of PVP during hydrate nucleation had also been reported by Zhao et al. (2015). Talaghat (2012) reported that presence of L-Tyrosine in liquid phase along with polyethylene oxide (PEO) and polypropylene oxide (PPO) had pronounced effect on CH4+C3H8 and CH4+iso C4H10 hydrate nucleation.
14
ACCEPTED MANUSCRIPT
3.3 Growth of Hydrate After nucleation, hydrate grows rapidly consuming both gas and water surrounding hydrate
RI PT
crystals. The amount of gas consumed during the hydrate formation was monitored to investigate the effect of inhibitors during hydrate growth. It is assumed that during hydrate formation, there is negligible change in composition of gas in equilibrium with hydrate (Veluswamy et al., 2015; Zhong et al., 2016; Linga et al., 2012). The amount of gas consumed during the hydrate
(1)
−
M AN U
∆ = − =
SC
formation was calculated from the following real gas equation
where, ∆n is the amount of gas consumed during hydrate formation, V is volume of gas, pi, Ti and pf, Tf are the pressure and temperature at initial and final condition respectively, R is the universal gas constant, zi, zf are compressibility factors measured by Peng-Robinson equation of
TE D
state.
Figure 8 shows the gas consumption curve along with temperature profile with time for 1.0%(wt.) PVP in water during CH4+C2H6+C3H8 hydrate formation. Before nucleation amount
EP
of gas consumed was negligible. At nucleation, as indicated by the sharp rise in temperature, there was sudden increase in gas consumption. After few hours hydrate formation ceased as
AC C
indicated by no further gas consumption.
15
ACCEPTED MANUSCRIPT
294 0.06 292
290
RI PT
Gas Consumption Curve Temperature Curve
0.04
288
0.03
286
SC
0.02
0.00 0
100
M AN U
0.01
200
300
284
Temperature (K)
Gas Consumption (mol)
0.05
282
280 400
Time (min)
Fig. 8. Gas consumption and temperature variation with time during hydrate formation in presence of
TE D
1.0% (wt.) PVP in water after nucleation.
The pressure change inside the autoclave cell was continuously monitored to study the hydrate growth behavior in presence of various inhibitors. The consumed gas during the experiments
EP
were calculated using Equation 1. Table 3 summarizes amount of gas consumption at the end of the experiments in presence of various inhibitors. All the experiments were repeated three times
AC C
to check the variability of the results and the standard deviation of the results of the fresh runs was also shown in the Table 3.
16
ACCEPTED MANUSCRIPT
Table 3 Summary of gas consumption in presence of various inhibitors
Water+1.0% (wt.) Tyrosine
Water+0.1% (wt.) PVP
Water+0.5% (wt.) PVP
Water+1.0% (wt.) PVP
Water+0.5% (wt.) PVP+0.5% (wt.) Tyrosine Water+0.5% (wt.) PVP+0.25% (wt.) NaCl+0.25% (wt.) Tyrosine
27 22 23 24 32 29 30 33 36 32 39 38 34 30 32 35 36 31 35 39 45 41 47 49 59 55 52 55 62 57 63 58 65 59 63 67
1.69
1.24
Gas Consumed at the End of Exp. (mol) 7.15×10-2 7.02×10-2 6.85×10-2 7.25×10-2 6.70×10-2 6.68×10-2 6.45×10-2 6.89×10-2 6.62×10-2 6.51×10-2 6.47×10-2 6.44×10-2 7.13×10-2 6.98×10-2 6.99×10-2 7.08×10-2 6.41×10-2 6.32×10-2 6.22×10-2 6.19×10-2 5.98×10-2 5.86×10-2 6.00×10-2 5.81×10-2 5.73×10-2 5.70×10-2 5.62×10-2 5.64×10-2 5.66×10-2 5.62×10-2 5.69×10-2 5.56×10-2 5.17×10-2 5.09×10-2 5.20×10-2 5.03×10-2
1.26
1.70
1.25
1.63
2.86
2.16
1.63
*The mean value and standard deviation are calculated based on fresh runs
17
Mean Gas Consumpti on (mol)
Standard Deviation
7.08×10-2
1.70×10-3
6.68×10-2
1.84×10-3
6.51×10-2
0.79×10-3
7.07×10-2
0.58×10-3
6.27×10-2
0.97×10-3
5.93×10-2
0.85×10-3
5.66×10-2
0.51×10-3
5.64×10-2
0.56×10-3
5.13×10-2
0.74×10-3
RI PT
Standard Deviation
SC
Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh
AC C
Water+0.5% (wt.) PVP+0.5% (wt.) NaCl
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Induction Time (min)
M AN U
Water+1.0% (wt.) NaCl
Sample State
TE D
Pure water
Exp. No.
EP
System
ACCEPTED MANUSCRIPT
Figure 9 shows the gas consumption profile in presence of various inhibitors. It is evident from the results that PVP is more effective compared to NaCl and L-tyrosine as inhibitors. After nucleation gas starts to get accumulated inside the cavities with rapid formation of hydrates.
RI PT
Thus the initial rate of gas consumption after nucleation is very fast. On the other hand inhibitors adsorb on the surface of hydrate crystal and slows down the hydrate growth. The total gas consumed over 350 minutes in pure water is 7.15×10-2 mol. While with addition of 1.0% (wt.)
SC
each of NaCl, L-tyrosine and PVP to the pure water system, the total amount of gas consumed comes down to 6.73×10-2 mol, 6.64×10-2 mol and 5.96×10-2 mol respectively. Thus addition of
M AN U
NaCl, L-Tyrosine and PVP inhibited the growth of hydrate resulting in lesser amount of gas consumption at the end compared to pure water. As expected it is found that the inhibition of PVP is more than the NaCl and L-Tyrosine which is also reported in any literatures. Talaghat (2013) studied the gas consumption of various gases like methane, propane, carbon di-oxide, iso-
TE D
butane during simple gas hydrate formation in presence of PVP and found that addition of PVP decreases the amount of gas consumption. Daraboina and Linga (2013) also reported that the growth of CH4+C3H8 hydrate is slowed down in presence of PVP. The mechanism of hydrate
EP
inhibition by KHIs is still not clear. But the general perception is that KHIs adsorbed on the surface of the nuclei, thus slowing down the hydrate growth rate by reducing the gas absorption
AC C
into the hydrate crystal. Previous studies suggest that hydrate inhibition by KHIs is a two-step process (Kvamme et al., 2005; Anderson et al., 2005, Sa et al., 2013). First, it raises the barrier to nucleation by disturbing the local water structure. Then the inhibitor binds to the surface of hydrate crystal and thus retards the further growth once nucleation occurs. King and his coworker (King et al., 2000) used small-angle neutron scattering to study mechanism of hydrate inhibition by polymers. They found that poly (N-vinyl-2-pyrollidone), poly (N-vinyl-2-
18
ACCEPTED MANUSCRIPT
caprolactam) and N-vinylacetamide/N-vinyl-2-caprolactam copolymer kinetically suppress the hydrate crystallization due the surface adsorption of polymer onto the growing crystals. Similar study was carried by Hutter er al. (2000). They too reported through small-angle neutron
RI PT
scattering that poly- (N-vinyl-2-pyrrolidone) adsorbed onto hydrate crystal surfaces and thus inhibit the hydrate formation. Figure 10 shows the gas consumption pattern with time in presence of different concentrations of PVP. It is seen from the Figure 10 that with increase in
SC
concentration the amount of gas consumed decreases. For example, in presence of 0.5%(wt.) PVP in water, the total amount of gas consumed after 350 minutes is 6.39×10-2 mol, but increase
M AN U
in PVP concentration to 1.0%(wt.) in water further decreases the gas consumption to 5.96×10-2 mol. Thus the growth of hydrate is found to decrease with the increase in the concentration of the PVP in the solutions (Daraboina and Linga (2013). The combined effect of inhibitors on the amount of gas consumption at the end is shown in Figure 11. Addition of both NaCl and L-
TE D
tyrosine to PVP in water further decreases the gas consumption compared to PVP alone in water. In presence of 0.5% (wt.) PVP+ 0.25% (wt.) NaCl+ 0.25% (wt.) L-tyrosine in water, the total amount of gas consumed after 350 minutes is 5.19×10-2 mol. It indicates that there is around
EP
27% decrease in gas consumption after addition of PVP+NaCl+L-tyrosine in water in compared to pure water system. Similar observations were reported in many literatures (Cha et al., 2013,
AC C
Daraboina et al., 2011). Zhao et al. (2015) studied the synergism of thermodynamic hydrate inhibitors on the performance of poly (vinyl pyrrolidone) in deepwater drilling fluid. They found that NaCl showed strong synergistic effect on the performance of PVP as hydrate inhibitor. The synergism effect of L-tyrosine on hydrate inhibitors had also been reported by Talaghat (2011).
19
ACCEPTED MANUSCRIPT
0.08 0.07
0.05
RI PT
0.04 0.03 0.02 0.01
Pure water Water+1.0% (wt) NaCl Water+1.0% (wt) L-tyrosine Water+1.0% (wt) PVP
0.00 -0.01 0
50
100
150
200
250
300
M AN U
Time (min)
SC
Gas Consumption (mol)
0.06
Fig. 9. Gas consumption profile in presence of NaCl, L-tyrosine and PVP after nucleation. 0.08 0.07
0.04 0.03 0.02
TE D
0.05
0.01
EP
Gas Consumption (mol)
0.06
Water+0.1% (wt) PVP Water+0.5% (wt) PVP Water+1.0% (wt) PVP
0.00
AC C
-0.01
0
50
100
150
200
250
300
Time (min)
Fig. 10. Gas consumption profile in presence of different concentrations of PVP after nucleation.
20
ACCEPTED MANUSCRIPT
0.06
Gas Consumption (mol)
0.05
0.04
RI PT
0.03
0.02
0.01
M AN U
SC
W +0 ate .5 r+0 % . (w 5% t.) (w Ty t.) ro P si VP ne W +0 ate . 0. 25 r+0 2 5 % .5 % % ( (w wt.) (w t.) N t.) Ty aC PV P l ro si + ne
W
at e
r+ 1
.0
%
(w
t.)
PV
P W +0 a t e .5 r+0 % . (w 5% t.) (w N t aC .) P VP l
0.00
Fig. 11. Combined effect of inhibitors on the end gas consumption.
4. Conclusion
TE D
The influence of L-tyrosine and NaCl on the hydrate inhibition strength of PVP during CH4+C2H4+C3H8 hydrate formation has been investigated. The studies of hydrate onset and growth are carried out by measuring the induction time and gas consumption profile. The
EP
induction time measured in pure water+ CH4+C2H4+C3H8 system is 27 minutes. Among the inhibitors used in this study, PVP delayed the hydrate nucleation most. Addition of 1% (wt.)
AC C
PVP to water increases the induction time to 45 minutes. It is further noticed that presence of both NaCl and L-tyrosine enhance the performance of PVP as inhibitor. The presence of NaCl+PVP and L-tyrosine+PVP in water increases the induction time to 59 minutes and 62 minutes respectively. It has been also noticed that there is around 27% decrease in gas consumption after addition of 0.5% (wt.) PVP+ 0.25% (wt.) NaCl+ 0.25% (wt.) L-tyrosine in water in compared to pure water system. Kinetic hydrate inhibitors (KHIs) are gaining interest as
21
ACCEPTED MANUSCRIPT
an efficient hydrate inhibitors in the industry, despite limited knowledge on the mechanisms involved. Inhibition effect of L-tyrosine, NaCl and PVP on hydrate nucleation and growth is very much encouraging with significant rise in induction time for different systems compared to pure
RI PT
water system
Acknowledgement
SC
We gratefully acknowledge the financial assistance provided by Science and Engineering
M AN U
Research Board (EMR/2015/002141) under Department of Science and Technology, New Delhi, India, to the Department of Petroleum Engineering, Indian School of Mines, Dhanbad, India.
TE D
References
1. Anderson, B. J., Tester, J. W., Borghi, G. P., Trout, B. L., 2005. Properties of inhibitors of methane hydrate formation via molecular dynamics simulations. J. Am. Chem. Soc.
EP
127, 17852–17862.
2. Cha, M., Shin, K., Seo, Y., Shin, J-Y, Kang, S-P, 2013. Catastrophic Growth of Gas
AC C
Hydrates in the Presence of Kinetic Hydrate Inhibitors. J. Phys. Chem. A 117, 13988−13995.
3. Cohen, J. M., Wolf, P. F., Young, W. D., 1998. Enhanced hydrate inhibitors: powerful synergism with glycol ethers. Energy Fuels 12, 216–218.
4. Daraboina, N., Linga, P., 2013. Experimental investigation of the effect of poly-N-vinyl pyrrolidone (PVP) on methane/propane clathrates using a new contact mode. Chem. Eng. Sci. 93 387–394. 22
ACCEPTED MANUSCRIPT
5. Daraboina, N., Linga, P., Ripmeester, J., Walker, V. K., Englezos, P., 2011. Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 2. Stirred Reactor Experiments. Energy Fuels 25, 4384–4391.
RI PT
6. Hutter, J. L., King, H. E., Lin, M. Y., 2000. Polymeric Hydrate-Inhibitor Adsorption Measured by Neutron Scattering. Macromol. 33, 2670-2679.
7. Jokandan, E. F., Naeiji, P., Varaminian, F., 2016. The synergism of the binary and
SC
ternary solutions of polyethylene glycol, polyacrylamide and Hydroxyethyl cellulose to methane hydrate kinetic inhibitor. J. Nat. Gas Sci. Eng. 29 15-20.
M AN U
8. Kakati, H., Kar, S., Mandal, A, Laik, S., 2014. Methane Hydrate Formation and Dissociation in Oil-in-Water Emulsion. Energy Fuels 28(7), 4440−4446. 9. Kakati, H., Mandal, A., Laik, S., 2015. Effect of SDS/THF on thermodynamic and kinetic properties of formation of hydrate from a mixture of gases (CH4+C2H6+C3H8) for
TE D
storing gas as hydrate. doi.org/10.1016/j.jechem.2016.01.018. 10. Kakati, H., Mandal, A., Laik, S., 2015. Phase Stability and Kinetics of CH4 + CO2 + N2 Hydrates in Synthetic Seawater and Aqueous Electrolyte Solutions of NaCl and CaCl2. J.
EP
Chem. Eng. Data 60 (6), 1835–1843.
11. Kakati, H., Mandal, A., Laik, S., 2016. Promoting effect of Al2O3/ZnO-based nanofluids
AC C
stabilized by SDS surfactant on CH4+C2H6+C3H8 hydrate formation. J. Ind. Eng. Chem. 35, 357–368.
12. Kashchiev, D., Firoozabadi, A., 2003. Induction time in crystallization of gas hydrates. J. Cryst. Growth 250, 499-515.
23
ACCEPTED MANUSCRIPT
13. Khodaverdiloo, K. R., Rad, S. A., Naeiji, P., Peyvandi, K., Varaminian, F., 2016. Synergistic effects of nonylphenol ethoxylates and polyethylene glycols on performance of gas hydrate kinetic inhibitor. J Mol. Liq. 216 268–274.
Monoethylene
Glycol
with
Poly(vinylcaprolactam)
Underinhibited System. J. Phys. Chem. B 118, 9065−9075.
RI PT
14. Kim, J., Shin, K., Seo, Y., Cho, S. J., Lee, D. J., 2014. Synergistic Hydrate Inhibition of in
Thermodynamically
SC
15. Kim, K.-S., Kang, J.W., Kang, S.-P., 2011. Tuning ionic liquids for hydrate inhibition. Chem. Commun. 47, 6341–6343.
M AN U
16. King, H. E., Hutter, J. L., Lin, M. Y., Sun, T., 2000. Polymer conformations of gashydrate kinetic inhibitors: a small-angle neutron scattering study. J. Chem. Phys. 112, 2523–2532.
17. Koh, C. A., Sum, A. K., Sloan, E. D., 2012. State of the Art: Natural Gas Hydrates as a
TE D
Natural Resource. J. Nat. Gas Sci. Eng. 8, 132−136.
18. Kumar, A., Kumar, R., 2015. Role of Metallic Packing and Kinetic Promoter in Designing a Hydrate-Based Gas Separation Process. Energy Fuels, 29 (7), 4463–4471.
EP
19. Kumar, A., Sakpal, T., Kumar, R., 2015. Influence of Low-Dosage Hydrate Inhibitors on Methane Clathrate Hydrate Formation and Dissociation Kinetics. Energy Technol. 3 (7),
AC C
717-725.
20. Kumar, A., Sakpal, T., Linga, P., Kumar, R., 2014. Impact of Fly Ash Impurity on the Hydrate-Based Gas Separation Process for Carbon Dioxide Capture from a Flue Gas Mixture. Ind. Eng. Chem. Res., 53 (23), 9849–9859. 21. Kvamme, B., Kuznetsova, T., Aasoldsen, K., 2005. Molecular Dynamics Simulations for Selection of Kinetic Hydrate Inhibitors. J. Mol. Graphics Modell. 23, 524−536.
24
ACCEPTED MANUSCRIPT
22. Larsen, R., Knight, C. A., Sloan, E. D., 1998. Clathrate hydrate growth and inhibition. Fluid Phase Equilib. 150–151, 353–360. 23. Lee, J. D., Englezos, P., 2005. Enhancement of the performance of gas hydrate kinetic
RI PT
inhibitors with polyethylene oxide. Chem. Eng. Sci. 60, 5323 – 5330.
24. Linga, P., Daraboina, N., Ripmeester, J. A., Englezos, P., 2012. Enhanced rate of gas hydrate formation in a fixed bed column filled with sand compared to a stirred vessel. Chemical Engineering Science 68, 617–623.
SC
25. Lou, X., Ding, A., Maeda, N., Wang, S., Kozielski, K., Hartley, P. G., 2012. Synthesis of
M AN U
Effective Kinetic Inhibitors for Natural Gas Hydrates. Energy Fuels 26, 1037−1043. 26. Phillips, N. J., Kelland, M. A., 1999. The application of surfactants in preventing gas hydrate formation. Industrial Applications of Surfactants IV; The Royal Society of Chemistry (RSC), RSC Special Publications, 230, 244−259.
27. Sa, J.-H., Kwak, G.-H., Lee, B. R., Park, D.-H., Han, K., Lee, K.-H., 2013. Hydrophobic
2428.
TE D
amino acids as a new class of kinetic inhibitors for gas hydrate formation. Sci. Rep. 3,
28. Salamat, Y., Moghadassi, A., Illbeigi, M., Eslamimanesh, A., Mohammadi, A. H., 2013.
EP
Experimental study of hydrogen sulfide hydrate formation: Induction time in the presence
AC C
and absence of kinetic inhibitor. J Energy Chem. 22, 114–118. 29. Seo, Y., Kang, S.-P., 2010. Enhancing CO2 Separation for Pre-combustion Capture with Hydrate Formation in Silica Gel Pore Structure. Chem. Eng. J. 161, 308−312.
30. Sharif, H., Ripmeester, J., Walker, V. K., Englezos, P., 2014. Kinetic inhibition of natural gas hydrates in saline solutions and heptane. Fuel 117, 109–117. 31. Sloan, E. D., 1998. Clathrate Hydrate of Natural Gases, 2nd ed.; Marcel Deckker, Inc.: New York.
25
ACCEPTED MANUSCRIPT
32. Sloan, E. D., Koh, C. A., Sum, A. K., Ballard, A. L., Shoup, G. J., McMullen, N., Creek, J. L., Palermo, T., 2009. Hydrates: State-of-the-Art Inside and Outside Flowlines. J. Pet. Technol. 61, 89−94.
hydrate crystallization. J. Am. Chem. Soc. 126, 1569–1576.
RI PT
33. Storr, M. T., Taylor, P. C., Monfort, J.-P, Rodger, P. M., 2004. Kinetic inhibitor of
34. Talaghat, M. R., 2011. Enhancement of the performance of kinetic inhibitors in the
SC
presence of polyethylene oxide and polypropylene oxide for binary mixtures during gas hydrate formation in a flow mini-loop apparatus. Can. J. Chem. Eng. 90, 79–86.
M AN U
35. Talaghat, M. R., 2012. Prediction of Induction Time for Natural Gas Components During Gas Hydrate Formation in the Presence of Kinetic Hydrate Inhibitors in a Flow MiniLoop Apparatus. Can. J. Chem. Eng. 9999, 1-8.
36. Talaghat, M. R., 2013. Experimental investigation of gas consumption for simple gas
TE D
hydrate formation in a recirculation flow mini-loop apparatus in the presence of modified starch as a kinetic inhibitor. J Nat. Gas Sci. Eng. 14, 42-48. 37. Talaghat, M. R., 2014. Experimental investigation of induction time for double gas
EP
hydrate formation in the simultaneous presence of the PVP and L-tyrosine as kinetic inhibitors in a mini flow loop apparatus. J. Nat. Gas Sci. Eng. 19, 215-220.
AC C
38. Veluswamy, H. P., Kumar, S., Kumar, R., Rangsunvigit, P., Linga, P., 2016. Enhanced clathrate hydrate formation kinetics at near ambient temperatures and moderate pressures: Application to natural gas storage. Fuel, doi:10.1016/j.fuel.2016.05.068.
39. Veluswamy, H. P., Yew, J. C., Linga, P., 2015. New Hydrate Phase Equilibrium Data for Two Binary Gas Mixtures of Hydrogen and Propane Coupled with a Kinetic Study. J. Chem. Eng. Data, 60 (2), 228–237.
26
ACCEPTED MANUSCRIPT
40. Villano, L. D., Kelland, M. A., Miyake, G. M., Chen, E., 2010. Effect of Polymer Tact icity on the Performance of Poly(N,N-dialkylacrylamide) s as Kinetic Hydrate Inhibitors. Energy Fuels 24, 2554−2562.
RI PT
41. Walker, V. K., Zeng, H., Ohno, H., Nagu Daraboina, N., Sharifi, H., Bagherzadeh, S. A., Alavi, S., Englezos, P., 2015. Antifreeze proteins as gas hydrate inhibitors. Can. J. Chem., 93(8): 839-849.
SC
42. Yang, J., Tohidi, B., 2011. Characterization of inhibition mechanisms of kinetic hydrate
M AN U
inhibitors using ultrasonic test technique. Chem. Eng. Sci. 66, 278–283. 43. Zeng, H., Lu, H., Huva, E., Walker, V. K., Ripmeester, J. A., 2008. Differences in nucleator adsorption may explain distinct inhibition activities of two gas hydrate kinetic inhibitors. Chem. Eng. Sci. 63, 4026.
44. Zeng, H., Walker, V. K., Ripmeester, J.A., 2007. Adsorption of antifreeze protein and a
Chem Ice 659–667.
TE D
commercial low dosage hydrate inhibitor on hydrophilic and hydrophobic surfaces. Phys.
45. Zeng, H., Wilson, L. D., Walker, V. K., Ripmeester, J. A., 2006. Effect of antifreeze
EP
proteins on the nucleation, growth, and the memory effect during tetrahydrofuran
AC C
clathrate hydrate formation. J. Am. Chem. Soc. 128, 2844–2850. 46. Zhao, X., Qiu, Z., Zhou, G., Huang, W., 2015. Synergism of thermodynamic hydrate
inhibitors on the performance of poly (vinyl pyrrolidone) in deepwater drilling fluid. J. Nat. Gas Sci. Eng. 23, 47-54.
47. Zhong, D. L, Wang, Y. R, Lu, Y. Y, Wang, W. C., Wang, J. L. 2016. Phase equilibrium and kinetics of gas hydrates formed from CO2/H2 in the presence of tetrahydrofuran and cyclohexane.
Journal
of
Natural
doi:10.1016/j.jngse.2016.03.036 27
Gas
Science
and
Engineering,
ACCEPTED MANUSCRIPT
Highlights
Hydrate formation experiments is carried out for a methane/ethane/propane
RI PT
•
(89.93/7.04/3.03 mol %) gas mixture in presence of various concentrations of PVP, LTyrosine and NaCl in water. •
Hydrate nucleation time and hydrate growth profile have been studied in presence of
SC
various inhibitors.
The presence of PVP, L-Tyrosine and NaCl inhibit the formation of hydrate.
•
Presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP.
AC C
EP
TE D
M AN U
•
S1875-5100(16)30574-1
DOI:
10.1016/j.jngse.2016.08.027
Reference:
JNGSE 1724
To appear in:
Journal of Natural Gas Science and Engineering
Received Date: 11 May 2016 Revised Date:
8 August 2016
Accepted Date: 8 August 2016
Please cite this article as: Kakati, H., Mandal, A., Laik, S., Synergistic effect of Polyvinyl Pyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4 + C2H4 + C3H8 hydrate formation, Journal of Natural Gas Science & Engineering (2016), doi: 10.1016/j.jngse.2016.08.027. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Synergistic effect of Polyvinyl Pyrrolidone (PVP) and L-tyrosine on kinetic inhibition of CH4+C2H4+C3H8 hydrate formation
RI PT
Himangshu Kakati, Ajay Mandal*, Sukumar Laik
Gas Hydrate Laboratory, Department of Petroleum Engineering, Indian School of Mines, Dhanbad 826004, India
SC
*Corresponding Author: E-Mail: [email protected], Fax: 91-326-229663
ABSTRACT
M AN U
Production and transportation of natural gas through pipeline is often hampered by formation of gas hydrates, which can be mitigated by using efficient inhibitors. In this work, the effect of Ltyrosine and NaCl on Polyvinylpyrrolidone (PVP) as kinetic inhibitor on formation of hydrate from methane/ethane/propane (89.93/7.04/3.03 mol %) gas mixture was studied. The effect of L-
TE D
tyrosine, NaCl and PVP on the nucleation and growth of hydrates was investigated by measuring the hydrate nucleation time and gas consumption profile. The addition of inhibitors was found to prolong the hydrate nucleation time and decrease the amount of gas consumption. The results
EP
showed that the presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP. Addition of 1.0% (wt.) PVP increased the induction time to 45 minutes compared to pure water
AC C
system where induction time was only 27 minutes. Again addition of 0.25% (wt.) NaCl, 0.25% (wt.) L-Tyrosine and 0.5% (wt.) PVP to the system increased the hydrate nucleation time further to 65 minutes and decreased the gas consumption 27% compared to pure water system. Keywords: Gas hydrate, Induction time, Synergist, Kinetic inhibitor, PVP, L-tyrosine, Gas consumption.
1
ACCEPTED MANUSCRIPT
1. Introduction Gas hydrates are solid, crystalline, non-stoichiometric compound formed when water and low
RI PT
molecular weight gas/gases (CH4, C2H6, C3H8, CO2, N2, H2S etc.) are kept at thermodynamically favorable pressure and temperature environment. Depending on the type and size of guest molecule(s) all known gas hydrate forms three types of structures, namely cubic structure I (sI),
SC
cubic structure II (sII) and hexagonal structure H (sH) (Sloan, 1998). Recently gas hydrate caught attention of many as it is a source of methane gas deposited in the sediment of ocean and
M AN U
permafrost region (Koh et al., 2012). Besides this, much research has also been going on to store gas in hydrate (Kakati et al., 2016, Veluswamy et al., 2016) as well as separation of gas using selective enclathration of gas molecules under specific pressure and temperature conditions (Seo and Kang, 2010, Kumar and Kumar, 2015, Kumar et al., 2014). But at the same time it is a concern for the oil and gas industry as it forms inside the offshore flowlines due to the favorable
TE D
pressure-temperature conditions resulting in blockage of the transmission lines (Sloan et al., 2009; Villano et al., 2010). This results in huge financial losses for oil and gas companies along with risk of pipeline explosions.
EP
There are a lot of measures that have been used by the petroleum industry to prevent the
AC C
problems associated with the formation of hydrate inside the oil and gas transmission lines. Some of these techniques are heating, lowering the pressure, insulation, water removal or the use of thermodynamic hydrate inhibitors (Talaghat, 2012). Thermodynamic hydrate inhibitors (THIs) include a variety of chemicals such as methanol, monoethylene glycol (MEG) etc. that are injected into the pipelines. These chemicals shift the hydrate equilibrium conditions outside the operating conditions of the transmission lines. This THI method is effective, but there are significant economic drawbacks. The volumes of inhibitors required for the inhibition are large 2
ACCEPTED MANUSCRIPT
(generally between 20 and 60% by weight). The cost of use and its recovery in such large volumes is very high (Lou et al., 2012). There is also concern for the not so environmentally friendly chemicals used as thermodynamic hydrate inhibitors (Phillips and Kelland, 1999). So
RI PT
industry is now moving toward risk management rather than complete prevention of hydrate formation inside the flowlines. This involves letting the formation of hydrate inside the flowlines but postponing nucleation of hydrate crystal or preventing agglomeration of hydrate particles
SC
using kinetic hydrate inhibitors (KHIs) or anti agglomerants (AAs), commonly called as lowdosage hydrate inhibitors (LDHIs) (Kim et al., 2014, Kumar et al., 2015).
M AN U
KHIs do not modify the thermodynamic conditions of hydrate formation, but delay the nucleation and/or retard growth of hydrates at low concentrations, typically less than 1% (wt.) of aqueous phase. Various types of KHIs include polymers (Larsen et al., 1998), antifreeze proteins (Zeng et al., 2006, Walker et al., 2015), ionic liquids (Kim et al., 2011), and quaternary
TE D
ammonium zwitterions (Storr et al., 2004). Though KHIs are gaining importance as a hydrate inhibitor, it is still unclear the mechanism of inhibition. Different authors propose different mechanism of hydrate inhibition. According to one mechanism based on simulation studies,
EP
perturbation of liquid water structure by KHIs prevents the growth of hydrate crystals to the critical cluster size or destabilizing partially formed hydrate clusters (Storr et al., 2004; Anderson
AC C
et al., 2005). In another study, Zeng et al. (2008) proposes that KHIs adsorb to the surfaces of “foreign” particles that would otherwise act as a site for heterogeneous hydrate nucleation. A third mechanism proposes that KHIs adsorb on the surfaces of growing hydrate crystal (subcritical or super-critical size), thus inhibiting further growth (King et al., 2000). Figure 1 shows the schematic diagram of hydrate inhibition by different proposed mechanism.
3
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig. 1. A schematic diagram of hydrate inhibition by different proposed mechanism
EP
For an effective design of KHI structure, it is important to study thoroughly all aspects of inhibition by KHI. Many different chemicals have been explored in the search for new LDHIs.
AC C
Generally, the effective KHIs are polymer with small cyclic amide groups such as pyrrolidone or capralactam as the active unit (Storr et al., 2004). Studies were also going on to improve the performance of exiting KHIs by using synergist materials. Cohen et al. (1998) reported that adding 2-butoxyethanol to VC- 713 in seawater increased the induction time from 40 min to over 1200 min. Kim et al. (2014) studied the hydrate inhibition performance of monoethylene glycol (MEG) and poly-(vinylcaprolactam) (PVCap) and found that mixing of a small amount of PVCap with MEG delayed the hydrate onset time. It also prevented the agglomeration of the 4
ACCEPTED MANUSCRIPT
hydrate particles. It is also found that polyethylene oxide (PEO) enhanced the performance of KHI, though PEO itself cannot inhibit the hydrate formation (Lee and Englezos, 2005). Yang and Tohidi (2011) studied the synergism of ether glycol for improving the performance of
RI PT
PVCap polymer and found that glycol ether compounds noticeably extend the hydrate nucleation time, and significantly prolong the delay of catastrophic growth. Khodaverdiloo et al. (2016) studied the synergistic effects of nonylphenol ethoxylates (NPEs) and polyethylene glycols
SC
(PEGs) on performance of PVP as hydrate inhibitor. They reported that presence of NPEs and PEGs increases the induction time and initial growth rate of ethane hydrate formation. The
M AN U
performance of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap) as kinetic hydrate inhibitors in saline solutions and n-heptane was studied by Sharif and his coworkers. They found that in presence of n-heptane, addition of kinetic inhibitor like PVP and PVCap decreased the induction time, but catastrophic growth did not occur. They also reported that in
TE D
presence of NaCl the above two KHIs significantly prolong the induction time (Sharif et al., 2014). Jokandan et al. (2016) studied the effect of polyethylene glycol (PEG), polyacrylamide (PAM) and hydroxyethyl cellulose (HEC) on hydrate inhibiting characteristics of PVP. They
EP
found that addition of PEG, PAM and HEC to PVP solution prolonged the hydrate nucleation and reduced the hydrate growth, thus enhanced the inhibition efficiency. Talaghat (2014) studied
AC C
the combined effect of PVP and L-Tyrosine on CH4+C3H8 and CH4+iso-C4H10 hydrate formation in a mini flow loop apparatus. Zhao et al. (2013) reported that NaCl showed strong synergetic effect on the performance of PVP. Therefore it is important to study the effect of synergist on inhibitors.
In this study the effect of L-tyrosine and NaCl on hydrate inhibition characteristics of Polyvinylpyrrolidone (PVP) have been studied with a mixture of gases having (mole) 89.93%
5
ACCEPTED MANUSCRIPT
CH4, 7.04% C2H6 and 3.03% C3H8. The formation of hydrate in presence of gas mixture is more complex than those formed from single gases or liquid hydrate formers (THF). Thus addition of inhibitors to such system complicate the process even more. So for a proper understanding of
RI PT
hydrate inhibition in actual oilfield conditions, it is important to study the hydrate formation in mixed gases system. In this work, the performance of the inhibitors is evaluated in terms of induction time. Induction time has been measured to analyze how much these inhibitors delaying
SC
the nucleation process. Growth of hydrate has also been studied by analyzing the gas
2. Experimental Section
AC C
EP
TE D
2.1 Experimental Apparatus
M AN U
consumption profile at various concentrations of different inhibitors.
Fig. 2. Schematic diagram of the experimental setup.
The schematic diagram of the experimental setup is shown in Figure 2. Our previous works (Kakati et al., 2014; 2015) describe the experimental setup in detail. Briefly, the setup consists of a stainless steel cell, a thermostatic bath, gas booster and data acquisition system. The bath contains a mixture of 85% water and 15% glycol to control the temperature inside the cell. The 6
ACCEPTED MANUSCRIPT
size of the bath is about 225 × 370 × 429 mm. The operating temperature range for the thermostatic bath is −10 to 60 °C with a maximum allowable pressure 20.68 MPa. The total capacity of the cell is 250 cm3. The temperature inside the cell is measured by a thermocouple
RI PT
(PT 100) through a port at the top of the cell. The uncertainty of the measurement is ±0.05 K. The accuracy of the pressure transducer, which measures the pressure inside the cell is 0.1% (Full scale). The fluid (water + additives) inside the cell is agitated with a magnetic stirrer with
SC
adjustable rotation speed (upto 1000 rpm) for proper mixing of the gas and the solution. The gas booster as seen in the Figure 2 is used to increase the gas pressure inside the cell. The data are
M AN U
recorded by a computer running an AppliLab (v6.0) software program.
2.2 Materials
The gas mixture used in the present study were supplied by Ultra Pure Gases (I) Pvt. Ltd. Gujrat, India. The composition of the gas mixture is given in the Table 1. NaCl and
TE D
Polyvinylpyrrolidone (PVP) were supplied by Merck Specialties Pvt. Ltd., Mumbai, India. While L-tyrosine were supplied by Central Drug House (P) Ltd (CDH), New delhi, India. Table 2 shows the structure molecular mass and supplier of the used chemicals. Distilled water produced
AC C
Table 1
EP
by a laboratory purification system was used in all experiments.
Composition of gas mixture
Component
Concentration (mole %)
Accuracy (%)
Propane
3.03
±1
Ethane
7.04
±1
Methane
Balance
-
7
ACCEPTED MANUSCRIPT
Table 2 The structure, molecular mass and supplier of the used chemicals. Structure
Purity
>99.0%
L Tyrosine
>99.0%
Merck Specialties Pvt. Ltd., Mumbai, India
M AN U
SC
PVP
Supplier
RI PT
Chemicals
2.3 Procedure
Central Drug House (P) Ltd (CDH), New delhi, India
TE D
Our previous work describes the experimental procedure in detail (Kakati et al., 2015). Briefly, initially the hydrate formers (i.e., gas and liquid) were kept at a pressure-temperature outside the hydrate phase stability region. Then the temperature of the cell was decreased to the nucleation
EP
temperature. Formation of hydrate was detected by an increase in cell temperature with a
AC C
simultaneous decrease in pressure. During the experiments induction time was measured and pressure decrease was recorded with time. The experiment was supposed to be completed when no further noticeable pressure drop was noticed.
3. Results & Discussion It is known that kinetic hydrate inhibitors (KHIs) could affect both the nucleation and growth of gas hydrate. In this study, experiments were performed to know the synergistic effect of NaCl, L-
8
ACCEPTED MANUSCRIPT
tyrosine and Polyvinylpyrrolidone (PVP) as hydrate inhibitor during CH4+C2H6+C3H8 hydrate formation. The performance of the kinetic hydrate inhibitors can be evaluated in terms of induction time. During growth stage, the effect of the inhibitors on the formation process can be
RI PT
assessed by the gas consumption pattern.
3.1 Hydrate Nucleation
SC
11.6 11.4
M AN U
11.2
Pressure (MPa)
11.0 10.8 10.6 10.4
10.0 9.8 9.6
TE D
10.2
Pure Water Water+1% (wt)Tyrosine Water+1% (wt)NaCl Water+1% (wt)PVP Water+0.5% (wt)PVP+0.5% (wt)NaCl Water+0.5% (wt)PVP+0.5% (wt)Tyrosine Water+0.5% (wt)PVP+0.25% (wt)NaCl +0.25% (wt)Tyrosine
EP
285
290
295
Temperature (K)
AC C
Fig. 3. Pressure-temperature plot during hydrate formation.
The onset of hydrate nucleation temperature was determined to know the effect of inhibitors on the hydrate formation temperature. To determine the nucleation temperature, the temperature of the cell that contains the samples (water + inhibitors) and the gas mixture was decreased stepwise. The initial pressure and temperature was 11.72 MPa and 20°C respectively. At each temperature the system was kept for one hour. So at start of the experiment the sample and the
9
ACCEPTED MANUSCRIPT
gas mixture were kept at 20°C for one hour. After one hour the temperature decreased to 19°C and kept the system at that temperature for the next hour. Similarly the temperature of the reactor decreased until the formation of hydrate. Hydrate formation was detected by the sudden decrease
RI PT
in pressure with simultaneous increase in temperature profile. Figure 3 shows the pressuretemperature plot during hydrate formation. The hydrate nucleation temperature in presence of various inhibitors is shown in Figure 4. As seen from the Figure 4 addition of inhibitors
SC
decreases the nucleation temperature. Initially in pure water the nucleation temperature for CH4+C2H6+C3H8 hydrate formation was around 14°C. But addition of the inhibitors decreases
M AN U
the nucleation temperature to around 9°C.
Water+0.5%(wt)PVP+0.25% (wt)NaCl+0.25%(wt)Tyrosine Water+0.5%(wt)PVP+ 0.5%(wt)Tyrosine
TE D
Water+0.5%(wt)PVP+ 0.5%(wt)NaCl Water+1%(wt)PVP
EP
Water+1%(wt)NaCl
AC C
Water+1%(wt)Tyrosine
Pure Water 0
2
4
6
8
10
12
14
Nucleation temperature (°C)
Fig. 4. The hydrate nucleation temperature in presence of inhibitors
3.2 Induction time
10
ACCEPTED MANUSCRIPT
When gas and water are kept within the appropriate pressure-temperature regime for natural gas hydrate to be stable, hydrate will not formed immediately. Gas hydrate formation initiates with a nucleation process, and the crystal growth process begins when the water-gas clusters reaches a
RI PT
critical nucleus size. A certain time is required for the first supernucleus sized hydrate cluster to appear (Kashchiev and Firoozabadi, 2003). This time lapse is known as induction time. There are many definitions of induction time as suggested by different authors. Sloan defined induction
SC
time as the time elapsed until ether the appearance of a detectable volume of hydrate phase or the consumption of a noticeable amount (moles) of hydrate forming gas (Sloan, 1998). It is basically
M AN U
the ability of the supersaturated system (gas in water) to remain in the state of metastability. Figure 5 shows the pressure-temperature response during hydrate formation in 1% (wt.) PVP in water. In this study induction time is measured from the time when the gas mixture (CH4+C2H6+C3H8) and the water are bought in contact (ts) to the time when the nucleation of
TE D
hydrate inside the reactor is detected by the sudden drop in pressure with simultaneous increase in temperature (t0). As seen from the Figure 5, initially there was gradual pressure drop due to gas dissolves in the solution. During nucleation the sudden pressure drop is due to gas goes into
EP
the cavities of the formed hydrate crystal. Prior to nucleation, gas molecules are in a state of disorder. During crystallization, these disorderly gas molecules arrange themselves into the
AC C
orderly hydrate crystal. During this process heat is evolved, which raises the temperature of the reactor.
11
ACCEPTED MANUSCRIPT
11.4
295
Temperature Pressure
11.2
RI PT
11.0 10.8 10.6
Induction Time
10.4 10.2
ts
280
t0 -50
0
50
M AN U
SC
285
100
150
200
250
300
10.0
Pressure (MPa)
Temperature (K)
290
9.8 9.6 9.4
350
400
Time (min)
TE D
Fig. 5. Temperature-Pressure response during hydrate formation in presence of 1.0% (wt.) PVP The induction time is an important characteristic in evaluating the inhibition effect of kinetic
EP
hydrate inhibitors (KHIs). Figure 6 shows induction time in presence of different inhibitors during CH4+C2H6+C3H8 hydrate formation. The induction time for CH4+C2H6+C3H8 hydrate
AC C
formation in pure water is 27 minutes. Addition of NaCl, L-tyrosine and PVP to water increases the induction time of hydrate formation. As seen from the Figure 6, in presence of 1% (wt.) NaCl and 1% (wt.) L-tyrosine in water, the induction time is 32 minutes and 36 minutes respectively, while addition of 1%(wt.) PVP increases the induction time to 45 minutes. So from the result obtained here, it is evident that PVP is effective in prolonging the hydrate nucleation. The increase in induction time in presence of PVP has also been reported by Salamat et al. (2013). They measured the induction time of H2S hydrate formation in presence of PVP and L-Tyrosine 12
ACCEPTED MANUSCRIPT
and found that PVP is more suitable than L-Tyrosine in prolonging the H2S hydrate nucleation. As expected the presence of NaCl slightly increases the induction time due to ions dissolved in water forming electrostatic bonds with dipoles of water molecules to form clusters (Sloan, 1998).
RI PT
This ionization allows fewer water molecules to form hydrate clusters and delays the hydrate nucleation. While as discussed earlier, PVP and L-tyrosine either adsorbed on the hydrate crystal through hydrogen bond or it may disturb the local water structure, thus increasing the barrier to
SC
nucleation (Zeng et al., 2007; Anderson et al., 2005).
(w t)T
P V
l
(w t)N aC
W at er +1 %
EP
Pu re W at er
0
TE D
10
(w t)P
20
W at er +1 %
30
W at er +1 %
Induction Time (min)
40
yr os in e
M AN U
50
AC C
Fig. 6. Induction time of hydrate formation in presence of NaCl, L-tyrosine and PVP
13
ACCEPTED MANUSCRIPT
70
50 40
RI PT
Induction Time (min)
60
30 20 10
W 0. ater 5% + (w 0.5% t)N ( aC wt) PV l P+ W a t 0. 5% er+ (w 0.5% t)T ( yr wt) os P W in VP (w ater e + t)N +0 aC .5% l+ ( 0. wt) 25 P % VP (w + t)T 0.2 yr 5% os in e
M AN U
SC
+1 % (w t )P V P W at er
Pu re
W
at er
0
Fig. 7. Induction time in presence of synergistic effect of NaCl and L-tyrosine on PVP as inhibitor during CH4+C2H6+C3H8 hydrate formation.
TE D
Figure 7 shows the synergistic effect of NaCl and L-tyrosine on PVP as inhibitor during CH4+C2H6+C3H8 hydrate formation. As seen from the figure, presence of both NaCl and Ltyrosine enhance the performance of PVP as inhibitor. The presence of NaCl+PVP and L-
EP
tyrosine+PVP in water increases the induction time to 59 minutes and 62 minutes respectively. Thus, the presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP, thus
AC C
prolonging the induction time and delaying hydrate formation (Talaghat, 2014; Zhao et al., 2015). The synergistic effect of NaCl on the performance of PVP during hydrate nucleation had also been reported by Zhao et al. (2015). Talaghat (2012) reported that presence of L-Tyrosine in liquid phase along with polyethylene oxide (PEO) and polypropylene oxide (PPO) had pronounced effect on CH4+C3H8 and CH4+iso C4H10 hydrate nucleation.
14
ACCEPTED MANUSCRIPT
3.3 Growth of Hydrate After nucleation, hydrate grows rapidly consuming both gas and water surrounding hydrate
RI PT
crystals. The amount of gas consumed during the hydrate formation was monitored to investigate the effect of inhibitors during hydrate growth. It is assumed that during hydrate formation, there is negligible change in composition of gas in equilibrium with hydrate (Veluswamy et al., 2015; Zhong et al., 2016; Linga et al., 2012). The amount of gas consumed during the hydrate
(1)
−
M AN U
∆ = − =
SC
formation was calculated from the following real gas equation
where, ∆n is the amount of gas consumed during hydrate formation, V is volume of gas, pi, Ti and pf, Tf are the pressure and temperature at initial and final condition respectively, R is the universal gas constant, zi, zf are compressibility factors measured by Peng-Robinson equation of
TE D
state.
Figure 8 shows the gas consumption curve along with temperature profile with time for 1.0%(wt.) PVP in water during CH4+C2H6+C3H8 hydrate formation. Before nucleation amount
EP
of gas consumed was negligible. At nucleation, as indicated by the sharp rise in temperature, there was sudden increase in gas consumption. After few hours hydrate formation ceased as
AC C
indicated by no further gas consumption.
15
ACCEPTED MANUSCRIPT
294 0.06 292
290
RI PT
Gas Consumption Curve Temperature Curve
0.04
288
0.03
286
SC
0.02
0.00 0
100
M AN U
0.01
200
300
284
Temperature (K)
Gas Consumption (mol)
0.05
282
280 400
Time (min)
Fig. 8. Gas consumption and temperature variation with time during hydrate formation in presence of
TE D
1.0% (wt.) PVP in water after nucleation.
The pressure change inside the autoclave cell was continuously monitored to study the hydrate growth behavior in presence of various inhibitors. The consumed gas during the experiments
EP
were calculated using Equation 1. Table 3 summarizes amount of gas consumption at the end of the experiments in presence of various inhibitors. All the experiments were repeated three times
AC C
to check the variability of the results and the standard deviation of the results of the fresh runs was also shown in the Table 3.
16
ACCEPTED MANUSCRIPT
Table 3 Summary of gas consumption in presence of various inhibitors
Water+1.0% (wt.) Tyrosine
Water+0.1% (wt.) PVP
Water+0.5% (wt.) PVP
Water+1.0% (wt.) PVP
Water+0.5% (wt.) PVP+0.5% (wt.) Tyrosine Water+0.5% (wt.) PVP+0.25% (wt.) NaCl+0.25% (wt.) Tyrosine
27 22 23 24 32 29 30 33 36 32 39 38 34 30 32 35 36 31 35 39 45 41 47 49 59 55 52 55 62 57 63 58 65 59 63 67
1.69
1.24
Gas Consumed at the End of Exp. (mol) 7.15×10-2 7.02×10-2 6.85×10-2 7.25×10-2 6.70×10-2 6.68×10-2 6.45×10-2 6.89×10-2 6.62×10-2 6.51×10-2 6.47×10-2 6.44×10-2 7.13×10-2 6.98×10-2 6.99×10-2 7.08×10-2 6.41×10-2 6.32×10-2 6.22×10-2 6.19×10-2 5.98×10-2 5.86×10-2 6.00×10-2 5.81×10-2 5.73×10-2 5.70×10-2 5.62×10-2 5.64×10-2 5.66×10-2 5.62×10-2 5.69×10-2 5.56×10-2 5.17×10-2 5.09×10-2 5.20×10-2 5.03×10-2
1.26
1.70
1.25
1.63
2.86
2.16
1.63
*The mean value and standard deviation are calculated based on fresh runs
17
Mean Gas Consumpti on (mol)
Standard Deviation
7.08×10-2
1.70×10-3
6.68×10-2
1.84×10-3
6.51×10-2
0.79×10-3
7.07×10-2
0.58×10-3
6.27×10-2
0.97×10-3
5.93×10-2
0.85×10-3
5.66×10-2
0.51×10-3
5.64×10-2
0.56×10-3
5.13×10-2
0.74×10-3
RI PT
Standard Deviation
SC
Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh Fresh Memory Fresh Fresh
AC C
Water+0.5% (wt.) PVP+0.5% (wt.) NaCl
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Induction Time (min)
M AN U
Water+1.0% (wt.) NaCl
Sample State
TE D
Pure water
Exp. No.
EP
System
ACCEPTED MANUSCRIPT
Figure 9 shows the gas consumption profile in presence of various inhibitors. It is evident from the results that PVP is more effective compared to NaCl and L-tyrosine as inhibitors. After nucleation gas starts to get accumulated inside the cavities with rapid formation of hydrates.
RI PT
Thus the initial rate of gas consumption after nucleation is very fast. On the other hand inhibitors adsorb on the surface of hydrate crystal and slows down the hydrate growth. The total gas consumed over 350 minutes in pure water is 7.15×10-2 mol. While with addition of 1.0% (wt.)
SC
each of NaCl, L-tyrosine and PVP to the pure water system, the total amount of gas consumed comes down to 6.73×10-2 mol, 6.64×10-2 mol and 5.96×10-2 mol respectively. Thus addition of
M AN U
NaCl, L-Tyrosine and PVP inhibited the growth of hydrate resulting in lesser amount of gas consumption at the end compared to pure water. As expected it is found that the inhibition of PVP is more than the NaCl and L-Tyrosine which is also reported in any literatures. Talaghat (2013) studied the gas consumption of various gases like methane, propane, carbon di-oxide, iso-
TE D
butane during simple gas hydrate formation in presence of PVP and found that addition of PVP decreases the amount of gas consumption. Daraboina and Linga (2013) also reported that the growth of CH4+C3H8 hydrate is slowed down in presence of PVP. The mechanism of hydrate
EP
inhibition by KHIs is still not clear. But the general perception is that KHIs adsorbed on the surface of the nuclei, thus slowing down the hydrate growth rate by reducing the gas absorption
AC C
into the hydrate crystal. Previous studies suggest that hydrate inhibition by KHIs is a two-step process (Kvamme et al., 2005; Anderson et al., 2005, Sa et al., 2013). First, it raises the barrier to nucleation by disturbing the local water structure. Then the inhibitor binds to the surface of hydrate crystal and thus retards the further growth once nucleation occurs. King and his coworker (King et al., 2000) used small-angle neutron scattering to study mechanism of hydrate inhibition by polymers. They found that poly (N-vinyl-2-pyrollidone), poly (N-vinyl-2-
18
ACCEPTED MANUSCRIPT
caprolactam) and N-vinylacetamide/N-vinyl-2-caprolactam copolymer kinetically suppress the hydrate crystallization due the surface adsorption of polymer onto the growing crystals. Similar study was carried by Hutter er al. (2000). They too reported through small-angle neutron
RI PT
scattering that poly- (N-vinyl-2-pyrrolidone) adsorbed onto hydrate crystal surfaces and thus inhibit the hydrate formation. Figure 10 shows the gas consumption pattern with time in presence of different concentrations of PVP. It is seen from the Figure 10 that with increase in
SC
concentration the amount of gas consumed decreases. For example, in presence of 0.5%(wt.) PVP in water, the total amount of gas consumed after 350 minutes is 6.39×10-2 mol, but increase
M AN U
in PVP concentration to 1.0%(wt.) in water further decreases the gas consumption to 5.96×10-2 mol. Thus the growth of hydrate is found to decrease with the increase in the concentration of the PVP in the solutions (Daraboina and Linga (2013). The combined effect of inhibitors on the amount of gas consumption at the end is shown in Figure 11. Addition of both NaCl and L-
TE D
tyrosine to PVP in water further decreases the gas consumption compared to PVP alone in water. In presence of 0.5% (wt.) PVP+ 0.25% (wt.) NaCl+ 0.25% (wt.) L-tyrosine in water, the total amount of gas consumed after 350 minutes is 5.19×10-2 mol. It indicates that there is around
EP
27% decrease in gas consumption after addition of PVP+NaCl+L-tyrosine in water in compared to pure water system. Similar observations were reported in many literatures (Cha et al., 2013,
AC C
Daraboina et al., 2011). Zhao et al. (2015) studied the synergism of thermodynamic hydrate inhibitors on the performance of poly (vinyl pyrrolidone) in deepwater drilling fluid. They found that NaCl showed strong synergistic effect on the performance of PVP as hydrate inhibitor. The synergism effect of L-tyrosine on hydrate inhibitors had also been reported by Talaghat (2011).
19
ACCEPTED MANUSCRIPT
0.08 0.07
0.05
RI PT
0.04 0.03 0.02 0.01
Pure water Water+1.0% (wt) NaCl Water+1.0% (wt) L-tyrosine Water+1.0% (wt) PVP
0.00 -0.01 0
50
100
150
200
250
300
M AN U
Time (min)
SC
Gas Consumption (mol)
0.06
Fig. 9. Gas consumption profile in presence of NaCl, L-tyrosine and PVP after nucleation. 0.08 0.07
0.04 0.03 0.02
TE D
0.05
0.01
EP
Gas Consumption (mol)
0.06
Water+0.1% (wt) PVP Water+0.5% (wt) PVP Water+1.0% (wt) PVP
0.00
AC C
-0.01
0
50
100
150
200
250
300
Time (min)
Fig. 10. Gas consumption profile in presence of different concentrations of PVP after nucleation.
20
ACCEPTED MANUSCRIPT
0.06
Gas Consumption (mol)
0.05
0.04
RI PT
0.03
0.02
0.01
M AN U
SC
W +0 ate .5 r+0 % . (w 5% t.) (w Ty t.) ro P si VP ne W +0 ate . 0. 25 r+0 2 5 % .5 % % ( (w wt.) (w t.) N t.) Ty aC PV P l ro si + ne
W
at e
r+ 1
.0
%
(w
t.)
PV
P W +0 a t e .5 r+0 % . (w 5% t.) (w N t aC .) P VP l
0.00
Fig. 11. Combined effect of inhibitors on the end gas consumption.
4. Conclusion
TE D
The influence of L-tyrosine and NaCl on the hydrate inhibition strength of PVP during CH4+C2H4+C3H8 hydrate formation has been investigated. The studies of hydrate onset and growth are carried out by measuring the induction time and gas consumption profile. The
EP
induction time measured in pure water+ CH4+C2H4+C3H8 system is 27 minutes. Among the inhibitors used in this study, PVP delayed the hydrate nucleation most. Addition of 1% (wt.)
AC C
PVP to water increases the induction time to 45 minutes. It is further noticed that presence of both NaCl and L-tyrosine enhance the performance of PVP as inhibitor. The presence of NaCl+PVP and L-tyrosine+PVP in water increases the induction time to 59 minutes and 62 minutes respectively. It has been also noticed that there is around 27% decrease in gas consumption after addition of 0.5% (wt.) PVP+ 0.25% (wt.) NaCl+ 0.25% (wt.) L-tyrosine in water in compared to pure water system. Kinetic hydrate inhibitors (KHIs) are gaining interest as
21
ACCEPTED MANUSCRIPT
an efficient hydrate inhibitors in the industry, despite limited knowledge on the mechanisms involved. Inhibition effect of L-tyrosine, NaCl and PVP on hydrate nucleation and growth is very much encouraging with significant rise in induction time for different systems compared to pure
RI PT
water system
Acknowledgement
SC
We gratefully acknowledge the financial assistance provided by Science and Engineering
M AN U
Research Board (EMR/2015/002141) under Department of Science and Technology, New Delhi, India, to the Department of Petroleum Engineering, Indian School of Mines, Dhanbad, India.
TE D
References
1. Anderson, B. J., Tester, J. W., Borghi, G. P., Trout, B. L., 2005. Properties of inhibitors of methane hydrate formation via molecular dynamics simulations. J. Am. Chem. Soc.
EP
127, 17852–17862.
2. Cha, M., Shin, K., Seo, Y., Shin, J-Y, Kang, S-P, 2013. Catastrophic Growth of Gas
AC C
Hydrates in the Presence of Kinetic Hydrate Inhibitors. J. Phys. Chem. A 117, 13988−13995.
3. Cohen, J. M., Wolf, P. F., Young, W. D., 1998. Enhanced hydrate inhibitors: powerful synergism with glycol ethers. Energy Fuels 12, 216–218.
4. Daraboina, N., Linga, P., 2013. Experimental investigation of the effect of poly-N-vinyl pyrrolidone (PVP) on methane/propane clathrates using a new contact mode. Chem. Eng. Sci. 93 387–394. 22
ACCEPTED MANUSCRIPT
5. Daraboina, N., Linga, P., Ripmeester, J., Walker, V. K., Englezos, P., 2011. Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 2. Stirred Reactor Experiments. Energy Fuels 25, 4384–4391.
RI PT
6. Hutter, J. L., King, H. E., Lin, M. Y., 2000. Polymeric Hydrate-Inhibitor Adsorption Measured by Neutron Scattering. Macromol. 33, 2670-2679.
7. Jokandan, E. F., Naeiji, P., Varaminian, F., 2016. The synergism of the binary and
SC
ternary solutions of polyethylene glycol, polyacrylamide and Hydroxyethyl cellulose to methane hydrate kinetic inhibitor. J. Nat. Gas Sci. Eng. 29 15-20.
M AN U
8. Kakati, H., Kar, S., Mandal, A, Laik, S., 2014. Methane Hydrate Formation and Dissociation in Oil-in-Water Emulsion. Energy Fuels 28(7), 4440−4446. 9. Kakati, H., Mandal, A., Laik, S., 2015. Effect of SDS/THF on thermodynamic and kinetic properties of formation of hydrate from a mixture of gases (CH4+C2H6+C3H8) for
TE D
storing gas as hydrate. doi.org/10.1016/j.jechem.2016.01.018. 10. Kakati, H., Mandal, A., Laik, S., 2015. Phase Stability and Kinetics of CH4 + CO2 + N2 Hydrates in Synthetic Seawater and Aqueous Electrolyte Solutions of NaCl and CaCl2. J.
EP
Chem. Eng. Data 60 (6), 1835–1843.
11. Kakati, H., Mandal, A., Laik, S., 2016. Promoting effect of Al2O3/ZnO-based nanofluids
AC C
stabilized by SDS surfactant on CH4+C2H6+C3H8 hydrate formation. J. Ind. Eng. Chem. 35, 357–368.
12. Kashchiev, D., Firoozabadi, A., 2003. Induction time in crystallization of gas hydrates. J. Cryst. Growth 250, 499-515.
23
ACCEPTED MANUSCRIPT
13. Khodaverdiloo, K. R., Rad, S. A., Naeiji, P., Peyvandi, K., Varaminian, F., 2016. Synergistic effects of nonylphenol ethoxylates and polyethylene glycols on performance of gas hydrate kinetic inhibitor. J Mol. Liq. 216 268–274.
Monoethylene
Glycol
with
Poly(vinylcaprolactam)
Underinhibited System. J. Phys. Chem. B 118, 9065−9075.
RI PT
14. Kim, J., Shin, K., Seo, Y., Cho, S. J., Lee, D. J., 2014. Synergistic Hydrate Inhibition of in
Thermodynamically
SC
15. Kim, K.-S., Kang, J.W., Kang, S.-P., 2011. Tuning ionic liquids for hydrate inhibition. Chem. Commun. 47, 6341–6343.
M AN U
16. King, H. E., Hutter, J. L., Lin, M. Y., Sun, T., 2000. Polymer conformations of gashydrate kinetic inhibitors: a small-angle neutron scattering study. J. Chem. Phys. 112, 2523–2532.
17. Koh, C. A., Sum, A. K., Sloan, E. D., 2012. State of the Art: Natural Gas Hydrates as a
TE D
Natural Resource. J. Nat. Gas Sci. Eng. 8, 132−136.
18. Kumar, A., Kumar, R., 2015. Role of Metallic Packing and Kinetic Promoter in Designing a Hydrate-Based Gas Separation Process. Energy Fuels, 29 (7), 4463–4471.
EP
19. Kumar, A., Sakpal, T., Kumar, R., 2015. Influence of Low-Dosage Hydrate Inhibitors on Methane Clathrate Hydrate Formation and Dissociation Kinetics. Energy Technol. 3 (7),
AC C
717-725.
20. Kumar, A., Sakpal, T., Linga, P., Kumar, R., 2014. Impact of Fly Ash Impurity on the Hydrate-Based Gas Separation Process for Carbon Dioxide Capture from a Flue Gas Mixture. Ind. Eng. Chem. Res., 53 (23), 9849–9859. 21. Kvamme, B., Kuznetsova, T., Aasoldsen, K., 2005. Molecular Dynamics Simulations for Selection of Kinetic Hydrate Inhibitors. J. Mol. Graphics Modell. 23, 524−536.
24
ACCEPTED MANUSCRIPT
22. Larsen, R., Knight, C. A., Sloan, E. D., 1998. Clathrate hydrate growth and inhibition. Fluid Phase Equilib. 150–151, 353–360. 23. Lee, J. D., Englezos, P., 2005. Enhancement of the performance of gas hydrate kinetic
RI PT
inhibitors with polyethylene oxide. Chem. Eng. Sci. 60, 5323 – 5330.
24. Linga, P., Daraboina, N., Ripmeester, J. A., Englezos, P., 2012. Enhanced rate of gas hydrate formation in a fixed bed column filled with sand compared to a stirred vessel. Chemical Engineering Science 68, 617–623.
SC
25. Lou, X., Ding, A., Maeda, N., Wang, S., Kozielski, K., Hartley, P. G., 2012. Synthesis of
M AN U
Effective Kinetic Inhibitors for Natural Gas Hydrates. Energy Fuels 26, 1037−1043. 26. Phillips, N. J., Kelland, M. A., 1999. The application of surfactants in preventing gas hydrate formation. Industrial Applications of Surfactants IV; The Royal Society of Chemistry (RSC), RSC Special Publications, 230, 244−259.
27. Sa, J.-H., Kwak, G.-H., Lee, B. R., Park, D.-H., Han, K., Lee, K.-H., 2013. Hydrophobic
2428.
TE D
amino acids as a new class of kinetic inhibitors for gas hydrate formation. Sci. Rep. 3,
28. Salamat, Y., Moghadassi, A., Illbeigi, M., Eslamimanesh, A., Mohammadi, A. H., 2013.
EP
Experimental study of hydrogen sulfide hydrate formation: Induction time in the presence
AC C
and absence of kinetic inhibitor. J Energy Chem. 22, 114–118. 29. Seo, Y., Kang, S.-P., 2010. Enhancing CO2 Separation for Pre-combustion Capture with Hydrate Formation in Silica Gel Pore Structure. Chem. Eng. J. 161, 308−312.
30. Sharif, H., Ripmeester, J., Walker, V. K., Englezos, P., 2014. Kinetic inhibition of natural gas hydrates in saline solutions and heptane. Fuel 117, 109–117. 31. Sloan, E. D., 1998. Clathrate Hydrate of Natural Gases, 2nd ed.; Marcel Deckker, Inc.: New York.
25
ACCEPTED MANUSCRIPT
32. Sloan, E. D., Koh, C. A., Sum, A. K., Ballard, A. L., Shoup, G. J., McMullen, N., Creek, J. L., Palermo, T., 2009. Hydrates: State-of-the-Art Inside and Outside Flowlines. J. Pet. Technol. 61, 89−94.
hydrate crystallization. J. Am. Chem. Soc. 126, 1569–1576.
RI PT
33. Storr, M. T., Taylor, P. C., Monfort, J.-P, Rodger, P. M., 2004. Kinetic inhibitor of
34. Talaghat, M. R., 2011. Enhancement of the performance of kinetic inhibitors in the
SC
presence of polyethylene oxide and polypropylene oxide for binary mixtures during gas hydrate formation in a flow mini-loop apparatus. Can. J. Chem. Eng. 90, 79–86.
M AN U
35. Talaghat, M. R., 2012. Prediction of Induction Time for Natural Gas Components During Gas Hydrate Formation in the Presence of Kinetic Hydrate Inhibitors in a Flow MiniLoop Apparatus. Can. J. Chem. Eng. 9999, 1-8.
36. Talaghat, M. R., 2013. Experimental investigation of gas consumption for simple gas
TE D
hydrate formation in a recirculation flow mini-loop apparatus in the presence of modified starch as a kinetic inhibitor. J Nat. Gas Sci. Eng. 14, 42-48. 37. Talaghat, M. R., 2014. Experimental investigation of induction time for double gas
EP
hydrate formation in the simultaneous presence of the PVP and L-tyrosine as kinetic inhibitors in a mini flow loop apparatus. J. Nat. Gas Sci. Eng. 19, 215-220.
AC C
38. Veluswamy, H. P., Kumar, S., Kumar, R., Rangsunvigit, P., Linga, P., 2016. Enhanced clathrate hydrate formation kinetics at near ambient temperatures and moderate pressures: Application to natural gas storage. Fuel, doi:10.1016/j.fuel.2016.05.068.
39. Veluswamy, H. P., Yew, J. C., Linga, P., 2015. New Hydrate Phase Equilibrium Data for Two Binary Gas Mixtures of Hydrogen and Propane Coupled with a Kinetic Study. J. Chem. Eng. Data, 60 (2), 228–237.
26
ACCEPTED MANUSCRIPT
40. Villano, L. D., Kelland, M. A., Miyake, G. M., Chen, E., 2010. Effect of Polymer Tact icity on the Performance of Poly(N,N-dialkylacrylamide) s as Kinetic Hydrate Inhibitors. Energy Fuels 24, 2554−2562.
RI PT
41. Walker, V. K., Zeng, H., Ohno, H., Nagu Daraboina, N., Sharifi, H., Bagherzadeh, S. A., Alavi, S., Englezos, P., 2015. Antifreeze proteins as gas hydrate inhibitors. Can. J. Chem., 93(8): 839-849.
SC
42. Yang, J., Tohidi, B., 2011. Characterization of inhibition mechanisms of kinetic hydrate
M AN U
inhibitors using ultrasonic test technique. Chem. Eng. Sci. 66, 278–283. 43. Zeng, H., Lu, H., Huva, E., Walker, V. K., Ripmeester, J. A., 2008. Differences in nucleator adsorption may explain distinct inhibition activities of two gas hydrate kinetic inhibitors. Chem. Eng. Sci. 63, 4026.
44. Zeng, H., Walker, V. K., Ripmeester, J.A., 2007. Adsorption of antifreeze protein and a
Chem Ice 659–667.
TE D
commercial low dosage hydrate inhibitor on hydrophilic and hydrophobic surfaces. Phys.
45. Zeng, H., Wilson, L. D., Walker, V. K., Ripmeester, J. A., 2006. Effect of antifreeze
EP
proteins on the nucleation, growth, and the memory effect during tetrahydrofuran
AC C
clathrate hydrate formation. J. Am. Chem. Soc. 128, 2844–2850. 46. Zhao, X., Qiu, Z., Zhou, G., Huang, W., 2015. Synergism of thermodynamic hydrate
inhibitors on the performance of poly (vinyl pyrrolidone) in deepwater drilling fluid. J. Nat. Gas Sci. Eng. 23, 47-54.
47. Zhong, D. L, Wang, Y. R, Lu, Y. Y, Wang, W. C., Wang, J. L. 2016. Phase equilibrium and kinetics of gas hydrates formed from CO2/H2 in the presence of tetrahydrofuran and cyclohexane.
Journal
of
Natural
doi:10.1016/j.jngse.2016.03.036 27
Gas
Science
and
Engineering,
ACCEPTED MANUSCRIPT
Highlights
Hydrate formation experiments is carried out for a methane/ethane/propane
RI PT
•
(89.93/7.04/3.03 mol %) gas mixture in presence of various concentrations of PVP, LTyrosine and NaCl in water. •
Hydrate nucleation time and hydrate growth profile have been studied in presence of
SC
various inhibitors.
The presence of PVP, L-Tyrosine and NaCl inhibit the formation of hydrate.
•
Presence of both NaCl and L-tyrosine enhanced the inhibition strength of PVP.
AC C
EP
TE D
M AN U
•