Comparison of Kinetic Hydrate Inhibitor Performance on Structure I

Subscriber access provided by RMIT University Library

Article

Comparison of Kinetic Hydrate Inhibitor Performance on Structure I and Structure II Hydrate-Forming Gases for a Range of Polymer Classes Eirin Abrahamsen, and Malcolm A. Kelland Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03318 • Publication Date (Web): 18 Dec 2017 Downloaded from http://pubs.acs.org on December 23, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Comparison of Kinetic Hydrate Inhibitor Performance on Structure I and Structure II Hydrate-Forming Gases for a Range of Polymer Classes

Eirin Abrahamsen* and Malcolm A. Kelland Department of Mathematics and Natural Sciences, Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway. *

Corresponding author: [email protected]

ABSTRACT A series of water-soluble polymers has been investigated for comparison of their potential as kinetic hydrate inhibitors (KHIs) for both Structure I (SI)- and Structure II (SII)-forming gas mixtures. A slow constant cooling test method and steel rocking cells have been used for these experiments. The average hydrate onset temperatures (To) have been used to rank the polymers according to their KHI ability, the lower To values gives a higher rank. The object of the study was a comparison of the KHI performance for SI versus SII inhibition for a range of polymers, not a study to find the optimal polymer for each hydrate structure. The most interesting comparative results were the large deviations of the ethyl derivative of poly(N-alkylglycine) for the two hydrate systems, where this polymer performed very well with the SI-forming gas, but had significantly less effect on the SII-forming gas. Also poly(2ethyl-2-oxazoline) (PEtOx) and poly(iso-propenyloxazoline)-01 (PiPOx-01) ranked better with SI hydrates in comparison with the SII hydrate system. In general the polymers that work well on the SI-forming gas, works well on SII-forming gas as well. KHI mechanistic insights from this study was discussed.

ACS Paragon Plus Environment

Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 29

Although other KHIs outside this study may be available with better performance, we found that the best KHIs for SII hydrates were two N-vinyl caprolactam polymers in the synergistic solvent 2-butoxyethanol and the best KHIs for SI hydrates were an N-iso-propylacrylamide homopolymer and the same two N-vinyl caprolactam polymers.

INTRODUCTION Production of oil and gas under certain temperature and pressure conditions can lead to gas hydrate formation, which can cause severe blockage of the pipelines.

1-3

Gas hydrates form

when there is free water together with gas at elevated pressures and low temperatures, which are typical conditions for fields in cold climate areas and for subsea pipelines. Common components of the produced natural gas mixtures that can promote the formation of gas hydrates include small hydrocarbons such as methane, ethane, propane, (iso-)butane as well as carbon dioxide and hydrogen sulfide. 2, 4, 5 To prevent plugging of the pipelines by gas hydrates, thermodynamic chemical inhibition has been commonly used for many decades. Low dosage hydrate inhibitors (LDHIs) such as kinetic hydrate inhibitors (KHIs) are becoming more widespread since they can be used at very low dosages (less than 5 wt. % of the aqueous phase). 6 This compares to conventional thermodynamic hydrate inhibitors (THIs) that often need to be dosed in very large amounts (up to 50 wt.% or more of the produced water). 2, 7, 8 The KHIs have also in many cases been used together with THIs in order to decrease the large amounts of chemicals needed to get sufficient inhibition. 9, 10 The majority of oil and gas fields produce natural gas mixtures that lead to Structure II (SII) gas hydrate as the most thermodynamically stable phase. 3 That is why studies on developing


Page 3 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

kinetic hydrate inhibitors have concentrated on using a SII-forming gas mixture. However, fields that are very rich in methane gas can give Structure I (SI) hydrate as the most stable phase. 3 In addition, SI hydrate can also form as a stable phase using SII-forming gas mixtures when the phase boundary for SI formation is past when cooling. The fluids will cool beyond both the SII and SI equilibrium curve in slow constant cooling experiments. An example is shown in Figure 1 with a graph of the SI- and SII equilibrium curves and the change in pressure/temperature (PT) profile during a slow constant cooling test. In this example two PT profiles are shown where the green curve starts at 110 bar and the red curve starts at 76 bar. In a closed system the pressure will decrease as the temperature decreases. The equilibrium temperature (Teq) for the SI-forming gas, at 110 bar, is approximately 15-16 °C and at 76 bar the Teq is approximately 12.5-13.5 °C. For the SII-forming gas, at 110 bar the Teq is approximately 21.5-22.5 °C and at 76 bar the Teq is approximately 20-20.5 °C. The range of the Teq values is based on various software such as PVTSim from Calsep and Mutiflash from KBC. 11


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Equilibrium temperature curves for SI (dotted red) and SII (dotted green). Pressure vs. temperature profile for the constant cooling experiments (SI red, SII green).

The potential for formation of SI hydrate may be the main reason for the subcooling limit for use of KHIs in SII-forming systems. Therefore, it is important to understand which KHIs are best suited for inhibiting SI hydrate-forming systems. Among the first commercial KHIs and probably of the most common classes to be used in KHI formulas are homo- and copolymers of N-vinyl lactams such as VP and VCap. These polymers were also found to give increased KHI performance with solvents such as BGE and MEG.

12-14

Similar polymers and copolymers with different ring sizes have also been

investigated as KHIs, where increasing the lactam ring size was found to give increasing KHI performance.15, 16


Page 4 of 29

Page 5 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Other polymers that have been investigated often contain amide groups, such as the lactam polymers. The amide group seems to help with good inhibition effects.17-19 For example polyaspartamides in which have been investigated mainly because of the potential of an allaround green KHI.20,

21

Other well-known KHI polymer classes are based on N-

alkyl(meth)acrylamides and hyperbranched polyesteramides.3, 22, 23 A more recent focus have been to find environmentally friendly KHIs, specifically with high biodegradation rates in seawater. One of the early ideas of hydrate inhibition came from natural anti-freeze proteins that can be found in certain species of fish, insects, plants and bacteria.18,

24

Since then, several proteins and peptides have been investigated as KHIs,

because they are expected to be readily biodegradable.

25

Amino acid and derivatives thereof

have also been investigated as KHIs, but the KHI performance on natural gas or CO2 hydrate is poor.26-28 Over the past 25 years, and particularly the last 10 years, a wide range of polymer classes have been tested for their KHI performance on a SII hydrate-forming gas mixture. This gives us a unique position to be able to test the KHI performance of the same polymers on SI methane hydrate for comparison. We report here our KHI performance results on a wide range of water-soluble polymers using the slow constant cooling test method in steel rocking cells. Both pure methane gas (giving SI hydrates) and a synthetic natural gas mixture (giving preferably SII hydrates) were used. We underline that this study is not designed to find the optimal polymers to inhibit either hydrate structure as more optimal polymers in the classes being studied could probably be found.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 29

EXPERIMENTAL METHODS: KINETIC HYDRATE INHIBITOR PERFORMANCE TESTS Materials Solvents and commercial products were used as received from supplier, without any further purifications. Polyacrylamide (PAM), 50 wt.% in H2O) Mw = 1500 and polyethylene glycol (PEG), Mw = 400 was supplied by Sigma Aldrich. Products supplied by Nippon Shokubai are poly(N-iso-propylacrylamide) (PNIPAM) as FXAAM

IP1000-11

(Mw

=

2.1k,

Mn

=

1.1k)

and

iso-propylacrylamide

/

(acrylamide)propanesulfonic acid (NIPAM/AMPS) copolymer (10 wt.% AMPS) as IP 1010 ASN. Products supplied by Ashland (ISP) are N-vinyl caprolactam (VCap / VOH) copolymer 36 wt.% in 2-butoxyethanol (or butyl glycol ether, BGE) as Inhibex BIO-800, poly(N-vinyl caprolactam) (PVCap) 50 wt.% in BGE, Mw = 2k as Inhibex 101, poly(N-vinyl pyrrolidone) (PVP) as PVP K-15 and butylated PVP (Bu-PVP) as Antaron P904. Products supplied by BASF are VCap / N-vinyl pyrrolidone (VCap/VP) (1:1) copolymer (53.8 wt.% in H2O) as Luvicap55 W, PVCap 41.1 wt.% in monoethylene glycol (MEG) low and high molecular (HM) weight as Luvicap EG and Luvicap EG HM. A hyperbranched polyesteramide-based KHI 30 wt.% in unknown solvent was supplied by Baker Hughes as HI-M-PACT 83701. Pectin Citrus was supplied by Alfa Aesar (purchased via VWR). Hydroxyethyl cellulose (HEC), Mw = 100k supplied by Schlumberger. The following polymers have been synthesized in our laboratories and/or have previously been tested in our group (see the references for further information): poly(N-vinyl piperidone) (PVPip)

16

, Mw = 25k, poly(N-vinyl caprolactam) UiS (PVCap UiS), Mw = 4000

15

, poly(N-

vinyl azacyclooctanone) (PVACO), 35.6 wt.% in iso-propanol (iPA) Mw = 4000-5000 poly(N-methylglycine) (PNMG) Mn = 1200

26

, poly(N-ethylglycine) (PNEG) Mn = 1900


15

,

26

,

Page 7 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

poly(N-propylglycine) (PNPG) Mn = 1700 26, poly(N-iso-propylglycine) (PNiPG) Mn = 3000 26

,

poly(N-iso-propylmethacrylamide)

(PNIPMAM)

29

,

poly(N-ethylmethacrylamide)

(PNEMAM), poly(N,N-dimethylhydrazidomethacrylamide) III (P(DMHMAM) III)

29

,

polyaspartamide (iso-butyl / methyl) (80/20) (PAsp iBu/Me) 44.6 wt.% in dimethyl sulfoxide (DMSO) 20, poly(dimethylamineoxide) ethylacrylate (PDMAOEA) 21.4 wt.% in H2O, poly(2ethyl-2-oxazoline) (PEtOx) 30, poly(iso-propenyloxazoline)-01 (PiPOx-01) Mn = 2000, PDI = 1.26

31

,

KHI

530

is

a

natural polymer,

40

wt.% in

aqueous

medium

tetraethylenepentaminebutylated amine oxide (TEPA-Bu-AO), 35.1 wt.% in H2O.

33

32

,

The

structures of the different polymers synthesized and/or previously tested in our lab are shown in Figure 2.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a)

O

Page 8 of 29

b)

R

c) R1

R1

N N H

H

n

n O

n

NH

O

NH

R

d)

N

e)

O

f)

H N N H

H

m

N

n

n

n

O

O O

NH

N

O

O

R

R

HN

h)

R

g)

n O

Bu

O

Bu

O N

N

N

Bu

N

Bu

O

O

O

N

Bu

Bu

O

Bu N O

j)

i)

k)

l)

n

n N

N

n O

N

n O

O

N

O

Figure 2. Molecular structures of the different polymers synthesized and/or previously tested in our lab. a) Poly(N-alkylglycine)s, b) poly(N-alkyl(meth)acrylamides, c) P(DMH(M)AM), d) polyaspartamides, e) PiPOx, f) poly(2-alkyl-2-oxazoline), g) TEPA-Bu-AO, h) PDMAOEA, i) PVP, j) PVPip, k) PVCap, l) PVACO. R = alkyl group and R1 = H or CH3.


Page 9 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

High-Pressure Rocking Cell Tests with Pure Methane Gas and Synthetic Natural Gas The procedure for the KHI performance tests were carries out by the same procedure as done previously in our group, for better comparison of the results.11, 34 The test equipment used was supplied by PSL Systemtechnik, Germany, a rocker rig that can hold up to five high-pressure steel rocking cells. Each cell can hold up to 40 ml where 20 ml was filled with an aqueous test solution. To simulate turbulent flow, a steel ball was placed in each cell so the liquid is properly agitated. The system was then pressurized using either a SI- or SII-forming gas. Pure methane gas was used as the SI-forming gas hydrates. Correspondingly, a synthetic natural gas mixture (SNG) containing the components listed in Table 1 was used as the SII-forming gas.

Table 1. Synthetic natural gas (SNG) mixture used in the KHI performance tests.

Component

mol %

N2

0.10

CO2

1.84

methane

80.67

ethane

10.20

n-propane

4.90

iso-butane

1.53

n-butane

0.76


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 29

The procedure for loading the cells and setup of the standard constant cooling test for the KHI performance tests are as follows:11, 34 1. The polymer was diluted to desired concentration in deionized water at least one day before testing it. 20 ml sample was loaded in each cell at room temperature and placed in the water bath at 20.5 °C to equilibrate. 2. Before purging the cells with 3-5 bar of the hydrate-forming gas, vacuum was applied in order to remove air in the system. After depressurizing the system, vacuum was applied again. 3. The system was pressurized to the desired test pressure, the cells were rocking at a rate of 20 rocks/min or 10 cycles/min through an angle of ± 40°. 4. The starting temperature was set to 20.5 °C and with a cooling rate of approximately 1 °C/hour, the minimum temperature was set to 2 °C. 5. Each cell is equipped with temperature- and pressure sensors. In addition, there is a sensor on the cooling bath. All the data is logged on a local computer.

For the SII-forming gas, a pressure of approximately 76 bar is used as in previous work in our group, where 20.5 °C is the Teq found from calculations done in Calsep’s PVTSim software. 15, 35

For the SI-forming gas, we had to increase the pressure to 110 bar in order to be able to

observe the pressure drop for the best performing KHIs reported in this paper. The SI envelope lies within the SII envelope at higher pressures and lower temperatures (as shown in Figure 1). Absolute pressure does affect KHI performance as several studies have shown, but results so far indicate that it does not appear to affect the ranking.

36-39

In these KHI

experiments, the hydrate that is first formed, as well as the finally formed macroscopic hydrates, is not analyzed. Thus, the exact composition of the clathrate structures involved are not known. ACS Paragon Plus Environment

Page 11 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Because the system is closed, the pressure will decrease correspondingly as the temperature decreases at a constant rate. In addition, the pressure will decrease a few bars at the start of the test as the gas dissolves in the aqueous phase. The pressure and temperature data are plotted against the time to give a pressure and temperature graph where we can find the onset temperature (To) and the temperature for rapid hydrate formation (Ta) (Figure 3 and Figure 4). To is the value of most interest because this is the temperature at which the first macroscopic hydrate formation is observed. The nucleation process is not detectable in these graphs and may have taken place earlier than the given time of To. From Figures 4, the data for each cell can be analyzed.

Figure 3. Summary of the results from a standard constant cooling test.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3 shows a summary of the graph from all five cells and from this, the graphs for each cell can be generated for analysis. The To value is found by the first deviation from the linear slope as shown in Figure 4. The Ta value is found by the point of the largest pressure drop in the slope after To. P1 is the pressure graph for cell 1, T1 is the temperature for cell 1. From the figure, the To was found at 12.1 °C after approximately 544 minutes and Ta was found at 11.1 °C after approximately 600 minutes.

Figure 4. Example of determination of To and Ta after a standard constant cooling experiment.


Page 12 of 29

Page 13 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

In total, 8-10 individual experiments were carried out for each polymer in these tests, using the slow constant cooling test method. Exceptions are for the polymers of limited amounts or if the polymer had poor performance in addition to causing problems such as foaming. There were no observations of any systematic error in any of the cells, i.e. none of the cells gave consistently better or worse results than the others for each experiment.

RESULTS AND DISCUSSION The results will be divided into the following categories for the main discussion; N-vinyl lactam-based polymers, poly(N-alkylglycine)s, miscellaneous polymers and PVP blends with other water-soluble polymers. This has been done to give the reader a better overview. In addition, we will summarize the most important results regarding KHIs that gave significant differences in ranking between the SI and SII gases. The complete list of tested polymers is summarized in Table 2 with the overall rank based on the average To values. For simplification, we illustrated only the To values in the figures. We underline that this is a comparative study to understand how structural differences may affect rankings between SI and SII. Comparisons of KHI rankings within one hydrate structure can be misleading since the optimum polymers within the polymer classes tested may not be represented, particularly those that are not commercial KHIs.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 2 Average To values and ranking of the tested polymers at 2500 ppm by weight.

To-av To-av Methane Rank SNG KHI 2500ppm [°C] [°C] 12.2 17.5 DIW DIW 4.4 2.6 1 PNIPAM VCap/VOH 36 wt.% in BGE 4.6 5.2 2 VCap/VOH 36 wt.% in BGE PVCap 50 wt.% in BGE 4.8 6.0 3 PVCap 50 wt.% in BGE PNPG 5.5 6.0 4 PNEG Hyperbranched polyesteramide 5.8 6.2 5 VCap/VP 53.8 wt.% in water PNIPAM 6.0 6.5 6 PNiPG VCap/VP 53.8 wt.% in water 6.4 8.0 7 VCap 41.1 wt.% in MEG PNiPG 6.7 8.2 8 PNPG TEPA-Bu-AO 35.1 wt.% H2O 6.8 8.3 9 PiPOx-01 VCap 41.1 wt.% in MEG 7.0 8.3 10 VCap HM 41.1 wt.% in MEG VCap HM 41.1 wt.% in MEG 8.7 7.2 11 PAsp iBu/Me 44.6 wt.% in DMSO Hyperbranched polyesteramide 7.5 9.5 12 PNIPMAM PNIPMAM 7.8 9.7 13 TEPA-Bu-AO 35.1 wt.% H2O PVACO 35.6 wt.% in iPA 8.0 10.0 KHI 530 (40 wt.% in aq. medium) 14 PVACO 35.6 wt.% in iPA 8.1 10.1 PVCap UiS 15 PVCap UiS 8.1 10.3 16 PVPip NIPAM/AMPS (10% AMPS) 8.1 10.5 PVPip 17 NIPAM/AMPS (10% AMPS) 10.5 Bu-PVP 18 PNEMAM 8.3 8.3 19 Bu-PVP 10.9 PNEMAM 9.3 11.1 PVP 20 PVP 9.5 11.1 PiPOx-01 21 KHI 530 (40 wt.% in aq. medium) a) 9.5 12.6 PNEG 22 PVP/PAM/HEC 13.6 P(DMHMAM) III 9.7 23 PVP/PAM/PEG 9.7 13.6 PVP/PAM/PEG b) 24 PVP/PEG 9.8 13.6 PVP/PAM b) 25 PEtOx 9.8 13.7 PVP/HEC b) 26 PVP/HEC a) 10.0 13.9 PVP/PAM/HEC b) 27 PVP/PAM 10.5 13.9 PVP/PEG b) 28 PAsp iBu/Me 44.6 wt.% in DMSO 11.9 16.6 PNMG 29 P(DMHMAM) III 12.0 16.7 Pectin Citrus 30 Pectin Citrus 12.1 16.8 31 HEC PDMAOEA 21.4 wt.% in H2O 12.1 17.0 PEG 32 PAM 50 wt.% in H2O 12.1 17.0 PEtOx 33 PNMG 12.2 17.1 HEC 34 PEG 12.2 17.4 PAM 50 wt.% in H2O 35 PDMAOEA 21.4 wt.% in H2O a) b) 5 experiments on SI-forming gas, 5 experiments on SII-forming gas (4 experiments for KHI 2500ppm

PVP/PAM/HEC)


Page 14 of 29

Page 15 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Main results of N-vinyl lactam-based KHIs The results for the N-vinyl lactam-based polymers are summarized in Figure 5. The KHI performance trend for this category, the lactam polymers, is similar for both SI and SII hydrates.

Figure 5. Average To for the N-vinyl lactam-based polymers.

Two of the best performing KHIs for both SI and SII hydrates, giving the second and third lowest To values of all the polymers tested (SI ranking) were two commercial KHI polymers, both are VCap-based and supplied in BGE solvent which is known to act as a good synergist. Compared to the SII ranking, the same two polymers ranked as the two best of all the polymers tested. Another low molecular weight PVCap supplied in MEG and a VCap/VP copolymer supplied in water, also performed well and ranked similarly for both SI and SII hydrates. The ranking


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of the homopolymers with different sizes of lactam rings (5-8-rings i.e. PVP, PVCap, PVPip and PVACO) of similar molecular weights and without organic solvents, had similar performance ranking for SI and SII hydrates. For the SII system, it is known that increasing the lactam ring size of the homopolymers will increase the KHI performance. This trend is similar for the SI system, however the To values are very close and not significantly different (except for PVP). This was checked with statistical t-tests, finding the p-value to be less than 0.05. 40 It is well known that 5- and 6-rings such as cyclopentane, tetrahydrofuran, 1,4 dioxane or tetrahydropyran are the largest rings that can be accommodated in the large SII (51264) cages, sometimes with a help gas such as methane. 1, 41 - 44 PVCap with synergists (particularly BGE) have a significantly better KHI performance than PVCaps with non-synergistic solvents or no solvent at all. Since most of the lactam ring sizes are too large to be accommodated in any 512, 51262 or 51264 cavity.41 The ranking results suggest that these polymers find some way to inhibit both the SI or SII hydrates. This shows that the polymer interaction is not structure specific to either of the hydrate surfaces (7-rings lactams cannot penetrate any of the 512, 51262 or 51264 cavities), but can still find a way to inhibit both hydrates. A more distance interaction to the surface, or perturbation of the bulk water structure are suggested as mechanisms that are more probable.

Main results of poly(N-alkylglycine)s A series of poly(N-alkylglycine)s were tested on SII hydrates by Reyes et al.26 The chosen polymers tested on the SI-forming gas had pendant alkyl groups varying in size from 1-4 carbon atoms. The results for the poly(N-alkylglycine)s are summarized in Figure 6.


Page 16 of 29

Page 17 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 6. Average To for the poly(N-alkylglycine)s category.

As seen previously for SII hydrates, often the polymers containing propyl and iso-propyl pendant groups are more effective as KHIs, whereas ethyl and methyl groups often show weaker KHI performance.

26, 45, 46

This trend might be related to the ability of the pendant

alkyl groups to penetrate 51264 cavities, whether on the hydrate surface or free cavities forming in solution. The graph in Figure 6 shows that PNPG and PNiPG have very good KHI performance for both SI and SII hydrates. The methyl derivative showed worst KHI performance on both hydrate structures. Interestingly, the ethyl derivative shows intermediate KHI performance on SII hydrate, however it gave very good performance on SI hydrates (slightly inferior to the best VCap-based polymers is BGE). PNEG also ranked better than PNiPG and PNPG for the SI system, showing To values that are close, however significantly different. This suggests that the ethyl group gives a weaker interaction with the SII hydrates (not the optimal size for


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

51264 cavities), but is small enough to interact properly with the SI cavities. Ethane can better penetrate and stabilize 51262 cages.

1, 2

This may be why PNEG with pendant ethyl groups

performs well with the SI-forming gas.

Main results of miscellaneous polymers Several different polymer classes have been investigated as KHIs where the following results are categorized as miscellaneous polymers. The results have been summarized in Figure 7, which shows the average To values for both the SI and SII system.

Figure 7. Average To values for the miscellaneous series.


Page 18 of 29

Page 19 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

The polymers that showed little or no significant KHI effect have small or negligible hydrophobic character in the side chains. The necessity of hydrophobic groups in watersoluble polymers is a well-known feature of KHI polymers. 18, 47 Surprisingly, PNIPAM ranked higher than PNIPMAM for both SI and SII hydrates. In fact, PNIPAM was ranked number one for the SI-forming gas, but with an average To value quite close to the best VCap-based polymers in BGE. However, neither the PNIPAM nor PNIPMAM were structurally optimized for inhibiting either hydrate structure. Studies by Exxon Mobil suggest that PNIPMAM when optimized will perform better than PNIPAM. 48 PEtOx has some effect as a KHI on the SI hydrates, however significantly weaker effect on SII hydrates. The KHI ability of the ethyl group on SI hydrate inhibition lines up with the result of the ethyl derivative of poly(N-alkylglycine), i.e. is more optimal in size for interaction with the large SI cages (51262) but not the large SII cages (51264). In addition, PEtOx has an amide group where the nitrogen atom, which could hydrogen-bond to water molecules, is more hidden in the polymer backbone than when the whole amide group is in the side chain. This may also explain the weaker KHI performance on SI hydrate compared to PNEG. The hyperbranched polyesteramide, Pasp iBu/Me and P(DMHMAM)III are higher up on the ranking in Table 2 for SII hydrates than SI hydrates, indicating that they are possibly better performing KHIs for SII hydrates. The hyperbranched polyesteramide also has a good KHI effect for SI hydrates, PAsp iBu/Me has a mediocre KHI effect and P(DMHMAM)III has little to no effect on SI hydrates. The large deviation of PAsp iBu/Me in the two systems (rank 28 for SI and rank 11 for SII) can indicate that the iso-butyl pendant group is not structurally compatible with the SI hydrate surface, as iso-butyl is too big to interact strongly with open SI cavities.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PiPOx-01 ranked surprisingly much better for SI hydrates than for SII hydrates (rank 9 versus rank 21). However the To value was still relatively good for both systems. For the SII hydrates, the performance is similar to PVP. For the SI hydrates, the performance is even better than some of the VCap-based polymers without solvent synergists. PiPOx-01 has a 5-ring pendant oxazoline group, roughly the same size as pyrrolidone, but it is not a polyamide like most of the polymers in this study. The superior performance on SI for PiPOx-01 could be due to a better direct interaction with the SI hydrate surface causing good crystal growth inhibition. This polymer has been shown to have very poor THF hydrate crystal growth inhibition, backing up its weaker performance on SII gas hydrates. 31 Although PVP is a crystal growth inhibitor, PVP has also been shown from computer modelling studies to work as an anti-nucleator, destabilizing SI hydrate clusters from a distance without sitting directly on the hydrate surface.

16, 49

If PiPOx-01 is assumed to be primarily a gas hydrate

anti-nucleator it would not explain the difference in performance between SI and SII gas hydrates, since the actual hydrate structure does not appear to be important when destabilizing these clusters from a distance.

Main results of PVP blends of PAM, PEG and HEC A study of PVP blended with other water-soluble polymers has been reported to give increased induction times on methane hydrate. 50 We investigated with similar polymer blends and concentrations using the slow constant cooling method with the rocking cells and with both SI- and SII-forming gas. The average To values are plotted in Figure 8.


Page 20 of 29

Page 21 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 8. Results from test series of PVP with synergists.

From our results, PAM, PEG and HEC were tested by themselves, and showed little or no inhibition effect with both types of gases. PVP improved the KHI effect of PAM, PEG and HEC when mixed. However, PVP by itself was the best performing KHI considering the SII system, with significantly lower To value compared to the PVP blends. For the SI system, there was little or no significant difference in the results with PVP by itself or PVP mixed with the other polymers.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

CONCLUSION A range of polymers have been tested and ranked for their KHI performance on both SI- and SII-forming gas, using the slow constant cooling test method and steel rocking cells. The rank was based on the average To values, where a lower To give the higher rank. The ranked results were compared for the polymers potential as a KHI. For SII system, a higher subcooling can be achieved before hydrate formation occurs compared to the SI system, i.e. hydrate formation happens faster within the SI envelope. In this case, for the SI system, we used a higher pressure in order to be able to observe the pressure drop for the best KHIs. However, this should not affect the ranking of the polymers. The polymers that had a good KHI performance on the SI hydrates, generally had a good performance on SII hydrates as well. A series of N-vinyl lactam-based polymers such as PVP, PVPip, PVCap, PVACO and copolymers thereof, with varying molecular weights were tested. The best performing lactams for both gas types are VCap/VOH copolymer and VCap homopolymers both with BGE as a synergist, in addition to a VCap/VP copolymer. All these rank among top ten of all the polymers tested in this paper. The lactam homopolymers show a similar inhibition trend for both types of gases, which suggests a probable inhibition mechanism that is not specific to either of the hydrate surface structures. A series of poly(N-alkylglycine)s from previous work done on SII-forming gas was retested on methane gas for comparison. For SI hydrates these polymers showed great potential as KHIs, with only the methyl derivative giving poor performance. One of the more interesting results in this study was the large deviation in KHI ranking of the poly(N-ethylglycine) (PNEG) between the two different gas systems. PNEG performed very well with the SI-


Page 22 of 29

Page 23 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

forming gas, but only had a mediocre performance with the SII-forming gas. These results suggest that PNEG has a better structural compatibility with the SI hydrates. Other miscellaneous polymers were also tested on the SI-forming methane gas for comparison, including (meth)acrylamide

polymers,

ring-closed/open

polyoxazolines,

polyaspartamides, hyperbranched polyesteramides and others. Amongst these polymers, some of the better performing KHIs were poly(N-iso-propylacrylamide) (PNIPAM), poly(isopropenyloxazoline) (PiPOx-01) and a commercial formulation based on hyperbranched polyesteramide, all with low molecular weights. (PiPOx-01) ranked surprisingly better with the SI-forming gas in comparison with the SII-forming gas. The PNIPAM performed better than the methacrylamide derivative, PNIPMAM, for both systems. However, these two polymers were made by different polymerization methods and were not optimized for these experiments. The ranked comparisons of PNEG and PiPOx-01 indicates that the inhibition mechanism is more structure specific i.e. the interaction with the SI hydrate surface is better than for the SII surface. Similarly for PAsp iBu/Me which is more structure specific to the SII surface than for the SI surface. The best SI KHIs may be useful to blend with the best SII KHIs to extend the subcooling limit for SII-forming gases further within the SI-forming envelope. This investigation is currently ongoing and will be reported on subsequently.

ACKNOWLEDGEMENTS Many thanks to my fellow co-workers in the group who have synthesized and previously tested some of the KHIs listed in this work.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

REFERENCES 1.

Sloan, E. D.; Koh, C. A., Clathrate hydrates of natural gases. 3rd ed. ed.; CRC Press:

Boca Raton, Fla, 2008; Vol. 119. 2.

Sloan, E. D., Natural gas hydrates in flow assurance. Elsevier Gulf Professional Publ.:

Amsterdam, 2011. 3.

Kelland, M. A., Production chemicals for the oil and gas industry. 2nd ed. ed.; CRC

Press: Boca Raton, Fla, 2014. 4.

Carroll, J. J., Natural gas hydrates : a guide for engineers. 2nd ed. ed.; Elsevier Gulf

Professional: Amsterdam, 2009. 5.

Fink, J., Petroleum Engineer's Guide to Oil Field Chemicals and Fluids. 2nd ed. ed.;

Elsevier Science: 2015. 6.

Swank, L.; Kapadia, K. P.; Webber, P. A.; Jones, R., Mitigation of Hydrates Using

Continuous KHI Injection in Deepwater GoM. In Offshore Technology Conference. 7.

Tohidi, B.; Anderson, R.; Mozaffar, H.; Tohidi, F., The Return of Kinetic Hydrate

Inhibitors. Energy & Fuels 2015, 29, (12), 8254-8260. 8.

Gupta, G.; Singh, S. K., Hydrate Inhibition -Optimization in Deep Water Gas Field. In

Society of Petroleum Engineers. 9.

Mozaffar, H.; Anderson, R.; Tohidi, B., Effect of alcohols and diols on PVCap-

induced hydrate crystal growth patterns in methane systems. Fluid Phase Equilibria 2016, 425, 1-8. 10.

Kim, J.; Shin, K.; Kim, J.; Chang, D.; Seo, Y.; Chang, K. P., Kinetic Hydrate

Inhibition Performance of MEG in Under-Inhibition System: Reduction Opportunities of MEG Injection for Offshore Gas Field Developments. In Offshore Technology Conference.


Page 24 of 29

Page 25 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

11.

Chua, P. C.; Kelland, M. A., Tetra(iso-hexyl)ammonium Bromide—The Most

Powerful Quaternary Ammonium-Based Tetrahydrofuran Crystal Growth Inhibitor and Synergist with Polyvinylcaprolactam Kinetic Gas Hydrate Inhibitor. Energy & Fuels 2012, 26, (2), 1160-1168. 12.

Cha, M.; Shin, K.; Kim, J.; Chang, D.; Seo, Y.; Lee, H.; Kang, S.-P., Thermodynamic

and kinetic hydrate inhibition performance of aqueous ethylene glycol solutions for natural gas. Chemical Engineering Science 2013, 99, 184-190. 13.

Fu, B., The development of advanced kinetic hydrate inhibitors. In Chemistry in the

Oil Industry VII: Performance in a Challenging Environment, Balson, T.; Craddock, H. A.; Dunlop, J.; Frampton, H.; Payne, G.; Reid, P., Eds. The Royal Society of Chemistry: 2002; pp 264-276. 14.

Hu, J.; Wang, Y.; Lang, X.; Du, J.; Li, Q.; Fan, S., Synthesis and application of a

novel combined kinetic hydrate inhibitor. Science China Technological Sciences 2011, 54, (12), 3289-3295. 15.

Chua, P. C.; Kelland, M. A., Poly(N-vinyl azacyclooctanone): A More Powerful

Structure II Kinetic Hydrate Inhibitor than Poly(N-vinyl caprolactam). Energy & Fuels 2012, 26, (7), 4481-4485. 16.

O’Reilly, R.; Ieong, N. S.; Chua, P. C.; Kelland, M. A., Missing Poly(N-vinyl lactam)

Kinetic Hydrate Inhibitor: High-Pressure Kinetic Hydrate Inhibition of Structure II Gas Hydrates with Poly(N-vinyl piperidone) and Other Poly(N-vinyl lactam) Homopolymers. Energy & Fuels 2011, 25, (10), 4595-4599. 17.

Kelland, M. A., History of the Development of Low Dosage Hydrate Inhibitors.

Energy & Fuels 2006, 20, (3), 825-847.


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

18.

Kelland, M.; Wytherst, M., A review of kinetic hydrate inhibitors: Tailor-made water-

soluble polymers for oil and gas industry applications. In Nova Science Publishers, Inc.: New York: 2011; Vol. 8. 19.

Lederhos, J. P.; Long, J. P.; Sum, A.; Christiansen, R. L.; Sloan Jr, E. D., Effective

kinetic inhibitors for natural gas hydrates. Chemical Engineering Science 1996, 51, (8), 12211229. 20.

Del Villano, L.; Kommedal, R.; Kelland, M. A., Class of Kinetic Hydrate Inhibitors

with Good Biodegradability. Energy & Fuels 2008, 22, (5), 3143-3149. 21.

Kelland, M., Additives for inhibiting gas hydrate formation. In Google Patents: 2008.

22.

Colle, K. S.; Costello, C. A.; Berluche, E.; Oelfke, R. H.; Talley, L. D. Method for

inhibiting hydrate formation. U.S. Patent 6,028,233, 2000. 23.

Klomp, U., A method for inhibiting the plugging of conduits by gas hydrates. In 29.

June 1995 ed.; 1995. 24.

Edwards, A. R., A Molecular Modeling Study of the Winter Flounder Antifreeze

Peptide as a Potential Kinetic Hydrate Inhibitor. Annals of the New York Academy of Sciences 1994, 715, (1), 543-544. 25.

Perfeldt, C. M.; Chua, P. C.; Daraboina, N.; Friis, D.; Kristiansen, E.; Ramløv, H.;

Woodley, J. M.; Kelland, M. A.; von Solms, N., Inhibition of Gas Hydrate Nucleation and Growth: Efficacy of an Antifreeze Protein from the Longhorn Beetle Rhagium mordax. Energy & Fuels 2014, 28, (6), 3666-3672. 26.

Reyes, F. T.; Guo, L.; Hedgepeth, J. W.; Zhang, D.; Kelland, M. A., First Investigation

of the Kinetic Hydrate Inhibitor Performance of Poly(N-alkylglycine)s. Energy & Fuels 2014, 28, (11), 6889-6896.


Page 26 of 29

Page 27 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

27.

Sa, J.-H.; Kwak, G.-H.; Han, K.; Ahn, D.; Cho, S. J.; Lee, J. D.; Lee, K.-H., Inhibition

of methane and natural gas hydrate formation by altering the structure of water with amino acids. Scientific Reports 2016, 6, 31582. 28.

Duncum, S. N.; Edwards, A. R.; Osborne, C. G., Method for inhibiting hydrate

formation. In Google Patents: 1993. 29.

Ree, L. H. S.; Mady, M. F.; Kelland, M. A., N,N-Dimethylhydrazidoacrylamides. Part

3: Improving

Kinetic Hydrate

Inhibitor Performance

Using Polymers

of

N,N-

Dimethylhydrazidomethacrylamide. Energy & Fuels 2015, 29, (12), 7923-7930. 30.

Villano, L. D.; Kommedal, R.; Fijten, M. W. M.; Schubert, U. S.; Hoogenboom, R.;

Kelland, M. A., A Study of the Kinetic Hydrate Inhibitor Performance and Seawater Biodegradability of a Series of Poly(2-alkyl-2-oxazoline)s. Energy & Fuels 2009, 23, (7), 3665-3673. 31.

Reyes, F. T.; Malins, E. L.; Becer, C. R.; Kelland, M. A., Non-Amide Kinetic Hydrate

Inhibitors: Performance of a Series of Polymers of Isopropenyloxazoline on Structure II Gas Hydrates. Energy & Fuels 2013, 27, (6), 3154-3160. 32.

Abrahamsen, E.; Magnusson, C.; Kelland, M. A.; Cely, A.; Kinnari, K.; Li, X.;

Askvik, K. M. In As Green As It Gets! – A Natural Product Kinetic Hydrate Inhibitor, 9th International Conference on Gas Hydrates, Denver, Colorado, 25-30 June, 2017; Denver, Colorado, 2017 (poster presentation). 33.

Magnusson, C. D.; Kelland, M. A., Nonpolymeric Kinetic Hydrate Inhibitors:

Alkylated Ethyleneamine Oxides. Energy & Fuels 2015, 29, (10), 6347-6354. 34.

Lone, A.; Kelland, M. A., Exploring Kinetic Hydrate Inhibitor Test Methods and

Conditions Using a Multicell Steel Rocker Rig. Energy & Fuels 2013, 27, (5), 2536-2547. 35.

Kelland, M. A.; Reyes, F. T.; Trovik, K. W., Tris(dialkylamino)cyclopropenium

chlorides: Tetrahydrofuran hydrate crystal growth inhibition and synergism with


Energy & Fuels 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

polyvinylcaprolactam as gas hydrate kinetic inhibitor. Chemical Engineering Science 2013, 93, 423-428. 36.

Arjmandi, M.; Tohidi, B.; Danesh, A.; Todd, A. C., Is subcooling the right driving

force for testing low-dosage hydrate inhibitors? Chemical Engineering Science 2005, 60, (5), 1313-1321. 37.

Kelland, M. A.; Mønig, K.; Iversen, J. E.; Lekvam, K., Feasibility study for the use of

kinetic hydrate inhibitors in deep-water drilling fluids. Energy and Fuels 2008, 22, (4), 24052410. 38.

Peytavy, J. L.; Glénat, P.; Bourg, P. In Kinetic hydrate inhibitors - Sensitivity towards

pressure and corrosion inhibitors, International Petroleum Technology Conference 2007, IPTC 2007, 2007; 2007; pp 328-335. 39.

Svartaas, T. M.; Kelland, M. A.; Dybvik, L., Experiments Related to the Performance

of Gas Hydrate Kinetic Inhibitors. Annals of the New York Academy of Sciences 2000, 912, (1), 744-752. 40.

Walpole, R. E., Probability & statistics for engineers & scientists. 9th ed. ed.;

Pearson: Boston, Mass, 2012. 41.

Carver, T. J.; Drew, M. G. B.; Rodger, P. M., Characterisation of the {111} growth

planes of a type II gas hydrate and study of the mechanism of kinetic inhibition by poly(vinylpyrrolidone). Journal of the Chemical Society, Faraday Transactions 1996, 92, (24), 5029-5033. 42.

Manteghian, M.; Mousavi Safavi, S. M.; Mohammadi, A., The equilibrium conditions,

hydrate formation and dissociation rate and storage capacity of ethylene hydrate in presence of 1,4-dioxane. Chemical Engineering Journal 2013, 217, (Supplement C), 379-384.


Page 28 of 29

Page 29 of 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

43.

Jager, M. D.; de Deugd, R. M.; Peters, C. J.; de Swaan Arons, J.; Sloan, E. D.,

Experimental determination and modeling of structure II hydrates in mixtures of methane+water+1,4-dioxane. Fluid Phase Equilibria 1999, 165, (2), 209-223. 44.

Trueba, A. T.; Rovetto, L. J.; Florusse, L. J.; Kroon, M. C.; Peters, C. J., Phase

equilibrium measurements of structure II clathrate hydrates of hydrogen with various promoters. Fluid Phase Equilibria 2011, 307, (1), 6-10. 45.

Chua,

P.

C.;

Poly(vinylalkanamide)s

Kelland, as

M.

Kinetic

A.;

Ajiro,

Hydrate

H.;

Sugihara,

Inhibitors:

F.;

Comparison

Akashi, of

M.,

Poly(N-

vinylisobutyramide) with Poly(N-isopropylacrylamide). Energy & Fuels 2013, 27, (1), 183188. 46.

Abrahamsen, E.; Kelland, M. A., Carbamate Polymers as Kinetic Hydrate Inhibitors.

Energy & Fuels 2016, 30, (10), 8134-8140. 47.

Gómez Gualdrón, D. A.; Aparicio-Martínez, S.; Balbuena, P. B., Computational

Studies of Structure and Dynamics of Clathrate Inhibitor Monomers in Solution. Industrial & Engineering Chemistry Research 2007, 46, (1), 131-142. 48.

Colle, K. S.; Costello, C. A.; Talley, L. D.; Oelfke, R. H.; Berluche, E., Method for

inhibiting hydrate formation. In Google Patents: 1996. 49.

Rodger, P. M. In Hydrate Nucleation and Inhibition: New Methods for Deeper

Understanding, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), 2011; 2011. 50.

Jokandan, E. F.; Naeiji, P.; Varaminian, F., The synergism of the binary and ternary

solutions of polyethylene glycol, polyacrylamide and Hydroxyethyl cellulose to methane hydrate kinetic inhibitor. Journal of Natural Gas Science and Engineering 2016, 29, 15-20.


Comparison of Kinetic Hydrate Inhibitor Performance on Structure I

Recommend Documents