Selection of Commercial Kinetic Hydrate Inhibitors Using a New Crystal Growth Inhibition Approach Highlighting Major Differences Between Them

The use of kinetic hydrate inhibitors (KHIs) is a well-known method for preventing gas hydrate formation in oil and gas production flow lines. The main ingredient in KHI formulations is one or more polymers with amphiphilic groups. Here, we report a series of citramide-based nonpolymeric KHIs. The KHI performance of these citramide derivatives has been studied using a synthetic natural gas mixture (forming structure II hydrate as the thermodynamically preferred phase) in slow constant cooling (ca. 1 °C/h starting from 20.5 °C) high-pressure (76 bar) rocking cell experiments. Isobutyl-substituted alkyl chains in the mono/bis(trialkyl citric acid) amide derivative gave better KHI performance than n -propyl-substituted citramide derivatives. Moreover, biscitramides with six alkylamide functional groups gave better performance than the equivalent monocitramides with three alkylamide groups. A solution of 2500 ppm of bis(tributyl citric acid) amide gave an average gas hydrate onset temperature ( T o ) of 8.4 °C compared to 8.9 °C for a low molecular weight N -vinyl pyrrolidone/ N -vinyl caprolactam 1:1 copolymer. For the bis(tributyl citric acid) amide, addition of liquid hydrocarbon ( n -decane) lowered further the average T o value to 6.2 °C, although this is at least partly due to lowering of the hydrate equilibrium temperature. This study demonstrates that good KHI performance can be obtained from molecules with as little as six amphiphilic alkylamide groups.

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“…There is also evidence that KHIs can totally inhibit hydrate crystal growth up to a certain subcooling level. 7 − 9 …”

Section: Introductionmentioning

confidence: 99%

Nonpolymeric Citramide-Based Kinetic Hydrate Inhibitors: Good Performance with Just Six Alkylamide Groups

Ghosh

Kelland

2022

ACS Omega

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“…This is because the polymer bonding would contribute to the stabilization of the formed hydrates, and consequently, the increase of hydrate dissociation temperature. The CGI method has been successfully applied to quantitatively evaluate the performance of KHI candidates. − An apparent advantage is that it can test KHI performances with the worst-case scenarios under flowing or shut-in conditions when a small fraction of hydrates may already be present …”

Section: Experimental Methods For Evaluation Of Khi Performancementioning

confidence: 99%

“…The most studied class of KHI polymers are those based on N -vinyl lactams. Several studies indicate that both nucleation and crystal growth inhibition mechanisms are operating with this polymer class. ,, In many gas hydrate KHI studies, it is impossible to differentiate between nucleation and crystal growth inhibition. However, there is experimental support for the nucleation inhibition mechanism by water perturbation, where it can be differentiated from mechanisms involving hydrate particle surface adsorption.…”

Section: Khi Mechanisms: Experimental and Computational Evidencementioning

confidence: 99%

Kinetic Hydrate Inhibitor Studies for Gas Hydrate Systems: A Review of Experimental Equipment and Test Methods

2016

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Kinetic hydrate inhibitors (KHIs) have been studied, developed, and used in the oil and gas industries for more than two decades. The main active ingredients in commercial KHI formulations are water-soluble polymers. When dosed at low concentrations (0.1−2.0 wt % active chemical), they are able to retard the gas hydrate formation process and facilitate reliable oil and gas transportation. A considerable amount of research effort on KHI technologies has contributed to an abundance of KHI knowledge, applications, and tailor-made solutions. Whereas previous reviews have concentrated on the chemistry of KHIs, this review article has a particular emphasis on the experimental equipment, hydrate detection tools, and test methods commonly applied in KHI investigations. The underlying mechanisms of KHIs are still not fully understood. The major hypotheses proposed in the literature and supporting experimental and computational evidence are also reviewed.

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“…1 Other complementary methods such as the CGI (crystal growth inhibition) test method can be used, also to better understand the actual field application limitations. [30][31][32][33] The constant cooling test procedure is as follows: 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 1. 20ml of aqueous solution of the test chemical at the desired active polymer concentration is added to each of the steel cells.…”

Section: High Pressure Gas Hydrate Kinetic Hydrate Inhibitor Testsmentioning

confidence: 99%

Acylamide and Amine Oxide Derivatives of Linear and Hyperbranched Polyethylenimine. Part 2: Comparison of Gas Kinetic Hydrate Inhibition Performance

Kelland

Magnusson²,

Lin

et al. 2016

Energy Fuels

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A series of acylamide and amine oxide derivatives of polyethyleneimine, both hyperbranched (HPEI) and linear (LPEI), have been synthesised and their performance as kinetic hydrate inhibitors (KHIs) with a Structure II-forming natural gas mixture investigated in high pressure steel rocking cell experiments. This is the first time the KHI performance of linear and polymers of with the same functional groups have been compared. The importance of quality control in KHI synthesis is also highlighted.In general the amine oxides showed better performance than the acylamides when comparing the structurally-optimised and best polymers from each class. The amine oxide polymers with best KHI performance were the low molecular weight butylated HPEI amine oxides. The performance was similar to those of oligomeric amine oxides reported previously with molecular weights as low as 660 g/mole. This contrasts with other KHI polymer classes where molecular weights below 1000-1500 g/mole generally give poor KHI efficacy. In previous work, the linear LPEI amine oxides were show to be excellent tetrahydrofuran Structure II hydrate crystal growth inhibitors, superior to hyperbranched HPEI derivatives. However, the LPEI amine oxides were poorer gas hydrate KHIs than the HPEI derivatives, suggesting that other mechanisms besides crystal growth inhibition, such as nucleation inhibition, may be the dominant mechanism for this class of KHI.Acyl amide polymers with n-propyl pendant groups performed only a little better than equivalent polymer with iso-propyl groups and far better than polymers with ethyl groups. This trend is in line with a lowering of the cloud points of the polymer as the hydrophobicity increases. Acylamides based on linear LPEI gave better performance than those based on hyperbranched HPEI. The reasons for this are discussed. Linear amine oxides based on LPEI gave lower performance than hyperbranched or oligomeric amine oxides, which may be related to the availability of primary amine groups in HPEI or oligomeric ethyleneamines.

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Selection of Commercial Kinetic Hydrate Inhibitors Using a New Crystal Growth Inhibition Approach Highlighting Major Differences Between Them

Cited by 15 publications

References 9 publications

Nonpolymeric Citramide-Based Kinetic Hydrate Inhibitors: Good Performance with Just Six Alkylamide Groups

Nonpolymeric Citramide-Based Kinetic Hydrate Inhibitors: Good Performance with Just Six Alkylamide Groups

Kinetic Hydrate Inhibitor Studies for Gas Hydrate Systems: A Review of Experimental Equipment and Test Methods

Acylamide and Amine Oxide Derivatives of Linear and Hyperbranched Polyethylenimine. Part 2: Comparison of Gas Kinetic Hydrate Inhibition Performance

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