Anomalous KHI-Induced dissociation of gas hydrates inside the hydrate stability zone: Experimental observations &amp; potential mechanisms

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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“…2 of 11 In this regard, kinetic hydrate inhibitors (KHIs) play an inhibition role at a lower dosage by retarding crystal formation and particle growth in ways that limit bulk [8][9][10][11]. Recently, KHIs were reported to cause anomalous hydrate dissociation inside the hydrate stability zone [12]. This provides flow assurance of the produced oil and gas, for which reason KHIs are applied in the field more often than THIs, although gas hydrate can still form in the pipelines under hydrate-forming conditions.…”

Section: Introductionmentioning

confidence: 99%

Anti-Agglomeration Effects of Biodegradable Surfactants from Natural Sources on Natural Gas Hydrate Formation

Kang

Lee

2020

Energies

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Kinetic hydrate inhibitors (KHI) and anti-agglomerants (AA) rather than thermodynamic hydrate inhibitors (THI) are often used for flow assurance in pipelines. This is because they require much lower dosages than thermodynamic inhibitors. Although the hydrate-phase equilibria are not affected, KHI and AA prevent the formed hydrate crystals from growing to a bulky state causing pipeline blockage. However, these KHIs might have huge environmental impact due to leakages from the pipelines. In this study, two biodegradable AA candidates from natural sources (that is, lecithin and lanolin) are proposed and their performances are evaluated by comparing them with and without a conventional AA (Span 80, sorbitan monooleate). At 30% and 50% water cut, the addition of AA materials was found to enhance the flow characteristics substantially in pipelines and hardly affected the maximum value of the rotational torque, respectively. Considering the cost-effective and environmental advantages of the suggested AA candidates over a conventional AA such as Span 80, the materials are thought to have potential viability for practical operation of oil and gas pipelines. However, additional investigations will be done to clarify the optimum amounts and the action mechanisms of the suggested AAs.

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“…An uninterrupted gas flow is essential to maintain efficiency in natural gas pipelines and other processing plants. − Usually, both the hydrocarbon gas and water are present in the fluids produced and transported. − Hydrate plugs can easily form at low temperatures (<293 K) and high pressures (>4 MPa) with diverse water/gas ratios. − Hydrate plugs can obstruct the pipelines, which can eventually lead to pipeline failure. , A conducive hydrate-forming environment is present in permafrost and the continental shelf regions. Offshore flowlines often operate in these regions and thus are prone to plugging due to hydrate formation. ,,,, The removal of hydrate plugs, if formed, from pipelines is inefficient and time-consuming. ,, Substantial damage to machinery can happen, especially when hydrate plugs are propelled due to significant pressure difference, creating a major safety and environmental hazard . Hence, to safeguard the cost-efficient working of pipelines, hydrate plug accumulation must be effectively prevented. − The most effective solution for hydrate plug inhibition is the use of hydrate inhibitors. − …”

Section: Introductionmentioning

confidence: 99%

“…KHIs are conventionally polymers or macromers that are soluble in water that decelerate the rate of hydrate nucleation − and further the crystal growth. , The primary monetary incentive of KHIs, especially in the offshore facilities, is the massive cutback on the CAPEX due to the decrease in storage size and pumping facilities . They also have the additional advantage of being more fire-proof and more environmentally friendly than THIs.…”

Section: Introductionmentioning

confidence: 99%

Review of Kinetic Hydrate Inhibitors Based on Cyclic Amides and Effect of Various Synergists

Singh

Suri

2021

Energy Fuels

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This Review presents a comprehensive literature review of an important class of kinetic hydrate inhibitors (KHIs) that is based on cyclic amides (lactams). The major aspects of the KHIs, such as their synthesis, inhibition mechanism, toxicity, biodegradability, performance, and cloud point, are thoroughly discussed. Data for 70 KHIs made of homo/co/terpolymers from 330 experiments are collected and evaluated for performance. The effects of the inhibitor concentration, molecular weight, monomer ratio of the co/terpolymers, and 35 different synergist chemicals on various KHIs are also studied. In conclusion, the top 10 KHIs with the highest performances that had a cloud point above 70 °C are presented. The copolymer (1:1) N-vinylpyrrolidone/N-vinyl-caprolactam (VP/VCap) is found to have the highest induction time (IT) of 13 to 14 h at 0.25 wt % and at a cooling rate of 1 °C/h. Some KHIs like Inhibex BIO-800 and poly(N-vinyl azacyclooctanone) (PVACO) also have a very high ITs (17 and 13.5 h, respectively) at 0.25 wt % and at a cooling rate of 1 °C/h, but they have low cloud points (<25 °C). Guanidinium salts (n-Bu6GuanCl/n-Bu6GuanBr) and a phosphonium salt, (n-Pe)4PBr, are found to be the best synergists for the cyclic-amide-based KHIs. When used at 0.15 to 0.30 wt % along with the KHIs, they further increase the IT by 3–5 h.

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Anomalous KHI-Induced dissociation of gas hydrates inside the hydrate stability zone: Experimental observations & potential mechanisms

Cited by 29 publications

References 17 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

Anti-Agglomeration Effects of Biodegradable Surfactants from Natural Sources on Natural Gas Hydrate Formation

Review of Kinetic Hydrate Inhibitors Based on Cyclic Amides and Effect of Various Synergists

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