Powerful Synergy of Acetylenic Diol Surfactants with Kinetic Hydrate Inhibitor Polymers—Choosing the Correct Synergist Aqueous Solubility

Malcolm A Kelland,Erik G Dirdal

doi:10.1021/acs.energyfuels.1c02152

Malcolm A Kelland, Erik G Dirdal

Open Access

https://doi.org/10.1021/acs.energyfuels.1c02152

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Abstract

The performance of injected kinetic hydrate inhibitor (KHI) polymer solutions can be boosted considerably by judicious choice of the polymer solvent system. We report the excellent KHI synergism of the low-foaming acetylenic diol gemini surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) with poly(N-vinyl caprolactam), N-vinyl caprolactam:N-vinyl pyrrolidone copolymer, and poly(N-isopropylmethacrylamide). High-pressure rocking cell tests, using the slow constant cooling method or the isothermal method, were carried out with a natural gas mixture giving structure II hydrates as the preferred thermodynamically stable phase. Poly(oxyethylene) derivatives of TMDD, which are far more water-soluble than TMDD, gave significantly lower synergetic KHI performance with the same polymers. It is conjectured that the low aqueous solubility of TMDD (1700 ppm at 20 °C) and its two isobutyl groups are key features contributing to the synergism. However, when decane was added to the system as a model liquid hydrocarbon phase, the synergetic performance decreases, probably due to partitioning of TMDD to the hydrocarbon phase. This highlights the need to choose synergist systems which are retained in the aqueous phase for optimal performance when condensate or oil is present in the produced fluids. Optimizing the structure and aqueous solubility of the synergist (solvent or otherwise) can be seen as complementary to the known principle of optimizing the structure and solubility of the KHI polymer.

Highlights

Gas hydrates are ice-like solids that are formed under conditions of elevated pressure and low temperatures, which are common conditions in gas and oil transportation flow lines.[1−3] These flow lines may be subsea or on land in coldclimate regions
We begin a discussion of the results by looking at the motivation for this study, that is, whether TMDD is a better synergist for kinetic hydrate inhibitor (KHI) polymers than the more water-soluble TMDD-EO10
We believe that the low aqueous solubility of TMDD (1700 ppm at 20 °C) and the presence of two isobutyl groups are key features contributing to the synergism

Summary

INTRODUCTION

Gas hydrates are ice-like solids that are formed under conditions of elevated pressure and low temperatures, which are common conditions in gas and oil transportation flow lines.[1−3] These flow lines may be subsea or on land in coldclimate regions. We proposed that a low polymer cloud point (i.e., near-hydrate-forming temperatures) is a useful property for high KHI performance as long as certain other criteria are met.[18] These included sufficient pendant amphiphilic groups with good hydrogen-bonding (e.g., amide or amine oxide) and correct-size hydrophobic groups. The solubility of TMDD in water is about 0.2 g/L (2000 ppm) at 20 °C which we thought was about the right level for a sparingly soluble KHI polymer synergist.[22] TMDD is made by the reaction of methyl isobutyl ketone with a base and two equivalents of sodium carbide or ethyne.[23] In the process of making TMDD, the intermediate 5-methyl-1-hexyn-3-ol (5MH) is formed Experiments to study the effect of the addition of a liquid hydrocarbon to the KHI test solution were carried out

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

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