A Simple and Direct Route to High-Performance Acrylamido-Based Kinetic Gas Hydrate Inhibitors from Poly(acrylic acid)

Qian Zhang,Malcolm A Kelland,Lilian S Ree

doi:10.1021/acs.energyfuels.0c00726

Qian Zhang, Malcolm A Kelland + Show 1 more

Open Access

https://doi.org/10.1021/acs.energyfuels.0c00726

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Abstract

(Meth)acrylamido-based polymers are used commercially in kinetic hydrate inhibitor formulations to prevent gas hydrate formation in upstream oil and gas flow lines. The monomers used to make these polymers are relatively expensive. We have now synthesized a series of acrylamido-based polymers directly from low molecular weight poly(acrylic acid) (PAA) in a high-yield process, avoiding the use of expensive monomers. Cloud points of the polymers made from PAA were similar to the homopolymers made from the acrylamido monomers, indicating a good conversion from the acid to the amide group. Slow constant-cooling KHI screening tests were carried out on the new polymers in a series of steel rocking cells using a structure II-forming natural gas mixture. Poly(N-isopropylacrylamide), poly(N-(n-propyl) acrylamide), and polyacryloylpyrrolidine prepared directly from PAA all gave an excellent KHI performance, comparable to the homopolymers made from the acrylamido monomers. This direct synthesis method also allows for a very controlled comparison of the activity of the acrylamido functional groups because every polymer can be derived from the same PAA starting material. Thus, the number of monomer units in each homopolymer is kept constant. Conversion of the poly(methacrylic acid) or poly(methyl methacrylate) by the reaction with amines to give the methacrylamido polymers was not successful, probably due to the steric effect of the backbone methyl groups.

Highlights

The gas-hydrate plugging of flow lines is considered one of the most serious production issues when developing subsea oil and gas fields, especially in deep water and/or in cold climates.[1]
The other direct route to acrylamido-based kinetic hydrate inhibitors (KHIs) polymers that we looked for in the open literature uses poly(acrylic acid) (PAA) as the starting material
We focused on the acrylamido polymers with isopropyl, n-propyl, and pyrrolidinyl groups in this study, as those are the ones known to have the best KHI effect.[16,32−34]

Summary

INTRODUCTION

The gas-hydrate plugging of flow lines is considered one of the most serious production issues when developing subsea oil and gas fields, especially in deep water and/or in cold climates.[1]. We did not find any reports of a single-stage synthesis with good yield, but we did come across a 2-stage route that proceeds via the polyacid alkylammonium salt (Figure 2).[22] This method is reported to give PNIPAM in good yield with a high conversion rate and short reaction times using low molecular weight PAA This is of particular interest because low molecular weight is good for KHI performance. We report the synthesis of PNIPAM, PNnPAM, and PAPYD from PAA and the amines isopropylamine, npropylamine, and pyrrolidine, respectively These polymers showed a very good KHI performance in high-pressure rock cell tests on a thermodynamically stable sII hydrate-forming system

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ REFERENCES