Designing Kinetic Hydrate Inhibitors—Eight Projects With Only Partial Success, But Some Lessons Learnt

Abstract

In our quest to develop new and improved kinetic hydrate inhibitors (KHIs) for practical use in the oil and gas industry, we have carried out a number of projects that, in our hands, proved ultimately unsuccessful. However, as with most laboratory research projects, useful data has been obtained and some important lessons have been learned. These lessons can be helpful in several ways. First, to understand the scope and limitations of chemicals that could be used as KHIs. Second, to highlight mechanistic aspects of KHI theory. Finally, the work may help inspire others to develop related but more successful research projects. In this article we present the results of eight partially successful KHI research projects and explain why each of these projects was undertaken and the results obtained. Seven of the projects concern new classes of polymers, and the other project describes what we hoped was a new class of nonpolymeric synergists for KHI polymers, but instead gave the opposite effect. All new KHI products were investigated for their performance in high pressure multiple steel rocking cells using a Structure II-forming gas mixture.

Reliability and Performance of Vinyl Lactam-Based Kinetic Hydrate Inhibitor Polymers after Treatment under a Range of Conditions

“…We have previously attempted to partially oxidize PVCap to convert the seven-ring caprolactam to a seven-ring adipimide (Figure 7). 60 We tried a variety of oxidizing agents, but none were able to accomplish the required oxidation, probably due to steric problems. (We are currently investigating oxidation of the caprolactam ring from the monomer, and we will report on this in a later study.)…”

Synthesis and Investigation of Polymers of 2-Methacrylamido-caprolactam as Kinetic Hydrate Inhibitors

“…Very few studies on polymers (other than VCap-based polymers) containing caprolactam rings as KHIs have been reported. In an earlier attempt in our research group, 2a m i n o c a p r o l a c t a m w a s r e a c t e d w i t h p o l y -(dichlorophosphazene) (PDCP) in order to make poly-(caprolactam-2-amino)phosphazene, which was water-soluble as a homopolymer 21 (Figure 2). This polymer showed some KHI effect, but it had two major drawbacks: First, the water solubility for even ethyl derivative was low; increasing the hydrophobicity (thereby probably increasing the KHI performance) by using pendant propyl groups would have been futile as the polymer became insoluble in water.…”

“…22 The making of these polymers was challenging, and in general the trend was that the longer the pendant alkyl group the more hydrolytically stable was the polymer, with the result of being less water soluble. 21 In one patent a research group reported that caprolactam groups can be attached to amines and polyamines via a Mannich reaction with formaldehyde. 23 In our hands, this reaction does not work and was unofficially confirmed by contact with the patent owners.…”

“…We presume the methacryloyl polymers, with extra methyl groups in the backbone, would also be difficult to make by radical polymerization. 21 In this study, we have synthesized a new class of caprolactam-containing polymers. They are based on 2methacrylamido-caprolactam (Figure 4).…”

Amphiphilic Optimization Enables Polyaspartamides with Effective Kinetic Inhibition of Tetrahydrofuran Hydrate Formation: Structure–Property Relationships

“…Polymers that contain lactam rings or acyclic amide groups in the side chain, such as poly­( N -vinyl caprolactam) (PVCap), poly­(acrylamide) derivatives, and copolymers of PVCap, PVP, and aminopropyl methacrylate (trade name VC713), can slow down the crystal growth rate at the early stages to prevent hydrate blockage in the pipelines . So far, much attention has been paid to the evaluation of certain water-soluble polymers acting as KHIs. − However, most of these inhibitors are not ecofriendly and are unable to meet the strict environmental regulations. Neither the structure–property relationship nor the inhibition mechanism is well-understood.…”