Study of the Kinetic Hydrate Inhibitor Performance of Poly(N-vinylcaprolactam) and poly(N-isopropylmethacrylamide) with Varying End Caps

Abstract

Poly­(N-vinylcaprolactam) (PVCap) is an effective kinetic hydrate inhibitor (KHI) that has been widely used in both industry applications and laboratory studies. Industrially, organic peroxides are often used as the N-vinylcaprolactam (VCap) polymerization initiator. In our own past studies, we usually make PVCap by polymerizing VCap with azoisobutyronitrile (AIBN), giving a 2-cyanoprop-2-yl polymer end cap. In this study, VCap was polymerized with AIBN and a series of mercaptocarboxylic acid chain transfer agents (CTAs) to modify the end groups of PVCap. These end-group-modified PVCaps were investigated as KHIs in high-pressure rocking cells. Some of them showed better KHI performance than PVCap made with AIBN alone. The mercaptoacetic-acid-group-modified PVCap (PVCapSCH2COOH) had significantly better inhibition performance than normal PVCap on both structure I (sI) and structure II (sII) gas-hydrate-forming systems in aqueous solution as well as a sII hydrate-forming system containing added decane. However, the most powerful sII gas hydrate inhibitor among these end-group-modified PVCaps in this study was found to be the mercaptosuccinic-acid-group-modified PVCap [PVCapSCH­(COOH)­CH2COOH]. For example, in slow constant cooling tests at 76 bar with the sII gas-hydrate-forming gas mixture, 2500 ppm of PVCapSCH­(COOH)­CH2COOH in deionized water gave the first detectable hydrate formation at an average temperature [T o(av)] of 8.5 °C. In contrast, PVCap made with AIBN alone gave a statistically significant and higher T o(av) value of 9.7 °C. In contrast, 4-mercaptobenzoic-acid-group-modified PVCap (PVCapSC6H4COOH) in deionized water increased the T o(av) value to 10.5 °C. We also introduced the mercaptoacetic acid and mercaptosuccinic acid groups into poly­(N-isopropylmethacrylamide) (PNIPMAA) polymers, again using AIBN as an initiator. Both of the end-group-modified PNIPMAAs gave superior KHI performance than PNIPMAA made using AIBN alone.

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

“…The initial step is to mix the desired monomer to be polymerized with four to five times its weight with a solvent. , The solvents generally used are organic solvents like propanol, , ethanol, dioxane, ,,− or dimethylformamide. − Subsequently, 1–20 wt % of the radical initiator is added. The radical initiator in most cases is 2,2′-azobis (2-methylpropionitrile) (AIBN). ,,,− After that, because the presence of oxygen is detrimental to the reaction, , the system is degassed and sealed under the protection of nitrogen. , Procedures like the freeze–pump–thaw method , or a high vacuum line are used for the degassing process. The freeze–pump–thaw method is more efficient; , however, a high vacuum line is commonly used because of its simplicity. , The reaction mixture is then vigorously stirred at 800–1000 rpm, ,, preferably using a magnetic stirrer at high temperatures between 60 and 80 °C for 16–20 h − for the monomer molecules to polymerize.…”

“…Many co/terpolymers have been synthesized using different macromonomers of alkyl pyrrolidone, alcohol, acetamide, , acrylate, imidazol, imidazolium bromide, acrylamide, thioglycolic acid, succinic acid, dodecanoic acid, hexadeconic acid, and benzoic acid . The structures of these macromonomer groups are shown in Figure .…”

“…Many co/terpolymers have been synthesized using different macromonomers of alkyl pyrrolidone, 176 alcohol, 93 acetamide, 61,118 acrylate, 177 imidazol, 86 imidazolium bromide, 86 acrylamide, 169 thioglycolic acid, 103 succinic acid, 103 dodecanoic acid, 103 hexadeconic acid, 103 and benzoic acid. 103 The structures of these macromonomer groups are shown in Figure 31. Table 22 shows the performance of these co/terpolymers at various concentra- tions, monomer ratios, and molecular weights and with a synergist.…”

Effect of the Ethylene Vinyl Acetate Copolymer on the Induction of Cyclopentane Hydrate in a Water-in-Waxy Oil Emulsion System

“…Gas hydrate, a type of cage-like crystal structure constructed by water and gas molecules, is generally formed in a low-temperature and high-pressure environment. − The gas molecules, such as methane, ethane, carbon dioxide, and so forth, − are able to be enveloped by the cages of water molecules, forming structure I, II, and H hydrate. − The formation of hydrate becomes a challenge in the development of deep-water fields, where the oil or gas is exposed to the environment of high pressure, low temperature, and water cuts. , Therefore, hydrate forms more easily in the deep water environment and increases the risk of plugging pipelines. − Webb et al studied the effect of water fraction in a water-in-dodecane emulsion on the rheological behavior of a hydrate slurry via a high-pressure rheology apparatus. The results show that the viscosity of the hydrate slurry increases apparently with the increase of water fraction from 5 to 30%.…”

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

“…The thermodynamic properties of natural gas hydrates depend on the size of the pores as well as the chemical composition of host sediments. The rate of formation of hydrate can be increased or decreased by the addition of different chemicals which can act as inhibitor [14,15] or promoter during the formation of hydrates [16]. A wide variety of methods have been introduced for the recovery of natural gas from gas hydrates, including depressurization, inhibitor injection, thermal stimulation, CO 2 sequestration [17], and CO 2 -CH 4 exchange [18,13].…”