Investigation of Solvent Synergists for Improved Kinetic Hydrate Inhibitor Performance of Poly(N-isopropyl methacrylamide)

Abstract

The synergistic effect of a range of solvents on the kinetic hydrate inhibitor (KHI) performance of poly­(N-isopropyl methacrylamide) (PNIPMAm) has been investigated in slow (ca. 1 °C/h) constant cooling high-pressure (76 bar) rocking cell experiments using a structure II forming synthetic natural gas mixture. We have tested the synergistic effects of several monoglycol ethers and compared them to those of corresponding diglycol ethers and alcohols. Compounds containing lactate, carboxylate, ammonium, and pyrrolidone headgroups have also been investigated as synergists. In general the monoglycol ethers were found to function best as synergists with PNIPMAm, and the performance improved going from n-butyl to isobutyl, cyclopentyl, and cyclohexyl alkyl substituents. The best performing synergist in this study was found to be 2-(cyclohexyloxy)­ethanol (CHexGE). Addition of 5000 ppm CHexGE to 2500 ppm PNIPMAm-II (made in isopropyl alcohol and precipitated out, M n = 8100 g/mol) dropped T o from 6.8 °C for pure polymer to the situation where no hydrate formation occurred in 9 out of 10 experiments down to 2 °C, the minimum test temperature and a subcooling of 17.3 °C. PNIPMAm identically made with similar molecular weight and kept in n-butyl glycol ether (nBGE), isobutyl glycol ether (iBGE), and tert-butyl glycol ether (tBGE) reaction solvents gave similar performances as KHIs. The performance of PNIPMAm sometimes varied depending on whether the polymer was made and kept in synergist solvent, or synergist was added to the isolated polymer. For example, nBGE added to pure PNIPMAm performed worse than PNIPMAm made in nBGE, even when the polymer molecular weights were similar. In contrast, PNIPMAm made in iBGE gave a performance similar to that of iBGE added to pure PNIPMAm. The seawater biodegradability according to the 28 day OECD306 test protocol is reported for some of the solvents tested for synergism. In particular, the high flash point solvent n-butyl lactate was found to be readily biodegradable. Combined with a reasonable effect as synergist with PNIPMAm, this makes n-butyl lactate a component to consider when developing more environmentally friendly KHI formulations.

Non-Amide Polymers as Kinetic Hydrate Inhibitors─Maleic Acid/Alkyl Acrylate Copolymers and the Effect of pH on Performance

“…MA precursor polymers were made in DME or xylene. We also knew that nBGE had been used previously to make maleamides from MA copolymers and has been reported to be a good synergist for many KHI series as well as a high-flash-point solvent. − Therefore, we used nBGE for the reaction of diamines and alkanolamines with MA/alkyl (meth)­acrylate copolymers. All maleic-based copolymers made in nBGE have a polymer concentration of 25.8 wt %.…”

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

“…Homo/copolymers of cyclic amides are generally synthesized using conventional free-radical polymerization. ,,, Although any flask can be used as the polymerization reaction vessel, a Schlenk flask is typically used. ,− It has a side arm connected to a gas line that replaces the air (having the reactive oxygen) inside the flask with an inert gas like nitrogen for air-sensitive chemical reactions . The flask is immersed in a water bath and is generally fitted with a reflux condenser.…”

“…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 .…”

“…Polymers based on cyclic amides (lactams) and acrylamide were the first commercially available and used KHIs. ,,− Numerous homo/co/terpolymers of cyclic amides (lactams) and acrylamide have been synthesized and tested for hydrate inhibition over the past two decades by several researchers. Thus a review of these KHIs is inescapable.…”

Dual-Function Synergists Based on Glucose and Sucrose for Gas Hydrate and Corrosion Inhibition

“…The use of synergists provides an effective method for enhancing the inhibition performance of KHIs . Small nonpolymeric compounds, salts, amino acids, solvents, ionic liquids, as well as some polymers are the most common synergists for the KHI formulations. ,− The compatibility issue between hydrate and corrosion inhibitors is another limitation of KHIs . Corrosion is a massive challenge for several industrial applications, especially for oil and gas pipelines .…”