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

Abstract

Poly(N-vinylcaprolactam) (PVCap) and related copolymers have been used as kinetic hydrate inhibitors (KHIs) for over 25 years to combat gas hydrate formation in oil and gas field production flow lines. The caprolactam groups in this polymer class have been shown previously to have a particularly strong interaction with hydrate surfaces, inhibiting crystal growth but probably also gas hydrate nucleation. We report here a study on an alternate class of copolymers with pendant caprolactam groups from the 2-methacrylamido-caprolactam (2-MACap) monomer. KHI experiments were carried out in high pressure steel rocking cells using a structure-II-forming natural gas mixture. The KHI performance of some of these copolymers exceeded that of PVCap of similar molecular weight, with further performance enhancement provided by solvent synergists.

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.…”

“…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.…”

Gas Hydrate and Corrosion Inhibition Performance of the Newly Synthesized Polyurethanes: Potential Dual Function Inhibitors

“…Gas hydrates represent nonstoichiometric compounds in which gas molecules stabilize the hydrogen-bonded network of water molecules through van der Waals forces at low temperature and high pressure conditions. − These compounds can block the flow in pipelines, which results in a severe economic loss and even leads to an explosion. Usually, inorganic salts, alcohols, and glycols as thermodynamic hydrate inhibitors (THIs) and water-soluble polymers as low-dosage hydrate inhibitors (LDHIs) are used in flow assurance to prevent formation of gas hydrate within pipelines and wellheads. − High concentrations of THIs alter the water activity which shifts the gas hydrate thermodynamic stability toward higher pressures and lower temperatures . LDHIs can be divided into anti-agglomerants (AAs) and kinetic hydrate inhibitors (KHIs).…”

“…LDHIs offer inhibitory activity at much lower concentrations than THIs (usually less than 2 wt %). Most of the KHIs are water-soluble polymers that do not affect the thermodynamic conditions of hydrate formation, but they interfere with the nucleation process and the growth of hydrate crystals. ,, Vinyl lactam-based polymers and copolymers, acrylamide-based polymers, and hyperbranched polyesteramides are the most well-known KHIs that have been used successfully in field applications. , Poly­( N- alkylacrylamide)­s, polyamine oxides, polyvinylaminals, polyvinylsulfonamides, ionic liquids, amino acids, waterborne polymers, proteins, pectin, and chitosan are some of the chemical classes that have been reported as KHIs in recent years. − The main role of AAs is to disperse formed hydrate particles in the hydrocarbon fluid. Phosphonium and quaternary ammonium compounds containing two or more n -butyl, n -pentyl, or isopentyl groups are common commercial AAs. , Corrosion is another major economic problem in the oil and gas industry.…”

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

“…But they increase operating costs dramatically and require particular infrastructure such as storage tanks and recovery equipment . In recent years, the use of low-dosage hydrate inhibitors (LDHIs) has been widely studied to overcome the environmental, economic, and handling issues. ,, Kinetic hydrate inhibitors (KHIs) and antiagglomerants (AAs) are two classes of LDHIs. ,,, KHIs directly affect the hydrate formation kinetics by delaying the nucleation process and/or slowing the growth of hydrate crystals. − AAs may have no kinetic effect, but they manage the size of hydrate particles to inhibit their agglomeration. ,, The phosphonium and quaternary ammonium surfactants as commercial AAs contain two or more n -butyl, n -pentyl, or isopentyl groups. The hydrophobic tail is the most important parameter for AA performance, which alters the hydrophilic–lipophilic balance and interfacial adsorption of surfactant .…”