Performance of Poly(N-isopropylacrylamide)-Based Kinetic Hydrate Inhibitors for Nucleation and Growth of Natural Gas Hydrates

Abstract

Hydrate prevention strategies for offshore flowlines are now moving toward hydrate risk management by delaying its nucleation and growth using water-soluble polymers, known as kinetic hydrate inhibitors (KHIs). This study investigates the natural gas hydrate inhibition performance of three poly(N-isopropylacrylamide) (PNIPAM)-based KHIs [poly(Nisopropylacrylamide-co-acrylic acid (PNIPAM-co-AA), poly(N-isopropylacrylamide-co-cyclopentylamine (PNIPAM-co-Cp), and poly(N-isopropylacrylamide-co-tert-butylamine (PNIPAM-co-C 4 t)] by determining the hydrate onset time, growth rate, and resistance to flow using a high-pressure autoclave. These data are compared to three control groups [water, Luvicap solution, and polyvinylpyrrolidone (PVP)] under various cooling rates (0.25, 0.033, and 0.017 K/min). The results show that the nucleation of hydrate crystals was delayed in the presence of the KHI candidates as assessed using the onset time at different cooling rates. The effect of the KHI candidate on the hydrate growth characteristics was also studied by determining the initial growth rate and torque changes with an increasing hydrate fraction in the liquid phase. The obtained results confirmed that the synthesized PNIPAM-based KHIs showed a high subcooling temperature, which is comparable to those of commercial KHIs. The modification of the base polymer (PNIPAM-co-AA) improves the kinetic inhibition performance for PNIPAM-co-Cp (13.9, 12.5, and 7.8 K for 0.25, 0.033, and 0.017 K/min cooling rates, respectively) but results in decreased performance for PNIPAM-co-C 4 t (9.6, 9.9, and 7.6 K for 0.25, 0.033, and 0.017 K/min cooling rates, respectively). After the hydrate onset, PNIPAM-co-C 4 t showed a slower growth rate and more stable torque during the hydrate formation than PNIPAM-co-Cp, suggesting its potential role as a crystal growth inhibitor. These results suggest that the performance of PNIPAM-based KHIs can be evaluated with the holistic investigation on nucleation and growth of hydrate crystals.

Kinetic Hydrate Inhibition Performance of Poly(vinyl caprolactam) Modified with Corrosion Inhibitor Groups

“…They do not prevent hydrate formation, as with thermodynamic hydrate inhibitors but instead of completely avoiding its formation. They are water-soluble polymers consisting of a hydrophobic backbone with pendant groups, which can interfere with the nucleation site of hydrate crystals. , There have been extensive studies to develop new KHIs which have typically been benchmarked against the early discovered homo- and copolymers of N -vinylcaprolactam (VCap), N -vinylpyrrolidone (VP), − and N -isopropylacrylamide (NIPAM). − Employing KHIs in the field lowers the risk of hydrate formation with relatively simple infrastructure due to its low dosage rate, which reduces the operational cost and the footprint in offshore platforms. To date, the performance of KHIs has been evaluated by measuring the subcooling temperature, which represents the temperature difference between the theoretical hydrate equilibrium temperature and the measured hydrate formation temperature at the corresponding pressure.…”

“…Varying the cooling rate of hydrocarbon fluids may affect the performance of KHIs as it changes the driving force for hydrate nucleation and growth. Our previous work presented the advanced test methodology to evaluate the performance of newly developed KHIs based on PNIPAM- co -AA by measuring the hydrate onset time and resistance-to-flow at various cooling rates . The primary objective of this study was to evaluate newly designed KHIs that carry corrosion groups using an advanced testing methodology, where the KHIs were designed to inhibit hydrate formation as well as corrosion of steel pipelines.…”

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

“…The advantages of the route to make acrylamido-based KHI polymers from poly­(acrylic acid) (PAA) include the simple two-stage synthesis procedure, the cheap starting material, and the fixed similar molecular weights of all the acrylamido products, thereby dismissing the molecular weight as an issue, and as a result, we can then better compare the functional groups. 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. ,− …”

Investigation on Methane Hydrate Formation in Water-based Drilling Fluid

“…THIs, such as methanol and ethylene glycol, are a kind of widely used hydrate inhibitor which prevent the hydrate formation by shifting the phase boundary of gas hydrates out of the prevailing conditions in the pipelines. − LDHIs are used in a much lower concentration which primarily takes effect by reducing the growth of hydrate particles. In specific, some LDHIs called kinetic hydrate inhibitors (KHIs) prolong the nucleation time of hydrate formation, and some prevent the agglomeration of hydrate particles, named antiagglomerants (AAs). − They do not change the thermodynamic conditions of hydrate formation. The addition of THIs is effective, but 20–50 wt % of the THIs are generally required.…”