6‑Ring Piperidine-Based Polymers with Both Upper and Lower Critical Solution Temperatures as Kinetic Hydrate Inhibitors

Kinetic hydrate inhibitors (KHIs) are a chemical method of preventing gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation giving a high performance is one or more water-soluble amphiphilic polymers. Many of these polymers exhibit a cloud point or lower critical solution temperature (LCST) in water, which can cause fouling problems if the polymer solution is above this temperature. A few polymers exhibit an upper critical solution temperature (UCST) such that the polymer is soluble only above this temperature. This could be advantageous for use as a KHI to avoid fouling issues at high temperatures, but only if the UCST was below the minimum temperature encountered by the hydrate-forming fluids. Here, we report the first study of a KHI polymer with a UCST in aqueous solution, poly(N-acryloyl-nipecotamide) (PNANAm). It gave a good KHI performance at 2500 ppm when screened using the slow constant cooling (1.0 °C/h) test method in high-pressure rocking cells with a synthetic natural gas blend, lowering the average hydrate onset temperature by 5.3 °C relative to tests with no additive. The related polymers poly(N-acryloylpiperidine) (PAPip) and poly(N-acryloyl-N,N-diethylnipecotamide) (PNADNAm) lowered the hydrate onset temperature by about 1 °C more, probably due to the increased hydrophobicity of the amphiphilic side groups.