N,N-Dimethylhydrazidoacrylamides. Part 2: High-Cloud-Point Kinetic Hydrate Inhibitor Copolymers with N- Vinylcaprolactam and Effect of pH on Performance

Abstract

Poly(N,N-dimethylhydrazidoacrylamides)s (PDMHAMs) and a series of copolymers of (N,N-dimethylhydrazidoacrylamide) and (N-isopropylacrylamide) were recently investigated as kinetic hydrate inhibitors (KHIs). Poly(Nvinylcaprolactam) (PVCap) and related copolymers have been used as a class of commercial KHIs in the oil and gas industry to prevent plugging of pipelines with gas hydrates. In this study, we have synthesized and investigated the ability of copolymers of DMHAM monomer and VCap monomer to inhibit structure II gas hydrate formation in high-pressure rocking cells at approximately 75 bar. Various polymer molecular weights have been investigated at various pH conditions. It was found that the novel polymers have high cloud points in deionized (DI) water or brine solutions at high or low pH under pressure compared to polyVCap. A 1:2 copolymer of DMHAM/VCap gave the best KHI performance for this class of copolymer with a cloud point at 50°C in DI water. Also, a 1:1 DMHAM/VCap copolymer gave excellent KHI performance, as well as giving no cloud point up to 100°C in DI water or high-salinity solutions (3.6−15 wt % NaCl) at pH 5.0. The cloud point was found to be 67°C at pH 12.0 for the 15 wt % NaCl solution, making it compatible for use in high-salinity water-based deep-water drilling fluids. It was also found that high pH improved the performance of the KHIs compared to otherwise identical tests at pH 5.0. This may be related to removing the structure I (SI)-forming and relatively more soluble acid gas CO 2 from the system at high pH.

Pectin as an Extraordinary Natural Kinetic Hydrate Inhibitor

“…As a result, kinetic hydrate inhibitors (KHIs), a kind of LDHIs and typically injected 0.5 ~ 2.0 mass% of produced water, have been an alternative solution to prevent gas hydrate formation 7 . Nonetheless, most representative commercial KHIs, such as polymers of N-vinylcaprolactam (PVCap), N-methyl-N-vinylacetamide and 2-alkly-2-oxazoline 8 9 10 , have been limited because of their high-cost and insufficient biodegradation 11 12 . Herein, developing “cheap and green inhibitor” is a wise choice.…”

First investigation of modified poly(2-vinyl-4,4-dimethylazlactone)s as kinetic hydrate inhibitors

“…Thus, poly(dimethylhydrazidoacrylamide) has no cloud point in water as a 1 wt.% aqueous solution at any temperature up to 100°C. This homopolymer or copolymers with NIPMAM or VCap are still very active KHIs with improved cloud points compared to PVCap or PNIPMAM (Mady and Kelland, 2015).…”

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

“…The cloud-point measurements for almost all the KHIs were done using a standard procedure where an aqueous solution of polymer was created mostly with a concentration of 0.25 , or 1 wt % , in some cases. This solution was heated carefully at ∼2 °C/min with constant stirring while under continuous surveillance .…”

“…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 .…”