Inhibition Performance of Chitosan-graft-Polyacrylamide as an Environmentally Friendly and High-Cloud-Point Inhibitor of Nucleation and Growth of Methane Hydrate

Gas hydrates are considered a major problem in the oil and gas transportation pipelines, and their crystallization involves nucleation and growth of hydrate crystals. Hence, developing inhibitors that can affect nucleation and growth of hydrates is essential to inhibit their formation. Acrylamide polymers are well-known hydrate inhibitors, but they show a low cloud point, causing precipitation problems for field applications. In this research, we used chitosan to synthesize chitosan-graft-polyacrylamide (CS-g-PAM) as a green and high-cloud-point kinetic hydrate inhibitor (KHIs). The inhibition performance of CS-g-PAM on nucleation and growth of methane hydrate crystals was assessed by a high-pressure autoclave and high-pressure microdifferential scanning calorimeter (HP-mu DSC). CS-g-PAM showed no cloud point in both deionized water and 3.5 wt % NaCl solutions, up to 100 degrees C. Autoclave experiments demonstrated that CS-g-PAM can increase the hydrate nucleation time 13 times (in 1 wt % sample) compared to the pure water system. According to HP-mu DSC results, by adding 0.1, 0.5, and 1 wt % CS-g-PAM, the onset methane hydrate formation temperature was decreased from -12.7 degrees C in the pure water system to -1.5.8, -17.0, and -19.0 degrees C, respectively. Also, CS-g-PAM can change the morphology of methane hydrate crystals from solid state into a viscous foam-like slurry. These results show that the modification of acrylamide-based KHIs with natural polymers is an attractive option to improve their deposition point and change the morphology of hydrate crystals.