Inhibition and promotion effects of modified HECs and modified starches on the growth rate of hydrate in methane-propane-water system

This paper investigates the potential of modified hydroxyethyl celluloses (HECs) and modified starches as novel inhibitors and promoters in hydrate formation with methane-propane gas mixture. A series of modified HECs and modified starches were synthesized by graft copolymerization and functionalization techniques. The effects of the HEC, starch, and synthesized products in the concentration range of 0.10 to 0.50 wt% were examined on the growth rate of hydrate crystals. Native HEC, starch, and all grafted copolymers which were synthesized by ceric ammonium nitrate and ammonium persulfate (modified HECs 1 and 2 and modified starches 1 and 2) showed inhibition effects. Interestingly, the modified HEC and modified starch which were produced by graft copolymerization of acrylamide on HEC and starch in the presence of a mixture of ammonium persulfate and sodium bisulfite (modified HEC 3 and modified starch 3), and also the functionalized products (modified HEC 4 and modified starch 4) showed kinetic promoting behavior for methane-propane hydrate formation. In this regard, functionalized products were good promoters such that the hydrate growth rate could be enhanced, even to 3 times higher than pure water. In addition, surface tension and zeta potential measurements showed the more adsorption of modified structures on hydrate crystals can lead to better performance of some modified products. The experimental results also indicated that some products can be applied for the development of new promoters in gas hydrate applications.