Synergistic Hydrate Inhibition by Iota-Carrageenan with Kinetic Hydrate Inhibitors

Abstract

The hydrate-inhibiting performance of a natural plant-based polysaccharide iota-carrageenan is evaluated as a standalone inhibitor and as a synergist with two well-known kinetic hydrate inhibitors (KHIs), polyvinyl caprolactam (PVCap) and polyvinylpyrrolidone (PVP), in order to achieve a higher hydrate inhibition performance. The hydrate inhibiting performance is assessed experimentally by measuring the induction time (IT) required for measurable hydrate formation and by the average hydrate growth rate (HGR) after measurable hydrate formation using a standard constant cooling rate of 1°C/h. Three inhibitor dosages at 0.5 wt% and 1 wt% are tested for the methane hydrate formation at 7.6 MPa and hydrate equilibrium temperature of 10.45°C. Synergy evaluation between the common KHIs and iota-carrageenan is done by making 50:50 ratio blends of iota-carrageenan with PVP and PVCap respectively (half iota-carrageenan and half KHI by wt%) and their performance is compared with the performance of individual PVP and PVCap performance at the same total inhibitor concentration for fair comparison. The individual inhibitor experimental results at 0.5-1 wt% showed that iota-carrageenan has a lower IT (around 4.5-5 h) than PVP (around 5.5-6.3 h) and PVCap (around 6.5-7.1 h), but has a lower average hydrate growth rate (HGR) between 0.07-0.08 m/h compared to PVCap (0.11-0.12 m/h) and PVP (0.13-0.18 m/h). The experimental results for the 50:50 blends of i-crgn with PVP and PVCap at a total concentration of 0.5-1 wt%, showed significant boost in the ITs (8.1-10.2 h for PVP and i-crgn blend) and (8.7-11.2 h for PVCap and i-crgn blend). These values were up 33-57% at the same total concentration of the individual inhibitor and the blend. The blends also have a much lower HGR with values 0.04-0.12 m/h at a total concentration of 0.5-1 wt% which is 16 - 64% lower than the individual HGRs of PVP and PVCap. Hence, iota-carrageenan, a natural, non-toxic, sustainable chemical can be used as hydrate inhibiting synergist additive to PVP and PVCap and other commercial hydrate inhibitors for enhanced hydrate inhibition performance and biodegradability.