Evaluation of a Novel Water-Immiscible Kinetic Hydrate Inhibitor Formulation

Abstract

The application of low dosage kinetic hydrate inhibitors (KHIs) for hydrate mitigation in hydrocarbon production operations can offer considerable practical benefits and cost savings. However, there are still concerns over KHI usage, particularly with respect to fouling problems in produced water handling/disposal. One possible solution to fouling is KHI polymer removal from produced waters by solvent extraction, with fatty alcohols showing particular promise for this purpose, these having a high affinity for common KHI polymers, but very limited miscibility with water. In this study, it is demonstrated that such solvents can also be used to create novel water-immiscible KHI formulations, with these offering potential for KHI recycling/reuse. The fatty alcohol 1-octanol has been successfully used as carrier solvent for PVCap to produce a KHI, which is immiscible with water, yet shows comparable hydrate inhibition performance to aqueous PVCap. Evaluation of this immiscible KHI using a crystal growth inhibition method shows that it can work well in various systems, including for dry/lean gases, with highly saline waters, and even in the presence of liquid hydrocarbons, despite strong dilution by these.

Solvent Synergists for Improved Kinetic Hydrate Inhibitor Performance of Poly(N-vinylcaprolactam)

“…For this reason, we did not test 1-octanol, also with eight carbon atoms, which has similar poor water solubility. It has been proposed as a solvent for removal and recovery of KHI polymers, such as PVCap …”

“…It has been proposed as a solvent for removal and recovery of KHI polymers, such as PVCap. 36 The next part of the study on solvent synergists for PVCap concerned cyclic alcohols. Figure 7 shows the synergist results for a series of cyclic alcohols, also summarized in Table 2.…”

“…Another research group has used 1-octanol as a water-immiscible carrier solvent for PVCap, to aid recycling of the polymer. This alcohol showed comparable hydrate inhibition performance to aqueous PVCap, i.e., no synergy . Another study using vinyl-lactam-based polymers and various solvent synergists showed that a lower interfacial tension corresponded to a longer onset time, i.e., a better kinetic inhibition performance .…”

“…This alcohol showed comparable hydrate inhibition performance to aqueous PVCap, i.e., no synergy. 36 Another study using vinyl-lactam-based polymers and various solvent synergists showed that a lower interfacial tension corresponded to a longer onset time, i.e., a better kinetic inhibition performance. 37 They suggested the lowest gas/liquid interfacial tension rule for developing amide class KHIs or KHI synergists as well as determining their suitable applied dosages.…”

Further Investigation of Solvent Synergists for Improved Performance of Poly(N-vinylcaprolactam)-Based Kinetic Hydrate Inhibitors

“…The PVCap polymer might partition to this phase and be less active in the water phase where hydrate formation first occurs, thus giving poorer performance. The effect can be considered similar to the addition of medium-size organic carboxylic acids such as pentanoic and hexanoic acid or 1-octanol, which have been found to be effective at displacing KHI polymers such as PVCap from produced water. , This indicates the importance of finding the right concentration in order to not under- or overinhibit the system.…”