Interaction of Antifreeze Proteins with Hydrocarbon Hydrates

Abstract

Recombinant antifreeze proteins (AFPs), representing a range of activities with respect to ice growth inhibition, were investigated for their abilities to control the crystal formation and growth of hydrocarbon hydrates. Three different AFPs were compared with two synthetic commercial inhibitors, poly-N-vinylpyrrolidone (PVP) and HIW85281, by using multiple approaches, which included gas uptake, differential scanning calorimetry (DSC) temperature ramping, and DSC isothermal observations. A new method to assess the induction period before heterogeneous nucleation and subsequent hydrate crystal growth was developed and involved the dispersal of water in the pore space of silica gel beads. Although hydrate nucleation is a complex phenomenon, we have shown that it can now be carefully quantified. The presence of AFPs delayed crystallization events and showed hydrate growth inhibition that was superior to that of one of the benchmark commercial inhibitors, PVP. Nucleation and growth inhibition were shown to be independent processes, which indicates a difference in the mechanisms required for these two inhibitory actions. In addition, there was no apparent correlation between the assayed activities of the three AFPs toward hexagonal ice and the cubic structure II (sII) hydrate, which suggests that there are distinctive differences in the protein interactions with the two crystal surfaces.

Recalcitrance of gas hydrate crystals formed in the presence of kinetic hydrate inhibitors

“…For oil field operators, the existence of multiple melting peaks means the elevated stability with chemical inhibitors which renders their use more challenging. Observations in experiments in stirred vessels were consistent with the calorimetric observations showing a two-stage decomposition for hydrate prepared in the presence of chemical inhibitors (Daraboina et al, 2011b;Ohno et al, 2010) and 5 C higher melting temperature compared to hydrate prepared in pure water (Makogon et al, 2000). It should be noted that the experiments reported in (Daraboina et al, 2011b) and (Daraboina et al, 2011a) were done with a methane/ethane/propane mixture and those in (Makogon et al, 2000) with a natural gas mixture.…”

“…The gas hydrate dissociation events were detected by endothermic peaks. The area under these peaks corresponds to the amount of the dissociated hydrates which were formed at the experimental conditions (Ohno et al, 2010). The uncertainty of the measured heat flow is 0.02 mW.…”

The chemistry of low dosage clathrate hydrate inhibitors

“…35 There has been considerable work probing the mechanism of action of AFPs at inhibiting ice growth, reporting a surface adsorption mechanism and the resulting Kelvin effect. 36,37 The mechanism of action for type-I anti-freeze proteins is believed to occur through hydrogen bond formation between four 5 threonine residues with oxygen atoms from the ice lattice.…”

“…When these 5 12 cavities are linked by their vertices the result is structure I hydrate, whilst those with face-sharing 5 12 cavities result in structure II. 24 The difference in linkages allows 35 for the formation of the larger voids within the structure I and structure II cavities (5 12 6 2 and 5 12 6 4 respectively).…”

“…4 In 1934 a pivotal report by Hammerschmidt acted as a catalyst for stimulating research in this area, by confirming that clathrate hydrates are responsible for the plugging of gas and oil pipelines and thereby dramatically increasing industrial 30 investment and research on the topic. 5 Today clathrate hydrates pose a major problem to the oil and gas industry with pipeline blockage causing many safety concerns in addition to requiring the shutdown of the pipeline for a time 35 whilst the plug is removed. This shutdown period results in reduced field site performance and may cause significant financial loss.…”