A Study of Natural Proteins and Partially Hydrolyzed Derivatives as Green Kinetic Hydrate Inhibitors

One of the first ideas explored for kinetic hydrate inhibitors (KHIs) for oil industry applications came from observing that some animals contain antifreeze proteins (AFPs) that protect them from fatal ice crystal formation at subzero temperatures. However, AFPs, or ice-structuring proteins, are designed to prevent ice formation not hydrate formation. Therefore, although several AFPs are known to show some KHI activity, it is possible that other proteins or peptides may be even more effective as KHIs. We have now tested a range of readily available natural protein-based products from animal and plant sources as green KHIs, as well as an AFP that is used to make ice cream smoother. Experiments on nearly all of these products were conducted in a high-pressure titanium autoclave and also in steel rocking cells on a Structure II-forming gas mixture. The AFP gave the best performance, although this is at least in part due to some thermodynamic inhibition from salts and other chemicals present in the sample. Some of the protein-based products (peptones and tryptones) were more effective as KHIs than poly(N-vinylpyrrolidone). The performance ranking was correlated to the molecular weight range and the ratio of amino acid monomer units. Finally, we have attempted to tailor-make short water-soluble peptide KHIs with exact structures and only 2 or 3 amino acid residues based on our knowledge that polymer side chains with small alkyl groups give good KHI performance. The promising results suggest that bespoke polypeptide KHIs may be a route to higher performing KHIs than those discovered so far.