| The formation of natural gas hydrate continues to be a serious, billion dollar/year problem for the oil and gas industry. Traditionally, the "thermodynamic inhibitors" (such as methanol and ethylene glycol) have been widely used to address this problem, however, these chemicals are costly and environmentally unfriendly. Recently developed synthetic kinetic inhibitors and anti-agglomerants can retard the nucleation or the growth of clathrate hydrate crystals at low dosage, but the mechanism of inhibition by these inhibitors is not understood clearly.; Antifreeze proteins (AFPs) have the ability to adsorb to ice crystals and depress the noncolligative freezing point of a solution below its melting point. In this thesis, the effect of AFPs (Type I fish AFP from winter flounder and insect AFP from spruce budworm) on water structures using differential scanning calorimetry and Raman spectroscopy showed that AFPs have stronger interaction with water than a control protein, bovine serum albumin. Because hydrates have a water lattice, AFPs might also associate with clathrate hydrates. The inhibition activities of AFPs on the formation and reformation of tetrahydrofuran (THF) hydrate were evaluated by measuring the induction time and by observing the crystal morphology. AFPs showed higher inhibition activities compared with a known kinetic inhibitor, polyvinylpyrrolidone. At 0.05mM wfAFP and CfAFP increased the average lag time for THF hydrate formation by 4-fold and 6-fold, respectively. AFP also showed inhibition activities toward gas hydrates (propane hydrate and methane hydrate). With 0.25mM wfAFP, the average lag time for propane hydrate formation was increased by 3-fold and the gas consumption rate was decreased by 5-fold. With 0.05mM wfAFP, the average conversion rate from aqueous solution to methane hydrate was decreased by 2-fold. As well as the inhibition acitivities, for both THF hydrate and propane hydrate, AFPs prevented the faster reformation of the hydrates (the "memory effect"). The inhibition mechanism was studied with respect to the status of water around AFP molecules, nucleation inhibition and adsorption kinetics. The understanding of these mechanisms, as well as the study on the influencing factors, have provided useful information to direct the development of new, superior hydrate inhibitors. |
