Kinetic studies of gas hydrate formation using in situ particle size analysis and Raman spectroscopy

In this study, actual particle size measurements were combined with Raman spectroscopy analysis to investigate the kinetics of hydrate formation from various natural gas hydrate formers. Experimental data on gas hydrates formation from methane, ethane, propane, and an equimolar ethane-propane mixture were collected with a semi-batch stirred isothermal-isobaric reactor that incorporates an in situ particle size analyzer and a Raman spectrometer. The particle size analyzer used is a LasentecRTM FBRM (focused beam reflectance measurement) probe capable of measuring particle chord lengths down to 0.5 microm.;Raman spectroscopy was used to identify the structure in which the gas hydrate former exists during the hydrate formation experiment to ensure that the reported intrinsic rate constant of each gas hydrate former correspond to the right hydrate structure.;The intrinsic rate constant for ethane hydrate formation in structure II hydrate was found to be significantly smaller than that in structure I. The kinetic model successfully captured the intrinsic nature of the hydrate growth phenomenon.;A procedure was developed to use the focused beam reflectance measurement (FBRM) probe to obtain satisfactory particle size measurements of the hydrate particles. Since the experimental measurements were made on the particle sizes and their distribution, the need to make assumptions with regard to initial nuclei size and particle size distribution during hydrate growth was eliminated for modelling the experimental data. The working equations used by Englezos et al. (1987a) were modified to incorporate the particle size measurement information in order to extract the intrinsic kinetic rate constant for hydrate growth by regressing the experimental data. The intrinsic kinetic rate constants for hydrate formation of methane gas in structure I, ethane gas in structure I, and propane gas in structure II were determined. Then, an equimolar mixture of ethane and propane gases was used where the experimental data and the a priori determined rate constant for hydrate formation of propane in structure II were used to extract the intrinsic rate constant of gas hydrate formation for ethane in structure II.