Co2 Hydrate Conversion From Microscopic Ice Powder Under Low Pressure And Low Temperature

The conversion rate of CO2 hydrate from microscopic ice powder was analyzed through the use of a laboratory experiment and numerical models. In the experiment, fine ice powder, the mean diameter of which was 5.2 mu m, was generated by means of an ultrasonic mist generator aimed at enhancing the formation rate under the constraint of the relatively low pressure and low temperature of 0.7 MPa and 253 K, respectively. The ice-to-hydrate conversion degree was obtained as a time variation through the measurement of the mass of the synthesized product of CO2 hydrate and the remaining ice at different timings. In the numerical part, a fugacity-driven formation model incorporated with a shrinking-core model was applied to a single spherical ice particle. The coefficient of the CO2 diffusion in the hydrate membrane was treated as an unknown parameter and was determined by the fitting of the model to the experimental results. The estimated diffusion coefficient was comparable with that proposed in the literature. It was also found that the conversion degree became no greater than about 60%. A possible explanation is the decrease of the CO2 supply due to shrinking of the inter-particle pores. This inter-particle effect was modeled to represent the drastic reduction of the formation rate.