Researches On Supercritical Ethylene Hydrated Extraction And Its Mathematical Model

Supercritical hydrated extraction that integrated hydrate separation with supercritical fluid extraction is an innovative separation technology for aqueous solution, and its theoretical foundation is that the theory of hydrate formation kinetics and that of supercritical fluid extraction.Though the domestic and overseas scholars have carried out many researches on these two fields at present, there were limited reports on hydrate formation kinetics under supercritical /near-critical conditions and mechanism of influences of hydrate formation on supercritical fluid extraction. On the basis of prophase studies in this laboratory , we in-depth researched the fundamental theory of supercritical hydrated extraction and its mathematical model.The kinetic experiments of ethylene hydrate formation under supercritical conditions were set down in methanol aqueous solution of different concentration, and the experiments also were supercritical hydrated extraction experiments.The hydrate formation kinetics behaviors under supercritical conditions were discussed in the paper. Under the supercritical conditions, the pressure declined firstly but abruptly quick increased during the beginning stage in the P-t curve ,and the temperature significantly rised and descended time after time in the T-t curve, ethylene hydrate secondary nucleation was overt.The influences of pressure, temperature and concentration on hydrate formation behavior under supercritical conditions were analyzed in the paper.The pressure increasing and temperature descending accelerated hydrates formation. Methanol is the thermodynamic inhibitors, and there was obvious inhibition on hydrate formation when the concentration of methanol aqueous solution was over 10.0 wt %.Along with hydrate formation, the influences of pressure,temperature and time on the methanol extraction rate under supercritical conditions were analyzed in the paper.Under supercritical conditions, pressure and temperature affected on supercritical ethylene fluid density and methanol mass transfer properties, so the result caused methanol extraction rate changing. Extraction time impacted surely the extraction process to some extent, and mass transfer rate could be impacted directly by extraction time. The mutual influence between hydrate formation process and supercritical fluid extraction process was inspected in the paper. Under supercritical conditions, the hydrate crystal constantly formed, enhancing the concentration of methanol solution and accelerating methanol extraction.Meanwhile,solid hydrate gradually covered gas-liquid interface, hampering the solute mass transfer and methanol extraction. In supercritical fluid extraction process, the pressure and temperature were major influence factors on hydrate formation ,and hydrate formation rate was fast under high pressure and low temperature conditions, generating a large amount of hydrate. There was large-scale temperature changing, and ethylene hydrate secondary nucleation phenomena was obvious.The hydrate formation kinetics model and supercritical fluid extraction mathematical model were established under supercritical conditions in the paper, and the two models were coupled and validation. But there was gap between calculations and experimental, so further ameliorative word was request.