Researches On Formation Kinetics Of Supercritical Hydrated Fluid And Supercritical Hydrated Extraction

Hydrated separation technology was based on the fundamental principle of that therewere only water molecule and hydrate former molecule included in the hydrate crystal, andthe contents of hydrate former were different between the crystal and primary mixture. Theapplication of hydrated separation technology could reach some purposes like concentratingdiluted solution, seawater desalination, gas mixtures separation, etc. Moreover, it couldcombine with other separation technologies to form novel ones. Supercritical hydratedextraction that integrated hydrate separation with supercritical fluid extraction was aninnovative coupling separation technology for aqueous solution, its theoretical foundationwas that the theory of hydrate formation/decomposition kinetics and supercritical fluidextraction. Choosing ethylene as supercritical hydrated fluid, the fundamental theory ofsupercritical hydrated extraction was studied in this paper.The 32 kinetic experiments of ethylene hydrate formation in n-propyl alcohol aqueoussolution under both the supercritical and normal conditions (16 experiments of eachcondition) were designed by orthogonal table. The sample of raffinate phase was analyzedby gas chromatography; it was proved that the concentration of n-propyl alcohol wasincreased with hydrate formation process. Besides, 3 kinetics data of ethylene hydrateformation in n-propyl alcohol aqueous solution with high concentration (more than 10wtï¼…)were measured.The hydrate formation kinetic behaviors under different conditions were discussed inthe paper. There was a phenomenon that pressure declined firstly, and then abruptlyincreased during the beginning stage in the P-t curve under the supercritical conditions. Itwas thought that this phenomenon was caused by the temperature of liquid phase increase.The acute dissolution of supercritical ethylene and crystal nuclei formation during the dissolution stage led to temperature increase. While the ethylene formation kinetics curvewas a smooth curve under normal conditions, the stages of gas dissolution, crystal nucleusformation and crystal growth could not be differentiated from each other; there were noinductive effect during the hydrate formation under these conditions. Be aimed at thespecially hydrate formation kinetics behavior of supercritical ethylene in n-propyl alcoholaqueous solution, it was explained by the novel dissolution point which were raised by ourlaboratory; this novel point was propitious to hydrate formation of supercritical liquid.Meanwhile, these special behaviors argument the point further more.The influences of pressure and temperature on ethylene hydrate formation werediscussed. The change of hydrate formation behavior with pressure and temperature wasnot obvious under the supercritical conditions because of the higher impetus. But the trendwas obvious under the normal conditions. The rate of gas dissolution, crystal nucleusformation and crystal growth during hydrate formation was increased with the pressureincreasing. Meanwhile, the hydrate formation rate increased with the decreasing oftemperature. The temperature affected the equilibrium pressure. The lower the temperatureis, the lower the equilibrium pressure.The influence of n-propyl alcohol's concentration on hydrate formation behavior undersupercritical conditions was studied. The n-propyl alcohol is a kind of thermodynamicinhibitor; it has overt inhibitory action on the hydrate formation when its concentration ismore than 10 percent in weight.The influence of supercritical hydrated extraction on organic aqueous solution wasresearched finally. It manifested that the supercritical hydrated extraction increased theconcentration of the raffinate phase, and the degree of enhancement ranged from 1.01 to1.52 fold. The extraction mechanism of supercritical extraction was discussed in the paper.