| Abstract: | 本研究採用半流動式相平衡實驗裝置來進行超臨界二氧化碳流體萃取實驗，為了證明本研究相平衡數據之準確性與可靠性，首先以萘(naphthalene)在超臨界二氧化碳流體中之溶解度作為測試系統，並與文獻值作比較，誤差值在4 %以內，與文獻值十分吻合。另外以二氧化碳作為萃取溶劑，分別量測廿烷酸(eicosanoic acid)與麥角固醇(ergosterol)在超臨界狀態下的平衡溶解度，廿烷酸之量測溫度為308.15 K、318.15 K與328.15 K，而麥角固醇之量測溫度則為318.15 K、323.15 K與333.15 K，壓力在119 bar至275 bar之間。 實驗結果顯示，廿烷酸在超臨界二氧化碳流體中之溶解度範圍在莫耳分率1.9×10-5 ~ 3.4×10-4間，而麥角固醇之溶解度略比廿烷酸低十倍，其溶解度範圍在莫耳分率2.9×10-6 ~ 3.0×10-5間。當系統定溫下升壓時，溶質的溶解度會隨壓力上升而增加，同時發現兩溶質於超臨界二氧化碳流體中之溶解度均有交錯現象發生，廿烷酸之交錯壓力在 150~180 bar之間，麥角固醇之交錯壓力在 130~170 bar間。 本研究將實驗所獲得之廿烷酸與麥角固醇的溶解度數據，分別以Chrastil、Schmitt-Reid、Giddings 及Santiago-Teja等半經驗關聯式進行關聯，各關聯式所獲得之最大平均相對誤差為8.5 %，其中廿烷酸與麥角固醇以Giddings關聯模式所獲得之誤差為最小，其誤差分別為4.8 %與4.2 %。 另一方面本研究亦使用Peng-Robinson狀態方程式，配合單一與雙交互作用參數之凡德瓦混合律，同時將昇華壓係數視為可調參數來關聯廿烷酸與麥角固醇在超臨界二氧化碳流體中之溶解度，結果則顯示使用雙參數之凡德瓦混合律對二系統之溶解度迴歸之趨勢較佳，廿烷酸與麥角固醇之平均相對誤差分別為7.7 % 與10.0 %。
In this work, a semi-flow type phase equilibrium apparatus was employed in a supercritical carbon dioxide extraction experiment. In order to ensure the accuracy and reliability of the measurements, the experimental apparatus was first tested by measuring the solubility of naphthalene in supercritical carbon dioxide, and the measured solubility data were compared with the literature data within 4 %. A good agreement between them was found. In addition, equilibrium solubility measurements were carried out at 318.15, 328.15, and 338.15 K and 318.15, 323.15, and 333.15 K in the pressure range from 119 bar to 275 bar for eicosanoic acid and ergosterol, respectively, using carbon dioxide as the supercritical extraction solvent. The experimental results showed that the observed eicosanoic acid solubilities were higher than those of ergosterol by one order of magnitude. Specifically, the solubilities of eicosanoic acid in terms of mole fraction are in the range of 1.9?10-5 - 3.4?10-4, while those of ergosterol are between 2.9?10-6 and 3.0?10-5. At constant temperature, it was found that the solubilities of both solutes increased with pressure. For eicosanoic acid, the crossover pressures appeared in the 150-180 bar region at the measured temperatures. On the other hand, the crossover region for ergosterol under the given experimental conditions was in the range of 130-170 bar. The measured solubility data of eicosanoic acid and ergosterol were correlated using four semi-empirical models including the Chrastil, Schmitt-Reid, Giddings, and Santiago-Teja equations. Experimental data and calculated results based on the four semi-empirical equations were in satisfactory agreement with a maximum average absolute relative deviation percentage (AARD) of about 8.5 %. The Giddings model resulted in the smallest deviations of 4.8 % and 4.2 % in correlating solubilities data for eicosanoic acid and ergosterol, respectively. Also, the Peng-Robinson equation of state using one-parameter and two-parameter van der Waals mixing rules was used to correlate the experimental solubilities data. Solute sublimation pressures were treated as adjustable parameters in regressing the data. The results showed that the Peng-Robinson equation of state with the two-parameter van der Waals mixing rule gave a better agreement with average deviations of 7.7 % for eicosanoic acid and 10.0 % for ergosterol. |
