supercriticalextract超臨界-wenkub
2023-05-22 18:13:59 本頁面
【正文】 e la Tour in 1822. ? He noted visually that the gasliquid boundary disappeared when the temperature of certain materials was increased by heating each of them in a closed glass container. ? From these early experiments, the critical point of a substance was first discovered. Historical ? The first workers have been done to demonstrate the solvating power of supercritical fluids for solids in 1879. ? In 1970 a significant development in supercritical fluid extraction(SFE), provided incentive for extensive future work, which involved decaffeination of green coffee with CO2. Historical coffee Historical ? Since 1980, there has been rapid development of SFE for the extraction of ? (1) hops。 ? (5) unsaturated fatty acids from fish oils. Hops(啤酒花 ) unsaturated fatty acids Properties of supercritical fluids ? A supercritical fluid is any substance above its critical temperature and critical pressure. In the supercritical area there is only one stateofthefluid and it possesses both gas and liquidlike properties. Phase diagram（ PT） Properties of supercritical fluids Properties gas SCF liquid 1bar， 15～ 30℃ Tc， Pc Tc， 4Pc 15～ 30℃ density/(g/mL) (~2) 103 ~ ~ ~ viscocity/ [g/(cm﹒s)] (1~3) 104 (1~3) 104 (3~9) 104 (~3) 102 diffusion coefficient /(cm2/s) ~ 103 103 (~3) 105 Properties of supercritical fluids ? A supercritical fluid exhibits physicochemical properties intermediate between those of liquids and gases. Characterisitics of a supercritical fluid are : ? Dense gas ? Solubilities approaching liquid phase ? Diffusivities approaching gas phase. 1 密度 類似液體，因而溶劑化能力很強(qiáng)，壓力和溫度微小變化可導(dǎo)致其密度顯著變化 2 粘度 接近于氣體 ,具有很強(qiáng)傳遞性能和運動速度 3 擴(kuò)散系數(shù) 比氣體小，但比液體高一到兩個數(shù)量級； 4 SCF的 介電常數(shù)，極化率和分子行為 與氣液兩相均有著明顯的差別 。 3）超臨界流體近氣體的性質(zhì)，使得超臨界流體的傳質(zhì)速率大于普通溶劑。超臨界流體的近氣體性質(zhì)，使得萃取的傳質(zhì)過程可以快速完成。 2）有優(yōu)良的傳質(zhì)性能，擴(kuò)散系數(shù)大，粘度低 3）與其它用作超臨界流體的溶劑相比， CO2具有相對較低的臨界壓力和臨界溫度，適合于處理某些熱敏性生物制品和天然物產(chǎn)品。臨界溫度相同的萃取劑，與被萃取溶質(zhì)化學(xué)性質(zhì)越相似，溶解能力越大。 ②從操作角度看，使用超臨界流體為萃取劑時的操作
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