supercriticalextract超臨界-展示頁
2025-05-16 18:13本頁面
【正文】 04 (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(yùn)動(dòng)速度 3 擴(kuò)散系數(shù) 比氣體小，但比液體高一到兩個(gè)數(shù)量級(jí)； 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) perfumes and flavors from natural products。Supercritical Fluid Extraction Historical ? The first reported observation of the occurrence of a supercritical phase was made by Baron Cagniard de 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。 ? (2) cholesterol from butter。 ? (4) residual solvents and monomers from polymers。 5 壓力和溫度的變化均可改變相變 由于超臨界流體的自擴(kuò)散系數(shù)大，粘度小，滲透性好，與液體萃取相比，可以很快地完成傳質(zhì)，達(dá)到平衡，促進(jìn)高效分離過程的實(shí)現(xiàn)。 2）在臨界點(diǎn)附近，超臨界流體的溫度或壓力的微小變化會(huì)引起密度的很大變化，使得超臨界流體的溶解度發(fā)生很大變化。 4）超臨界流體接近液體的性質(zhì)，使得超臨界流體具有接近普通溶劑的溶解能力。 利用超臨界流體在不同的密度下溶解度的不同， 控制 對(duì)溶質(zhì)的 溶解 和 釋放 ，從而實(shí)現(xiàn)對(duì)溶質(zhì)的萃取過程。微小的壓力或溫度波動(dòng)可以引起溶解度的較大變化，萃取的循環(huán)過程的能耗相對(duì)較低。 溫度和壓力的關(guān)系 二氧化碳的密度與 此外，超臨界 CO2具有一些特殊的優(yōu)點(diǎn)： 1）無毒，無腐蝕性，不可燃燒，純度高且價(jià)格低。 在超臨界區(qū)內(nèi)，通常將 1 ≤ Tr ≤ ，
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