removal of water and extractives from softwood with supercritical carbon dioxide
超臨界co2萃取系統(tǒng)分離木片中的水分和提取物
salonika aggarwal, shelly johnson, and marko hakovirta*
department of forest biomaterials, north carolina state university, campus box 8001, raleigh, north carolina 27695, united states
bhima sastri
u.s. department of energy,germantown road, germantown, maryland 20874, united states
sujit banerjee*
school of chemical & biomolecular engineering, georgia tech, atlanta, georgia 30332, united states
abstract:
supercritical co2 (sco2) removes both water and extractives from wood chips and flakes at 60 °c. the water appears to be mostly displaced by sco2 because its nominal concentration in sco2 exceeds its solubility limit. sem imaging and contact angle measurements show no major differences in surface properties between sco2-treated and thermally dried flakes, which suggests that their interaction with resin should be similar. an economic analysis for the removal of water and extractives from pine flakes for the manufacture of oriented strand board shows that sco2 treatment is potentially much more cost-effective than thermal drying from both capital and operational perspectives. the main reasons are that the water is removed by displacement rather than through evaporation, environmental control costs are drastically reduced, and the extractives removed represent a value stream instead of pollutants whose emissions need to be controlled. because the sco2 is largely recirculated, the process is greener than conventional direct dryers that generate co2 from the combustion of wood fines used as a fuel.
超臨界co2(sco2)在60°c時(shí)能去除木屑和木片中的水分和抽出物。由于sco2中的名義濃度超過(guò)其溶解度極限，水似乎大部分被sco2置換。掃描電鏡(sem)成像和接觸角測(cè)量表明，經(jīng)sco2處理的鱗片和經(jīng)熱干燥的鱗片在表面性質(zhì)上沒(méi)有顯著差異，這表明它們與樹(shù)脂的相互作用應(yīng)該是相似的。從生產(chǎn)定向刨花板的松片中除去水和抽出物的經(jīng)濟(jì)分析表明，從資本和操作角度來(lái)看，sco2處理可能比熱干燥更具成本效益。其主要原因是水是通過(guò)置換而不是蒸發(fā)去除的，環(huán)境控制成本大幅度降低，去除的提取物是一種價(jià)值流，而不是需要控制排放的污染物。由于sco2大部分是再循環(huán)的，這一過(guò)程比傳統(tǒng)的直接烘干機(jī)更環(huán)保，后者通過(guò)燃燒用作燃料的木屑產(chǎn)生二氧化碳。