超臨界二酸化炭素を用いた高含水率木材の高速脱水処理

摘要

This paper reports on a novel use of supercritical carbon dioxide for super-rapid dewatering of water-saturated wood and green wood. In this treatment, sugi (Cryptomeria japonica D. Don) heartwood of high moisture content was simply incubated in supercritical carbon dioxide (120°C /17MPa) for 20 min until the pressure was quickly released to atmospheric pressure. It was found that the moisture contents of the specimens were reached to about 1/2-1/4 of the initial values after this treatment. It is supposed that a large amount of supercritical carbon dioxide was penetrated and diffused in free water within wood in a short period of time, and then free water was immediately driven out of wood because of the release of pressure to gasify carbon dioxide. Furthermore, it was found that this dewatering treatment was also effective to improve the water permeability of the specimens. This may be caused by the effects of supercritical carbon dioxide in removing the occluding substances from bordered pits and/or lumens of tracheids.%1．はじめに 　環境や人体に有害な有機溶媒の代替として利用されている環境調和型溶媒の一つに超臨界二酸化炭素（臨界温度：31．3℃，臨界圧力：7．3MPa）がある。超臨界二酸化炭素は気体並の拡散浸透力と液体並の溶解力を有しており1），コーヒー豆のカフェイン抽出溶媒やビールのホップエキス抽出溶媒として既に用いられている2）・3）。毒性が低く，化学的にも安定で，値段が安いことに加え，利用後の回収・再利用も容易であり，環境負荷の低い溶媒として，食品分野以外においてもその用途が広まりつつある。