Abstract:

The characteristics of sub- and supercritical extraction of wood with ethanol or ethanol-water were studied in a semi-continuous experimental apparatus using the non-isothermal dynamic extraction technique,the effects of pressure and water on the sub- and supercritical extraction of wood with ethanol were mainly investigated.The results showed that the main extraction process of wood could be classified as two phases roughly,the temperature range in the first phase was from 200℃ to 280℃,and the extract formation rate had the maximum value at about 250℃.The temperature range in the second phase was from 280℃ to 380℃,and the extract formation rate had the maximum value at about 350℃,a great quantity of gas was generated in this phase simultaneously.Wood conversion and extract yield increased and gas yield decreased with the increasing of pressure and the molar fraction of water in ethanol-water mixture.The effect of pressure mainly reflected after 250℃,and the effect of water mainly reflected before 300℃.From an engineering standpoint,the sub- and supercritical extraction technology could be suited to the different conversion ways of wood resources through regulating and controlling process variables such as temperature,pressure and the molar fraction of water in ethanol-water mixture.

Key words: Wood, Subcritical extraction, Supercritical extraction, Ethanol, Water