Liquefaction of bio-mass in hot-compressed water for the production of phenolic compounds

Direct liquefaction of lignocellulosic wastes (sawdust and cornstalks) and two model bio-mass compounds (pure lignin and pure cellulose as references) has been conducted in hot-compressed water at temperatures from 250 to 350 °C in the presence of 2 MPa H2, for the production of phenolic compounds that may be suitable for the production of green phenol–formaldehyde resins. The liquefaction operations at 250 °C for 60 min produced the desirable product of phenolic/neutral oil at a yield of about 53, 32, 32 and 17 wt.% for lignin, sawdust, cornstalk and cellulose, respectively. The yield of phenolic/neutral oil for each feedstock was found to decrease with increasing temperature. As evidenced by GC–MS measurements, significant quantities of phenolic compounds such as 2-methoxy-phenol, 4-ethyl-2-methoxy-phenol, and 2,6-dimethoxy-phenol, were present in the resulting phenolic/neutral oils from the two lignocellulosic wastes and pure lignin. The relative concentration of phenolic compounds in the lignin-derived oil was as high as about 80%. As expected, the liquid products from cellulose contained essentially carboxylic acids and neutral compounds. Addition of Ba(OH)2 and Rb2CO3 catalysts were found to significantly increase both phenolic/neutral oil and gas yields for all feedstocks except for lignin.