Capture and Recovery of Indole from Methylnaphthalene Oil in a Continuous Supercritical CO2 Extraction Apparatus over a Fixed Bed of Anion-Exchange Resin

Abstract

Capture and recovery of nonbasic aromatic nitrogen compounds such as indole from crude methylnaphthalene oil in coal tar fractions were examined using a continuous supercritical CO2 extraction apparatus with the fixed bed of an anion-exchange resin. A model feed consisting of 10 wt % indole with 10 wt % quinoline in 1-methylnaphthalene and crude methylnaphthalene oil (CMNO) was used for the supercritical CO2 separation procedures. Indole was selectively adsorbed on an anion-exchange resin (Amberlite IRA-904) for the first 120 min, with quinoline and 1-methylnaphthalene being eluted under the supercritical CO2 (323 K, 80 atm) conditions. After the resin was saturated with indole, the feed was stopped and the adsorbed indole was recovered. Preextraction of the resin with supercritical CO2 before the recovery of indole from the adsorbent improved the concentration of recovered indole through the selective elution of quinoline and 1-methylnaphthalene remaining in the dead space in the flow line and fixed bed. Indole in CMNO was also effectively separated by the same procedures as described above. The adsorption and desorption mechanisms of indole are briefly discussed based on the above results.