Capture and recovery of quinoline bases from methylnaphthalene oil were examined using a semicontinuous supercritical CO2 extraction apparatus equipped with the fixed bed of supported aluminum sulfate as a solid acid adsorbent; A model methylnaphthalene oil (quinoline and isoquinoline in 1- and 2-methylnaphthalenes) mixed with supercritical CO2 (323 K, 80 atm) was continuously fed over the fixed bed of the adsorbent. The nitrogen compounds were selectively adsorbed on the solid acid, giving purified methylnaphthalenes by the feeding of 120 min. Quinoline and isoquinoline started to elute by 140 and 180 min, respectively, with the composition at the outlet gradually approaching to the initial one by 220 min. After the feeding was stopped and then the adsorbent was washed with supercritical CO2 at 353 K for 25 min, the adsorbed nitrogen compounds were effectively recovered by mixing a small amount of tetrahydrofuran (THF) as an entrainer to the supercritical CO2 to regenerate the adsorbent at the same time. The adsorbent was confirmed to be repeatedly used by the above adsorption/desorption cycle, with purified methylnaphthalenes and concentrated quinoline bases being alternatively recovered at the adsorption/desorption steps, respectively.