PURPOSE: To obtain the aimed compound in high yield by distilling a raw material to give concentrated fraction having aimed ingredient and non-aimed ingredient at a specific ratio, feeding the concentrated fraction to two-stage melt crystallizers, circulating a filtrate in the latter stage to the former stage and simultaneously keeping concentration of the aimed compound to a specific value or above.
CONSTITUTION: A raw material reduced in 3,4-dimethylphenol (3,4-DMH) or 3,5-DMH is distilled so as to afford a concentrated DMH fraction having ≥35wt.% aimed DMH concentration and non-aimed DMH concentration U expressed by the formula [x is aimed DMH concentration (%) in concentrated DMH fraction; P is aimed DMH concentration (%) in liquid at crystallization temperature obtained from solid solution equilibrium diagram] and the concentrated DMH fraction is fed through lines 1 and 4 to a crystallizer 5 in previous stage. The aimed DMH crystal is separated by a separator 6 and a part of filtrate is circulated and the crystal is dissolved and fed to a crystallizer 15 in latter stage. The solution is similarly treated and a part of filtrate is fed to the crystallizer 5 in previous stage and the remainder is fed to the crystallizer 15 in latter stage and the aimed product is obtained in a tank 2. When the aimed DMH concentration in concentrated DMH fraction is ≥70wt.%, the concentrated DMH fraction is directly fed to the latter stage 15.
TABATA KOJI
KASHITANI TOSHIHIKO
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