Abstract: A process and an apparatus therefor are described for separating p-xylene from a p-xylene containing hydrocarbon liquid feed material by crystallization, said process comprising (1) mixing a p-xylene containing hydrocarbon feed material with an inert liquid refrigerant, (2) feeding the mixed liquid into a lower part of a bubble tower type crystallization tower as an ascending current, (3) evaporating the refrigerant by the lowering of the liquid static pressure caused by ascent of the mixed liquid and by the transfer of heat into the refrigerant due to solidification of p-xylene and by the lowering of the temperature of the mixed liquid, cooling the ascending liquid to form a slurry of p-xylene crystals in the hydrocarbon liquid, (4) separating the inert refrigerant as a vapor from the liquid surface of the upper part of the crystallization zone, and (5) separating p-xylene crystals from the slurry discharged from the upper part of the crystallization zone.