A process for recovering solid reaction products during partial oxidation of hydrocarbons in a liquid solvent as a reaction medium by multi-stage evaporative crystallization includes determining a final temperature of the multi-stage evaporative crystallization based on a melting point of the solvent. The pressure and temperature of the solvent is reduced in steps via successive crystallization stages until the final temperature is reached. Each of the crystallization stages includes a compressor configured to perform the reducing of the pressure and to withdraw vapors formed. The vapors from the compressor of a lower expansion pressure crystallization stage are introduced into a vapor discharge conduit of a next successive higher expansion pressure crystallization stage upstream of the compressor of the higher expansion pressure crystallization stage.