Process for the preparation of sump product

In the distillation of a solution comprising an organic substance, and non-volatile material which is precipitated as solid in the distillation, in a thin layer evaporator, comprising the steps of distilling the solution in the thin layer evaporator to evaporate the organic substance as overhead distillate product of the distillation and precipitate the non-volatile material as solids, collecting the precipitated solids as sump products, and adding a solvent which is at a lower temperature than the walls of the evaporator to the sump to take up the precipitated solids and removing the solvent containing the solids from the sump, the improvement which comprises introducing the solvent from outside the evaporator directly into the sump and providing a vapor lock adjacent to and above the level of the introduction of the solvent by injecting a stream of inert vapor through a first spray ring obliquely and upwardly and opposite the direction of the solvent to prevent condensation of distillate vapors by the solvent.