Patent ID: 8106240

Claim:
A process for operating a (A) continuous removal of a target product X in the form of crystals of the target product X from a liquid phase P which consists of the target product X and of constituents B i other than the target product X and whose total mole fraction of the constituents B i has a value M B tot , the process comprising: (a1) conducting a stream of the liquid phase P and, as a constituent thereof, a mass flow {dot over (m)} X of the target product X into a secondary chamber of an indirect heat transferrer comprising the secondary chamber and at least one primary chamber, in which the secondary chamber and the at least one primary chamber are each separated spatially from one another by at least one material dividing wall which serves as a surface for transfer of heat out of the secondary chamber into the at least one primary chamber; (a2) simultaneously flowing at least one fluid cooling medium through the at least one primary chamber wherein the at least one fluid cooling medium is fed to the at least one primary chamber with a temperature T K in , such that the crystals of the target product X are formed from the liquid phase P in the secondary chamber to form a suspension S comprising the crystals of the target product X and a liquid residual phase R in which the crystals of the target product X are suspended, said liquid residual phase R, compared to the liquid phase P, comprising the constituents other than the target product X in enriched form and having a content of the target product X of at least 70% by weight, and said suspension S having a degree of crystallization Y of the crystals of the target product X in the liquid residual phase R; and (a3) continuously conducting a stream of the suspension S out of the secondary chamber of the heat transferrer, wherein the heat transferrer cools the suspension S under different operating states I and II: (I) the at least one fluid cooling medium with a temperature T K in (I) is fed to the at least one primary chamber, and the stream of liquid phase P with a mass flow {dot over (m)} X (II) of the target product X is fed to the secondary chamber, and (II) the at least one fluid cooling medium with a temperature T K in (II) is fed to the at least one primary chamber, and the stream of liquid phase P with a mass flow {dot over (m)} X (II) of the target product X is fed to the secondary chamber, with the proviso that {dot over (m)} X (II)>{dot over (m)} X (I) and T K in (II)<T K in (I), wherein a total mole fraction M B tot of the constituents B i other than the target product X in the liquid phase P fed to the secondary chamber is greater in operating state II than in operating state I, and wherein the target product X is acrylic acid, methacrylic acid, p-xylene, or N-vinvlpyrrolidone.