Separation of impurities in a process for hydrolytically depolymerizing a polyamide

A process for separating at least one ε-caprolactam oligomeric compound CPO from a stream SR comprising said at least one CPO and ε-caprolactam monomeric compound CPM, the process comprising

• (i) providing an aqueous liquid stream SR comprising CPM dissolved in water at a concentration cR(CPM), CPM having a boiling point TCPM, wherein SR further comprises the at least one CPO at a concentration cR(CPO), CPO having a boiling point TCPO with TCPO>TCPM;
• (ii) preparing an aqueous liquid mixture ME comprising the stream SR provided according to (i);
• (iii) subjecting the mixture ME according to (i) to evaporation conditions in an evaporation unit E1, obtaining an aqueous vapor stream SV1 and an aqueous liquid stream SL1, wherein SV1 comprises CPM at a concentration cV1(CPM) with cV1(CPM)>cR(CPM), wherein SL1 comprises the at least one CPO at a concentration cL1(CPO) with cL1(CPO)>cR(CPO) and comprises CPM at a concentration cL1(CPM) with cL1(CPM)<cR(CPM);
• (iv) dividing the stream SL1 according to (iii) into a first stream SL11 and a second stream SL12, wherein SL11 and SL12 have the same chemical composition as SL1;
• (v) passing the stream SL12 obtained according to (iv) to a downstream treatment stage;
• wherein preparing the aqueous liquid mixture ME according to (ii) comprises mixing the stream SR with the stream SL11.