Process for filtering polyamide oligomers from aqueous streams containing the same

A filter element surface is coated with particulate polyamide which serves as a filter aid to trap polyamide oligomers suspended in water. The particulate polyamide is preferably coated onto a surface of a bag filter so that polyamide oligomers flowing through the coated bag filter surface will adhere to the polyamide particles forming an oligomer cake thereon which encapsulates the polyamide particles. Momentarily equalling the pressure differential across, or reversing flow through, the coated bag filter surface (i.e., back-pulsing) will cause the oligomer cake and polyamide particles encapsulated thereby to break into relatively large-sized solid aggregate particles which may be easily recovered. Since the polyamide particles which are encapsulated by the oligomer cake are chemically compatible with one another, the entire particulate aggregate may be subjected to depolymerization processing so as to recover monomers from which the polyamide is formed (e.g., caprolactam). Filter coating and back-pulsing may be automated using a programmable controller and flow control valves.