The present invention provides a continuous process for producing ammonium sulfate crystals, wherein said process comprises: (a) feeding to a first group of crystallization sections, which crystallization sections are heat integrated in series, a first aqueous ammonium sulfate solution that contains one or more impurities; (b) feeding to a second group of crystallization sections, which crystallization sections are heat integrated in series, a second aqueous ammonium sulfate solution that contains one or more impurities; (c) crystallizing ammonium sulfate crystals in each crystallization section respectively from each of said solutions of ammonium sulfate that contain one or more impurities; (d) purging a fraction of the ammonium sulfate solution that contains one or more impurities from each of said crystallization sections; and (e) discharging ammonium sulfate crystals from each crystallization section, characterized in that: (i) both the first group of crystallization sections and the second group of crystallization sections are together heat integrated in one series of crystallization sections; wherein the first group of crystallization sections operates at higher temperature than the second group of crystallization sections; and (ii) the composition of the first aqueous ammonium sulfate solution that contains one or more impurities is different to the composition of the second aqueous ammonium sulfate solution that contains one or more impurities. Further provided is apparatus suitable for producing ammonium sulfate crystals.

A process for producing high-purity -caprolactam includes the following steps: (1) cyclohexanone oxime is subjected to a gas phase Beckmann rearrangement reaction; (2) the reaction product obtained from step (1) is successively subjected to gas-liquid separation, solvent removal, and light impurity removal to produce a crude caprolactam; (3) the crude caprolactam is subjected to crystallization to produce a crystallization product and a crystallization mother liquor; (4) the crystallization mother liquor is subjected to crystallization to produce a crystal slurry. At least a part of the crystal slurry is returned to step (2) and/or step (3). The purification process can obtain high-purity caprolactam through only one crystallization and one mother liquor crystallization without reducing the overall yield of caprolactam.

The present invention relates to a process for separating at least one -caprolactam oligomeric compound CPO from a stream S.sub.R comprising said at least one CPO and -caprolactam monomeric compound CPM.

The present invention relates to a process for separating at least one -caprolactam oligomeric compound CPO from a stream S.sub.R comprising said at least one CPO and -caprolactam monomeric compound CPM.

The present invention provides an improved process for the recovery of -caprolactam from Nylon 6 comprising multi-component material, in particular multi-layered film. Further, the invention provides a plant configured to carry out the process of the invention, and the recovered e-caprolactam obtainable by the process of the invention that has a product carbon footprint of less than 2.5 kg CO.sub.2 equivalent per kg purified e-caprolactam (based on data originating from ecoinvent version 3.7.1; location: Europe).

A process for the recovery of -caprolactam from extract water of polycaprolactam obtained by hydrolytic polymerization, wherein the extract water is concentrated, subsequently contained oligomers are depolymerized, non-depolymerizable impurities are separated, water and low-boiling impurities are removed, wherein for adjusting the purity of the recovered -caprolactam and the energy consumption used for the process a part of the product is removed from the process as intermediate products.

A process for the recovery of -caprolactam from extract water of polycaprolactam obtained by hydrolytic polymerization, wherein the extract water is concentrated, subsequently contained oligomers are depolymerized, non-depolymerizable impurities are separated, water and low-boiling impurities are removed, wherein for adjusting the purity of the recovered -caprolactam and the energy consumption used for the process a part of the product is removed from the process as intermediate products.

The present invention provides a process and a plant for recovering purified-caprolactam from polyamide 6 comprising fishing nets, wherein the plant comprises a depolymerization section [B], a recovery section [C], and a purification section [D]. The present invention also provides purified -caprolactam that has a particularly low product carbon footprint and is obtained via depolymerization of polyamide 6 from fishing nets.

The present invention provides a process and a plant for recovering purified-caprolactam from polyamide 6 comprising fishing nets, wherein the plant comprises a depolymerization section [B], a recovery section [C], and a purification section [D]. The present invention also provides purified -caprolactam that has a particularly low product carbon footprint and is obtained via depolymerization of polyamide 6 from fishing nets.

A method for recovering a cation component of a neutralized-salt type ionic liquid, characterized by comprising a first step, in which an aqueous solution of the neutralized-salt type ionic liquid is mixed with a water-incompatible organic solvent to prepare a liquid separating into two phases, i.e., an aqueous phase and an organic phase, a second step, in which the liquid separating into two phases is mixed with a water-soluble strong alkali so that the amount of the strong alkali is 20% by mass or larger with respect to the water contained in the aqueous phase, thereby regenerating the cations of the neutralized-salt type ionic liquid present in the aqueous phase, into a neutral substance and moving the neutral substance from the aqueous phase to the organic phase, and a third step, in which the organic phase containing the neutral substance is recovered by a liquid-separating operation.