(56p) Crude Caprolactam Purification Processing

Session: Distillation/Separations

Title: Crude Caprolactam Purification Processing

Authors: Fenil Shah, MS Graduate Student (Texas A&M University – Kingsville), fenilshah017@gmail.com

Dr Matthew Alexander, Associate Professor (Texas A&M University – Kingsville), matthew.alexander@tamuk.edu

Topic Description:

Caprolactam [(CH₂)₅CONH] is an organic compound which is used to produce tire cords, nylon fibers for textile, carpet and industrial yarn. Every year, approximately 5 million tons of caprolactam is produced by the manufacturers. The main method for manufacturing of caprolactam is a reaction between cyclohexanone (Anone) and hydroxylamine sulfate (HAS), followed by Beckmann rearrangement using oleum. Anone can be produced by oxidation of cyclohexane, and HAS can be produced by oxidation of ammonia to nitrous oxide, followed by hydrogenation in the presence of sulphuric acid. The crude caprolactam which is processed from cyclohexanone and HAS has different types of impurities like water, ammonium sulfate, light impurities (cyclohexanone, aniline and benzene) and heavy impurities (valeramide, cyclohexanone oxime and octahydrophenazine). So, crude caprolactam must be purified before it goes under polymerization to give nylon fibers.

This research work focuses on simulation and optimization of a crude caprolactam purification process using the Aspen Plus simulator. This crude caprolactam purification plant consists of six distillation columns, one extraction tower and one stripping tower. Currently, we have a design specification for a crude caprolactam purification plant of 150 metric tons (MT)/day. When the plant load is increased to 180 MT/day multiple problems are observed. During the higher material throughput, problems observed are extraction tower temperature remains lower than desired, quality of separation in extraction tower decreases, distillation column pressure drop across the packing materials increases, and bottom operating temperatures remain high, which deteriorates the quality of the product. This research includes the identification of problems during higher material throughput, and subsequent design of the columns for higher feed flowrates using Aspen Plus. After optimization of crude caprolactam purification plant, the capital cost evaluation is also performed using CAPCOST software.

Keywords: Crude caprolactam, high-purity caprolactam, distillation of caprolactam