Cyclohexanone is typically produced by the oxidation of cyclohexane, or the hydrogenation of phenol. These methods may also generate various contaminants that are difficult to separate from the desired products, and that can render the cyclohexanone product substandard or unusable to downstream processes, for example in the manufacture of caprolactam or adipic acid. Thus, certain treatment means have been described to remove those contaminants from cyclohexanone.
The production of phenol from cyclohexylbenzene is an emerging technology, interesting in that it co-produces cyclohexanone, rather than acetone. Cyclohexylbenzene may be produced, for example, by direct alkylation of benzene with cyclohexene, or as disclosed in U.S. Pat. No. 6,037,513, by contacting benzene with hydrogen in the presence of a catalyst. The cyclohexylbenzene may then be oxidized to the corresponding hydroperoxide and the hydroperoxide cleaved to phenol and cyclohexanone using a catalyst.
The production of phenol and cyclohexanone from cyclohexylbenzene also produces various contaminants that are difficult to separate from the desired products. However, the nature of those contaminants and the separations thereof are significantly different from those in the conventional Hock process for the production of phenol and acetone, and/or the conventional cyclohexanone production from cyclohexane or phenol. For example, hydroalkylation of benzene produces significant amounts of, among others, cyclohexane and lesser amounts of methylcyclopentane, cyclohexene, phenylcyclohexene, and phenylcyclohexyldiene. Similarly, the oxidation of cyclohexylbenzene typically produces peroxide species alien to the Hock process, such as the desired cyclohexyl-1-phenyl-1-hydroperoxide (CHBHP), and undesired byproduct hydroperoxides such as cyclohexyl-1-phenyl-2-hydroperoxide, cyclohexyl-1-phenyl-3-hydroperoxide and cyclohexyl-1-phenyl-4-hydroperoxide. The cleavage of these various hydroperoxides produces a wide variety of contaminant species which are not produced by the chemistry and technology of either the Hock process, the cyclohexane oxidation process, or the phenol hydrogenation process.
Caprolactam is an important industrial material for making nylon-6, a widely used polymer material. The purity of caprolactam has significant impact on the quality such as strength of nylon-6 made therefrom. Caprolactam can be made from cyclohexanone via the following Route-1:

In the various industrial processes for making cyclohexanone, methylcyclopentanone may be produced as a contaminant. Even at a very small amount, such as on the level of several ppm, methylcyclopentanone, by undergoing similar reactions to those of cyclohexanone in reaction Route-1 above, may lead to the formation of highly undesirable contaminants, particularly methylvalerolactam having one or more of the following formulae:

Methylvalerolactam is very difficult to remove from caprolactam. During further reaction of caprolactam to produce nylon-6 via reaction Route-2 below:
the various isomers of methylvalerolactam, shown above, by polymerization with each other and/or with caprolactam, may significantly reduce the quality and performance of the nylon-6 product, even if at a low concentration.
As such, there is a strong need of producing a cyclohexanone product with very low methylcyclopentanone concentration. Due to the very close boiling points of cyclohexanone (156° C. at 101 kPa), 2-methylcyclopentanone (140° C. at 101 kPa) and 3-methylcyclopentanone (145° C. at 101 kPa), separation of a physical mixture of cyclohexanone and methylcyclopentanone using traditional fractionation to purify cyclohexanone is quite difficult, especially if the concentration of methylcyclopentanone in the final cyclohexanone product is desired to be as low as several ppm by weight. Usually, this would entail the use of complicated, costly, and high maintenance equipment and processes such as one of more of (i) high vacuum inside the column; (ii) fractionation column with high number of distillation trays and/or a high reflux ratio; and (iii) multiple fractionation columns in a series to achieve the desired level of separation.