A Simplified Overall Kinetic Model for Cyclohexanone Oximation by Hydroxylamine Salt

Abstract

Cyclohexanone oxime (ONEOX) is the precursor of ε-caprolactam, a monomer used within the nylon-6 industry. This work studies the production of ONEOX from cyclohexanone (ONE) oximation with hydroxylammonium sulfate (HAS). The reaction involves two liquid phases: HAS is present in the aqueous phase, and ONEOX and ONE are present in the organic phase. The influence of pH, the interfacial area between phases, and the concentration of reagents on the oximation rate have been studied, taking into account the effect of these variables on the proposed model for the overall rate. Oximation runs have been carried out in a batch reactor at low agitation speed to control the interfacial area between phases. The pH ranged from 3 to 5.5, and the temperature was set at 353 or 358 K. The contact model proposed for the two liquid phases was based on the two-film theory, and it was assumed that the oximation reaction takes place in the aqueous film. Because of the low solubility of organic species in the aqueous phase (salting-out effect), the concentration of salts was considered negligible in the organic phase and the concentration of hydroxylamine was assumed to be constant in the aqueous film. The rate expression obtained was first order for ONE and 0.5 for HAS, using a pseudokinetic constant that included the transport coefficient of ONE in the aqueous film, and the pH effect. It was found that this apparent kinetic constant shows a slight increase when the pH is increased within the studied range. The kinetic model proposed predicts well the overall oximation rate under the experimental conditions studied. This model includes quantitatively the influence of the main variables: temperature (353−358 K), pH (3−5), and concentration of reagents.

Linear Amides in Caprolactam from Linear Ketone Impurities in Cyclohexanone Obtained from Cyclohexane: Kinetics and Identification

“…34 As can be seen, the pH has an opposite effect on stages 1 and 2 of the oximation mechanism. As found elsewhere in the cyclohexanone oximation reaction, 30 pH has a slight positive effect on the ONE conversion, which was experimentally confirmed as shown in Figure 2. As seen above, the higher the pH, the higher the cyclohexanone conversion.…”

“…Temperature and pH were kept constant in each reaction. As used elsewhere, 30 an IKA laboratory agitator (RW 20 digital) was used for mixing in these runs in order to obtain a low agitation speed (A w = 100 rpm) that produces a defined interface between both phases. This area corresponds to the transversal section of the batch reactor (S).…”

Green synthesis of benzonitrile using ionic liquid with multiple roles as the recycling agent

“…As for the rst step, it is believed that benzaldoxime is produced through the nucleophilic attack of nitrogen electron pairs in the NH 2 OH to the C]O carbon in the benzaldehyde. 29,30 Free NH 2 OH, 31 resulted from the decomposition of hydroxylamine salt, is the nucleophile necessary for conversion of benzaldehyde to the corresponding benzaldoxime. It was evident that, the aromatic hydrocarbon solvent, such as toluene, ethylbenzene and paraxylene, demonstrated an obvious promotion on the decomposition of hydroxylamine salt to form free NH 2 OH, 32,33 since high benzaldehyde conversions were obtained in these solvents.…”

“…Based on the reported reaction mechanism for aldehyde and hydroxylamine to produce aldehyde oxime, 30,31 followed by benzaldoxime dehydration to benzonitrile, 35,36 a plausible mechanism for the present reaction was proposed and depicted in Scheme 2. Firstly, free NH 2 OH and [HSO 3 -b-Py]$HSO 4 were released by the decomposition of (NH 2 OH) 2 $[HSO 3 -b-Py]$HSO 4 .…”

Biorenewable Strategy for Catalytic ε-Caprolactam Production Using Cellulose- and Hemicellulose-Derived γ-Valerolactone

“…ε-Caprolactam (EC) is primarily used as a precursor for its catalytic ring-opening polymerization to nylon-6. , The global market size of EC was approximately $8–10 billion in 2012, when more than 4.0 million metric tons (Mt) per year were produced and with current market prices of around $2,000–2,500 per Mt . The commercial-scale production process of EC follows a two-step petro-based route. − Cyclohexanone oxime is first produced from benzene-derived cyclohexanone with hydroxylamine sulfate. The oxime is then converted to EC through Beckmann rearrangement with fuming sulfuric acid.…”