A kinetic model to describe the dimer formation (D) in the process of cyclohexanone self-condensation was developed, including different variables such as temperature, catalyst concentration and equilibrium concentrations. Basic catalytic self-condensation of cyclohexanone in the liquid phase was conducted in a batch reactor by using sodium hydroxide as catalyst (C NaOH values from 1.6 to 30.0 mmol/kg). The reaction temperature was varied from 127 to 149 °C; to study the equilibrium conditions, the temperature was varied from 100 to 160 °C. Cyclohexanone conversions up to 80% were reached. Dimers, trimers, and tetramers from consequent-parallel condensation reactions were identified and quantified by gas chromatography/mass spectroscopy (GC/MS). Three dimer species were found: the adduct 1′-hydroxy-[1,1′-bicyclohexyl]-2one (D1) is first formed, and then, this compound is in situ dehydrated, yielding an isomeric mixture of reaction products, namely, 2-(1-cyclohexen-1-l)cyclohexanone (D2) and 2-cyclohexylidencyclohexanone (D3), being D2 the main dimer formed. Under all the tested experimental conditions, trimer and tetramer concentrations were obtained in traces. A lumped specie D was defined as the sum of all dimers. The effect of water on the cyclohexanone conversion and selectivity was also studied. To achieve this, several experiments were conducted at vacuum pressure to remove the formed water and at 10 bar to ensure that all the formed water remains in the reaction media. A remarkable influence of water content on the cyclohexanone conversion profiles was observed. Therefore, it had to be considered in the kinetic model. Reaction enthalpy was experimentally calculated and an endothermic reaction was determined (ΔH r °= 59.2 kJ/mol). The kinetic parameters were estimated by data fitting. The estimated activation energy of D formation was 132.6 kJ/mol. This kinetic model reproduces quite well the experimental results. Moreover, experimental data from other authors in literature can be also reasonably well predicted with the model developed.

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.

α, β and γ-hexachlorocyclohexane (HCH) are persistent and bioaccumulative pollutants and they were included in the Stockholm Convention on Persistent Organic Pollutants (POPs). Old lindane factories generated high amounts of wastes with HCH and other Chlorinated Organic Compounds (COCS). These were often dumped in the surroundings of the production sites, polluting soil and groundwaters with the associated risk of surface pollution. This is the case of the Sardas and Bailin landfills, located in Sabiñánigo (Huesca, Spain). Among the waste from lindane production, a liquid residue was detected in the landfill subsurfaces, forming a dense non-aqueous phase liquid (DNAPL) composed of HCH isomers, benzene and chlorobenzenes, with a high impact on groundwater pollution. In this study, six DNAPL samples obtained from the Bailin and Sardas landfills were analyzed by GC/MSD and GC/FID/ECD. Compounds were identified using mass spectra and the retention index from pure standards and literature information. Pure positional isomers of dichlorobenzene (DCB), trichlorobenzene (TCB), tetrachlorobenzene (TetraCB), HCH and pentachlorocyclohexene (PentaCX) were distinguished and quantified. In addition, heptachlorocyclohexane (HeptaCH) isomers, precursors of hexacholorocylohexene (HexaCX), were also identified and quantified in the DNAPL samples, although the corresponding isomers could not be discriminated. Information about PentaCX, HexaCx and HeptaCH identification is very limited in the literature. HCH contents in the DNAPL ranged from 22% to 30% in weight, the major isomers being lindane and δ-HCH, followed by α-HCH. The β isomer was the least abundant. HeptaCH contents were present in the same order of magnitude as HCHs in the DNAPL. PentaCXs and HexaCXs could have appeared as dehydrochlorination derivatives of HCHs and HeptaCHs, respectively. Two of the DNAPLs analyzed showed a higher content of TCBs and TetraCBs, associated with lower HCH and HeptaCH contents. Variations of these compounds in the DNAPL could be related to an alkaline dehydrochlorination in the landfill conditions.

In the cyclohexanone purification process, some impurities, such as pentanal, hexanal, and 2-cyclohexen-1-one, must be removed in order to ensure good quality of nylon fibers in the caprolactam polymerization step. To do this, an industrial common practice is to add a homogeneous basic catalyst (such as sodium hydroxide, NaOH) to promote the condensation of these impurities with cyclohexanone because the condensation products are easily separated by distillation. In this study, a kinetic model for the catalytic condensation of each impurity was developed, including variables such as temperature, impurity concentration, and catalyst concentration. In order to fulfill this purpose, runs were carried out in a batch reactor containing 70 g of cyclohexanone and different contents of impurities. NaOH was used as the catalyst (C NaOH values ranging from 2.5 to 30.0 mmol/kg). Runs were carried out by a nonisothermal procedure; the reaction temperature was changed from 298 to 423 K, and several temperature ramps were applied. All of the experiments were conducted at a pressure of 10 bar to ensure that all of the volatile compounds remained in the liquid phase. The products of the condensation reaction of each impurity with cyclohexanone were identified and quantified by gas chromatography/mass spectrometry. The reaction products found were as follows: 2-(1-pentenyl)cyclohexanone (A1) and 2-pentylidenecyclohexanone (A2), in which both isomers were lumped together and quantified as A; 2-(1-hexen-1-yl)cyclohexanone (B1) and 2-hexylidenecyclohexanone (B2), in which these isomers were lumped together and quantified as B; [1,1′-bicyclohexyl]-2,2′-dione (C1) and [1,1′-bicyclohexyl]-2,3′-dione (C2), in which both were lumped together as C. The kinetic parameters were estimated by data fitting. The estimated activation energies of impurity elimination were 3.47 kJ/mol for pentanal, 3.99 kJ/mol for hexanal, and 24.23 kJ/mol for 2-cyclohexen-1-one. This kinetic model reproduced the experimental results quite well. Moreover, experimental data from isothermal experiments were also reasonably well predicted with the model.

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