CATALYTIC OXIDATION OF CYCLOHEXANE IN THE PRESENCE OF SUBSTANCES THAT AFFECT ON THE SURFACE TENSION

2018;
: 57-62
1
Lviv Polytechnic National University
2
Lviv Polytechnic National University
3
Lviv Polytechnic National University

Oxidation of cyclohexane is one of few organic synthesis processes industrially made in Ukraine. Oxidation of cyclohexane is characterized by relatively low conversion of hydrocarbon (4-5%) and selectivity for aim products – cyclohexanole and cyclohexanone (around 78%). Analysis of literature data shows that the most perspective way of increasing of selectivity for aim products in cyclohexane oxidation is use of catalytic systems based on industrial catalysts and organic modifiers of different nature. It is known that use of catalytic systems based on variable valence metal salts and organic modifiers of different nature: salts of perfluoric sulfoacids, craun-ethers, polyglicols and quarter oniec salts. Mentioned catalytic systems allow to increase speed of oxidation as well as selectivity for aim products and at the same time shifting ratio between cyclohexanole and cuclohexanone.

Due to the fact that majority of mentioned modifiers influences surface tension (e.g. oniec salts), we can assume that influence of catalytic systems can be partially explained by this fact. Change of surface tension can lead to changes in equilibrium concentration of dissolved oxygen in reaction mixture and in speed of reaction mixture components diffusion.

We researched oxidation of cyclohexane in the presence of catalytic systems based on cobalt naphtenate and two groups of catalytic additives: quarter ammonium salts and esters of polyglicols. In order to define impact of organic additives we also researched their impact on surface tension in the systems cyclohexane/air and cyclohexane/water.  

We found that use of quarter ammonium salts, tetraethylammonium iodide, allows to increase selectivity for aim products at 5,8% under conversion of cyclohexane around 4% (close to industrial) and at 26,6% under conversions close to 6%. Analysis of received data showed certain correlation between surface tension in system cyclohexane/water and conversion of cyclohexane, and molar ratio cyclohexanole/cyclohexanone; and between surface tension in the system cyclohexane/air and selectivity for aim products for catalytic systems containing quarter ammonium salts.

We conducted linearization of curves of use of cyclohexane and creation of aim products, received effective constants of process speed. We also made conclusions about dependence of technological indicators from change of surface tension.

As a conclusion we can state that use of catalytic systems containing quarter ammonium salts allows to increase total selectivity for aim products, selectivity for cyclohexanone and to decrease selectivity for esters. Alongside we can not state define correlation between change of surface tension in reaction systems and effective speed constants.

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