Phase Transfer Catalysis-Continuous Contact
Advancing the chemical engineering fundamentals
Catalysis - III (T2-13c)
Keywords: continuous contact, phase transfer catalysis
When two immiscible liquids containing reactants are brought together the reaction will be slow or will not take place at all due to inaccessibility of the reactants. The reaction can be made faster by adding a little amount of phase transfer catalyst. These types of reactions have been investigated mostly using batch reactors. The catalyst will be present in one of the phases or either of the phases depending on their solubility. The removal of the catalyst which is present in small quantities, after the reaction will be cumbersome and the reactions cannot be carried out under continuous conditions. Hence some of the reactions were investigated by supporting the catalyst on solids like polymer, silica gel, alumina etc. In such cases removal of catalyst becomes easy and also the reactions can be carried out under continuous flow conditions. However the literature indicates, in most of the cases the rate of reaction decreases when the catalyst is supported on a solid compared to when it is not supported. But with catalysts which are soluble in one of the phases and the product formed in the other phase, the reactions can be carried under continuous contact conditions. In the present study, the aqueous phase containing potassium permanganate is used to oxidize n-hexanol in benzene phase. The phase transfer catalyst is tri caprylyl methyl ammonium chloride (Aliquat 336) and is insoluble in the aqueous phase. The product thus formed will be in the aqueous phase. Under continuous contact conditions, the aqueous phase containing the product can be easily separated from the organic phase. The organic phase containing unconverted alcohol and the catalyst can be recycled. For this a column of 0.7 m in length and 0.01m in diameter was used. The inlets for organic and aqueous phases were at the bottom. The organic liquid was dispersed in the aqueous phase under continuous co-current conditions. At the outlet(top) the two phases were separated and analysis was made when required. The experimental runs were made for different flow rates of organic and aqueous phases and also varied the catalyst and alcohol concentration in the organic phase.
The enhancement in the conversions was observed with the catalyst. The rate of extraction of potassium permanganate was found to increase with the catalyst concentration. With increase in n-hexanol concentration the rate of extraction was found to remain same. For a particular concentration of the catalyst the extent of extraction decreased with the flow rate of potassium permanganate solution. With increase in the flow rate of organic phase, the percentage of extraction of potassium permanganate increased. A model equation has been developed.
Presented Thursday 20, 14:40 to 15:00, in session Catalysis - III (T2-13c).
