Partition Phenomena and Equilibrium of Esterification Reactions

The high molar conversion obtainable in esterifications catalyzed by dry mycelia encouraged us to investigate the partition of water in these heterogeneous systems further. The objechve was to verify whether mycelia were able to affect the thermodynamic equilibrium of the reactions by modifying the parhtioning of the water formed during the esterificahon. The synthesis of two esters by lyophilized mycelia of R. oryzae CBS 112.07 was studied and the results were compared with those obtained with a commercial immobilized CALB (Novozym 435). 

In all cases the conversions achieved by using R. oryzae CBS 112.07 were slightly higher, although both systems led to 90% conversions. 

In order to understand whether the observed differences were ascribable to any effect of the mycelia on the reaction equilibrium, a series of measurements was aimed at monitoring the variations in the water vapour pressure in the gas phase, expressed as relative humidity (RH). A hygrometer specifically conceived for providing fast measurements in systems involving organic solvents was used for this. 

Solvent Temperature (°C) Molar conversion at equilibrium (%) R. oryzae CBS 112.07 Novozym 435  

It must be underlined that, in those cases where the system had reached an apparent equilibrium (constant reading for at least 1 h), such values were considered as an acceptable approximation of the value of the system. Firstly, the water content of the two dry biocatalysts was evaluated and it was found that 11% of the water was stiU present in the mycelia after lyophilization (weight variation after 6h in an oven at 110°C). The two biocatalysts were then equilibrated in toluene for 24 h and the amounts were chosen so as to obtain the same water content in both systems. The results of Table 6.7 indicate that the mycelia led to a lower water activity, hence suggesting that water might partition inside the mycelia. 

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