Optimisation of Heterogeneous Catalysed Esterification Reaction for n-Hexyl Acetate Synthesis part 6

Optimisation of Heterogeneous Catalysed Esterification Reaction for
n-Hexyl Acetate Synthesis part 6

Results and Discussions:

Effect of Catalyst Loading

The evolution of the ester was studied at three different catalyst loadings i.e. 1% (w/w), 2.5% (w/w) and 5% (w/w) using Purolite CT-124. It can be seen from Figure 6 that with increasing catalyst loading, speed of reaction and
conversion of acetic acid also increases. At 5% (w/w) catalyst  loading, equilibrium was achieved in about 1 h whereas with catalyst loading of 1% (w/w) and 2.5% (w/w), equilibrium was reached after 2 h and 5 h respectively. As a result, all the further experiments
were conducted at 5% (w/w) catalyst loading.

At higher catalyst loading there are more available active catalytic sites to be attacked by the molecules. Kinetics suggest that the greater the catalyst weight loading, the   greater the number of sites accessible to the reactants,
and ultimately faster initial reaction rates and conversion (Patel and Saha, 2007; Chuang and Xu, 2009). The figure above is notable in the sense that whilst equilibrium is attained faster, catalyst loading will not bear influence on the extent of the overall
conversion of acetic acid, this was also identified by Teo and Saha (2004).

Effect of Feed Molar Ratio

Feed molar ratio (FMR) is one of the pertinent parameters for reaction optimization.
n-Hexyl acetate synthesis reaction using Purolite CT-124 at three feed molar ratio (n-hexanol to acetic acid). i.e. 2:1, 3:1, 4:1 was studied. Figure 7 shows the acetic acid conversion with respect to time over 6 hours for all three molar
ratios. It is evident from the figure that the extent of conversion at equilibrium state is influenced by the amount of
n-hexanol used (Patel and Saha, 2007; Teo and Saha 2004).

At 2:1 molar ratio (n-hexanol to acetic acid), conversion of acetic acid achieved was about 83% at completion of reaction. On the other hand, acetic acid conversions reached with 3:1 and 4:1 feed molar ratio are 88% and
92% respectively after 1 h. On the basis of the results obtained, 4:1 (n-hexanol : acetic acid) molar ratio was used in the later experiments.

These findings vindicate our use of molar ratios higher than 1:1 (as reported in classic organic chemistry) to obtain higher conversion. Selection between 3:1 and 4:1 feed ratios may come down to economic considerations. The findings
of Teo and Saha (2004) and Patel and Saha (2007) reinforce our decision not to use greater than 4:1 FMR because it was found that
n-hexanol in great excess (i.e. 10:1) will not drive conversion significantly higher.

Essentially, there is no economic merit to charge such amounts of alcohol, as only the equilibrium state is reached slightly quicker and the surplus alcohol will need to be recovered and recycled at great cost to the operators.

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Posted by Ahmed Tariq on Jan 4 2012. Filed under Sci-Tech. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry