Optimisation of Heterogeneous Catalysed Esterification Reaction for n-Hexyl Acetate Synthesis part 5

Optimisation of Heterogeneous Catalysed Esterification Reaction for
n-Hexyl Acetate Synthesis part 5

Experimental findings for the n-hexyl acetate synthesis are detailed in this section. The most striking feature of the resulting figures is the shape that they all share the same steep rise in conversion to a point whereby
the equilibrium is observed, a plateau where the conversion remains static until experimental termination.

Elimination of Mass Transfer Resistances

The results of the experiments carried out confirm the findings of Gangadwala
et al. (2003) whom established that facilitating mass transfer by higher speeds of agitation had no effect on overall conversion achieved.

The n-hexyl acetate synthesis reaction was studied in the presence of Purolite CT-124 at two different agitation speeds of 300 rpm and 500 rpm. Figure 4 shows the results obtained from the conducted experiments.

 It is very clear from the figure that speed of agitation does not have any significant influence on the conversion of acetic acid (93% for both speeds) during the whole reaction time of 6 h for 300 rpm and 500 rpm speeds.

Thus it was concluded that n-hexyl acetate synthesis reaction is not affected by the facilitating mass transfer within the reacting mixture at this agitation speed range.

An estimation of the Reynold’s number of the reactant mixture to establish laminar/turbulent flow conditions could assist in establishing if the diffusion step has any influence whatsoever on the outcome of the reaction.

Effect of Different Type of Catalyst

The effect of different types of catalyst i.e. Purolite CT-124, Purolite CT-175 and Purolite CT-151 on conversion of acetic acid was studied. The results are shown in Figure 5. It was observed that the Purolite CT-124 obtained
a conversion of acetic acid of 92% within 1 h while CT-151 and CT-175 gave about 92% and 88% respectively, note the marginal differences between conversion, one can infer that initial conversion rates (i.e. initial reaction rate), under these conditions, are
not determined by a particular catalyst brand.

This does not concur well with the concept of the macroporous resins possessing a greater specific surface area (Alexandratos, 2009). The absence of improved yield may be attributed to the water molecules (released by reaction)
attaching themselves to the sites on the resin, denying access of the acetic acid molecule to the resin’s  catalytic  sites, therefore limiting the initial reaction rate and conversion (Umar
et al., 2009; Patel and Saha, 2007).

Since the CT-124 gel resin’s size is accentuated by swelling in alcohol solvent/water media, of course which would tend towards a greater frequency of reactant species contacting with the sites. Hence the rest of experiments were
carried out with Purolite CT-124. CT-124 would be the resin of choice, since industrial operations would encounter more aqueous acetic acid feeds, which the macroporous resins are rightfully predicted to be unsuitable for (Patel and Saha, 2007; Sharma and
Saha, 1996).

Essentially, the macropore resins didn’t perform as well predicted (in spite of possessing a superior specific surface area; (Alexandratos, 2009)). Purolite CT-124 was considered to be the optimal catalyst to contend with variable
aqueous acetic acid feeds.

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Posted by Ahmed Tariq on Dec 31 2011. 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