Optimisation of Heterogeneous Catalysed Esterification Reaction for n-Hexyl Acetate Synthesis part 7

Optimisation of Heterogeneous Catalysed Esterification Reaction for n-Hexyl Acetate Synthesis part 7

Results and Discussions:

Effect of Acetic Acid Concentration

Figure 8 shows data that is relevant to industrial conditions. There is a significant difference in conversion achieved between the control concentration (@ 99.8% concentration acetic acid) and the dilute system, 30% concentration.
Most notable in the 30% run is the non-establishment of an equilibrium point, which is achieved in virtually all other trials. So limiting reactant concentration strength is a key determinant of final conversion and initial reaction rate.

Arguably, a major industrial concern is the absence of an equilibrium point, which would need to be addressed by running the batch vessel to times of perhaps 8 hours or upwards, which would pose more of an economic constraint to
run for a longer duration.

The trend displayed by the aqueous acetic acid curve and the final conversion of acid achieved is in good agreement with the findings of Patel and Saha (2007). Singh and Tiwari (2006) also noted the industry-standard values for
acetic acid strength, to be in the order of 30-35% in the case of cellulose acetate synthesis, so this underlines the significance of the observations deduced from figure 8.

Catalyst Reusability

Reusability of Purolite CT-124 catalyst was tested for
n-hexyl acetate synthesis reaction. Results can be seen from the Figure 9.  Fresh catalyst   and a ‘once used’ catalyst were both employed and it was concluded that the conversion of acetic acid remained same from both the fresh and used CT-124 catalyst.

Hence, it is predicted that Purolite CT-124 could be used several times without affecting acetic acid conversion. The results above concur well with the findings of Patel and Saha (2007). This is concurrent with the findings of
Teo and Saha (2004) that catalytic activity is not compromised upon multiple usage of re-claimed catalyst. This is naturally a foremost advantage for commercial applications of this reaction.

Effect of Reaction Temperature

Effect of temperature was identified as one of the most influential factor on the conversion of acetic acid. As is evident from Figure 10, the temperature variations elicit a graph not too dissimilar to the catalytic loadings figure,
in the sense that at 353 K, the conversion becomes constant at 2.5 hours [akin to 2.5% (w/w) loading] and similarly, the lowest temperature setting here (338 K) generated a curve that shows equilibrium attained at approximately 4 hours.

The figure above correlates very well with Patel and Saha (2007) and Peng
et al. (2009), in the aspects of increased conversion at higher temperatures and increased reaction rate. It can be observed from the Figure 10 that the overall conversion cannot be expressed as a function of the reaction temperature, only the initial
reaction rate (slope of the conversion curve in Fig. 10) is strongly correlated to temperature of the system.

This was purported by Peng et al. (2009) and is demonstrated by this study. Teo and Saha (2004) and Chuang and Xu (2009) also concluded that the forward reaction of this equilibrium system was accelerated by the effect
of higher temperatures.

Continued to part 8

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Posted by Ahmed Tariq on Jan 5 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