A Statistical Approach for Optimizing the High Yield Green Production of the Flavor Ester Butyl Butyrate

Abstract

Being the prevailing approach for producing esters such as butyl butyrate, the use of chemical route has been linked to numerous disadvantages. Hence, a green alternative method for higher yield production of butyl butyrate by esterification reaction utilizing Novozyme 435 as biocatalysts in a solvent-less system may prove useful. Such approach can be further improved by optimizing the relevant reaction parameters using the Response Surface Methodology by the Box-Benkhen Design attempted in this present study. The reaction parameters evaluated were: substrate molar ratio, time and temperature, and the response of each parameter was measured as percentage conversion yield. Using the Design Expert 7.1.6 optimization functions, the two sets of optimum conditions selected viz. [i] molar ratio butyric acid:butanol 1:3.93, 9.93 h at 56.09°C and [ii] molar ratio butyric acid:butanol 1:3.35, 9.79 h at 53.90°C had afforded the highest yield of butyl butyrate i.e. 99.62% and 99.55%, respectively. The ester product obtained from the reaction were confirmed as butyl butyrate by FTIR and GC. Therefore, the results substantiated the applicability of the RSM prediction technique as well as efficacy of Novozyme 435 as biocatalysts in the high yield solvent-less synthesis of butyl butyrate, adhering to the philosophy of Green Chemistry.

Novozym 435: the “perfect” lipase immobilized biocatalyst?

“…261 For example, butyl butyrate was produced by esterification in a solvent-less medium. 262 Optimization via the response surface methodology gave a yield of butyl butyrate near 100%. In a very interesting paper, N435 was used to esterify 1-butanol and butyric acid using diesel as the reaction medium, with a 90% yield.…”

Simplified Method to Optimize Enzymatic Esters Syntheses in Solvent-Free Systems: Validation Using Literature and Experimental Data

“…The reduction in the reaction rate seems clear in this case due to the long reaction times (30 h) compared to the synthesis of isobutyl propionate carried out by Kuperkar and co-workers (10 h) [4]. The study of Rahman and co-workers (2017) [64] reinforces the relevance of water maintenance in the esterification of short-chain acids and alcohols, and although only one condition was tested, the optimum SER value in this study (91) is above the supposed optimum range.…”

“…For different reasons, we can observe that large stoichiometric excesses of one of the reagents seem to be unfavorable to enzymatic esterifications since it increases the solvation of the limiting reagent requires the use of high biocatalyst loading or other strategies to avoid inhibition of lipases. Nevertheless, some high conversion results showed in Table 1 were attained with a large stoichiometric excess of one of the reagents [4,8,64], diminishing the inhibition potential of the utilized acid by increasing its solvation. Vadgama et al (2015) [5] did not observe deleterious effects on Novozym 435 ® above 4% biocatalyst loading using a substrate molar ratio acid:alcohol of 1:15.…”

“…The classical approach of evaluating independent variables once a time is still commonly used for enzymatic esterification reaction optimization, even in recent studies [7][8][9][53][54][55][56]. However, it has been shown that correlation among some of the studied variables makes the independent optimization incomplete, and, thus, statistical tools, such as response surface methodology (RSM), became popular for optimization studies [49,[57][58][59][60][61][62][63][64]. Although interactions between variables may be discovered using RSM, the molar ratio of reagents and biocatalyst loading are generally considered independent variables.…”