Lauric esterification

By the enzymatic esterification of diglycerol with lauric acid, the corresponding monolaurate ester is obtained [84]. This is an important industrial reaction for the cosmetic, pharmaceutical and feed industries, since this ester is used as biodegradable non-ionic surfactant. In recent years, the synthesis of this and other polyglycerols with fatty acids has attracted growing interest in industry, leading also to a demand for enantiomerically and isomerically pure products. 

Organic synthesis 12 [OS 12] Esterification of diglycerol with lauric add with... 

The failure to fit the data over the complete conversion range from 0 to 100% to a third-order plot has sometimes been ascribed to failure of the assumption of equal functional group reactivity, but this is an invalid conclusion. The nonlinearities are not inherent characteristics of the polymerization reaction. Similar nonlinearities have been observed for nonpolymerization esterification reactions such as esterifications of lauryl alcohol with lauric or adipic acid and diethylene glycol with caproic acid [Flory, 1939 Fradet and Marechal, 1982b]. 

Jacobs and coworkers reported the catalytic activity of a mesoporous silica-supported sulfonic sites in the esterification of sorbitol with lauric acid [130]. This reaction affords in a one step process the dilauryl isosorbide (dehydration of sorbitol/esterification). In contrast to zeolites, it is found that mesoporous silica-supported sulfonic sites afford the corresponding dilauryl isosorbide with 95% selectivity at 33% conversion (Scheme 13). 

Sorbitol. Sorbitol is the sugar alcohol obtained by reduction of glucose and it can be dehydrated to either isosorbide or to 1,4- and 2,5-sorbitan in acid or base catalyzed processes, respectively. Using sulfonic acid functionalized MCM-41 type materials lauric acid esters of isosorbide can be achieved quite selectively starting from sorbitol (>95% selectivity towards isosorbide dilaurate at 33% lauric acid conversion) in a dehydration-esterification... 

Enzyme activity was determined as the initial rates in esterification reactions between lauric acid and propanol at a molar ratio of 1 3, a temperature of 60°C, and an enzyme concentration of 5 wt% in relation to the substrates. At the beginning of the reaction, samples containing the mixture of lauric acid and propanol were collected and the lauric acid content was determined by titration with 0.04 N NaOH. After the addition of the enzyme to the substrates, the mixture was kept at 60°C for 15 min. Then, lauric acid consumption was determined. 

The objective of the present work was to study the synthesis of monolaurin by direct lipase-catalyzed esterification between glycerol and lauric acid without any solvent or surfactant. The effects of lauric acid/ glycerol molar ratio, enzyme concentration, and temperature were studied using an experimental design. The reuse of the commercial immobilized lipase, to reduce the process cost, was also investigated. 

The esterification activity of Lipozyme IM-20 was measured according to the method described by Langone and Sant Anna (9), which determines the consumption rate of fatty acid at 60°C in a reaction system containing glycerol, lauric acid, and a given amount of the commercial enzyme preparation. One international unit of esterification activity is the quantity of enzyme that consumes 1 pmol of lauric acid/min under the reaction conditions. The enzyme used has an esterification activity of 20 IU/g. 

This section deals with the conceptual design of a catalytic distillation process for the esterification of lauric acid (LA) with 2-ethyl-hexanol (2EtH). Laboratory experiments showed that a superacid sulfated zirconia catalyst exhibits good activity over a large interval, from 130 to 180 °C with no ether formation. On the contrary, the catalyst is sensitive to the presence of free liquid water. Raw materials are lauric acid and 2-ethylhexyl alcohol of high purity. The conversion should be over 99.9%, because the product is aimed at cosmetic applications. 

Figure 8.3 Equilibrium constants for esterification of lauric acid with 2-ethylhexanol.

Figure 8.7 Concentration and temperature profiles for the esterification of lauric acid with 2-ethylhexanol with an equilibrium-based model. Top Pressure 0.3bar. Seven reactive stages, acid feed on 3 and 5 with 0.5 split, alcohol feed on 7.

In the following, the strategy presented before will this time be applied for developing a process for the esterification of lauric acid with methanol. All the thermodynamic data for pure components and binary mixtures are available in Aspen Plus. A residue curve map of the reactive mixture at equilibrium can be computed as described in Appendix A. A useful representation can be done in reduced coordinates defined by Xx = water + add and X2 = add + ester. The diagram displayed... 

Figure 8.15 Dual esterification of lauric acid with methanol and 2-ethyl-hexanol liquid concentration, reaction rate and temperature profiles.

In the case of esterification of lauric acid with methanol, the RCM analysis shows two alternatives (1) reflux of alcohol, but secondary methanol distillation, and (2) acid reflux (reactive absorption instead reactive distillation). The last alternative seems to be generic for any type of alcohol, but in practice it is limited by low volatility of fatty acids and high sensitivity to operating conditions. A better alternative is offered by dual reactive distillation, in which 2-ethyl-hexanol is added in the top as a coreactant and a mass-separation agent. 

Figure 13.3 shows the profiles of the DBSA-catalysed reaction of lauric acid with 3-phenyl-1-propanol (1 1) at 40°C in water (closed circle). The reaction reached its maximum yield of 84% in 170 hours. We also conducted hydrolysis of the corresponding ester (open square). Both esterification and hydrolysis finally led to the same composition of the reaction mixture, indicating that the reaction reached its equilibrium position. 

FIGURE 13.3. Reaction profiles for DBSA-catalysed reactions in water. Closed circle esterification of lauric acid with 3-phenyl-l-propanol (1 1). Open square hydrolysis of 3-phenyl-1-propyl lauratc. 

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