Reaction kinetics are presented for the reversible esterification reaction of citric acid with ethanol to form tri-ethyl citrate via mono-ethyl and di-ethyl citrates. The reaction was studied in batch isothermal experiments, self-catalyzed homogeneously by citric acid and the formed mono-and di-ethyl citrates, and heterogeneously catalyzed by macroporous Amberlyst-15 ion-exchange resin catalyst. Experimental data were obtained between 78 and 120 °C at different mole ratios of ethanol to citric acid and catalyst concentrations up to 5 wt % ion-exchange resin. The kinetics of ethanol etherification to form di-ethyl ether were included in the investigation. Kinetic modeling was performed using a pseudo-homogeneous UNIQUAC-based activity model, taking into consideration the rate of self-catalyzed esterification and the side reaction to form diethyl ether. The activity coefficients for the tri-ethyl citrate-ethanol and tri-ethyl citrate-water binary pairs were obtained from experimental vapor-liquid equilibrium data. Kinetics of the di-ethyl citrate to tri-ethyl citrate reaction limit the overall tri-ethyl citrate formation rate, as citric acid and mono-ethyl citrate are esterified rapidly to their equilibrium compositions. Higher temperatures lead to faster reaction kinetics but significantly increase the production of the undesired byproduct di-ethyl ether. The kinetic model developed is useful for the design and simulation of processes such as reactive distillation for tri-ethyl citrate formation.

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The kinetics of esterifying lactic acid and its oligomers with ethanol over Amberlyst 15 cation-exchange resin have been determined via batch reaction studies. The kinetic model for esterification of lactic acid and its oligomers uses nth-order, reversible rate expressions for esterification and oligomerization reactions. Rate constants, activation energies, and equilibrium constants were generated via regression of experimental results. Model predictions for esterification of 20%, 50%, and 88% lactic acid solutions in water are in good agreement with experimental results over a wide range of experimental conditions.

The continuous formation of ethyl lactate (L1E) from aqueous lactic acid solution and ethanol is carried out in a reactive separation column. Nearly complete conversion of lactic acid can be achieved with L1E yield exceeding 85%; byproduct lactate oligomer esters and acids formed can be further converted to additional L1E. Concentrated (88 wt % in water) lactic acid feedstock gives the best results, with as little as 40% excess ethanol required to achieve >95% conversion of lactic acid. Similar conversion can be obtained using 50 wt % lactic acid feed solution, but with much higher ethanol feed rates. Optimal column operation in both cases is observed with no reflux, so that operation is as a reactive stripping column. Limiting the quantity of ethanol added or vaporizing feed ethanol makes it possible to eliminate ethanol and water from the bottom stream of the column, thus simplifying recovery and purification of L1E product and facilitating the recycle of byproduct oligomers. Reaction of oligomeric byproducts with excess ethanol over Amberlyst 15 cationic exchange resin in a batch reactor gives a high yield of L1E, indicating that process yields of L1E approaching 100% are feasible.

The reaction kinetics of the reversible esterification reaction of succinic acid with ethanol to form monoethyl and diethyl succinate are presented. The reaction was studied in batch isothermal experiments catalyzed by macroporous Amberlyst-15 ion-exchange resin. Experimental data were obtained between 78 and 120 °C at different mole ratios of ethanol to succinic acid and at ion-exchange resin catalyst concentrations from 1 to 5 wt % of solution. Kinetic modeling was performed using a pseudohomogeneous mole fraction model which acceptably fits the experimental data. The kinetic model is useful for the design and simulation of processes such as reactive distillation for diethyl succinate formation.