(119e) Systematic Evaluation of Triethyl Citrate Purification By Using a Falling Film Evaporator System

The triethyl citrate is a bio-based plasticizer for different polymers, and also a fixative agent widely used in cosmetic and food industry. As fragrance and flavor ingredient, triethyl citrate must fulfill certain organoleptic properties such as transparency, clarity, brightness and neutral odor. Because esterification of citric acid requires large excess of ethanol to overcome solubility and chemical equilibrium limitations, purification of the ester requires ethanol stripping. In general citric acid esterification is carried out under batch operation, where the jacketed reactor is also used as reboiler for the stripping stage.  During ethanol removal, the ester gets undesirable color and odor mainly because large residence time is required to reduce volatiles concentration up to commercial specifications, and also because of the low heat transfer area to volume ratio.

In order to improve organoleptic characteristics of triethyl citrate during ethanol removal, a falling film evaporation system was evaluated for product purification. In this system the heat transfer area to volume ratio is much larger than in traditional heat transfer equipments, and also reduced residence times are obtained. A simple lab scale methodology was developed to evaluate the preferable operating conditions for a continuous falling film evaporation system. Time dependent evaporation profiles were obtained gravimetrically at different temperatures (50, 80, 100 and 120 °C) in a vacuum oven. Based upon organoleptic panels, this methodology allowed establishing the range of operating conditions where the product remained stable and no degradation was observed. Besides, It was possible to estimate the residence time required in a continuous evaporation system.

In subsequent experiments, lab scale (40 cm high and 5 cm diameter, electrically heated), and pilot scale (1m high and 12 mm diameter, steam heated) falling evaporators were ran under different operating conditions (residence time and temperature). It was possible to demonstrate that the developed methodology can be used to predict best operating conditions for falling film evaporation systems.