Microencapsulation of essential oils

A matter of gas flow management

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Encapsulation Process in Closed Cycle Mode

Compared to a single-path process, the encapsulation process in closed cycle mode results in clearly less contaminated air that needs to be treated prior to being discharged into the environment. Since it is only the amounts of gas introduced in the cycle operation (e.g. atomizing gas, pneumatic filter cleaning) that have to be removed from the system and treated, the energy and material input for cleaning the exhaust air is significantly lower for the same granulation performance.

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Operating a continuous microencapsulation process in closed cycle mode requires an additional processing step for the treatment of the exhaust air. Condensable components, for example water used as a solvent for the solid matter, have to be condensed and discharged from the cycle as otherwise the supply air would be saturated with solvents which prevents a proper drying process of the granules.

Increasing Oil Concentration

The redesign of the entire process allows the oil concentration in the supply air to the granulator to be varied. The closed gas cycle offers the opportunity of providing a better supply air quality with less humidity and a higher oil concentration. An encapsulation process operating with gas recirculation (cycle mode) allows up to 10 % higher oil recovery rates to be achieved compared to the single-pass gas operation under comparable processing parameters. The loss of oil via processing air can be reduced by up to 99 % with the use of a condenser located in the loop; and there is also a comparably low exhaust gas mass flow rate.

However, when using just a condenser, none of the two gas flow options will be able to ensure compliance with the legally required limiting values for volatile organic substances. A specific exhaust air cleaning unit that uses heterogeneous catalysis for the treatment of contaminated exhaust air from the encapsulation process makes it possible for the first time to arrive at a concentration that is up to 50% below the limiting value. This type of exhaust air cleaning unit operates at a temperature of 250 °C and needs no additional fuel for the treatment of the exhaust gas when compared to the conventionally applied thermal systems where the contaminating materials are combusted at temperatures of up to 900 °C. Since only the amounts of gas have to be removed from the system and treated that had previously been introduced, the energy and material input for cleaning the exhaust air is significantly lower at the same granulation performance. The exhaust air stream from the cycle operation is approximately 95% less than the air stream in single-pass mode.

From the energy point of view, the cycle operation offers a much more favorable way of integrating an exhaust air cleaning unit while complying with the legally required limiting values. Apart from using less energy, there is also less technical equipment needed for the heterogeneous-catalytic oxidation of volatile oils in a closed cycle operation.

* The author is process engineer im Bereich Process Technology Food, Feed & Fine Chemicals at Glatt Ingenieurtechnik, Weimar/Germany.

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