SHORT NOTE Vacuum vapor distillation of organic compounds

101/2013
R-210/215, R-II, R-3
SHORT NOTE
Vacuum vapor distillation of organic compounds
Vacuum vapor distillation is a mild method to obtain aroma compounds, fragrances and essential oils from aqueous solution. A
vacuum vapor distillation set-up with two Rotavapor® in series was employed for vapor distillation of compounds typically used
in the aroma and fragrance industry. Recovery rates of up to 99 % are reported by GC-FID analysis. Higher concentrations of
the compounds were measured by liquid nitrogen cooled condensation compared to condensation at 5-10 °C and applying a
vertical condenser.
Introduction
In this short note, an experimental set-up to perform
vacuum vapor distillation is presented. The performance of
the set-up was assessed by the Center for Ingredient and
Beverage Research of the Zurich University of Applied
Sciences (ZHAW). Therefore, an aqueous mixture of
organic compounds, typically employed in the aroma and
fragrance industry, was evaporated and the recovery rates
analyzed (table 1).
Distillation of these compounds is not straightforward due
to their high boiling point (120-243 °C) and possible
decomposition at elevated temperatures. However, by
directing water vapor trough the evaporation vessel,
containing organic compounds and water, the boiling point
of the liquid is lowered (only if the organic compounds are
not miscible with water). In general, the immiscible mixture
of organic compounds and water starts to boil as soon as
the sum of the pure vapor pressures equals the
atmospheric pressure. Hence, by applying a vacuum the
boiling temperature of the mixture is further lowered such
that distillation is possible at mild conditions.
To evaluate the performance of the set-up 50 µl of a
standard sample mixture of 15 benchmark compounds
(table 1), was diluted in 50 ml of ultrapure water. Three
fractions where collected, each after 5, 10 and 15 min of
process time respectively, resulting in about 50 ml per
fraction. The cooling medium temperature was kept
constant between 5-10 °C. Prior to GC-FID analysis, an
internal standard (4-methyl-2-pentanol) was added to each
fraction.
Results
All compounds were detected in the first distillate fraction.
Some compounds were also found in the second or third
fractions (table 1). Highest recovery (99.1 %) was
measured for 2-methylpyrazine, a component of the aroma
of roasted sesame seeds.
Experimental
In Figure 1, the set-up is shown. Two Rotavapor® were
connected in series. The heating bath of the first Rotavapor
(left), employed as a water vapor generator, was heated to
60 °C. The water vapor was directed by a tube to the
sample in the evaporation flask of the second Rotavpaor®
(right), equipped with a V-condenser. The temperature of
the second heating bath was set to 40 °C to protect the
substances from heat. A vacuum of 73 mbar was applied
and the sample rotated at 90 rpm.
Table 1. Recovery rates for 15 organic compounds in three fractions using a
V-condenser and the total recoveries for the V- and C-condenser set-up.
Interestingly, significantly higher recovery rates were
recorded when using the liquid nitrogen cooled Ccondenser set-up. Hence, a low cooling temperature of the
condenser is beneficial to trap and condensate the
compounds analyzed.
Conclusion
Figure 1. Experimental set-up for vacuum vapor distillation. The R-3 (left)
and the R-215 are connected by a water vapor tube (black).
For comparison of the condenser performance a liquid
nitrogen cooled C-condenser was used in a control
experiment employing similar conditions (total process time
30 min, 1 l liquid nitrogen consumed).
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By combining two Rotavapor® in series – one used for
vapor generation and the other vapor distillation – vacuum
vapor distillation was performed. The findings confirm that
with this set-up of two Rotavapor® aroma compounds,
fragrances and essential oils are vapor distilled with high
yields.
Acknowledgement
Sandro Dossenbach of the Center for Ingredient and
Beverage Research at the Zurich University of Applied
Sciences is kindly thanked for sharing his results.
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