Optimization of the device after the first tests and discussions with specialists

Discussion with specialists...

Hosepipe for the vapors

Écrit par Rohan NOWAK et Waldan GIRARD le . Publié dans Optimization of the device after the first tests and discussions with specialists

When meeting with distillation specialists, Dr Jalil Belkamel, a Moroccan aromatherapist who is a specialist in plant extractions, and also Philippe Bertrand, a consultant on plant extraction processes, we clearly noticed their reluctance about the use of a hosepipe (used for in bathroom showers) because the internal surface is covered with rubber which is probably non-food grade. With a high temperature, the rubber deteriorates, solidifies and cracks. In this way, particles from this rubber could pollute the oils.


Fig. 20: Cracks formed in the rubber                         Fig. 21: Inside the hosepipe


We immediately decided to sacrifice one of these hoses to analyze its composition.

Firstly, the inside of the hosepipe did seem to be made of rubber. The problem is the rubbers used are synthetic and so they probably comprise some compounds added during the synthesis such as phthalates or other molecules to increase their flexibility or their lifetime.


Fig. 22: Skeletal formula of a phthalate 


Hypothesis: The oils contain impurities because of the rubber

Experiment: To check for potential impurities in the distilled waters, we decided to do 3 extractions on distillates obtained using 3 different hosepipes (made of 3 different materials) having the same diameter (10mm) and under the same distillation conditions (same heating power from a gas burner, same plants (dry rosemary) and same volume of perfumed waters obtained). The pipes were:

-Annealed copper;

-Shower hosepipe

-Multilayer food-grade hosepipe made of several layers of polyethylene;


We analyzed the floating oils by GC, but this time, we did it more slowly and followed it by mass spectrometry.



Black: Multilayer polyethylene

Pink: slow distillation (1h)

Blue: Hosepipe

Brown: Annealed copper


Fig. 23: Chromatogram of the oils obtained with different pipes

Conclusion: We did not detect any difference in the oils obtained. However it is not improbable for phthalates to be present in the oils, but in too much weak concentrations to be detected by the technique used. The shower hosepipe used for this experiment had not been used a lot and it is only after a series of heating and cooling cycles that it deteriorates. So, it is possible to use a copper pipe as Moroccans do but the device will lose mobility. Therefore we would need to put the dish+the condenser on the same rotating plate.


Vapor outlet

Écrit par Rohan NOWAK et Waldan GIRARD le . Publié dans Optimization of the device after the first tests and discussions with specialists

During the previous experiment, we were surprised by the fact that we obtained a layer of what looked like dust between the aqueous phase and the oils. An effect of the hosepipe was quickly eliminated because all the pipes lead to the same quantity of dust.

Hypothesis: According to Philippe Bertrand, the dust could be the consequence of the output being too high. He told us again that a good distillation had to last about one hour and not only 30 minutes or less as we did distilling with the gas burner.

Experiment: We immediately repeated the previous experiment, reducing the heating power provided by the gas burner to the water.




Fig. 24: Distillate from

1) High power heating, distillation in 20min

2) Low power heating power, 60min distillation


Observation/conclusion : Le résultat est probant : la couche de « poussière » est nettement moins importante ! En effet, le débit des vapeurs étant moins important, elles n’entraînent pas autant de particules avec elles.

Observations/Conclusion: The result was compelling: the layer of “dust” is clearly less significant! Indeed, when the vapor output was lower less particles were carried with the vapor..

A second comment from M. Bertrand and M. Belkamel concerned the vapor outlet of the pressure cooker which, according to them, was too narrow. Indeed, when we observed the traditional still, the vaporoutlet narrowed progressively (gooseneck).

This allows:

-a reduction in the velocity of the vapors at the outlet and also

-avoidance of excessive pressure, and at the same time a rise in temperature in accordance with the perfect gas law. It is worth noticing that this elevation of the temperature, even if only slight, could facilitate some oxidation reactions of the oils, commonly called a Maillard reaction (caramelization is a Maillard reaction).

Experiment: We decided to enlarge the outlet hole for the vapors to see whether or not there would be a visual change in the quality of the oils. The best would be to have a hosepipe which narrows progressively like a gooseneck but our aim was to make this device affordable to everybody, so we made the progressive reduction by using fittings. We decided to use an outlet with a diameter of 16mm instead of the 10mm outlet we used beforehand. This increases the cross-sectional area of the vapor outlet by 2.6 (s’/s = R’²/R² ) and therefore, according to the Venturi effect, divides the velocity of the vapor at the outlet by the same factor.


Results: The temperature recordings indicated that under the same distillation conditions, there was an average decrease in temperature of only 0.8° compared to the 10mm outlet.

Conclusion: This small difference in temperature cannot produce caramelization of the oils and cannot denature the oils.


Fig. 25: Enlarged vapor outlet

Cooling the water

Écrit par Rohan NOWAK et Waldan GIRARD le . Publié dans Optimization of the device after the first tests and discussions with specialists

For the condenser, it is best to have the largest surface area possible for heat exchange between the copper coil and the cold water. The perfumed waters have to cooled as much as possible before they exit from the condenser because the higher the temperature is, more volatile the oils are so we will lose their olfactory properties (the saturation vapor pressure increases with temperature). We did tests with a coil cut to half the length but this obliged us to change the cooling water two times during distillation.

With 10L of cold water, we wanted to determine what final temperature the water inside the condenser would reach at the end of distillation. The water in the condenser is used to liquefy the vapors and cool the distillate obtained. To do the calculation we are going to make some simplifying hypotheses.

- The perfumed water will exit the condenser at a constant temperature, whereas in fact it will be colder at the beginning of distillation than at the end;

- All the water in the condenser/distillate is in a closed system, meaning that there are no external exchanges;

-The distillate is purely water;



- qi = 20C, the initial temperature of the water in the condenser;

- qf, the final temperature of the water of the condenser;

- Vwater = 10 L the water volume in the condenser tank ;

- Vhydrolat = 0.75 L, the volume of the hydrolat (=distillate) obtained;

- Lliq = - Lvap = -2250 kJ.kg-1, latent heat of condensation for water ;

- cwater = 4,18 kJ.kg-1.°C-1 specific heat capacity for water

If we neglect the exchanges with the outside:

DHwater + DHhydrolat = 0

With DHwater = mwatercwater(qf-qi)

HDhydrolat = -Lvap.mhydrolat + mhydrolatcwater(qf-100).

So : mwatercwater(qf-qi) -Lvap.mhydrolat + mhydrolatcwater(qf-100) = 0

qf =   so qf = 63°C

This is why we have to change the water during the distillation, because at the end, the temperature will be too high.

We tried to find a way to cool the water in the condenser. In electric power plants, water drops on grids or fans are used to cool the water but for us it is impossible to do that. However, we thought about a way using evaporation, as is used in the desert to keep drinks cold. We wanted to see if having a damp cloth around the condenser would have an efficient effect. If a damp cloth surrounds the tank, the water in the cloth will evaporate and since the vaporization is an endothermal phenomenon it will absorb heat energy from the condenser.

The factors favoring vaporization are:

- increasing the surface area exposed (spreading the cloth favors vaporization) : we have to cover the whole tank with a damp cloth

- the type of wet material used (wool, cotton, nylon...) : what is the best for our use?

- the wind : windier it is, more efficient it will be, but in Morocco, it is not really the case... → forced convection

- heat input such as the sun favors drying by vaporization because it is an endothermic phenomenon, which means that it will take heat from its environment. So we should use a white cloth to avoid the drying by absorption of the solar radiation and keep the condenser out of the sun, in the shade of the dish. The cloth has to dry by absorption of the energy from the water and not thanks to the sun effect.

- The lower the relative humidity of the air the higher the rate of vaporization will be. This is one of the advantages in Morocco where the climate is dry.

During our previous trip to Morocco, we tested this hypothesis. At the end of the experiment, the temperature of the water inside the condenser was 51°C. Indeed, we noticed that the damp cloth used to surround the condenser dried quickly, but it was generally helped by the wind which was quite strong that day. We hope to repeat this experiment during our next trip to confirm or refute this hypothesis, by doing two distillations in parallel.