1. EFFECT OF OPERATING CONDITIONS ON THE SOLVENT RECOVERY BY THE METHOD OF
EVAPORATION CONDENSATION
Authors: Adel OUESLATI (1)
, Mohamed JEMAIEL(2)
(1)Process engineering department, College of technological studies in Zaghouan, Mogran
Tunisia.adel.oueslati@laposte.net.
(2) Fabrication Nord Africaine de Chimie, Z.I. BenArous.
Abstract
Liquid discharges, paint factories, may contain more than forty solvents, pigments and solid
particles. These solvents are expensive, polluting and their colours are usually black dense.
Their recovery in the pure state is extremely difficult and costly. In this article, the solvent
recovery is in the form of colourless condensate using a rotary vacuum evaporator-condenser.
The influence of operating conditions such as the flow and temperature of cooling water, the
volume and temperature of the crude mixture and the speed of rotation of the evaporator, the
flow of the condensate were studied.
Keywords: solvents, Liquid discharges, operating conditions, recovery
I INTRDOUCTION
The industry of manufacture of paints, inks and adhesives produces a large amount of
hazardous waste. These are for the most toxic products including chemicals such as acetone,
butanols, acetates, cyclohexanes, alcohols and water [1, 2, 3, 4]. These toxic wastes are
hazardous to health and the environment. Handling of unstable waste involves risks of serious
accidents [4, 5]. Solvent regeneration uses simple distillation, fractional distillation column
and / or distillation by steam distillation to separate the different components of spent
solvents. After distillation, the solvents were "dried". The residual water is removed by
attachment to a support which does not react chemically with the solvent [3, 6, 7].
The performance of these processing techniques, waste, are limited by the complexity of
mixtures of solvents. Indeed these solvents have boiling temperatures of neighboring, more
they are not totally immiscible azeotropic and mixtures thereof are [8, 9, 10]. Hence their
separation by distillation and extraction proves beneficial not.
Other attempts at separation of a ternary mixture hetero azeotropic were conducted by Stathis
Skouras and SigurdSkogestad. This attempt uses a hybrid extraction-distillation column
wherein there is a decanter [11]. This method is beneficial for a ternary mixture, but it is still
inadequate for mixtures containing more than three solvents.
On an industrial scale, solvent recovery is effected using a recycling apparatus comprising an
enclosure in which the crude mixture is heated by an electric heater. The generated vapours
are conducted to a heat exchanger cooled by a condenser-air fan [12].
In this article, we performed tests recovering solvents using a rotary evaporator under
vacuum. The generated vapors are condensed on the outer walls of a coil. We seek to study
the influence of certain parameters such as the speed of rotation of the evaporator, the system
temperature and the initial volume of the mixture to evaporate the condensate flow.

2. II MATERIALS AND METHODS
Figure 1 shows the diagram of the vacuum rotary evaporator. It is used in the chemical
industry to quickly distilled solvents, in order to partially concentrate the solution. The
apparatus consists of a balloon to the crude mixture, another balloon for condensate, a glass
coil whose inclination is adjustable, a hot water bath where the temperature is controlled by a
temperature controller, a system vacuum, a water cooler and the condenser used in a control
panel. The positions of the balloons and the condenser are adjustable.
The principle of this device is based on the discontinuous distillation in vacuo. The flask
containing the crude mixture is immersed in the hot water bath. It is rotated with a rate. The
vapors generated are led to the condenser where it condenses on the walls and fall into the coil
condensate flask. The cooling water circulating inside the heat absorbing coil tube and move
to the cooler. Its temperature is controlled by an instruction. The system is evacuated by a
vacuum pump.
We will study the effects of the bath temperature, the rotational speed, the initial volume of
the crude mixture in the evaporator, the temperature of the cooling water to the flow rate of
condensate. Concerning the effect of the chemical composition of the crude mixture on the
flow of the condensate was examined by comparison with pure water.
Figure-1:Diagram of the rotary vacuum evaporator used in the solvent recovery
recoveryflask
Water outlet
closing
valve
Cooler
Water inlet
vacuo
hot water bath

3. III RESULTS AND DISCUSSION
Figure 2 shows the flow variation as a function of the distillate flow of cooling water.
Figure-2:Varying the flow rate depending on distillate cooling
Increasing the cooling water flow through the coil causes an increase of two parameters: the
Reynolds number and the turbulence. These two parameters represent factors favorable to the
growth of the coefficient of heat exchange between the cooling water and steam.
The effect of the initial volume of the crude liquid mixture in the flask at the rate of
evaporation of the distillate is shown in Figure 3.
Figure-3: Effect of volume of departure of the crude mixture on the flow of distillate

4. We observe that the flow rate of condensate increases with increasing initial volume of the
liquid in the evaporating flask. This increase in volume of recovered condensate is explained
by the presence of a high heat flux density between the hot water bath and the crude mixture
of solvents.
Ifmsamp, mevap, Lv, Cpsamprepresent respectively the initial mass, the mass evaporated to the
latent heat of vaporization and heat capacity of the crude mixture of solvents. Either Tin and
Teb and the initial boiling temperatures of the solvent mixture.Then the heat delivered,
QHeatbath, by the hot water bath, the crude mixture of solvents is understood by the equation (1)
below:
݉௦௔௠௣ ൈ ‫݌ܥ‬௦௔௠௣ ൈ ሺܶ௘௕ െ ܶ௜௡ሻ ൅ ݉௘௩௔௣ ൈ ‫ܮ‬௩ ൌ ܳு௘௔௧௕௔௧௛(1)
From this equation, we deduce the mass of the solvent evaporated:
m௘௩௔௣ ൌ ቀ
ଵ
௅ೡ
ቁ ൫ܳୌୣୟ୲ୠୟ୲୦ െ m௦௔௠௣ ൈ Cp௦௔௠௣ ൈ ሺT௘௕ െ T௜௡ሻ൯ (2)
Thus, the term m௦௔௠௣ ൈ Cp௦௔௠௣ ൈ ሺT௘௕ െ T௜௡ሻis small compared to the amount of heat
ܳୌୣୟ୲ୠୟ୲୦.
The effect of the temperature of the warm water bath on the amount of condensate is shown in
Figure 4. Condensate flow increases with increasing the temperature of the hot water bath.
But at a temperature higher than 85 ° C bath, the throughput decreases because of the
condensate return condensate to the flask containing the crude mixture of solvents. This is
because the inclination of condenser.
Figure-4:Effect of the bath temperature on the flow of distillate
Figure 5 shows the flow of distillate based on the rotational speed of evaporator flask. The
evaporation rate (mevap) increases as the rotational speed increases. This is explained by the

5. effect of turbulence on the heat transfer coefficient by convection. Therefore, if the Reynolds
number increases, so the heat transfer coefficient increases. On the other hand, the rotation of
the evaporating flask creates a thin liquid film on the wall of the balloon which promotes heat
exchange between the hot water bath and the crude mixture of solvents.
Figure-5:Effect of the rotational speed on the speed of the distillate
The crude mixture of the composition has an effect on the rate of evaporation of solvents.
This may be elucidated by comparing the rate of evaporation of a crude mixture of solvents
with one of pure water.
IV CONCLUSION
Mixtures of liquid discharges from factories paint may contain more than forty solvents,
water, pigment and solid particles of different sizes and densities. Much of these solvents are
characterized by boils neighboring points. Furthermore their densities are as close to one
another. Each solvent among them may form one or more azeotropic mixtures with other
solvents. Therefore, their separation by conventional methods of chemical engineering, is
very difficult and expensive.
In this study we used a rotary evaporator-condenser for solvent recovery in the form of
colorless mixture. The performance of this method of recovery depends on the operating
conditions such as the initial volume, composition and temperature of the crude mixture to be
separated, the speed of rotation of the evaporator, the temperature and flow of cooling water
in the condenser.
The increase of the initial volume, the temperature of the crude mixture, flow of cooling water
and the rotational speed of the evaporator has a positive effect on the flow rate of condensate.
The latter also increases by decreasing the temperature of the cooling water.

6. The effect of the initial composition of the raw liquid to be separated has been shown in
comparison with distilled water. Indeed, the distilled water is placed on the rotary evaporator-
condenser in the same operating conditions of crude mixture of solvents to recover. If the
mixture contains more volatile solvent than water, then the flow of condensate will be higher
than that of pure water. If not, the contrary is obtained.
Acknowledgement
We thank the managers of the company "FNAC" for technical assistance for this work.
REFERENCES BIBLIOGRAPHIQUES
[1] World Bank Group: - Pollution Prevention and Abatement Handbook. July 1998
[2] André Beguin, Dictionnaire technique de la peinture (3 volumes), Vander
[3] Regionalrecycling rates for municipal solidwaste, 2008/2009 [archive], site de l'Agence
européenne pour l'environnement consulté le 8 avril 2014.
[4] François Perego, Dictionnaire des matériaux du peintre, Belin, Paris, 2005, 896
pages. (ISBN 2-7011-2135-3)
[5] Jean-Pierre Brazs, Manières de peindre, carnets d'atelier, éd.Notari, Genève,
2011. (ISBN 978-2-940408-48-1)
[6]J.F. Montagne, R. Szkudlarek, G.Toulemonde, Peintures et Revêtements, Paris,
Casteilla, coll. « Mémotech », juin 2007, 400 p. (ISBN 978-2-7135-2927-6), (ISSN 0986-
4024)
[7] Anne-Marie et Jean-Claude Misset, Cahier de recettes de la marchande de couleurs,
Paris, Charles Massin, 110 p. (ISBN 978-2-7072-0452-3).
[8] M. Durand, V. Molinier, W. Kunz et J.-M. Aubry, Classification of Organic Solvents
Revisited by Using the COSMO-RS Approach, Chem. Eur. J., 2011, 17, 5155–5164.
DOI:10.1002/chem.201001743
[9] L. Moity, M. Durand, A. Benazzouz, C. Pierlot, V. Molinier et J.-M. Aubry, Green
Chemistry, 2012, 14, 1132-1145.
[10] P. De Caro et S. Thiébaud-Roux, Biosolvants, Éditions techniques de l'ingénieur, IN 102,
2008.
[11] Stathis Skouras and SigurdSkogestad.SEPARATION OF TERNARY
HETEROAZEOTROPIC MIXTURES IN THE CLOSED MULTIVESSELBATCH
DISTILLATION COLUMN.Norwegian University of Science and Technology, NTNU,
Trondheim, Norway.
[12] www.tricolor-industries.fr/EPA/recyclage.htm. February 18, 2013