Predicting Azeotropic Batch Distillation Equilibrium conditions

Jassim Alajmi

November 12, 2019

Jassim Alajmi, Ashraf Al Shekaili, and David Luong

ChE 450

Group Number 5

Dr. Larry Jang

California State University-Long Beach

Department of Chemical Engineering


Table of contents:


1. Abstract

1. Introduction

1. Materials and methods

1. Results

1. Dissections

1. Conclusion

1. References










Vapor liquid equilibrium is very important now a days where most separation plants uses it. It helps to separate gas from liquid or liquid from gas to use it for some other purpose. In this experiment the goal was to Predict VLE of non-ideal mixture of water and 2-propanol at atmospheric pressure. Additionally, the group focus on Find the relationship between batch distillation and VLE. The results were satisfying where the data that was collected where converted to a point in the that was under equilibrium curve.


The vapor liquid equilibrium (VLE) is very important in chemical engineering field where it relate the distribution of a chemical species among the vapor phase and a liquid phase. Batch distillation is one of the essential processes in chemical engineering field nowadays, where it refer to the use of distillation column in order to separate mixture components into fraction of that mixture. The goal of this lab exercise is to study and analyze the conditions necessary for the azeotropic conditions which include but not limited to, bubble point, VLE composition and dew point. The name given to the liquid whose physical characteristics include boiling at a given composition and at a constant temperature is azeotrope. In this lab exercise, a mixture of water and 2-propanol was used as the specimen to evaluate the hypothesis when using batch distillation method (Gorak, 2014). This type of distillation has its applications in water treatment plants. It is also a common process used to perform separation of various materials in pharmaceutical plants. These, among other applications, makes this process very important in daily application.

On the sections that follows, the list of equipment, materials, results and discussions are well explained. All the tests were carried out at normal atmospheric pressure. Enthalpies of mixing for such system has been reported before. The extensive knowledge obtained from testing the vapor-liquid equilibria in a water-n-propanol can be used for further testing of equilibrium systems such as the vapor-liquid equilibria in water-n-propanol-n-butanol system (Gunawan, 2010).

Below are some of the important equations that shall be used when performing the analysis of the results obtained experimentally.

The Antoine equation

. .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . … . . . . . . . . . . . . . . .Equation 1

Where i= 1,2. At point 1, the saturation pressure of 2-proponol is obtained while at point 2, the saturation pressure of 2-propanol is obtained.

. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . Equation 2

When the value of x and y in the equation 2 above are equal azeotropic point is achieved, it is the point where the mole fraction of the liquid and the gas are equal. It follows then that the Raoult`s Law is as follows;

. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . Equation 3

When x=y, the values ( activity coefficient) can be obtained.

Material and method


i. Boiling chips

ii. Boiling flask

iii. Electronic balance

iv. Othmer still distillation apparatus

v. Refractometer

vi. Heating mantle

vii. Beakers/ vials

viii. Condensers


The binary mixture shouldn’t, under any circumstance be drunk by students whether in lab or anywhere else. It was also necessary that students worn safety goggles and lab coat to protect them in case the mixture ever flashed while carrying out the experiment. Students were also advised to not spill any liquid on electrical equipment to avoid damaging it and also to prevent electrocution. It was also important for student to note that other than being highly flammable liquid, isopropanol was capable of causing eye irritation (Cunningham, 2011).

i. The batch distillation was set up as shown in the figure and the reflux turned on. The following ratios were used for water and 2-propanol during the experiment, 10%, 15% and 20%. A 100g of the solution was used during the experiment.

Figure 1: The distillation set up for the lab exercise

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Figure 2: The actual lab set up for the distillation

ii. the mixture was weighed on the electronic balance after which it was poured into the boiling flask. A beaker was placed on the electronic balance where the distillate would pour. The balance was first zeroed to avoid errors during the measurements. The refractometer was zeroed using the DI water. The reflective index of the initial mixture was obtained so that the mass fraction of the 1- propanol could be obtained (Kagaku , & Kōgakkai , 2018).

iii. The mixture was heated. The reflective index of the mixture heated was recorded after every degree rise in temperature. The refractive index pf the distillate was also obtained.

iv. The process continued until the weight percent of the alcohol vapor ran out.


Parameters for equations 1, 2 and 3 obtained from the experiment.


  Van Laar


Table 1: Equation parameters

Run 1 : not adding anything        
Time (s) Condensate wt % 2-propanol mol % Pool wt % mol %
0 1.37021     1.3626    
180 1.37062     1.36286    
360 1.3716     1.35401    
540 1.37133     1.36284    
720 1.37146     1.36138    
1005 1.37167     1.36261    
1200 1.37194 60.73846 0.3168695 1.36255 36.82 0.14874552

Table 2: The model parameter results

Table 3:The refractive index to wt% 2-propanol



Run 2 : adding 2-Propnol          
Time (s) Condensate wt % 2-propanol mol % Pool wt % mol %
0 1.36799     1.36276    
180 1.37072     1.3627    
360 1.37121     1.36259    
540 1.37116     1.36266    
720 1.3712     1.36261    
900 1.37147 59.2333 0.30345284 1.36249 36.58 0.14744214
    87.7 0.68130923     0.31869077


Table 4: Run 2 mole fraction of the water and wt% 2-propanol

Run 3 : adding water          
Time (s) Condensate wt % mol % Pool wt % mol %
0 1.34096     1.36219    
180 1.34096     1.36215    
360 1.34096     1.36234    
540 1.34107     1.3621    
720 1.34147     1.3623    
900 1.34179 9.79 0.03151387 1.36228 36.16 0.14517535







Table 5: Run 3 mole fraction of the water and wt% 2-propanol



The following graphs were obtained when Van Laar model was used. The liquid composition of the liquid is in the x-axis and vapor composition is in the y-axis.


Figure 3: The graph above is a vapor-Liquid equilibrium diagram developed using the Van Laar model

Figure 4: The bubble point and dew point diagram for the parameters predicted using the Van Laar Model

Table 1 indicate and where they are the parameter for the Van Larr equation which they been used to find model parameter for azeotropic condition. Table 2 indicate the model parameter that was obtained. Table 3-5 are the three trials that was done in the experiment. Trial one was without adding anything to the apparatus, trial two wad run by adding 2-propanol, and trail 3 was done by adding water and the date shown in the table was obtained.

The refractive indices and densities of the binary system were recorded in the table 4 at room temperature (Nevers, 2013). The excess volumes of mixing the binary system have been calculated from the densities recorded before used to plot the figure 4 above. The asymmetry seen in the curve is probably not real at all since many thermodynamic functions are not asymmetric at all. The tables 4 and 5 contain the equilibrium results for the water-n-propanol system. The absolute deviation of the above values from smooth curve is probably less than 0.001. it was also found that from the curves plotted. ===.. At low alcohol concentration, there challenges encountered when operating the equilibrium because the boiling region did rapidly change. The graphical boiling point values for n-propanol and water through extrapolation in a t-x diagram at 760 mm Hg are 97.1 and 100. respectively. The values differ from those obtained through Antoine equations which were 97.1and 100.00 respectively. The estimated errors from the extrapolation process is approximately 0.C.


The lab exercise was success because the state objective was achieved. The conditions necessary for azeotropic equilibrium were determine. For this type of equilibrium to take place the mole ratio of the vapor and liquid propanol must be equal. Other than plotting several figures which assisted in analysis, several other equations were introduced in the process which were used to validate the results obtained from the experiment.

Batch distillation methods gives results with a higher degree of accuracy compared to other methods of distillation. The conditions for processing the type of feeds involved helped in the analysis of the product. This method is useful in pharmaceutical process because the exact ratio and quantities are needed when developing certain drugs whose components can prove lethal if they are used in excess.

Though the errors were minimal during the experiment, the possible sources of errors could be failure to zero the electronic balance and thereby false values of mass were obtained. When determining the ratio of water and propanol, it was possible some errors occurred and thereby falsifying the results (Rousseau, 2017).















Gorak, A. (2014). Distillation: Fundamentals and Principles. Academic Press.

Kagaku Kōgaku Kyōkai (Japan), & Kagaku Kōgakkai (Japan). (2018). Journal of chemical engineering of Japan. Tokyo: Society of Chemical Engineers, Japan.

Rousseau, R. W. (2017). Handbook of separation process technology. New York: John Wiley & Sons.

Nevers, N. . (2013). Physical and chemical equilibrium for chemical engineers. Hoboken, N.J: Wiley.

Gunawan, R. J. (2010). Experimental measurement of liquid-fluid equilibria of dodecane + carbon dioxide and methyl oleate + carbon dioxide.

Cunningham, J. R., & Jones, D. K. (2011). Experimental results for phase equilibria and pure component properties. New York, N.Y: American Institute of Chemical Engineers


X-Y Plot for IPROPNOL and H2O (Thermo = VANL01, P = 14.696 psia)

x = y 0 1 0 1 Equilibrium curve 0 5.0000001000000002E-2 0.1 0.15000000999999999 0.2 0.25 0.30000000999999998 0.34999998999999998 0.40000001000000002 0.44999999000000002 0.5 0.55000000999999998 0.60000001999999997 0.64999998000000003 0.69999999000000002 0.75 0.80000000999999998 0.85000001999999997 0.89999998000000003 0.94999999000000002 1 0 0.40579680000000001 0.49524072000000002 0.52741735999999995 0.54168749000000005 0.54979621999999995 0.55638145999999999 0.56359844999999997 0.57256383 0.58392453 0.59811400999999997 0.61548102000000005 0.63636285000000004 0.66113186000000002 0.69023204000000005 0.72421318000000001 0.76376957000000001 0.80978846999999998 0.86341625 0.92615241000000004 0.99998719000000003

Liquid Composition, Mole Fraction IPROPNOL

Vapor Composition, Mole Fraction IPROPNOL