Abstract

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.

Introduction

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
Apparatus
i. Boiling chips

ii. Boiling flask

iii. Electronic balance

iv. Othmer still distillation apparatus

v. Refractometer

vi. Heating mantle

vii. Beakers/ vials

viii. Condensers

Procedure
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 , & Ko?gakkai , 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.

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

Van Laar

2.470754

1.090241

Table 1: Equation parameters