Methods and Materials

 

PROPERTY PACKAGES (UNIFAC)

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The UNIFAC (Universal Functional Activity Coefficients) method is a group contribution method. As it is group contribution model, it is used to predict the activity coefficients. Mainly used to calculate fugacity, enthalpy, entropy, and Gibbs free energy.

 

We use this method, as it requires no experimental data for the particular mixture of interest. Here, the mixture is “ACETONE/PHENOL” mixture. As the pressure is below 10atm i.e UNIFAC method is the best model to highly non-ideal liquid mixtures at low pressures (below 10atm).

 

 

THERMODYNAMICS OF THE MODEL

 

Separation operations are major problems in part of chemical engineering design. Many of these are diffusion operations which are phase-contacting type, distillation, absorption, and extraction are the most common operations. We need quantitative information on phase equilibrium in multi-component mixtures such as temperature, pressure, and compositions. These parameters are rarely available to acquire the desired experimental equilibrium data in a particular design. Therefore, it is necessary to estimate and interpolate existing data to determine the desired equilibrium from required conditions. UNIFAC model can be used for this kind of purposes. The UNIFAC group contribution method is a reliable and fast method for predicting liquid phase activity coefficients in non-electrolyte, non-polymeric mixtures at low temperatures, pressures to moderate temperatures, pressures between 300 K and 425K. This method widely used in practical chemical engineering applications mostly in phase equilibrium calculations where little or no relevant experimental information is available.

 

Advantages

·      Flexibility, as UNIFAC method has a well founded basis for estimation and establishing group sizes and shapes.

·      Simplicity, because UNIFAC parameters are nearly independent of temperature.

·      Large range of applicability.

 

Disadvantages

·      All components must be condensable.

·      Doesn’t apply to mixtures of polymers.

 

Applications of UNIFAC method

 

UNIFAC method is used in many areas such as

 

·      To calculate vapour-liquid equilibrium (VLE)

·      To calculate liquid-liquid equilibrium

·      To calculate solid-liquid equilibrium and also vapour pressures for pure components

·      To determine flash points of solvent mixtures, solubility’s of gases, estimation of excess enthalpies.

 

 

 

 

 

 

 

DISTILLATION (DISTL) COLUMN

 

We have chosen a distillation column (Distl) in ASPEN PLUS. It uses Edmister method for separating the components in a process.

·      Number of stages

·      Feed location

·      Reflux ratio

·      Pressure profiles

·      Distillate to feed ratio

 

This distillation column is used for a single feed and two product distillation. As mentioned earlier, this method uses Edmister method. Basically, this method can be used when everything in the column is mentioned. The results are verified. The following parameters are specified in this DISTL column

We get the feed stage temperature, bottom stage temperature, top stage temperature and feed quality as well as composition of the products.

 

 

 

This distillation column is used for a single feed and two product distillation. As mentioned earlier, this method uses Edmister method. Basically, this method can be used when everything in the column is mentioned. The results are verified. The following parameters are specified in this DISTL column.

·      Number of stages

·      Feed location

·      Reflux ratio

·      Pressure profiles

·      Distillate to feed ratio

 

We get the feed stage temperature, bottom stage temperature, top stage temperature and feed quality as well as composition of the products. Simulation of this mixture is done by using three DISTL distillation columns.

 

We have given the input conditions (Temperature, Pressure, molar flow rates) from DSTW distillation column to DISTL distillation column as these values provides satisfactory results. In this process simulation,  process begins with defining composition of feed values, electing a thermodynamic model (UNIFAC), information on component, such as acetone, phenol, cumene and water. Thereafter, the process is made to run to check it step wise, if got any errors, one can change the values as required. Afterwards, the DISTL column 2 is given its parameters such as number of stages, Reflux ratio, and distillate to feed ratio, feed stage to obtain the desired product of acetone in this distillation and water is separated from acetone in this distillation stage. Similarly, when the DISTL column 3 provided with the values of column parameters, phenol and cumene components gets separated from the mixture in this distillation