user guide gpec 2012 1

7/26/2019 User Guide Gpec 2012 1

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GPEC V3.2.0

Martn Cismondi and Martn Gaitn, 2012

This user guide by:

SofaStellin, Melisa Gomez, Martn Gaitnand Martn Cismondi

December 2012

IDTQ (UNC-CONICET)

www.idtq.efn.uncor.edu

http://gpec.phasety.com

E-MAIL: [email protected]

Global Phase Equi l ib r ium Calculat ion s


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BACKGROUND

GPEC is a software originally created over the years 2005-2009 in PLAPIQUI-

CONICET (Bahia Blanca, Argentina) in a project promoted and supervised by Professor

Esteban Brignole. It is based in methods and algorithms developed mainly by Professor

Martin Cismondi in collaboration with Professor Michael Michelsen (Technical

University of Denmark) and Professor Marcelo Zabaloy (UNS-PLAPIQUI). The front-end

or visual interface in the original version was developed by Diego Nuez at PLAPIQUI,

and used to be available atwww.gpec.plapiqui.edu.ar

Nowadays, GPEC continues to be updated and developed by Phasety, in

collaboration with the IDTQ Group in the FCEFyN-UNC (Universidad Nacional de

Crdoba, Argentina).

So far, no other software is known with the same or equivalent capabilities.

That is why GPEC has a growing user community in most of Europe, Latin America,

USA, Asia and Africa, and belonging not only to academic and research institutions but

also to industries.

This user guide, corresponding to the present front-end developed by Martn

Gaitn at IDTQ first and Phasety at present, is based on and includes fragments from

the last guide for the previous version of GPEC, authored by Gerardo Pisoni and Martin

Cismondi, and delivered in February 2010.
http://www.gpec.plapiqui.edu.ar/http://www.gpec.plapiqui.edu.ar/http://www.gpec.plapiqui.edu.ar/http://www.gpec.plapiqui.edu.ar/


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1. WHAT IS GPEC AND WHAT CAN I USE IT FOR?

GPEC is a computer program that allows you to obtain phase diagrams and

other thermodynamic plots for binary systems, as calculated with equations ofstate. It can be helpful for either educational, academic or development

purposes.

It is easy to use and you do not have to provide any initial guesses or other

inputs.

The diagrams you can calculate and see with GPEC are: 3-D diagrams (P-T- and

P-T-z, 2-D diagrams (global phase equilibrium diagrams in different projections,

P-xy diagrams for constant temperature, T-xy diagrams for constant pressure

and isoplethes for a constant composition).

In the present version of GPEC five different equations of state can be used:

The SRK or Soave-Redlich-Kwong EOS (Soave, 1972).

The PR or Peng-Robinson EOS (Peng and Robinson, 1976).

The RK-PR EOS (Cismondi and Mollerup, 2005).

The SPHCT or Simplified Perturbed Hard Chain Theory EOS (Kim et al.,

1986).

The PC-SAFT or Perturbed Chain Statistical Associating Fluid Theory (Gross

and Sadowski, 2001).


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2. HOW DO I USE GPEC?.

When you first run the GPEC program, you will see the main screenshown in

Figure 1.

2.1. The main screen.

Figure 1.The main screen.

In this screen you can recognize four panels, whose titles or names are

highlighted with a red oval in Figure 1:

1. Cases panel: is the place where your defined system will appear in its

respective tab.

2. Manager panel: is the site where all the calculated d iagrams will be listed.


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3. Plots panel:in this part of the screen, graphics will be displayed in their

respective tab.

4. Info panel:is where the program gives detailed information including the

following tabs:

Log. Its arecord of computer activity used for statistical purposes as

well as backup and recovery. Log files are written by the operating

system or other control program for such purposes as recording

incoming dialogs, error and status messages and certain transaction

details. Message types that can appear are:

Error

Info

Ok

Warning

Input/output. An input is data that is ready for entry into the

computer. An output is any computer generated information displayedon screen.

Shell. The outer layer of a program that provides the user interface,

or a way of commanding the computer.

About terminology, there are different references on the web that can be

consulted, for example:http://www.pcmag.com/encyclopedia/ .
http://www.pcmag.com/encyclopedia/http://www.pcmag.com/encyclopedia/http://www.pcmag.com/encyclopedia/http://www.pcmag.com/encyclopedia/


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2.2. Creating a Case.

The first step required before running any application is to define a binary

system by choosing two components from the list

1

. This can be done by clicking on the

Define system button ( ). Immediately, the program shows you the following

window (Figure 2).

Figure 2.Defining a binary system.

On the left side you can find the list of the different components from de DIPPR

database. (R.L. Rowley, Wilding, W.V., Oscarson, J.L. and collaborators, 2003)

From that list you can select the two compounds that define your binary system by

using the arrow to the right . You can deselect a compound using the arrow to the

left .

Note that in the figure, the compounds (Carbon Dioxide-Ethane) have already

been selected (see the System box).

Once you have already defined your system (shown in the Case 1tab), you have

to choose the equation of state you want to use and specify pure compound and

interaction parameters. The program shows you the following window (Figure 4). You

1Alternatively, you can open a project saved in a previous session, which already contains two

compounds and parameters (see section 4).

Searching bar


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can choose the model to be used from the Model drop-down list. The five equations

of state available are:

The PC-SAFT or Perturbed Chain Statistical Associating Fluid Theory.

The PR or Peng-Robinson EOS.

The RK-PR EOS.

The SPHCT or Simplified Perturbed Hard Chain Theory EOS.

The SRK or Soave-Redlich-Kwong EOS.

Note that in Figure 4 on the left side you can see the selected compounds. The

program shows you in the first place the lighter compound (more volatile) and below it

the heavier one.2

Figure 4.A view of the window after defining the binary system.

2The mathematical criterion in GPEC is that the more volatile compound is the one with the lowest value

for Tc12

/Pc.


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2.2.1. Pure compound parameters.

As you change the model from the Model drop -down list, the parameter

columns in the component boxes will change accordingly. There are two different waysfor defining each pure compound parameter set that will be used in the calculations:

For each compound, on the left side you can see the experimental values of the

critical temperature, pressure and the acentric factor, as taken from the DIPPR

data base. Then you can obtain the corresponding values of the parameters for

the selected model by clicking the arrow .

Note that the experimental critical volume is also shown initially on the left

side, but then it changes to the predicted value after clicking the arrow .

If you choose the RK-PR EOS you need to provide either a temperature

(absolute or reduced) for matching the experimental saturated liquid density,

or a specification for the value of the Vc ratio.

Alternatively, you can choose to specify numerical values for the parameters, for

example the original parameters for PC-SAFT (Gross and Sadowski, 2001). In this

case, you have to activate first the parameters column by clicking the small

circle in the top of the right side. After typing the numbers, by clicking the


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arrow you can see the predicted critical constants in the corresponding

side3.

2.2.2. Binary interaction parameters: Quadratic Mixing Rules K ijand Lij.

These parameters modify the value of the cross energetic and size parameters

respectively, according to the default mixing rule for each model (default values are

zero).

You can choose either the Van der Waals combining Rule or the Lorentz-

Berthelot combining rule (see the Other case variables box), except for PC-SAFT and

SPHCT, that were developed based on Lorentz-Berthelot combining rules.

Theoretically, these models would not admit using van der Waals combining rules due

to the physical meaning of their attractive and repulsive parameters.

In the next version of GPEC there will be an option that will allow you to make

the attractive interaction parameter Kij temperature-dependent.

3. HOW DO I GENERATE A DIAGRAM?

Once you have parameters and critical constants consistent with each other you

are ready to run a diagram calculation by clicking the run button4. You can also

specify a maximum pressure for the liquid-liquid critical line (the default value is 2000

bar, you can change this in the option Maximum pressure for LL critical line see figure

1 in the left down corner.

The types of diagrams that you can generate with GPEC are (see the Diagrams

drop-down list):

3The reason why it is important to have the predicted critical constants for each component is that the

construction of a global phase equilibrium diagram is started from pure compound critical points.

Besides this, it might be important for you to know what critical point your parameters are predicting

actually.4If you did not click the arrow corresponding to your specification (constants or model parameters), the

calculation will be performed automatically anyway, before proceeding to the calculation of the global

phase equilibrium diagram.


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Global phase equilibrium diagrams (or univariant lines diagrams): they are

shown through 3 dimensional (3-D) graphics such as P-T-x and P-T-, and also 2

dimensional (2-D) projections, including: P-T, P-z, T-z, T- and P- .

P-xy diagrams (for a specified constant T).

T-xy diagrams (for a specified constant P).

Isopheths (for a specified constant composition).

In the following sections you'll read about these different diagrams that you can

calculate using GPEC.

3.1. Generating a global phase equilibrium diagram: 3-D diagrams.

The inclusion of this type of diagrams is the main new feature in the present

version of GPEC. A global phase equilibrium diagram is a collection of critical lines, pure

compound vapor pressure lines and in some cases also LLV and/or azeotropic lines in

the P-T-x- space, calculated for a given binary system. All these lines are automatically

detected and calculated by GPEC according to the computational strategy and methods

proposed by Cismondi and Michelsen (2007a) and Cismondi et al. (2008).

After clicking the run button ( ) in the main screen you will see in the

Manager panel a tree organizing the different diagrams generated. First of all, you

have the 3-D diagrams such as: P-T-x and P-T- (Figure 5 and 6, respectively).

Next to the Manager panel you have the Plots panel where you can visualize

the diagrams generated.

If you click on the button you will see the plot in a full screen size. Note that

you can rotate the graphic by holding the left mouse button.


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Figure 5. The P-T-x diagram for the defined system.

Figure 6.The P-T- diagram for the defined system.

Below the graphic area you have a series of buttons with different functions:


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(HOME):undoes all changes made in the graphic at that moment so that the

original view is restored.

(BACK FORWARD): is used to undo or redo an action, respectively.

(PAN): it changes the ranges for the plot by clicking and dragging indiferrent

directions (up/down or left/right) with your mouse.

(ZOOM): is useful to explore a specific area of the diagram by clicking and

selecting that area of interest with your mouse.

(CONFIGURE SUBPLOTS): is used to adjust the size of the graphic area. When

you click this button a new window will emerge (Figure 7). There, you can click

on a slider to adjust the subplot.

Figure 7. Configure subplots window.

(SAVE): this button enables you to save the image of the current diagram in

your computer.

The same buttons and possibilities are also available in the 2-D diagrams.

Then, if you click on the plot area with the right mouse button you have the

posibility to:

1. Eliminate some lines (and also points in the case of isopleths) just by demarking

the corresponding check box, which can be useful when some lines are very


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close and overlapping or crossing with each other. The colors assigned to the

different types of lines, in order to distinguish them, are as follows:

Vapor pressure greenCritical black

LLV red5

Azeotropic violet

2. Change the scales. You can choose to express the 'x' and/or 'y' scales in a

logarithm form (Log x/Log y) by marking the corresponding check box.

3. Add a grid by marking the corresponding check box.

4. Add Legends. This option was not available in the previous versions of GPEC.

5. Set plot title. This enables you to change the title of the plot.

6. Set perspective. You can choose the perspective from which you want to display

and analyze the graph. This option is only logically possible for 3-D graphics.

Options 1 to 5 are also available to be used for the 2-D diagrams.

3.1.1. Visualizing different projections of a global phase equilibrium diagram: 2-Ddiagrams.

The P-T projections are the ones most frequently seen in books and scientific

papers, and probably the most useful in general. Nonetheless, the information they

provide is not complete for the analysis or understanding of global phase equilibrium

diagrams. Using GPEC you can visualize different projections of the calculated global

phase equilibrium diagram (see the Manager panel): P-T diagrams, T-x diagrams, P-x

diagrams, T- diagrams, P- diagrams. These graphics are displayed in the Plots panel

in their corresponding tab. The appearance order of the different projections is: P-T, T-

x, P-x, T- and finally P-. Note that on each tab, the case number appears in round

brackets.

In the following figures you can see the P-T and T- projections corresponding to

the examples in Figure 5 and 6.

5In projections with composition or density as one of the variables, the liquid branches appear in blue.


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Figure 8. The P-T projection of a calculated global phase equilibrium diagram.

Figure 9. The T- projection of a calculated global phase equilibrium diagram.

3.2. Generating P-xy diagrams.

Now we will focus on the P-xy diagrams. You can choose this option from the

Diagrams drop-down list by clicking on the P-xy option. Then you will see a white field

where you can enter a temperature value in Kelvin degrees (default is 300 K). After

clicking the Plot button ( ) the calculated P-xy diagram for the specified


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temperature will appear in the screen as a new tab in the Plots panel. An example is

shown in Figure 9 for a temperature value of 250 K, in this case with an azeotropic

point, in accordance with the global projections previously shown for the

corresponding case.

Figure 10. Example of a P-xy diagram.

An advantage of this new version of GPEC is that you can view the generated P-

xy diagrams included in the 3-D Global phase diagrams (Figure 11). Note that the

isothermal line is shown with a black dotted line on the 3-D graph.


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Figure 11. Global phase equilibrium diagram with oneP-xy diagram included.

P-xy as well as T-xy diagrams are automatically calculated by GPEC according to

the computational strategy and methods proposed by Cismondi and Michelsen

(2007b). No other input than the temperature (or pressure) is required.

3.2.1. The pressure-density plot.

Also, you have the option to visualize the pressure-density diagram for the

phases appearing in the P-xy diagram (Figure 12). This plot is generated jointly with the

P-xy diagram and available in a consecutive tab in the Plots panel.


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Figure 12. Example of a P- diagram (corresponding to the P-xy diagram in Figure 10).

3.3. Generating T-xy diagrams.

In the same way you proceed to obtain a P-xy diagram you can do it for a T-xy

diagram. You only need to specify a pressure value (in bar, default is 100) and click the

corresponding button ( ). An example is shown in Figure 13 for 2 bar, corresponding

to same case as for the previous examples.


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Figure 13. Example of a T-xy diagram.

Similar to the P-xy diagram, you can view the generated T-xy diagramsincluded

in the 3-D Global phase diagrams (Figure 14).

Figure 14. Global phase equilibrium diagram with the T-xy diagram included.


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3.3.1. The temperature-density plot.

Analogous to the P-xy case, you can access the temperature-density plot

corresponding to the T-xy diagram at the specified pressure just by clicking the T- tab.

An example is shown in Figure 15.

Figure 15.Example of a T- diagram (corresponding to the T-xy diagram in Figure 13).

3.4. Generating isoplethic diagrams.

Another possible and useful phase diagram is the constant composition diagram

or isopleth. You can generate it choosing the option Isopleths in the Diagrams drop-

down list. Once you have selected this type of diagram, a white field will appear. There,

you have to specify the global composition of the binary system (as molar fraction of

component 1, default is 0.97). Then, after clicking the Plot button ( )the P-T plot

will be displayed. As an example, in Figure 16 an isopheth for z =0,5 is shown for the n-

Butanen-Decane binary system.


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Figure 16. Example of an isopheth in a P-T diagram.

Note that the critical point is indicated in the graphic with a black dot.

Similar to the P-xy and T-xy diagrams, you can view the present isoplethic

diagram included in the 3-D Global phase diagram for the corresponding case (Figure

17). Note that the isopleth is shown as a green dashed line on the 3-D graph.


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Figure 17.Global phase equilibrium diagram with an isopleth included.

Besides, you can choose among other projections, which are shown below. The

black lines correspond to incipient phases while the green color denotes the saturated

phase.

3.4.1. The temperature-x and pressure-x projections.

Figure 18. Example of an isoplethic T-x diagram (corresponding to the P-T diagram in Figure 16).


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Figure 19. Example of an isoplethic P-x diagram (corresponding to the P-T diagram in Figure 16).

3.4.2. The temperature-density and presure-density projection.

Figure 20.Example of an isoplethic T- diagram (corresponding to the P-T diagram in Figure 16).


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Figure 21. Example of an isoplethic P- diagram (corresponding to the P-T diagram in Figure 16).

4. HOW DO I WORK WITH CASES?.

First of all, its necessary to define the therm Case. A Case is defined once you:

Define the compounds for your binary system.

Select an EOS model.

Establish values or a procedure to work with pure compound parameters,

provide values for interaction parameters such asKijand Lijfor quadratic mixing

rules, and a maximum pressure for the liquid-liquid critical line. There are

default values or choices in all cases.

So, when all these points are defined you will have your Case already specified.

The first time you do this, it will be named Case 1 (the tab name is Case 1). Then, if

you create a new Case by clicking the add button ( ), this new one will be

displayed in another tab named Case 2, and so on.

Besides, once you have defined a Case and ploted it, if you want to change

something, for example an interaction parameter, while keeping the rest in order to

make a comparison, you can do it in a new case, just by clicking the Clone case button

( ). This will enable you to change any of the selections that defined the original

case, so you can then compare and analyze different situations.


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Finally, you can open a Case that has been created previously and edit it or

continue working with it. This last action will be explained in the next section.

5.

HOW DO I USE THE MENU BAR?

In the menu bar, you have the following options:

File.

View.

Help.

The File option includes:

Open. You have to choose a case from the list displayed.This allows you

to continue working in a previoussession, without having to make your

choices and type your parameters again.

Save as. You can save information about the system, model, parameters,

etc. you are working with. It causes a copy of the current case and it lets you

make a copy of the file in a different folder or make a copy with a different

name.

Save. You can store the data back to the file and folder it originally came

from.

Exit. To get out of the current Case or quit the program.

The View option enables you to restore the default views of the different

panels if their size has been modified.

The Help option gives you information about the current version of the

software.


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6. REPORTING A BUG OR ANY PROBLEM WHEN USING GPEC.

In case the program does not work as it should in a particular case, you may

contact us to report the problem. Just follow the indications in the web page:

http://gpec.phasety.com

7. UPDATES.

Remember also to visit the web page regularly for updates that may be released

from time to time. These updates may contain:

Improvements, in case bugs were detected and fixed.

New models implemented.

New types of calculations or particular features, etc.

The new changes and improvements we are developing and that wouldbe

available in the next version of GPEC are related to:

Parameter Kij. There will be an option that will allow you to make the attractive

interaction parameter Kij temperature-dependent.

Other features. Features independent of global equilibrium diagrams such us:

pressure-density isotherms for mixture or specified compositions, single P-xy and T-

xy regions from given starting points and fugacity-composition plots for specified

temperature and pressure.


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8. GLOSSARY.

,density.

,azentric factor.

Kij, mixing rules parameter

Lij, mixing rules parameter

LLV, liquid-liquid vapour equilibrium line

T, temperature.

Tc, critical temperature

P, pressure.

Pc, critical pressure

V, volume.

Vc, critical volume.

x, dew point composition, molar fraction.

y, bubble point composition, molar fraction.

z, global composition, molar fraction.


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9. REFERENCES.

Cismondi, M.,Brignole, E. A., Mollerup, J. (2005) Rescaling of Three-Parameter

Equations of State: PC-SAFT and SPHCT. Fluid Phase Equilibria, 234, 108-121.

Cismondi, M., Michelsen, M. L. (2007a) Global Phase Equilibrium Calculations:

Critical Lines, Critical End Points and Liquid-Liquid-Vapour Equilibrium in Binary

Mixtures. The Journal of Supercritical Fluids, 39: 287-295.

Cismondi, M.,Michelsen, M. L. (2007b) Automated Calculation of Complete Pxy

and Txy Diagrams for Binary Systems. Fluid Phase Equilibria, 259: 228-234.

Cismondi, M., Michelsen, M. L., Zabaloy, M.S. (2008) Automated generation of

phase diagrams for binary systems with azeotropic behavior. Industrial and

Engineering Chemistry Research, Vol. 47 Issue 23, 97289743.

Cismondi, M., Mollerup, J. (2005) Development and Application of a Three-

Parameter RK-PR Equation of State. Fluid Phase Equilibria, 232: 74-89.

Gross J., Sadowski G. (2001) Perturbed-Chain SAFT: An Equation of State Based

on a Perturbation Theory for Chain Molecules, Ind. Eng. Chem. Res., 40: 1244

1260.

Kim, C.H., Vimalchand P., Donohue, M.D., Sandler, S.I. (1986) Local Composition

Model for Chain-Like Molecules: A New Simplified Version of the Perturbed Hard-

Chain Theory, AIChE J., 32: 1726-1734.

Peng, D.-Y., Robinson, D.B. (1976) A New Two-Constant Equation of State, Ind.

Eng. Chem. Fundam., 15: 59-64.

R.L. Rowley, Wilding, W.V., Oscarson, J.L., Yang., Zundel, N.A., Daubert, T.E.,

Danner, R.P., DIPPR Data Compilation of Pure Compound Properties. Desing

Institute for Physical Properties, AIChE, New York, 2003.

Soave G. (1972) Equilibrium constants from a modified Redlich-Kwong equation

of state, Chem. Eng. Sci., 27: 1197-1203.

user guide gpec 2012 1

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