Sulfuric Acid

Navigation: User Guide ➔ Stream Properties ➔ Sulfuric Acid

Standard Species Model		Stream Properties								Special Cases
Standard Species Model	Stream Properties Calculations	Density	Heat of Formation	Heat of Dilution	Specific Heat (Cp)	Solubility	Boiling Point Elevation	pH	Charge	Steam and Water	Sulfuric Acid

Related Links: Species Database, Heat of Dilution, Phase Change

---

Introduction

Sulfuric acid (H2SO4) is a strong acid that is widely used in the hydrometallurgical industry. It has a strong affinity for water and is soluble at all concentrations.

Concentrated sulfuric acid, consists of 98.3% H2SO4(l) and 1.7% water. Any solution containing a lower concentration of acid, will contain the aqueous form, H2SO4(aq).

When water and sulfuric acid mix, or when streams with different concentrations of H2SO4 mix, there is an exothermic reaction and the resulting stream is hotter. This is known as the Energy, or Heat, of Dilution.

SysCAD has been designed to automatically handle the complexities of sulfuric acid dilution.

Adding or Removing Sulfuric Acid

SysCAD will automatically add both H2SO4(l) and H2SO4(aq) to all SysCAD species databases.

• If these species are not required in the project, then you simply do not add them to the configuration file.
• If you wish to Add sulfuric acid to a project, you need to include both species in the configuration file. SysCAD will expect both H2SO4(l) and H2SO4(aq) in the configuration file. Therefore, if you select one of these species to add to the configuration file, then SysCAD will automatically add the other species.
• If you wish to Remove sulfuric acid from the project, you need to remove both. You can simply select either H2SO4(l) or H2SO4(aq) from the display list and click on the Remove button. SysCAD will automatically remove both the liquid and aqueous species from the display list.

Please see Adding or Removing a Species for further information.

Editing the Properties of Sulfuric Acid

The SysCAD database will contain hardwired values for sulfuric acid. If the user has other data that they wish to use in the project, then they can type the required data into the fields in the species database, as described in Editing User Species Database.

Note: All fields that have hardwired data are indicated by a button on the right hand side with a ''.

When you view the data for either H2SO4(l) or H2SO4(aq), the data fields that are using hardwired data will be greyed out.

To edit the data, or to override it with your own data:

• Click on the button on the right hand side of the required data field
• A list of the available data will be visible from the popup window
• To use your own data, double click to edit the user data, a pop up dialog box will allow entry of user data. Note the input dialog boxes will vary with the function being edited.
• When changes are complete, click on the 'Update' button. To ignore any changes at this point, click on the 'Undo' button.
• If you wish to return to the hardwired data at any time you can simply click on the button and select the required data source from the list.

Please refer to Editing User Species Database for more information.

Sulfuric Acid in SysCAD Projects

If you have included sulfuric acid in the project configuration (cfg file), then SysCAD will use the data in the species database to calculate all of the normal properties of streams that contain sulfuric acid. In addition to this, SysCAD will do the following specific calculations:

Heat of Dilution

If the species database contains Heat of Dilution data (see Heat of Dilution in the Species Table) SysCAD will use this to calculate the temperature change when streams with different acid concentrations mix.

• If Heat of Dilution data is being used, it will usually be in the form of Spline data with Enthalpy of Formation at 25°C as a function of percentage acid mass in solution.
• If you do NOT want to include this functionality (enthalpy of mixing) in a project, then you must edit the species database and carry out the following steps:

1. Click on the button on the right hand side of H25
2. Select either Edit User Data or a hardwired constant value.
3. If you have chosen Edit User Data, then you will need to enter a constant value for the H25.
4. Click on 'Update'.
5. When you reload your project, the enthalpy of mixing will no longer occur.

• If you wish to re-enable the heat of mixing, then you must edit the species database and carry out the following steps:

1. Click on the button on the right hand side of H25
2. Select the a set of heat of dilution data from the popup list.
3. Click on 'Update'.
4. When you reload your project, the enthalpy of mixing will be enabled.

Note: In an open project in SysCAD to see the Enthalpy of Formation at various mass fractions of H2SO4, go to the Species Properties page (Species - View Properties) and adjust the Mass Fraction.

Automatic Phase Change between Liquid and Aqueous Forms

SysCAD will use the Phase Change data to automatically change H2SO4 from the liquid form to the aqueous form (and visa versa, although this seldom occurs in a hydrometallurgical facility).

• When you enter H2SO4 (aqueous or liquid) mass fraction data into SysCAD, for example in a Feeder, SysCAD will compare the mass fraction to the value in the species database. If the mass fraction is equal to or above the mass fraction of phase change, then SysCAD will use the Liquid form. If the mass fraction is less than the mass fraction of phase change, then SysCAD will use the Aqueous form.
• The hardwired SysCAD data for sulfuric acid specifies that the phase change occurs at a mass percentage in water of 98.3% H2SO4. Above this mass percentage, H2SO4 occurs in the liquid form, and below this it will occur as the aqueous form.

Example

User Input		SysCAD Result		Description
Species	Mass Percentage	Species	Mass Percentage
H2SO4(aq)	98.5%	H2SO4(l)	98.5%	Automatic change from Aqueous to Liquid form, 98.5% > 98.3%
H2SO4(l)	98%	H2SO4(aq)	98%	Automatic change from Liquid to Aqueous form, 98% < 98.3%
H2SO4(aq)	55%	H2SO4(aq)	55%	No change
H2SO4(l)	98.3%	H2SO4(l)	98.3%	No change

Your project must meet two conditions for automatic phase change between H2SO4(l) and H2SO4(aq) to occur:

1. The species database must contain Phase Change data - see Phase Change at Mass Fraction in the Species Table; and
2. The field PhaseChange@MF on the Plant Model access window is set to ON.

If the first condition is met, i.e. Phase Change data is present in the species database, but the PhaseChange@MF field is set to OFF, SysCAD will generate a single message every time that the project is solved - PhaseChange@MF switched off on the Settings Variations tab of the Messages window. This is to alert the user to the fact that while data does exist for the automatic phase change to occur, it has been disabled in the project.

Enabling H2SO4 Phase Change in a Project

1. In a new SysCAD project the user does not have to do anything to obtain this functionality for sulfuric acid. SysCAD will automatically detect if Phase Change data exists in the species database and will set the field PhaseChange@MF on the Plant Model access window to ON.
   • To disable or enable the Phase Change functionality, go to View - PlantModel and on the Species tab page, change the PhaseChange@MF field to OFF or ON.

Disabling H2SO4 Phase Change in a Project

There are two methods for disabling this functionality in a project. Both methods require H2SO4(aq) and H2SO4(l) to be included in the configuration file list of project species. The first method is simpler and does not involve closing the project or removing any data:

1. Go to View - PlantModel and on the Species tab page, set the PhaseChange@MF field to OFF.
2. Edit the species database as follows:
   • Go to H2SO4(aq)
   • Double click on the button next to the 'PhaseChange' field to edit the user data. (see Editing the Properties of Sulfuric Acid)
   • Select Undefined for the Phase Change Type
   • Click on the Yes button if asked to change configuration to USER
   • Click on the Update Button
   • Click on the OK button and reload the project.

Changing H2SO4 Phase Change Data

The default data for H2SO4 will change sulfuric acid from the liquid to the aqueous form at 98.3% H2SO4. However, some users may wish to use a different value for the phase change, such as 98%. To do this edit the species database as follows:

1. Go to H2SO4(aq)
2. Double click on the button next to the 'PhaseChange' field to edit the user data. (see Editing the Properties of Sulfuric Acid)
3. Select Change @ MF : Constant for the Phase Change Type
4. Select H2SO4(l) for the Paired Species
5. Enter the desired value in the Function section, e.g. 0.98
6. Click on the Yes button if asked to change configuration to USER
7. Click on the Update button
8. Click on the OK button and reload the project.