Solvent Extraction Unit

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Contents 1 General Description 1.1 Diagram 2 Inputs and Outputs 3 Model Theory 4 Data Sections 4.1 Requirements 4.2 Results 4.3 Isotherm Section 5 Adding this Model to a Project 6 Hints and Comments

General Description

The Solvent Extraction unit is designed for use as a solvent extraction model, which can also be configured to do organic stripping. The model ensures that mainly aqueous phases leave via the aqueous stream and organic phases leave through the organic stream.

The user is responsible for setting up a suite of species which accurately portrays the application that is being evaluated e.g. H₂O, H₂SO₄, Cu, Fe, CuSO₄, FeSO₄, Fe₂[SO4]₃, Kerosene, RH, R₂Cu, R₂Fe, R₃Fe. This suite of species is typically set up for chelating type of organic solvents such as the LIX hydroxy oxime copper extractants available from the Henkel Corporation i.e. LIX 64N, 65N, 860, 864, 865, and 622.

The model is capable of the following:

1. Based on a user specified separating density it is able to distinguish between an organic and an aqueous phase. The aqueous species are denser than the separating density and the organic species less dense. e.g. with a separating density of 950 kg/m³, water and all dissolved aqueous species will report to the aqueous phase and the organic species, normally with densities less than approximately 850 kg/m³, will report to the organic phase.
2. The user would select a primary metallic element of interest that is to be extracted, e.g. Primary Metal 'Cu'
3. The user should supply a reaction which utilises the specified Primary Metal, e.g. .
   Or in the case of stripping:
   
4. The model may be configured to use Isotherms (McCabe-Thiele diagrams) to determine the extent of the reaction, or the user may specify the reaction extent directly.
5. If the Isotherm method is chosen, the model uses the concentration of the primary metal in the streams entering the unit and the extraction (or stripping) isotherm, provided by the user, to determine the required primary metal concentration within the aqueous and organic phases. The model then calculates the extent to which the defined reaction should proceed to give the desired concentrations.
6. The ratio of the organic phase volume flow to the aqueous phase volume flow within the unit also fulfils a crucial role in the equilibrium extraction calculation. It provides the slope of the McCabe-Thiele operating line (a straight line). The Y-intercept is calculated by SysCAD using the data provided by the user. It is called MinOrgConc in the case of extraction, and MinAqsConc in the case of stripping.
7. The model is not currently sensitive to pH and assumes that the pH is correct for a particular equilibrium isotherm.

Diagram

The diagram shows the default drawing of the Solvent Extraction unit, with all of the streams that have to be connected for the unit to operate.

The physical location of the streams connecting to the Solvent Extraction unit is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label	Input / Output	No. of Connections		Description
		Min	Max
Aqueous Inlet	In	1	20	Aqueous feed to Solvent Extraction unit.
Organic Inlet	In	1	20	Organic feed to Solvent Extraction unit.
Aqueous Outlet	Out	1	1	Aqueous outlet from Solvent Extraction unit.
Organic Outlet	Out	1	1	Organic outlet from Solvent Extraction unit.

Model Theory

The Isotherm Method of modelling a Solvent extraction unit is based on the M^cCabe-Thiele method. This assumes that the operating line on the xy diagram, representing a single solvent extraction stage, is linear. The diagram below illustrates the graphical representation of the unit:

The operating line is the ratio of the incoming organic stream to the incoming aqueous stream.

The Equilibrium line is determined from experimental test data.

(This is the Isotherm that the user is required to input to the model. For extraction, the x axis is the concentration of the primary metal in the aqueous phase and the y axis is the concentration of the primary metal in the organic phase. For stripping, the x axis is the concentration of the primary metal in the organic phase and the y axis is the concentration of the primary metal in the aqueous phase.)

If the Metal (in this case Copper) concentration in the incoming Aqueous stream is 1.7 g/l, then, move vertically up the red line to the operating line, then horizontally to the Equilibrium line to find the equilibrium values of the Copper concentrations in the exiting Aqueous and Organic streams.

In this case the Organic Stream will contain 5g/l Cu and the Aqueous 0.4g/l Cu at equilibrium.

The values will be adjusted to take into account the stage efficiency, as the two phases are not usually in contact long enough to achieve perfect equilibrium.

In this example, the user will insert the Equilibrium curve into the model, and then the Reaction file should contain a reaction with the following form:

Extent:Fraction

Where (aq) denotes the aqueous phase and (o) the organic phase.

The model will adjust the extent of the reaction to produce the required aqueous and organic Copper concentrations.

Data Sections

The default access window consists of several sections,

1. The first tab has the same name as the model tag, contains general information relating to the unit.
2. Optional tab RB, or Reaction Block, is fully described in Reaction Block (RB).
3. The Info section, contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents. This is fully described in Common Data Sections.
4. Links tab, only visible in SysCAD 9.2, contains a summary table for all the input and output streams.
5. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Class: SolvExtr-1 The first tab page in the access window will have this name.

Tag / Symbol	Input / Calc	Description/Calculated Variables / Options
Common First Data Section
Requirements
RhoSep	Input	The required liquid separation density. This must be a value between the density of the aqueous and organic streams. Note: The density of water is a function of temperature, and is often less than 1000 kg/m3; therefore it is safer to specify a separation density below 950 kg/m3.
AqLoss	Input	The fraction of Aqueous liquid lost to the Organic product stream.
OgLoss	Input	The fraction of Organic liquid lost to the Aqueous product stream.
Method	None	The model does not use Isotherms to determine the extent of the extraction or stripping reaction. The user sets the extent/s of the reaction/s manually.
	Isotherm Method	The model uses Isotherms to determine the extent of the extraction or stripping reaction. Reactions will be switched on by SysCAD if the isotherm method is chosen. The user must still specify the reaction file and the reaction/s, but the model will set the extent of the extraction or stripping reaction/s manually. Note The reaction file may contain more than one reaction. The model will set the extent of the First reaction in the file. The user must set the required extents of the other reactions.
The following fields will be visible if the Isotherm Method is chosen.
AllowOveride	Tickbox	This allows the user to override the reaction extent calculated by the isotherm and manually set the reaction extent on the RB tab page.
Mode	Extraction	This mode is selected if the unit is used to extract the metal from the aqueous into the organic phase.
	Stripping	This mode is selected if the unit is used to strip the metal from the organic into the aqueous phase.
StageEff	Input	The efficiency of the solvent extraction stage.
Solute?	Input	The liquid containing the primary metal, e.g. for Extraction it may be CuSO4, and for Stripping R2Cu.
Primary Metal	List	The user must select the metal of interest from the list of available elements in the project. A valid element must be selected if the "Isotherm" method is selected. It is optional for the method "None", however it is useful to set this so that the feed and product concentrations can be shown.
Reactions	List	The user may turn the reactions 'On' or 'Off'. If this is 'On' then the RB tab page will become visible. Reactions will be switched 'On' by SysCAD if the isotherm method is chosen.
OperatingP... (available in SysCAD 9.2 or later)
Method	List	Atmospheric -- outlet streams will be at Atmospheric Pressure. The atmospheric pressure is calculated by SysCAD based on the user defined elevation (default elevation is at sea level = 101.325 kPa). The elevation can be changed on the Species tab page of the Plant Model.
		LowestFeed -- outlet streams will take the lowest pressure of the feeds.
		HighestFeed -- outlet streams will take the highest pressure of the feeds.
		RequiredP -- outlet streams will be at the user specified pressure.
Result	Display	The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).
Results
MinOrgConc OR MinAqsConc	Output	This field is only visible if the Isotherm Method has been chosen. The Y-intercept of the McCabe-Thiele operating line, MinOrgConc in the case of extraction, and MinAqsConc in the case of stripping. NOTE this is defined by the feed streams entering the unit operation.
ReactExtent	Feedback	This field is only visible if the Isotherm Method has been chosen. This is the reaction extent as appears in the RB tab page. Displayed here for easy access.
MaxLoadedConc	Output	If the Isotherm Method has been chosen, this field will only be visible if Extraction Mode is chosen. Displays the maximum concentration based on 100% extraction and calculated by mass balance. This will serve as a warning for incorrectly supplied data if the results differ to those expected.
MaxStripConc	Output	If the Isotherm Method has been chosen, this field will only be visible if Stripping Mode is chosen. Displays the maximum concentration based on 100% strip efficiency and calculated by mass balance. This will serve as a warning for incorrectly supplied data if the results differ to those expected.
Feed Conditions
AqsConcIn	Calc	The concentration of the Primary metal in the incoming Aqueous stream.
OrgConcIn	Calc	The concentration of the Primary metal in the incoming Organic stream.
OARatio	Calc	The calculated volumetric ratio of Organic to Aqueous liquid entering the unit.
AORatio	Calc	The calculated volumetric ratio of Aqueous to Organic liquid entering the unit.
Product Conditions
AqsConcOut	Calc	The concentration of the Primary metal in the outgoing Aqueous stream.
OrgConcOut	Calc	The concentration of the Primary metal in the outgoing Organic stream.

Isotherm Section

The user types in the Isotherm describing the Solvent Extraction process, either in the space required, or as a csv file (saved in Excel.)

Tag / Symbol	Options	Description
The black rectangle is for display purposes only. The user can configure the Information data to display the Isotherm curve.
Equation	Data Only XYFunction	The data is entered in a csv file, or on this page, in two columns. For example, for extraction, x represents the mass fraction of solute in raffinate, and y represents the mass fraction of solute in extract. The model interpolates linearly between the points and beyond the first and last points.
	Cubic-Spline	The data is entered in a csv file, or on this page, in two columns. For example, for extraction, x represents the mass fraction of solute in raffinate, and y represents the mass fraction of solute in extract. The model fits a curve between the points, but beyond the first and last points it assumes a horizontal straight line relationship.
Equation	+ / -	This is used if the user wishes to use an equation. In this case the model only accepts a data function.
Information	+ / -	The user clicks on the + to obtain the following buttons, these allow the user to configure the display.
	Lin > Log X	Toggles between normal and log on the x scale
	Lin > Log Y	Toggles between normal and log on the Y scale
	Auto>Manual Scale Display	Toggles between automatic and manual display parameters. If the display is in auto mode, then the model sets the minimum and maximum display parameters. Changing to manual allows the user to set these parameters.
	Graph : Width & Height	These numbers determine the size of the graph on this page.
	Display Min	The minimum display point on the graph
	Display Max	The maximum display point on the graph
	Lower Boundary	The lower boundary of the actual data points, i.e. the lowest point to which the data may be extrapolated.
	Upper Boundary	The upper boundary of the actual data points, i.e. the highest point to which the data may be extrapolated.
Data Points	+ / -	The user clicks here to enter the data points.
	File	The user may type in the file and path if the points are stored in a csv file.
	Length	The number of data points. If the user wishes to type the data points directly into the model, then this value needs to be filled in. Once a number has been typed in, the X and Y columns will be visible with the required number of lines.
	Load Points	This will load the points from the file.
	Save Points	This will save the points into the file.
	Sort	This will sort the data points into ascending x values.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

	DLL:	Separ1.dll	→	Units/Links	→	Separation: Mixer/Settler
OR	Group:	Mass Separation	→	Units/Links	→	Separation : Mixer/Settler

See Project Configuration for more information on adding models to the configuration file.

Insert into Project

Insert Unit

→

Separation

→

Mixer/Settler

See Insert Unit for general information on inserting units.

Hints and Comments

1. Check that the Separation Density specified in the model is a value between the aqueous and organic densities.
2. Isotherm data plot X and Y axes are in concentrations (g/L). For extraction, the x axis is the concentration of the primary metal in the aqueous phase and the y axis is the concentration of the primary metal in the organic phase. For stripping, the x axis is the concentration of the primary metal in the organic phase and the y axis is the concentration of the primary metal in the aqueous phase.
3. If the isotherm is required to be used outside the range of the data points entered, then SysCAD will linearly extrapolate from the nearest set of 2 points.