Incorporating Kinetics into a Lithium Purification Process Model

Table of Contents

Objective

Process Overview

Defining Kinetics in the Chemistry Model

Using the Optimizer for Kinetic Variables

Replacing Kinetic Parameter Values in the Chemistry Model

Detailed Video Tutorial

Conclusion

Objective

This article demonstrates how OLI Flowsheet: ESP can be used to align lithium purification model predictions with field or experimental data. By combining measured product compositions with OLI’s kinetic modeling and Optimizer tools, users can adjust reaction parameters to match observed process performance. In addition to model calibration, the article also highlights several important considerations in lithium purification modeling, including setting up nanofiltration, pH neutralization, and process configuration.

Disclaimer: The user interface, calculations, and results displayed in this article are from OLI Flowsheet: ESP Version 12.0. Other software versions may appear different due to continual developments to the software.

Process Overview

Figure 1. Lithium purification process model in OLI Flowsheet: ESP 

In this example, a LiCl-containing feed stream with contaminants enters a Component Splitter, simulating a nanofiltration module. Key parameters include:

• Li-containing species: Generally assigned a permeate fraction of 0.99.
• Contaminants: Assigned a permeate fraction of 0.8, contributing primarily to the "NF Concentrate" stream.

Note: The permeate fractions assigned to lithium-containing species and contaminants are based on manufacturer-provided data describing nanofiltration (NF) ion rejection performance. Actual values will vary depending on the specific membrane type and operating conditions used by the user.

The "NF Permeate" stream, treated to a pH of 8 via a pH Controller, consists of O(-2), H(+1), Cl(-1), Na(+1), and Li(+1). This stream is mixed with NaOH and fed into a Concentrator, which evaporates water to concentrate the lithium solution. The concentrated solution then enters a Crystallizer—a kinetic reactor—producing LiOH·H₂O (solid) and NaCl (solid).

Defining Kinetics in the Chemistry Model

Figure 2. Kinetics definition window in OLI Flowsheet: ESP

In OLI Flowsheet: ESP, all reactions are assumed to proceed to equilibrium. However, for this model, we aim to control the precipitation rates of LiOH·H₂O and NaCl to more closely match predictions with sample data. 

1. Access the Kinetics tab in the Chemistry Model.
2. Define the two chemical reactions using the OLI Tag name convention.
3. Enter initial estimates for the Arrhenius kinetic parameters for each reaction. For additional guidance, please see our Support Center article on Arrhenius kinetics.

Figure 3. Defining a Kinetic Reactor in OLI Flowsheet: ESP

In the Flowsheet tab, the Crystallizer is a kinetic reactor which leverages the reaction rates defined in the Chemistry model.

Figure 4. Configuring the Number of Stages and Residence Time for the Kinetic Reactor

The reactor’s Kinetics Parameters include Number of Stages and Residence Time. For more information on these parameters, please refer to our Support Center article. 

Using the Optimizer for Kinetic Variables

The Optimizer tool in Flowsheet: ESP allows users to define Objective Functions to maximize/minimize, based on Variables to fix/free. In this case, it serves to refine the model's alignment with experimental data by minimizing prediction errors from the kinetic reactor. Please refer to our Support Center article for more information on available mathematical functions and naming rules for the Optimizer. 

Figure 5. Optimizer user interface in OLI Flowsheet: ESP

Objective Functions:

• Minimize the model prediction error compared to experimental datapoint for LiOH.1H2O precipitation
• Minimize the model prediction error compared to experimental datapoint for NaCl precipitation

To meet these Objective Functions, we identified two Variables:

• KF (Forward Reaction Rate Constant) for LiOH.1H2O precipitation
• KF for NaCl precipitation

The simulation concludes when the Objective Value achieves the specified tolerance (e.g., 1e-3).

Replacing Kinetic Parameter Values in the Chemistry Model

Replace the existing forward reaction rate constants in the Kinetics tab of the Chemistry Model with the regressed values from the converged Optimizer run. 

Then, the model can be run without the Optimizer. To do so, please uncheck the “Enable optimizer in the simulation” checkbox in the Optimizer tab.

Figure 6. "Enable optimizer" checkbox

Detailed Video Tutorial

Watch our step-by-step tutorial for constructing this model and fine-tuning the kinetic reactor outputs to match experimental data using the Optimizer tool.

Lithium Purification Tutorial | Nanofiltration, Kinetics & Optimizer in OLI

Conclusion

This article provides a framework for building lithium purification models tailored to experimental or operational data. For further assistance with model development or troubleshooting, please submit a support ticket at support.olisystems.com.