Thermogravimetric Analysis of Molten Salts' Kinetics

Ali Z. Fadhel, John Cameron, Hussam Al Khasawneh, and Zaki Yusuf. Paper Engineering, Chemical Engineering, and Imaging, Western Michigan University, A-217 Parkview Campus, Western Michigan University, kalamazoo, MI 49008


The purpose of this study is to generate kinetics data and to build a kinetic model for borate autocausticizing using thermogravimetric techniques. Furthermore, borate autocausticizing is a promising approach for the improvement of operational and environmental operations in Kraft pulping and its chemical recovery. The advantages of utilizing borate autocausticizing include partial or total elimination of the lime cycle (which is the biggest energy consumer in modern papermaking operations), pulp strength improvement and capital and maintenance cost savings.

The process of borate autocausticizing involves the use of an amphoteric salt, sodium metaborate, to decarbonize sodium carbonate and produces trisodium borate. This reaction occurs at high temperatures, it is suggested to carry out this reaction in the chemical recovery boiler. Furthermore, the reactions suggested by Tran and Cameron (1999) are shown below; trisodium borate reacts with water in the green liquor tank to produce sodium hydroxide. Moreover, the produced sodium hydroxide is used in the chemical cooking of the wood chips to extract the lignin

NaBO2 + Na2CO3 → Na3BO3 + CO2 (1)

Na3BO3 + H2O → 2NaOH + NaBO2 (2)

This research aims at a systematic analysis of borate autocausticizing kinetics. The uniqueness of this research is the usage of a ThermoGravimetric Analyzer (TGA) to study the kinetics of the borate/carbonate reaction. The experiments are designed with three control variables: stoichiometric ratio of borate to carbonate, reaction temperature and amount of carbon dioxide in the reactants environment. The response variable is the amount of carbon dioxide generated from the reaction. The weight loss as a result of carbon dioxide emission is measured by the TGA and the results can be displayed graphically or exported to an Excel spreadsheet. Moreover, the data are analyzed through material balance, kinetics modeling and statistics.

The analysis of the system shows good material closure within 3% in agreement with reaction 1. The kinetics are studied with an Arrhenius' type analysis to estimate the orders of reaction, the activation energy, and the pre-exponential factor.