Synthesis and Characterization of Hydrotalcite-like Compounds Produced via Hydrothermal Treatment
Advancing the chemical engineering fundamentals
Crystallization (T2-9P)
Keywords: Hydrotalcite,crystallization, hydrothermal
Hydrotalcites-like compounds (HTlc) are stacks of metal hydroxides layers with anions in between, compensating the charges, and also water. Despite of many possible application of HTlc, currently they are used commercially in pharmaceutical, PVC and catalyst industry. Wide spread use of the material is still limited due to their complex production process. HTlc is generally produced by precipitation of acid/basic solution in batch reactor. This process includes the removal of acid/base material from the starting solution via a washing process, which is of course time consuming, expensive and waste productive. A novel hydrothermal method to produce HTlc has been proposed. This method does not use acid/basic starting materials, thus eliminating the requirement of product washing.
In this research project, the production of HTlc via direct hydrothermal treatment of magnesium oxide and aluminium trihydroxide with Mg/Al ratio of 2 is studied in a batch process. An optimization of the process is performed with respect to the conversion of the magnesium oxide, reaction rate and crystal polytype. The optimization parameters include nature of the reactant, reactant pre-treatment and reaction temperature profile. The product characterization includes the determination of crystal structure, product size distribution and degree of crystallinity.
Optimization of the hydrothermal process for producing HTlc has resulted in a drastic reduction in batch time combined with an increase in the product purity. Two different HTlc polytypes can be produced at different operating temperatures. Polytype 3R1 is produced at temperature below 90°C and the other polytype, 3R2, is produced at higher temperature. The reaction rate is especially enhanced by the milling of the starting material prior to the reaction.
Presented Wednesday 19, 13:30 to 15:00, in session Crystallization (T2-9P).
