Public defence in Chemical Engineering, M.Sc. Mitra Ila

Title of the thesis: Toward higher purities of diols and polyols by solid-liquid equilibrium modeling and cooling crystallization

Thesis defender: Mitra Ila
Opponent: Prof. Dr.-Ing. habil. Dr. h.c. Joachim Ulrich, Martin Luther University Halle-Wittenberg, Germany
Custos: Prof. Marjatta Louhi-Kultanen, Aalto University School of Chemical Engineering

Optimizing purification of bio-based diols and polyols using crystallization techniques

This research focused on optimizing the purification of key compounds such as monoethylene glycol (MEG), glycerol, mannitol, and xylitol by employing cooling crystallization techniques to achieve high purity products. These compounds were derived from sustainable biomass sources through the conversion of cellulose and hemicellulose into hydrolysates, which were subsequently utilized in fermentation and chemical processes. The research addressed purification challenges associated with close-boiling and azeotrope-forming impurities, heat sensitivity, and high viscosity of the main components, alongside the purification and isolation of xylitol and mannitol obtained from fermentation broth.

The study demonstrated the effectiveness of solvent-aided melt crystallization in purifying MEG and glycerol from both thermodynamic and kinetic perspectives, offering key insights into changes in operating temperatures, crystallization driving force, crystal growth rates, product purity, and yield. It further explored the melt crystallization method for purifying xylitol derived from xylose fermentation, addressing efficiency and challenges. These findings provided the necessary information for refining crystallization techniques to improve product purity and yield while minimizing operation time and reducing the number of crystallization and post-treatment steps needed to achieve the desired purity. Additionally, this study offered insights into controlled cooling crystallization methods for purifying mannitol in the presence of fermentation by-products, using predicted solid-liquid equilibrium diagrams. It examined how variations in impurity levels influenced the effectiveness of this method and the overall yield in D-mannitol production.

The methodologies and results from this study can be applied by industries involved in chemical production and biomass processing to optimize purification steps and improve product outcomes. An efficient downstream purification method allows higher yields of ultra-pure bio-based products, which can be integrated into various sectors, including cosmetics, pharmaceuticals, food industry, and in general biomaterial production.
 
Keywords: Cooling crystallization, solid-liquid phase equilibrium, melt crystallization, purification, diols, polyols

Thesis available for public display 10 days prior to the defence at Aaltodoc.