Thermal Unit Operations / Separation Technology

The main research areas of the Thermal Unit Operations group are crystallization and advanced oxidation processes.


Because it is economical and efficient, crystallization is a widely used separation and purification procedure in water treatment processes and the chemicals, pharmaceutical and food industries. The crystallization research of the Thermal Unit Operations group utilises modern measuring methods to optimise and monitor crystallization processes. In the future, the need for making use of side streams by recovering chemicals will probably grow, and crystallization is one of the potential separation methods available. Crystallization can also be utilised in other Cleantech applications in order to achieve low emission rates. In years to come, crystallization may, for instance, have a significant role in separating biomass-based compounds.

About crystallization in general

The starting point for crystallization is that the equilibrium state between the crystal and solution phase, that is the thermodynamics of the material system at various temperatures, must be sufficiently well known. In general, solubilities in different crystallization applications are determined through experiments carried out in the temperature range specified for the solution being examined. In the case of relatively pure solutions, solubility values from reference materials can be used. The effect other components have on the solubility of the crystallisable component can be assessed with the help of thermodynamic models, such as the Pitzer model for aqueous solutions containing inorganic salts.  These equilibrium concentrations can then be further used to determine the driving force behind crystallization, i.e. supersaturation, and the crystal yield. The momentary supersaturation level of a solution affects the degree of core formation and crystal growth precipitating from the supersaturation. Thus the level of supersaturation greatly affects the crystal product obtained in the process.

Evaporation crystallization research focuses on determining the evaporation rates of solvents and their effects on the crystal product. By using the evaporator chamber developed at LUT, it is possible to determine the exact evaporation flow of a solvent (amount of evaporated solvent per cross-sectional evaporation area and time unit, kg/(m2 h)). The evaporation rate has a significant effect on the supersaturation of the solution and the resulting crystal product.

Freezing research examines how different concentrations of dissolved substances affect the freezing point and whether dissolved substances crystallize simultaneously with the forming ice.

Pure crystals, nanocrystals, new forms of crystals, polymorphism control

In industrial crystallization, the general aim is to produce a crystallized product with the desired crystal size distribution, size of crystal, level of purity and crystal structure (polymorphism). Since polymorphism control is an essential factor in the crystallization process, it has also been one of the LUT Crystallization group's main areas of research. The effect a pulsed electric field has on the precipitation of photocatalytic nanocrystals has also been examined at LUT, using titanium oxide as a sample compound. The produced TiO2 nanocrystals were used to determine the degradation of different pollutants at various wavelengths of visible light in a photocatalytic research project. The effects of an electric field have also been examined in the cooling crystallization of amino acids.

Wastewater treatment by natural freeze crystallization in winter, carbonate precipitation using CO2
Diluted aqueous solutions can be concentrated by freezing part of the water. With some compositions, it is possible to reach the eutectic point of the system where solute substances will crystallize at the same time as the ice. This method is called eutectic freeze crystallization (EFC). Ice is formed on top of the solution due to its lower density, while the rest of the crystal mass in the suspension tends to sink.

The carbon dioxide found in combustion gases can be used to precipitate carbonate compounds from alkaline wastewater solutions. Modern process monitoring methods, such as Raman analytics, can be used to monitor both the mother liquor and the solid phase (Raman sensor immersed in the crystallizer). Current research projects include a wastewater project based on freezing and a project examining the use of carbon dioxide in the precipitation of various carbonates. 
The Crystallization group's research capabilities


  • Crystallization methods used: cooling, evaporation and vacuum crystallization, reactive crystallization, precipitation using an anti-solvent, crystallization using electrodes
  • Eutectic freeze crystallizer, winter simulator, melt crystallizer
  • Crystallizers in laboratory, bench and pilot scale
  • Evaporating chamber
  • Batch, semi-batch and continuous crystallization processes

Examples of methods of analysis

  • crystal size and crystal form analysis
  • powder X-ray diffraction
  • thermal analysis (DSC, TG/ DTA-MS)
  • spectroscopic methods (ATR-FTIR, Raman, FTIR)

Further information and the research group

Professor Marjatta Louhi-Kultanen, D.Sc. (Tech),
tel. +358 40 701 8078
Bing Han, D.Sc. (Tech)
Mehdi Hasan, M.Sc. (Tech)
Johanna Puranen, M.Sc. (Tech)

Advanced oxidation processes

In the areas of water treatment and the modification of chemicals, the Thermal Unit Operations research group has studied advanced oxidation processes and photocatalytic water treatment. The Thermal Unit Operations research group has also developed a Pulsed Corona Discharge (PCD) method that can be used to degrade pollutants and disinfect waters in a cost effective way. The PCD method is an example of a non-thermal plasma technology.

PCD oxidation

In PCD oxidation, the solution to be treated is conveyed to a reactor containing air or oxygen, where a short high-voltage pulse creates a corona discharge. The pulse generator connected to the reactor generates high-voltage discharges lasting 100 to 400 nanoseconds. The maximum voltage levels are typically between 20kV and 30kV.

The corona discharge generates a plasma field between the electrodes in the reactor, and ozone is produced from oxygen and strong hydroxyl radicals from water molecules. As water flows through the perforated plate at the top of the reactor and through the plasma field as droplets or films, the oxidants formed during the discharge efficiently degrade the non-biodegradable organic pollutants in the water.

Such pollutants include pharmaceuticals that often enter waterways unchanged after being used and treated at traditional wastewater treatment plants. At LUT, researchers have examined the degradation of common analgesics, such as ibuprofen (e.g. Burana) and paracetamol (e.g. Panadol) using the PCD method. The degradation of paracetamol, in particular, is a very slow process in natural environments.

Other pharmaceuticals that have been researched at LUT include carbamazepine (used in the treatment of epilepsy and affective disorders, very slowly biodegradable), indometacin (an anti-inflammatory drug) and various types of antibiotic and hormone compounds. PCD research has focused on the treatment of wastewater containing small concentrations of biologically active pollutants (micropollutants, often slowly biodegradable) and the identification of generated oxidation products, the oxidation of harmful dissolving chemicals used in the extractive industry, the modification of macromolecules using PCD oxidation, and the examination of antibiotic mixtures and temperature effects in PCD oxidation.

Energy efficient wastewater treatment using PCD oxidation

As a result of its energy efficiency, high oxidation potential and simple process solution, the PCD method has great potential for improving water quality and the recycling of process waters in the treatment of industrial and municipal wastewaters. The research theme is very topical in South Karelia since the region will need to modernise its existing wastewater treatment plants or build new plants in the future. A collaborative project with the LUT Membrane Technology group is currently in progress. The aim of the project is to combine membrane separation with PCD oxidation in order to recycle food industry washing water.
If the quality of water treated using traditional treatment methods needs to be further improved, the PCD method is more cost effective than UV treatment, which is often used in hygienisation. The PCD oxidation equipment used in the research project has been developed in collaboration with Tomsk Polytechnic University.

Research equipment

  • 100W and 250W PCD reactors (temperature adjustment)

Further information and the research group

Professor Marjatta Louhi-Kultanen, D.Sc. (Tech),
tel. +358 40 701 8078
Petri Ajo, M.Sc. (Tech)
Alexander Sokolov, M.Sc. (Tech)

Other research


The long-term effects peat production has on the water quality of Lake Pien-Saimaa have been studied using the national Oiva database in collaboration with Docent Satu-Piia Reinikainen from the Chemometrics research group. The research project is part of the doctoral dissertation of Eija Sääksjärvi, Lic.Sc. (Tech.).


The aim of Nicolus Rotich's doctoral dissertation project is to develop a model for determining optimal conditions for particle classification equipment. Rotich has carried out the research in collaboration with Associate Professor Ritva Tuunila, D.Sc. (Tech). A set of prototype equipment was built to verify the results of mathematical models and to examine the impact the vibration frequency, feed, and deck angle of inclination have on classification efficiency and screening capacity.


Research has been carried out in collaboration with Docent Jaakko Partanen, D.Sc. (Tech), and Kari Vahteristo, D.Sc. (Tech). The most recent freezing point depression modelling results have provided researchers with thermodynamic parameter values that can be used to determine the activities of electrolyte solutions more accurately in temperatures below room temperature.



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