Crystallization is often the best alternative when distillation is difficult, or even impossible. High purity products are manufactured from close boiling or azeotropic mixtures or components that are thermally unstable at their boiling point. The technology has proven to be the most reliable and environmentally friendly crystallization process, because crystals grow directly from the melt without the use of solvents. Selection of the most suitable technology is supported by bench and pilot scale testing. Typical applications are the purification of Monomers, Carboxylic acids, Tar chemicals, Waxes, Organic and inorganic chemicals at high purities.
The Sulzer Chemtech static crystallizer is equipped with vertical plates immersed in a stagnant melt. Crystal layers grow on the cooled plates. Following crystallization, the remaining impure melt is drained from the crystal layer, which then is further purified by sweating. Hereafter, the purified product is recovered by melting the crystal layer. Sweating and melting is established by heating the plates.
The falling film crystallizer contains vertical tubes through which the melt flows as a falling film. The crystal layers grow in the form of cylindrical shells inside the cooled tubes. Crystallization is followed by sweating and subsequent melting of the product. A high thermal gradient can be imposed and crystal growth rates are fast.
Sulzer Chemtech’s suspension crystallization is an advanced, highly selective, energy efficient separation process. Crystals are formed in one or more scraped wall crystallizers. A stirred growth vessel provides the needed residence time for the crystals to grow to a separable size. Crystals are separated from the mother liquor in one or more wash columns and subsequently melted to produce a high purity product.
Freeze concentration is a special application of suspension crystallization. Freeze concentration of food and beverage products leads to selective removal of water at sub-zero temperatures. It is the preferred technology for supreme quality liquid food concentrates because all flavour and aroma components are retained. Typical applications are the concentration of juices, wine and beer, coffee and tea.