Designed for the production of organic and inorganic chemicals at extreme purity levels, Sulzer's suspension crystallization technology delivers high separation efficiency in a single process step. At the same time, the technology enables efficient impurity concentration in wastewater streams supporting zero liquid discharge and the recovery of valuable chemicals. Based on melt crystallization principles, the process combines a compact layout with low energy consumption making it the benchmark solution for aromatic isomers, halogenated chemicals and monomers.

What is suspension crystallization?

Name: Suspension crystallization
Brand: Sulzer

Suspension crystallization is an industrially proven melt crystallization technology used to achieve high separation efficiency for organic and inorganic chemicals in a single process step. Unlike layer-based alternatives such as static or falling film crystallization, suspension crystallization generates crystals in a slurry phase using a scraped surface crystallizer, which removes crystallization heat, followed by a growth vessel where crystals reach a separable size.

The purified crystals are then separated from the mother liquor in a wash column or centrifuge, delivering product purities that are difficult to achieve through conventional distillation or extraction. This industrial crystallization process is particularly well-suited for temperature-sensitive compounds, aromatic isomers, halogenated chemicals, high-value monomers and waste water streams.

Key Innovation / USP

Sulzer's suspension crystallization system achieves high separation efficiency in one single processing step eliminating the need for multiple separation stages. The integration of a proprietary scraped surface crystallizer with a wash column or centrifuge delivers consistently superior crystal quality and mother liquor separation, even for chemically complex feeds.

How suspension crystallization works

Step 1: Crystallization: Crystal formation and growth
In the first step the target component must be separated from the feed mixture. By cooling down the liquid in the crystallizer slightly below the equilibrium temperature of the mixture a partial phase change is reached. The seed crystals are kept in a suspension where they further grow in a controlled manner during a defined residence time.

Step 2: Separation
The separation of the crystals from the mother liquor takes place in a wash column; the selection is based upon operating parameters, such as product feed quality and target purity, capacity, yield, etc. After leaving the wash column, the crystallized product melts directly into pure product.

Technical specifications & process parameters

Technology type	Melt crystallization (suspension)
Crystallizer type	Scraped surface crystallizer
Separation unit	Wash column or centrifuge
Typical purity achieved	Application-dependent
Process configuration	Continuous or batch
Layout	Compact; skid-mounted unit available depending on capacity
Energy consumption	Low relative to distillation for high-purity targets
Scalability	Pilot to industrial scale

Advantages of Sulzer suspension crystallization

High separation efficiency
Achieves product purities in a single crystallization and separation stage, eliminating multi-step purification sequences and reducing overall process complexity. Particularly suitable for medium concentration feed.

Low energy consumption
Operates at or near the melting point of the target compound, requiring significantly less energy than distillation for high-purity targets, particularly for close-boiling or heat-sensitive mixtures.

Compact layout and low installation costs
The integrated crystallizer–wash column design minimizes plot space requirements and reduces capital expenditure compared to multi-stage separation trains, especially attractive for grassroots or retrofit installations.

Broad chemical applicability
Suitable for a wide range of organic and inorganic compounds, including aromatic isomers, halogenated chemicals and monomers, as well as fractional crystallization or freeze concentration applications such as wastewater streams.