Industrial Crystallization
Industrial crystallization is a separation and purification process in which solute molecules are transferred from a supersaturated solution into an ordered solid crystal lattice structure. It is widely used in the chemical, pharmaceutical, and food industries to produce high-purity solids such as sugar, salt, fertilizers, and active pharmaceutical ingredients. The process is controlled by manipulating temperature, solvent composition, or evaporation rate to achieve a desired crystal size distribution and purity.
Key Formula
σ = (c − c*) / c*
LaTeX: \sigma = \frac{c - c^*}{c^*}
| Symbol | Meaning | Unit |
|---|---|---|
| σ | Supersaturation ratio (dimensionless) | — |
| c | Actual solute concentration | kg/m³ |
| c* | Equilibrium (saturation) solute concentration | kg/m³ |
Worked Example
Problem
A crystallizer operates with a solution of potassium nitrate. The actual concentration is 320 kg/m³ and the saturation concentration at the operating temperature is 250 kg/m³. Calculate the supersaturation ratio.
Solution
Step 1: Identify values — c = 320 kg/m³, c* = 250 kg/m³. Step 2: Apply the supersaturation formula: σ = (c − c*) / c* = (320 − 250) / 250 = 70 / 250 = 0.28.
Answer
σ = 0.28 (28% supersaturation), indicating moderate driving force for crystal nucleation and growth.
Common Crystallization Methods in Industry
| Method | Driving Force | Typical Product | Temperature Change |
|---|---|---|---|
| Cooling crystallization | Reduced solubility at low T | KNO₃, sugar | Decrease |
| Evaporative crystallization | Solvent removal | NaCl, urea | Moderate increase |
| Anti-solvent crystallization | Reduced solubility in mixed solvent | APIs, dyes | Minimal |
| Reactive crystallization | Chemical reaction produces sparingly soluble salt | CaCO₃, BaSO₄ | Varies |
| Melt crystallization | Solidification from melt | Naphthalene, paraxylene | Decrease below melting point |
Interactive Tools
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Related Terms
Industrial Filtration
Industrial filtration is a mechanical separation process that removes solid particles from a liquid or gas stream by passing the mixture through a porous medium that retains the solids (filter cake) while allowing the fluid (filtrate) to pass through. It is fundamental to chemical processing, wastewater treatment, food and beverage production, and pharmaceutical manufacturing. The efficiency of filtration depends on particle size, filter medium properties, applied pressure, and the characteristics of the slurry.
Membrane Separation
Membrane separation is a process in which a semi-permeable membrane selectively allows certain molecules or ions to pass through while retaining others, driven by a concentration, pressure, or electrical potential gradient. Common forms include reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and pervaporation, each distinguished by the size range of species separated. Membrane processes are highly energy-efficient alternatives to thermal separation methods and are critical in water purification, food processing, and pharmaceutical applications.
Engineering Adsorption
Engineering adsorption is a surface-based separation process in which molecules (adsorbate) from a fluid phase adhere to the surface of a solid material (adsorbent) via physical or chemical interactions, enabling removal or recovery of target species from gases or liquids. It is used industrially for air purification, solvent recovery, water treatment, and chromatographic separation. The process is characterized by equilibrium isotherms and mass transfer kinetics, with the adsorbent regenerated by temperature or pressure changes to allow repeated cycles.
From Latin "crystallus" (clear ice, crystal), derived from Greek "krystallos" (ice), referring to the ordered, transparent solid structure formed when solutes solidify from solution. Industrial application developed prominently in the 19th century sugar-refining industry.