For wastewaters containing high phenol concentrations, solvent extraction reduces the phenol to acceptable levels. Occasionally, recovered phenol is reused in the manufacturing process or solid as a by-product. In solvent extraction, two immiscible or partially soluble liquids are brought into contact for transfer of one or more components. Using a solvent such as benzene, phenol can be extracted from the wastewater. The extracted phenol is then washed out with caustic to form the sodium salt, and the benzene is reused. In the petroleum industry, light catalytic cracking oils are used as extractors, and in the coking industry, coke oven light oils are used as extractors. Process efficiency depends on solvent choice and system design.
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