How Is Mineral Oil Manufactured?
Mineral oil is a by-product produced after the fraction distillation of crude oil takes place and the petroleum is separated to different parts. Conventionally, mineral oil is refined from raw distillates of crude oil by techniques such as solvent extraction, solvent dewaxing, acid treating and hydrogenation.
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Fractional Distillation
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Crude oil is refined to produce petroleum using the method called fractional distillation. One of the main byproduct of this method is mineral oil. The mineral oil thus obtained has to be refined to relieve from impurities such as sulfur, nitrogen, oxygen, inorganic salts and even soluble salts. Fractional distillation separates the petroleum products into different groups based on the boiling point of the liquids in the mixture.
Solvent Extraction
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Solvent extraction process removes the impurities from the distillate obtained from fraction distillation process during the refining stages. The method used for separating the impurities from the distillate in solvent extraction process is either precipitation or dissolving. In the dissolving process, the distillate is first washed with a liquid so that the impurities which are to be separated are more soluble in it than in the resulting product. In the precipitation process, certain solvents are added to the distillate that make the impurities precipitate out. Thus, the product stream from the fractional distillation process is heated or evaporated, and then the residual traces of impurities are removed by steam stripping or vacuum flashing. If inorganic impurities are present, then electric precipitation is used to refine. Commonly used solvents include phenol and cresylic acid.
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Solvent Dewaxing
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Solvent dewaxing is a process used to remove wax from the distillate. First, the distillate is mixed with a solvent. Then, it is chilled in order for the wax to precipitate from the mixture. After this, the solvent is obtained from the wax by distillation and steam stripping. The commonly used solvents for this method are toluene, which dissolves the oil, and methyl ethyl ketone (MEK), which dissolves the wax. At low temperatures, MEK acts as the precipitating agent for wax and toluene maintains the fluidity. Solvent dewaxing is a costlier refining method because the operation has high refrigeration requirements.
Acid Treatment
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In acid treatment method, the distillate is treated with acid, normally fuming sulfuric acid. Once it is treated with acid, the oil obtained is purified by neutralizing, washing and treatment with clay. This procedure is called contact finishing--a method by which the impurities which are formed during the acid treatment is removed. The difficulty encountered in this method is to dispose off the strong acid waste produced during the acid treatment.
Hydrogenation
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In hydrogenation method, the distillate is first treated with hydrogen in the presence of sulfur-resistant catalyst. This forms hydrogenated oil. It is then treated with hydrogen in the presence of a second catalyst to form refined oil.
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