The application of solvents in the petroleum industry

Solvents are primarily used in the petroleum industry for the refining of petroleum hydrocarbons, such as the refining of lubricating oils, diesel fuel oils, kerosene, and other special oils, as well as for the extraction and refining of aromatic hydrocarbons.

Main applications of solvents in the petroleum industry

Uses	Purpose	Main solvents
Extraction of aromatic hydrocarbons	Mainly to extract hydrocarbon oil, while separating cyclic hydrocarbons and chain hydrocarbons	Liquid sulphur dioxide, ethylene glycol, ammonia-containing ethylene glycol, diethylene glycol (containing water)
Wax removal	Use solvent to extract paraffin	Propane, benzene-acetone, benzene-liquid sulphur dioxide, butanone, various chlorides
Asphalt removal	Remove asphalt	Liquid propane, aliphatic alcohols
Lubricating oil	Remove impurities from distillation residue oil	Furfural, phenol, dichloroethane, nitrobenzene, liquid sulfur dioxide, benzene, propane, propane-phenol mixed solvent, aniline, cresol, acetone, phenol

Solvent extraction methods include single-solvent and mixed-solvent extraction. Generally, extraction solvents are selected based on their good solubility, high solubility for the components being extracted, ease of recovery, and a significant difference in relative density between the extract and the solvent, ensuring easy separation between the two liquid phases. Additionally, the solvents should be non-toxic, non-corrosive, and have good thermal stability.

Solvents commonly used in the petroleum industry

Solvent	Advantages	Disadvantages	Application
Liquid sulphur dioxide	Good selectivity, low solubility of lubricating oil components, can be used with 15–16% benzene	High vapour pressure, low solubility	Extraction of aromatic hydrocarbons (benzene, toluene, xylene) from reformed naphtha and refining of kerosene, crude diesel oil, and lubricating oil
Aniline	Good selectivity and solubility	High toxicity	Refining of lubricating oil
Phenol	Chemically stable, easy to recover, selectivity and solubility can be adjusted according to moisture content, usage is 1–2 times the amount of raw oil	High toxicity, high freezing point, raw oil with high aromatic content is not suitable for use	Refining of lubricating oil
Toluene	High solubility of aromatic hydrocarbons, can precisely separate alkanes and cycloalkanes	High boiling point, difficult to recover Due to high solubility, extraction must be carried out at low temperatures	Refining of lubricating oil
Formaldehyde	Excellent selectivity between 32–138°C, suitable for high-viscosity, high-wax content feedstock oils, capable of removing asphalt, sulphides, and coloured substances	Slightly toxic	Modification of light oil and catalytic cracking feedstock oil for lubricating oil refining
Dichloroethane	Thermally stable, resistant to hydrolysis, good selectivity and solubility, easy to separate from refined oil, extraction dosage is 1/2–3/4 of the feedstock oil, temperature 75–100°C	Acid is generated during recovery	Modification of light oil and catalytic cracking feedstock oil for lubricating oil refining
Methylphenol	Phenol dissolves aromatic hydrocarbons and cycloalkanes; propane dilutes the feedstock oil, causing asphalt to precipitate		Refining of lubricating oil, deasphalting.
Ethylene glycol-water composite	It exhibits excellent selectivity and solubility for aromatic hydrocarbons, with adjustable mixing ratios, and is non-corrosive		Extraction of aromatic components in petroleum fractionation