Refining of Petroleum Products

the removal from petroleum products, such as distillates and distillation residues, of undesirable components that adversely affect the useful properties of fuels and oils. Such components include sulfurous and nitrogenous compounds, and also tars and resins. Chemical, physicochemical, and catalytic refining methods are used in industry.

Chemical refining. Chemical refining is carried out by the action of various reagents on the components to be removed. The simplest methods are (1) purification with 92–98-percent sulfuric acid and oleum, which is used for removing unsaturated and aromatic hydrocarbons, tars and resins, and nitrogenous and sulfurous compounds; and (2) purification with bases (solutions of sodium hydroxide and soda ash), for the removal of certain oxygen-containing compounds, hydrogen sulfide, and mercaptans. Sodium plumbite is used for the removal of sulfurous compounds.

Physicochemical refining. Physicochemical refining is carried out using solvents that selectively remove undesirable components. Nonpolar solvents, such as liquefied propane and butane gases, are used to remove tars, resins, and polycyclic (heavy) aromatic hydrocarbons from petroleum distillation residue (tars and asphalts); this is called the deasphalting process. Polar solvents, such as phenol and furfurol, are used to remove polycyclic aromatic and naphthene-aromatic hydrocarbons with short side chains, unsaturated hydrocarbons, sulfurous and nitrogenous compounds, and tars from oily distillates and the products of deasphalting. Ketones mixed with toluene, and also chlorinated hydrocarbons mixed with benzene and other polar and nonpolar solvents and their mixtures, are used in the deparaffination process to remove solid hydrocarbons from the raffinates (products of the selective refining of oily distillates and residues). Solid paraffins are removed by crystallizing them from solutions of the product being refined. Carbamide deparaffination, which is based on the formation of complexes by normal paraffin hydrocarbons and carbamide (urea), is also used for the purification of diesel fuels, kerosines, heavy gasolines, and low-viscosity petroleum oils.

In adsorption purification, unsaturated hydrocarbons, resins, and acids, as well as polycyclic aromatic and naphthenearomatic hydrocarbons, are removed from petroleum products. Adsorption purification is carried out by contact of the heated product with finely disperse adsorbent (contact purification) or by filtration of the product through adsorbent granules. Selective adsorption using molecular seives (zeolites) permits the separation of normal paraffins for the light gasoline and kerosine-gas oil fractions.

Catalytic refining. Methods of catalytic refining include (1) hydrogenation under mild conditions, for removal of sulfurous, nitrogenous, and oxygen-containing compounds by converting them into hydrocarbons and easily removed compounds (hydrogen sulfide, ammonia, and water); and (2) hydrogenation under vigorous conditions, for deparaffination of oily raw material. In this case, degradation of the solid hydrocarbons takes place, with the formation of low-molecular-weight hydrocarbons, which solidify only at low temperature. Oils with a high viscosity index may also be produced using vigorous modes of hydrogenation.

In the technology of refining of petroleum products, wide use is made of efficient equipment that permits automation. Such equipment includes extraction columns, centrifugal extractors, rotary disk contractors, vacuum filters, and injection mixtures.