Chemical processing of crude oil:

Chemical processing of crude oil:

Crude oil is a mixture of thousands of different hydrocarbons (compounds of hydrogen and carbon). There are four primary activities that occur in crude refinery processes: (a) Separating hydrocarbons (e.g., distillation), (b) Creating hydrocarbons (e.g., cracking/coking), (c) Blending hydrocarbons, (d) Removing impurities (e.g., sulfur removal).
A. Chemical processing is nothing but changing one fraction into another. Chemical process generally has three methods, such as, (i) Breaking large hydrocarbons into smaller pieces (i.e., cracking); (ii) Combining smaller pieces to make larger ones (i.e., unification); (iii) Rearranging various pieces to make desired hydrocarbons (i.e., alteration).
(i) Cracking: Cracking takes large hydrocarbons and breaks them into smaller ones. Generally, there are two types of cracking; Thermal and Catalytic. In thermal cracking, you heat large hydrocarbons at high temperatures (sometimes high pressures as well) until they break apart. In catalytic cracking, a catalyst is used to speed up the cracking reaction. Catalysts include zeolite, aluminum hydrosilicate, bauxite and silica-alumina. After various hydrocarbons are cracked into smaller hydrocarbons, the products go through another fractional distillation column to separate them.
(ii) Unification: To combine smaller hydrocarbons to make larger ones is called unification. The major unification process is called catalytic reforming and uses a catalyst (platinum, platinum-rhenium mix) to combine low weight naphtha into aromatics, which are used in making chemicals and in blending gasoline. A significant by-product of this reaction is hydrogen gas, which is then either used for hydrocracking or sold.
(iii) Alteration: Sometimes, the structures of molecules in one fraction are rearranged to produce another. Commonly, this is done using a process called alkylation. In alkylation, low molecular weight compounds, such as propylene and butylene, are mixed in the presence of a catalyst such as hydrofluoric acid or sulfuric acid. The products of alkylation are high octane hydrocarbons, which are used in gasoline blends to reduce knocking.

B. Treating and blending the fractions: Distillated and chemically processed fractions are treated to remove impurities, such as organic compounds containing sulfur, nitrogen, oxygen, water, dissolved metals and inorganic salts. Treating is usually done by passing the fractions through: (i) a column of sulfuric acid which removes unsaturated hydrocarbons (those with carbon-carbon double-bonds), nitrogen compounds, oxygen compounds and residual solids (tars, asphalt); (ii) an absorption column filled with drying agents to remove water; (iii) sulfur treatment and hydrogen-sulfide scrubbers to remove sulfur and sulfur compounds. After the fractions have been treated, they are cooled and then blended together to make various products, such as:
(a) Gasoline of various grades, with or without additives;
(b) Lubricating oils of various weights and grades;
(c) Kerosene of various grades;
(d) Jet fuel;
(e) Diesel fuel;
(f) Chemicals of various grades for making plastics and other polymers.