What Is Refinery Gas?

Gaseous hydrocarbons by-product from petroleum refineries. Mainly from crude oil distillation, catalytic cracking, thermal cracking, petroleum coking, hydrocracking, catalytic reforming, hydrofining and other processes. Refinery gas from different sources has different compositions (see table). The main components are paraffins and olefins below C4, hydrogen and a small amount of nitrogen and carbon dioxide. The yield of refinery gas varies with the depth of crude oil processing. Generally, refinery gas for deep processing is about 6% (mass) of crude oil processed. About 2% of ethylene, 60% of propylene, and 90% of butene in the United States come from refinery gas.

Refinery gas

Refinery gas processing is one of the important tasks of petroleum refineries. The choice of process depends on the output, composition and product requirements of the refinery gas. Generally, the refinery gas first passes through a gas separation device and is used.

Gases below C2 can be used as raw materials for hydrogen and ethylene production or as fuel gas after ethanolamine desulfurization and sulfur recovery (see Claus method). If there is a large ethylene plant near the refinery, the desulfurization gas can be sent directly to cryogenic separation after drying and compression (see cracking gas cryogenic separation) to obtain polymer-grade ethylene and hydrogen with a purity greater than 95%; or using molecular sieve or activated carbon As an adsorbent, at a temperature of 5-40 ° C and a pressure of 1-4.2 MPa, a multi-bed pressure swing adsorption method is used (concentration of hydrogen on the adsorbent under high pressure, and then recovering hydrogen rich under low pressure) Gas) to purify hydrogen, with a hydrogen recovery rate of 60% to 85%, and a purity of more than 99.999%; or use a membrane permeation method (see membrane separation) to purify hydrogen. The above methods are economically advantageous.

Refinery gas

The C3 and C4 fractions from the gas fractionation device are fractionated to obtain C3 and C4 components. The C3 component is mainly used for superposition (see olefin superposition) to produce superposed gasoline (the research method can reach 94).

C4 component dealkylation device, using sulfuric acid or hydrofluoric acid as a catalyst to convert isobutane and butene (see alkylation of petroleum hydrocarbons) into alkylated gasoline based on C8 isoparaffin (research method (Octane number is about 94). The alkylation reaction requires a volume ratio of isobutane to olefin of 1.15 to 1.35: 1. The isobutane content in the existing raw materials is low and cannot be adapted. The n-butane in the refinery gas can be converted by the butane isomerization process Alkane (nC ) is converted to isobutane (iC ) (see Petroleum Hydrocarbon Isomerization) as a supplementary feed for alkylation.

The propane and butane fractions by-produced in the above process can also be used to produce corresponding olefins through dehydrogenation, or to produce aromatic hydrocarbons through dehydroaromatization.