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C4 has a wide range of downstream applications, which can be applied to mixtures or to individual components within them. Butane has the lowest added value as a LPG fuel, and its high olefin content also affects its combustion performance. Butadiene, which is present in the C4 fraction of plants that produce cracked ethylene, is one of the most widely produced commodities; other well-established applications include products such as MTBE, ethyl methyl ketone, and maleic anhydride. Common downstream applications of tetrahydrocarbons are as follows: 01 Aromaticized low-molecular-weight hydrocarbons are converted into mixed aromatic hydrocarbons containing benzene, toluene, and xylene through aromaticization reactions. Through a series of separations, standard-compliant mixed aromatics, light aromatics, and heavy aromatics are ultimately produced, while liquefied gas with low olefin content and a small amount of dry gas are generated as by-products. During periods of shortage of refined oil, local refineries added a lot of aromatization capacity, mainly for use in oil blending, but the economic viability of this approach has now significantly declined. 02 Butadiene carbon tetra is one of the most important products; it is primarily used in the synthesis of rubber (styrene-butadiene, cis-butadiene, nitrile rubber, etc.), ABS, styrene-butadiene latex, elastomers (SBS, SEBS, etc.), adiponitrile, thiophene, **phthalic anhydride, and other substances. Butadiene is difficult to store; it is usually stored under pressure or at low temperatures to prevent self-polymerization. Butadiene tanks and tank cars can be used interchangeably with LPG tanks and tank cars, but the required pressure levels, oxygen content, and other specifications are more stringent. 03 Isobutylene: Since isobutylene and butylene are usually present together in mixed C4 hydrocarbons, it is difficult to separate them by physical methods; generally, methanol etherification is used, in which isobutylene reacts with methanol to produce MTBE. MTBE can be used in gasoline blending or re-cracked to produce high-purity isobutylene. High-purity isobutylene is a raw material for producing butyl rubber; it can also be used to synthesize products such as MMA, polyisobutylene, and antioxidants. In recent years, the number of plants producing isobutylene through isobutane dehydrogenation has also been increasing. 04 1-butene and 2-butene can undergo isomerization conversion with each other. 1-butene can be used as a comonomer for LLDPE to synthesize poly-1-butene and similar materials ； 2-butene is used in the production of methylethyl ketone, sec-butyl acetate, and others. Butadiene is produced from butylene through oxidative dehydrogenation (rather than direct dehydrogenation), but the material and energy consumption for the raw materials is high, resulting in higher costs compared to carbon tetraolefin extraction. 05 Butane is divided into n-butane and isobutane; aside from its use in combustion, n-butane can be used as a feedstock for the production of ethylene and for the synthesis of maleic anhydride, among other things ； The synthesis of maleic anhydride from n-butane will compete with the route using pure benzene as a starting material. Isobutane has a poor yield when used for the cracking of ethylene; it can be isomerized into n-butane, but isomerization becomes economical only on a sufficiently large scale. Isobutane can be combined with butylene to produce isooctane for alkylating gasoline, or it can be dehydrogenated to yield isobutylene.