What is the ideal composition of gasoline?

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We know that crude oil can yield some very light fractions after distillation, but these cannot be used directly in cars, as they do not meet the basic requirements of gasoline for use in vehicles. Take octane rating, the most important indicator for measuring gasoline quality – the current requirement is at least 90, which refers to what is known as 90-octane automotive gasoline. The octane number of the light fractions obtained directly from crude oil distillation is at most 60, which is far from meeting the requirements. To this end, our country has made significant efforts to develop the catalytic cracking process in recent years; at present, the majority of gasoline used in vehicles is produced through this process, and its octane rating is close to 90. However, modern cars now require gasoline with an octane rating of at least 93, and some even demand 97 or even 98 octane gasoline; therefore, other measures must be taken to further increase the octane rating of gasoline. After all, the combustion performance of gasoline is closely related to its composition. As we all know, gasoline products mainly contain hydrocarbons such as alkanes, olefins, cycloalkanes, and aromatics. In terms of octane rating, straight-chain alkanes are the worst, while branched alkanes, olefins, and aromatic hydrocarbons are relatively ideal components. Therefore, refineries also need to have specialized facilities for producing aromatic hydrocarbons and branched-chain alkanes, in order to incorporate their high-octane products into gasoline to meet the requirements for 93, 97, or 98 octane rating motor fuels. In the production of aromatic hydrocarbons, a catalytic reforming process using platinum as a catalyst is employed, which allows for the dehydrogenation of naphthenes to produce aromatic hydrocarbons. In the production of branched-chain alkanes, the alkylation process is primarily used; this involves using propylene, butylene, and isobutane from catalytic cracking gases as raw materials, along with sulfuric acid or hydrofluoric acid as catalysts, to synthesize alkylated oils (industrial octane) ； Isomerization processes can also be used to convert straight-chain alkanes into branched-chain alkanes. Therefore, gasoline products with octane ratings of 93, 97, or 98 are usually mixtures prepared from catalytic cracking gasoline, catalytic reforming gasoline, and alkylated oils, in accordance with the requirements of quality standards. In recent years, it has been discovered that although olefins and aromatic hydrocarbons in gasoline have a high octane rating and good combustion properties, they have adverse effects on the environment; therefore, their content in gasoline needs to be restricted. As a result, people have to find other substances that have a high octane rating and do not pollute the environment. Research has shown that oxygen-containing organic compounds such as ethers generally meet these requirements; therefore, methyl tert-butyl ether (MTBE) has been widely used in recent years. It is produced from isobutylene and methanol present in refinery gases. Furthermore, similar compounds include ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME). However, recently it has been suggested that although MTBE does not pollute the atmosphere, it can contaminate groundwater when it seeps into the ground, which has sparked debate over whether MTBE should be banned. Currently, new oxygen-containing compounds are being developed, such as dimethyl ether, diisopropyl ether, and dimethyl carbonate (note: dimethyl carbonate, sec-butyl acetate, methylal, amines, etc., have already been listed as substances prohibited in gasoline), all of which hold promise as components for high-quality gasoline.