Why are the octane ratings for new national standard gasoline being reduced?

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　Why are the octane ratings for new national standard gasoline being reduced? 　　We know that in the past, the octane ratings for vehicle gasoline were 90#, 93#, and 97#. Phase 5 was changed to 89#, 92#, and 95#. What’s going on here? 　　First, one needs to understand what the gasoline octane rating means. We know that gasoline is flammable and explosive; even in the absence of an open flame, it can explode under severe shock. So how is the anti-knock property of gasoline measured? Or simply put, how can we evaluate a type of gasoline to determine whether it is stable? 　　We’ll use the gasoline octane rating. To be precise, the octane rating of gasoline refers to its octane number. We selected two hydrocarbons with opposing properties: isooctane and n-heptane. Isooctane is relatively stable under compression and impact, so we rate it 100. N-heptane is exactly the opposite: it explodes easily after being compressed by impact, so we give it a score of 0. If a certain type of gasoline has an anti-knock property equivalent to that of a mixture of 70% isooctane and 30% n-heptane, then we say that this gasoline has an octane rating of 70; it is therefore 70# gasoline. The commonly used 93# gasoline means that its anti-knock property is the same as that of a mixture of 93% isooctane and 7% n-heptane. And so on. 　　Secondly, what factors determine the octane rating, or level of octane, of gasoline? The octane rating of gasoline is determined by its components. The octane ratings of the various components in gasoline differ, and when they are mixed in different proportions, the octane rating as well changes. Everyone should understand that gasoline is not a single substance, but a mixture. So, never say that a certain brand of gasoline is purer – that’s nonsense. What are the components of gasoline? Simply put, the components of gasoline fall into several main categories: straight-chain hydrocarbons with carbon atoms from C4 to C12 ； Naphthenes, aromatic hydrocarbons. The olefins and aromatic hydrocarbons among them can significantly increase the octane rating of gasoline. 　　In addition to olefins and aromatic hydrocarbons, the octane rating of gasoline can also be increased by adding anti-knock agents. The most common anti-knock agent in the past was tetraethyl lead, but it is toxic and causes lead pollution in the environment, which is why it was banned. As some of you may still remember, gasoline for cars used to be red; it was actually gasoline to which tetraethyl lead had been added. For more information on petroleum products, as well as details on oil blending techniques, please follow the WeChat official account \"Youpin Quan\"; its ID is ypq0910. Since tetraethyl lead is toxic, leaded gasoline is colored red intentionally, so as to prevent people from mixing it with lead-free solvent gasoline and thereby suffering poisoning. After the discontinuation of tetraethyl lead, carbonyl manganese antiknock agent (MMT) was used for some time, but manganese is also toxic and can pollute the environment; therefore it is now banned as well. 　　The commonly used antiknock agents at present are methyl tert-butyl ether (MTBE), as well as ethanol and isooctane. MTBE also has certain environmental toxicity; some developed countries have begun to restrict its use, and China has imposed strict limits on the amount of MTBE that can be used. Ethanol has a certain degree of water solubility; its compatibility with gasoline is poor, and it can cause damage to engines. Additionally, it has a low calorific value, which leads to increased fuel consumption. Isooctane is the best anti-knock agent; in fact, the indicator for a gasoline’s anti-knock properties is named after it! However, the current production of isooctane is still very low and far from meeting the demand. 　　For environmental protection reasons, we must reduce the sulfur content in gasoline, which requires hydrodesulfurization to convert the sulfur in gasoline (present in the form of sulfides, thioalcohols, heterocycles, etc.) into hydrogen sulfide, which is then removed through washing with water. However, during hydrogenation, olefins and aromatic hydrocarbons are also reduced, resulting in a decrease in octane rating. Due to the unsaturation of olefins and aromatic hydrocarbons, which leads to the formation of gums, increased carbon deposits, a high carbon content, and incomplete combustion compared to alkanes, Phase 5 also limits the levels of olefins and aromatic hydrocarbons. 　　This leads to a paradox: in an effort to protect the environment, we have reduced the presence of high-octane components in gasoline (such as olefins and aromatic hydrocarbons), which has resulted in a lower octane rating. As a result, anti-knock agents are needed, but tetraethyl lead and manganese carbonyl can no longer be used; MTBE is subject to restrictions, ethanol has shortcomings and cannot be used on a large scale, and isooctane is the best option yet its production cannot keep up with demand. What should we do? 　　Thus, the five-stage process can only reduce the octane rating of gasoline; it is a reluctant compromise. If it is not reduced, then in order to maintain the octane rating of their products, companies will be forced to increase the amount of anti-knock agents used, as well as the levels of olefins and aromatic hydrocarbons. In such a case, environmental protection becomes an empty slogan, and the original purpose of the five-stage system is lost. 　　What should we do in the future? Two options: First, improve processes and equipment to enhance the quality of oil products ； Second, increase the supply of high-octane substances, especially isooctane. At present, there are only a few isooctane production lines in operation in our country, and their capacity is quite low; however, this industry holds great potential in the future.