There are two methods to produce isoprene by dehydrogenation: isopentane dehydrogenation and isopentene catalytic dehydrogenation. 1、 Isopentane dehydrogenation method The two-step catalytic dehydrogenation method of isopentane was first developed by the former Soviet Union and was industrialized in 1968. The raw material isopentene used in the isopentene dehydrogenation process is from catalytic cracking or straight-run gasoline. The process is mainly divided into three steps: first, the isopentane is dehydrogenated to isopentene, and a fluidized bed reactor similar to catalytic cracking is used, and the catalyst is spherical chromium-alumina oxide; Then isoprene is obtained by catalytic dehydrogenation of isoprene, and the plate-shaped calcium-nickel-phosphoric acid catalyst and adiabatic fixed-bed reactor are used; Finally, the dehydrogenation product is extracted and distilled with dimethylformamide or acetonitrile in two extractive distillation columns to obtain crude isoprene, and then the high-purity product is obtained after alkali treatment, hydrogenation and acetylene removal. In order to obtain the conversion rate beneficial to industrial production, the reaction must be carried out at high temperature (above 500~600 ℃), resulting in the increase of side reactions such as pyrolysis and isomerization. Therefore, although the raw materials of this method are cheap and easy to obtain, the cost and consumption quota are high, the process for preparing high-purity products is complex, and the development prospect is lacking. At present, only some enterprises in Russia and Eastern Europe apply this method to produce isoprene, with a total production capacity of about 300000 t/a. 2、 There are three isomers of isopentene by catalytic dehydrogenation of isopentene: 2-methyl-1-butene, 2-methyl-2-butene and 3-methyl-1-butene, of which 2-methyl-2-butene is the most suitable precursor for the synthesis of isoprene. In 1961, Shell Company of the United States built a 18000 t/a isoprene production unit using isoprene catalytic dehydrogenation method, and the production capacity of this method has reached 190000 t/a. The process flow is divided into three steps: extracting and separating isopentene from C5 fraction, a by-product of the catalytic cracking unit of the refinery; Isopentene was dehydrogenated at 600 ℃ in a fixed-bed adiabatic reactor using iron oxide, chromium oxide and carbonate catalysts; The dehydrogenation product is extracted, distilled and refined to obtain isoprene product with purity of 99.2%~99.7%. This method can use isopentene (10%~30%) with a wide range of mass fraction as raw material. Among the many methods for producing isoprene, extractive distillation has certain advantages in technology and economy. In economy, only alkenal method can be compared with extractive distillation, and the production cost of other methods is higher. Summary: From an economic point of view, the isoprene dehydrogenation technology developed by the former Soviet Union to produce isoprene has been declining and cannot be compared with the cracking C5 separation method. For the students participating in the chemical design competition, it is even more difficult to check the documents of the former Soviet Union decades ago. Even if they find them, they are still in Russian, and they can’t understand them. From a technical point of view, the reaction part is similar to the catalytic cracking unit, which is extremely complex, with many side reactions, more complex components and great difficulty in product separation. It is conceivable that such a huge workload and technical difficulty will defeat a large number of heroes.