The main method for producing isopropanol at home and abroad is propylene hydration. According to whether or not intermediate products are produced, it can be divided into two methods: indirect propylene hydration and propylene direct hydration.
Indirect hydration, also known as sulfate hydrolysis. This method uses concentrated sulfuric acid to absorb propylene, and then it is hydrolyzed to isopropyl alcohol. This method has the disadvantages of large consumption of sulfuric acid, severe equipment corrosion, and high energy consumption, which limits its development and has been eliminated. Direct hydration is a new technology that uses highly active catalysts and is compatible with environmental protection. This method overcomes the shortcomings of indirect hydration, has the advantages of high efficiency, low consumption, and short process flow, and is the main direction of hydration development today.
There are three main types of direct hydration depending on the catalyst:
a. Phosphoric acid (Veba) method: Using diatomaceous earth phosphate as a catalyst. The reaction process takes place in the gas phase and the dissolution of phosphoric acid is inhibited by selecting the reaction conditions which keep the water in the gas phase. The method has low conversion per pass of propylene and large amount of gas circulation, and it is preferable to use a high concentration of propylene as a raw material.
b. Texaco Method: A highly active zeolite catalyst or cation exchange resin is used as a catalyst. Because the catalyst has good activity and water resistance, the reaction can be carried out at a lower reaction temperature and a larger ratio of water to alkene, and the single-pass conversion rate is more than 10 times higher than the phosphoric acid method.
c. Heteropolyacid (Deshan-Suda) method: A tungsten-based heteropolyacid is used as a catalyst. The reaction is carried out under high temperature and high pressure conditions. Since the high temperature is unfavorable to the chemical balance, in order to increase the conversion rate of propylene, a high pressure, a ratio of a large water to a olefin is used. Among the above three methods, the solid acid method has the advantages of milder reaction conditions, higher conversion of propylene, and lower energy consumption compared to the other two methods, and has attracted people's attention. In recent years, most countries and regions have adopted new technologies for the production of isopropyl alcohol, such as South Korea and Taiwan. At present, most isopropanol production facilities in China still use the phosphoric acid method and traditional sulfuric acid method to produce isopropyl alcohol, which lags behind the advanced level in foreign countries and cannot meet the needs of economic development.