Propylene oxide is an important derivative of propylene, and about 7% of propylene is used in the production of Propylene oxide every year. Nowadays, the main industrial production methods of Propylene oxide in the world are chlorination and co-oxidation, among which co-oxidation is divided into ethylbenzene co-oxidation and isobutane co-oxidation. In recent years, the isopropylbenzene oxidation method and hydrogen peroxide direct oxidation method have been successfully developed and industrialized successively, and the direct oxidation method using oxygen as an oxidant is also under development. The following is to introduce a few specific Propylene oxide production process
1. Chlorohydrin method
2. Co-oxidation method
3. Direct oxidation method
Chlorohydrin method
The chlor-alcohol process has a long history of production and has been industrialized for more than 60 years. The main process of the chlor-alcohol method is the chlorination of propylene, lime milk saponification and product refining, which is characterized by a mature production process, flexible operating load, good selectivity, the purity of the raw material propylene requirements are not high, which can improve the safety of production and low investment in construction. Due to the low investment in fixed assets and low product cost, its products have strong cost competitiveness. Today, about 40% of the world's production capacity of propylene oxide is chlorhydrin.
The disadvantage of the chlor-alcohol method is the consumption of water resources, generating a large amount of wastewater and waste residue, each production of 1t Propylene oxide produces 40 ~ 50t of chlorinated saponification wastewater and more than 2t of waste residue, the wastewater has a high temperature, high pH, high chlorine content, high COD content and high suspended matter content of the "five high " characteristics, difficult to treat. At the same time, the chlorine alcohol method also consumes a large amount of energy-intensive chlorine and lime raw materials, while chlorine and calcium are discharged in the wastewater and waste sludge, and the hypochlorite produced during the production process is also serious corrosion of the equipment.
Co-oxidation method
Co-Oxidation method, also known as the Haakon method, includes 2 types of isobutane co-Oxidation method and ethylbenzene co-Oxidation method, which are co-Oxidation reactions of isobutane or ethylbenzene with propylene to produce tert-butanol or styrene, and co-production of propylene oxide at the same time.
The co-oxidation method overcomes the disadvantages of the chlor-alcohol method, such as high corrosion and sewage, and has the advantages of low production cost and less environmental pollution. Since its industrialization in 1969, it has developed rapidly worldwide, and today, the capacity of the co-oxidation method of propylene oxide has accounted for about 55% of the world's total capacity.
The disadvantages of the co-oxidation process are long process flow, many varieties of raw materials, high propylene purity requirements, process operation under high pressure, equipment materials mostly use alloy steel, high equipment cost and large construction investment. At the same time, propylene oxide in the production of co-oxidation, only a small amount of co-products, each ton of propylene oxide to co-produce 2.2 ~ 2.5t styrene or 2.3t test-butanol, raw material sources and product sales constraints on each other, must be properly addressed, only propylene oxide and co-products market demand match the advantages of the process can be revealed. In addition, the COD of the effluent produced by the co-oxidation method is relatively high, and the treatment cost accounts for about 10% of the total investment.
Direct Oxidation
Lyondell is developing a direct oxidation technology for the conversion of propylene, hydrogen and oxygen to propylene oxide using a bifunctional catalyst consisting of a silicate of palladium and titanium to produce hydrogen peroxide with hydrogen and oxygen and then immediately convert propylene to propylene oxide, the entire process being completed in a single reactor. The process is still in the pilot stage.
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