Propylene oxide is an important propylene derivative, and about 7% of propylene is used for propylene oxide production every year. The production processes mainly include chlorohydrinization, co-oxidation (also called indirect oxidation), and direct oxidation. Nowadays, the main industrialized methods for producing propylene oxide in the world are the chlorohydrinization method and the co-oxidation method. The co-oxidation method is divided into the ethylbenzene co-oxidation method and the isobutane co-oxidation method. In recent years, the cumene oxidation method and the hydrogen peroxide direct oxidation method have been successfully developed and successively realized in industrial production, and the direct oxidation method using oxygen as the oxidant is also under development. The following is how to make propylene oxide.
The production methods are divided into the following·
Chlorohydrin method· ·
Co-oxidation
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Cumene oxidation method
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HPPO method
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The production of chlorohydrins has a long history and has been industrialized for more than 60 years. The main process flow of the chlorohydrin method is propylene chlorohydrin, saponification of lime milk, and product refining. It is characterized by mature production technology, large operating load flexibility, good selectivity, low requirements for raw material propylene purity, improved production safety, and low construction investment. Due to the low investment in fixed assets and low product costs, products made from propylene oxide
are highly cost-competitive. Today, about 40% of the world's propylene oxide production capacity is the chlorohydrin process.
The disadvantage of the chlorohydrin method is that water resources are consumed, and a large amount of wastewater and waste residue is produced. For every Chlorohydrin method
1t of propylene oxide produced, 40~50t chloride-containing saponification wastewater and 2t or more waste residues are produced. The wastewater has a high temperature, high pH value, and chlorine. The "five high" characteristics of high root content, high COD content, and high suspended solids content are difficult to handle. At the same time, the chlorohydrin method also consumes a large amount of high-energy-consuming chlorine and lime raw materials, while chlorine and calcium are discharged in wastewater and waste residues, and the hypochlorous acid produced during the production process also causes serious corrosion of equipment.
Co-oxidation method
The co-oxidation method, also known as the Hakon method, includes the isobutane co-oxidation method and ethylbenzene co-oxidation method. The co-oxidation reaction of isobutane or ethylbenzene and propylene is carried out to generate tert-butanol or styrene. Producing propylene oxide.
The co-oxidation method overcomes the shortcomings of the chlorohydrin method, such as large corrosion and more sewage, and has the advantages of the low product cost (co-product cost-sharing) and less environmental pollution. Since its industrialization in 1969, it has developed rapidly worldwide. Today, the production capacity of co-oxidation propylene oxide accounts for about 55% of the world's total production capacity.
The shortcomings of the co-oxidation method are the long process flow, the variety of raw materials, the high purity of propylene, the process operation is carried out under higher pressure, the equipment materials are mostly alloy steel, the equipment cost is high, and the construction investment is large.
Cumene oxidation method
The cumene oxidation method uses a fixed-bed reactor with titanium-based catalysts and uses cumene hydroperoxide (CHP) as the oxidant. CHP epoxidizes propylene to obtain propylene oxide and two Methylbenzyl alcohol, the latter is dehydrated to α-methyl styrene, and then hydrogenated to produce cumene, which is oxidized to CHP and recycled. The cumene oxidation method is an improvement of the co-oxidation method.
The main difference from the co-oxidation method is that cumene is used instead of ethylbenzene, and the cumene is recycled and does not produce co-products. Since this process does not require auxiliary equipment for the co-production of styrene, the equipment investment cost is about 1/3 lower than that of the co-oxidation method, and the anti-corrosion equipment is required for the chlorohydrin process using chlorine gas is not required.
HPPO method
Hydrogen peroxide direct oxidation method (HPPO method) is a new process of epoxidizing propylene to propylene oxide by hydrogen peroxide (hydrogen peroxide). Only propylene oxide and water are generated in the production process. The process flow is simple and the product yield is high. , There are no other co-products, basically pollution-free, and it is an environmentally friendly cleaner production system.
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