Ethylene oxide (EO), also known as ethylene oxide, is the simplest cyclic ether. Ethylene oxide is an important product in the petrochemical industry, and is also a basic organic chemical raw material. It is widely used in the production of ethylene glycol, non-ionic surfactants, ethanolamine, ethyl alcohol ether solvents, pharmaceutical intermediates, oilfield chemicals, pesticide emulsifiers and other fine chemicals.

In the early 1920s, UCC company carried out industrial production, and then the company based on Lefort's research results on silver catalyst, using silver catalyst, launched the direct oxidation of ethylene by air to produce ethylene oxide process. In the late 1950s, Shell Company used nearly pure oxygen instead of air as the oxygen raw material for the production of ethylene oxide, and introduced the process of direct oxidation of ethylene by oxygen method to produce ethylene oxide. After continuous improvement, the current more advanced production method is to react with pure oxygen and ethylene with silver as catalyst in a tubular fixed bed reactor. Ethylene oxide was produced by direct oxidation of ethylene. Now these methods are analyzed and compared.

1.Chlorol method

The production of ethylene oxide chlorol process is divided into two steps: first, chlorine gas reacts with water to produce hypochlorous acid, and then reacts with ethylene to produce chloroethanol; The chloroethanol is then saponified with lime milk to produce ethylene oxide. The serious disadvantages of this method are as follows: 1) oxygen consumption, discharge of a large amount of sewage, causing serious pollution; 2) When ethylene hypochlorite is used to produce chloroethanol, by-products such as carbon dioxide are produced at the same time. The ethylene oxide produced during the saponification of chloroethanol can be isomerized into acetaldehyde, resulting in the loss of ethylene oxide and high single consumption of ethylene; 3) ethylene oxide, the mass fraction of aldehyde is very high, about 4×10-6-5×10-6 and the minimum is 2×10-6

The production of ethylene oxide by chloroalcohol method, due to the small device, low output, poor quality, high consumption, and therefore high cost, has lost its market competitiveness compared with the high-quality products produced by large device oxidation method.

2. Direct oxidation method

Ethylene direct oxidation method is divided into air direct oxidation method and oxygen direct oxidation method.

Direct air oxidation method

Direct air oxidation method uses air as an oxidizer, so there must be an air purification device in the production to prevent harmful impurities in the air from taking the reactor and affecting the activity of the catalyst. The air method is characterized by two or more reactors in series, that is, the main reactor and the secondary reactor, in order to keep the activity of the main reactor catalyst at a high level (63% to 75%), usually operated at a low conversion rate (20% to 50%). Oxygen direct oxidation method

This method uses the preparation of pure oxygen or other oxygen sources as oxidants. Due to the use of pure oxygen as an oxidizing agent, the continuous introduction of inert gases into the system is greatly reduced, and the unreacted ethylene can be basically recycled completely. The circulating gas from the top of the absorption tower must be decarbonized to remove the carbon dioxide and then recycled back to the reactor, otherwise the carbon dioxide mass exceeds 15%, which will seriously affect the activity of the catalyst.

3.Comparison between air direct oxidation method and oxygen oxidation method

Both of these oxidation methods use a tubular fixed bed reactor. The reactor is the key equipment, which is closely related to the reaction effect, and its reaction process is basically the same, including reaction, absorption, stripping and distillation refining processes. However, compared with the air oxidation method, the oxygen oxidation method has obvious advantages, mainly reflected in the following aspects:

① Process: Air method requires air purification system, secondary reactor and absorption tower, as well as tail gas catalytic converter and heat recovery system; The oxygen process requires a separation unit and a carbon dioxide removal system. Compared with the air oxidation method, the oxygen oxidation method has a shorter process, less equipment and less investment in plant construction.

② Catalyst: The amount of catalyst in production directly affects the level of product cost. There are two main factors that affect how much catalyst is used. On the one hand, the performance of the catalyst, such as the selectivity and conversion rate of the catalyst. The oxidation method is more advantageous in this respect, because of the high selectivity and the small amount of catalyst required. On the other hand, the mass fraction of silver in the catalyst, the mass fraction of silver in the air method catalyst of Germany Hals company is about 20%; The mass fraction of silver of Shell's oxygen catalyst is only about 10%, which is the same volume of catalyst. The difference in silver content is almost 50%.

③ Reactor: under the premise of the same production scale, the oxygen method requires fewer reactors, and the reactors are all operated in parallel. The air process requires a secondary reactor, as well as secondary absorption and stripping towers, which increases the equipment investment. Yield and unit consumption: The yield of ethylene oxide by oxygen method is higher than that by air method, and the unit consumption of ethylene is lower.

Reaction temperature: the reaction temperature of oxygen oxidation method is lower than that of air method, which is more favorable for extending the life of catalyst and maintaining the smooth operation of production.

In summary, oxygen oxidation method has obvious advantages in production process, production equipment, product yield and reaction conditions, so EO/EG devices in the world generally use oxygen oxidation production. However, because the oxygen oxidation method uses pure oxygen as raw material, when the oxygen price rises, the total production cost of ethylene oxide produced by the oxygen method will have a certain impact, while the air method does not have the total cost change caused by the change of oxygen price, and the oxygen method has high purity requirements for the raw material, such as low oxygen purity, it will significantly increase the amount of hydrocarbon containing gas. Ethylene consumption increases. However, the production cost of oxygen oxidation is usually about 10% lower than that of air oxidation.