How to separate styrene and ethylbenzene in continuous distillation column?

How to separate styrene and ethylbenzene in continuous distillation column?

In chemical production, styrene and ethylbenzene are important organic compounds, which are widely used in synthetic resins, plastics and rubber. The physical properties of styrene and ethylbenzene are very similar, and direct separation is difficult. In this case, the continuous distillation column becomes an efficient and commonly used separation technology. This paper will discuss in detail how to use continuous distillation column to separate styrene and ethylbenzene, and its practical application in industrial production.

1. Distillation technology basic principle

Distillation is a process of separation by heating the mixture and using the difference in the volatility of the components. In the rectification process, the mixture is heated to boiling, and the different components partition between the vapor and liquid phases due to differences in volatility. Through multiple partial condensation and partial evaporation, high volatility components (such as styrene) or low volatility components (such as ethylbenzene) are gradually enriched. The continuous rectification column realizes the countercurrent contact of the vapor and the liquid phase through the tray or packing, thereby efficiently separating the mixture.

2. Styrene and ethylbenzene separation characteristics

Styrene (C≡H≡C) and ethylbenzene (C≡H≡C) are structurally similar isomers with boiling points of 149°C and 136°C, respectively. Although their boiling points are not very different (about 13°C), this difference is sufficient to achieve separation using distillation techniques. The relative volatility (α) of styrene is about 1.09, which is slightly higher than that of ethylbenzene, which means that under the same conditions, the volatility of styrene is slightly higher than that of ethylbenzene.

3. Continuous distillation tower works

In a continuous rectification column, the mixture enters at the top of the column and undergoes several partial condensation and partial evaporation. Through the tray or packing, the vapor and liquid phase are fully contacted, and the low volatile component (ethylbenzene) is gradually enriched in the liquid phase, while the high volatile component (styrene) is enriched in the vapor. Eventually, styrene and ethylbenzene flow out of the top and bottom of the column, respectively.

The following are the key steps for the separation of styrene and ethylbenzene in a continuous distillation column:

1. Feed: the mixture from the top of the column into, through the distributor uniform distribution.
2. Partial evaporation: the mixture is heated to boiling in the column, part of the components are evaporated into vapor, and the remaining components remain in the liquid phase.
3. Countercurrent contact: vapor and liquid phase in the tray or packing countercurrent contact, through mass transfer effect to achieve separation.
4. Partial condensation: the vapor rises to the top of the tower and is condensed, while the liquid phase falls to the next tray.
5. Product separation: styrene is enriched in vapor and flows out from the top of the tower; ethylbenzene is enriched in liquid phase and flows out from the bottom of the tower.

4. Factors Affecting Separation Effect

In order to efficiently separate styrene from ethylbenzene, the following key factors need to be considered:

4.1 raw material purity and proportion

The ratio of styrene and ethylbenzene in the mixture directly affects the separation difficulty. If the concentrations of the two components in the feed are close, more trays or more efficient separation equipment is required.

4.2 temperature control

Temperature is an important parameter affecting the separation effect. The temperature in the column needs to be strictly controlled to ensure sufficient separation of styrene and ethylbenzene. Too high a temperature may result in entrainment of ethylbenzene in the top product, while too low a temperature may result in entrainment of styrene in the bottom product.

4.3 pressure control

The pressure has a significant effect on the relative volatility of the mixture. In the distillation process, it is usually necessary to maintain a constant pressure to ensure the stability and efficiency of the separation process.

4.4 reflux ratio

The reflux ratio is the ratio of the liquid phase reflux flow rate to the product flow rate in the distillation process. Appropriate reflux ratio can improve the separation efficiency, but too high reflux ratio will increase energy consumption.

5. Industrial applications in practical considerations

5.1 packing or tray selection

The design of the continuous distillation column requires the selection of the appropriate packing or tray type. High efficiency packing (such as corrugated packing) or tray (such as bubble cap tray) can improve the separation efficiency.

5.2 system design

In industrial applications, the design of continuous distillation columns needs to consider the flow rate, component properties and separation requirements of the mixture. Thermodynamic calculations and hydrodynamic analysis are often required to optimize column performance.

5.3 Operation and Maintenance

Continuous distillation column requires strict process control and daily maintenance. Operators need to monitor temperature, pressure and flow parameters in real time to ensure the stability and safety of the separation process.

6. Summary

Continuous distillation column is an efficient and commonly used separation technology, which can effectively separate styrene and ethylbenzene. By controlling the parameters such as temperature, pressure and reflux ratio, combined with appropriate packing or tray design, the efficient separation of styrene and ethylbenzene can be achieved. The core of how to separate styrene and ethylbenzene in a continuous distillation column is to make full use of the volatile difference between the two components and to achieve separation through multiple countercurrent contacts. This technology has a broad application prospect in the chemical industry, and with the progress of technology, its separation efficiency and safety will continue to improve.