How is the operating pressure of a distillation column generally determined?

First, consider the requirements of distillation; second, consider the economic availability of refrigerants or heat transfer fluids; third, take into account the investment required for equipment...... In short, various factors should be considered comprehensively, and various parameters optimized so that the distillation system can be constructed and operated at a relatively economical cost. This post was last edited by processimu on 2008-1-15 at 14:45.]

It depends on the following factors: (1) The properties of the material. If the material tends to polymerize or decompose at high temperatures, reduced pressure is used. If it is a gas at normal pressure, apply pressure. (2) Specific determination of decompression or compression: Considering that an appropriate tower top temperature is achieved, circulating water can be used as the cooling medium ； The bottom temperature of the tower is considered to be appropriate, provided that steam at a certain pressure is used, or the temperature does not exceed a certain level ； Taking equipment investment into account, the lower the absolute pressure, the relatively larger the tower diameter; therefore, a technical and economic analysis is necessary.

1. The distillation results required to meet the process specifications, namely the separation efficiency of light and heavy components, taking into account the physical properties of the materials (boiling point, solubility, etc.). 2. Economic analysis. The comparison of steam, circulating water, and electricity consumption under different pressures (after recycling) has been determined. Recycling is possible; for example, the light-component steam from the tower top can be used as a heat source for other materials.

Determining the pressure in a distillation column is a matter that takes various factors into consideration. Firstly, the capabilities of the auxiliary systems play a role: using circulating water for cooling at the top of the column is cost-effective, while using air coolers is the most energy-efficient approach. In other words, the temperature at the top of the column needs to be high enough, at least above 50 degrees. The pressure at the top of the column can then be determined based on the vapor pressure curve at that temperature. Another factor is the heating provided to the bottom of the column; the higher the column pressure, the easier it is to cool the vapor at the top, and thus the smaller the area required for the condenser. However, the temperature at the bottom of the column also increases, and the requirements regarding the heat source used there rise as well, or else the heat exchange area of the reboiler at the bottom of the column becomes larger. Secondly, the separation requirements between light and heavy components within the column are important: as the column pressure increases, the relative volatility of some components decreases, which means more trays are needed to achieve the same level of separation. Therefore, a higher column pressure isn’t necessarily advantageous. Thirdly, the higher the column pressure, the lower the gas phase volume load within the column, and since the column diameter is determined by this gas phase load, the investment required is reduced. Fourthly, there are other considerations as well; for example, the temperature at the bottom of the column cannot be too high, as high temperatures can cause polymerization. Hence, some columns need to operate under vacuum conditions. This post was last edited by 1681818 on 2008-1-18 at 21:05

I understand, thank you all for your answers