The issue of hydrogen pressure and boiling point

It is recommended to pick up a book on \"Principles of Chemical Engineering\" to read; it can serve as a reference if you are interested in this type of problems.

Dalton’s law of partial pressures, a concept from high school physics. The principle behind methods such as introducing steam at the bottom of the vacuum distillation column in crude oil distillation to lower the distillation temperatures of various components in the mixture, and introducing steam into the catalytic diesel stripping column to reduce the light components in diesel thereby controlling its flash point, is based on this same principle. The boiling point of pure *** is 210; when hydrogen is added to the system, the partial pressure of *** in the system decreases, and its boiling point drops as well.

It is recommended to get a copy of \"Physical Chemistry\" to read; it can serve as a reference if you are interested in this type of problems.

This post was last edited by qugd on 2022-4-30 at 20:28. The boiling point of a pure substance refers to the temperature at which its saturated vapor pressure reaches 1 atmosphere under normal conditions. From a thermodynamic perspective, the boiling point is merely a function of temperature and is independent of pressure. I think 1. The original poster’s description of the problem is incorrect ； 2. The person in the problem described by the OP has an issue with the way the problem is presented. If, as the original poster described, crude oil distillation didn’t require vacuum distillation – if high-boiling-point components could have their boiling points reduced by adding an inert gaseous medium – that would be an excellent thing for refineries. I personally guess that the problem described by the original poster is similar to that encountered in distillation or steam distillation: taking advantage of the fact that volatile substances have a certain vapor pressure at a specific temperature, a gaseous medium with a lower boiling point than that of the volatile substance – such as water vapor or other low-boiling-point media – is used to vaporize and separate the desired volatile substance at a temperature below its normal boiling point, thereby extracting it. Although the principle is also related to partial pressure, it does not result in a decrease in boiling point, because that’s not how the boiling point is defined. It would be better for the poster to learn about distillation or steam distillation. Steam distillation is often used to extract substances with high boiling points or those that are prone to decomposition at high temperatures from certain natural plants, allowing them to be separated from the matrix at temperatures lower than their normal boiling points.

Thermodynamically speaking, the saturated vapor pressure is merely a function of temperature and has nothing to do with pressure. When the vapor pressure exceeds the external pressure, the liquid begins to boil. Therefore, the boiling point is related to pressure. Crude oil distillation does indeed employ a stripping process; the principle is to use steam to carry away the vapor of hydrocarbons, keeping their partial pressure below the saturated vapor pressure so that equilibrium cannot be reached, and thus the hydrocarbons are continuously distilled out.

This should not be a closed system; rather, it should be a system with a continuous inflow of hydrogen and an outflow of materials. 0.18 Mpa is the operating condition. ***I haven’t looked up the vapor pressure-temperature relationship; I assume that 150 degrees corresponds to 0.05 Mpa. In a closed system at 150 degrees, when the vapor pressure reaches 0.05 Mpa, liquid evaporation and gas liquefaction reach equilibrium. At this point, hydrogen gas is introduced into the system, and gas flows out of it. The volume ratio of hydrogen gas flowing in is 100%; conversely, the volume ratio of *** flowing out is 0.05/0.18 = 27.7%, while that of hydrogen gas is 72.3%. If the hydrogen flow rate is higher, it’s possible that 10% *** and 90% hydrogen will flow out; this principle is similar to that of vacuum distillation and stripping

Yes, *** and hydrogen enter while exiting at the same time

For pure substances, there is a specific relationship curve between the saturated vapor pressure and temperature. ***The boiling point temperature actually corresponds to the saturated vapor pressure value at 1 standard atmosphere (for pure substances). Generally, the higher the temperature, the greater the saturated vapor pressure. In non-hermetically sealed containers or mixed systems, different substances have their own saturated vapor pressures; the combination of these substances results in the system’s current pressure. The proportion of gas molecules from each substance in the gas phase determines its respective partial pressure. At this point, strictly the saturated partial pressures of various substances corresponding to the temperature. When there is an adequate supply of hydrogen, under the given operating conditions, most of the partial pressures in the gas phase are due to hydrogen; the partial pressure of *** accounts for only a small portion. The effect resulting from this is equivalent to placing *** in a vacuum state where its partial pressure corresponds to the absolute pressure under the current operating conditions. This absolute pressure corresponds to the vapor pressure of *** at 150 degrees Celsius; therefore, boiling occurs naturally. This pressure division is what explains why, even though the temperature has not reached the boiling point, there is a large amount of solvent in the air of the painting workshop (air accounts for the majority of the partial pressure in the air, while solvents evaporate at a much lower partial pressure). ) This is also why many high-boiling-point substances can be separated by distillation at lower temperatures using stripping (water vapor occupies most of the partial pressure under operating conditions, thereby reducing the boiling point of these high-boiling-point substances)