【Daily Question】Chemical Engineering Principles 251: Theoretical Plates (December 2)
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The last edit to this post was made by Zaihui Kangqiao on 2015-12-24 at 13:47. The Chemical Engineering Theory section is now launching a \"One Question per Day\" activity aimed at helping everyone reinforce their basic knowledge in chemical engineering. Subsequent series will include those on \"Principles of Chemical Engineering\", \"Mass Transfer and Separation\", \"Thermodynamics in Chemical Engineering\", and \"Chemical Process Engineering\". We hope for your active support! Answers to the questions in the \"One Question per Day\" activity can be viewed directly, and the thread will be closed after 1 day ! You receive 3 wealth rewards just for participating, and an additional 3 wealth points if you answer correctly~ Short answer question: What is a theoretical plate? Theoretical plate: a plate from which the gas and liquid phase compositions satisfy the equilibrium relationship ；
The idealized tray section in which the gas and liquid phases are fully mixed, and the resistances to heat and mass transfer are both zero#
Theoretically, if the vapor-liquid phase contact is good and sufficient time is allowed, the vapor-liquid phases leaving plate n may reach an equilibrium state, with the equilibrium temperature being Tn; the vapor phase composition Yn and the liquid phase composition Xn are related by an equilibrium relationship. A tray that brings the vapor and liquid phases into equilibrium is called one theoretical plate.
This tray enables the vapor rising to the upper tray and the liquid descending to the lower tray to reach vapor-liquid equilibrium through heat and mass transfer; such a tray is known as an ideal tray.
The number of theoretical plates, n, is equal to the column length L divided by the theoretical plate height H. The theory of theoretical plates was first proposed by Martin and Synge; they compared the chromatography column to a distillation tower, considering a continuous chromatography column as being composed of many small segments. Within each of these segments, part of the space is occupied by the stationary phase, while the rest is filled with the mobile phase. Once the components enter the chromatography column along with the mobile phase, they undergo distribution between the two phases. It is assumed that within each segment, the components can quickly reach distribution equilibrium between the two phases. Such a segment is referred to as a theoretical plate, and the length of one theoretical plate is called the theoretical plate height H. After multiple cycles of distribution equilibrium, the components with lower distribution coefficients leave the column first, while those with higher distribution coefficients leave later. Since there are a large number of theoretical plates in the chromatography column, even slight differences in the distribution coefficients of the components can still result in good separation effects.
Answer: In theory, if the vapor and liquid phases are in good contact and enough time is allowed, the vapor and liquid phases leaving plate n may reach an equilibrium state. The equilibrium temperature is Tn, and there is a equilibrium relationship between the vapor phase composition Yn and the liquid phase composition Xn. A tray that brings the vapor and liquid phases into equilibrium is called one theoretical plate.
Answer: A theoretical plate refers to an idealized tray on which the gas and liquid phases are fully mixed, and the resistance to heat and mass transfer is zero.
In a theoretical scenario, if the gas and liquid phases are in good contact and sufficient time is allowed, the gas and liquid phases leaving the nth tray may reach an equilibrium state. The equilibrium temperature is Tn, and there is an equilibrium relationship between the gas phase composition Yn and the liquid phase composition Xn. Such a tray that brings the gas and liquid phases to equilibrium is referred to as a theoretical tray.
A tray that enables the vapor rising to the upper tray and the liquid descending to the lower tray to reach vapor-liquid equilibrium through heat and mass transfer is known as a theoretical tray.
It is the number of separation plates required theoretically, with each plate having an efficiency of 100%.