化工原理 考试 重要

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• Assuming the equilibrium relationship can be used, then
• The average composition of top product y
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1.2.2 Simple distillation
t B
A x2 x1 x或y
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xD
• 1.2.2 Simple distillation
Simple distillation can be used in primary separation of liquid mixture. Characteristics: (1) batch (un-steady), single-stage distillation. (2) Instant equilibrium
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• (2) Bubble point equation（泡点方程）
• (3) Dew point equation （露点方程）
• (4) The equilibrium equation（相平衡方程） phase equilibrium constant
1.3 Principle of rectifying and flow 1.4 Continuous rectifying of binary 1.5 Uncontinuous distillation and special distillation
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When the total pressure is not high, the gas is the ideal gas, the equilibrium constitution of gas is
if
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then
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1.1.3 Volatility and relative volatility
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In bi-component solution, when the total pressure is not high, we can get
Specification:
– (1) If α > 1, it shows component A is more volatile than the component B, the bigger deviation of α to 1 is, the bigger difference of volatility is, the easier to separate. – (2) If α = 1, we can get y=x, we cannot separate the components by the general distillation, we should use the special distillation or other methods.
• Characteristic
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• Category
– (1)The operation manner – (2)The process manner
simply equilibriu m fractional special
• 1.1.1 The ideal system
– (a) The liquid is ideal solution, following Raoult`s law （拉乌尔定律）. – (b) The gas is ideal gas, following Dalton‘s law（道 尔顿 定律）. • (1) Phase rule（相律） – F=C-Ф+2 – where F:the freedom （ 自 由 度 数 ） , Ф: the number of the phase（相数） and C: the number of the independent component （独立组分数）.
The introduction of Distillation
• Application
– separating, purifying or recovering the useful components ( the homogeneous liquid mixtures or vaporizing gas mixture). – (1) Getting the products directly and operating process easily. – (2) The wide application. – (3) Be suitable to mixtures with all concentrations. – (4) Costing lots of energy in the operation.

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Calculation of simple distillation
• Assuming at certain moment t, stream of the bottom is L kmol, composition is x , After the differential time dt, stream of the bottom is L-dL, composition is x-dx, gas evaporation is dD, and composition is y. • Total material balance dL=dD • Balance of the volatile components
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Equation of equilibrium
For the non-ideal solution, the equilibrium partial pressure can be shown: （γ: activity efficiency of the component 活度系数）
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• Heat balance(te—equilibrium temperature of separator)
ignoring the heat loss
• The equilibrium relationship(ideal system)
– (3)The number of components in the system – (4)The operation pressure
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1.1 The equilibrium relationship between gas and liquid
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equilibrium stage
又称接触级
饱和液相
x0 t0 L t
B T0
y V t
y y0
B A
t-y t-x
接触级
t0 x y0 x0 y
A
x x0
Hale Waihona Puke x L tThe principle of chemical engineering
y0 T0 V 饱和汽相
T0 >t0
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1.3 Principle of rectifying and flow
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1.2 Equilibrium distillation & simple distillation
1.2.1 Equilibrium distillation
• Equilibrium distillation is also called flash distillation（闪蒸）, is a continuous and steady single-distillation process （连续、稳态的单级蒸馏 操作 ）.
• 简单蒸馏、平衡蒸馏（闪蒸）、精馏和特殊精馏 • Batch(间歇) distillation,Continuous(连续) distillation • Bicomponent, multi-component • High-pressure, Atmospheric, Reduced distillation
• 1.3.1 Principle of rectifying
Partial vaporizing and condensing several times Basic principle of the fraction distillation: the liquid mixture can separate completely through partially vaporizing and condensing several times.
– material balance（物料衡算）, heat balance（热 量衡算） 、 equilibrium relationship（汽液平衡关 系）