第 17章 相际扩散与传质原理
概 述
扩散是一种
在物理驱动下单
组分通过混合物
的运动。扩散最
通常的原因是扩
散组分浓度梯度
的存在。
Diffusion is the movement,
under the influence of a
physical stimulus,of an
individual component through
a mixture,The most common
cause of diffusion is a
concentration gradient of the
diffusing component,
A concentration
gradient tends to move
the component in such a
direction as to equalize
concentrations and
destroy the gradient,
浓度梯度驱使扩
散组分朝着使浓
度均匀化的方向
扩散，从而使浓
度梯度趋于消失。
? When the gradient is
maintained by constantly
supplying the diffusing
component to the high-
concentration end of the
gradient and removing it
at the low concentration
end,there is a steady-state
flux of the diffusing
component,This is
characteristic of many
mass-transfer operations,
当不断地向
高浓度一端提供
扩散组分，从低
浓度一端除去扩
散组分时，扩散
组分便具有稳定
的传质通量。这
就是许多传质操
作的特点。
例如，当在填料塔
中用水吸收气体中
的 NH3时，在塔内的
任意一点上，在气
相浓度梯度的驱使
下,NH3由气相主体
扩散至气～液界面，
在界面上溶解，然
后，在液相浓度梯
度驱使下，扩散至
液相主体。
For example,when ammonia is
removed from a gas by
absorption in water in a packed
column,at each point in the
column a concentration gradient
in the gas phase causes ammonia
to diffuse to the gas-liquid
interface,where it dissolves,and
a gradient in the liquid phase
causes it to diffuse into the bulk
liquid.
In stripping a solute from a
liquid the gradients are
reversed; here diffusion
brings solute from the bulk
liquid to the interface and
from there into the gas
phase.
当从吸收液中
解吸溶质时，
浓度梯度与吸
收过程相反。
在此，扩散作
用使溶质从液
相主体移至界
面，再从界面
移至气相。
In some other mass-
transfer operations such
as leaching and
adsorption,unsteady-
state diffusion takes
place,and the gradients
and fluxes decrease with
time as equilibrium is
approached.
在其它一些诸如
浸取和吸咐操作
中发生的是不稳
定扩散，随着过
程趋于平衡，扩
散组分的浓度梯
度和通量随时间
而降低。
Although the usual cause of
diffusion is a concentration
gradient,diffusion can also be
caused by an activity gradient,
as in reverse osmosis,by a
pressure gradient,by a
temperature gradient,or by
the application of an external
force field,as in a centrifuge.
虽然扩散的一般
原因是浓度梯度，但
能动梯度也能引起扩
散如反渗透过程，压
力梯度、温度梯度和
外场力都可引起扩散，
如离心分离。
Molecular diffusion induced
by temperature is thermal
diffusion,and that from an
external field is forced
diffusion,Both are
uncommon in chemical
engineering,Only diffusion
under a concentration
gradient is considered in this
chapter.
由温度引起的分子
扩散称为热扩散，
由外场力引起的扩
散称为强制扩散。
这两种扩散方式在
化学工程中并不常
见。本章仅讨论由
浓度梯度引起的质
量扩散。
Diffusion is not restricted
to molecular transfer
through stagnant layers
of solid or fluid,It also
takes place when fluids
of different compositions
are mixed.
扩散并不局
限于分子通过固
体或液体停滞膜
的传递。当不同
组成的流体相混
合时也会发生扩
散。
The first step in mixing
is often mass transfer
caused by the eddy motion
characteristic of turbulent
flow,This is called eddy
diffusion,The second step
is molecular diffusion
between and inside the
very small eddies,
混合过程首先
是因湍流的涡流特
性引起的质量传递。
这一过程被称为涡
流扩散。其次是在
微小的漩涡间及其
内部的分子扩散。
Sometimes the
diffusion process is
accompanied by bulk
flow of the mixture in
a direction parallel to
the direction of
diffusion.
有时扩散过程
还伴随着与扩散
方向相平行的混
合物主体流动。
In all the mass-transfer
operations,diffusion
occurs in at least one
phase and often in both
phases,In distillation,
the low boiler diffuses
through the liquid phase
to the interface and
away from the interface
into the vapor.
在所有的质量传
递操作中，扩散
至少在一相中发
生，更多则是在
两相中发生。蒸
馏时，低沸物由
液相扩散至界面，
离开界面进入汽
相。
Role of diffusion in mass transfer 扩散在质量传递中的角色
The high boiler
diffuses in the reverse
direction and passes
through the vapor into
the liquid,In leaching,
diffusion of solute
through the solid phase
is followed by diffusion
into the liquid.
高沸物逆向扩
散从汽相进入液
相。浸取时，溶
质扩散穿过固相，
然后再扩散进入
液相。
In liquid extraction,the
solute diffuses through the
raffinate phase to the
interface and then into
the extract phase,In
crystallization,solute
diffuses through the
mother liquor to the
crystals and deposits on
the solid surfaces.
液～液萃取
时，溶质从萃余
相扩散至液～液
界面，然后进入
萃取相。结晶时，
溶质由母液扩散
到晶体，然后积
淀于晶体表面。
In humidification or
dehumidification there is no
diffusion through the liquid
phase because the liquid
phase is pure and no
concentration gradient
through it can exist; but the
vapor diffuses to or from
the liquid-gas interface into
or out of the gas phase.
增湿和减湿时，
因液相是纯液体，
无浓度梯度存在。
故液相无扩散。但
增湿时，蒸汽离开
气液界面，扩散进
入气相；而减湿时，
则为蒸汽朝向气液
界面，扩散离开气
相。
In membrane
separations diffusion
occurs in all there
phases,in the fluids
on either side of the
membrane and in the
membrane itself.
膜分离时，
所有相中即膜
两侧的流体中
和膜自身内均
会发生扩散现
象。
Chap.8 Gas absorption
This chapter deals with the mass-transfer operations
known as gas absorption and stripping or desorption.
⒈ 气体吸收, 利用 气体混合物 各组份在 吸收剂 中的 溶
解度 不同，而使气体混合物得以 分离 的单元操作。
In gas absorption a soluble gas is absorbed from its
mixture with an inert gas by means of liquid in which
the solute gas is more or less soluble.
§ 8-1 Introduction
气体混合物,Mixture or Rich Gas ～ A+B
溶质,Solute ～ A
惰性气体,An Inert Gas ～ B
吸收剂,Solvent ～ S
溶解度,Solubility
分离,Separation
可溶的,Soluble
单元操作,Unit Operation
吸收液,Absorbing liquid or The strong liquid
尾气,Dilute gas or Lean gas
K
E
Y
W
O
R
D
S
§ 8-1 Introduction
2 规定
3 Examples（ P546）
⑴ A major application of absorption technology is
the removal of CO2 and H2S from natural gas
（天然气） or synthesis gas （合成气） by
absorption in solutions of amines （有机胺） or
alkaline salts（碱式盐）,
⑵ Another example is the washing of ammonia
from a mixture of ammonia and air by means of
liquid water,
§ 8-1 Introduction
4 The solute & the absorbing liquid
The solute is subsequently recovered from the liquid
by distillation,and the absorbing liquid can be either
discarded or reused,
5 Adsorption
sometimes a solute is removed from a liquid by
bringing the liquid into contact with an inert gas;
such an operation,the reverse of gas absorption,is
desorption or gas stripping.
§ 8-1 Introduction
A common apparatus used in
gas absorption and certain other
operations is the packed tower,
The rich gas enters the
distributing space below the
packing and flows upward
through the interstices (空隙 )in
the packing countercurrent to
the flow of the liquid.
填料,Packing
填料塔,Packed tower
6 The process of gas absorption
§ 8-1 Introduction
⑴ The packing provides a large area of contact
between the liquid and gas and encourages
intimate contact between the phases.
⑵ The solute in the rich gas is absorbed by the
fresh liquid entering the tower,and dilute,or
lean,gas leaves the top.
⑶ The liquid is enriched in solute as it flows
down the tower,and concentrated liquid,
called the strong liquid,leaves the bottom of
the tower through the liquid outlet,
§ 8-1 Introduction
7 Major applications for gas absorption in
commercial industry
⑴ Purification of the material gases 原料气净化
CO2 and H2S are removed from natural gas or
synthesis gas by absorption in solutions of amines salts.
在合成 NH3工艺中，来自变换工段的变换气
约含 28％ CO2。 因 C02可使 catalyst中毒。所以，变
换气进合成塔前，必须经过水洗和铜洗两个工段，
将 CO2的含量减小到 0.01％ 以下。
§ 8-1 Introduction
⑵ Recovering of using materials
⑶ Preparation of some solution
For examples,
NO2 is absorbed by liquid water,→HNO 3 ～ 化学吸收
HCl is absorbed by liquid water,→HCl ～ 物理吸收
⑷ Purification of waste gas
8 Classification
⑴ Absorption and absorption with chemical reaction
物理吸收与化学吸收
⑵ Isothermal absorption and no-isothermal absorption
等温吸收与非等温吸收
§ 8-1 Introduction
In general,当气体溶解于液体时，常常伴
随有溶解热。若有化学反应存在，还会有反应
热。这些因素最终导致溶液温度逐渐升高。但
若 热效应较小,或 气相中 A的浓度很低,或 吸收
剂用量很大 时，温度升高不显著，便可以认为
是 Isothermal absorption。
⑶ Single and multiple component absorption
单组份吸收与多组份吸收
Single component,混合气中 只有一个组份 进入液相。
Multicomponent, 混合气中有 两或更多组份 进入液相。
This chapter deals with the isothermal single absorption。
§ 8-1 Introduction
9 This chapter will discuss some questions,
⑴ 吸收过程进行的限度和影响因素
～ Phase-equilibrium ～ 相平衡
⑵吸收剂用量的计算（操作型问题）
～ Calculation of amount of the liquid
⑶ 吸收塔高度的计算 （设计型问题）
～ Calculation of tower height
⑷ 提高吸收塔生产能力的措施
～ Methods to enhance the ability of absorption tower
10 吸收设备
吸收设备有多种结构。
但以 塔设备 最为常用。 ★ 填料塔 packed tower
板式塔 plate tower
§ 8-1 Introduction
概 述
扩散是一种
在物理驱动下单
组分通过混合物
的运动。扩散最
通常的原因是扩
散组分浓度梯度
的存在。
Diffusion is the movement,
under the influence of a
physical stimulus,of an
individual component through
a mixture,The most common
cause of diffusion is a
concentration gradient of the
diffusing component,
A concentration
gradient tends to move
the component in such a
direction as to equalize
concentrations and
destroy the gradient,
浓度梯度驱使扩
散组分朝着使浓
度均匀化的方向
扩散，从而使浓
度梯度趋于消失。
? When the gradient is
maintained by constantly
supplying the diffusing
component to the high-
concentration end of the
gradient and removing it
at the low concentration
end,there is a steady-state
flux of the diffusing
component,This is
characteristic of many
mass-transfer operations,
当不断地向
高浓度一端提供
扩散组分，从低
浓度一端除去扩
散组分时，扩散
组分便具有稳定
的传质通量。这
就是许多传质操
作的特点。
例如，当在填料塔
中用水吸收气体中
的 NH3时，在塔内的
任意一点上，在气
相浓度梯度的驱使
下,NH3由气相主体
扩散至气～液界面，
在界面上溶解，然
后，在液相浓度梯
度驱使下，扩散至
液相主体。
For example,when ammonia is
removed from a gas by
absorption in water in a packed
column,at each point in the
column a concentration gradient
in the gas phase causes ammonia
to diffuse to the gas-liquid
interface,where it dissolves,and
a gradient in the liquid phase
causes it to diffuse into the bulk
liquid.
In stripping a solute from a
liquid the gradients are
reversed; here diffusion
brings solute from the bulk
liquid to the interface and
from there into the gas
phase.
当从吸收液中
解吸溶质时，
浓度梯度与吸
收过程相反。
在此，扩散作
用使溶质从液
相主体移至界
面，再从界面
移至气相。
In some other mass-
transfer operations such
as leaching and
adsorption,unsteady-
state diffusion takes
place,and the gradients
and fluxes decrease with
time as equilibrium is
approached.
在其它一些诸如
浸取和吸咐操作
中发生的是不稳
定扩散，随着过
程趋于平衡，扩
散组分的浓度梯
度和通量随时间
而降低。
Although the usual cause of
diffusion is a concentration
gradient,diffusion can also be
caused by an activity gradient,
as in reverse osmosis,by a
pressure gradient,by a
temperature gradient,or by
the application of an external
force field,as in a centrifuge.
虽然扩散的一般
原因是浓度梯度，但
能动梯度也能引起扩
散如反渗透过程，压
力梯度、温度梯度和
外场力都可引起扩散，
如离心分离。
Molecular diffusion induced
by temperature is thermal
diffusion,and that from an
external field is forced
diffusion,Both are
uncommon in chemical
engineering,Only diffusion
under a concentration
gradient is considered in this
chapter.
由温度引起的分子
扩散称为热扩散，
由外场力引起的扩
散称为强制扩散。
这两种扩散方式在
化学工程中并不常
见。本章仅讨论由
浓度梯度引起的质
量扩散。
Diffusion is not restricted
to molecular transfer
through stagnant layers
of solid or fluid,It also
takes place when fluids
of different compositions
are mixed.
扩散并不局
限于分子通过固
体或液体停滞膜
的传递。当不同
组成的流体相混
合时也会发生扩
散。
The first step in mixing
is often mass transfer
caused by the eddy motion
characteristic of turbulent
flow,This is called eddy
diffusion,The second step
is molecular diffusion
between and inside the
very small eddies,
混合过程首先
是因湍流的涡流特
性引起的质量传递。
这一过程被称为涡
流扩散。其次是在
微小的漩涡间及其
内部的分子扩散。
Sometimes the
diffusion process is
accompanied by bulk
flow of the mixture in
a direction parallel to
the direction of
diffusion.
有时扩散过程
还伴随着与扩散
方向相平行的混
合物主体流动。
In all the mass-transfer
operations,diffusion
occurs in at least one
phase and often in both
phases,In distillation,
the low boiler diffuses
through the liquid phase
to the interface and
away from the interface
into the vapor.
在所有的质量传
递操作中，扩散
至少在一相中发
生，更多则是在
两相中发生。蒸
馏时，低沸物由
液相扩散至界面，
离开界面进入汽
相。
Role of diffusion in mass transfer 扩散在质量传递中的角色
The high boiler
diffuses in the reverse
direction and passes
through the vapor into
the liquid,In leaching,
diffusion of solute
through the solid phase
is followed by diffusion
into the liquid.
高沸物逆向扩
散从汽相进入液
相。浸取时，溶
质扩散穿过固相，
然后再扩散进入
液相。
In liquid extraction,the
solute diffuses through the
raffinate phase to the
interface and then into
the extract phase,In
crystallization,solute
diffuses through the
mother liquor to the
crystals and deposits on
the solid surfaces.
液～液萃取
时，溶质从萃余
相扩散至液～液
界面，然后进入
萃取相。结晶时，
溶质由母液扩散
到晶体，然后积
淀于晶体表面。
In humidification or
dehumidification there is no
diffusion through the liquid
phase because the liquid
phase is pure and no
concentration gradient
through it can exist; but the
vapor diffuses to or from
the liquid-gas interface into
or out of the gas phase.
增湿和减湿时，
因液相是纯液体，
无浓度梯度存在。
故液相无扩散。但
增湿时，蒸汽离开
气液界面，扩散进
入气相；而减湿时，
则为蒸汽朝向气液
界面，扩散离开气
相。
In membrane
separations diffusion
occurs in all there
phases,in the fluids
on either side of the
membrane and in the
membrane itself.
膜分离时，
所有相中即膜
两侧的流体中
和膜自身内均
会发生扩散现
象。
Chap.8 Gas absorption
This chapter deals with the mass-transfer operations
known as gas absorption and stripping or desorption.
⒈ 气体吸收, 利用 气体混合物 各组份在 吸收剂 中的 溶
解度 不同，而使气体混合物得以 分离 的单元操作。
In gas absorption a soluble gas is absorbed from its
mixture with an inert gas by means of liquid in which
the solute gas is more or less soluble.
§ 8-1 Introduction
气体混合物,Mixture or Rich Gas ～ A+B
溶质,Solute ～ A
惰性气体,An Inert Gas ～ B
吸收剂,Solvent ～ S
溶解度,Solubility
分离,Separation
可溶的,Soluble
单元操作,Unit Operation
吸收液,Absorbing liquid or The strong liquid
尾气,Dilute gas or Lean gas
K
E
Y
W
O
R
D
S
§ 8-1 Introduction
2 规定
3 Examples（ P546）
⑴ A major application of absorption technology is
the removal of CO2 and H2S from natural gas
（天然气） or synthesis gas （合成气） by
absorption in solutions of amines （有机胺） or
alkaline salts（碱式盐）,
⑵ Another example is the washing of ammonia
from a mixture of ammonia and air by means of
liquid water,
§ 8-1 Introduction
4 The solute & the absorbing liquid
The solute is subsequently recovered from the liquid
by distillation,and the absorbing liquid can be either
discarded or reused,
5 Adsorption
sometimes a solute is removed from a liquid by
bringing the liquid into contact with an inert gas;
such an operation,the reverse of gas absorption,is
desorption or gas stripping.
§ 8-1 Introduction
A common apparatus used in
gas absorption and certain other
operations is the packed tower,
The rich gas enters the
distributing space below the
packing and flows upward
through the interstices (空隙 )in
the packing countercurrent to
the flow of the liquid.
填料,Packing
填料塔,Packed tower
6 The process of gas absorption
§ 8-1 Introduction
⑴ The packing provides a large area of contact
between the liquid and gas and encourages
intimate contact between the phases.
⑵ The solute in the rich gas is absorbed by the
fresh liquid entering the tower,and dilute,or
lean,gas leaves the top.
⑶ The liquid is enriched in solute as it flows
down the tower,and concentrated liquid,
called the strong liquid,leaves the bottom of
the tower through the liquid outlet,
§ 8-1 Introduction
7 Major applications for gas absorption in
commercial industry
⑴ Purification of the material gases 原料气净化
CO2 and H2S are removed from natural gas or
synthesis gas by absorption in solutions of amines salts.
在合成 NH3工艺中，来自变换工段的变换气
约含 28％ CO2。 因 C02可使 catalyst中毒。所以，变
换气进合成塔前，必须经过水洗和铜洗两个工段，
将 CO2的含量减小到 0.01％ 以下。
§ 8-1 Introduction
⑵ Recovering of using materials
⑶ Preparation of some solution
For examples,
NO2 is absorbed by liquid water,→HNO 3 ～ 化学吸收
HCl is absorbed by liquid water,→HCl ～ 物理吸收
⑷ Purification of waste gas
8 Classification
⑴ Absorption and absorption with chemical reaction
物理吸收与化学吸收
⑵ Isothermal absorption and no-isothermal absorption
等温吸收与非等温吸收
§ 8-1 Introduction
In general,当气体溶解于液体时，常常伴
随有溶解热。若有化学反应存在，还会有反应
热。这些因素最终导致溶液温度逐渐升高。但
若 热效应较小,或 气相中 A的浓度很低,或 吸收
剂用量很大 时，温度升高不显著，便可以认为
是 Isothermal absorption。
⑶ Single and multiple component absorption
单组份吸收与多组份吸收
Single component,混合气中 只有一个组份 进入液相。
Multicomponent, 混合气中有 两或更多组份 进入液相。
This chapter deals with the isothermal single absorption。
§ 8-1 Introduction
9 This chapter will discuss some questions,
⑴ 吸收过程进行的限度和影响因素
～ Phase-equilibrium ～ 相平衡
⑵吸收剂用量的计算（操作型问题）
～ Calculation of amount of the liquid
⑶ 吸收塔高度的计算 （设计型问题）
～ Calculation of tower height
⑷ 提高吸收塔生产能力的措施
～ Methods to enhance the ability of absorption tower
10 吸收设备
吸收设备有多种结构。
但以 塔设备 最为常用。 ★ 填料塔 packed tower
板式塔 plate tower
§ 8-1 Introduction
