-
Chemical Reaction Engineering
化学反应工程
Every
industrial chemical process is designed to produce
economically a desired product
from a
variety of starting materials through a succession
of treatment steps.
每一个工业化学
过程的目的是从不同的原材料，经过一系列的处理步骤生产经济所
需的产品。
Fig. 4-1 shows a typical
situation.
图
4-1
展示了一个典型的情况。
The raw materials undergo a number of
physical treatment steps to put them in the form
in which they can be reacted
chemically.
原料进行了一些物理处理的步骤，使它们能够发生化学反应。
They then pass through the reactor.
然后让他们通过反应器。
The
products of the reaction must then undergo further
physical
treatment
—
—
separations,
purifications, etc.
—
—
for the final
desired product to be obtained.
产物要经历进一步的物理处理—
—
分离，净化提纯等等—
—
以获得期望的最终产品。
Design of equipment for the
physical treatment steps is studied in the unit
operations.
物理处理步骤设备的设计在单元操作中研究。
Here we are concerned with the chemical
treatment step of a process.
在这里我们关心的是一个过程的化学处理步骤。
Economically this may be an
inconsequential unit, say a simple mixing tank .
1
从经济的角度说，这可能是个不
重要的单元，比如说一个简单的混合槽。
More
often than not, however, the chemical treatment
step is the heart of the process, the
thing that makes or breaks the process
economically.
然而通常，化学处理步骤是一
个过程的核心，它决定这个过程经济的成败。
Design of the reactor is no
routine matter, and many alternatives can be
proposed for a
process .
反应器
的设计不是普通的事，对于一个过程有许多可供选择的建议。
In searching for the optimum it is not
just the cost of reactor that must be minimized.
寻找最佳的条件，不仅是反应器成本的最小化。
One design may have low reactor cost,
but the materials leaving the unit may be such
that
their treatment requires much
higher cost than alternative design.
<
/p>
一个设计可能使反应器的成本较低，但材料离开装置可能比其他的设计需要更高的
处理费。
Hence, the
economics of the over-all process must be
considered.
因此，必须要考虑整个过程的经济。
Reactor
design
uses
information,
knowledge,
and
experience
from
a
variety
of
areas
thermodynamics,
chemical
kinetics,
fluid
mechanics,
heat
transfer,
mass
transfer,
and
economics.
反应器的设计使用了各个领域的信息，
知识和经验，比如热力学，化学动力学，流
体力学，传热，传质，和经济学。
2
Chemical
reaction
engineering
is,
the
synthesis
of
all
these
factors
with
the
aim
of
properly designing a
chemical reactor.
化学反应工程，是这
些因素的综合学科，旨在设计出合适的化学反应器。
The design of chemical reactors is
probably the one activity which is unique to
chemical
engineering, and it is
probably this function more than anything else
which justifies the
existence of
chemical engineering as a distinct branch of
engineering.
化学反应器的设计对于化学工程而言可能是一个独特的活动
，它的这个功能可能比
任何东西都更能证明化学工程作为一个独特的分支工程的存在。<
/p>
In chemical
reactor design there are two questions which must
be answered:
（
1<
/p>
）
What change can we expect to
occur
？
（
2
）
How
fast will they take place
？
化学反应器的设计有两个必须回答的问题：
（
1
）我们
预期发生什么变化？（
2
）它们发生的有多快？
The
first
question
concerns
thermodynamics,
the
second
the
various
rate
processes-
-chemical
kinetics, heat transfer, etc.
第一个问题涉及热力
学，第二个问题涉及各种速率过程—
—
化学动力学，传热等。<
/p>
Putting these all together
and trying to determine how these processes are
interrelated can
be an extremely
difficult problem; hence we start with the
simplest of situations and build
up
our
analysis
by
considering
additional
factors
until
we
are
able
to
handle
the
more
difficult problems.
3
把这些放在一起，
试图确定这些过程
是怎样相关联的，
是一个非常困难的问题；
< br>因
此，我们从最简单的情况着手，考虑附加因素，建立我们的分析，直到我们能处
理
更难的问题。
1.
Thermodynamics
1.
热力学
Thermodynamics
gives
two
important
pieces
of
information
needed
in
design,
the
heat
liberated or absorbed
during reaction and the maximum possible extent of
reaction.
热力学给出设计中需要的两条重要的信
息，反应放出和吸收的热量与最大可能的反
应进度。
2
Chemical reactions are invariably
accompanied by the liberation or absorption of
heat,
the magnitude of which must be
known for proper design. Consider the reaction
aA
→
rR+sS
,
Δ
H
r
positive, endothermic negative ,
exothermic
化学反应
总是伴随着热量的释放或吸收，为了合理的设计，必须知道它的大小，考
虑下面的反应：
aA
→
rR+sS
,
Δ
H
r
,
正值，吸热；负值，放热。
The
heat
of
reaction
at
temperature
T
is
the
heat
transferred
from
surroundings
to
the
reacting system when
a
moles of A disappear to
form
r
moles of R and
s
moles of S, with
the system measured at the same
temperature and pressure before and after
reaction.
温度为
T
时，
a
mol
的
A
消失生成了
r
mol
的
R
和
s
< br>
mol
的
S
< br>，反应的热量是环境
传递给反应体系的，这是在反应前后相同的温度和压力下对体
系测量的结果。
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With heats of reaction known or
estimable from thermochemical data, the magnitude
of
the heat effects during reaction can
be calculated.
从热化学数据中可以得到或
估算反应的热量，反应中产生的热量大小可以计算。
Thermodynamics also allows calculation
of the equilibrium constant K from the standard
free energies of the reacting
materials.
热力学也可以从反应物的标准自由能来计算平衡常数。
With
the
equilibrium
constant
known,
the
expected
maximum
attainable
yield
of
the
products
of reaction can be estimated.
< br>由于平衡常数已知，可以估算出反应中可以得到的预期产品的最大产量。
2. Chemical Kinetics
2.
化学动力学
Under appropriate conditions feed
materials may be transformed into new and
different
materials which constitute
different chemical species.
适当的条件下，供给的材料可能转变为新的不同的材料，形成不同的化学物质。
If
this
occurs
only
by
rearrangement
or
redistribution
of
the
constituent
atoms
to
form
new molecules, we say that a chemical
reaction has occurred.
如果发生
这种情况只是由于构成原子的重排或再分配，形成新的分子，我们就说一
个化学反应已经
发生了。
Chemistry is concerned
with the study of such reactions.
化学关注的是这种反应的研究。
5
It
studies
the
mode
and
mechanism
of
reactions,
the
physical
and
energy
changes
involved and the rate of formation of
produces.
它研究反应的模式和机制，反应中涉及
的物质和能量的变化，及产品形成的速率。
It is the last-mentioned area of
interest, chemical kinetics, which is of primary
concern to
us.
这
是最后提到的，我们感兴趣并且主要关心的领域，化学动力学。
Chemical kinetics searches for the
factors that influence the rate of reaction.
化学动力学寻找影响反应速率的因素。
It measures this rate and proposes
explanations for the values found.
化学动力学测量反应速率，并提出对已有数值的解释。
For
the
chemical
engineer
the
kinetics
of
a
reaction
must
be
known
if
he
is
to
satisfactorily design equipment to
effect these reactions on a technical scale.
对于化学工程师，如果他想设计出令人满意的设备在技术规模
完成这些反应，就必
须知道一个反应的动力学。
Of course, if the reaction is rapid
enough so that the system is essentially at
equilibrium,
design is very much
simplified.
当然，如果反应足够迅速以至于体
系基本上是平衡的，那么设计是非常简单的。
Kinetic
information is not needed, and thermodynamic
information alone is sufficient.
不需要动力学的信息，仅凭热力学信息就足够了。
3. Homogeneous and Heterogeneous
Reactions
3.
均相反应和非均相反应
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Homogeneous reactions are
those in which the reactants, products, and any
catalyst used
form one continuous
phase: gaseous or liquid.
均
相反应的反应物，产物，和所用的催化剂形成一个连续相：气相或液相。
Homogeneous
gas phase
reactors will always be operated continuously;
whereas liquid
phase
reactors may be batch or continuous.
<
/p>
均匀的气相反应器将连续的运作；然而液相反应器可连续或间歇操作。
Tubular (pipe-line) reactors are
normally used for homogeneous gas-phase reactions;
for
example,
in
the
thermal
cracking
of
petroleum
crude
oil
fractions
to
ethylene,
and
the
thermal decomposition of
dichloromethane to vinyl chloride.
管式（管道）反应器通常用于均相气相反应；例如，在热裂解石油中，原油分裂为
乙烯，二氯甲烷热分解为氯乙烯。
Both
tubular and stirred tank reactors are used for
homogeneous liquid-phase reactions.
管式反应器和搅拌斧式反应器都用于均相液相反应。
In a heterogeneous reaction
two or more phases exist, and the overriding
problem in the
reactor design is to
promote mass transfer between the phases. The
possible combinations
of phase are:
在非均相反应中，存在两种或更多的相，在反应器设计中，最
重要的问题是，提高
相之间的传质。可能的相结合是：
（
i
）
Liquid
-liquid: immiscible liquid phases; reactions such
as the nitration of toluene or
benzene
with mixed acids, and emulsion polymerizations.
（
i
）液体
—液体：不混溶的液相；例如甲苯或苯与酸混合的硝化反应，和乳胶的聚
7