大学化工专业英语Lesson 4

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 .

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.

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。

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。

In chemical reactor design there are two questions which must be answered:

（1）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。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.

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；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 ,ΔH 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 ,ΔH 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 mol的S，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。

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.

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。

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

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.

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

合反应。

（ii）Liquid-solid: with one, or more, liquid phases in contact with a solid. The solid may be a reactant or catalyst.

（ii）液体—固体：一种或多种液相与固体接触。固体可能是反应物或催化剂。（iii）Liquid-solid-gas: where the solid is normally a catalyst; such as in the hydrogenation of amines, using a slurry of platinum on activated carbon as a catalyst. （iii）液体—固体—气体：固体通常是催化剂；如胺类氢化中，使用活性炭上铂的悬浮液作为催化剂。

（iv）Gas-solid: where the solid may take part in the reaction or act as a catalyst. The reduction of iron ores in blast furnaces and the combustion of solid fuels are examples where the solid is a reactant.

（iv）气体—固体：固体可能参与反应，或作为催化剂。高炉中铁矿石的还原和固体燃料的氧化，都是固体作为反应物的例子。

（v）Gas-liquid: where the liquid may take part in the reaction or act as a catalyst.

（v）气体—液体：液体可能参与反应，或作为催化剂。

4. Reactor Geometry (type)

4. 反应器几何学（反应器的类型）

The reactors used for established processes are usually complex designs which have been developed (have evolved) over a period of years to suit the requirements of the process, and are unique designs.

对于已建立的过程，反应器通常是复杂的设计，这些设计已经经过一段时间的发展，适应了过程的需要，是唯一的设计。

However, it is convenient to classify reactor designs into the following broad categories. 然而，把反应器的设计分成以下几大类是很方便的。

Stirred tank reactors

搅拌釜式反应器

Stirred tank (agitated) reactors consist of a tank fitted with a mechanical agitator and a cooling jacket or coils.

搅拌釜式（搅拌）反应器由装有机械搅拌器的釜体和冷却套管或线圈组成。

They are operated as batch reactors or continuously. Several reactors may be used in series.

他们即可间歇操作，又可连续操作。几个反应器可以连续使用。

The stirred tank reactor can be considered the basic chemical reactor, modeling on a large scale the conventional laboratory flask.

搅拌釜式反应器被认为是基本的化学反应器，在较大的尺度上，模仿实验室常见的烧瓶。

Tank sizes range from a few titers to several thousand liters.

搅拌釜的尺寸从几升到几千升。

They are used for homogeneous and heterogeneous liquid-liquid and liquid-gas reactions; and for reactions that involve finely suspended solids, which are held by the agitation.

它们应用在均相和非均相的液—液和液—气之间的反应；对于包含细微悬浮固体的反应，通过搅拌来保持它们反应。

As the degree of agitation is under the designer's control, stirred tank reactors are particularly suitable for reactions where good mass transfer or heat transfer is required.

由于搅拌的程度是由设计师来控制，搅拌釜式反应器特别适合的反应是，有好的传质或传热的反应。

When operated as a continuous process the composition in the reactor is constant and the same as the product stream, and, except for very rapid reactions, this will limit the conversion that can be obtained in one stage.

操作一个连续的过程时，同产品流一样，反应器中的合成物是不变的，除了非常快的反应以外，这将会限制可以在一个阶段获得的转化。

The power requirements for agitation will depend on the degree of agitation required and will range from about 0.2 kW/ms for moderate mixing to 2 kW/ms for intense mixing.

搅拌功率的要求，将取决于搅拌所需的程度，从约0.2 kW/ ms 的轻度混合到2 kW/ms 的强烈混合。

Tubular reactor

管式反应器

Tubular reactors are generally used for gaseous reactions, but are also suitable for some liquid-phase reactions.

管式反应器一般用于气体反应，但也可用于液相反应。

If high heat-transfer rates are required, small-diameter tubes are used to increase the surface area to volume ratio.

如果需要高的传热率，小口径管可以用来增加表面积与体积的比值。

Several tubes may be arranged in parallel, connected to a manifold or fitted into a tube sheet in a similar arrangement to a shell and tube heat exchanger.

几个管可能被平行放置，与总管相连，或者是按照想相似的布置装进管板，形成列管式换热器。

For high-temperature reactions the tubes may be arranged in a furnace.

对于高温反应来说，管可能布置在炉子里。

Packed bed reactors

填充床反应器

There are two basic types of packed-bed reactor: those in which the solid is a reactant, and those in which the solid is a catalyst.

填充床反应器有两种基本类型：一种是固体是反应物，一种是固体是催化剂。Many examples of the first type can be found in the extractive metallurgical industries.

可以在湿法冶金工业中发现第一种类型的很多例子。

In the chemical process industries the designer will normally be concerned with the second type: catalytic reactors.

在化学过程工业中，设计师通常会关注第二类：催化反应器。

Industrial packed-bed catalytic reactors range in size from small tubes, a few centimeters diameter lo large diameter packed beds.

工业上的填充床催化反应器的大小由直径是几厘米的小管子到大直径的填充床。Packed-bed reactors are used for gas and gas-liquid reactions.

填充床反应器适用于气体反应和气—液反应。

Heat-transfer rates in large diameter packed beds are poor and where high heat-transfer rates are required fluidized beds should be considered.

在大直径填充床中，传热率是很低的，如果需要高的传热率，应该考虑流化床。Fluidized bed reactors

流化床反应器

The essential features of a fluidized bed reactor is that the solids are held in suspension by the upward flow of the reacting fluid; this promotes high mass and heat-transfer rates and good mixing.

流化床反应器的基本特征是，利用反应流体向上的流动来保持固体的悬浮；这促进了高的传质、传热率和良好的混合。

The solids may be a catalyst; a reactant in fluidized combustion processes; or an inert powder, added to promote heat transfer.

固体可能是一个催化剂；可能是流化床燃烧过程中的反应物；或着是促进传热的惰性粉末。

Though the principal advantage of a fluidized bed over a fixed bed is the higher heat-transfer rate, fluidized beds are also useful where it is necessary to transport large quantities of solids as part of the reaction processes, such as where catalysts are transferred to another vessel for regeneration.

虽然，流化床超过固定床的主要优势是更高的传热率，对于反应过程中需要传输大量的固体，流化床也是有用的，如催化剂被转移到另一个容器中再次使用。

Fluidization can only be used with relatively small sized particles, < 300μm with gases. 流化作用只适用于尺寸相对较小的颗粒，小于300μm的气体。

A great deal of research and development work has been done on fluidized bed reactors in recent years, but the design and scale up of large diameter reactors is still an uncertain process and design methods are largely empirical.

近年来，对于流化床反应器，大量的研究和开发工作已经完成，但是，大尺寸反应器的设计和扩大仍是一个不确定的过程，设计方法主要凭经验。

Batch or continuous processing

间歇和连续加工

In a batch process all the reagents are added at the commencement; the reaction proceeds the compositions changing with time, and the reaction is stopped and the product withdrawn when the required conversion has been reached.

在间歇过程中，一开始加入所有的试剂；反应成分随时间变化，当达到需要的转化时，反应停止，取出产物。

Batch processes are suitable for small-scale production and for processes where a range of different products, or grades is to be produced in the same equipment; for instance, pigments, dyestuffs and polymers .

间歇过程适合小规模生产和加工一系列不同的产品，或是在相同的设备中生产不同等级的产品；例如，颜料，染料和聚合物。

In continuous processes the reactants are fed to the reactor and the products withdrawn continuously; the reactor operates under steady-state conditions.

在连续过程中，反应物流入反应器及产物的流出是连续不断的；反应器在恒定的条件下运行。

Continuous production will normally give lower production costs than batch production, but lacks the flexibility of batch production.

连续生产通常会比间歇生产成本低，但缺乏间歇生产的灵活性。

Continuous reactors will usually be selected for large-scale production.

连续反应器通常应用于大规模的生产。

Processes that do not fit the definition of batch or continuous are often referred to as semi-continuous or semi-batch.

不符合间歇或连续生产定义的过程通常被称为半连续或半间歇操作。

In a semi-batch reactor some of the reactants may be added, or some of the products withdrawn, as the reaction proceeds.

在半间歇反应器中，随着反应的进行，一些反应物被加入，一些产品被取出。

A semi-continuous process can be one which is interrupted periodically for some purpose; for instance, for the regeneration of catalyst.

一个半连续的过程是，因为某种目的被周期性地中断的过程；例如，催化剂的再生。