题目

英语翻译
The unit operations are as applicable to many physical processes as to chemical ones.Forexample,the process used to manufacture common salt consists of the following sequence of the unit operations:transportation of solids and liquids,transfer of heat,evaporation,crystallization,drying,and screening.No chemical reaction appears in these steps.On the other hand,the cracking of petroleum8,with or without the aid of a catalyst,is a typical-chemical reaction conducted on an enormous scale.Here the unit operations — transportation of fluids and solids,distillation,and various mechanical separations — are vital,and the cracking reaction could not be utilized without them.The chemical steps themselves are conducted by controlling the flow of material and energy to and from the reaction zone.

提问时间：2020-07-26

答案

单元操作不但适用于许多物理工艺过程,对化学工艺过程也同样如此.
例如,生产普通食盐的工艺过程包含以下依次进行的单元操作：运输固体/液体原料；传递热量；蒸发；结晶；干燥；筛渣.这些步骤中并不产生化学反应.
另一方面来说,不管是否用到催化剂,石油的裂解都是典型的化学反应.对于裂解石油而言,其涉及的单元操作（运输液体/固体原料；蒸馏；各种机械分离法）都是不可或缺的,少了这些步骤,裂解反应根本无法实现.这些单元操作所服务的化学工序主要通过控制原料/能量流入流出反应区而实现.