The scale of a chemical process refers to the rough ranges in mass or volume of a chemical reaction or process that define the appropriate category of chemical apparatus and equipment required to accomplish it, and the concepts, priorities, and economies that operate at each. While the specific terms used—and limits of mass or volume that apply to them—can vary between specific industries, the concepts are used broadly across industry and the fundamental scientific fields that support them. Use of the term "scale" is unrelated to the concept of weighing; rather it is related to cognate terms in mathematics (e.g., geometric scaling, the linear transformation that enlarges or shrinks objects, and scale parameters in probability theory), and in applied areas (e.g., in the scaling of images in architecture, engineering, cartography, etc.).
Practically speaking, the scale of chemical operations also relates to the training required to carry them out, and can be broken out roughly as follows:
For instance, the production of the streptomycin-class of antibiotics, which combined biotechnologic and chemical operations, involved use of a 130,000 liter fermenter, an operational scale approximately one million-fold larger than the microbial shake flasks used in the early laboratory scale studies.
As noted, nomenclature can vary between manufacturing sectors; some industries use the scale terms pilot plant and demonstration plant interchangeably.
Apart from defining the category of chemical apparatus and equipment required at each scale, the concepts, priorities and economies that obtain, and the skill-sets needed by the practicing scientists at each, defining scale allows for theoretical work prior to actual plant operations (e.g., defining relevant process parameters used in the numerical simulation of large-scale production processes), and allows economic analyses that ultimately define how manufacturing will proceed.
Besides the chemistry and biology expertises involved in scaling designs and decisions, varied aspects of process engineering and mathematical modeling, simulations, and operations research are involved.