The field of process concept design with the discipline of chemical engineering is still expanding and new terms appear. Here is a brief description of these novel terms entered into the vocabulary:

Process Concept Design

Process Concept Design is a systematic procedure to find the best flowsheet, i.e., to select the best process units and the interconnecting streams among these units and estimate the optimum design conditions [Douglas]. With process units Douglas means conventional unit operations.


The term flowsheet means the representation of the process design by process units and their connecting streams [Douglas and Smith]. The term is also be used for computer programmes by which the connecting stream compositions are calculated based on mathematical models of the process units.

Process Synthesis

Process Synthesis is also a term used for process concept design, to generate the best flowsheet structure to convert feedstock into product [Schaschske]. However, process synthesis is also used for process concept design, not based on conventional unit operations, but based on functions (also called tasks) and streams. The functions are simple transformations, such as reaction, mixing, and enthalpy change, describing what transformation is needed, but not how. In a second step the functions are further defined for physical and chemical conditions. In a third design step functions and also streams are integrated as much as is optimal. For the other functions suitable unit operations are selected. Finally, a flow sheet is generated which can contain a novel process step, such as a reactive, extractive, distillation column combining several functions [Siirola].

Unit Operations

Unit operations is a process step characterised by the same physical and chemical rules as for any application. The term was introduced by AD Little in 1916. Perry’s Chemical Engineers’ Handbook describes most of them [Green, 2019]. By process intensification research novel unit operations are generated based on novel dynamic operations, and different external fields, such as gravity, microwaves, and light [Stankiewicz].


  • Douglas JM. Conceptual design of chemical processes. New York: McGraw-Hill; 1988.
  • Smith R. Chemical process: design and integration. John Wiley & Sons; 2005.
  • Siirola JJ. Industrial applications of chemical process synthesis. In Advances in chemical engineering 1996 Jan 1 (Vol. 23, pp. 1-62). Academic Press.
  • Green DW, Southard MZ. Perry’s chemical engineers’ handbook. McGraw-Hill Education; 2019.
  • Stankiewicz A, Van Gerven T, Stefanidis G. The fundamentals of process intensification. John Wiley & Sons; 2019.