Aromatics Process Unit Design

This chapter covers topics related to the process design and optimization of a typical aromatics complex including aromatics fractionation, aromatics extraction, transalkylation, xylene isomerization, and para-xylene separation units. In addition, it discusses important process design considerations including design margin philosophy, operational flexibility, fractionation optimization, and safety considerations. An aromatics complex producing para-xylene and benzene products, as well as by-products including nonaromatic raffinate and heavy aromatics streams, contains upto 14 different fractionation services not including those associated with the upstream naphtha hydrotreating and reforming units. Additional columns are required if other xylene products such as ortho-xylene are produced. Some of these columns are included in the aromatics extraction, transalkylation, xylene isomerization, and para-xylene separation units. While there are many different aromatics extraction processes in operation and offered by licensors, there are two main types: processes that combine liquid-liquid extraction and extractive distillation (ED) and processes that solely use ED.