ABSTRACT
Distillation has been widely accepted for product separation, purification, and waste removal in chemical process industries. Depending on whether the industry is handling petrochemicals, bulk chemicals, specialty chemicals, or pharmaceuticals, the distillation process can be divided into two categories: (1) batch distillation, which is mainly used in specialty chemical, biochemical, and pharmaceutical industries; and (2) continuous distillation, which is primarily implemented in the petrochemical and bulk chemical industries. Figure 5.1a shows a conventional batch distillation column where the feed is initially charged into the reboiler at the beginning of operation. After a total reflux operation (i.e., all condensates are recycled to the column), the distillate is continuously withdrawn while the bottom residue with a high-boiling-temperature component is concentrated, making this a time-varying process. In continuous distillation (Figure 5.1b), the feed is constantly supplied to the column, and the top and bottom products are simultaneously obtained under a steady-state operation. The upper section of the feed point is referred to as the
rectifying
section
, as a low-boilingtemperature component is enriched. The lower section is referred to as the
stripping section
, as a low-boiling-temperature component is stripped off. Batch distillation is the oldest separation process and the most widely used
unit operation in the batch industry. Batch distillation is highly preferable to continuous distillation when high-value-added, low-volume chemicals must be separated. It is also widely used in chemical processing industries where small quantities of materials are to be handled in irregularly or seasonally scheduled
periods, and it is implemented when the feed composition varies widely from period to period or where completely different feed stocks have to be handled.
