Table of Contents

What is Batch Distillation?

Batch distillation is a separation process that takes in a fixed amount of feed to be separated, as opposed to a continuous distillation process in which a feed stream would constantly be going into the separation unit. Batch distillation can also be run as a single-stage or multi-stage process. A single-stage batch process could resemble a flash distillation unit, in which a finite amount of liquid feed is heated and passed into a flash drum where the more volatile component is vaporized and exits the drum at the top outlet stream, while the less volatile component exits the drum at the bottom outlet stream. Batch process can then also be conducted as a multi-stage process either by taking an outlet stream of a single stage batch process and putting it through another consecutive single stage operation, or by utilizing a multi-stage distillation column in a batch process. Batch distillation processes often operate on the principal that more volatile and lighter components will collect at the top of a distillation column as vapour while heavier and less volatile components collect at the bottom as liquid. This results in volatile components being extracted earlier in the distillate and over time leaving a high concentration of the less volatile component in the batch distillation unit [1].

Figure 1: Batch Distillation vs. Continuous Distillation [2]

How to Build a Batch Distillation Unit

To build a singl- stage batch distillation unit, you could build a simple separation unit with just a heater to raise the temperature of the feed, a flash drum to enable the more volatile component to flash, a top outlet stream for the vapor to exit, and a bottoms exit stream for less volatile liquid to leave. However if you want to build a multi-stage batch distillation unit with a distillation column you would require more components. In a batch distillation column, a reboiler is used to heat the batch feed and have it rise through the multi-stage distillation column. The reboiler also acts as a pot where the initial liquid batch is placed. When the heated vapour moves up through the distillation column, packed material improves gas-liquid contact which helps in the separation of materials. After the vapour rises through the trays of the column, it exits as overhead vapour and begins the condense in the condenser unit. This resulting condensate is collected in a reflux tank or reflux drum which then leads to either collection tanks for the final products of the separation, or are returned into the distillation column as reflux and passed through again [1]. Typically in a batch distillation the first condensate is known as the head and the final condensate in the batch is called the feints. These condensates are undesirable and are usually used as reflux for the distillation column. The condensate in the middle is known as the heart, which is what begins to return desired product as some of the overhead distillate will be removed will be progressively removed over time and placed into receiver tanks [2]. Main cuts receive the desirable product while off cuts receive any by-products [1].

Figure 2: Example of Batch Distillation Column [1]

Advantages and Disadvantages of Batch Distillation

Advantages	Disadvantages
Good to produce high purity products Batch distillation is capable of separating multiple components [1] Ideal for small volume separation Good flexibility as units can be modified to operate based on the different chemical compositions of each batch [4]	Batch processes require more energy to operate than a continuous process [1] Higher risk of contamination between different batches if processing units are not cleaned out Not as good as continuous distillation for very high volume processes [4]

Industry Applications

Batch distillation processes are typically used to separate small amounts of fine chemicals and give a high purity of desired product. Batch distillation is also good for the recovery of solvent containing the product of interest. These factors make batch distillation a common separation process in the pharmaceutical industry in which separating high purity products is important. The recovery of solvent in batch distillation also makes it so that almost all of the desired pharmaceutical product can be extracted through a multi-stage batch distillation [1]. The water purification industry also benefits from using batch distillation as the high purity return of the desired product makes it an effective separation unit to distil clean drinking water. Batch distillation is also effective at separating multiple components since the most volatile component can be boiled off early and extracted from the system. This process is then repeated until every component is separated. This process could be seen in the purification of certain oils which may require separation from a mixture of many other hydrocarbons [3].

References

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Faculty Advisor: Sarah Meunier

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