Batch Distillation refer to the use of distillation in batches, means that a mixture is distilled to seperate into its component fraction before the distillation. Still is again charged with more mixtures and the process is repeated. This is in contrast with continuous distillation where the feedstock is added and the distillate drawn off without interruption. Batch Distillation has always been an important part of the production of high purity of substance or material. It is very frequent seperation process in pharmaceutical industry.
The simplest and most frequently used Batch distillation configuration is the batch rectifier, including pot still. It consist of pot or reboiler, rectifying column, a condenser.(for splitting off a portion of the condensed vapours/distillate) as reflux and one or more receivers. Pot is filled with liquid mixtures and heated. Vapours flow upward in the rectifying column and condenses at the top. Usually, this contacting of vapour and liquid considerally improves the separation. Generally, this step is named as startup. The first condensate is the head, and it contain undesirable components.
- They are economical for small volumes.
- They are flexible in accomodation changes in product formulation.
- They re flexible in changing production rate.
- Allow the use of standardised multipurpose equipment for the production of variety of product from the same plant are best if equipment needs regular cleaning because of fouling or needs regular sterlization.
- Allow the better product integer each batch of product can be clearly identified in terms of the feed involved and condition of processing. This is particulary important in industry such as a pharmaceutical and food stuff.
Batch distillation is still widely used in chemical industry. Many smaller chemical plants operate in batch mode with batch reaction and batch rectifiers. The main source is production flexibility where differnent chemicals are being made in the same equipment in short compaigns.
- It may be difficult to establish when to switch from one cut to another.
- It is difficult to establish optimal reflux ratio, since the pot composition continuously changes.
- operating instabilites are there while changing parameters.
- It is impractical sometime
- When the product obtain in crude is too small, it is not able to recover then product needs to concentrated and then processed in a separate batch distillation.
The batch stripper consist of the same part as the batch rectifier. In this case , the pot is located above the stripping column. During operation the high boiling constituents are primarily separated from the charge mixtures. The liquid in pot is deplted in the boiling constituents, and enriched in low boiling ones. The high boiling product is riched into the bottom product. The residual low boiling product is withdrawn from the charge pot. This mode of batch distillation is very seldom applied industrial processes.