Distillation is a process where more volatile components (lower boiling points) can be separated from less volatile materials (higher boiling points). This particular process is a batch distillation where the feed stock (a mixture of A and B) is fed into the base of a still. A is more volatile than B. The still is fitted with a column and a reflux condenser. The column is a vertical vessel fitted with perforated plates (trays) where vapour and liquid can mix. The still is heated with steam and as the mixture starts to boil, vapour passes up the column to the condenser where it condenses. Some of this ‘condensate’ is removed as product into the product receiver but most of the condensate is fed back to the column. This ‘reflux’ liquid meets the vapour coming up the column. On each plate, more of the volatile A is evaporated from the liquid flowing down the column but more B is condensed from the vapour coming up. The use of many stages and a high reflux gives a high purity product (A).
The challenge is to produce as much product A as possible in the allowed batch time. Increasing the steam rate will increase the distillation rate but at very high rates, the trays in the column won’t work efficiently and the product purity will suffer.
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