Continuous distillation

If this vapor is then separated and condensed into a liquid, it becomes richer in the lower boiling point component(s) of the original mixture.

On entering the column, the feed starts flowing down but part of it, the component(s) with lower boiling point(s), vaporizes and rises.

However, as it rises, it cools and while part of it continues up as vapor, some of it (enriched in the less volatile component) begins to descend again.

The bottoms reboiler may be a steam-heated or hot oil-heated heat exchanger, or even a gas or oil-fired furnace.

Steady state means that quantities related to the process do not change as time passes during operation.

Unless the process is disturbed due to changes in feed, heating, ambient temperature, or condensing, steady state is normally maintained.

The height of the feed point along the column can vary on the situation and is designed so as to provide optimal results.

For a multi-component feed, computerized simulation models are used both for design and subsequently in operation of the column as well.

Large-scale industrial fractionation towers use reflux to achieve more efficient separation of products.

Distillation towers (such as in images 3 and 4) use various vapor and liquid contacting methods to provide the required number of equilibrium stages.

The vapor–liquid equilibrium for each feed component in the tower reacts in its unique way to the different pressure and temperature conditions at each of the stages.

Hence, a distillation column needs more plates than the required number of theoretical vapor–liquid equilibrium stages.

These offer the advantage of a lower pressure drop across the column (when compared to plates or trays), beneficial when operating under vacuum.

The total packing height required is the number of theoretical stages multiplied by the HETP.

The number of theoretical stages required to make a given separation is calculated using a specific vapor to liquid ratio.

[9][10] Images 4 and 5 assume an overhead stream that is totally condensed into a liquid product using water or air-cooling.

However, in many cases, the tower overhead is not easily condensed totally and the reflux drum must include a vent gas outlet stream.

In yet other cases, the overhead stream may also contain water vapor because either the feed stream contains some water or some steam is injected into the distillation tower (which is the case in the crude oil distillation towers in oil refineries).

In particular, it is the arrangement in a single column shell of the Petlyuk configuration[11] that has been proved to be thermodynamically equivalent.

Although crude oils generally do not contain olefins, they are formed in many of the processes used in a petroleum refinery.

[13][14] For example, the crude oil fractionator produces an overhead fraction called "naphtha" which becomes a gasoline component after it is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value.

After these come the heavy fuel oil cuts and finally the bottoms product, with very wide boiling ranges.

A typical application for distilling cannabis concentrates is butane hash oil (BHO).