Distillation is defined as a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat. Distillation is the most commonly used separation process in the chemistry and petrochemical industry, mostly employed in continuous processes but also used in discontinuous processes.
Batch distillation is widely used for the separation of specialty and fine chemicals and for the recovery of small quantities of solvent during the production of high purity and added value products. Batch processing is the main feature of the pharmaceutical, biochemical, and specialty chemical industries. Sometimes distillation is carried out in batches rather than continuously. Batch stills are more labor-intensive than continuous distillation. After each batch, the still has to be unloaded and then cleaned out. However, batch distillation can be more flexible and is to small scale processes.
One advantage of batch distillation is the possibility to separate a mixture of several components with only one column and, although a batch distillation column uses more energy than a continuous column, many times it is convenient to operate in batch mode. For these reasons the design, analysis, and optimization of batch distillation columns have obtained attention by several researchers. Figure 1 shows a conventional batch distillation column consisting of a rebuild or pot, a column with plates or packing, a condenser, a reflux tank, accumulative recipients for products (main outs), and byproducts (off cuts).
Figure 1. 1: Batch distillation column with three receivers for products (main cut) and three receivers for mixtures (off cut). Although many people have a fair idea what “distillation” means, the important aspects that seem to be missed from the manufacturing point of view are that: distillation is the most common separation technique it consumes enormous amounts of energy, both in terms of cooling and heating ARQ reorients it can contribute to more than 50% of plant operating costs The best way to reduce operating costs of existing units, is to improve their efficiency and operation via process optimization and control.
To achieve this improvement, a thorough understanding of distillation principles and how distillation systems are designed is essential. 2. 0 TYPE OF DISTILLATION COLUMN 1 . Continuous distillation Figure 2. 1 : Type of continuous distillation column Continuous distillation column is a form of distillation, is an ongoing separation in which a mixture is continuously (without interruption) fed into the process and separated fractions are removed continuously as output streams.
A distillation s the separation or partial separation of a liquid feed mixture into components or fractions by selective boiling (repatriation) and condensation. A distillation produces at least two output fractions. These fractions include at least nonvolatile distillate fraction, which has boiled and been separately captured as a vapor condensed to a liquid, and practically always a bottoms (or residuum) fraction, which is the least volatile residue that has not been separately captured as a condensed vapor. Continuous distillation is a process used in industry to separate chemical compounds.
It works using the principles of distillation, but is particularly useful in dealing with large volumes of industrial chemicals by allowing distillation to happen without interruption. The process is especially important in the petroleum industry, where it is used to refine crude oil. When a mixture of chemicals is boiled, certain chemicals those with the lowest boiling points undergo a change of state from liquid to gas and rise as vapor. In distillation, this vapor is passed through a device known as a condenser, which consists of a sealed tube surrounded by a hollow area filled with coolant.
As the vapor is cooled, it condenses back from a gas into a liquid and runs down the tube into a container. By controlling the temperature of the boiler, specific chemicals can be separated out from a liquid mixture using this process. Continuous distillation uses this principle to separate and purify industrial chemicals. A column, or tower, is filled with “feed,” the mixture to be purified. The mixture is then heated, and certain compounds rise as vapor. As they rise, however, they also cool, and some chemicals may fall back as liquid while others continue on as vapor.
This progressively purifies the mixture and allows for more specific and controlled separation of the various compounds. The chemical vapors are run through separate condensers and into receiving vessels. Figure 2. 2 : A typical set-up for continuous distillation operation 2. Batch distillation Figure 2. 3 : The picture of batch type of distillation column Batch distillation refers to the use of distillation in batches, meaning that a mixture is distilled to separate it into its component fractions before the distillation still is again charged with more mixture and the process is updated.
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 seasonal, or low capacity and high-purity chemicals. It is a very frequent separation processing the pharmaceutical industry and in wastewater treatment units. Batch distillation is an unsteady state operation. It is usually carried out in a batch still to which a column equivalent to a number of equilibrium stages is attached.
Alternatively, packing may be used. In a batch process, the main steps are operated discontinuously. In contrast with a continuous process, a batch process does not deliver its product continuously but in discrete manner. This means that mass, temperature, concentration, and other properties vary with time. In practice, most batch processes are made up of a series of batch and semi- continuous steps. A semi-continuous step runs continuously with periodic start- ups and shutdowns.
Batch processes: are economical for small volumes re flexible in accommodating changes in product formulation are flexible in changing production rate allow the use of standardized multi-purpose equipment for the production of a variety of products from the same planter best if equipment needs regular cleaning because of fouling or needs regular sterilization allow better product integrity: each batch of product can be clearly identified in terms of the feeds involved and conditions of processing. This is particularly important in industries such as pharmaceuticals and foodstuffs.
