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Destructive Distillation

What is Destructive Distillation?

Destructive distillation can be defined as the chemical process through which unprocessed materials are subjected to decomposition by heating them and thereby producing ‘cracks’ in the relatively large molecules. Generally, the term ‘destructive distillation’ is used to refer to the processing of certain organic materials along with limited amounts of oxygen and certain reagents, solvents, or catalysts such as phenols and steam. It can also be used to denote the processing of organic material in an environment void of air (pyrolysis in the absence of air). The process of destructive distillation can be viewed as an application of the concept of pyrolysis (the thermal decomposition of certain substances at very high temperatures under relatively inert atmospheres).

The process of destructive distillation is known to create ‘cracks’ in relatively large molecules. It is not uncommon for these large molecules to break apart completely when subjected to destructive distillation. For example, when coal is subjected to destructive distillation, a wide range of commercially important products are formed (such as coke, coal oil, ammonium hydroxide, coal tar, gas carbon, and coal gas).

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What are the Products formed during Destructive Distillation?

It can be noted that when inorganic materials are subjected to destructive distillation, only a few products are generated. However, when organic materials are subjected to this process, a wide range of different products are produced. In fact, it is not uncommon for hundreds of products to be obtained from the destructive distillation of some organic materials. However, most of these products are usually not of any commercial importance.

The distillates of destructive distillation processes are often of relatively low molecular weights. However, some fractions of these distillates are known to have the ability to undergo polymerization and form relatively large molecules. Larger molecules can also be formed from certain chemical reactions that are undergone by the distillate molecules. Common examples of the products formed from such interactions between distillate molecules include chars and tars that are heat-stable. Furthermore, it can be noted that the cracking of the relatively large molecules in the feedstock and their subsequent conversion into volatile compounds and liquids, the polymerization of the distillate molecules, and the formation of solids and chars, can all occur during the same process. All of these products may be valuable commercially.

In the past, the process of destructive distillation, along with other different forms of pyrolysis, have helped in the discovery of new chemical compounds and the elucidation of the chemical structures of these compounds. Furthermore, this process has helped chemists understand the chemical nature of several natural materials. For example, insight into the structures of furanoses and pyranoses was obtained from the destructive distillation of certain organic materials.

Process of Destructive Distillation

The process of destructive distillation involves the pyrolysis of the organic (or inorganic) feedstock inside a distillation apparatus and the collection of the volatile products that are formed during the pyrolysis. However, it must be noted that only a fraction of the mass of the initial feedstock will be accounted for by the collected products. This is because a significant portion of the initial feedstock are retained by the distillation apparatus in the form of ash, non-volatile tar, and char. When compared to combustion, a significantly lower quantity of the organic matter is consumed during destructive distillation (post combustion, the mass of the products formed are almost equal to the mass of the initial feedstock and the required amount of oxidant).

The process of destructive distillation can be viewed as a modified version of the traditional practice of charcoal burning. It is worth noting that this process is of industrial significance in several regions of the world, the most notable of which is Scandinavia. It can also be noted that modern destructive distillation practices have been optimized in many ways in order to maximize the extraction of valuable products from the feedstock.

Applications of Destructive Distillation

  • Destructive distillation can be employed to obtain methanol and turpentine from wood. Furthermore, the destructive distillation of wood is also known to leave behind a residue of solid charcoal, a substance that has a wide range of commercial applications.
  • The destructive distillation of wood is also known to produce several other compounds of commercial value, such as terpenes and tar.
  • One of the most prominent applications of destructive distillation is in the processing of coal in order to obtain several commercially important compounds such as coke, ammonium hydroxide, coal gas, and coal tar.
  • The waste processing of polymers via destructive distillation can afford their constituent monomers, which can be reused in suitable processes.

Apart from these applications of destructive distillation, the process is also known to have played a vital role in the discovery of many important organic compounds. For example, isoprene was discovered when natural rubber was subjected to destructive distillation. This compound was crucial in the production of many synthetic rubbers, the most prominent of which being neoprene. Thus, destructive distillation is a very important form of pyrolysis that can be employed to derive numerous useful substances from organic and inorganic feedstock. To learn more about the process of destructive distillation and other important types of distillation, such as fractional distillation, register with BYJU’S and download the mobile application on your smartphone.

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