Aby-product orbyproduct is a secondary product derived from a production process,manufacturing process orchemical reaction; it is not the primary product or service being produced.
A by-product can be useful and marketable or it can be considered waste: for example,bran, which is a byproduct of themilling ofwheat into refinedflour, is sometimescomposted or burned for disposal, but in other cases, it can be used as a nutritious ingredient inhuman food oranimal feed.Gasoline was once a byproduct ofoil refining that later became a desirable commercialproduct asmotor fuel. The plastic used inplastic shopping bags also started as a by-product of oil refining.[1] By-products are sometimes calledco-products to indicate that although they are secondary, they are desired products. For example, hides and leather may be called co-products of beef production. There is no strict distinction between by-products and co-products.
In the context of production, a by-product is the "output from ajoint production process that is minor in quantity and/ornet realizable value (NRV) when compared with themain products".[2] Because they are deemed to have no influence on reported financial results, by-products do not receive allocations ofjoint costs. By-products also, by convention, are not inventoried, but the NRV from by-products is typically recognized as "other income", or as a reduction ofjoint production processing costs when the by-product is produced.[3]
TheInternational Energy Agency (IEA) definesby-product in the context oflife-cycle assessment by defining four different product types: "main products,co-products (which involve similar revenues to the main product), by-products (which result in smaller revenues), andwaste products (which provide little or no revenue)."[4]
While some chemists treat "by-product" and "side-product" as synonyms in the above sense of a generic secondary (untargeted) product, others find it useful to distinguish between the two. When the two terms are distinguished, "by-product" is used to refer to a product that is not desired but inevitably results from molecular fragments of starting materials and/orreagents that are not incorporated into thedesired product, as a consequence ofconservation of mass; in contrast, "side-product" is used to refer to a product that is formed from a competitive process that could, in principle, be suppressed by an optimization of reaction conditions.[5]
Plastic is obtained as a by-product from the oil refining process [...]
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