Biochemical engineering is a branch of chemical engineering that mainly deals with the design and construction of unit processes that involve biological organisms or molecules. Biochemical engineering is often taught as a supplementary option to chemical engineering due to the similiarities in both the background subject curriculum and problem-solving techniques used by both professions. Its applications are used in the pharmaceutical, biotechnology, and water treatment industries.

Important aspects

Important aspects of biochemical engineering include

Reactor design

A reactor utilizes biological cells, called biomass, to perform catalytic reactions on a substrate, called the media, to produce one or more useful chemical species, called the product. The reactor is often called a continuous-stirred tank reactor (CSTR), a fermentor, a chemostat, or a turbostat, depending upon its operating conditions. The objective is to produce the maximal quantity of the product, constrained by both economical and technological criteria. Typical products include antibiotics, protein inhibitors, insulin, and alcoholic beverages.

Additionally, a reactor may utilize only the proteins that specifically catalyze desired reactions, called enzymes. Instead of growing biological cells and using them as 'mini-reactors' to produce the desired product, one can extract the necessary enzymes from the cell and use them to catalytically synthesize the product. The design of enzyme catalytic reactors is similar to those for inorganic catalysts, including the use of packed or fluidized bed reactors.

Biological reactor design features mild operating conditions, high specificity and yields, and exothermic, self-regulated reactions. Important aspects of design include preventing oxygen deprivation, un-mixed regions, and build up of toxic byproducts.

Separation

Separation processes extract the desired product from the output stream of a reactor. The pharmaceutical and biotech industries typically require extreme purification of the product in order to meet federal regulations, making the separation process the most expensive part of a production plant. Commonly, the output stream of a reactor is passed through multiple separation processes, each designed to either remove a fraction of the waste from the stream while leaving the product or to remove only the product. There are numerous types of separation proceses, including

• Filtration -- The stream of fluid containing the product is passed through a membrane, containing holes of varying sizes, which then prevent the product from passing through the membrane or allow only the product to pass through. Multiple sizes of holes and designs exist, including direct flow and tangential flow.

• Chromatography -- The stream is passed through a long hollow column, which has its internal edges coated with a specific chemical species that will interact with the stream is a desired manner. Depending upon the type of coating used, either the product or the waste chemical species may bind or adhere to the inside of the column walls. Once bound, the product or waste may be unbound, in a process called elution, by changing the pH or temperature of the column, destabilizing the force which keeps the product or waste from binding to the coating. To separate the waste from the product, one changes the containers in which the outflow enters prior to elution. The different types of chromatography are named based on the type of coating they employ. Some types include

i) Affinity chromatography -- Uses antibodies to bind to product molecules

ii) Ionic chromatography -- Uses negative or positive ions to either repulse or attract product or waste molecules

Products may be specifically altered to make the separation process easier by including 'tags' that bind to specific coatings in the chromatography column.

• Centrifugation -- The stream is passed into a centrifuge that, while spinning, uses centrifugal force (centripetal acceleration) to push molecules with higher molecular weights outward. Centrifugation is often used to remove excess water and concentrate the outflow of a reactor.