Equilibrium in Biochemical Separations

The fermentation of sugars (and starches) to ethanol is presumably the oldest known example of humans domesti- 

The production of penicillin shows the classic example of producing a high value biochemical by biochemical means. In a very well-managed soup of nutrients, a mold grows and excretes the antibiotic product we want. When the mold will produce no more, the concentration of penicillin in the soup is about 1 % (1 part penicillin to 99 parts of waste products). The two challenges in the process are first, to get the mold to produce as much as possible, as quickly as possible, and second to separate the pure (easily destroyed) penicillin away from the waste products at an acceptable cost. 

Chemical equilibrium plays little if any role in the growth step, but physical equilibrium is very important in the separation steps. In industrial organic chemistry the separation tools (distillation, crystallization, extraction) all depend on using differences in equilibrium concentration to enrich one species in a mixture relative to the others. The same is tme in industrial biochemistry. The main differences are 

The starting concentrations of biochemical products are generally much smaller than in industrial organic chemistry. Biochemical processes often start the separation with much less than 1% of the desired product in the mix. Industrial organic chemistry rarely does. 

The desired product is often very unstable. Penicillin is destroyed by heating, and by long exposure to acids or bases. The same is not true of most industrial organic chemicals. 

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