Upon Fermentation Penicillin is put through a Recovery Process to obtain its crystallized form, Which can than be dissolved in saline and injected into a patient for treatment.

Recovery Process:

1. Broth Filtration :
    • The main objective is to remove any microbial cells and any large solid particles such as, cell fragments, soluble and insoluble medium components, other metabolic products, Intact micro-organims.
    • During the filtration the micro-organisms are captured in a concentrated cake, which looks like sand, sludge or paste.
    • There are many factors that influence the type of filtration to be used:
      1. Viscosity.
      2. Density of filtrate.
      3. Solid liquid ratio.
      4. Size and shape of particles.
      5. Scale of operation.
      6. Need for aseptic conditions.
      7. Need for batch or continuous operation.
      8. Need for pressure or vacuum suction to ensure an sufficient for rate for liquid.

    • The rotary type is the most often used filtration, its features include:
      1. The Filter Drum: Cylindrical, hollow drum which carries the filter cloth. On the inside it is segmented into rows to which a vacuum can be applied or shut off in sequence as the drum slowly revolves.
      2. Trough: Filter is partially immersed in through which contains the penicillin broth. The trough is sometimes fitted with an agitator to maintain solids in suspension.
      3. Discharge Nodes: Filter cakes are produced from the filtration of to penicillin broth. Because of this a node is devised to scrap off the cake after filtration. When this happens the vacuum is broken.
    • The filter drum, partially submerged in the trough of broth, rotates slowly. Filtrateand washings are kept separate by the segments in the drum. The liquid is drawn throughthe filter and a cake of solids builds up on the outer surface. Inside the drum, the filtrate is moves from the end of the cylindrical drum onto a storage tank. As our penicillin cellsmove from the broth, the vacuum is used to remove as much moisture as possible fromthe cake, and to hold the cake on the drum. The section at the node/knife, which scrapes off the filtrate can get air pressure to burst out, helping contact with the node.

2. Filtrate cooled:
    • From filtration, the penicillin rich solution is cooled tp 5°C.
    • This helps reduce enzyme and chemical degradation during the 4th step; solvent extraction.

3. Further Filtration:
    • More filtration is done with rotary filtration method.

4. Extraction of Penicillin with solvent:
    • This method is carried out under the basis that the extraction agent and the liquid in which the extract is dissolved cannot be mixed.
    • Solvent extraction is suitable for the recovery of penicillin because of its operation at low temperatures, greater selectivity and is less expensive compared to distillation, evaporation and membrane technology.
    • A Podbielniak Centrifugal Contractor is used for this method.

5. Carbon Treatment:
    • The penicillin rich solution is then treated with 0.25-5% activated carbon to remove pigments and impurities.
    • Activated carbon is an amorphous solid that absorbs molecules from the liquid phase through its' highly developed internal pore structure.
    • It is obtained in powered, pelleted or granular form and is produced from coal, wood and coconut shells.

6. Transfer Back to Aqueous state:
    • Using a Podbielniak Centrifugal Contractor, like the one used in solvent extraction, the penicillin rich solvent is passed into a fresh aqueous phase.
    • This is done in the presence of Potassium or Sodium Hydroxide to bring the pH back to 5.0-7.5, creating the penicillin salt.

7. Solvent Recovery:

    • The penicillin solvent is usually recovered by distillation.
    • Distillation is carried out in three phases:
      1. Evaporation.
      2. Vapour-liquid seperation in a column.
      3. Condensation of vapour.
    • Firstly the solvent is vaporised from the solution, then the low boiling volatile components are separated from the less volatile components in a column, and finally condensation is used to recover the volatile solvent fraction.
    • Solvent recovery is an important process, as solvent is a major expense in the penicillin extraction process.

8. Crystallisation:
    • Crystallisation is essentially a polishing step that yields a highly pure product and is done through phase separation from a liquid to a solid.
    • To begin the process a supersaturated solution, where there are more dissolved solids in the solvent than can ordinarily be accommodated at that temperature, must be obtained through cooling, drowning, solvent evaporation, or by chemical reaction.
    • The two main methods are Cooling and Drowning.
    • Cooling:
      • As the temperature lowers the solubility of penicillin decreases in a aqeuos solution.
      • Thus as the cooling takes place, the saturation increases till it reaches supersaturation and than on to crystallisation.
    • Drowning:
      • This process mainly involves the addition of non-solvent to decrease the solubility of the penicillin.
      • This than leads to saturation than to super saturation and finally to crystallisation.
    • Crystallisation process after supersaturation has two phases:
      1. Phase 1 Primary Nucleation:
        • This phase is mainly the growth of new crystals.
        • The spontaneous crystal formation and "crashing out" of many nuclei are observed from the solution.
      2. Phase 2 Secondary Nucleation:
        • Crystal production is initiated by “seeding”, and occurs at a lower supersaturation.
        • Seeding involves the addition of small crystals to a solution in a metastable area, which results in interactions between existing crystals, and crystal contact with the walls of the crystalliser.
        • The crystals will grow on those crystals until the concentration of the solution reaches solubility equilibrium.
    • Batch crystallisation is the most the most used method for polishing penicillin G. Batch crystallisers simply consist of tanks with stirrers and are sometimes baffled. They are slowly cooled to produce supersaturation. Seeding causes nucleation and growth is encouraged by further cooling until the desired crystals are obtained.
    • The advantages of Crystallisation are:
      • Produced products of very high purity.
      • Improves products appearance.
      • And has a low energy input.
    • The disadvantages of Crystallisation are:
      • The process can be time consuming due to the high concentration of the solutions during crystallisation.
      • It can also be profoundly affected by trace impurities.
      • Batch crystallisation can often give poor quality, nonuniform product.

9. Crystal washing:

    • Even though the penicillin crystals are pure in nature, adsorption and capillary attraction can cause impurities from its mother liquor on their surfaces and within the voids of the particulate mass.
    • Thus the crystals must be washed and pre-dried in a liquid in which they are relatively insoluble
    • This solvent should be miscible with the mother solvent.

    • For this purpose anhydrous lpropanol, n-butanol or another volatile solvent is used.

10. Drying of Crystals:
    • Drying stabilizes heat sensitive products like penicillin.
    • The drying of penicillin must be carried out with extreme care to maintain its chemical and biochemical activity, and ensure that it retains a high level of activity after drying.
    • The 3 most used methods for drying would be:
      1. Lyophilization:
        • Another name for freeze-drying

        • The wet penicillin is frozen to solidify it.
        • Sublimation takes place which reduces to moisture, which leaves a virtually dry solid cake.
        • Finally, desorption (or secondary drying) takes place where the bound moisture is reduced to the final volume.
      2. Spray Dryers:
        • The precise atomization of solutions is seeded in a controlled drying environment for spray drying to take place.
        • Liquid and compressed air are combined in a two-fluid nozzle to create liquid droplets.
        • Warm air streams dry the droplets and a dry powder is created.
      3. Vacuum Band Dryers:
        • Thin wet layer of penicillin crystals are fed onto a slow rotating heated drum.
        • Radiant heat dries the layer and scalpels remove the product from the end.

The Whole Recovery Process in a diagram: