Antibiotics recovery process

Another example is the purification of a P-lactam antibiotic, where process-scale reversed-phase separations began to be used around 1983 when suitable, high pressure process-scale equipment became available. A reversed-phase microparticulate (55—105 p.m particle size) C g siUca column, with a mobile phase of aqueous methanol having 0.1 Af ammonium phosphate at pH 5.3, was able to fractionate out impurities not readily removed by hquid—hquid extraction (37). Optimization of the separation resulted in recovery of product at 93% purity and 95% yield. This type of separation differs markedly from protein purification in feed concentration ( i 50 200 g/L for cefonicid vs 1 to 10 g/L for protein), molecular weight of impurities (<5000 compared to 10,000—100,000 for proteins), and throughputs ( i l-2 mg/(g stationary phasemin) compared to 0.01—0.1 mg/(gmin) for proteins). 

The product is extracted from the culture fluid by adsorption onto caibon or resins rather than by solvent. This illustrates an important general point that antibiotic manufacturing processes differ from one another much more in their product recovery stages than in their fermentation stages. Figure 7.4 illustrates a typical production ronte from inoculum to bulk antibiotic. 

Figure 30.6 shows a typical recovery process for antibiotics, and a schematic overview of a typical downstream process in an enzyme plant is given in Figure 30.7. From these diagrams it is apparent that most recovery...

Production takes place in the fermenter which normaly is a stirred reactor with feedsys-tems and various instrumentation equipment. Nutritional compounds either in solution or as a slurry are added to the fermenter, an inoculum of the desired micro-organisms is added, the whole mash will be stirred, air for oxygen supply is passed through the mash and the fermentation process goes on. After the fermentation the products are isolated in a recovery process. The products are the micro-organism itself (e.g.yeast) or its metabolites like enzymes or antibiotics. Typical properties of a fermentation process are ... 

Antibiotic effects over longer periods of recovery at 20 C suggests the presence of protein synthesis as part of the repair mechanism. At 5 C the effect of antibiotics are less noticeable than at higher temperatures as noticed by Greer et al (8). Both chloramphenicol and cycloheximide appear to be efficient in reducing the recovery suggesting that synthesis of chloroplastic and nuclear encoded proteins take part in the recovery process. 

Figure 24.15 shows a typical recovery process for antibiotics, and Fig. 24.16 presents a flowsheet for an enzyme plant. It is apparent from these diagrams that most recovery processes involve combinations of the following procedures ... 

Membrane-retained components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. It is the objective of ultrafiltration to recover or concentrate particular species in the retentate (eg, latex concentration, pigment recovery, protein recovery from cheese and casein wheys, and concentration of proteins for biopharmaceuticals) or to produce a purified permeate (eg, sewage treatment, production of sterile water or antibiotics, etc). Diafiltration is a specific ultrafiltration process in which the retentate is further purified or the permeable sohds are extracted further by the addition of water or, in the case of proteins, buffer to the retentate. 

Occurrence, Fermentation, and Biosynthesis. Although a large number of Streptomjces species have been shown to produce carbapenems, only S. cattkja (2) and S. penemfaciens (11) have been reported to give thienamycin (2). Generally the antibiotics occur as a mixture of analogues or isomers and are often co-produced with penicillin N and cephamycin C. Yields are low compared to other P-lactams produced by streptomycetes, and titres are of the order of 1—20 p-g sohdusmL despite, in many cases, a great deal of effort on the optimization of the media and fermentation conditions. The rather poor stabiUty of the compounds also contributes to a low recovery in the isolation procedures. The fermentation and isolation processes for thienamycin and the olivanic acids has been reviewed in some detail (12). 

Before leaving ionic liquids it is worth mentioning their potential value in separation processes. Organic solvents are frequently used in multiphase extraction processes and pose the same problems in terms of VOC containment and recovery as they do in syntheses, hence ionic liquids could offer a more benign alternative. Interesting applications along this line which have been studied include separation of spent nuclear fuel from other nuclear waste and extraction of the antibiotic erythromycin-A. 

The growing interest in various )5-lactam antibiotics, especially the cephalosporins, over the last decade has called upon improvement in their production methods via modification of either the basic process and the microbial strain or the downstream processing techniques. The product recovery may involve various methods of extraction and purification which play an important role in the overall process economics [12]. During recent years much attention has been given to the development of liquid membrane (LM) processes which usually exhibit high extraction rates and selectivity as compared to those achievable in conventional solvent extraction and adsorption processes. 

Antibiotics. The history of antibiotics is one of remarkable success in saving lives. Penicillin, although discovered earlier, began to be manufactured for sale as a drug in 1942. Tetracycline followed in 1955 and amoxicillin in 1981. These, other variants developed over the years, and some new recent classes of antibiotics treat bacterial infections by killing the bacteria or preventing them from multiplying. In the process, they save lives and speed recovery. Except for some products sold for external use, antibiotics require a prescription. 

In the chemical processing industry, extraction is used when distillation is impractical or too costly. Extraction may be more practical than distillation when the relative volatilities of two components are close. In other cases, the components to be separated may be heat sensitive like antibiotics or relatively nonvolatile like mineral salts. When unfortunate azeotropes form, distillation may be ineffective. Several examples of cost-effective liquid-liquid extraction processes include the recovery of acetic acid from water using ethyl ether or ethyl acetate and the recovery of phenolics from water with butyl acetate. 

The economic feasibility of a bioreaction process clearly depends on the characteristics of the associated bioseparation process, especially in the usual case when the product is present at low concentration in a complex mixture. For example, the existence of an extremely efficient and low-cost separation process for a particular compound could significantly lower the final concentration of that compound required in the bioreactor to achieve a satisfactory overall process. After noting that special approaches and processes are needed for efficient recovery of small molecules (ethanol, amino acids, antibiotics, etc.) from the dilute aqueous product streams of current bioreactors, I shall discuss further only separations of proteins. These are the primary products of the new biotechnology industry, and their purification hinges on the special properties of these biological macromolecules. 

Examples of sorption processes using packed beds include recovery of crude antibiotics from fermentation broth filtrate, heavy metal removal from product streams, and separation of amino acids from solutions. 

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