Downstream product recovery

The complexity of biological processes generally requires many stages to produce a final, purified product from a particular composition of raw materials. Although a typical bioprocess consists of two main parts, upstream fermentation and downstream product recovery, it is not unusual to have between 10 and 20 steps in the overall process. This reflects the complex nature of a typical fermentation broth, which will consist of an aqueous mixture of cells, intracellular or extracellular products, unreacted substrates, and by-products of the fermentation process. From this mixture, the desired... 

Although the parameters governing a whole cell-based process are numerous, the key limitation of the low productivity was clearly idenhfied as substrate and product inhibition. Substrate inhibition could conveniently be overcome by continuous feeding. A pilot-scale fed-batch experiment (551) was carried out [101] in which the feeding rate was adjusted to maintain the ketone concentrahon below 0.7 g/1. A final concentration of about 4g/l of lactones was reached within 4h. After downstream product recovery on charcoal, over 200 g of combined lactones was obtained, corresponding to a 76% yield. 

Continuous releases of concentrated HjS streams must be segregated in a separate flare system to limit the extent of fouling and plugging problems. Releases of HjS such as diversion of sour gas product to flares during shutdown or upset of a downstream sulfur recovery unit are considered to be continuous, but safety valve releases are not included in this category. However, if a special HjS flare system is provided for continuous releases, the concentrated HjS safety valve releases should be tied into it rather than into the regular flare system. Due to the nature of HjS one should plan on frequent inspection and flushing of HjS flares to remove scale and corrosion products. 

In a chemical production process at least one of the unit operations (the chemical reactor) is the place in which chemical conversion takes place. However, the chemical upstream reactor is proceeded by a series of unit operations in which the new materials are downstream prepared (the upstream operations). After conversion has taken place, the products are operations subjected to a further series of unit operations (the downstream operations). These downstream operations include product recovery and purification steps. A typical example of a production process is illustrated in Figure 1.1. 

The first consideration in any design and optimization problem is to decide the boundaries of the system. A reactor can rarely be optimized without considering the upstream and downstream processes connected to it. Chapter 6 attempts to integrate the reactor design concepts of Chapters 1-5 with process economics. The goal is an optimized process design that includes the costs of product recovery, in-process recycling, and by-product disposition. The reactions are... 

After fermentation, subsequent midstream to downstream processes such as cell disruption, centrifugation, extraction and drying will be carried on for product recovery. Fig. 9 shows a white sheet of PHB obtained from fermentation of sweet sorghum juice (SSJ) by Bacillus aryahhattai. 

One of the most important advantages of the bio-based processes is operation under mild conditions however, this also poses a problem for its integration into conventional refining processes. Another issue is raised by the water solubility of the biocatalysts and the biocatalyst miscibility in oil. The development of new reactor designs, product or by-product recovery schemes and oil-water separation systems is, therefore, quite important in enabling commercialization. Emulsification is thus a necessary step in the process however, it should be noted that highly emulsified oil can pose significant downstream separation problems. 

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. 

Search for natural flavour compounds with additional functionalities (e.g. antimicrobial properties) Improved downstream processing, especially in situ product-recovery techniques... 

Product recovery and capture can be carried out in a series of condensation stages, at different temperatures, in order to achieve different fractions enriched in target compounds. The temperature of each condenser has to be adjusted according to the downstream pressure in the circuit and the character of the compounds to be separated and recovered [37, 38]. Capture of the target-permeating compounds by condensation remains one of the main problems for competitive use of pervapora-tion systems, due to the energy costs involved to keep an adequate downstream pressure and to cool down the permeating stream. 

When production volume is sufficient, it is economical to build one plant for one product. Batch production in a single unit may be limited by maximum reactor size. Holdups of greater than 20,000 gal are handled in separate parallel reactors. To use common upstream and downstream facilities, the reactors may not be operated simultaneously but on overlapping schedules. When long reaction times cannot be avoided, the reaction sections operate batch wise however, feeding reactants and recovering products may be continuous for economic reasons. This practice is typical of many processes, such as the saponification of natural fats in intermediate quantities. In the production of ethanol by fermentation, two reactions (saccharification and fermentation) are operated on a batch basis, while hydrolysis (conversion of starch to dextrin) and product recovery by distillation are continuous. 

Although this technique is not limited to the initial cell recovery stages of a downstream process, cross-flow filtration is commonly used for product recovery operations, particularly in lower volume processes where stringent hygiene requirements apply, as in the pharmaceutical and food industries. 

Lean solvent from the bottom of the recovery column is returned to the extractor. The extract is recovered overhead and sent on to distillation columns downstream for recovery of the individual benzene, toluene and xylene products. The raffinate stream exits the top of the extractor and is directed to the raffinate wash column (4). In the wash column, the raffinate is contacted with water to remove dissolved solvent. The solvent-rich water is vaporized in the water stripper (5) and then used as stripping steam in the recovery column. The raffinate product exits the top of the raffinate wash column. The raffinate product is commonly used for gasoline blending or ethylene production. 

When the production of the secondary metabolites coincides with the death and general lysis of the cells, the recovery of the product is simply a matter of separation from the spent production solution downstream of the reactor. An example of this type of operation was initially used in Japan during the production of shikonin. However, if the secondary metabolites are stored in the vacuole of the cells and the cells remain viable but dormant during the production phase, then a permeabilizing agent such as dimethylsulfoxide (DMSO), detergents, proteins, and antibiotics may be employed in some cases in concentrations that make the cells leak product out but maintain cell viability. Success for this type of product recovery has been reported in C. roseus, Datura innoxia, and Daucus carota cell cultures. 

A downstream production process must achieve the required purity and recovery with complete safety and reliability, and within a given economic framework. 

After biological reactions have generated a product of interest, it is necessary to recover this product from a liquid mixture that typically contains several undesirable components. The treatment of any culture broth after bioreactor cultivation is known as downstream processing. Downstream processing can account for 60-80%) of the total production cost, particularly in the production of modern recombinant proteins and monoclonal antibodies. A typical downstream process requires several steps in the areas of solid-liquid separation, cell rupture, product recovery, and product purification. It is important to minimize the number of downstream processing steps required because significant product losses inevitably occur during each step.f ... 

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