Fed-batch

Fed - batch process (English fed " fed" batch " stack " ) also feed process is an established concept in process engineering. It refers to batch processes ( feeding ) are operated on precursors to the maximum level as a " stack " that is, one after the other, and are processed by an influx.

Time course

A typical fed-batch process has the following time schedule:

• Partially filling the reaction vessel with the starting materials ( reactants )
• Reaction of the reactants to products. From a defined concentration is now starting material " fed ". Here, you can try to keep the reactant concentration in the reactor constant, or it will be a constant feed stream fed.
• Evacuation of the reaction vessel ( harvest) and forwarding of products for downstream processing
• Preparation of the reaction vessel to the next filling (cleaning, maintenance)

Accounting

Material balance

For the change of the molar amount to the reaction volume, the fuel change rates, the flow rate at the input of the system and the molar concentrations in the reactor or in the feed stream where:

The reaction volume is in contrast to the continuous and discontinuous operation variable time:

Therefore is:

One obtains:

Benefits

The fed-batch process provides both the ability to limit the reaction rate by the low position of the reactant concentration to a certain level, which in highly exothermic reactions offers the particular advantage completely dissipate the heat of reaction. Most often, the Fed - batch mode in the cultivation of microorganisms (fermentation) is employed. By a low substrate concentration in this case a substrate inhibition of the growth rate can be prevented. In contrast to the batch process, wherein the final concentration of biomass due to the stoichiometry of the initial substrate concentration is dependent, can markedly higher final concentrations of biomass and of product are thus also achieved here. Similarly, in a substrate - limited fed-batch process, the risk of secretion of (often toxic ) secondary metabolite ( overflow products) decreases. In contrast to the simple batch process can regulate the growth rate in a fed - batch process, which can significantly improve the reproducibility of fermentations.

Disadvantages

Due to the time-varying reaction volume accounting for a fed-batch reactor is much more complex. This results in difficulties in predicting or scale-up. To control the reactant concentration at a constant level, a high level of technical or a high automation effort is to operate.