Air lift reactor

Like enzymes, whole cells are sometime immobilized by attachment to a surface or by entrapment within a carrier material. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for transformation of substrate. A great variety of reactor types have been proposed including packed beds, fluidized and spouted beds, and air-lift reactors. A semicommercial process for beer used an air-lift reactor to achieve reaction times of 1 day compared with 5-7 days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavour profile that was attributed to mass transfer limitations. 

ALR air-lift reactor AOS active oxygen species C constant in Eq. (13)... 

Siegel, M. FL, Merchuk, J. C., and Schugerl, K., Air-Lift Reactor Analysis Interrelationships between Riser, Downcomer, and Gas-Liquid Separator Behavior, including Gas Recirculation Effects, AIChE J., 32 1585 (1986)... 

The system used by Stevens et al. [79] consisted of an air-lift reactor with an external lamella settler. They did not need to pump the cell suspension through the settler, since free flow convection was achieved by cooling the cell suspension (20 °C) before entering the sedimentation device. As also found by other authors, they could achieve selective retention of viable cells by varying the perfusion rate. 

J.C. Merchuk, S. Yehuda, Local holdup and liquid velocity in air-lift reactors, AIChE J. 27 (1981) 377-388. 

The range of culture flasks and reactor types employed is quite wide, both for suspension and adherent cultures, from small Carrel s or Roux s flasks to roller bottles. Fixed- and fluidized-bed bioreactors, air-lift reactors and even stirred and aerated tanks with capacities up to 15 m3 are common in large plants producing monoclonal antibodies (mAbs) for anticancer therapies (Adams and Weiner, 2005 Griffiths, 1988). 

Figure 9.5 Principle of fermentation realtors stirred tank reactor (left) air lift reactor (right). (Source Schugerl, K., 1982)...

Yahiro et al. [115] conducted itaconic acid production from glucose using stirred-tank and air-lift reactors. Results indicate that the air-lift reactor has a much higher productivity (0.64 g/l/h) than the stirred-tank reactor (0.48 g/l/h). Final itaconic acid concentration reached 65 g/1 after 96 h of fermentation. Likewise, Okabe et al. [116] used an air-lift bioreactor using a modified draft tube for itaconic acid production and obtained an enhanced itaconic acid yield. 

Class 1 equipment are also called column-type equipment. Under this category, there are the various multiphase contactors. Gas-liquid contactors include bubble columns, packed bubble columns, internal-loop and external-loop air-lift reactors, sectionalized bubble columns, plate columns, and others. Solid-fluid (liquid or gas) contactors include static mixers, fixed beds, expanded beds, fluidized beds, transport reactors or contactors, and so forth. For instance, fixed-bed geometry is used in unit operations such as ion exchange, adsorptive and chromatographic separations, and drying and in catalytic reactors. Liquid-liquid contactors include spray columns, packed extraction... 

Bubble column, packed bubble column, sectionalized bubble column, plate column, external- and internal-loop air-lift reactors, static mixer, venturi scrubbers... 

FIGURE 11.23 External-loop air-lift reactor (a) riser sparging, (b) downcomer sparging. 

In addition to low pressure drop, external-loop air-lift reactors have several advantages over bubble-column reactors. The former offer much flexibility in design in terms of height-to-diameter ratio, area ratio of downcomer to riser, sparger locations, and so on. Conditions can be manipulated... 

When the total reactor volume is small (< 5 to 10 m ), an air-lift reactor can be used in the form of an internal loop as shown in Eigure 11.24. 

As indicated in Section 11.4.2.1.4, the energy requirement of a bubble column can be reduced with an external-loop air-lift reactor (Figure 11.23a). As an illustration, consider case 2 in Table CS7.2. This case was shown to be optimum on the basis of bottom pressure or the pressure at which the gas phase enters the column. Furthermore, there is no complication of desorption. 

This case study on oxidation of sodium sulfide illustrates the design of a variety of gas-liquid reactors and compares their performances. Bubble column reactors are particularly attractive, as they offer advantages such as simplicity of construction and operation, but they suffer from such drawbacks as high pressure drop and backmixing in the liquid phase. To reduce the pressure drop, two modifications have been considered an external-loop air-lift reactor and a horizontal sparger reactor. Both result in substantial energy savings (because of low AP) under similar conditions of capacity and conversions in the gas and liquid phases. 

In the simplest type of bubble column, gas is dispersed at the bottom and bubbles are present throughout the reactor, as shown in Figure 7.10a. In a loop or air-lift reactor (Fig. 7.10b), gas is introduced beneath a central draft tube, and rising bubbles carry liquid upward. After most of the bubbles disengage, liquid flows downward in the annulus. The direction of flows could be reversed by feeding gas to the annulus. The columns may have internal coils for heat transfer and baffles to decrease axial mixing. 

Barbosa MJ, Janssen M, Ham N, et al Microalgae cultivation in air-lift reactors modeling biomass yield and growth rate as a function of mixing frequency, Biotechnol Bioeng... 

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