Gas-liquid stirred reactors

Fig. 7.4 Schemes for mathematical models of a gas-liquid bubble column (a) and a gas-liquid stirred reactor (b). B = bubble phase, H = reactor head, L = liquid phase, Fg = gas flow rate ...

FIGURE 1.8 Flov regimes of gas-liquid stirred reactor (from Middleton, 1992). 

In bubble columns and gas-liquid stirred reactors, the estimation of parameters is more difficult than in gas-solid or liquid-solid fluidized beds. Solid particles are rigid, and hence the fluid-solid interface is nonde-formable, whereas the gas-liquid interface is deformable. In addition, the effect of surface-active agents is much more pronounced in the case of gas-liquid interfaces. This leads to uncertainties in the prediction of all major parameters, such as the terminal bubble rise velocity, the bubble diameter, the gas holdup, and the relation between the bubble diameter and the terminal bubble raise velocity. 

Litz LM. (1985, Nov) A novel gas-liquid stirred reactor. Chem. Eng. Prog., 81(ll) 36-39. Malpani V, Ganeshpure PA, Munshi P. (2011) Determination of solubility parameters for the p-xylene oxidation products. Ind. Eng. Chem. Res., 50 2467-2472. 

Flow Reactors Fast reactions and those in the gas phase are generally done in tubular flow reaclors, just as they are often done on the commercial scale. Some heterogeneous reactors are shown in Fig. 23-29 the item in Fig. 23-29g is suited to liquid/liquid as well as gas/liquid. Stirred tanks, bubble and packed towers, and other commercial types are also used. The operadon of such units can sometimes be predicted from independent data of chemical and mass transfer rates, correlations of interfacial areas, droplet sizes, and other data. 

In the second class, the particles are suspended in the liquid phase. Momentum may be transferred to the particles in different ways, and it is possible to distinguish between bubble-column slurry reactors (in which particles are suspended by bubble movement), stirred-slurry reactors (in which particles are suspended by bubble movement and mechanical stirring), and gas-liquid fluidized reactors (in which particles are suspended by bubble movement and cocurrent liquid flow). 

Andersson, B. (2003) Important factors in bubble coalescence modeling in stirred tank reactors. 6th International Conference on Gas liquid and Gas-Liquid -Solid Reactor Engineering, 2003, Vancouver. 

Three-phase slurry reactors are commonly used in fine-chemical industries for the catalytic hydrogenation of organic substrates to a variety of products and intermediates (1-2). The most common types of catalysts are precious metals such as Pt and Pd supported on powdered carbon supports (3). The behavior of the gas-liquid-sluny reactors is affected by a complex interplay of multiple variables including the temperature, pressure, stirring rates, feed composition, etc. (1-2,4). Often these types of reactors are operated away from the optimal conditions due to the difficulty in identifying and optimizing the critical variables involved in the process. This not only leads to lost productivity but also increases the cost of down stream processing (purification), and pollution control (undesired by-products). 

Gas-liquid-solids reactors Stirred slurry reactors, three-phase fluidized bed reactors (bubble column slurry reactors), packed bubble column reactors, trickle bed reactors, loop reactors. 

Sudiyo R (2006) Fluid Dynamics in Gas-Liquid Stirred Tank Reactors Experimental and Theoretical Studies of Bubble Coalescence. PhD Thesis, Chalmers Uiuversity of Technology, Gbteborg... 

Equation 4.20 shows that mass transfer is a determining factor in anionic polymerisation of PO, a high surface area of the liquid reaction mass giving high rates of PO consumption. On the other hand, due to the very high efficiency of stirring, the gas-liquid contactor reactor type assures a very narrow MW distribution of the resulting polyether. For the ethoxylation of intermediate propoxylated polyethers (in block copolymers PO-EO... 

After the addition of the calculated quantity of monomer, a very important step is the consumption of the unreacted monomer, by maintaining the reaction mass at the polymerisation temperature (100-125 °C), under continuous stirring or/and recirculation of the reaction mass. Because the PO addition was stopped, the pressure decreases from 0.35-0.45 MPa to less than 0.1 MPa, in 1.5-2 hours. This step is very important for the improvement of polyether yields and for the loss of a minimum quantity of monomer. The very intensive gas-liquid contactor reactors are extremely efficient in this step of digestion, because the remaining quantity of unreacted monomer decreases very much, in a short digestion time. 

Litz (1985) published an article in Chemical Engineering Progress entitled, A novel gas-liquid stirred tank reactor, from which some key introductory statements are quoted here to emphasize the fact that (1) the liquid-phase reaction is more important than reaction in the gas phase and (2) interphase mass transfer is extremely important. In most gas-liquid reaction systems, the bulk of the reaction occurs between the liquid, or species dissolved in the liquid phase, and... 

A.3 HYDRODYNAMIC REGIMES IN TWO-PHASE (GAS-LIQUID) STIRRED TANK REACTORS... 

Flow regimes in two-phase (gas-liquid) stirred tank reactor... 

FIGURE 7A.8 Hydrodynamic regimes in two-phase (gas-liquid) stirred tank reactor. 1, flooding of the impeller 2, gas dispersion above the impeller 3, gas circulation above the impeller with marginal dispersion helow the impeller 4, gas circulation both above and below the impeller 5, recirculation of the gas resulting in the formation of secondary loops besides main discharge streams from the impeller. (Reproduced from Middleton 2000 with permission from Elsevier. 1997, Elsevier.)... 

---