Liquid-gas, continuous-stirred tank

Gas-liquid continuous-stirred tank reactor This is a CSTR, where the liquid and gas phases are mechanically agitated (Figure 3.4). 

Figure 3.4 A gas-liquid continuous-stirred tank reactor.

Modeling of Gas-Liquid Continuous-Stirred Tank Reactors (CSTRs)... 

Some specific aspects in the modeling of gas-liquid continuous-stirred tank reactors are considered. The influence of volatility of the liquid reactant on the enhancement of gas absorption is analyzed for irreversible second-order reactions. The impact of liquid evaporation on the behavior of a nonadiabatic gas-liquid CSTR where steady-state multiplicity occurs is also examined. 

System 1 In a gas-liquid continuous-stirred tank reactor (Figure 13-1), the gaseous reactant was bubbled into the reactor while the liquid reactant was fed through an inlet tube in the reactor s side. The reaction took place at the... 

System 1 In a gas-liquid continuous-stirred tank reactor (Figure 13-If. the gaseous reactant was bubbled into the reactor while the liquid reactant was fed through an inlet tube in the reactor s side. The reaction took place at the gas-liquid interface of the bubbles, and the product was a liquid. The continuous liquid phase could be regarded as perfectly mi.xed. and the reaction rate was proportional to the total bubble surface area. The surface area of a particular bubble depended on the time it had spent in the reactor. Because of their different sizes, some gas bubbles escaped from the reactor almost immediately, while others spent so much time in the reactor that they were almost coin-... 

Figure 1-1 CSTR performance curve for the production of monochlorobenzene from chlorine and benzene in a gas-liquid continuous-stirred tank reactor, and the corresponding total reactor volume required to achieve these outlet molar densities of CeHsCl.

Agitated Slurry Reactors The gas reactant and solid catalyst are dispersed in a continuous liquid phase by mechanical agitation using stirrers. Most issues associated with gas-liquid-solid stirred tanks are analogous to the gas-liquid systems. In addition to providing good... 

In addition to processes involving gas-liquid reactions, stirred-tank reactors can also be used for single (liquid)-phase reactions. Moreover, their operation is not limited to the continuous mode, and they can be easily adapted for use in semibatch and batch modes. The absence of a gas phase does not pose important structural and operational differences from those stated earlier for multiphase systems. However, in the case of single-phase operation, the aspect ratio is usually kept lower ( 1) to ensure well mixing of the reactive liquid. Regardless of the number of phases involved, stirred-tank reactors can approach their ideal states if perfect mixing is established. Under such conditions, it is assumed that reaction takes place immediately just... 

ALLreviations reactors Latch (B), continuous stirred tank (CST), fixed Led of catalyst (FB), fluidized Led of catalyst (FL), furnace (Furn.), multituLular (MT), semicontinuous stirred tank (SCST), tower (TO), tuLular (TU). Phases liquid (L), gas (G), Loth (LG). Space velocities (hourly) gas (GHSV), liquid (LHSV), weight ( VHSV). Not available, NA. To convert atm to kPa, multiply Ly 101.3. 

Three basic fluid contacting patterns describe the majority of gas-liquid mixing operations. These are (1) mixed gas/mixed liquid - a stirred tank with continuous in and out gas and liquid flow (2) mixed gas/batch mixed liquid - a stirred tank with continuous in and out gas flow only (3) concurrent plug flow of gas and liquid - an inline mixer with continuous in and out flow. For these cases the material balance/rate expressions and resulting performance equations can be formalized as ... 

Fig. 45.4 Left Schematic diagram of a continuous stirred tank reactor with gas and liquid inlet and outlet. Right A Rushton-type turbine (adapted from [3]).

Chapter 1 reviews the concepts necessary for treating the problems associated with the design of industrial reactions. These include the essentials of kinetics, thermodynamics, and basic mass, heat and momentum transfer. Ideal reactor types are treated in Chapter 2 and the most important of these are the batch reactor, the tubular reactor and the continuous stirred tank. Reactor stability is considered. Chapter 3 describes the effect of complex homogeneous kinetics on reactor performance. The special case of gas—solid reactions is discussed in Chapter 4 and Chapter 5 deals with other heterogeneous systems namely those involving gas—liquid, liquid—solid and liquid—liquid interfaces. Finally, Chapter 6 considers how real reactors may differ from the ideal reactors considered in earlier chapters. 

The slurry tank, when well mixed, can be considered a continuous-stirred tank reactor for both the gas phase and the liquid phase. When the solid is retained in the reaction vessel, it behaves in a batch mode however, catalyst can be removed and regenerated easily in a slurry tank, so activity can be maintained. 

FIGURE 22 Cell (Kampers et al., 1989) that functions as a continuously stirred tank reactor (a) sample holder (b) heater/cooler cylinder (c) hollow tubes for coolant and electrical wires (d) reservoir for coolant liquid (e) thermocouple (f) flange enclosing in situ chamber (g) O-ring (h) X-ray transparent window (i) gas inlet/outlet. Reprinted with permission from J.A. van Bokhoven, T. Ressler, F.M.F. de Groot, and G. Knopp-Gericke, in In situ Spectroscopy of Catalysts , B.M. Weckhuysen, Ed., published by American Scientific Publishers (2004). Copyright American Scientific Publishers. 

The Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

To derive the overall kinetics of a gas/liquid-phase reaction it is required to consider a volume element at the gas/liquid interface and to set up mass balances including the mass transport processes and the catalytic reaction. These balances are either differential in time (batch reactor) or in location (continuous operation). By making suitable assumptions on the hydrodynamics and, hence, the interfacial mass transfer rates, in both phases the concentration of the reactants and products can be calculated by integration of the respective differential equations either as a function of reaction time (batch reactor) or of location (continuously operated reactor). In continuous operation, certain simplifications in setting up the balances are possible if one or all of the phases are well mixed, as in continuously stirred tank reactor, hereby the mathematical treatment is significantly simplified. 

Continuous stirred-tank reactors (CSTRs) have been routinely employed for producer gas fermentations. A two-stage reactor system has also been used to maximize ethanol production and minimize the formation of byproducts. Carbon monoxide and hydrogen conversions of 90% and 70%, respectively, were observed in the first reactor, while they were about 70% and 10% in the second reactor. High ethanol-to-acetate ratios were achieved by the use of such a dual reactor system. Bubble colunms are also commonly used for industrial fermentations. A comparative study was performed between a CSTR and a bubble column reactor for CO fermentation using Peptostreptococcus productus. Higher conversion rates of CO were observed with the bubble column without the use of any additional agitation. Producer gas fermentation with packed bubble colunms and trickle bed reactors has also been studied. The trickle bed reactor has a low pressure drop and liquid hold-up, and the conversion rates were the highest compared to CSTRs and bubble columns. 

In fact, since the leaving group, methyl carbonate, decomposes (reaction 3), the base is restored and can be used in truly catalytic amounts. This feature allows utihzation of continuous-flow (c-f) procedures (i.e. gas-liquid phase-transfer catalysis, GL PTC, and continuously stirred tank reactor, CSTR ). 

---