Stirred-flow reactors laboratory scale

Batch reactors often are used to develop continuous processes because of their suitabiUty and convenient use in laboratory experimentation. Industrial practice generally favors processing continuously rather than in single batches, because overall investment and operating costs usually are less. Data obtained in batch reactors, except for very rapid reactions, can be well defined and used to predict performance of larger scale, continuous-flow reactors. Almost all batch reactors are well stirred thus, ideally, compositions are uniform throughout and residence times of all contained reactants are constant. 

Reactor design usually begins in the laboratory with a kinetic study. Data are taken in small-scale, specially designed equipment that hopefully (but not inevitably) approximates an ideal, isothermal reactor batch, perfectly mixed stirred tank, or piston flow. The laboratory data are fit to a kinetic model using the methods of Chapter 7. The kinetic model is then combined with a transport model to give the overall design. 

There is an additional point to be made about this type of processing. Many gas-phase processes are carried out in a continuous-flow manner on the macro scale, as industrial or laboratory-scale processes. Hence already the conventional processes resemble the flow sheets of micro-reactor processing, i.e. there is similarity between macro and micro processing. This is a fimdamental difference from most liquid-phase reactions that are performed typically batch-wise, e.g. using stirred glass vessels in the laboratory or stirred steel tanks in industrial pilot or production plants. 

Chakrabarti, T. and Subrahmanyam, P.V.R., Biological hydrolysis of urea in a continuous flow stirred tank reactor under laboratory conditions—a bench scale study, Proc. 36th Industrial Waste Conference, Purdue University, pp. 477, 1981. 

Equation 8.3.4 may also be used in the analysis of kinetic data taken in laboratory scale stirred tank reactors. One may directly determine the reaction rate from a knowledge of the reactor volume, flow rate through the reactor, and stream compositions. The fact that one may determine the rate directly and without integration makes stirred tank reactors particularly attractive for use in studies of reactions with complex rate expressions (e.g., enzymatic or heterogeneous catalytic reactions) or of systems in which multiple reactions take place. 

A chemical reaction is being studied in a laboratory scale steady-state flow system. The reactor is a well-stirred 1000 cm3 flask containing an aqueous solution. The reactor contents (1000 cm3 of solution) are uniform throughout. The stoichiometric equation and data are given below. What is the expression for the rate of this reaction Determine the reaction order and the activation energy. 

The corresponding semibatch process is a rather slow reaction at 90 °C with simultaneous exothermic decomposition of DAST. Thus, the processed volume is restricted to laboratory scale (< 11) [ 50]. The transfer to production in a stirred tank is prohibited because of these safety reasons. A micromixer-tube reactor approach was chosen using the convective-flow-driven bas-relief caterpillar micromixer and tubes with diameters of 1-5 mm and lengths up to 20 m, respectively, and tube reactor volumes up to 500 ml (see Figure 5.16). 

A continuously stirred tank reactor (CSTR) would probably be the reactor vessel of choice for most liquid-scC02 systems, to ensure that efficient mixing of the phases occurs. Apart from this, the setup is likely to be similar to that employed for solid-C02 applications with regard to product isolation. A typical reactor setup for laboratory-scale exploratory explorations is depicted in Figure 6. Examples of continuous-flow systems using IL-SCCO2 mixtures using apparatus of this type... 

Semibatch and continuous stirred-tank reactors (CSTRs) are much more commonly found in polyolefin production. Semibatch reactors are the standard choice for laboratory-scale polymerizations, while CSTRs dominate industrial production, as will be seen in Section 2.5. The equations derived above are easily translated into semibatch and CSTR operation mode by simply adding terms for the inflow and outflow streams in the reactor. For instance, consider Equation 2.49 for the zeroth moment of dead chains. The molar flow rate [mol s ] leaving the reactor is given by... 

Continuous-flow stirred-tank reactors (CSTRs) can be cooled in three ways. The most elegant method is to allow boiling of the monomer or solvent so that the heat of reaction is removed in an overhead condenser. The pressure in the vessel is set to give the desired temperature. The condensate can be returned to the vessel or recycled back to the feed. This process is commonly used for polystyrene. Chilling the feed is another means for managing the exotherm in a CSTR. Refrigeration to -40°C has been used for the bulk, continuous polymerization of PMMA. Laboratory reactors and small-scale industrial reactors can be cooled using jackets or internal coils, but this method scales up poorly. 

The construction of a laboratory-scale continuous stirred tank reactor (CSTR) resembles of that of a BR, but the reactor is equipped with an inlet and an outlet. Concentration and temperature gradients should be absent because of vigorous stirring. For a homogeneous CSTR, a constant volume and pressure are reasonable assumptions. The concentrations at the reactor outlet are measured as a function of the space time, that is, volumetric flow rate. The steady-state mass balance is written as (Chapter 3)... 

The scale of operation of these HT developments has been limited thus far to laboratory-scale experimentation. Much of the work has been performed in small batch reactors from 5 to 1000 mL. In most cases these reactors are agitated either with internal stirring or by a shaker in order to minimize mass transfer limitations considering the several phases involved (hydrogen gas, hydrocarbon, and water vapor solid heterogeneous catalyst aqueous liquid, hydrocarbon liquid, and polar biomass-derived liquids, which are likely immiscible). The HT process is envisioned as a continuous-flow operation, so the limited amount of laboratory-scale HT in continuous-flow systems provides the most useful information for consideration of scale-up and in-process modeling for economic analysis (Jones et al., 2014). 

This chapter treats the effects of temperature on the three types of ideal reactors batch, piston flow, and continuous-flow stirred tank. Three major questions in reactor design are addressed. What is the optimal temperature for a reaction How can this temperature be achieved or at least approximated in practice How can results from the laboratory or pilot plant be scaled up ... 

ABSTRACT A novel reactor configuration has been developed in our laboratory which addresses the heat transfer limitations usually encountered in vacuum pyrolysis technology. In order to scale-up this reactor to an industrial scale, a systematic study on the heat transfer, the chemical reactions and the movement of the bed of particles inside the reactor has been carried out over the last ten years. Two different configurations of moving and stirred bed pilot units have been used to scale-up a continuous feed vacuum pyrolysis reactor, in accordance with the principle of similarity. A dynamic model for the reactor scale-up was developed, which includes heat transfer, chemical kinetics and particle flow mechanisms. Based on the results of the experimental and theoretical studies, an industrial vacuum pyrolysis reactor, 14.6 m long and 2.2 m in diameter, has been constructed and operated. The operation of the pyrolysis reactor has been successful, with the reactor capacity reaching the predicted feed rate of 3000 kg/h on a biomass feedstock anhydrous basis. 

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