Flow reactors laboratory scale

B. Flow Reactors. Laboratory-scale catalytic reactors and reactors for the reaction of solids with gases arc often constructed from metal. One of the principal objectives in the use of laboratory-scale catalytic reactors is the determination of rate data which can be associated with specific physical and chemical processes in a catalytic reaction. Descriptions are available for these kinetic analyses as they relate to reactor designs and reaction conditions. ... 

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. 

Peclet number independent of Reynolds number also means that turbulent diffusion or dispersion is directly proportional to the fluid velocity. In general, reactors that are simple in construction, (tubular reactors and adiabatic reactors) approach their ideal condition much better in commercial size then on laboratory scale. On small scale and corresponding low flows, they are handicapped by significant temperature and concentration gradients that are not even well defined. In contrast, recycle reactors and CSTRs come much closer to their ideal state in laboratory sizes than in large equipment. The energy requirement for recycle reaci ors grows with the square of the volume. This limits increases in size or applicable recycle ratios. 

Most kinetic experiments are run in batch reactors for the simple reason that they are the easiest reactor to operate on a small, laboratory scale. Piston flow reactors are essentially equivalent and are implicitly included in the present treatment. This treatment is confined to constant-density, isothermal reactions, with nonisothermal and other more complicated cases being treated in Section 7.1.4. The batch equation for component A is... 

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. 

The use of glutaric dialdehyde as a coupling agent bound the enzymes trypsin or glucose-6-phosphate dehydrogenase to the surface. A large part of the enzymic activity was retained (Fig. 4), and the activity was such that the particle-enzyme conjugate could be used in laboratory scale continuous-flow reactors. 

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. 

It is to be expected that in the near future more of such concepts will find application, simply for cost reasons. Laboratory-scale investigations with precisely microfabricated reactors in advance of the use of such devices can give valuable information, providing a best-case scenario. From then, one can look for alternative micro-flow solutions of lower cost, higher reliability, higher flexibility and so... 

Liquid transport is achieved by hydrostatic action, pumping or electroosmotic flow (EOF). So far, chip reactors have been employed at low to very low flow rates, e.g. from 1 ml min to 1 pi min. Applications consequently were restricted to the laboratory-scale or even solely to analytics. However, this is not intrinsic. By choosing larger internal dimensions, similar throughputs as for the other classes of liquid or liquid/liquid micro reactors are in principle achievable. 

GL 23] [R 12] [P 16] Conversions near 70% were determined for a mini trickle-bed reactor (flow rate 20 mg min ) [36]. The corresponding reaction rate was 10 times larger than in typical batch operation on a laboratory-scale, which is restricted to milder conditions. 

Collect together all the kinetic and thermodynamic data on the desired reaction and the side reactions. It is unlikely that much useful information will be gleaned from a literature search, as little is published in the open literature on commercially attractive processes. The kinetic data required for reactor design will normally be obtained from laboratory and pilot plant studies. Values will be needed for the rate of reaction over a range of operating conditions pressure, temperature, flow-rate and catalyst concentration. The design of experimental reactors and scale-up is discussed by Rase (1977). 

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. 

Large-scale ultrasonic irradiations are extant technology. Liquid processing rates of >200 L/min are routinely accessible from a variety of modular, flow reactors with acoustic powers of tens of KW per unit (14). The industrial uses of these units include 1) degassing of liquids, 2) dispersion of solids into liquids, 3) emulsification of immiscible liquids and 4) large-scale cell disruption. While these units are of limited use for most laboratory research, they are of potential importance in eventual industrial application of sonochemical reactions. 

For gas phase heterogeneous catalytic reactions, the continuous-flow integral catalytic reactors with packed catalyst bed have been exclusively used [61-91]. Continuous or short pulsed-radiation (milliseconds) was applied in catalytic studies (see Sect. 10.3.2). To avoid the creation of temperature gradients in the catalyst bed, a single-mode radiation system can be recommended. A typical example of the most advanced laboratory-scale microwave, continuous single-mode catalytic reactor has been described by Roussy et al. [79] and is shown in Figs. 10.4 and... 

A plug-flow reactor (PFR) may be used for both liquid-phase and gas-phase reactions, and for both laboratory-scale investigations of kinetics and large-scale production. The reactor itself may consist of an empty tube or vessel, or it may contain packing or a fixed bed of particles (e.g., catalyst particles). The former is illustrated in Figure 2.4, in which concentration profiles are also shown with respect to position in the vessel. 

A laminar-flow reactor (LFR) is rarely used for kinetic studies, since it involves a flow pattern that is relatively difficult to attain experimentally. However, the model based on laminar flow, a type of tubular flow, may be useful in certain situations, both in the laboratory and on a large scale, in which flow approaches this extreme (at low Re). Such a situation would involve low fluid flow rate, small tube size, and high fluid viscosity, either separately or in combination, as, for example, in the extrusion of high-molecular-weight polymers. Nevertheless, we consider the general features of an LFR at this stage for comparison with features of the other models introduced above. We defer more detailed discussion, including applications of the material balance, to Chapter 16. 

Measurement of biofilm activity can be performed based on laboratory reactor experiments or with a technique combining biofilm growth taking place in a sewer followed by measurements in laboratory scale (Raunkjaer et al., 1997 Bjerre et al., 1998). Huisman et al. (1999) developed a sewer in situ biofilm respiration chamber. It includes a DO sensor and a chamber that can be pressed onto the sewer wall. It is designed to achieve an even and unidirectional flow distribution over the entire measurement area. Pure oxygen is injected for oxygenation. 

Figure 7.4 Collection of commercial Raman probes designed for different installations (a) laboratory scale probe with interchangeable immersion or noncontact optics, shown with immersion option (b) probe shown in (a) installed in laboratory fermentation reactor (c) production scale immersion probe (d) probe shown in (c) installed in a glass reactor (e) gas phase probe with flow through cell (f) probe shown in (e) installed in process piping (g) wide area illumination (WAI) noncontact probe after completion of a pharmaceutical tablet coating operation. Adapted, with permission. Copyright 2004 Kaiser Optical Systems, Inc.

The success of these selective nitrations relies on the application on recent nitration technology - the use of flow reactors. The following is a discussion of some important work conducted at DERA and illustrates the research and development transition from laboratory to pilot plant scale synthesis of energetic materials. ... 

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