Tubular reactor control

The constant-flux reactor Tubular reactors control better than batch STR Stable temperature control when scaled up and fine chemical reactions... 

Because the characteristic of tubular reactors approximates plug-flow, they are used if careful control of residence time is important, as in the case where there are multiple reactions in series. High surface area to volume ratios are possible, which is an advantage if high rates of heat transfer are required. It is sometimes possible to approach isothermal conditions or a predetermined temperature profile by careful design of the heat transfer arrangements. 

Economic evaluations of algal production indicate that production costs vary from 0.15 to 4.00/kg of algal product, depending on type of bioreactor, culture technique, and operating conditions (51). For systems with controlled agitation and carbonation, including raceways and tubular reactors, production costs ate estimated to range from 2.00 to 4.00/kg. 

Initiators. The degree of polymerization is controlled by the addition rate of initiator(s). Initiators (qv) are chosen primarily on the basis of half-life, the time required for one-half of the initiator to decay at a specified temperature. In general, initiators of longer half-Hves are chosen as the desired reaction temperature increases they must be well dispersed in the reactor prior to the time any substantial reaction takes place. When choosing an initiator, several factors must be considered. For the autoclave reactor, these factors include the time permitted for completion of reaction in each zone, how well the reactor is stirred, the desired reaction temperature, initiator solubiUty in the carrier, and the cost of initiator in terms of active oxygen content. For the tubular reactors, an additional factor to take into account is the position of the peak temperature along the length of the tube (9). 

Continuous-flow stirred-tank reactors ia series are simpler and easier to design for isothermal operation than are tubular reactors. Reactions with narrow operating temperature ranges or those requiring close control of reactant concentrations for optimum selectivity benefit from series arrangements. 

Low Leak Rate If friendly equipment does leak, it does so at a low rate, which is easy to stop or control. Examples already mentioned are spiral-wound gaskets, tubular reactors, and vapor phase reactors. 

Figure 2.2.4 (Berty 1983) shows a tubular reactor that has a thermosiphon temperature control system. The reaction is conducted in the vertical stainless steel tube that can have various diameters, 1/2 in. being the preferred size. If used for fixed bed catalytic studies, it can be charged with a single string of catalytic particles just a bit smaller than the tube, e.g., 5/16 particles in a l/2 O.D. tube. With a smaller catalyst, a tube with an inside diameter of up to three to four particle diameters can be used. With such catalyst charges and a reasonably high Reynolds number— above 500, based on particle diameter—this reactor...

Hydrochloric acid may conveniently be prepared by combustion of hydrogen with chlorine. In a typical process dry hydrogen chloride is passed into a vapour blender to be mixed with an equimolar proportion of dry acetylene. The presence of chlorine may cause an explosion and thus a device is used to detect any sudden rise in temperature. In such circumstances the hydrogen chloride is automatically diverted to the atmosphere. The mixture of gases is then led to a multi-tubular reactor, each tube of which is packed with a mercuric chloride catalyst on an activated carbon support. The reaction is initiated by heat but once it has started cooling has to be applied to control the highly exothermic reaction at about 90-100°C. In addition to the main reaction the side reactions shown in Figure 12.6 may occur. 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

Donnet, M., Jongen, N., Lemaitre, J., Bowen, P. and Hofmann, H., 1999. Better control of nucleation and phase purity using a new segmented flow tubular reactor Model system Precipitation of calcium oxalate. In 14th International Symposium on Industrial Crystallization. Cambridge, U.K., September 12-16, Institution of Chemical Engineers, CD ROM, pp. 1-13. 

The maximum rate of polymerization has been confirmed to occur at the laminar-turbulent flow transition. The rate of polymerization was observed to be maximum at the transition for both straight reactors as well as for the helically-coiled reactor for which the transition is at a Reynolds number higher than that of the straight tube. The helically coiled tubular reactor is of industrial interest since it is much more compact and, consequently, the cost and the temperature control problems are more tractable. 

There are many interesting reports in the literature where computer simulations have been used to examine not only idealized cases but have also been used in an attempt to explain segregation and viscosity effect in unperturbed polymerization reactors (6). Some experimental work has been reported (7, 8). It is obvious, however, that although there is some change in the MWD with conversion in the batch and tubular reactor cases and that broadening of the MWD occurs as a result of imperfect mixing, there is no effective means available for controlling the MWD of the polymer from unperturbed or steady-state reactors. 

Figure 2.10. Control of deposition uniformity in a tubular reactor (a) susceptor parallel to gas flow, (b) titled susceptor.

For catalyst testing, conventional small tubular reactors are commonly employed today [2]. However, although the reactors are small, this is not the case for their environment. Large panels of complex fluidic handling manifolds, containment vessels, and extended analytical equipment encompass the tube reactors. Detection is often the bottleneck, since it is still performed in a serial fashion. To overcome this situation, there is the vision, ultimately, to develop PC-card-sized chip systems with integrated microfluidic, sensor, control, and reaction components [2]. The advantages are less space, reduced waste, and fewer utilities. 

In this chapter the simulation examples are described. As seen from the Table of Contents, the examples are organised according to twelve application areas Batch Reactors, Continuous Tank Reactors, Tubular Reactors, Semi-Continuous Reactors, Mixing Models, Tank Flow Examples, Process Control, Mass Transfer Processes, Distillation Processes, Heat Transfer, and Dynamic Numerical Examples. There are aspects of some examples which relate them to more than one application area, which is usually apparent from the titles of the examples. Within each section, the examples are listed in order of their degree of difficulty. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

For fast reactions (i.e., < 1 min.), open tubular reactors are commonly used. They simply consist of a mixing device and a coiled stainless steel or Teflon capillary tube of narrow bore enclosed in a thermostat. The length of the capillary tube and the flow rate through it control the reaction time. Reagents such as fluorescamine and o-phthalaldehyde are frequently used in this type of system to determine primary amines, amino acids, indoles, hydrazines, etc., in biological and environmental samples. 

The tubular reactor consists of a stainless steel tube (3/8 OD) in which approximately 300 mg of 2% Rh/Al203 is held in place with glass wool and 22 mg of catalyst is loaded in DRIFTS cell. The temperatures are monitored with a K type thermocouple connected to an omega temperature controller. Both pulse and step reaction studies were carried out at 250 °C. 

Polymer production technology involves a diversity of products produced from even a single monomer. Polymerizations are carried out in a variety of reactor types batch, semi-batch and continuous flow stirred tank or tubular reactors. However, very few commercial or fundamental polymer or latex properties can be measured on-line. Therefore, if one aims to develop and apply control strategies to achieve desired polymer (or latex) property trajectories under such a variety of conditions, it is important to have a valid mechanistic model capable of predicting at least the major effects of the process variables. 

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