Tubular flow reactors laboratory scale

Tubular-flow reactors are used both as laboratory units, where the purpose is to obtain a rate equation, and for commercial-scale production. In fact, it is a desirable and common practice to develop a rate equation for data obtained in a laboratory-sized reactor of the same form as the proposed large-scale unit. 

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. 

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. 

Olefin polymerization in batch reactors is not common. Laboratory-scale high-throughput reactors are perhaps one of the few examples of such reactors applied to olefin polymerization. Some olefin polymerization tubular reactors can also be treated as batch reactors, where a polymerization-time to reactor-length transformation can be made and directly applied to the equations derived above if the tubular reactor has plug-flow residence time. 

A successful micromixer-assisted pilot plant was designed by researchers at Axiva (formerly Aventis) [8] for the production of acrylates. In the scale-up of the above-described laboratory-scale experiments, the numbering-up approach was used as the performance of the micromixer is direcfly related to its small dimensions. Therefore, 28 micromixers were used to mix the inlet flows of four tubular reactors (Figure 12.3). A capacity of 2000tons per year was achieved without any fouling problem. Axiva filed a patent [9] on the use of such a micromixer for the continuous production of polymers. 

Figure 4 shows the CO conversion curves (calculated from a mass balance on the amount of carbon in CO and of all the hydrocarbons, revealed by the detector of the gas-chromatograph) vs time for two RU/AI2O3 samples (1% Ru w/w). The runs were performed at 275 C, 5 bar in a tubular continuously fed reactor, with a molar ratio H2/CO = 2. Pd/C catalysts were tested in the hydrogenation of acetophenone in ethanol at 25°C and atmospheric pressure with flowing H2 as reactant in a slurry laboratory-scale plant. The activity values were measured by the consumed hydrogen in mL-min i. 

Two alternative reactor configurations were then investigated in the laboratory (1) agitated thin-film reactor and (2) tubular reactor with static mixers. The reaction time was found to be at most a few tenths of a second and yield increased with increasing agitator speed in the thin-film reactor and increasing flow rate in the tubular reactor. Semicommercial scale reactors of both types were assembled and tested. 

However, no general correlation is yet available for ki,a and kca in vertical tubular reactors when the two-phase flow regime is different from bubble flow. So for design, scale-up should be based on laboratory data for mass-transfer coefficients and on the ratio of eneigy dissipation terms as in the method defined by Jepsen (J3). For any tubular reactor, great care must be taken with the distributor design and with the size of the inlet section so as to minimize the entrance effects. 

Tubular reactors are commonly used in laboratory, pilot plant, and commercial-scale operations. Because of their versatility, they are used for heterogeneous reactions as well as homogeneous reactions. They can be run with cocurrent or counter-current flow patterns. They can be run in isothermal or adiabatic modes and can be used alone, in series, or in parallel. Tubular reactors can be empty, packed with inert materials for mixing, or packed with catalyst for improved reactions. It is often the process that will dictate the design of the reactor, as discussed in this entry. 

Exercise 9,5,4, Laboratory experiments on the dehydration of ethyl alcohol indicate that the reaction, C2H5OH —> C2H4 + H O, is second order with respect to the alcohol concentration. The rate constant is 0.52 1 gm-mole" sec at 150 C. It is proposed to construct a small scale tubular reactor which will operate at 2 atm and 150"C to give 35% conversion of the alcohol when the feed rate is 9.9kg/hr. If the reactor has a diameter of 10cm, what length will be required Ideal gas behavior and piston flow through the reactor may be assumed and... 

The experience of using small-scale tubular reactors [1], which operate in a quasi-plug flow mode, for fast chemical and many mass exchange physical processes, together with the results of laboratory research and mathematical modelling for processes of... 

Concentric cells provide another method of maintaining a uniform and small interelectrode gap. The cell shown in Fig. 2.33(b) was developed as a simple annutar-flow tubular reactor for laboratory and pilot-scale organic electro-synthesis. While the space-time yield is relatively low (due to the use of essentially two-dimensional electrodes and a dead space within the inner electrode) the reactor is robust and a separator may be incorporated much more readily than for the stacked-disc cell The resulting reactor provides a convenient modular flow-through cell, which has been utilized for industrial-scale processes. 

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