Scaling laboratory reactor

The criteria for selection of laboratory reactors include equipment cost, ease of operation, ease of data analysis, accuracy, versatility, temperature uniformity, and controllabihty, suitability for mixed phases, and scale-up feasibility. 

The ROTOBERTY internal recycle laboratory reactor was designed to produce experimental results that can be used for developing reaction kinetics and to test catalysts. These results are valid at the conditions of large-scale plant operations. Since internal flow rates contacting the catalyst are known, heat and mass transfer rates can be calculated between the catalyst and the recycling fluid. With these known, their influence on catalyst performance can be evaluated in the experiments as well as in production units. Operating conditions, some construction features, and performance characteristics are given next. 

This study was run in a laboratory bench-scale unit with 0.75-in. reactor tubes. The catalysts were sized to 10 X 12 mesh and diluted nine-to-one with Si02 in order to spread the reaction out through the bed and to permit measurement of temperature profiles, the profile being an... 

The value for is conservatively interpreted as the particle diameter. This is a perfectly feasible size for use in a laboratory reactor. Due to pressure-drop limitations, it is too small for a full-scale packed bed. However, even smaller catalyst particles, dp 50 yum, are used in fluidized-bed reactors. For such small particles we can assume rj=l, even for the 3-nm pore diameters found in some cracking catalysts. 

Scahng up will probably continue to be a problem since large reactors carmot be as efficient as small laboratory reactors. However, it may be possible to make laboratory or pilot-plant reactors that are more similar to large-scale reactors, allowing more rebable validation of the simulations and process optimization. The time from laboratory-scale to full-scale production should be shortened from years to months. 

Worz et al. give a numerical example to illustrate the much better heat transfer in micro reactors [110-112]. Their treatment referred to the increase in surface area per unit volume, i.e. the specific surface area, which was accompanied by miniaturization. The specific surface area drops by a factor of 30 on changing from a 11 laboratory reactor to a 30 m stirred vessel (Table 1.7). In contrast, this quantity increases by a factor of 3000 if a 30 pm micro channel is used instead. The change in specific surface area is 100 times higher compared with the first example, which refers to a typical change of scale from laboratory to production. 

As illustrated by the examples above, the possibility of removing the generated heat from the reaction zone decreases with an increase in reactor size. As proven above, it can happen that the temperature of the reaction mixture in a full-scale reactor becomes higher than in the laboratory flask reactor. If multiple chemical reactions of distinctly different temperature sensitivities take place, differences in yields and selectivities between small and large reactors will be observed. This has a large influence on safety also. The laboratory reactor might still show satisfactory performance, while the industrial reactor might even explode. 

Stability tests of catalyst. All catalysts deactivate during their life by various causes (see Chapter 3). The aim of stability tests is to examine the cause and rate of deactivation. These experiments are usually performed at conditions similar to those planned for the commercial unit. In some cases, accelerated tests are carried out using a feedstock with an elevated level of impurities or at a temperature significantly higher than that anticipated for the full-scale reactor. A laboratory reactor used for such tests is usually a down-scaled reactor or a part of the full-scale-reactor. Standard analytical equipment is used. 

Quality control tests or improvement of existing processes. Raw materials from various sources can be used in the manufacture of fine chemicals and pharmaceuticals. The raw materials can contain different impurities at various concentrations. Therefore, before the raw material is purchased and used in a full-scale batch its quality should be tested in a small-scale reactor. Existing full-scale procedures are subject to continuous modifications for troubleshooting and for improving process performance. Laboratory reactors used for tests of these two kinds are usually down-scaled reactors or reactors being a part of the full scale-reactor. 

Laboratory reactors and industrial scale equipment are seldom operated under similar flow and heat transfer conditions. To obtain a... 

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. 

Another issue that needs attention is that in large-scale beds, phenomena absent in the laboratory reactor may develop. For example, in commercial beds, axial gradients of temperature may appear, which are absent in bench beds due to the small diameters usually used in them. In the worst scenario, the controlling mechanism, and thus the whole behavior of the system, could change from the small to the large scale. 

These factors are introduced in the experimental plan at the bench-scale before the pilot--plant stage. On the bench-scale, glass or steel laboratory reactors of about 1 to 2 L will be used for MSSR and a 30 cm diameter and 2 m height for BSCR. 

Choosing a laboratory reactor for the purpose of investigating a particular reaction is rather like choosing a reactor for an industrial scale operation, in that the choice depends mainly on the intrinsic speed of the reaction—/as/, moderately fast, or slow. As with large scale reactors, the value of P- lk2CBLDA /kL is a useful... 

Calculated and experimental maleic anhydride yields for the three fluid bed reactors involved in the scale-up of the Mitsubishi process are shown together in Figure 7. The yield value for the 45 cm dia. reactor was used to determine the reaction rate constant k, but the calculations for the 15 cm dia. bed and for the laboratory reactor with 4 cm diameter were performed without any parameter fitting. The calculation for the 15 cm bed is surprisingly close to the measurement whereas there is some deviation between theory and experiment on the laboratory scale the reason of which ist not quite clear. It should be noted however that in the laboratory reactor 1-butene was used as feed while on the pilot scale C -fractions of the naphtha cracker i.e. mixtures of various hydrocarbons were used. 

In spite of the differences in construction all reactors suited for kinetic studies can be classified into the three ideal reactor types mentioned above. It is stressed here that kinetic data should be acquired in laboratory reactors that are suited for kinetic studies and should not be a small-scale replica of the reactor intended to be used in practice. 

Evaluation of literature data on the correlation between the particle Peclct number (also referred to as Bodenstcin number) and particle Reynolds number for single phase and trickle flow yielded Fig. 6. At low Rep (<20) a value between 0.3 and 0.7 holds for single phase flow, whereas for trickle flow this is one order of magnitude lower. These conditions are usually encountered in small scale laboratory reactors. 

Decomposition of Ti(0-iC 3117)4 dissolved in supercritical isopropanol leads to the formation of titanium oxide. The reaction is studied in the temperature range 531 to 568 K under 10 MPa and a mechanism is proposed. The obtained kinetic results are further used to optimize a continuous reactor producing submicronic TiC>2 powder at a laboratory pilot scale. 

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