Properties of slurry reactors

Typical properties of slurry reactors, and of packed bed co-current downflow trickle flow reactors, are summarized in Table 1. Most properties indicated for slurry reactors also hold for three-phase fluidized beds. These properties can be advantageous or disadvantageous, depending on the application ... 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

In 1976 he was appointed to Associate Professor for Technical Chemistry at the University Hannover. His research group experimentally investigated the interrelation of adsorption, transfer processes and chemical reaction in bubble columns by means of various model reactions a) the formation of tertiary-butanol from isobutene in the presence of sulphuric acid as a catalyst b) the absorption and interphase mass transfer of CO2 in the presence and absence of the enzyme carboanhydrase c) chlorination of toluene d) Fischer-Tropsch synthesis. Based on these data, the processes were mathematically modelled Fluid dynamic properties in Fischer-Tropsch Slurry Reactors were evaluated and mass transfer limitation of the process was proved. In addition, the solubiHties of oxygen and CO2 in various aqueous solutions and those of chlorine in benzene and toluene were determined. Within the framework of development of a process for reconditioning of nuclear fuel wastes the kinetics of the denitration of efQuents with formic acid was investigated. 

This latter interpretation would mean that with the approach depicted in Fig. 10, the catalyst itself could be monitored. The authors reported that the silica-supported Nafion could not be observed in the beginning of their experiments and appeared in the spectra only after the catalyst interacted with octanol. This observation may indicate that the octyl groups promote the sticking of the catalyst particles onto the ATR probe, within the evanescent field. However, the example also shows that this approach may not be without problems, because it depends on the adsorption of the particles from the slurry reactor onto the ATR element. This process is accompanied by the adsorption of molecules on the catalyst surface and complicates the analysis. More important, as also indicated by the work of Mul et al. (74). this adsorption depends on the surface properties of the catalyst particles and the ATR element. These properties are prone to change as a function of conversion in a batch process and are therefore hardly predictable. 

Except for continuous weighing, control of the flow of solids is less precise than that of fluids. Several devices used for control of feed rates are shown schematically in Figure 3.7. They all employ variable speed drives and are individually calibrated to relate speed and flow rate. Ordinarily these devices are in effect manually set, but if the solid material is being fed to a reactor, some property of the mixture could be used for feed back control. The continuous belt weigher is capable ordinarily of 1% accuracy and even 0.1% when necessary. For processes such as neutralizations with lime, addition of the solid to process in slurry form is acceptable. The slurry is prepared as a batch of definite concentration and charged with a pump under flow control, often with a diaphragm pump whose stroke can be put under feedback control. For some applications it is adequate or necessary to feed weighed amounts of solids to a process on a timed basis. 

Stirred tanks are typically used for the thermochemical pretreatment. To simulate flow of corn stover slurries in stirred tanks, the rheologic properties of these suspensions must be known. The corn stover slurries in stirred tank reactors typically range from 10 to 40% solids (3). 

Reaction Order. Rate Constants and Activation Energy (Slurry-Reactor). Hydrogentation of a-methylstyrene was selected for a test reaction. This reaction has been studied extensively by a number of investigators (6, 11. 14, 15, 17). Previous studies used Pd/A 203 or Pd-black catalysts in a-methylstyrene-cumene mixtures. We wanted to verify the kinetics of this reaction in various solvents of different physical properties (cyclohexane, hexane (u.v.), hexane (A.C.S), toluene, 2-propanol) and examine the effect of Pd concentration on the rate. The above solvents were to be utilized in trickle-bed reaction studies also to provide a range of liquid physical properties. 

If the catalyst deactivates rapidly or whenever good heat transfer properties are essential and where local hot spots cannot be accepted, the slurry reactor should also be considered. Finally, the slurry reactor can be an attractive alternative to multitube gas-solid packed-bed processes, particularly where large heat effects ask for thousands of thin tubes to control the reactor temperature in the packed beds. Also here, the much better heat transfer characteristics of slurries relative to gas-solid packed beds are deciding. 

In Japan, ureaform is also produced as a component of compound fertilizers by the addition of formaldehyde solution to the urea solution fed to the granulator.49 In one process a methylene urea reactor is used to react urea and formaldehyde solution to produce a slurry that feeds directly to a granulation plant with other materials to make compound fertilizers.50 Some slow-release nitrogen is formed, and the physical properties of the products are improved. 

The range of operating conditions for the 276 experimental run in the 12.7 cm column and 20 experimental runs to date in the 30.5 cm column are shown in Ta ble I. Relevant physical properties of the liquids are listed in Ta ble II., and compared with estimated data for the slurry phase Fischer-Tropsch pilot plant reactor at Rheinpreussen (12). Solid densities were obtained from the literature (13). As received, the isoparaffin (lM) sample was saturated with water. However, this ppm level of water was soon removed during the initial experiments by the dry nitrogen gas. Additional isoparaffin was added when required to maintain the solid concentration weight-percent. All water based runs used humidified air. 

Bubble column reactors (BCR) are widely used in chemical process industries to carry out gas-liquid and gas--liquid-solid reactions, the solid suspended in the liquid phase being most frequently a finely divided catalyst (slurry reactor). The main advantages of BCR are their simple construction, the absence of any moving parts, ease of maintenance, good mass transfer and excellent heat transfer properties. These favorable properties have lead to their application in various fields production of various chemical intermediates, petroleum engineering, Fischer-Tropsch synthesis, fermentations and waste water treatment. 

Bubble columns are convenient for catalytic slurry reactions also (67). It is therefore important to know how the hydrodynamic properties of the gas-in-liquid dispersion is influenced by the presence of suspended solid particles. In the slurry reactor absorption enhancement due to chemical reaction cannot be expected. However, if particle sizes are very small, say less than 5 yum, and if, in addition, the catalytic reaction rate is high a small absorption enhancement can occur ( 8). Usually the reaction is in the slow reaction regime of mass transfer theory. Hence, it is sufficient to know the volumetric mass transfer coefficient, kj a, and there is no need to separate k a into the individual values. 

Heat transfer in bubble column slurry reactors was studied by Kolbel and coworkers (75-77) and Deckwer et al. (13). The addition of solids increases the wall-to--suspension heat transfer coefficient. However, this increase is only due to changes in the physico-chemical properties and represents no independent contribution of the particles. Therefore, the heat transfer model, i.e. eqn. (17), developed by Deckwer (<53) for two-phase BCR also applies to slurry reactors as was proved for particle sizes up to 120 yum. This confirms that solids and liquid in the slurry can be regarded as a pseudo-homogeneous phase provided the gas velocity is large enough to provide for complete fluidization of the particles. 

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