Internal recycle, reactor with

Internal recycle reactor with a stationary packed bed... 

Internal recycle reactors with moving catalyst bed... 

Jankowski et al (1978) discuss in detail the great variety of gradientless reactors proposed by several authors with a pictorial overview in their paper. All of these reactors can be placed in a few general categories (1) moving catalyst basket reactors, (2) external recycle reactors, and (3) internal recycle reactors. 

The operational characteristics of the older Berty reactors are described in Berty (1974), and their use in catalyst testing in Berty (1979). Typical uses for ethylene oxide catalyst testing are described in Bhasin (1980). Internal recycle reactors are easy to run with minimum control or automation. 

The experimental setup uses the ROTOBERTY internal recycle reactor. The catalyst basket of this is charged with W = 35.5 g or V = 44.3 cm of OXITOX that contains 0.25 mol, i.e., 26.5 g of sodium carbonate. 

Internal recycle reactors are designed so that the relative velocity between the catalyst and the fluid phase is increased without increasing the overall feed and outlet flow rates. This facilitates the interphase heat and mass transfer rates. A typical internal flow recycle stirred reactor design proposed by Berty (1974, 1979) is shown in Fig. 18. This type of reactor is ideally suited for laboratory kinetic studies. The reactor, however, works better at higher pressure than at lower pressure. The other types of internal recycle reactors that can be effectively used for gas-liquid-solid reactions are those with a fixed bed of catalyst in a basket placed at the wall or at the center. Brown (1969) showed that imperfect mixing and heat and mass transfer effects are absent above a stirrer speed of about 2,000 rpm. Some important features of internal recycle reactors are listed in Table XII. The information on gas-liquid and liquid-solid mass transfer coefficients in these reactors is rather limited, and more work in this area is necessary. 

Differential internal recycle reactors have become important tools in recent years for the investigation of catalytic processes and a number of such reactors have been reported in literature with the main emphasis on the actual reactor design [1,2]. In this work a similar reactor, which has been developed by the main investigator for gas-phase reactions under low pressure and high temperature, where it proved its suitability, is described. [3]... 

Many authors have proposed reactors with similar basic principles. The best known are those of Garanin et al. [44], Livbjerg and Villadsen [45] and new versions of Berty reactor [34]. Variants of internal recycling reactors have also been proposed by Bennett et al. [43] who tried to decrease the ratio of reactor volume to catalyst volume. In this arrangement the amount of reactant adsorbed increases compared to that in the gas space as a result the dynamics of the adsorption - desorption processes can be detected through the gas phase measurements. 

Equation (2) (as an ordinary differential equation) and Eq. (3) apply now with Eq. (4). As already implied, a laboratory well-mixed reactor for heterogeneous catalysis is more difficult to realize than a PFR. Many versions have been used 12), and Froment and Bischoff 13) illustrate reactors with external recycle, with internal recycle 1,14), and with an internal spinning basket 15). When using these reactors for experiments in the transient regime, it is important to keep to a minimum the volume outside the bed of catalyst. Internal recycle reactors involve bearings exposed to hot reactive gases and require a magnetic drive system for leak-proof operation. Exter-... 

The results at differential conversions with water addition can be compared with methanol production at the finite conversion in the internal recycle reactor where the water concentration as a result of water production was similar (Table 3). The two types of experiment are analogous in that at differential conditions in the microflow reactor the catalyst was uniformly exposed to the feed concentration, whereas at finite conversions in the internal recycle reactor the catalyst was uniformly exposed to the product concentration. The methanol production rate at finite conversion was similar to the methanol production rate from COj/Hj/HjO at differential conditions for both the Cu/Zn/Al-1 and Pd impregnated catalyst. Therefore, the kinetics at the particular finite conversions, well away from equilibrium, can also be described by methanol production by CO2 hydrogenation, and the inhibition of this reaction associated with the presence of the product water. Furthermore, the Pd promotion was similar under the two reaction regimes (Table 3), reinforcing the conclusion that Pd promotion of CO2 hydrogenation is active only in the presence of water. 

The reactor used for these studies is the Autoclave Engineer s Berty internally-recycled reactor (19) which is supplied with a 3-kW heater. Temperature control is achieved via a Nanmac Model PC-1 temperature controller which operates a mercury relay switch-variac combination which powers the heaters. 

They found the reaction order for H2 (6) was positive but the reaction order for CO (a) was negative, suggesting inhibition by adsorbed CO. Samp and Wojciechowski [16] compared six different possible mechanisms to FT synthesis data they obtained with a cobalt catalyst used in a Berty internal recycle reactor. They found the best fit was obtained with the expression ... 

Recycle reactor [3.48, 3.54] with natural circulation through a central tube (mammoth recycle reactor), with cocurrent slip stream of liquid and gas phase (slip stream recycle reactor) and internal tube (jet tube recycle reactor) (Fig. 3-15 a-c). 

The negative reaction order was confirmed by measurements with industrial-size catalyst pellets in an internal recycle reactor (CSTR, Berty reactor), as shown in Figure 3.27. 

The internal recycle reactor as described elsewhere ( ) used for the experiments was charged with about 60 g of catalyst which was thermally pretreated and reduced with hydrogen before the synthesis reaction. During the synthesis recycle ratios (recycled volume per time and weight of catalyst divided by space velocity under operating conditions) of more than 20 were used to establish ideal mixing as well as isothermal operation and to avoid transport limitation due to film resistance. 

Fig. 8. Combined flow reactor models (a) parallel flow reactors with longitudinal diffusion (diffusivities can differ), (b) internal recycle—cross-flow reactor (the recycle can be in either direction), comprising two countercurrent plug-flow reactors with intercormecting distributed flows, (c) plug-flow and weU-mixed reactors in series, and (d) 2ero-interniixing model, in which plug-flow reactors are parallel and a distribution of residence times dupHcates that...

Various experimental methods to evaluate the kinetics of flow processes existed even in the last centuty. They developed gradually with the expansion of the petrochemical industry. In the 1940s, conversion versus residence time measurement in tubular reactors was the basic tool for rate evaluations. In the 1950s, differential reactor experiments became popular. Only in the 1960s did the use of Continuous-flow Stirred Tank Reactors (CSTRs) start to spread for kinetic studies. A large variety of CSTRs was used to study heterogeneous (contact) catalytic reactions. These included spinning basket CSTRs as well as many kinds of fixed bed reactors with external or internal recycle pumps (Jankowski 1978, Berty 1984.)... 

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

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. 

The RR developed by the author at UCC was the only one that had a high recycle rate with a reasonably known internal flow (Berty, 1969). This original reactor was named later after the author as the Berty Reactor . Over five hundred of these have been in use around the world over the last 30 years. The use of Berty reactors for ethylene oxide process improvement alone has resulted in 300 million pounds per year increase in production, without addition of new facilities (Mason, 1966). Similar improvements are possible with many other catalytic processes. In recent years a new blower design, a labyrinth seal between the blower and catalyst basket, and a better drive resulted in an even better reactor that has the registered trade name of ROTOBERTY . ... 

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