Catalytic semibatch

Other variations of catalytic and noncatalytic coal Hquefaction schemes were also developed (27,28). Additionally, bench-scale and semiworks systems have been operated in Germany by researchers at Bergbau-Forschung in Essen (29). A 2.5 ton per day pilot plant is being operated by the National Coal Board in the United Kingdom at Point of Ayr in Wales (30). This facdity is notable for the use of semibatch or candle filters for removal of mineral matter and unreacted coal from the primary Hquefaction products. 

Single phase Gas-liquid or liquid-liquid (semibatch reactors) Catalytic (three-phase) (semibatch or continuous) ... 

Column reactors can contain a draft tube - possibly filled with a packing characterized by low pressure drop - or be coupled with a loop tube, to make the gas recirculating within the reaction zone (see Fig. 5.4-9). In recent years, the Buss loop reactor has found many applications in two- and three-phase processes About 200 Buss loop systems are now in operation worldwide, also in fine chemicals plants. This is due to the high mass-transfer rate between the gas and the liquid phase. The Buss loop reactor can be operated semibatch-wise or continuously. As a semibach reactor it is mostly used for catalytic hydrogenations. 

Price and Schiewetz Ind Eng. Chem. 49 (807), 1957] have studied the catalytic liquid phase hydrogenation of cyclohexene in a laboratory scale semibatch reactor. A supported platinum catalyst was suspended in a cyclohexene solution of the reactant by mechanical... 

Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10-15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. 

Heterogeneously catalyzed hydrogenation reactions can be run in batch, semibatch, or continous reactors. Our catalytic studies, which were carried out in liquid, near-critical, or supercritical C02 and/or propane mixtures, were run continuously in oil-heated (200 °C, 20.0 MPa) or electrically heated flow reactors (400 °C, 40.0 MPa) using supported precious-metal fixed-bed catalysts. The laboratory-scale apparatus for catalytic reactions in supercritical fluids is shown in Figure 14.2. This laboratory-scale apparatus can perform in situ countercurrent extraction prior to the hydrogenation step in order to purify the raw materials employed in our experiments. Typically, the following reaction conditions were used in our supercritical fluid hydrogenation experiments catalyst volume, 2-30 mL total pressure, 2.5-20.0 MPa reactor temperature, 40-190 °C carbon dioxide flow, 50-200 L/h ... 

Monoliths exhibit a large flexibility in operation. They are well suited for optimal semibatch, batch, continuous, and transient processing. Catalytic conversion can be combined with in situ separation, catalytic reactions can be combined, heat integration is possible, and all lead to process intensification. In the short term, catalytic monoliths will be applied to replace trickle-bed reactor and slurry-phase... 

As an application example, the dynamic model was used for the simulation of the steady-state and semibatch production of methyl acetate, performed in a packed column with a catalytic packing. For the model validation, several experiments were carried out in a pilot-plant column. For the investigated operation range, the simulation results are in good agreement with the experimental data. 

Although a wide variety of catalysts have been employed to crack PE, zeolites have proven particularly effective. For example, Garforth et al. reported that activation energies (La) measured when PE was catalytically cracked by HZSM-5, HY, and MCM-41 were much lower than when no catalyst was present. [66] They concluded that HZSM-5 and HY have similar activities and that both of these zeolites were more effective than MCM-41. Manos and co-workers found that catalytic cracking of PE by HZSM-5 and HY was effective in producing gasoline size hydrocarbons in a laboratory semibatch reactor [67, 68]. Mordi and co-workers reported that H-Theta-1 and H-Mordenite... 

S. C. Cardona and A. Corma, Tertiary recycling of polypropylene by catalytic cracking in a semibatch stirred reactor. Use of spent equilibrium FCC commercial catalyst, Appl. Catal. B Env., 25, 151 (2000). 

S. C. Cardana. and A. Corma, Kinetic stndy of the catalytic cracking of polypropylene in a semibatch stirred reactor, Catal. Today, 75, 239 (2002). 

The large spectrum of reactors is shown in Fig. 2 with the vertical axis showing the progression from the simplest types such as a delayed coker (a semibatch reactor) to the highly complex fluid catalytic cracking (FCC) unit, which has both the reaction phase and the catalyst being transported through the reactor. 

Propylene epoxidation with O2/H2 mixture in MeOH or BuOH solvent can proceed with a selectivity above 88% over Pd/TS-1 catalyst in semibatch reactors. The addition of a small amoimt of Pt is effective to maintain cationic Pd and enhances the catalytic performance. 

The key issue in effective catalytic oxidation of organics is finding a suitable catalyst. Oxidation of aqueous phenol solutions by using different transition metal oxides as heterogeneous catalysts is already known [4-6]. On the other hand, the potential of molecular sieves to catalyze oxidative phenol destruction has not been examined yet. The objective of this contribution is to provide kinetic and mechanistic data on the catalytic liquid-phase oxidation of aqueous phenol solutions obtained in the presence of various transition metal oxides and molecular sieves. The reaction was studied in a semibatch slurry as well as two-and three-phase continuous-flow reactors. Another matter of concern was the chemical stability of catalysts under the reaction conditions. 

Figure 2. Percentage of CO2 formed during the course of catalytic liquid-phase phenol oxidation carried out in a semibatch slurry reactor.

In a kinetic investigation of the catalytic liquid-phase phenol oxidation carried out in a semibatch slurry reactor [6], it has been found that homogeneous stepwise polymerization reactions are enhanced in the bulk liquid-phase due to the high liquid-to-solid volumetric ratio. The rate of phenol disappearance has been expressed on the basis of power-law kinetics as a sum of heterogeneous and homogeneous (polymerization) contributions, thus... 

Batch, semibatch, and continuous stirred tank reactors residence time 600 to 15,000 s (10 min to 4 h) heat of reaction primarily exothermic reaction rate slow to moderate. High-pressure autoclaves <100 L. Unique to semibatch phases liquid, gas-liquid, liquid-liquid, gas-liquid catalytic solid. Use where a batch operation is appropriate (Section 16.11.6.24), but one reactant (e.g., gas) needs to be added continuously or if the initial reaction rate is very high. Selectivity is best for parallel reactions. For more details, see CSTR, Section 16.11.6.26. 

Catalytic reactions can be run in batch mode or as a continuous process. In a batch process the reactants, catalyst, and other reaction components are loaded in an appropriate vessel, the reaction is run, and the produets are removed from the vessel after some time and separated from the catalyst. In a continuous system the reactants are passed over the eatalyst and the products removed at the same rate as the reactants are added. Another, intermediate, option is semibatch operation one of the reaetants is added, gradually or step-wise, to the reaetor, which has been loaded with catalyst and the other reaetant(s). 

Different types of reactors are applied in practice (Figure 1.14). Stirred tank reactors (STR), very often applied for homogeneous, enzymatic and multiphase heterogeneous catalytic reactions, can be operated batchwise (batch reactor, BR), semi-batchwise (semibatch reactor, SBR) or continuously (continuous strirred tank reactor, CSTR)... 

Catalytic sites of formation of DCH seemed to be specific and rather reactive. They were easily deactivated or poisoned. The addition of sodium carboxylates (5% of nickel surface coverage) lowered the 1,2-DCH formation by 40% during the hydrogenation of adiponitrile without any loss of activity (semibatch test). 

A kinetic investigation of the Co-catalyzed hydroformylation in a semibatch reactor [44] showed that the pseudo-first-order rate constant for the reaction is a function of pressure if the rate law known from liquid organic solvents is used for data analysis. However, a nonlinear relationship between the reaction rate and the catalyst concentration was observed and is not in agreement with the simple kinetic scheme. From a practical viewpoint, the large catalyst loadings and the relatively forcing conditions are still severe limitations of this catalytic reaction. 

PE = polyethylene PP = polypropylene PS = polystyrene ASR = automobile shredder residue VGO = vacuum gas oil LCO = light cycle oil. SA = Si02/ AI2O3 MOR = mordenite. TD/CD = thermal degradation followed by catalytic degradation COMB = mixed polymer and catalyst in a batch reactor COMS = mixed polymer and catalyst in a semibatch reactor FB = fixed bed flow reactor BIRR = Berty internal recycle reactor. 

The catalytic hydrogenation of nitrobenzene to aniline in a solvent was studied using a stirred semibatch reactor with 25-/rm particles of catalyst. The reaction was first order to hydrogen and zero order to nitrobenzene. Tests at 70°C and 90 psia gave the results listed in Table 8.8. 

The safety technical assessment of continuous CSTR processes and discontinuous processes performed in batch or semibatch reactors is of special importance. In the case of reactions conducted in tube reactors the amoimt of substance is comparatively smaller. On the other hand, reactions performed in such tube reactors are often very complex catalytic equilibrium processes, which need an individual evaluation for an adequate safety assessment. Generalizations are hardly possible. 

This problem has been adapted with permission from the late Professor C. N. Satterfield of MIT. R. H. Price and R. B. Schiewetz [Ind Eng. Chem., 49, 807 (1957)] studied the catalytic liquid-phase hydrogenation of cyclohexene in a laboratory-scale semibatch reactor. A supported platinum catalyst was suspended in a cyclohexene solution of the reactant by mechanical agitation of the solution. Hydrogen was bubbled through the solution continuously. The reactor is described in their words as follows ... 

A large number of liquid-phase organic reactions are carried out in batch or semibatch reactors. For large volume, liquid-phase reactions, the use of a series of CSTRs is quite common. For large volume, vapor-phase catalytic reactions, tubular reactors are often the reactors of choice. 

Donati, G., and Paludetto, R. (1999), Batch and semibatch catalytic reactors (from theory to practice), Catalysis Today, 52(2-3) 183-195. 

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