Three-phase Slurry Reactor Research Articles

Bubble Column Reactors and Fischer-Tropsch Synthesis

Abstract Three-phase slurry bubble column reactors have been used extensively in a number of chemical, petrochemical, and biochemical process engineering applications. For the success of these operations and their large scale industrial exploitation, it is essential that their transport and chemical characteristics be adequately understood on a mechanistic basis so that appropriate design criteria and optimum operating conditions can be established. It is the purpose of this review to present such available knowledge in relation to chemical catalytic operations. The mass transfer characteristics, catalytic activity, and mixing patterns of different phases necessitate a detailed understanding of the hydrodynamic behavior and catalyst dispersion in slurry bubble column reactors. The current status of these aspects is presented, discussed, and assessed in this review. Chemical and biochemical reactions are exothermic in nature and hence efficient heat removal devices must be installed in the reactor to prese...

Determination of gas-liquid mass-transfer and solids-suspension parameters in mechanically-agitated three-phase slurry reactors

This paper describes methods for determining gas-liquid mass-transfer and off-bottom solids-suspension parameters, and the interactions between these parameters, for mechanically-agitated three-phase slurry reactors. A steady-state sodium sulphite feeding method was used to obtain estimates of the overall volumetic mass-transfer coefficient ( k La ). In this work, the effectiveness of performing a gas-phase oxygen mass balance (in place of a sulphite balance on the liquid phase) to determine the sulphite oxidation rate was demonstrated. Mass-transfer data for a high-solidity ratio axial-flow impeller were generated over a range of air flowrates and impeller speeds. The ‘just-off-the-bottom suspension’ criterion (JOBS) is a useful and widely-used criterion for solids suspension in slurry reactors. This criterion was used to obtain solids-suspension data for a finely-ground, fast-settling mineral slurry with a wide particle-size distribution, in both two- and three-phase systems. The effect of increasing gas flowrates on the ability to maintain solids in suspension was demonstrated. The effectivenessand limitations of these methods to characterise three-phase systems was illustrated using bacterial sulphide oxidation as the reacting system. The results obtained in this work emphasise the importance of incorporating the effects of physical gas-liquid-solid interactions in the design of mechanically-agitated three-phase slurry reactors.

A mathematical model for multiple hydrogenation reactions in a continuous stirred three-phase slurry reactor with an evaporating solvent

A mathematical description is given of reactor system with a continuously operated stirred three-phase slurry reactor and an evaporating solvent to remove a large fraction of the heat of reaction from the reactor. Some characteristic properties of the reactor system and the influence of the operating parameters on the performance of the reactor are illustrated by the catalytic hydrogenation of 2,4- dinitrotoluene in methanol as a model reation, which can be described by a reaction pathway of five consecutive and parallel reactions with three stable intermediate products. It is concluded that the appropriate operating parameters to set and fine-tune the conditions in the stable operating point of the reactor are the reactor pressure and the catalyst concentration. The interrelation of the many operating and design variables is so complex that a computer model is needed to predict the behaviour of the reactor system and to monitor the selectivity.

The catalytic hydrogenation of 2,4-dinitrotoluene in a continuous stirred three-phase slurry reactor with an evaporating solvent

An experimental study of the catalytic hydorgenation of 2,4-dinitrotoluene (DNT) in a mini-installation with a continuously operated stirred three-phase slurry reactor and an evaporating solvent is discussed. Some characteristic properties of the reactor system and the influence of the operating parameters on the performance of the reactor are illustrated. The experimental results are compared with the predictions based on a mathematical model of the reactor system. The results indicated that the assumption of complete saturation with solvent vapors of the gas exit stream out of the reactor does not hold for our small laboratory reactor. It is concluded that, for the mini-installtion, the model describes well the operation and further the behavior of the reactor system, and that the model should be fully adequate for large industrial reactors. Further, it was concluded that the kinetics cannot be based on the overall hydrogen conversion determinations alone, and reevaluation of chemisorption constants by analysis of the reactor product composition also is required as soon as a new batch of catalyst is taken into use.

A novel single-step dimethyl ether (DME) synthesis in a three-phase slurry reactor from co-rich syngas

The productivity of liquid phase methanol synthesis reactor in limited by the chemical equilibrium barrier caused by high local methanol concentration in the liquid phase. This barrier can be partly lifted by either selective physical remoal of methanol from the liquid phase or in-situ conversion to other chemical species. A novel process for manufacturing dimethyl ether (DME) from CO-rich syngas in the liquid phase has been developed. Two functionally different catalysts are slurried in the inert liquid phase, in this dual catalytic mode of operation. The (methanol+DME) co-production approach is extremely effective in increasing the per-pass syngas conversion and reactor productivity over those of methanol synthesis alone. The co-production approach can also co-produce methanol and DME in any fixed proportion, from practically pure DME to pure methanol. Scientific aspects of the process including the process feasibility domain, reaction kinetics, catalytic management, and thermodynamic modeling will be discussed.

The ethynylation kinetics of formaldehyde in a three-phase slurry reactor

Investigations were undertaken on the ethynylation of formaldehyde over a Cu 2C 2/MgSiO 4 catalyst in a slurry reactor to study the reaction kineics. The result show that this catalyst is highly selective to the main product 1,4-butynediol. It was found that the reaction rate is first order with respect to catalyst loading and zeroeth order in acetylene partial pressure at above 1.0 kg/cm 2. The activation energy was found to be 51.88 kJ/mol ensuring that the rate controlling step is a surface reaction. We chose to use a mechanistic model to explain our experimental data. We postulated a reaction mechanism in which reactants are adsorbed on different active sites respectively. According to this, the following rate expression of Langmuir-Hinshelwood type were obtained for the ethynylation of formaldehyde at 363 K: ▪ We also found that the ethynylation reaction can be expressed with a simple empirical power law model with a reaction order of 0.59 with respect to formaldehyde.

Hydrodynamic and mass transfer characteristics of sectionalized aerated slurry reactors

The effect of selected construction and operating variables (number of column stages, distributing plate geometry, gas and liquid flow rates, and solid phase concentration) on hydrodynamic and mass transfer characteristics of multi-stage three-phase slurry reactors was studied in a countercurrent-flow bubble column reactor 0.29 m in diameter, sectionalized by perforated plates with downcomer tubes, using the system air-aqueous suspension of ZnO particles ( c s = 0−5 wt.%). Experimental results proved the favourable effect of column sectionalization on gas holdup and k L a L values, while the effect of increasing solid phase concentration on these system characteristics was negative within the whole region of experimental conditions. The relationship between k L a L and gas holdup was independent of the solid phase concentration and gas flow rate. However, values of k L a L corresponding to given gas holdup ratios increased substantially with increasing number of column stages. Axial mixing of the liquid (slurry) phase was well described by a model of perfectly mixed tanks in series with backflow, with the number of series terms equal to the number of column stages. Evaluation of the backflow coefficient confirmed the importance of plate design optimization for particular flow conditions.

Dynamic response of an isothermal three-phase slurry reactor—II. The PM-PM-HS/ID model: analytical solutions for two kinds of batch operation

The dynamics of an isothermal batch, three-phase slurry reactor with a first-order reaction occurring in uniform spherical catalyst particles have been investigated. Two kinds of batch operation were considered: variable and constant reactant concentrations in the gas phase. Analytical solutions were presented in both cases. The solutions are based on the PM-PM-HS/ID model, which considers perfect mixing (PM) in both gas and liquid phases, homogeneous suspension (HS) of the catalyst particles, and intraparticle diffusion (ID). The solutions are valid for any mode of input perturbation with non-negative and constant initial conditions. For an input perturbation with which the catalyst particles are suddenly introduced into the reactor after the gas and liquid are in equilibrium, the gas reactant in the liquid phase reveals two responses for both kinds of batch operation. In the case of constant gas reactant in the gas phase, the critical condition which distinguishes two responses can be expressed explicitly, and is independent of liquid—solid mass transfer coefficient and intraparticle diffusion coefficient. This makes it possible to determine experimentally the rate constant from the critical condition without evaluating these two mass transfer processes simultaneously.

Slurry-phase hydrogenation of aromatic compounds over supported noble metal catalysts

The hydrogenation of benzene, naphthalene and biphenyl over monometallic (Pt, Rh, Ru) and bimetallic (Pt, Rh, Ru-Pd, Ir, Re ) catalysts supported on γ-Al 2O 3 or TiO 2 is investigated in a three-phase slurry reactor at a temperature of 300 °C and a hydrogen pressure of 66 atm. Under the conditions employed in this study, of the primary metals investigated platinum was found to possess the highest specific hydrogenation activity while biphenyl was found to be the most reactive molecule. The hydrogenation of benzene over platinum and naphthalene over platinum and rhodium were found to be structure insensitive reactions. In most cases, bimetallic formulations were found to exhibit significantly higher hydrogenation activity as compared to their monometallic counterparts. The enhancement factor was found to be larger when the bimetallic formations were supported on TiO 2 as opposed to Al 2O 3 carriers. Bimetallic catalysts, especially those containing rhenium were also found to exhibit enhanced resistance to sulfur poisoning.

Dynamic response of an isothermal three-phase slurry reactor—I. The PM-PM-HS/ID model: analytical solutions for continuous and semi-batch operations

Based on the PM-PM-HS/ID model, the dynamic response of an isothermal three-phase catalytic reactor with a first order reaction in uniform spherical catalyst particles was presented analytically. The solution is valid for any mode of input perturbation with non-negative and constant initial conditions, and for continuous and semi-batch operations. Two critical Thiele moduli divide the solution into five cases and the dynamic response depends on the magnitude of the Thiele modulus. For the semi-batch operation with a sudden introduction of catalyst into the reactor, there exists two types of response for the effluent reactants in both gas and liquid phases, and the responses are distinguished by the first critical Thiele modulus. Based on the difference of the responses, a method which is able to determine the rate constant directly from the experiments was also proposed. For the continuous operation, two types of response always exist if the inlet liquid stream is pre-equilibrated with a gas which has the same composition as the inlet gas stream. The criterion to distinguish these two responses was also given. However, if there is no gas reactant dissolved in the inlet liquid stream, it is possible to have only the decay type response as the liquid flow rate is larger than some critical value.

Effect of hydrogenation catalyst activity on adsorption and surface reaction rates

Dynamic studies of the hydrogenation of α-methyl styrene in a three-phase slurry reactor showed that catalyst reduction temperature appreciably affects individual values of adsorption equilibrium constants, adsorption rate coefficients and surface reaction rate coefficients. Measurements were made in a well-stirred slurry reactor with Pd/Al 2O 3 catalyst particles at 22, 38 and 50°C. Increasing the temperature for reducing, in hydrogen, PdCl 2 to Pd from 250 to 420 to 510°C decreased the palladium dispersion, and caused a reduction in equilibrium adsorption, adsorption rate and surface reaction rate coefficients. The heat of adsorption and the activation energy for surface reaction, 3.8 and 10 kcal/mole, respectively, were constant with reduction temperature. The relative magnitudes of metal dispersion at the three catalyst reduction temperatures were estimated from equilibrium adsorption coefficients, and found to agree with an experimental study by Boitiaux et al. (1983a).

Dynamic response and poisoning studies of a liquid-solid catalytic reaction: Effects of metal content on adsorption and surface reaction rates

Individual adsorption equilibrium, adsorption rate, and surface reaction rate coefficients were determined for three supported-metal ( Pd Al 2O 3 ) catalysts of 0.050, 0.150, and 0.450 wt% palladium content. The data were obtained by a hydrogen-gas, pulse response technique in a well-mixed, three-phase slurry reactor at 25, 38, and 50 °C and atmospheric pressure. The reaction, hydrogenation of α-methyl styrene to cumene in pure methyl styrene, is first-order in H 2 and zero-order in methyl styrene. Adsorption equilibrium coefficients for hydrogen on Pd increased with Pd content. The heat of adsorption, 13.7 kJ/mole, was the same for the three catalysts. Adsorption and surface reaction rate coefficients based on mass of catalyst also increase, while those based on mass of Pd decrease with Pd content. The energy of activation increases for adsorption and decreases for the surface reaction rate as Pd content increases, but remains constant for the overall rate constant. The number of active sites on the catalyst surface for these metal loadings was estimated from experimental data of CS 2 poisoning. The number of active sites per gram of catalyst increases, and the number per gram of Pd decreases with Pd content. Adsorption equilibrium, adsorption rate, and surface reaction coefficients increase with number of active sites for unpoisoned catalyst. The results suggest that the dynamic response technique combined with poisoning studies is a useful tool in the study of heterogeneous catalysis.

MATHEMATICAL MODELING OF FISCHER- TROPSCH SLURRY BUBBLE COLUMN REACTORS

Three-phase slurry bubble column reactors are used in a wide variety of biological and chemical operations. This work is a comprehensive review of the mathematical modeling of such reactors for the Fischer-Tropsch (F-T)synthesis as applied to indirect coal liquefaction. The salient features of the F-T slurry bubble column reactors are described, and the fundamental mass transfer and kinetic rate processes that are needed to model the reactor performance are discussed. A brief description of the F-T chemistry, including principal F-T reactions, properties of commonly used F-T catalysts, and the Schulz-Flory distribution, is also given. All of the mathematical models for the F-T slurry process that have been developed to date are presented in enough detail to highlight the basic relations as well as the implicit assumptions. The refinements introduced by different workers are emphasized, as well as the numerical results obtained from these models either in the perspective of comparison with experimental data or in relation to design implications. The controversy surrounding the importance of relative mass transfer resistance in F-T slurry reactors is discussed. It is concluded that none of the available models includes enough details in relation to hydrodynamics, kinetics, and F-T chemistry to provide a reliable base for either prediction of conversion or optimum reactor design. Suggestions are given to develop such a comprehensive model, and the particular features that must be included in its formulation are elaborated.

Enhancement of gas absorption rate as a function of the particle size in slurry reactors

Exact relationships are given for the enhancement of gas absorption rate as a function of particle size in a three-phase slurry reactor. The solid-liquid mass transfer in the liquid film at the gas-liquid interface is considered as a transfer through spherical surface. The solid phase is the catalyst or reactant. The enhancement of the gas absorption rate calculated by the given equations are in very good agreement with the experimental data as a function of particle size and solid phase concentration.

Transient response of three-phase slurry reactors

Analytical time domain solutions are provided for the transient response of three-phase slurry reactors, with diffusion and first-order irreversible ch input of the reactant in the inlet gas stream; and (b) when the catalyst particles are suddenly introduced into the reactor which has otherwise reached obtained for the general case of continuous slurry reactors but can be easily reduced for application to semi-batch slurry reactors in which there is n and are expected to be useful for evaluating the rate and equilibrium constants from dynamic response experiments. Asymptotic solutions have also been obtained for the case of large Thiele parameter (φ ≥ 3) and some other simpler expressions have been derived as only for gaseous reactants of moderate or high solubility in the liquid phase and are not applicable to those with low solubility.

ChemInform Abstract: Promoting Action of Water on Slurry Phase Hydrogenation of p‐Nitrotoluene on Raney Nickel.

Enhancement in the reaction rate of hydrogenation of p-nitrotoluene on Raney nickel in a three-phase slurry reactor due to the presence of water in the reaction mixture has been observed. The promoting action was found to be dependent on the initial concentration of water, the reaction rate passed through a maximum when the initial water concentration varied from 0.0 to 10.85 (mmol cm-3). A two to three fold increase in the reaction rate dependent on the temperature has been observed at the optimum water concentration. However, at very high concentrations (above 8.0 mmol cm-3) water inhibited the hydrogenation. The reaction is not influenced significantly by the presence of p-toluidine.

Estimation of batch time of a semi-batch three-phase slurry reactor

Estimation of batch time of a semi-batch three-phase slurry reactor

Dynamics of three-phase slurry reactors

The dynamic behavior of three-phase slurry systems is presented in terms of the response characteristics of the reactor to a pulse or step input. Equations are derived for the steady-state conversion and the first moment of the response in the gas phase to pulse input of concentration. Overall irreversible and reversible first-order reactions, and adsorption-reaction processes at the catalyst surface have been considered from the viewpoint of evaluating rate coefficients from measured response data. Analysis of two-step adsorption-reaction processes is particularly interesting since dynamic data offer the possibility of separate evaluation of adsorption and surface reaction rate constants, which is not possible from steady-state measurements.

Effectiveness factors in a three-phase slurry reactor: the reduction of crotonaldehyde over a palladium catalyst

Rate measurements are described of the reduction of liquid crotonaldehyde by hydrogen in a slurry reactor using palladium deposited on the surface and a porous γ-alumina. Measurements were made at ambient pressure and temperatures between 30° and 70°C using: (a) 3 16 in. cylindrical catalyst pellets and (b) powdered pellets for which the mean particle size was 30 μ. The effectiveness factor for the commercial palladium catalyst is calculated to be ca. 0.1 with an average tortuosity factor of 1·6.