Trickle-bed reactor performance

Industrial gas-liquid hydrogenation reactions are carried out in slurry and trickle-bed reactors (Ref. 3). Modeling of the latter has been advanced significantly in the last two decades (Refs. 4-6). Predictions of trickle-bed reactors performance were in good agreement with experimental data (Ref.7). 

T. Tsukamoto, S. Morita, and J. Okada, Oxidation of D-glucose on immobilized glucose oxidase trickle-bed reactor performance, Chem. Pharm. Bull., 31 (1983) 3785-3795. 

An appropriate model for trickle-bed reactor performance for the case of a gas-phase, rate limiting reactant is developed. The use of the model for predictive calculations requires the knowledge of liquid-solid contacting efficiency, gas-liquid-solid mass transfer coefficients, rate constants and effectiveness factors of completely wetted catalysts, all of which are obtained by independent experiments. 

The above issues associated with prediction of trickle-bed reactor performance has motivated a number of researchers over the past two decades to perform laboratory-scale studies using a particular model-reaction system. These are listed in Table I. Although a more detailed summary is given elsewhere (29), a general conclusion seems to be that both incomplete catalyst wetting and mass transfer limitations are significant factors which affect trickle-bed reactor performance. 

A few reactor models have recently been proposed (30-31) for prediction of integral trickle-bed reactor performance when the gaseous reactant is limiting. Common features or assumptions include i) gas-to-liquid and liquid-to-solid external mass transfer resistances are present, ii) internal particle diffusion resistance is present, iii) catalyst particles are completely externally and internally wetted, iv) gas solubility can be described by Henry s law, v) isothermal operation, vi) the axial-dispersion model can be used to describe deviations from plug-flow, and vii) the intrinsic reaction kinetics exhibit first-order behavior. A few others have used similar assumptions except were developed for nonlinear kinetics (27—28). Only in a couple of instances (7,13, 29) was incomplete external catalyst wetting accounted for. 

The above discussion on previous experimental studies in trickle-bed reactors suggests that both liquid-solid contacting and mass transfer limitations play a role in affecting trickle-bed reactor performance. Except for a few isolated cases, the reactor models proposed in the literature for gaseous reactant limiting reactions have not incorporated particle-scale incomplete contacting as paft of their development. For cases where it was used, this parameter served as an adjustable constant to match the observed conversion versus liquid mass velocity data so that the true predictive ability of the model... 

If one has intrinsic and apparent reaction kinetics available, then Equation 10 may be viewed as a three-parameter model (t)ce, b wo> B -d f°r prediction of isothermal trickle-bed reactor performance. However, Biwo depends on two mass transfer coefficients and a priori model parameter evaluation is no simpler than before. 

In addition to the flow regimes characteristic of trickle-bed reactors, there are also the usual controlling regimes, as described previously for MASRs. We summarize in Table 17.7 the effects of different variables on trickle-bed reactor performance in these regimes. 

Gas-liquid-solid reactors with a trickle-flow regime are the most widely used type of three-phase reactors and are usually operated under steady-state conditions. The behavior of this kind of reactor under the other three-phase fixed-bed reactors is rather complex due to gas and liquid flow concurrently downward through a catalyst packing. For process intensification it is required to improve some of the specific process steps in such chemical reactors. Figure 4.1 shows an overview of different factors that influenced the trickle-bed reactor performance. 

Figure 4.1 Influence factors on the trickle-bed reactor performance.

The experimental and simulation results of Liu et al. [16] showed also for a complex reaction system (2-ethylanthrahydroquione-hydrogenation) an improved trickle-bed reactor performance under unsteady-state-operation conditions. The selectivity of the consecutive reaction was increased up to 12% in comparison to steady-state conditions. 

The main conclusion of the Iliuta et al. [120] simulation results resides in the fact that the fine particle deposition process does not change appreciably the trickle-bed reactor performance, so the unique undesirable consequences of the fine particle deposition process reflects in an almost exclusive hydraulic effect of bed clogging. 

Goto S, Smith JM. Trickle bed reactor performance. AIChE J. 1975 21 706. 

Goto, S. and J. M. Smith. Trickle-Bed Reactor Performance. Part 2. Reaction Studies. AICHE Journal 21 (1975) 714-720. Goto, S. and J. M. Smith. Performance of Slurry and Trickle-Bed Reactors Application to Sulfur Dioxide Removal. AICHE J. (1978) 286-293. 

Tsukamoto, T., S. Morita and J. Okada. Oxidation of Glucose on Immobilized Glucose Oxidase Trickle-Bed Reactor Performance. (1983). 

The trickle-bed reactor performances can be expressed in terms of mass transfers between F, C and S zones, in the gaseous and liquid phases, as shown on Figure 4. In the liquid phase the mass transfer limitations arise from the hydrogen absorption into F and S zones ( g) and from its transport between these zones ( l). In the gaseous phase the transfer limitations arise from the ketone vaporization on the F and S zones ( r), from its transport ( q) and its condensation onto the C zones... 

Goto, S., Smith, J.M. 1975. Trickle-bed reactor performance. Part I. Holdup and mass transfer effects. A/C/t 7. 21(4) 706-713. 

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