Slurry reactors mass balance

Vasco de Toledo et al. (2001) developed dynamic models for catalytic slurry reactors. Mass and energy balances, as well as an equation for a coolant fluid were proposed for the hydrogenation of o-cresol on Ni/Si02 to produce 2-methylcyclohexanol. 

The catalytic reactor is an example where reaction occurs only at the boundary with a solid phase, but, as long as the solid remains in the reactor and does not change, we did not need to write separate mass balances for the soHd phase because its residence time Tj is infinite. In a moving bed catalytic reactor or in a slurry or fluidized bed catalytic reactor... 

Note that the same mass-balance equations apply whether the reaction in the liquid phase is homogeneous or catalyzed by solid particles as in a slurry reactor. The difference between catalyzed and noncatalytic systems is accounted for in the global rate. If the reactants are introduced only in the gas phase, a mass balance is needed only for that phase. This situation exists for some slurry reactors where the liquid phase is inert and its purpose is simply to suspend the.catalyst particles. 

In the absence of any catalyst, no conversion of HEP was ever observed, up to 8 h of reaction. The trend of Chep obtained in preliminary standard runs in the presence of some of the most significant samples is shown in Fig. la, while the Yvp values obtained after 4 h of reaction are reported for all catalysts in Table 1. Protonated Y-zeolites appear as the most interesting catalysts. The trend reported in Fig. la was observed also by slurrying the same amount (2 g) of catalyst in an initially larger amount (30 g) of HEP. This allowed to close the mass balance around the reactor very near to 100%, by reducing the influence of the hold-up of the various parts of the apparatus. Under these conditions mol % selectivity to VP (Svp) was always very close to 100%, the only detectable by-product being 2-methyl-pyridine in trace amounts. After reaction every catalyst appeared pale-straw coloured, due to the presence of some organic material ( coke ). 

For the case of continuous feed of particles to a bubble column slurry reactor, with an exit age distribution of particles E(0), a mass balance gives... 

Figure 4 shows the CO conversion curves (calculated from a mass balance on the amount of carbon in CO and of all the hydrocarbons, revealed by the detector of the gas-chromatograph) vs time for two RU/AI2O3 samples (1% Ru w/w). The runs were performed at 275 C, 5 bar in a tubular continuously fed reactor, with a molar ratio H2/CO = 2. Pd/C catalysts were tested in the hydrogenation of acetophenone in ethanol at 25°C and atmospheric pressure with flowing H2 as reactant in a slurry laboratory-scale plant. The activity values were measured by the consumed hydrogen in mL-min i. 

Let us consider the mass balance of two kinds of three-phase reactors bubble columns and tube reactors with a plug flow for the gas and the liquid phases, and stirred tank reactors with complete backmixing. Modeling concepts can be implemented in most existing reactors backmixing is typical for slurry reactors, bubble columns, and stirred tank reactors, whereas plug flow models describe the conditions in a trickle bed reactor. The interface between the gas and the liquid is supposed to be surroimded by gas and liquid films. Around the catalyst particles, there also exists a liquid film. In gas and liquid films, physical diffusion, but no chemical reactions, is assumed to take place. A volume element is illustrated in Figure 6.15. 

Equation 12.3 is the mass balance of liquid reactant B, which is well-mixed. In Eq. 12.4, the inlet concentration of A in the liquid phase is zero, and therefore, the total mass of A transferred from the gas to the liquid phase should be equal to the sum of species A leaving the reactor and the amount of this species consumed by the reaction. Since the liquid phase is well-mixed, both Cal and Cbl are uniform throughout the liquid phase. Equations 12.2 through 12.4 completely describe the slurry reactor provided that the global rate is expressed in terms of bulk-liquid concentrations, i.e., Rg)a[Cal,Cbl]-... 

For the slurry reactor shown in Figure 12.2, a mass balance for the gas phase (bubbles) can be written as ... 

If the process is continuous and under plug flow, for both the gas and slurry phases, the equations derived for trickle bed reactors are applicable (see Section 3.7.2) (Hopper el al., 2001) by using the appropriate mass transfer coefficients. Note that in trickle beds, the material balances are based on the reactor volume. 

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