*5.2.1. Styrene hydrogenation*

**Figure 10** shows a scheme of the reaction of selective hydrogenation of styrene to ethylbenzene. In this reaction the hydrogenation of the aromatic nucleus is undesired.

**Figure 10.** Scheme of the reaction of selective hydrogenation of styrene to ethylbenzene.

The reaction of hydrogenation of styrene to ethyl benzene is used as a reaction test for the process of purification of some refinery hydrocarbon streams. In this reaction the interest is to hydrogenate the vynillic external C═C bond, while keeping unaltered the bonds of the aromatic ring [34, 35].

In order to determine the mass transfer limitations in the inside of the catalyst particles, the effectiveness factor (η) was used:

$$\eta = \frac{\text{real reaction rate}}{\text{unstretrected reaction rate}} \tag{1}$$

The real reaction rate corresponds to the measured rate of the reaction at the conditions of temperature and concentration of the bulk reaction medium.The unrestricted reaction rate corresponds to the ideal reaction rate of a catalyst particle with no intraparticle or fluidparticle gradients of concentration or temperature that has the temperature and concentration of the bulk fluid phase.The unrestricted reaction rate was measured by grinding the catalyst pellets to a particle size smaller than 100 μm. For this particle size and the reaction conditions used it was estimated that all mass and heat transfer gradients were negligible.

The results of styrene conversion as a function of reaction time for the pelletized and powder catalysts are shown in **Figure 11**. The catalysts prepared with the composite supports UTAl and BTAl have higher activities (higher conversion values) than the catalysts prepared with commercial supports.

**Figure 11.** Styrene conversion as a function of reaction time.Catalysts with 1% Pd. Reaction conditions: toluene solvent, *C*0 styrene = 0.445 M, 2.0 MPa H2, 353 K, *W*cat = 0.3 g (pellet) or 0.01 g (powder).

In all the tests, for all catalysts, at all reaction conditions used, the obtained values of selectivity to ethylbenzene were higher than 99%.

Initial reaction rates were calculated by calculating the conversion rate as a function of time and extrapolating to zero conversion. With the values corresponding to the pellet and powder catalyst the effectiveness fact or could thus be estimated using the following equation:

New Strategies for Obtaining Inorganic-Organic Composite Catalysts for Selective Hydrogenation http://dx.doi.org/10.5772/65959 195

$$\eta = \frac{\text{Initial reaction rate of pellets catalyst}}{\text{Initial reaction rate of powder catalyst}} = \frac{r\_{p\text{ollder}}^0}{r\_{p\text{ouder}}^0} \tag{2}$$

**Table 3** contains the values of pellet <sup>0</sup> , powder 0 , and for the different catalysts. It can be seen that the composite supports have highervalues than PdRX and PdAl catalysts. The higher effec‐ tiveness values are directly related to the lower mass transfer limitations when using the composite catalysts.

hydrogenate the vynillic external C═C bond, while keeping unaltered the bonds of the

In order to determine the mass transfer limitations in the inside of the catalyst particles, the

The real reaction rate corresponds to the measured rate of the reaction at the conditions of temperature and concentration of the bulk reaction medium.The unrestricted reaction rate corresponds to the ideal reaction rate of a catalyst particle with no intraparticle or fluidparticle gradients of concentration or temperature that has the temperature and concentration of the bulk fluid phase.The unrestricted reaction rate was measured by grinding the catalyst pellets to a particle size smaller than 100 μm. For this particle size and the reaction conditions used it

The results of styrene conversion as a function of reaction time for the pelletized and powder catalysts are shown in **Figure 11**. The catalysts prepared with the composite supports UTAl and BTAl have higher activities (higher conversion values) than the catalysts prepared with

**Figure 11.** Styrene conversion as a function of reaction time.Catalysts with 1% Pd. Reaction conditions: toluene solvent,

In all the tests, for all catalysts, at all reaction conditions used, the obtained values of selectivity

Initial reaction rates were calculated by calculating the conversion rate as a function of time and extrapolating to zero conversion. With the values corresponding to the pellet and powder catalyst the effectiveness fact or could thus be estimated using the following equa-

styrene = 0.445 M, 2.0 MPa H2, 353 K, *W*cat = 0.3 g (pellet) or 0.01 g (powder).

to ethylbenzene were higher than 99%.

= (1)

real reaction rate unrestricted reaction rate

h

194 New Advances in Hydrogenation Processes - Fundamentals and Applications

was estimated that all mass and heat transfer gradients were negligible.

aromatic ring [34, 35].

commercial supports.

*C*0

tion:

effectiveness factor (η) was used:


**Table 3.** Styrene hydrogenation initial reaction rate for catalyst pellets (*r*<sup>0</sup> pellet) and catalysts powders (r0 powder). Effectiveness factor (η) [31].

Catalysts with a metal loading lower than 0.5 Pd wt% were also tried with this reaction test. The catalysts are named 0.3PdUTAl and 0.3PdBTAl in the case of the composites (with 0.3% Pd). LD265 is a procatalyse Pd/Al2O3 catalyst (0.3% Pd) and Engelhard is a BASF Pd/Al2O3 catalyst (0.5% Pd).The results are plotted in **Figure 12**.

**Figure 12.** Styrene hydrogenation catalysts with less of 0.5 wt % of Pd. Reaction conditions: toluene solvent, *C*0 styrene = 0.445 M, 2.0 MPa H2, 353 K, *W*cat = 2 g pellet.

It can be seen that for all catalysts the pattern of conversion as a function of time are quite similar, though the catalytic activity is slightly better for the composite 0.3PdUTAl and 0.3PdBTAl catalysts.
