固定床反应器中催化剂孔结构英文文献和中文翻译(7)

Fig. 3. Predicted velocity ﬁeld (left), temperature proﬁle (right) of the reference case.

Fig. 4. Predicted concentration proﬁle for C4H10 (left) and C4H2O3 (right) of the reference case.

304 Y. Dong et al. / Chemical Engineering Science 142 (2016) 299–309

Position 1

Position 2

Position 3

Dimensionless pellet coordinate 

Position 4

Position 5

Fig. 5. Concentration proﬁles of C4H10 (left top), C4H2O3 (right top), CO2 (left bottom) and temperature proﬁle (right bottom) inside the pellet at ﬁve sampling positions in the reactor. Position 1: r ¼ 0 m, z ¼ 0.1 m; Position 2: r ¼ 0 m, z ¼ 0.25 m; Position 3: r ¼ 0 m, z ¼ 0.4 m; Position 4: r ¼ 5:25 · 10 — 3 m, z ¼ 0.1 m; Position 5: r ¼ 10:5 · 10— 3 m, z ¼ 0.1 m.

the progress of reaction, the concentration gradient is ﬂattened as expected. The ﬂattened proﬁles along the reactor are a sign for the decreasing reaction rates along the bed due to lower concentration of the reactants and decreasing temperature along the bed.

If the entire reactor for n-butane oxidation is packed with the same catalyst material, one can image that the catalysts in the lower part of the bed are not used as efﬁciently as at the bed inlet (Triﬁrò and Grasselli, 2014). From an economic point of view, a more structured catalyst packing where catalysts with different kinetics are packed at different sections of the reactor may be a good approach (Guettel and Turek, 2010). Positions 1, 4, and 5 are taken from the same axial coordinate but different radial coordi- nate. One can observe rather different concentration proﬁles

inside the pellet. Position 1 is almost in the hot-spot region as one

can see in the temperature plot and that may explain the higher concentration gradient with higher reaction rates. Figs. 4 and 5 show that the catalyst pellet located in different sections of the reactor may experience different conditions (concentration of the reactants and temperature). It is possible that these catalysts are chemically different from each other especially on the surface in

Fig. 6. Effect of the macro-pore porosity εM on the simulated ﬁxed-bed reactor performance for n-butane oxidation.

outlet of the ﬁxed-bed. These were calculated as integral average at the outlet:

N — N

accordance to the exposed conditions. In future work, incorpora-

tion of the surface dynamics in the model can be an insightful reﬁnement of the model.

3.2. Effect of pore structure parameters

In total, there are four pore structure parameters in the model of Wakao and Smith (1962) which can be varied or optimized. In the presented study, only three parameters were studied since the total porosity of the catalyst pellet was kept ﬁxed to 0.5. By ﬁxing the total porosity, the pellet density and bed density were kept unchanged with varying distribution of the macro and micro pores porosity in the pellets. The following question is addressed in this work: which pore structure of the catalyst pellet is more efﬁcient for a given mass of active catalyst and ﬁxed pellet shape. All simulations were carried out at the same operational conditions as for the reference case.

Firstly, the macro-pore porosity εM was varied from 0 to 固定床反应器中催化剂孔结构英文文献和中文翻译(7):http://www.youerw.com/fanyi/lunwen_78853.html