66
CHANG ET AL.
TABLE 2
Effect of Reactant Ratio and Temperature Upon Deactivation and Selectivity of K–ZSM-5(50)
1
Toluene
Constant b in Eq. [1] (min
)
Initial para-/ortho-chlorotoluene selectivity
concentration
3
mol cm
313 K
323 K
333 K
313 K
323 K
333 K
03
03
03
02
03
03
02
0.00868
0.00537
0.00121
1.88 10
7.44 10
3.18 10
9.82 10
8.76 10
2.73 10
5.90 10
8.99 10
3.72 10
1.4
1.4
1.5
1.4
1.3
1.5
1.4
1.2
1.3
03
02
narrow to allow additional SO2Cl2 molecules to approach temperature, or the identity of the exchange cation, but it
toluene closely enough to produce a similar effect. is significantly higher on a high-silica form of ZSM-5 than
Finally, Table 2showsthat there are some trendsin the de- on other samples of the same zeolite.
activation behavior as the composition is varied. Generally,
at each temperature the constant, b, increases as the toluene
concentration decreases (and the sulfuryl chloride concen-
tration increases). This is consistent with the idea that de-
activation is caused primarily by formation of polychlori-
nated aromatics that block the pores. As the concentration
of chlorinating agent increases and the concentration of
toluene decreases, it becomes more likely that polychlori-
nated materials will form, and thus it would be expected
that the catalysts would deactivate more rapidly.
ZSM-5 is a more promising catalyst for chlorination of
toluene than Na–X, Na–Y, or NaK-L mainly because it can
be regenerated after deactivation whereas the others can-
not. However, the reaction takes place at near-ambient con-
ditions while the regeneration requires treatment at an el-
evated temperature in air or oxygen. Furthermore, the rate
of deactivation is so high that a continuous process could
only be implemented if catalyst regeneration and recycle
were integrated into it. This kind of integration is very ele-
gantly employed in the catalytic cracking process. For chlo-
rination, the extreme differences in temperature and phase
between the reaction and the regeneration stages would
appear to make such integration practically impossible. It
might be interesting to determine whether the chlorination
process could be effected in the vapor phase, in which case
it would be easier to integrate catalyst regeneration with
the reaction process.
ACKNOWLEDGMENTS
This material is based upon work supported by the National Science
Foundation under Awards CTS-93-21392 and CTS-97-27315.
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