(457a) High Throughput Testing of Catalysts with Different Time Scales of Deactivation for Methanol-to-Hydrocarbons (MTH)

The MTH reaction has been thoroughly investigated
with current state-of-the-art catalysts based on ZSM-5 (slow deactivation) and SAPO-34
(fast deactivation) and represents a challenging application for parallel
testing of catalysts.^1,2 This challenge was met by appropriate test
protocols for both types of catalysts and an advanced analytical setup to
detect complex multi-component products in connection with a fully automated
data evaluation.

For fast deactivating catalysts such as SAPO-34,
a low severity protocol (low MeOH partial pressure, low WHSV) was developed
which allows for the formation of all secondary and tertiary stable products at
full conversion. Subsequent band aging until MeOH and DME breakthrough delivers
additional information on the behavior of catalysts at partial conversion under
kinetic control. Slow deactivation of ZSM-5 materials on the other hand
requires much higher severity (high MeOH partial pressure, high WHSV) to
observe partial conversion in a reasonable time on stream (TOS).

The common variable to compare activity,
selectivity and deactivation of both protocols is cumulative MeOH converted on
zeolite and the activity, selectivity and deactivation can be differentiated as a
function of cumulative MeOH converted on zeolite and reaction parameters
(temperature, WHSV, MeOH partial pressure). This is demonstrated in Figure 1, in which the effect of using TOS or cumulative MeOH
converted on zeolite as an x-axis is shown for the deactivation curves and
olefin yields of various zeolites and mesoporous materials (grey data points)
in the MTH reaction in comparison with state-of-the-art
catalysts SAPO-34 and ZSM-5.

Figure
1. Breakthrough curves for MTH conversion versus TOS
(top) and versus cumulated carbon on zeolite (middle). The olefin yields
versus cumulated carbon on zeolite are shown in the bottom chart. The
reference catalysts SAPO-34 (green circles) and ZSM-5 (orange squares under low
severity conditions / red diamonds under high severity conditions). Transparent
data points demonstrate how different catalysts can be differentiated by high
throughput catalyst testing.

Figure
2. Product yields in carbon percent for SAPO-34 (left) and
ZSM-5 (right) for low nad high severity conditions, respectively. From top to
bottom, the product yield is shown for different TOS events such as the initial
activity at startup (top), the maximum olefin yield (middle) shortly before
breakthrough of MEOH and after breakthrough (bottom)

While the MeOH breakthrough under low severity conditions
occurs at 13 h TOS for SAPO-34, partial conversion for ZSM-5 is not observed up
to 1900 h TOS. Utilizing high severity conditions, the breakthrough of ZSM-5
can be shifted to 75 h TOS.  In the middle and lower part of Figure 1 the conversion
and olefin yields are plotted versus cumulated carbon on zeolite, which
can be obtained by multiplication of TOS and WHSV. It can be seen that the olefin
yield under high severity conditions is in line with the low severity protocol with
the advantage of reducing the screening time from > 1900 h TOS to 75 h TOS.
Maximum olefin yield is obtained shortly before breakthrough of MeOH for both
ZSM-5 and SAPO-34. Each data point contains detailed information on PIANO
distribution based on product yields of 95 components. In Figure 2, these
product yields are shown for selected TOS events SAPO-34 under low and ZSM-5
under high severity conditions.

It can be concluded that catalysts for fast deactivating
systems such as MTH can be successfully tested in parallel fixed-bed reactors
and it will be shown that catalysts can be precisely characterized and
differentiated by activity, selectivity and deactivation.

References

1.        
C. D.
Chang, Catal. Rev.-Sci. Eng. 25 (1983) 1.

2.        
U.
Olsbye, , S. Svelle, M. Bjørgen, P. Beato, T. V. W. Janssens, F. Joensen, S.
Bordiga, K. P. Lillerud, Angew. Chem. Int. Ed. 51 (2012) 5810.