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The decrease in silicon utilization seems mainly related to cocatalyst composition of
the fraction: it seems that higher amount of cocatalyst in this fraction is detrimental to
the productivity of the transferred catalytic site.
Impact of cocatalyst and additive on copper transport at room temperature
In these experiments, the mixing between contact mass and fresh silicon is performed
at room temperature for 2 hours. Quantity of zinc added together with fresh silicon
was identical as in the previous experiments: Aluminium was added (as Si
2
Al
3
Fe) in
equimolar amount to Zn.
In these experiments, Al content in the two fractions was also measured.
Table 3 :
Mixing silicon and contact mass with cocatalyst under nitrogen at fixed temperature
before MCS reaction : analysis of fractions from day 1 and from day 2
Catalyst content
Cu transfer
Exp Temp Cocatalyst Si Fraction
Weight
Si consump. Cu Sn
Zn Al
Cu
(°C) added
(day)
(g)
rate (wt%) (wt%)(ppm) (ppm)(ppm) (%)
1
25°C
/
-100µm (d1)
106g
49%
3,3 170 1405 2400
1
25°C
/
+100µm (d2)
32g
36%
0,8 70
490 1950 3.0%
4
25°C
Sn/Zn -100µm (d1)
113g
46%
2,8 190 2090 1690
4
25°C
Sn/ Zn +100µm (d2)
44g
11%
0,8 210 800 1070 6.5%
7
25°C
Zn -100µm (d1)
100g
52%
3,3 210 3370 1970
7
25°C
Zn +100µm (d2)
46g
8%
0,8 140 1360 1170 5.0%
8
25°C
Al
-100µm (d1)
128g
39%
2,3 170 1390 1860
8
25°C
Al
+100µm (d2)
34g
32%
0,6 100 490 1130 2.8%
The two experiments giving the highest silicon reactivity are the one without any
addition and the one with Al addition. In both cases, a low percentage of Cu was
transferred to the fraction +100µm and the amount of tin and zinc on this fraction was
low.
Zn addition led to a high Zn concentration in both fractions, much higher than when
added together with tin. The activity for this experiment was significantly increased
and Me
2
SiCl
2
selectivity decreased.
The addition of Al does not increase the concentration of Al in either fraction,
indicating that it does not react with the surface or that it is evaporated from the
silicon. The concentration of other elements seems to decrease in the contact mass as
well. A mass balance of the different element for the 4 experiments above is given in
the table below :
134