Catalysis : an Integrated Approach to Homogeneous ...

32 2 -CATALYTIC PROCESSES IN INDUSTRY
Typical process conditions are:
Temperature: 350420°C
Pressure: 40-100 bar
LHSV: 1-6 h-'
The severity of the processing conditions depends on the feed; for light petro-
leum fractions it will be milder than for heavy residues. Moreover, it is common
practice to compensate for deactivation of the catalyst by increasing the tempera-
ture of the reactor. A simplified flow scheme involving a trickle flow reactor is
shown in Fig. 2.5.
Cutulysts
M
watr
I I
high pressure low pressure
furnace reactor sepora t or stripper separator
Fig. 2.5. Simplified scheme of hydrotreatment involving a trickle flow reactor.
Catalysts are mixed metal sulphides on a carrier. The major examples are
supported mixed phases of CoS and MoS3 of NiS and MoS2 and NiS and WS2.
There is as yet no full agreement on the structure. For the first catalyst the best
description is small MoS2 clusters with CoS units at the edges. Typical dimen-
sions of these clusters are 1 nm and a stacking between 1 and 3.
Environment
From the point of view of clean technology hydrotreatment is gaining increas-
ing interest. A recent example is diesel fuel. Sulphur-containing compounds in
diesel fuel cause serious difficulties in catalytic cleaning of the exhaust gases.
Undoubtedly, in the near future, novel processes will be needed for the deep
desulphurization of diesel.