Chemistry Reference
In-Depth Information
All of the above processes are carried out mainly in
the liquid phase. However, processes now have been
commercialised for phenol hydroxylation [8] and
caprolactam manufacture (via ammonia oxidation
to hydroxylamine) [9] using H
2
O
2
with a heteroge-
neous catalyst—the Ti-substituted zeolite TS-1. This
has been disclosed [10] as an effective catalyst for
epoxidation, raising the possibilities of large-scale
use in the manufacture of epichlorhydrin and propy-
lene oxide, neither of which currently is manufac-
tured using H
2
O
2
. What is of more fundamental
significance is that the technology for large-scale use
of H
2
O
2
in the liquid phase with a heterogeneous
catalyst is now available, paving the way for many
future developments of this nature.
Processes using H
2
O
2
with a homogeneous cata-
lyst, often in two-phase liquid systems with a phase-
transfer agent, have been commercialised but on a
smaller scale. In these cases too, the attributes of
H
2
O
2
as a waste-avoiding reagent have been demon-
strated in practice.
2500
2000
1500
1000
500
0
1985
1990
1995
2000
Year
Fig. 11.1
Global production of hydrogen peroxide.
100
Other
Environment
Textiles
Chemicals
Pulp & Paper
80
60
40
20
0
1987
1990
1992
1998
Year
Fig. 11.2
Breakdown of hydrogen peroxide usage by
application.
Recent trends in H
2
O
2
application
[11a]
Global production of H
2
O
2
now is probably over 2
million tonnes, of which about 75% is made in North
America, Western Europe and Japan. Fig. 11.1 shows
the rapid rise in production since the late 1980s,
roughly doubling inside 10 years.
By far the major driving force has been the growth
in its use for pulp and paper processing. It is used
both to bleach and to delignify wood fibres and
is applied to mechanical, chemical and recycled
pulps. A number of factors have contributed to this
growth. Development of the technology has been
driven by the desire to move away from elemental
chlorine—traditionally used in the industry—
for environmental reasons. This has been accompa-
nied by big improvements in the performance of
H
2
O
2
, owing to better understanding and control of
the role of metals and chelating agents (both natural
and artificial) in the processes, and by improvements
in the use of oxygen for primary 'cooking' of the
pulp.
To show the effect of the pulp and paper usage
on overall H
2
O
2
consumption, Fig. 11.2 gives a
breakdown of the percentage of H
2
O
2
devoted to the
main application areas. Production devoted to persalt
manufacture for laundry use is conventionally
omitted from this breakdown—it is of similar size to
the chemicals application. During the period 1990-
1998, usage in chemicals grew by 16% and in envi-
ronmental applications by 63%, but such was the
dominance of pulp and paper (which more than
doubled in the same period) that the contribution of
both of these important uses actually fell in percent-
age terms.
The rapidly growing pulp and paper application
has changed the face of the H
2
O
2
market, causing a
sharp reduction in prices and a move towards com-
modity character. Manufacturers, although continu-
ing to give advice on safe handling and use, can no
longer afford to maintain the previous high levels
of R&D applications, and the onus for process dis-
covery and development has passed to the user.
However, one beneficial effect of this price reduction
has been to bring H
2
O
2
in range for a series of appli-
cations for which it was ruled out previously on eco-
nomic grounds. This has, in fact, given new impetus
to the development of new technology for chemical
synthesis and environmental uses, which should
lead to an increased growth rate in the chemicals
area and sustained progress in the environment in
years to come.
