Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
73~
-1- 63293-2452
PROCESS OF THE PREPARATION OF A HYDROGEN-RICH GAS
The present invention relates to a process for the pre-
paration of a hydrogen-rich gas carried out by transforming a
carbon monoxide-containing gas with steam according -to the wa-ter-
gas shift reaction:
CO + H2O ~ 2 2
This conversion, which constitutes an important part in most of the
industrial processes for the preparation of hydrogen, is generally
effected in two steps in the presence of a catalyst. The first
conversion step, which is performed at a temperature of over
300C, is known as water-gas shift reaction at elevated temperature.
In the second conversion step, the water-gas shift reaction at low
temperature, a temperature below 300C is used. As most of the
catalysts proposed hitherto for the water-gas shift reac-tion are
only sufficiently active in a fairly limited temperature range,
it is customary to use different catalysts in each of the two
conversion steps as mentioned above.
It has now been found that certain spinels are excellent
catalysts for the water-gas shift reaction both in low and high
temperature operations.
The invention therefore relates to a process for the
preparation of a hydrogen-rich gas, which is carried out by
transforming a carbon monoxide-containing gas with steam, charact-
erized in that the reaction is performed at a temperature from
~' ~
~7~
-la- 63293-2452
175to 500C, a pressure of 10 to 100 bar, a space velocity of
1,500 to 4,500 litres of gas per hour per litre of catalyst at
normal temperature and pressure and in a molar ratio of steam in
relation to carbon monoxide of 0.5 to 50, and that the conversion
is effected in the presence of a catalyst containing a spinel
whose composition corresponds to the formula
CuxMn(l_x)FeyCr(l-y)o4 in which O < X < 1 and O< Y <2.
~.."'
oJ~
-- 2 --
The catalysts used according to the inveneion are conveniently
obtained by kneading a mixed powder of the metals~containing
constituents together with water or by precipitating the me~als-
containing constituents in the desired proportion starting from a
solucion of their salts, for preference a solution of carbonates
and/or nitrates, by drying the kneaded paste or the precipi~ate and
subsequently calcining it, for preference at a temperature from 400
to 1000 C for a period of three to 20 hours. It has moreover been
found that it is possible to stabilize the above-mentioned cata-
lysts by adding an oxide of at lea9t one alkali metal and~or ofvanadium. Catalysts containing these constituents retain their
activity longer during use, and as a result it is less frequently
n~cessary to regenerate or replace them. It is advantageous to use
catalysts containing from 0.1 to 15% by weight of ~i20, ~a20,
K20, Rb20, Cs20 and/or V205.
The abova-mentioned catalysts can be used as such:
they will be advantageously applied in the form of particles having
a length and/or a diameter of 0.2 to 0.6 mm. ~owever, it is also
possible to precipitate the catalysts an a carrier and to use them
on this carrier, after drying and calcination, for the water~gas
conversion reaction. If desired, aluminium trloxide can be used as
carrler; the quanti~y of carrier will suitably be such that it
conseitutes from 40 to 80Z by weight of the total catalyst.
The water-gas conver~ion reaction, which in principle may take
place at temperatures ranging from 175 ~o 500 C, ls generally
performed in practice in severa1 steps, for reasons of reactlon
rate and state of equilibriu~, partly above 300 C (water-gas
conversion reaction at eleva~ed temperat~re) and partly below
300 C (water-gas shift reaction at low te~pera~ure~. For
preference the reaction is performed by passing the gas to be
transformed through two or more reactors a~ a temperature ranging
from 300 to 500 C, the sald reactors containing a catalyst for
water-gas shift reaction at elavated temperature, and subsequenely
passing the mixture of partially cransformed gas through a reactor
at a temperature ranging from 175 ~o 300 C, the said r~actor
containing a catalyst for water-gas shift reaction at low
tempera~ure.
j If the water-gas shift process is applied to several
steps at different temperatures, partly above and partly below
300 C, a process according to the invention ls an~way preferred
for ~he step at low temperature. Since the catalysts used to be
used according to the in~ention generally feature a sufficient
activity and stability also above 300 C, it is advantageous to use
a catalyst according to the invention in all the steps of the
water-gas shift reaction, both above and below 300 C.
- The pressure at which the water-gas shift reaction is
perfor~ed may vary between wide limits. The reaction is for
preference performed at a pressure in the range from 10 to 100 bar
in particular from 20 to 80 bar. The quantity of steam present in
~he gas mixture subjected to the water-gas shift reaction is for
prefersnce from 0.5 to 50 moles per mole of carbon monoxide.
The rate at which ehe gas is to be eransformed is passed over
2a the catalyst may vary between wide limits, but is for preference
fro~ 1,500 to 4~500 litres of gas per hour per litre of catalyst,
at normal temperature and pressure.
As has already been m~ntioned, the preparation of hydrogen-
rich gas by conversion of a carbon monoxide-containing gas
with steam according to the water-gas shift reaction for~s an
important part of most of the industrial proc~sses for the
preparation of hydrogen. The process according to the invention is
very ser~iceable as part of such a process for the preparation of
hydrogen. The carbon monoxlde-containing gas is generally obeained
in these processes by incomplete combustion of a hydrocarbon or a
mixture of hydrocarbons with oxygen. It is preferred to add steam
as a modifler to the mixture. The incomplete combustion yields a
crude gas which comprises principally car6On monoxide and hydrogen.
:, ,
: -,
-- 4 --
The mixture of hydrocarbons used is for preference a petroleum
fraction. Petroleum fractions, both from distillation and residual,
are serviceable for this purpose. U~der certain condi~ions, coal,
for example in the form of a slurry in a hydrocarbon oil, may also
be used as feed. It is customary in most of the processes to
withdraw heat from the crude gases leaving the combustion reactor
and which are at a very elevated temperature.
This can be effected very conveniently by causing heat to be
exchanged by the gases with the water in a waste heat boiler; as a
result high-pressure steam is formed and the temperature of the
crude gas falls.
According to the starting maeerial selected and the conditions
uset in the combustion reactor, the gas thus cooled which, however,
ls still at a relatively high te~perature, can contain a
IS conslderable quantity of soot.
Because of ~he rapid clog~ing of the catalyst by the soot, the
latter has to be removed from the gas before the latter ~s
sub~ected to the water-gas catalytic shift reaction, if a
conventional reactor is used. However, since re~ently a reactor has
been available which allows the catalyeic transformatlon of gases
containing solid impurlties, such as soot, without the catalyst
becoming rapidly clogged by the solid impurities. In this reactor,
which contains hollow channels for gas in which the gas can
circulate and whose walls are gas-per~eable, the catalyst is
present behind the walls. Thi~ reactor is based on the princlple
that the constituent~ to be transformed present 1~ the gas ~pread
out f rom the gas channels, through the walls of these channels,
come into contact with the catalyst, and spread out again in the
gas channels after conversion.
The reactor described above is e~tremely serviceable if the
carbon monoxide-containing gas to be tran formed in the process
according to the invention contains soot. According eo the soot
content of the gas, some of the soot, may, if desired, be separated
from the gas in advance.
:` :
J~3~
Upon comple~ion or the water-gas conversion reaction, the
resultant hydrogen-rich gas for che preparation of pure hydrogen
mus~ be purified again. If the crude gaseous ~ixture leaving the
combustion reactor contained sulphur and/or soot, while no sulphur
and/or soot has been removed or only some of the soot has been
rPmoved before the water-gas conversion reaction, the sulphur
and/or the soot must still be removed from the hydrogen-rich gas.
The purification of the hydrogen-rich gas further comprises in
particular the removal of carboxylic anhydride ormed and of
non-transformed carbon monoxide.
The following non-limitative examples will show clearly how
the invention can be carried out.
EXAMPLE 1
~ . ~
A catalyst having a composition as defined by the formula
~CuO 5MnO 5Fel gCrO 1)4 was prepared by 8rinding 57-5 g
MnC03, 120-75 g Cu(~03)~,3H20, 175.6 g Fe203,1.4H20
(15107 g based on anhydrous Fe203) and 40.0 g
Cr(N0~)3.9H20 to obtain a powder, kneading this po~der with
66 cm water during 35 minutes and by drying the resultant paste
at 110 C for 4 hours. The mass was subsequently calcined by
gradually increasing the temperature to 300 C during about 20
hours and by keeping the temperature at 300 C during 2 hours.
By means of X-ray diffraction it has been found that the
resultant mixed oxides had assumed the crystalline shape of a
spinel.
The calcined material was screened, and the particles of a
diameter from 0.4 to 0.6 mm were used for the conversion of carbon
monoxide into hydrogen with steam.
To this end, a gas having the followlng composition, together
with steam, was passed over a bed ormed by the cataly~t par~icles:
tdJ 3 ~
% by vol.
C0 6
C2 29
H2 65
The following reaction conditions were used:
Temperature 250 C
Pressure 40 bar
Space Velocity 1,500 litres at normal temperature and
pressure/l of catalyst/h
Steam/gas
molar ratio ~V/V) 0.65
63% of the carbon monoxide present in the gas was transformed
during the process according to the following reaction:
CO + H20 ~ H2 + CO~
EXAMPLE 2
A catalyst having a composition as de~ned by the formula:
85(Cuo 5MnO 5Fel gCro 1)4 12R2-3 2 5 (P
weight) was prepared by grinding. 57.5 g MnC03, 1~0.75 g
Cu(~03)2,3H20, 175-6 g Fe203.1.4H20 (151-7 g on
anhydrous oxide basis), 40.0 g Cr(~O3)3.9H20, 48.6 g
K2C03 and 10.66 g NH4V03 and using the same procedure as in
Example 1.
~he calcined material was screened, and the partlcles of a
diameter from 0.4 to 0.6 mm were used for the conversion of carbon
monoxide into hydrogen with steam, using the same reac~ion
conditions as described in Example 1.
In ehis case, 75% of carbon monoxide present in the ga~ was
transformed durlng the process, thus showing ehe advan~ageous
effect of adding an oxide of alkalimeeal and vanadium on the
catalyst activity ~t low temperature.
3~
-- 7 --
EXAMPLE 3
In this example the catalyst described in Example 2 was used
for the conversion of carbon monoxide with steam at higher
temperature: 350 C.
S The gas composition was the same as in Example 1 and the
following reaction conditions were used:
Temperature 350 C
Pressure 40 bar
Space Velocity 1,500 lltres at normal temperature
and pressure/l of catalyst/h.
Steam/gas
molar ratio (V/V) 0.65
The activity and stability of the catalysts are shown in the
following table:
C0 conversion
at thermadynamic 68
equilibrium (%)
. . . _ . .
C0 conversion (%)
after 10 h on stream 64
50 h 62
100 h 61
150 h 59
200 h 58
As shown in the table, ~he use of a catalyst according to the
invention leads to an aetive and stable opera~ion at 350 C. about
94% of the thermodyna~ic equilibrium value for C0 converslon had
been reached, with an activlty loss with t~me on stream of about 3%
C0 conversion per 100 h.
