Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~0 6Zt~
The invention relates to a process for taking out of
operation a catalyst-filled reactor for the catalytic
hydrogenation of a liquid or gaseous feed, in which
-. hydrogenation the feed i5 passed over a catalyst in the
presence of added hydrogen. In general, hydrogenations
of this type ~lill be carried out at a temperature above
; 300C. In many cases the feed will contain sulphur com-
pounds, from which H2S is formed during hydrogenation.
The above-mentioned catalytic hydrogenations often
occur in the refining of mineral oil, but are also applied
~ outside that field.
.` An example of the use of liquid feed is the catalytic
desulphurization of certain petroleum fractions, such as
a distillate fraction or a residual fraction. In this
process the feed together with hydrogen is passed through
a reactor filled with desulphurization catalyst at a temper- ~
ature at which the reed is not yeb or only slightly con- . -
verted by cracking or isomerization. Sulphur compounds
~,; pre~ent in the liquid feed are hydrogenated With the form-
: 20 ation of hydrogen sulphide. A desulphurized feed on the
one hand and a hydrogen sulphide and unused hydrogen-
1~ containing gas on the other are discharged from the re-
:~3 actor. The latter gas~ for example~ can be passed to the
:3
, Clau~ plant mentioned below.
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~06Z641
An example Or the above-mentioned catalytic hydrogen-
ation involving a gaseous feed is the catalytic reduction
of a Claus of~-gas originat,ing from a Claus plant ~or
the preparation of elemental sulphur by reaction o~
sulphur dioxide and hydrogen sulphide. Claus off-gas
still contains a percentage of unreacted sulphur compounds
which must usually be removed, which may be effected by
total reduction of the sulphur compounds with hydrogen
to hydrogen sulphide, after ~hich the hydrogen sulphide
Drmed is removed from the Claus off-gaR (for example by
; absorption) and i8 recycled to the Claus plant~ Claus
plants are not only found on refinerie8 but also in
natural gas fields, for processing the hydrogen sulphide
removed from the natural gas.
A phenomenon which almost invariably occurs during
the catalytic hydrogenation of sulphur compounds is the
deposition of carbon on the catalyst. This carbon often
originates either from hydrocarbons of the feed (for
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~ example in the desulphurization of petroleum fractions)
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or from combustion gases admixed for heating (for
3 example at the reduction of Claus off-gas). In the de- ;~
1 sulphurization of liquid products, for example, tarry
products are also deposited on the catalyst.
~i Solid particles, such as scale, silica, me~al salts
and iron particles, are usually deposited at the beginning
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062641 ~.
of the cataly~t bed, the sulphides and carbon being
present over the entire length in the catalyst bed.
In the regeneration of this catalyst the carbon
and the tarry products are burnt off, while sufficient
oxygen mixed with a large quantity of steam or nitrogen
is invariably supplied to maintain the temperature in
the reactor at an acceptable level. Temperatures applied
in practi~e often lie between 300C and 500C, since
the carbon is not burnt off below this temperature.
` 10 In this regeneration the sulphides are oxidized
simultaneously with the carbon and the tar and with a
view to the desirability of limited heat generation this
oxidation may only proceed very gradually. The regener-
ation, therefore, usually takes a very long time, with
large reactors up to some days.
In some cases, for example in the desulphurization
~l of residual petroleum fractions, the total quantity of
i~ catalyst in the reactor is very large, for example 500
tons. In these cases the quantity of catalyst on which
' 20 no solid particles have been deposited becomes, in an
;l absolute sense, very large compared with the quantity of
catalyst on which such deposition has occurred. A draw-
back is then that of the total quantity of catalyst the
metal sulphides present are oxidized in order to cause
the carbon and the tarry products to be burnt off.
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~062~4
When the reactor must be opened for some reac;on or
other, it will not be sufricient for the reactor to be
cooled and pur~ed with an inert gas~ as would be expected.
It has, in fact, ~een found that when the reactor is
5 purged with low~temperature inert gas ~or a long period
o~ tlme and subsequently opened, the catalyst begins to
glow in the open air and releases sulphur dioxide in case
sulphur compounds have been present in the feed. Under
these conditions the catalyst content consequently ha~ a
pyrophoric character, and the per~ormance o~ work on or in
the reactor is impossible or dangerous.
.i Up to now this problem has been solved by fully
regenerating the catalyst Content before opening the re-
actor. ThiS solution, howeverJ is expensive and time-
consuming and the invention aims at providing other
routes.
I For example, it has been found to occur in practice
:~:J that the reactor must be opened, while the activity of
` the catalyst has not yet decreased to such an extent
` that the catalyst requires regenerating. Another object
of the invention is to provide a process in which this
; regen~ation is not necessary in such cases and the re-
actor can nevertheless be opened.
- It has now been found that the pyrophoric character
of the catalyst is entirely removed by performing a fully
25 controlled oxidation, in which mea~ures are taken to
maintain the temperature continuously below 300C.
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Surprisingly, this "passivation" of the catalyst
takes place without the active sulphides, such as cobalt,
nickel, molybdenum and/or tungsten sulphide, being oxidized.
The passivation, therefore, takes considerably less time
5 than the regeneration customary hitherto, in which latter
treatment these sulphides are in fact oxidized.
It has further been found that also the carbon and
the tarry products are hardly if at all oxidized in the
passivation. There are distinct indications that the
catalyst derives its pyrophoric character from the
presence of finely divided iron and/or iron sulphide,
which seem to be oxidized at low temperature.
The invention, therefore, relates to a process as
stated above, in which:
a) the temperature in the reactor is reduced to below
300C in caqe it was above 300C and kept at a
temperature below 300C until the reactor has been
, opened;
;~ b) the supply of feed is discontinued and the added
j 20 hydrogen is replaced by an inert gas before, after ~ -
or during the said reduction in temperature;
c) the reactor is purged with a purge gas consisting of
1 the said inert gas for some time,
.~,
d) subsequently an oxygen-comprising gas is introduced~
25 ~ into the purge gas in such a quantity that the
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` ~062641
initial oxygen content is at most 1% by volume;
e) the oxygen content of the purge gas is increased
and the supply of purge gas is continued until
no further appreciable heat generation in the re-
actor is found to occur;
f) the oxygen partial pressure of the purge gas is
brought to at least 0.2 kg~cm2, and
g) the reactor is opened.
Because in general the temperature in the reactor
during the catalytic ~drogenation i5 above 300C, the
temperature in the reactor has to be reduced in most
cases to below 300C by cooling.
If the supply of feed is discontinued before the re-
duction of the temperature in the reactor, it is possible
to,effect the reduction of that temperature by means of
the hydrogen supplied or with the purge gas. Especially
in those cases where a heavy feed, such as a residual
petroleum fraction is used, it is advisable already to
discontinue the supply of feed at high temperature, to
prevent hardening of the feed in the reactor. -~
In the event of the feed being liquid, it is possible
and preferred to change over to another, lighter feed,
such as naphtha or gas oil, immediately before putting
the reactor out of operation and to reduce the temper-
ature in the reactor with this lighter feed. In this
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manner any rests oP residual products are removed which
may have deposited on the catalyst particles.
The catalyst is cooled more rapidly with a 1iqllid than
with a gas.
It is also possible to reduce the temperature in
the reactor during or partly during the interruption of
the supply of feed, this interruption beihg effected
gradually and therefore lasting a longer period of time.
This simultaneous cooling and interruption of the feed
occurs, for example, when hydrogen is supplied to the
reactor and subsequently the supply of feed is gradually
discontinued or when a colder feed i8 supplied than
before .
~The supply of feed may also be interrupted after the
cooling and the cooling may be at least partly effected with
the feed. In this case, o~ course, only a small part of
the feed is hydrogenated, 80 that under certain conditions
it may be advisable during cooling to use a feed which
need not be hydrogenated.
It is preferred to reduce the temperature in the re-
', actor with the aid of a hydrocarbon oil in particular with
naphtha or gas oil.
The final object is to have a reactor in which the
: j
, temperature i8 below 300C and which contains neither
feed nor hydrogen. The latter is obtained by purging the
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1062~;41
reactor wi~h an inert gas before, during or after cooling.
The said inert gas may, for example, consist of carbon
; dioxide, and is preferably nitrogen.
After substantially all the hydrocarbon and hydrogen
residues have been removed from the reactor, for example
less than 1% by volume is present by sufficient purging
with inert gas, a small quantity of air or oxygen is ad-
mitted into the purge gas. This initial quantity must
in any case be so low that less than 1% by volume o~
oxygen is present in the gas and must ~so be sufficiently
low to ensure that the temperature in the reactor does
not exceed 300C.
The passage through the reactor of the purge gas
with the low percentage of oxygen is now continued. A
quantity of oxygen is consumed which is attended by a
rise in temperature uhich, as already stated, should
always remain limited to a maximum increase to 300C.
The oxygen content of the purge gas is preferably
so controlled that the temperature of the purge gas
discharged from the reactor remains below 150C. This
temperature of the purge gas used is a reliable in-
dication of the temperature in the reactor and is easy
-~ to determine.
J According to an embodiment of the invention the
oxygen-containing purge gas is recycled after it has been
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-lo- 106Z64~
passed through the reactor, the purge ~as being cooled
and the oxygen content being supplemented. It will be
clear that this provides a saving compared with the
situation in which fresh purge gas is invariably supplied.
When the rise in temperature in the reactor begins
to decrease at the oxygen percentage in the purge gas
below 1% by volume, the oxygen content of the purge gas
is gradually raised in the range above thi~ limit o~ lS
by volume. It is then continuously ensured that the temper-
ature in the reactor does not rise above 300C.
Also, during this period in which the oxygen content
in the purge gas is higher than 1% by volume, the purge
gaæ is preferably recycled and oxygen or air is made up.
The rises in temperature will generally be lower in this
period, since the controlled oxidation is in an advanced
stage. The consumption of oxygen will also be lower.
In an embodiment o~ the invention the oxygen content
of the purge gas is increased at a predetermined rate, a
~!
~ further rise being invariably postponed, however, as long
20~ as the temperature in the reactor exceeds a predetermined
value. In this manner the pas~ivation can be performed
in a relatively simple manner from the control point
of view.
~he oxygen content o~ the recycling purge gas is
pre~erably made up to the desired value by the addition
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106Z64~
of less air ~ccording as the rise in temperature in
the reactor is higher. The oxidation is thus fully
controlled and the rise in temperature is limited to a
relatively constant value, since in the case of an ex-
; 5 cessive temperature rise the cause thereof - namely too
~ high an oxygen content - is removed and in the case of
; too low a temperature rise the insufficient oxygen
content is raised, An excessive rise in temperature
involves the disadvantage of components being oxidi~ed
in the reactor which in fact need not be oxidized and
too low a rise in temperature means that the controlled
oxidation proceeds more slowly than is strictly necessary.
~ According to the invention the oxygen partial pres-
`,~ sure is by preference ultimately maintained at at least
! 15 0.2 kg/cm2, in particular at least 0.8 kg/cm2, for some
3 time before the reactor is opened. The reactor i8, prefer-
ably, further purged for some time, while no further `
, appreciable heat generation is found to occur. Depending
on the circumstances, this may take place at an oxygen ~ ;
~ 20 partial pressure of at least 0.2 kg/cm2 or below. The
;1 latter two measures guarantee optimum safety.
It has been experienced that under certain conditions
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there is a risk for local burning off of coal, which may
lead to an uncontrolled temperature increase in the zone
~ 25 wherein the coal is burned off, and which undesired
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temperature increa~e may spread to other areas of the
catalyst. Conditions in which such a phenomenon may
occur are, e.g., the presence of large amounts of pyrophoric
compounds in the reactor, or cases in which during the
catalytic hydrogenatiOn and/or the coding of the reactor
not all sites of the catalyst have been wetted by the
cooling medium (e.g., naphtha or gas oil) and local dry
zones exist. The latter phenomenon may happen in
particular in cases in which the catalyst is polluted to
an appreciable extent, which results in a poor distribution
of the cooling agent over the catalyst.
In order to avoid any danger of uncontrolled temper-
ature increase in the reactor, it is preferred that the
reactor is purged with a hydrocarbon oil together with
the purge gas. The hydrocarbon oil is very suitably
` petroleum-based, and may, e.g., consist of naphtha, or
~ preferably of gas oil. The rate of hydrocarbon oil supplyj
to the reactor may vary between wide limits. Preferably,
the said rate amounts to at least 5% of the designed rate
of the supply to the reactor of the feed to be catalytically
hydrb~genated~ In particu]ar, the said percentage amounts to
at least 10. The rate of circulating gas oil is, prefer-
ably, increased to about the design rate during the purge
gas circulation.
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1062641
In order to obtain a complete wetting of the catalyst,
it is of advantage to fill the catalyst-containing re-
actor completely or substantially completely with a
hydrocarbon oil (in particular a gas oil) before oxygen-
~ 5 containing purge gas is supplied to the reactor. Very
-j suitably, the reactor is filled up with the hydrocarbon
~i oil from below, after the hydrogen has been substantially
removed from the reactor. After the hydrocarbon oil has
. subsequently been removed from the reactor, circulation
o~ purge gas is started. To this purge gas a circulating
hydrocarbon oil can be added immediately or after some
time. -
j It is desirable that the temperature in the reactor
should be relatively low before it is opened. This temper-
ature is preferably at most 60C. This low temperature may
, already have been reached during purging. It is also pos-
~1 sible to cool the reactor after purging. It is then
;~ ensured that maximum conversion of iron sulphide, etc.,
l can take place for as long as possible at a relatively
1 20 high temperature. In the latter case forced cooling is
, :J' ' pre~ferred, for example with air, since the reactor - if ~ ;
l left to itself - will cool of r only very slowly.
, ~
`~ The invention can, for example, be applied to a
reactor for the cataYytic desulphurization of a liquid ~ ;
hydrocarbon feed. Examples of such desulphurization
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processes are the desulphurization of light distillate
fractions of petroleum and the desulphurization of
residual petroleum fractions.
The invention may, however, also be applied to other
proces es, for example ~e catalytic reduction to hydrogen
sulphide of sulphur compounds in a gaseous feed.
In the latter case the feed may, for example consist
of the off-gas of a Claus plant Por the~reparation of
elemental sulphur from sulphur compounds-containing gases.
In the above-mentioned types of desulphurization
processes the catalyst very suitably consists of cobalt
;;~ sulphide and/or nickel sulphide combined with molybdenum
sulphide and/or tungsten sulphide, on a carrier at least
the greater part of which consists of silica and/or alumina.
Such catalysts have been found to exhibit pyrophoric
properties. It will be understood, however, that any
other type of catalyst which exhibits pyrophoric properties
can be treated according to the present invention.
The invention provides an improvement of the process
,¦ 20 for the continuous catalytic hydrogenation of one or more
I sulphur compounds in a liquid or gaseous feed with the
formation of hydrogen sulphide, in which hydrogenation
the feed is passed through a catalyst-filled reactor in
f the presence o~ added hydrogen at a temperature above
, 25 200C. The improvement consists in that by the time a
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predetermired increase in pressure drop across the re-
act~r has occurred as a r~Ult Or contamination of the
catalyst layer on the feed end of the reactor, the re-
! actor is taken out of operation by the process of one ~ ~
or more of the above embodiments of the invention, the -
contaminated catalyst layer is ~ubsequently replenished
and the reactor again put into operation. An advantage
o~ this method is that the total quantity of catalyst
need not - as hitherto - be replenished or regenerated.
,.
lC Especially in the case of a reactor for the catalytic
desulphurization of a residual petroleum fraction the
above-mentioned process of the invention has great
advantages, since in such a case very large quantities
~ ,
of catalyst are use~d. In practice a total quantity of
catalyst of about 750 m3 per reactor is currently used,
in which the steam-air regeneration often involves
difficulties owing to the fact that about 0.5-1.0 ton
of steam per ton of catalyst per hour is required for
regeneration, which often constitutes a very high peak
load for the refinery. In this connection an advantage
of the process of the invention is that the purge gas ~ `
3 can-be recycled. -
Especially in the case of liquid feed the pressure
; drop across a reactor for catalytic hydrogenation o~ten
rises owing to the deposition of scale on the first
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-16- iO6Z64~
catalyst layer. This deposit often contains a high
percentage of metals, such as metallic iron or metal
salts originating from the apparatus or feed. The de-
position of scale, however, does not imply that the
catalyst is deactivated. In the desulphurization of
liquid feeds the catalyst in a reactor for the desulphur-
ization of residual petroleum fractions is, for example,
so blocked after about half a year that the upper layer
must be replenished, whereas this period is generally much
longer for the catalyst for desulphurization of distil-
late petroleum fractions~ for example about 3 months to
about 2 years. Further, too high a pressure drop re-
peatedly occurs before the catalyst has been deactivated.
An advantage ~ the passivation according to the
present invention compared with the regeneration of the
catalyst as previously effected, is that the catalyst need
not be resulphided. In the case of the catalyst con-
taining molybdenum a further drawback of the regener-
ation is that it occurs at a much higher temperature
under oxidative conditions, so that there is a risk of
sublimation of molybdenum trioxide. In this connection
it should be noted that during the regeneration the
burning-off generally takes place at a temperature
between 370C and 470C. Further, the above-mentioned
~ 25 embodlment of the invention is also based on the fact
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that the catalyst activity has been found not to be in-
creased appreciably by the burning-off of the carbon, ~-~
provided it is present in the usuai percentages, the
latter again being present again rather rapidly after
the reactor has again been put into operation, without
affecting the activity in a high degree. For this reason
the burning-off of carbon is there~ore not strictly neces-
sary for regeneration. 1
` The above-mentioned improvement of the process ~or `
; 10 continuous catalytic hydrogenation is preferably carried
out in such a way that while the reactor is taken out of
., ,~ , :
operation the C02 content in the purge gas leaving the
reactor is controlled during the period when oxygen is .
present in the purge gas supplied to the reactor and this ;
quantity of oxygen is reduced, or brought to zero, as
long as the quantity of C02 exceeds a predetermined
~i value. As soon as the C02 ccntent becomes too high, this
~ fact in itself is already an indication of too much carbon
! being burnt off. It is preferably ensured that the C02
i 20 content remains below 0.04% by volume.
The invention will now be illustrated with reference ;~
to the following Examples.
, EXAMPLE I
` The appertaining figure is a diagrammatic represent-
ation of the course of the oxygen content of the purge gas
used in the passivation in this example.
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-18-
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In a semi-commercial plant for the catalytic de-
sulphurization of residual petroleum fractions, l470 tons
of residual petroleum fracti~S were desulphurized. The
plant consisted o~ a catalyst-filled desulphuriæation
reactor. The catalyst comprised 3.2% by weight of Co ald
9.2% by weight of Mo on a carrier mainly consisting of
alumina, which had previously been sulphided. The reactor
contained the catalyst as a fixed bed, the residual
fraction to be treated was supplied at the top of the
reactor and discharged at the bottom, in parallel flow
with hydrogen.
Immediately before the passivation according to the
invention, 3.2% by weight of Co and 9.2% by weight of Mo
were present on the catalyst. At the top ~ the reactor
the catalyst contained lO.2~ by weight of V; 4.4% by
weight of Ni; 0.7% by weight of Na and 0.40% by weight
of Fe. At the bottom Or the reactor the catalyst con-
tained 0.8% by weight of V; 0.3% by weight of Ni; 0.2%
by weight of Na and 0.04% by weight of Fe.
The reactor was now passivated, in which the reed
of the residual ~raction was first changed into gas oil
with the continuous supply of a hydrogen-rich gas mixture.
~ ~he reactor was cooled over a period of io hours. During
.!, this cooling period the ~all in temperature was con-
tinuously less than 40C/hour. The temperature of the gas
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supplie~ to the reactor was 15C and after the said
cooling tne temperature of the gas discharged from the
reactor was a~so 15C.
The gas oil feed was now discontinued and the re-
actor was purged with a hydrogen-rich gas over a period
of about 6 hours. The hydrogen was subsequently replaced
by nitrogen and the reactor was purged with nitrogen
. "
until the hydrogen concentration was below 1% by volume.
The nitrogen pressure was raised to 6 kg/cm2 and the ;
nitrogen was recycled by meanS Of a Compressor.
Subsequently air was injected into the recycling
nitrogen. The oxygen content of the purge gas supplied
-~ to the reactor was continuously recorded and is shown
in the Figure. In this Figure the time "t" has been
¦ 15 plotted in hours on the horizontal axiS and the oxygen
percentage in % by volume on the vertical axis. As is
shown, the injection of oxygen was performed dis-
~ continuously. The duration of the injections, how~ver,
?
increased continuously.
The Table shows, for the same period of time as
in the Figure, the process pressure (superatmospheric
pressure), the duration of the air injections and the
~l C2 percentage in the purge gas leaving the reactor.
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10626~1
TABLE
Time in ¦ Superatmospheric Duration of C02 percent-
minutes pressure in kg/cm2 air injection age in vol.%
in minutes
_
0 3.4 1 _
3.4 3 ~
3.8 2 0.018
4.9 5 _
120 5.4 5 o.ols
150 6.o 5 0.020
180 5~9 lo 0.025
225 5.8 12 . 0,020
285 5.5 15 0.020
330 4.7 40 0.020
450 o. 8 full air 0.030
circulation
510 _ end of pas- 0.040
sivation . . :~
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. The Figure shows that oxygen is used during pas-
sivation. The passivation process was also controlled
by continuously determining the C02 content. It is
found that a large oxygen consumption occurred between
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~06Z64~ ~
2.5 and 4 hours after the beginning of the purging. It
is noted that the C02 content increases by the injection
. . . .
of air into the purge gas owing to the C02 present in ;~
this air.
The temperature of the purge gas wa~ continuously
- 15C at the moment it left the reactor. The passivation
process ac~ording to the present Example has, therefore,
been carried out very cautiously.
After purging for 7.5 hours by means of oxygen-con-
taining nitrogen with increasing oxygen content, the
; passivation process was completed with forced-air
circulation ~rough the reactor for 30 minutes, after
which the reaotor was opened. The catalyst then had no
more pyrophoric properties.
Analysis of the catalyst subsequently revealed that,
dependent on the place of origin in the reactor, about
7-15% by weight of carbon and about 7-8% by weight of
j sulphur w~epresent.
EXAMPLE II
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l 20 In the semi-commercial plant described in Example I
.. i .
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sulphurized. The catalyst was polluted to an appreciable-
~ extent, and contained much pyrophoric material.
i The reactor was cooled to 40C, the hydrogen was
....
replaced by nitrogen and the pressure of nitrogen increased
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to 6 kg/cm2, oxygen was supplied to the purge gas and
the oxygen content of the purge gas was gradually in-
creased as described in Example I.
The temperature wa~ measured at 3everal sites in the
reactor and the C02 content of the off-gas was measured
periodically. A~ter about 20 hours (at an oxygen con-
centration in the purge ga~ of about 18% by volume) the
amount of C02 in the off-gas increased drastically (from
0.0~ to 0.3% by volume) and in the end part of the re-
actor a rapid temperature increase was ~asured (~rom
the original 40-50C to 100C). Subsequently, the re-
actor was opened and the catalyst was discharged. The
, catalyst originating from the end part of the catalyst
,, was hot and gas oil vapour and S02 were emerged therefrom.
;l 15 Although the catalyst was not pyrophoric, it will be
clear that the risk exists that at further temperature
~ increase uncontrolled burning-off of coal may occur.
; This risk i~ avoided when taking the reactor out of
~, operation according to Example III.
,,!, 20 EXAMPLE III
A catalyst which had been used for the catalytic de- ~
sulphurization of about the same amount of residual ;~ -
, petroleum fract~ns as described in Example II, was cooled
', and the amount of hydrogen in the reactor was reduced
to lg by volume with the aid of nitrogen as a pur~e gas
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1~6264~
as described in Example II, The reactor was evacuated,
and gas oil was pumped into the reactor from below
until the total catalyst content of the reactor was
completely submerged. Subsequently, the gas oil wa~
removed ~rom the reactor, and nitrogen was supplied to
a presQure of 6 kg/ cm2 . The nitrogen was circulated
~- ~nd simultaneously an amount of gas oil (10% of the
. amount for which the installation was designed) was
- circulated. Then 1% by ~olume of oxygen was added to the
purge ~as. After one hour the circulation of nitrogen
+ oxygen was stopped and circulation of air at 6 kg/cm2
.,.~
was commenced. The gas oil circulation was gradualIy
increased to about the design rate. After three hours
of air and gas oil circulation, during which time no
trace of temperature increase or undesired oxidation
of coal had been experienced, the reactor was opened.
The catalyst proved to be not pyrophoric.
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