Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR CATALYST REGENERATION
This invention relates to a process for regenerating
used hydroprocessing catalysts having contaminants
comprising carbonaceous and/or sulfur-containing
materials deposited on their surface.
A number of catalytic processes are used in the
petroleum and petrochemical industries for purposes of
treating and converting process streams into a variety of
useful products. Among the refining processes utilizing
catalysts are cracking, hydrocracking, hydrodesul-
furization, hydrodenitrification and reforming. The
catalysts used in these processes decline in activity
and/or selectivity during the course of use as a result,
in major part, of an accumulation of carbonaceous
materials commonly containing hydrogen and sulfur on the
surface of the catalyst.
Catalysts deactivated by carbonaceous materials
deposition can be regenerated by in-situ carbon burn-off
in a controlled oxidative atmosphere in a fixed bed
apparatus or a fluidized bed apparatus. For example,
U.S. Patent No. 4,007,131, discusses a process for
regenerating catalyst from hydroprocessing operations by
passing hot inert gas containing 0.1-4.0 % volume oxygen
through the catalyst while in-situ in the reactor. Such
in-situ regeneration, however, requires shutdown of the
reactor for the time period needed to perform the
regeneration, which may require many days. In addition,
some channelling of the hot gas flow in the catalyst bed
usually occurs and results in undesired variation in the
degree of regeneration obtained. Thus, more effective
external catalyst regeneration processes not involving
extensive reactor downtime have been sought. However,
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available external type commercial catalyst regeneration
processes have not been entirely satisfactory due to lack
of total-control over gas temperatures, oxidative
atn:iospheres and physical breakage. Catalysts regenerated
by these processes often_have incomplete recovery of
sur.face area and pore volume, a high content of residual
sulphur_and carbon,__ and'-substantial---fgnes--losses-. - 'Fhis----
situation arises because heat is necessary to remove
--- coritaminants, yet-excessive heat - causes --co~]:apse--of-p
structure, loss of surface area and agglomeration of
- meta}.s e-Release-- of contaminants--from deep in tfie-
6s _ ~ _- - -- ._ . - -_ - -. -
catalyst pores often requires a long "heat soak" period
in order to achieve high removals. Accomplishing the
conflicting objectives of surface area retention, which
suggests controlled heat for a short time, and complete
rentoval of carbon _ which auQQPr.ita 1- c~ncsar hPat i nrr t-; .,,A~
------ - --- -- --------. -------- --~~---- -a-- -__...,..,. _~
..........,..,.,.
has long been an elusive goal. Thus, it would be
advarr~a~t5t~~t~~iave a ca a ys regeneration process
whereby the recovery of catalytic and physical properties
as well as the levels of contaminant removal are
enhanced.
US-A 4,621,069 discloses the continuous regeneration
of used catalyst containing carbon and sulphur in a.
multiple stage process. The first preparatory stage
consists of stripping the particulate catalyst with hot
inert.gas for 1-2 hours to evaporate low boiling liquid
con:iponents and the second through the fourth substantive
stages consist of burning the oil-free catalyst with (per
stage) increasing concentrations of oxygen at increasing
temperatures and for an increasing duration of time (i.e.
4-6 hours, 4-6 hours and 6-10 hours respectively). The
stripping stage may be conducted in a fluidised bed, and
---tht-_-btxrnsng- stages--may- 33e--corrd'txct-L-cr-iYr" a movtng
e .
US-A-3,647,714 discloses a process for.reducing the
carbon content of spent silica-alumina or zeolite
AMENDED SHEET
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--2a -
catalyst from at least 0.5 wtt to less than 0.25 wtk by
burning in a catalyst regenerator chamber, whereby the
residence time of the catalyst in the regenerator chamber
is reduced to not more than 15 minutes by keeping the
temperature in the regenerator chamber at at least 660 C
(1220 F) and by introducing 10 to 100 percent of the
combustion air to the transfer line leading the catalyst
to be regenerated into the regenerator chamber, wherein
the velocity in the transfer line reaches 6.10 to 18.29 cn
(20 to 60 feet) per second. The catalyst is fluidised in
the transfer line as well as in the regeneration chamber.
WO-A-9201511 discloses-a process for regenerating
spent fluidised bed cracking catalyst in a fluidised
catalytic cracking--regenerator with a C combustion
promoter [such as Pt], -characterised by regenerating the
spent catalyst in at least-two stages under controlled
conditions, whereby hot regenerated catalyst containing
the CO combustion promoter is recycled from the second
stage to the first stage and at least 90t CO combustion
is maintained in both stages. - None of the above documerits addresses the
problem of
preserving the physicaI{properti.es of the spent catalysts
during their regeizeration.
It has now been found that a process for regenerating
catalysts which comprises subjecting a spent catalyst to
a. fluidized bed treatment_step f -o-llowed by a moving belt
treatment sten results in a reQenerated catalvst from
which the contaminants havebeen removed and the physical
properties of the catalyst have been substantially
recovered and/or enhanced.
The present invention, accordingly, relates to a
process for regenerating used catalyst particles
contaminated with carbonaceous and/or sulphur-containing
materials, which process comprises the steps of:
AMENIDEC SHEE~g
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a) contacting said particles in a fluidised bed with an
oxygen-containing gas at a temperature in the range of
from 204 C (400 F) to 593 C (1100 F) and for a time
which does not exceed 20 minutes wherein at least part of
the contaminants is removed; and
b) passing the thus treated catalyst particles to a
moving belt and causing the belt to move said catalyst
particles through a furnace zone which is maintained at
a temperature in the range of from 371 C (700 F) to
593 C (1100 F) for at least two hours, wherein the
remaining portion of the contaminants is removed.
The present process provides a process in which a
used hydroprocessing catalyst deactivated by
contamination with carbonaceous materials and sulphur-
containing compounds, normally by deposition of such
contaminants on the surface of the catalyst particles or
by plugging of the catalyst pores by such contaminants,
is regenerated by a two step process. The first step of
the regeneration process is a fluidized bed treatment,
and the second step is a moving belt treatment. A
combination of these steps results in regenerated
catalysts which show low attrition, i.e., little or no
reduction in size of the particles. In some cases,
enhanced surface areas can also be seen. In addition, in
the process of the present invention, the throughput may
be doubled and the end result is a much more optimal
regeneration process.
The regeneration process of the present invention is
particularly suitable for regenerating hydroprocessing
catalysts, especially hydrotreating catalysts. These
catalysts typically comprise Group VIB, VIIB, VIII
metals, or mixtures of two or more of these metals
supported on various supports such as, for example,
alumina, silica, silica-alumina, aluminosilicates,
MCS13/TH636PCT
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zeolites, and the like. The catalysts typically have a
cylindrical, spherical or multi-lobe shape, a diameter
ranging from 0.50 millimeters to 3.5 milli-meters, and a
length between 1.5 millimeters and 6.5 millimeters. 5 The first step of the
regeneration process of the
present invention is a fluidized bed treatment. Briefly,
a fluidized bed consists of a mass of particles.contained
in a chamber through which a gas is passed. The
particles are typically heated and if the velocity of the
gas entering the chamber is properly adjusted, the
particles separate and move about in a random manner such
that the entire bed behaves like a liquid.
In the present invention, the spent catalyst is
placed in a fluidized bed apparatus or chamber of any
suitable construction and is supported on a bottom plate
or other suitable device having a plurality of ports
designed to permit flow of an oxygen-containing gas
upwardly and to prevent the catalyst partieles from
moving downwardly such that the flow of gas would be
restricted. The oxygen-containing gas is normally
introduced into the chamber prior to the introduction of
material to be treated. The oxygen content of the gas
can vary in the range of from 4 percent by volume to
100 percent by volume. Preferably, the oxygen component
of the gas stream is from 4 to 30 percent by volume, and
more preferably from 15 to 22 percent by volume. A
convenient gas stream is atmospheric air, although pure
oxygen may also be utilized. After the oxygen-containing
gas is passed upwardly through the ports into the chamber
and contacted with the spent catalyst particles, the
exhaust gas exits the chamber and suitably is subjected
to a further treatment, such as, for example, it may be
passed to equipment downstream for discharge by
procedures well known in the art.
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The velocity of the gas stream must be sufficiently
high for the catalyst particles to remain in fluidized
state in the chamber. The minimum velocity is that
needed to overcome the gravitational pull on the catalyst
particles. The velocity may not be so high that catalyst
particles are transported out of the chamber. The
oxygen-containing gas is preferably introduced.into the
chamber at a superficial velocity in the range of from
12.2 meters per minute (m/min) (40 feet per minute
(ft/min)) to 488 m/min (1600 ft/min).
Generally, the oxygen-containing gas is introduced
into the chamber at a temperature sufficient to initiate
the desired reaction in the column, and is desirable that
the temperature of the gas stream in the chamber be
maintained constant at the temperature it was introduced.
Therefore, the temperature of the gas at the inlet is
adjusted so that the temperature of the chamber is
maintained at the desired temperature, i.e:, a
temperature in the range of from 204 C (400 F) to
593 C (1100 F) , preferably from 399 C (750 F) to
538 C (1000 F). The pressure in the chamber is
typically atmospheric pressure.
After the gaseous atmosphere has been established at
the desired temperature and velocity, the spent catalyst
materials are added to the chamber. The residence time
of the catalyst particles in the fluidized bed apparatus
or chamber is suitably from 1 minute to 20 minutes,
preferably from 5 minutes to 15 minutes. These residence
times at the temperatures specified above suitably result
in the removal from the spent catalyst of at least
50 percent by weight of the sulfur contaminants. The
first step, i.e., the fluidized bed step, of the
regeneration process also suitably results in the removal
of from 5 percent by weight to 40 percent by weight of
the carbon contaminants and from 25 percent by weight to
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50 percent by weight of the total volatilities present on
the spent catalyst. Preferably, at least 55 percent by
weight of the sulfur contaminants, and from 10 percent by
weight to 25 percent by weight of the carbon
contaminants, and from 30 percent by weight to 40 percent
by weight of the total volatilities present on the spent
catalyst are removed during the fluidized bed treatment.
As one skilled in the art would readily recognize, the
above-described fluidized bed treatment is quite
effective for removing contaminants from used or spent
catalysts, but the constant agitation is quite abrasive
and thus detrimental to the integrity of the catalysts.
Thus, if the catalysts are subjected to such a treatment
for prolonged periods of time, attrition becomes a
significant problem. For this reason, the present
invention is a process in which the most volatile portion
of the contaminants are removed in a first step to
control the exotherm, i.e., a fluidized bed treatment,
and the remainder of the contaminants are removed in a
second step, i.e., a moving belt treatment, in which
there is a minimal amount of catalyst particle motion.
Following the fluidized bed treatment, the spent or
used catalyst is subjected to a moving belt treatment.
In this second step of the regeneration process of the
present invention, catalyst particles are withdrawn from
the fluidized bed apparatus or chamber and transferred to
a continuous belt driven by mechanical means such as, for
example, a motor and which moves through a furnace zone.
The furnace zone may comprise a single furnace com-
prising one or more heating zones, but may also comprise
two or more distinct furnaces as will be discussed in
more detail hereinafter. The belt is advantageously
constructed of wire mesh, suitably made of stainless
steel, but any other known material capable of being used
as a moving belt resistant to high temperatures could
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also be used. The belt moves in a horizontal direction
through a furnace zone such that the catalyst particles
are subjected to only a minimal amount of agitation. The
catalyst particles will normally be placed onto the belt
in the form of a layer or bed, although this is not
strictly required. Such bed suitably has a thickness of
0.64 cm (14 of an inch) to 6.4 cm (2&1 inches), preferably
from 1.9 cm (3/4 inch) to 3.8 (11,~ inches). As the bed
containing the catalyst particles is in motion through
the furnace zone, hot air, either in the presence or
absence of combustion gases is passed through the wire
mesh belt. The direction of the air flow may be upwardly
or downwardly, as desired, but must flow through the
moving belt containing the catalyst particles. The
temperature of the air flowing upwardly or downwardly
through the moving belt and contacting the catalyst
particles should be sufficiently high to achieve the
removal of the remaining portion of the contaminants
still present on the catalyst particles. It has been
found particularly advantageous to increase the
temperature as the particles move through the furnace.
Very good results are obtained when the temperature of
the oxygen-containing gas used -suitably air- increases
over a range within the range from about 370 C (700 F)
to about 595 C (1100 F) as the catalyst particles
continue on the belt. Accordingly, the temperature in
the furnace is suitably maintained in the range of from
371 C (700 F) to 593 C (1100 F) and preferably from
371 C (700 F) to 510 C (950 F) . The time required for
the moving belt treatment and the removal of the
remainder of the carbon and sulfur contaminants suitably
is at least two hours, and is generally from four hours
to eight hours.
In one embodiment of the present invention, the
catalyst particles are passed through a furnace zone
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consisting of a series of zones where the temperatures
are controlled in each zone, suitably in such way that
the temperature increases in each successive zone. In
this embodiment, the zones are distinguished by physical
separation means, so basically the furnace consists of a
number of smaller furnace zones. The number of zones
will normally be less than 8, and suitably is in the
range from 3 to 8. However, the number of zones utilized
is not critical. In this embodiment, the catalyst
residence time in each zone is maintained at the desired
time by controlling the belt speed. Initially, the
temperature of the oxygen-containing gas in the first
zone is 371 C (700 F) to 482 C (900 F) , preferably
from 412 C (775 F) to 468 C (875 F) . Following a
residence time in each zone of 0.5 hours to 2 hours, the
catalyst particles are passed to additional zones in
which the temperature of the oxygen-containing gas is
increased to 427 C (800 F) to 593 C (1100 F) ,
preferably from 432 C (810 F) to 510 C (950 F) . The
total residence time for the moving belt treatment is
suitably again in the range of from two hours to eight
hours, although longer residence times may be utilized,
if desired. The regenerated catalyst is then withdrawn
from the moving belt and passed to a cooling step before
packaging and return of the catalyst for reuse.
The regeneration process of the present invention is
particularly advantageous from an economic standpoint for
continuous operations in that the throughput can be
significantly increased.
The process of this invention will be further
described by the following embodiments which are provided
for illustration and are not to be construed as limiting
the invention.
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The following Example and Comparative Examples
utilized spent/used catalysts having the following
characteristics:
Catalyst Composition Ni/Mo on
A1203
Carbon, %wt. 10.3
Sulfur, %wt. 6.4
Surface area, m2/g.(1) 230
Attrition Index(2) 53.4
(1) Surface area is determined by the B.E.T. method for
determining specific surface area as described in
Brunauer, S., Emmet, P. Y. and Teller, E., J. Am. Chem.
Soc., 60, 309-316 (1938).
(2) Attrition index is defined as the number percent of
particles which are less than the averaged length of 2.5
millimeters.
Example 1
Spent catalysts having the above characteristics were
regenerated using the process of the present invention.
The conditions used were as follows:
The gas atmosphere, i.e., air containing 21 volume
percent of oxygen, was entered into a fluidized bed
chamber, i.e. pretreater, at a superficial velocity of
131 m/min (430 ft/min) and an initial temperature of
510 C (950 F). The fluidized bed chamber had a
staggered, perforated type of distributor plate at the
bottom, a reaction zone having a 45.7 cm (18 inch)
diameter and a height of 160 cm (5 feet, three inches), a
.
transition zone of conical shape having 45 included
/ angles and having a height of 28.6 cm (11.25 inches), and
a disengagement zone having a diameter of 91 cm
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(36 inches) and a height of 91 cm (3 feet). There was a
cyclone downstream and a wet scrubber for collecting fine
catalyst particles entrained from the fluidized bed
chamber and for removing the sulfur dioxide produced in
the pretreater.
The spent catalysts, having a trilobe shape averaging
0.13 cm (1/20 inch) in diameter and 2.5 millimeters (mm)
in length, were fed continuously from a 7.6 cm (three
inch) pipe on one side of the disengagement section. The
partially regenerated catalysts were discharged
continuously from a 15.2 cm (six inch) pipe on the
opposite side of the reaction zone. The catalyst
discharge rate was controlled by means of a flapper
valve, while the spent catalyst feed rate was controlled
using a vibrator connected to a hopper. The bed height
of the catalyst in the pretreater was maintained at about
15 cm (six inches).
Initially, 19.5 kg (43 pounds) of regenerated
catalysts were charged to the pretreater for facilitating
control of the initial reactor temperature. In order to
achieve a steady state, prior to the fluidized bed
treatment step, the spent catalyst feed rate and the
discharge rate were set at 1.0 kg/min (2.2 lb/min). The
inlet air temperature was then gradually decreased
from 510 C (950 F) to 466 C (870 F) after 20 minutes
of start-up. The feed and discharge rate were then reset
to about 2.0 kg/min (4.3 lb/min) (10 minute residence
time) and the inlet air temperature was gradually reduced
to 293 C (560 F). One drum of partially regenerated
catalysts was collected at 60 minutes after the start-up.
The feed and the discharge rate were then further
increased to 2.5 kg/min (5.5 lb/min) (7.8 minute
residence time), and the inlet air temperature was
maintained at 293 C (560 F). Another drum of the
partially regenerated catalysts was collected at
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120 minutes after the start-up. The catalyst temperature
inside the fluidized bed pretreater fluctuated from
393 C (740 F) to 416 C (780 F) when both drums of
catalysts were collected. For the first drum, the sulfur
content from this step was 2.6 wt%, i.e., 59 wt% of the
sulfur contaminants had been removed, and the carbon
content was 8.6 wt%, i.e., 16.5 wt% of the carbon
contaminants had been removed. For the second drum, the
sulfur content was 2.7 wt%, i.e., 58 wt% of the sulfur
contaminants had been removed, and the carbon content was
8.6 wt% i.e., 16.5 wt% of the carbon contaminants had
been removed.
The drums of partially regenerated catalysts frcm the
pretreater were then sent to the moving belt for the
second step of the regeneration process. The catalyst
passed through Zone 1 which had a temperature ranging
from 432 C (810 F) to 443 C (830 F) , Zone 2 which had
a temperature ranging from 382 C (720 F) to 438 C
(820 F), Zone 3 which had a temperature ranging from
432 C (810 F) to 454 C (850 F) , and Zone 4 which had a
temperature ranging from 432 C (810 F) to 460 C
(860 F). The catalyst bed thickness on the belt was
maintained at 1.9 cm (3/4 inch) and the belt speed
corresponded to a production rate of 3402 kg
(7500 pounds) per day.
The results are presented in Table 1 below.
Comparative Example 1
Spent catalysts having the above characteristics were
regenerated using a fluidized bed treatment, but without
a subsequent moving belt treatment. The conditions used
were as follows:
The catalysts remaining in the pretreater in Example
1 above were gradually heated from a temperature of
393 C (740 F) up to a temperature of 482 C (900 F)
over a period of 75 minutes. The superficial air
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velocity in the reactor was maintained at about 131 m/min
(430 ft/min) during the regeneration process.
The results are presented in Table 1 below.
TABLE 1
Ex. 1 Comp. Ex. 1
Carbon, %wt. 0.2 0.1
Sulfur, %wt. 0.3 0.5
Surface area, m2/g.(1) 229 228
Attrition Index (2) 54.2 57.4
(1) Surface area determined by the B.E.T. method for
determining specific surface area as described in
Brunauer, S., Emmet, P. Y. and Teller, E., J. Am. Chem.
Soc., 60, 309-316 (1938).
(2) Attrition index is defined as the number percent of
particles which are less than the 2.5 millimeters
averaged length. The number percent is 53.4 for
spent/used catalysts as indicated in the table above
summarizing the characteristics of the spent catalyst.
As can be seen in Table 1, the spent catalyst
regenerated according to the present invention (Example
1) has a much lower attrition index than catalysts
regenerated using a fluidized bed process alone
(Comparative Example 1).
