Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
108~893
B~CKGROUND_OF__HE_INVENTION
2 Fi_ld_of the_I_v_____n
3 This invention relates to a process for regenerating
4 dsactivated catalyst carrier particles. More particularly, it
relates to rejuvenating a metal-sulfide-contaminated hydrocarbon-
6 treating catalyst.
7 The dwindling of world petroleum reserves has made it
8 necessary to squeeze more and more refined products from every
9 barrel of crude oil. The heavy, high-boiling, metal- and sulfur-
containing portion of crude oil which formerly was ~urned as low-
11 grade fuel or used as a material for the construction of roads
12 must now also be catalytically hydrotre~ted for the recovery of
13 refined products. Because of the high-metal and sulfur content
14 of this material, hydrotreating catalyst lives frequently become
unduly shortened because of the fouling of catalyst pores. ~he
16 problem is magnified because catalysts satisfactory for
17 hydrotreating require for their production the use of customized
18 carriers having relattively large surface areas and unique pore
19 diameter characteristics. Such carriers, in contrast to conven-
tional materials, now represent a significant fraction of the
21 catalyst cost. Consequently, there is a need for an effective
22 process for the rejuvenation of these carriers that they may be
23 reused for the production of rejuvenated hydrotreating catalysts.
24 D---Ei~t----o----e---Ei--r-AEt
Various methods have been disclosed for removing metal
26 sulfide contaminants from catalyst carrier particles. These
27 methods are reviewed in large part and a yet further method is
28 disclosed in U.S. Patent 3,791,989. In general, the object of
29 these methods is to achieve some improvement in a used catalyst
3~ by selectively dissolving contaminants present in the pores of
31 hydrogenation catalyst carrier particles. While a moderate
32 degree of success appears to be achieved from the use of these
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methods, the activities and catalyst lives of the resulting
regenerated catalysts usually are inferior relative to those of
the new catalysts.
It is an object of this invention to provïde a process L
for the regeneration of porous catalyst carriers comprising
alumina and to produce rejuvenated catalysts from these
rejuvenated carriers.
SUMMA:RY OF THE INVENTION
According to the present invention, a process for
rejuvenating a catalyst comprising an effective amount of a
catalytic component disposed on an alumina carrier, said
catalytic component comprising a Group VI metal or compound
thereof and a Group VIII metal or compound thereof, and said
catalyst having pores which are plugged or fouled by metal
sulfide contaminants as a result of use of said catalyst in
hydrotreating a hydrocarbon feed which contains an organometallic
compound and sulfur-contaminants, which comprises: leaching at
least 50~ of said metal sulfide contaminants, calculated as
metal, from said catalyst with aqueous nitric acid solution,
` 20 said solution having a nitric acid concentration in the rangefrom about 0.8-3 molar, said leaching being (a) carried out at
a temperature in the range from 0C to the reflux temperature
of said solution, and (b) effected by using for each gram of
- said catalyst an amount of said solution in the range of 4-20
ml, said amount being in excess of the stoichiometric
quantities required for said metal sulfide contaminant; oxidiz-
ing residual oxidizable matter from said leached catalyst by
contacting said catalyst with molecular oxygen at a temperature
below the sintering temeprature of said catalyst.
In a yet further aspect of the present invention, a
process is provided for rejuvenating a catalyst comprising an
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effecti~e amount of a catalytic component disposed on a carrier
selected from the group consisting of particles of alumina and of
alumina-silica mixtures, the particles containing pores plugged
or fouled by metal sulfide contaminants as a result of contact
with a hydrocarbon feed containing organometallic compounds and
sulfur-containing compounds under hydrotreating conditions, which
comprises, in addition to the two steps described above for the
rejuvenation of the catalyst carrier partïcles, the restoring of
the effective amount of a catalytic component by impregnating the
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1 leached particles vith at least one solution of the catalytic
2 component or a precursor thereof and calcining the resulting
3 impregnated particles at a temperature below their sintering
4 temperature.
In a yet further and preferred aspect of the present
6 invention, the catalytic component of the hydrotreating catalyst
7 comprises a Group VI metal or compound thereof and a Group VIII
8 metal or compound thereof.
9 EMBODIMENT
In a preferred embodiment, the carrier particles of a
11 spent, select, high-activity hydrodesulfurization (HDS) catalyst
12 are first rejuvenated and then used for the preparation of a
13 rejuvenated select, high-activity HDS c~talyst. The spent
14 catalyst, which has not been treated other than to wash off
residual hydrocarbons to give a free-flowing material, is used as
16 the feed for the process.
17 The spent catalyst and aqueous nitric acid are charged
18 to a suitable leaching vessel, which is resistant to the
19 corrosive action of nitric acid, for example a glass-lined or
stainless-steel vessel. For each gram of the catalyst, about 5
21 ml of 12.5% weight aqueous nitric acid are charged to the vessel.
22 Vigorous exothermic leaching action ensues upon the contacting of
23 the spent catalyst with the nitric acid. Desirably the
24 temperature is maintained in the range 10-22C. Nitrogen oxides
are produced and evolved as the leaching proceeds, and is
26 substantially complete for the removal of sulfide contaminants
27 after about 1 hour, when the evolution of nitrogen oxides more or
28 less ceases~ The leaching may be continued for 1-3 hours,
29 particularly where the metal contamination is severe.
In a typical leaching operation in vhich the HDS cata-
31 lyst comprises porous alumina, cobalt, molybdenum and phosphorus
32 and the metal contaminants are sulfides of vanadium, nickel and
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1 iron, all but about 6% of thc cobalt, about 15% of the vanadium
2 and about 12~ of the nickel (all calculated as metal) is removed
3 from the carrier particles, and only very little (less than 4
4 weight) of the alumina is leached from the particles. In
addition, the acid leaching action removes about 75~0 of the
6 sulfur content and little or none of the carbon content of the
7 spent catalyst.
8 The leached carrier particles are next impregnated with
9 an aqueous solution containing sufficient cobalt in the form of
cobalt nitrate and molybdenum in the form of phosphomolybdic acid
11 as reguired to reconstitute the cobalt and molybdenum (calculated
12 as the metals) catalytic components of the original fresh
13 catalyst. The impregnation is effected by conventional means,
14 for example imbibation of the impregnation solution by the
carrier particles and evaporation of the water solvent and
16 loosely bound water.
17 Next the residual oxidizable matter, for example carbon
18 and sulfur contaminants, is removed from the leached and
19 impregnated carrier particles by contacting them with an inert
gas, for example nitrogen, containing 1-5 volume percent of
21 molecular oxygen, while maintaining the particles at a tem-
22 perature in the range 340-400C. This contacting is continued
23 until the major portion, if not all, of the carbon contaminant on
24 the carrier particles has been converted to CO2 and vented from
the carrier particles. For practical purposes, the oxidation
26 with molecular oxygen results in the removal of all of the carbon
27 and sulfur contaminants. Surprisingly, the pore volume of the
28 resulting rejuvenated HDS catalyst is usually within experimental
29 limits of accuracy the same as that of the fresh catalyst, as is
30' likewise the average pore diameter. The surface area of the
31 rejuvenated catalyst is as large as, if not larger than, that of
32 the fresh catalyst, while the crush strength of the regenerated
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1 catalyst is excellent.
2 Most surprising is the result noted that after an
3 initial break-in period on stream, the rejuvenated catalyst (see
4 FIG. 3) exhibits a markedly improved fouling rate relative to a
fresh HDS catalyst.
6 BRIEF DESCRIPTION OF THE DRAWINGS
7 FIG. 1 shows the removal of metal from a spent catalyst
8 carrier as a function of nitric acid strength.
9 F.IG. 2 shows the weight percent metals removal as a
function of the amount of nitric acid used for leaching.
11 FIG. 3 shows a comparison under comparable conditions
12 of the performance of a fresh catalyst vs. the performance of a
13 rejuvenated catalyst.
14 DETAILED DESCRIPTIQN OF THE INVENTIQN
Ca rier Mate___l_
16 Porous particulate carrier materials comprising alumina
17 sized for use in a fixed-bed hydrotreating reactor and ordinarily
18 employed as carrier particles for hydrotreating (hydro-
19 desulfurizing, hydrocracking, hydrodemetallation and hydrode-
nitrification) catalysts are in general rejuvenated by the
21 present process and are contemplated for use as feeds herein.
22 The particle sizing usually varies in the diameter range from 0.5
23 to 10 mm and may be any suitable shape. Preferably the carrier
24 material is a mixture of silica and alumina in any proportions.
Still more preferably, the carrier material consists essentially
26 of alumina. This process is advantageously applied to particles
27 having a surface area of at least 50 mZ/gram and is especially
28 - advantageous when used to rejuvenate high-surface-area carriers
29 comprising alumina ordinarily used in the preparation of HDS
30' catalysts for use in hydrotreating sulfur-containing and metals-
31 contaminated hydrocarbons. Such feeds routinely plug or foul the
32 pores and surfaces of the catalyst.
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1 C_taly_i _C__p_n_n_
2 The present process is preferably applied to spent
3 hydrotreating catalyst particles comprising Group VI and/or Group
4 VIII metals and a carrier material as described above. Effective
amounts of the catalytic components of these catalysts vary, and
6 ordinarily are in the range, calculated as metal, from 1 to 25
7 weight percent of the composite catalyst. Other components, such
8 as promoters and stabilizers, may also be present in minor
9 amounts, for example phosphorus. Usually these catalysts are
prepared using conventional solution impregnation methods. They
11 may also be prepared by gelation, cogelation, and the like
12 methods, of the carrier component wherein the catalytic
13 components are incorporated into the carrier at any convenient
`;
14 time, for example during gelation, after gelation, after
calcination of the carrier, and the like. Preferably the spent
16 catalysts used as feeds in the process have in their preparation
17 been subjected, either as the total composite or as the carrier
18 per se, to calcination at a temperature in the range 426-871C,
19 preferably 482-593C, prior to use. Such catalysts in general
appear to suffer little or no loss of support material by
21 dissolution in the nitric acid leaching solution of the present
22 process. They also appear to suffer but a minor loss, if-any, of
23 crush strength as a result of the leaching.
24 Le _hin~_C_n_ltl__s
A. A_id_C____nt_at_on
26 For the leaching of metal sulfide contaminants from
27 spent hydrotreating catalysts, a sufficiently concentrated
28 aqueous nitric acid solution must be used. Although the relative
29 ease of dissolution of metal sulfide contaminants varies
depending upon a number of factors, including the specific metal,
31 the degree of pore plugqing and the like, a satisfactory concen-
32 tration for the nitric acid is, in general, in the range 5 to 10
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1 weight percent (e.g., about 0.8 to 1.7 molar). Preferably the
2 concentration of the nitric acid is in the range 10 to 17.5
3 weight percent (e.g., about 1.7 to 3 molar). Higher
4 concentrations may be used, but such use is relatively disadvan-
tageous in terms of increasing dissolution of the carrier
6 particles and increasing loss of crush strength of the particles.
7 8ecause the leaching reaction is exothermic and gas is evolved,
8 the use of nitric acid having an excessive concentration is
9 disadvantageous for further reasons in that such use includes
problems of temperature control and foam-up control. There
11 appears to be no redeeming counteradvantage to the foregoing
12 - disa~vantages in the use of n-itric acid having a concentration
13 above about 20 weight percent (e.g., about 3.4 molar).
14 ~. Tem~erature
The temperature which should be used for the leaching
16 varies, depending upon factors such as the acid concentration
17 used, the particular carrier particles involved, and the degree
18 of the leaching. Usually the initial temperature should be lower
19 than the final temperature as a matter of convenience in
controlling the more exothermic phase of the leaching and the
21 evolution of gaseous by-products. In general, a satisfactory
22 temperature is in the range 0C to the reflux temperature for the
23 leaching solution. The use of higher temperatures tends to
24 result in increased dissolution of the carrier particles
themselves. Preferably a temperature in the range from about
26 10C to 30C is employed. More preferably a temperature in the
27 range 10-20C is employed.
28 Residual-Matter Oxid__ion
29 The oxidizable residual matter present OD the leached
30' carrier varies in composition, depending upon the prior service
31 of the spent catalyst. In general, the material appears to be
32 ~ainly carbonaceous matter, i.e., coke, sulfocàrbon solids, and
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1 the like. It is readily oxidizable to gaseous products at a
2 temperature below the sintering temperature of the particles.
3 Usually the oxidation of this material is so exothermic that it
4 is desirably effected, at least in the initial stage, by using
molecular oxygen diluted by an inert gas, for example nitrogen or
6 carbon dioxide, in order to avoid subjecting the leached carrier
7 particles to a temperature which exceeds their sintering
8 temperature. Otherwise, the particles tend to suffer a severe
9 loss in surface area and may suffer undesirable changes in the
pore characteristics. Preferably the oxidizing of this residual
11 matter is effected in the main by contacting an oxidizing gas
12 comprising nitrogen containing from 1 to 5 volume percent of
13 molecular oxygen with the leached carrier particles, the
14 contactinq being at a temperature in the range from about 260C
to 540C, more preferably 340C to 400C. The oxidation is
1~ satisfactorily complete when the effluent gas contains little or
17 no carbon dioxide and/or sulfur oxide gas.
18 I_Preqn_t_Q_
19 For the rejuvenation and/or reconstitution of the spent
catalyst, the catalytic components removed by the leaching must
21 be restored, or if a new combination of catalytic components is
22 desired by impregnating the leached and partially rejuvenated
23 carrier with a suitable solution. While the impregnation is
24 desirably effected prior to completing the carrier rejuvenation
by the oxidizing step, it may also be conveniently effected
26 afterwards. Routine impregnation methods are contemplated and
27 used in this step. The carrier particles are immersed in a
28 solution containing one or more of the desired catalytic
29 components or a suitable precursor thereof, and the absorbed
30' solvent, which is usually water but not necessarily so, is
31 evaporated from the leached carrier particles. The impregnation
32 may be achieved in a single-dunk-type operation with the
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1 catalytic components all present, or by the use of two or more
2 impregnating solutlons. The single-dun~ method is preferred.
3 That is, a single solution containing sufficient of the catalytic
4 components, for example cobalt nitrate and phosphomolybdic acid,
is used to restore the metal contents of these components to that
~ of the fresh catalyst before use in a hydrotreating process.
7 Calci__t_on
8 Depending upon whether or not the fresh catalyst prior
9 to its use was desirably calcined, the _omposite resulting from
the above-described impregnation step is also calcined.
11 Calcination, in any event, is carried out after any oxidizable
12 residue on the leached carrier is removed by an oxidation step.
13 Calcination is carried out at a temperature below the sintering
14 temperature of the particles, preferably at a temperature in the
range 426C to 871C, and more preferably 482C to 593C.
16 EXAMPLES
17 The following examples are for the further illustration
18 -but not limitation of the present invention.
19 Exa_~
In this example the effect of nitric acid concentration
21 upon the leaching of metal sulfide contaminant and sulfur-
22 containing contaminant is demonstrated in a series of runs using
23 water alone and by using a series of nitri~ acid concentrations
24 in which the acid and spent catalyst particles are contacted in a
glass reactor. For each gram of the spent catalyst, 6.5 mls, an
26 excess, of nitric acid was used. Except for the acid
27 concentrations (see FIG. 1), the conditions employed in these
28 runs were as follows:
29 Temperature, C 10-21
Pressure Atmospheric
31 Time, hours 4
32 The spent catalyst used in these runs had been expended
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.
1 in hydrodesulfurization service in which the hydrocarbon feed had
2 a high sulfur and a high metals content. The fresh catalyst
3 contained molybdenum and cobalt, calculated as metals, in the
4 weight percents 12 and 3, respectively. ~he spent catalyst
contained vanadium, nickel, iron, carbon and sulfur in the weight
6 percents 5.4, 1.7, 0.2, 13.4 and 11.0, respectively. The metals
7 contents were determined using x-ray fluorescence (estimated
8 uncertainty ~10% of value) and the carbon and sulfur were
9 determined by combustion (estimated uncertainty ~5% of value).
The results of the runs are shown in FIG. 1. These data
11 establish that for effective removal of metal sulfide
12 contaminants (vanadium and nickel), for example removal of at
13 least 75 weight percent, a substantial nitric acid concentration
14 must be employed, that is, a concentration which is at least in
the ran~e 0.8 to 1.7 molar, and preferably is in the range 1.7 to
16 3 molar. Th-ese data also establish that there is no apparent
17 advantage in the use of an acid concentration in excess of about
18 3.5 molar.
19 Exampl__2
In this example, the effect of the amount of nitric
21 acid used upon the removal of metal sulfide and sulfur from the
22 spent catalyst particles by leaching is demonstrated in a series
23 of runs. The conditions and spent catalyst used were as in
24 Example 1, except that the nitric acid used was 3 molar and the
relative amounts of acid used were varied (see FIG. 2). These
26 data establish that provided at least sufficient acid is employed
27 for the effective ~for example at least 75X) removal of the metal
28 sulfide contaminants, there is no apparent advantage in the use
29 of a large excess of the acid for removal of metal sulfide
30! contaminants. In the case of the spent catalyst used in these
31 examples, a satisfactory amount is at least about S mls of acid
32 per gram of spent catalyst. These runs also suggest that the
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1 amount of acid desirably used per unit weight of the spent
2 catalyst varies depending in the main upon the relative amount of
3 the spent catalyst metal, sulfur impurity, and metal sulfide
4 impurity components present in the spent catalyst which are
leached from the carrier particles.
6 In general, it appears from these examples that the use
7 per gram of spent catalyst of an amount of a suitable con-
8 centrated nitric acid in the range from about 4 to 20 mls results
9 in an effective removal of metal sulfide contaminant from a spent
hydrotreating catalyst. Preferably, when the acid concentration
11 is in the range 1 to 3 molar, and the amount of acid employed, in
12 general, should be in the range from about 4 to 10 mls per gram
13 of spent catalyst, more preferably 4 to 7 mls.
14 ExamPl__3
In this example the performance in hydrodesulfurization
16 service of a rejuvenated catalyst as herein was compared with the
17 performance of a fresh catalyst. The hydrocarbon feed was an
18 Iranian heavy atmospheric residuum containing about 2.7 weight
19 percent of sulfur and a high metals content. Within experimental
limits for molybdenum and cobalt determination, the respective
21 catalysts contained the same amount of molybdenum and cobalt
22 catalytic components. In addition, the rejuvenated catalyst
23 prior to use contained about 0.8 weight percent of vanadium
24 (calculated as metal) and trace amounts of nickel, iron and
sulfur.
26 The surface areas (BET nitrogen method~ for the fresh
27 catalyst and the rejuvenated catalyst were 164 and 187 m2/g,
28 respectively, and the densities were each 1.3 g/cc. The larger
29 surface area for the rejuvenated catalyst is attributable to the
rejuvenation process, because the carrier particles employed were
31- the same for the fresh comparison catalyst and for the parent to
32 the rejuvenated catalyst. (The improvement in surface area,
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1 about 14~, of the rejuvenated catalyst over the fresh catalyst is
2 therefore an unexpected bonus.)
3 The process conditions in the comparative runs were:
4 Pressure, atmospheres 139
H2 feed, SCM/100 liters 177
6 LHSV 1.6
7 The results from the above-described comparative runs
8 are shown in ~IG. 3. These data establish that during an initial
9 break-in period of about 140 hours, both catalysts, the fresh
~10 catalyst and rejuvenated catalyst, exhibited for practical
11 purposes the same fouling rate. Thereafter, the fouling rate for
12 the rejuvenated catalyst was markedly superior to that of the
13 fresh catalyst, i.e., a negligible rate vs. a rate of about
14 0.08C per hour.
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