Note: Descriptions are shown in the official language in which they were submitted.
~i7Z7Z2
1 This invention relates to an improved sorbent and
2 to a method of using the same in the ;elective removal of
3 sulfur oxides Erom gaseous mixtures. The sorbent comprises
4 copper and/or copper oxide as the active component, supported
on an alumina carrier assoc~at:ed with a stabllizing amount of
6 magnesium oxide.
7 Sulfur dioxide is a constituent in various waste
8 gases, such as flue gas, smelter gas, and off~gases from var-
9 ious chemical and pe~roleum refining processes. Flue gas
formed by combustion of a sulfur~containing fuel such as
- 11 coal or fuel oil constitutes a major source of sulfur dioxide
. .
l2 pollution. Flue gas usually also contains trace amounts of
13 sulfur trioxide and small quantities of oxygen, the latter
14 due to the use of excess airO As is well known, sulfur di-
oxide is irritating to the respiratory system and is harm~
16 ful to plant life.
17 Heretofore9 several sorben~s have been proposed
18 for the selective removal or separation of sulfur oxides
19 from such gaseous mixturesO These include gaseous sorbents ~;
~ such as ammonia9 liquid sorbents such as a solution of ammo-
21 nia and/or of an ammonium salt3 and solid sorbents sush as a
22 transition metal or a transitîon metal oxide supported on a
23 suitable carrier such as alumina or silica. As is well
24 known, each of these sorbents depends upon a chemieal reac-
2~ tion between the sulfur oxide or oxides and the active com-
26 ponent of the sorbent to effect separation. As is also well
27 known, any one of these types of sorbents might advantageous~
28 ly be used in a particular situation depending upon the par-
29 ticùlar circumstances involved~ As a general proposition,
however, the solid sorbents offer the broadest range of ad-
31 vantages both in economy and ease of use. Of the solid sor-
32 bents, CuO supported on alumina has been found to ke
. ~
7 ~7 Z Z
1 particularly effective.
2 Generally9 the solicl sorbents are used in cyclic
3 operations wherein a gaseous mlxture containing one or more
4 sulfur oxides is first contact:ed with the solid sorbent un-
;, 5 til the sulfur oxide concentraltion in the off-gas reaches a
6 predetermined maximum valueO The contacting is then discon-
7 tinued and the solid sorbent is regenerated with a suitable
8 regenerating gas or by thermal means. During the initial
9 contacting, the sul~ur oxidPs are absorbed by reaetion with
the active component or components of the solid sorbent.
11 During the regeneration, the acti~e component or components
12 are restored to an active form and the sulfur oxides are
13 liberated Such a process, wherein copper oxide on alumina ;~
14 is used as the sorbent, is described in several patents in-
cluding British Patent No. ~,0899716 and UOSo 3,501,987.
16 Although processes of the type jus~ described,
17 using a solid sorbent, offer several distinct advantages
- 18 and generally yield excellent separation results, the amount
19 of sulur oxides actually absorbed during each subsequent
absorption cycle is generally less than in any previous cy-
21 cle. The difference is, of eourse, only slight as between
22 any two consecutive cycles but as the n~mber o cycles in~ ~-
23 creases, the difference between th~ absorption capacity dur-
24 ing the first cycle and the most recent cycle becomes greater
~5 and greater. The net resul~ is that each subsequent absorp-
26 tion cycle is shorter, in time, and less sulfur oxides are
27 absorbed and regeneration is required on a more requent
28 basisO Ultimately, the absorption capacity becomes so low
29 that replacement of the sorbent is absolutely required if
the sulfur oxide content in the treat~d gas is to be main~
31 tained at the desired level. While this relatively frequent
32 replacement of the sorbent is, of itself, an economic dis-
107Z7;~:Z
advantage, a much more ser:lous dlsadvantage is the signi~i-
cant decrease in operating e:Eficiency resulting from the
shorter absorption cycles and more fre~uent regeneration9
required for each sorbent bed~ The need, then, for an im-
proved sorbent offering impro~ed operating efficiencies is
believed to be readily apparlentO
- Thus the present invention provides a cyclic
: process for removing Sx from a gaseous mixture containing
SOx, oxygen and at least 2.0 mol % water vapor comprising
conducting a plurality of desulfurization/regeneration
cycles, each cycle comprising (i) contacting said gaseous
mixture with a solid sorbent contained in a reaction zone
at desulfurizing conditions to remove Sx from the gaseous
mixture and (ii) subsequently regenerating said sorbent at
regeneration conditions in the absence of said gaseous
mixture, said sorbent comprising a carrier comprising at
least about 70 mol ~ alumina combined with copper oxide
and a stabilizing amount of magnesium oxide, the capacity
of said sorbent after more than 600 cycles being at least
equal to the initial capacity of said sorbent times the ~ :
quantity (number of cycles)-0.02.
It has now surprisingly been discovered that the
foregoing and other disadvantages o ~he prior art solid
sorbents and particularly ~ho~e comprising a copper oxide
active component on an alumina carrier can be avoided or at
least minimized with a solid sorbent that comprises copper
and/or copper oxide as the active component supported on an
alumina carrier, which carrier is impregnated or otherwise
combined with a stabilizing amount of magnesium oxide. Ge~-
erally, the copper and/or copper oxide may be combined with
the carrier either before or after the MgO has been incor-
~ 4
~ ~7 ~7
porated, or simultaneously therewith~ using any suitable
technique known in the prior art to be useful or combining
copper and/or copper oxide wi.th a conventional alumina car-
rier.
In general, any of the porous alumina based sup~
ports known in the prior art to be useful for preparing sup-
ported catalysts and/or sorbents can be uged to prep~re the
improved sorbents of the present invention. These include
-~ those types of alumina exhibiting various crystalline struc-
tures such as eta~alumina,.or gamma-alumina, as well as mix-
tures thereof and mixtures comprising one or more of such
aluminas in comblnation~with one or more other refractory
metal oxides such as silica or titania, Such other refrac- :
tory metal oxides will be present either as a constituent
of the carrier, eOg. co-precipitated with the alumina, as a
support for the alumina, or as an impurity therein. Usually
:
-4a-
,.
. , , , ~,. . . .
7 ~ 7 2 ~
when the other metal oxides are present only as impurlties,
they will be present in small amounts. When they are pres-
ent as a corprecipitate or as a support for the alumina car-
4 rier, on the other hand, they could be present in grea~er
concentrations. It should be noted, however, that because
6 acidic refractory metal oxid2s such as silica will adversely
7 affect sulfur oxlde absorption, the concentration of such re-
8 fractory o~ides should be ~1inimized~ Moreover, since maxi-
9 mum advantages are realized in the present invention only
when alumina is the major, if not the sole, constituent of
11 the carrier, the concentration of any other metal oxide will
l2 generally be minimized, and in all cases, alumina will con~
13 stitute at least 70 mol % and preferably a~ leas~ 98 mol %
14 of the carrier material.
In general, the carrier may be used in any desired
l6 form or shape, as for example, in the form or shape that it
17 is ordinarily obtained or pr~pared, or the carrier might be
8 ground or otherwise divided and screened so as to obtain par-
19 ticles of any desired size. Alternatively, the carrier mate-
rial might be fashioned into various shap-es, such as spheres,
21 cylindrical extrudates9 rings or ~he like, in accordance with ~-
22 known techniques, or it may be coated on a support material,
23 as for example, as a high ~ur~ac~ area film adherently bonded
24 to a low surface area support, which support might itself be
fashioned in any desired shape from any suitable material
26 such as alumina or other refrac~ory material or a non-reac-
27 tive metal screen or other e~panded shape. In any case, how-
28 ever, the carrier material, as used, will generally exhibit
29 a surface area of a~ least 75 m2/g, and preferably a sur~ace
area within the range f~om about 90 to about 400 m2/g and
31 most preferably with~n the range from about lO0 to about
32 200 m2/g. Moreover, the carrier will generally exhibit a
,. .. .
- ~ ~ 7 ~ 7 ~Z
1 porosity, as a result of pores having a radiu~ greater than
2 about 400 A, of at least 0.27 cctg~ and preferably such a
3 porosity withln the range from about 0.30 to about 0.36 cc/g
4 and a total porosity of at least 0.27 cc/g and preferably a
total porosity within the range from about 0.3 to about 0.92
6 ~c/g.
7 With respect to carrier properties, lt should be
8 noted that, initially at least, both the ~urface area and
9 pore volume of an alumina carrier are controlled, inter alia,
by the particular raw ma~erials and methods used to prepare
11 the same and by the method and condition~ used to shape the
12 carrier. Once the carrier is formed, however~ these proper~
13 ties can be altered and, indeed, adversely affected by sev-
14 eral factors~ the most significant of which is the maximum
temperature to which the carrier is exposed after prepara~
l6 tion. For this reason, best results are achieved in the
17 method of this invention when the ma~1mum temperature to
18 which the carrier is exposed af~er preparat~on is minimized~ : :
19 In this regard, it should be noted that the carrier can be
exposed to temperature~ as high as 1400Fo or periods as
21 long as 12 to 24 hours without significantly affacting the
22 performance of a sorbent prepared therewithO The effect is,
23 however, even less significant when the maximum temperature
24 to which the carrier is subjected is no more than about
1200F. and a minimum change in surface area and pore volume
26 characterist:ics will be realized if this temperature is no
27 greater than about 1125F. For these reasons, then, the
28 carriers used in the sorbents of this invention will, ge~er-
29 ally, be calcined a~ a temperature between about 800 and
about 1400F'., preferably between about 950 and about 1200F.
31 and most preferably between 1075 and about 1125F.9 before
32 the carriers are combined with the stabllizer and the artive
-- 6 -
.. . .. . .
~727~
C omponent .
2 In general, the magnesium oxide may be combined
3 with the carrier material in essentially any manner known in
4 the prior art to be effective in achieving the desired com-
bina~ion. For example7 the carrier material could be physi-
6 cally admixPd and bonded with magnesium oxide in accordance
7 with known techniques; both the carrier material and the mag-
8 nesium oxide could be slmultaneously formed via coprecipita-
9 tion in accordance with known techniques, or the carrier ma-
terial could simply be impregnated with the requisite amount
11 of magnesium oxide~ also in accordance with prior art tech-
12 niques. It has been found most effective, however, to de-
13 posit the magnesium oxide stabilizer on the surface of the
14 carrier, rather than coprecipitating or otherwise combining
the same such that the magnesium oxide is distributed uni-
16 formly throughout the carrier. In this regard, it should be
17 noted that the effect of the magnesium oxide is, apparently,
18 to block or otherwise prevent agglomeration of the active
19 cnpper oxide and/or the conversion of the active copper ox~
~ ide to an inactive, nonregeneratable form and/or to prevent
21 the loss thereof from the surface of the carrier such as by
22 penetration into an inaccessible portion of the carrier.
23 . This is, then~ apparently accomplishad only when the neces~
24 sary concentration of magnesium oxide is available at the
2s carrier surface. Deposition of the magnesium oxide directly
26 on the surfac:e is therefore preferred.
27 It is believed that the prior ar~ copper oxide on
28 alumina sorbents gradually lose their absorption capaclty as
29 a result of t:he active copper oxide agglomerating and/or COM~
bining with Al203 of the alumina carrier to form an inactive
31 spinel-like structure, CuAl~04. To the extent that the re-
32 action of CuO with Al203 is the cause of the observed,
- 7
,, , . . , . , . . ., -, . .
4 ~>
J 7 ~
1 gradual deactivation, it is believed th.lt, while, initially,
2 this formation would occur at or near the carrier surface
3 and involve only a small portiLon of the available CuO, as
4 the sorbent is continuously cycled between the absorption
and regeneration cycles and the varying conditions ~hereof,
6 the availabLe CuO mlgrates or otherwise penetrates into the
7 carrier, thus forming additional inactive CuA1204 and fur~
8 ther reducing the total amount of CuO available for subse-
9 quent absorptlon. It is believed that a portion of the MgO
combined with the alumina carrier in accordance with this
11 invention prevents surface agglomeration while the remaining
l2 portion forms a spinel or spinel~like crystalllne structure,
13 MgAl2O4, at the surface thereof in substantially the same
14 manner as the GuO would, if the MgO were not used. Because
of the unusually stable surface struc~ure of the MgO modi-
16 fied carrier, however, once the MgA1204 struct~re is formed9
17 there is llttle,if any, change in the availability of either
18 MgO or CuO for S02 sorption, and hence, little, if any, de-
19 terioration of the sorbent as the result of continued use.
As indica~ed previously, then, the carrier u ed in
21 the sorbent of this invention will be impregnated or other-
22 wise combined with magnesium oxide. G~nerally, this may be
23 accomplished in accordance with any of the techniques kno~n
24 in the prio,r art to be useful for this purpose, For exampLe,
this can be accomplished by combining the carrier material,
26 either before or after the same has been formed lnto the de-
27 sired shape for use, with a solution of a salt or other com
28 pound which will deeompose or otherwise yield the desired
29 stabilizing agent; viz., magnesium oxide~ Although essen-
tially any magnesium salt could be used as the magnesium ox-
31 ide precursor and the same could be combined with the car
32 rier material as a solution in essentially any solvent
~ 8 ~ -~
~ 7 ~ 2
1 therefor, preferably only those salts comprisin~ anions,
2 which are themselves easily separated from the carrier mate-
3 rial, as well as solvents, which are ~ rly separated, will
4 be used. Salts comprising ea!~ily separated anions include
magnesium nitrate and magne~ n acetateO Solvents which can
6 be easlly separated include water and the lower alcohols.
7 Generally, the carrier material will be combined
8 with the sal~ solution~ which may contain one or more solu~
9 ble salts therein~ in a suitable manner to insure a thorough
w~tin~ thereof and a corresponding even distribution of the
11 ~agnesium salt or salts thereoverO The mixture is then gen-
l2 erally dried so as to remove excess solvent and any free wa- `~
13 ter or other volatile material contained therein. The dried
14 mixture is then usually calcined so as to yield the desired
magnesium-oxide~impregnated carrier. In this regard, it
l6 should be noted that the anion or anions origlnally assocl~
17 ated with the magnesium will, generally, be separated there-
18 from durlng the calcining step, and that an oxygen-contain~
9 ing or similar gas could be used during the calcining step
~ to facilitate the formation of magnesi~m oxide.
21 An improvement 1n absorption capacity maintenance
22 can be expected when the surface of the carrier is treated
23 or combined with essentially any amount of magnesium oxide
~4 ranging from9 and generally including, what might be termed
a "trace" amount up to any amount short of that which would
26 completely coat or cover the entire surface of the carrier.
27 Because the exact amount of magnesium oxide actually required
28 for optimum o~ maximum effect1veness will vary with the par-
29 ticular carrier employed and particularly the amount of
Al203 at or near the surface thereof and available for or
31 to the formation of a spinel~like crystalline structure9 the
32 required amount is not subject to precise definition~ None-
~ g ~
:'
~0727~
1theless, it can be stated as a general proposition that sig- !
2 nificant improvements will be realized when the amount of
3 magnesium oxide deposited or otherwise disposed upon the sur-
4 face of the carrier is within the range from about 0 1 to
about 10 wtl%, based on the we!ight of carrier, and that op-
6 timum,or maximum effectivenessl wlll generally be realized
7 when the amount of magnesium oxide deposited or disposed
8 upon the surface is within the range from about 0O5 to about
9 3 0 wt %, again based on the weight of carrler.
10As also indicated previously, eopper oxide, CuO,
11 will be used as the principal active component in the solid
2 sorbent of this invention. The copper oxide may9 howeve~ be
13 used in combination with other materials, such as the vari~us
14 non~noble transition me~al oxides that are known to be effec-
tive in absorption of sulfur oxides from gaseous mixtures
16 containing the same7 The magnesium oxide treatment is not,
17however, believed to offer any particular advantage in the -:
18 absorption process except when the same is used in combina-
19 tion with an active material capable of agglomeration on the
surface and/or of forming a spinel~like crystalline struc~
~1 ture w~th A1203 and, then3 only when used with the smaller
22 metal o~ide molecules which might be subject to migration
23 and/or penetration into the earrierO Such active materials
24 include the smaller oxides of metals having a valence of two
and particularly copper oxide. The magnesium oxide treat-
26 ment will, then, be most effective when copper is the princi-
27 pal or sole active material and this combination is particu
28 larly preferred.
29The copper oxide and/or any o~her act~ve material
30 that might be used in combination therewith may be deposited
31 on the surface of the carrier either before or after ~he mag-
3~ nesium oxide or simultaneou~ly therewith9 all ln accordance
`:
- 10 -
~7 ~ 7 Z ~
1 with prior art techniques and, indeed, the same may be de-
2 posited in ~he same manner as has been prevlously described
3 with respect to the magnesium oxide. I~ should be noted,
4 however, that when the copper oxide is depos~ted on the sur~
face before the magnesium oxide, the copper~oxide on~alumina
6 sorbent should not be subjected to the oxidation~reduction
7 variations and/or temperature variation normally encoun~ered
8 in cyclic sorption;regeneration operations before the magne-
9 sium oxide is deposited since such exposure would result in
a reduction of available copper oxide. Such care is not re-
11 quired, however, when the magnesium oxide is deposited on
2 the carrier surfa~e be~ore the copper oxide or when the two
13 oxides are deposited simultaneously. For this reason, then9
14 it ~s preferred that the magnesium oxide or its precursor be
deposi~ed on the carrier surface either before or simNltane-
16 ously with the copper oxide or its precursor. Simultaneous
17 deposit~on is most preferred because this can be accomplished
18 with a minim~m of process steps. Simultaneous deposition
1~ will be accomplished from a solution contain~ng one or more
salt& of both magnesium and copper, which salts will yield
21 the corresponding oxides upon contacting or su~sequent-treat-
22 ment such as drying and/or calcining. In any case, however,
~3 the amount of eopper oxide actually present on the carrLer
24 or the magnesium oxide stabilized carrier will, generally,
range between about O.l and about lO wt.% based on carrier
26 material, including any MgO ~hereon
27 Independent o the particular method used to im-
2~ pregnate the carrier used in the sorbent of this invention
29 and/or the particular order of impregnation, the same will,
generally, be dried to remove excess solvent and then cal~
31 cined at a temperature generally wlthin the range from about
32 800 to about llO0~ and in the presence of oxygen or ar r
' ~ 1 1
1~7;~:7Z2
1 oxygen-containing gas so as to convert the metal salt or
2 salts used for impregnation to the corresponding oxide or
3 oxides. It will be appreciated that in those cases where
4 separate, rather than simultaneous impregnation is used, the
carrier will usually be dried and calcined after each lmpreg-
~ nation. To avold high temperature damage to the sorbent,
7 however, and for economic reasons, the calcining in all cases
8 will, preferably be accomplished at the lowest possible tem
9 perature consistent with the desired conversion and most
preferably at a temperature between about 800 and 850F.
11 It should be understood that, as an alternative
l2 procedure, the desired conversion of the metal salts could
3 be accomplished by reducing the salts to free metal and there-
14 after, such as in the 1nitial portion of a desulfurization
cycle, oxidizing the metal or metals to the corresponding
l6 oxlde or oxides.
17 As ind-Tcated previously, the sorbents of this in~
18 vention will, generally, be used under known conditions for
19 gas desulfurization and sorbent regeneratlon and the process
of this invention will employ su~h a sorption-regeneration
21 cycle. During the sorption portion of the cycle, a stream
.~
22 of flue gas or other gas mixture containing sulfur oxides,
23 (iOe., sulfur dio~de, sulfur trioxide, or both~ and oxygen
24 is contacted with the sorbent, preferably by passing the gas
stream through a f~xed bed of the sorbent, under desulfuriz-
26 ing conditions. Desulfurizing conditions in the case of a
27 stabilized copper oxide on alumina sorbent include a gas in-
28 let temperature of about 600-900F , preferably 625~850F.
29 and most preferably about 650-750F., and a space velocity
of about lO00 to about lO,000 v/v/hr. These conditions are,
31 of course, generally known in the art. As is also known3
32 optimum inlet temperatures and space velocities will vary
,~ .
- 12 -
; ,
~LCI1~2722
1 slightly from sorbent to sorbent depending on the active ma-
2 terial used. During the course of the sorption period, the
3 active material becomes partially sulfa~:ed (e.g., part of
4 the copper oxide is converted to copper sulfate) and an ef-
fluent gas stream of greatly reduced sulfur oxide content is
6 obtained. The amount of sulfur oxides in the effluent gas
7 is very small at the start of a sorption period, and gradu-
8 ally rises as sorption continues. Sorption ls stopped and
9 the sorbent is regenerated when the amount o effluent Sx
(the symbol S0x is used to denote S02, S03 and mixtures
11 thereof) reaches a pre-determined level. For 90% removal,
12 sorption is stopped when the total amount of Sx in the ef-
13 fluent gas over a whole cycle reaches 10% o~ the total in~
coming Sx over the cycle. The percentage of active mate-
rial which is utilized (i.e. rPacted with sulfur oxides)
16 during the sorption period is, of course, a measure of sor-
bent act~vity,
8 The sorbent is usually regenerated by passing a
19 reducing gàs9 such as hydrogen, carbon monoxlde, various hy-
drocarbons and/or m~xtures thereof, through the sorbent bed.
21 A mixture of hydrogen and steam containing at least 50 mol %
22 of steam is a particularly preferred regeneration gasO Re-
23 generation gas inlet tempera~ures are, generallyg in the
24 range of about 600 to about 900F. During regeneration o
the stabilized copper oxide on alumina sorbent of this inven-
26 tion, the mixture o copper sulfate and copper oxlde which
27 is present at the end of the sorption period is reducèd
28 either to metallic copper or to a mixture of copper and cop-
29 per oxide, and a regeneration off gas containing S0~ in a
substantially higher concentration than the orlginal SOx
31 contain~ng gas is evolved. Strong reducing agen~s, e.g.,
32 hydrogen and hydrogen-steam mixtures reduce the copper con-
- 13 -
7~ 2
1 ten~ to ~etallic copper. The presence of steam suppresses
2 cop~er sulfide and sulfur formation. Any metallic copper
3 formed in the sorbent during regcneration is, o course,
4 quickly and quantitatively oxidized to copper oxide at the
start of the next sorption cycle by oxygen in the S~x--con-
b taining gas. This in turn permits a repetition of the sorp-
7 tion-regeneration cycles just described. Sulfur dioxide in
8 the regeneration off~gas can be converted to sulfur or to
9 sulfuric acid by means known in the art. A complete oper-
~ ating cycle may include purge periods either after the sorp-
11 tion period, after the regeneration perlod, or after both,
l2 using any desired purge gas such as steam or nitrogen.
13 In such use as previously described, the stabilized
14 sorbents of the present invention surprisingly exh;bit re-
markably improved absorp~lon capaci~y and activity mainten-
16 ance after continued use when compared to their unstabilized
17 counterparts and no~withstanding that the presence of the
18 MgO ~tabili~er results in a signi~icantly lower ini~ial ac~
1g tivity. Moreover, the rate of activity and capacity decline
is mNch lower with sorbents of the present inventio~ t~an
21 with known unstabilized sorbents and, as has been indicated
22 previously3 approaches zero with the sorbents ~f this inven~
23 t~on and, in fact, both ma~ increase slightly, with the most
24 preferred sorbents of this invention. In this regard, ~t
should be noted that with prior art type sorbénts and with ~
26 sorbents of this invention when a decline is, in act, re-
27 alized, the capacity generally declines logarithmically ac-
28 cording to the equa~ion:
29 Capacity -- (initial capacity) (no. o cycles) K
where 1'capacity" ref~rs to the capacity after any given num-
31 ber of cycles and K is a constant, dependent upon the sever-
~ty o operation, partlcularly the inlet temperature to the
- 14 -
~, ' .
1~72t722
1 absorber, but independent of the oper~tional history, which
2 constant will be referred to as a capacity retention con~
3 stant hereinafter. The value of K is then much gre~t~r Qe~s
4 negative) for sorbents of this invention than for their cor-
responding but unstabilized equivalents. In this regard,
6 and as discussed more fully hereinafter, the value of K for
7 sorbents of this invention is essentially zero and more par-
8 ticularly, generally within the range of about ~0.02 to 0,
9 while that of an unstabillzed equivalent ls, generally, with~
in the range of about -0.12 to 0.06 for operations with in-
11 let temperatures within the range from 650 to 750F.
2 Comparative plots showlng the relati~e change in
13 absorption capacity with number of cycles for representative
14 sorbents are given in the accompanying Figure as curves (I) 9
(II) and (III). The curves shown are for certain sorbents
l6 prepared in the Examples hereinafter. Curve I is for a con
17 ventional, unstabilized sorbent while Curves II and III were
18 obtained with sorbents of the present invcntion. As will
19 readily be apparent from the curves, the value of the capa-
city retention constant9 K" for both of the sorbents within
21 the scope of the present invention is essentially zero. The
22 value of K for the conventional sorbent, on the other hand9
23 is -0.116. All curves reflect adiabatic operation
24 As will also be apparent from the appended Figure,
the initial activity of the unstabilized sorbent (Curve I)
26 was substantially higher than tha~ of either stabilized sor-
,~! 27 bent. This difference does, of course, reflect the signifi=
28 cant adverse effect that MgO is known to have on the CuO ac-
29 tivity, and in light of this significant difference, it was
3~ indeed surprising to discover that the activ~ty of the sta-
31 bilized sorbent would, ultimately, surpass that of the un~
32 stabilized sorbent The curve for the conventlonal sorbent fell
below the curve of the stabilized sorbent at values as low as about 600
" cycles.
-15-
~ , . .. .. .
~ ~ 7 ~ 7 Zz
1 In a preferred embodiment of the present invent~oll,
2 a gamma alumina having a surface area wi.thin the range from
3 about 100 to about 200 m2/g and a total porosity within the
4 range of about 0.30 ~o about 0~92 cct~ and a po~oslty due to
pores having a radius of at least 400 A within the range
6 from about 0.30 to 0O36 cc/g will be used as the support ma~
7 terialO Typically, this support will be extruded into hol
8 low cylindrical pellets having a dlameker between about 1/4"
9 and 1" and a length between about 1/4" and 1~9 said pellets
having holes parallel to the eylindrical axls so as to limlt
11 the partlcle wall thickness to about 1/8'~ ~nd thereby mini
l2 mize pressure dropO Once formed and calcined, the extruded
13 pellets will then be impregnated with between about 005 and
14 300 wt. /0 MgO (based on the weight of carrier material)O The
impregnation will preferably be accomplished by firs~ con~!
16 tacting the extrudates with an aqueous solution of magnesium
17 nitrate under conditions favoring an even d~stribut~on of -
18 the salt throughout the extrudate followed by drying at a
19 temperature within the range from about 180 to about 205Fo
and calcining, in the presenee of an o~ygen~containing gas
21 at a temperature within the range of about 800 to about r
22 850Fo Once the extruded support has been impregnated with
23 MgO, the same will then be surace impregnated with CuO, by
24 first filling the carrier pores with a suitable liquid such
as a Cs Clo alcohol and then contacting the filled carrier
26 with an aqueous solution of copper nitrate to effect impreg
27 nation in substantially the same mann~r as was used ~o ac
28 compl~sh the MgO impregnation. The surfaoe impregnation
29 technique w~lich ~s most preferred in preparlng the sorbents
of this invention is disclosed in Belglan Patent 790,816,
31 granted Apri.l 30, 1973. The preferred sorbent will comprise
32 between about 4 and 8 wt.% CuO (based on the weight of gamma-
~ 16 ~
.
~L~7;~:72;;~
1 alumina in the reglon where ~he coppe~ is placedO~
2 Once prepared, the preferred sorbent w~ll be used
3 to absorb SOx from a gaseous m~xture co~prising the same and
4 water vapcr. In a most preferred embodiment9 ~he sorbent
will be used to separate SOx from a flue gas, whlch gas also
6 contains at least 2 mol % H2O vapor and most preferably be~
7 tween about 8 and 12 mol % H2O vapor.~.~n this regard, it
8 should be noted that maximNm lmprovement has been realized
9 with all of the sorbent of this invention while treating gas-
eous mixtures also containing ste~m or water vapor generally
1 within the range of that normally encountered in.flue gas
2 streamsO For this reason~ lt is cOntemplated that steam
13 could be added within the range heretofore specified to an
l4 otherwise dry gas so as to enhance performance of ~he pres
ent sorbents and, indeed9 this would ba a preferred method
of separating Sx from gas streams which do not contain
17 waten vapor in th2 d~sired concentration~
18 In a preferred me~hod of operating, the absorption
19 will be accomplished at temperatures in;the lower portion of .
the ranges her~tofore speci~led and particularly within the
21 range of inlet temperatures from about ~50. to ~bbut 750Fo
: . .......... . .
22 and such that the outlet temperature from.the b~d~is iess
23 than abou~ 900Fo The regeneration9: on ~he other han~, will
24 be accomplished with an inlet temperature equal to about the
outlet temperature from the absorber, but at least about
26 600F~, and the regeneration temperature wlll be controlled
27 such the same does not exceed about 1000F. at any point
28 within the bed. Moreover, and whlle essent~ally any pres~ -
2~ sure, including superatmospheric pressures, ml~ht be used,
both the absorpt~on and regeneration will preferably be ac~
31 complished at or near atmospheric pressure.
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7 2 ~ ~Z
EXAMpLE 1
:
2 A copper oxide on alumina sorbent was prepared by
3 first shaping gamma~alum~na into hollow cylindrical pellets
4 having an outside dlameter of 0.5'~, an inside dlameter of
0.25" and a length of 0.51lo Then 7146 g. of the~e pellets
6 were mixed with 5933 gO of an aqueous hydrated magnesium ni
7 trate ~Mg~N03)2 6H20~ solution containing 1507 wt.% hydrated
8 magnesium nitrate, this being don~ by dipping the pellets
9 into the aqueoussolution so as to ~nsure an even dlstribu~
tion of the magnesium salt throughout the carrier pellets~
11 The pellets thus treated were then dried at a temperature of
12 190F. for 16 hours while being blown with a~r. Following
13 the drying, ~he treated pellets were calcined at a tempera~
14 ture o~ 800F. for 3 hours after being slowly heated ~o this
lS temperature. The magneslum~3xide~c~ated pellets were soaked
16 in hexyl alcohol at ambient temperature ~70F.) and then ..
17 dipped, while st~ll saturated with the alcohol9 into an aque
18 ous solut~on contaln~ng 700 gO Cu(N03)2'3H20 per liter of
19 soluticn ~approx. a .2 g/ml Cu~) in the same manner a~ was
used in contacting the pelle~s with the aqueous magnesium
21 salt solutionO The thus treated pellets were dried with air
22 blowing3 to remove H20 and hexyl alcohol and then calc~ned
23 in a manner paralleling that used in d~ying and ealcining
24 the magnesium~treated pellets. The resulting sorbent was
analyzed ancl found to contain 1 wt. % MgO and 1.5 wto % CU++
26 tbased on total s~rbent)O
27 The ga~ma~alumina used to prepare the sorbent of
28 this Example exhibited a surface area 3f 182 m2/g ~BET
29 method) and a porosity of 0,32 cc/g (BET m~thod~O The sor~
bent of thi~; Example was used ln the test runs described in
31 Example 2.
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` ~ O 7'~7 Zz
1 OOM~A~A } L~ A
2 A copper oxide on fllumina sorbent was prepared by first
3 shaping a gamma~alumina into hollow cyliradrical pelletA~ having
4 an outside diameter of 0O5 ~n. and an inside dlameter of O.X5
in, and a length of appro~imately 5 inO After 2924 gn cf these
6 pellets h~d b0en soaked ln hexyl alcDh~l for 1 hrO ~nd while
7 they were still saturated with the alcohol, th2y were dipped
8 into an aqueous copper nitrate soluticn containing 0O~9 g Cu~+
~ /ml. for 2~ min. The resulting combination was then dried and
calcined. The calcined pellets were analyzed and found to con
11 tain 1055 wto % Cu+~ which Cu++ was unifonmly distributed over
12 the alumina pel~etA~O
l3 EXAMPLE 2
14 A 3" diameter, 44~' deep fixed bed absorber containing
2512 g~ of the absorb2nt of Example l was used to separate S2
l6 from a gaseous mixture containing the same in a cyclic9 absorp-
17 tion~regeneration operation. During thP absorpticn phase ~f
18 the cycle9 a synthetic flu~ gas containlng 2800 ppm of S02~2O~O
19 oxygen, 7,5% water vapor and 90% nitrogen (all parts by vol.)
was passed downwardly through the r~actor at an lnlet temp, of
21 65QFo and a space ve1Ocity of 2000 V/V/HrO The absorption time
22 in each cycle was adjusted to giv2 about 90~/O absorption of S02~ ~
23 that is~ the absorption pha~e of each cycle was stopped when ~:
24 the accumulative total S02 in ~he exit g~s was 10% ~f ~e total
S02 in the inlet gasO The sorbent was then regenerated by pas~-
26 ing a regeneration gas containing 40/0 hydrogen an~ 60b water va~
27 por (both by volO) downwardly through the reactor at an inlet
28 temp. of ~50Fo and at a rate which provided about a 30% excess
29 H2 over the 1% min. regenera~on period ~asedona ~ consumpt~on of 1
mol/mslof Cu+~l H~/mol SO2c~ptu~e~0 Af~r ~e regenerat~n ~,the
31 absorption and regeneration cycles were repeated in succession
32 until in all 7000 absorption and regeneration cycles were com-
~L9
11[~727ZZ
1 pleted ~o as to insure a complete and ~ccurate determination
2 of the absorbent performance~ life and stabillty~ Generally,
3 the conditions of each cycle were ~ubstantlally identical to
4 those previously noted although other operatlng conditions
were occasionally interposed.
6 During each cycle9 the effluent S02 was measured
7 with a continuous analyzer whlch ~lso integrated the tot~l
8 amount, with time, such that the point of ~g~/O S02 absorp~
9 tion" could be accurately determined and the absorption dis-
continued at this pointO The percentage of copper oxide
11 uti~ization at 9~% S02 absorption ~i~eO the mol ~/~ CuO con~
12 verted to CuS04) wa5 also determined for several cycles dur-
13 ing this runO The efective utilization thus determined has
14 been plotted in the appended F~gure (Curve II) against the
cyrle number.
16 COMPARATIVE EXAMPLE B
17 The run of Example 2 was repeated using the abs~r-
18 bent o Comparative Example A (no MgO~. During that portion
19 of the run of this Ex~mple used for comparison with the run
in Example ?., the conditions during each absorption and re-
21 generation cycle were, within experiment~l error, identical
22 to those u~ed in Example 2~ Generally, however3 the time re-
23 quired for a "lO% S02 breakthrough" was shorter in thls run
24 and the hydrogen required for regeneration was reduced~accor~
ingly. Ag~ln, the peroent of copper oxide utilization was
2~ de~ermined for several cycles during the run and this is
27 plotted in the Figure ~Curve I)o
28 As will be seen from the Figure9 the effective
29 utilization of ~he copper o~ide reduces significantly with
the number of cycles when MgO is not used (Curve I) while
31 there is little, if any, reduction therein when MgO is used
32 (Curve II~. It must, then, be concluded that the use of MgO
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~ ~7 2~ ~ Z
1 as a stabilizer is effective, and that absorbentg which are
2 thus stabilized will exhibit a substantially longer and more
3 effective life.
4 EXAMPLE 3
A copper oxide on alumina sorbent was prepared by
6 first shaping a gamma ~lumina into pellets identical in ~ize
7 and shape to tho~e prep~red in Ex~mple 1. The alumina used,
8 however, exhibited a surface area of 17~ m~g ~nd ~ total
9 porosity of 0.51 cc/g~ of which about 60% wa~ attributed to
pores having a radius of at least 40ûA. After ~978 g. of
11 these pellets were lmmersed in hexyl ~lcohol~ for one hour,
12 w~ile ~till saturated with alcohol9 they were dipped into an
13 aqueous solution containing 0006 g Cu+~/ml and 0,035 g Mg+~/
14 ml., both as nitrate~9 for two and one half minutes. The
pellets were then dried and calcined in the prPsence of air.
l6 The finished sorbent contained G~64 wto % MgO and ~2 wto ~/o
7 Cu~
1B EXAMPLE 4
19 The sorbent prepared in E~ample 3 w~s tested as an
S02 sorbent in a manner identical to that described in Exam-
21 ple 2 and 14,000 cycles were completed~ Again~ the percent
22 copper oxide utiliz~t~on was periodically determined and the
~3 results obt~ined are plotted in the appended Flgure as Curve
24 III.
As will be readily apparent from a eomp~rison of
26 Curves II and III in the Figureg the results obtained with
27 the sorbent o:f Example 3 are about 7.5~/~ better than those
28 obtained with the sorbent of Example 1. This difference is
29 believed to be due to the reduced amount of MgO present on
the sorbent of Example 3 ~nd the corresponding reduction in
31 its inhibiting effect upon the CuOO
32 From the foregoing~ it will be apparent that the
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1~7;~:'7Z~
1 magnesium oxide stabilized absorbents of this invention ex~
2 hibit improved activity maintenance and lmproYed absorption
3 capacity stability during use arld thus provide an improved
4 proces~ f~r~sul~4r oxide removal from g~seous mixtures when
they are used as the absorbents ln such process.
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