Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
io~,g3~
This invention comprises a process for the
vapor phase dehydra-tion of ~-alkylbenzyl alcohols and
substituted analogues thereof to form styrene and sub-
stituted styrenes.
Dehydration of alcoh~ls to their corresponding
unsaturated structural compounds is well known in the art.
; Dehydration techniques are not generally employed in the
manufacture of styrene and many homoloyues thereof because
standard dehydrogenation of ethyl benzene is considered to
be a more economic route. In addition, styrenes produced
by conventional dehydration techniques o~ten contain enough
ethyl benzene and other impurities to require extensive
purification.
It is characteristic of standard dehydrogenation
techniques employed in the production of styrene that fairly
large quantities of unreacted ethyl benzene be present in
the styrene fraction~ Such quantities of ethyl benzene in
the styrene fraction are substantial enough to cause loss
of properties in polymers of such styrenè fractions. Fur- ~:
thermore, due to the closeness of the boiling points of
styrene and ethyl benzene, removal of ethyl benzene by
distillation is expensive.
Moreover~ normal dehydrogenation of many substi-
tuted ethyl benzenes, particularly the tertiary alkyl sub~
~` 25 stituted ethyI benzenes, destroys or alters the substituted : :
group. For example, dehydrogenation of ar-~t-alkyl)-ethyl
benzene to form;thelr corresponding styrenes usually
results in nlpture~and/or loss of the t-alkyl group as
well az dehydrogenation of the athyl group.
:
:: :: . :
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~ 14,774A-F
;: :: : :
~0'~3~'Y
Attempts to prepare ar-(t~alkyl)styrenes by con-
ventional dehydration of the corresponding ar-(t-alkyl)-a-
-methylbenzyl alcohols have not been satisfactory due to
the formation of other byproducts and the rupture of the
t-alkyl group which frequently accompanies dehydration.
As a result of this ruptl~e, appreciable quantities of
ethyl benzene and under certain conditions, diole~inically
unsaturated aromatic monomers are foxmed in addition to the
desired ar-(t-alkyl)styrene. These diolefinically unsatu-
rated aromatic monomers, e.g., ar-(i-propenyl)styrene in
dehydration of ar-(t-butyl)-~-methylbenzyl alcohol, are very
difficult to separate from the de~ired ar-(t-alkyl)styrene.
During polymerization of the ar-(t alkyl)styrene monomer,
the diolefinically unsaturated aromatic monomer acts as a
crosslinking agent thereby producing a substantially cross~
linked styrene polymer which is insoluble in many organic
solvents such as toluene and benzene. Thi~ lack of solu-
bility is undesirable in many applications employing such
styrene polymers.
Conventional dehydration techniques for preparing
sty~ene and substituted styrenes are not completely satis
factory in that substantial amounts of ethyl benzene and
othçr~difficult to separate impurities often remain or are
produced~ Such difficulties ha~e been pointed out in U.S.
,.
Patent No. 2,399,395 and U.S~ Patent No~ 3,442,963, ~or
; example.~ ~
Therefore, it would be highly desixable to pro- -
vide a new, improved technique for produ¢ing styrene and
substltutéd styrenes in high yield which contain little or
no ethyl benzene and other impurities, particularly diole-
finicalIy unsaturated aromatic monomers.
: ~ : ,. .. .
~ 14,774A-F ~ -2-
; ~ `"^''"''"''
10~930~
Accordingly -the present invention is an improved
process for dehydrating ~-alkylbenzyl alcohols and to form
the corresponding styrene monomer in high yield and purity.
The present invention resides in a process for
preparing a monovinylidene aromatic monomer by dehydrating
an a-alkylbenzyl alcohol represented by the general
formula
R R OH
R ~ fH2
R R Rl H : :.
wherei.n R is hydrogen, alkyl having from 1 to 12 carbon atom3
or halogen and Rl is hydrogen or alkyl having 1 to 4 carbon
atoms, comprising the step of contacting the a alkylbenzyl
alcohol in vapor phase with a dehydration catalyst con-
sisting essentially of silica gel in the presence of from
0.03 to 25 parts by weiyht of added watsr per part by
weight of alcohol, said dehydration step being carried
out at temperatures from 200 to 510~C.
: Prior art teachings indicate that water produced
during dehydration of an alcohol should be removed from the
reaction mixture ln order to move the reversible dehydra- -
tion reaction to the right and thereby increa~e the yield ;:
: of the unsaturated productO In the process of this in
vention, a siIica gel of a type which has hereto~ore
25~ often been employed as a support for another catalyst
, ~ . .
is used as the dehydration catalystO Surprisingly, in
the practice of this process, it is found that the presence
.
of water, (p:referably aceomplished by addition of from
0.03 to 25 weight parts per weight part of alcohol
~ to;the al~cohol~prior to dehydration and/or during
-
,,
.
~ ~'4,77-A-F ~ _3_ .
~ 3~
dehydration)~ efEectively increases the yield of the desired
styrene and substantially reduces, and under optimum
conditions, almost completely eliminates the formation
of ethyl benzene and other impurities which are difficult
to separate, In general, the desired monovinylidene
aromatic monomer is produced in purity greater than about
99 mole percent and contains less than about 1, preferably
less than about 0O5 mole percent of alkyl benzene impurity,
so-called ethyl benzene impurity.
As a result, styrene monomers produced by this
method require little or no further purification to remove
impurities having boiling points nearly the same as the
monomer; thus expensive dis~illation procedures are elim- ;
inated. Styrene polymers produced from these styrene
monomers are found to have improved properties as a result
of the increased purity. As a result of low concentrations,
i.e., less than 0.02 mole percent based on total monomer,
of diolefinic impurity, ar-(t-alkyl)styrenes produced by
this process can be polymerized directly into polymers
which are soluble in toluene, benzene and other organic
solventsO Such organic soluble polymers are particularly
useful in various coatings~ thermoplastic moldings, reactive
diluents, polyester varnishes and chemical applications that
require a monomer essentially free of diolefinic species.
For the purposes of this invention, the term
"a-alkylbenzyl alcohol" includes ~-alkylbenzyl alcohols,
.. ~ . - , .-:
especially ~-methylbenzyl alcohol and substituted analogues
` thereof. Such aIcohols are represented by the general
~ : ~.,~
formula-
14,774A-F -4-
~ 30'~
R R OH
R ~ C - CH2
wherein R is hydrogen, alkyl having from 1 to 12 carbon
atoms, e.g., for example, methyl, t-butyl, t-amyl and
other t-alkyl; halogen, e.g., for example, bromo, chloro,
and fluoro; and Rl is hydrogen or alkyl having from l to
4 carbon atoms.
Exemplary a~alkylbenzyl alcohols include, for
example, a-methylbenzyl alcohol, ar chloro-a-methylbenæyl
alcohol, ar-bromo-~-methylbenzyl alcohol, ar-fluoro-a-
-methylbenzyl alcohol, ar-dichloro-a-methylbenzyl alcohol,
ar-dibromo-ar-chloro-~-methylbenzyl alcohol, ar-chloro-
-~-ethylbenzyl alcohol, 4-chloro-2,5-difluoro-~-methyl-
benzyl alochol, ar-(t~butyl) a-methylbenzyl alcohol,
ar-chloro-ar-(t-butyl)-~-methylbenzyl alcohol, ar-bromo-
-ar-~t-butyl) a-methylbenzyl alcohol, ar-(t-amyl)-a-
-methylbenzyl alcohol, ar,~-dimethylbenzyl alcohol,
-ethyl-2-isopropyl-5-methylbenzyl alcohol, or a-iso- ~ -
::
butyl-2,4,5-trimethylbenzyl al~ohol.
Preferred ~ alkyl benzyl alcohols are -methyl-
benzyl alcohol, ar-halo-~-methylbenzyl alcohol such as
ar-chloro and ar-bromo u-methylbenzyl alcohol and ar-
-(t-alkyl)~-m~thylbenzyl alcohols such as p-(t-butyl)-
~;25~ -methylbenzyl alcohol, p-(t-amyl)-~-methylbenzyl alcohol
and sl~ilar a]cohols ~herein t-alkyl has 4 to 8 carbon
:
atoms. The abo~e alcohols are known compounds and can
be prepared by synthasis obvious to those skilled in the
art. ~IllustraLtively, ar-alkyl-~-methylbenzyl alcohols
:
~ 14,774A-F~ -5-
:
~ ~ ,
~07~3~J
can be prepared by the stepwise synthesis of (l) alkylating
ethyl benzene with olefin in the presence of sulfuric
acid in accordance with the me1:hod of Ipatieff et al.,
J~CS, Vol. 58, 9l9 (1936)J
. .
~ 14,774A-F -Sa- .
~0~3a~
(2) oxidizing the alkylated ethyl ben~ene to the corres-
ponding acetophenone-alcohol mixture as described by H. J~
Sanders et al., I 6 E Chem, Vo] 45, 2(1953), and (3) reduc-
ing the mixture by catalytic hydrogenation to the desired
alcohol.
The silica gel employed in this invention may
be in any of the several forms of silica gel which will
permit intimate contact between the silica gel and
alcohol vapor during the dehydration. It is desirable
that the silica gel be in the form of a divided solid, pre-
ferably in the form of particles not measuring more than
about an inch in any dimension. Further the silica gel
should be of a type that is not decJraded or des~royed when
contacted with large quantities of water. Although good
results are obtained with a number o grades of particulate
silica gel, bes~ results are obtained with the silica gel
in the form of a particulate solid having a mesh size
ranging from 2 to 400 and a surface area of at least about
300 square meters per gram, preferably from 300 to 900
m2/g. Of special preference are the commercial grades
of silica gel that have here~ofore been employed as sup
ports for other catalysts. In these preferred ~mbodiments~
the possibility of complete contact be~ween the silica
gel and the alcohol is maximized. It is especially pre-
ferred that the sLlica gel be inely divided porous particles
having an average pore diameter ranging from 2 to 200
Angstrom UnitsO Methods for preparing silica gel are
well known to skilled artisans. Also any of several com-
mercial grades of silica gel fitting the above general
description may be employed.
14,774A-F -6-
~ .
~ 3~
In the practice o~ this invention the u-alkyl-
benzyl alcohol in vapor phase ls contacted with the silica
gel in the presence of from 0.03 to 25 parts by weight
of water per part by weight of alcohol~ preferably from
0.5 to 20 weight parts, especially from 1 to 2 parts of
water per weight part of alcohol. It is generally pre-
ferable that the alcohol be inl:imately mixed with specified
amounts of water in the form of steam prior to dehydration.
This is easily accomplished by passing liquid or vaporous
mixtures of the alcohol and water over or through a bed
or column of an effective heat transfer material such
as silicon carbide, fused ceramic packing or non-corrosive
metal packing. In such embodiments, a column having a
lower portion of a bed of silica gel and an upper portion
of the heat transfer agent can be made and the alcohol
containing water is then passed dow~ward into the column
through the heat transfer agent and then through the silica
gel bed. It is often desired to employ an organic carrier
liquid which is a solvent for the alcohol, e.g. t toluene
or benzene, but which can be easily removed by simple
distillation. In such embodi~ents, the alcohol and
~ carrier liquid are mixed together prior to vaporization
; ~ of the alcohol mixture. It is understood that the addition
of water to the reaction may be made after the alcohol
has passed through the heat transfer agent. Also the
; water need not be added in the form of steam or super-heated
steam although it is preferred to do so.
Generally, the desirable temperatures of opera- -
.
~ ~ ~ tion of the process of this invention are in the range of
.: ,
~ 3Q ~ 200'C to 510"C, preferably from 260QC to 500C, especially
~, : :
~ 14,77~A-F ~ ~7~
~ 30'~
from 300 to ~00C. In the dehydration of ar-(t-alkyl)-
-~-methylbenzyl alcohols, it is desirable to employ dehydration
temperatures above 260C, preferably from 325C to 425C,
in order to insure contact between the silica gel and the
alcohol in the vapor state. It is generally desirable
to carry out dehydration at atmospheric pressure, although
it is possible to achieve dehyclration with relatively
good purity and yield at subatmospheric to superatmospheric
pressure, e.g., from 0.2 to 5 atmospheres. Vaporization
of the alcohol, however, may be advan~ageously achieved
by using reduced pressure. Vaporiæation may also be
achieved by contacting the alcohol with steam or super-
heated steam substantially prior to dehydration~
The quantity of silica gel which effectively
dehydrates the alcohol depends in part upon the rate at
which the vaporous alcohol is to be passed through the
silica gel bed or column, upon the surface area of the gel
per unit of weight, upon the amount of water to be employed.
Generally higher vapor flow rates and larger quantities of
water require more silica gel to achieve effective dehy-
dration.
Practice of the present invention as described
hereinbefore yields the desired monovinylidene aromatic
monomer, particularly the ar-(t-alkyl)styrene, in purity
greater than 99 mole percent based on total product after
simple distillation which removes unreacted ketones and
alcohols. Accordingly, the alkyl benzene impurity is held
below about 1, preferably below about 0.5 mole percent.
In the dehydration of the ar-(t-alkyl)~-methylbenzyl
alcohols by the method of this invention, diolefinic and
.
'~
14,774A-F -8-
~0~93~
other polyolefinic impurity is held below 0.02 mole percent
based on total procluct after simple distillation.
The invention is urt:her illustrated by the
Eollowing examples which shoulcl not be construed as limit-
ing the scope of the invention. ~11 parts and percentages
are by weight unless otherwise indicated.
Example l
A first mixture of 50 parts of ~-methylbenzyl
alcohol and 50 parts of toluena is preheated to 300C and
mixed with 100 parts of steam at 300C. The resulting
steam/alcohol mixture is passed downward at a rate equi-
valent to that employed in Example 2 through a glass
coL~In (l" outside di~meter x 27" length) e(~ui~ped with
an electric furnace and containin~ a 14-incll upper layer
of silicon carbide (8 mesh) preheated to 350C and a
6-inch lower layer (20 g) of silica gel (on 10 mesh, 300 m2
of surface area/g and having a pore volume of 1 cc/g, sold
as a catalyst support under the trade name Davison Silica
Gel Grade 57 by Davison Chemical). Water and dehydrated
organic product are condensed in the lower part of the
column, collected and separated4 The organic product is
dried and distilled. The distilled product is determined
by inrared spectroscopy and vapor phase chromatography
.:: -.
to be 99~ mole percent styrene containing less than 0.5
mole percent of ethyl benzene. Overall yield on the basis
of starting alcohol is greater than 95 percent.
Example 2 ~ ~
A~mixture of 50 parts of 4-(t-butyl)-~-methyl- - ~;
benzyl alcohol and 50 parts of toluene is prepared. A
reaction col~n (l" outside diameter x 27i' length) is
filled to a bed height of 8-9 inches with silica ~el (8-10
~: ' ,' '
14,774A-F ~ -9-
~O~9307
mesh, 340 m2 of sur~acc area/g, 140~ average L)ore cliameter
and sold as a catalys-t support under the trade name D~vison
Silica Gel Grade 70 by Davison Chemical) and sufficient
amount of silicon carbide (6 mesh) is added to the tube
to increase total bed height to 16 inches. The reaction
column is heated to 300C. Water preheated to 300C and
the mixture are added simultaneously into the feed end
of the column at rates of 9~ m:L~hr and 45 ml/hr re-
spectively. An intimate admixture of steam and the
alcohol mixture in vapor phase i~ formed and passes down-
ward through the silicon carbide preheated to 350C which
acts as a preheat section for the vapor and then through
the silica gel to effect dehydration~ Following passage
through the silica gel, water and organic product are con-
densed in the column, and collected. The dehydrated
organic product is decanted, dried a~d distilled. The
distilled product is determined by infrared spectroscopy
and vapor phase chromatography to be 4-(t-butyl)styrene at
99 percent or greater purity. Overall yield on basis of
amount of starting alcohol is ~reater than 90 percent.
Polymerization of the 4-(t-butyl)styrene by heat-
ing in the presence of benzoyl peroxide yields a polymer
which is soluble in toluene at 20C.
Example 3
Several sample runs are carried out generally -~-
according to the procedure of Example 2. In these runs,
mixtures of 50 parts of 4-(t-butyl)-~-methylbenzyl alcohol --~-
and 50 parts of toluene are prepared and mixed with varying ~-
amounts of steam. The vaporous steam-alcohol mixture is
~ 30 passed downwaxd into a glass column (1" OD x 27" length)
:: : . :~ 14,774A-F -10- -
~ ' ,'.
: :- . . ~. :~. .
~J930~
having a 14" upper bed of silicon carbide (10 mesh) pre-
heated to varying temperatures and a 6" lower bed of silica
gel (same as in Example 2). ~ater and dehydrated organic
product are condensed, collected and separated as in Example .
2. The results are recorded i:n Table I.
To show the ~articulax advantage of employing
added water in this system, a control run (Cl) is made
under conditions similar to the above runs with the ex-
ception that no water is added to the alcohol at any point
prior to or during dehydration, the results of this control
run are also recorded in Table I~ To indicate upper limits :
as to temperature during dehydration, two control runs (C2
and C3) employing varying amounts of ~water are also carried
out in accordance with the procedures employed in the above
sample runs. The results are recorded in Table I.
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Example 4
Several sample runs are carried out e6sentially
according to Example 2 except that a wide range of temper-
atures are employed~ In the several runs, mixtures of 50
parts of ar-(t-butyl)-~-methylbenzyl alcohol containing
~7 mole percent of ar-(t-butyl)acetophenone and 50 parts
of toluene are prepared. A glass column (l" OD and l6"
length) equipped with an electric furnace is filled to a
heiyht of 3.5" with silicon carbide (8 mesh, 42 grams),
to a total height of 13.5" with silica gel (same as in
Example 2, 50 grams), and to total height of l6.0" with
s.ilicon carbide (8 mesh, 40 grams) and preheated to varying
temperatures from 200 to 500C for the several runs.
Steam superheated to at least 550C and the alcohol/toluene
mixture are added simultaneously into the feed end of the
column at rates of l00 ml/hour (measured as condensed
water) and 50 ml/hour respectively, An intimate admixture
of steam and the alcohol mixture in vapor phase is formed
and passes downward through the heat transfer agent and
the silica gel to effect dehydration. The water and organic
product are then condensed, collected and separated. The ~ ..
organic product is distilled and dried, and its constitu- :
ency is dete.rmined by infrared spectroscopy and vapor phase
chromatography. The xesults are shown in Table II. .
.:
.:
'
-
-
14,774A-F
:-: :., , . ., . ~ ,
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~ 30'~
To point out the advantage of silica gel cata-
lysts over conventional dehydration catalysts, several
control runs (C4-C8) are made employing essentially the
same procedure used above except that a titania dehydration
catalyst (4-8 mesh, and 70 m2 of surface area/g) is
substituted for silica gel. The dehydra~ion column has
a 3.5" bottom layer of silicon carbide (8 mesh), a 10"
middle layer of titania catalyst and a 2.5" top layer of
silicon carbide. The organic product is recovered and
analyzed by infrared spectroscopy and vapor phase chroma-
tography and the results are recorded in Table IIo
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AS eviclenced by Table II, signii-icantly larger
quantities of ar-(t-butyl)-ethyl benzene are generally
produced in dehydrations employing titania as catalyst
than those employing silica geL under essentially the same
conditions. The ar-(t-butyl)-ethyl benzene is dii-ficult
to separate from ar-(t-butyl)styrene whereas ar~(t-butyl)-
acetophenone is separated from either of the above by
simple distillation,
Example 5
A solution of 50 parts of ar-(t-butyl)-a-methyl-
benzyl alcohol containing ~7 mole percent of ar-(t-butyl)-
acetophenone in 50 parts of toluene is mixed with super-
heated steam (550C) in a ratio of 2 parts of water to one
part of tha mixture. The steam-alcohol mixture is passed
downward through a glass column (1" OD x 21" length) con- -
taining a 10" upper layer oi- silicon carbide and a 10"
lower layer of silica gel (same as in Example 2). The
temperature at the top of the column is 350C and at the
bottom of the column is 325C. The water and organic pro-
duct i5 distilled and dried, and its constituency is deter-
mined by infrared spectroscopy and vapor phase chroma-~
tography. The results are shown in Table III.
For the purposes o comparison a control run (C
is carried out by following the above process except that
alumina (4-8 mesh and 210 m2g of sur~ace area/gram~ is
substituted i-or~silica gel as dehydration catalyst. The
organic product is distilled and dried and its constituency
is de~ermined~by the means described above~ The results
are also recorded in Table III.
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14, 774A--F -18 ~ :
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Exam~le 6
The dehydratlon process of the pre~ent invention
is carried out in a continuous manner by continuously ~ee(l-
ing molten ar-(t-butyl)-a-methylbenzyl alcohol at 200 lb/hr
and water superheated to 550C at 400 lb/hr into a column
(18" OD x 6'8" length~. The column contains a 3'4" upper
bed of metallic heat transfer material preheated to 350C
and a 3'4" lower bed of silica gel (same as in Example 2).
The temperature at the lower end of the column is 325C.
The dehydrated orgarlic product is continuously collected
at the lower end of the column and then recovered at
99~ percent purity by simple distillation. The de-
hydrated product is determined by infrared spectroscopy
to be ar-(t-butyl)styrene.
Example 7
Several samples of ar-chloro a-methylbenzyl
alcohol containing small amounts of ar-chloro-acetophenone
are continuously dehydrated hy mixing the liquid alcohol
with varying amounts of superheated s~eam ~550C) and
passed as vapor phase through the column descri~ed in
Example 3. Dehydration temperatures for the various runs
are also varied. The amounts of low boiling components
are shown in Table IV. .:
For the purposes of comparison, similar samples
of ar-chloro~ methylstyrene also containing small amounts
. .
of ar-chloro~acetophenone are continuously dehydrated ln
the same manner except that no water is added during the
process. The amounts of low boiling components for these . .~ :
( 10 r Cll ~ Cl2) are also shown in Table IV
. ~'-' '
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L.l ~ ~ S l .~
~4 O O O O C~ cn O r~l O
~1 ~: ~ ~I c~ cn cn
,. ~ , . . . O ~1
h
I ~ ~D 1`Lt~I~ In 1~ ~P O
~1 a~
d u~
C~ ~,X :,
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O ~ --I O
~rl ~ O O O O O O O O ~ ~ ~.. .
: ~ : O O OIn L0 O O rl ~rl 0
~ a)
::
E~ , ,~
O rl .
'0 ~ O f~
~ o~ In o ~r~ o o o
3 x a) u~ ,., . "
O ~ ~ O O .'
)r~lIt) ~1 Z Z
X c~ * ~c r-l
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14, ~ 7 4~-F: ~ : ~ 2 0- . :
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: ;, ,; . : ~ . -
~7~3~7
Examples 8-13
-
In accordance with the con-tinuous dehydra-tion
process of Example 3, several substituted ~-methylbenzyl
alcohols are dehydrated to the corresponding substituted
styrenes thereof. The results obtained are comparable
to khose obtained in Example 3. The alcohols successfully
dehydrated are as follows:
ar-t-butyl~ -dimethylbenzyl alcohol
ar-dichloro-~-methylbenzyl alcohol
ar-dibromo-a-methylbenzyl alcohol
ar-di-t-butyl-a-methylbenzyl alcohol
ar~tl-ethyl l-methylpentyl)-~,-methylbenzyl alcohol
ar-t-butyl-ar-methyl-~-methylbenzyl alcohol.
Several dehydration runs are also carried out -~
using silica gel catalysts having different mesh sizes in
the range from 2 to 400 and surface areas in the range
from 300 to 900 m2/g with good results.
''.
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:"
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.
.,
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~ 14,774A-F i -21-
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