Sept. 15, 1953
B. L. GRAHAM
2,651,922
ICRYSTALLIZATION PROCESS AND APPARATUS
Filed Sept. 2, 1949
3 Sheets-Sheet l
WE.\
IN VEN TOR.
B. L_v GRAHAM
Sept. 15, 1953
2,651,922
B. |_, GRAHAM
CRYSTALLIZATION PROCESS AND APPARATUS
Filed Sept. 2, 1949
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INVENTOR.
B L GRAHAM
BY hi My.‘ 8' W
A TTORNEYS
Sept. 15, 1953
2,651,922
B L, GRAHAM
CRYSTALLIZATION PROCESS AND APPARATUS
Filed Sept. 2, 1949
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LOW MELTING PRODUCT COMPOSITION, WEIGHT PER CENT BENZENE
I00
F/G. 4
IN VEN TOR.
B L GRAHAM
A TTORNEKS‘
Patented Sept. 15, 1953
2,651,922
UNITED STATES ir‘ATEN-T OFFICE
GRYSTALLIZATION PROCESS AND‘
APPARATUS
Benton‘ L. Graham, Cactus, Tern, assignor to
Phillips Petroleum. Company, a corporation of
Delaware‘
Application September 2, 1949, SerialNo; 113,861
9‘ Claims.
1.
This invention relates to‘ the separation of
mixtures of organic compounds by crystalliza
tion. In a more speci?c aspect, it relates’to the
separation of binary, mixtures into two fractions,
one of. which is substantially pure. ’ In another
(01. 62-424)
2.
Figure‘ 1 is an elevational view of a single stage
apparatus for carrying out my process.
Figure 2 is an elevational view of a'multi-st'age
modi?cation of my apparatus;
Figure 3 is aschematic flow- diagram showing
speci?c aspect‘,.it relates to the. multi-stage sep
the flow of materials through my multi-stage
aration of‘ binary mixtures. In another specific
process.
aspect,v it relates to an apparatus for carrying
Figure 4 is a series of’curves showing thecom
out these separations.
position of‘ the'products obtained in a single-stage
In the separation of binary mixtures'of com 10 crystallizer using benzene and normal‘ hexane
pounds by crystallization methods, ity is’ theoreti
as a starting mixture.
cally possible to obtain at least one of the com
In Figure 1, an internally-cooled‘ drum Bis p0‘
ponents in substantially pure form. If the start
sitioned above and‘di'ps‘into trough 1 into which
ing mixture is a eutectic-forming mixture, a one
the starting mixture is fed‘ through‘ inlet 81 A‘
step process would theoretically give one fraction 15 cooling liquid is passed into drum 6 through in
comprisingthe saturation component of the orig
let i l and is removed therefrom'through'outlet 9.
inal mixturein substantially pure‘ form and an
other fraction comprising the eutectic mixture.
Ifthe starting mixture is a solid solution-form
ing mixture, a multi-stage separation process
should result in complete separation into two, '
substantially pure components.
Various processes and machines have been;
used'for effecting the‘ separation of binary mix~~
tures by crystallization. The processes usually
comprise the- step of freezing a portion of the
liquid, removing» the solidified portion and“ re+
melting it' to form a new mother. liquor‘ from
which a new portion i‘s-frozen and-removed. By
The material which freezes on the surface of drum
ii is removed by a‘ scraper blade l2'and falls into
a‘ receptacle it which is heated by'means of coil
it. The melted product‘ is‘removedfromrecep
t'acle“ It’ through“ outlet: It; Outlet l'l'is pro
vided for removing the mother liquor from'trough
l. Positioned above‘ drum 6" and in contact
therewith is a second drum l8‘ Which is biased
i against‘ drum 6" by means'of springs l9.‘ Drum‘
i8 is‘geared to'drum (Shy-means of gears 2| and‘
drum 5 is driven by a motor or engine, not shown;
A‘ heating liquidv is‘ passed into'drum' l8" through‘
inlet 23 and is removed therefrom through out
a sufficient number of: these-steps, it is possible
let 22.
to separate the starting mixture into at least one 30
Figure 2 is a three-stage apparatus‘ having;
pure" component and- a- second fraction; which
freezing drums t; troughs T, scraperblades I2;
may ‘or- may notibe pure.
receptacles I3; coolant inlet [1, and upper drums
The'amount of’ mother liquor o‘ccludedor en
l8‘.
trappedlby th'ecrystals formed’ is ordinarily'so
FigureSshowsthe flow of‘ material through a
great that it is necessary to have some‘positive
four-stage process; This diagram shows four
means for! excluding‘ the occludedv impurities'if
freeze troughs 26-, 2'5’, 28'; and 29 and four melting
a" reasonable degree ofseparation‘is to be accom
receptacles 3t, 32; 33-, and 34‘. The fresh feed-is
plished by- each crystallization. I have discovered‘
introduced‘ into freeze trough 274 through feedv
a process and apparatus by which'it is posssible
line 35;‘ The material removed from freeze
to ‘remove substantially all of1 the occluded im 40 trough 2'3" by the freeze drum rotating therein’
purities from the crystal's'so that I am able to
is deposited in melt‘ receptacle 33 and the un--v
obtain at least one of the-components-oii the
frozen mother liquor over?ows intofreeze trough
starting mixture in substantially pure form.
2B? The over?ow from trough 28' flows into‘
An object of .my invention is to provide a proc-_
freeze trough 25'»- and the over?ow therefrom is
ess: for separating binary mixtures into their 45 rem'oved'from the system through outlet 31. The
components.
ineltec’rmaterialj in‘ each melt receptacle, exceptv
Another objectis to provide‘ a multi-stage crys
receptacle (it, flows into the‘opposit'e side of the
tallization process.
next adjacent freeze‘ troug-liupstream. The melt‘
Stillanother object is to provide an apparatus
in receptacle 34 may be recycledv into‘. freeze
for effecting these separations by crystallization 50 trough‘ 26‘ by means of line 38' or itlmay be re
andfor excluding the occluded impurities from
moved through' product line :39.
the crystals formed‘in each step.
The. curves shown in Figure 4: represent‘ the.
Other objects and advantages of my invention
composition ofv the'products that can be obtained‘
will be apparent from a study of the following,
inasingle unitiapparatus; vsuch-asitha't shown
drawings, description and claims.
55 Figure 1. The various curves show the separa
2,651,922
3
.4
applied by each according to its length. The ex
tion obtained at the indicated cylinder speeds.
The force supplied to the upper cylinder was 400
pounds and the feed comprised benzene and nor
mal hexane.
In explaining my process, I shall refer to 6 as 5
act pressure exerted by the drums on the crys
tals is not known because the contact area could
not be measured.
The rotary crystallizer was placed in operation
by ?lling the freezing trough with the feed mix
ture, adjusting the feed rate, adjusting the com
freeze drum must be cooled to a temperature
pression springs to give the desired force on the
below that at which crystals begin to form in the
squeeze cylinder, starting the motor which drove
mixture in the trough. The particular refriger
the cylinders and then starting the flow of the
10
ant used will, of course, depend upon the partic
refrigerant through the freeze drums. When the
ular feed. For very low temperatures, I have
crystals began to form on the freeze cylinder,
used acetone cooled by passing it through a coil
the flow of warm water through the squeeze cyl
submerged in a bath of acetone and Dry Ice.
inder was started. The crystals were then
For large scale operation, less expensive cooling
scraped from the freeze cylinder and deposited in
should be used.
the freeze drum and I8 as the squeeze drum. The
the melting compartment.
A heat transfer liquid is circulated through
squeeze drum !8. The temperature therein must
be higher than the temperature in the freeze
drum but should not be above the melting point
After about 30 minutes operation, the process
had become lined out and the test period was
started. During the test periods, which were nor
freeze drum. Preferably, the temperature of the
nally 30 minutes, the crystal and liquid products
were collected, measured, and their compositions
squeeze drum is maintained as low as possible to
determined. For tests 1 through 4, the feed ma
still give the requisite purity of product.
terial was a benzene-n-hexane mixture.
of the material being removed as a solid on the
The
nearer the temperature of the squeeze drum ap
EXAMPLE I
proaches the temperature of the material being 25
removed as a solid, the purer will be the material,
but the lower will be the yield.
The multi-stage apparatus can be one such as
that shown in Figure 2 wherein the squeeze
drums have a common axle and rotate at the
This test Was carried out to determine the ef
fect of varying the pressure of the squeeze cyl
inder on the freeze cylinder. The freeze cylinder
temperature was —40° F. and the squeeze cylin
30 der temperature was 75° F. The cylinder speed
same speeds. If desired, a plurality of the units
shown in Figure 1 may be used and each unit
may have a particular speed of its own. If the
was 3.6 R. P. M.
Table 1
freeze drums are on a common axle, the speed is
regulated to give maximum removal from the
trough in which crystal formation is slowest.
This means that the drums in the other troughs
may not always be completely coated. This type
of apparatus is not as ?exible as that wherein a
plurality of single unit crystallizers are used but
it has the advantage of being simpler in construc
tion and operation.
The operating variables include the force ap
plied to the crystals by the squeeze cylinder, cyl
inder speed, freeze-cylinder temperature, squeeze
cylinder temperature, and feed composition. If
The results are shown in the
following table:
-
Force
Ap-
S gueeze
plied béry1'
mder’ lbs‘
Feed
Rate
mL/hr’.
Ylelcl of
Compositions
High-Melt-
ingt
P‘r/vod
uc ’
O '
Pegging of
‘
Feed
9
0
0
400
400
600
600
'
Weight Per
cent Benzene
High-
Low
Meltiu
Melting
Product
Product
—
——
33. 2
49. 9
76
76
78
77
75
75
880
760
730
700
35. 5
38. 2
41. 5
41. 5
76
76
76
76
92
90
97
97
68
68
61
61
It is seen that the separation achieved with
out the application of pressure is negligible. In
creasing the pressure on the crystals is shown to
cake, the force applied by the squeeze-cylinder
increase the purity of the products.
may be high. If, however, the material forms a
gummy mass on freezing, the force applied must 50
EXAMPLE II
the material freezes out on the drum as a hard
be reduced because too much pressure will cause
the crystals. to slough off or refuse to pass.
The pressure applied by the squeeze-cylinder
has a dual purpose.
Any liquid occluded or en
_ This test was carried out to determine the ef
fect of cylinder speed upon the performance of
the crystallizer. The operating conditions for
trapped within the crystal mass is squeezed out. 55 this test were the same as those for Example I
except that the force on the freeze cylinder was
The high pressure applied to the crystals as they
maintained constant at 400 pounds and the speed
pass between the cylinders increases the freez
ing point of the materials which causes an addi
of the cylinders was varied.
tional amount to solidify.
pected, the purity of the products decreases with
The heat given up
As was to be ex
when this additional amount solidi?es melts a 60 an increase in the speed of rotation.
At slower
portion of the lower melting component which is
speeds, slight increases in the speed of rotation
present as a solid to result in better separation.
The liquid squeezed from the crystals runs down
the freeze drum and has a reflux action on the
have no substantial effects.
?lm of material deposited thereon.
65
The advantages of my invention will be better
understood from a study of the following speci?c
examples which have been selected to explain
the operation of my invention.
These tests were carried out with a machine 70
similar to that shown in Figure 1. The squeeze
and freeze drums were each three inches in di
ameter and four inches in length. The drums
were forced together by four springs, which were
calibrated to permit determination of the force 75
The results were as
indicated in the following table:
Table ‘2
-
Speed of
yllnders,
P. M.
0. 55
1. 28
3. 6
8. 5
Feed
Rate,
ml.[hr.
250
280
600
670
Hiin?lgiglfb
ing new
ugt V01
Peréent o'f
Compositions, Weight Per
cent Benzene
Feed
Feed
30. 7
28. 5
29. 1
19. O
51
53
51
51
High-
Melting
Low
Melting
Product
Product
88
89
82
77
35
44
42
44
21,6513'922
5
6
III;
This ‘test ,wascarried out .toidetermine. the. Bf‘,
Ther-resultsnf this; test -‘ were as indicated ' in -. the
following table :
fectof. the freezecylinder. temperature, on the
purity of. theproducts, The cylinder speed was
1,281R. P. M.,.the squeezecylinder temperature
was 75°‘ F. andthe force.- on thefreeze cylinder
was 4001 pounds“. ‘The. following resultsindicate
an increase-in the, purity of .the product with an
increase in the.freezecylindertemperature. The
temperature differential between the freezecyl 10
ind'er and. the. freezing. point of _ the , test mixture
decreased, as thefreeze cylindertemperature was
increased. The increase in product purity. was
probably due to slowerrate of crystal growth on
the freeze'cylinder and less, occlusion of liquid.
The results of ‘this .test.wer_e__.as,- shown in the fol
lowing ,table ; .
;
.
.
?vilgfl’glglfh
, Cylinder
Teinp_._, FF.
Feed‘
Rate,
ml./hr.
1 in
Compositionsy, Weight Per
cent Benzene
Pr0d_
11-5: V01
Peréent o'f
Feed
High-
Feed
‘
Low
Melting
Melting
Product
Product
~80
110
20.3
76
95
72
—70l:
280...
75:0
76 '
93
46
—60
_
Hyilelgllo1ft~
Feed Rate
’
mum‘
-
1g 7'
Compositions; Weight Percent
Para Xylene
e '
lngvProduct,
Vol. Percent
of Feed
‘
Feed
HighMelting
Low
Melting _
Product
Product
' Total-re?ux600 >
30
21
60
so 80
500
22
60
81
54 .
550.‘-
20
60
79
561
V
24
52
The» foregoing examples have been presented
for the purpose of more fully explaining the'iop
eration of my invention. It is not intended that
my" invention be limited tothe speci?c systems
used; but it is applicable to any system whose
componentsare not'decomposed‘ by melting or
Tcbleii.
Freeze~
Table 5
290
60. 0
76
97
—40
1801
52.1 0
76 ‘
97 ‘
57
w20
360
16. 3
76
99. 5
73
52
freezing; The scope-of my invention is de?ned
by the following claims.
Having described my invention, I claim:
1. The method of resolving a mixture of- com
pounds into a higher-melting fraction and a
lower-melting fraction which comprises freezing
a portion of the mixture, removing the frozen
portion from contact with the liquid, mechan
ically expressing the occluded mother liquor from
the solid, returning the expressed liquid as re
over the removed‘ frozen portion to the
mother liquor, re-melting the solid out‘ of con
EXAMPLE IV
tact with its mother liquor to form a- new mother
To test the effectof-the squeeze temperature
cylinder on-the-~crystallizer‘performance, a cyl
inderspeed‘of 055R. P. M., a freeze cylindertem
peratureof —64°
and-‘a force of ‘400 pounds on
2. The method of separating a mixture of com
pounds into a higher-melting fraction and a
the squeeze cylinder was-used.
lower-‘melting fraction which comprises main
The data indi
liquor and repeating the step described;
cate that the purity of the high-melting product
taininga body of the mixture as a liquid, con
increases with an increase in the squeeze cylinder
tinuously removing and simultaneously freezing
temperature. This probably results from in
creased fractional melting of the crystals as the
temperature is increased. The additional wash
ing resulting from the additional amount of the
crystals melted is probably another factor in the
increased purity. The data also indicate that the
yield decreases as the temperature increases.
This was to be expected. The following results
a ?lm of said mixture, maintaining said ?lm at
a temperature between the freezing point of the
lower-melting fraction and that of the higher
melting fraction, pressing the frozen ?lm to ex
press the occluded mother liquor, recovering the
were obtained:
3. A crystallization apparatus which comprises,
in combination, a pan for containing the liquid
material to be separated, a ?rst internally cooled
rotatable drum adapted to dip into said pan, a
scraper blade biased against said drum for re
moving frozen material therefrom, a second drum
positioned above and parallel with said ?rst drum
and biased against said ?rst drum, and means for
maintaining said second drum at a temperature
higher than said ?rst drum.
4:. A crystallization apparatus which com
Table 4
-
Squeeze
Cylinder
Temp, °F.
Feed
Rate,
nil/hr.
Hgrl?grgfb
in; Pmd_
Compositions, Weight Per
cent Benzene
not V01
Peréent o'f
F d
_
Feed
ee
60
75
80
90
380
380
350
170
37. 8
25. 3
25. 7
25. 9
53. 0
51. 0
51. 0
51. 0
High-
Low
Melting
Melting
Product
Product
86. 0
87. 0
88. 0
95. 0
33. 0
37. 0
37. 0
41. 0
frozen ?lm as a, higher-melting fraction, and re
turning the expressed liquid to the body of liquid
mixture as re?ux over the ?lm of said mixture.
prises, in combination, a shallow pan, a lower
60 drum rotatably mounted above said pan and
adapted to dip into said pan, means to cool said
EXAMPLE? V
This test was carried out to determine the
separation to be achieved with a feed mixture
of meta-xylene and para-xylene.
The cylinder
speed was 2.82 R. P. M., freeze cylinder tem
perature was -40“ F., squeeze cylinder tempera
ture was 60° F. and the force applied by the
squeeze cylinder was approximately 200 pounds.
It was necessary to use a smaller force with the
meta, para-xylene system than with the benzene
n-hexane system because the mixed xylene crys
lower drum interiorly, a scraper blade biased
against said lower drum on the down-side with
respect to the rotation thereof, an upper drum
rotatably mounted above and parallel with said
lower drum, said upper drum being biased against
said lower drum and cooperating therewith to ro
tate in the opposite direction, means for warm
ing said upper drum interiorly, and means for
rotating said drums.
A crystallization apparatus comprising, in
combination, a rotatable flaker drum, a trough
tals were somewhat pasty and sloughed oif the
under said drum, said drum being positioned to
freeze cylinder when the pressure was too high. 75 dip into said trough, a scraper blade biased
2,651,922
8
7
tinuously removing and simultaneously freezing
against the periphery of said drum, means for in
ternally cooling said drum, a second drum rotat
ably mounted above and parallel with said ?aker
drum, said second drum being biased against said
a ?lm of said mixture, maintaining said ?lm at a
temperature between the freezing point of the
lower-melting fraction and that of the higher
melting fraction, continuously pressing the frozen
?lm to express the occluded mother-liquor, pass
?aker drum, means for maintaining said second
drum at a temperature higher than said ?aker
drum and means for rotating said drums.
6. A crystallization apparatus which comprises,
in combination, an elongated trough having an
_ ing the expressed occluded mother-liquor over
the frozen ?lm as reflux, and recovering the
frozen ?lm as a higher-melting fraction.
9. The method of resolving a mixture of com
inlet at one end and an outlet at the other, a 10
pounds into a higher melting fraction and a
plurality of transverse ba?les dividing said trough
lower melting fraction which comprises pass
into a plurality of shorter troughs, a plurality
of in-line, internally-cooled ?aker drums rotat
ably mounted above said troughs and dipping
ing said mixture of compounds successively
through a plurality of freeze zones, freezing a
thereinto, a scraper blade at the rear of each 15 portion of the mixture on a rotating body in
each said freezing zone, removing the frozen por
drum for removing frozen material therefrom, a
receptacle behind each drum for receiving the
tion from contact with the liquid mixture, me
chanically expressing the occluded mother-liquor
material so removed, a conduit connecting each
from the solid, returning the expressed liquid
receptacle with the next adjacent trough towards
the inlet end, an internally heated roll positioned 20 as re?ux over the removed frozen portion to the
mother-liquor, remelting the solid out vof con
above and biased against said flaker drums, and
means for rotating said drums.
7. A crystallization apparatus which comprises,
tact with its mother-liquor to form a new mother
liquor, and passing the new mother-liquor to a
freezing zone upstream of the freezing zone from
in combination, a ?rst roller, means for deposit
ing a layer of the mixture to be processed on the 25 which it is obtained as a solid.
BENTON L. GRAHAM.
periphery of said ?rst roller, a second roller par
allel with and biased towards said ?rst roller,
References Cited in the ?le of this patent
means for maintaining said second roller at tem
UNITED STATES PATENTS
perature higher than said first roller, said ?rst
and second rollers cooperating on being rotated 30 Number
Name
Date
to apply pressure to the material deposited on
306,543
Smith ___________ __ Oct. 14, 1884
the periphery of said ?rst roller, and means for
1,560,473
Howard _________ __ Nov. 3, 1925
removing said layer of material from said ?rst
roller after the squeeze treatment.
8. The method of separating a mixture of com 35
pounds into a higher-melting fraction and a
1,906,534
2,131,333
2,308,541
2,435,792
Burke __________ __ May
Schweinitz ______ __ Sept.
Raver ___________ __ Jan,
McArdle et a1 _____ __ Feb.
lower~melting fraction which comprises main
2,470,116
Swietoslawski et al.__ May 17, 1949
taining a body of the mixture as a liquid, con
2,
27,
19,
10,
1933
1938
1943
1948