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Патент USA US2134331

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Oct. 25, 19358.>
y
2,134,331
W. P.- GEE
SEPARATION OF WAI` FROM MINERAL OIL BY FILTRATION
4 ‘Sheds-Sheet 1 l
ì Filed March 31, 1934
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INvENToR
ATTORNEY
Oct. 25, 1938.
W. PA GEE
'
2,134,331 n
SEPARATION OF WAX FROMl MINERAL OIL BY FILTRATION
Filed March 31, , 1954
-4 Sheets-Sheet, 2
.
' Oct. 25, 1938.
w;l P. GEF.>
l2,134,331
SEPARATION OF WAX FROM MINERAL OIL BY FILTRATION
Filed March 31, 1934
4 sheets-snaai 5 y
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Klv@
INVENTOR
_ BYvfwWAM,
ATTORNEY
Oct. 25, -1938.
y2,134,331
W. P. GEE
SEPARATION OF WAX FROM MINERAL
Filed March 3l ,
BY FILTRATION
1934
4 sheets-sheet '4
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INVENTOR
W/Y//à/r/f/.gâee
BY/z/s
A TORNEY
2,134,331
Patented Oct. 25, 1938
f -UNITED STAT
kSEPARATION
»
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`2,134,331>
0FA WAX
FROM'.
MINERAL> _, ,
BY FILTRATION
"
william P. Gee, Plainfield, N. 1.-,'assimor :one _
- Texas Company, New York, N. Y., a corpora- '
tion of Delaware
Application March 31, >193:4, Serial No. .718,347
«4 Claims.
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(cl. 19o-1s)
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` VThis invention relates to an improved process j tempting to .meer preeipltated wax freinr cold
of dewaxing mineral oil by filtration, and to an wax-bearing oil, or mixturesfof such oil and sol
improved process of continuous filtration ap
vent, with a continuous or intermittent typeof
, plicable thereto: and the presentapplication is t filter where changev of >temperature is involved,
5 a continuation-in-part of my application Serial the initial filtering rate may be fairly high >but
` it almost immediately decreases and. drops of!"
No. 607,270, filed April 25, 1'932.
exceedingly rapidly.. This is due torplugging up
'I'he invention contemplates a process of filter
ing solid hydrocarbons or paramn wax vfrom liquid . of the pores'or interstices ofthe filter fabric >with
hydrocarbons comprising consecutively submerg
waxy »material which has- vbecome liquid and
penetrated the. fabric'duringthe time- the cake.vk
10 ing a hollow filtering surface within a cold mix
and -filter surface is exposed- -in the relatively*
warmer zone above the> cold- ñltering. mixture.>
.During ,this time the filter cake _and the fi1ter_
surface to form a ñlter cake while the liquid Y
ñows through the surface into its’interior, then ` cloth or fabric become substantially'wa'r'mer due
15 moving the surface out ` of the mixture to‘ contact .t with the vvsurrounding atmosphere,
' ture of solid and liquid hydrocarbons during
which solid hydrocarbons are deposited on the
particularly duringthe cake drying, operation
where air or gasis drawn throughthe cake vand
through a zone of cake washing, dryingl and
discharge while maintaining the filter cake and
filtering surface at a temperature below that "at ' the cloth from‘the relatively warmer »surround
which the solid hydrocarbons tend to soften or v ings. t Contact with the .warmer gas and'exposure
liquefy. During passage of the ñlter surface to the warm surrounding'sf causes. the- wax ~toV
through this zone, chilled gas is forced through soften and redissolve inthe oil vadhering toor
the> cake and the ñlter surface to maintain the absorbed in the cake, or in the wash liquid, and
this solution penetrates the fabric or filtering
cake and surface in a cold condition thus pre
venting vsoftening or re-solution- of the wax in medium along with thek gas or air which isbeing
drawn therethrough».l Upon submergenceof the
25 the liquid contained in. thevcake, or applied
25
thereto as a wash, `with consequentpenetration >'fabric in the cold. niixturein >the bowl of thè .
and plugging of the filter 4fabric by the dissolved ' `ñlter, lsolidiilcation of this wax occurs within
waxy material.
the interstices of .the fabric and >also within the
.
fibres of the ,fabric itself. Consequently, 'the nl
My invention may be employedfin connection
30 with either continuous or intermittent filters. ¿ tering surface soon becomes substantially kcom-_ _`30
One form- of ñlter may, for example, comprise a pletely plugged and iìltration is rendered prac
hollow rotating cylinder or hollow rotating leaves
tically impossible.
with means for creating vacuum within the in- _.
I have. found that by completely enclosing and
surrounding the exposed illteringrsurface, and
terior of the ñlter element or for exerting posi
35 tive pressure upon the exterior thereof.
In operation, the rotating cylinder is kept
.,
l
' circulating -chilled gas throughthe surface dur
ing the time it is out of contact with the cold
partially submerged in ~the Afiltering mixture. ' filteringmixture so as yto maintain the tem
Solids are deposited on the submerged portion #perature of the cake as well as that ofthe fabric
of the surface to form a cake while liquid ñows . at -substantially `that of the- coldmixture, >or
nearly so, I am able to prevent the aforemen
>40 through the surface into the interior of the cyl
~ _ inder from which it is withdrawn asfñltrate. tioned plugging effect. By this means, I am
As the. cylinder rotates the cake is exposed
able .to maintain a continual high economic rate
whereupon it may be dried and washed byap
of
plying `solvent liquid to the surface ofthe cake,
45 the liquid being drawn through thecake into the
interior ofthe cylinder for removal. The'cake
filtration. v
g
,
Y
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50 pressure to the interior of the filtering element
.
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Fig. l is a diagrammatic `view of apparatus
for carryingv out the method of the present- in
vention;
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t
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causing distention of the fabric and consequent
- Flg.».2 is a diagrammatic viewof a modified
loosening of the cake, complete removal of which
arrangement, .illustrating t, the `invention as lap
plied to a ñlter aid dewaxing process with'VA re
is facilitated by suitable means located adjacent
‘ to the exterior surface of the filter fabric. , f
55
.
ing drawings which >>disclosepreferred embodi-VY
may bey subjected to further drying to remove ’l ments of the invention, and in which ~
remaining wash liquid following which the cake
is removed, usually by applying a slight reverse
.~
In orderto better understand the invention,
reference will now be made to the accompany
Experiments have indicated that when at
covery` of illter aid;
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Fig. 3-is a diagrammatic view of still another
amasar
modified form of apparatus for carrying out the
ing liquid, such as naphtha,_for example, from
method of the present invention in a plant in
which filter aid is not employed;
Fig. 4 is a diagrammatic view illustrating the
filtering cycle and the method of supplying wash
f ing solvent to the filter cake;
Fig. 5 is an elevational view of a continuous*
filter suitable for carrying out thepresent inven
tion, certain> parts being broken away and in
10 section in order to illustrate the construction
a tank I3 is applied to the surface of the nlter
cake through a pipe I4 and a nozzle I5 positioned
within the hood G adjacent to the filter cake.
'I'his spray liquid is drawn through the cake into
the interior of the drum and is separately with
drawn therefrom through the'hollow shaft l,
filter valve l and pipe IO into the storage tank
Il. The vacuum pump I I also communicates
with the tank Il by means of a pipe I1 for the 10
purpose of creating a vacuum in the tank and
Fig. 6 is a perspective’view of a portion yof'- also within the interior of the filter drum. This
the filtering surface;
vacuum is continued «after the filter cake has ad
Fig. 7 is a partial sectional view taken on the _vanced beyond the nozzle I5 to permit drying the
15 plane of the line 1-1 of Fig. 6; and
cake and maintaining it in a cold condition by
Fig. 8 is a partial sectional view taken on the drawing cold gas therethrough as will now be 15
plane of the line 3_8 of Fig. 6.
.
explained in more detail.
»Referring to Fig. 1, the wax-bearing mineral
While the vacuum pump II is shown as taking
oil, such as cylinder stock, is advantageously direct suction on the tanks `III and I3, it may be
20 mixed with a solvent liquid or wax-fprecipitating _ _advantageous to interpose a foam' trap between
medium. This solvent liquid may comprise a these tanks and the vacuum pump to remove
thereof;
.
light petroleum fraction, such as naphtha or vari
"entrainedmatter from the gas. _Such a trap is
preferably mounted about 35 or'40 feet above the
ous otherV organic solvent liquids or mixtures
thereof, including alcohols, ketones, aldehydes,
tank and ' provided with a water' leg through
cyclic hydrocarbona‘benzolor its homologues, or
which liquid matter removed in the trap may be
derivatives of these various‘materials. ‘
drawn
The mixture of oil and solvent liquid is deliv
ofi'.
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The exhaust gases from- the vacuum pump II
ered from a source not shown in the diagram and ' arel advantageouslyk conducted, directly to _ a gas
conducted through a chilling coil I wherein it
may be cooled to a temperature of around 0° F.
or below. The chilled mixture is then introduced
to a mixer 2 wherein itis admixed if desired, with
a comminuted solid filter aid material introduced
to the mixer from a hopper 3. The mixer is pref
erably provided with a jacket into which a refrig
erant may be introduced. or through which it may
be circulated in order to maintain the mixture in
a chilled condition.
Y
cooler I9. If desired, a fan or blower I8 may be
used to reduce the back lpressure on the vacuum
The cooler I! comprises a column packed with
Raschig rings or other'sultable packing means.
Cooling liquid, preferably the solvent being used
such as cold naphtha, at a temperature, for ex-`
ample, of about >--40° F., is sprayed overlthe
packing by which means it is brought into inti
mate contact with the gas passing upwards there
o _’
This chilled mixture of oil, precipitated wax
40 and filter aid material is then conducted to the
bowlzfâ' of a filter 4.
through. The naphtha collecting in the bottom
of the column, and at a temperature of about-
This filter is advantageously ' +40° F., is withdrawn by a pump 20 and passed
of the continuous rotating drum type, somewhat
through a >chiller 2| wherein it is again chilled by
similar -" in general principles to that ' employed
interchanging heat with a refrigerant. Liquid
heretofore in industrial .iiltrationg The exterior
ammonia may be expanded into the shell of the
vchiller to effect the necessary refrigeration.
The temperature to which the naphtha is
45 of the filter shell is'covered` with heat-insulating’
materialto facilitate maintaining the interior in
>a cool condition.
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' chilled depends on the extent to which it is de
During rotation of the hollow drum 5, the cy
sired to cool the gas, -and this in turn depends
lindrical surface thereof, comprisingv a filtering ~ upon the character of th'e solid material being
Y50 surface or medium formed from cloth or metal
fabric or any porous' filtering material, passes’
through the body of filtering mixture maintained
in the bowl 3' of the filter, and then .emerges
therefrom during passage through the upiîe?’and
Filtered. 'Usually it is desirable to keep the cake
at’ substantially the same temperature as the
rntering mixture. ‘By maintaining the ybottom of
the column at a temperature above +32° F. any
water removed from the gas may be withdrawn
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from the bottom of the column. It is desirable 55
55 hooded portion 6 of the filter.
The precipitated wax and admixedá‘ïfllter aid ~ to keep the circulatinggas free from water which
material is deposited upon thelexterior and sub:
merged portion of thesurface to' form î‘a filter
might penetrate the cake and the fabric'and deter
filtration.
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cake, while the solvent'ari‘d dissolved oil are forced Y `
The chilled gas at a temperature, for example,
60 through the filter surface into the interior of the of about _30° F., is then conducted through a 60
drum. The liquid~ within-the interior of the drun-l pipe 22 to the hood 6 of the filter wherein it _sur
is withdrawn therefrom through the hollow ro- ~ rounds the filtering surface during its emergence
tating shaft ‘L_„the filter valve 8, the pipe 9 in com
from the filtering solution. This chilled' gas is
munication therewith, and into a. filtrate'storage forced through the filter fabric prior tovandy sub
sequent tothe removal of the filter cake there
tank _HIJ -'The tank Ik is maintained under a re
duced _ pressuregfby. ‘means of vacuum exerted from.4 In this way, the cake and- the filter sur
through a vacuum‘punip o II communicating with
face are continually maintained at a temperature
the top of the _tank through a pipe I2.'v
When that portion o_f filter surface over'which
70 ñlter cake is deposited emerges from the _cold
filtering, mixture into the hooded portion, of the
filter, the application of vacuum upon thein
terior -of that portion of the surface .is continued
substantially nearly the same as that of the cold
mixture undergoing filtration; for' example, in
this case at a temperature of from about 0° F. to
_10°
F.
‘
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70
'
‘ To take care of gas losses, fresh gas may be
drawn from the storage tank or gasometer 23 by
the fan I8. Q The gas referred to herein may in
75 tained in the cake. Upon further rotation, wash-_ ' clude air, flue gas, hydrocarbon vapor, fixed gases 75
_ ~for the purposeyof removing mother' liquor con
I have found it
of advantage to use -ñue gas which~ is relatively
~ auch as `nitrogen and so forth.
inexpensive.
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' - The cake is discharged from the ñlter'surface
lafter washing and drying by introducing, for a
short period of time, a positive gas pressure to
the interior of the particular segment of the'filter
drum in> question, causing the- filter fabric to
bulge and loosen the cake which is then removed
10’ therefrom by scrapersv24. This reverse gas pres
sure may be effected by introducing chilled gas
through the filterv valve >8 from a line 25 leading
Y from a suitable Vsource of supply, aszfor example,
the cooler
y15
I9.
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covery. The wash- nltrate ~-discharge may' be` in
common with'the oil filtrate discharge, as shown,
where' the wash filtrate is passedV froxn'ta‘nk 50
» by pump t4 through lines 65 -a'nd 62 to discharge
63~for solvent recovery. Lines 4| andïf5|ï~are
- 'provided with valves 4|" and 5|’ respectively.-> so
f that the vacuum 'producedby-pump ` 46 inthe
" tanks`40 and 58 may be independently controlled.y
-’ Inl-some gases, fit 'is found «desirable to‘maintain 10
La higher vacuum or pressure’l differential’on they `
`filtering surfaceduring the _washingstage than
during the- pick-up' or cake forming'stag'e. vFor i
examplepimproved results have been> secured by
»
The dislodged cake removed'from the filter sur
face falls through thev chutes 26 into a closed
storage tank 21 from which it may be withdrawn
lfor further treatment including the removal
therefrom of retained Aoil and solvent as well as
1 for the Aseparation and recovery of the filter aid
.materiaL
point of `storage for `distillation forflolvent re-l
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While a vacuum type of continuous ñlter has
maintaining a vacuum'v or pressure differential of 15
about vl5 inches of -mercury on the filtering sur- , ,
face during the time that the -filtering’ sur'iîface'ïis'`
immersed in the chilled wax-bearing mixture and
when the cake is being built up on the filtering
surface, and` a vacuum orY pressuredifferential 20 l
`of about 25> inches of mercury onthefiltering
surface throughout the washing and drying vpor
been described, it is contemplated that the in
tion of the. cycle.v> This‘ is conveniently effected
vention is equally well adapted `to pressure filtra
by adjustment of the valves~ 4|* and 5|’j`which
tion wherein superatmospheric pressures may be «controlthe‘ application of suction to the men- " as
maintained on the exterior .of the filtering sur
tioned stages' of the filtering cycle ,through the
face.
lines`39 and 49 respectively.
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Referring to Fig. 2,v there is disclosed a plant
for filter` aid dewaxing by continuous filtration
with continuous recovery'of filter aid, in which
a foam trap is mounted between the filtrate and
the wash solvent tanks and the vacuum pumpin
the manner described above.Y Wax-bearing oil
is supplied from line 30 by pump 3| through heat
exchanger 32’~ and chilling coils 33 to a mixing
tank 34, where it is mixed‘with recovered filter
aid supplied through chute 35.
'I'he mixture
then passes by line 36 to an enclosed rotary vac
uum `filter 31 `of the type described above, and
which operates with a. continuous filtering cycle
\- The mixed wax and filter aid continuously re- '
moved by blow-back 58, assisted if desired bya `
suitable- scraper of defiector blade, falls vinto a-` so
discharge trough 18 containing 'a scroll 1 I, which '
»feeds the material to a discharge 12 terminating
in' 'a -hopper -13, `which in'turn feeds through
chute- `14into~a hot mix tank 15. A solvent, such
as vnaphtha, is» supplied tothe >'tank by linej_16. l35
The tank-is equipped vwith a suitable agitator and
a steam ~ coilV or .ietÀ (not shown)`, whereby the
contents are mixed and heated to dissolve >the
waxin the’sol'vent andv to form a pumpable'
>slurry of‘the’filter aid suspendedin the 'wax
including pick-up or cake forming, washing, dry ` solution; The slurry iswithdrawn through line
ing -and cake discharge. In the cake forming 11 by pump 18 and passed by lln'e`_19\to a‘conf
`stage, filtered oil is discharged from thefvalve 38 tinuousenclosed filter 88, which may be of simi
of the `filter through line 39 to tank 49. >Thelat A.lar constructionv to the ñlter 31, operatingjwith
45 ter is connected by line 4| to a common suction stages of pick-up, washing, Adrying and Acake >dis 45
line 42 leading to a` foam trap 43‘having a gravity charge. _In rthe pick-upv or" cake.P forming stage
leg 44 through which any trapped or entrained ofthe'cycle, the; filtrate of wax >solution is'dis'
liquidi» is discharged into a barometric’seal or chargedfthrough the line 82 into tank 83, from
' drum, the separated gas passing by line 45` to the which the wax solution maybe withdrawn by
suction side of vacuum pump 46. Chilled wash
solvent, supplied by pump 41 through chiller`4'l'
and line 48 to the distributing means of the filter
31 at the washing stage of the filtering cycle,
passes through the filter cake; and the mixed
55 Wash solvent and extracted oil discharges
through line 49 to solvent storage tank 58. The
latter is connected by pipe 5| to the common suc
tion line 42 leading to the foam trap 43 and,
thence to suction pump 46 as described above.
The separated gas'is suppliediby pump 46 under
pump 84 andy passed through line 85 for‘recovery 50
of thev solvent from the contained.. wax.v The
upper portion of -tank 83 communicates by lines
86 and`81 with a foam trap 88 having .agravity4
discharge leg 89 for any enti'alned liquid, and >a
gas discharge‘90 communicating with thesuction 55
side ofavacuumjpump 9|` which dischargesv into
an equalizlng tank`92. Gas from tank 92 passes
through lines 93 and 94, the latter- containing
pressure reducing valve 95, tothe interior of the
casing ofthe filter'88, to completethe‘g'as cycle 60
pressure through a preliminary cooling tank 53 which minimizes solvent loss.- During thewash
and- a chiller 54 to`line 55, and then’through ing stage on filter 80'„`heated wash lsolvent,'such '
pressure- reducing valve 56 to the interior of asnaphtha, supplied from line l96 by pump „91
the filter casing, to continuously maintain the through heater 98 -and line 99, is' directed Lonto
chilled gaseous atmosphere surrounding the fil
the formed~filtercake lto remove contained'wax es
tering surface. Chilled gas at a suitablev presi
solutionl therefrom. -The vresulting “solution is
sure, such as about 2 to 5 pounds gauge, may Withdrawn iìhrougii‘llrie- |00 tó Solution tank Inl,
be passed through branch >58 to the proper pas
the' vapor spacev'of which’j is connected by line
sage .in the valve 38 Voi’ the filter, to assistV in ` |02 with the common 'suctioniine a1 leading to"
70 the discharge of the cake in the blow-back por-- foam trap 88 and vacuum pump 9|.' The 'resulte 70'
tion of the cycle. Dewaxed oil is withdrawn from ing solution is_ withdrawn from tank |8| byv pump
tank 40 by pump 60 and supplied through lines
6| and 62 to the heat exchanger 32, where it
serves to partially cool the incoming oil »to be
75 dewaxed; and then passes by line 63 toa suitable
|03 andï‘returnedby line 16 tovserve,asfsolventl
liquid in the hotrmlx tank 15. "Pressure'gas from
line 93 is >supplied by'branchy line '|05 as bloW-.
back tov remove the washedand drled‘ cake of
,
.
4
arena:
nlter aid material from nlte'r l0. VThis cake is «ma m. ma thence by une m controlled by
discharged into chute Il, which returns the filter valve |24- to »continuous enclosed filter indi
aidto mixer“ for reuse in the process.
'
cated generally at |24. A drain line |25 con
, VA- pump |05 withdraws flue gas from a genera
trolled by valve |25 is provided for draining the
tor -|01 through a scrubber and dehydrator |00, filter tank.;Í . i
.
and forces the gas under a controlled pressure
'I'he continuous filter may be of the type pre
intoa gasometer |08, which maintains a bal
viously described, operating with stages of pick
_anced pressure on the system. vFlue. gas is sup
up, washing, drying and cake discharge. In
p1ied¿from_the gasometer |09 throughv line ~||0 the pick-up or cake forming stage of the cycle,
to the interior ofthe filter casing 51 by means filtrate is discharged from the usual control4T
of line |I|, and t9 the interior of> filter 00 by valve> |20 throughl line |29 to tank |30. Wash 10
ymeans `of line H2.. Thevgasorneter thus fioatszon 2filtrate is discharged through line |32 to tank
the system, supplying a small amount of make
|33. 'I'he upper portions cftanlrsv |30 and |35
up gasas required-to maintain the desired-quan
communicate through lines |35 and |31, respec
15 tity andpressure of gas within the system. The tively provided withvalves |35and |39, with a
pressure within the gasometer |09 isV controlled
4to the desired pressure which is to bemaintained
withinv the filter casings by suitable regulation
of pump |05.
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common suction line |40 leading to a foam trap
|4| having a gravity discharge leg |42. >Gas is
withdrawn from 'foam trap> |4| through line |43
l
by vacuum pump |44, and supplied under‘low
pressure to preliminary cooler |45 and thence 20
ploy filter aid kin connection with the dewaxing through chiller |45 and line | 41 containing pres
of certain distillateand residual oils by filtra vsure reducing valve |48 to the interior of the
tion. It has now been found that the use of filter closed filter casing to maintain the-chilled gas
It was formerly considered essential to em
aid can be dispensed v with in certain dewaxing
-processes employing filtration. »This is advan
tageously accomplished-by the >employment of
certain selective solvents . or solvent mixtures.
which at lowered temperatures aresolvents for
the oil, but in which the precipitated wax is sub
stantially completely insoluble; or by the use of
solvents'of low viscosity which give a crystalline
wax on chilling. Examples of such selective sol
vents include a ’mixture of acetone and benzol,
and a mixture of acetone, benzol and toluol; and
propane is an example of thelatter. typeof; sol
vent >of low'viscosity.` Very satisfactory results
have been secured where a `solvent consisting
of substantially 35% by volume of acetone and
65% by volume of benzol is employed in the ratio
>of from two to four parts of solvent mixture to
one part of wax-bearing oil. ~'In the case .of
residual oils, a very satisfactory solvent mixture
consists of about 28-35% acetone, ifi-57% ben-_
zol and 15-l8% >toluol in substantially the same
proportions of solvent mixture to oil'. In „such
case, it is also found highly desirable to wash
with the same selective solvent mixture. By
the use of a solventmixtureV of this character,
the wax is precipitated in a formwhich admits
of satisfactory filtration at commercial rates.
By the Ause of such a selective solvent mixture
for washingv the formedA wax filter cake, re-solu
tion of some of the wax is avoided, and conse
quentlythe oil removed in the wash stage has
substantially the same pour test as the filtrate,
whereby the two `may be mixed to give an in
creased dewaxed oil yield of the desired low pour
test. l When this is coupled with a gas recircu
lation system of the character disclosed herein,
which maintains the filtering surface >at all times
at substantially the -temperature of the wax
. bearing mixture being filtered,- successfuliopera
tion of the fllter'over substantial periodsof time
is assured. Thus, by the cooperation of the
several features,- including the precipitation of
the wax in a Vmore suitable form for filtration,
the maintenance of the filtering surface vin a
. condition of high effectiveness, and the avoid
ance of re-solution Vof the wax cake, separation
70 of wax by continuous filtration may be accom
plished without the use of filter` aid. _
.
Referring to Fig. 3, there is shown a simpli
fied plant for continuous filtration, in vwhich
filter aid is not employed. The chilled wax
bearing oil is supplied through line |20 to feed
- eous atmosphere therein.
_
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» Where a solvent.l mixture of the character offv
acetone-benzol'is employed for dewaxing, it is
found desirable to u_se an indirect chiller'. |45,
rather tharï>4 the direct chiller shown vin Fig'. l.
For’example,- the chiller maybeof suitable heat
exchanger construction, having a bank of tubes
through which the> gas passesin indirect'heat
exchanger relationship with a refrigerant,l such
for example y.as chilled brine,- ammonia, SO2 or
other suitable- refrigerant. A branch line |49
leads from chiller |45 to an auxiliary pump |50, »
which serves to force chilled gas at a regulated
positive pressure, which is independent of fluc
tuations of pressure in the main circulation sys
tem, through the blow-back line | 5| for discharge
of the cake.y
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.
A liquid dischargepump |53 servesto dis
charge the oil filtrate and the wash filtrate
through lines |54 and |55, respectively controlled
by valves `|55 and |51, to a'discharge line |55
leading `to solvent` recovery. Pump |52 draws
flue gas from .generator |53 through scrubber
and dehydrator |54, andY discharges the gas into
.gasometer |55. From the latter, gas is supplied
through line |55 to line |41 beyond valve |40, `
and ythus to the interior of the filter casing, to
make up for any gas loss and to maintain the
quantity and pressure of gas within the circu
lating system. Inasmuch as the gas loss is very
small, the quantity of gas passing from the
gasometer to the, filter casing is insufficient to
materially affect the temperature ofV the gaseous
atmosphere therein.
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Fig. 4 shows diagrammatically and in outline
'a rotary vacuum continuousÍ filterof the type
used in Fig. .1 to 3 for wax filtration, with the fll
teringy cycle indicated thereon. rThe filtering sur
face is shown at |1||,A and is divided by division
strips | 1| into a plurality- of longitudinal seg
mentafindicated as 2,4 in vnumber about the pe
riph’ery of the filter, although of course' the
number >may bevaried. The customary filter
valve which controls the application of suction
and the'` supply of pressure blow-back gas to
the interior of the filtering segments at various
stages in the cycle of rotation of the filter, is
indicated Aat |12. The liquid level of the chilled
wax-bearing mixture within the vat or casing
of the filter is shown at |13. The filter rotates
in the >direction of the arrow |14, and cake
formation starts at |15. Atrthis'point. the filter u
5
2,184,831
valve opens to communicate suction to the ñlter-V the terminationv of the vacuum andthe initia
ing surface, which suction continues throughout , tion of _blowfback at„|9i.` At this point, chilled
gas~ under pressureisdischarged throughr the n
the extent of the _immersed portionof` the filter, ‘
rpassage in the valve to'theuinteriorsof the seg
to provide the pick-up'or cake forming'uare‘a y|16.
ments of the filter, _#causing distention v‘of the
vassisted
through the> filtratezline as previously, described. ’ filter cloth asindicated »at |82.`
Á As the ñltering’segments consecutively -emerge by’thejscraper|93,"serves to` remove the formed
from the "chilled mixture, their communication and dried filtercake. ‘The reverse'ìflow of chilled
with the filtrate outlet is cut ,oi‘fa’t'` |18;‘and gas or blow-backterminates jat |84, and a; full
.'I'hefiltered oil fromv this section is discharged
10
afterashort rotation, _communication with Vthe
' block indicated‘at |95vseparates'thetermination 10
washing'and drying discharge po'rt of the valve
is initiated at |18.
Theaction of the vacuum
then creates .a pressure differential on` the filter
, ing surface, which causes the chilled gaseous at
of 'the'cake discharge` zone from> _the beginning
of the rcake forming,v zone at l'lñçfwhereupon the
cycle is repeated. ' "_"
'_
y
.
n
c In fdewaxingI ,byy pressure filtration, it `has ¿been
surrounding the -filter to act upon'fthe customary ~to employ pressures, ‘of from about
15 mosphere
cake. during the drying stage |80, to Adrain or ' >>‘foto oofpoundsper squareA inch or. higher. Í In '
_strip retained oil from the cake. The washing applying‘the principles of pressure',` `filtration tor
.of the drained cake then commences, asjindi-A , an ‘enclosed vacuum filter, the, obvious thing
cated at I8I.
y
So far as I am aware„all prior suggestions for
washing a wax _cake on a filter have beento l
is to use a gas pressure’within the’ filter casing
ofv substantially thisA amount, Mini.’ order n to` in
crease v_the pressure` differential" acting onjthe
apply sprays of washing solvent thereto. I have filteringv surface, with‘a view to increasing fil-v`
discovered that superior resultsl are obtained by ltering'rates and capacity. ¿I have found, how
supplying the washingy solvent- to the cake in -ever, that instead of being'beneiicial, such in
theform of a continuous- liquid film 'which iiows creased pressures may beyaçtually harmful, `due 25
._ continuously onto the cake. This is accomplished Y to the reduction in filterirígffrates. This' is'> ap
by the weir feed, comprising the trough |82 parently vdue -tothe fact Y, that' the wax‘cake,l
which is mounted yto extend- longitudinally ` tends to compact under >the increased pressure,
"throughout the length ofthe ñlter, ’beingsup
thereby` losing its pervióus'__fo_rm of interwoven
_ walls. ‘Washing solvent is continuously sup
" imperviousi‘mass." -In accordance with the "pres
ported in any >suitable manner from the casing ' crystals, and becoming more'or lessl of va slimy
plied to the trough by"supply pipe |83 so as to ' ent invention, the 'u chilled 'gaseousatmosphere!` e
maintain a continuous overñow‘at ,the Weir |80.
within :the viilter’casing' vis purposely maintained
tion opposite to the direction of rotation of the
ed. This'is preferably 'accomplished by' main- .
'I'his forms a sheet or vfilm of liquid throughout >at'such a pressure that a pressure‘differential on
the length of` the filter, which flows down an "thejfiltering surface equivalent to notA more than 35
about 15 to 20 poundsper square inchjisaffo'rd
inclined guide |85 onto the filter cake in a direc
filter. Sufiicient washing liquid is supplied so a taining the gaseousv atmosphere within theiilter
casing- at substamtiallyï'atmospheric- pressure, `or‘
as to maintain’a thin liquid film over the ex
posed portion of the filtering surface substantial- ’ at, onlya few pounds above atmospheric'l pressure, 40
ly throughout the extent of the washing zone the pressure diiîerentialfbeing then secured'byv
indicated at |86, the film being of course thick- ' means of vacuumappliedbyi‘thevacuum pump.:
er at the upper portion adjacent the weir feed.
The outer portion of the film flows downwardly
over the filter cake countercurrent to the direc
tion of the rotation of the filter, _while the in
yThis is-` efiectedin Figs. Zand 3 by staging down
the pressure‘of the gas being vreturned -tothe
filter casing, as bythe pressure_.reducin'g,valves
56_and |48 respectively. This' has' the further
ner portionof the >film adjacent thecake as- ` advantage of" minimizingfgas leakage, thereby .
sumes movement along with the filter cake. The c avoiding loss of associated solvent vapor.
pressure >differential existing upon opposite sides
of the cake land liquid `film, tends to force the
-wash liquid down into the cake to'displace re
`Previous practice in connection with enclosed
vacuum filters employing a pressure gas atmosf 50
phere therein, has been to either enclose the
entire filter in alarga casing Vforrningin effect y
of wash liquid supplied, and the extent of the` Va filtering room,vor'tofattempt to secure the
washing zone, is controlled to afford substantially 'cover of the filter casing to the vatY creasing
maining oil therefrom. Preferably, the quantity
complete displacement of retained oil _from the
proper is gas tight relationship byy bolting' with 55
the aid of sealing gaskets.` The former'pr'actice
solvent which would needlessly drain` through
the cake after oil has been expelled. This dis
the objection that frequent removal of the cover,
55 cake, while avoiding the use of an excess of
is highly expensive; andthe latter practice has ,
which is `necessary for adjustment, repairor re
use of wash solvent, obtains an increased yield placement of parts, renders it diiliculttol main 60
of dewaxed oil, and avoids solvent loss which I ' tain the proper- sealing »relationship when> the
'
have found toi'be inherent in the use of sprays, cover is replaced.
The presentinvention overcomes these objec
when volatile solvents are employed.
placement weìr wash affords ìeconomy lin-the
Following the washing zone, the cake is then
subjected tofurther pressure differential during
the drying stage |88, at which time cold gas from
tions in the manner ‘shown inA Fig. l15,'in'which
a commercial formfofuenclos‘ed vacuum @filter is
shown inl end elevation. The_iilter casing 200
the atmosphere surrounding the filter is drawn lisxformed. ,at its upper endwlth an 'outwardly
through the ñltering surface to displace 'wash extending flange 20|." Entirelyv about the'inner
_solvent as well as to maintain the filtering sur- j 1periphery of the‘upper portion‘of casing Y200 is
' a narrow trough 2702, 'to which is suppliedy a `suit
70 face chilled to a low temperature. The liquids able sealing liquid 203. The removable cover 204
and gases drawn through the filter during the
zone from |19 to |88, at which latter point the yis formed with a surrounding reinforcing bar
discharge passage is closedby the valve, are
202iV carryingan outwardly extending flange A206
discharged through» the _wash solvent line as adapted to seat upon the` flange 20| to support
the cover. The latter carries-a'ldownward‘ly ex
75 previously described. A full block |90 separates `
65
70.
.
8,184,881
tending flange 2li about lits periphery, which features of -the present invention were incor
depends nearly- to theV bottom of the troughV 202, porated. The advantages of this method of con
and thus provides a liquid seal. Due tothe fact . tinuous filtration over the heretofore used inter
that only- a.. comparatively small gas pressure is " mittent pressure filtration include such consider
` maintained'within the filter casing, a >compara
ations as greatly increasedplant capacityl for a
tively shallow trough .202 suflices to maintain 'given - amountfof ,fllten area, simplified _plant
, the liquid seal. V_The cover is equipped with longi ' operation;y simplified means of applying a `dis-v
`>t'udinally extending handles 208'at opposite sides placement wash tothe filter _cake so' ‘as to obtain
thereof, by which the cover may be attached to highen yields, Y and
lconsiderable reduction.` in 1
suitable chains or hooks of a conventional lift
installation costs, l*
ing mechanism or hoist, so that the >cover may
. -beeasily and instantly removed andreplaced.
ll has been to fasten‘the filtering cloth- over the
filter .by `means of an exteriorwire wrapping, _’
generally in >the fermer a splrauy wound wire. 1
factory` discharge of >awax cake. The scraper
,
.
s
tinuous filtration 'for' yvax separation has >here
tofore proved impractical in the industry, two
fPrior practice ingthe' -construction of rotary
drum ñlters of the lcharacter disclosed herein,
~ have found that this `may interfere with the satis
_
" While thereare a'nuìnber of reasonswhy con
of thev outstanding reasons are no doubt
First: _ The inability to maintain `the filtering
surfacev in highly effective filtering condition
throughout a long period of continuous'operation, .
and
,
,
‘y
i
Second:;The inability to `continuously form a
filter cake at commercially 'practical rates which
or deiiector, which assists in removal. of ythe
, cake, generallybears against or near this outer s could be satisfactorily removed from lthe con
wire wrapping.l Consequently. there ,is a sub
tinuously rotatinglfilter.
‘.`
'
'
'
lstantialsgap between the scraper and thefilter
The
first_reason
for
failure
asl
notedabove,
ing’surface depending on the size of the wire has been overcome by aV combination of features
used; Due to the peculiar natureof the „wax of the present invention, including the chilled
_, cake, a portion fof the wax tends to be ,retained
about the wires on either sidey thereof, which
` eventuallymay slime or plug the filtering sur
faceto a certain~ extent, reducingfiltering rates.
gas recirculation/system which maintains the fil
tering surfaceat all times at a temperature ap
proximating that’of the chilledVwax-bearing mix
ture being'filtered," such as to prevent re-solutlon
of the wax'with plugging ofthe Afilter cloth; the
This is overcome in >accordance with the present
invention by the construction shown in Figs. 6 use of wax-bearing mixtures resulting _from sol- ‘
to 8 inclusive.
Two ofthe longitudinal segments yent dew’axin'g of suchv character that the lpre
y
' ' ofva
sealing
V.conventional
blocks'for the,
filter
ends
areofshown,
the filter
thechambers
>annular
as ofthe segments being indicatedat 2li. and the
division between >two segments at 2li. Indi
vidual filterV clothsA 2l2 are provided> foreach
segment. Along’ the end surfaces of each seg
ment. as indicated at 12H; the filter cloth is
4o caulked in place within a. mortise and tenori type
of >groove >2M (Fig, 7) >extending about the pe'
riphery of the blocks 2|0.` The filter cloth >is
laid over the grooves, with a substantial extent
overlapping the blocks 2N;V and then a cotton
45 rope or other suitable cord is pounded into the
groove as shown at- 2lb, thereby forcing the filter
cipitated wax is in a better: form for filtration;
`the employmentl for washing >of the cake of a
selective solvent 'mixture'of such character that
the wax is substantially completely insoluble
>therein- at the temperature of treatment; and the
use offiltration pressures or pressure differentials,
together with a reduced filtering timeper cycle”
i to which'jtheöwax cake is subjected to such 40
pressure differential, such that compactlng of the
*_ cake down 'into the pores of the ~filter-cloth is
avoidedT
y
Y
Y
l
r
, .In explanation of thes'econ'd reason for failure
noted above', comparison is4 herein: made with the
customary practice of dewaxing on intermittent
cloth securely into the groove and lockingit in pressure filters. A typicalfilteringz cycle vonrthel
place therein. 'I‘he construction is such that vthe _latter is the following:
„ adjacent portions yof the cloth at the upper end
The period~ of filtration, in `which the filter
of the groove, indicatedy at 2IS, are substantially . press -or pressure filter is filled with the chilled
50
in contact witheach Aother.Y Fig. 8 shows the. wax-bearing mixture under pressure, and the oil
vmanner in which the side _edges ofthe individual forced through the filter cloths while the wax
filter cloths are fastened in place. 2|! is’a ,builds upin a cake on the exterior thereof, gen-4
division strip which extends longitudinally of
erallyl consuming .about 20~ to 30 minutes; the
period of >blow-back, in which the wax-bearing
2i9. yOverlapping portionssoftwo adjacent cloths mixture
remaining in the filter at the termina
2|2 are secured within the groove by a longi -tion of the filtering operation is blown back to
_Ítudinally extending caulking rope 220. kThe
55 the filter,land is provided with a slmilargroqve
>outer surfaces of the cloths »arethus free and
fully exposed, giving full filtering area, and en
abling the cloths to be more euectively distended
by the blow-back gas, to thereby secure an efii
'i cient discharge ofthe calce.` Í-v
_
The advantages'of continuous filtration on ro
65 tary vacuum filters> orv analogous ~continuous
filters as opposed to intermittent'V filtration on
pressure filters orfilter presses, has long been
recognized in the filtration art generally. 'I'here
¿. have been lscattered proposals to employ con- ‘
70 tinuous rotaryfilters for dewaxing. The fact Are
mains, however, that priorvto the invention dis
closed herein, `the dewaxing art continued to em
_ ploy the old intermittent pressure filters or filter
presses. Successful dewaxing on continuous fil
75 ters on a commercial scale was not achieved until
the supply tanks,- generally consuming about 3
to 5‘minutes; the period of washing, in-,which
the filteris filled with wash solventV under «pres
sure to wash- retained-oil out of the cake,_gen-
erally consuminguabout 15 to 20 minutes; ythe
period of drying, in which gas pressure .is ap
V.plied to the filter cake >to remove retained solvent', `
generally consuming about 10 minutes; andthe~
period, of removing the wax >cake from the filter,
generally >consuming about 10 minutes.
It is
thus apparentvthat the overall filtering cycle
consumes approximately 5‘0 >to' 65 minutes, in
Y which less than 50% of that time is‘employed in 70
actual wax filtration;
A
Applying the above periods of time to a con
tinuous filtration cycle necessitates that the filter»A
rotate at an extremely low rate of speed, given
difficulties in the drive and reduction gearing 75
2,134,331»
7 .
therefor. In attempting to speedup the. con nitrati@ rates' during continuous nltr'anoh. „In
tinuous 4filter by reducing the time for-,the ~`vari explanation, it is pointed .outA that Vthe actual
ous operations vcarried out in theY cycle, difficulty rate of ñow of a ñltrate for agivenrlengthof
was experienced in the building up of a cake .of filtering time -at' a constant effective pressure _ dif- l
sufficient thickness to enable satisfactory con
ferentlal is about the same for both a pressure
tinuous removal. In general, it may be stated
that-a cakeV of not substantially lessthan 1/4". in
flow» is ¿ at lthe „ beginningî~ ofv the filtering`> period, y
filter and a vacuum filter. `The highestrateof
and this rapidlydecreases as `’the thickne’ssof rthe
deposit of solids increasesbeyond a certain value.
In an intermittent pressurey filter, for example, 10
thickness should be formed for satisfactory „re
moval. However, where the cake is compacted
during the cycle, a still thicker cake appears nec
essary for securing -satisfactory removal. r`The
use of filter aid'has assisted in- this problem.
substantially _70% to 80% of _the/filtrate may ,
pass >through the filter in thefirst>2 to 4 minutes
of the filtering time. Continuedßpplication of
In accordance with the present invention, this
the .pressure ,upon the cake _thus builtl upcom
pacts this cake, so that the filtering rate then 15
drops off rapidly. However, due to the length of'
objection has been satisfactorily overcome, and a _
cake forming time of ‘as short as from .about -1
to 4 minutes or even less has been made prac
ticable. This is accomplished by the use of a wax
time consumed in the 'other treatments. ofy wash-V '
crystal 4modifying material of suchy .character ing, drying, dumping of _the cake'. etc.„inf,the
that crystal formation .is modified upon- chilling ’intermittent filtration cycle, it ismcommercially
the wax-bearing oil in thc presence of such ma
.impractical to terminate ythe filtrationfperiód>
ferial, coupled with'other> features of the 'present
invention including the comparatively low pres
sure differential which' avoids compacting of- the
cake. By the use -of waxcrystal modifying ma
' terials of this character, filtration -rates of the
oil may be increased as much as 100% or more.
`'I'his is of peculiarcooperation with continuous
filtration, because‘it enables a cake of -satisfac
tory thickness to be built up while employing a
30 commercially practicalv rate of rotation: of ¿the
filter, such as to give a cake. forming time of not
. more than 4 minutes per cycle. In addition, -it
is pointed out that a 100% increase’in filtration
rate on a continuous filter results in' a `100% in
crease-in capacity‘of the plant; whereas, a sim-k
1 until a cake approaching about 1". >in thickness
L'nas-been built up, which as set forth above'nor'
mally requires-‘fromabout 20 to 30minutes. vOn
-the other hand, the cakev forming'timel ofthe.y
present method of -continuous filtration is limited 25
to onlythat initial part of the filtration> period
of the intermittent filter, in which substantially
the highest filtering rates occur.: This further
.improvesfthe overall efiiciencyof vthe continuous
filtration, giving a materially increased-'plant
capacity. For example, the cake forming-time isY
coordinated `with the filtration rate so that only
the ,highflltration »rates normally obtained with
an >uncompactedcakejof a thickness less thanv
1/2" are utilized, such a` cake forming time being y
ilar increase in filtration rate in an intermittent ' generally not more ‘than 4 minutes in extent, and
filtration process gives only a fraction of such `often as little as 1 minuteI or'less. Nevertheless,
increase in plant capacity, due to the ‘fact that with such a short period ofcake formation, the
the actual filtering time is only -a fraction of the high filtration rates .enable arwaxfcake of a.
[thickness in excessof 1/4" to be formed; and 40
I
Various wax crystal modifying materials vmay » often a Vcake of about %" to 1/2'1 or ,more in ’
be employed for this purpose, such’for example, thickness results. This is readily? removed in
continuous operation.`
'
'
‘as a cracked pitchy residue resulting from the re
The successive steps of> thev filtering cycle ’arel
craoking of a cracked'cycle fuel, as' set forthin
40 complete operating time in the cycle.
co-pending application Serial No. 686,244, filed
also performed in proportionatelyshort intervals
August 22, 1933; the high vacuum distillation of time.` In connection with the washing time,
residue of a condensation product of naphthalene it is vfound :that the,v yields j of- dewaxed oil in- ,
in the presence of valuminum chloride,ïas de» . crease with an increase in ratio of washing time
scribed in co-pending ,application Serial No. _. to pick-up time.l 'Ordinarily, fa .washingl time
710,564, filed March 21,- 1934. Also', other types , which is not less than one-third _the pick-up time
of wax crystal modifying »'materials, such as a is employed,.which means that the peripheral ex- _
condensation product of a chlorinated‘wax with tent of the washin'gzone'isat least one-third the“
peripheral extent of the> pick-up or "cake forming
an aromatic hydrocarbon in the presence of Aalu
minum chloride,` certain mineral oil distillation ' zone; `andthe highestylelds appear to '_'be >ob->
. residues, coal tar residues, etc., may be‘used for _tained when the washingtimeis increased so as
this purpose. As the methods of» forming such
materials and of using themas wax crystal mod
ifying materials generally, form no Hpart' of the
present invention, apart from their particular
60 adaptation to continuous filtration, no further
description thereof‘is thought needed. However,
it may be stated that such materials are gener
ally added in a proportion of from about 0.3%
to 6% by weight on the weight of the wax-bear
ing oil and are dissolved in the oil; the oil is
then chilled in the presence of the materials, and
wax is precipitated in a resulting form which
to` be substantially _equal _to [the pick-up time.
However, ,the Iactual differences in yields. ’of de
waxed o_ilfor variation in >the' washing time from
one-third the pick-uptime to a Atime [equal to
the pick-up time,- are comparatively small, so
that operations Within this range are. satisfac
tory.,_ The resulting -'average orcyc’le _rate _of
fflow of the continuousfllteroperating inaccord
ance withthe present .invention is thus much
higher than that commonly obtained on _anin-.l
termittent filter. By way of example, _a filtration
rate of about 0.4 to 0.6 gallons of Vwax-,free oil
yper hour >per square footof filtering surface is
increases filtration rates.
» . `
In accordance with the present invention, there considered a very-satisfactory rate for an inter 70
is coupled with the increased filtration rates at -mittent pressure filter. By operating> in accord
tributable to solvent dewaxing with ',the solvent ance „with the present invention. a filtration
‘ mixtures specifiedabove, and the use of wax rateof from 2.0 to as high as 3.5 gallons per hour
crystal modifying materials, a coordinated con- . persquare foot of` filtering surface hasI been ob-'
trol of the pick-up or cake .forming time. soas tained,- thus >givingÍa plant `capacity.' of _ about
75 to employ only the highest or peak portion of the four ormore times thatof the intermittent filter.
9,184,381
s
At the same time,
~
the dewaxed oil yield is in
emerges from the chilled ,mixture after which
creased, due to the superior‘washing and drying
vthe said cake on theemerged filtering surface is
oi' the cake. For example, a dewax'ed oil yield of
about 80% to 85% has been regularly obtained
continuously washed,'dried `and discharged there
from; the` steps ywhich comprise supplying a
in practic'ze,l as compared to a dewaxed oil Vyield
6r' around 75% or lower onthe yintermittent pres
sure
filter.v
-
'
~
'
_
-
chilled gaseous atmosphere to surround `exposed 5
portions of 'the filtering surface after emergence
>from the chilled mixture and tol maintain a pres
sure Vslightly ‘in excess ofl atmospheric pressure
upon the wax cake during the washing and dry
1
VThe following are examples of results obtained
in the dewaxing of oil‘by continuous nltration
10 without the employment of Ai‘llter aid in accord
‘ing operations, Ithe gaseous atmosphere having 10
ance with the present invention: '
A
l
~a temperatureapproxim'ating that of the chilled
A Mid-Continent distillate oil and an Illinois
wax-bearing mixture'being filtered, supplying a
l Kentucky distillate oil were employed, these oils .chilled solvent mixture in which the wax is sub-_
having the following tests:`
`
-
stantially yinsoluble rfor rthe washing operation
14sl
’_
Mid-Con-
,
_
Kentucky
Gravity, "'A. P. I
2l. 7 ~
Fissa-"1F _____ _.
,_ 45o
, Fire, °F_-__-.
23.1
46o
. 550
vis. @ 21o°F .............. ._
>
_
filtering" surface during the washing and drying
550
;, 7i
_Pour test,_°F-'. .......................... _.
and applying the said solvent mixture to the wax
cake on the filtering surface by-fiowing .the sol
vent mixture by gravity onto the wax cake to
forma continuousliquid film on the> said cake,
and regulating the pressure differential on the
Illinois
tlnent
`
105
,
so
operations so as, to maintain said-pressure dif
90
ferentialat less than twenty‘pounds per square
inch to avoid compactingfof the wax cake.
A selective'solvent mixtureicomposedof ace
2. The method of continuouslyseparating wax
tone 35%,- benzol 52% and‘toluol 13% 'was em
>from a wax slurry on a rotary Vfilter, element
ployed in the’ratio of 4.parts ofv‘solvent to _1
, mounted within a filter casing having an enclos- .
part kof ycharge stock.v The oil was> then-,chilled
ing cover, which comprises immersing said ele
to aA temperature of about _10° F. or slightly
ment'in a wax slurry under a pressure differential
ulower, and the chilled wax-bearing `_mixture
'I'he lfollowing
sumcient to force filtrate through the element and
to build-,up a wax cake thereon, removing the
>filter cake from the` slurry, washing said filter
cake, .drying said cake by means of a stripping
gas, continuously removing saidcake from said
element, introducing a stripping medium into
said casing to provide a chilled gaseous atmos
phere therein between said-filter casing with en
30 passed to the continuous filter.
tabulation indicates the operations and results
obtained:
`
-
"
'
MidCont.
'run #l
35
MidCont.
run #2
Filtering temperature, aF ~
Wax dist. mix_-__
_ `
'
-13
-4
-10
-12
-12
cous atmosphere is at a temperature approxi
`> mating that of the wax slurry being filtered and
‘ 120
120
120
60
supplies-f‘said‘stripping gas, and regulating the
-14_ f
Drying stage._«_
40
30
10
10
Washing stage.
Drying stage...
40
40
, 00
30
60
50
60
50
48
4.8
12.6
48
. 4. 8
12. 6
i 35
_ 3. 6
16. 8
9i
2. 7
3.0
82. 9
17. l
82.3
17. 7
85. 6
14. 4
_.
48
4. 8
12.6
_
Cake thickness in inches _________ .-'.._
Filtering rate of dewaxed oil
in gai/sq. ft./hr.-.-. ...... _.
Dewaxed oil _____ _. .... -Slack wax ........ _; ____ -_
- closing cover and said filter element, which gas
-13‘
_
}í-%
_
2.6
Yields percent by weight: .
_
2.5 `
-
,
80. 3
19. 7
Solid point °F. of dewaxed
50
K'
" y'
“m n
'
CakeA discharge stage__-._
Total cycle time in minutes .
Cycles per hour ____________ __ f
45
’
-9
‘
Wash solvent_-.__
Time of filtration in secs.
Pick-up stage.-
m K
" y‘
n
1
oi _______________________ __
-8
-12
-10
-8
Dewaxing differential °F-. _ _
1
1
3
6
pressure of the said gaseous atmosphere and the
pressure differential through said filter element
to maintain a pressure differential throughsaid
filter element which is less than 20#/sq. in.v to
, avoldjobjectionable compression of the said wax 45
_ cairel on the filter‘element.Y
_ 3. _'I'he method of. _continuously separating wax
froml a wax slurry, on a rotary filter element
mounted within a- filter casing having an enclos
ing cover, which comprises immersing saidk ele 50
ment in a wax slurry under a pressure difieren-_
` 'While the invention hasbeen described in con
_nection with the separation of’wax from wax
bearing oils, it is'to be understood that it is also
55 applicable to the removal of similar types _of solid
jmaterials from liquids v‘wherein it is desirableto
maintain the resulting cake- of'solids ata tem
60
perature below that at which the solids tend
‘to liquefy and reach a condition where they pen
etrate the fabric and ultimately result in plug
gms,
‘
_
l
,
'
‘i
Obviously many modiflcationsand variations
of the invention, as hereinbefore set forth, may
be made without departing fromfthe spirit and
65 scope thereof, and therefore only such limitations
should be imposed as are indicated in the ap
pended claims.
I
claim:
_
,
,
`
'
-l. In the continuous 'process of' dewaxing min
70 eral oil by continuously filtering the chilled wax
bearing mixture at temperatures of around 0° F.
tial sufiicient to force filtrate through the element
_ and‘to build up a wax lcake thereon, removing
the filter cake fromthe slurry, washing said filter
cake, drying saidcake by means of a stripping 55
gas, continuously removing said cake from said .
element, introducing a stripping medium into
said >casing toprovide a chilled gaseous atmos
phere >therein between said filter casing with en
closing cover and lsaid filter element, which gas 50
eous _atmosphere is at a temperature approxi
mating that of the wax slurry being filtered and
supplies said stripping gas, and regulating the
pressure of _ the said gaseous atmosphere and the
pressure difîerentialthrough said filter element 65
to maintain a _pressure differential through >said - filter element which is less than 15#/sq. in to
avoid Vobjectionable compression of the said wax
cake on the filter element.
4. The method of continuously separating wax 70
from` a wax slurry on a rotary filter` element
or lower, and wherein a wax ñlter cakeïis'con
tinuously formed on a moveable filtering surface
-mounted within a filter casing having enclosing
which consecutively submerges `within the chilled
ment in‘a wax slurry under a pressure differen
75 mixture to deposit a filter cake thereon, and then
cover, which comprises immersingthe said ele
tial sufl‘lcient to force filtrate throughthe element 75
9,184,881
and to build up a wax cake thereon. removing
the ñlter cake from the slurry, washing said
ñlter cake with dewaxing solvent chilled to a
.5.
temperature approximating that of -the wax
slurry being filtered by preforming the solvent
>as a continuous liquid ñlm and leading this ‘co'ri
tinuous i‘llm onto the cake, drying said cake by
means of a stripping gas, continuously removing
said cake from said element, introducing a strip
10 ping medium into said casing to> provide a chilled
gaseous atmosphere therein between said ñlter
casing with enclosing cover and said ßlter ele
ment, which- gaseous ~atmosphere is at a> tem
perature approximating that of the- wax slurry
being tlitered. and supplies 'said stripping gas,
andv regulating thepressure of the `said gaseous
atmosphere and the pressure diiierential through
^ said filter element to maintain a pressure diiïer
ential through said illter element which is lesa v
than iifteen pounds per square inch to avoid ob
Jectionable compression of the said` wax cake on
v the nlter'element.
O
wnmm r». om.
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