Note: Descriptions are shown in the official language in which they were submitted.
3~
P~C. 6096A
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PROCES5 FOR TREATING XANT~IOMONAS FERMENT~TION
BROTH FOR IISÆ IN DISP~ACEMENT OF OIL FROM
PARTIALLY DEPLETED_RESERV0 ~S
The hydrophilic colloids produced by Xanthomonas
species are polysaccharides which contain mannose,
glucose, glucuronic acid, 0-acetyl radicals and acetal-
linked pyruvic acid. These gums and their derivatives
have found wide food and industrial applioations. Of
special interest is the increasing focus on the use of
Xanthomonas gums in displacement of oil from partially
depleted reservoirs.
Typically, oil is recovered from underground reser-
voirs via a series of sequential operations. A new well
will senerally produce a limited amount of oil as a
result of release of internal pressure in the well.
As this pressure becomes depleted, it is necessary to
pump further quantities of oil by mechanical means.
These measures recover only about 25% or less of the
total oil stored in the reservoir. A great deal of oil
is still trapped within the pores of the ~ormation.
Further enhancement of recovery can then be eff~cted
by secondary methods. In one method of recovery, a
waterflood is ~arried out by pumping water into a well
or series o~ wells, displacing part of the trapped oil
from the porous rock and collecting the displa~ed oil
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from surrounding wells. However, waterflooding st.ill
leaves about 55-60~ of the available oil trapped in
the formation. The e~planation for this is thak the
water haæ a very low Vi3C05i ty comp~red to the c~udie
oil and teinds to follow the path o~ least resistance,
fingering through the oil and leaving large pockets
untouched. In addition, surface forces in the forma-
tion tend to bind the oil and prevent itsi displacement.
A number of processes have been developed in
recent years to recover further quantities of oil from
these reservoirs by the use of mobility control 501u-
tion~ which enhance oil displacement by increasing the
viscosity or permeability of the displacing fluid. Of
interest are those enhanced recovery processes employing
polymer ~looding with a polysaccharide or polyacrylamide
to increase the vi~cosity of the displacing fluid.
Varia~ions of this process include the use of surfactants
and co-surfactants to release the oil from the rock
formation. Polyacrylamides have been found to suffer
such deficiencies as visco~ity loss in brines and severe
shear sensitivity. Since, as was well documented in the
prior art, xanthan gum is relatively insensitive to
salts (does not precipitate or lose v~scosity under
normal conditions), is shear stable, thermostable and
viscosity stable over i~ wide p~ range, xanthan gum is
a good displacing agent. Moreover, the gum is poorly
adsorbed on the elements of the porous rock formations
and it yives viscosities useful in enhanced oil recovery
(5 to 90 centipoise units at 1.32 sec. 1 shear rate) at
10~J concentrations (100 to 3000 ppm). The use of solu-
tions of xanthan gum or derivatives of xanthan gum for
oil recovery is described in U.S. Patents 3,243,000;
3,198,268, 3,532rl66; 3,305,016; 3,251,417; 3~319,606;
3,319,715, 3,373,810; 3,434,542, 3,729~460 and 4,119,546
, .. .,. , ;. ., : : .:
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It is suggested in U.S. Patent 3,305,016 that aqueous
solutions containing heteropolysaccharide in sufici~-n~
q~antity to increase the viscosity be employed as the
thickening agent in preparing viscous waterflooding
solutions. The polysaccharide may be prepared, separated,
purified and then added~ Alternatively, according to
this reference, the entire culture after adding a
bactericide (e.g., formaldehyde) to kill the bacteria,
may be added to the flood water.
It has been found that various hea tr~atments
result in enhanced viscosities or filterability of
whole and diluted Xanthomonas fermentation broths.
U.S. Patent 3,501,~78 provides ~hat a heat step is
carried out prior to the precipitation of xanthan.
Viscosity increases of 1.5 to 3.5 fold are obtained in
the h~at-treated broth. ~.S. Patent 3,773,752 describes
a process for heating diluted fermentation broth after
addition of an alkali metal salt until coagulation
occurs and filtering the hot solution preferably after
the addition of a coagulating agent such as alum. The
process of U.S. Patent 3,801,502 calls for the addition
of an alcohol, phenol, ketone or non-ionic surfactant
during the heating process. In the process of U.S.
Patent 3,355,447, the heat-treated fermentation broth is
diluted, filtered and the xanthan removed by alcohol
precipitation.
This invention is concerned with an improved
process for preparing an oil reco~ery mobility control
solution having activity enhancement of greater than 15
and a filter ra~io of less than 3 through a Millipoxe~
filter with a pore size of 1.2 microns which process
.
` ~39~3~
comprises heating an aqueous solution of Xanthomonas biopolymer at
an equîvalent xanthan concentration of 0.14 to 1.5 and a salt con-
tent of less than 0.2~ for a period of from about 5 to 20 minutes a-t
a -temperature of about 80-98C, and when the equivalent xanthan
concentration exceeds 3000 ppm diluting the solution to an e~ui-
valent xanthan concentration of from about 100 to 3000 ppm, the
solution of Xanthomonas biopolymer being substantially free of
insoluble matter having a particle size greater than about 3
microns. Preferably said solution is a fermentation broth.
The present invention likewise embraces a process for
preparing an oil recovery mobility control solution which comprises
the steps of:
(a) diluting a whole Xanthomonas fermentation broth to an
equivalent xanthan concentration of 0.14-1.5% with water having a
salt content of less than 0.2%;
(b) heating the broth for a period of from about 5 to 20
minutes at a temperature of about 77-98C; and
(c) filtering the broth to yield a filtrate with activity
enhancement of greater than 15% and a filter ratio of less than 3
through a Millipore* filter with a pore size of 1.2 microns or
even finer, said broth being substantially free of in~oluble matter
having a particle size greater than about 3 microns, and the process
being carried out in the absence of an alkali metal hydroxide.
Preferably step (c) is conducted at from 77 to 98~, and
preferably also the heat treated solution is diluted to an
equivalent xanthan concentration of from about 100 to 3000 ppm when
the equivalent xanthan concentration exceeds 3000 ppm.
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In all cases final dilution of the heat-treated
solution to use concentration, where required, i5
preferably effected with water haviny a salt cvnt~nt
of at le~st about 0.6%.
Whereas previously described heat treatments were
individually concerned with enhancing either vis~osity or
filterability of whole Xanthomona~ fermentation broths,
., _
the present invention is concerned with an integrated
process for preparing mobility control solutions charac~
terize~ by each of these desirable properties, i.e.
enhanced viscosity and improved filterability, as well
as enhanced injectability and good thermal stability.
Methods are described for treating Xanthomonas biopolymer
solutions or broths of two types: those substantially
lS ~ree of insolubles having a particle size greater than
about 3 microns, and those containing such insolubles.
For solutions of the former type, the process of the
invention provides a product suitable for direct injection
without filtration, although for use in oil fields of
low permeability, filtration may be resorted to. For
Xanthomonas pol~mer solutions of the latter type, the ~;
process of the invention includes a fil~ration step.
For purposes of describing the process of the present
invention, the following terminology is used. As a
measuxe of xanthan activity, solution viscosity in centi-
poises is determined at 6 P~PM and 25C using a Brookfield
viscometer with UL adaptor, corresponding to a shear
rate of 7.3 sec 1. For a given solution, the degree of
dilution ~with 500 ppm salt solution, NaCl: CaC12 = 10~
necessarY to ~rield a viscosity of 10 cp. is determined.
With untreated Xanthomonas polymer this viscosity is
.
observed at a polymer concentration of 0.05~ (500 ppm).
~.~3~
The dilution factor observed with a given solu~:ion,
multiplied by 0.05%~ yields the e~uivalent xankhan
concentration of that solution (also termed th~ acti~e
Xanthomonas polymer aoncentrAtion).
Injectability (not used interchangeably h~rein with
the term filterability) is an important property of
mobility control solutions. It is coxrelated with a
Millipore test, as described later in detail, a procedure
that measures flow rate through a Millipore filter (0.45
to 3.0 micron pore size) as a function of volume under a
constant pressure of 40 psig. The filter ratio (F.R~)
is the ratio of the time required to collect the fourth
250 ml. of mobility control solution to the time to
collect the first 250 ml. of mobility control solution.
A filter ratio of 1.0 indicates that the solution has
no plugging tendencies. An acceptable mobility control
solution generally has a filter ratio of 1 to 3 (0.45
to 3 micron Millipore filter~, and preferably below 1.7.
The desirable filter ratio and filter pore size for
a particular mobility control solution are dependent
on the permeability of the subterran~an stratum of the
oil field ~or which oil displacement is planned.
Xanthan mobility control solutions may be subjected
to subterranean temperatuxes of 80C. or higher. The
thermal stability of these solutions is affected by
their salt concentrations as well as other factors.
Thermal stability is measured as the viscosity ratio
of the diluted broth after 7 days storage at 80C. to
that before storage (10 cps)~
Studies of heat treatment of whole
Xanthomonas fermentation broths show that the temperature
required for achieving enhanced viscosity of whole broth
is con~iderably higher than that for diluted broth~
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The wnol~ hroth is far more stable and resistant to ~anthan
polymer reconfiguration by heating ~han is diluted broth.
This can be ~plained by the presence of a higher salt
concentration (.ionic strength) in the whol~ ~ro~h, as
well as by reduced mol~culax mo~ility.
Further st~dies demonstrate that although enhance~
ment of xanthan activity is achieved by heating, heat-
treated whole broth does not retain its injectability
(measured as filter ratio). The injectability decreases
as the heating temperature and holding time are increased.
Further investigations indicated that neither
chemical (surfactants, phenols, etc~) nor physical
(shear rate) treatments were effective in improving the
injectability of heat-treated whole Xanthomonas fermenta-
tion broths.
Studi~s leading to the present invention show thatXanthomonas polymer reconfiguration is the main reason
for the injectability change on heat treatment.
Xanthomonas polymer configuration i~ dependent upon the
trea~ment temperature, time and salt concentrationO
In turn, the configuration determines the viscosity,
injectability and thermal stability of the Xanthomonas
solutior..
The novelty and ad~ance over the prior art o~ the
present invention reside in the findings that (a)
- significant enhancement of xanthan activity is obtained
by the moderate (60-~8C.) heat treatment ~or a brief
period of time, ~rom about 2 to 60 minutes, of a
Xanthomonas fermentation broth diluted with deionized
water or water of low salinity, (b) that the moderate
heat treatment of diluted whole Xanthomona fermentation
broth causes minimum Xanthomonas cell deterioration and
so does not materially affect the injectability of the
mobility control solution and (c3 final dilution of the
mobility control solution to use xan-~han concentration
with water of high salinity favors thermal stability.
3~
In one preferred embodiment of the present in~en~ion
a whole Xant omonas fermentation bro~h subst~tially
free of insoluble matter having a par~icle ~iz~ greater
than about 3 microns is treated to provide mobility
control solutions with favorable filter ratios such
as described in U.S. 4,119,546~
Whole Xanthomonas fermentation broth substantially
free of insoluble matter having a particle size greater
than about 3 microns is diluted to a xanthan concentra-
tion of ahout 0.05 to 2% with deionized water or with
field water having a salt content below 0.2%. The
diluted broth is then heated with agitation at a temp-
erature of 60-98C. for about 2 to 60 minutes, pre~erably
about 5 20 minutes. The heat-treated broth is then
if necessary diluted to use level (lO0 to 3000 ppm
xanthan), preferably with water having a salt content
of at least about 0.6%. The diluent may also contain
other additives such as preservatives, surfactants and
scale inhibitors.
Thus, the inte~rated process of the present invention
offers a method for preparing mobility control solutions
for use in oil recovery having the following practical
and economic advantages:
1. Increased xanthan activity.
2. Improved thermal stability ~when salt water
is used for use dilution).
3. Elimination of need for Xanthomona cell
f~ltration with retention of good injectability.
Mobility control solutions prepared from the whole
fermentation broths by the process of the present inven-
tion have filter ratios suitable for use in most oil fields.
~ ~ 3~3~
Where subterranean s~rata are highly impervlous,
mobility control solutions with low filter ratios (1-3)
through finer Millipore~filters l0.45-0.65 micron pore
size) must be used. Under such circumstances, mobility
control solutions free of Xanthomonas cells and other
insoluble matter must be employed.
For this limited alternative process, the fermenta-
tion medium can be selected from any of those described
in the literature for the production of xanthan. A simple
and useful medium containing an extract of distillers'
solubles (Stimufla ~ H.iram ~alker), dipotassium hydrogen
phosphate, glucose and magnesium sulfate is described
in Biotech. & Bioeng., XII, 75-83 (1970~. The whole
Xanthomonas fermentation broth is dilu~ed with water
having a salt content below 0.2% to a xanthan concentra-
tion of 0.05 to 2.0~, preferably 0.14%-1.5%. The pH
is optionally ad~usted to 6.5 with an alkali metal base.
The solution is stirred (preferably using low shear
mixin~) until the xanthan i5 uniformly dispersed (approxi-
mately l hour). Low sheax mixing gives a higher solutionviscosity after heat treatment than does high shear
mixing.
The diluted broth is heated to a temperature of
60-98C., pre~erably 77-g8C, and filtered. A filter
aid, e.g., diatomaceous earth (Dicalite Superaid), at
a level of about 4 times the xanthan concentration
per liter of diluted broth is added with stirring at
77-98C. and the broth filtered through a pressure leaf
~ilter heated during the run to 77-g~C. Total time
at the elevated temperature, including filtration time,
should be from about 2 to 60 minutes. Filtration can
also be done at ambient temperature after holding at
the elevated temperature for the time period selected.
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Final dilution to use xanthan concentration (100-
3000 ppm) can be made with water, preferably having
a salt content of at least about 0.6%. The filtration
step may optionally be conducted after final dilution
if desired.
Typical sparkling filtrates with doubled viscosities
have filter ratios of 1.5 to 2 through a Millipore filter
with a pore size of 0.45 micron. In addition, 1000 ml.
of ~illipore filtrate is collected within 20 minutes.
Thus, this alternative process provides mobility control
solutions that have enhanced viscosities and that are
injectable into the strata of highly impervious oil fields.
Millipore Injectability Test
Prepare 1050 ml of S00 ppm xanthan solution in
500 ppm salt solution (10:1 - NaCl:CaC12) as follows:
In a Waring type blender equipped with a rheostat,
measure sufficient broth (based on xanthan content) to
provide 0.525g. xanthan solids. Dilute 1 to 6 with salt
solution. Shear this mixture at 50 volts for 2 minutes.
Dilute in the blender to 1050 ml with salt solution
and shear at 50 volts for 1 minute. Use an experi-
mental set-up that allows measurement of the flow rate
through a Millipore filter disc (47 mm, 0.45-30 microns
pore size) as a function of volume under a constant
pressure of 40 psig. Use a reservoir that will accomodate
at least 1000 ml. filtrate~
Ch~rge the reservoir with 1050 ml of xanthan solution
(500 ppm). Set the pressure at 40 psig. Open the valve
and start recording filtrate volume vs. time (seconds).
time to collect the 4th 250 ml of solution
Fllter ratlo =
time to collect the 1st 250 ml of solution
~,
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The following examples are provided for illustrative
purposes and should not be deemed to limit the invention,
the scope of which is defined by the appended claimsO
EXAMPLE 1
_
Xanthomonas fermentation broth substantially free
of insoluble matter having a particle size greater than
about 3 microns may be prepared in the following way:
Cells of Xan~homonas cam~estris NRRL B-1459a from
-
a YM agar slant are transferred to 300 ml o~ YM broth
contained in a 2.8-liter Fernbach flask and shaken on a
rotary shaker for about 31 hours at 28C. A 25 ml aliquot `
is transferred to a 2.8-liter Fernbach flask containing
500 ml of a medium of the followin~ composition:
Ingredient Gram/liter
Glucose-fructose (Isosweet 100,
Corn Products) 10.1
Crude glucose ~Cerelose) 25.7 ~;
NH4NO3 ' 1.0
MgSO4 7~2 0.10
MnS4-H2 0~03
FeSO 47H2O 0.01
AnhydrGus citric acid 1.0
X2HPO4 4.1
KH2PO4 0.69
The Cerelose and Isosweet 100 are dissolved in
distilled water and autoclaved separately. The rest of
the ingredients are combined, adjusted to pH 6.4 and
autoclaved. The separately autoclaved materials are then
combined.
A~ter shaking at 28C. for about 33 hours a 200 ml
portlon is transferred to a 4-liter mechanically agitated
fermentor containing 2 liters ~f the following medium:
: ,: :: . :, . :,, . : ::, : . : ; :
.: : : , :;,. ,:.: . : :. .. :
3 ~ 3~3~
-12
Ingredient Grams/liter
Cerelose (autoclave separately) 25.7
Isosweet 100 (autoclave separately~ 10.1
NH4NO3 1.0
g 4 7H2 0.10
MnS4 H2 0-03
FeSO 7H 0 0.01
Anhydrous citric acid 1.0
CaCl 2H O 0.20
Na2 4
2 4 0.70
The sugars dissolved in 30Q ml of water are auto-
claved separately. The rest of the ingredients dissolved
in 1700 ml of water are autoclaved, and the two solutions
then combined. Aeration is at a rate to provide 1.5
millimoles of o~ygen per liter per minute. The fermen-
tation is conducted at 30C. for 48 hours during which
time the pH of the medium is maintained between 5.9 and
7.5 by the addition of a sodium phosphate buffer made
up with tap water. Ethylenediaminetetraacetic acid is
also added to the sodium phosphate buffer to prevent the
precipitation of calcium phosphate salts. At the end
of the fermentation, the viscosity of the broth exceeds
7800 centipoise units at 5.~7 sec. 1 shear rate and the
xanthan concentration is above 1.5~.
EXAMPLiE 2
Xanthomonas whole fermentation broths substantially
.
free o~ insoluble matter having a particle size greater
than about 3 microns were treated by the process of the
invention. A portion of each was diluted with deionized
water to a xanthan concentration of 0.6% and heated for
5 minutes at 80C. Th heat-treated solutions wexe then
further diluted to a viscosity of about 10 cps. and com-
pared with similarly diluted samples which were not heat
treated~ The test results were as follows: -
: ' , ' ` '" ', ` .,.", ', , ' - : .:'`, ~ ,
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Broth Heat 1.2 micron Activity Thermal
No. Treatment Filter Ratio Enhancement (c) Stabil_ty
1 (a) - 1.06 - 0.77
1 (a) + 1.07. ~70~ 0.82
1 (b) - _ _ 0.22
2 (b) - 1.01
2 (b) ~ 1.01 +65%
(a) Final dill1kion with 0.6% sodium chloride
(b) Final dilution with 500 ppm sodium chloride
~c) Activity enhancement = Ratio of dilution required ~ -
to give 10 cps. at 6 RPM on the Brook~ield
viscometer after heat treatment to the dilution
required to give 10 cps at 6 RPM on the Brook- :
~ield viscometer before heat treatment, multiplied
by 100. :
EXAMPLE 3
A series of Xanthomonas broths with xanthan concen- :
trations above about 3% were diluted with deionized water
to a xanthan concentration of 0.75%, heated for 5 minutes
at a temperatuxe of 85C and diluted to lD cps. visco~ity.
The results are summarized as follows:
1.2 micron Activity
Broth Number Heat Treatment Filter Ratio Enhancemen~
1 - 1.22
+ 1.15 ~56~ ;
2 - 1.12
~ 1.13 +67 ~:
3 - 1.12
+ 1.22 +67
4 - 1~12
+ 1.07 +67
- 1.16
+ 1.08 +67
- 1.27
+ 1.16 +57 .
~:
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1.~ micron Activity
Broth Number ~eat Treatment Filter Ratio Enhancement
7 - 1.21
+ 1.11 l67%
8 - 1.22
+ 1.09 ~4
9 - 2.11
~ 1.31 ~67
- 1.28
~ 1.10 +67
11 1.37
~ l.OS ~84
12 - 1.13
+ 1.04 ~78
Averaye - 1.28
~ 1013 ~70
EXAMPLE 4
,
~ sample of whole Xanthomonas fermentation broth
having an initial 0.65 micron FR of 2.59 was treated using
the invention to improve its viscosi~y and mobility r ;
characteristics. A 1% solution of xanthan in 500 ppm salt
solution (10:1 Na:Ca) was heated to 85C. for 5 minutes,
then cooled to room temperature, diluted to 0.14% using
the same salt solution, 5600 ppm diatomaceous earth
bodyaid was added, and the heat-treated diluted solu-
tion was filtered at room temperature on a precoated
pressure leaf filter. The sparkling filtrate exhibited
a 40% activity enhancement and an improved 1.71 filter
ratio at 0.65 microns filter pore size.
~343~
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EXAMPLE 5
A sample of whole Xanthomonas fermentation broth -
which initially plugged a 0.45 micron Millipore filter,
was treated to improve its viscosity and injectivity
characteristics. The broth was diluted ~o 1% with 500 ppm
salt solution, heated to 85C and then diluted to 0.14%
by adding 500 ppm salt solution at 85C. containing
sufficient diatomaceous eaxth bodyaid to s~eed ~ubse-
quent filtrations. The heat-treated solutien was then
filtered on a precoated pressure leaf filter at about
85C. and a flux of 13.1 gal/hr ft2 obtained. Total
time at 85C. was about 20 minutes. The sparkling
filtrate exhibited an activity enhancement in excess
of 18~i and improved injectivity as demonstrated by
Millipore filter ratios of 1.94 at 0.45 micron and 1.23
15 at 0.65 micron pore size. `
EXAMPLE 6
Xanthomonas fermentation broth containing insoluble
matter having a particle size greater than 3 microns
may be prepared in the following way:
Cells of Xanthomonas campestris NRRL B-1459a from
a YM agar sfant are transferred to 300 ml of YM Broth
contained in a 2.8 liter Fexnbach flask and shaken on a
rotary shaker for about 31 hours at 28C. A 25 ml aliquot
is transferred to a 2.8 liter Fernbach flask containing
500 ml of a medium of the following composition:
Ing'redie'nt Grams/100 ~rams
Part A
*Distillers' soluble extract 18
2EIP4 0.5
Antifoam (GE 60) 0.08
Distilled water 57
p~ ~.1 Autoclave separately
`
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Grams~100 grams
Part B
G1UCOSQ 2.5
MgSO4 0.01
Distilled water 2
p~ 4.~5
* The extract is prepared by boiling a 10~ w/w
aqueous slurry of distillers' dried solubles for 5
minutes, cooling, making up evaporation losses with
fresh water, adding 4% diatomaceous filter aid, and
vacuum filtering.
After shaking at 28C. for about 33 hours, a 200 ~1
portion is transferred to a 4-liter mechanically agitated
fermen~or containing 2 liters of the above medium.
Aeration is at a rate to provide 1.5 to 3.5 millimoles
of oxygen per liter per minute. The fermentation is
conducted at 30C. until the level of reducing sugar is
0.3% and a viscosity of at least 4500 centipoise units
and a xanthan concentration of at least 1.0~ is obtainedO
Treatment of the Xanthomonas fermentation broth by
the present process is illustrated by the following:
The whole brcth is diluted to 750 ppm xanthan with water
containing 500 ppm sod~ium chloride and calcium chloride
in a 10:1 ratio. The diluted broth is stirred for
about an hour using low shear mixing until the xanthan
is uniformly dispersed and is then heated for about 5
minutes at a temperature of about 95 4C ~ Dicalite
Superaid ~3 grams p~r liter of diluted broth) is stirred
in at a temperature of about 95C. and the broth filtered
through a vertical leaf test filter with a cotton duck
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cloth filter medium and no precoat. The filter area
is 0O025 square feet. The filter is heated with an
electric tape before and during the run to 93-98C. :~
The filtration is done at a constant pressure of
40 psi. The first filtrate is recycled until it
becomes clear. The filtrate is cooled to 20-30C.
This treatment ~ill typically yield a filtrate having ~:
a viscosity of about 30 cps~ and a filter ratio below
2 thorugh Millipore filters with pore sizes of 0.45 :
and 1.2 microns.
