Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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; SUMMARY OF THE INVENTION
In accordance with the invention r it has now been
found that heteropolysaccharides having increased viscosity
in aqueous media are obtained by heating the beer in which
the heteropolysaccharides are fermented to a temperature of
from about 210F to about 220F for from about 1 to about
5 minutes.
DETAILED DESCRIPTION
The present invention relates to polymers for
; 10 altering the rheological properties of aqueous media and
more particularly related to modified heteropolysaccharides
which are particularly effective for increasing the vis-
cosities of brine and similar solutions.
The hateropolysaccharides which are modified in
15 accordance with the invention are heteroglycans produced
by the action of bacteria of the genus Xanthomonas upon
carbohydrates. Representative species of these bacteria
include Xanthomonas begoniae, Xanthomonas campestris,
Xanthomonas carotae, Xanthomonas hedrae, Xanthomonas incanae,
20 Xanthamonas malvacearum, Xanthomonas papavericola, Xantho-
monas phaseoli, Xanthomonas plsi, Xanthomonas vesicatoria,
Xanthomonas vasculorum, and Xanthomonas translucens. The
production of the heteropoIysaccharides is a characteristic
trait of all members of the genus Xanthomonas. It has been
25 shown that certain species of these bacteria produce the
polymers with particular efficiency and are therefore more
attractive for purposes of the invention than are others.
Xanthomonas begoniae, Xanthomonas campestris, Xanthomonas
incanae, and Xanthomonas pisi are particularly outstanding
30 in this respect and are therefore preferred for purposes
of the invention.
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Organisms of the Xanthomonas genus act upon a wide
variety of carbohydrates to produce the heteropolysaccharides
utili~ed for purposes of this invention. The fermentation
medium generally contains a suitable carbohydrate at a
concentration of about 1 to about 5% by weight. Suitable
carbohydrates include, for example, dextrose, sucroseJ maltose~
fructose, lactose, corn starch, glucose, soluble starch, and
the like. Fermentation studies have shown thae the carbohydrates
employed need not be in a refined state and may instead be
utilized in the form of crude materials derived from natural
sources. Specific examples of such crude materials include
raw sugar, crude molasses, sugar beet juice, raw potato starch
and the like. Since the crude materials are generally much
less expensive than the corresponding refined carbohydrates,
they are, in most cases, preferred for use as substrates in
preparing the heteropolysaccharides.
The heteropolysaccharides are normally produced
from carbohydrates such as those described above by employing
an aqueous fermentation medium from about one to about five
weight percent of the carbohydrate. From about 0.1 to about
0.5 weight percent of dispotassium acid phosphate and from
about 0.1 to about 10 weight percent of a nutrient containing
suitable trace elements and organic nitrogen sources is usually
added to the carbohydrate solution to complete the fermentation
medium. The nutrient employed will normally be a byproduct
material such as distillers' solubles or the like. A mixture
containing 2 weight percent raw sugar, .4 weight distillers'
solubles has been found to yield excellent results. The use
of such a mixture is not necessary in all instances however~
The trace elements and organic nitrogen sources contained in
the nutrient are apparently also present in certain of the
,` crude carbohydrate source materials--raw sugar beet juLce, for
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example -- and hence, it has been found that the addition of a nutrient
to such materials may not be necessary.
The actual fermentation conditions are known to those skilled in
the art and are not part of the present invention. Fermentation procedures
~ are described, for example, in U.S. Patents 3,391,060; 3,391,061, 3,427,226;
; 3,433,708; 3,446,796 and 3,729,460.
At the end of the fermentation, the fermentation beer is pasteurized
by heating to a temperature of from 195 F to 205 F for 1 to less than 3
minutes and the gum separated by conventional means, e.g., precipitation,
extraction of solids, removal of precipitating agent and milling. The
resulting gum, when added either directly or through a stock solution to a
brine solution for secondary recovery operations in the petroleum industry
at a concentration of about 500 ppm, yields a brine having a viscosity of
about 6.5 - 7 cps.
In contrast to the foregoing prior art product, it has now been found
that a xanthan gum having increased viscosity in aqueous media is obtained by
increasing both the temperature and duration of the conventional pasteurization
step and heating the fermentation beer, before separating the gum, to a
temperature of from about 210F to about 220F for from about 1 to about 5
minutes at a pH of from about 6 to about 7. The gum separated from a fermenta-
tion beer treated in the foregoing manner produces a substantially higher
viscosity in a~ueous media. For example, when added to a brine solution for
secondary recovery in the petroleum industry at a concentration of about 500 ppm,
such a gum yields a brine having a viscosity of from about 13 to about 14 cps.
While French Patent 1,575,756 indicates that the viscosity
- of xanthan gum is increased by heating to a
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temperature of from 80C - 130C for lO minutes to 2 hours,
it has been found according to the present invention that
a heating period ~f from about 3 to about 5 minutes is critical
and that heating beyond about 5 minutes results in a decreased
viscosity.
In oil well flooding operations, 1:he user generally
prepares an aqueous concentrate of xanthan gum containing from
about 0.25% to about 1.5% by weight of xanthan gum. This
concentrate may be held at ambient temperature for a period
of hours or days. Shortly prior to injection of the solution
into the well bore, the xanthan gum solùtion is diluted to
"use" concentration of from about 200 - 2,000 ppm.
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The following examples illustrate the present invention '
without, however~ limiting the same thereto,.
'
Example 1
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The following data shows the viscosity of brine water con- '
~ 5 taining 500 ppm of xanthan gum produced from beers fermented ~,
; under similar conditions and pasteurized for the indicated
' time and temperature.
The viscosity was measured at 7.3 sec
Time~ Minutes
: 10 ~ Temperature~ F 0 3 5
1 180 603
2 180 5.9 ~'
3 1~0 8~2
4 190 806 ~ '~
200 9.0 ~'
' 6 200 9.7 9.7
': 7 210 9.7 , ,,
., 8 220 10~3
'' Example 2
,~
,: 20 T,he following table shows the effect on viscosity of brine
containing 500 ppm of xanthan gum obtained by subjecting
aliquots of a fermentation beer produced by fermentation beer
produced by fermentation of Xanth =onas campestris to differing
pasteurization temperatures:
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Brookfield Viscosity (cps) of
500 ppm Brine Sol~tion at Shear
Rate of 7.32 sec
Time ~minutes)
Aliquot Temperature F 1 3 5
: 1 200 13.30
2 210 13.97
3 220 13.77
E ample 3
The following table shows the effect on viscosity of brine
containing 500 ppm of xanthan gum obtained by subjecting
aliquots of a fermentation beer produced by fermentation
of Xanthomonas compestris to differing pasteurization
temperatures:
Brookfield Viscosity (cps) of
500 ppm Brine Solution at Shear
Rate of 7~32 sec-l
Tlm ~Minutes)
~ Temperature F 1 3 5
1 200 10.80
2 210 11.37
3 220 11.43
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