Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEUTSOElE HEFEWERXE GMBH - 1 -- O . Z . 4 4 41
Process for acidifying solutions of molasses
The invention relates to a novel process for acidifying
dilute solutions of molasses.
The molasses which are obtained as mother liquor in the
production of sugar contain approximately 50% ~ugars,
20~ water and furthermore organic and inorganic compounds
containing nitrogen and pho~phoru~. It is therefore well
suited a~ a nutrient for microorganisms. However, the pH
of the molasses, which is u~ually about 7 to 9, i8 too
high for many applications.
In yeast, anaerobic or aerobic metabolism is possible at
a pH of between 2 and 7. However, a pH of 4 to 5.5 is
usually preferred for yeast fermentation since this pH
range i8 a aelection advantage for yeasts and furthermore
guarantees good protection against infection by con-
taminants. A certain acid p~ i8 also established when
yeast is cultured for baking purposes.
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After having been diluted with water, the molas~es are
therefore acidified with sulphuric acid 80 that the
~esired pH i~ established, before using thQm for the
formation of alcohol or for propagating yeast (cf. DRP
641 742 and L. Nacher, Die Hefe, Volume II (1962),
420-23). Sulphuric a~id i8 u~ed because it is extra-
ordlnarily inexp4n~lve and, in contrast to other acids,ha~ no effect on the phy~iology of the yeast cells. At
the end of the fermentation or yeast culture, the ~ul-
phuric acid which has been added remains in the exhausted
liquid culture medium in the form of sulphates.
~hese days, yeast waste waters are increasingly purified
anaerobically or used for producing methane (bio~as). The
sulphates are undesirable in the methanization of the
organic material contained in the wa~te water, since they
are reduced to hydrogen sulphide and exert a negative
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influence on the quality of the biogas (cf. D.8. Archer,
Enzyme Microb. Technol. 1983, 162-70, and G. R. Anderson
et: al., Process Biochemi~try 1982, 28-32). Indeed, high
concentrations of sulphate can lead to an inhibition of
tlle formation of bioga~, or bring it to a halt. Moreover,
sulphate in waste waters can corrode cement or concrete
components and contribute to the destruction of waste
water equipment. It is therefore desirable to employ, in
the methanization, waste waters whose sulphate concen-
trations are as low as possible.
Accordingly, the ob~ect was to reduce the amount of~ulphuric acid when acidifying solutions of mola~ses.
Surpri~ingly, the ob~ect is achieved by treating the
dilute solution~ of molas~es with ion exchangers. The
fact that sufficient changes in the pH could be brought
about with relatively low amount~ of ion exchangers could
not have been anticipated.
First, the molasses are converted to preferably 10 to 70~
strength aqueous solution by adding water. Particularly
preferred ~olutions of molasses in this context are tho~e
fro~ 30 to 60%. The~e percentage~ do not take into
account any water contents initially present in the
molasses.
The dilute ~olution~ of molasses are treated with lon
exchanger~, lt being po~sible to use strongly acid or
weakly acid cation exchanger~. Weakly acid cation ex-
changers are preferably employed. In this con~ext, use
can be made of 811 commercially available cation exchan-
ger~.
~he amount of ion exchangers i~ generally 100 to 700 ml
relative to 1 kg of undiluted molasse~. Amounts of 120 to
300 ml of ion exchangars per kg of molasses are preferred
in this context.
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The type and amount of ion exchanger used depend on the
de~ired pH. pH value~ in the range of from 5 to 5.5 can
readily be ad~usted using weakly acid cation exchanger~
in the preferred amount~.
The acidification can take place at 10 to 80C, tempera-
tures of 20 to 30C being preferred. The period in which
the treatment with ion exchangers take~ place can be 10
minutes or even 2 hours.
The treatment can be carried out in a stirred reactor. At
the end, the ion exchanger can be filtered off, or the
~olution of molasses can be decanted. It is also possible
to introduce the ion exchanger into a column and then to
pass the solution of molasses through this column. This
treatment can be effected batchwise and al~o continuous-
ly.
The ~olutions of molasses, which have been acidified inthis way, are highly suitable for producing fermentation
products. In particular, the solutions of molasses are
used for produc~ng yeast biomass, for example for produc-
ing baker's yeast, and also for synthesizing organicsub~tances with the aid of microorgani~ms, such as, for
example, for producing alcohol by fermentat~on. The
solution~ of molasse~, according to the invention, are
certainly equal when compared with conventional, ~ulpha~
tized solutions of molasses. When the fermentation i~
complete, however, exhau~ted fermentat~on solutions which
have been prepared u~ing a ~olution of molasses, accord-
ing to the inventlon, can advantageou~ly be degraded
anaerobically to give bioga~, since the formation of
hydrogen ~ulphide is completely absent, or considerably
reduced.
The examples which follow are intended to illustrate the
invention.
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xample 1
In a 6-litre reactor, 2 kg of molas~e~, con~isting of 25%
of crude molasses and 75% of beet molasses, are diluted
with 2 kg of water. The solution of molasses has a pH of
7.40. 500 ml of weakly àcid ion exchanger (type IV, made
by Merck, D-6100 Darm~tadt) are now added. The solution
i~ then stirred for 30 minutes at 25C. After this, the pH
of the ~olution of molasses is 5.10.
Example 2
The procedure i~ a~ in Example 1, with the difference
that 2 kg of wash water from the ion exchanger is u~ed
for dilution.
After the treatment with ion exchanger, the solution of
mola~ses has a pH of 5.20.
Example 3
3 kg of molasses of Example 1 are diluted with water to
give 6 kg of solution of molasses.
500 ml of ion exchanger (LEWATIq~ CNPLF, made by Bayer,
D-5090 Leverku~en) are introduced into a chromatography
column. The solution of molas~es is then passed through
the column at ~ flow rate of 1.70 l/h. This gives 6 kg of
~olutlon of mola~se~ of a pH of 5.08.
Exa~ple 4
The procedure i8 a~ in Example 3, with the difference
that 3.5 kg of mola~se~ are diluted to give 7 kg of
solution of molas~e~, which are passed through the column
at a flow rate of 2.8 l/h. Thi~ give~ 7 kg of solution of
mola~ses of a pH of 5Ø
A furth~r 6 kg of ~olution of molasses are passed through
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the column. This now gives a solution having a pH of
5.35.
ExamPle 5
1.25 kg of beet molasse~ (from Clauen) are diluted with
1.25 kg of water. The solution of molasses now ha~ a pH
of 9.2. The subsequent procedure iB as in Exsmple 3, with
the difference that 500 ml of ion exchanger of Example 1
are used. $he flow rate is 1 l/h, and the temperature is
25C.
lQ Thi~ give~ 2.5 kg of solution of molasses having a pH of
5Ø
A further 3.5 kg of the ssme solution of molasses are
then passed through the column. This procedure gives a
solution having a pH of 5.4.
Example 6
3 kg of beet molasses of Example 5 are diluted with 3 kg
of water.
~he conditions of Example 5 are then ad~usted, but the
ion exchanger of Example 3 i~ used.
This gives 6 kg of eolution of molas~es havinq a pH of
4.9.
Exsmple 7
1.5 kg of beet molasse~ (from Belgium) are diluted with
1.5 kg of wster. ~he resulting solution of mola~ses has
a pH of 8Ø
The procedure is a8 in ~xample 5. Thi~ proces~ giYes 3 kg
of ~olution with a pH o~ 5Ø
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A further 3 kg of solution of mola~ses are then pa~sed
through the column. This now gives a solution having a pH
of 5.3.
Example 8
Example 6 is repeated with the alteration that beet
molasses of Example 7 are employed.
~his gives 6 kg of solution of molasses having a pH of
4.7.
Example 9
Molasses consisting of 25~ cane molasses and 75% beet
molasses are diluted with the same amount of water. The
pH of the solution of mola3~es is 7.2.
~he procedure is as in Example 6. After 6.9 kg have been
put through, the pH is 4.7. A pH of 5.0 is measured after
8.8 kg have been put through.
Rxample 10
Produ¢tion of baker' 8 yeast
5 kg of solution of molasses having a pH of 5.0 are
prepared in accordance with Example 4.
In a 20-litre fermenter, 21 g of NH~Cl and 10 ml of
concentrated H3P04 are treated with 10 1 of water, and
400 g of perpetuated yeast (strain DHW S-3, by Deut~che
Hefewerke, D-4370 Narl) are added. The fermentation takes
place at 30~C under aerobic conditions and with molass~s
being fed in. The pN is kept constsnt at 5.0 by metering
in ammonia solution. After a fermentation time of 24
hours, about 2,400 g of baker's yea~t (43 to 47~
protein, light colour) are harvested. The yeast produced
in thi~ way corresponds qualitatively to a baker's yeast
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which is fermented by a solution of mola~ses acidified
with ~ulphuric acid (the amount~ of yea~t are based on
27~ dry matter).
Example 11
Production of alcohol
In a 20-litre fermenter, 6 kg of solution of molasses
from Example 3 are d~luted with 4 kg of water, and a pH
of S.5 is then established with NH3-water. To thi~ there
are added 200 ml of a nutrient salt solution containing
25 g of RH2P0~ per litre and 50 g of MgS0~ per litre, and
also 100 g of Saccharomyces cerevisiae (27% dry matter,
strain DHW S-3, by Deutsche Hefewerke, D-4370 Marl),
after which an anaerobic fermentation takes place for 30
hours at 30C and at a p~ of 5.5.
After this period, the concentration of alcohol is 9.45%
by volume, which corresponds to a yield of 750 g of
alcohol.
