Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is concerned with a process
for the selective extraction of fats and/or oils from
vegetable, animal or microbial solid natural materials
with a mixture of the two compressed gases propane and
carbon dioxide.
In the case of extractive processes for obtaining
oils and fats from natural materials, in principle
liquid or gaseous solvents are used under normal
conditions. Usually, on a large technical scale,
extractions are frequently carried out with hexane or
light benzine (petroleum ether), whereby, however, the
selectivity of the processes is often not sufficient,
for which reason a multi-stage refinement of the
extracts must subsequently be carried out. Furthérmore,
the liquid solvent must be removed not only from the
extract but also from the extraction residue which, in
some cases, makes necessary increased process temper-
atures. In particular, when, in this way, deoiled or
defatted extraction residues are to be used as
starting materials for the foodstuff industry, a
substantial removal of the solvent can give rise to
technological problems insofar as sensitive products
can thereby undergo thermal damage. An increasingly
- more critical user attitude in connection with solvent
residue problems in foodstuffs and also the stricter
legal requirements and regulations require process
improvements from the modern foodstuff technology.
2165387
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From the point of view of the residue situation,
extractions which use compressed gases as solvents
offer decisive advantages since the actual solvent
residue problem in foodstuffs (extraction residue and/or
extract) can be disregarded. Of the gases
unrestrictedly permitted for foodstuff technology by
the present EU regulations, namely butane, carbon
dioxide, propane and nitrous oxide, in particular
carbon dioxide and propane are described as solvents
for deoiling and defatting. Admittedly, in the case of
gentle process conditions, carbon dioxide displays a
very high extraction selectivity but it often only
shows a satisfactory dissolving ability in the super-
critical state (T >31C, p >73 bar). Especially in the
case of fats and oils, as a rule a process pressure of
>500 bar is necessary in order to keep the process times
within technically acceptable limits (see E. Stahl,
K.-W. Quirin, D. Gerard, Verdichtete Gase zur
Extraktion und Raffination, pub. Springer Verlag,
Berlin, 1988). Consequently, from economic points of
view, in spite of many potential possibilities of using
supercritical carbon dioxide, it must be considered
that defatting and deoiling processes with the use of
supercritical carbon dioxide are not very attractive.
In contradistinction to carbon dioxide, compressed
propane shows a very good dissolving ability for
lipophilic materials, even in the case of a very much
2165387
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lower process pressure (<50 bar). This advantage has
already been described for quite a long time in the
case of the gas extraction of fats and oils, for
example in U.S. Patent Specifications Nos. 2,254,245;
2,560,935; 2,548,434 and 2,682,551, as well as also in
U.S. Patent Specification No. 4,331,695. However, a
serious disadvantage of compressed propane as
extraction solvent is generally its lower selectivity
in comparison with carbon dioxide, which is especially
manifested in the undesired co-extraction of
accompanying materials, for example coloured materials
and phospholipids. Additionally, by careful choice of
the process parameters, the selectivity of the propane
extraction can be increased (cf. DE 43 26 399 Al) but
this is not sufficient for numerous uses so that the
extracted fats and oils must be further worked up and
refined.
According to DE 34 29 416 Al, with a process
for the extraction of oil from oil-containing vegetable
materials, an attempt was made to improve the low
dissolving capacity of supercritical carbon dioxide for
vegetable oils by feeding a supercritical entraining
agent, for example propane or butane, into the
extraction. With this process variant, it is
admittedly possible distinctly to improve the
solubility for oil in comparison with pure carbon
dioxide but the necessary process pressures must still
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be from 80 to 300 bar in order to keep the carbon
dioxide in the supercritical state. Furthermore, the
specific gas throughput rates necessary for the
achievement of the object of the extraction are still
very high so that a long and thus uneconomic
extraction time must be taken into account.
Thus, it is an object of the present invention to
overcome the disadvantages of the known processes with
the help of a process for the selective extraction of
fats and/or oils from solid natural materials and to
provide an economic process with improved selectivity
for obtaining fats and/or oils with the use of
compressed gases. Furthermore, in general, gentle
process conditions are to be achieved with regard to
a good product quality and especially a lower process
pressure and a favourable specific gas throughput rate.
Thus, according to the present invention, there
is provided a process for the selective extraction of
fats and/or oils from solid natural materials, wherein
the extraction is carried out with a mixture of propane
and a maximum of 50% by weight carbon dioxide at
temperatures of <96C and pressures of <73 bar, the
two pure gases each being present in the subcritical
state.
Surprisingly, we have found that the gas mixture
under these conditions possesses, on the one hand, a
very high dissolving ability for oils and fats (in
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comparison with pure compressed propane) but, at the
same time, displays the dissolving selectivity of
supercritical carbon dioxide. However, the favourable
process pressure can thereby be maintained similarly
to the extraction with pure propane. In contra-
distinction to the earlier processes, in the case of
the process according to the present invention, the
proportion of compressed carbon dioxide, which is
always selected at ~ 50% by weight, can be regarded as
being a "selectivity modulator" with which a
surprisingly high increase of selectivity can be
achieved.
Thus, the process according to the present
invention combines the decisive advantages of gas
extraction with supercritical carbon dioxide (high
extraction selectivity) and compressed propane (high
dissolving ability in the case of low process pressure)
without displaying their disadvantages.
As already mentioned, in the case of the
extraction of fats and oils from natural materials,
depending upon the selectivity of the process, a number
of undesired accompanying materials are also co-
extracted which, in the case of the known processes,
must often have to be separated off in subsequent
process steps in order to achieve a good product
quality. Typical fat accompanying materials include,
for example, phospholipids (lecithins), coloured
~ 2165~87
materials and waxes. In the case of the process
according to the present invention, by the addition of
carbon dioxide to compressed propane, the undesired
co-extraction of these materials can be suppressed in
a targeted manner, whereby essentially the composition
of the starting material and the quality of the product
to be achieved determines the proportion of the carbon
dioxide.
Amounts of carbon dioxide are preferably between
20 and 40% by weight, whereby, in this case, the
process pressure is from 25 to 40 bar and an extraction
temperature of <50C is selected. Thus, for example,
in the case of the deoiling of soya flakes, in the case
of a proportion of 10% by weight of carbon dioxide, a
recognisable decrease of the phospholipids in the
extracted soya oil is ascertained. In the case of a
carbon dioxide content from about 40% by weight, a
highly deslimed soya oil can be obtained which has a
total phosphorus content of < 5 ppm. In addition, the
increase of the selectivity of the extraction is to be
very well recognised by the optical advantages in the
form of a distinctly clearer colour of the oil obtained.
The amount of gas needed for the extraction can be
varied within a relatively wide range and depends
essentially upon the starting material of the gas
composition and the desired aim of the extraction.
Typical extraction amounts are from 1 to 10 g of
- ~165~87
extraction mixture for 1 g of oil or fat to be
extracted.
The process according to the present invention is
very well suited for the extraction of sensitive
natural materials since it can be carried out under
process conditions which are very gentle for the
product. Important for the process is the fact that it
is always carried out at extraction temperatures of
< 96C (the critical temperature of propane) and
extraction pressures of < 73 bar (the critical pressure
of carbon dioxide). Under these conditions, the two
pure gases are subcritical (propane: Tc = 96C, Pc =
42 bar; carbon dioxide: Tc = 31C, Pc = 73 bar).
Especially in the case of the extraction of temperature-
sensitive natural materials, a process temperature of< 60C is preferably selected in order to avoid thermal
damage of special component materials, for example of
highly unsaturated fatty acids or proteins. Considered
generally, in the case of an extraction temperature
predetermined by the process, only such an extraction
temperature is necessary which keeps the gas mixture in
a liquid state; however, it must not exceed 73 bar,
the critical pressure of carbon dioxide.
After the extraction, the extracted fats and/or
oils are separated off from the extraction mixture by
increasing the temperature and/or lowering the pressure
since, under such changed conditions, the dissolving
216~387
g
ability of the gas mixture is very considerably
decreased. The extent of the temperature increase
and/or of the pressure lowering depends very consider-
ably upon the selected composition of the gas mixture
which is used for the extraction in question.
Process technically, two possibilities are
preferred for the separation of the extracts:
(i) The pressure and/or the temperature are decreased
or increased, respectively, in an extract separator to
such an extent that the gas mixture is completely
converted into the gaseous phase. On the basis of the
low solubility of the extracts in the gas phase, as a
result these are separated out from the gaseous mixture.
In a preferred embodiment, for the minimisation of the
thermal stressing of the extracts, the separation
temperature is kept at < 60C. Depending upon the
composition of the extraction mixture, the pressure
in the separator is then from 8 to 30 bar.
(ii) Especially in the case of low proportions of
carbon dioxide in the extraction mixture, the reverse
dissolving ability of propane in the region of the
critical state can be utilised, i.e. the extraction
mixture is not converted into the gaseous state but
rather, starting from the liquid state in the case of
the extraction, is brought into the region of the
critical state in the case of the extract separation,
whereby the dissolving ability for fats and oils can
- 216~3~7
- 1 o -
be very greatly reduced. However, in contradistinction
to the first-mentioned possibility, the second one is
less temperature gentle since, according to a preferred
variant, in the case of proportions of carbon dioxide
of < 20% by weight, it is necessary to work with
separation temperatures in the range of 90 to 100C,
i.e. in the region of the critical temperature of
propane (Tc = 96C), and at a separation pressure which
is from 42 to 80 bar.
In the case of a preferred embodiment of the
process according to the present invention, the
extraction gas mixture is recovered directly in an
extraction plant after separation of the extracts in
an extract separator, again adjusted to the extraction
state and then returned to the extraction process
(cyclic process). Thus, due to the low extraction
pressure and the favourable solvent requirement, with
the process according to the present invention there
can be carried out a selective gas extraction of fats
and oils with distinctly improved economy than hitherto.
Quite generally, the process according to the
present invention can be used advantageously for work-
ing up numerous sensitive natural materials. There
can thereby be used all solid starting materials of
vegetable, microbial and animal origin which are also
otherwise used for obtaining oils and fats. Examples
from the field of vegetable starting materials include
2165~87
- 1 1 -
seeds, such as soya beans and rape seed, and plant
seedlings, such as wheat germ. As microbial starting
materials, there can be used, for example, dried
fermentation residues which have a high content of
desired lipid components. As products of animal origin,
there can be mentioned, for example, wool from which
wool fat (lanolin) can be obtained in very good quality.
The following Examples are given for the purpose
of illustrating the present invention, whereby, in
particular, the targeted control of the selectivity
properties is illustrated.
Examples
Examples 1 to 6 describe the use of the process
according to the present invention in the case of soya
as vegetable starting material.
In a high pressure extraction plant, in an
extraction autoclave with a volume of 4 1 were, in
each case, introduced 1.7 kg of flaked soya beans
(oil content 21.0%) and in each case extracted at an
extraction temperature of 40C under the conditions
given in the following Table 1. With the particular
given specific gas throughput, there was achieved the
corresponding extraction yield. The analysis of the
total phosphorus took place X-ray fluorimetrically.
~16~ 387
--12--
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2165387
Examples 7 to 11 describe the process in the
case of the extraction of oils from dried fermentation
residues for obtaining PUFA-rich oils (PUFA = poly-
unsaturated fatty acids).
The starting material was a dried fermentation
residue (water content ~ 5%) which was pelleted
(pellet size about 2 mm). At the beginning of the
extraction, the total oil content was 46% by weight.
The starting material was introduced in amounts of,
in each case, 0.5 kg into a high pressure extraction
plant with an autoclave volume of about 1 1. In each
case, the extraction temperature was 40C.
- 216S~87
-14--
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~16~387
-15-
Examples 12 and 13 describe the advantages of the
process according to the present invention in the case
of the extraction of wool fat from sheep wool (starting
material of animal origin).
For this purpose, in each case into the 4 1 auto-
clave of a high pressure extraction plant were introduced
1 kg of raw wool tamount of wool fat 11.5% by weight as
dichloromethane-extractable proportion) and in each case
extracted at 40C under the conditions given in the
following Table 3 with the given results.
Table 3
Examp-e propane/CO2 extraction separation specific gas extract colour of the
No. (wt.-%) pressure pressure temper- throughput yield extracted
(bar) (bar) ature (C) (kg/kg starting (wt.-%) wool fat
material )
12 100/0 20 8 50 5 8.5 dark brown
(comparison)
13 60/40 55 25 50 8 7.3 bright
yellow
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