Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND APPARATUS FOR RECOVERING VEGETABLE FATS AND OILS
FROM OIL-CONTAINING NATURAL SUBSTANCES
SPECIFICATION
Field of the Invention
My present invention relates to a process and apparatus
for recovering vegetable fats and oils from oil-containing
natural plant substances, especially oil-bearing seeds and
fruits.
My invention particularly relates to a process and a plant
or apparatus for recovering vegetable fats and oils from
natural substances in which the natural substances are mixed
with a solvent, extracted, fats and/or oils are separated from
the solvent, and the solvent is recirculated or recovered.
Backqround of the Invention
To obtain vegetable fats and oils from oil-containing
fruits and seeds both continuous and discontinuous processes
are used.
According to the kind of natural product before the actual
oil recovery process is performed a husking or shelling can be
necessary since the quality of the oil can be considerably
reduced by shell-specific material (e.g. wax) which can appear
in the oil on extraction with the solvent.
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The conventional pressing frequently employed with
fat-rich fruits and seeds is very cost intensive and has lost
considerable importance although in a single pressing process a
residual fat content of 4 % in the pressed residue is
attainable. Today processes for continuously recovering oil
usually comprise a combination of pressing and extraction with
a solvent. First the oil-containing natural materials are
subjected to a preliminary pressing to a fat content of about
25~ and then extracted to a residual content of 1%. With
oil-bearing seeds whose fat content is about 20%, direct
extraction is performed without preliminary pressing.
With many plant raw materials a preliminary mechanical
treatment involving comminuting or grinding up into smaller
pieces is necessary to destroy as much as possible of the
storage tissue to attain a high yield. Usually the seeds are
subjected to a pressing process after a conditioning. They are
moistened and preheated in a unit prepared expressly for this
purpose.
By this preliminary treatment the oil flows more readily
(with a lower viscosityj and separates better on pressing.
Moreover a further coagulation of the protein is attained and
undesirable enzyme systems and microorganisms are inactivated
at temperatures over 80~. With cotton seeds there is also a
disinfecting action of the conditioning.
2S Continuously operating straining screw presses, whose
operating principles can be found in the appropriate literature
and also are used in the processes described in European Patent
0 129 739 and European Open Patent Application 0 187 877, are
generally used currently in processing heavy oil-bearing seeds
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3 28500-1
and fruits. Working comparisons have clearly shown that in
principle a certain screw design or structure only yields optimum
results with seed sorting. Different crops require different
processing conditions which forces a considerable compromise
between quality and operating requirements.
As an extraction medium an industrial grade n-Hexane
fraction with a boiling range between 55 and 70C is generally
currently used. For a few special cases however other solvents
are used. Moreover processes are known, e.g. from German Open
Patent Application 2 127 596 and the cited European Patent
Document 0 187 877 A 1 in which the fat or oil is extracted with
supercritical gases.
Solvent separation occurs from the crude oil
comparatively easily at temperatures under 100 and in vacuum.
The residual content of oil in the solvent is under the current
analytical detection limit. The solvent is driven out from the
solid extraction residue usually with steam.
Despite many attempts it has not been possible to
optimize the combination of pressing and solvent extraction in
continuous processing and also it has not been possible to obtain
satisfactory end product processing in a given plant or unit for a
variety of oil bearing seeds and fruits.
Aims of the Invention
This invention seeks to provide an improved process and
apparatus for recovering vegetable fats and oils from oil-
containing natural substances which are more economical for a
variety of natural substances than the processes and apparatuses
currently used.
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This invention also seeks to provide an improved process
and apparatus for recovering vegetable fats and oils from oil-
containing natural substances, which are more economical but which
guarantee a satisfactory product quality despite the type of
natural substance being processed.
Summary of the Invention
These ob~ects and others which will become more readily
apparent hereinafter are attained in accordance with my invention
in a process for recovering vegetable fats and oils from natural
substances in which the natural substances are mixed with a
solvent, extracted and subsequently the fats and/or oils are
separated and the solvent is recirculated.
According to my invention the natural products are mixed
with a solvent phase obtained in the process to form a mixture and
the mixture is fed into the shear field of at least one rotor-
stator unit for intensive processing, mixing and extraction in
which the solvent phase takes up the oils and/or the fats from the
solid phase. The solvent containing the oils and/or the fats and
the solids from a suspension leaving the rotor-stator unit are
separated in a subsequently connected separator and subsequently
the solvent is removed in a distillation column from the oils
and/or the fats.
By the intensive treatment of the mixture of the natural
products and the solvent in the shearing field of a rotor-stator
unit in many cases a preliminary comminuting or similar
conditioning can be omitted. This has the advantage that the
danger of overheating connected with the conditioning can be
avoided. This overheating can lead to an impairment in
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the nutrient valve of the pressed cake and in the color and
taste characteristics of the oil which results in a considerably
increased expense in subsequent raffination and bleaching of the
oil. Also the oil yield can be considerably poorer, especially
at higher moisture content.
We can use Hexane as the solvent and/or extraction means for
the process according to my invention, although other solvents,
e.g. ethanol, isopropanol, methylene chloride, among others, can
be used with certain oil-containing natural substances.
The advantage of the process according to my invention for
recovering oil from oil-bearing seeds and oil-containing fruits
is based on the fact that in the rotor-stator unit a combination
of extraction with solvent and simultaneous preparation of the
oil-bearing seeds and oil-containing fruits (by cell breakdown)
until cell decomposition nearly occurs so that the principle of
extreme diffusion path length reduction providing for a short,
intracellular material transport is used.
This cell breakdown occurs by a strong dispersion of the
oil-containing solid particles from the destroyed, oil-carrying
seeds and fruit cells and there is thus a constant boundary
surface renewal with an optimization of the concentration
gradient between the oil and the oil-receiving solvent phase as
is important for the solubilization of the oil in the solvent.
That is, the extraction process takes place simultaneously
2S with the decomposition and the dispersion of the oil-containing
seeds or fruit flesh pieces. A substantially shorter total
process time results.
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Advantageously the process is controlled so that the
extraction occurs in the rotor-stator unit in a temperature
range between room temperature and a few degrees below the
boiling point.
Also when in many cases a comminuting and conditioning is
not required in the process according to my invention, it can
also be important according to the guality or type of the seeds
or fruit meat to be processed when before starting the process
described previously, to provide a preconditioning and/or a
possible comminution of the substances.
The process according to my invention permits both heat
treatment required for conditioning of the oil-containing seeds
and fruits and a partial grinding up or cell destruction to be
carried out in a connected rotor-stator unit with suitably
formed rotor-stator assemblies.
For the heating or heat treatment a feed of hot steam into
the natural substances can be effected directly through the
stator elements at suitable places or before the actual feed of
the natural substances into this dispersion and extraction
unit. The process according to my invention can understandably
be used for treatment of the pressed oil-containing seeds and
fruits with considerable advantage.
It can be particularly advantageous that mixing and/or
subsequent processing and extracting occurs continuously in one
or more stages and a solvent phase containing some oil is fed
in a counterflow to the solids. Thus the solid phase is
subjected to an intensive treatment, mixing and extraction in
continuous processes in individual connected extraction stages
with solvent-containing oil fed back in a counterflow. It is
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thus possible to optimize the concentration gradient for each
stage and to enrich the solvent phase with oil in stages.
The residual solvent from the solid phase in the last
extraction stage is advantageously removed by heat treatment,
liquefied in a condensor and fed back into the solvent cycle.
The removal of the residual solvent happens advantageously at
the surrounding pressure and at temperatures under lOO~C. The
return of the residual solvent occurs advantageously together
with the pure solvent from the distillation stage to the mixer
of the last stage. However understandably it can also be fed
back to other locations according to the requirements of the
process.
In cases in which the suspension issuing from the first
rotor-stator unit has a high fraction of fine particles for
reliable and trouble-free operation of the distillation column,
an oil-containing liquid phase from the first separator can be
filtered to separate the finely divided solid particles before
feeding them to the distillation column, and in the case of a
multistage treatment, the filter cake from the filtration step
can be delivered to one of the mixers in a subsequent stage.
An apparatus in which simultaneous treatment, mixing and
extraction occurs which is especially suited to performing the
process according to my invention and which also satisfies some
of the aims of my invention can comprise a mixer with feed
means for oil- or fat-containing natural substances which is
connected by a pipe with a rotor-stator unit whose outlet is
connected by another pipe with a separator.
The separator outlet for the liquid phase from the
separator is connected with a distillation column by still
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another pipe. In the rotor-stator unit the force acting on the
oil-containing cells for their decomposition is the result of
both a purely mechanical action of a specially designed
rotating element against a similarly appropriately designed
S stationary opposing piece and also by action of the solvent
itself.
The rotor-stator unit in which the extraction also occurs
as well as the decomposition and dispersion of the
oil-containing seeds and fruit meat or flesh pieces thus can be
characterized as a homogenizing and extraction unit operating
with a rotor-stator unit in which different rotor-stator
assemblies can be used according to the requirements in regard
to the structure and operation and indeed in all stages in case
of a multistage process.
It can be significant according to the natural raw material
to be processed when a conditioning and an eventual comminuting
of the starting material before running the above-described
process according to my invention occurs.
An additional rotor-stator unit with a suitably structured
rotor-stator assembly is provided in the apparatus. In this
rotor-stator unit a partial pulverizing like the heat treatment
required for conditioning of the oil-containing seeds and
fruits is possible so that for heat treatment the input of hot
steam in the natural product can be effected directly through
the stator element of the rotor-stator unit at suitable
locations or can be effected in this dispersion and extraction
unit before the actual introduction of the natural product.
Advantageously the choices among the different rotor-stator
assemblies vary according to the product to be processed. The
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following tool types are available and can be exchanged with
each other in the rotor-stator unit when the product is changed
without special effort.
For comminuting an interlocking conical rotor-stator
assembly designated as a cone tool provided with elongated
grooves oriented radially can be used. The gap width between
the conical rotor and the similarly conical stator can be
adjusted as desired to provide a certain desired seed and/or
fruit flesh particle size. Also in this rotor-stator assembly
already an intimate mixing with the solvent (e.g. hexane)
occurs.
Furthermore a rotor-stator assembly made from a plurality
of concentric rings can be used in which the concentric rings
of rotor and stator are provided with radial slots and are
interlocking. In this assembly, which is called a chamber tool
the oil-containing natural substances are jointly delivered
with the solvent in the middle of the rotor-stator assembly.
The centrally delivered slurry made from the natural material
and the solvent is subjected to pressurization by the
centrifugal force of the rotor which forces the dispersion
radially to the outlet located on the periphery of the unit.
On its way through the rotor-stator assembly the individual
particles of the slurry are subjected to the action of the
frictional forces, shear and tangential stresses. Moreover the
discrete volumes of the slurry on the way through the narrow
ducts of the chamber tool experience extreme direction changes
and accelerations which depending on the speed of the rotor and
the number of radial slots in it lead to high frequency
microcavitation in the discrete volume of the slurry and thus
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to cell rupture of the oil-containing cells.
Further an intimate mixing of the solid particles and the
solvent occurs and thus an extreme improvement of the solution
kinetics in the extraction process.
Another rotor-stator assembly, an orifice and/or nozzle
tool, is constructed with additional concentric cylindrical
surfaces in which radial passages are provided. The passage
size is designed according to fluid mechanics so that the
slurry passing through as in a nozzle flow is accelerated so
strongly that the slurry stream is divided and dispersed in
many extremely small discrete droplets from the slurry located
upstream of it. This has the advantage that the previously
formed agglomerates of oil-containing solid particles are
destroyed and thus a boundary surface renewal with an optimum
material exchange or replacement in regard to the oil transport
by the solid particles is attained in the solvent.
Examples of the process and apparatus of my invention are
provided in the following detailed description and accompanying
drawing however my invention is not intended to be limited to
the details provided below and it will be understood that
various omissions, modifications, substitutions and changes in
form and detail are possible. Particularly conveying, measuring
and control systems and their combinations which are
conventional in the art have not been described in detail.
Brief DescriPtion of the Drawing
The above and other objects, features and advantages of my
invention will become more readily apparent from the following
description, reference being made to the accompanying highly
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diagrammatic drawing in which:
FIG. 1 is a flow diagram of the apparatus for recovering
fats and oils according to my invention;
FIG. 2 is a cross sectional view through a conical tool for
a rotor-stator unit;
FIG. 3 is a cross sectional view through a chamber tool for
a rotor-stator unit;
FIG. 4 is a cross sectional view of a nozzle or orifice
tool for a rotor-stator unit; and
FIG. 5a is a perspective view, FIG. 5k is a diagrammatic
top view and FIG. 5c is a diagrammatic top view of the tool
structure of a rotor-stator assembly and the path of the
particles.
Specific Description
FIG. 1 shows a multistage process for recovering vegetable
oil and fat from natural substances comprising four stages I,
II, III and IV.
The oil-containing natural products in the form of
oil-bearing seeds or oil fruits -- either subjected to a
preliminary treatment or not -- are fed in a first stage I to a
funnel-like mixer 3 by a feeder 1 and there they are mixed with
a solvent partially containing oil which reaches the mixer 3
from a separator 15 in a second stage II through the feed duct
The mixture is fed to the homogenizing and extracting unit
5 operating according to the rotor-stator principle through the
pipe 4 where the solvent phase containing some oil receives
more- oil up to a certain maximum amount which is removed from
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the solids or the solid phase.
For separation of the solid and the solvent phase the
solid-solvent mixture is fed from rotor-stator unit outlet 6'
by the pipe 6 to a separator 8 in the first stage I for gross
separation of the solids and the solvent. In an actual case
this separator 8 usually comprises a straining screw conveyor
so that simultaneously with the solid-liquid separation the
feed of the solid occurs. The solvent phase with the maximum
possible oil content is fed from the separator outlet 8'through
the pipe 7 to a distillation column 39 which is operated as a
vacuum distillation column for separation of the supplied oil
and solvent.
The oil is taken off the distillation column 39 through the
pipe 37. The pure solvent which leaves the distillation column
39 as a head product by the pipe 35 is fed to the final mixer
24 in the fourth stage IV as a pure solvent phase freed from
all oil.
Depending on the nature of the oil-containing natural
substances used because of the fraction of fine particles in
the solvent phase containing oil issuing from the separator 8
the necessity may arise to feed this solvent phase through a
pipe 47 to a filter 42 in which it is freed from the finely
divided solid fraction present before further processing in the
distillation column 39.
The dense oil-containing filter cake is continuously taken
from the filter 42 through a pipe 44 by a conveying unit 45
comprising a screw conveyor. The filter cake material is then
fed through the pipe 46 to the mixer 10 where it is subjected
to an additional extraction process. In the following straining
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screw conveyor or separator 15 it forms an agglomerate with the
gross solid materials and follows the path of these solid
materials through the subsequent process stages. It leaves the
process at 36 in a final stage together with the extract
residue.
The solid phase partially de-oiled in the first stage I is
fed to the mixer 10 through the pipe 9 and there premixed with
the oil containing solvent from the separator 22 which is also
a straining screw conveyor through the pipe 12.
The slurry is then fed for the purpose of intensive mixing,
processing and extraction over the pipe 11 to the second
homogenizing and extracting unit operating according to the
rotor-stator principle.
This rotor-stator unit 13 is connected to a following
separator 15 which is also a straining screw conveyor which is
supplied through the feed pipe 14 with the slurry intimately
exchanging material and a separation of the solvent phase
containing the oil and the solids is performed.
The subsequent additional extraction stage III corresponds
to those previously described and utilizes a feed pipe 16,
mixer 17, pipe 18, rotor-stator unit 19, feed pipe 20 and pipe
21 over which the mixture of solid and solvent phase is fed to
the downstream separator 22.
The final mixer 24 in the last stage IV is fed the solid
2S phase already largely de-oiled through the feed pipe 23. The
principal flow coming from the distillation column 39 through
the pipe 35 is combined together with the partial flow coming
from the condensor 33 through the pipe 34 into a total solvent
phase flow and is fed through the pipe 38 to the mixer 24. From
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there the slurry is fed through the pipe 25 to the rotor-stator
unit 26.
The slurry is fed through the pipe 27 to the separator 28
which operates according to the principle of a straining screw
conveyor like the other separators 8, 15 and 22. Here a
further separation of solid and partially loaded solvent phase
occurs.
While the liquid phase partially containing oil is taken
off through the pipe 29 and is fed in a counterflow to the
solid flow to stage III immediately downstream of the stage IV
containing the separator 28. For example the quasi-de-oiled
solids (oil content 1 %) are fed through a pipe 30 to a
solvent remover 31, advantageously a fluidized bed evaporator,
in which the solvent (e.g. hexane) dissolved in the solids is
removed by heating and is fed through pipe 32 so that it can be
recovered by condensation in the condensor 33 and is then
recycled through the pipe 34 to the solvent cycle. The dried
solids are taken off through the pipe 36.
In this process leakage and other solvent losses depending
on the production details are compensated by the addition of
solvent from a solvent reservoir 40 through the pipe 41.
In FIGS. 2 to 4 examples of the rotor-stator assembly are
illustrated for applications corresponding to the requirements
which result from different natural products and different
product steps. A rotor 49 which carries the rotor ring or rings
50 is attached to a rotor shaft 48.
These rings 50 are mounted interlocking or facing each
other adjacent the stator rings 52 mounted in the stator 51.
The actual tool 53 and/or 54 which forms the shear region of
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the rotor-stator assembly acts between the rotor ring 50 and
the stator ring 52.
In the case of the cone tool of FIG. 2 the rotor-stator
assembly is basically conical. The tool elements 53 do not have
interlocking elements but they simply face each other and a
variable gap 54 can be provided by axial sliding, e.g. axial
sliding of the stator.
The rotor-stator assembly is still formed basically
conically in the chamber tool illustrated in FIG. 3, however
the tool elements 53k on the rotor and/or stator rings 50c to
50f and/or 52_ to 52e forming the shear field interlock in each
other. Thus properties deviate from those of the cone tool of
FIG. 2 according to the purpose of the application.
Also in the nozzle and/or orifice tool shown in FIG. 4 the
tool elements 53_ and/or 53_ on the rotor-stator rings 50~ to
50k and/or 52f to 52_ engage in each other like rings so that
the rotor-side tool elements 53_ also have recesses, however
the stator-side tool elements 53c are also provided with
passages 55. Also the most exterior rotor ring 50~ is provided
with passages 55. The special properties of these rotor-stator
assemblies result from the nozzle or orifice action of these
passages 55.
The path of particles 56 in a rotor-stator assembly is
illustrated in FIGS. 5a and 5b. The individual pieces of
material are accelerated, retarded and guided many times on
their path 56 and/or 59 from the interior to exterior through
the tool elements 53_. The high crushing, dispersing and
extracting performance of the rotor-stator unit for recovering
oil is based on these detailed features. Residual
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still-existing agglomerations are further divided on impinging
on the housing wall 57.
In FIG. 5c the course 58 of the particles in a conventional
rotor-stator unit are illustrated in contrast to the path 59 of
the particles in a rotor-stator assembly in a unit according to
my invention.
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