Fat crystallization method and apparatus therefor

Process for crystallizing fatty substances for their subsequent fractionation especially by pressure filtering, consisting in particular in melting the fatty substances, dividing the molten mass into beads, feeding these beads into a pre-refrigerated aqueous solution, adjusting the concentration of the fatty substance relative to the aqueous solution, adjusting the feed rate of said beads, adjusting the temperature of the beads/solution mixture, maintaining said mixture temperature until the crystallization of each bead has completely stabilized, subsequently transferring the beads/solution mixture to the filtration location, separating the fatty substance beads under a low pressure from the aqueous solution, and finally extracting from said fatty substance beads, under high pressure, the liquid portion of the fatty substance, and apparatus for applying this process.

The present invention relates to a process for crystallising fatty 
substances, in particular lauric fats and lauric or non-lauric fatty acids 
for their subsequent fractionation especially by pressure filtering. 
In the field of nutrient fats, the area relating to the total or partial 
substitution of cacao butter is the subject of many research, this being 
mainly due to the high price of cacao butter, the main characteristic of 
which resides in its capacity to melt entirely at the human body 
temperature while still remaining sufficiently solid and manageable there 
below. The main use of cacao butter is in confectionery and in 
chocolate-factory, but the excipient market in pharmacology is not 
negligible. 
The substitution products for cacao butter are classified in two large 
categories, depending whether they are of the lauric or nonlauric type, 
i.e. according to whether they are produced starting from fats which are 
rich in lauric fatty acids or not. 
The invention relates in particular to substitution products of the lauric 
type and more particularly to fats, rather than to oils, since the 
physical characteristics of the concerned products range generally within 
those of the category of fats. 
However, the invention also relates to the production of fractionated fatty 
acids of the lauric or non-lauric type which may substitute, at a lower 
cost, the distilled fatty acids. 
The fat which is used the most for manufacturing a substitute of the lauric 
type is indisputably palm fat, which is extracted from palm nut kernels. 
Other exotic fats, such as coconut oil, karite nut fat, fats originating 
from cuphea, babassu, mangue or sal kernels can also be used. 
With respect to palm fat, in order to obtain, starting therefrom, a product 
which is similar to cacao-butter, the palm fat is fractionated in order to 
withdraw a solid portion thereof. Starting from palm fat with a iodine 
number of about 17 to 19, the object of the fractionation is to obtain a 
solid portion with a iodine number not higher than 7. In this field, the 
use of the iodine number, i.e. of the measurement of the insaturation 
degree of the fat, is quite widespread because it is quickly done and 
gives a good approximation of the product quality. Other analyses relative 
to the composition of the products and to their physical behaviour are 
used for a sharper definition. 
For doing this, the processes for fractionating fatty substances which are 
used nowadays are of four different types, namely: 
A process according to which the fatty substance is admixed with a solvent, 
in general acetone. Then, the miscella is refrigerated by convection or 
evaporation until germination and growth of crystals occur within the 
miscella. After stabilisation of these crystals by tempering, they are 
separated from the fluid portion by filtration, decantation or by another 
separation process. 
A process according to which the fatty substance is crystallised, without 
solvent, by cooling down and subsequently admixed with a surfactant which 
allows to separate the crystallised portion by centrifugation, this 
process being known under the denomination Lanza process. 
A process according to which the fatty substance is crystallised and 
solidified in trays placed in a cold chamber or conveyed into 
refrigeration tunnels, the plates of solidified fatty substance being then 
introduced into filtering bags which are subsequently stacked up in the 
cage of a hydraulic press. Thanks to the available high pressure, the soft 
portion of the fatty substance is exuded until the quality of the rigid 
part thereof which remains within the press is as desired. The filtering 
bags are then unstacked and the cakes formed by said rigid part are 
demolished. 
A process according to which the fatty substance is partially solidified in 
a crystallisation vessel until the point that the fatty substance is in 
the super-cooling state, at the limit of the pumping possibilities. It is 
then fed by pumping into the chambers of a filter press equipped with 
plates with refrigerated walls and provided with membranes. After having 
fed the fatty substance into the filter, this filter is left the time 
which is necessary for its solidification and for the stabilisation of the 
crystalline phase. Then, an important pressure, of 25 to 70 bars according 
to the case, is applied onto the backside of each membrane in order to 
exude the fluid portion from the fatty substance. The pressure is then 
relieved and the filter is opened for demolishing the solid material 
cakes. 
From these four known processes, it is the last one which is developing the 
most, taken into account the fact that the costs for the first three 
processes are high, namely: in the first process, energy costs caused by 
the recovery of the solvent and costs for replacing the lost solvent; for 
the second process, costs for the surfactant and costs for the loss of 
fatty substance and, for the third process, costs of labour. 
However, notwithstanding the advantages that it shows with respect to the 
first three processes, the fourth aforementioned known process causes also 
difficulties with respect to the control of the fatty substance 
crystallisation and with respect to the transfer of the crystallised mass 
into the filter to fill all of the chambers and to avoid plates braking by 
compression onto empty or partially empty filter chambers. 
An object of the invention is to provide a simple and efficient solution to 
the aforesaid difficulties which arise when carrying out the above 
mentioned fourth process. 
To this end, the process according to the invention consists in melting the 
fatty substance, dividing the molten mass into beads which are as 
homogeneous as possible and which have dimensions as regular as possible, 
feeding these beads into an aqueous solution refrigerated previously to a 
temperature lower than the melting point of the fatty substance, adjusting 
the concentration of the fatty substance relative to the aqueous solution 
in function of the capacity of this solution to absorb the amount of heat 
required for solidifying the fatty substance beads, controlling the feed 
rate of said beads into said solution in order that each fatty substance 
bead is subjected instantaneously to a beads/aqueous solution heat 
exchange which causes the surface of the beads to solidify quickly and 
progressively the entire mass thereof, maintaining the fatty substance 
beads in suspension in said aqueous solution, adjusting the temperature of 
the beads/solution mixture to enable the crystallisation of each bead to 
stabilise, maintaining said mixture temperature until said crystallisation 
is completely stabilised, subsequently transferring the beads/solution 
mixture to the filtration location whose surfaces which come into contact 
with said mixture are kept at a temperature near the temperature of the 
mixture, separating the fatty substance beads under a low pressure from 
the aqueous solution, and finally extracting from said fatty substance 
beads, under a high pressure, the liquid portion of the fatty substance. 
A further object of the invention is an apparatus for carrying out said 
process. 
According to the invention, this apparatus comprises a crystallisation 
chamber connected to a source of molten fatty substance, to a source of 
aqueous solution adapted to make the temperature of the solution 
adjustable and to a filter press equipped with plates the walls of which 
being arranged to be suited for being brought to a determined temperature, 
means disposed within the chamber, near the location where the molten 
fatty substance is fed therein, and arranged to divide this fatty 
substance into beads, means arranged for controlling the feed rate of the 
molten fatty substance in the chamber and the concentration of the fatty 
substance beads into the aqueous solution, means arranged within the 
chamber for maintaining the fatty substance beads in suspension in the 
aqueous solution, means provided within the chamber and connected to an 
external source of cooling fluid, which means are arranged for maintaining 
the temperature of the fatty substance beads/aqueous solution mixture at a 
determined value, and means arranged to enable said mixture to be 
transferred from the chamber to the filter.

In the different figures, the same reference numerals indicate identical or 
analogous elements. 
First of all, one will notice that, within the scope of the present 
invention, the expression "fatty substance" has a meaning which is as 
large as possible and which will comprise consequently as well fats 
containing fatty acids as fatty acids as such, whether these fats and 
fatty acids are of the lauric or non-lauric nature. However, as was set 
forth already previously, the process of the invention is particularly 
suited for the treatment of lauric fats and lauric or non-lauric fatty 
acids. 
The process according to the invention illustrated in the drawings is more 
particularly destined for crystallising fats of the lauric type, in an 
aqueous solution, in view of their later fractionation by pressure 
filtering, with recovery of this aqueous solution during the filtering. 
This process consists first of all, in 1, in melting the fats and in 
dividing, in 2, the molten fatty mass 3 into beads 4 which are as regular 
as possible and which are fed in an aqueous solution 5 previously 
refrigerated to a temperature lower than the one of the melting point of 
the fat. The concentration of the fat beads relative to the aqueous 
solution is adjusted in function of the capacity thereof to absorb the 
necessary amount of heat for solidifying the fat beads and, in 6, the feed 
rate of the beads 4 in the solution 5 is controlled so that each fat bead 
is instantaneously subjected to a beads/aqueous solution heat exchange 
which causes the surface of the beads to solidify quickly and the entire 
mass thereof progressively. The fat beads are kept in suspension, in 7, in 
the aqueous solution and the temperature of the beads/solution mixture 8 
is adjusted to enable the crystallisation of each bead to stabilise and 
this mixture temperature is maintained, in 7, until said crystallisation 
is completely stabilised. Then, the beads/solution mixture is transferred, 
for example by pumping 9, to the filtering location 10 whose surfaces 
which come into contact with said mixture are kept at a temperature near 
the temperature of this mixture. First of all, the fat beads are 
separated, under a low pressure, from the aqueous solution and then the 
liquid portion of the fat is finally extracted, under a high pressure, 
from said fat beads. 
In the process illustrated in FIG. 1, the fat beads 4 are crystallised 
discontinuously by feeding, in 7 in order to form the beads/aqueous 
solution mixture, a given volume of fat beads in a given volume of aqueous 
solution, which is prepared in 11 where it is recycled after filtering of 
said mixture. After having composed said mixture, it is maintained, as set 
forth hereinabove, in 7, until the crystallisation of the fat beads is 
completed. Only when this crystallisation is stabilised, the mixture is 
transferred to the filtering location. 
According to the invention, one could also provide to crystallise the fat 
beads of said mixture continuously and this by circulating the 
refrigerated aqueous solution in counter-current with respect to the flux 
of the fat beads until the crystallisation of said beads, which are kept 
in suspension in the aqueous solution, is stabilised. An advantageous way 
for doing this would be to feed the molten fat at the bottom of a vertical 
column, through a device for dividing the fat into beads as illustrated by 
any one of the FIGS. 2, 3, 4 or 5. Through the vertical column flows then 
a flux of aqueous solution, going from the top towards the bottom of the 
column in a continuous or pulsed way. The formed and progressively 
solidified beads are thus moved upwards due to their specific, weight 
which is lower than that of the solution. The beads/solution mixture flows 
then over, at the top of the column, into a stabilisation vessel. When the 
crystallisation is stabilised, the beads/aqueous solution mixture is 
directed towards a battery of filters where the filters are filled and 
actuated one by one so as to separate the aqueous solution, by pressure, 
from the fat beads, these beads being then put under pressure so that 
their liquid portion is exuded. 
In the process illustrated in FIG. 1, there is fed in 7, i.e. in a 
crystalliser, an amount of aqueous solution which is determined by the 
desired concentration of the mixture formed by this solution and the fat 
beads 4 which will be fed therein, the temperature of the aqueous solution 
being adjusted, prior to this feeding, to a temperature lower than that of 
the melting point of the fat. For palm fat, the temperature of the aqueous 
solution will be comprised between 5.degree. and 27.degree. C. and 
preferably between 8.degree. and 20.degree. C. The fat is fed into this 
aqueous solution in the form of homogeneous beads, the diameter of which 
is comprised between 0.1 and 5 mm, but which is preferably situated 
between 1 and 3 mm. The aforementioned concentration of the fat beads 
relative to the aqueous solution will be from 10 to 70%, and will 
preferably be comprised, for palm fat, between 20 and 50%. The fat beads 
are kept in suspension in the aqueous solution by a stirring movement 
until the feeding of said beads into this solution is stopped. Once the 
beads/aqueous solution mixture is formed, its temperature is kept between 
10.degree. and 23.degree. C., and preferably between 17.degree. and 
20.degree. C., such as to stabilise the crystallisation of each bead of 
the mixture. Keeping the mixture at temperature is done by controlling, in 
a precise way, the temperature of said mixture through that of a cooling 
liquid 12 and takes between 2 and 24 hours, and preferably, for palm fat, 
from 4 to 10 hours. When the beads/aqueous solution mixture has been kept 
for the desired period at temperature, it can easily be transferred either 
by pumping, as shown in FIG. 1, or by pressure difference, into the filter 
10 which will be described hereinafter and which has previously been 
brought to a temperature close to that of the mixture; in the filter, the 
aqueous solution will first of all be separated from the mixture at a 
pressure comprised between 1 to 4 bars, so as to be recovered in 11, the 
liquid portion of the fat beads being then exuded at a pressure comprised 
between 15 to 70 bars and preferably, for palm fat, of 20 to 40 bars. 
As aqueous solution use can simply be made of water but in order to avoid, 
on one hand, an untimely saponification of the free fatty acids contained 
in the fat and, on the other hand, a mutual agglomeration of the fat 
beads, an aqueous solution is provided which contains an acid and a 
surfactant. Before feeding the fat beads in the solution, this acid is 
dosed therein to obtain a pH situated between 6.8 and 7.0 and this weak 
acidity of said solution is maintained. Preference will be given, for its 
anti-oxidising effect, to citric acid although there would not be any 
inconvenient in using other, more economical acids. As to the surfactant, 
there will be chosen advantageously, for palm fat, an emulsifier of the 
anionic, cationic or zwitterionic or non ionic type. 
According to the invention and as shown in the drawings, the apparatus for 
carrying out said process comprises a crystallisation chamber 13 connected 
to a source 14 of molten fatty substances, to a source 15' of aqueous 
solution adapted to make the temperature of the solution adjustable and to 
a filter press 10 equipped with plates the walls of which being arranged 
to be suited for being brought to a determined temperature. Means 15 are 
disposed within the chamber 13, near the location 16 where the molten 
fatty substance is fed therein, and arranged to divide this fatty 
substance into beads 4. Means 6 are arranged for controlling, on the one 
hand, the feed rate of the molten fat in the chamber 13 and, on the other 
hand, the concentration of the fat beads in the aqueous solution. Means 17 
are arranged within the chamber 13 for maintaining the fat beads in 
suspension in the aqueous solution, whilst means 18 are provided within 
the chamber and connected to an external source 12 of cooling fluid, for 
maintaining the temperature of the fat beads/aqueous solution mixture at a 
determined value, means 19 being arranged for transferring said mixture 
from the chamber 13 into the filter 10, the walls of which are tempered by 
a cooling fluid contained in a tank 20 and circulated by a pump 21. Means 
22 are moreover provided for recycling the aqueous solution, which has 
been separated in the filter from the fat beads, towards the source 15' of 
aqueous solution. 
Although use could be made of no matter what type of crystallisation 
chamber, it is advantageous to use a crystallisation chamber 13 shown in 
FIGS. 1 and 2 which is of the cylindrical vessel type with a vertical axis 
and an insulated wall 22, wherein the molten fatty substance is fed at the 
bottom, in 16, which vessel comprises, over an important portion of its 
height, on the one hand, a heat exchanger 23 which is co-axial to the 
vessel and which forms said means 18 for maintaining the temperature of 
the fat beads/aqueous solution mixture at a determined value and, on the 
other hand, an agitator 24 formed by a shaft mounted on the vessel so that 
the axis of its shaft 25 coincides with the vessel axis. Blades 26, which 
are preferably directional, are regularly distributed according to the 
longitudinal direction of the shaft and according to planes passing 
through the axis of this shaft, said agitator forming said means 17 for 
maintaining the fat beads in suspension in the aqueous solution. Said 
means 15, arranged for dividing the molten fat into beads, are formed in 
the chamber 13, as shown in FIGS. 1 and 2, by a regularly perforated plate 
27 which is fixed, by its circumference, into the lower portion of the 
vessel to the inner wall thereof, this plate 27 which is flat and 
perpendicular to the vessel axis, could, according to the invention, also 
be arched, either convex or concave, the dimensions of the perforations 28 
being chosen in function of the desired volume of the beads 4. The cooling 
liquid, which circulates in the heat exchanger 23, is constantly 
controlled with respect to both its temperature and its flow rate by means 
of the pump 29. Most often, this liquid will be water or, when required by 
the temperature, a mixture of water and propylene glycol. 
As shown in FIGS. 3 and 4, the aforementioned means 5, arranged for 
dividing the molten fat into beads, may also be of the circular or 
longitudinal bell-type and disposed onto a plate 30 fixed within the 
vessel at right angles to the axis thereof and provided with a central 
opening 31. A duct 32, which is open at its both extremities, is fixed to 
the circumference of this opening 31 so as to extend above said plate 30, 
a bell 33, also fixed to this plate, capping the duct 32 in such a way 
that a space 34 remains between the upper extremity 35 of said duct and 
the bell 33, this bell being regularly perforated 36, over its entire 
circumference, in the zone thereof comprised between the level of the 
plate 30 and that of the upper part of the duct 32. As shown in FIG. 5, 
these means 15 could also be formed by a flat plate 30 fixed within the 
vessel at right angles to the axis thereof and showing parallel elongated 
openings 36. Each of these openings 36 is capped by a box 37 having a 
U-shaped section with unequal heights of the flanges 38 and 39, this box 
being fixed to the upper side of the plate 30 by the free edge 40 of its 
longest flange 38 whilst the free edge 41 of its shortest flange 39 shows 
notches 42 which are regularly divided over its entire length. This box 37 
comprises between the two flanges 38 and 39 of the U-shape and parallel 
thereto a flat vertical partition 43 fixed to said plate and disposed 
between said elongated opening 36 and the lowest flange 39 of the U-shape, 
the height of this partition 43 being such that a space 44 remains between 
its upper edge 45 and the web 46 of the U. 
The filter 10, one element of which is schematically shown in FIGS. 6 to 9, 
is a chambered plate filter-press known per se, each filter element 
chamber 47 being provided with a flexible membrane 48 behind which, in 49, 
it is possible to feed a pressurised fluid. 
The operation sequences of the filter are as follows 
Feeding of the filter with fat beads/aqueous solution mixture, in 50 (FIG. 
7), filtering from the mass the fat beads in suspension, then increasing 
the pressure to a pressure of 1 to 4 bars in order to extract the aqueous 
solution which is immediately recovered, in 51, so as to be reused in 11. 
Compacting each chamber 47 by bringing the back of each membrane 48 at a 
pressure comprised between 15 and 70 bars, during which the liquid portion 
of the fat is exuded, in 52, and leaves in each chamber 47 a product cake 
56 with a high melting point (FIG. 8). 
Blowing the beads/aqueous solution mixture feeding ducts 53. 
Blowing the filtrate outlet ducts 54. 
Evacuating the circuit 55 for pressurising the membranes 48. 
Demolishing the cakes 56 (FIG. 9). 
Closing the filter and preparing it for the transfer of a new amount of 
said, after a possible washing cycle. 
It has to be understood that the invention is in no way limited to the 
described embodiments and that many modifications could be applied thereto 
without leaving the scope of the present patent. 
Of course, any fatty substance other than a lauric fat could be treated in 
the same way or in a way substantially similar to the illustrated process. 
It is so that the use of the aqueous solution composed of water and an 
acid for avoiding saponification of the free fatty acids of the fat is to 
be conceived of course only in the case of the treatment of a fat.