Apparatus for separating a solid substance from a liquid mixture of substances

Apparatus for separating solid substances from liquid mixtures of substances, wherein the liquid substances contained in the mixture are separated from the solid substances by countercurrent extraction with a solvent which, during the extraction process, is in a liquid or supercritical state and which, under standard conditions, is gaseous. The solvent is fed to a cylindrical extraction chamber at the lowest point of the extraction chamber. The solvent leaves the nozzles with a Reynold's number of 40,000 and flows upward in the extraction chamber with a Reynold's number of 2,700 to 8,000.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for separating a liquid mixture 
of substances comprised of dissolved solid substances and liquid 
substances, in which the liquid substances are separated from the solid 
substances by countercurrent extraction in an extraction chamber with a 
solvent to form a solvent phase which is loaded with the liquid substances 
and an extraction phase. During the extraction process, the solvent, 
which, under standard conditions, is gaseous, is in a liquid or 
supercritical state. The solvent phase which is loaded with the liquid 
substances is removed from the extraction chamber, and subsequently, by 
pressure reduction and/or temperature changes, resolved into its component 
parts. Solvent is recovered during this resolving and the recovered 
solvent is returned to the extraction chamber. The present invention also 
relates to an apparatus for implementing this process. 
A process of the type described above is known from DE-OS 3 229 041. There, 
a process is suggested to separate lecithin from mucilage, a by-product of 
the production of vegetable fats and oils, by extraction of the mucilage 
with a solvent which is gaseous under standard conditions. In this 
process, the mucilage is extracted under a pressure of 2.times.p.sub.k to 
500 bar and at a temperature of 0.degree. C. to &lt;T.sub.k, within 15 to 60 
minutes. The loaded, compressed solvent phase which forms is first 
separated from the insoluble lecithin, and then the extracted liquid 
substances are separated from the loaded, compressed solvent phase. The 
gaseous solvent which is recovered is returned to the extraction chamber. 
The extraction phase which forms in the extraction chamber contains 
lecithin and solvent, and after the extraction phase is removed from the 
extraction chamber, the lecithin is recovered from the extraction phase in 
solid form by evaporation of the solvent. As used herein, the symbol 
p.sub.k =critical pressure of the solvent; the symbol T.sub.k =critical 
temperature of the solvent; and standard conditions=0.degree. C., 1 bar. 
Carbon dioxide, ethane and/or ethylene or a mixture of one or several of 
these gases with methane, propane and/or propylene are used as gaseous 
solvents. In this process, it is difficult to recover the solid substance 
(lecithin) consistently in powder form since in some charges, the 
recovered solid substance was in the form of blocks or large clumps which 
had a negative effect on the quality of the product. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an apparatus for 
implementing a process of the type mentioned above in which the solids to 
be separated from the liquid mixtures always are recovered in powder form. 
Additional objects and advantages of the present invention will be set 
forth in part in the description which follows and in part will be obvious 
from the description or can be learned by practice of the invention. The 
objects and advantages are achieved by means of the processes, 
instrumentalities and combinations particularly pointed out in the 
appended claims. 
To achieve the foregoing objects and in accordance with its purpose, the 
present invention provides an apparatus for separating a liquid mixture of 
substances comprised of a dissolved solid substance and liquid substances, 
in which the liquid substances are separated from the solid substance by 
countercurrent extraction in an extraction chamber with a solvent to form 
a solvent phase which is loaded with the liquid substances and an 
extraction phase, the solvent, during the countercurrent extraction, is in 
a liquid or supercritical state and under standard conditions, is gaseous, 
the solvent phase which is loaded with the liquid substances is removed 
from the extraction chamber, the solvent phase is resolved by pressure 
reduction and/or temperature change into its component parts to recover 
gaseous solvent, and the recovered gaseous is returned to the solvent 
extraction chamber, comprising: effecting the countercurrent extraction by 
(a) feeding the solvent to a cylindrical extraction chamber at the lowest 
point of the extraction chamber through nozzles, and (b) controlling the 
flow of the solvent through the extraction chamber so that the solvent 
leaves the nozzles with a Reynolds' number of &gt;40,000 and flows upwards in 
the extraction chamber with a Reynolds' number of 2,700 to 8,000. 
The present invention is based on the discovery that the solid substances 
to be separated are recovered only as powders when a specific condition is 
maintained for the mass flow of the solvent in the extraction chamber, 
which flow is between the extremes of laminar and turbulent flow. This 
condition of mass flow can only be realized if the solvent is fed into the 
extraction chamber in a highly turbulent state in the manner set forth 
above. 
In accordance with a preferred embodiment of the present invention, the 
liquid mixture to be treated contains 5 to 75% by weight solid substances 
dissolved in the liquid mixture to be treated, and the mass flow of the 
liquid solvent feed into the extraction chamber is between 140 to 170 
kg/m.sup.2. h in relation to the cross sectional area of the extraction 
chamber. By maintaining the above mass flow and the content of solids in 
the mixture, a solid in powder form is produced by economical means. The 
process of the invention can be implemented especially well if the liquid 
mixture which is treated comprises, by weight, 50 to 70% of lecithin and 
remainder of vegetable oil. 
In another aspect of the present invention, there is provided an apparatus 
for separating a dissolved solid substance from a liquid mixture of 
substances by countercurrent extraction in an extraction chamber with a 
solvent to form a solvent phase which is loaded with the liquid 
substances, the apparatus containing at least one separator connected to 
the extraction chamber for separating the solvent from the liquid 
substances, means for returning the separated solvent to the extraction 
chamber; comprising a cylindrical pressure-resistant countercurrent 
extraction chamber having a diameter-heigth ratio of 1:5 to 1:10, and 
nozzles at the bottom of the extraction chamber for supplying solvent to 
the extraction chamber. 
The use of a slender, cylindrical extraction chamber without anything built 
into it, in conjunction with the nozzles built directly into the bottom of 
the extraction chamber, assures that the mass flow maintained is in 
accordance with the present invention. 
In a preferred embodiment of the apparatus of the present invention, the 
nozzles are in the form of bores located radially on at least one tube 
ferrule that is fastened to the bottom of the extraction chamber wherein 
the axes of the radial bores form an angle of 0.degree. to 60.degree. with 
the axis of the extraction chamber. Alternatively, the nozzles are in the 
form of bores which are located on a plate fastened to the bottom of the 
extraction chamber wherein the axes of the bores run parallel to the axis 
of the extraction chamber. Both arrangements provide for even distribution 
of the solvent in the extraction chamber. 
Preferably, the means for returning the separated solvent to the extraction 
chamber comprises a compressor connected to the separator for compressing 
the separated solvent and a heat exchanger connected to the compressor for 
heating the compressed solvent; It is to be understood that both the 
foregoing general description and the following detailed description are 
exemplary and explanatory, but are not restrictive of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIG. 1 a storage tank 10 
which contains the liquid mixture which is to be treated. The liquid 
mixture which is to be treated is fed from storage tank 10 into the top of 
an extraction chamber 1 by way of a pipe 11. Extraction chamber 1 contains 
no built-in device to facilitate separation of the substances in the 
liquid mixture and is designed as a cylinder with a diameter to height 
ratio of 5 to 1:10. Extraction chamber 1 contains a bottom 2 on which 
nozzles are provided. The nozzles are the means by which the solvent is 
fed into extraction chamber 1 and towards the liquid mixture in 
counterflow to the liquid mixture. During the countercurrent flow of the 
solvent upwardly through extraction chamber 1, a solvent phase is formed 
which comprises solvent and liquid substances which have been extracted 
from the liquid mixture. At the head of extraction chamber 1, the solvent 
phase, which is loaded with the liquid substances, is drained or removed 
by a pipe 12, and then is relaxed (pressure is reduced) in a valve 13, is 
heated in a heat exchanger 14, and conveyed by a pipe 15 into a separator 
3 where the liquid substances drop out (separate, as by gravity) from the 
solvent. The so separated liquid substances are withdrawn from separator 3 
by pipe 16. Thus, the solvent phase is resolved into its components, that 
is, the solvent phase is separated into solvent and liquid substances. 
The gaseous solvent developed in separator 3 reaches a compressor 4 by way 
of a pipe 17 and, subsequently, a heat exchanger 5 by way of a pipe 20. In 
these devices, the solvent is liquified and the extraction pressure and 
temperature are adjusted. Loss of solvent is compensated by feeding a 
specific amount of solvent from a storage tank 18 through a pipe 19 into 
pipe 17. The solvent, which is in a liquid or supercritical state, is fed 
into extraction chamber 1 by a pipe 21. After the liquid substances have 
been extracted from the mixture in extraction chamber 1, an extraction 
phase comprised of solids mixed with solvent is present in extraction 
chamber 1 and this extraction phase then is conveyed from extraction 
chamber 1 by a pipe 22 into a chamber 23 where the remaining solvent is 
evaporated and reaches storage tank 18 by way of a pipe 25. The solids in 
powder form are removed from chamber 23 by a pipe 24. 
The solvent is fed into extraction chamber 1 by nozzles 6 which are located 
directly at bottom 2 of extraction chamber 1. Suitable as nozzles 6 are 
bores which are arranged in a tube ferrule (tubular ring) 7. The solvent 
is expelled upwardly through extraction chamber 1 from nozzles 6. Axes of 
the bores can form an angle of 0.degree. to 60.degree. with axis 9 of 
extraction chamber 1. The bores in extraction chamber 1 can be arranged to 
be parallel with axis 9 as shown by axis 8' in FIG. 2b, or can be arranged 
to be aligned toward the inside of extraction chamber 1 as shown in FIG. 
2b by axis 8", or toward the outside of extraction chamber 1, as shown by 
axis 8" in FIG. 2b. Tubular ferrule 7 is fastened by a mounting 26 on 
bottom 2 of extraction chamber 1. The solvent is placed into tube ferrule 
7 by way of a pipe that is not shown in the drawing. 
Instead of tube ferrule 7, a plate 10, as shown in FIGS. 3a and 3b directly 
attached to bottom 2, can be utilized in which the bores, acting as 
nozzles 6, are arranged in such a way that axes 8 of the bores are 
parallel to axis 9 of extraction chamber 1. 
Plate 10 is designed as a hollow body which is fastened to bottom 2 of 
extraction chamber 1 and to which the solvent is conveyed by way of a pipe 
that is not shown in the drawing. Both nozzle arrangements (FIGS. 2a and 
3a) provide for even distribution of the solvent over the cross section of 
the extraction chamber which results in excellent extraction output. 
The solvent used in the present invention is one which is gaseous under 
standard conditions, that is to say, at 0.degree. C. and 1 bar. This 
solvent is suitable for extraction when it is in liquid or supercritical 
state. The liquid state is defined by the pT-diagram and is achieved by 
cooling a gas and compressing it to a specific pressure. The supercritical 
state exists when the gas exhibits a pressure and temperature which are 
above the critical pressure or, respectively, the critical temperature. As 
solvents which are gaseous at standard conditions, carbon dioxide and 
low-molecular hydrocarbons are appropriately used to implement the process 
of the invention. 
The Reynold's number Re.sub.E for the extraction chamber is defined as 
##EQU1## 
u=flow velocity of the extraction agent in the extraction chamber; 
d=diameter of cylindrical extraction chamber; 
.gamma.=kinematic viscosity of the extraction agent; 
m.sub.g =mass flow of extractive agent; 
.eta.=dynamic viscosity of extractive agent. 
The Reynolds number Re.sub.B for the bore diameter is defined as 
##EQU2## 
u.sub.B =current velocity of the extraction agent in the nozzle; 
d.sub.B =nozzle diameter; 
.gamma.=kinematic viscosity of extractive agent; 
m.sub.g =mass flow of extractive agent; 
n=number of nozzles. 
On the basis of these relationships, there is some leeway in setting the 
number and diameter of the nozzles which is restricted by construction 
considerations and by the need for even distribution of gas in the 
extraction chamber. It is, therefore, possible within certain limits to 
vary the number and diameter of the nozzles in relation to the size of the 
extraction chamber and the quantity of the substance transferred. 
EXAMPLE 
In a cylindrical extraction chamber, standing vertically, with an inside 
diameter of 109 mm, a height of 850 mm, and a volume of 7.93 1, 700 g raw 
lecithin with an oil content of 40% by weight was fed in over a period of 
one hour. Carbon dioxide flowed through the extraction chamber at 350 bar 
and 60.degree. C. as well as at a mass flow of 80 kg CO.sub.2 /h. At the 
bottom of the extraction chamber, a tube ferrule with an external diameter 
of 90 mm and a tube diameter of 3 mm was installed as solvent distributor, 
whose wall had 20 bores with a diameter of 0.3 mm. The bores were inclined 
toward the cylindrical axis of the extraction chamber at an angle of 
0.degree. and 60.degree. , whereby the inclinations were oriented toward 
the inside of the extraction chamber. The solvent was fed to the tube 
ferrule by way of a soldered pipe. The pressure difference between the 
inside of the tube ferrule and the extraction chamber was 20 bar. 
The oil-loaded carbon dioxide was withdrawn from the top of the extraction 
chamber whereby the small lecithin particles were prevented from being 
carried along by a packing of steel wool. After cutting off the supply of 
raw lecithin at the end of one hour, the solvent flow was kept going for 
another hour. During the two-hour extraction, the extracted oil was 
separated from the loaded solvent phase by reducing the pressure to 60 
bar. 
After the two-hour extraction period, the pressure in the extraction 
chamber was relieved (reduced) and the de-oiled lecithin was withdrawn 
from the extraction chamber. It was in pulverized form, the medium grain 
size was about 50 .mu.m, and the lecithin content was 95.6%. The extracted 
oil still contained 1.0% lecithin. 
All percentages shown above are related to weight. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.