Process for selective removal of volatile substances from liquids, as well as unit and device for carrying out the process

For selective removal of volatile substances from liquids, the initial liquid is fed to a crosscurrent diaphragm separation device (2), in which the permeate consisting of water and volatile substances is separated by increased transdiaphragm pressure and concentration difference. Then, the permeate is fed into a further liquid-volatile separation device (8), in which the alcohol is distilled out. The permeate now only consisting of water, salts, acids and extracts is then fed back into the crosscurrent diaphragm separation device (2), where it flows through the permeate side in countercurrent to the flow of the retenate. Excess permeate can be introduced into the dealcoholized initial liquid. By the process according to the invention the economic efficiency of the unit and the quality of the end product are significantly improved.

The invention relates a process for selective removal of volatile 
substances from liquids, particularly of alcohol from beverages such as 
wine, beer or fermented fruit juices by diaphragm separation processes and 
at least one additional separation process. 
In the dealcoholization of liquids one distinguishes between alcohol 
reduction (for example 40 %) and total dealcoholization (0.5%). In the 
process the characteristic taste substances in the initial liquid, for 
example wine or beer, are to remain as unaltered as possible in the 
dealcoholized beverage. 
To attain this goal, thermal processes have become known which have been 
developed from evaporating units. A known unit for the extraction of 
alcohol-free wine exhibits a multi-stage evaporator, in which the alcohol 
is evaporated along with the aromatic substances. The condensate is fed to 
a distilling column with several separation substances, in which the 
alcohol is distilled out. Afterwards the separated aromatic substances are 
again mixed with the dealcoholized wine. The disadvantage of the known 
thermal processes lies in that as a result of thermal stress boiling 
products which diminish taste are produced and an undesirable aftertaste 
occurs in the dealcoholized beverage. Moreover the energy use in thermal 
processes is very high and the unit, particularly with the use of several 
evaporation stages and a distilling column with several separation stages, 
is relatively expensive. 
In addition diaphragm separation processes for dealcoholization of liquids 
have become known, in which the alcohol is filtered out of the initial 
liquid, for example, beer or wine by reverse osmosis in the crosscurrent 
diaphragm process. With the addition of water the liquid to be 
dealcoholized is fed through the diaphragm filter modules with the help of 
a circulating pump. In the course of this the volatile substances are 
removed by diafiltration along with the water on the permeate side of the 
diaphragm filter module. To improve the yield a reconcentration or 
preconcentration of the retentate is often also carried out. Since in 
these known diaphragm processes there is no heat treatment, the peculiar 
taste or boiled taste resulting in thermal processes is not present. But 
with increasing concentration, the aromatic substances contained in the 
initial liquid still diffuse through the diaphragms of the diaphragm 
filter module, particularly if the diaphragm is not precisely adjusted to 
the initial liquid. The consequence of this is a taste alteration of the 
beverage, which becomes worse with increasing dealcoholization. This leads 
to wine, for example, losing its characteristic taste in total 
dealcoholization by diaphragm filtration. 
A further known process of dealcoholization of liquids is the dialysis 
process (EP-OS 0021247). In contrast to the reverse osmosis processes, in 
which the transdiaphragm pressure works as a driving force for the 
permeate flow through the diaphragm, in the dialysis process the 
separation of the alcohol from the initial liquid results almost 
exclusively from the concentration differences of the two liquids 
separated by a diaphragm. The initial liquid to be dealcoholized flows 
through the retentate side of the dialysis module. On the permeate side 
water is fed through the dialysis module countercurrent to the retentate 
flow. As a result of the concentration differences the volatile substances 
(alcohol) pass out of the retentate through the diaphragm and are carried 
off along with the water on the permeate side as dialyzate. In a similar 
manner as in reverse osmosis, with the diffusion of the alcohol other low 
molecular substances, particularly aromatic substances, pass through the 
diaphragm into the dialyzate. In the production of alcohol-reduced 
beverages these aromatic losses have no significant impact on the general 
character of the beverage. In contrast with total dealcoholization by 
dialysis, the taste and full-bodied character of the initial product 
suffer significantly. In addition the small specific yield of the unit 
given by the action principle declines with significantly increasing 
reduction of the alcohol content and the energy use rises correspondingly. 
The dialysis process is therefore unsuited for total dealcoholization; 
Further a process for dealcoholization of wine has become known, which 
consists of a combination of dialysis processes and thermal processes. The 
wine as initial liquid flows through the retentate side of the dialysis 
module and as result of the concentration differences gives off the 
alcohol off through the diaphragm to the dialyzate, which flows through 
the permeate side of the dialysis module countercurrent to the retentate 
flow. The dialyzate is fed into a distilling column, in which a further 
separation of the alcohol from the dialyzate takes places by vacuum 
distillation at low temperature. The valuable substances remaining in the 
recirculating dialyzate as a result cause an only slight concentration 
difference with the retentate, so that after a certain start-up time and 
reaching of equilibrium essentially only alcohol diffuses from the 
retentate into the dialyzate and a considerable portion of the valuable 
substances remains in the retentate. The disadvantage of this process lies 
in that as a result of the dialysis the yield goes down significantly with 
increasing alcohol reduction, so that in total dealcoholization the 
profitability of the unit is no longer guaranteed. 
Theretofore the object of the invention is to avoid the disadvantages 
attached to the known processes for dealcoholization of liquids, and to 
improve the economic efficiency of the unit and the quality of the product 
not only in the case of alcohol reduction but also in total 
dealcoholization. 
This object is achieved according to the invention in that the permeate 
consisting mainly of water and volatile substances is separated from the 
initial liquid by increased transdiaphragm pressure, in comparison with 
the dialysis process, and by concentration difference, subsequently the 
alcohol is removed by at least one additional liquid-volatile separation 
process, and then the resulting residue is fed back at least partially 
into the permeate side circuit between diaphragm separation processes and 
at least one of the additional liquid-volatile separation processes. 
Additional advantageous and suitable configuration of the invention can be 
gathered from the claims. 
The advantages obtained with the invention consist particularly in the fact 
that the disadvantages of the known processes can be largely eliminated 
while maintaining their advantages by the combination according to the 
invention of reverse osmosis, dialysis and thermal processes. The 
crosscurrent diaphragm separation device according to the invention is 
constructed so that the liquid-volatile separation takes place through the 
diaphragm by increased transdiaphragm pressure relative to the dialysis 
and by concentration difference. The driving force in this is the 
transdiaphragm pressure, which significantly improves the given small 
yield in the pure dialysis process and sharply reduces the yield decrease 
resulting from the increasing alcohol reduction. A further advantage 
consists in the fact that the aromatic substances, salts, acids and 
extracts passing through the diaphragm along with the alcohol remain in 
the permeate after the removal of the alcohol by at least one additional 
liquid-volatile separation process, for example, thermal distillation, 
diaphragm processes and a part of the permeate is fed back again into the 
retentate. Thereby the original taste and bouquet substances contained in 
the initial liquid, for example wine, are preserved largely unchanged even 
in total dealcoholization.

In the embodiment according to FIG. 1 the wine to be dealcoholized is 
introduced by a feed pipe 1 into the retentate side of a countercurrent 
diaphragm separation device 2. Crosscurrent diaphragm separation device 2 
consists of one or more crosscurrent diaphragm modules 3, in which mainly 
alcohol and water are removed from the wine as well as first, unwelcome, 
in addition aromatic substances, salts, acids and extracts to an extent 
not to be ignored. The specific design of crosscurrent diaphragm modules 
3, which cause a liquid-volatile separation on the basis of the 
transdiaphragm pressure and concentration difference, is described later. 
In crosscurrent diaphragm module 3 the wine flows through the retentate 
side separated from the permeate side by a diaphragm 4 in the direction of 
arrow 5 and leaves crosscurrent diaphragm module 3 after separation of the 
volatile substances as dealcoholized or alcohol-reduced wine by discharge 
pipe 6. The permeate consisting of alcohol, water and also aromatic 
substances, salts, acids and extracts is introduced by way of a permeate 
discharge pipe 7 into a further liquid-volatile separation device 8, which 
in the embodiment consists of a distilling column. In the distilling 
column the alcohol is distilled out of the permeate at low temperatures, 
which are made possible by a vacuum pump 9. By a return pipe 10 and a 
buffer tank 11 the residue consisting of aromatic substances, salts, acids 
and extracts is fed back again into diaphragm module 3 of crosscurrent 
diaphragm separation device 2. Circulating pumps 12 and 13 see to it that 
the permeate flows through the permeate side of crosscurrent diaphragm 
module 3 in the direction of arrow 14 countercurrent to the flow of the 
retentate. 
Although diaphragm 4 is selectively chosen for the separation of alcohol, 
by reason of the initial concentration difference between retentate and 
permeate, at first along with the alcohol and water also aromatic 
substances, salts, acids and extracts from the wine pass into the 
permeate. With increasing concentration of these substances which remain 
after separation of the alcohol in the liquid-volatile separation device, 
the concentration difference decreases, so that after reaching equilibrium 
the above mentioned valuable substances now diffuse only to an 
insignificant extent into the permeate and are thereby contained in the 
dealcoholized wine. The effect is improved by addition of aromatic 
substances, salts, acids and extracts which correspond to the contents of 
wine, to buffer tank 11 and/or into connecting pipes 10 and/or pumps 12, 
13. These substances can also be extracted by enrichment by distillation 
or diaphragm processes from the recirculating permeate or excess permeate 
or can also be mixed together synthetically. 
Diaphragm module 3 is operated with increased transdiaphragm pressure, 
which is over 5 bars. The driving force for the diffusion of alcohol is 
thus less the concentration difference between retentate and permeate than 
primarily the pressure, which is necessary to overcome the osmotic 
counterpressure of the alcohol. The osmotic counterpressure of salts, 
acids, extracts and aromatic substances increases with increasing 
concentration in the permeate, so that compared with pure reverse osmosis 
fewer valuable substances are lost and after a certain start-up time 
essentially only alcohol still diffuses into the permeate. 
From liquid-volatile separation device 8 a connection pipe 15 leads to 
discharge pipe 6 for the retentate. Through connection pipe 15 excess 
permeate, after passage through liquid-volatile separation device 8 is fed 
to the dealcoholized wine, which is thereby additionally enriched with 
valuable substances. With increasing transdiaphragm pressure the amount of 
permeate rises. As a consequence more permeate must be carried off as 
excess by connection pipe 15. As a result, the concentration of the 
permeate fed back by return pipe 10 decreases in proportion to the 
concentration in the retentate. As a result, the concentration gradient 
rises and thus also the quantity which diffuses from the retentate into 
the permeate. The valuable substances in the excess permeate are not 
present in equal quality as originally in the wine, as a result of the 
thermal stress, slight as it is, in liquid volatile separation device 8 
embodied as a distilling column. Therefore one must optimize between yield 
and quality, particularly, when one is working without addition of 
aromatic substances, salts, acids and extracts to the recirculating 
permeate. It has turned out that with a transdiaphragm pressure in the 
range of 5 to 25 bars a high quality with significantly increased 
throughput is attained compared with the pure dialysis process. With 
addition of aromatic substances, salts, acids and extracts to the 
recirculating permeate the permissible pressure for reverse osmosis 
systems can be exploited and thus additional improvement of the yield 
along with good quality is attained. 
With lesser alcohol reduction, for example to 50% of the original content, 
one can dispense with feeding the excess permeate back to the wine when 
quality demands are lower. Instead, beverage thinning water can be 
supplied to the retentate before its entry into crosscurrent diaphragm 
separation device 2. The result of this is that while using the same unit 
a less mild distillation can be carried out, which leads to increased 
yield and savings in energy costs. 
Along with the separation of undesired volatile substances, for example 
alcohol from liquids, the process according to the invention can be used 
to advantage for the separation of valuable volatile substances, for 
example aromatic substances from liquids. In the first case diaphragm 4 of 
crosscurrent diaphragm module 3 must exhibit a high salt retention 
capacity, while in the extraction of aromatic substances the salt 
retention capacity ought to be a low as possible. With corresponding lay 
out it is therefore possible by switching the crosscurrent diaphragm 
modules to use the same unit during the harvest season for aroma recovery 
and after the season for dealcoholization of fermented fruit juices. In 
comparison with purely thermal aroma recovery the quality if significantly 
improved with the process according to the invention, since no thermal 
separation of the aromatic components from the fruit juice takes places, 
but rather a cold separation Through this multiple use of the unit 
according to the invention its economic efficiency is substantially 
improved, which is not possible with the known systems. 
If the process according to the invention is used for the extraction of a 
concentrated, dealcoholized liquid, it is suitable to connect upstream to 
countercurrent diaphragm separation device 2 an ordinary reverse osmosis 
device 16 for preconcentration of the initial liquid, for example raw 
juice (FIG. 2). The preconcentration in this instance preferably takes 
place only to the extent that the losses in aroma which thereby result are 
insignificant. The raw juice, which is preferably already clarified by an 
ultrafiltration or microfiltration device connected upstream, not 
represented, is fed to reverse osmosis device 16 and reconcentrated. The 
concentrate is fed by pipe 17 into the retentate side feed pipe 1 of 
crosscurrent diaphragm separation device 2. With a preconcentration of 
about 50% and a relatively high transdiaphragm pressure of crosscurrent 
diaphragm separation device 2 a quality improvement is attained with high 
throughput. The reason for this is that with preconcentration by reverse 
osmosis device 16 only slight losses of valuable substances occur, however 
a sharp decrease in the quantity of permeate in dealcoholization takes 
place, and thereby a decrease in excess permeate. This in turn results in 
an increased concentration of valuable substances when the permeate is fed 
back into crosscurrent diaphragm separation device 2. 
When there is high preconcentration in reverse osmosis device 16 it is 
advantageous, because of the higher losses in valuable substances which 
result thereby, to feed a part of the permeate by way of pipe 18 into 
permeate discharge pipe 7 of crosscurrent diaphragm device 2. It has 
turned out that by preconcentration by reverse osmosis device 16, 
crosscurrent diaphragm separation device 2 can be built significantly 
smaller for dealcoholization or aroma recovery and consequently subsequent 
liquid-volatile separation device 8 can be built smaller. The 
ultrafiltration or microfiltration device connected upstream to reverse 
osmosis device 16 forms the prerequisite for clean juices, to be able to 
use, instead of pipe modules, also more cost-effective non-pipe modules, 
for example hollow fiber, roll or plate modules, for preconcentration by 
reverse osmosis device 16. 
In FIG. 3 of the drawing an embodiment of crosscurrent diaphragm module 3 
for crosscurrent diaphragm separation device 2 is represented in the form 
of a modified hollow fiber reverse osmosis module. Crosscurrent diaphragm 
module 3 exhibits on its forward front side an intake opening 19 for the 
initial liquid to be dealcoholized, which forms the retentate. On the 
opposite front side is located an outlet opening 20 for the retentate, 
which flows through a hollow fiber body of crosscurrent diaphragm module 3 
forming diaphragms 4 in direction of arrow 5. In one casing 21 surrounding 
diaphragms 4 of crosscurrent diaphragm module 3 there is located near of 
intake opening 19 a permeate outlet opening 22, which is connected with 
permeate discharge pipe 7 of crosscurrent diaphragm separation device 2. 
On the opposite end of crosscurrent diaphragm module 3 in casing 21 there 
is placed a permeate intake opening 23, which is connected with return 
pipe 10 of crosscurrent diaphragm separation device 2. The permeate coming 
out on the outside of diaphragm 4 accumulates in the space between 
diaphragm outside and casing 21 and flows through the permeate side of 
crosscurrent diaphragm module 3 in direction of arrow 14 with the help of 
circulating pumps 12 and 13 countercurrent to the flow of the retentate. 
A further embodiment of crosscurrent diaphragm module 3 for crosscurrent 
diaphragm separation device 2 is represented in FIG. 4 in the form of a 
modified reverse osmosis pipe module. An inner pipe 24 of crosscurrent 
diaphragm module 3 exhibits along with diaphragm 4 intake opening 19 and 
outlet opening 20 for the retentate. The wall of inner pipe 24 is provided 
with flow-through openings 25 for diaphragm 4, through which the permeate 
can flow and is collected in the space between inner pipe 24 and a casing 
pipe 28 surrounding the inner pipe. Tubular casing 28 exhibits near intake 
opening 19 outlet opening 22 for the permeate. On the other end of 
crosscurrent diaphragm module 3 there is located in tubular casing 28 
intake opening 23 which is connected with return pipe 10 of crosscurrent 
diaphragm separation device 2. With the help of recirculating pumps 12 and 
13 the permeate flows through the space between tubular casing 28 and 
outer pipe 26 in direction of arrow 14 in countercurrent to the flow of 
the retentate. 
FIGS. 5 through 9 show as a further embodiment of crosscurrent diaphragm 
module 3 a reverse osmosis plate module, which consists of plate element 
29 and end plate 30, between which diaphragm 4 supported by support 
elements 31 and consisting of separation diaphragm 40 and support 
diaphragm 41 is placed. End plate 30 exhibits a space 32 for the retentate 
and plate element 29 a space 33 for the permeate. Spaces 32 and 33 are 
separated from one another by diaphragms 4 and the retentate and the 
permeate flow through them in opposite directions. 
Plate element 29 exhibits on its back side an attachment 34, to which a 
further plate element 29 can be attached. By diaphragm 4 placed between 
the two plate elements 29 there result further spaces 32 and 33, through 
which the retentate or the permeate flows (FIGS. 6 and 7, arrows 5 and 
14). 
From FIG. 6 in connection with FIGS. 8 and 9 it can be seen that space 32 
exhibits, on its upper right end, intake opening 19 for the retentate and, 
on its lower left end, outlet opening 20 for the retentate. FIG. 7 shows 
in connection with FIGS. 8 and 9 that in space 33 on the lower right end 
there is located permeate intake opening 23 and on the upper left end 
permeate outlet opening 22. 
When several plate elements 29 are strung together intake openings 19 and 
outlet openings 20 of individual spaces 32 for the retentate are connected 
with one another by pipes or passages 35 (FIG. 8) and 36 (FIG. 9). The 
connection of permeate intake openings 23 and of permeate outlet openings 
22 of individual spaces 33 occurs in each case by pipes or passages 37 
(FIG. 8) and 38 (FIG. 9).