Use of a microporous membrane constructed of polyether sulfon and hydrophilization agent for the filtration of beer

The invention concerns the use of a microporous membrane constructed of polyether sulfon and a hydrophilization agent having a pore size which is within the range of between 0.1 and 1.2 microns for the filtration of beer. This membrane filter proves to be particularly suitable for the microbiological stabilization of the beer and for the separation of the turbid substances. The membrane makes it possible to remove the germs which are harmful to the beer and the harmful turbid substances and to simultaneously filter the beer with a high throughput and therefore economically and with low costs.

FIELD OF THE INVENTION 
This invention relates to the use of polysulfon membranes for filtration of 
beer in breweries. 
BACKGROUND OF THE INVENTION 
The effective separation of undesirable substances comprises an important 
step in brewing beer. Mechanical processes, such as centrifugation and 
filtration have the advantage against thermal processes, for example 
heating for short periods, and conservation agents, that the products are 
neither thermally nor chemically burdened. 
The quality of the product and/or its purity as well as the production 
costs play dominating parts in the brewing of beer. It is therefore 
required of the filtration installations which are used in the brewing 
process that they remove the accumulating turbid substances and yeasts and 
the microorganisms which are harmful to the beer, and simultaneously they 
do not adversely affect the aroma, taste and foreign body neutrality of 
the beer, while operating economically. A maximal filtration effect with 
small filter surfaces, high filtration speeds and long filter service life 
are expected. The filtration processes which are most used at present in 
the breweries are cake filtration with diatomaceous earth as the 
filtration ancillary agent and layer filtration using fiber and filter 
layers which contain diatomaceous earth. The separation of the particles 
is based on a screening effect and on the adsorption effect of the filter 
material. The great consumption of diatomaceous earth and the lack of 
possibility of regeneration of this filtration ancillary agent leads to 
great strains on the environment, so that alternative methods are being 
sought for a less problematical clarification of the beer. Great progress 
could be achieved with the development of membrane filtration, in which 
thin and highly porous membranes having a defined pore size, composed of 
plastic or ceramic materials, are used as the screen. Preference is given 
to the use of polymer materials of cellulose mixed esters, polyamides, 
polyimides, polyurethanes, polysulfons and nylon 66, as well as 
polyolefins, in particular PTFE. The pore sizes and the pore size 
distribution can be deliberately controlled by the manufacturing process 
so that the membranes are adjusted to predetermined particle size, wherein 
the maximal pore size should not exceed the size of the particles which 
are to be separated. In contrast to the diatomaceous earth and sheet 
filters, by suitable selection of the filter membranes, a predetermined 
particle size can be separated (detained) with defined certainty 
irrespective of the flow speed, of fluctuations of the throughput and of 
pressure surges. Further advantages of the membrane filters are that they 
do not adversely influence the filtered beer by emitting particles or by 
changing the contents. The membrane filters can be easily checked for 
their modus operandi, are easily handled, have an unproblematical 
endurance behaviour and a low maintenance expenditure. The membranes are 
produced either as highly porous films or in capillary and/or tubular form 
and can be applied on a support. A distinction is made between flat 
membranes (disc filters, spiral wound cartridge or pleated cartridge, 
plate and frame filters, dynamic pressure filters) and tubular or 
capillary membranes, while the membranes can be arranged in the 
corresponding modular form. 
The membrane process can be classified in accordance with the size of the 
particles to be separated. As regards the permeability of the respective 
filter membrane, a differentiation is made between reverse osmosis, 
ultra-filtration, micro-filtration and conventional filtration, while the 
borders between the individual filtration stages overlap: 
__________________________________________________________________________ 
SEATION LIMITS 
MG of the separable 
Size of separable 
Separable 
substances [g/mol] 
substances [.mu.m] 
substances 
__________________________________________________________________________ 
Reverse Osmosis 
.ltoreq.10 000 
5.10.sup.-4 -5.10.sup.2 
molecules, ions 
Ultrafiltration 
10,000-300,000 
5.10.sup.-3 -0,5 
macromolecules (proteins, 
polysaccharides), kolloids 
viruses 
Microfiltration 
100,000-1,000,000 
5.10.sup.-2 -50 
microorganisms, bac- 
teria, colloids, fine 
particles 
Conventional Filtration 
.gtoreq.1,000,000 
&gt;5 particles 
__________________________________________________________________________ 
The individual membranes are frequently different not only in their pore 
sizes, but also in the membrane structure. Thus a differentiation is made 
between symmetrical membranes, the pores of which pass through the 
membrane layer with the same width, and asymmetrical membranes, the pores 
of which expand from one side of the membrane to the opposite side of the 
membrane. If the open pore side of the membrane is facing the non-filtered 
portion the membrane has a higher capacity for impurities. If the open 
pore side of the membrane is facing the filtered portion, particles, which 
are smaller than the pore diameter can more easily pass through the 
membrane and are not retained in the interior of the membrane. 
The filtration technologies can be subdivided into conventional dead-end 
filtration and into dynamic cross-flow filtration or dynamic pressure 
filtration. In the first case the filtration is performed in such a way 
that the solution to be filtered is applied under pressure on the filter 
and permeates the filter, while the retained particles remain on the 
filter surface or are arrested in the pores. The entire liquid to be 
filtered is pressed through the filter. Because when using this process a 
filter cake rapidly forms on the surface, which increases the flow 
resistance greatly and reduces the throughput, only small amounts or 
quantities which have already been largely clarified can be filtered. The 
dynamic filtration avoids this disadvantage in the process technology 
because the liquid to be filtered is not simply brought under pressure 
onto the filter surface but the major proportion is guided tangentially, 
i. e. parallel to the filter surface and perpendicularly to the flow of 
filtrate at great speed over the filter surface (cross-flow filtration) or 
because the filter surface is moved at greater speed (dynamic pressure 
filtration), and therefore respectively only a proportion of the liquid 
penetrates through the filter. The retained substances therefore are not 
stored on the surface of the filter, do not form any impermeable filter 
cake and do not block the pores of the filter, but are led away by the 
high flow speed along the surface of the filter and are concentrated in 
the non-filtered portion. Thereby a high filtrate quantity is achieved 
until the filter is clogged. 
In the filtration processes in brewing, it is advantageous that germs which 
are harmful to the beer should be filtered out. This filtration is 
conventionally performed using a membrane in accordance with the dead-end 
filtration principle. The membrane filters which are used in practice 
having a pore size of 0.8 microns indeed possess a high throughput and 
high permeability at acceptable pressures and therefore function 
economically, but microbiological sterility with respect to the bacteria 
damaging to the beer cannot be guaranteed. If membranes are used with a 
smaller pore diameter (0.45 microns, 0.20 microns), the bacteria which are 
harmful to the beer are removed by the membranes, but an economical modus 
operandi and therefore low cost beer production is no longer possible, as 
a rule, because of the low throughput and the increased tendency to 
clogging. 
In another important filtration process, the beer is freed on its way from 
the storage tank from yeast, turbid substances and bacteria. In the case 
of dead-end filtration as the filter agent for the separation of the chill 
haze which consists of protein agglomerates, diatomaceous earth is still 
used, which however has the disadvantages listed above of high 
consumption, lack of regeneration possibility and great environmental 
pollution. Filter materials such as ceramics, Al.sub.2 O.sub.3 or 
polypropylene were tested as the membranes in a dynamic filtration for the 
separation of yeast and turbid substances, but they could not as yet 
achieve any technical breakthrough because of the low throughput. 
In European patent application EP-A2 0 228 072 filter membranes are 
disclosed of polyethers, polyimides, polyamides and polyether sulfons 
having a pore size in the range from 0.02 to 20 microns. These membranes 
are used for preference in the electronic and pharmaceutical industries. 
There is no discussion in more detail of the use of these filters for the 
microbiological filtration of beverages, and in particular indications of 
the special problems of beer filtration are lacking. 
BRIEF SUMMARY OF THE INVENTION 
The invention is based on the object of discovering a membrane filter for 
the filtration of beer which on the one hand retains the bacteria harmful 
to the beer, on the other hand has high permeability (maximal filtrate 
volume until the clogging of the filter) for the beer to be filtered and 
which has a high throughput. The permeability influences the dimensions of 
the filter device and the frequency of replacement of the filter and it 
therefore constitutes a decisive economic factor. In order to guarantee 
great purity of the beer, the membrane used should as far as possible not 
contain any of the components which dissolve out during filtration of the 
beer, and moreover no filter particles should detach themselves from the 
membrane during the filtration process. For economic reasons and in order 
to prevent clogging of the filter by the coating of the internal filter 
surface the membrane should not bind large quantities of the material to 
be filtered. For sterlization and regeneration of the membrane filter, 
furthermore, high hydrolytic and chemical stability are required at 
extreme pH values and under extreme oxidation conditions, and moreover the 
membrane must be thermally resistant and have good mechanical properties. 
Apart from the filtration of the beer, for the separation of germs harmful 
to the beer, a suitable membrane filter is also to be found for the 
separation of the yeast and of the turbid substances from the beer, which 
overcomes the disadvantages of diatomaceous earth filters and of sheet 
filters and meets the same criteria as the membrane for microbiological 
stabilization of the beer. 
The problem according to the invention is solved by a microporous membrane 
which contains polyether sulfon and hydrophilization agents and which 
possesses a pore size within the range between 0.1 and 1.2 microns. A 
membrane of this construction is suitable for the filtration of beer 
because it fulfills the conditions stated above. It is especially suitable 
for filtering out germs harmful to the beer by means of a dead-end 
filtration process while obtaining a microbiologically stable beer and 
also for the separation of turbid substances (protein agglomerates) and 
yeast by means of dynamic filtration. The membrane which is used for beer 
filtration in accordance with the invention contains preferably as the 
polyether sulfon a polyarylether sulfon having the units [--C.sub.6 
H.sub.4 --SO.sub.2 --C.sub.6 H.sub.4 -O--]. Preferably the polyether 
sulfon is composed exclusively of this group. As the hydrophilization 
agent, hydrophile groups can be used which are integrated as substituents 
in the polyether sulfon or in the polyarylether sulfon. These groups are 
preferably selected from the series --NR.sub.2, --SO.sub.3 H, --COOR, 
--OR, where R is an alkyl, aralkyl or aryl radical or a hydrogen atom. An 
adequate hydrophilization of the membranes can also be achieved if as the 
hydrophilization agent at least one hydrophile polymer is used which is 
copolymerized with the polyether sulfon or is mixed in a mixture with the 
polyether sulfon. In particular polymers such as polyethylene glycol, 
polyvinylpyrrolidon, polyvinyl alcohol, polyvinyl acetate, polyacrylic 
acid, polyacrylic acid ester, but also various derivatives of cellulose 
and combinations thereof have been found to be suitable. 
In a preferred embodiment the membrane used in accordance with the 
invention possesses an amount of the hydrophilization agent of from 0.05 
to 20 % by weight based on the weight of the polyether sulfon, the range 
between 0.1 and 8 % by weight being especially favourable. Preferred 
hydrophile polymers are polyethylene glycol and polyvinylpyrrolidon which 
are advantageously used in an amount of 0.1 to 6 % by weight with respect 
to the amount of polyether sulfon. 
The pore size of the membrane filter is preferably in the range from 0.2 to 
0.8 microns, in particular from 0.45 to 0.65 microns. In another 
favourable application form, the membrane is slightly asymmetrical, 
whereby the magnitude ratio of the pores on one side of the membrane to 
those on the other side of the membrane opposite the first side may cover 
a range from 1.5 : 1 to 2.5 : 1. The membranes which are used show a high 
porosity, and the void volume amounts as a rule to more than 70 %. 
The membrane filters which are favourable for breweries have at a pressure 
of 0.7 bar a water flow rate of from 10 to 200 ml/min.cm.sup.2. 
Particularly advantageous are filters having a rate of from 30 to 65 
ml/min.cm.sup.2, which is high enough to guarantee, apart from a 
filtration which is sterile as regards the germs harmful to the beer, an 
economically advantageous filtration as well. The air flow rate has at a 
pressure of 0.7 bar values between 1 and 24 l/min.cm.sup.2, the range from 
4 to 8 l/min.cm.sup.2 being particularly favourable. The bubble point with 
water in the case of the membranes used in accordance with the invention 
is within the range from 0.7 to 7.5 bar. Preferably membranes are used 
having a bubble point from 1.2 to 2.5 bar. The hydrophile membranes, after 
washing the membranes with a lower alcohol, for example methanol, have a 
contact angle with glycerine on the one side of the membranes of less than 
40.degree., and on the opposite side of the membranes of less than 
25.degree.. The membranes which are used in accordance with the invention 
for beer filtration, after they have been washed with a lower alcohol and 
subsequently dried, are spontaneously and completely wettable with water 
so that no additional wetting agent is necessary for filtration. 
In a particularly advantageous embodiment, in which a beer which is 
reliable microbiologically stabilized is obtained with sufficiently high 
throughput and therefore with low costs, the membrane filter has a pore 
diameter of 0.45 to 0.65 microns, a porosity greater than or equal to 70 
%, a water flow rate of 30 to 65 ml/min.cm.sup.2 (pressure: 0.7 bar), an 
air flow rate of from 4 to 8 l/min.cm.sup.2 (pressure 0.7 bar), a bubble 
point with water of 1.2 to 2.5 bar and, after washing of the membranes 
with a lower alcohol, a contact angle with glycerine on the one side of 
the membranes of less than 40.degree., as well as on the opposite side of 
the membranes of less than 25.degree.. 
The membranes which are used according to the invention have a thickness of 
50 to 300 microns, a range of 120 to 180 microns being preferred. The 
basis weight is preferably from 1.3 to 8.0 mg/cm.sup.2 The range between 
3.2 and 4.8 mg/cm2 is to be regarded as being especially favourable. The 
membranes are resistant against hydrochloric acid and caustic soda and 
therefore can be easily regenerated. Furthermore, the membrane filters can 
be treated in boiling water, in which process the share of material which 
is extractable amounts to less than 1.0 % by weight, preferably to less 
than 0.5 % by weight. 
For use as filters, the membranes are advantageously provided with support 
materials for mechanical stabilization and are designed as flat filters 
(disc filters, spiral wound cartridge or pleated cartridge, plate and 
frame filters, dynamic pressure filters) or as tubular or capillary 
filters. The filters are arranged frequently in corresponding modules. 
The membranes used according to the invention for beer filtration can be 
prepared by precipitation from a suitable solution. This solution 
comprises a polar, aprotic solvent, polyether sulfon, hydrophilization 
agents, wherein in particular polyethylene glycol and polyvinylpyrrolidon 
are suitable. The solvent is preferably selected from the series 
dimethylformamide, dimethylacetamide and N-methylpyrrolidon and is used in 
an amount of from 17 to 45 percent by weight based on the total solution. 
The weight of the polyethersulfon in the solution amounts preferably to 
from 10 to 15 %, while the weight of the polyethylene glycol amounts to 
from 40 to 70 %, respectively based on the total solution. If use is made 
of polyvinylpyrrolidon, the latter is preferably used in an amount of less 
then 1 percent by weight, based on the amount of the polyethersulfon. For 
the production of the membranes, polyethersulfon is dissolved in the 
aprotic, polar solvent, polyethylene glycol and polyvinylpyrrolidon are 
added to the solution and this is also dissolved. The solution thus 
obtained is pured as a layer and this is moistened subsequently to a 
sufficient extent to precipitate the membrane.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The membrane filters which are used according to the invention in breweries 
fulfill the requirements initially listed. By comparison with the 
conventionally used membranes they make possible, with the given pore size 
and therefore with the given retention capacity, a particularly high flow 
rate and a large throughput. Therefore a sterilizing filtration with 
respect to the germs harmful to the beer can be achieved with sufficiently 
high throughput and in an economically favourable modus operandi. On the 
other hand, the high throughput which is attainable and the easy 
regenerability of the membranes make it possible that the diatomaceous 
earth layer filters can be replaced advantageously during the separation 
of the turbid substances and of the yeast. The advantages of the membranes 
used in accordance with the invention are made clear in the following 
Table 1, in which the maximal permeability V.sub.max (hl beer/m.sup.2) of 
a selected type of beer is compared for various membrane materials which 
are all suitable for sterile filtration of beverages. 
TABLE 1 
__________________________________________________________________________ 
V.sub.max [hl beer/m.sup.2 ]; pressure = 
1 bar 
__________________________________________________________________________ 
Pore Size 0,2 .mu.m 
Seitz (polysulfon) 0,86 
Millipore (cellulose mixed ester) 
3,2 
Enka PP high flux (polypropylene) 
0,69 
Inventive Membrane: 
Gelman Supor 200 (polyethersulfon) 
4,8 
Water flow rate: 22 ml/min.cm.sup.2 (0,7 bar) 
Air flow rate: 3 l/min.cm.sup.2 (0,7 bar) 
Bubble-Point (H.sub.2 O): 3,1 bar 
Membrane thickness: 150 .mu.m 
extractable share: .ltoreq.1% 
Pore Size 0,45 .mu.m 
Brunswick (asym. polysulfon) 
0,30 
Cuno (Nylon 66) 
4,1 
Millipore (polytetrafluorethylene) 
0,97 
Millipore (polyvinylidendifluoride) 
3,2 
MSI (Nylon 66) 
4,3 
Nuclepore (polycarbonate) 
1,6 
Nuclepore (polyester) 
0,81 
Pall (nylon 66) 
2,6 
Seitz (polysulfon) 
2,0 
Inventive Membrane: 
Gelman Supor 450 (polyethersulfon) 
13,7 
Water flow rate: 35 ml(min.cm.sup.2 (0,7 bar) 
Air flow rate: 5 l/min.cm.sup.2 (0,7 bar) 
Bubble-Point (H.sub.2 O): 1,8 bar 
Membrane thickness: 150 .mu.m 
extractable share: .ltoreq.1% 
Pore Size 0,8 .mu.m 
Pall (Nylon 66) 8,4 
5,6 
Schleicher und Schull (cellulose mixed ester) 
Inventive Membrane: 
Gelman Supor 800 (polyethersulfon) 
21 
Water flow rate: 100 ml/min.cm.sup.2 (0,7 bar) 
Air flow rate: 11 l/min.cm.sup.2 (0,7 bar) 
Bubble-Point (H.sub.2 O): 1,1 bar 
Membran thickness: 150 .mu.m 
extractable share: .ltoreq.1% 
__________________________________________________________________________ 
The test arrangement with which the maximal beer volume which can pass 
under the defined conditions and with a selected type of beer through a 
membrane disc filter with a diameter of 47 mm is detected is shown in FIG. 
1. 
In carrying out the test, the membranes are first placed in the filter 
holder, in which process hydrophobe membranes such as PP, PTFE, are 
completely wetted with ethanol. In the pressure filtration apparatus, 
approximately 230 to 250 ml water are poured into the pressure filtration 
apparatus, the water having been previously filtered through a 0.22 micron 
membrane to be particle-free, and the filtration apparatus is closed using 
the upper sealing plug. The CO.sub.2 pressure flask, which is adjusted by 
an adjustable pressure reducer to 1 bar, is now connected via a plug to 
the filter holder. Thereby the selfclosing fast-couplings are opened and 
the pressure filtration apparatus is exposed to 1 bar CO.sub.2 pressure. 
At the point in time t.sub.0, the jamming clamp at the filtrate exit is 
opened. The filtered water is intercepted by a measuring cylinder, and the 
times t.sub.1 and t.sub.2 are measured at 100 ml and 200 ml throughput 
respectively. From this the water value of the membrane can be computed as 
volume/time in ml/min. The water value of the membrane is used to control 
the similarity of a membrane type. Subsequently the water is pressed 
completely through the filter, the rapid separation couplings are detached 
and the jamming clamp at the filtrate exit is closed. 
The plug for the beer line of the container which holds maximally 18 1 of 
beer is connected with the rapid separation coupling on the pressure 
filtration apparatus. Subsequently the jamming clamp on the upper tube 
olive is cautiously opened until the liquid level becomes visible in the 
area of the observation window. In the observation window it can be 
checked whether the membrane is still completely covered with liquid and 
therefore no partial blocking of the membrane surface takes place due to 
gas bubbles from the carbon dioxide content of the beer. The state of the 
liquid in the observation window does not change substantially because of 
the constant pressure conditions during filtration. Because of the supply 
pressure in the container from the pressure flask, there is also a 
pressure of 1 bar in the pressure filtration apparatus. 
The jamming clamp at the filtrate exit is opened at the time t.sub.0 =0 and 
the filtered beer is intercepted using a measuring vessel. Consecutively 
the volume values V.sub.1, V.sub.2, . . . , V.sub.n as well as the 
associated times t.sub.1, t.sub.2, . . . , t.sub.n are recorded. The beer 
is filtered until such time as the flow in ml/min. amounts to 
approximately 1/5 of the initial flow (after the first 30 to 50 ml of 
beer). 
In the evaluation the degree of regression is computed by the points 
##EQU1## 
for 0 less than or equal i less than n and V.sub.0 =0. For V.sub.0 =0 the 
maximal initial flow results, and for V/t=0 one obtains the maximal volume 
which can be filtered at 1 bar with the given filter surface. This can be 
recalculated into the unit hl beer/m.sup.2 of filter surface and is shown 
in the Table 1 as V.sub.max. 
The test was carried out at 4.+-.1.degree. C. It is dependent on the type 
of beer which is used, so that the maximal volumes obtained do not 
represent absolute values, but are only used for purposes of comparison. 
From Table 1 it can be seen that the different membrane filters for the 
special case of beer filtration have clear differences with respect to the 
maximal throughput quantity. At the given pore size, the maximal 
throughput of the membranes used according to the invention achieves 
respectively the highest values. The superiority is particularly clear and 
is surprising in its amount in the case of membranes having a pore size of 
0.45 microns, of which in the enclosure a screen electron microscope 
photograph (FIG. 2), an infrared spectrum (FIG. 3) and a NMR spectrum 
(FIG. 4) are enclosed. Using this membrane, great progress in beer 
filtration is achieved, because with this pore diameter, together with a 
guaranteed separation of bacteria which are harmful to the beer, the beer 
can be filtered with a high throughput and therefore with low costs.