CA2135077A1 - A system and a process for membrane filtration of a dispersion - Google Patents

Abstract

A dispersion having an aqueous continuous phase is membrane filtrated in one or more membrane filtration steps, where a feeding dispersion fed to a filtration membrane is separated in each step into a retentate retained by the filtration membrane and a permeate passing through said filtration membrane, whereby the retentate from one step can be used, if desired, as a feeding dispersion or a portion thereof in one or more succeeding steps. The permeate resulting from one or more steps is subjected to a concentration to form a concentrated fraction containing an increased concentration of the dry matter or a portion thereof present in the permeate, and this concentrated fraction is returned as a portion of the feeding dispersion in one or more membrane filtration steps. A
system for membrane filtration of such dispersion comprises one or more membrane filtration units each associated with a feeding pipe, a retentate exit pipe, and a permeate exit pipe, one or more of the permeate exit pipes (8n-1, 8n, 8n+1, ...) being coupled to one or more concentrating units (10n-1, 10n, 10n+1, ...) adapted to separate the permeate into a diluted fraction and a concentrate, each concentrating unit being provided with an exit (12n-1, 12n, 12n+1, ...) for the diluted fraction and a concentration exit pipe (14n-1, 14n, 14n+1, ...) for the concentrate, said concentration exit pipe being coupled to a return pipe (16n-1, 16n, 16n+1, ...) opening on to one or more of the feeding pipes (2n-1, 2n, 2n+1, ...) of the membrane filtration units.

Description

W093t22037 213 5 0 7 7 PCT/DK93/0014X 1,~

A system and a process for membrane filtration of a dispersion Technical Field The present invention relates to a system for membrane filtration of a dispersion having an aqueous continuous phase, said system comprising one or more membrane filtra-lQ tion units, also called primary membrane filtration units,where each unit is associated with a feeding pipe, a reten-tate exit pipe, and a permeate exit pipe, said retentate exit pipe of one unit, if desired, being coupled to or being the only inlet to the feeding pipe of one or more succeeding units.

Furthermore, the invention relates to a process for membrane filtrating a dispersion having an aqueous continuous phase in one or more membrane filtration steps, where a feeding dispersion fed to a filtration membrane is separated in each step into a retentate retained by the filtration membrane and a permeate passing through said filtration membrane, whereby the retentate from one step can be used, if desired, as a feeding dispersion or a portion thereof in one or more succeeding steps.

A specific embodiment of the invantion relates to a process for regulating milk solids components in concentrated milk products in connection with their manufacture by ultrafil-tration of milk. The concentrated milk products achieved bythis embodiment of the invention are preferably intènded for the manufacture of cheese, in particular fresh unripened i~
cheese, curd or cheese in brine, such as White Cheese, Feta, Domiaty, Mozzarella, Kaskaval and Kefalotyri.
Background Art W093t22037 ~ 1 3 ~ o 7 7 1 ` ~
. PCT/DK93/~0148 ~?

In order to support the understanding of the application some expressions used in the present specification and claims have been defined below. ~ ;

5 Membrane filtration: Filtration through a membrane where ~;
a dispersion, here called a feed dispersion, is separated into a retentate not passing through the membrane and a permeate passing through said membrane. The retentate is a fluid dispersion in which the amount of dispersing phase has been increased relative to the amount thereof in the feed dispersion. Examples of membranes to be used by the membrane filtration are MF, UF, NF, and R0 membranes, which have been defined in greater detail below.

Retentate: The fraction of a feed dispersion which is retained by a filtration membrane.

Permeate: The fraction of a feed dispersion which passes through a filtration membrane.
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Microfiltration tMF): Filtration through an MF-membrane, i.e. a membrane of a pore size of 0.08 ~m to 2.5 ~m corresponding to a molecular cutoff value of 150 000 to 5 000 000.
~5 Ultrafiltration (UFl: Filtration through a UF-membrane, i.e.
a membrane of a pore size of 0.002 ~m to 0.4 ~m correspon-ding to a molecular cutoff value of 500 to 8Q0 000.
30 Nanofiltration (NF): Filtration through an NF-membrane, i.e.
a membrane of a pore size of 0.0007 ,um to 0.007 ~um corre-sponding to a molecular cutoff value of 140 to 15 000. ~, HvDerfiltration (HF) or reverse osmosis (R0): Filtration ~-through an RO-membrane. When an RO-membrane is used, the permeate is nothing but water in some cases. In other cases metal ions and aqueous salts may also pass through an R0-W O 93/22037 2 1 3 5 0 7 7 PC'r/D K93/0014N
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membrane. In connection with an R0-membrane it is hardly possible directly to refer to a pore size, but at least theoretically speaking a pore si~e of between 0 and 0.0015 ~m corresponding to a molecular cutoff value of between 0 and 300 applies.

Diafiltration: Filtration through a membrane, especially a UF-membrane or an NF-membrane, where water has been added to the feed dispersion~ It is possible to reduce the amount of permeable solids in the retentate by using diafiltration.

Feed disPersion: The material fed to a membrane filtration unit. The feed dispersion can be any type of dispersion where the disperse phase can include particles of molecu:Lar-disperse, colloid-disperse, and/or coarse-disperse particle sizes. In practise the present invention only refers to feed dispersions in which the continuous phase of the dispersion is based on water.

Permeable solids: Solids capable of passing through the used filtration membrane, i.e. in practise all permeate ingre-dients apart from water. The ingredients of the feed dis-persion to be considered permeable solids are determined by the filtration membrane used.
During the membrane filtration, the permeate containing permeable solids and water passes through the iiltration - membrane. The remaining portion of the feed dispersion, viz.
the retentate, leaves the filtration unit without passing throuyh the filtration membrane. The weight ratio of per-meate to retentate depends on various factors, such as the pressure difference above the membrane, the pore size of said membrane, the area as well as coating or fouling degree of said membrane. The individual membrane units may be coupled in series or in parallel. For some purposes, such as ultrafiltration of milk or milk products, the membrane capacity is advantageously utilized by the individual mem-W093~22037 213 3 0 7 7 PCT/DK93/00l48 ~ ~

brane units being coupled in series in such a manner thatthe retentate of the first membrane unit is used as feed dispersion in the succeeding membrane unit etc.

The retentate leaving a membrane filtration unit represents per se a dispersion and accordingly it includes a disperse phase and a continuous phase. When the disperse phase exclusively contains particles unable to pass through the filtration membrane, and the continuous phase exclusively contains permeable solids and water, the continuous phase of the retentate is at least approximately of the same composition as the permeate. An exception may be the situation where in addition to particles being too large to pass through the membrane the dispersion also contains particles being permeable per se but which in practise adhere to the impermeable particles in the retentate with the result that the amount of said permeable particles in the permeate is lower than the amount thereof in the continuous phase of the retentate.
When it is desired that also relatively small particles or molecules are separated off as retentate, it is possible, at least theoretically, to carry out the filtration by means of a filtration membrane having a small pore size. In prac-tise problems do, however, arise as the filtration capacityis heavily reduced in connection with a reduced pore size.

The choice of pore size of the membrane is thus of decisive importance for the capacity of a membrane filtration plant.
A too large pore size has, however, the effect that some of the ingredients desired in the retentate follow the perme-at2.
'~' When it is desired to ensure a retaining of ingredients of a relatively low molecular weight by usins a membrane of a small molecular cutoff value, said membrane is, as previous-ly mentioned, quickly fouled with the result that the fil-. W093/~2037 21 3 ~ 0 7 7 PCT/DK93/00148 tration capacity is reduced. Accordingly, a demand existsfor a system and a process ensuring on one hand a commer-cially acceptable filtration capacity and on the other hand that relatively low-molecular ingredients, or at least a portion thereof, can be maintained in the retentateO

It is known to reduce the amount of permeable solids in the continuous phase of the retentate simply by diluting the continuous phase of the feed dispersion with water, i.e. by carrying out a so-called diafiltration. Then it is possible to obtain a larger permeate fraction while the amount of retentate is unchanged. In case of dissolved permeable solids, the concentration thereof in the continuous phase of the feed dispersion is reduced by the diafiltration, whereby the concentration and conse- quently also the amount of the permeable solids are reduced in the continuous phase of the retentate.

Attempts at increasing the amount of the permeable solids in the retentate have revealed, that such an increase requires a feeding of said solids to the feed dispersion.
In connection with production of retentate to be used in articles of food, such an addition is, however, undesired and in some cases, such as in connection with milk products, even directly forbidden in some countries.

The above problems of membrane filtrating fat and protein-containing aqueous dispersion are within the food industry for instance found in the production of many dairy products 3~ where a starting material or an intermediary product, such as milk, milk products or milk-like products, is concen-trated by way of ultrafiltration in an ultrafiltration plant. This ultrafiltration plant is based on an ultrafil-tration membrane (UF membrane) retaining fat and protein whereas lactose, low-molecular protein substances, salts, and wat~r can pass through the UF membrane.

2 1 ~ ~ 0 7 7 PCT/DK93/00148 j~ ~

Cow's milk, which may be homogenized, is generally used as a starting material in the manufacture of cheese according to the classic method. The milk may be used as whole milk, i.e. with its total solids content, or with a reduced fat content, or with an increased fat content by the addition of cream.

In the manufacture of cheese it is known to ultrafiltrate the milk to the desired solids content in the finished cheese. This is normally done in a commercial ultrafiltra-tion system comprising a plurality of modules, each of which is composed of a plurality of membrane coated plates which together provide the desired membrane area in each module.
Ducts are arranged in the module and conduits between the modules such that the liquid to be concentrated is conveyed through the modules substantially in series, while the permeate is conveyed in parallel from these to a collector.
Such ultrafiltration of milk primarily involves concen-trating the protein and fa~ content of the milk, while a major portion of lactose and salts enters into the permeate from the ultrafiltration.

US patent specification No. 4 497 ~36 discloses a process for producing a whey concentrate which is suitable for use 25 in infant food formulas, wherein cheese whey is subjected to ultrafiltration to produce a protein-xich retentate frac-tion and a lactose-rich permeate fraction, said permeate fraction having a mineral salt content from the whey of 9-12~ on dry solids basis, the permeate fraction is subjected to ! concentrating and demineralization by reverse osmosis or concentrating by vacuum evaporation followed by deminera-lization by electrodialysis, and the demineralized permeate is blended with the protein-rich retentate from the ultra-filtration in such proportions as to provide the desired lactose and mineral salt contents in the blended product.
This process thus involves ultrafiltration of whey, wherein mineral salts are removed from the permeate, while lactose ; W093/22037 PCT/DK93~00l48 p 7 !:' is retained to the greatest extent possible and added to the concentrated product from the ultrafiltration.

Lactose is a low-molecular su~stance and is therefore only 5 retained to a slight degree by ultrafiltration. Thus the lactose usually follows the aqueou~ permeate in dissolved form, which means that the concentration of lactose in the retentats is usually substantially lower than the concen-tration of lactose in the feed material.
1~ ; .
The ultrafiltration of dispersions is often performed as a stepwise process, the retentate of the first step being used as feed dispersion in the succeeding step. The ultrafiltra-tion can often be combined th diafiltration, according to 15 which water is added to th~- feed dispersion in one or more of said steps.

If the ultrafiltered dispersion for instance is a milk product, it is possible to reduce the content of lact3se in 20 the retentate by way of diafiltration independent of the amount of fat and protein contained therein as it is pos-sible to vary the amount of water being added to the feed dispersion. The addition of large amounts of water ha~ the effect that the concentration of lactose in the water phase 25 is reduced. The portion of the water phase remaining in the retentate contains thus a lower amount of lactose. In other words, a higher amount of lactose enters the permeate phase.

The diafiltration can also be used for regulating the 30 content of minerals in the retentate, such as dissolved salts.
f.i The permeate resulting from the membrane filtration is often a waste product involving disposal problems due to the high 35 content of permeable solids, such as lactose, as such solids may have a strongly polluting effect on the environment.

213aO77 ~

~1' ' ' In addition, some of the substances present ir. the permea~e are desirable in some type of products, and accordingly a selective retaining of some of these su~stances in ~he rete~tate resulting from the membrane filtra~ion would be advantageous.

E~ publication No. 460 339 (Perry et 21. ), cf. in particul2-Example VII and Fig. l, discloses a proce~s and an apparatus for removing undesired ingredients, such as citric acid, from materials based on water, such as citrus juice. Accor-ding to the process, the juice is first separated by micro-filtration into a retentate con~aining the dispersed, sub-s~antially solid pulp substances of Ihe juice, and a depulped permeate. Subsequently, the depulped permeate is subjected to an electrodialysis, whereby the citric acid is removed without change of the water content of the permeate.
The resulting deacidified and depulped permeate is carried to an intermediary tank in which it is remixed with ~he pulp-containing retentate from the microfiltra.ion, whereb~
i~ is possible ~o remove rep-oduced, deaci~ fied ci_-us juice ~rom ~he intermediary tank.

In order to ensure a possibilit~ of regulating the produc~
flows in such a manner ~ha. the microfiltration and the electroanalysis can be carried out in an optimum manner, the apparatus known from EP 460 339 has in a manner known pe-se been provided with a recirculation pipe carr~ing the ma~erial from the intermediary tank back to the feed side of the microfiltration unit. The returning of the deacidi-fied permeate fraction is, however, not carried out direct-ly, but not until said permeate frac~ion has been mixed with the retentate, whereby the weight ratio of th~ dispersing pulp phase to the contin~ous phase is almost ldentical with the weight ratio in the original, nontreated cltrus juice.
Due to ~he fact that the deacidified permeate fraction is not a fraction of the permeate having increased content of permeable solids it is not possible o obtain a retentate 213~077 ~;

-- 8c with a high content of solics and ar. increaseà con~ent of ¦ :
- permeable solids. ¦ :

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~ W093/22037 213 5 ~ 7 7 PCT/DK93/00148 DE Offenlegungsschrift No. 36 26 498 (Roiner) discloses a process for preventing a coating or fouling of an ultrafil-tration membrane by returning the retentate to the feed side prior to the actual concentration and in addition by subjec-ting the permeate to a desalting and/or pH-adjustment by way of ion exchange, electrolysis or dialysis in such a manner that a portion of the permeate flow is also re~urned to the feed side of the UF membrane. By being mixed with the reten-tate, the desalted or pH-adjusted permeate ensures that the proteins contained therein provide a reduced tendency to fouling. When the conductivity of the mixed phase has dropped below a predetermined value, the concentration of the feed dispersion by way of ultrafiltration can be carried out with a reduced fouling and consequently an increased filtration capacity. The DE Offenlegungsschrift do not suggest a returning of the permeate alone to the feed dispersion, and the returned permeate has been desalted and/or pH-adjusted and cannot thus be considered a con-centrated fraction of the permeate with an increased ; 20 concentration of permeable solids.

Thus none of the above publications provide the person skilled in the art with a guideline for meeting the above demand for a process and a system ensuring both a commer-cially acceptable filtration capacity and that relativelylow-molecular compounds or at least a portion thereof can be maintained in the retentate.

Brief Description of the Invention `
A demand still exists for a way of increasing the content of permeable solids in a retentate resulting from a membrane filtration. This object has been obtained by the system and the process according to the invention.
The system according to the invention for membrane filtra-tion of a dispersion having an aqueous continuous phase 2 1 3 ~ O ~ 7 ~ ~
W093/22037 PCT/DK93/00148 ,.. ~

' ~' comprises one or more membrane filtration units, also called primary membrane filtr~tion units, where each unit is asso~
ciated with a feedin~ pipe, a retentate exit pipe, a~d a permeate exit pipe, said retentate exit pipe of one unit, .
5 if desired, being coupled to or being the only inlet to the :.
feeding pipe of one or more succeeding units, and is charac-terized in that one or more of the permeate exit pipes (8n-1, 8~, 8n~ are coupled to one or more concentrating units (lOn-', lOn, lOn~1, ...) adapted to separate the permeate into a diluted fraction and a concentrate, each concentrating unit being provided with an exit (12n-1, 12n, 12n~1, ...) for the diluted fraction and a concentration exit pipe (14n-1, 14n, 14n~l, ...) for the concentrate, said concentration exit pipe being coupled to a return pipe (16n-1, 16n, 16n~l, ...) opening on to one or more of the feeding pipes (2n-1,`2n, 2n~l, ...) of the membrane filtration units.
~ .
The return pipe may advantageously be coupled to one or more feeding pipes of the associated membrane filtration unit 20 (4n) and/or one or more of the preceding membrane filtration : : units (... 4n-2 4n-, ,, : According to an advantageous embodiment of the system accor-ding to the invention, said system may comprise one or more ~ 25 groups of intercoupled concentrating units coupled to a :~:; common return pipe.

Such groups may include concentration units coupled in series, where the concentrate exit pipe of a first concen-trating unit is coupled to a succeeding second concentratingunit.

According to an alternative embodiment, the system may as concentrating unit comprise a first membrane unit and a second m~mbrane unit of a pore size being smaller than the pore size of the first membrane unit, and by the permeate exit pipe of the first membrane unit being coupled to the '~

, ~ ~ wn 93/22037 ~13 5 o 77 PCT/DK93/0ol4~

11 `I
second membrane unit. In such a system, a permeable solid matter of an average molecular weight in the permeate from the first membrane unit can be removed from the retentate resulting from the first membrane filtration, while a rela-tively low-molecular permeable solid matter i9 returned to the first membrane unit in such a manner that the content of such a relatively low-molecular permeable solid matter is increased in the first retentate.

In the system according to the invention, the membrane filtration system may advantageously be a microfiltration unit or an ultrafiltration unit.

In the system according to the invention, the concentrating unit may advantageously be a centrifugal unit, an evapora-tion unit or a secondary membrane filtration unit or a com-bination thereof.
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According to an advantageous embodiment of the system, the concentrating unit is a secondary membrane filtration unit, which comprises a membrane, called a secondary membrane, of a smaller pore size than the membrane, called a primary membrane, provided in the primary~membrane filtration unit ~ (4)--- 2~5 - According to a further advantaa~ous embodimen~ of the system - according to the lnvention, the primary membrane filtration ; unit is an ultrafiltration unit, and the concentrating unit ` comprises a nanofiltration unit (120) with a retentate exit , 30 pipe (124) for the retentate and a permeate exit pipe ~22) for the permeate, where the permeate exit pipe (12~ is coupled to an RO-unit (126) provided with a permeate exit pipe (112) and a retentate exit pipe (114), and where the retentate exit pipe (114) is coupled to the return pipe (116) opening on to one or more of the feeding pipes ( 2 ~; ~ 2n, 2n-~', 102) of the primary membrane units.

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W093~2037 213 ~ 0 7 7 PCT/DK93/0014X ~ ~

12 , `
The process according to the invention for membrane filtra-ting a dispersion having an aqueous~continuous phase in one ¦
or more membrane filtration steps, where a feeding disper- i sion fed to a filtration membra~e is separated in each step 5 into a retentate retained by the filtration membrane and a 1-~-permeate passing through said filtration membrane, whereby the retentate from one step can be used, if desired, as a feeding dispersion or a portion thereof in one or more succeeding steps, is characterized by subjecting the perme-ate resulting from one or more steps to a concentration to ~;form a concentrated fraction containing an increased concen-tration of the dry matter or a portion thereof present in the permeate, and by the concentrated fraction being return-ed as a portion of the feeding dispersion in one or more membrane filtration steps.

Such~a~;concentration may advantageously be carried out by way~of centrifuging,~evaporation or membrane filtration or by~a combination of several of said concentrating methods.

When ~the~concentration is carried out by way of membrane filtratlon, a secondary membrane is advantageously used, said secondary membrane having a smaller pore size than the pore~size~of~the primary filtration~membrane used for mem-~-25- ~ ;br~ane~iltratlng the féeding dispersion.

When~the prlmary~membrane is an ultrafiltration membrane, tha~con~entratlon~may~advantageously be carried out by way ~`
i ~ of one~ or more secondary membrane filtrations while using ;" , 30 one or mo~e~ NF-membranes, RO-membranes or a combination - thereof. Such a combination allows a selective concentration of deslred permeable sollds.

By the process according to the invention, the dispersio~- ~ 35~ used as starting material may advantageously be a fatty and proteln-con`taining dispersion to be used within the food industry.

, -, .
.., ~
, . - .. -, W093/22037 2 13 5 0 7 7 PCrIDK93/00148 The process according to the invention may advantageously be carried out by way of diafiltration. As a result, it is for instance possible to reduce the amount of undesired permeable solids in the retentate, the permeate being subjected to a selective concentration and returning of particularly selected permeable solids desired in the retentate.

According to a particular embodiment, the concentration may thus be carried out by way of a combination of a nanofil-tration membran~ and an RO-membrane, the permeate of the nanofil.ration ~brane being used as feed dispersion for the ROv embran~ and by the concentrate resulting from the RO-membrane being returned to the feed dispersion for the primary membrane filtration by way of ultrafiltration~

It is possible by means of the system according to the invention to obtain an economical profit by enriching the content of solids with permeate ingredients as the solid ingredients following the permeate are usually rather - ineXpensive relative to the fat and the protein substances.
- An increase of the content of lactose and/or~the mineral content in the retentate renders it possible to affect the properties of the product, such as the consistency and the taste, so as to be a more creamy sweet product, said properties being preferred in specific product types.

An important advantage gained by using the system according to the invention is that foreign substances are not added to,the product, because the concentrated permeate contains exactly the substances deriving from the feed material used ~ as startin~ material. This advantage makes the process -~ according to the inventlon particularly attractive in connection with treatment of articles of food.
In a specific embodiment of the invention the object is to provide a process for regulating milk solids components in concentrated milk products in connection with their manu-facture by ul~rafiltiation of milk, making it possible to regulate the percentage of the individual solids compo~ents individually, in particular the content of protein and lactose with respect to total solids and fat content. This enables direct manufacture of a very great variety of cheese products having very different organoleptic properties.
; ~ Further, it generally involves better utilization of the solids components of the milk, and it also makes it possible to regulate the consistency of the final cheese product, since~more lactose~with respect to protein generally gives a more ~spreadable product. A special advantage of the invention is that the regulation ¢an be performed in line in the manufacture of cheese so that no foreign ingredients are added~to the cheese. Finally, the process of the inven-tion~entails that the excess products (perméates) are either so clean that they can be discharged directly without envi-ronmental problems, or æo concentrated that they can be sold , , as they~are for use in feeds or for production of lactose powdér~

his~ is~achieved by an embodiment of the process of the invention~wh:ich is characterized in that the permeate from a` first~step of the ultrafiltration, optionally together ~ 25 with~a portion of the permeate from a second step of the i2~ ultrafiltration, is subjected to hyperfiltration or nano-flltration or evaporation, and a portion of or the entire aoncentrate obtained is introduced into the second step of the ultrafiltration which is carried out to the desired -30 isol:ids cont,ent. ~ `

Whole milk is pretreated by separation and pasteurization.
For certain products the fat portion is homogenized as a cream. Optionally, all the milk may be homogenized. Also, ~=-x ~ 39 the fat -ontent may be reduced by separating cream, or be ~ lncreased by addition of cream.

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~, .. ~, , ;,, ~ . , _ _ W093/22037 213 5 0 7 7 PCT/DK93~00l4$ ~ ~
~. :

Ultrafiltration is employed for concentrating the fat and protein of the milk. The ultrafiltration is generally per-formed at a temperature in the range of 40-60 C to a salids concentration of 18-50 %. J, In the process according to this embodiment of the invention the ultrafiltration is carried out in at least two steps.
Both step 1 and step 2 of the ultrafiltration normally com-prise several ultrafiltration modules. The permeate from UF
step 1 is concentrated by hyperf ltration, nanofiltration or evaporation, in line or batchwise. To adjust protein and lactose, the concentrated retentate from the HF/NF system is added in the part of the ultrafiltration system having the greatest concentration of S, i.e. UF ste~ 2. The effect 15 of this is that a larger water soluble s ids contènt, -~
primarily lactose, enters into the produc~ ~he ~ f hyperfiltration or evaporation increases the --~ose -nt as well as the content of salts and ash comp ~a~-s. The use of nanofiltration increases the lactose conter one, while the ash and salt content is reduced.

When hyperfiltration is used, the UF 1 permeate is cooled from the ultrafiltration temperature 40-60 C to approxi- ~;
mately 30 C. pH is adjusted to 5.9-6.1 prior to the intro-duction into the HF system. The working pressure is ad~usted on the retentate valve to max. 3 MPa.
.:
Depending on the adjustment, the solids content is increased during the concentrating from the introduction value 5.7-10%
t~o the maximum value at the adjusted pressure. Any variation between 10 and Z2% S may be selected, as desired. The pre-ferred solids content in the retentate from the hyperfiltra-~- tion is 15-19%.
: ' i-In nanofiltration, a varied temperature may be used, de-pending upon the type of the nanofi ! tration system. It is the type of system and membrane that decides the working W093/22037 Z135077 PCT/DK93/00148 i~

temperature. The variations are in the range of 20-60 C, and solids concentrations of 10~-40 ~ may generally be obtained at these temperatures.
.: .
When evaporation is used, the permeate from UF step 1 is conveyed at the ultrafiltration temperature 4~-60 ~C to an evaporator for concentration to the desired final solids content, which may be 10-50%, preferably 20-40%.

Regulation of the solids components of the milk may be effected individually for each solids component. The fol-lowing milk solids components are involved: fat, protein, lactose, ash and salt.

The membrane(s) used in the system according to the inven-tion as well as by the process according to the invention for the concentration of the permeate or a portion thereof is/are below~called secondary membranes or membrane type II
or merely membrane II in order to distinguish these membra-nes from the membrane receiving the feed dispersion, said; membrane in~ the present specification also being called a primary membrane or membrane type I or merely membrane I.

The scope of applicability of the invention will become -apparent from the detailed description given hereinafter.
, However, it should be understood that the detailed descrip-tion and specific examples, while indicating preferred - ~ embodiments of~the invention, are given by way of illustra-tion only, since various changes and modifications within thq spirit and scope of the invention will become apparent to persons skilled in the art from the detailed description.

Detailed Description of the }nvention - !
The present invention is based on the principle that some of the solid matter ingredients passing through the primary membrane in form of a permeate are concentrated by centrifu-~'~

-- wog3/22037 213S077 ~.~
PCT/DK93/0014~ ~;

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ging, evaporation or by membrane filtration on a secondary membrane being tighter than the primary membrane, and in such a manner that a concentrated fraction of the permeate can be returned to the primary membrane unit. In this manner it is possible to increase and regulate the content of solid matter ingredients in the retentate, even when a primary membrane is used which is of a pore size usually causing portions of the solid matter ingredients to enter the - permeate.
.' 10 Fig. 1 illustrates the basic principle of the system accor-ding to the invention comprising a single membrane filtra-tion unit and the associated concentration unit.

Fig. 2 illustrates an intercoupling of several of the basic units shown in Fig. 1.

Fig. 3 illustrates a basic unit of a particular embodiment, where the membrane filtration unit is an ultrafiltration unit, and where the concentration unit comprises a nano-filtration unit and an R0-unit.

Fig. 4 illustrates an embodiment of the system according to the invention including a plurality of ultrafiltration units ;~25 coupled in series and two R0-units as concentration units, ~-~where`the flows of permeate from the individual ultrafil-tration units together are carried to the R0 units, and where the total amount of concentrated permeate is returned and distributed over suitably selected ultrafiltration units of,the unit$ coupled in series.

Fig. 5 is a flow diagram illustrating an embodiment of the process according to the invention as defined in claim 18.

Fig. 6 is a flow diagram illustrating an embodiment of the process according to the invention as defined in claim 19.
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wO93~22n37 213 ~ 0 7 7 PCT/DK93/00148 The basic principle of the invention appears from Fig. 1, where the material to be membrane filtered is introduced through a feed pipe 2 to a membrane filtration unit 4r in which a separation is carried out into a retentate leaving through a retentate exit pipe 6, and a permeate leaving through a permeate exit pipe 8. The permeate exit pipe is connected to a concentration unit lO, in which a separation is carried out into a diluted fraction discharged at 12, and a concentrate removed through a concentrate exit pipe 14.
The concentration process can be carried out in any conven-tional manner, such as by way of centrifuging or evapora-`~ tion, where the "diluted fraction" discharged at 12 is water steam being evaporated, or membrane filtration, which can - be carried out by means of one or more membrane filtration units o the same type or different types. The concentrate or a portion thereof removed through the concentrate exit pipe 14 i~s~carried by means of a return pipe 16 to the feed pipe~2~before the membrane filtration unit, where said concentrate is mixed with the introduced feed material.
The ba~sic principle shown in Fig. 1 has been further deve-~ loped in Fig. 2, in which a membrane filtration is performed .~ ~ in a manner known per se by means of several membrane units coupled~in series. Thus the féed dispersion is fed through a feed pipe~2n~1 to a membrane filtration unit 4n~1, where a permea~e 8n-1 and a retentate 6n-1 are formed. The retentate 6n-1 is carried through a fèed pipe 2" to the succeedins membrane filtration unit 4n, where a separation is again performed into a permeate 8n and a retentate 6", which in turn are carried to the succeeding membrane filtration unit 4n~ etc. Thus each membrane filtration unit 4" is provided with a permeate exit pipe 8n coupled to a concentration unit on with a permeate exit pipe 12n and a concentrate exit i pipe 14A which can be returned through a return pipe 16" to the feed pipe 2n of the same membrane filtration unit 4n, ; The concentrate can, however, also be returned through one , ~ . . . . . .... ... . . ... . . . . . .. . . ... . . . ... . . . . . . . . ...

W093/22037 213 3 ~ 77 PCT/DK93/00148 or more pipes 18n, 18n-1 ... to one or more of the preceding membrane filtration units 4n~l ~ 4n-2 . . .

Fig. 3 illustrates a particular embodiment of the system according to the invention where the feed dispersion is introduced through a feed pipe 102 to an ultrafiltration unit 104 while forming a retentate drained off through a retentate exit pipe 106 and a permeate drained off through a permeate exit pipe 108. The permeate or a portion thereof is carried to a nanofiltration unit 120 while forming a retentate drained off through a retentate exit pipe 124. In addition, a permeate is formed which is drained off through a permeate exit pipe 122. The permeate from the nanofiltra-; tion unit 120 or a portion thereof is carried to an R0-unit 126 provided with a permeate exit pipe 112 and a retentate exit pipe 114. The retentate from the R0-unit or a portion thereof is returned through a return pipe 116 to the feed ~- dispersion feed pipe 102. When such a system unit is used, the solids capable of passing through the ultrafiltration membrane, but not the nanofiltration membrane can be remo-- ved, while desired solids capable of passing through the nanofiltration membrane, but not through the R0-membrane can be concentrated and returned to the ultrafiltration unit.
The unit shown in Fig. 3 can, of course, be coupled to 25~ several corresponding units in the same manner as shown for the un t in Fig. 1 coupled in series as shown in Fig. 2.

A practical embodiment of the system according to the inven-tion is shown in Fig. 4. By this em~odiment, a plurality of - 30 ultjrafiltration units are coupled in series (UF), and the concentration units are here formed by two R0-units (R0) coupled in series. The system comprises an inlet 201 for the -~- starting material to be filtered, such as milk, said inlet being coupled via a vessel 203 to a feed pipe 202 to a first ultrafiltration unit 204. The ultrafiltration unit 204 is in a manner known per se provided with a recirculation circuit 205 on the feed/retentate side, said recirculation W093/22037 2 1 3 s o 7 7 PCT/D~93/00l48 circuit 205 comprising a pump 207 ensuring the necessary filtering pressure, as well as a retentate exit pipe 206 coupled to a feed pipe 209 to the succeeding ultrafiltration unit 21I. As illustrated in Fig. 4, the ultrafiltration unit 211 and the succeeding ultrafiltration units are designed in the same manner as the ultrafiltration unit 204, as all said units are provided with corresponding recirculation circuits with pump and retentate exit pipe.

A permeate exit pipe 208 of the first ultrafiltration unit 204 is together with the permeate exit pipes of the remai-ning ultrafiltration units coupled to a common permeate pipe 213 in turn coupled to a first RO-unit 210. Like the ultra-filtration units, the first RO-unit 210 is provided in a conventional manner with a recirculation circuit 215 with a pump 217 and a concentrate exit pipe 214, here an RO-., ~
~ retentate pipe, as well as an exit 212 for a diluted frac-- ~ ~ tion, here~RO-permeate. The concentrate exit pipe is coupled ~to a succeeding RO-unit 219 designed in the same manner as the ~O-unit 210. A concentrate exit pipe 221 from the RO-unit 219 is coupIed to a return pipe 216 in turn coupled to one or more of the recirculation circuits of the ultrafil-tration units. In the embodiment shown in Fig. 4, the return pipe 216 is coupled to the third, the fourth, and the fifth ultraflltration unit in a series of six ultrafiltration units. The ultrafiltration membrane of the ultrafiltration ;~ unit is typically of a molecular cutoff value of between 10 000 and 20 oob M.

Fig.~4 also shows the following material flows~

~(A): starting material in form of a dispersion with o ~ an aqueous continuous phase.

~-~35 (B): UF-permeate.
!
(Bl): Excess permeate.

. W093/22037 213 ~ 0 7 7 PCTJDK93/001~8 ... ,. ~.

(B2): UF-permeate to RO.

~C): UF-retentate. ~ i 5 (D): RO-retentate.

(E): RO-permeate.

In the embodiment where the concentration is carried out by way of membrane filtration, the process can be performed as shown in Fig. 1, the membrane filtration unit 4 bein~ mem-brane type I and the concentration unit 10 being membrane type II. In this embodiment, a feed material is fed as feed dispersion to a membrane of the type I, such as an ultra-filtration membrane while forming a retentate and a permeateI. A large or small portion of the permeate I can then be subjected to a further membrane filtration on a membrane of membrane type II, i.e. for instance an NF-membrane, an RO-membrane or a UF-membrane of a smaller pore size than membrane I. As result a permeate II is formed, and a concentrate is formed as retentate. The concentrate or a portion thereof can be returned so as to be mixed into the fed feed dispersion, whereby the resulting retentate is enriched wi~h substances from the concentrated permeate.
25 ~ ~
Several parameters can be used for obtaining the desired composition of the r~tentate. Thus the entire amount of the concentrated permeate or only portions thereof can be returned. It is also possible to carry out a concentration of jthe permeate in one or more steps. By using a multi-stepped concentration of the permeate, it is also possible to use various types of membranes of their respective pore size. Such a fractioning in several steps can, of course, be carried out both during a posttreatment of the initially formed concentrate or during a posttreatment of the initi-ally formed permeate.

~ , .

Examples of such processes are for instance:

The permeate resulting from ultrafiltration is subjected to reverse osmosis (RO) r and the RO-concentrate or a portion 5 thereof is returned to the UF-system.` ~-. .
- The permeate resulting from the ult~afiltration is subjected to a nanofiltration (NF), and the NF-concentrate or a por-tion thereof is returned to the UF-system.
' The permeate resulting from the ultrafiltration is subjected to an NF-filtration, and the NF-permeate is then subjected to an RO-filtration, whereafter the RO-concentrate or a portion thereof is returned to the UF-system.
It appears that by a suitable selection of the concentration unit, such as by the selection of membrane sizes, in a ;
selective and regulated manner it is possible to return desired substances to the primary membrane filtration unit, ;20 and thereby to obtain an increased and controlled concen-tration of these substances in the obtained retentate.

The returning of a desired fraction of the permeate con-centrate renders it possible to develop many interesting product improvements and new products. Thus the use of the system according to the invention for treatment of milk ~- products based on a suitable fractioning renders it possible ;~ ~ to increase and regulate~ the content of lactose in the retentate without thereby involving an increase in the retentate of, monovalent salts to a significant degree. On - the other hand it is also possible to increase the content of monovalent salts without increasing the content of lactose. The latter can thus be obtained by combining an NF-membrane and an RO-membrane unit, where the lactose is retained in the NF-retentate and where the NF-permeate containing monovalent salts is returned to the RO-unit so W093/2~037 2 1 3 5 0 7 7 pCT/~93/00148 as there to be returned in form of retentate to the primary membrane filtration unit.

The content of lactose and minerals in the resulting reten- 1 5 tate has a high effect on many important properties of the t'' finished product, such as taste, consistency, gelling capa-city, heat stability, colour etc., and accordingly a great demand exists for the possibility of regulating the concen-trations of such ingredients.
It is, of course, an advantage that it is possible to maintain the content of solids in the retentate using a ;~ product which was previously considered a by-product, as it is possible to obtain a high yield with respect to weight and to reduce the amount of by-products which are difficult to dispose.
-The system and the process according to the in~ention have been developed in connection with ultrafiltration of milk ;~ 20 or milk products. It is, however, possible as feed dis-~ persion to use any dispersion having àn aqueous continuous , ; phase. In addition to milk and milk products, blood and was~e water can be mentioned as examples of such dispersions.
:, The various possible combinations in the specific embodiment of the invention relating to a process for regulating milk solids components in concentrated milk products are illu- ~-strated more fully by the following flow diagrams with reference to Figs. 5 and 6 on the accompanying drawings.
;
Flow diaaram Fia. S t`

Milk treatment Centrifugation.
Optional cream homogenization.
Pasteurization 72-75 C/lS s.

,~
",~
;~
.~

213~077 W093/22037 PCT/DK93/00148 t``~

24 ~, .
Ultrafiltration step 1 Temperature 40-55 C. ', Permeate B, 5.7-10% S.
Retentate C, 15-35% S.

5 Hyper/nanofiltration Permeate B from UF step 1 is .
or evaporation concentrated to desired solids.
Permeate D for discharge.
Retentate/concen~rate E,+E" 10-20%
S by hyperfiltration, 10-40~ S by nanofiltration and 10-50~ S by evaporation.

Ultrafiltration step 2 Part of the retentate/concentrate E, from HF/NF or evaporation is conveyed toge~her with the reten-tate C from UF step 1, and the mixture F is introduced into UF
step 2 and concentrated to 25-50~
S in the retentate H. The permeate :.
G is conveyed together with excess . retentate/concentrate E" and the ; mixture can be sold as a feed or be used for the production of lactose powder.
Flow diaq~am Fi~. 6 Milk treatment Same as above .Ul,trafiltration step 1 Same as above Hyper/nanofiltration Permeate B from UF step 1 is t or evaporation conveyed together with a recycled portion of permeate G. from UF
step 2 and is concentrated to desired S. Permeate D for W093/~2037 213 5 0 7 7 PCTiDK93/00l48 discharge. Retentate/concentrate E
same S as above.

Ultrafiltration step 2 The retentate/concentrate E from '~
HF/NF or evaporation is conveyed ~-~
together with retentate C from UF
step 1, and the mixture F is introduced into UF step 2 and concentrated to 25-50~ S in the retentate H.
Part of the permeate G,~is recycled for HF/NF or evaporation;
the residue G2 can be sold as a feed or be used for the production of lactose powder.

Danish cow's milk contains the following solids ingredients on an average:
Protein 3.40~, of which NPN 0.25%, real protein 3.15%
Lactose 4.70%
Acid 0.30%
Ash 0.63%
Fat 4.20%
I a low fat content in the concentrated milk product is desired~, the fat content of the milk is lowered by removing part of the cream by separation. In the ultrafiltration all the fat is retained in the retentate, while protein is ; 30 re~ained with more than 90% depending~upon membrane density.
Thus, the protein/fat ratio in the concentrated milk product .
~ is adjusted by the fat percentage. ~
, :~
- - Depending upon the desired final S in the product, S is selected in UF. Between 25 and 31% S in the UF 1 retentata C is chosen in most of the following examples. In a couple ~, of cases with a final S in the retentate H from UF 2 of 30%

~: ~

W093/22037 2 1 3 ~ ~ 7 7 PCI'/DK93/00148 !~

(examples 5 and 9), 16~ S is chosen in the retentate C from UF 1.

The parameter most frequently used for adjusting lactose in the product is the amount of retentate/concentrate E, which is added to UF 2, combined with S in the retentate C from UF 1, compared with the final S in the retentate H from UF
2. A lower S in the UF 1 retentate C and/or a larger amount of E, and/or a higher S in E~ results in an increased lac-tose percentage in the final product~ A lower S percentagein the retentate from UF 1 necessitates a greater system capacity of the~ HF/NF/evaporation system. The above para-~meters~ are therefore selected on the basis of the mosteconomical operation with respect to system size, membrane area and energy consumption.

The system and the process of the invention will be illu-strated more~fully by the following working examples with referenae to the drawings.

The present example illustrates the use of a system as shown in Fig.~ 4 for ultrafiltration of milk. The used ultrafiltra-~tion membranes have a molecular cutoff value of approximate-,~
ly 15~000 M~ In the Table shown below the weight ratios arestated in kg/h for the individual materials, the solid content ~(S) in~ ~by weight, and the content of the most important ingredients are stated in % by weight relative to thç total amount of solids. The Table shows both the compo-,, . . i ~
sition by means of the system according to the invention and ` by means o~ a corresponding conventional ultrafiltration system structured in the same manner as shown in Fig. 4, but ~, without the concentration and returning of a concentrate with an increased concentration of permeable dry substances.

'~

f 213~077 1~
; .
,. I ~;-Table - Ultrafiltration of_milk I ' .,, ., _ _ _ _ ~
¦Mate~ial . Amount (kg/h) Composition (% by weight) - . __ .....
System accor- Conventional I l ding to the system inven~ion . . . _ (A) Milk 10,000 TS: 13.5% TS: 12.5%
1 : Fat: 4.6% Fat: 3.6%
1~ ¦ Protein: 3,4% Protein: 3.4%
~ ~1 ¦ ~ Lactose: 4.. 6% Lactose: 4.6%
I -----.- . __ . .
: ¦(B) UF-perme- 9,222 TS: 7.3~ . TS: 5.8%
ate . Fat: 0.0~ Fat: 0.0%
~- ¦ . : Protein: 0.3% Protein: 0.2%
: Lactose: 6.2% Lactose: 4.9%
~ : _ ¦~B1)~ Ex¢ess : :4,430 As (B) : ~pe~meate ~ ~ . .
~ , : - ~ - .
¦~B2~j~perméate 4,792 As (B) ¦to RO .
I .
¦(C) UF-reten-2,594 TS: 39~5% TS: 39-5% .
~tate Fat: 17.7% Fat: 17.7%
¦ ~ Protein: Protein:
12.7% 16.3%
¦ I :~ Lactose: 7.0~ Lactose: 3.4%
¦~(D~ RO-reten- 1,816. TS: 19.0%
¦~tate Fat: 0.0%
I i l , ~ . Protein: 0.6%
Lactose:
. 16.3% .
:, _ . I (E) RO-perme- 2,976 TS: 0.1%
ate ~ . _ .

.';` ',': ~ ' ; ' ' ", ~ ~
' ` ? ~

WO 93/221)37 2 1 3 5 0 7 7 PCI/DIC93/0014ei j It appears that it is possible produce a UF-retentate having a desired content of solids and fat, here 39.5% by weight j-and 17.7% by weight, respectively, with a content of ~only 12.7% by weight of protein representing the most expensive ,-ingredient by means of the system according to the inven-tion. On the other hand 16.3~ by weight of protein are necessary for the production of a UF-permeate containing 39.5% by weight of solids and 17.7% by weight of fat when a conventional ultrafiltration system without a returning of permeable solids is used.

Regulation of solids composition by concentrating whole milk to a product which is useful for the manufacture of fresh soft spreadable cheese having a low fat content.

-~ ~ Desired Pro~erties Solids, ~ Approx. 30 Fat in solids, incl. 1.20 % salt, ~ Approx. 35 Protein, % Approx. 11 Lactose, % Approx. 7 The procedure proceeds according to the flow diagram in Fig.
5, the fat content in the starting milk being reduced to

3.25% by separation of cream, the ultrafiltration in step ~- 1 being run to a solids content of 27~ in the retentate C, and 20~ HF retentate E, being added to the retentate C from UF 1, the residue E, of the HF retentate being conveyed together with the~permeate G from UF 2 to provlde a mix$ure that can be sold as a feed or be used for the production of lactose powder. This procedure results in the following amounts and compositions of the various process flows: ' ~:

/. W093~2037 2135~77 PCT/DK93/00l4X

UF step 1 HF
Whole milk Permeate Retentate Permeate ~E~n~e A B C D E,+E, J

Amounts, 1 11000 7784.623215.38 5244.37642~08 1897.17 Protein, % 3.15 0.0110.75 0 0.03 NPN, ~ 0.25 0.230.30 0.06 0.46 Lactose~ 4~.70 ~ 5.13~3.66 0.02 16.31 Aoid,~ 0.3~0; ~ 0.200.54 0 0.71 Total ash, ~0.~63~ ~ 0.6~30.63 0.01 1.49 Fat,~%~ 3.25 0 ~11.12 0 ~; 0 Solids, % 12.~28 6.20 27 0.09 19 ~ UF step 2 s~ Feed ~Permeate ~k~l~

nts~`385~8.;46 ~ 643.08 3215.38 in~ %~ 8.g7~ 0.01 10.7~ -NPN,~%~ 0~33 0.23 0.39 Lacto~e, ~ ~~5.77 7.88 6.92 Acid,~-%~ 0.~57 ~ 0.30 0.68 a~ àsh,~ %~ 0~.~77~ 0.63 ~.93 9'67~ .05 ~ 30 80 , ~ ~

21~5077 l~
W093~22037 PCT/DK93/00148 ~': ;~.~.?-, ~, EXAMPLE 3 .
... ` , 1 Regulation of solids COmpQSitiOn by concentrating whole~milk to a product which is useful.for the manufacture of feta .
cheese in brine.

Desired ProPerties: .
Solids, % Approx. 40 Fat in solids, incl. 3.50 salt, ~ Approx. 40 lO Protein, ~ Approx. ll : Lactose, % Approx. lO
:
The procedure proceeds according to the flow diagram in Fig~
5, the uItrafiltration in step l being run to a solids content of 28% in the retentate C, 20~ HF retentate E. being added to the retentate C from UF l, the residue E, of the HF
retentate being conveyed together with the permeate G from ~: UF 2 to provide a mixture that can be sold as a feed or be used for the production of lactose powder. This procedure 20;~:~ results :in the following amounts and compositions of the various process flows.
~ .' , , ~
.~ . I

i., . ~
`:

~ .

`::

,~. W093/22037 PCT/~K93~0014X `;~
~.

UF step l HF
Whole milk Permeate Retentate Permeate ~ein~ I
A B C DE,~E, ¦-Amounts, 111000 6594.71 4405.29 4442.75881.06 1270.90 : Protein~ ~3.15 0.01 7.85 0 0.03 NPN, % 0.25 0.23 0.28 0.06 0.46 Lactose, %4.70 5.13 ~4.~06 0.0216.31 ~ .Acid, ~ 0.30 0.20 0.45 0 0.71 .~ Total ash, %: : 0.63 0.63 0.63 0.01 1.49 Fat, ~% ~ ~:5.50 0 13.75 0 0 Sol~ids, % 14.53 6.20 27 0.09 l9 : : -UF step 2 Feed ~ Permeate ~
F : G H
Amounts~5286.35 1919.25 3367.10 Proteln, %` ~ 6.55 ~ 0.01 10.28 NPN,:~%~ ~ 0.31 : 0.23 0.49 LaCtose,~ %: ~6~10 7.88 9.57 .~%~ 0.49 ~ 0.30 0.77 ~
Total`~ash~, %~ :0.77 0.63 1.21 t,~%~ -11.44 : ~ ~ 0 17.97 `;
So1ids~ % ~ 25~.67 ; ;: ~ ~ ~ 9.0S 40.30 EPLACEM ENT SH E~Er 2135~
WO93~22037 PCT/DK93/00148 Regulation of solids composition by concentrating whole~ilk to a product which is useful for the manufacture of feta cheese in brine.

Desired ProPerties:
Solids, % Approx. 40 Fat in solids, incl. 3.50~ salt, % Approx. 50 ;
Protein, ~ Approx. 7 Lactose, % Approx. 8 ::
- ~ . .
The procedure proceeds according to the flow diagram in Fig.
5~, the ultrafiltration in step 1 being run to a solids content of 30.12% in the retentate C, 20~ HF retentate E.
being added to the retentate C from UF 1, the residue E, of the HF retentate being coneyed together with the permeate ~-G from UF 2 to provide a mixture that can be sold as a feed or be used for the production of lactose powder. This - 20 procedure results in the following amounts and compositions of the various process 1OWS:

,.-. ~, -"~ - ~

: : ~ '.
!
- ':

.~ 2 : ~
~' ': ~ .

~' , : : :

. W093/22037 213 5 0 7 7 PCT/DK93/00148 .. ,........................................................... . l ~-.' 33 ~-I
UF step 1 HF
Whole milk Permeate Retentate Permeate ~oenb~
A ~ C DE,+E. ~, Amounts, l11000 5099.92 5900.08 3435.73 1180.02 ;'~
484.17 Protein, %3.15 0.01 5.86 0 0.03 NPN, ~ 0.25 0.23 0.27 0.060.46 Lactose, %4.70 5.13 4.33 0.0216.31 Acid, %: Q.30 0.20 0.39 0 0.71 Total ash, % 0.63 0.63 0.630.01 1.49 Fat, ~ 10 0 18.64 0 0 Solids, % 19.03 : 6.20 30.12 0.09 19 - .
UF step 2 Feed Permeate F~
F G H
Amounts, 1 : 7080.10 2022.89 5057.21 Protein,~ % ~ :4.89 : 0.01 6.85 NPN,~: 0.30 0.23 0.42 La¢tose~, % 6.3:3 7.88 8.86 Acid,;:~%~ ~ 0.44 0.30 0.62 Total ash, % 0.77 0.63 1.08 Fat,~:~% 15.5~ 0 21.75 Solids, % ~ 28.~7 9.05 39.57 ~, ~, . , i ! I /
:" -'~
- , " ~
,,-: ~: -. 3 ;~'':.

. ~, , .

REpLAcEMENTsHEET

W093/22 21350~7 ~:
037 , PCT/DK93/00148 ,~
~, .

Regulation of solids composition by concentrating whole m~lk to a product which is useful for the manufacture of feta cheese in brine.

Desired Properties:
Solids, % Approx. 42 Fat in solids, incl. 3.50% salt, ~ Approx. 45 Protein, % Approx. 10 Lactose, % Approx. 10 The procedure proceeds according to the flow diagram in Fig.
5, the fat content in the starting milk being increased to 6.90% by addition of cream, the ultrafiltration in the step 1 being run to a solids content of 28.58~ in the retentate C, 20% HF retentate E, being added to the retentate C from UF 1, the residue E, of the HF retentate being conveyed together with the permeate G from UF 2 to provide a mixture ~that can be sold as a feed or be used for the production of , .
lactose powder. This procedure results in the following amounts and compositions of the various process flows:

: : :
,.; ~
~"

., ~ , .

. W093~22037 2 1 3 ~ 0 7 7 Pn /DKg3/00l4g i~ ~
. . I i, .

UF step l HF
Whole milk Permeate Retentate Permeate ~k~l~ .
A B C DEl~EI , Amounts, l 11000 6217.39 4782.61 4188.56956.52 1072.31 Protein, % 3.15 0.01 7.23 0 0.03 NPN, % 0.25 0.23 0.28 0.060.46 Lactose, % 4.70 5.13 4.14 0.0216.31 ~ Acid, % 0.30 0.20 0.43 0 0.71 T~tal ash, %0.63 0.63 0.63 0.011.49 Fat, % 6.90 0 lS.87 0 0 Solids, % 15.93 6.20 28.58 0.09 19 UF step 2 Feed Permea~e ~e~d~
F G H ;~

Amounts, l 5739.13 2060.20 3678.93 Protein, % 6.03 . 0.01 9.41 NPN, %: 0~31 0.23 0.48 Lactose, % : ~ 6.17 7.88 9.62 Acid, ~ 0.48 0.30 0.74 Total ash, % 0.77 0.63 1.21 Fat, % 13.23 :0 20.63 Solids, ~ 26.98 9.0S 42.09 ': L
', ' ~.

: ~

.

REPU~CEMENT SHEE~

- W093/22037 2 1 3 ,3 0 7 7 PCT/DK93/00148 Regulation of solids composition by concentrating whole milk to a product which is useful for the manufacture of light - ', 5 feta cheese in b~ine or spreadable cheese. ,' Desired Properties:
Solids, % Approx. 30 Fat in solids, incl. 2.50 % salt, ~ Approx. 20 Protein, ~ Approx. 10 Lactose, % Approx. 12 The procedure proceeds according to the flow diagram in Fig.
5, the fat content in the starting milk being reduced to 2.20% by separation of cream, the ultrafiltration in step 1 being run to a solids content of 16.26~ in the retentate ; C, 20~ HF retentate E, being added to the retentate C from ~ UF 1, the residue E, of the HF retentate being, conveyed : -:
; together with the permeate G from UF 2 to provide a mixture that can be sold as a feed or be used for the production of lactose~powder. This procedure results in the following amounts and compositions of the various process flows:

,.: ~. ::

,:
-'" '' :

, ~.

- W093~22037 21 ~ S 0 7 7 PCTtDK93~00148 ; -UF step 1 HF
Whole milk Permeate Retentate Permeate h~ln~e A B C DE.+E.

Amounts, 1 11000 5500.00 5500.00 3705.26 1100.00 694.74 Protein, % 3.15 0.01 6.29 0 0.03 NPN, % 0.25 0.23 0.27 0.060.46 Lactose, ~ 4.70 5.13 4.27Q.02 16.31 Acid, % 0.30 0.20 0.40 0 0.71 Total ash, % 0.63 0.63 0.630.01 1.49 Fat, ~ ~ ~2.20 0 4.40 0 0 Solids, % 11.23 6.20 ` 16.26 0.09 19 UF step 2 Feed Permeate ~srn~e F G H

~Amounts~, l 6600.00 3032.43 3567.57 Protein, % ~ ~5.25 0.01 9.71 NPN, % 0.30 0.23 0.56 Lactose, % 6.28 7.88 11.61 AGid, ~ % 0 . 4 5 0 . 30 0 . 84 Total ash, % 0.77 0.63 1.43 Fat,~% ~3.67 0 6.78 Solids, ~ 16.72 9.05 30.93 ~' ~

,~:
:: ~

' REPLACEMENTSHEET

W093/22037 213 .S O 7 7 PCT/DK93/00148 ,`

Regulation of solids composition by concentrating whole m~lk to a product which is useful for the manufacture of fetaS cheese in brine.

Desired Pro~erties:
Solids, ~ Approx. 40 Fat in solids, incl. 4.20~ salt, % Approx. 40 Protein, % Approx. 15 Lactose, ~ Approx. 6 : - :
;The procedure proceeds according to the flow diagram in Fig.
5, the fat content in the starting milk being reduced to

4.00% by separation of cream, the ultrafiltration in step 1~ -1 being run to a solids content of 30.11~ in the retentate C, 5% HF retentate E, being added to the retentate C from UF
the residue E, of the HF retentate being conveyed together with the permeate G from UF 2 to provide a mixture 20; that can~be sold as a feed or be used for the production of ` ~~ lactose powder. This procedure results in the following amounts and compositions of the various process flows:

r-~
.. , 1.

'~ ~

-; W093~22037 21 3 5 0 7 7 PCT/DK93/0014X ~ ~
,,. ' ~ ~, UF step 1 HF ¦ -Whole milk Permeate Retentate Permeate ~eIn~
A B C DE,+E.
Amounts, 1 11000 7857.14 3142.86 5293.23 157.14 ~ `
2406.77 Protein, % 3.15 0.01 11.00 0 0.03 NPN, ~0.25 0.23 0.30 0.060.46 Lactose, ~4.70 5.13 3.63 0.0216.31 Acid, % 0-30 0.20 0.55 0 0.71 Total ash, ~ 0.63 0.63 0.63 0.01 1.49 Fat, ~ 4.00 0 14.00 0 0 Solids, %13.03 6.20 30.11 0.0919,00 UF step 2 - Feed Permeate ierr~e ~ F G H
- ~:

Amounts, 13300.00 873.53 2426.47 Protein, ~10.48 0.01 14.25 NPN, % 0.31 0.23 0.42 L:actose, ~ 4.23 7.88 5.75 Acid, ~0.56 0.30 0.76 Total ash, % 0.67 0.63 0.91 Fat, ~13.33 0 18.13 ; Solids, ~29.58 9.05 40.22 . ~

~:.

, ~ , REPLACEM ENT SH EET

W093/22037 213507~ PCT/Dh93/00148 ,~:

1`
EXaMPLE 8 ¦

Regulation of solids composition by concentrating whole milk to a product which is useful for the manufacture of feta - '

5 cheese in brine. ~, Desired ProPerties:
Solids, % Approx. 40 Fat in solids, incl. 4.20% salt, ~ kpprox. 40 Protein, % ~ Approx. 8 Lactose, ~ Approx. 12 The procedure proceeds according to the flow diagram in Fig.

6, the ultrafiltration step 1 being run to a solids content of 26.49% in the retentate C, 6% UF 2 permeate G, being added to the permeate B from UF 1 and 4~% HF retentate E
eing added to the retentate C from UF 1, the residue G, of the pérmeate from UF 2 being recovered and being useful as ~- a feed or for the production of lactose powder. This ;
procedure results in the following amounts and compositions o~ the various process flows:

,~

, 1.

213~077 ~ I
- ~ W093/22037 PCT/DK93/00148 ~ '' 41 ~ ~
j ~
UF step 1 ~F !
Whole milk Permeate Retentate Permeate Re~ntr~ `
A B C D E

Amiounts, 111000 5500.00 5500.00 3627.112200.00 Protein, %3.15 0.01 6.29 0 0.03 NPN, % 0.25 0.23 0.27 0.060.46 Lactose, %~ 4.60 5.40 3.80 0.021~.31 Acid, % 0.30 0.20 0.40 0 0.71 Total ash, ~ 0.63 0.63 0.63 0.01 1.49 Fat, ~ 7.55 0 15.10 0 0 Solids, % 16.4B 6.47 26.49 0.0919,00 UF step 2 ' -Feed . Parmeate ~æ
F G.~G. H

Amounts, 1 7700.00 327.11 4666.67 2706.22 Proteln, % ~ 4.50 0.01 7.43 NPN,~%~ 0.32 0.23 0.54 Lactose, % 7.37 7.88 ~12.17 Acid, % 0.49 0.30 0.81 Total ash, % 0.88 0.63 1.44 Fat~, ~ 10.79 0 17.80 Solids, ~ 24.35 9.05 40.18 ~ ! ~ . ii . j : i i' .', ' .

: , FlEPl~CEMENT SHEEr - , , . . . . . . . .. ... ~ . .. .. . . . . ... . . . .. ..

213~077 ~
... , `~,.
,,, .

Regulation of solids composition by concentrating ~hole milk -to a- product which is useful for the manufacture of feta 5 cheese in brine. ~-Desired Properties: `
Solids, % Approx. 40 Fat in solids, incl. 4.20% salt, % Approx. 40 Protein, % Approx. 12 Lactose, % Approx. 8 The procedure proceeds according to the flow diagram in Fig.
6 with evaporation of the UF 1 permeate, the ultrafiltration in step 2 being run to a solids content of 20% in the retentate C, 20~ evaporation concentrate E. being added to the retentate C from UF 1, the residue E, of the concentrate being conveyed together with the permeate G from UF 2 to provide 2 mixture that can be sold as a feed or be used for the production of lactose powder. This procedure results in the following amounts and compositions of the various process flows:

1 ;"
, ~ . ;,, :: . ~- .;

. . . .
,' . :~ ' ' ' . ' ~ W O 93/22037 ~13 S o 7 7 PC'r/D ~93/00148 ~ `.
UF step 1 HF !~ :
Whole milk Permeate Retentate Pe~meate ~En~
A B C DE,~E. '.
Amounts, 111000 7071.43 3928.57 4861.61 785.71 1424.11 Protein, %3.15 0.01 8.80 0 0.03 NPN, % 0.25 0~23 0.29 0.020.67 .
Lactose, %4.47 5.40 2.80 017.28 Acid, ~ 0.30 0.20 0.48 0 0.64 Total ash, % 0.63 0.63 ` 0.63 0.01 1.98 `.
Fat, ~ 4.90 0 13.72 0 0 ..
Solids, % 13.70 6.47 26.71 0.0320.61 ',~
UF step 2 Feed Permeate Fe~
F G H
Amounts, l 4714.29 1730.56 2983.73 Protein, % 7.34 0.01 11.60 NPN, % ~0.35 0.23 0.55 Lactose, % 5.21 7.88 8.23 Acid, ~ 0.51 0.30 0.80 Total ash, ~ 0.86 0.63 1.35 Fat, % 11.43 0 18.06 Solids, % 25.70 9.05 40.60 . ~

;

REPLACEMENTSHEET

213~077 ~:
~.
4L - .

Regulation of solids composition by concent~ating ~hole mi~k to a product which is useful for the manufacture of light ~- 5 feta cheese in brine or spreadable cheese.

Desired ProPerties:
Solids, % Approx. 30 Fat in solids, incl. 2.50~ salt, % Approx. 20 Protein, ~%~ ~ Approx. 10 Lactose~ Approx. 12 ~ The~pro~cedùre proceeds according to the flow diagram in Fig.
"- 6, the ultrafiltration in step 1 being run to 2 solids content of 27~ in the retentate C, I6.07% HF retentate E~
bel~ng~addèd~to~the retentate C from~VF 1, the residue E, of the~ F~re~tentàte~being~ conveyed together with the permeate G from UF'~2~to~provlde~a~mixture that~can be sold as a feed or~be~used for;the producti;on of lactose powder. Workin~ ln 20 ~;thl~s ~,manne~ results ~in the ~following 'amoun~s and ,s~ compositlons~of~the various process flows:

'"'`` t ~j~ " ~

.:~. W093/22037 213 5 0 7 7 PCT/DK93/00148 ~
.. . ~,, .
, ,, l :' UF step 1 HF :
Whole milk Permeate ~etentate Permeate ~unb~ ~-;
A B C DE,~Ei, I

Amounts, 111000 5500.00 5500.00 3781.251485.00 ~:
233.75 Protein, ~3.15 0.01 6.29 0 -0.03 ~
NPN, % 0.25 0.23 0.27 0.02 0.67 :~.
Lac~ose, %4.59 5.40 3.78 0 17.28 Acid, % 0.30 0.20 0.40 0 0.64 Total ash, %0.63 0.63 0.63 0.01 1.98 .
Fat, % 2.25 0 4.70 0 0 Solids, % 11.27 6.47 16.07 0.03 20.61 UF step 2 Feed Permeate ~1n~e -~
F G H

Amounts, 16985.00 3104.44 3880.56 i~
:Protein, %4.96 0.01 8.93 NPN, ~ 0.36 0.23 0.64 ~ ~ Lactose, %6.65 7.88 11,97 -. ~ Acid, ~ 0.45 0.30 0.81 Total ash, ~ 0.92 0.63 1.65 Fatj % 3.70 0 6.66 Solids, ~17.03 9.05 30.66 .
,, The invention being thus described, it will be obvious that ; ' I 'the same may be varied in many~ways. Such variations are not to be regarded as a departure from the spirit and scope of 5 the invention, and all such modifications as would be obvi- ~:
ous to one skilled in the art are intended to be included ; within the scope of the following claims.
i: ~ :

:: :

REP~ACEMENr SH EET

Claims (26)

. 46 PATENT CLAIMS

1. A system for membrane filtration of a dispersion having an aqueous continuous phase said system comprising one or more membrane filtration units (4n-1, 4n, 4n+1....), also called primary membrane filtration units, where each unit (4n-1, 4n, 4n+1....) is associated with a feeding pipe (2n-1, 2n, 2n-1....), a retentate exit pipe (6n-1, 6n, 6n+1....) and a permeate exit pipe (8n-1, 8n, 8n+1....), said retentate exit pipe (6n-1, 6n, 6n+1....) of one unit ( n-1, 4n, 4n-1....), if desired, being coupled to or being the only inlet to the feeding pipe (2n, 2n+1, 2n+2....) of one or more succeeding units (4n, 4n-1, 4n+2....), c h a r a c t e r i z e d by one or more of the permeate exit pipes (8n-1, 8n, 8n+1, ...) being coupled to one or more concentrating units (10n-1, 10n, 10n-1, ...) adapted to separate the permeate into a diluted frac-tion and a concentrate, each concentrating unit being provi-ded with an exit (12n-1, 12n, 12n+1, ...) for the diluted fraction and a concentration exit pipe (14-1, 14n, 14n+1, ...) for the concentrate, said concentration exit pipe being coupled to a return pipe (16n-1, 16n, 16n+1, ...) opening on to one or more of the feeding pipes ( 2n-1, 2n, 2n-l, ...) of the membrane filtration units.

2. A system as claimed in claim 1 wherein the membrane fil-tration unit (4n), which is coupled through its associated permeate exit pipe (8n) with a concentrating unit (10n), is termed the associated membrane filtration unit with respect to said concentrating unit and vice versa, c h a r a c t e -r i z e d by the return pipe (16n), which is coupled with the concentrate exit pipe (14n) from said contentrating unit (10n), being coupled to one or more feeding pipes (...2n-2, 2n-1, 2n) of the associated membrane filtration unit (4n) and/or one or more of the preceding membrane filtration units (,,, 4n-2, 4n-1).

3. A system as claimed in claim 1, c h a r a c t e r i -z e d by comprising one or more groups of intercoupled concentrating units (210, 219) having concentrate exit pipes (214, 221) coupled to a common return pipe (216).

4. A system as claimed in claim 3, c h a r a c t e r i -z e d by comprising one or more groups of concentrating units (210,219) coupled in series, where the concentrate exit pipe (214) of a first concentrating unit (210) is coupled to a succeeding second concentrating unit (219).

5. A system as claimed in claim 3, c h a r a c t e r i -z e d by comprising as concentrating unit a first membrane unit (120) and a second membrane unit (126) of a pore size being smaller than the pore size of the first membrane unit, and by the permeate exit pipe (122) of the first membrane unit (120) being coupled to the second membrane unit (126).

6. A system as claimed in claim 1, c h a r a c t e r i -z e d by the membrane filtration unit (4) being a micro-filtration unit or an ultrafiltration unit.

7. A system as claimed in claim 1, 2 or 3, c h a r a c -t e r i z e d by the concentrating unit (10) being a centrifugal unit, an evaporation unit or a secondary membrane filtration unit or a combination thereof.

8. A system as claimed in claim 7, c h a r a c t e r i -z e d by the concentrating unit (10) being a secondary membrane filtration unit, which comprises a membrane, called a secondary membrane, of a smaller pore size than the mem-brane, called a primary membrane provided in the primary membrane filtration unit (4).

9. A system as claimed in claim 1, c h a r a c t e r i -z e d by the primary membrane filtration unit being an ultrafiltration unit (104), and by the concentrating unit comprising a nanofiltration unit (120) with a retentate exit pipe (124) for the retentate and a permeate exit pipe (122) for the permeate, where the permeate exit pipe (122) is coupled to an RO-unit (126) provided with a permeate exit pipe (112) and a retentate exit pipe (114), and where the retentate exit pipe (114) is coupled to the return pipe (116) opening on to one or more of the feeding pipes (2n-1, 2n, 2n-+2, 102) of the primary membrane units.

10. A process for membrane filtrating a dispersion having an aqueous continuous phase in one or more membrane filtra-tion steps, where a feeding dispersion fed to a filtration membrane is separated in each step into a retentate retained by the filtration membrane and a permeate passing through said filtration membrane, whereby the retentate from one step can be used, if desired, as a feeding dispersion or a portion thereof in one or more succeeding steps, c h a -r a c t e r i z e d by subjecting the permeate resulting from one or more steps to a concentration to form a con-centrated fraction containing an increased concentration of the dry matter or a portion thereof present in the permeate, and by the concentrated fraction being returned as a portion of the feeding dispersion in one or more of the membrane filtration steps.

11. A process as claimed in claim 10, c h a r a c t e r i -z e d by carrying out the concentration by way of centrifuging, evaporation or membrane filtration or by a combination of several of said concentrating methods.

12. A process as claimed in claim 11, c h a r a c t e r i -z e d by carrying out the concentration by way of membrane filtration while using a secondary membrane of a smaller pore size than the pore size of the primary filtration mem-brane used for membrane filtrating the feeding dispersion.

13. A process as claims in claim 12, c h a r a c t r i -z e d by the primary membrane being an ultrafiltration mem-brane, and by the concentration being carried out by way of one or more secondary membrane filtrations while using one or more NF-membranes, RO-membranes or a combination thereof.

14. A process as claimed in any of claims 10 to 13, c h a -r a c t e r i z e d by the dispersion used as starting material being a fatty and/or protein-containing dispersion, preferably a milk product.

15. A process as claimed in any of claims 10 to 14, c h a -r a c t e r i z e d by carrying out the primary membrane filtration by way of diafiltration.

16. A process as claimed in claim 13, c h a r a c t e r i -z e d by carrying out the concentration by means of a com-bination of a nanofiltration membrane and an RO-membrane, the permeate of the nanofiltration membrane being used as a feeding dispersion for the RO-membrane, and by the concen-trate resulting from the RO-membrane being returned to the primary ultrafiltration feeding dispersion.

17. A process according to claim 10 for regulating milk solids components in concentrated milk products in con-nection with their manufacture by ultrafiltration of milk, c h a r a c t e r i z e d by subjecting the permeate from a first step of the ultrafiltration, optionally together with a portion of the permeate from a second step of the ultra filtration, to hyperfiltration or nanofiltration or evaporation, and introducing a portion of or the entire obtained concentrate into the second step of the ultrafil-tration which is carried out to the desired solids content.

18. A process according to claim 17, c h a r a c t e r i -z e d by introducing a portion of or the entire concentrate from hyperfiltration/nanofiltration/evaporation of the per-meate from step 1 of the ultrafiltration to step 2 of the ultrafiltration.

19. A process according to claim 17, c h a r a c t e r i -z e d by introducing the entire concentrate from hyperfil-tration/nanofiltration/evaporation of a combination of the permeate from step 1 of the ultrafiltration with a portion of the permeate from step 2 of the ultrafiltration to step 2 of the ultrafiltration.

20. A process according to any of claims 17-19, c h a -r a c t e r i z e d by carrying out the ultrafiltration in step 1 to a solids content in the retentate of 15-35%, pre-ferably 25-31%.

21. A process according to any of claims 17-20, c h a -r a c t e r i z e d by carrying out the ultrafiltration in step 2 to a solids content in the product of 18-50%, prefe-rably 25-50%.

22. A process according to any of claims 17-21, c h a -r a c t e r i z e d by using hyperfiltration at approx-imately 30 °C and pH 5.9-6.1 of the permeate from step 1 of the ultrafiltration to a solids content in the concentrate of 10-22%, preferably 15-19%.

23. A process according to any of claims 17-21, c h a -r a c t e r i z e d by using nanofiltration at 20-60 °C of the permeate from step 1 of the ultrafiltration to a solids content in the concentrate of 10-40%.

24. A process according to any of claims 17-21, c h a -r a c t e r i z e d by using evaporation of the permeate from step 1 of the ultrafiltration to a solids content in the concentrate of 10-50%, preferably 20-40%

25. A process according to any of claims 17-24, c h a -r a c t e r i z e d by regulating the protein/fat ratio in the concentrated product by adjusting the fat percentage of the starting milk.

26. A process according to any of claims 17-25, c h a -r a c t e r i z e d in that the proportion of lactose in the concentrated product is increased by a lower solids con-tent in the retentate-from step l of the ultrafiltration and/or greater introduction of concentrate from the hyper-filtration/nanofiltration/evaporation to step 2 of the ultrafiltration and/or a greater solids content in the concentrate from the hyperfiltration/nanofiltration/eva-poration, and vice versa.