EP3105356A1

EP3105356A1 - Method and plant for producing lactose crystals

Info

Publication number: EP3105356A1
Application number: EP15705553.4A
Authority: EP
Inventors: Reinhard Scholz; Jan A.M.V. Van Esch; Christian Melches; Hermann Plate
Original assignee: GEA Messo GmbH
Current assignee: GEA Messo GmbH
Priority date: 2014-02-13
Filing date: 2015-02-10
Publication date: 2016-12-21
Also published as: WO2015121238A1; DE102014101843A1; US20160340750A1; DE202015009329U1; AU2015217727A1

Abstract

For continuous production of qualitatively high-grade lactose monohydrate crystals from a solution, the invention proposes the preparation of a highly concentrated solution in a falling film evaporator (1), from the pre-concentrated solution (L2), which is then subjected to continuous cold crystallization (2) with forced circulation (KR) and from which a lactose suspension (SP) is drawn off that forms the product crystals following separation of the transported solution. The product crystals (K) are thereby obtained directly by solid/liquid separation (3), without further crystallization steps from the suspension that was drawn off from the cold crystallization (2). A portion of the mother solution separated off from the product crystals (K) is fed back to a point prior to the inlet to the falling film evaporator (1), the remainder of the mother solution (A) is discarded.

Description

The invention relates to a process for the continuous production of a lactose crystallizate from an aqueous lactose solution and to a plant for carrying it out.

Aqueous lactose solutions are obtained in milk processing, especially as a result of the treatment of whey, which has been extracted from proteins, for example by membrane filtration such as ultrafiltration. By withdrawal of the

Water content can be obtained from the solution, the lactose as a solid. For crystallization, batch processes have conventionally been used. In many cases, an aqueous lactose solution is first replaced by a

Nanofiltration extracted about 98% of the contained proteins. The then e.g. 1 to 3% of the TS (here and in the following always containing as dry matter by weight) lactose solution is then added e.g. withdrawn by reverse osmosis water, so that a content of about 5 - 8% TS results. The thus preconcentrated solution is then heated to about 70 ° C with evaporation of water (for example in a falling film evaporator) and concentrated to 60-70% DM and then into a series of

Refrigerated containers filled and cooled to form lactose crystals. The individual cooling vessels are then each emptied into a centrifuge combination (e.g., decanter and screen screw centrifuge) to separate the lactose crystal formed from the mother liquor. The mother solution will continue in

Worked up alternative processes, since a return to the evaporation before the batch crystallization stage would lead to viscosity problems due to the entrained residual content of proteins, which are now concentrated in the mother liquor higher concentration. The yield of lactose crystallizate is in this known

Usually in the range of 62-68%.

The publication WO 03/075643 A2 discloses a process for the continuous recovery of lactose crystallizate from an aqueous lactose solution which first preconcentration of the solution by evaporation of water to 45-65% solids content and then a high concentration to about 70-80%. Solid content provides. The highly concentrated solution is then in a

Cascaded multi-stage system for simultaneous concentration, cooling and crystallization in which the lactose solution is cooled by a gas stream so that a partial crystallization of the lactose takes place and increases the solids content to 78 - 88%. Subsequently, this suspension is injected for complete crystallization in a spray chamber operated with hot air, from which a product with 90-99% solids content is removable, wherein 70-100% of the water still contained therein are bound as lactose monohydrate crystals. The individual stages of the system for simultaneous concentration, cooling and

Crystallization are each formed as a horizontal cylindrical container whose volume is only partially filled with solution and through the longitudinal axis of a paddled, driven shaft runs, which promotes the solution under constant circulation in the next stage, the air for cooling above the Liquid level is passed through the container. This method requires a comparatively complex system technology and a high energy consumption for operation.

Another method for obtaining lactose crystallizate is from

Published patent application WO 2012/047122 A1, which starts from a lactose solution with less than 80% solids content. This solution is in one

Heat exchanger, in particular a riser or a thermosyphon heat exchanger, heated to 50 - 90 ° C and passed into an evaporation vessel in which water evaporates and lactose crystallized. The heat exchanger is connected in a circuit with the evaporation tank, so that the solution circulates with the formed crystals as a suspension. A partial stream of the suspension is discharged continuously and fed, for example, to a hydrocyclone, in which by separation of mother liquor which is recycled, a suspension with increased solids content is produced. The suspension thus obtained is then placed in batch-wise operated cooling tanks in which the original grain size of the crystallizate formed in the evaporation vessel is further increased by further crystallization as a result of the cooling of the entrained solution fraction. The suspension removed from the cooling tanks is then decanted and the separated mother solution is discharged from the process. The obtained moist crystals are washed, centrifuged and finally dried. US Pat. No. 4,955,363 A discloses a process for obtaining lactose crystallizate from whey, which first undergoes a multistage falling film evaporation at a maximum temperature of 75 ° C. and is concentrated to, for example, 58% DM. The solution thus concentrated is then charged into a crystallization tank and cooled therein with stirring the solution over a period of several hours at a cooling rate of 2 ° C / h to 15 ° C, wherein lactose crystallizate precipitates out of the solution. The crystallization tank is emptied via a decanter centrifuge, in which the lactose crystallizate is separated from the mother liquor. The mother liquor is transferred to a buffer while the crystals are washed and dried after centrifugation. The mother solution separated from the washed crystals in the centrifuge is also incorporated into the

Buffer passed. The mother solution in the cache becomes one

Purification by adjusting the pH to 5.8 - 7.9 and the

Mother solution is heated to 60 - 70 ° C. The precipitated solids are removed by centrifugation. The mother liquor separated is subjected to a chromatographic fractionation yielding three fractions, namely a protein fraction to be removed, a middle fraction containing lactose and other impurities, which is recycled to chromatographic fractionation, and a lactose fraction entering the crystallization tank is returned.

The published patent application DE 198 39 209 A1 discloses a process for obtaining lactose crystallizate from whey, which after a protein removal by

Ultrafiltration to concentrate the whey uses a nanofiltration, wherein 80-90% of the solution in the permeate (water and salts) are transferred. The on

Lactose supersaturated retentate is placed in a crystallization tank in which a lactose crystallizate is formed by addition of seed crystals and optional cooling. The crystals are separated by decantation, then washed and dried. The mother liquor is at least partially recycled before nanofiltration.

Another method for obtaining lactose from ultrafiltered whey is known from the publication US 2006/0278217 A1. The whey is first subjected to an ion exchange treatment by means of an anionic and a cationic resin filling in two columns connected in series and then in by unspecified process steps by

Water evaporation concentrated and crystallized. After the crystallization of the lactose, the crystals are separated and the mother liquor is recycled wholly or partly for the regeneration of the resin fillings in the columns. However, the separated mother solution can also completely or partially a chromatographic

Treatment are obtained, on the one hand, a lactose-enriched fraction and on the other hand, a raffinate is obtained, which can be used for the regeneration of the resin fillings. Of the above-described methods of lactose production, only published patent application WO 03/075643 A2 has a continuously operated one

Process stage for the crystallization of lactose. However, the apparatus provided for this purpose is a comparatively complicated, operated with a cooling air flow mechanical device. The previously commonly used batch-wise operated crystallization tanks are structurally very simple design, but not only require significant space and Verrohrungsaufwand for a plurality of parallel tanks, but also require considerable effort for the regular cleaning work on the emptied tanks to prevent contamination by bacteria.

In lactose recovery, it is generally desirable to obtain the solid in the form of the lactose monohydrate, in as constant a quality as possible. This is generally best done by a continuous

Achieve procedural control.

The object of the present invention is to improve a process for producing a lactose monohydrate crystallizate from a continuously fed aqueous lactose solution such that the production of the lactose crystallisate remains as constant as possible with energy as well as energetically and in terms of plant and plant technology low effort and the highest possible yield is guaranteed.

This object is achieved by a process for the continuous production of a lactose monohydrate crystallizate from a continuously fed aqueous lactose solution preconcentrated to about 5-8% TS, from which the original contained proteins by a membrane filtration largely (95 - 99% of the original content) were removed, so that at most slight residual amounts of protein are present. In this case, the preconcentrated solution is under

Heat supply in a falling film evaporation highly concentrated and then fed to a continuous cooling crystallization for lactose crystallization, from which then a lactose suspension is withdrawn, which forms after removal of the entrained solution, the Produktkristallisat. According to the invention, at the outlet of the falling film evaporation, the temperature of the solution is kept in the range of about 50-90 ° C. and the solution brought to a content of 60-80% of DM and the continuous cooling crystallization at 10 ° -55 ° C. with continuous circulation the

Make suspension. The product crystals according to the invention are directly, i. without further crystallization steps, from the suspension coming out of the

Cooling crystallization was withdrawn, recovered by solid / liquid separation. Of course, this is followed by the usual further treatment steps for the crystals, such as crystal washing and drying. Essential for the increase in the yield is that part of the mother liquor separated from the product crystallization is recycled before the entrance of the falling film evaporation and only a remainder of the mother liquor is rejected. Typically, yields in the range of about 75-85% can thus be achieved.

It is characteristic of the process according to the invention that no crystallization takes place in the heat exchanger upstream of the continuous cooling crystallization, ie in the falling-film evaporator, but the crystallization takes place exclusively in the continuous crystallization stage. All process steps take place in a continuous mode of operation and ensure a consistently high product quality.

In principle, it is of course possible to carry out the cooling crystallization by means of surface cooling. Conveniently, however, the cooling crystallization is operated with a continuous vacuum cooling to the time and

Space requirement and the energy consumption as low as possible. A

Continuous vacuum cooling crystallization protects very well against the risk of contamination by bacteria because of the outward complete conclusion and therefore also allows a considerable saving in cleaning effort compared to a batch-wise crystallization. Added to this is the advantage that in the Vacuum generation from the cooling crystallizer water vapor is constantly withdrawn and thus after the falling film evaporation still a further reduction of

Water content in the solution is effected, which increases the overall yield of lactose crystals of the inventive method. Incidentally, compared to a batch-wise operated crystallization in tanks, as has hitherto been customary in a continuous cooling crystallization and the cost of the piping and valves reduced.

It has proven to be particularly advantageous for the cooling crystallization in

Temperature range of 35 - 50 ° C, in particular at about 40 ° C. This type of crystallization allows compared to known methods very high crystallization performance at relatively low investment costs.

The falling film evaporation is expediently operated at 65-75 ° C., preferably at about 70 ° C. Preferably, the dehydration in the falling film evaporation is driven so far that the lactose solution then has a solids content of 65-70% DM. In the event that preconcentration of the lactose solution by

Water evaporation takes place, there is the great advantage that the heating of the falling film evaporation is very good in the appropriate on similar

Temperature level settled thermal management in particular one

Integrate multi-stage pre-evaporation.

In some cases, in terms of thermal management, it is advantageous to perform falling film evaporation in several successive stages.

Particularly advantageously, the portion of the mother liquor separated from the product precipitate is previously subjected to membrane filtration (e.g., micro, ultrafiltration, or nanofiltration) to remove protein from falling film evaporation. This can be expected otherwise problems in terms of a strong

Viscosity increase can be avoided, so that even increases in yield to values of over 80% up to 95% are made possible. The cost of this additional membrane filtration is relatively low, since the masses to be handled are much lower than in the preparation of the preconcentrated lactose solution. It is sufficient for a small and correspondingly inexpensive system for this. With regard to the best possible product quality, ie the highest possible degree of purity of the lactose monohydrate crystallizate, it is advisable to subject the portion of the mother solution attributable to falling film evaporation to mineral precipitation and separation. This is especially about the

Removal of calcium and phosphates, which could also crystallize on lactose crystallization and contaminate the product.

The circulation of the suspension in the crystallizer can be carried out appropriately by stirring or by pumping in a circuit.

A plant for carrying out the method according to the invention is equipped

with a crystallization device designed as a continuously operated cooling crystallizer with forced circulation,

- having a supply line for preconcentrated lactose solution

Falling film evaporator, out of which a supply line for highly concentrated

Lactose solution leads to the crystallizer,

- With a solid / liquid separator, in which by a suspension line crystal suspension from the crystallizer can be introduced and

- With a mother solution return line, through which a part of the separated in the solid liquid separator mother liquor is traceable to the entrance of the falling film evaporator.

The falling film evaporator can advantageously also be designed as a multi-stage system.

Advantageously, the crystallization device is connected to a vacuum generating device.

Furthermore, it is advantageous if a membrane filter system (for example a micro, ultra or nanofilter system) for the separation of proteins is switched on in the line leading from the solid / liquid separator to the falling film evaporator.

It may also be provided to turn into the leading from the solid / liquid separator to the falling film evaporator line means for precipitation and separation of minerals (especially calcium and phosphates) to a To produce a particularly pure product.

The invention will be explained in more detail with reference to the embodiment shown schematically in the figures.

Show it:

FIG. 1 shows a plant scheme for the method,

Figure 2 shows a system example with falling film evaporator and cooling crystallizer. The plant scheme exemplified in Fig. 1 provides that from an unillustrated source (e.g., cheese making) an aqueous lactose solution L0 is first fed to a membrane filtration NF (e.g., nanofiltration) in which, for example, 98% of the originally contained protein is removed. The solution L1 thus obtained then passes into a device for Vorkonzentrierung the solution. This may be formed, for example, as a pre-evaporation or as in the illustrated scheme as a reverse osmosis device RO. In preconcentration, most of the water is removed from the solution so that it reaches a content of about 4-8% DM. This preconcentrated solution L2 is, as shown in the more detailed partial representation with the same reference numerals for functionally identical parts in Fig. 2, in a falling-film evaporator 1 for high concentration of the solution L2 by water evaporation. This falling film evaporator 1 could also be designed in several stages. The one at a

Operating temperature of the falling film evaporator 1, for example, 70 ° C vaporized water content is withdrawn as vapors and condensed in a condenser C1. From the lower part of the falling film evaporator 1, for example by means of a pump P1, a highly concentrated solution L3, which typically has a content of e.g. 65-70% TS, a cooling crystallizer 2, which has the constant circulation of crystal suspension via an equipped with a pump P2 external line circuit KR. Instead of the line circuit KR, e.g. also an internal agitator may be provided in the crystallizer 2. The supply line of the highly concentrated solution L3 can, as shown, open into the circulation line or directly into the crystallization space of the cooling crystallizer 2. The

Cooling crystallizer 2 is preferably used to withdraw the vapors formed in its upper part by evaporation to a non-illustrated

Vacuum generator V connected, the vapors to Condensation can be performed by a capacitor C2. As a result of the cooling of the continuously circulated in the cooling crystallizer 2 solution whose temperature is depending on the temperature of the supplied solution L3 in the range of 10 - 55 ° C, typically in the range of about 40 ° C, the saturation limit of the solution is exceeded, so that lactose crystallized and grows to ever-growing grains. This means that in the circulation line KR not only the pure solution is circulated but with this also the already formed crystals in the form of a suspension. The lactose monohydrate crystallizate continuously formed in this way can be withdrawn from the lower part of the cooling crystallizer 2 through a line SP as a suspension and fed to a solid / liquid separation device 3 (eg decanter and / or centrifuge) in which the entrained mother solution is separated from the lactose product crystallizate K. A portion of the separated mother liquor may be returned to the inlet of the falling film evaporator 1 through a conduit MR, while a smaller portion of the mother liquor is discharged as reject A from the process to avoid concentrating contaminants. The usual further steps for working up the lactose crystallizate produced have not been shown.

The inventive method of completely continuous lactose monohydrate crystallization requires a relatively low energy and

Apparatus expense, since it leads to a good separable from the mother liquor crystals whose mean grain size is typically prove to be about 0.1 - 0.2 mm leads. The energy required for the evaporation of water can in particular by a

Vacuum generation in the cooling crystallization can be minimized. In addition, the inventive method allows a particularly high yield of highly pure lactose without large amounts of wastewater, especially when the recycled mother liquor is subjected to a removal of protein and minerals. LIST OF REFERENCE NUMBERS

1 falling film evaporation

2 crystallizer

3 solid / liquid separator

A rejection line

C1 capacitor

C2 capacitor

E proteins

K product crystallizate

KR circulation line

L0 fresh lactose solution

Lactose solution largely liberated from proteins

L2 preconcentrated lactose solution

L3 highly concentrated lactose solution

MR line for returned mother solution

NF membrane filter system

P1 pump

P2 pump

P3 pump

RO reverse osmosis device

SP line for the withdrawal of the suspension with the product crystallizate V vacuum generation

Claims

claims

1 . A process for the continuous production of a lactose monohydrate crystallizate from a continuously fed aqueous lactose solution preconcentrated to 5 to 8% TS, from which the originally contained proteins were removed by membrane filtration, the preconcentrated solution being concentrated under

Heat supply in a falling film evaporation highly concentrated and then a continuous cooling crystallization for lactose crystallization is fed, from which a lactose suspension is withdrawn, which forms after removal of the entrained solution, the Produktkristallisat, wherein the temperature of the solution at the exit of the falling film evaporation in the range of 50 -. 90 ° C is maintained and the solution reaches a content of 60 - 80% TS and wherein the continuous

Cool crystallization is carried out at 10 - 55 ° C with constant circulation of the suspension and wherein the product crystals directly without further crystallization steps from the suspension, which was withdrawn continuously from the cooling crystallization, by solid / liquid separation and by carrying out a crystal washing and drying is obtained and wherein a part of the separated from the product crystallizate

Mother liquor is returned before the entrance of the falling film evaporation and repelled the rest of the mother liquor.

2. The method according to claim 1, characterized in that the cooling crystallization is operated with a continuous vacuum cooling.

3. The method according to claim 1 or 2, characterized in that the

Cooling crystallization in the temperature range 35-55 ° C, especially at 40 ° C is operated.

4. The method according to any one of claims 1 to 3, characterized in that the falling film evaporation at 65-75 ° C, in particular at 70 ° C is operated.

5. The method according to any one of claims 1 to 4, characterized in that the attributable to the falling film evaporation part of the separated product from the mother liquor is subjected to membrane filtration for the separation of proteins.

6. The method according to any one of claims 1 to 5, characterized in that the attributable to falling film evaporation part of the separated from the product mother liquor of a precipitation and separation of mineral substances, in particular of calcium and phosphates, is subjected.

7. The method according to any one of claims 1 to 6, characterized in that the circulation of the suspension takes place in the crystallization device by stirring or pumping in a circuit.

8. The method according to any one of claims 1 to 7, characterized in that the falling-film evaporation is carried out in several stages connected in series.

9. The method according to any one of claims 1 to 8, characterized in that the dehydration in the falling film evaporation is driven so far, the

Solids content in the lactose solution is 65-70% TS.

10. Lactose recovery plant for carrying out the method according to claim 1,

- With a designed as a cooling crystallizer with forced circulation

Crystallization device (2),

with a falling film evaporator (1) having a supply line (L2) for preconcentrated lactose solution, from which a supply line (L3) for highly concentrated lactose solution leads to the crystallization device (2),

- With a solid / liquid separator (3), in which by a suspension line (SP) crystal suspension from the crystallization device (2) can be introduced and

- With a mother solution return line (MR) through which a part of the separated in the solid liquid separator (3) mother solution to the input of

Falling film evaporator (1) is traceable.

1 1. Plant according to claim 9, characterized in that the

Crystallization device (2) to a vacuum generating device (V) is connected.

12. Plant according to claim 10 or 1 1, characterized in that in the of the solid / liquid separator (3) to the falling film evaporator (1) leading line (MR) a membrane filter system (NF) for the separation of proteins is turned on.

13. Plant according to one of claims 10 to 12, characterized in that in the of the solid / liquid separator (3) to the falling film evaporator (1) leading line (MR) means for precipitation and separation of minerals is turned on.

14. Plant according to one of claims 10 to 13, characterized in that the falling film evaporator (1) is formed in multiple stages.