DK178799B1 - Clarifier with acid for low ash lactose - Google Patents

Abstract

A process for the production of low ash levels lactose crystals comprising clarifying a whey permeate after calcium precipitation followed by pH-adjustment to dissolve precipitates of calcium phosphates not removed by clarification.

Description

TITLE

Clarifier with acid for low ash lactose FIELD

The invention relates to a method of combined calcium precipitation, separation by use of clarifier and pH adjustment prior to further processing in the production of lactose from whey permeate with very high purity and very low ash levels after wash.

BACKGROUND

In the production of crystalline lactose from whey or whey permeate the presence of salts, which may co-precipitate with lactose during lactose crystallization, is a persisting problem. The concentration of mineral salts in the whey is typically from 5-40 mM with calcium salts, in particular calcium phosphates, being particularly problematic for the efficient production of lactose from whey permeate due to calcium's high content in milk and the atypical precipitation behavior of calcium phosphates, exhibiting a reduced solubility with increased temperature.

In the industry it is common to concentrate the whey permeate to a higher solids content using evaporation prior to the precipitation of lactose, see e.g. WO 2012/047122. However when evaporating and if calcium phosphates are not inactivated prior to the whey permeate entering the evaporator, the salts may precipitate on the heat surfaces in the evaporator causing reduced heating efficacy and additional downtime for maintenance and cleaning.

Traditionally, the calcium phosphate is precipitated in the permeate by adjusting the pH to about 7.2 e.g. by addition of caustic Mg(OH)2 or NaOH after which the permeate is heated to about 80°C. The precipitated calcium phosphate can then be removed by centrifugation or membrane filtration. Usually, the discharged product is then dried and sold as "milk calcium" as food additives or used in the manufacture of fertilizers, e.g. in the Odda-process.

However, with the traditional industrial methods of precipitating calcium phosphates it is difficult to get consistent ash levels below 0.3% in the resulting lactose powders due to incorporated Ca and P in the lactose crystals. This ash level, however, is important as 0.3% ash content is the current maximum limit in lactose used for infant formulas. As a result thereof, lactose for infant formulas must currently undergo additional processing to reduce the ash levels therein to meet current standards for infant formulas, thereby increasing cost to the detriment of industry and families with infants that rely on infant formulas for the nutrition of their children.

Accordingly, there is a need in the art for industrial scale methods of precipitating calcium phosphates from whey permeate for obtaining crystallized lactose with low ash levels of calcium phosphates.

This problem has traditionally been solved by submitting the whey to ultrafiltration and ion-exchange at high temperatures, to obtain whey permeate with low ash levels of calcium phosphates. However this method is generally considered expensive in establishing and operating costs.

An alternative method exists which combines submitting the whey to ultrafiltration to obtain a permeate enriched in calcium and phosphate, followed by calcium precipitation at elevated temperature and basic pH, followed by cooling, and separation of the calcium precipitate by use of a clarifier to remove precipitated calcium phosphates and obtain a whey permeate with reduced ash levels of calcium phosphates of 0.2%, see e.g. http://us.westfalia-separa tor. com/f ileadmin/GSA WS US/'Documents/Brochures/Dai ry/Processing Lines for Whey Brochure.pdf; accessed

February 26, 2015. In this process, calcium phosphate is separated from whey permeate. The purpose of this method is to obtain calcium phosphate as a food additive and also to achieve longer operating times in the concentration processes due to the effect of demineralizing the permeate. US 4,202,909 describes methods of precipitating calcium salts from whey at the pH of milk, while leaving phosphate-ions in the whey permeate, the methods involving precipitating by heating and removing the resulting precipitate, primarily calcium citrate salts, by clarifying using filtration either using filters or with flocculants. The resulting crystallized lactose products are 98.8% pure, which can be improved to 99.1% purity by washing the formed lactose crystals in acidified water.

The current inventors have now realized that by modifying the above alternative process, an improved process for the separation of calcium phosphates from whey permeate is obtained which in one step can yield ash levels below 0.2% and as low as 0.1% without the need for further purification of the whey permeate. Further, improvements in energy savings are thereby achieved. The process of the present invention is particularly suitable in the dairy industry where large quantities of whey permeate are handled and where improvements to process economy is of particular importance. A further advantage of the presently suggested process is increased versatility of a production line implementing the process, permitting the line to produce both high grade and low grade lactose using the same equipment, thereby reducing CAPEX and OPEX for the production line.

SUMMARY OF THE INVENTION

In a first aspect and embodiment, the present invention concerns a process for producing lactose from concentrated whey permeate comprising between 10 to 40 % dry solids, said process comprising the steps of: i. Independently, adjusting the pH of the concentrated whey permeate to between pH 6.0 to pH 8.5 in a pH-adjustment step (3) and/or heating the whey permeate to between 60°C to 90°C in a heating step (4); ii. Holding the concentrated whey permeate of step i. for a retention time of at least 30 minutes in a precipitation step (5) in order to allow precipitates of calcium phosphates having a size larger than a centrifugal clarifier cut-off value of 0.5 pm to form in the whey permeate; iii. Clarifying the whey permeate of step ii. in a clarification step (7) to remove precipitates of calcium phosphates with sizes above said centrifugal clarifier cut-off value to obtain a calcium phosphates reduced whey permeate; iv. Adding acid to the calcium phosphates reduced whey permeate of step iii. in an acid addition step (8) to dissolve precipitates of calcium phosphate smaller than said centrifugal clarifier cut-off value, thereby obtaining a precipitate free whey permeate; v. Concentrating the precipitate free whey permeate of step iv. in a lactose concentration step (9) to obtain a high lactose content whey permeate; and vi. Precipitating lactose from said high lactose content whey permeate of step v. in a lactose precipitation step (10).

In a second embodiment of the invention, the process of the first aspect and embodiment comprises both a pH-adjustment step (3) and a heating step (4).

In a third embodiment of the process of either said first or said second embodiment, said step i. is preceded by a permeate concentration step (2) and optionally, a riboflavin removal step.

In a fourth embodiment of the process according to any of previous embodiments, the process comprises addition of a base to maintain the pH during said precipitation step (5) at the pH of the pH-adjustment step (3).

In a fifth embodiment of the process according to any of the previous embodiments said centrifugal clarifier cutoff value is 1 pm.

In a sixth embodiment of the process according to any of the previous embodiments the process comprises adjusting pH down by 0.05 to 0.5 pH degrees in said acid addition step (8).

In a seventh embodiment of the process according to any of the previous embodiments the process comprises said lactose concentration step (9) being concentration by evaporation.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: Flow-diagram of prior art and exemplary processes for the separation of calcium phosphates from whey permeate according to the present invention.

DETAILED DESCRIPTION

The improved process for the separation of calcium phosphates from whey permeate according to the present invention is described below with reference to the drawing, Figure 1. The processes described in the flow-diagram are meant as an illustration of the inventive concept, and the skilled person will be able to make modifications thereof, following the contents of the present disclosure, without departing from the disclosed inventive concept.

Whey permeate comprising calcium phosphates dissolved in the aqueous phase is used as a starting material (1) . It is normally contemplated that the whey permeate comprises calcium phosphates in concentrations equal to those found in the milk from which the whey originated, however, whey permeates comprising calcium phosphates in concentrations higher or lower than this are equally suitable for use with the process of the invention. The whey permeate will typically originate from ultrafiltration of whey, however, other methods of isolating whey proteins from whey permeate yield equally useful starting materials and hence, the present invention is not limited by the manner in which whey proteins are separated from whey permeate.

In accordance with the process of the invention as detailed in the exemplary flow-diagram of figure 1, whey permeate is concentrated to remove surplus water in a permeate concentration step (2). It is generally preferred that concentration is by reverse osmosis, but other methods of concentrating whey permeate are equally useful. Whey permeate is concentrated to between 10 to 40% dry solids (DS) , between 15 to 35% DS, between 17 to 30% DS, preferably between 18 to 25% DS, and most preferably 20% DS.

The permeate concentration step (2) may be combined with a riboflavin removal step for the removal of riboflavin present in the whey permeate, e.g. by passing the concentrated whey permeate through a column comprising active carbon, thereby removing riboflavin by adsorption.

The permeate concentration step (2) is followed by adjusting the pH in a pH-adjustment step (3) , and/or a heating step (4) and a precipitation step (5), preferably a precipitation step at an elevated temperature. As will be detailed below, the steps of adjusting pH (3) and of heating (4) can be used individually without the other or in combination, the combination being preferred.

Whey permeate in general has a pH below 6.3. Once pH is raised above six (see e.g. US 6558717 Bl) calcium phosphates can be expected to precipitate from solution. Already at pH 6.5 at least 50% precipitation can be expected and raising the pH to moderate basic conditions, such as pH 7.2, will cause more than 65% of the calcium phosphate to precipitate due to the influence of pH alone. Raising the pH to above 8 does not further benefit the precipitation of calcium phosphates. Accordingly, in the pH-adjustment step (3) as contemplated in the present invention, pH is adjusted to lie between at least 6.0 and not more than 8.5, between 6.1 and 8.0, between 6.2 and 7.8. More preferably, pH is adjusted to lie between 6.3 and 7.5, between 6.4 and 7.2, or between 6.5 and 6.9. Most preferably, pH is adjusted to be 6.5. The skilled person will know how to adjust to the pH for use in the present process, if further optimization is contemplated beyond what is stated here.

The heating step (4) involves heating the concentrated whey permeate to a temperature of precipitation above 60°C and below 90°C. Improved results are achieved when the temperature is between 65°C to 85°C, more preferably between 70°C to 80°C, more preferably between 73°C to 78°C, and most preferably around 75°C. These temperatures of precipitation are well known in the art and the skilled person will know how to adjust to the temperature for use in the present process, if further optimization is contemplated beyond what is stated here.

In order to achieve the beneficial high level removal of ash in crystallized lactose made from permeate treated using the presently suggested process, heating (4) and pH-adjustment (3) must be combined, however, due to the permeate concentration step (2), significant precipitation of calcium phosphates can be achieved with the process without the use of both pH-adjustment or heating, as long as at least one of these process steps are used. Thereby a lactose crystallization plant or production line operating according to the present process gains additional versatility, as it may produce both low grade and high grade lactose without the need for dedicated low grade and high grade production lines. Also, and in general, omitting a process step reduces production costs, which may be crucial for competitive low grade products.

The pH-adjustment step (3) and/or heating step (4) is followed by a precipitation step (5) in which the concentrated permeate is retained in a precipitation vessel for a retention time sufficient to allow calcium phosphate crystals larger than at least 0.5 ym to form. An average retention time for precipitation is preferably from between 30 min to 120 min, most preferably around 60 minutes, as is known in the art. The skilled person will know how to optimize the retention time to the process economy desired. For high level ash removal retention times of 60 minutes or more are usually sufficient, when both the pH-adjustment step (3) and the heating step (4) have been implemented.

The precipitation step (5) is followed by a clarification step (7), preferably at the temperature of the precipitation step. In the preferred embodiment energy is saved as cooling or further heating can be omitted. Further, when operating the process for obtaining high level ash removal, it will help to drive the equilibrium towards precipitation as calcium phosphates can be continuously removed during precipitation, thereby further reducing the ash levels in lactose produced based on the presently suggested process.

Current centrifugal clarifiers, such as the SPX Seital Separation Technology clarifier range, allow the recovery of fine particles above a given centrifugal clarifier cutoff value, typically 0.5-500 ym. Hence, retention times in the precipitation step must be sufficient to obtain calcium phosphate crystals of at least a centrifugal clarifier cut off value of 0.5 pm. However, in the present process, it is preferable that the retention time is sufficient to generate crystals of a centrifugal clarifier cut-off value of at least 1 pm for optimal efficacy of the centrifugal clarifier employed.

Clarification in step (7) is followed by an acid addition step (8) wherein the calcium phosphates reduced permeate is pH-adjusted down by 0.05 to 0.5 pH degrees. The pH may, depending on the needs in the further downstream processes, in some instances be reduced further. By reducing the pH of the permeate, precipitates of calcium phosphates which were too small to be removed in the clarification step (7) will be dissolved. Due to the removal of phosphate from the permeate during precipitation pH changes, and the buffering capacity of the permeate reduces, it may be beneficial to add base continuously during precipitation, if the pH-adjustment step (3) option is used. Alternatively, pH drop during precipitation. Since the mass of the very fine calcium phosphates particles in the permeate is very low and the buffer capacity is reduced by the significant removal of phosphate, the required amount of acid needed for neutralization is relatively small.

The permeate, which has now become a calcium phosphates reduced permeate, is subsequently submitted to further concentration, in order to concentrate the lactose comprised therein in a lactose concentration step (9) prior to precipitation of lactose in a lactose precipitation step (10) to yield crystalline lactose (11). Methods of concentration and precipitation of lactose as generally known in the art are all suitable for these subsequent steps . A particularly suitable lactose concentration step (9) is by evaporation according to known methods in the art. When lactose concentration is performed by evaporation of the calcium phosphates reduced permeate, it is an additional advantage of the presently suggested process that when a heating step (4) is employed prior to and during calcium phosphates precipitation (5) and clarification (7) , the permeate reaching the concentration step (9) is already heated to the precipitation temperature and less or no heating is needed to get the desired inlet temperature of the evaporator.

The below examples show the effect of producing crystalline lactose according to the presently suggested process following the preferred process of pH-adjustment and heating to obtain low ash level lactose crystals.

EXAMPLES

Ash results in crystallized lactose powder according to: Prior Art - Comparative:

Crystallization tank without clarifier and acid: 0% of a 67% lye, 40 min at 75C and no acid gave an ash result of 0,29% and 0,24% measured as sulfated ash

Present Disclosure:

Crystallization tank with clarifier and acid: 0,075% of a 67% lye to a 20% DM whey permeate, 60 min at 75C, with clarifier and 0,1% of a 37% acid gave an ash result of 0,10% and 0,11% measured as sulfated ash.

When mother liquor of this was purified and processed again at 0% lye, 60 min at 75C with clarifier and 0,1% of a 37% acid then this gave an ash result of 0,12% and 0,12% measured as sulfated ash.

Using clarifier and acid gave a consistent and very good result measured on ash content in the final lactose powder.

CLOSING COMMENTS

The term "comprising" as used in the claims does not exclude other elements or steps. Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

Claims (7)

A process for preparing lactose from concentrated whey permeate comprising between 10 and 40% solids, comprising the steps of: i. Independently adjusting the pH of the concentrated whey permeate to between pH 6.0 to pH 8.5; a pH adjustment step (3), and / or heating the whey permeate to between 60 ° C to 90 ° C in a heating step (4); ii. retention of the concentrated whey permeate from step i. for a retention time of at least 30 minutes in a precipitation step (5) to allow precipitates of calcium phosphates having a size greater than a clearance centrifuge cut-off value of 0.5 µm can be formed in the whey permeate; iii. clearance of the whey permeate from step ii. in a clearance step (7) to remove precipitates of calcium phosphates having sizes above the clearance centrifuge cutoff value to obtain a calcium phosphate-reduced whey permeate; iv. addition of an acid to the calcium phosphate-reduced whey permeate from step iii. in an acid addition step (8) to dissolve calcium phosphate precipitates less than said clarification centrifuge cutoff value, thereby obtaining a precipitate-free whey permeate; v. concentration of the precipitate-free whey permeate from step iv. in a lactose concentration step (9) to obtain a high lactose whey permeate; and we. precipitation of lactose from said whey permeate with high lactose content from step v. in a lactose precipitation step (10). The method of claim 1, which comprises both a pH adjustment step (3) and a heating step (4). The method of either claim 1 or claim 2, wherein step i. Precedes a permeate concentration step (2) and optionally a step of removing riboflavin. A method according to any one of claims 1 to 3, comprising adding a base to maintain the pH during the precipitation step (5) at a pH as in the pH adjustment step (3). A method according to any of claims 1 to 4, wherein the clearance centrifuge cut-off value is 1 µm. A method according to any one of claims 1 to 5, which comprises lowering the pH by 0.05 to 0.5 pH degrees in the acid addition step (8). A process according to any one of claims 1 to 6, wherein the lactose concentration step (9) is concentration by evaporation.