Method for Mixing of Particles

Abstract

Continuous mixing in a static mixer possible can be used to add one kind of particles (such as an enzyme granular product) in a small amount to a larger amount of a different kind of particles (such as a powder stream of detergent powder), even if the powder characteristics are substantially different, with substantially no damage to the enzyme particles and with a high degree of homogeneity.

Claims

1. A method for mixing of at least two kinds of particles, wherein a first and a second stream of particles are mixed in a static mixer, and wherein the first and the second stream of particles have a weight ratio below 1:20.

2. The method of claim 1 wherein the ratio is below 1:50, particularly in the range from 1:1000 to 1:100, or from 1:500 to 1:125.

3. The method of claim 1, wherein the average particle size of the first stream of particles is in the range 100-2000 μm.

4. The method of claim 1, wherein the average particle size of the first stream of particles is in the range 300-1200 μm.

5. The method of claim 1, wherein the coefficient of variation of the amount of particles from the first stream, in the resulting mixture of the first and second stream of particles, is less than 40%.

6. The method of claim 5, wherein the coefficient of variation is measured using at least 9 samples and a sample size of at least 5 g.

7. The method of claim 1, wherein the first stream comprises enzyme particles.

8. The method of claim 7, wherein the enzyme particles comprise a protease, an amylase, a carbohydrase, a lipase, a cellulase, an oxidoreductase, a mannanase or a pectate lyase or a phosphatase, or a deoxyribonuclease.

9. The method of claim 7, wherein the resulting mixture of the enzyme particles and the second stream of particles has an amount of free enzyme dust below 20 parts per billion.

10. The method of claim 1, wherein the second stream comprises detergent granules or detergent powder particles.

11. The method of claim 1, wherein the second stream comprises animal feed particles.

12. The method of claim 1, wherein the second stream comprises flour.

13. A method for mixing of at least two kinds of enzyme particles, wherein a first and a second stream of enzyme particles are mixed in a static mixer.

Description

DETAILED DESCRIPTION

First Particle Stream

[0011] The first particle stream typically comprises one or more kinds of enzyme particles or other active or functional particles, such as bleach activators, polymers, colorants, perfume particles etc. The enzyme particles typically have particle sizes in the range 100-2000 μm, preferably an average particle size in the range 300-1200 μm. They generally consist of a core comprising the enzyme surrounded by a coating. The core may additionally comprise finely divided cellulose fibers. The coating may comprise a wax such as polyethylene glycol or a salt such as sodium sulfate. Some formulations of enzyme particles are described in U.S. Pat. No. 4,106,991, WO9212645, WO0001793, WO0104279, WO06034710, WO2011134809, WO200024877, WO 2003000625 and WO2007044968.

Second Particle Stream

[0012] As examples, the second powder stream may consist of powder detergent (granular detergent), animal feed or flour premix for baking where it is of interest to add minor ingredients in very small dosages. The particles should be free flowing as determined by an angle of repose being less than 45°, particularly less than 40° or less than 35°.

[0013] Thus, the invention may be used to add minor ingredients such as enzyme particles to powder detergent (granular detergent), Relevant enzymes include one or more of the following: a protease, an amylase, a carbohydrase, a lipase, a cellulase, an oxidoreductase, a mannanase and a pectate lyase. Examples are described in U.S. Pat. No. 4,106,991, WO9212645, WO0001793, WO0104279, WO2011134809, WO200024877 or WO 2003000625.

[0014] Another example is the addition of feed enzymes to animal feed. Relevant enzymes include one or more of the following: a protease, an amylase, a carbohydrase, a lipase, a cellulase, and a phosphatase such as phytase. Examples are described in WO9212645, WO 2001/004279, WO06034710, WO2007044968, WO9623062.

[0015] The invention may also be used to add enzymes to a flour premix for baking. Relevant enzymes include alpha-amylase. maltogenic amylase, lipase, phospholipase, xylanase. Examples are described in WO9104669, WO9826057.

Mixing of Enzyme Particles

[0016] A static mixer can also be used for mixing of two or more kinds of enzyme particles. Examples of relevant enzymes are those listed above.

Static Mixer

[0017] The static mixer is a device which can provide continuous mixing of streams of solid particles using no moving components. It may be a helical mixer consisting of mixer elements housed in a cylindrical tube, where the static mixer elements consist of a series of baffles. The static mixer should have a diameter which is at least 10 times of the particle size.

EXAMPLES

Example 1-3

In-Line Mixing of Enzyme into Detergent Powder

[0018] Streams of two types of particles were used, as follows: [0019] (a) Detergent: commercial European powder detergent without enzyme. [0020] (b) Enzyme: Commercial protease granules (Savinase™, product of Novozymes A/S). The average particle size is in the range 300-1200 microns.

[0021] The equipment for dosing and mixing was as follows: [0022] The detergent powder and the enzyme granules were each dosed by a vibrating feeder giving essential constant volumetric flow rates. A flow rate of 20 kg/min (+/−1 kg/min) was used for dosing the detergent powder and the enzyme feeder set-point was set to dose 16, 31, and 62 g enzyme/min., corresponding to with dosages of 0.15%, 0.3 and 0.6% of enzyme by weight, respectively.

[0023] Measurements were done as follows: [0024] Full flow samples were collected over 1 minute corresponding to about 20 kg. The homogeneity of the mixing was measured by scooping out nine samples (2a, 2b, 2c, 4a, 4b, 4c, 6a, 6b, 6c) of ˜5 g scoop size randomly from each test. It was secured that no additional mixing took place during the sampling procedure. [0025] The results were as shown in the following Tables.

TABLE-US-00001 TABLE 1 Product activity Enzyme granules Scoop size [activity Sample ID [wt. %] [g] units/scoop] Example-1-2a 0.6 5.15 0.201 Example-1-2b 0.6 5.14 0.171 Example-1-2c 0.6 5.21 0.167 Example-1-4a 0.6 5.18 0.364 Example-1-4b 0.6 5.18 0.345 Example-1-4c 0.6 5.22 0.352 Example-1-6a 0.6 5.23 0.281 Example-1-6b 0.6 5.18 0.278 Example-1-6c 0.6 5.26 0.294

TABLE-US-00002 TABLE 2 Product activity Enzyme granules Scoop size [activity Sample ID [wt. %] [g] units/scoop] Example-2-2a 0.3 5.17 0.0787 Example-2-2b 0.3 5.19 0.1100 Example-2-2c 0.3 5.18 0.0988 Example-2-4a 0.3 5.22 0.0726 Example-2-4b 0.3 5.24 0.1080 Example-2-4c 0.3 5.24 0.1310 Example-2-6a 0.3 5.16 0.0832 Example-2-6b 0.3 5.18 0.0801 Example-2-6c 0.3 5.21 0.0681

TABLE-US-00003 TABLE 3 Product activity Enzyme granules Scoop size [activity Sample ID [wt. %] [g] units/scoop] Example-3-2a 0.15 5.22 0.0664 Example-3-2b 0.15 5.16 0.0534 Example-3-2c 0.15 5.19 0.0480 Example-3-4a 0.15 5.19 0.0304 Example-3-4b 0.15 5.17 0.0706 Example-3-4c 0.15 5.16 0.0340 Example-3-6a 0.15 5.14 0.0514 Example-3-6b 0.15 5.15 0.0363 Example-3-6c 0.15 5.21 0.0468

TABLE-US-00004 TABLE 4 Mixing homogeneity as function of dose. Enzyme granules Cv Cv (scoop size: 5 g) Mean Std. Dev. measured minimum 0.15 wt. % 0.049 0.014 28% 24.7%  0.3 wt. % 0.092 0.021 23% 17.5%  0.6 wt. % 0.273 0.077 28% 12.4%

[0026] The mixing quality is determined by doing activity analysis of a number of scoops of product taken randomly. The scoop size is selected according to the application.

[0027] The best mixing quality that is possible to achieve corresponds to a statistical random distribution of the enzyme particles among the particles of the major powder stream(s). From the particle size distribution it is possible to calculate the distribution of the number of particles which is in a completely randomly mixed product for a given dosage and a given sample size (also called scoop size). When the distribution is known the standard deviation of the total amount of enzyme present in a scoop may be calculated. The average value will be equal to the dosage, so the Cv (coefficient of variation) can be calculated as the standard deviation divided by the average value. In Table 4, this Cv (Cv min) has been calculated for the three different dosages and a scoop size of 5 g. It is seen that the measured Cv, which includes the fixed value of the analytical Cv of the enzyme assay, gets close to the best possible Cv—especially for the smaller enzyme dosages.

[0028] The amount of free enzyme dust that is present in a sample is measured using a standard fluidization assay (J. Liu et al., Building and Environment, 44 (2009), 2327-2334). Table 5 shows the obtained results for the three tested dose levels: 0.15, 0.3 and 0.6 wt. % enzyme. The results are plotted in units of PPB (parts per billion or ng (10.sup.−9 g) active enzyme/g product. The blank-level of the method is ˜2 ng/g, and typical commercial laundry powders have active enzyme dust levels in the range 5-20 ng/g. Thus, the results show an extremely low level of active dust in all samples.

TABLE-US-00005 TABLE 5 Enzyme granules Total dust Active dust Sample ID [wt. %] [mg/60 g] [ng/g product] Example-1-2a 0.6 855 2.21 Example-1-2b 0.6 875 2.04 Example-1-4a 0.6 1390 3.60 Example-1-4b 0.6 1170 3.03 Example-1-6a 0.6 960 4.30 Example-1-6b 0.6 952 7.85 Example-2-2a 0.3 1140 2.96 Example-2-2b 0.3 899 2.93 Example-2-4a 0.3 1680 5.74 Example-2-4b 0.3 1490 7.26 Example-2-6a 0.3 966 2.47 Example-2-6b 0.3 1000 2.48 Example-3-2a 0.15 861 1.55 Example-3-2b 0.15 668 3.28 Example-3-4a 0.15 1200 1.93 Example-3-4b 0.15 990 2.35 Example-3-6a 0.15 1020 0.98 Example-3-6b 0.15 1180 2.26

[0029] The results demonstrate efficient mixing to a high degree of homogeneity, with a coefficient of variation close to the theoretical value for the sample size and particle size in question. The results also demonstrate an extremely low dust formation, well below the commonly accepted limit of 60 ng/m.sup.3.