WO2002051785A1

WO2002051785A1 - Benzoic acid particles

Info

Publication number: WO2002051785A1
Application number: PCT/NL2001/000911
Authority: WO
Inventors: Mantijn Leonardus Johannes Van Leeuwen; Reinier Grimbergen
Original assignee: Dsm N.V.
Priority date: 2000-12-22
Filing date: 2001-12-14
Publication date: 2002-07-04
Also published as: NL1016974C2

Abstract

Benzoic acid particles with a particle size substantially between 0.3 and 3 mm, a total diphenyl content substantially less than 300 ppm calculated relative to the amount of benzoic acid, and a total content of phthalic acid and phthalic anhydride substantially less than 900 ppm calculated relative to the amount of benzoic acid. Preferably, the particle size is between 0.5 and 1.5 mm. Preferably more than 5% by weight, in particular more than 10% by weight of the particles have a particle size larger than 1 mm. The concentration of phthalic acid and phthalic anhydride preferably is lower than 500 ppm, in particular lower than 100 ppm. The benzoic acid particles preferably exhibit less than 33% pulverisation and have a bulk density higher than 550 kg/m3. Preferably, the total diphenyl content is less than 100 ppm.

Description

BENZOIC ACID PARTICLES

The invention relates to benzoic acid particles with a particle size substantially between 0.3 and 3 mm, a total diphenyl content substantially less than 300 ppm calculated relative to the amount of benzoic acid, and a total content of phthalic acid and phthalic anhydride substantially less than 900 ppm calculated relative to the amount of benzoic acid.

It is known that benzoic acid intrinsically has a very high caking tendency. Consequently, benzoic acid particles that are currently available exhibit a relatively high caking tendency. For a number of applications solid benzoic acid is required that is free-flowing, that can be mixed relatively homogeneously with other substances and that consists of particles which are sufficiently strong to avoid breakage or pulverization of the particles during transport. This is particularly important, because breakage and pulverization of the particles during transport increases the caking tendency of the product. Pulverization also increases the concentration of inhalable particles, which is harmful to persons who are exposed to these particles. This applies to for example the application of benzoic acid in cattle feed. The invention provides such benzoic acid particles.

Surprisingly, the applicant has found that a distinct relationship exists between the caking tendency and the impurity content, in particular the diphenyl content, notably the methyldiphenyl content, present in the benzoic acid particles. Surprisingly, the caking tendency is enhanced more by the presence of methyldiphenyls that by the presence of diphenyl.

The total diphenyl content of the benzoic acid particles is less than 300 ppm, preferably less than 100 ppm. In the context of the present invention total diphenyls are understood to mean compounds that contain 2 phenyl groups, for example o, m or p-methyldiphenyl, o, m or p dimethylphenyl and diphenyl. The total diphenyl content is expressed in ppm (mg/kg), calculated relative to the total amount of benzoic acid. The diphenyl content usually is a fraction of the total diphenyl content, for example between 40 and 95 % by weight, in particular between 45 and 80 % by weight, calculated relative to the amount of total diphenyls. The phthalic acid content and phthalic anhydride content of the benzoic acid particles are preferably less than 500 ppm, in particular less than 300 ppm and most preferably less than 100 ppm, calculated relative to the amount of benzoic acid. Surprisingly, it has been found that the presence of larger amounts of phthalic acid or phthalic anhydride affects the crystal shape and disturbs crystal growth on further processing to for example alkali metal salts of benzoic acid, which may result in the incorporation of impurities. The benzoic acid particles according to the invention substantially have a particle size of between 0.3 and 3 mm, preferably between 0.5 and 1.5 mm. In the context of the present invention, this means that less than 15% by weight, in particular less than 5% by weight, of the particles is larger than 3 mm and less than 15% by weight, in particular less than 5% by weight, of the particles is smaller than 0.3 mm. Preferably less than 15% by weight, in particular less than 5% by weight, of the particles is larger than 1.5 mm and less than 15% by weight, in particular less than 5% by weight, of the particles is smaller than 0.5 mm. The caking tendency increases when the particle size decreases. In practice, when the mean particle size is smaller than 1 mm, a proportion of the particles, for example more than 5 % by weight, in particular more than 10 % by weight, is preferably larger than 1 mm. The particle size is determined by screen analysis (in accordance with DIN 4188).

The caking tendency of benzoic acid particles may be determined by for example the sleeve test. The caking tendency determined by the sleeve test may be related to the caking tendency of bagged product expressed by the number of days of storage.

Rubber sleeves of 100 ml are filled with product, with the sleeves being vibrated. The sleeves are sealed and consolidated for a few (3 to 7) days at 1 bar and at room temperature.

Subsequently, a vertical pressure is applied to the sleeve with the aid of a cylinder. Fracture of the column that has formed in the sleeve is revealed by a recorder. From this is derived the pressure, in bar, required for fracture, which is a measure of caking. The caking tendency is denoted as the caking figure, expressed in bar, which indicates the pressure at which the sleeve containing benzoic acid particles fractures. Another important measure of caking is the number of lumps. The mass percentage of lumps relative to the total amount of benzoic acid is determined by carefully separating large lumps, i.e. lumps larger than 4.75 mm, with a screen. The higher the percentage of lumps, the more the product cakes.

The hardness of the lumps is determined by hand. There are 3 categories. Soft lumps can be crushed easily by closing the hand without really exerting any force. Medium hardness lumps can be crushed in the hand by exerting pressure. Hard lumps cannot be crushed in the hand.

Pulverisation of particles during transport increases the caking tendency. Preferably, measures are taken to ensure that less than 33% of the particles are pulverised. Pulverisation is tested by the ball-pressure test.

In the ball-pressure test, 50 g of particles (from the fraction larger than 1 mm) is transferred to a screen together with 36 steel balls having a diameter of 15 mm and a mass of 13.70 g. The screen has a diameter of 200 mm and a height of 50 mm. The whole is placed on a shaking screen and shaken for 5 minutes. The shaking screen is in circular motion in the horizontal plane at a frequency of approx. 250 per minute and an amplitude (top to top) of 15 mm.

The product may be further analysed by for example screen analysis (according to DIN 4188). Pulverisation is expressed as the mass of particles having a diameter less than 500 micrometers relative to the total mass of particles before the test.

The benzoic acid particles of the invention preferably have a bulk density (measured according to ASTM 1895) higher than 450 kg/m³, in particular higher than 550 kg/m³.

Benzoic acid particles of the invention may be prepared from for example liquid benzoic acid employing known shaping techniques, for example prilling, (fluid bed) granulation, pelleting, flaking and the like. The liquid benzoic acid preferably has a total diphenyl content (calculated relative to the total amount of melt/amount of benzoic acid) of less than 300 ppm, in particular less than 100 ppm.

The total diphenyl content admissible for a desired caking tendency may be different for different shaping techniques and conditions and composition. The total diphenyl content that is admissible for the given caking tendency requirement may readily be determined for each shaping technique and the prevailing conditions, for example the storage and transport temperatures, storage period and particle shape. Especially the (bagging) temperature and the particle size are important parameters affecting caking. The applicant has found, for example, that if the desired storage period is 300 days, use may be made of for example prills with a mean particle diameter of 0.8 mm and a total diphenyl content of less than 100 ppm, pellets with a mean particle diameter of 3.5 mm and a total diphenyl content of less than 40 ppm, and flakes with a mean particle diameter of 1 mm and a total diphenyl content of less than 100 ppm. Benzoic acid is preferably melt-shaped. Especially the manner in which heat is removed from the product is important in this process. This may be effected by for example cooling on a belt cooler or flaker, direct cooling with a gas stream or direct cooling with a liquid stream. The traditional cooling technique takes place on a flaker or belt cooler. A product layer forms on the flaker, which subsequently needs to be scraped and/or crushed. A well-known example of this is for example flaking. The traditional belt cooler has a number of variants in the form of the various pelleting processes. In these processes the product is given a defined shape (pellets) with cooling being continued via a flaker or a plate-type cooler. Another variant is for example the micropelleting machine supplied by Sandvik (Rotoform process) wherein the pellets are cooled on a belt cooler.

Examples of shaping techniques with cooling being effected by a gas stream are prilling, spray cooling and the commonly known fluid bed granulation. In prilling, the melt is divided in a gas stream in the form of droplets.

Besides pressure-atomization, other techniques are available for dividing a melt in a gas stream in the form of droplets, for example distributing the melt with the aid of a rotating atomizer and spraying the melt in a sprayer with the aid of a vibrating diaphragm. In spray cooling, the molten product is atomized at a pressure of for example 0.5-3 MPa with the aid of a sprayer. A typical tower design using a pressure nozzle is shown in Figure 1 (C = cooling air inlet, E = air outlet, S = solid product, M = liquid benzoic acid inlet). Figure 1 shows a countercurrent tower design. A cocurrent spray cooler design is also possible. A drawback of cooling techniques based on a gas stream is that a substantial amount of benzoic acid may enter the gas stream. As a result, the gas stream may need to be inertized to prevent the benzoic acid-air mixture from posing an explosion hazard. In addition, the gas stream needs to be treated in order to prevent contamination of the surrounding area before the stream is discharged or reused in the process. This drawback is eliminated by cooling with a liquid stream, for example in the jet-priller (GMF). Basically, this is a traditional prilling tower except that cooling is effected with atomised liquid nitrogen.

The invention is now elucidated with reference to the examples, without being limited thereto. EXAMPLES

Example I. Caking of benzoic acid prills as a function of the total diphenyl content Properties of the benzoic acid prills The prills were prepared by means of jet-prilling technology, and had a mean particle diameter, determined by screen analysis, of 0.86 mm. 10 % by weight consisted of prills having a diameter smaller than 0.57 mm. 10 % by weight consisted of prills having a diameter larger than 1.27 mm. 27 % by weight consisted of prills having a diameter larger than 1 mm. After pulverization applying the ball-pressure test, 18.3 % by weight consisted of prills having a diameter smaller than 0.5 mm, and 81.7 % by weight consisted of prills having a diameter larger than 0.5 mm.

Caking of the bezoic acid prills

The caking tendency was determined using the sleeve test at 40^SC for 3 days.

Prills with a total diphenyl content of 1 ppm yielded a caking figure of 0.45 bar and a lump percentage of 4.5%; qualification: soft.

Prills with a total diphenyl content of 39 ppm yielded a caking figure of 0.33 bar and a lump percentage of 20.1%; qualification: soft to medium. Prills with a total diphenyl content of 76 ppm yielded a caking figure of 0.67 bar and a lump percentage of 47.3%; qualification: medium to hard.

Prills with a total diphenyl content of 204 ppm yielded a caking figure of 1.5 bar and a lump percentage of 57.5%; qualification: hard.

Example II. Caking of benzoic-acid flakes

The caking tendency of benzoic acid flakes as a function of the particle size was determined using the sleeve test at 20 ^eC during 3 days.

The unscreened benzoic acid flakes fractured at a pressure of 0.71 bar.

The fraction of benzoic acid flakes larger than 2.0 mm fractured at a pressure of 0.54 bar.

The fraction of benzoic acid particles smaller than 2.0 mm and larger than 0.85 mm fractured at a pressure of 0.91 bar.

The fraction of benzoic acid flakes smaller than 0.85 mm and larger than 0.6 mm fractured at a pressure of 1.53 bar. Example III. Caking of benzoic-acid flakes as function of the total diphenyl content of the benzoic acid melt and the particle size

Caking tests were performed using the sleeve test at 20 ^eC during 3 days.

111.1. Total diphenyl content of benzoic acid melt less than 50 ppm

III.1.1

Mean particle diameter 1.82 mm. 10 % by weight of the particles larger than 2.77 mm 10 % by weight of the particles smaller than 1.14 mm. Caking figure 0.89 bar. Soft lumps. Percentage of lumps relative to the total amount of benzoic acid: 6.3%.

.1.2

Mean particle diameter 1.02 mm. 10% by weight of the particles larger than 1.33 mm. 10% by weight of the particles smaller than 0.57 mm. Caking figure 0.96 bar. Soft lumps. Percentage of lumps relative to the total amount of benzoic acid: 28.9 %.

.2. Total diphenyl content of benzoic acid melt less than 100 ppm

.2.1

Mean particle diameter 2.81 mm. 10% w/w by weight of the particles larger than 3.84 mm. 10% by weight of the particles smaller than 1.74 mm. Caking figure 0.93 bar.

Percentage of lumps relative to the total amount of benzoic acid: 0%.

III.2.2

Mean particle diameter 1.11 mm. 10% by weight of the particles larger than 1.28 mm. 10% by weight of the particles smaller than 0.65 mm.

Caking figure 1.01 bar.

Lumps of medium hardness.

Percentage of lumps present relative to the total amount of benzoic acid: 19.1 %.

111.3. Total diphenyl content of benzoic acid melt about 3500 ppm (comparison)

111.3.1 Mean particle diameter 1.02 mm.

10% by weight of the particles larger than 1.33 mm.

10% by weight of the particles smaller than 0.57 mm.

Caking figure of > 1.53 bar.

Hard lumps. Percentage of lumps relative to the total amount of benzoic acid: 78.8%.

Example IV: Jet-prilling technology

The caking tendency of benzoic-acid prills produced by jet-prilling technology and having a mean particle diameter of 0.86 mm was determined at 20°C (7 days) as a function of the impurities.

The benzoic-acid prills that were contaminated with 240 ppm of 3- methyl-diphenyl fractured at a pressure of 0.26 bar and contained 20% by weight of lumps, which were classified as medium to hard.

The benzoic-acid prills that were contaminated with 410 ppm of 4- methyl-diphenyl contained 21 % by weight of lumps, which were classified as medium to hard.

The benzoic-acid prills that were contaminated with 430 ppm of 3,3- dimethyl diphenyl contained 23% by weight of lumps, which were classified as medium to hard. The benzoic-acid prills that were contaminated with 260 ppm of diphenyl contained less than 1 % by weight of lumps, which were classified as soft.

Claims

1. Benzoic acid particles with a particle size substantially between 0.3 and 3 mm, a total diphenyl content substantially less than 300 ppm calculated relative to the amount of benzoic acid, and a total content of phthalic acid and phthalic anhydride substantially less than 900 ppm calculated relative to the amount of benzoic acid.

2. Benzoic acid particles according to Claim 1 , with more than 5 % by weight, preferably more than 10% by weight of the particles having a particle size larger than 1 mm.

3. Benzoic acid particles according to Claim 1 or Claim 2, with a particle size between 0.5 and 1.5 mm.

4. Benzoic acid particles according to any one of Claims 1 -3, with a total content of phthalic acid and phthalic anhydride of less than 500 ppm, in particular less than 100 ppm.

5. Benzoic acid particles according to any one of Claims 1 -4, with less than 33% pulverisation.

6. Benzoic acid particles according to any one of Claims 1 -5, with a bulk density higher than 550 kg/m³.

7. Benzoic acid particles according to any one of Claims 1 -6 with a total diphenyl content of less than 100 ppm.

8. Benzoic acid particles according to any one of Claims 1 -7, the particles being flakes or prills.

9. Benzoic acid particles according to any one of Claims 1 -8 with a methyldiphenyl content of between 40 and 95 % by weight relative to the amount of total diphenyls.

10. Process for the preparation of benzoic acid particles according to any one of Claims 1-9, wherein liquid benzoic acid is subjected to a shaping technique with cooling.

11. Process according to Claim 10, wherein the liquid benzoic acid has a total diphenyl content of less that 300 ppm.

12. Process for the preparation of benzoic acid particles according to Claim 11 , wherein the liquid benzoic acid has a total diphenyl content of less that 100 ppm!

13. Process according to any one of Claims 10-12, wherein flaking is applied as the shaping technique.

14. Use of benzoic acid particles according to any one of Claims 1-9 or obtained by the process according to any one of Claims 10-13 in the preparation of cattle feed.