WO2010133952A1

WO2010133952A1 - Emulsions of refinery residue and asphalt in water and method for preparing same

Info

Publication number: WO2010133952A1
Application number: PCT/IB2010/001182
Authority: WO
Inventors: Hercilio José RIVAS SIERVO
Original assignee: Hra Colombia S.A.S.
Priority date: 2009-05-22
Filing date: 2010-05-13
Publication date: 2010-11-25
Also published as: CO6180082A1; PE20121199A1

Abstract

The present invention relates to stable emulsions of refinery residue, as well as to a method for producing such emulsions of refinery residue and asphalts in water. The emulsions of the present invention contain 60 wt% to 90 wt% of the hydrocarbon, and display levels of viscosity several orders of magnitude lower than the viscosity of the hydrocarbon. Said viscosity of the emulsions can be controlled by changing the average diameter and the distribution of drop diameters in the emulsion. The emulsions according to the present invention are suitable for use as fuel in electric power plants and as asphalt for roads, since the low viscosity and stability of said emulsions allows said emulsions to be transported, handled and stored at room temperature.

Description

EMULSIONS OF REFINERY RESIDUES AND ASPHALTS IN WATER. AND PROCEDURE FOR PREPARATION

FIELD OF THE INVENTION

The present invention is developed in the field of hydrocarbons. Particularly, the present invention relates to emulsions of refinery residues and asphalts in water, as well as its preparation process. The present invention reveals emulsions and a process for stabilizing emulsions of refinery residues or asphalts in water. The final product turns out to be a stable and low viscosity fluid, which can be stored for extended periods of time; it can be transported long distances through pipelines and tankers, and it can be handled and used as fuel in electricity generating plants.

BACKGROUND OF THE INVENTION

Highly viscous hydrocarbons, especially those from the oil refining process and the production of asphalts, which have API severities of less than 10, are produced in large quantities during daily refining operations by oil companies worldwide. AND! Industrial use of these materials is restricted for several technical reasons, especially those related to handling and storage. To overcome these types of technical restrictions, various techniques have been proposed, including the preparation of hydrocarbon emulsions.

And in the state of the art the art of forming hydrocarbon emulsions, such as natural bitumen, refinery waste or Asphalts in water. Such emulsions are formed to facilitate the handling and transport of these highly viscous materials. Some typical processes are described in US Patents No. 3,380,351; 3,467,195, 3,519,006; 3,943,954; 4,099,357; 4,795,478; 4,801,304; and 4,976,745. In addition to the above, the state of the art also teaches that oil-in-water emulsions formed with natural bitumens or refinery residues can be used as fuels in electricity generating plants, as indicated in US Pat. No. 4,144,015; 4,378,230 and 4,618,348.

However, these processes and the resulting conventional emulsions are not suitable and effective for highly viscous hydrocarbons; and its application is not advantageous for such purposes. Consequently, it is clear that there is still an urgent need in the state of the art for new developments that allow the handling and transport of highly viscous hydrocarbons such as bitumens, refinery waste or asphalt in water.

DESCRIPTION OF THE FIGURES

Figure 1 corresponds to a graph illustrating the bi-modal distribution of the drop diameter of emulsions of refinery waste in water as those of the present invention.

Figure 2 corresponds to a simplified scheme of the flow chart of a plant to prepare emulsions of refinery waste or asphalt in water, as described in the present invention.

Figure 3 corresponds to a schematic representation of the effect of the percentage of ionization of oleic acid and linoleic acid on the average drop diameter of emulsions of refinery waste in water, such as those disclosed in the present invention.

Figure 4 corresponds to a graph illustrating the effect of the percentage of ionization of TOFA fatty acids and the concentration of TOFA on the drop diameter of emulsions of refinery waste in water, such as those disclosed in the present invention.

Figure 5 corresponds to a graph illustrating the effect of the concentration of refinery waste on the average drop diameter of waste emulsions in water, such as those disclosed in the present invention.

Figure 6 corresponds to a graph that illustrates the effect of the number of units of Ethylene Oxide (UOE) and the hydrocarbon / water ratio on the average diameter of drops in emulsions of refinery waste in water, such as those disclosed herein. invention, stabilized with mixtures of TOFA and Ethoxylated Nonyl Phenol.

Figure 7 corresponds to a graph illustrating the effect of the Cut Rate, on the viscosity of emulsions of refinery waste in water, such as those disclosed in the present invention, for mono-modal emulsions with different average drop diameters and for a bi-modal emulsion

Figure 8 corresponds to a graph illustrating the effect of storage time at 25 "C on the viscosity of emulsions of refinery waste in water, such as those disclosed in the present invention.

Figure 9 corresponds to a graph illustrating the effect of storage time at 25 ° C on the average emulsion drop diameter of refinery waste in water, such as those disclosed in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In view of the drawbacks present in conventional developments for the handling of highly viscous hydrocarbons, the present invention reveals a novel alternative that is highly effective for the treatment of said materials.

In this way, the principal! The object of the present invention is to provide emulsions and a process for the production of a liquid fuel using such highly viscous refinery residues by means of the formation of said easily manageable emulsions to pave communication paths.

A characteristic aspect of the emulsions of the present invention is that they are constituted as an emulsifier package containing fatty acid and monoethanolamine; These components alone are not emulsifiers, but when they react they form a compound that acts as an emulsifier, which constitutes a fundamental and significant difference of the product of the present invention with respect to conventional products of this type.

On the other hand, the formation and structure of the emulsion of the present invention is of bi-modal characteristics which allows reducing the water content without an increase in viscosity.

The two previous characteristics allow the emulsion of the present invention to be more stable and for better use as fuel. Although there are asphalt emulsions in the state of the art, it is clear that they are not mono-modal and with a high water content: There are emulsions as fuels, but they are of water in waste, which also constitutes a substantial difference with the emulsions of the present invention that are of residue in water.

There is also in the state of the art an emulsion based on natural bitumen in water (30% water) and mono modal, which differs from the emulsions of the present invention because they are a product from refinery funds, with lower water content and bi-modal structure.

In this way, the particular objective of the present invention is to produce a low viscosity fluid using refinery residues or highly viscous asphalts, by forming emulsions of said materials in water.

It is also an objective of the present invention to provide emulsions of refinery residues or asphalts in water that behave as low viscosity fluids at room temperature, with the appropriate characteristics to be used as fuels in electricity generating plants or for paving of roads.

Thus, in a first embodiment, the present invention reveals hydrocarbon emulsions in water characterized in that it comprises a hydrocarbon selected from refinery wastes and asphalts in water and having viscosities greater than 10 Pa. S (10,000 centipoise) at 50 ⁰ C (122 ° F), and an aqueous solution containing water soluble additives comprised of amines and a surfactant.

Thus, the present invention provides stable emulsions of hydrocarbons in water, where said emulsions have very low viscosities with respect to hydrocarbons, which have very high viscosities. According to the present invention, the hydrocarbon can be a refinery residue or an asphalt, which have the following physicochemical characteristics: carbon from 78 to 88% by weight, hydrogen from 9 to 11% by weight, oxygen from 0 , 2 to 1, 4% by weight, nitrogen from 0.5 to 0.7% by weight, sulfur from 0.5 to 4.0% by weight, API gravity below 12 ⁰ API, viscosity at 50 ⁰ C (122T), 10 Pa.s (10,000.00 centipoise) up to 70 Pa.s (70,000.00 centipoise), viscosity at 23.3 ⁰ C (74 ° F) from 100 Pa.s (100,000.00 centipoise) to 250 Pa .s (250,000.00 centipoise) and calorific value from 23,240 kJ / kg (10,000.0 BTU / lb) to 44,150 kJ / kg (19,000.00 BTU / lb).

In accordance with the present invention, emulsions of refinery residue or asphalts in water are stabilized with a surfactant or a mixture of two or more surfactants. The mixture of surfactants promotes a synergistic effect which confers greater stability to the emulsion. The mixture of surfactants used includes anionic and non-ionic surfactants, cationic and non-ionic surfactants and preferably mixtures of fatty acids, non-ionic surfactants and amines. When the surfactant used is of the non-ionic type, e! Preferred non-ionic surfactant is selected from the group of polyoxyethylene alcohols, from the group of alkyl polyoxyethylene phenols or from a mixture of both groups. AND! Preferred non-ionic surfactant is a phenol or a polyoxyethylene alcohol, which has approximately 12 carbon atoms in the hydrophobic chain and at least 30 units of ethylene oxide in the hydrophilic chain, with an HLB greater than 13. When the surfactant used is a fatty acid, the preferred acid is selected from oleic acid, linoleic acid or stearic acid. These acids can be used separately, or mixed in the way that they are normally produced commercially.

When fatty acids are used as surfactants, the presence of a water soluble amine is required to promote the ionization of fatty acid. The amines used are selected from the group formed by Ia ethylamine (EA), di-ethylamine (DA), monoethanolamine (MEA), di ethanolamine (DEA) or propanolarnine (PA). When emulsions are prepared using mixtures of fatty acids, non-ionic surfactants and amines, the fatty acid dissolves in the oil phase, while the non-ionic surfactant and the amine dissolve in the aqueous phase. The total concentration of surfactant varies between 0.1 and 5.0% by weight and preferably between 0.5 and 3.0% by weight.

In another embodiment, the present invention provides hydrocarbon emulsions in water characterized in that they contain hydrocarbons selected from refinery residues or asphalts in water, water and a surfactant consisting of a pure fatty acid, selected from oleic acid, linoleic acid or acid stearic The fatty acid must be dissolved in the refinery residue, while the aqueous phase must contain a water soluble amine, particularly monoethanolamine (MEA), in a concentration that promotes a partial ionization of the fatty acids present in the refinery residue.

In a preferred embodiment, the emulsions resulting from the present invention are characterized in that it contains at least 60 to 90% (w / w) of a hydrocarbon selected from refinery residues or asphalts in water having a viscosity greater than 10 Pa. S (10,000 centipoises) at 50 ⁰ C (122 ° F), 10% by weight of water, a lower concentration of surfactant 1% by weight of the hydrocarbon, a resultant viscosity equal to or less than 3 Pa. s (3000 centipoise) at 50 ⁰ C (122 ° F) and an average droplet diameter of not more than 100 microns.

In another embodiment of the present invention, a process for the formation of hydrocarbon emulsions in water is disclosed, characterized in that it comprises the steps of: (i) preparing an aqueous solution containing water soluble additives, such as a non-ionic surfactant and an amine;

(ii) pre-mixing the aqueous solution of (i) with a hydrocarbon selected from a refinery residue or asphalt in water, which has previously been added with a fatty acid or a mixture of fatty acids;

(iii) divide pre-mix into two streams to form two emulsions with different average drop diameters;

(iv) mixing the emulsions from the two streams again until the resulting emulsion is achieved with the required drop diameter and viscosity; Y

(v) homogenize the resulting emulsion and store.

The hydrocarbon emulsions in water, prepared according to the process described in the present invention, show an average diameter and a distribution of diameters of drops, as well as a constant viscosity, when said emulsion is stored for prolonged periods of time (See Figure one). This characteristic determines the stability of the product and allows it to be transported and stored without any risk of separating the hydrocarbon from the water.

According to the present invention, an aqueous solution containing water soluble additives, such as a non-ionic surfactant and an amine (monoethanolarnin) is mixed with the refinery residue or asphalt, which has previously been added with a fatty acid. or with a mixture of fatty acids, to form an emulsion of refinery residue or asphalt in water, which contains between 5 and 40% by weight of water. The aqueous solution and the refinery residue or asphalt are mixed using a stirrer. Variable speed mechanic When increasing the speed of the mixer, the average diameter of drops of the emulsion decreases. Emulsions with different average diameters of drops, 2 and 30 microns for example, can be mixed in certain proportions, to obtain a final product with a fairly wide distribution of diameters (See Figure 1), which allows to obtain an emulsion with a viscosity much less than the viscosity of the original emulsions.

However, according to Figure 2 a simplified diagram of the flow chart of a plant for preparing emulsions of refinery waste or asphalt in water is shown, as described in the present invention. Thus, the viscous material from the refinery 1 is stored in the tank 2. The refinery residue is added with the mixture of acids grade 3 using a static mixer 4. On the other hand, the aqueous solution is prepared by mixing the water 5 with the surfactant 6 and the amine 7 with the static mixer 8. The aqueous solution and the refinery residue are then premixed with the static mixer 9 and the stream is divided into two flows, each of which is passed through the mechanical mixers (colioid mil!) 10 and 11, respectively, which operate at different speeds. The emulsions formed with each of the mechanical mixers, have different average diameters of drops. Both emulsions are given to me in a proportion such that the required final droplet diameter and the desired viscosity are obtained, using static mixer 12. The final water content in the emulsion can be adjusted, when necessary, by adding water. stored in 13, to the emulsion and homogenizing the mixture with the static mixer 14. The final product in specifications is stored in the tank 15.

The following examples illustrate the simple way to achieve the hydrocarbon emulsions in water of the present invention and its advantages in handling and transporting viscously hydrocarbons: EXAMPLE 1

In order to demonstrate the effect of the formulation on the average drop diameter of the emulsions of refinery residues in water, such as those of the present invention, several hydrocarbon samples emulsions were prepared, with viscosities of 55 Pa s (55,000 centipoise) at 50 ⁰ C (122 ⁰ F), at 135 Pa s (135,000 centipoises), at 23 3 ⁰ C (74 ⁰ F) and API severity of 7, were added with oleic or linoleic acid at a concentration of 0.8% in By weight, they are used as surfactants Subsequently, the refinery residue, containing fatty acids, was mixed with water, using a mechanical stirrer rotating at 1000 RPM, to form hydrocarbon emulsions in water which contained 30% by weight of water The formulation was added by adding different concentrations of monoethanolamine (MEA) in the aqueous phase. The presence of MEA in the water promotes the ion! 7, a fatty acid present in the hydrocarbon. Tsar and ionized which adsorbs to the hydrocarbon water inferred, act as an emulsifying agent As the concentration of MEA in the aqueous phase increases, the percentage of ionization of adsorbed fatty acids in the interface also increases the effect of ionization of the fatty acids (concentration of MEA) are the average droplet diameter of the emulsions formed in Figure 3. The data in this Figure 3 indicate that the droplet diameter drops, as the percentage of ionization laughs the fatty acids increases, until reaching minimum values, from which in average diameter of drops increases again R! average droplet diameter also decreases with the total concentration of fatty acids present in the emulsion

EXAMPLE 2

To demonstrate the effect of the mixtures of fatty acids on the formulation of emuis'nπes so emulsions of residues of water refinery, containing different concentrations of the commercial TOFA product, which contains a mixture of fatty acids. The emulsions prepared in the manner described in Example 1, contained 30% by weight of water and different concentrations of TOFA (0.6 and 0.8% by weight with respect to the hydrocarbon). The data of Figure 4 indicate that the average diameter of drops decreases, until reaching minimum values, from which the diameter of drops increases again; in the same way the diameter of drops decreases with the concentration of the fatty acid mixture (TOFA)

EXAMPLE 3

To demonstrate the effect of the hydrocarbon concentration on the average droplet diameter of the emulsions formed, several emulsions of the refinery residue in water were prepared, containing different weight ratios of hydrocarbon / water. In these experiments the same refinery residue used in the EXAMPLE 1 experiments was used. The concentration of TOFA used as a surfactant was 0.6% by weight with respect to the hydrocarbon. The concentration of MEA present in the aqueous phase was necessary to obtain an ionization of approximately 50%, in the mixture of fatty acids. The results obtained are shown in Figure 5, and it is observed that the average drop diameter of the emulsions of refinery waste in water increases as the concentration of the hydrocarbon increases.

EXAMPLE 4

To demonstrate the influence of the synergistic effect of mixtures of surfactants on the average droplet diameter of emulsions of refinery waste in water, stabilized emulsions were prepared with mixtures of fatty acids and nonionic surfactants of the ethoxylated nonylphenol type, containing different numbers of units of ethylene oxides (UOE) per surfactant molecule. The total concentration of surfactant used was 0.6% by weight with respect to the hydrocarbon, the total being 50% by weight TOFA, 50% ionized and the rest ethoxylated nonylphenol. Figure 6 shows that there is a range of UOE in nonyl phenol, where the average diameter of drops reaches their minimum values. Figure 6 also shows that the average diameter of drops decreases when the ratio in weight of the refinery residue / water increases. These experiments were also performed with non-ionic surfactants of the ethoxylated alcohols type, obtaining similar results

EXAMPLE 5

To demonstrate the effect of the average diameter of drops and the distribution of diameters on the viscosity of the emulsions of refinery waste in water, emulsions were prepared with 30% by weight of water and different average diameters. The emulsifying agent used was a mixture of 50% by weight of TOFA (50% ionized) and 50% by weight of an ethoxylated nonylphenol surfactant containing 50 UOE. The total concentration of the emulsifying agent was 0.6% by weight with respect to the hydrocarbon. The prepared emulsions, with average droplet diameters of 2 and 30 microns respectively, had monomodal type drop diameters distributions. Figure 7 shows the viscosities as a function of the cutting rate for both emulsions, being observed that for single mode emulsions, the viscosity decreases, at each cutting rate, with the average diameter of drops. Figure 7 also shows the viscosity as a function of the cutting rate, for an emulsion with bimodal diameter distribution, obtained by mixing the single mode emulsions in a 50/50 weight ratio. The bimodal emulsion with an average diameter of drops of 17 microns has lower viscosities than the single mode with 30 microns of average diameter. It is concluded that bimodal emulsions have lower viscosities than their similar ones with monomodal distributions. EXAMPLE 6

To demonstrate the stability of the emulsions object of the present invention, Figures 8 and 9 show the viscosity and the average drop diameter of two emulsions of refinery waste in water, as a function of storage time at 25 ° C. None of the mentioned parameters changed substantially with the storage time, which is an indication that during this period of time there was no coalescence and that therefore the emulsions possess very good stability.

In this way, the emulsions of the present invention are constituted as a package of emulsifiers containing fatty acid and monoethanolamine; These components alone are not emulsifiers, but when they react they form a compound that acts as an emulsifier, which represents a fundamental and significant difference of the product of the present invention with respect to conventional products of this type.

Therefore, the emulsion of the present invention is more stable and for better use as fuel. Although in the state of the art there are asphalt emulsions, it is clear that they are not mono-modal and with a high water content: In addition there are emulsions as fuels, but they are of waste water, which also constitutes a substantial difference with emulsions of the present invention that are waste in water.

Now, any person in the art, particularly a versed person who has access to the teachings of the present invention, will recognize without difficulty that any modification or variation on the emulsions or the procedure, disclosed herein, is possible, without them departing from the scope and spirit of the invention. For example, it will be recognized that any variety of components that fulfill the purposes of the invention can be used. So that all the embodiments and variations set forth in the present invention should not be understood as limiting the scope of the invention, which is determined by the content of the following claims.

Claims

1. An emulsion of oil in water characterized in that it comprises a selected refinery waste water and hydrocarbon asphalts and having higher viscosities at 10 Pa s (10,000 centipoise) at 50 ⁰ C (122 ° F).; and an aqueous solution containing water soluble additives comprised of amines and a surfactant.

2. An emulsion of hydrocarbons in water according to claim 1, characterized in that the hydrocarbon has the following physical-chemical characteristics: carbon from 78 to 88% by weight, hydrogen from 9 to 11% by weight, oxygen from 0.2 to 1.4 wt%, nitrogen 0.5 to 0.7 wt%, sulfur from 0.5 to 4.0% by weight, API gravity below 12 ° API, viscosity at 50 ⁰ C (122 ° F), from 10 Pa.s (10,000.00 centipoise) to 70 Pa. S (70,000.00 centipoise), viscosity at 23.3 ° C (74 ° F) from 100 Pa.s (100,000.00 centipoise) to 250 Pa .s (250,000.00 centipoise) and calorific value from 23,240 kJ / kg (10,000.0 BTU / lb) to 44,150 kJ / kg (19,000.00 BTU / lb).

3. An emulsion of hydrocarbons in water according to claims 1 to 2, characterized in that the hydrocarbon is an asphalt.

4. An emulsion of hydrocarbons in water according to claims 1 to 3, characterized in that the hydrocarbon is present in a concentration ranging from 60 to 90% (w / w).

5. An emulsion of hydrocarbons in water according to claims 1 to 4, characterized in that the water is present in a concentration ranging from 5 to 40% by weight with respect to the hydrocarbon.

6. An emulsion of hydrocarbons in water according to claims 1 to 5, characterized in that the surfactants are selected from anionic and non-ionic surfactants, cationic and non-ionic surfactants, or mixtures of fatty acids, non-ionic surfactants and amines.

7. An emulsion of hydrocarbons in water according to claim 6, characterized in that the non-ionic surfactant is selected from the group of polyoxyethylene alcohols, alkyl polyoxyethylene alkyl phenols or a mixture of both groups.

8. An emulsion of hydrocarbons in water according to claim 6, characterized in that the fatty acid surfactant is selected from oleic acid, linoleic acid or stearic acid, or mixtures thereof.

9. An emulsion of hydrocarbons in water according to claim 6, characterized in that the surfactant is a mixture of a pure fatty acid selected from oleic, linoleic or stearic acid and a non-ionic surfactant selected from the group of polyoxyethylene alcohols, polyoxyethylene alkyl phenols or their mixtures

10. An emulsion of hydrocarbons in water according to claim 6, characterized in that the fatty acids correspond to a mixture of 40% oleic acid, 40% linoleic acid and 10% stearic acid.

11. An emulsion of hydrocarbons in water according to claim 6, characterized in that the non-ionic surfactants have between 20 and 70 units of ethylene oxide (UOE).

12. An emulsion of hydrocarbons in water according to claim 11, characterized in that the non-ionic surfactants have 50 units of ethylene oxide (UOE).

13. An emulsion of hydrocarbons in water according to claims 1 to 12, characterized in that the non-ionic surfactant is a phenol or a polyoxyethylene alcohol having approximately 12 carbon atoms in the hydrophobic chain and at least 30 ethylene oxide units ( UOE) in the hydrophilic chain with an HLB greater than 13.

14. An emulsion of hydrocarbons in water according to claims 1 to 13, characterized in that the amines are selected from the group consisting of ethylamine (EA), di-ethylamine (DA), monoethanolamine (MEA), di ethanolamine ( DEA) or propanolamine (PA).

15. A hydrocarbon emulsion in water according to claims 1 to 14, characterized in that the surfactant is present in a concentration ranging from 0.1 to 6.0% by weight

16. An emulsion of hydrocarbons in water according to claims 1 to 15, characterized in that the surfactant is present in a concentration ranging between 0.5 and 3.0% by weight.

17. An emulsion of hydrocarbons in water, characterized in that it comprises a hydrocarbon selected from refinery wastes and asphalts in water and having viscosities greater than 10 Pa.s (10,000 centipoises) at 50 ⁰ C (122 ⁰ F), and a aqueous solution comprising a surfactant consisting of a pure fatty acid selected from oleic acid, linoleic acid or stearic acid; and a water soluble amine corresponding to the monoethanolamine (MEA).

18. An emulsion of hydrocarbons in water according to claims 1 to 17, characterized in that it contains at least 60 to 90% (w / w) of a hydrocarbon selected from refinery residues or asphalts in water having a viscosity greater than 10 Pa.s (10,000 centipoises) a 50 ° C (122 ° F), 10% by weight of water, a concentration of surfactant less than 1% by weight with respect to the hydrocarbon, a resulting viscosity equal to or less than 3 Pa.s (3000 centipoise) at 50 ⁰ C ( 122 ° F) and an average droplet diameter of not more than 100 microns.

19. An emulsion of hydrocarbons in water according to claims 1 to 18, characterized in that it exhibits a resulting viscosity equal to or less than 3 Pa.s (3000 centipoises) at 50 ⁰ C (122 ° F) and an average droplet diameter not greater than 100 microns.

20. An emulsion of hydrocarbons in water according to claims 1 to 19, characterized in that it has a monomodal or bimodal drop diameter distribution.

21. A process for the formation of hydrocarbon emulsions in water as in claims 1 to 20, characterized in that it comprises the steps of:

(i) preparing an aqueous solution containing water soluble additives, such as a non-ionic surfactant and an amine;

(iii) divide the pre-mixture into two streams to form two emulsions with different average drop diameters;

(iv) mixing the emulsions from the two streams again until the resulting emulsion is achieved with the required drop diameter and viscosity; Y (v) homogenize the resulting emulsion and store.

22. A process according to claim 21, characterized in that the mixture of monomodal emulsions allows obtaining emulsions with bi-modal distribution with viscosities lower than the viscosity of the initial emulsions

23. A process according to claims 21 to 22, characterized in that monoethanolamine is added to the aqueous solution until an ionization of the fatty acids greater than 20% is produced.

24. A process according to claims 21 to 22, characterized in that the mixing of the solutions is carried out in a static mixer.

25. A process according to claims 21 to 23, characterized in that the two streams from the division of the pre-mix are mixed in mechanical mixers at different speeds.