EP3897966A1

EP3897966A1 - Composition based on sodium bicarbonate and on fatty acids

Info

Publication number: EP3897966A1
Application number: EP18833037.7A
Authority: EP
Inventors: Karine Cavalier; Jean-Yves SEGUIN; Jordi LOPEZ LAUNES
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2018-12-20
Filing date: 2018-12-20
Publication date: 2021-10-27
Also published as: WO2020126012A1

Abstract

Composition based on sodium bicarbonate and on fatty acids Powder comprising at least 93% of sodium bicarbonate and from 0.01% to 7% of an unsaturated C6-C22 carbon fatty acid, or of a branched saturated C6-C2 carbon fatty acid, or of a saturated linear C6-C12 fatty acid, or of an alkali metal or alkaline earth metal salt thereof, and having less than 1% of sodium carbonate or less than 0.02% of ammonia equivalent. Use of unsaturated C6-C2 carbon fatty acid, or of a branched saturated C6-C2 carbon fatty acid, or of their alkali metal or alkaline earth metal salt, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders.

Description

Composition based on sodium bicarbonate and on fatty acids

Technical field

The invention relates to a composition based on sodium bicarbonate and on unsaturated fatty acids or on their alkali metal or alkaline earth metal salts.

It also relates to a method for the preparation of such a composition.

It also relates to the use of unsaturated fatty acids or of their alkali metal or alkaline earth metal salts for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders.

State of the art

Substances such as alkali metal bicarbonates, carbonates or

sesquicarbonates are commonly used in the form of powders of solid particles. Such powders are used in particular in the food industry, animal feed and as reactants for the purification of flue gases.

The tonnages produced worldwide and used annually (2016) are high: of the order of 4 million tonnes for sodium bicarbonate, 65 million tonnes for sodium carbonate and a few hundred thousand tonnes for potassium carbonate, potassium bicarbonate, sodium sesquicarbonate or trona (natural ore of sodium sesquicarbonate). These tonnages are produced mainly in the form of powders.

Many uses of such carbonates, bicarbonates and sesquicarbonates require fine powders, having a weight-average particle size (D₅₀) of at most 100 pm, indeed even yet finer. This is the case in the food industry for baking powders, or powders used in industry for the purification of flue gases from acid gases, such as HX gases (X indicating a halogen element, such as fluorine, chlorine, bromine or iodine) or such as SOx gases (for example sulfur dioxide SO₂ or sulfur trioxide SO₃).

It is known to use fatty acids, such as stearic acid or its salts (sodium, magnesium or calcium stearate) as anticaking agent for alkali metal carbonates, bicarbonates or sesquicarbonates or as mill antifouling and lubricating agent for such powders, in particular for fine ready-for-use powders.

For example, JP5058622 describes the addition of 0.5% to 1% of calcium or magnesium stearate to sodium bicarbonate powders, comprising sodium carbonate at the surface, as anticaking agent for the storage of such powders, in particular in closed bags. W02007/071666 describes the use of 0.2% to 7% of fatty acids or of their salts, such as the stearate, as a cleaning agent of the grinder, wherein fatty acids or their salts are used as a mixture with sodium bicarbonate, during the milling of sodium bicarbonate powders.

WO2015/118166 describes the use of fatty acids to limit the ammonia release during storage of ammoniated compositions, used with in a content of 0.01% to 5% by weight of fatty acids reported to weight of alkali ammoniated solids. Fatty acids are chosen from: lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, behenic acid or their salts. The ammonia- comprising compositions comprises from 60% to 98% of sodium bicarbonate,

1% to 40% of sodium carbonate and 0.02% to 2% of ammonia- compounds.

W02016/102603 describes the use of C₆-Cis fatty acids at a content of 0.1 to 20% as a mixture in a fluid bed or in comilling with sodium bicarbonate, in order to reduce the rates of dissolution of the powders thus obtained, and uses as baking powders for cake making. The preferred fatty acids are palmitic acid or stearic acid.

WO2017/178623 describes the use of fatty acids, as a mixture with sodium bicarbonate powders, at a content of 16.7% to 60% by weight of fatty acid and the remainder as bicarbonate in order to reach 100%, for formulations of extruded sodium bicarbonate aggregates, in particular in application as blowing agents for polymers.

However, the use of fatty acids or of their salts as a mixture with alkali metal bicarbonate, carbonate or sesquicarbonate powders, in particular in the purification of flue gases, presents a problem due to the amounts of fatty acids added to the powders, which reduce their purities, and during the recycling for the recovery in value of the waste salts from the purification of the flue gases during the use of such powders. Such fatty acid salts are insoluble in brines and have to be separated on activated carbon or phase separators, during the reprocessing of these salts in order to regenerate alkali metal bicarbonate or carbonate.

Summary of the invention

The inventors of the present invention have found that:

- unsaturated C6-C22 carbon fatty acids or their salts compared to corresponding saturated linear fatty acids of same number of carbons, and also that - saturated branched C₆-C₂₂ carbon fatty acid or their salts compared to saturated linear fatty acids of same number of carbons, and even

- saturated fatty acids having a short chain in particular from 6 to at most 12 carbon atoms, such as caproic acid or lauric acid, or their salts,

bring improved free-flowing (fluidity) characteristics of powders of alkali salts such as bicarbonate, carbonate or sesquicarbonate, enabling to reduce the amount of said organics in said powders to improve handling and storage capabilities.

Consequently, the present invention relates to the use of unsaturated C₆-C₂₂ carbon fatty acid, or of saturated branched C₆-C₂₂ carbon fatty acid, or of a saturated C₆-C₁₂ carbon fatty acid, or of their alkali metal or alkaline earth metal salt, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders.

The present invention also relates to a powder comprising at least 93% of sodium bicarbonate and from 0.01% to 7% of an unsaturated C₆-C₂₂ carbon fatty acid, or of a saturated C₆-C₁₆ carbon fatty acid, or of their alkali metal or alkaline earth metal salt.

The present invention also relates to a method for the preparation of a powder with improved fluidity properties, comprising a step of mixing an unsaturated C₆-C₂₂ carbon fatty acid, or a branched saturated C₆-C₂₂ carbon fatty acid, or their alkali metal or alkaline earth metal salt, with a sodium bicarbonate powder having a reduced content of ammonia compounds or having a reduced content of sodium carbonate.

A first advantage of the present invention is the possibility of improving the fluidity of alkali metal bicarbonate, carbonate or sesquicarbonate powders with respect to the uses already known and in comparison with equivalent powders non-additivated with fatty acids or their salts, or in comparison with commonly used fatty acids

A second advantage of the present invention is the possibility of reducing the amounts of fatty acids added to alkali metal bicarbonate, carbonate or sesquicarbonate powders and thus, during their use in the purification of flue gases, of reducing the steps and costs associated with the removal of the organics from the waste salts during the recovery in value and the recycling of the waste salts, for the renewed manufacture of alkali metal bicarbonate, carbonate or sesquicarbonate.

A third advantage of the present invention is the improvement in the behaviour of the powders to compaction, making possible a reduced compaction of the latter with such fatty acids, making them easier to store and transport in bulk.

A fourth advantage of the present invention is the improvement in the behaviour of the powders to bulk storage in a silo, making it possible to reduce the diameter of the channels (often called‘ratholes’) which are created during the emptying of the said silos and making it possible to limit the number of beaters or arch breakers in storage hoppers for such powders.

A fifth advantage of the present invention is the improvement in the behaviour of the powders to transportation by road tankers, tank wagons, bulk ore carriers or container ships, making possible an improved fluidization in pneumatic transportation for the emptying of the said tanks or containers.

A sixth advantage is the improvement in the angles of repose of the powders poured as powder, making possible storage in a silo having a less pointed conical bottom.

A seventh advantage is the improvement in the Carr index of the powders thus obtained, making possible a reduced compaction during the transportation and easier emptying of the powders transported in road tankers, in particular over lengthy stretches of road or over roads in a poor condition, causing vibrations and compaction of the said powders and difficult emptying.

An eighth advantage of the present invention is the improvement in the behaviour towards handling of the said powders after transportation by sea, in particular through humid and/or hot regions of tropical or equatorial regions (Azores, Suez Canal, Panama Canal, Pacific Ocean, and the like).

Definitions

In the present descriptive specification, some terms are intended to have the following meanings.

Powder is understood to mean an assembly of solid particles. In general, the said solid particles have small dimensions, generally of less than a millimetre or of less than a tenth of a millimetre (100 pm).

Angle of repose of a powder is understood to mean the measurement the angle of the angle of repose, in particular according to the method described in the present descriptive specification.

Specific weight by flow (SWF) is understood to mean the density measured by free flow in a 500 ml cylindrical container according to the method described in the present descriptive specification. Specific weight by tapping (SWT) is understood to mean the density of solid powder measured on a 100 ml graduated measuring cylinder with 70 g of powder after 1000 tapping blows obtained by rotation of a scalloped wheel with a lift of 9 mm over a time of 7 minutes, according to the method described in the present descriptive specification.

Carr index is understood to mean the measurement of the compressibility of a bed of particles, defined by the relationship:

Cl = "SWT - SWF'V'SWT" x 100 (dimensionless)

where:

· SWF (Specific Weight by Flow) is the poured bulk density, expressed in kg/m³

• SWT (Specific Weight by Tapping) is the tapped bulk density,

expressed in kg/m³

The Carr Indices obtained are then generally interpreted in the following way:

Table 1 : Determination of the flow of a powder as a function of its Carr index.

In the present specification, the expression "C_x-C_y carbon fatty acid" denotes fatty acids, the molecules of which have a minimum of x carbons and a maximum of y carbons.

In the present specification, the expression "saturated fatty acid" denotes a fatty acid, the molecule of which does not have available a carbon-carbon double or triple bond.

In the present specification, the expression "monounsaturated fatty acid" denotes a fatty acid, the molecule of which has available a carbon-carbon double bond (C=C).

In the present specification, the expression "polyunsaturated fatty acid" denotes a fatty acid, the molecule of which has available more than two carbon- carbon double bonds (C=C). In the present specification, the expression "branched fatty acid" denotes a fatty acid molecule, wherein the carbon atoms are connected to other carbon atoms forming a chain of carbon atoms and wherein at least one carbon of the chain is directly connected to more than 2 carbon atoms (ie 3 or to 4 carbon atoms). Therefore said carbon atom chain is not linear, and comprises at least one branch.

In the present specification, the term fatty acid "salt", except when the type of fatty acid salt is explicitly described, corresponds to the alkali metal salts of fatty acids, or alkaline earth metal salts of the corresponding fatty acid.

In the present specification, the choice of an element from a group of elements also explicitly describes:

- the choice of two or the choice of several elements from the group,

- the choice of an element from a subgroup of elements consisting of the group of elements from which one or more elements have been removed.

In addition, it should be understood that the elements and/or the

characteristics of a process or a use, described in the present specification, may be combined in all possible ways with the other elements and/or characteristics of the process, or of the use, explicitly or implicitly, this being done without departing from the scope of the present specification.

In the passages of the present specification which will follow, various embodiments or items of implementation are defined in greater detail. Each embodiment or item of implementation thus defined may be combined with another embodiment or with another item of implementation, this being the case for each embodiment or item unless otherwise indicated or clearly incompatible when the range of one and the same parameter of value is separated. In particular, any alternative form indicated as being preferred or advantageous may be combined with another alternative form or with the other alternative forms indicated as being preferred or advantageous.

In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments where the variable is chosen, respectively, within the range of values: excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.

The term "comprising" includes "consisting essentially of' and also "consisting of'.

If the term "approximately" is used before a quantitative value, this corresponds to a variation of ± 10% of the nominal quantitative value, unless otherwise indicated.

Detailed description of the invention

Consequently, the invention relates to the use of an unsaturated or of a branched saturated C6-C22 carbon fatty acid, or of a saturated C6-C10 carbon fatty acid, or of their alkali metal or alkaline earth metal salt, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders.

The present invention also relates to a powder comprising at least 93% of sodium bicarbonate and from 0.01% to 7% of an unsaturated C6-C22 carbon fatty acid or of a branched saturated C6-C22 carbon fatty acid, or of a saturated C6-C12 carbon fatty acid, or of their alkali metal or alkaline earth metal salt.

The present invention also relates to a method for the preparation of a powder according to the invention, comprising a step of mixing the unsaturated C6-C22 carbon fatty acid, or the saturated C6-C12 carbon fatty acid, or their alkali metal or alkaline earth metal salt, with a sodium bicarbonate powder having a reduced content of ammonia compounds or having a reduced content of sodium carbonate.

The invention relates to different preferred embodiments ('Item') described below.

Item 1. Powder comprising at least 93% of sodium bicarbonate and from 0.01% to 7% of an unsaturated C6-C22 carbon fatty acid, or of a branched saturated C6-C22 carbon fatty acid, or of a saturated C6-C12 carbon fatty acid, or of their alkali metal or alkaline earth metal salt.

Item 2. Powder according to item 1, the unsaturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 8, or at least 10 carbons.

Item 3. Powder according to item 2, the unsaturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 12, or at least 14 carbons.

Item 4. Powder according to any one of the preceding items, the unsaturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at most 20 carbons, or at most 18 carbons.

Item 5. Powder according to any one of the preceding items, the unsaturated fatty acid of which, or its alkali metal or alkaline earth metal salt, is monounsaturated, such as oleic acid. Item 6. Powder according to any one of the preceding items, the unsaturated fatty acid of which, or its alkali metal or alkaline earth metal salt, is polyunsaturated, such as linoleic acid.

Item 7. Powder according to item 1, the saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 8 carbons.

Item 8. Powder according to item 1, the saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 10 carbons.

Item 9. Powder according to item 1 or 7, the saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at most 10 carbons.

Item 10. Powder according to item 1, the saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 8 or at least 10 carbons.

Item 11. Powder according to item 1 or to item 7 or item 8, wherein the fatty acid is a branched saturated fatty acid, or its alkali metal or alkaline earth metal salt, and comprises at least 12 carbons.

Item 12. Powder according to item 11, the branched saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, comprises at least 14 carbons.

Item 13. Powder according to any one of items 1, 10, 11, or 12, wherein the fatty acid is a branched saturated fatty acid, or its alkali metal or alkaline earth metal salt, and comprises at most 20 carbons, or at most 18 carbons.

Item 14. Powder according to item 1 or anyone of items 11 to 13, the branched saturated fatty acid of which, or its alkali metal or alkaline earth metal salt, is isostearic acid.

Item 15. Powder comprising at least 93% of bicarbonate and from 0.01% to 7% of fatty acid selected among: caproic acid, linoleic acid, lauric acid, oleic acid or isostearic acid, or their alkali metal or alkaline earth metal salts, and having less than 0.02% of ammonia equivalent or having less than 1% of sodium carbonate.

Item 16. Powder according to any one of the preceding items, wherein the fatty acid is selected among unsaturated C6-C22 carbon fatty acids different from oleic acid and linoleic acid, and their alkali metal or alkaline earth metal salt.

Item 17. Powder according to any one of the preceding items, wherein the fatty acid is selected among branched saturated C6-C22 carbon fatty acids different from isostearic acid and its alkali metal or alkaline earth metal salt. Item 18. Powder according to any one of the preceding items, comprising at least 0.05%, preferably at least 0.20% of fatty acid, or or of their alkali metal or alkaline earth metal salt.

Item 19. Powder according to any one of the preceding items, comprising at least 0.30% of unsaturated fatty acid, or of saturated fatty acid, or of their alkali metal or alkaline earth metal salt.

Item 20. Powder according to any one of the preceding items, comprising at most 4% of fatty acid, or of their alkali metal or alkaline earth metal salt.

Item 21. Powder according to any one of the preceding items, comprising at most 2% of fatty acid, or of their alkali metal or alkaline earth metal salt.

Item 22. Powder according to any one of the preceding items, comprising at most 1.5% of fatty acid, or of their alkali metal or alkaline earth metal salt.

Item 23. Powder according to any one of the preceding items, the fatty acid of which is in the form of fatty acid salt chosen from sodium, potassium, magnesium or calcium salts.

Item 24. Powder according to any one of the preceding items, in the form of solid particles with a mean diameter of at most 500 pm or of at most 200 pm.

Item 25. Powder according to the preceding item, in the form of solid particles with a mean diameter of at most 100 pm or of at most 50 pm.

Item 26. Powder according to the preceding item, in the form of solid particles with a mean diameter of at most 30 pm.

Item 27. Method for the preparation of a powder according to any one of the preceding items, comprising a step of mixing the fatty acid, or their alkali metal or alkaline earth metal salt, with a sodium bicarbonate powder.

Item 28. Method according to the preceding item, the mixing step of which is carried out by a mixing device chosen from: a blade mixer equipped with lifter blades, a ploughshare mixer, a screw mixer, a mill, a fluid bed or any

combination of at least two of them.

Item 29. Method according to item 27 or 28, wherein the step of mixing the fatty acid and the powder is carried out with the fatty acid in molten state or its salt in the molten state.

Item 30. Use of unsaturated C6-C22 carbon fatty acid, or of a branched saturated C6-C22 carbon fatty acid, or of a saturated C6-C12 carbon fatty acid, or of their alkali metal or alkaline earth metal salt of fatty acid, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders. Item 31. Use of fatty acid or of its salt according to the preceding item, which consists in adding from 0.01% to 7% of unsaturated and/or saturated fatty acids, or their alkali metal or alkaline earth metal fatty acid salts, to the alkali metal bicarbonate, the alkali metal carbonate or the alkali metal sesquicarbonate powder, in order to improve the fluidity of the said powder, such as the angle of repose, or the Carr index, or the rathole diameter.

Item 32. Use of fatty acid or of its salt according to item 30 or 31 , for producing a powder according to any one of item 1 to 26.

Item 33. Use of fatty acid or of its salt according to any item 30 to 32, which consists in adding at least 0.05% or preferably at least 0.10% of fatty acid or of its alkali metal or alkaline earth metal salt.

Item 34. Use of fatty acid or of its salt according to the preceding item, which consists in adding at least 0.20% or 0.30% of fatty acid or of its alkali metal or alkaline earth metal salt.

Item 35. Use of fatty acid or of its salt according to any one of the preceding items, which consists in adding at most 4% or at most 2% of fatty acid or of its alkali metal or alkaline earth metal salt.

Item 36. Use of unsaturated C6-C22 carbon fatty acid, or of a branched saturated C6-C22 carbon fatty acid, or of a saturated C6-C12 carbon fatty acid, or of their alkali metal or alkaline earth metal salt of fatty acid, according to the preceding item, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders with a fine particle size and intended to be injected in a dry condition in purification of flue gases.

This is because it has been observed that the quality of flow of powders additivated with monounsaturated fatty acids, indeed even preferably with polyunsaturated fatty acids, or with their respective salts, substantially increases in comparison with the linear saturated fatty acids having a comparable number of carbons.

Likewise, the use of saturated fatty acids having a branched carbon chain, in comparison with the saturated fatty acid having a linear carbon chain with the same carbon number (or respectively of their salts), makes possible a substantial improvement in the quality of flow of the said powders.

Finally, saturated fatty acids having a shorter carbon chain (less carbon) also improve the quality of flow of the said powders, in comparison with the use of fatty acids having a longer carbon chain. This makes it possible to use less fatty acid, in comparison with the known fatty acids of the prior art.

This is particularly interesting for the production of fine alkali carbonate salts (such as bicarbonate, carbonate or sesquicarbonate) ready to use for acidic gas mitigation in industrial fumes, wherein such powders are injected and dispersed in fumes to react with acidic gas before being collected on filters such as bag filters or electrostatic precipitators.

Furthermore, the adjustment in the amount of fatty acid or of its salt may be adapted according to:

- the particle size of the particles constituting the bicarbonate, carbonate or sesquicarbonate powder,

- and the surface condition of the said particles.

This is because the more the powder is divided into fine particles and/or particles of irregular shapes, the more the amount of corresponding fatty acid or of its salt has to be increased in order to cover the solid particles and to prevent bonds (or bridges) of Van der Waals type or of electrostatic type.

Moreover, an excessively large amount of fatty acid exhibits the disadvantage of producing a tacky powder, generally when used above 7% in weight reported to the total weight of the powder.

A simple test, of the type of the measurement of the angle of repose of the powder with a reduced number of different contents of additive, between 0.01% and 7%, makes it possible to adapt the amount of fatty acid to be added to the powder, in order to find an optimum with the least cost/amount of additive.

For large particles with a mean diameter of several hundred microns, amounts of additive of the order of at least 0.01%, or at least 0.05%, up to 0.10%, indeed even up to 0.30%, by weight, are generally highly suitable.

For very fine particles with a mean diameter of less than 20 pm, or of less than 10 pm, amounts of fatty acids or of their salts of at least 0.50% by weight, up to 7% for the finest particles, are highly suitable.

Angle of repose of a powder is understood to mean the measurement the angle of the angle of repose, in particular according to the ISO 4324:1977 method (equivalent to standard AFNOR T73.008).

Specific weight by flow (SWF) of a powder is understood to mean the bulk density of the powder measured by free flow in a 500 ml cylindrical container according to procedure No. 320016 of 12/08/2010, of Solvay Carbonate France, available on request. Specific weight by tapping (SWT) of a powder is understood to mean the bulk density of solid powder measured on a 100 ml graduated measuring cylinder with 70 g of powder after 1000 tapping blows obtained by rotation of a scalloped wheel with a lift of 9 mm over a time of 7 minutes, according to the comprehensive procedure No. 32011 of 26/03/2014, of Solvay Carbonate France, available on request.

Content of ammonia compounds is understood to mean, in the present specification, compounds of the ammonium bicarbonate or of ammonium carbonate or of carbamate type which give off ammonia (NFfi) when they are heated at temperatures above ambient temperature. The measurement of their content, expressed in ammonia equivalent, is described in WO2015/118166.

The following examples serve to illustrate the invention.

Example 1

In these examples, use was made, as starting substance, of a technical-grade bicarbonate with a starting particle size of D50= 80 +/- 10 pm (weight-average diameter), ground without additive or with additive according to the procedure described in WO 2007/071666A1 in Example 1 on page 7. The additives are mixed beforehand using a test weight of 1.8 kg of bicarbonate, occupying a volume of approximately 3 litres, in order to suitably fill (at 2/3) a mixing chamber of a Lodige ploughshare mixer with a volume of 5 litres. This mixing is carried out at 250 revolutions/min and over 3 minutes. The acids are added in the solid form or in the liquid form (molten fatty acids) sprayed by a nozzle giving a circular jet, the flow rate of which is 1 g/min. Such a pre-spreading jet of the fatty acid makes possible a better distribution of the fatty acid over the solid particles and makes it possible to slightly reduce the amounts of fatty acid used per given angle of repose targeted.

The following particle size characteristics were measured (by laser particle sizing) on the powders thus obtained after grinding, with or without additive (confirmed for each test and batch of powder obtained):

• D90: 24 +/- 3 pm

· D50: 11 +/- 1 pm

• D10: 2 +/- 0.5 pm

The additives tested were:

• Stearic acid (saturated, linear chain)

• Isostearic acid (saturated, branched chain)

· Oleic acid (monounsaturated, linear chain)

• Linoleic acid (polyunsaturated, linear chain) • Olive oil (consisting of fatty acid triglycerides)

• Linseed oil (consisting of fatty acid triglycerides)

• Castor oil (consisting of fatty acid triglycerides)

• Ca (P04)2 (Tricalcium phosphate)

· CaO (quicklime, as powder)

• T1O2 (rutile, as powder).

Table 2 - Angle of repose of the powders obtained without additive and with different contents of additive between 0% and 0.90% of additions of additives.

Table 3 - Comparative characteristics of the powders obtained without additive and with 0.50% of additive relating to SWF, SWT, Carr index and Angle of repose.

Additional behavioural characteristics of the powders under stress on a Brookfield PFT (Powder Flow Tester) powder rheometer are produced. The powder rheometer is an instrument which measures the stress necessary for the flow of a powder, under different compressive stresses between 0 and 11 kPa, in order to establish the flow function (or ff coefficient) of the said powder, by plotting the unconfined yield stress fc of the powder as a function of the major consolidation stress sΐ :

fc = f(al).

The PFT measures enables also to calculate the rathole diameter for a given powder function of an equivalent height of the powder, usually between 0.8 to 8.0 m.

The comparison of these curves, or of the flow no-flow ratholes diameters, or the arching diameters, between different powders makes it possible to quantify the quality of flow of the powder and to compare the effectiveness of the different additives.

Conventional tests at low stresses (SWT, SWF, Carr index and Angle of repose) and also PFT tests at high stresses show that, among organic additives, polyunsaturated fatty acids, such as linoleic acid, and short-chain acids, such as lauric acid, exhibit a better behaviour in flow than saturated long-chain fatty acids, such as stearic acid. Likewise, saturated branched- chain acids, such as isostearic acid, greatly improve the quality of the flow of the powder, in comparison with saturated linear-chain fatty acids. Linoleic acid, for example, makes possible virtually an easy flow (ff = 4) and lauric acid makes possible a weakly cohesive flow (ff < 4).

Moreover, the values of arch diameter or channel diameter in storage in a silo which may be deduced from the combined flow function and wall friction characteristics with a powder rheometer were significantly lower when the polyunsaturated acid, such as linoleic acid, was present at lower concentrations than 7%, preferably lower than 4%, or lower than 2%, and preferably for amounts of between 0.80% and 0.50%. The calculated diameters show a favourable behaviour of the powder in a confined medium (silo).

Example 2

In these examples, use was made, as starting substance, of a technical-grade bicarbonate with a starting particle size of D50= 80 +/- 10 pm (weight-average diameter), ground without additive or with additive according to the procedure described in WO 2007/071666 A1 in Example 1 on page 7. The additives are mixed beforehand using a test weight of 1.8 kg of bicarbonate, occupying a volume of approximately 3 litres, in order to suitably fill (at 2/3) a mixing chamber of a Lodige ploughshare mixer with a volume of 5 litres. This mixing is carried out at 250 revolutions/min and over 3 minutes. The acids are added in the solid form or in the liquid form (molten fatty acids) sprayed by a nozzle giving a circular jet, the flow rate of which is 1 g/min. Such a pre-spreading jet of the fatty acid makes possible a better distribution of the fatty acid over the solid particles and makes it possible to slightly reduce the amounts of fatty acid used per given angle of repose targeted.

• D90: 30 +/- 4 pm

• D50: 13 +/- 2 pm

· D10: 2.9 +/- 0.9 pm

The additives tested were:

• Behenic acid (saturated C22, linear chain)

• Erucic acid (unsaturated C22 : 1 ( 13), linear chain)

• Stearic acid (saturated Cl 8, linear chain)

· Isostearic acid (saturated Cl 8, branched chain)

• Linoleic acid (polyunsaturated C18:2(9,12), linear chain)

• Laurie acid (saturated C12:0, linear chain)

• Caproic acid (saturated C6:0, linear chain)

At: 0, 0.2%, 0.5%, 0.8%, and 1.5% reported to the total weight of the powder.

Results are reported on Table 4.

The results on Table 4 show:

Carr Index and repose angle are decreased (fluidity of the powder is increased) when fatty acid additive are added at same level:

When unsaturated fatty acids are used compared to saturated equivalent fatty acid (Powders 6 to 8 compared to powders 3 to 5; and Powders 9 to

11 compared to powders 18 to 20);

With branched fatty acid used rather than linear fatty acid (Powders 12 to 15 compared to powders 9 to 11).

Also particular good characteristics are obtained with saturated low carbon (C6-C12) fatty acids (Samples 21 to 26).

Additional behavioural characteristics of the powders under stress on a Brookfield PFT (Powder Flow Tester) powder rheometer were produced under different compressive stresses between 0 and 11 kPa,

All ratholes diameters extrapolated from 0.8 to 8.0 m height of product showed decreased ratholes diameters of fatty acid addtive at same level:

When branched fatty acid were used rather than linear fatty acid or When unsaturated fatty acids were used compared to equivalent saturated fatty acids.

Table 4 - Comparative characteristics of the powders obtained without additive and with various content of additive relating to SWF, SWT, Carr index and Angle of repose.

Claims

1. Powder comprising at least 93% of sodium bicarbonate and from 0.01% to 7% of an unsaturated or of a branched saturated C6-C22 carbon fatty acid, or of an alkali metal or alkaline earth metal salt of such an acid, and having preferably less than 1% of sodium carbonate and/ or less than 0.02% of ammonia expressed as NH4+ equivalent.

2. Powder according to the preceding claim, wherein the fatty acid is an unsaturated C6-C22 carbon fatty acid, or an alkali metal or alkaline earth metal salt thereof.

3. Powder according to claim 1, wherein the fatty acid is a branched saturated C6-C22 carbon fatty acid, or an alkali metal or alkaline earth metal salt thereof.

4. Powder according to claim 1, wherein the fatty acid is a linear saturated C6-C12 carbon fatty acid, or an alkali metal or alkaline earth metal salt thereof.

5. Powder according to any one of the preceding claims, wherein the fatty acid, or its alkali metal or alkaline earth metal salt thereof, comprises at least 10 carbons.

6. Powder according to any one of the claims 1 to 3 or 5, wherein the fatty acid, or its alkali metal or alkaline earth metal salt thereof, comprises at most 18 carbons.

7. Powder according to any one of the claims 2 or 5, wherein the unsaturated fatty acid, or its alkali metal or alkaline earth metal salt thereof, is monounsaturated, such as oleic acid.

8. Powder according to any one of the claims 2 or 5, wherein the unsaturated fatty acid, or its alkali metal or alkaline earth metal salt thereof, is polyunsaturated, such as linoleic acid.

9. Powder according to any one of the preceding claims, the fatty acid of which, or its alkali metal or alkaline earth metal salt, is saturated and comprises at most 14 carbons.

10. Powder according to any one of the preceding claims, the fatty acid of which, or its salt, is chosen from: linoleic acid, lauric acid, oleic acid or isostearic acid, or their mixtures, or their alkali metal or alkaline earth metal salts.

11. Powder according to any one of the preceding claims, the fatty acid of 5 which is in the form of fatty acid salt chosen from sodium, potassium,

magnesium or calcium salts.

12. Method for the preparation of a powder according to any one of the preceding claims, comprising a step of mixing the unsaturated C6-C22 carbon fatty acid, or the branched saturated C6-C22 carbon fatty acid, or the saturated Ce lt) C12 carbon fatty acid, or their alkali metal or alkaline earth metal salt, with a sodium bicarbonate comprising less than 1% by weight of sodium carbonate and/or less than 0.02% of ammonia compounds, expressed as ammonia.

13 Use of an unsaturated C6-C22 carbon fatty acid, or of an alkali metal or alkaline earth metal salt thereof, for improving the fluidity of alkali metal 15 bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders, in particular to reduce the angle of repose of the powder or the carr index.

14. Use of a branched saturated C6-C22 carbon fatty acid, or of an alkali metal or alkaline earth metal salt thereof, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate 0 powders, in particular to reduce the angle of repose of the powder or the carr index.

15. Use of saturated linear C6-C12 carbon fatty acid, or of an alkali metal or alkaline earth metal salt thereof, for improving the fluidity of alkali metal bicarbonate, alkali metal carbonate or alkali metal sesquicarbonate powders, in 5 particular to reduce the angle of repose of the powder or the carr index.