WO2005053429A1

WO2005053429A1 - Salt containing flow aid and processes for its manufacture

Info

Publication number: WO2005053429A1
Application number: PCT/EP2004/012243
Authority: WO
Inventors: Amitava Pramanik
Original assignee: Unilever N.V.; Unilever Plc; Hindustan Lever Limited
Priority date: 2003-11-21
Filing date: 2004-10-27
Publication date: 2005-06-16

Abstract

The present invention relates to particulate free flowing common salt and in particular to a process for producing particulate common salt of high flow characteristics by way of a cost-effective and simple process of manufacture. The free flow salt of the invention is storage stable and also of desired taste and flavour. The invention provides food grade flow aid and/or enhancing additives for common salt comprising calcium and/or magnesium salt obtainable by subjecting a calcium and/or magnesium ion impurity of salt to treatment with a selective solution of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate of sodium or potassium.

Description

SALT CONTAINING FLOW AID AND PROCESSES FOR ITS MANUFACTURE

Field of the Invention

The present invention relates to particulate free flowing common salt and in particular to a process for producing particulate common salt of high flow characteristics by way of a cost-effective and simple process of manufacture. The free flow salt of the invention is storage stable and also of desired taste and flavour.

Background Art Common salt is usually manufactured following two basic methods; a) by way of mining of salts in areas which have salt deposits and b) by extracting salt from seawater or sub-soil brine. Usually in places where underground salt deposits are not readily available it is mostly the manufacture of salt from seawater or sub-soil brine that is commonly followed.

In such existing methods of manufacture of salt from seawater or sub-soil brine, the processes usually involve the steps of collecting seawater and evaporating the moisture from the residual salt water at ambient temperature and humidity to produce table salt.

Impurities in raw salt, process for refining them to prepare common salt, and additives that are permitted to be added to common salt are summarized in Chapter 6 of the book "Salt lodization for the Elimination of Iodine Deficiency" (1995) by M.G. Venkatesh Mannar and John T. Dunn.

Purification of raw salt by washing with rain water has been described in "Rain Washing of Common Salt Heaps" in Salt Research and Industry, 10(2), (1974), 13 to reduce the levels of calcium, magnesium and sulphate in salt.

International Journal of Salt Lake Research 6, (1998), 331 reports methods to reduce the levels of calcium, magnesium and sulphate impurities using fractional crystallisation of salt from sub-soil brines which contain high levels of those impurities. US2003/0080066 describes processes for recovery of common salt and other chemicals from brine.

In order to meet the standards of a common table salt (a food grade salt) the raw salt produced from any possible source including as discussed above is required to be refined and also to include additives such as potassium iodide to make it fortified to meet iodine deficiency.

In such conventional methods presently followed for refining of the salt , the raw salt (%wt NaCI = 90-99%wt, %wt Ca = 0.02-0.20%wt, %wt Mg = 0.02-0.8%wt) is initially washed with brine solution (%wt NaCI = 20-25%wt usually) either on a heap or on a washery or refinery. A salt of higher %wt NaCI purity (96-99%wt NaCI, %wt Ca= 0.02-0.16%wt, %wt Mg= 0.02-0.20%wt) is thus obtained. The solid is then separated from the liquid either by draining or in a centrifuge, to get a salt with 3-5%wt moisture. This is then dried either in open sun or in a dryer preferably a fluid bed dryer. For producing iodized salt, potassium iodide/iodate is sprayed on salt before drying.

While the above refining of raw salt and the possible addition of iodide make the salt of desired iodine content and food grade, due to its hygroscopic nature, salt particles usually absorb moisture during storage which lead to lumping or caking of the salt which makes it inconvenient to use and also affected its taste.

It is also known in the art to treat the salt by external aids such as food grade anti- caking, free flowing or conditioning agents to avoid problems of caking/lumping during storage and provide the salt in a free flowing form for effective and proper use and/or application and retain its desired taste/flavour. In order to provide salt with anti-caking and free flowing characteristics, usually up to 2%wt of suitable food grade anti-caking and/or free flowing agents are allowed. Some of the commonly used anti-caking/free flowing agents include sodium ferrocyanide, ferric ammonium citrate, silicon dioxide, aluminium calcium silicate, calcium silicate, magnesium silicate, magnesium carbonate and sodium alumino silicate. Usually the anti-caking and/or free flowing agents are sprayed on salt before drying, and after drying, an inorganic porous water-insoluble powder for example silica, Ca or Mg salts of carbonate or phosphate or silicate, or sodium aluminosilicate is added. Such additives added to the salt facilitate enhancing and retaining the flow properties of the salt by absorbing any moisture present in the salt and aid in keeping the salt surface dry as well as coating the salt surface and preventing inter/granular bridge formation, thereby preventing caking or lumping.

Salt which is a very basic and essential food commodity is required to meet both the standard of a safe food grade product as well as to be cost-effective so that the same can be affordable to one and all. However, it is found that compared to the basic salt which is a readily and cheaply available, the additives such as the flow aids required to impart stable flow properties to the salt are very expensive which in turn add to the cost of the salt produced. Moreover, since the homogeneity of solid-solid mixing at a high throughput is not very good essentially it requires higher dosages/amounts of such flow aids/additives at a level of >0.2% w/w on salt to meet its required purpose.

Thus while salt is a basic necessity and is supposed to be for the consumption of all, the need for avoiding its lumping/caking characteristics for better and effective use of the product by use of the expensive flow aids presently available add to the cost of the salt and make the salt expensive for the common man.

Objects of the Invention

Thus the basic object of the present invention is directed to provide cost-effective flow aids which could provide common salt with the desired storage stability and free flow characteristics without the need of expensive flow aids presently in use.

Another object of the present invention is to provide food grade common salt having free flowing characteristics to avoid caking and lumping on storage which would also be simple and cost-effective to manufacture and thereby affordable to the common man. Another object of the present invention is to provide for common salt, which would have the desired characteristics of free flowing and storage stable character without the need for high levels/ dosages of expensive flow enhancing additives.

Yet another object of the present invention is to provide for common salt of food grade which would maintain desired standards of table salt and achieve homogeneous distribution of flow aids in the salt particles whereby at lower dosage levels of such flow aids the desired high free flow-characteristics can be achieved.

Yet another object of the present invention is directed to provide for a process for manufacture of common salt which would on the one hand provide for better refining of the salt and on the other hand enable production of free flowing table salt without the need to add cost-extensive additional flow aids and the like.

Yet another object of the present invention is directed to providing a free flowing table salt which would achieve the flow aid/properties during the usual refining process of the salt and thereby avoid complications and higher dosage of flow aids additives to favour cost-effective and safe food grade table salt.

Yet another object of the present invention is directed to providing process for manufacture of free flowing salt which would be storage stable wherein the free flow characteristics to the salt are provided during refining of the salt which apart from being simple and cost-effective also enables high homogeneous distribution of the flow aid properties in the salt produced to be achieved.

Yet another object of the present invention is directed to providing table salt having free flow properties involving the conventional manufacturing/refining stages and which would require lower dosage levels but yet achieve better flow behaviour than that achieved by addition of external expensive flow aids.

The present invention seeks to address one or more of the above problems. Summary of the invention

Thus according to the first aspect of the invention there is provided a food grade flow aid and/or enhancing additives for common salt comprising calcium and/or magnesium salt obtainable by subjecting a calcium and/or magnesium ion impurity of salt to treatment with a selective solution of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate of sodium or potassium.

According to a further aspect of the invention there is provided a food grade common salt comprising salt particles with flow enhancing calcium and/or magnesium salt formed thereon obtainable by subjecting the calcium and/or magnesium ion impurity of salt to treatment with a selective solution of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate of sodium or potassium.

According to a further aspect of the present invention there is provided a free flowing salt composition comprising: basic common salt particulates and calcium and/or magnesium salt based flow enhancing agent obtainable from calcium and/or magnesium ion impurity of salt.

It is preferred according to the present invention that the free flowing salt composition is synergistic.

The above salt compositions of the invention can additionally comprise other food grade additives such as ferric ammonium citrate, green iron ammonium citrate, green ferric citrate, green ferric ammonium citrate, silicon dioxide, yellow prussiate of soda (YPS, sodium ferrocyanide decahydrate), aluminum calcium silicate, calcium silicate (calcium metasilicate), magnesium silicate, magnesium carbonate, sodium aluminosilicate (Zeolex), sodium silicoaluminate or tricalcium silicate. According to a further aspect of the invention there is provided a process for the manufacture of a free flowing salt composition comprising : a. providing refined common salt ; and b. providing calcium and/or magnesium salt based flow enhancing agent obtainable from calcium and/or magnesium ion impurities of the salt, c. and mixing a) and b) together.

In the above process of the invention the salt composition is obtained preferably from refined salt having %wt NaCI= 96-99%wt, %wt Ca= 0.02-0.16%wt, %wt Mg = 0.02- 0.20%wt and 3-5% moisture.

According to a preferred aspect of the process of the invention there is provided a process for manufacture of free flowing salt as according to the invention, the process comprising the steps of: 1. providing salt, preferably with %NaCI purity 96-99%wt, 0.02-0.16%wt calcium, 0.02 - 0.20%wt magnesium and 3-5% moisture; 2. providing a solution of Na and/or K salt of at least one of carbonate, bicarbonate, phosphate, silicate or aluminate; 3. spraying the solution of step 2 on the salt; and 4. subjecting the thus sprayed solution and salt to drying to thereby obtain the free flowing salt.

It is especially preferred that in step 3 of the above method the spraying occurs with additional food grade additives preferably potassium ferocyanide and potassium iodate solution.

Detailed Description of the Invention

It is thus possible by way of the present invention to provide solid inorganic particulates from refining solar salt by spraying a solution of water soluble salts on moist salt pre-drying. These particulates after drying serve as effective flow enhancers and can be used in generating and maintaining free flow common salt. Solar salt always contains calcium and magnesium ions as impurities along with sodium chloride. It is found byway of the present invention that when a solution of carbonate, bicarbonate, phosphate, or silicate of sodium or potassium is sprayed on salt, precipitates of the corresponding calcium and/or magnesium salts can be produced which are surprisingly found to be cost-effective and better flow enhancers of common salts. Such flow aids can be generated in-situ by spraying of cost-effective sodium/potassium salt on moist common salt and upon drying, the flow behaviour of the latter improves. Alternately, it is also possible to produce such flow aids separately and then mixing with refined salt to provide salt with higher free flow characteristics.

The salt obtained as above with the flow aid obtained by refining of calcium and magnesium ion impurities is found to provide for cost-effective as well as high purity salt suitable as food grade salt. Advantageously, it is also found that the present in- situ generated flow aid incorporated salt of the invention could achieve enhanced flow properties at lower dosages than the externally added flow aids such as potassium ferrocyanide of the known art. This would enable good quality free flowing salt to be produced cost-effectively.

As discussed above in accordance with a preferred aspect of the present invention the method involves providing in situ such flow aids during drying of solar salt itself in a refinery. Solar salt is always accompanied with calcium and magnesium ion as impurities. Thus, when a selective solution of sodium and/or potassium salt of carbonate or bicarbonate or phosphate or silicate is sprayed on moist solar salt, it precipitates the corresponding calcium and/or magnesium salt on the salt surface and during drying of salt, gets dried with high homogenous distribution. Thus the flow behaviour of the salt is enhanced at a low dosage of the spray of sodium or potassium salt of carbonate or bicarbonate or phosphate or silicate. Since the sodium and/or potassium salts of carbonate or bicarbonate or phosphate or silicate are cheaper and the dosage level for getting equivalent flow behaviour is lower, the cost for flow enhancement of salt is significantly lower than post dosage of flow aids. The details of the invention its objects and advantages are explained hereunder in greater detail in relation to non-limiting exemplary illustrations hereunder:

Examples Exemplary preparation of the salts according to the invention were carried out under Examples 1 to 6 using varied solutions of the selected sodium salt with or without additional external flow aid such as silica as detailed in Table I. Further examples within the scope of the present invention will be apparent to the person skilled in the art.

TABLE - 1

The process followed was as discussed hereunder: Providing the refined salt with high %wt NaCI purity 96-99%wt, %wt Ca = 0.02- 0.16%wt and %wt Mg = 0.02 - 0.20%wt and 3-5%wt moisture; providing the selected solution of Na salt of carbonate/bicarbonate, and spraying the same on the salt with or without additional flow aid silica, subjecting the thus sprayed solution and salt to drying to thereby obtain the free flowing salt.

The flow properties of the salt obtained under Example 1 to 6 above were compared with flow properties of the conventional salt having only externally added flow aid magnesium carbonate/silica (Examples A to D). For the purpose the flow property was measured following conventional method wherein the respective salts were allowed to pass through a 300 ml glass cylinder and the rate of flow (volume flowed per unit time) was measured. The results were noted and detailed hereunder in Table-ll

TABLE - II

As is clearly apparent from Table II above the salt of the invention incorporating the Ca/Mg impurity transformed flow aid using solution of sodium/potassium salts of silicate/orthophosphate/carbonate/sodium bicarbonate (Examples 1 to 6) achieved much improved flow properties in the range of 180-230 ml/sec. vis-a-vis the externally added flow aid (Examples A to D) of 80-170 ml/sec.

It is thus possible by way of the present invention to cost-effectively provide common salt with free flow properties by selective use of the Ca/Mg impurities of the raw salt. Such a salt of the invention on one hand achieves the required flow properties and on the other hand is cost-effective. Advantageously, the process of manufacture of the free flow salt of the invention is such that the same can be obtained following the known conventional process of refining of salts whereby on one hand the salt is refined to greater purity and on the other hand the flow properties can be enhanced cost-effectively.

Claims

1. Food grade flow aid and/or enhancing additives for common salt comprising calcium and/or magnesium salt obtainable by subjecting a calcium and/or magnesium ion impurity of salt to treatment with a selective solution of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate of sodium or potassium.

2. Food grade flow aid/enhancing additives for common salt as claimed in claim 1 having flow properties in the range of from 180 to 230 ml./sec.

3. Food grade common salt comprising salt particles with flow enhancing calcium and/or magnesium salt formed thereon obtainable by subjecting the calcium and/or magnesium ion impurity of salt to treatment with a selective solution of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate of sodium or potassium.

4. A food grade common salt as claimed in claim 3 having flow properties in the range of from 180 to 230 mlJsec.

5. A free flowing salt composition comprising: basic common salt particulates and calcium and/or magnesium salt based flow enhancing agent obtainable from calcium and/or magnesium ion impurity of salt.

6. A free flowing salt composition as claimed in claim 5 comprising: basic common salt particulate and calcium and/or magnesium salt based flow enhancing agent obtained from calcium and/or magnesium ion impurity of raw salt provided selectively as particulates and/or at least partial deposits or coating on the salt particles.

7. A free flowing salt composition as claimed in either one of claims 5 or 6 comprising other food grade additives preferably selected from ferric ammonium citrate, green iron ammonium citrate, green ferric citrate, green ferric ammonium citrate, silicon dioxide, yellow prussiate of soda, aluminum calcium silicate, calcium (meta) silicate, magnesium silicate, magnesium carbonate, sodium aluminosilicate, potassium ferrocyanide and potassium iodide.

8. A free flowing salt composition as claimed in any one of claims 5 to 7 wherein the salt is iodized.

9. A free flowing salt composition as claimed in any one of claims 5 to 8 having an improved flow property in the range of from 180 to 230 ml./sec.

10. A process for the manufacture of a free flowing salt composition comprising : a. providing refined common salt ; and b. providing calcium and/or magnesium salt based flow enhancing agent obtainable from calcium and/or magnesium ion impurities of the salt, c. and mixing a) and b) together.

11. A process as claimed in claim 10 wherein the salt composition is obtained from refined salt comprising 96-99%wt NaCI, 0.02-0.16%wt calcium, 0.02-0.20%wt magnesium and 3-5%wt moisture.

12. A process as claimed in either one of claims 10 or 11 wherein the salt composition additionally comprise other conventional additives selected from ferric ammonium citrate, green iron ammonium citrate, green ferric citrate, green ferric ammonium citrate, silicon dioxide, yellow prussiate of soda, aluminum calcium silicate, calcium (meta) silicate, magnesium silicate, magnesium carbonate, sodium aluminosilicate silicate, potassium ferrocynide and potassium iodate solution.

13. A process for manufacture of free flowing salt as claimed in any one of claims 10 to 12, the process comprising the steps of:

1. providing salt, preferably with 96-99%wt %NaCI purity, 0.02-0.16%wt calcium, 0.02 - 0.20%wt magnesium and 3-5% moisture; 2. providing a solution of Na and/or K salt of at least one of carbonate, bicarbonate, phosphate, silicate and aluminate; 3. spraying the solution of step 2 on the salt; and 4. subjecting the thus sprayed solution and salt to drying to thereby obtain the free flowing salt.

14. A process for manufacture of free flowing salt as claimed claim 13 wherein in step 3 the spraying occurs with additional food grade additives preferably potassium ferocinite and potassium iodate solution.

15. A process as claimed in any one of claims 10 to 14 wherein the calcium or magnesium ion impurity based flow aids are generated in-situ by spraying the sodium or potassium salt on moist common salt followed by drying.

16. A process as claimed in any one of claims 10 to 12 wherein said calcium or magnesium ion impurity based flow aids are separately obtained and then mixed with refined salt to provide salt with higher free flow characteristics.

17. A process as claimed in any one of claims 10 to 16 wherein a spray of sodium and/or potassium salt of carbonate or bicarbonate or phosphate or silicate or aluminate with or without additional flow aids is applied and is chosen from 0.1 %wt sodium carbonate, 0.2%wt sodium carbonate, 0.1 %wt sodium carbonate plus 0.1 %wt silica, 0.2%wt sodium carbonate plus 0.1%wt silica, 0.05%wt sodium bicarbonate, 0.05%wt sodium bicarbonate plus 0.1% silica.

18. A process as claimed in anyone of claims 10 to 17 comprising adding external flow aid.

9. A food grade flow aid/enhancing additives for common salt and a process for manufacturing the same substantially as hereindescribed with reference to the accompanying examples.