Title of Invention	A PROCESS FOR PREPARING FREE-FLOWING COATED SALTS OF SODIUM SELECTED FROM SODIUM NITRITE, SODIUM NITRATE OR A MIXTURE THEREOF
Abstract	The present invention relates to a process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof comprising (a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residual moisture content of less than 0.2% by weight, (b) the step of cooling the dried salt to below about 40°C and (c) the step of coating said salt/salts with either silica or tricalcium silicate or a combination thereof. PRICE: THIRTY RUPEES

Title of Invention

A PROCESS FOR PREPARING FREE-FLOWING COATED SALTS OF SODIUM SELECTED FROM SODIUM NITRITE, SODIUM NITRATE OR A MIXTURE THEREOF

Abstract

The present invention relates to a process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof comprising (a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residual moisture content of less than 0.2% by weight, (b) the step of cooling the dried salt to below about 40°C and (c) the step of coating said salt/salts with either silica or tricalcium silicate or a combination thereof. PRICE: THIRTY RUPEES

Full Text	! The present invention relates to an improved process for prepar-.ng free-flowing sodium nitrite and/or sodium nitrate. ?he preparation of sodium nitrite or sodium nitrate has long been mown and is therefore extensively described in the literature. .'he preparation usually proceeds, as described for example in Dl DE-A 3125616), by reacting nitrous gases with sodium hydroxide solution at about from 20 to 80°C (Dl, p. 2 and 4), The product :hus obtained is precipitated out by evaporating the mother .iquor and is then dried, for example in a rotary tubular fur-lace, and then cooled (Dl, Example). Jodium nitrite and sodium nitrate are used in many ways. Typical ireas of use are, for example, in fertilizers, the production of jlass and surface and heat treatment of metals and, in particu¬lar, in the food industry, for instance as additives in the pro¬duction of curing salt. iowever, because of their relatively high hygrosccpicity, the two salts, in particular sodium nitrite, have a marked tendency to slumping. Even when relatively small amounts of these salts are stored, this causes large and hard agglomerates to form rapidly tfhich need to be treated at great expenditure before further pro¬cessing in order to obtain them in a transportable and dosable Eorm. figure 1/shows by way of example a hitherto conventional treat¬ment stage for aggregated sodium nitrite and/or sodium nitrate. The salt agglomerates (1) are fed to a roller crusher (2), where the agglomerates are crushed with high energy consumption. The crushed products are discharged (3) from the roller crusher and fed (5) via a belt (4) to the screen (6). In this screen, the crushed material is separated into a coarse fraction (7) and a fine fraction (10). The coarse fraction is" re¬turned to the roller crusher via the belts/elevators (8) and (9) for further crushing. The fine fraction is run into a fine-mate¬rial hopper (11). Because of the hygroscopicity mentioned at the outset and the associated tendency to form large and hard agglomerates, further¬more, loose storage of relatively large amounts of sodium nitrite and/or sodium nitrate, for example in a silo or in a relatively large container (eg. in a "Big bag") has not been able to be jracticed economically, since withdrawal from these containers iven a short time later was only possible at best with great ex-)enditure. although the use of silicas to improve flowability in products laving a tendency to agglomeration is generally known and is de¬scribed, for example, in document D2 (publication by Degussa AG, Jr. Horst Ferch, Rolf Oelmuller, "Synthetische Kieselsauren als fliefihilfsmittel und als Tragersubstanz" [Synthetic silicas as iid to free running and as carrier substance]), those skilled in ;he art did not expect any advantages of using these aids in the ;ase of sodium nitrite and/or sodium nitrate. This is verified lot only by the hitherto conventional procedure described at the cutset involving the further processing of corresponding agglom¬erates, but also by the fact that in D2, despite extensively Listing of suitable substances, there are no references to the suitability of these substances in the case of sodium nitrite jnd/or sodium nitrate. besides the extensive examples, only the addition of silicas in ;he case of inorganic salts and industrial salts is mentioned in general, it being stated also, however, that in the case of high-density and finely divided substances and highly hygroscopic products, good flowability causes difficulties (see page 33). En the surface treatment and heat treatment of metals, metal parts to be tempered are generally immersed in melts which, in addition to usual additives, essentially contain molten sodium nitrite. Here, to produce the melt, attempts were made to use so¬dium nitrite whose flowability had been improved by the addition af sodium salts of phenylethylnaphthalenesulfonic acid. However, enrichment of this organic additive at the surface of the melt due to flotation was observed in this case and at the prevailing temperatures of from about 300 to 400C, a vigorous exothermic reaction of this additive with oxygen could sometimes be ob¬served. Therefore, in these applications, untreated sodium ni¬trite is generally used which, however, must be treated in ad¬vance with the expenditure described at the outset. Since both sodium nitrite and sodium nitrate can serve as inter¬mediates for the production of substances for which there are high requirements of product purity and safety, other known coat¬ings or aids such as, for example, amines, are also not used here. It is an object of the present invention to find an improved pro¬cess which enables readily free-flowing sodium nitrite and/or so¬dium nitrate to be prepared in a simple and economical manner in terms of processing technique. The process should further enable products having long-term good flowability to be produced in such a purity that they can also satisfy high requirements such as are encountered, for example, in the food industry. We have found that this object is achieved by a process for pre¬paring free-flowing sodium nitrite and/or sodium nitrate, which comprises, after drying and cooling, coating the sodium nitrite and/or sodium nitrate with silica and/or tricalcium phosphate. The invention further relates to the use of the salts obtainable according to the invention for producing curing salt and to the use of silica and/or tricalcium phosphate for coating sodium ni¬trite and/or sodium nitrate suitable for producing curing salt. The novel process is described schematically in more detail below with reference to Figure 2. The moist sodium nitrite and/or sodium nitrate is passed via (1) into a drying stage (2). Drying apparatuses which are suitable are, for example, rotary tubular furnaces or fluidized-bed dryers. The drying is usually performed at from about 100 to 300°C, and the residence time is from about 0.25 to 0.50 hours. The salt is generally dried to a residual moisture content of less than 0.2, preferably 0.05> % by weight. The dried salt is then fed via (3) to a cooling stage (4). The product is cooled here to below about 40C, preferably below about 30°C. Rotary drums or fluidized-bed coolers, for example, can be used for the cooling. The cooled crystals are passed by the conveying means (6) to a mixer {7). In addition, the coating substance is fed to the mixer from the storage vessel (8) via the metering apparatus (9) and line (10). The two components are brought into contact with one another in the mixer so intensively that the surface of the salt crystals is furnished with a homogeneous layer of the coating substance. This mixing process can be performed either continu¬ously or discontinuously. Mixing apparatuses which can be used are, for example, simple concrete mixers (discontinuous) or, pre¬ferably, continuous flowthrough mixers having internal paddles, such as are distributed, for example, by the Drais company under the Tornado type. The percentages by weight of added salt and coating substance are from about 0.1 to 1.0% by weight, prefer¬ably from 0.2 to 0.4% by weight, particularly preferably from 0.2 to 0.3% by weight, based on the mixture. The residence time in the mixer is from about 1 to 10 min, preferably from 1 to 2 min, and the temperature in the mixing operation is from about 20 to 40°C. The mixing operation is performed with relatively little shear stress, the essential aim in this process step being to wet the surface of the salt intensively with the coating substance. The thickness of the layer of the coating substance on the salt crystals can be influenced by varying process parameters such as the ratio of salt to coating substance or residence time in the mixer. Usually, attempts are made to keep the layer thicknesses as low as possible in order not to cause any significant impair¬ment in the solubility and reactivity of the salt crystals. The layer thicknesses achieved are from about 50 μm to 500 μm, prefer¬ably from 100 μm to 200 urn, particularly preferably from 100 nm to 150 \|μm. The layer thicknesses were calculated from the amounts of sub¬stances required when samples were prepared. In order to ensure a constantly beneficial and reproducible ratio between salt and coating substance in the mixer, the two streams can be linked by a control method in a known manner. The coated sodium nitrate and/or sodium nitrite crystals thus ob¬tained are fed to a storage vessel via line (11). Advantageously, the salt crystals thus treated have long-term good flowability, so that the storage vessels used can also be relatively large and thus more economical vessels such as silos or Big bags. Further advantages result directly therefrom; thus, for example, this en¬ables economic buffering between production and logistics. In addition, the complex precomminution of hardened salt crystals previously described can be dispensed with. This proves to be ad¬vantageous, in particular, when the salts are later used in pro¬cesses where there are high requirements of product purity, since avoidance of this processing stage can avoid possible sources of » contamination. As coating substance, use is made of silica and/or tricalcium phosphate. Coating with one of these substances prevents both di¬rect contact of the crystals with one another and diffusion of i moisture to the crystal surface. Furthermore, the two coating substances do not react with sodium nitrate or sodium nitrite un¬der the usual conditions. Surprisingly, in the case of both coat- ing substances, even relatively small amounts are sufficient in order to ensure good flowability of sodium nitrate and sodium ni¬trite which have a strong tendency to agglomerate formation. De¬pending on the application, the use of silica as, eg., synthetic silica, or of tricalcium phosphate is particularly advisable. Since the two coating substances are also permitted in the food industry, this gives further advantages. Thus, sodium nitrite coated with small amounts of silica, because of its good flow-ability, can be used in the production of curing salt simply and economically in terms of processing technique. Curing salt con¬ventionally comprises a mixture of common salt and small amounts, about 0.5% by weight, of sodium nitrite. The process according to the invention offers the possibility of preparing readily free-flowing sodium nitrite and/or sodium ni¬trate in a simple and economical manner in terms of processing technique. The products produced by this process have longer-term good flowability with high purity, so that they can satisfy even high requirements as are made, for ex""-'!«- i« the food industry. Accordingly, the present invention provides a process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof comprising (a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residual moisture content of less than 0.2% by weight, (b) the step of cooling the dried salt to below about 40°C and (c) the step of coating said salt/salts with either silica or tricalcium silicate or a combination thereof. To test the processing properties of sodium nitrite coated with finely divided silica in the production of curing salt, approxi¬mately 1000 kg of sodium nitrite were dried to a residual mois¬ture content of less than 0.2% by weight, then cooled to below about 30*C and coated with finely divided si02 batchwise in a con¬crete mixer as follows. For this purpose, batches each of 50 leg containing 100 g of Si02 were charged into a 150 1 concrete mixer and mixed at 34 rpm. for approximately 10 minutes. To improve mix¬ing, the mixer was equipped with a double blade. The coated product was packaged from the mixer directly into the conventional packaging. Despite a storage time of some weeks, the sodium nitrite coated with finely divided silica could be processed directly completely without the expenditure on treatment necessary hitherto. WE CLAIM: 1. A process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof comprising (a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residua! moisture content of less than 0.2% by weight, (b) the step of cooling the dried salt to below about 40°C and (c) the step of coating said salt/salts with either silica or tricalcium silicate or a combination thereof. 2. The process as claimed in claim 1, wherein the sodium nitrite and/or sodium nitrate and silica and/or tricalcium phosphate are placed in a mixer, the proportion of silica and/or tricalcium phosphate being from 0.1 to 1.0% by weight. 3. A process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof substantially as herein described and exemplified.

Full Text

!

The present invention relates to an improved process for prepar-.ng free-flowing sodium nitrite and/or sodium nitrate.
?he preparation of sodium nitrite or sodium nitrate has long been mown and is therefore extensively described in the literature. .'he preparation usually proceeds, as described for example in Dl DE-A 3125616), by reacting nitrous gases with sodium hydroxide solution at about from 20 to 80°C (Dl, p. 2 and 4), The product :hus obtained is precipitated out by evaporating the mother .iquor and is then dried, for example in a rotary tubular fur-lace, and then cooled (Dl, Example).
Jodium nitrite and sodium nitrate are used in many ways. Typical ireas of use are, for example, in fertilizers, the production of jlass and surface and heat treatment of metals and, in particu¬lar, in the food industry, for instance as additives in the pro¬duction of curing salt.
iowever, because of their relatively high hygrosccpicity, the two salts, in particular sodium nitrite, have a marked tendency to slumping. Even when relatively small amounts of these salts are stored, this causes large and hard agglomerates to form rapidly tfhich need to be treated at great expenditure before further pro¬cessing in order to obtain them in a transportable and dosable Eorm.
figure 1/shows by way of example a hitherto conventional treat¬ment stage for aggregated sodium nitrite and/or sodium nitrate. The salt agglomerates (1) are fed to a roller crusher (2), where the agglomerates are crushed with high energy consumption. The crushed products are discharged (3) from the roller crusher and fed (5) via a belt (4) to the screen (6).
In this screen, the crushed material is separated into a coarse fraction (7) and a fine fraction (10). The coarse fraction is" re¬turned to the roller crusher via the belts/elevators (8) and (9) for further crushing. The fine fraction is run into a fine-mate¬rial hopper (11).
Because of the hygroscopicity mentioned at the outset and the associated tendency to form large and hard agglomerates, further¬more, loose storage of relatively large amounts of sodium nitrite and/or sodium nitrate, for example in a silo or in a relatively large container (eg. in a "Big bag") has not been able to be

jracticed economically, since withdrawal from these containers iven a short time later was only possible at best with great ex-)enditure.
although the use of silicas to improve flowability in products laving a tendency to agglomeration is generally known and is de¬scribed, for example, in document D2 (publication by Degussa AG, Jr. Horst Ferch, Rolf Oelmuller, "Synthetische Kieselsauren als fliefihilfsmittel und als Tragersubstanz" [Synthetic silicas as iid to free running and as carrier substance]), those skilled in ;he art did not expect any advantages of using these aids in the ;ase of sodium nitrite and/or sodium nitrate. This is verified lot only by the hitherto conventional procedure described at the cutset involving the further processing of corresponding agglom¬erates, but also by the fact that in D2, despite extensively Listing of suitable substances, there are no references to the suitability of these substances in the case of sodium nitrite jnd/or sodium nitrate.
besides the extensive examples, only the addition of silicas in ;he case of inorganic salts and industrial salts is mentioned in general, it being stated also, however, that in the case of high-density and finely divided substances and highly hygroscopic products, good flowability causes difficulties (see page 33).
En the surface treatment and heat treatment of metals, metal parts to be tempered are generally immersed in melts which, in addition to usual additives, essentially contain molten sodium nitrite. Here, to produce the melt, attempts were made to use so¬dium nitrite whose flowability had been improved by the addition af sodium salts of phenylethylnaphthalenesulfonic acid. However, enrichment of this organic additive at the surface of the melt due to flotation was observed in this case and at the prevailing temperatures of from about 300 to 400*C, a vigorous exothermic reaction of this additive with oxygen could sometimes be ob¬served. Therefore, in these applications, untreated sodium ni¬trite is generally used which, however, must be treated in ad¬vance with the expenditure described at the outset.
Since both sodium nitrite and sodium nitrate can serve as inter¬mediates for the production of substances for which there are high requirements of product purity and safety, other known coat¬ings or aids such as, for example, amines, are also not used here.

It is an object of the present invention to find an improved pro¬cess which enables readily free-flowing sodium nitrite and/or so¬dium nitrate to be prepared in a simple and economical manner in terms of processing technique. The process should further enable products having long-term good flowability to be produced in such a purity that they can also satisfy high requirements such as are encountered, for example, in the food industry.
We have found that this object is achieved by a process for pre¬paring free-flowing sodium nitrite and/or sodium nitrate, which comprises, after drying and cooling, coating the sodium nitrite and/or sodium nitrate with silica and/or tricalcium phosphate.
The invention further relates to the use of the salts obtainable according to the invention for producing curing salt and to the use of silica and/or tricalcium phosphate for coating sodium ni¬trite and/or sodium nitrate suitable for producing curing salt.
The novel process is described schematically in more detail below with reference to Figure 2.
The moist sodium nitrite and/or sodium nitrate is passed via (1) into a drying stage (2). Drying apparatuses which are suitable are, for example, rotary tubular furnaces or fluidized-bed dryers.
The drying is usually performed at from about 100 to 300°C, and the residence time is from about 0.25 to 0.50 hours. The salt is generally dried to a residual moisture content of less than 0.2, preferably 0.05> % by weight.
The dried salt is then fed via (3) to a cooling stage (4). The product is cooled here to below about 40*C, preferably below about 30°C. Rotary drums or fluidized-bed coolers, for example, can be used for the cooling.
The cooled crystals are passed by the conveying means (6) to a mixer {7). In addition, the coating substance is fed to the mixer from the storage vessel (8) via the metering apparatus (9) and line (10). The two components are brought into contact with one another in the mixer so intensively that the surface of the salt crystals is furnished with a homogeneous layer of the coating substance. This mixing process can be performed either continu¬ously or discontinuously. Mixing apparatuses which can be used are, for example, simple concrete mixers (discontinuous) or, pre¬ferably, continuous flowthrough mixers having internal paddles, such as are distributed, for example, by the Drais company under

the Tornado type. The percentages by weight of added salt and coating substance are from about 0.1 to 1.0% by weight, prefer¬ably from 0.2 to 0.4% by weight, particularly preferably from 0.2 to 0.3% by weight, based on the mixture. The residence time in the mixer is from about 1 to 10 min, preferably from 1 to 2 min, and the temperature in the mixing operation is from about 20 to 40°C. The mixing operation is performed with relatively little shear stress, the essential aim in this process step being to wet the surface of the salt intensively with the coating substance.
The thickness of the layer of the coating substance on the salt crystals can be influenced by varying process parameters such as the ratio of salt to coating substance or residence time in the mixer. Usually, attempts are made to keep the layer thicknesses as low as possible in order not to cause any significant impair¬ment in the solubility and reactivity of the salt crystals. The layer thicknesses achieved are from about 50 μm to 500 μm, prefer¬ably from 100 μm to 200 urn, particularly preferably from 100 nm to 150 |μm.
The layer thicknesses were calculated from the amounts of sub¬stances required when samples were prepared.
In order to ensure a constantly beneficial and reproducible ratio between salt and coating substance in the mixer, the two streams can be linked by a control method in a known manner.
The coated sodium nitrate and/or sodium nitrite crystals thus ob¬tained are fed to a storage vessel via line (11). Advantageously, the salt crystals thus treated have long-term good flowability, so that the storage vessels used can also be relatively large and thus more economical vessels such as silos or Big bags. Further advantages result directly therefrom; thus, for example, this en¬ables economic buffering between production and logistics. In addition, the complex precomminution of hardened salt crystals previously described can be dispensed with. This proves to be ad¬vantageous, in particular, when the salts are later used in pro¬cesses where there are high requirements of product purity, since avoidance of this processing stage can avoid possible sources of » contamination.
As coating substance, use is made of silica and/or tricalcium phosphate. Coating with one of these substances prevents both di¬rect contact of the crystals with one another and diffusion of i moisture to the crystal surface. Furthermore, the two coating substances do not react with sodium nitrate or sodium nitrite un¬der the usual conditions. Surprisingly, in the case of both coat-

ing substances, even relatively small amounts are sufficient in order to ensure good flowability of sodium nitrate and sodium ni¬trite which have a strong tendency to agglomerate formation. De¬pending on the application, the use of silica as, eg., synthetic silica, or of tricalcium phosphate is particularly advisable.
Since the two coating substances are also permitted in the food industry, this gives further advantages. Thus, sodium nitrite coated with small amounts of silica, because of its good flow-ability, can be used in the production of curing salt simply and economically in terms of processing technique. Curing salt con¬ventionally comprises a mixture of common salt and small amounts, about 0.5% by weight, of sodium nitrite.
The process according to the invention offers the possibility of preparing readily free-flowing sodium nitrite and/or sodium ni¬trate in a simple and economical manner in terms of processing technique. The products produced by this process have longer-term good flowability with high purity, so that they can satisfy even high requirements as are made, for ex*""-'!«*- i« the food industry.

Accordingly, the present invention provides a process for preparing free-flowing coated salts of sodium selected from sodium nitrite, sodium nitrate or a mixture thereof comprising (a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residual moisture content of less than 0.2% by weight, (b) the step of cooling the dried salt to below about 40°C and (c) the step of coating said salt/salts with either silica or tricalcium silicate or a combination thereof.

To test the processing properties of sodium nitrite coated with finely divided silica in the production of curing salt, approxi¬mately 1000 kg of sodium nitrite were dried to a residual mois¬ture content of less than 0.2% by weight, then cooled to below about 30*C and coated with finely divided si02 batchwise in a con¬crete mixer as follows. For this purpose, batches each of 50 leg containing 100 g of Si02 were charged into a 150 1 concrete mixer and mixed at 34 rpm. for approximately 10 minutes. To improve mix¬ing, the mixer was equipped with a double blade.
The coated product was packaged from the mixer directly into the conventional packaging.
Despite a storage time of some weeks, the sodium nitrite coated with finely divided silica could be processed directly completely without the expenditure on treatment necessary hitherto.

WE CLAIM:
1. A process for preparing free-flowing coated salts of sodium selected from
sodium nitrite, sodium nitrate or a mixture thereof comprising
(a) the step of drying the moist sodium nitrite and/or sodium nitrate at from 100 to 300°C to a residua! moisture content of less than 0.2% by weight,
(b) the step of cooling the dried salt to below about 40°C and
(c) the step of coating said salt/salts with either silica or tricalcium silicate
or a combination thereof.
2. The process as claimed in claim 1, wherein the sodium nitrite and/or sodium
nitrate and silica and/or tricalcium phosphate are placed in a mixer, the
proportion of silica and/or tricalcium phosphate being from 0.1 to 1.0% by
weight.
3. A process for preparing free-flowing coated salts of sodium selected from
sodium nitrite, sodium nitrate or a mixture thereof substantially as herein
described and exemplified.

Documents:

1238-mas-1996 abstract.pdf

1238-mas-1996 claims.pdf

1238-mas-1996 correspondence others.pdf

1238-mas-1996 correspondence po.pdf

1238-mas-1996 description (complete).pdf

1238-mas-1996 drawings.pdf

1238-mas-1996 form-1.pdf

1238-mas-1996 form-26.pdf

1238-mas-1996 form-4.pdf

1238-mas-1996 petition.pdf

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Patent Number

194956

Indian Patent Application Number

1238/MAS/1996

PG Journal Number

08/2007

Publication Date

23-Feb-2007

Grant Date

05-Jan-2006

Date of Filing

12-Jul-1996

Name of Patentee

M/S. BASF AKTIENGESELLSCHAFT

Applicant Address

67056, LUDWIGSHAFEN

Inventors:

#	Inventor's Name	Inventor's Address
1	HANS JURGEN EISEN,	NEBRUNING-STR.7, 67071 LUDWIGSHAFEN

PCT International Classification Number

C01D9/20

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA