CA1275607C - Sodium phosphate composition and process - Google Patents

Abstract

ABSTRACT

A Particulate hydrated trisodium phosphate composition useful in heavy duty cleansers has a core and shell structure, the shell being of trisodium phosphate hexahydrate and the core comprising trisodium orthophosphate dodecahydrate and sodium hydroxide. The composition may be made by prilling to form an intermediate body with solid shell and a liquid or solid/liquid core followed by further cooling.

Description

SODIUM PHOSPHATE COMPOSITION AND PROCESS
.

This invention relates to phosphate compositions, in particular ones comprising trisodium phosphate, and processes for making them.

Trisodium phosphate c~ystalliæes ~n anhydrous and many hydrated forms including ~he hemi-, hexa-, octa- and dodeca- hydrate forms (see J.R. Van Wazer "Phosphorus and its Conpounds" Yol.1 page 494).
Foremost among these commercially is the dodecahydrate (Na3 P04.
12H20) but this compound, as crystallized~ usually has an analysis showing the presence of an excess of sodium hydroxide with an Na:P
atom ratio of 3.14 or 3025:1. Mixtures of trisodium phosphate with sodium nitrite or nitrate etc, also crystallize to give mixed salt crystals with small extra amounts of the nitrite or nitrate, etc anion. (see Van Wazer Phosphorus and Its Compounds Vol 1, page 494 and 495). The dodecahydrate is usually obtained by crystallization but there have been proposals and uses many years ago of spray drying and spray cooling to give solid dodecahydrate ~see BIOS
Report 1557, Manufac~ure of Technical Phosphates in West Germany, 1946, pages 30-33) and disclosures of flaking and also spraying into a cooling chamber (Phosphoric Acid Phosphates and Phosphatic Fertilizers by W.H, Waggaman published by Reinhold 1952, Second Edition page 236). However these processes were not con~inued later and the commercial dodesahydrate has for very many years been the crysta11ine material w~th the excess of alkali. But this product is well known to cake on storage and not be a free flowing powder, making its handling more difficult.

We have now discovered a trisodium phosphate composition which can have reduced caking properties and improved flow properties compared to the crystalline dodecahydrate.

The present invention provides a particulate solid hydrated phospha~e composition co0prising ~risodium phosphate and sodium hydroxide w~th the ratio of the number of atoms to sodium to the number of atoms of phosphorus to the number of moles of hydroxyl group (here~nafter called the rat~o of Na:P:OH) being 3.1-3.2:1:0.1-.27~ )7 ~2--0.2, and the overall ratio of the number of phosphorus atoms to thenumber of water molecules (hereinafter called the P:H20 ratlo) of 1:8-11, the solid composition having an outer layer comprising trisodium phosphate hexahydrate and a core containing trisodium phosphate dodecahydrate and sodium hydroxide, which are believed to be present as a solid solution.

The present invention also provides a process for preparing a particulate solid hydrated phosphate composi~ion, wherein an aqueous solution at 90-120C of trisodium phosphate and sodium hydroxide, wherein the atomic ratio of Na:P:OH is 3.1-3.2:1:0.1-0.2 and a P:H20 ratio of 1:10-14 is formed into droplets and rapidly chilled substantially out of contact with one another by counter current contact with air to produce particles of an intermediate body with a solid outer layer of trisodium phosphate hexahydrate enclosing a core containing aqueous medium comprising trisodium phosphate and sodium hydroxide and the said particles of the inter~ediate body are cooled further to give a so7id phosphate composition of P:H20 ratio of 1:8-11 having an outer layer comprislng trisodium phosphate hexahydrate and a core containing trisodium phosphate dodecahydrate and sodium hydroxide. Preferably the par~icles of the intermediate body are separated from said counter current air before the subsequent cooling, though at ~he separation stage the core usually contains solid trisodium phosphate and sodium hydroxide as well as said aqueous medium.

In the hydrated solid composition of the invention, the molar ra~io of P to hydroxide is preferably 1:O.12-0.18 e.g. about 1:0.15. In the hydrated solid the overall ratio of P:H20 is 1:8-11, preferably 1:9-11 such as 1:9.5-11 bu~ espec~ally 1:10-11. However the P to water ratio is not constant throughout the solid, because it is 1:6, or sl~ghtly above, in the outer l~yer and 1:12, or slightly below, ~n the inner core; the thickness of core and outer layer are such as to g~ve the desired overall P to water ratio. The corelouter layer structure may be shown by X-ray crystallographic analysis of samples taken across a diameter of the particles~ The solid composition of S6~7 the invention is substantially completely water soluble at 20C.
While the solid compositions usually consist essentially o~ the two trisodium phosphates and sodium hydroxide~ they may contain small amounts, e.g. up to 1%, especially up to 0.5% (by welght based on the weigh~ of Na3P04) of sodium carbonate, either present as an intentional or accidental ingredient in ~he sodium hydroxide solution used in the production of the aqueous solution being solidified or bec~use of absorptîon by the droplets of carbon dioxide from the air used in the solidification process.

The solid compositions of the invention are particles obtained by ejecting droplets of the hot aqueous solutiqn from a sprayer into a stream of gas moving countercurrent to the droplets which subsequently continue to move in countercurrent to the air and essentially out of contact with each other until the intermediate body with the solid outer layer or shell of trisodium phospha~e hexahydrate and core containing liquid is produced. After separa~ion i~ desired from the countercurren~ air flow, the particles of this ~ntermediate body are allowed to cool further in or out of contact with each other until the body solidifies completely and its temperature is less than 30QC. The gas in~tially contacting the droplets as they emerge from the sprayer is at a t~mperature less than that of the droplets, preferably at less than 60ÇC e.g. at 30-~0C and that finally contacting the partly solidified intermediate body ~ith solid shell and 1iquid or 1iqu~d/
solid core is also at less than the temperature of that body, e.g.
at 0-30C such as at 10-20C. Advantageously the droplets during sol~dification contact gas of progressively reduced temperature e.g.
as happens when the droplets fall under gravity in countercurrent to an upward stream of ~as e.g. air, the air being cold e.g. 0-20C at the bottom and being warmed progressively by the molten droplets passlng through it. This solidiP~cation may be perPormed in a prill tower in which the hot aqueous solution is pumped to the top oP the tower and under sufficient pressure to atomize it, the solution is ejected from one or more, e.g. 1-6 or 2-~, nozzles in a spray head in the ~orm of droplets wh~ch fall down the tower agains~ an upward .L2756~7 flow of alr. The nozzles may be of the sol~d cone or the hollow cone type and are arranged to minimize overlap between the sprays of droplets and to m~nimize impact of the droplets on the walls of the tower and to maximize spraying of droplets down ~he tower. The partly solidified body with the solid shell and liquid or liquid/solid core may be collected from the bottom of the tower and subsequently cnoled. The ejection of hot solution into the gas usually causes evaporation of some of the water in the solution, thereby increasing the P:water ratio fron 1:10-14 to 1:8-11.

In the process there is initial cooling of the droplets to cause surface solidification of the hexahydrate while at the same time there is evaporat~on of water fram the solution to reduce its water to P ratio. The gas initially contac~ing the hot droplets preferably has a Relative Humidity of 10-90%. If the hot solutiGn already has a water to P content of 9.5-11:1, e.g. 10-11:1, then the gas may be saturated with water vapour, but advantageously hot phosphate solutions of water to P ratio of 12-13:1 are used and the water to P ratio is redueed in the spraying and solidification steps; ~n order to obtain products of the desired structure it is then essential tha~ wa~er vapour is evaporated from the droplets before the solidl~ication of the ou~er shell is complete, as happens when the vapour pressure of the water in the gas contacting the hot molten droplets is less than the vapour pressure of water over the droplets at the temperature of the droplets. When the inlet gas has a high relatlve humidity and a higher temperature, lt is capable of effecting less cooling and less ~ncrease of the P:water ratio of the particles than with colder inlet gas of lower relative humidity. The flow of droplets and the P:H20 content of the input liquid may be ad~usted during continuous operation to compensate for varlations, if any, in temperature and humidlty of the air and to produce a solid product, with the higher the air inlet temperature at constant air flow rate the lower the liquid flow rate, and the higher the humid~ty the higher the P:H20 ratio of the input liquid. In addition the higher the flow rate of ~he air~ the higher can ~e the flow rate of khe liquid being solidified; there may be used ratios ~ 275iÇi~7 of the volume of liquid per hour to the volume per hour of gas, e.g.
air of not more than 1:10, e.g. not more than 1:15 or 1:20 such as 1:10-50 or 1:15-30.

The in~enmediate body has a solid shell of hexahydrate and a core which contains a liquid phase of trisodium phosphate dodecahydrate, and sodium hydroxide. The core usually al so contalns solid dodecahydrate, sodium hydroxide and/or sodium phosphate hexahydrate so the core may have partly, e.g 50-90~, solidified but not completely solidifled. The intermediate body is usually at 30~70C, e.g. 40-70C or 30-50C, these temperatures being the measured average for ~he body because ~ has a relatively cold solid shell and a relatiYely hot core containiny the crystallizing liquid phase and usually solid phase as described above. The intermediate body has sufficient strength that the particles do not coalesce on cuntact wth one another.

The production of the intermediate body is usually performed in a prill tower of height at least sufficient so that the inter~ediate body has sufficient strength not to break when hitting the prill tower bottom. The tower is usually 10-30M high, e.g. 12-20M. The warm inter~ediate produ~t is then cooled further to below 35C, e.g. to below 30C. The cool~ng may occur ~n the tower but preferably is o~tside the tawer. Thus the intermediate body may be cooled at the bottom of the tower by passin~ air countercurrent through it. This cooling could occur while the particles of lntermediate body fall under gravity out of contact w~th one another ~n a tower, e.g. with the droplets of hot liquid being sprayed down a tower 50-70M long against a countercurrent stream of air to produce at the bottom a completely solid composition of the invention at below 30C. Alternati~ely a shorter tower could be used so long as the droplets fall out of contact with one ano~her until the intermedia~e boqy is produced and then ~he part~cles of intenmediate boqy, a signi~icant proportion of which are ~n contact with one another, e.g. ~n the $orm of spheroids with sem~ molten centres, are cooled by passing air countercurrent through them, before they lea~e the tower at the bottom a~ below 30C.

:~.2'~61~
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Complete cooling in the tower inevitably raises the temperature of the air contacting the drop1ets at the top of the ~ower. Therefore it is preferred to cool the intenmediate body outside the tower. The intermediate body is advan~ageously separated from the countercurrent air stream and is subsequently cooled outside the tower~ Th~s la~er cooling can take place with at least a por~ion of the particles in contact with one another, e~g. when air is passed through a mass of particles o~ the intermediate body or is passed through or over a moving optionally perforated conveyor or table on wh i ch the intermediate body lies. However the i ntermediate body is preferably significantly further cooled with the particles substantlally out of contast wi~h one another. Thus the par~icles of intermediate body may be passed from the tower~ e.g. by conveyor or vibrating table, into a chamber where they are mixed with air, e.g. tumbled with air and then separated in a cyclone. Most preferably the particles of intermediate body are passed from the tower into a second tower or conduit where they are contacted cocurrent with air having a temperature of 0-30C e.g. by be~ng passed into an upwardly moving air stream in which they move cocurrently and are cooled to 15-30C, e.g. in an air lift.

If desired, before the second cooling outside the tower, any oversize part~cles may be removed. The cooled product of the Invention is then obtained of substantially uniform particle size with few fine materla1s, in con~rast to the product obtained by spray drying which gives particles with a breadth of sizes including ma~y fines, e.g. at least S0~ of less than 0.25mm and at least 10 and often at least 2~ o~ less than 0.075mm. The process can therefore glve a h~gher yield of product of substantially uniform size, e.g. greater than 0.18~m, than sprqy drying.

The particles of product of the invention, which are usually substantially spherical are preferably of 0.1-2mm, e.g. 0~25-1.5mm;
at least 95% may be of 0.18 to 1.5mm. The vast majority, e.g~ at least 90~ by weight are usually of 0.25-lmm and a large major~ty, e.g. at least 80% are o~ 0.35-0.7mm, e.g. about 0.5mm diameter. The 7tjÇj~7 particles of product usual7y contain less than 1% of less than 0.075mm. The particles of product of the invention are usually obtained from hot droplets of substantially the same size sprayed from nozzles which are 0.7~4.0mm e.g. 1.6-3.6 or about 2.5mm in diameter.

The aqueous feed solution to the sprayer may conveniently be made by reacting a concentrated aqueous solution containing orthophosphate values of Na:P atom ratio less than the desired figure with the requisite amount of concentrated sodium hydroxi~e solution to give the solution of desired Na:P:OH ratio. The neutralization of the sodium phosphate solution is exokhermic and the hot solution may advantageously be used as such for the solidification process of the 1nvention, though extra heat may be provided if required in order to keep the solution of that concentration liquid before the solidification. Examples of solutions of orthophosphate values are those with Na:P ratio nf 0-2.2:1, e.g~ phosphoric acid or monosodium phosphate or mixures thereof, or disodium phosphate or mixtures therefore with mono- or tri- sodium phosphate.

The solid phosphate c~nposit~ons of the invention have a reduced tendency to cake, and they flow more freely than the crystalline produc~s. They may be used in solid cleanser compositions e.g.
household cleansers.

Such cleaning composit~ons may comprise by weight 1-40%, e.g. 10-35%
of the solid composition of the invention, 40-99g, e.g. 60-~OX of other alkaline compounds such as sodium carbonate or sesquicarbonate sodium tripolyphosphate, or sodium sil~cate and optionally O.l-20%
of filler, e.g. sodium sulphate, and/or 0.1-2~ surfactants, e.g.
alkyl-benzene sulphonate such as dodecylbenzene sulphonate and/or 5 15X of a bleaching agent, e.g. a trichloro isoeyanurate. Abrasives may be present or absent. These cleaning compositions may be made by dry blending the various ingredients, e.g. by tumb1e blending.

~Z'7S~i~7 , ~

The compositions of the invention may also be used in industrial applications, e.g. for the phosphating of steel or ~or the treatment of boiler water.

In a modification of the composition and process of the invention at least a portion of the sodium hydroxide content of the solid composition and hence solution to be solidified is replaced by a sodium salt of a monobasic inorganic acid, e.g. chloride, nitrite, ni trate or hypochl ori te.

Thus the present invention also provides a particula~e solid hydrated phosphate composition comprising trisodium phosphate and a sodium c~mpound of fonmula NaX, wherein X is selected fron hydroxyl and a monovalent inorganic anlon Z and mixtures thereof with the a~omic ratio Na:P:X being 3.1-3.2:1:0.1-0.2, and the atomic ratio P:Z:OH being 1: up to 0.2: up to 0.2, eOg. 1:0.01-0.2:0-0.19 and the overall P:H20 ratio of 1:8-11, the solid composition having an outer layer comprising trisodium phosphate hexahydrate and a core containing trisodium phosphate dodecahydrate and the sodium compound which is believed to be present as a solid solution.

The present invention also provides a process for preparing a part~culate solid hydrated phosphate composition wherein an aqueous solut~on at 90-120C of trisodium phosphate and a sodium compound of formula NaX, where X is selected from hydroxyl and a monov21ent inorganic anion Z and mixtures thereof with the atomic ratio of Na:P:X be~ng 3.1-3.2:1:0.1-0.2 and ~he atomic ratio of P:Z:OH being 1: up to 0.2: up to 0.2, e.g. 1:0.01-0.2:0 0.19, and the overall P:H20 ratio of 1:9-11 ~s ~ormed with droplets and droplets rapidly chilled substantially out of contact with one another by countercurrent contact with aîr to produce particles of an intenmediate body w~th a solid outer layer of trisodlum phosphate hexahydrate enclosfng a core oF aqueous med~um comprising trisodium phosphate and sodium cGmpound and then said particles of intermediate body are cooled further to give a solid phosphate composition of P:H20 ratio oF 1:8-11 havin~ an outer layer comprising trisodium phosphate hexahydrate and a core containing ~.~7S~)7 trisodium phosphate dodecahydrate and sodium compound. Apart fron the change in the chemical composition of the modified solids and the solution used to make them, the mod~,ied solids and the process for making them are essentially the same as the solids of the invention without the added NaZ compound, and the process for mak~ng them.

The inorganic anion Z is monovalent from a monobasic inorganic acid of formula HZ. The group Z may be a halide, e.g. fluoride or chloride, nitrite, nitrate, permanganate, hypohalite, e.g.
hypochlorite or borate. Preferably the group Z is a nitrite or chloride. The group Z may constitute the only group o~ formula X, but there may also be present hydroxyl group, the proportion of phosphorus ~o Z to hydroxyl being 1:0.01-0.2:0-0.19 especially 1:0.1-0.15:0-0.04, with the ra~io of P to X being prefera~ly 1:0.l-0.18 especially 1:0.12-0.18, e.g. about 1:0.15. The modified solids of the invention may also contain the small amounts of sod~um carbonate as described for the solids free of ~he NaZ compound.

The aqueous solution which is converted to the modified solids of the ~nvention~may conveniently be made by reactin~ a concentratPd aqueous solut1On containing orthophosphate values as described above with an Na:P ratio less than the desired ~igure with the requisite amount of concentrated sodium hydrox~de solution in the presence of the sodium compound NaZ to give the solut~on of desired Na:P:Z and X:Z ratlo. If the desired product ~s to contain no excess of a1kali, ~.e. X is constituted by Z only, then enough alkali is added iust ~o titra~e the last acidity of the disodium hydro~en phosphate, i.e. to Na:P ratio 3:1. Examples of the solution containing orthophosphate values are as described above.

The modified solid phosphate compositions have a reduced tendency to cake, and hence flow more freely than the corresponding crystalline products. Their de~ree o~ free alkalinity per uni~ volume of powder is also reduced over the phosphate compositions without the NaZ
camponent, a benef~t in those solid cleanser compositions~ e~g.

~';75~;~7 particular household cleansers where an excess of alkali is undesired. Furthermore the compositions comprlsing nitrite may advantageously be used in water treabment to combine alkalinity and nitrite content, while those with hypochlorite may be used in solid bleaching compositions.

The process may be per~ormed in apparatus as illustrated in the accompanying figure which is a schematic representation of a prilling tower with associated pipework.

Tower 1 has inlets, 29 for air at its bottom and exits, 3, for wanm alr in its top, 4. Also fitted in its top, 4, are two ~nlet pipes, 5, with four fixed spray nozzles, 6, through which hot liquid may be ejected. The tower has an inverted conical bottom, 7, the inside surfaces of which, toyether with the end of the vertical sides of the tower, define the air inlets, 2. On one side of ~he conical bottom is an exit, 8, for any large lumps with a movable door~ 13, and on the other side of the conical bottom, 7, is a grating, 9, e.g. of 30mm spacing for removal of particles of product. The particles pass through grating, 9, down line 10 whiGh may contain conveying means, e.~. a vibrat~ng table or screen, and are then separated by gravity into any residual large bodies which fall down line 11 and desired partlcles which move up line 12 carried by a cocurrent stream of air, which enters line 11 and passes up line 12.
A suctlon f~n and cyclone (not shown) may be attached to the upper end of line 12 ~nally to separate the particles of product from the a~r.

In use the hot aqueous solution of sodium phosphate and sodium hydroxide, optionally with e.g. sodium nitrite, is sprayed down the tower 1 in countercurrent to cooler air passing up the tower from ~nlet 2 to exits 3~ The liquid is partly soli~ified to give ~ntermediate product with solid shell and partly solidified core and the intermediate product is separated at the bottom of the tower by the gratingJ 9, into large lumps wh~ch are retained and the rest of the product wh~ch passes through the gratlng and is cooled and J.i2~;~S~g~7 separated further as described above to give completely solidifed part~culate product~

The lumps, which are agglomerations of particles and/or ma~erfal from the tower walls, fall off the grating, 9, and periodically are removed dcwn exlt line 8 by opening the door 13~ The air leaving ex~ts 3 may contaln ul~ra fine dust particles of the solid, whose phosphate values may be recovered by scrubbing (not shown).

The process Is illus~ra~ed in the ~ollowing Examples, in Example 1-6 of which the solidification apparatus was substantially as described in and with reference to the accompanying Figure and was used in a manner generally as described above.

488 parts of an 85% w/w aqueous phosphoric acid solution and 1135 parts of a 47% w/w aqueous sodium hydroxide solution were added simultaneously with stirring to 248 par~s of water. The resultant liquid of Na:P atom ratio 3.15:1 became hot (about 100C) and was heated to 110C and its density adjusted by addition of wa~er to 1.53kg/m3 a~ 110C, corresponding ~o a P to H20 atom ratio of 1:12.8. The hot liquor was then solidified in the solidification apparatus. The hot liquor was conveyed to the top of a tower, 1, whfch was 4.~M diameter and 13.7M high (as shown in the accompanwing Flgure) down which it was sprayed from four fixed atom~zation hollow cone spr~y nozzles, 6, of 2.5mm orifice against a countercurnent stream o~ a~r w~th a ra~io of the volume of aqueous liquor per hour to volume of air per hour oP about 1:16.7. The temperature of the a~r when the liqu~d from the nozzle first contacted it was 35~, while the air entering the tower had a temperature of 18C and a relative humidity in the range 40-90g. The process gave a semi-solid product which substantially separated ~rom the coun~er current air f10w which passed up the tower. The semi-solid product was sieved by grating, 9, of 30m~ spacing to remove oversize pieces and the particles of semi-solid product passing through the grating were 75 6l~7 passed alony line 10 by meAns of d vibrating table contained therein. The particles, the intermediate body, had a solid outer shell and a core of partly solidified aqueous medlum; the temperature o~ the particles was measured as 33C. The particles passed from the vibrating table into line 12, wherein they were cooled further to 26C in cocurrent with an upward stream of air at 18C passing through line 11 through line 12. A ve~y small percentage of larger product such as flakes fell down line 11. The particles leaving line 12 at 26CO were completely solid and were collected via a cyclone. The completely solid particles had an analysis of 4S.6~ Na3P04 1.8X NaOH, 52.6% H20, P:H20 of 1:10.5 and Na:P of 3.15:1. The completely solid product was in the form of substantially spherical particles with a solid shell of Na3P04 6H20 and a solid core comprising Na3P04 0.25NaOH 12H20. The completely solid product particles had the following partic1e size distribution: greater than 0.7mm 1.2%, 0.36-0.7mm 58.9~, 0.25-0.36mm 32.6%, 0.18-0.25mm 6.8~ and 0.07~-0.18mm 0.6~.

Example 2 In another experiment the solid particles were made as descr1bed in Example 1.

The ease of flowing nf the solid particles was found by detennining their angle of repose which was 20, compared to an angle of 32 for crystall~ne Na3P04 0.25NaOH 12H20. The solid particles also were much less prone to caking compared to the crystalline Na3P04.
0.25NaOH 12H20.

~x~ples-3-6 In the same manner as described ~n Example 1 were made solid particles having the following analyses on a weight basis:

~.2~5~

Example _ %Na3PO~ _ NaOH -- Na2~-3 P:H~O _ Na_P

3 46.5 1.7 0.1 1:10.3 3.157 4 47.5 1.7 0.2 1:9.7 3.161 44.8 1.9 0 1:10.8 3.174 6 47.4 1.6 0.2 1:9u8 3.1~2 :

In the process of Example 3 the input air had a temperature of 20.5C and a Relat~ve Humidity of 59X.

The particle size oP ~he product of Example 3 leaving line 12 was as follows - greater than 0.7mm, 19.3%, 0.36-0.7mm ~6.~g, 0.25-0.36mm 18.0~, 0.18-0.25mm 5.1~, 0.075-0.18mm 0.6~.

The particle size oP the product of Example 6 after leaving line 12 and sievlng to remove particles larger than 0.75mm was as follows -greater than 0.7mm 1,4%, 0.36-0.7mm 69.4%, 0.2S-0.36mm 22.6~ 0.18-0.25mm 5.0~, 0.075-0.18mm 1.6~.

Example 7 Commercial trisodium phosphate dodecahydrate crystals were dissol~ed hot in the m~nimum amount of water to gi~e an aqueous solution of speclfic gravlty 1.535 at 100C. The aqueous solution was pumped at 100C through a prehea~ed hollow cone atomizing nozzle of lmm orif~ce diameter situated at the top of a 13.7M ~ower, up which air flowed~ The a~r en~ered the tower at ~ts bottom at ambient temperature. The nozzle produced a spray of droplets wh~ch moved downwards countercurent ~o the upward air and solidified to give wanm solid particles with a partly molten core which separated from the upward air, were collected Prom the bottcm of the tower and allowed to cool to below 250a~ OYersized ma~erial was removed fron a sample of the part~cles by sieving ~hrough a 1.2mm sieYe and a sample oP the substantlally spherical particles passing through this sieve were s~

analyzed as containing 46.7X Na3P04 3.195:1 Na:P and P:N20 of 1:10.33. These particles were shown by Xray crystallography to have a solid shell of Na3P04.6H20 and a solid core comprising Na3P04Ø25NaOH 12H20. Xray crystallography on a sur~ace layer of the solid, i.e~ its shell, showed i~ to contain Na3P04 6H20 and on a crushed sample of the solid showed It to contain both Na3P04 6H20 and Na3P04 0.25NaOH 12H20. d lines for the compounds in order o~ decreasing intensities were as follows:
Na3P04.6H20~ 4.283 2~.80, 2~62~ 3.29, 2.88, 2.55, 2.64, 2.70, and for Na3P04 0.25 NaOH 1~H20, 4.34, 10.3, 2.61, 5.39, 3.32, 2.70,

2.87 and 2.86.

Exa ~ 8 678 parts of 46% w/w aqueous sodium hydroxide solution were added to an aqueous solution of 470 parts of monosod~um phosphate and 54 parts sodium nitr~te ~n 320 parts water. The density of the hot solution was adjusted to 1.54 kg/m3 at 105C. The hot solution was converted to a solid product by atomization and solidification in the manner descrlbed in Example 1. The product had an analysis of 46.1~ Na3P04, 3.8% NaN02, 0.1X NaOI~, 0.1X Na2C03, 49.8~
H20; wi~h a P:H20 ratio of 1:9.8 and conta~ned a shell 1~yer of Na3 P04 6H20 surroundin~ a core of Na3P04 0.25 NaN02 12H20 and NaOH~Na2C03.

A surface san~t~ng product had the ~ollow~ng compos~tion on a we~ght basfs and was made by dry blending the ~ngredients ~n the proportlons quoted:

Sol~d part~cles of Example 1 30X
Sod~um carbonate 40X
Pentasod~um tr~polyphosphate 20X
Tr~chloro~socyanurate sold under the trade mark FICLOR CLEARON 10X

.~, ~75~i~7 -lS-Example 10 A carpet cleaning formulation had the follcwing composition on a weight bas~s and was made by dry blend~ng the ~ngredients ~n the proportions quoted:

Solid part~cles of Example 1 25~
Pentasodium ~ripolyphosphate 25%
Tetrasodium pyrophosphate 15 Sod~um s~licate pentahydra~e sold wnder the trade mark METSO 35%

A domest~c hard surface cleaner had the follaw~ng co~position on a weight bas~s and was made by dry blending the fngredlents in the proport~ons quoted:

Solld part~cles o~ Example 8 30X
Penta sodium tr~polyphospha~e 15 Sodium sesquicarbonate 54X
Surfactant dodecylbenzene sulphonate lX

Claims (22)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A particulate solid hydrated phosphate conposition comprising trisodillm phosphate and sodium hydroxide with the atomlc ratio of Na:P:0H being 3.1-3.2:1:0.1-0.2, and the overall P:H20 ratio of 1:8-11, the solid composition having an outer layer comprising trisodium phosphate hexahydrate and a core containing trisodium phosphate dodecahydrate and sodium hydroxide.

2. A phosphate composition according to claim 1 of particle size 0.25-1mm.

3. A phosphate composition according to claim 1, wherein the overall P:H2O ratio is 1:-10-11.

4. A phosphate composition according to claim 2, wherein the overall P:H2O ratio is 1:10-11.

5. A phosphate composition according to claim 1, 2 or 3 wherein the ratio of Na:P:0H is 3.12-3.18:1:0.12-0.18.

6. A particulate solid hydrated phosphate composition comprising trisodium phosphate and a sodium compound of formula NaX, wherein X is selected from hydroxyl and a monovalent inorganic anion Z and mixtures thereof with the atomic ratio of Na:P:X
being 3.1-3.2:1;0.1-0.2, and the atomic ratio P:Z:0H being 1: up to 0.2: up to 0.2 and the overall P:H20 ratio of 1:8-11, the solid composition having an outer layer comprising trisodium phosphate hexahydrate and a core containing trisodium phosphate dodecahydrate and the sodium compound.

7. A phosphate composition according to claim 6 wherein the atomic ratio of P:Z:0H is 1:0.01-0.2:0-0.19.

8. A phosphate composition according to claim 7 wherein the atomic ratio of P:Z:0H is 1:0.1-0.15:0-0.04.

9. A phosphate camposition according to claim 6 or 8 of average particle size 0.25-1mm.

10. A process for preparing a particulate solid hydrated phosphate composition wherein an aqueous solution at 90-120°C of trisodium phosphate and sodium hydroxide, wherein the atomic ratio of Na:P:0H is 3.1-3.2:1:0.1-0.2 and a P:H20 ratio of 1:10-14 is formed into droplets and rapidly chilled substantially out of contact with one another by countercurrent contact with air to produoe partfcles of an intermediate body with a solid outer layer of trisodium phosphate hexahydrate enclosing a core comprising aqueous medium comprising trisodium phosphate and sodium hydroxide and then said particles of the intermediate body are cooled further to give a solid phosphate composition of overall P:H20 ratio of 1:8-11 having a solid outer layer comprising trisodium phosphate hexahydrate and a solid core containing trisodium phosphate dodecahydrate and sodium hydroxide.

ll. A process according to claim 10 wherein particles of the intermediate body with a solid outer layer and a core comprising partly solidified aqueaus medium are separated fron said counter current air before being cooled further.

12- A prooess according to claim 10 wherein droplets of 0.1-2mm size initially contact the countercurrent air, which has a temperature of less than 60°C, the particles of intermediate body have an average measured temperature of 70-30°C and are cooled to give the solid phosphate campositions at less than 30°C.

13. A process according to claim 11 or 12 wherein the particles of intermediate body are cooled further substantially out of contact with one another.

14- A process according to claim 11 or 12 wherein the particles of intermediate body are cooled further in an upward cocurrent stream of air.

15- A process according to claim 11 wherein droplets of 0.25-1mm of said aqueous solution pass down a tower countercurrent to an upwardly moving air stream to give particles of intermediate body having an average temperature of 35-50°C, said particles are then separated from said air stream and passed into an upwardly moving air stream in which they move cocurrently and are cooled to 15-30°C to produce said solid particulate phosphate composition.

16. A process according to claim 10 wherein said aqueous solution is prilled to give said particulate solid composition.

17- A process for preparing a particulate solid hydrated phosphate composition wherein an aqueous solution at 90-120°C of trisodium phosphate and a sodium compound of formula NaX, where X is selected from hydroxyl and a monovalent inorganic anion Z
and mixtures thereof with the atomic ratio of Na:P:X being 3.1-3.2:1:0.1-0.2 and the atomic ratio of P:Z:0H being 1: up to 0.2: up to 0.2 and the overall P:H20 ratio of 1:10-14 is formed into droplets and rapidly chilled substantially out of contact with one another by countercurrent contact with air to produce particles of an intermediate body with a solid outer layer of trisodium phosphate hexahydrate enclosing a core comprising aqueous medium comprising trisodium phosphate and sodium compound and then said particles of intermediate body are cooled further to give a solid phosphate composition of P:H20 ratio of 1:9-11 having an outer layer comprising trisodium phosphate hexahydrate and a core containing trisodium dodecahydrate and sodium hydroxide.

18. A process according to claim 17 wherein said particles of the intermediate body with a solid outer layer and a core comprising partly solidified aqueous medium are separated from said counter current air before being cooled further.

19. A solid cleanser composition comprising a solid particulate sodium phosphate composition according to claim 1. together with sodium sesquicarbonate.

20. A solid cleanser composition comprising a solid particulate sodium phosphate composition according to claim 1 together with sodium sesquicarbonate and an abrasive.

21. A solid cleanser composition comprising a solid particulate sodium phosphate composition according to claim 1 and wherein the ratio of Na:P:OH is 3.12-3.18:1:0.12-0.18, together with sodium sesquicarbonate.

22. A solid cleanser composition comprising a solid particulate sodium phosphate composition according to claim 1 and wherein the ratio of Na:P:OH is 3.12-3.18:1:0.12-0.18, together with sodium sesquicarbonate and an abrasive.