US3210154A - Molecularly dehydrated phosphates - Google Patents

Description

Oct. 5, 1965 KLEIN ETAL MOLECULARLY DEHYDRATED PHOSPHATES Filed March 7, 1962 Y mm m mwWE H b wipe, E. BH m% w wmA GL2 G F BY ATTORNEY.

United States Patent MOLECULARLY DEHYDRATED PHQSPHATES George I. Klein, Park Forest, Leo B. Post, Chicago, and

Ralph E. Newby, Steger, IlL, assignors to Stauifer Chemical Company, New York, N.Y., a corporation of Delaware Filed Mar. 7, 1962, Ser. No. 178,182 10 Claims. (Cl. 23-106) This application is a continuation-in-part of our prior copending applications, Ser. No. 861,618, filed on Dec. 23, 1959, and Ser. No. 93,074 filed Mar. 3, 1961 which in turn was a continuation-in-part of our prior application Ser. No. 826,234, filed July 10, 1959. All of the aforesaid applications have now been abandoned.

This invention relates to a method of manufacturing alkali metal pyrophosphates and polyphosphates and mixtures thereof. More specifically, the invention relates to a method of heating a feed material containing alkali metal and phosphate components in a suspended, fluidized state to produce pyrophosphates and polyphosphates of predetermined composition and bulk density.

The pyrophosphate and polyphosphate products of this invention are defined as those partially or completely molecularly dehydrated pyroand polyphosphates having a M O:P O ratio of about 1.0 to about 2.0 where M is at least one alkali metal, preferably from the group consisting of Na and K.

Bulk density (lbs/unit of volume) of alkali metal pyrophosphates and polyphosphates is a quality of great commercial importance. Most of the granular pyrophosphates and polyphosphates are tailored to the density most suitable for the desired end uses existing in industry. For example, sodium tripolyphosphate (Na P O the most popular of the current detergent builders is manufactured in at least three densities: so-called light density at about -40 lbs./cu. ft. is employed where the fastest rate of solution is desired, where a detergent is to be dry-mixed with the tripolyphosphate, or in certain types of detergent tablets, etc.; the medium density at about 55 lbs/cu. ft. is the standard builder in packaged granular detergents; and the high density at about -75 lbs/cu. ft. is used where it is desirable to decrease the bulk and container sizes, in low-foamer detergents, or in detergent tablets, etc. Tetrasodium pyrophosphate (Na P O and tetrapotassium pyrophosphate (K4P20q) are also commercially supplied in agglomerated (light or medium density) and powder (high density) forms. With the partially molecularly dehydrated pyrophosphates, such as sodium acid pyro hosphate (Na2H2P2O7), density is again an important factor; food grades usually have a high density while technical grades used in general chemical applications may be supplied in lighter densities.

Heretofore, manufacture of molecularly dehydrated phosphates in a plurality of widely differing densities has required more than one method of preparation and major processing unit, or, said another way, several principal methods and types of apparatus have been required in commercial chemical plants capable of producing light, medium, and high density molecularly dehydrated phosphates. Of course, other than the major units, every plant would comprise minor units for preparing the raw feed and blending and/or drying the same. In addition, with the methods employed heretofore, it was commonplace for individual products to require a two-step preparation which necessitated two major pieces of equipment.

Sodium tripolyphosphate is an example of a compound which required several methods to prepare the various commercial grades: the lightest grades of sodium tripolyphosphate have usually been produced by flash-drying a liquid feed, e.g., in spray drying equipment; the medium ice density materials have normally been prepared by moderately fast heating of a dry feed mixture, e.g., in a dry feed, directly-fired kiln; and the high density materials have usually been prepared by fast heating of a liquid feed in a special kiln in which a heating flame impinges upon a tumbling bed of the product.

Sodium tripolyphosphate has two known crystalline modifications, the so-called high temperature form (hereafter referred to as Na P O I or form I) and the low temperature form (Na P O II or form 11). Under atmospheric pressure these polymorphic forms are reported to be enantiotropic with a transition temperature at about 470 C.

The sodium and potassium pyrophosphates, as well as the two forms of sodium tripolyphosphate, have excellent chelating properties useful for softening hard water. Their ability to deflocculate and suspend water-insoluble substances acounts for the success of the pyrophosphates and tripolyphosphates in detergent and cleaning compounds, Where they are presently used in mixtures or individually. Other uses for the polyphosphates and mixtures thereof include cement defiocculation, paper production, cheese production, food processing, and clay conditioning.

The two forms of Na P O exhibit markedly dilferent water solubility characteristics. Because of these solubility characteristics, considerable commercial demand for mixtures of these compounds with other polyphosphates has been found. For commerce, however, such mixtures must be uniform and reproducible from day to day throughout sustained production. Furthermore, mixtures have often been desired which have varying bulk densities, e.g., specifications may call for individual lots of light, medium, and high density materials, each of which has the same percentage of forms I and II sodium tripolyphosphate. By the methods available heretofore, it was often difficult, and even more often impracticable, to provide material having the desired combination of mixed forms and density. The prior methods for commercially manufacturing mixtures usually involved mixing the components mechanically and, although acceptable mixtures might be made in this manner, extensive testing and blending with fluctuation of quality made this method somewhat unsatisfactory.

Heretofore, the usual method of making form I Na P O involved intermolecular dehydration of watercontaining meta, ortho, or pyrophosphates at temperatures above about 470 C., but below the melting point of Na P O i.e., about 620 C. Form II was usually made by a like procedure at temperatures of about 250470 C. By means of the invention, predetermined, controlled mixtures containing both forms of Na P O can be produced at uniform and constant bed temperatures as low as about 350 C. This discovery would not be anticipated from the prior art.

Sodium acid pyrophosphate, one of the compounds within the general scope of this invention, is usually prepared commercially in several grades by reacting phosphoric acid containing trace quantities of stabilizing additives, as disclosed, for example, in U.S. Patents 2,844,437 and 2,408,258, with a sodium base to produce monosodium orthophosphate which is then convetred to sodium acid pyrophosphate by heating at a temperature of about ZOO-245 C.

After the conversion to sodium acid pyrophosphate is substantially (e.g., 94-96%) complete, the material is usually treated by either exposing it at elevated temperatures to an atmosphere containing steam at a partial pressure of about 760 mm. of mercury for about /2 to 4 hours, or by reheating or continued heating at a temperature of about 200-245 C. for prolonged periods,

usually about 2 to 6 hours. Steam treatment is used primarily to promote stability in the inherently less stable fast-reacting grades of sodium acid pyrophosphate, whereas heat treatment is used to further depress the reaction rate of the slower reacting types.

Conversion and treatment of sodium acid pyrophosphate have heretofore been accomplished commercially by application of such conventional heating equipment as static heaters, rotary kilns, rotary flight heaters, drum dryers, and rotary dryers. The common disadvantage of this equipment is in producing appreciable temperature gradients which may exceed 30 C. within the mass of heated material, with the consequent production of hot spots and localized heating leading to the deleterious formation of metaand/ or polyphosphates by pyrolysis. Further, because of residual moisture and the water liberated during conversion, intimate contact of the fusible particles during conversion and treatment by the methods heretofore employed results in the formation of lumps, large agglomerates, and crusted heating surfaces. These formations, ultimately composed of underor overconverted material, are discharged with the salable product or built up on the heater surface.

The baking industry has found considerable use for sodium acid pyrophosphate as a baking acid in the preparation of doughnuts, cake, and prepared mixes, and as a leavening agent in comercial-type baking powders and creams. In such use, sodium acid pyrophosphate per forms best at higher percentages of pyro and, therefore,

at lower percentages of monosodium orthophosphate and the undesirable pyrolysis products. Monos'odium orthophosphate is objectionable by virtue of its extremely fast reaction rate as a baking acid and because its inclusion, even in small quantities, in sodium acid pyro-phosphate baking acid results in a significant loss of leavening gas during the mixing of a batter or dough. The presence of polyor metaphosphates lowers the neutralizing strength (N-S value) of the acid, thus requiring increased amounts to produce equivalent acidity. High pyro" contents and N-S values, therefore, are quantitative measurements of the quality of sodium acid pyrophosphate baking acid.

We have now discovered that the alkali metal pyrophosphates and polyphosphates and mixtures thereof having any of the aforementioned commercially-required bulk densities may be produced by means of a single basic method utilizing fluidization technique. The method of this invention involves preparing a phosphate feed mater-ial, especially a finely commingled mixture of orthophosphates or its equivalent, and charging this feed to a pro-established bed of fluidized particles of the approximate composition as that to be produced. Thereafter, these materials are retained for a specific time and at a specific temperature in the fluidized state until a product of the predetermined composition has been made. By the method of the invention, any of the above-described polyphosphates, and particularly mixtures of the sodium polyphosp'hates, can be produced directly in predetermined compositions. We have found that the relative quantities ofNa P O I and Na P O II produced, at constant feed ratios, is proportional to both retention time and bed temperature in a fluidized bed. Thus, a principal feature of this invention involves the discovery that the total so dium tripolyphosphate produced can be accurately apportioned between form I and form II, in predetermined percentages, by application of controlled temperatures and retention times during thermal conversion. This, combined with our ability to obtain any desired proportion of the other polyphosphates by selecting the proper M O:P O ratio in the feed material, enables us to produce a plurality of mixtures of the polyphosphates in a single processing step.

We have also discovered that agglomeration, uncontrolled by the prior art methods, can be sufiiciently moderated in a fluidized bed to permit the Well-controlled manufacture therein of molecularly dehydrated phosphates having highly desirable quality and suitable for commercial uses. It is well-known that alkali metal pyroand polyphosphates agglomerate during manufacture as the phosphate feed looses water of constitution. Moreover, persons familiar with the art of fluidization have heretofore doubted the desirability and practicability of processing agglomerative materials in a fluidized bed. Nevertheless, the present invention illustrates that agglomerative materials, at least the alkali metal pyrophosphates and polyphosphates, may not only be processed in a fluidized state, but that agglomeration may be beneficially utilized to produce materials having a wider range of properties than obtainable by the conventional methods of the prior art.

In the manufacture of mixed sodium tripolyphosphate (forms I and II) by the method of the present invention, it has been found that, at a fluidized bed temperature between about 400 C. to about 550 C., a 1 C. increase in bed temperature effects an increase of about 0.9% in the amount of Na5P301Q I in the final product, at a fixed retention time within the range between 2 and 8 hours. On the other hand, at a given bed temperature the percentage of Na P O I increases about 6% for each one hour increase in retention time.

For a mixture containing substantially all form I and form II Na P O we have formulated these findings in an empirical mathematical relationship which can be used to predict the percentage of form I in a mixture produced by the method of this invention from the bed temperature and retention time variables:

Percent Na P O I= i where T is the bed temperature expressed in C. in the range of about 400 C. to about 550 C. and R is the retention time expressed in hours in the range of about 2 to about 8 hours. This equation is useful for predicting positive percentages of form 1 between about 2% to about 99%. Mixtures containing appreciable quantities of each form will normally have a form I content which will fall within about 15% of that predicted by this equation. For small quantities of one form or temperatures and/or retention times outside the range given this equation is less accurate, but it can be used as a general indication of the product to be expected.

The composition of a product consisting of alkali metal pyrophosphates and tripolyphosphates produced by intermolecular dehydration can be controlled, by adjustment of the M O:P O feed ratio in the range of about 1.0 to about 2.0, to give any desired percentages of the two compounds in the mixture. For mixtures consisting of sodium pyrophosphate and tripolyphosphate this relationship can be expressed by the approximate equation:

PeI'CEHl. Na4P207 300[ (NflgOiP205) where (Na O:P O is the molar feed ratio expressed to three decimal places.

Because the compound Na P O exists in two known polymorphic forms, the above formula was not, heretofore, applicable to three component mixtures containing Na P O N21 P O I, and Na5P301o The findings previously correlated for binary mixtures can be represented mathematically by empirical equations which are useful for predicting the percentage of forms I and II in tertiary mixtures consisting of the two forms of Na P O as well as Na P O when produced by our method:

Percent N315P3O10 I fi) (6.01% 4s.0)][3 (2.0Na2O 9 05 Percent NP301Q Each equation can be used to predict positive percentages of one form between about 2% to about 98% where T and R are the same as for binary mixtures. The accuracy of these equations, since they are based upon the same data, is about the same as for binary sodium tripolyphosphate mixtures.

Usually by the present invention the polyphasphates and pyrophosphates are prepared by the intermolecular dehydration of acidic phosphates resulting from the reaction of phosphoric acid and alkali metal bases. Monoand dialkali metal orthophosphates and mixtures thereof are highly suitable as feed materials for conversion to the polyphosphates. Equivalent mixtures of various phosphate and alkali metal components are obviously suitable for conversion to polyphosphates wherein the M O:P O ratios are controlled within the range necessary for the desired polyphosphate product. Compounds conforming to the formulas H PO MOH, M CO MCl, H1 0 4 2 1 z i Z i: s, 4 2 7 z z z 'r, etc., can be employed as sources of phosphate and metal, where M is an alkali metal, and preferably Na or K.

For a dry feed process we have found that very fine milling, at least about 50% through 325 mesh, is most desirable. Granular or unmilled feed apparently does not agglomerate well in the bed and hence does not allow as good a density control as with finely milled feed. From a standpoint of operating efliciency it is very desirable to employ multiple beds for the processing of polyphasphates. A separate bed or spray drying chamber, for removing the water of solution from liquid feed, conserves process heat and is otherwise advantageous. This may be located above the conversion bed for gravity feed.

A most significant feature of the present invention is the finding that the basic method, with modification of several variables, may be used to produce molecularly dehydrated phosphates of all bulk densities. Among the conditions which must necessarily be controlled by the method of the present invention, probably the most critical is the composition of the fluidized bed. Smooth and effective fluidization can only be accomplished if the starting bed is composed of a large amount of previously dehydrated pyroor polyphosphates. Any attempt to fluidize and dehydrate a starting bed consisting of substantially all, or even a predominant amount, of alkali metal orthophosphates will normally result in excessive agglomeration and fusion of the bed. For the same reason it is important that the feed rate during continuous fluidization be sufiiciently moderated so as to prevent the build-up in the bed of a predominant amount of unconverted orthophosphates at any one time. In practical applications, however, little difliculty is encountered during continuous fluidization since it is possible to maintain a large volume of converted material in the bed and since the high heat transfer rate of the fluidized bed quickly converts incoming feed through the tacky phases.

There are four principal variables which influence the bulk density of the final product by our method; these are (1) retention or sojourn time in the bed, (2) bed temperature, (3) location of the incoming feed, and (4) type of feed. A longer sojourn time for the feed through the bed causes the final product to have a higher bulk density. In this regard it is thought that the feed particles fuse quickly to the larger particles of the bed, building up an agglomerate through successive fusions, but after agglomeration has ceased, the particles undergo gradual attrition from the impingement and collision in the bed. When all of the other variables are maintained constant, an increase in bed temperature causes an increase in bulk density; usually about a 5-10 lbs/cu. ft. rise in bulk density accompanies a 100 C. rise in bed temperature at temperatures between about 200 C. and 400 C. At either extreme of the broad temperature range this phenomenon is less pronounced.

As will be shown hereafter, the method of the present invention allows for incoming feed above and below the level of the fluidized bed. Generally, if the feed enters above the bed (in the freeboard area) the final product will have a lower density than when the feed is furnished directly to the bed. However, distribution of incoming feed is also important. For example, the lightest density material possible is produced where the feed is distributed or sprinkled on top of the bed from an inlet in the freeboard area. Materials produced from both liquid and solids feed are influenced by the distribution condition. To improve distribution of a solid feed to the freeboard, various mechanical devices may be used. One particularly suitable device is a cone distributor (not shown in the drawing discussed hereafter) placed immediately above the bed. Incoming feed is dropped on the cone; then it spreads into a thin layer before falling into the bed. On the other hand, liquid feed may be dispersed to almost any desired degree by proper selection of a suitable feed nozzle. Distribution of dry feed entering under the bed may be influenced by baflles, etc., but is not subject to the same degree of control as a freeboard feed. A liquid feed entering the bed directly may be varied to increase or decrease distribution by selection of the desired type of spray nozzle and the desired orifice. A two-fluid nozzle using air to disperse the liquid feed may be used when it is desirable to decrease density and/ or when the liquid feed is too thick to be sprayed by ordinary nozzles.

The type of feed used is very influential on the density of the final product. In general, liquid feed promotes formation of high density material and solid feed (and feed mixtures) tends to give a light product. Solid feed under the bed, however, may yield a product which is classified as high, or at least medium-high, density. By contrast, a well-distributed solid feed entering from the freeboard will normally yield light density material (30-40 lbs./ cu. ft. for Na P O produced in this manner). A poorly distributed feed entering immediately above the bed will yield an intermediate, or medium density product (about 4055 lbs./ cu. ft with Na P O The figure shows a typical single bed reactor which may be used to produce the pyrophosphates and polyphosphates by the method of this invention.

Screw type feeders 1 are used to charge the dry feed to the fluid bed reactor 19. Ambient air is supplied from an external compressor 3 to support combustion of a hydrocarbon fuel passing through line 13 into the burner 12. The hot gases formed in the windbox-combustion chamber 16 proceed upward through the bed plate 17 into the fluidized bed 2. Thermocouple 15 and the manometer 14 supply the necessary temperature and bed depth information and, by means of well-known electrical control mechanisms, can regulate the combustion, feed, and product discharge rates. The cooler gases rising out of the fluidized bed 2 pass upward into freeboard section 18 and by way of the outlet 4 into dust collector 8 where any entrained particles are separated. The collected particles are then either returned through line 9 to the bed or withdrawn from the process through line 10.

Product materials are discharged either from the top of the conversion bed through line 5 or from the bottom of the bed through line 7. As an alternate method, liquid feed may be sprayed from spray nozzle 22 into the freeboard space or from spray nozzle 21 located under the bed.

Because a great number of equivalent mechanical combinations may be effectively used, and because our process is not limited to any particular type of fluid bed apparatus, no limitations should be implied to the invention from the details of the figure.

Many combinations of series and parallel beds may be used to dry, convert, and cool the products of this invention, and these are largely dependent upon the desired production rates and the type of feed, whether dry or in solution. Other sources of fiuidizing gases, e.g., the discharge from a spray dryer, may be used.

We have produced polyphosphates using bed temperatures as low as 120 C. Temperatures up to and higher than the melting point of sodium tripolyphosphate (about 620 C.) are also practical. However, the preferred temperature range for eflicient operation is about 250- 580 C. Similarly, retention times of a few minutes to over hours have been used, but the preferred range is about minutes to 8 hours.

Obviously, our method is not limited to 8 hours as a maxium retention time. Retention times of 40 hours or more are quite possible. However, 8 hours has been selected as the maximum retention time for a commercially feasible process using our invention. The upper temperature limitation for our process is the melting point temperature of sodium tripolyphosphate, about 620 C., but because of the control problems existing at such temperatures it is usually more practical to run commercial units at somewhat lower temperatures.

In a continuous process, the phosphates leave the bed by fluo-static pressure in quantities about equal to the phosphates entering in the feed. The gases leaving the bed usually contain some entrained phosphate particles which are collected and either returned to the bed or removed from the process.

Because high processing temperatures make the polyphosphate product somewhat diflicult, even hazardous, to handle, another bed for cooling the material prior to discharge from the reactor is very desirable. This cooling bed can be fluidized with ambient air which warms considerably by contact with the hot polyphosphates.

The next stage of fluidization can conventiently use the warmed air to support combustion, again allowing excellent conservation of the process heat.

Any mixture or single pyrophosphate or polyphosphate as defined herein can be produced by our method. With feed ratios (M O:P O of about 1,667, we can produce 98-99% yields of Na P O containing form I and form II of any desired proportions. Using feed ratios between about 1.6 and about 2.0 we can produce, at exceedingly good production rates, compositions containing any desired proportions of Na P O II and Na P O At higher temperatures and feed ratios between 1.6 and 2.0, compositions containing Na P O I and Na P O in all desired proportions can be manufactured by the invention. The three component mixtures are produced at temperatures and retention times of about 350550 C. and about 2-8 hours, respectively, and feed ratios of about 1.6 to about 2.0. Feed ratios of about 1.5 to about 1.6 give a product containing considerable quantities of metaphosphates and/or polyphosphates higher than tripolyphosphate. Mixtures containing measurable quantities of form I Na P O are invariably made at temperatures above 350 C. by our method. The equivalent compounds containing K and Li can be produced at tempera tures of about 120 C. to 620 C. and retention times of about 0.2 hour to about 10 hours.

The examples which follow describe our manufacture of pyrophosphates and polyphosphates and mixtures thereof. Sodium tripolyphosphate, both forms, and tetrasodium pyrophosphate percentages in the product were obtained mainly by ion exchange and chromatographic methods. In determining the percentages of each form of sodium tripolyphosphate in a mixture, the well-known TRT (Temperature Rise Test) was used. Although generally used for commercial applications, this test has its highest accuracy with compositions containing high percentages of form II sodium tripolyphosphate. This test is explained in an article by J. D. McGilvery in the ASTM Bulletin, No. 191, July 1953.

Although not usually reported in the examples, some of the products contained small amounts of the metaor polyphosphates higher than tripolyphosphate, usually about 0.1l.0%. Because this process is applicable to a very broad range of polyphosphate mixtures, as well as the single components, the examples were selected to show operating conditions for only a relatively small number of the more commercially desirable mixtures. These examples, together with methods of controlling the product composition by variation of the M O:P O ratio, can be interpreted to define a considerable number of mixtures not specifically shown.

Example 1 As the starting bed for this run, a 680 kilogram batch of sodium tripolyphosphate, containing about 10% tetrasodium pyrophosphate was charged to a 4 ft. diameter fluid bed reactor. This bed was expanded by fluidizing gases generated in an external combustion chamber employing natural gas and about 650 c.f.m. ambient air. Temperature equilibration was obtained with the bed at 440 C. and the windbox at 630 C. These temperatures were maintained essentially constant throughout the entire run. Entrained particles separated in the collector were returned to the bed. A dry, crystalline mixture containing Na HPO NaH PO NEIQHZPZOI'I, and Na4P207, but comprising the former two components in larger quantitics, and having a Na O:P O ratio of about 1.69, was used as feed material. Before feeding, this material was milled to pass about 6065% through a 325 mesh screen and had a bulk density of about 60-70 lbs./ cu. ft. The sodium phosphate feed was delivered to the reactor at a point about 1 ft. above the top of the bed at a rate of about 111 kilograms/ hour during the 6 hours of this run. The analyzed product showed 59.9% Na P O II and 29.2% Na5P301B I, with the remainder substantially all Na P O The product showed a bulk density of 50 lbs./ cu. ft. with about 66% retained on a 30 mesh screen.

Example 2 Using the same apparatus and procedure as Example 1, a 4900 kilogram batch of milled feed of about the same composition as that given in the previous example, with a ratio of 1.67, was processed. The bed temperature was held at 295 C. and the material was retained in the conversion bed for 55 minutes. The product showed 97.1% Na P O II and the remainder substantially all Na P O Example 3 With a procedure similar to Example 1 and bed temperatures of about 460483 C., a granular material containing mainly Na P O II was fed to the conversion bed. Continuous operation, feeding about 400 lbs/hour to the bed and employing a retention time of 4.4 hours, was maintained. About 50% Na P O I and the remainder substantially all Na P O II and Na P O was found by a product analysis.

Example 4 A starting bed of Na P O was charged to the bed section of a fluid bed reactor. This was expanded by hot gases passing through the bed at an apparent space velocity of 1.30 ft./sec. giving a bed pressure drop of 12" H O. The bed temperature was fixed at 412 C. for the duration of this 9 hour run. A dry, crystalline feed containing only Na i-IP0 milled to pass about 50% through a 325 mesh screen was fed to the initial bed at a rate of 270 lbs/hour. The product of this thermal dehydration contained substantially all Na P O Example 5 A batch of about 337 lbs. of the sodium tripolyphosphate mixture manufactured during the run of Example 3 was used as the bed for this run. The bed was fluidized and brought to a temperature of 287 C. A 2,220 lb. feed lot containing mainly the sodium orthophosphates, milled to pass 60% through a 325 mesh screen and having a Na O:P O ratio of about 1.70 was fed continuously to the reactor. The feed rate was fixed at 600 lbs/hour, allowing a retention time of about 32 minutes. Product was intermittently withdrawn from the bed at about 5 9 minute intervals. A composition containing 22.0% NH4P207 with the remainder substantially all Na P O II was produced by this run. The bulk density of this polyphosphate composition had become 32 lbs/cu. ft. with about 18% passing through a 30 mesh screen.

Example 6 A continuous run employing a 1,750 lb. bed containing mainly Na P O II was made. The retention time was about 5.4 hours, and the bed and windbox temperatures were 483485 C. and 580 C. respectively. Granular, dry feed containing mostly Na P O II previously prepared to about equivalent composition as that produced in Example 2 was fed to the expanded bed. This operation yielded compositions containing high percentages of form I sodium tripolyphosphate with the remaindersubstantially all form II. Samples of the product taken at one hour intervals showed 64.4%, 66.0% and 72% form I. The first two samples were taken while the bed temperature was at 483 C., and the last at about 485 C.

Example 7 Using the same procedure and apparatus as in Example 6, a low temperature run was made. The bed temperature was adjusted to 270 C. and held constant throughout this run. To a 472 lb. initial bed of the same composition as in the foregoing example, a feed rate of 500 lbs/hour was established. The orthophosphate feed mixture had been finely milled to pass 60-65% through a 325 mesh screen and had a ratio of Na O:P O somewhat greater than 1.67. These materials were retained in the conversion zone for about 56 minutes. This operation lasted 6.5 hours. The product showed 89.9% form II Na P O with the remainder substantial- 1y all Na P O Example 8 For this run a 1,200 lb. bed of granular Na P O was fluidized in a 4 ft. diameter fluid bed reactor. During the run the bed temperature was varied between 299 C. and 325 C. by controlling the rate of combustion in an external combustion chamber. For these conditions the windbox and free board temperatures were 3994l8 C. and 248260 C., respectively. A finely milled, thoroughly commingled lot of dry orthophosphate feed containing a Na O:P O ratio of about 1.68 was fed to the initial bed at a rate of 800 lbs/hour and retained therein for 1.5 hours. The material so produced contained 4.6% Na P O 94.8% Na P O II, and had a moderate bulk density of 40.7 lbs/cu. ft.

Example 9 A fluid bed reactor was fitted with spray nozzles to produce polyphosphate mixtures directly from a liquid feed containing mainly the orthophosphates. These nozzles were situated about 24" above the upper level of fluidized particles, each giving a spray pattern of about 24" diameter. A solution containing about 50% by weight H and the remainder mainly sodium orthophosphates was used as feed. The conversion bed consisted of about 1,200 lbs. of dry Na P O II produced in a prior liquid feed run and was fluidized with gases generated externally. The feed was sprayed at the rate of 200 lbs/hr. above the fluidized particles maintained at a temperature of 300 C. The free board temperature was found to be 190-255 C., and the maximum windbox temperature 600 C. A spray nozzle pressure of 15-25 p.s.i.g. was used. In this manner a continuous run producing 1,935 lbs, of polyphosphate Was completed. During the first part of the run the feed contained a low Na O:P O ratio and the material produced had an assay of about 94.9% Na P O II with the remainder substantially all Na P O The second prt of the run used a higher Na O:P O feed ratio to produce 88.3%

10 Na P O II with the remainder substantially all Na P O Example 10 A continuous run employing a 337 lb. bed was made. A moist consisting of Na HPO and NaI-I PO previously milled to pass about 60% through a 325 mesh screen, and with a Na O:P O ratio of about 1.62 was fed to the pre-established bed at a rate of 350 lbs/hour. The retention time was adjusted to about 54 minutes, and the bed and windbox temperatures were maintained at 292 C. and 450 C., respectively. This run was continued for 5.5 hours. The product of this operation analyzed 86.1% form II Na P O 5.3% Na P O and 8.6% NaPO cu. ft. and 15.2% was retained on a mesh screen.

In all the examples given herein, the pre-existing or starting bed contained materials analytically equivalent to the product which was ultimately produced therein.

' Usually, during these runs the bed weight did not vary appreciably from that initially established because product was discharged at about the same rate as new materials were fed.

Examples 11 To act as the starting bed for fluidization, a 2,000 lb. sample of Type IV (see Table I) untreated sodium acid pyrophosphate, milled to pass 93.2% through a 200 mesh screen, was charged to the tuyere plate of a fluid bed react-or having a diameter of 4 feet. This material was fluidized to give a bed depth of 4 ft. by gases supplied from the combustion of natural gas in an external combustion chamber and air supplied from a turboblower, together creating a superficial gas velocity of 0.86 ft./sec. Materials entrained and recovered in the overhead dust colector were refluxed to the bed. The combustion rate was controlled to give a bed temperature of 230 C. A 2,500 lb. unconverted batch of monosodium orthophosphate, coresponding in additives to Type IV in Table I, was milled to pass 78.1% through 200 mesh and fed at a rate of 500 lbs/hr. to the top of the previously established bed where it fluidized. Product material was discharged from the bed at about 5 minute intervals, maintaining approximately a 2,000 lb. bed during the 5 hours of operation. The product discharged of this process showed essentially complete conversion of the monosodium orthophosphate to sodium acid pyrophosphate.

Example 12 Approximately 1,000 lbs. of the sodium acid pyrophosphate produced in Example 11 was left in the 4 ft. reactor as the starting bed for this run. The gas velocity was increased to 1.02 ft./sec. to give a bed depth of 2 ft. while continuing to reflux the entrained materials back to the bed. The combustion rate was adjusted to give a bed temperature of 210 C. A 500 lb. batch of granular, unmilled monosodium orthophosphate, 76.3% through 30 mesh, was fed to the top of the bed where it fluidized. For this one hour run product material was withdrawn from the bed at about 5 minute intervals, maintaining the 1,000 lb. bed, and the remaining material of the bed was discharged from the reactor at the end of the run. It was found that this run had produced essentially complete conversion of monosodium orthophosphate to sodium acid pyrophosphate.

Example 13 An initial bed consisting of approximately 1,500 lbs. of sodium acid pyrophosphate, milled to pass about 83 to through a 325 mesh screen, was charged to a fluid bed reactor having a diameter of 4 feet. This material was fluidized to give a bed depth of 3 /2 ft. by a stream of gases passing through the bed at a velocity of 0.77-0.82 ft./sec. A bed temperature of 210 C. was obtained and maintained by regulating the windbox temperatures The bulk density of the product was 35.0 lbs./ I

to an average of 335 C. but at no time exceeding 390 C. During fluidization, the outlet gas temperature (at the dust collector) was found to be 160 C. and the freeboard draft pressure 0.2 in. of water. A 4,200 lb. lot of untreated sodium acid pyrophosphate, milled to pass about 8390% through 325 mesh, and containing 0.08% CaO additive was used as feed material. It was fed to the top of the previously established bed at a rate of 1,400 lbs./hr. while injecting 20 p.s.i.g. steam into the windbox through a /2" orifice. Product material was discharged from the bed throughout the 3 hours of operation. The tempered and steam treated product was found to be stable, not differing by more than 4% from the originally established reaction rate after being subjected to the accelerated storage test, and showed a neutralizing strength of 73.7.

Example 14 A 4 ft. fluidized bed of milled sodium acid pyrophos phate corresponding to that produced in Example 11 was established in a 5 /2 ft. diameter fluid bed reactor. The bed temperature was stabilized at 225 C. and the superficial gas velocity was adjusted to 0.69 ft./sec. A total of 3,300 lbs. of untreated sodium acid pyrophosphate having a pyro content of 95.3%, N-S value of 73.4, and milled to pass 98.0% through a 200 mesh screen and 90.0% through a 325 mesh screen, was fed to the top of the previously established bed at the rate of 1,750 lbs/hr. Product material was withdrawn from the bed at about 5 minute intervals, maintaining the 4 ft. bed and retaining the feed in the bed for 1.9 hours. The product of this heat treating operation was found to contain 98.1% sodium acid pyrophosphate, an increase of 2.8% from the feed. The sievings of the product proved that some of the larger particles had been broken up (99.0% through 200 mesh) but with fewer small particles (only 88% through 325 mesh).

Example 15 An initial bed of approximately 3,300 lbs. of sodium acid pyrophostate, milled to pass 83% through 325 mesh, was charged to a reactor having a diameter of 5 /2 feet. The bed was fluidized with a gas stream at a velocity of 0.77 ft./sec. and the bed temperature was adjusted to 245 C. A 3,300 lb. batch of untreated, sodium acid pyrophosphate, milled to pass 83% through 325 mesh, and containing 0.15% CaO and 0.15% Al O additives, was fed to the bed at the rate of 1,150 lbs/hr. and retained in the bed for 2.9 hrs. The product of this heat treating process was discharged at 5 minute intervals, maintaining the original weight bed for the duration of the run. This material was found to have an initial 2 min. reaction rate of 26% which, after exposure to the accelerated storage test explained herein, increased to 28%.

Example 16 A 1,700 lb. bed of sodium acid pyrophosphate was established in a 4 ft. diameter fluid bed reactor. This initial bed was fluidized by gases supplied from the combustion of natural gas and air at 20% relative humidity supplied from a turboblower, together creating a superficial gas velocity of 0.86 ft./sec. Steam was injected into the hot gases at the windbox at a rate of 50100 lbs/hr. to establish and maintain throughout this run 100% relative humidity in the fiuidizing gases. The bed temperature was maintained at 7095 C. by controlling combustion rate at the burner, and the temperature of the gas being discharged to the atmosphere was found to average about 60 C. Approximately 9,600 lbs. of untreated sodium acid pyrophosphate, with 0.10% Cat) and 0.10% A1 additives and relatively poor stability, showing a reaction rate change of about 6-9% from the initially established rate after exposure to the accelerated storage test described herein, was fed to the bed. The feed rate was established at 1,000 lbs/hr. and the original bed weight was maintained by extracting'materials from the bed at about 5 minute intervals. The product of this stream treatment run was found to have become more stable showing a reaction rate change of not more than 4% from the initially established rate after exposure to the accelerated storage test.

The following examples will serve to illustrate our method of producing sodium acid pyrophosphate directly from a monosodiurn orthophosphate liquid by a one step procedure. By comparison, the methods used heretofore typically required three separate operations, viz., drying, conversion, and treatment, to produce sodium acid pyrophosphate from the liquid phosphoric acid-soda ash reaction product.

Example 17 An initial bed consisting of finely divided sodium acid pyrophosphate, corresponding in additives to Type III in Table I infra, was charged to the bed chamber of a fluidization unit. This material was then expanded to a dense fluidized phase and heated to a temperature of 210215 C. by hot gases uprising from the windbox. A liquid feed consisting of 60% monosodium orthophosphate having Type III additives, and 40% water was then sprayed directly into the expanded bed through a two fluid nozzle (utilizing air as the secondary fluid) positioned about as shown in the accompanying drawing. As feed was passed into the bed, particles of sodium acid pyrophosphate were removed therefrom at about an equivalent stoichiometric rate. Fines escaping the bed by entrainment in the dilute overhead phase were collected in a cyclone and returned to the dense phase. A feed rate to bed weight ratio (retention time) of about 3.0, based on moisture-free monosodium orthophosphate feed, was maintained, While an air to liquid ratio of 0.3 ft. lb. was used for the two fluid feed. The total duration of this run was 72 hours. At the end of the run the entire bed was discharged and the unit was inspected and found to be substantially free of crustations and agglomerates of any sort. Samples of the product were tested and found to be a sodium acid pyrophosphate baking acid of high quality and good stability having a pyro content of about 97%, a 2 minute reaction rate ranging from 31% to 37% and a neutralizing strength ranging from about 71 to 74.

Example 18 Utilizing the same techniques described in Example 17, a liquid feed run of 40 hours duration was carried out in which a sodium acid pyrophosphate baking acid, having the Type V additives of Table I infra, was produced.

In accordance with the foregoing examples, the conversion of sodium orthophosphate to sodium acid pyrophosphate, as well as such subsequent heat or steam treatment thereof as is desired, is carried out in'a-fluidized bed at a temperature above about 200 C. but below the decomposition temperature of sodium acid pyrophosphate. We have found that conversion and heat treating are most satisfactorily accomplished at temperatures only slightly below the decomposition temperature of sodium acid pyrophosphate, which varies slightly under the influence of different additives, pH values, etc. The process of the invention permits the production of sodium acid pyrophosphate compositions having desirably high stability, pyro content, neutralizing strength, and absence of fines.

An advantage of our invention is that it yields sodium acid pyrophosphate of more commerically desirable stability, pyro content, neutralizing strength, and particle size. Continuous and large-scale production of sodium acid pyrophosphate by our method yields a composition consistently having a pyro content of 9698% and on occasion as high as 99%.

Of no less importance is the remarkable and totally unexpected agglomeration control, heretofore virtually unknown in this field. This ease of control permits not only the continuous production at high rates for long periods of a uniform product free of lumps and agglomerates, but also quick, trouble-free change-overs to the processing conditions required for each of the several commercial grades.

By our method, a bed of sodium acid pyrophosphate, having the same approximate composition as the material to be ultimately produced, is first charged to the bed chamber of a fluidization unit where it is expanded to a dense turbulent state by uprising hot gases. When the turbulent bed reaches a temperature suitable for the desired operation, the feed material, either liquid or finely divided solids, is slowly, usually continuously, passed into the fluidization chamber where it disperses in and becomes fluidized together with the pre-established bed. As feed enters, particles of sodium acid pyrophosphate (the preponderant substance present in the bed at any given time) are withdrawn at a substantially equivalent stoichiometric rate.

In accordance with the method of the invention, dry crystalline monosodium orthophosphate (or sodium acid pyrophosphate) is fed to a fluid bed reactor near the top of the fluidized bed at a point preferably above or within the upper level of the bed. Upon contacting a stream of hot gases moving upward through the bed at velocities of about 0.4-1.5 ft./sec., and preferably about 0.75 ft./sec., the charged material fluidizes to give a bed having a typical density of about 35 lbs./ft. After about 1-4 hours of intimate contact with the hot gases, the monosodium orthophosphate is converted to sodium acid pyrophosphate, and when desirable, by adjusting to the proper retension time and/or adding steam to the bed, it is possible to convert and treat the material simultaneously without using an additional bed. Concurrently with feeding, processed particles are withdrawn from the bed through valved outlets located within the bed section. A small portion of the very small particles, up to about 15% at high gas velocities, are entrained by the rising gases and carried overhead where they are collected and either returned to the bed or removed from the process.

A liquid feed comprising monosodium orthophosphate and a solvent, preferably water, may also be advantageously employed by the present method. When water is used as the liquid feed solvent, monosodium orthophosphate solute concentrations of at least 5%, and up to the saturation point of such solution, about 75% monosodium orthophosphate, produce a suitable feed. Preferably, the liquid is sprayed directly into the bed through a constriction-type nozzle. Although it is possible to feed the orthophosphate-containing liquid into the freeboard area, this results in the formation of substantial quantities of entrained dust which must be collected and returned to the bed. Critical positioning of a feed nozzle located Within the fluidized bed is not necessary. Thus it may be located at the wall of the fluidization unit or extended in towards the center of the bed, and may have its opening pointed in any direction, either up, down, or to the side.

A particularly advantageous device for feeding liquids into our dense fluidized bed is the so-called two fluid nozzle. Such nozzle employs, as a secondary fluid, a compressed gas, e.g., air, nitrogen, steam, etc., to mix with the primary fluid, in the present case containing the solubilized feed, and reduce its apparent density. Lowering the liquid feed density in this manner gives it greater buoyancy in the uprising fluidization gases and allows it to be heated and dispersed more rapidly. We have found by our method that a gas to liquid ratio for a two fluid nozzle of 0.1 to 1.0 ft. /lb., based on air at standard temperature and pressure, produces the most desirable spray pattern when feeding below the surface of the bed. A particularly satisfactory location for such nozzle is shown in the accompanying drawing, wherein the nozzle is depicted in the center of the bed, pointing downward with its opening about one foot from the top of the bed plate.

Although largely dependent on bed temperature and type of material processed, retention times in the bed of 14 3, 2, and 1 hours are most common for conversion, heat treating and steam treating, respectively, and for multiple operations in a single bed the proper retention time is somewhat less than the sum of the individual times.

Although the temperature range 200-245 C. has proven to be most satisfactory for conversion and treatment, it is also possible to convert and treat sodium acid pyro-phosphate at temperatures higher than 245 C. to possibly as high as 310 C., in a fluid bed reactor using methods similar to that described in US. Patent 2,021,012.

For the purpose of efliciency and economy, steam treatment, as a separate step after conversion and/or heat treatment, may be accomplished at lower temperatures, i.e., about 50100 C., and preferably at about 60 C. However, steam treatment is often performed concurrently with conversion or heat treating and as such is subject to the temperatures of these operations.

During fluid bed conversion of orthophosphate, it was found that this material becomes tacky and has a tendency to stick together in agglomerates while undergoing the transition to pyrophosphate. To obtain fluidization in the conversion step, without fusion of the bed or blocking of the gas risers, it was discovered that improved operation can be obtained by exceeding the normal gas velocity, with an attendant increase in entrainment rate, and returning the collected solids to the bed.

We have also found that very fine milling of the raw material, about 100% through 200 mesh, gives the most desirable, i.e., the fastest processing rates for sodium acid pyrophosphate. Nevertheless, coarse material, even unmilled feed, may be fluidized and processed, but less efliciently and at higher retention times.

Even in cases where, through operator error or otherwise, some large agglomerates or lumps form, they immediately fall to the bottom of the bed, coming to rest on the tuyere plate, and may be removed later during a routine suspension of operations. Impingement and collison within the bed and on the walls tend to selectively break up the larger particle sizes while having a negligible effect on the smaller sizes. Very small particles or dust formed during a prior milling operation or by collision within the bed are too buoyant to stay suspended in the bed and are carried overhead and collected. Thus, the method of the invention has been found to be a very effective means of classifying and removing undesirable particle sizes during the processing operations.

Pilot runs using a liquid monosodium orthophosphate feed were accomplished for all of the various sodium acid pyrophosphate grades shown in Table I infra. The stability of all the sodium acid pyrophosphate produced was excellent. Samples which were evaluated by the accelerated storage test described below were found to change on the average of only about 2.5% in reaction rate as a result of exposure to the severe conditions of temperature and humidity.

To meet the varied demands of the baking industry, sodium acid pyrophosphate is supplied for commerce in a plurality of grades which differ mainly in their speed of reaction. This speed of reaction is known in the art as the reaction rate or reactivity and is a measure of the speed at which sodium acid pyrophosphate will react (in a doughnut or biscuit dough) with sodium bicarbonate to liberate carbon dioxide. Values for the reaction rates mentioned herein are given as percentages of the total carbon dioxide content which is liberated in 2 minutes in a doughnut dough at a temperature of 27 C.

Baking acids of the sodium acid pyrophosphate type may have a tendency to gradually increase in reaction rate upon exposure to atmospheric conditions of high temperature and humidity, the faster reacting grades showing the greater propensity to change. Because it is often advantageous in the baking industry to store baking acids for prolonged periods under non-ideal atmospheric conditions, stability of these acids is a commercially important quality.

The following table shows commercially available sodiurn acid pyrophosphate baking acid compositions employing the additives recently suggested by US Patent 2,844,437 and various combinations of the heat and steam treatments mentioned previously. The compounds listed in the table are typical examples of the baking acids that can be produced by our method in large-scale fluidized bed equipment at high production rates.

The stability of these compounds is determined by an accelerated storage test which involves testing the baking acid by the standard 2 minute rate test, then exposing this material to an atmosphere having a relative humidity of 75% at 140 F. for five hours, after which the material is retested by the 2 minute rate test, The neutralizing strength (N-S) values given in this table represent the amount of baking soda required to react with 100 grams of sodium acid pyrophosphate to completely liberate its carbon dioxide leavening gas, and were determined by standard titration methods. The pyro content values were determined by chromatographic or titration methods. Quantitative data describing the stability of our improved sodium acid pyrop'hosphate are given in the table. It may be seen that the reaction rates do not change by more than 3% to 7% from the initially established rate produced, maintaining a feed rate and bed temperature which will prevent the loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being in the range between 200 C. and 620 C., and withdrawing molecularly dehydrated phosphate prod ucts from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the aqueous feed.

3. A process for producing a molecularly dehydrated phosphate mixture consisting essentially of Na P O Na P O I, and Na 0 II which comprises preparing a feed consisting essentially of Na HPO and NaHPO and having ratio of alkali metal to phosphorus the same as the ratio of the molecularly dehydrated phosphate to be be produced, feeding said feed to a pre-established fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature bein in the range between 350 C, and 620 C., and withdrawing molecularly dehydrated phosphate product from the fluidized bed at a after exposure to the accelerated storage test. rate approximately equal to the rate at which alkali TABLE I l I I 7 i a g gg 2 Min. Rate After Additives, Treatment After phate Content) N-S (Neutralizing 2 Min. Accelerated Storq Type Percent By Conversion Percent By etrength), Gms. Rate, age Test,

Weight Weight Percent Percent None 97 0 73. 6 Steam treatment 97. 5 73. 4 36 40 do 96.9 72. 9 31 36 do 97. 5 72. 1 25 30 do 07. 8 73-74 24 27 The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

We claim:

1. A process for producing a molecularly dehydrated phosphate selected from the group consisting of alkali metal pyrophosphate, alkali metal polyphosphate and mixtures thereof, which comprises preparing a finely divided dry feed consisting essentially of alkali metal orthophosphates said feed having substantially the same ratio of alkali metal to phosphorus as the molecularly dehydrated phosphate to be produced, feeding said dry feed to a preestablished fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being in the range between 200 C. and 620 C., and withdrawing molecularly dehydrated phosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

2. A process for producing a molecularly dehydrated phosphate selected from the group consisting of alkali metal pyrophosphate, alkali metal polyphosphate, and mix tures thereof which comprises preparing an aqueous feed consisting essentially of alkali metal orthophosphates and water said feed having substantially the same ratio of alkali metal to phosphorus as the molecularly dehydrated phosphate to be produced, feeding said aqueous feed to a ire-established fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be metal and phosphorus components enter the fluidized bed in the feed.

4. A process for producing a molecularly dehydrated phosphate mixture consisting essentially of a Na P O I and Na 0 II which comprises preparing a feed material containing Na HPO and NaH PO having a ratio of alkali metal to phosphorus of 5 to 3, feeding said feed to a pre-established fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining the feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being within the range between 350 C. and 620 C., and withdrawing molecularly dehydrated phosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

5. A process for producing a molecularly dehydrated phosphate mixture consisting essentially of Na P O and Na P O II which comprises preparing a feed material containing Na HPO and NaH PO said feed having sub stantially the same ratio of alkali metal to phosphorus as the molecularly dehydrated phosphate to be produced, feeding said feed to a preestablished fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being within the range of 250 C. and 450 C., and withdrawing molecularly dehydrated phosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

6. A process for producing a molecularly dehydrated phosphate mixture consisting essentially of Na P O and Na P O I which comprises preparing a feed material containing Na HPO and NaH PO said feed having substantially the same ratio of alkali metal to phosphorus as the molecularly dehydrated phosphate to be produced, feeding said feed to a preestablished fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being within the range between 450 C. and 620 C., and withdrawing molecularly dehydrated phosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

7. A process for producing a molecularly dehydrated phosphate selected from the group consisting of Na P O Na P O I, and Na P O II which comprises preparing a feed material containing at least one member selected from the group consisting of Na HPO and NaH PO said feed having substantially the same ratio of alkali metal to phosphorus as the molecularly dehydrated phosphate to be produced, feeding said feed to a pre-established fluidized bed of particles of molecularly dehydrated phosphate having at all times substantially the same composition as the product to be produced, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being within the range between 200 C. and 620 C., and Withdrawing molecularly dehydrated phosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

8. A process for producing sodium tripolyphosphate which comprises preparing a finely divided dry feed consisting of a mixture of monosodium orthophosphate and disodium orthophosphate and having an Na O:P O ratio of 1.67, feeding said dry feed to a fluidized bed of particles containing at all times substantially all sodium tripolyphosphate, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being in the range between 200 C. and 620 C., and withdrawing sodium tripolyphosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

9. The process of claim 8 wherein the feed is milled to pass about by weight through a 325 mesh screen.

10. A process for preparing sodium acid pyrophosphate which comprises preparing a finely divided dry feed of monosodium orthophosphate which is sized to pass about 50% by weight through a 325 mesh screen, feeding said dry feed to a pre-established fluidized bed having at all times substantially all sodium acid pyrophosphate, maintaining a feed rate and bed temperature which will prevent loss of fluidization due to excessive agglomeration within the fluidized bed said temperature being within the range between 200 C. and the decomposition temperature of sodium acid pyrophosphate, and withdrawing sodium acid pyrophosphate product from the fluidized bed at a rate approximately equal to the rate at which alkali metal and phosphorus components enter the fluidized bed in the feed.

References Cited by the Examiner Kalbach: Chemical Engineering, January 1947, pp. -108.

MAURICE A. BRINDISI, Primary Examiner.

CERl I E I CATE OF CORRECTION Patent No 3 ,210, 154 October 5, 1965 George I. Klein et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 18, for "acounts" read accounts line 62 for "convetred" read converted column 3, line 27 for "comercial-type" read commercial-type column 1 lines 32 to 34 in the formula, after "48 D0" insert a closing parenthesis; lines 69 to 71, for that portion of the formula reading "P 05" read R 0 column 5 lines 7 and 28, fc

"polyphasphates", each occurrence, read polyphosphates column 9, line 74, for "prt" read part column 10, line after "moist" insert feed line 23, for "Examples", in italics, read Example in italics; line 35, for "colector" read collector same column 10, line 38, for "coresponding" read corresponding column 12 line 3, for "stream" read steam column 13, lines 30 and 31 for "retens ion" read retention column 15, TABLE "I third column, line 4 thereof, for "do" read Heat treatment column 16, line 22, for "bein" read being Signed and sealed this 24th day of May 1966.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of. P'atem ERNEST Wu SWIDER Attesting Officer

Claims (1)

1. A PROCESS FOR PRODUCING A MOLECULARLY DEHYDRATED PHOSPHATE SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL PYROPHOSPHATE, ALKALI METAL POLYPHOSPHATE AND MIXTURES THEREOF, WHICH COMPRISES PREPARING A FINELY DIVIDED DRY FEED CONSISTING ESSENTIALLY OF ALKALI METAL ORTHOPHOSPHATES SAID FEED HAVING SUBSTANTIALLY THE SAME RATIO OF ALKALI METAL TO PHOSPHORUS AS THE MOLECULARLY DEHYDRATED PHOSPHATE TO BE PRODUCED, FEEDING SAID DRY FEED TO A PREESTABLISHED FLUIDIZED BED OF PARTICLES OF MOLECULARLY DEHYDRATED PHOSPHATE HAVING AT ALL TIMES SUBSTANTIALLY THE SAME COMPOSITION AS THE PRODUCT TO BE PRODUCED, MAINTAINING A FEED RATE AND BED TEMPERATURE WHICH WILL PREVENT LOSS OF FLUIDIZATION DUE TO EXCESSIVE AGGLOMERATION WITHIN THE FLUIDIZED BED SAID TEMPERATURE BEING IN THE RANGE BETWEEN 200*C. AND 620*C., AND WITHDRAWING MOLECULARLY DEHYDRATED PHOSPHATE PRODUCT FROM THE FLUIDIZED BED AT A RATE APPROXIMATELY EQUAL TO THE RATE AT WHICH ALKALI METAL AND PHOSPHORUS COMPONENTS ENTER THE FLUIDIZED BED IN THE FEED.

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