IL25062A - Process for the production of concentrated phosphoric acid - Google Patents

Description

Process for the production of concentrated phosphoric acid CHEMICALS ft PHOSPHATES This invention relates to the production of phosphoric acid of high decomposition of rock phosphate with sulfuric acid and is a modification of the main invention claimed Patent Specification According to the main invention the rock phosphate is heated by itself before being contacted with the sulfuric acid and the latter is to the hot rock phosphate that the reaction takes place under certain ned conditions of temperature and absence of water from the reaction and the substantially solid and as a rule granular reaction product is leached with water for separating the phosphoric acid from the calcium sulfate containing It is the object of the present invention so to modify the main invention that on the one hand the phosphoric acid can be obtained at a still higher concentration on the other the calcium sulfate is obtained in a dry state in which it can more readily be separated from the phosphoric In accordance with the the reaction mass obtained by the decomposition of heated rock phosphate with sulfuric acid under the conditions set out in the main invention is extracted with an solvent at a ture below that at the solvent boils under the conditions of the The solvent dissolves the phosphoric acid but leaves the remaining reaction products contained in the reaction mixture The solvent may be that is or miscible to a limited or even completely with where a very highly concentrated phosphoric acid is to be recovered and it is desired to leave the calcium sulfate residue in a dry even solvents should be used in a virtually anhydrous As with the extraction of the reaction mass with its extractio with anhydrous or almost anhydrous solvents among the advantages that a given the extract the density and viscosity of the solvent extract are lower than those of aqueous extract and that less energy is required for the evaporation of the organic solvent from the extract than is required the evaporation of the being of the order of 95 to 99 Moreover the solvent stabilizes the granules already present in the solid reaction mass and also causes coagulation and agglomeration of any fines entrained with extract which can then easily be separated from Suitable solvents for the following cycloaliphatic or aromatic ethers and oxygenated hydrocarbon The solvents can be used either by themselves or in mixtures with other solvents which latter are not necessarily solvents for phosphoric The proper choice of the solvent or solvent mixture depends on their selectivity with respect to phosphoric and sulfuric acids and also to other impurities initially present in the rock It also depends on their physical and chemical properties which determine the conditions in which a solvent is most suitable use in the process according to the some can be an advantage to carry out the extraction under pressure and at elevated temperatures in order to increase the extraction The choice of the solvent and the extraction conditions will be adapted in each specific By another feature of the the main invention is further modified by maintaining the reaction before being leached with either wate or a solvent or solvent for some time at an elevated temperature allowing it to cool and reheating it for some Another intermediate treatment of the reaction mass may consist in denning it for some time at a lower It is found that by all of these measures the decomposition of the phosphate is completed in spite of substantially anhydrous tions of the reaction which otherwise make the completion of the reaction unless a considerable excess of sulfuric acid is By this prolonged reheating operation or denning it becomes possible to use substantially not more than the amount of sulfuric acid stoichiometrically required for the decomposition of those components of the rock phosphate which undergo decomposition in the that primarily tricalcium phosphate and secondarily calcium calcium fluoride and other It is one of the advantages of the main invention that the liberated silicon tetrafl oride and hydrogen fluoride largely expelled from the reaction mixture and an almost phosphoric acid calcium and calcium sulfate are This advantage is even enhanced by the modification according to the present invention since the heating or free sulfuric acid contained in the decomposition mixture is apt to be with the phosphoric acid by most of the solvents usable for the purposes of the present In order theless to obtain pure phosphoric substantially free of sulfuric several different procedures are By one of the decomposition of the rock phosphate is effected by means of a slightly quantity of sulfuric acid in order to avoid the presence in the reaction mixture of sul uric In this ease the amount of the residue can be retrieved by heating the residue again with sulfuric whereafter the mixture of sulfuric and phosphoric acids is extracted from the reaction mixture with either water or a solvent and used again for the decomposition of more rock where the reaction mixture contains some amount of free sulfuric acid the extraction may be effected in stages since it is possible to choose appropriate solvents which preferentially phosphoric such as The first contains a mixture of phosphoric and sulfuric acids and can be used either for such purposes where the phosphoric acid is needed and the presence of sulfuric acid does not in the manufacture of or else it can be recycled for in the decomposition of rock The raffinate of the first is then subjected to a second tion stage which yields a virtually pure phosphoric acid In some cases the solvent extract containing the reactions of phosphoric acid where the presence of a solvent is desirable or even In other cases it might prove an advantage to separate the product acid from the extract by treatment with and precipitation of ammonium In this case the solvent separates as a distinct liquid phase containing most of the organic colouring matter initially present in the phosphate rock or produced during the treatment of the latter with sulfuric and the ammonium phosphate obtained is of high purity and free of organic colouring method according to the invention also provides a possibility of reducing the amounts of Fe and Al oxides with the product By choosing an appropriate solvent or solvent mixture which selectively removes ratio of solvent and reaction mixture and by working under such decomposition conditions of the rock phosphate that no excess of sulfuric acid is present in the reaction it is possible to obtain a concentrated phosphoric acid low in and Al oxide Phosphoric acid obtained by processes in which the reaction mixture is extracted water generally contains a considerable part of the impurities initially present in the phosphate possibly at least in part by the Of the Fe and Al contained as commonly referred to as troublesome since they cause the reversion of into phosphate in form insoluble precipitates in aqueous solution of water soluble phosphates of such phosphoric acid with the increase the viscosity of the phosphoric the more so the higher the concentration of the In the process according to the invention it is by the judicious choice of the appropriate solvents for the to reduce the amount of impurities with the phosphorie acid or even to prevent their extraction virtually anhydrous calcium sulfate residue obtained as a in the process according to the present invention a cheap and clean starting for the manufacture of cement or calcium In the calcining is split off and can be recovered the generation of sulfuric For this latter purpose the liberation of the decomposition reaction mixture from the bulk of fluorine originally contained therein is an important advantage since if any fluoride in the residue and silicon tetrafluoride or hydrogen from the latter in the course of the with the liberated they would contaminate and destroy the catalyst in case the contact process is used sulfuric The invention isillustrated by the following Examples to which it is not Example 1 400 kg of rock phosphate from the of of of of sieve particle size of minus 100 heated to 500 C and then contacted with 350 kg of which the amount required to convert all calcium contained in the rock phosphate into calcium The practically dry mixture was divided into two equal portions A and Δ was allowed to cool to the ambient temperature and then extracted with ethyl o Portion was cooled to 100 maintained at this temperature for 24 allowed to cool and then extracted wit ethyl Th extraction was carried out by the passage of ether condensate through fixed bed of reaction mixture held on a filter which permitted the free passage of solvent but held back the solid From the elutriate the ether was continuously the ether vapour was condensed and the condensate passed again through the reaction extraction was continued for 2 The Table below shows the recovery of in the form of product in per cent of the the rock as well as the concentration and composition of the product acid after the of the Portion A B Recovery of Composition of product acid 89 P Weight of anhydrous residue kg 265 of residue When product acid obtained from both portions was neutralized with to a of about no precipitate was 2 Begev rock phosphate of of of of grain size of minus 100 was heated to and then mixed in a pug mill with rock phosphate of parts by This amount of sulfuric acid is of the theoretical amount needed for the complete conversion of all the calcium contained in the rock During the mixing proces and silicon fluoride some hydrogen fluoride were evolved from the When no more gas evolved the reaction mixture was cooled to about by the passage of and then contacted in a counter current extractor with five times its volume of ethyl Some of the ether evaporated during the extraction and was condensed and After evaporation of the ether the extract a highly pure phosphoric acid of concentration containing of fluorine and traces of other impurities was The solid residue leaving the extractor consisted mainly of substantially dry in the form of It was freed from residual solvent by heating with a stream of inert The residual dry material of total of of In order to recover this remainder of the residue was heated again to and contacted in a second pug mill with a large excess of The reaction mixture thus obtained was cooled to the ambient temperature and extracted currently with The solvent was evaporated from the extract and the acid obtained of of corresponding to of y of F This acid was returned to the first stage of the process and made up with so much acid that the aforesaid feed ratio of rock phosphate was The residual anhydrous obtained in the second step of the operation contained of and of F and conetituted a suitable raw material for simultaneous production of sulfuric acid and of In the course of the two stages of this process the fluorine content of the rock phosphate was expelled and the final reaction the phosphoric acid and were practically free of 5 203 kg of coarsely ground phosphate rock from Oron of of of of particle of minus 20 were heated C and then contacted with 180 of The reaction mixture was allowed to cool to the ambient temperature and then extracted twice in succession with ethyl The acids remaining after Extraction I Extraction In both acids no precipitate formed upon neutralization with alkali hydroxide or 202 kg phosphate containing of of of ground to pass through a 100 mesh and heated to were reacted with 178 kg of mixture which wae a paste for a short of time rapidly set and solidified into a solid mixture of powder and After cooling this mixture was divided into portions which were extracted each with a different The following results were Yield Acid Analysis Solvent 5 P 99 Acetone Ketone Methyl alcohol 98 alcohol 0 93 4 acetate 10 Tetrahydrofurane not The several acid extracts differed in their composition owing to the fact that on the hand the reaction mixture used was not mixed well enough and was therefore not and on the other hand some solvent remained in the but this solvent can be readily Exampl The phosphate rock described in 1 was heated to and found to react better with the sulphuric acid than at which would be the ture which the reaction mixture would spontaneously assume owing to the exothermal reaction of the originally cold acid and phosphate The hot phosphate rock mixed with acid in the proportions indicated below after the mixture was extracted with ethyl ether and the solvent was The results obtained are given in the following Analysis of Temperature of Type of per 100 g of Phosphate phate rock used Phosphate rock 4 4 Oron 100 mesh 89 Oron 100 mesh Example 200 kg of phosphate rock as specified in Example 1 were reacted without preliminary heating with 229 kg of 75 The mixture obtained was damp and did not After eooling to ambient temperature the reaction was extracted with methyl Less than of the recovered in the After the product analyzed of of The amount of fluorine left in the residue was The residue was reheated to and kept 24 hours at this after which a second extraction was carried The amount of fluorine in the residue was thus reduced to but was much higher than in any of the previous The comparative test shows that when solvent extraction is applied to a reaction mixture obtained without preliminary heating of the rock phosphate the extraction efficiency is much lower and the separation of the extract from the residue is Example kg of Florida pebble phosphate rock containing of of of of of were ground to minus on a 200 USS sieve and minus on a 100 mesh USS sieve and heated to The hot phosphate rock was reacted with 185 kg of cooled to ambient temperature and then extracted with ethyl The recovery of in the product acid was and the acid contained of of If instead of ethyl ether methyl alcohol was used as the solvent the product acid and of Example 200 kg of Christmas Island phosphate rock containing of of were ground to plus 27 on a 100 mesh sieve and to minus on a 200 mesh USS and heated of and after cooling down to ambient temperature the mixture extracted with The product acid obtained after evaporation of the solvent contained of of of and of More than of the of the rock phosphate was recovered as product insufficientOCRQuality

Claims (12)

HAVING NOW particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim isj-

1. . A process for the production of phosphoric acid of a high JP2°5 con-fcen* ¾y *ae decomposition of rock phosphate with sulfuric acid, wherein the rock phosphate is heated by itself before being contacted with the sulfuric acid, and the latter is admixed to the hot phosphate, the temperature to which the phosphate is pre-heated and the degree of concentration of the sulfuric acid being so chosen that in the resulting reaction mixture highly concentrated sulfuric acid reacts with the phosphate at a temperature of about 100 to 200°Cj the substantially dry, solid and as a rule granular reaction product is extracted with an organic solvent or solvent mixture at a temperature below the boiling temperature of the latter, and the solvent is evaporated from the extract,

2. . A process according to Claim 1 , wherein prior to the solvent extraction the reaction mixture is maintained at a temperature of 100-3GG°C for 10 minutes to 24 hours.

3. . A process according to Claim 1 , wherein prior to the solvent extraction the reaction mixture is cooled or allowed to cool, and then reheated to about 200°C.

4. A process according to Claim 1 , wherein prior to " ~~ the solvent extraction the reaction mixture is denned.

5. · A process according to any of Claims 1 to 4, wherein the extraction operation is repeated once or several times.

6. A process according to any of the preceding Claims, wherein the sulfuric acid is used in a proportion of 90-955& of the stoichiometrical quantity needed for converting all the calcium contained in the rock phosphate into calcium sulfate, and the raffinate left after the solvent extraction is treated again with sulfuric acid in a proportion in a _ excess of the residual ^ ^5 con*en* of ¾ne raffinate, and the solvent extraction is repeated.

7. A process according to Claim 6, wherein the acid recovered by the second extraction is recycled to the operation of heat-decomposition of the rock phosphate.

8. A process according to any of the preceding Claims wherein the solvent or solvent mixture used in the extraction operations consists of aliphatic, cycloaliphatic or aromatic alcohols, esters, aldehydes, ketones, acids, ethers or other oxygenated hydrocarbon derivatives.

9. Δ process according to Claim 8, wherein solvents capable of dissolving phosphoric acid are used in mixture with solvents which, by themselves, are not so capable.

10. A procees for the production of phosphoric acid of high ?2^5 con"t©n* ¾y decomposition of rock phosphate with sulfuric acid substantially as described herein.

11. Concentrated phosphoric acid of high purity when produced by the process according to any of Claims 1 to 10.

12. Dry calcium sulfate anhydrite of low fluorine content when obtained as a residue from the process according to any of Claims 1 to 11. Bated this 27th day of January, 1966 Fo the Applicants PC:I£