US3387929A - Method and apparatus for producing polyphosphoric acid - Google Patents

Method and apparatus for producing polyphosphoric acid Download PDF

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Publication number
US3387929A
US3387929A US212773A US21277362A US3387929A US 3387929 A US3387929 A US 3387929A US 212773 A US212773 A US 212773A US 21277362 A US21277362 A US 21277362A US 3387929 A US3387929 A US 3387929A
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Prior art keywords
acid
circuit
heat
combustion
concentration
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US212773A
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English (en)
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Beltz Klaus
Cremer Joseph
Muller-Schiedmayer Gunther
Thomas Friedrich
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Knapsack AG
Knapsack Griesheim AG
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Knapsack AG
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Priority to US719285*A priority Critical patent/US3526482A/en
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/24—Condensed phosphoric acids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S159/00—Concentrating evaporators
    • Y10S159/19—Acid

Definitions

  • the present invention relates to a method of producing polyphosphoric acid, a mixture of condensed phosphoric acids which are present as pyro-, tripolytetrapolyand hi her phosphoric acids, by burning phosphorus and absorbing the phosphorus pentoxide from the combustion gases in phosphoric acids, as well as an apparatus for the carrying out of the method of the invention.
  • polyphosphoric acid there are understood phosphoric acids having an H PO -content of more than 100% H PO (72.5% P which are produced by adjusting the corresponding ratio between the phosphorus pentoxide and water in suitable manner.
  • H PO -content of more than 100% H PO (72.5% P which are produced by adjusting the corresponding ratio between the phosphorus pentoxide and water in suitable manner.
  • two regions free of crystallization exist above 72.5% P 0 namely between 76.0 and 77.5% P 0 (105% and 107% H PO and above 81.0% P 0 (112% H PO
  • the phosphorus pentoxide content is limited to these ranges.
  • the intermediate range of polyphosphoric acids crystallizes upon cooling.
  • the P 0 content of the polyphosphoric acids can reach metaphosphoric acid with 89% P 0 and even be higher than this.
  • steam is injected into the combustion gases of white phosphorus in such an amount that the oxidation products are hydrated to a phosphoric acid having a concentration of between 104.9 and 116% H PO
  • the cooling is effected by absorption of the hot reaction products in an acid film covering the Wall of the combustion chamber, the acid film having a concentration of between 104.9% and 116% H 'PO Satisfactory space-time yields can, however, only be obtained if a sutficiently rapid removal of the large heat of States Patent 0 Patented June 11, 1968 combustion of the phosphorus and of the heat of hydration of the phosphorus pentoxide which must be taken up by the acid covering the wall can be assured.
  • Temperature and concentration of this acid determine the relative vapor pressure of the oxidation and hydration products over the liquid phase. If the vapor pressure of the acid exceeds the partial pressure of said products in the gaseous phase, no absorption takes place but the acid evaporates. If the concentration of the oxidation products in the gaseous phase exceeds the partial pressure over the liquid phase, absorption occurs and the volume of acid increases. The vapor pressure of the acid serving as absorption medium therefore determines the top temperature limit. Another reason not to permit the temperature of the acid to exceed a given temperature limit is its corrosive properties which increase considerably with a decrease in the P 0 concentration, and an increase in the temperature.
  • the acid film which protects the wall of the combustion chamber against overheating forms a coherent layer more readily, the higher the concentration and the lower the temperature. If the viscosity of the acid is increased, either by increasing the P 0 concentration or reducing the temperature to below 180 C., and preferably below 140 C., a coherent acid film of corresponding thickness is formed.
  • the heat of the acid serving as absorption medium must be transmitted through a boundary layer to a cooling medium.
  • the combustion chamber is so designed that the absorption of the main portion of the heat liberated upon the reaction is separated from the formation of the after-concentrated phosphoric acid.
  • the combustion chamber therefore comprises two acid circuits, the first of which sprinkles on the Wall of the combustion chamber and is operated with phosphoric acid of low concentration, for instance less than 107% H PO and preferably to 107% H PO Via this recirculated acid, the heat of combustion is dissipated in a suitable cooling system.
  • the H PO concentration of the acid is maintained constant by the addition of Water or commercial phosphoric acid.
  • the phosphorus pentoxide contained in the combustion gases is absorbed in a polyphosp-horic acid which has the desired final concentration of, for instance, more than 107% H PO
  • the P is converted into polyphosphoric acid by adding water or phosphoric acid, preferably phosphoric acid obtaincd in the first acid circuit.
  • the heat in the two circuits is so divided that the heat of combustion of the phosphorus is mainly removed by transfer into a more dilute acid coolant in a first circuit; the more highly concentrated acid absorbent in a second circuit acts as a vehicle for transfer of a minor proportion of heat produced, which corresponds to the heat of hydration of the phosphorus pentoxide absorbed in said second circuit.
  • the present invention makes possible the production of a highly concentrated polyphosphoric acid of, for instance, more than 107% H PO without encountering difficulties in cooling or becoming uneconomical.
  • the combustion chamber is divided into two chambers 1 and which are partially inserted one in the other and taper slightly downward to assure better acid sprinkling.
  • the heat evolved in the combustion of the phosphorus effected by means of the nozzle 2 and a given part of the phosphorus pentoxide formed are absorbed by the more weakly concentrated phosphoric acid of lower concentration sprinkled over the wall 3A.
  • the acid is charged onto the wall at the top of the tower through a suitable device, for instance, a spray ring 4.
  • the acid is removed at 5 and recycled by means of a pump 7 via a storage container 6 provided with a discharge outlet and a connecting pipe to circuit II (18).
  • the heat exchange takes place via the cooled tower wall and a heat exchanger 8.
  • the acid in circuit I is maintained at a constant P 0 concentration by introducing water or phosphoric acids of lower concentration through the inlet 9.
  • a large part of the phosphorus pentoxide is absorbed in the inner funnel 10 in concentrated polyphosphorlc acid of, for instance, more than 107% H PO which is charged onto the wall at the upper edge by a suitable device, for instance an overflow II.
  • the uppermost edge 21 of the inner funnel which is directly exposed to the area of combustion consists of a material particularly resistant to hot phosphoric acid, preferably graphite.
  • an absorption tower which is sprinkled with the acid contained in circuit II, containing, for instance, more than 107% H PO
  • the absorption tower can be arranged directly below the combustion tower, as well as to the side thereof.
  • the absorption tower advantageously is designed as a pipe 12 provided for the distribution of the acid with centrifuges which are fed with a part of the acid film trickling down the walls.
  • Other absorption devices may also be employed.
  • the highly concentrated acid leaves the collecting funnel 13 and is circulated by means of a pump 15 out of the receiving tank 14 through a small heat exchanger 16 to carry off the residual heat in the circuit.
  • the polyphosphoric acid produced containing, for instance, more than 107% H PO is recovered from the storage tank 17.
  • the removed acid is replenished by the addition of acid from circuit I via the connection 18 or by the addition of water or commercial phosphoric acid.
  • the addition of acid from circuit I can be effected continuously or batchwise.
  • the blower 19, produces a slight vacuum in the combustion tower and the stream of gas is conducted through a cyclone 20 to completely remove entrained acid.
  • the advantage of the two-circuit method is that the difiiculties which occur in discharging the heat from highly concentrated phosphoric acids are avoided since the amounts of heat evolved upon the reaction are discharged by means of the more dilute acid circulating in circuit I before the acid becomes more highly concentrated in circuit II by absorption of the still remaining portion of the P 0 whereby the heat transfer coefiicient is impaired.
  • the plant can be operated either exclusively for the production of highly concentrated polyphosphoric acid containing, for instance, more than 107% H PO or for excess production of acid in circuit I containing, for instance, less than 107% H PO and preferably to 107% H PO the quantitative ratio of the acids obtained in circuits I and II being dependent on the distribution equilibrium.
  • the ratio of the phosphorus pentoxide absorption depends on the P O -concentration of the acid selected in the two circuits and on the P O -concentration of the commercial phosphoric acid added in circuit I.
  • the absorption coefficient corresponds to the ratio of phosphorus pentoxide absorbed in circuit I to the total phosphorus pentoxide. If the absorption coeth cient a is greater than the equilibrium value, an excess production of acid in circuit I is the result; if a is smaller, a further addition of water or of commercial phosphoric acid in circuit II becomes necessary.
  • orthophosphoric acids of low concentrations can also be added in circuit I, but this results in an impairment of the heat distribution so that it is recommended to use acids having a P O -content which is greater than that of the commercial concentrated phosphoric acid.
  • a desired excess production of acid having less than, for instance, 107% H PO in circuit I can be obtained by increasing the coefiicient of absorption referred to the added water, or by the addition of commercial phosphoric acid, or a mixture having a given ratio of water and phosphoric acid.
  • the value of the absorption coefficient is determined by the size and design of the acid-sprayed surface of the combustion chamber.
  • the absorption coefficient results as a function of several variables, represented by the size of surface, radius and inclination of the combustion chamber, length of the funnel, velocity of flow and temperature of the combustion gases, as well as the concentration of the phosphorus pen-toxide in the combustion gases.
  • the plant is designed beforehand for a given absorption coefficient.
  • a change in the absorption surface of the tower relative to the P O -charged combustion gas stream is obtained by vertical displacement of the phophorus nozzle in the combustion tower.
  • the phosphorus combustion nozzle is so designed that it can be displaced vertically through the cover of the tower into the combustion tower, and its depth of immersion can be varied.
  • the absorption surface of circuit I is at the same time decreased and the absorption coefficient is lowered, which corresponds to an increase of the P proportion in circuit II.
  • circuit I is so designed that it corresponds to the maximum desired absorption coefiicient which attains its larger value in circuit I upon the reaction of phosphorus pentoxide with water, and the maximum possible acid concentration, and additional increase of the absorption is possible by imparting a rotary motion to the combustion gases.
  • the rotary motion is best produced by the imparting of a twist to the gas fed to the combustion nozzle. The two effects are in opposition to each other, and can be applied either separately or in combination.
  • a change in the absorption coefficient is furthermore obtained by increasing or reducing the velocity of flow of the combustion gases in the tower.
  • An increase in the velocity of flow can be obtained by increasing the amount of combustion air above the minimum value necessary for the burning of the phosphorus. Air or a mixture which is strongly enriched with oxygen can be used.
  • An increase in the velocity of flow of the P 0 containing combustion gases corresponds to a reduction of the absorption coefl'icient.
  • the process of the present invention for the production of polyphosphoric acids of high concentration by burning elementary phosphorus with air/ or an oxygen-containing gas and subsequently absorbing the P 0 formed in phosphoric acids is carried out as follows: the main portion of heat set free during the combustion reaction is removed by means of phosphoric acid circulated in circuit I through a reaction zone comprising a first absorption zone and an appropriate cooling system, while a portion of the P 0 obtained is absorbed simultaneously with such removal of heat, and the remaining portion of the P 0 is absorbed in polyphosphoric acid circulated in circuit II through a second absorption zone and an appropriate cooling system, the polyphosphoric acid used in circuit II having a concentration of P 0 higher than the acid circulated in circuit I.
  • At least about 30% and at most about 70%, preferably 40 to 60% of the P 0 produced are absorbed in circuit I within the first absorption zone, and at least about 75% of the reaction heat are dissipated within circuit 1.
  • the phosphoric acid used in circuit I contains less than about 77.5% by weight P 0 preferably about 76.0 to 77.5% by weight.
  • the phosphoric acid used in circuit II contains more than about 77.5 by weight P 0 preferably about 84% by weight.
  • the acids used in circuit I and circuit II have a temperature of less than about 180 C. and generally a 6 temperature within the range of about 60 C., advantageously C., to about 40 C.
  • the concentration of the acid circulated in circuit I is kept constant by adding water and/or commercial phosphoric acid, and so is the acid circulated in circuit II by adding water and/ or phosphoric acid.
  • the phosphoric acid used in latter case is withdrawn from circuit I.
  • a portion of the absorbed and thereby concentrated polyphosphoric acid is withdrawn continuously or batchwise from circuit II as the final product.
  • the reaction and absorption zones comprise two chambers (1 and 10) which are partially inserted one into the other and slightly taper downward, of which the upper chamber 1 carries at its head a phosphorus combustion nozzle 2 and a spraying means 4 and at its side walls a cooling jacket 3 and a short outlet pipe 5.
  • the short outlet pipe 5 is connected via a storage tank 6, a pump 7 and a heat exchanger 8 as circuit I to the spraying means 4.
  • the lower chamber 10 which is open at its lower end and taken together with the surrounding jacket forms an overflow 11, is connected with a tower 12 provided with absorbing means and projecting into a collecting funnel 13.
  • the collecting funnel 13 communicates via a cyclone 20 and a blower 19 with the atmosphere and further communicates at its outlet side with a collecting tank 14, which in turn is connected to the storage tank 6 and via a pump 15 and a heat exchanger 16 in circuit II to the overflow 11, and is further connected through a pump 17a to the storage tank 17.
  • the upper funnel edge of the lower chamber 10 is advantageously covered with a material especially resistant to hot phosphoric acid, preferably graphite.
  • the absorption means used in tower 12 are centrifuges which are fed with a portion of the acid flowing down the tower walls.
  • the combustion nozzle 2 is disposed so as to be displaceable in the direction of its longitudinal axis.
  • EXAMPLE 1 50 kg./ hr. elementary, yellow phosphorus were burned in a combustion tower 1 with the aid of combustion nozzle 2. 250 to 300 m. /hr. air were necessary for the combustion.
  • the walls of combustion tower 1 were sprinkled per hour with 25 m. of circulated polyphosphoric acid of 76% P 0 (circuit I), and the lower chamber 10 which is open at its upper end and connected to tower 12 provided with customary absorption means, was sprinkled per hour with 20 m. circulated polyphosphoric acid of 84% P 0 (acid circuit 11).
  • the P 0 obtained from the combustion gases was used to absorb the combustion heat and the hydration heat evolved in the two acid circuits.
  • the acid in circuit I on passing the tower was heated from 89 C. to 102 C. and the acid in circuit II from C. to C.
  • the heat evolved was dissipated in heat exchangers 8 and 16 and via the water-cooled wall 3 of combustion tower 1.
  • Heat exchanger 8 was operated per hour with 10 rn. cooling water at 18 C. the temperature of which rose to 31 C.
  • heat exchanger 16 was operated per hour with 15 m. cooling water at 18 C. the temperature of which rose to 22 C.
  • the tower jacket 3 was charged per hour with 10 m. cooling water which was heated from 18 to 26 C.
  • EXAMPLE 2 Under the conditions specified in Example 1 the process was conducted in a manner such that 90 kg./hr. polyphosphoric acid of 76% P 0 were produced in circuit I while adding 21.5 kg./hr. water. The acid so obtained was introduced through acid line 18 into circuit II. In circuit II 136 kg./hr. polyphosphoric acid of 84% P 0 were obtained while adding 90 kg./hr. polyphosphoric acid of 76% P 0 emanating from circuit I. The polyphosphoric acid produced in circuit II was withdrawn through acid line 17a. The P O -yield thus amounted to 99.7%.
  • EXAMPLE 3 Under the conditions specified in Example 1 the process was conducted in such a manner that 131 kg./hr. polyphosphoric acid of 76% P 0 were produced in circuit I while adding 82 kg./hr. commercial phosphoric acid of 85% H PO The acid so obtained was introduced into circuit II through acid line 18. 196 kg./hr. polyphosphoric acid of 84% P 0 were produced in circuit I] while adding 131 kg./hr. polyphosphoric acid of 76% P 0 emanating from circuit I. The acid produced in circuit II was removed through acid line 17a. The yield was 99.7%.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Gas Separation By Absorption (AREA)
  • Treating Waste Gases (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
US212773A 1961-08-05 1962-07-25 Method and apparatus for producing polyphosphoric acid Expired - Lifetime US3387929A (en)

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US719285*A US3526482A (en) 1961-08-05 1968-02-19 Apparatus for producing polyphosphoric acid

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DEK44440A DE1159403B (de) 1961-08-05 1961-08-05 Verfahren und Vorrichtung zur Herstellung von Polyphosphorsaeure

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CH (1) CH449595A (de)
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GB (1) GB965728A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3954381A (en) * 1973-03-02 1976-05-04 Societe Pour L'equipement Des Industries Chimiques Speichim Method of and apparatus for incinerating an aqueous solution containing nitro compounds
US4135965A (en) * 1976-01-15 1979-01-23 Societe Lab Process and apparatus for the treatment of liquids containing solid particles
CN116534819A (zh) * 2023-05-17 2023-08-04 武汉联德化学品有限公司 一种利用五氧化二磷超细粉制备多聚磷酸的方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1159403B (de) * 1961-08-05 1963-12-19 Knapsack Ag Verfahren und Vorrichtung zur Herstellung von Polyphosphorsaeure
CN107226460A (zh) * 2016-03-25 2017-10-03 云南派博科技有限公司 利用磷燃烧热量浓缩稀磷酸生产过磷酸的方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1898541A (en) * 1929-06-17 1933-02-21 G D Jenssen Company Means for producing acid liquor
US2026519A (en) * 1935-05-15 1936-01-07 Tennessee Valley Authority Apparatus for making phosphoric acid
US2999010A (en) * 1957-03-25 1961-09-05 Tennessee Valley Authority Manufacture of superphosphoric acid
US3015540A (en) * 1960-11-23 1962-01-02 Tennessce Valley Authority Manufacture of superphosphoric acid
DE1159403B (de) * 1961-08-05 1963-12-19 Knapsack Ag Verfahren und Vorrichtung zur Herstellung von Polyphosphorsaeure
US3193350A (en) * 1960-03-05 1965-07-06 Knapsack Ag Method of producing higher polyphosphoric acids

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2303318A (en) * 1940-09-03 1942-12-01 William H Baskervill Separating hydrated phosphorus pentoxide
DE1041481B (de) * 1953-08-11 1958-10-23 Fmc Corp Verfahren zur Herstellung von waessriger Phosphorsaeure

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1898541A (en) * 1929-06-17 1933-02-21 G D Jenssen Company Means for producing acid liquor
US2026519A (en) * 1935-05-15 1936-01-07 Tennessee Valley Authority Apparatus for making phosphoric acid
US2999010A (en) * 1957-03-25 1961-09-05 Tennessee Valley Authority Manufacture of superphosphoric acid
US3193350A (en) * 1960-03-05 1965-07-06 Knapsack Ag Method of producing higher polyphosphoric acids
US3015540A (en) * 1960-11-23 1962-01-02 Tennessce Valley Authority Manufacture of superphosphoric acid
DE1159403B (de) * 1961-08-05 1963-12-19 Knapsack Ag Verfahren und Vorrichtung zur Herstellung von Polyphosphorsaeure

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3954381A (en) * 1973-03-02 1976-05-04 Societe Pour L'equipement Des Industries Chimiques Speichim Method of and apparatus for incinerating an aqueous solution containing nitro compounds
US4135965A (en) * 1976-01-15 1979-01-23 Societe Lab Process and apparatus for the treatment of liquids containing solid particles
CN116534819A (zh) * 2023-05-17 2023-08-04 武汉联德化学品有限公司 一种利用五氧化二磷超细粉制备多聚磷酸的方法

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GB965728A (en) 1964-08-06
CH449595A (de) 1968-01-15

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