CA2070949A1 - Production of phosphorous acid using gas plasma - Google Patents
Production of phosphorous acid using gas plasmaInfo
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- CA2070949A1 CA2070949A1 CA 2070949 CA2070949A CA2070949A1 CA 2070949 A1 CA2070949 A1 CA 2070949A1 CA 2070949 CA2070949 CA 2070949 CA 2070949 A CA2070949 A CA 2070949A CA 2070949 A1 CA2070949 A1 CA 2070949A1
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- phosphorus
- plasma
- phosphorous acid
- oxides
- gas
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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
- C01B25/163—Phosphorous acid; Salts thereof
-
- 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
- C01B25/12—Oxides of phosphorus
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- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
ABSTRACT
The present invention relates to a process for the production of phosphorous acid of high purity by reacting gaseous phosphorus and steam in a gas plasma to form predominantly phosphorus trioxide and then quenching the phosphorus trioxide with water before it has the opportunity to decompose. The phosphorus tri-oxide itself may be recovered by rapidly quenching the phosphorus trioxide to a stable temperature using an inert quenching medium in place of water. The present invention also relates to a corrosion-free anode for a plasma torch which is used in the production of phos-phorous acid.
The present invention relates to a process for the production of phosphorous acid of high purity by reacting gaseous phosphorus and steam in a gas plasma to form predominantly phosphorus trioxide and then quenching the phosphorus trioxide with water before it has the opportunity to decompose. The phosphorus tri-oxide itself may be recovered by rapidly quenching the phosphorus trioxide to a stable temperature using an inert quenching medium in place of water. The present invention also relates to a corrosion-free anode for a plasma torch which is used in the production of phos-phorous acid.
Description
2~7~9 The present invention relates to the production of phosphorus chemicals, particularly phosphorous acid and phosphorus trioxide from phosphorus oxidation under gas plasma conditions.
The preparation of phosphorous acid (H3PO3) by the direct oxidation of elemental phosphorus and dis-solution of the resulting oxides in water has been difficult to accomplish selectively because of the variety of oxides of phosphorus that can be formed.
A thermodynamic analysis of the oxidation prod-ucts resulting from reacting phosphorus with an oxi-dant indicates that, under no circumstances, would15 P4O6 be a stable phase. Any P4O6 formed should quan-titatively disproportionate into P4 and P4Olo at higher temperatures. However, if one assumes that P2O3 can be formed, this compound is a stable phase over an approximate temperature range from 1500 to 2100K, with the fraction of phosphorus initially pre-sent reporting as P2O3 depending on the nature of the oxidant. The P2O3 so formed can be dissolved in water to form the phosphorous acid or allowed to dimerize to P4O6 and recovered as such.
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Oxidants which may be considered for this reac-tion are oxygen, carbon dioxide and water. The heat release using pure oxygen in stoichiometric amounts is so great that the reaction temperature will exceed the desired range and some form of cooling is required. In addition, precise metering of the reac-tants must be effected since a deficiency f 2 will result in lower oxides of phosphorus while an excess of 2 will generate higher oxides, notably P4Olo.
2~7~9 United States Patent 4,980,142 issued on December 25, 1990, discloses a process for producing phosphorous acid. Although the process of this patent uses phos-phorus and steam, the reaction is not effected under S gas plasma conditions.
In accordance with the present invention, a novel procedure for forming phosphorous acid is pro-vided wherein reaction between phosphorus and steam is effected in a gas plasma and the resulting phosphorus trioxide is quenched with water. The quenching also may be effected with an inert medium to recover P4O6 as the product.
Accordingly, in one embodiment of the inven-tion, there is provided a process for the production of phosphorus chemicals, which comprises a sequence of steps. An inert gas, such as hydrogen, nitrogen or argon, is subjected to a high frequency and high volt-~0 age discharge to form a gas plasma. Sometimes referred to as the fourth state of matter, the plasma state is a partially ionized gas containing free elec-trons, positive and negative ions and neutral atoms.
The plasma overall is electrically neutral, as the positive and negative charges cancel each other, how-ever, due to the presence of free electrons, the plasma has typically high electrical conductivity.
The so-formed gas plasma is passed to an enclosed reaction zone.
Phosphorus and steam are introduced into the plasma torch flame in the enclosed reaction zone such as to effect contact of the phosphorus and steam and to react the same in the plasma torch flame at a tem-- . ::: :.: ~. . .
, 2~9~9 perature of about 1500 to about 2500K, so as to effect substantially complete conversion of phosphorus to phosphorus oxides which are at least about 90% of P203 ~
The phosphorus oxides at a temperature of above about 1400C are contacted with a quench medium which is water or an inert quenc:h medium in the enclosed reaction zone to quench the phosphorus oxides to a temperature below about 1100K sufficiently rapidly to prevent substantial decomposition of the P2O3 from occurring.
When the quench medium is water, there is formed from the phosphorus oxides, phosphorous acid in the quenching step having a purity of at least about 90%, wherein the major impurity in the phosphorous acid is phosphoric acid. When the quench medium is an inert quench medium such as nitrogen or argon, there is formed from the phosphorus oxides stable P203 hav-ing a purity of at least about 90% wherein the majorimpurity is P205. The product, whether phosphorous acid or P2O3, is substantially uncontaminated with unreacted phosphorous.
The phosphorous acid or stable P2O3 product is recovered from the enclosed reaction zone.
In another aspect of the present invention, the plasma arc is attached on the anode to prevent the phosphorus attack of the anode which inevitably lead to the anode corrosion.
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Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, show:ing by way of illustration a preferred embodiment thereof, and wherein:
s Fig. 1 is a schematic represen~ation of one embodiment of apparatus ~or effecting the production of phosphorous acid or stable phosphorus trioxide according to the present invention; and Fig. 2 is a schematic representation of the plasma arc attachment on the anode (A) exterior sur-face and (B) interior surface.
In the present invention, phosphorus is reacted with water (steam) at a high temperature in the range of about 1500 to 2500K form phosphorus trioxide, which is quenched with water to form phosphorous acid or with an inert quenching medium to recover stable P2O3; The dominant chemical reactions which occur in the high temperature region are represented by the following equations:
P4 ~ 2P2 - (1) 2P2 + 6H2O ~ 2P2O3 + 6H2 - (2) 2 + lH2O ~ 2P2Os + lOH2 _ (3) The phosphorus pentoxide produced by equation (3) is an impurity in the desired product obtained in equa-tion (2) and consumes about 5% of the pho~phorus fed to the reactor.
Phosphorus trioxide is unstable between 1500K
and 1100K and undergoes decomposition in this temper-ature range and hence rapid quenching is required to prevent its decomposition and to enable phosphorous .. -:,, , ,.,: . . . :, ~0709919 acid or stable P203 to be obtained. The quenching is most conveniently achievecl using cold water, with hydrolysis of the phosphorus oxides proceeding in accordance with the following equations:
2P23 + 6H2 -~ 4H3P03 _ 2P205 + 6H2 ~ 4H3Po4 _ (~;) Although the reaction of phosphorus and steam accord-ing to equation (2) above, in effect, is a dynamic equilibrium, some residual unreacted phosphorus was expected to be present in the phosphorous acid prod-uct, but no unreacted P4 was observed provided the appropriate gas plasma reaction conditions were observed.
The present invention utilizes a plasma torch to generate the temperatures required for the reaction of phosphorus and steam. The principles of operation of a plasma torch are well known and hence need only briefly to be described. The plasma is initiated by a high frequency, high voltage discharge between a cath-ode and an anode while a gas is blown through a noz-zle. The discharge causes local ionization of the gas and electrons near the cathode are accelerated towards the anode by the high intensity electric field, thereby acquiring enough energy to ionize any atoms with which they collide. The continual process of collisions of the electrons with the gas atoms increases the kinetic energy of the gas. Upon recom-bination of the electrons with positive ions upon exiting the anode, large quantities of thermal energy are released.
The reactants, namely phosphorus and steam, are introduced into the high temperature region downstream .
: , :, .
21370~9 of the anode and the chemical reaction favored by the thermodynamics of the system occurs, resulting in the establishment of a high temperature chemical equilib-rium. Following reaction in the high temperature gas plasma, the products enter a quench zone wherein the temperature is rapidly decreased, so as to maintain the species existing in the high temperature reactant-product equilibrium and to remove residual heat to permit recovery of the products.
The gas passed between the electrodes of the plasma torch to generate the plasma for carrying out the high temperature reaction may be any convenient gas stream, such as hydrogen, argon, nitrogen and mix-tures thereof.
The desired plasma temperature ranges fromabout 1000 to about 2500K, usually about 1500 to about 2000K, preferably from about 1700 to about 1800K.
A d.c. discharge is required to be produced between the electrodes of the plasma torch to achieve the high temperature plasma. The power applied to the plasma torch affects the temperature of the plasma produced by the torch and generally varies from about 5 to about 80kW, preferably about 60kW. The tempera-ture of the plasma is also affected by the particular inert gas employed and the flow rate of the gas through the torch. The gas flow rate generally varies from about 30 to about 200 sL/min, preferably from about 50 to about 140 sL/min depending on the inert gas used.
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2~7~949 In some of the inventors' experiments, corro-sion of the anode of the plasma torch was observed.
It was found that this resulted from the plasma arc extending outside the torch. It was further found S that, if the anode is si:zed sufficiently that the plasma arc does not extend outside the torch, then such corrosion is absent. Accordingly, it is pre-ferred to construct and operate the plasma torch such that the arc between the electrodes is confined within the torch and does not extend into the region into which the reactants are injected.
The reactants are introduced in vapor form into the region of the hot plasma emanating from the plasma lS torch in such a manner that their straight-line paths would intersect the axis of flow of -the hot gas, such as by employing feed ports angled with respect to the axis of the reactor. Fxom the observations with respect to corrosion of the anode noted above, it is ~0 believed that, rather than follow such straight-line paths. The reactants are aspirated directly into the hottest region of the plasma, following injection into the reactor. This effect is thought to result from the formation of a relatively low pressure region near the face of the anode by the rapidly expanding and cooling jet of gas, as well as circulation of steam in the reactor from the quench operation. The aspiration of the reactants is beneficial in achieving good mix-ing of reactants in the hottest part of the plasma, permitting short residence times and subsequent rapid quenching.
Thle production rate of phosphorous acid or sta~
ble P203 attainable also is affected by the power 207~94~
applied to the plasma torch, production rates increases with higher power supplies since the power supply affects the amount of heat available for reac-tion.
s The ratio of H2O/P4 which is fed to the reactor can be over a wide range without significantly affect-ing the production of P2O3. The ratio of H2O/P4 affects the extent to which the reaction of equation (2~ is effected. The yield of P2O3 which is obtained by the reaction can be increase by increasing the ratio of H20/P4. Further when the feed ratio of steam to phosphorus H2O/P4 is about 6 to 10, phosphorus con-version is excellent and phosphorous acid purity of 95~ is achieved.
The nature of the phosphorus oxide impuritiesformed in the phosphorus oxidation reaction depend on the temperature of reaction and the phosphorus to oxi-dant ratio. In general, at temperatures below 1800K,mainly P4O7 to 10 oxides are formed, while above 1800K, P02, P0 and P2O4 become the major impurities.
If an excess of oxidant is used, the first-mentioned group of oxides tend to form as the impurities.
From a practical standpoint, the ability to form relativelY pure P2O3 over a wide temperature range and over a broad range of reactant ratios is beneficial, since only rough controls need to be exer-cised on the relative rates of feeding of the tworeagents.
An amount of unreacted phosphorus is present in the e~uilibrium mixture at the high temperature of - : - . : .: . . :
. -.: , :
: ~ .. ..
2~7~
operation and may amount to about :L0 to about 35~ of the total phosphorus, dependent mainly on the molar ratio of water to P4 as noted above. The temperature of reaction of P4 with H2O largely coincides with the temperature range where at P2 begins to appear and by 2200K, essentially all the phosphorus is present in the P2 form.
The phosphorous acid which is produced by the process of the present invention has a purity which can exceed 90%, with the major contaminant being phos-phoric acid. High purity phosphorous acid is useful in the production of phosphonates, in salt or ester form, for use in a variety of water treatments, from descaling to corrosion inhibition.
The relatively pure phosphorous acid also may be used to produce high purity phosphine and phospho-ric acid by thermal decomposition at a temperature above about 250C, in accordance with the equation:
~H3PO3 3H3PO4 + PH3 - (6) The ability to produce high purity PH3 by this thermal decomposition is insensitive to the presence of phos-phoric acid in the phosphorous acid.
Phosphorous acid also is useful in the stabi-lization of polyvinyl chloride and other polymers to prevent their discoloration by heat or U.V. light.
The textile and pulp and paper industries also use phosphorous acid, in the sizing of products and in making surface active additives.
As described above, quenching of the phosphorus trioxide to rapidly cool the products produced by the ::
, ~7~9~9 plasma may be effected using an inert quenching medium, which may be nitrogen or argon, so as to recover P2O3 in a stable form. The recover~ o~ P2O3 is advantageous, in that it is a more flexible start-S ing material than H3P03 for the provision of useful derivatives. Further, PzO3 is more easily purified and feed from contaminants than ~3PO3.
Referring to Fig. 1 there is shown one embodi-ment of apparatus 10 for carrying out the process ofthe present invention. As seen therein, the apparatus 10 comprises a reactor 12 which the reactions of phos-phorus trioxide formation and quenching to form phos-phorous acid or stable P2O3 occur.
Phosphorus vapor and steam are fed respectively by lines 14 and 16 into the high temperature region of the reactor 12. The high temperature region of the reactor 12 has a temperature of about 1500 to about 2500K, preferably about 1700 to about 1800K, which is achieved by a plasma torch 18.
Water is fed via a metering pump 20 into a tank 22 containing phosphorus. The bath containing the phosphorus is maintained at a temperature above about 45C, preferably about 50 to about 60C, to maintain the phosphorus in liquid form. A dip tube 24 in the tank 22 carries phosphorus into an evaporator 26 which is maintained at a temperature of about 500 to about 600C, typically about 550C. The phosphorus vapor is swept out of the evaporator 26 by a nitrogen gas stream fed by line 28 and then passes by line 14 into the reactor 12. The steam in line 16 is produced by a boiler 30.
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2~9~9 Within the reactor 12, the phosphorus and steam react in the high temperature region and the products of the reaction, predominamtly P203, are carried in the rapidly cooling plasma gas downwardly within the reactor 12 into contact with quench sprays 32 fed by water having a temperature generally of about 5~ to about 15C, preferably about 10, from an external source 34 by line 36. Alternatively, an inert quench medium, such as nitrogen or argon, may be employed, so as to recover stable P203 .
The quenching of the products of the reaction is effected sufficiently rapidly to decrease the tem-perature of the product gas stream below about llOOK
in less than about 1 sec, so as to prevent decomposi-tion of the P203.
Solid products o~ the quench reaction, com-prising mainly phosphorus are collected in a catch pot38 at the lower end of the reactor 12 and phosphorous acid product is recovered in line 40. The phosphorous acid product is obtained generally is greater than about 90% yield, with the balance comprising phospho-ric acid. Any unreacted phosphorus settles out in the catch pot 38 and may be removed by line 42 for recy-cle, intermittently or continuously.
Gases present in the reactor 12, comprising mainly by-product hydrogen and including nitrogen plasma gas, steam, PH3 and any unscrubbed phosphorus oxides, leave the reactor 12 by line 44 and pass through a scrubber 46 containing scrubber solution for removal of phosphine, before venting by line 48. The 2~7~9 scrubber solution may comprise any convenient mate-rial, for example, an approximately 3% NaCl solution buffered to pH10 with sodium bicarbonate. A cooling coil also may be present in the scrubber 46 to con-S dense steam present in the line 44.
The expanding plasma flame exiting the torch 18created a strong aspiration action, thereby drawing the reactants into the high temperature plasma tail-flame where reaction occurred. However, this aspira-tion also drew the phosphorus vapour into contact with the copper anode surface 50, whereby the phosphorus reacted with the copper to form a copper phosphide that was found in the liquid samples (Yig. 2). This reaction resulted in severe corrosion, and usually within a short time (20 minutes) anode 50 failure occurred. The corrosion always developed at the same position 51 on the anode 50. The plasma gas exited the torch 18 with a tangential component, imparted to ~0 it within the torch 18 for flame stabilization and as the phosphorus vapour entered the reactor 12, the plasma gas swept around the perimeter of the anode 50 and aspirates the vapour into contact with the anode whereupon the phosphorus attacked the copper anode 50.
A thermodynamic analysis indicated that the reaction between phosphorus and copper, seen below, occurs at temperatures of 500K:
P4 + Cu <===> 2P + CuP2 - (7) An investigation of the plasma arc 52 behaviour showed that the plasma arc 52 attached itsel~ onto the exterior surface 54 of the anode 50 at position 51 as shown in Fig. 2A. This explains why the 500 K temper-ature required for Reaction (7) to occur was achieved.
Decreasincl the anode 50 internal diameter and modify ., ~
207~949 ing the secondary gas distribution head to increase the swirl component of the plasma gas along with a reduction in gas flow rate caused the arc 52 to rotate within the anode 50 with the anode arc 52 foot onto the anode interior surface 56 at position 53. Since a thermodynamic analysis revealed that boron nitride as well as some ceramic materials resist the chemical attack of phosphorus, torc:h anodes 50 with smaller diameters were assembled, complete with boron nitride, stainless steel and ceramic barriers. Experimental trials were extremely successful and no visible corro-sion was observed. The ceramic barriers were then removed from the smaller anode diameter and tests repeated. No anodic corrosion was observed.
The invention is illustrated by the following Examples, wherein the results of experiments carried out in an experimental apparatus to produce phospho-rous acid are described.
This Example describes details of the apparatus used to carry out the process in accordance with the present invention.
An experimental reactor having the arrangement generally seen in the drawing (Figure 1) was con-structed comprising a carbon steel cylinder with an outside diameter of 66 cm and a height of 122 cm. The inside surface was insulated with 15.3 cm of insula-tion comprising 5.1 cm of Cerlite lOOCTM next to the shell and 10 cm of Emerald GVMTM vibratable plastic on the inner surface, having an inside diameter of 30.5 cm. The exterior of the reactor was insulated using - ~ . .
207~4~
- 1'1-2.5 cm of CerwoolTM, which was covered with an aluminum sheet.
The roof of the reactor was made of carbon steel with an opening in the centre, onto which was fitted a copper roof designed to hold the plasma torch and protect it from the heat load rising from the reactor. Two quenches were! positioned at the centre line of the reactor, pointed in the direction of gas flow and ports in the wall of the cylinder were located for thermocouple placement and gas sampling.
At the bottom of the reactor was a conical sec-tion made of carbon steel, 30.5 cm in height with a 5.1 cm diameter side exhaust port for the exit gas. A
second 10.2 cm side gas exhaust port was located at the bottom of the reactor. At the base of the cone was a liquid seal of 10.2 cm i.d. and 25.4 cm in height. A catch pot was attached to collect any unre-acted phosphorus. A liquid sampling port was locatedin the downspout of the liquid to permit representa-tive samples to be withdrawn. The product acid passed through the seal to collection tanks.
2~ The exit gas was passed through a water-cooled gas scrubber before being vented to atmosphere. The scrubber consisted of a stainless steel cylinder of 25.4 cm o.d. and 7~.2 cm in height with a cooling coil positioned in the interior. The scrubbing solution, used to remove any phosphine present, was a mixture of sodium bicarbonate and sodium hypochlorite.
The plasma torch was a modified Norton Model AA61 DCT~ having two gas inlets and a small diameter ~ . .
~7~9 anode. The torch was powered by a 60 kW rectifier (Miller Welder Model SRS-1500F7~M) and was initiated by a high frequency starter (Miller Welder Model HF-2000TUI) .
The Example illustrates a material balance inaccordance with the present invention.
A material balance ~Eor phosphorus reactant and products was determined for two experiments carried out in the experimental reactor of Example 1 and the data is presented in Table I below:
Table I
Experiment No. _ 2 _ Mole P Mole H2 Mole P Moie H2 Input - P (gas) 27.5 18.3 Output (liquid) - H3P2 0.01 0 0.12 0 - H3P03 16.8 25.2 8.3512.5 H3PO4 1.01 2.52 0.77 1.9 - PH3 0.05 0 0.04 0 Total P 17.87 9.28 Difference 9.02 (P4OX vented)9.63 ~ P4O6 (as P)9.14 13.71 8.2412.4 :~ ~ P4Olo (as P) 0.55 1.370.75 1.8 - Calculated 42.81 28.6 - Found 46.25 26.1 - Mass BalanCe ~2 108% 92%
2~7~9 As may be seen Erom this data, the quantity of hydrolyzed oxides accounts for between 50 (expt. 2) and 77~ (expt. 1) of the phosphorus fed to the reac-tor. Assuming the vented oxides have the same concen-tration as the liquid, the proportions of each werecalculated and, from this, the quantity of hydrogen that would be expected to be observed. This value was compared with the actual amount of hydrogen observed.
The differences in the hydrogen balance arises from the time lag between gas samples leaving the reactor and entering the gas chromatograph for analysis. No unreacted phosphorus was observed in either experi-ment.
This Example sets forth the results of a series of experiments.
A series of experiments was carried out in the experimental apparatus described in Example 1 in which the ratio of steam to phosphorus was varied and the effect of this variation on purity of phosphorous acid produced was observed. The results obtained are set forth in the following Table II:
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Table II
H2O/P4 ~ H3PO3 H3PO4 Expt. No. Molar Production Rate Purity ratio Mole/Min . -- . .. .,.. _............. .. .. I .
la 9.40.075 0.028 73%
b 4.30.214 0.046 82~
2a 9.820.064 0.042 61%
b 5.550.100 0.057 76%
c 3.270.206 0.049 81%
d 2.240.536 0.125 81%
3a 1.75 0.679 0.067 91%
b 1.64 0.828 0.073 92%
c 1.56 0.836 0.068 93%
d 1.12 0.723 0.056 93%
4 0.83 1 0.850 0.051 94%
The stoichiometric requirement of the reaction to produce H3PO3 is H2O:P4 of 1.5:1 while that for S H3PO4 is 2.5:1. As may be seen from the results in Table II, the purity of product phosphorous acid increases with decreasing steam : P feed mole ratios.
It was also observed that the purity of the product also is dependent on the feed rates of the reactants.
In each of these experiments, no unreacted phosphorus was observed, with the exception of the 1~ experiment 4, in which unreacted phosphorus was pre-sent.
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: : , : . ~.. ~. . , ,., :, 2~70949 While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skillecl in the art. Accordingly, S the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.
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The preparation of phosphorous acid (H3PO3) by the direct oxidation of elemental phosphorus and dis-solution of the resulting oxides in water has been difficult to accomplish selectively because of the variety of oxides of phosphorus that can be formed.
A thermodynamic analysis of the oxidation prod-ucts resulting from reacting phosphorus with an oxi-dant indicates that, under no circumstances, would15 P4O6 be a stable phase. Any P4O6 formed should quan-titatively disproportionate into P4 and P4Olo at higher temperatures. However, if one assumes that P2O3 can be formed, this compound is a stable phase over an approximate temperature range from 1500 to 2100K, with the fraction of phosphorus initially pre-sent reporting as P2O3 depending on the nature of the oxidant. The P2O3 so formed can be dissolved in water to form the phosphorous acid or allowed to dimerize to P4O6 and recovered as such.
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Oxidants which may be considered for this reac-tion are oxygen, carbon dioxide and water. The heat release using pure oxygen in stoichiometric amounts is so great that the reaction temperature will exceed the desired range and some form of cooling is required. In addition, precise metering of the reac-tants must be effected since a deficiency f 2 will result in lower oxides of phosphorus while an excess of 2 will generate higher oxides, notably P4Olo.
2~7~9 United States Patent 4,980,142 issued on December 25, 1990, discloses a process for producing phosphorous acid. Although the process of this patent uses phos-phorus and steam, the reaction is not effected under S gas plasma conditions.
In accordance with the present invention, a novel procedure for forming phosphorous acid is pro-vided wherein reaction between phosphorus and steam is effected in a gas plasma and the resulting phosphorus trioxide is quenched with water. The quenching also may be effected with an inert medium to recover P4O6 as the product.
Accordingly, in one embodiment of the inven-tion, there is provided a process for the production of phosphorus chemicals, which comprises a sequence of steps. An inert gas, such as hydrogen, nitrogen or argon, is subjected to a high frequency and high volt-~0 age discharge to form a gas plasma. Sometimes referred to as the fourth state of matter, the plasma state is a partially ionized gas containing free elec-trons, positive and negative ions and neutral atoms.
The plasma overall is electrically neutral, as the positive and negative charges cancel each other, how-ever, due to the presence of free electrons, the plasma has typically high electrical conductivity.
The so-formed gas plasma is passed to an enclosed reaction zone.
Phosphorus and steam are introduced into the plasma torch flame in the enclosed reaction zone such as to effect contact of the phosphorus and steam and to react the same in the plasma torch flame at a tem-- . ::: :.: ~. . .
, 2~9~9 perature of about 1500 to about 2500K, so as to effect substantially complete conversion of phosphorus to phosphorus oxides which are at least about 90% of P203 ~
The phosphorus oxides at a temperature of above about 1400C are contacted with a quench medium which is water or an inert quenc:h medium in the enclosed reaction zone to quench the phosphorus oxides to a temperature below about 1100K sufficiently rapidly to prevent substantial decomposition of the P2O3 from occurring.
When the quench medium is water, there is formed from the phosphorus oxides, phosphorous acid in the quenching step having a purity of at least about 90%, wherein the major impurity in the phosphorous acid is phosphoric acid. When the quench medium is an inert quench medium such as nitrogen or argon, there is formed from the phosphorus oxides stable P203 hav-ing a purity of at least about 90% wherein the majorimpurity is P205. The product, whether phosphorous acid or P2O3, is substantially uncontaminated with unreacted phosphorous.
The phosphorous acid or stable P2O3 product is recovered from the enclosed reaction zone.
In another aspect of the present invention, the plasma arc is attached on the anode to prevent the phosphorus attack of the anode which inevitably lead to the anode corrosion.
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Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, show:ing by way of illustration a preferred embodiment thereof, and wherein:
s Fig. 1 is a schematic represen~ation of one embodiment of apparatus ~or effecting the production of phosphorous acid or stable phosphorus trioxide according to the present invention; and Fig. 2 is a schematic representation of the plasma arc attachment on the anode (A) exterior sur-face and (B) interior surface.
In the present invention, phosphorus is reacted with water (steam) at a high temperature in the range of about 1500 to 2500K form phosphorus trioxide, which is quenched with water to form phosphorous acid or with an inert quenching medium to recover stable P2O3; The dominant chemical reactions which occur in the high temperature region are represented by the following equations:
P4 ~ 2P2 - (1) 2P2 + 6H2O ~ 2P2O3 + 6H2 - (2) 2 + lH2O ~ 2P2Os + lOH2 _ (3) The phosphorus pentoxide produced by equation (3) is an impurity in the desired product obtained in equa-tion (2) and consumes about 5% of the pho~phorus fed to the reactor.
Phosphorus trioxide is unstable between 1500K
and 1100K and undergoes decomposition in this temper-ature range and hence rapid quenching is required to prevent its decomposition and to enable phosphorous .. -:,, , ,.,: . . . :, ~0709919 acid or stable P203 to be obtained. The quenching is most conveniently achievecl using cold water, with hydrolysis of the phosphorus oxides proceeding in accordance with the following equations:
2P23 + 6H2 -~ 4H3P03 _ 2P205 + 6H2 ~ 4H3Po4 _ (~;) Although the reaction of phosphorus and steam accord-ing to equation (2) above, in effect, is a dynamic equilibrium, some residual unreacted phosphorus was expected to be present in the phosphorous acid prod-uct, but no unreacted P4 was observed provided the appropriate gas plasma reaction conditions were observed.
The present invention utilizes a plasma torch to generate the temperatures required for the reaction of phosphorus and steam. The principles of operation of a plasma torch are well known and hence need only briefly to be described. The plasma is initiated by a high frequency, high voltage discharge between a cath-ode and an anode while a gas is blown through a noz-zle. The discharge causes local ionization of the gas and electrons near the cathode are accelerated towards the anode by the high intensity electric field, thereby acquiring enough energy to ionize any atoms with which they collide. The continual process of collisions of the electrons with the gas atoms increases the kinetic energy of the gas. Upon recom-bination of the electrons with positive ions upon exiting the anode, large quantities of thermal energy are released.
The reactants, namely phosphorus and steam, are introduced into the high temperature region downstream .
: , :, .
21370~9 of the anode and the chemical reaction favored by the thermodynamics of the system occurs, resulting in the establishment of a high temperature chemical equilib-rium. Following reaction in the high temperature gas plasma, the products enter a quench zone wherein the temperature is rapidly decreased, so as to maintain the species existing in the high temperature reactant-product equilibrium and to remove residual heat to permit recovery of the products.
The gas passed between the electrodes of the plasma torch to generate the plasma for carrying out the high temperature reaction may be any convenient gas stream, such as hydrogen, argon, nitrogen and mix-tures thereof.
The desired plasma temperature ranges fromabout 1000 to about 2500K, usually about 1500 to about 2000K, preferably from about 1700 to about 1800K.
A d.c. discharge is required to be produced between the electrodes of the plasma torch to achieve the high temperature plasma. The power applied to the plasma torch affects the temperature of the plasma produced by the torch and generally varies from about 5 to about 80kW, preferably about 60kW. The tempera-ture of the plasma is also affected by the particular inert gas employed and the flow rate of the gas through the torch. The gas flow rate generally varies from about 30 to about 200 sL/min, preferably from about 50 to about 140 sL/min depending on the inert gas used.
.
2~7~949 In some of the inventors' experiments, corro-sion of the anode of the plasma torch was observed.
It was found that this resulted from the plasma arc extending outside the torch. It was further found S that, if the anode is si:zed sufficiently that the plasma arc does not extend outside the torch, then such corrosion is absent. Accordingly, it is pre-ferred to construct and operate the plasma torch such that the arc between the electrodes is confined within the torch and does not extend into the region into which the reactants are injected.
The reactants are introduced in vapor form into the region of the hot plasma emanating from the plasma lS torch in such a manner that their straight-line paths would intersect the axis of flow of -the hot gas, such as by employing feed ports angled with respect to the axis of the reactor. Fxom the observations with respect to corrosion of the anode noted above, it is ~0 believed that, rather than follow such straight-line paths. The reactants are aspirated directly into the hottest region of the plasma, following injection into the reactor. This effect is thought to result from the formation of a relatively low pressure region near the face of the anode by the rapidly expanding and cooling jet of gas, as well as circulation of steam in the reactor from the quench operation. The aspiration of the reactants is beneficial in achieving good mix-ing of reactants in the hottest part of the plasma, permitting short residence times and subsequent rapid quenching.
Thle production rate of phosphorous acid or sta~
ble P203 attainable also is affected by the power 207~94~
applied to the plasma torch, production rates increases with higher power supplies since the power supply affects the amount of heat available for reac-tion.
s The ratio of H2O/P4 which is fed to the reactor can be over a wide range without significantly affect-ing the production of P2O3. The ratio of H2O/P4 affects the extent to which the reaction of equation (2~ is effected. The yield of P2O3 which is obtained by the reaction can be increase by increasing the ratio of H20/P4. Further when the feed ratio of steam to phosphorus H2O/P4 is about 6 to 10, phosphorus con-version is excellent and phosphorous acid purity of 95~ is achieved.
The nature of the phosphorus oxide impuritiesformed in the phosphorus oxidation reaction depend on the temperature of reaction and the phosphorus to oxi-dant ratio. In general, at temperatures below 1800K,mainly P4O7 to 10 oxides are formed, while above 1800K, P02, P0 and P2O4 become the major impurities.
If an excess of oxidant is used, the first-mentioned group of oxides tend to form as the impurities.
From a practical standpoint, the ability to form relativelY pure P2O3 over a wide temperature range and over a broad range of reactant ratios is beneficial, since only rough controls need to be exer-cised on the relative rates of feeding of the tworeagents.
An amount of unreacted phosphorus is present in the e~uilibrium mixture at the high temperature of - : - . : .: . . :
. -.: , :
: ~ .. ..
2~7~
operation and may amount to about :L0 to about 35~ of the total phosphorus, dependent mainly on the molar ratio of water to P4 as noted above. The temperature of reaction of P4 with H2O largely coincides with the temperature range where at P2 begins to appear and by 2200K, essentially all the phosphorus is present in the P2 form.
The phosphorous acid which is produced by the process of the present invention has a purity which can exceed 90%, with the major contaminant being phos-phoric acid. High purity phosphorous acid is useful in the production of phosphonates, in salt or ester form, for use in a variety of water treatments, from descaling to corrosion inhibition.
The relatively pure phosphorous acid also may be used to produce high purity phosphine and phospho-ric acid by thermal decomposition at a temperature above about 250C, in accordance with the equation:
~H3PO3 3H3PO4 + PH3 - (6) The ability to produce high purity PH3 by this thermal decomposition is insensitive to the presence of phos-phoric acid in the phosphorous acid.
Phosphorous acid also is useful in the stabi-lization of polyvinyl chloride and other polymers to prevent their discoloration by heat or U.V. light.
The textile and pulp and paper industries also use phosphorous acid, in the sizing of products and in making surface active additives.
As described above, quenching of the phosphorus trioxide to rapidly cool the products produced by the ::
, ~7~9~9 plasma may be effected using an inert quenching medium, which may be nitrogen or argon, so as to recover P2O3 in a stable form. The recover~ o~ P2O3 is advantageous, in that it is a more flexible start-S ing material than H3P03 for the provision of useful derivatives. Further, PzO3 is more easily purified and feed from contaminants than ~3PO3.
Referring to Fig. 1 there is shown one embodi-ment of apparatus 10 for carrying out the process ofthe present invention. As seen therein, the apparatus 10 comprises a reactor 12 which the reactions of phos-phorus trioxide formation and quenching to form phos-phorous acid or stable P2O3 occur.
Phosphorus vapor and steam are fed respectively by lines 14 and 16 into the high temperature region of the reactor 12. The high temperature region of the reactor 12 has a temperature of about 1500 to about 2500K, preferably about 1700 to about 1800K, which is achieved by a plasma torch 18.
Water is fed via a metering pump 20 into a tank 22 containing phosphorus. The bath containing the phosphorus is maintained at a temperature above about 45C, preferably about 50 to about 60C, to maintain the phosphorus in liquid form. A dip tube 24 in the tank 22 carries phosphorus into an evaporator 26 which is maintained at a temperature of about 500 to about 600C, typically about 550C. The phosphorus vapor is swept out of the evaporator 26 by a nitrogen gas stream fed by line 28 and then passes by line 14 into the reactor 12. The steam in line 16 is produced by a boiler 30.
9 . . .. .
2~9~9 Within the reactor 12, the phosphorus and steam react in the high temperature region and the products of the reaction, predominamtly P203, are carried in the rapidly cooling plasma gas downwardly within the reactor 12 into contact with quench sprays 32 fed by water having a temperature generally of about 5~ to about 15C, preferably about 10, from an external source 34 by line 36. Alternatively, an inert quench medium, such as nitrogen or argon, may be employed, so as to recover stable P203 .
The quenching of the products of the reaction is effected sufficiently rapidly to decrease the tem-perature of the product gas stream below about llOOK
in less than about 1 sec, so as to prevent decomposi-tion of the P203.
Solid products o~ the quench reaction, com-prising mainly phosphorus are collected in a catch pot38 at the lower end of the reactor 12 and phosphorous acid product is recovered in line 40. The phosphorous acid product is obtained generally is greater than about 90% yield, with the balance comprising phospho-ric acid. Any unreacted phosphorus settles out in the catch pot 38 and may be removed by line 42 for recy-cle, intermittently or continuously.
Gases present in the reactor 12, comprising mainly by-product hydrogen and including nitrogen plasma gas, steam, PH3 and any unscrubbed phosphorus oxides, leave the reactor 12 by line 44 and pass through a scrubber 46 containing scrubber solution for removal of phosphine, before venting by line 48. The 2~7~9 scrubber solution may comprise any convenient mate-rial, for example, an approximately 3% NaCl solution buffered to pH10 with sodium bicarbonate. A cooling coil also may be present in the scrubber 46 to con-S dense steam present in the line 44.
The expanding plasma flame exiting the torch 18created a strong aspiration action, thereby drawing the reactants into the high temperature plasma tail-flame where reaction occurred. However, this aspira-tion also drew the phosphorus vapour into contact with the copper anode surface 50, whereby the phosphorus reacted with the copper to form a copper phosphide that was found in the liquid samples (Yig. 2). This reaction resulted in severe corrosion, and usually within a short time (20 minutes) anode 50 failure occurred. The corrosion always developed at the same position 51 on the anode 50. The plasma gas exited the torch 18 with a tangential component, imparted to ~0 it within the torch 18 for flame stabilization and as the phosphorus vapour entered the reactor 12, the plasma gas swept around the perimeter of the anode 50 and aspirates the vapour into contact with the anode whereupon the phosphorus attacked the copper anode 50.
A thermodynamic analysis indicated that the reaction between phosphorus and copper, seen below, occurs at temperatures of 500K:
P4 + Cu <===> 2P + CuP2 - (7) An investigation of the plasma arc 52 behaviour showed that the plasma arc 52 attached itsel~ onto the exterior surface 54 of the anode 50 at position 51 as shown in Fig. 2A. This explains why the 500 K temper-ature required for Reaction (7) to occur was achieved.
Decreasincl the anode 50 internal diameter and modify ., ~
207~949 ing the secondary gas distribution head to increase the swirl component of the plasma gas along with a reduction in gas flow rate caused the arc 52 to rotate within the anode 50 with the anode arc 52 foot onto the anode interior surface 56 at position 53. Since a thermodynamic analysis revealed that boron nitride as well as some ceramic materials resist the chemical attack of phosphorus, torc:h anodes 50 with smaller diameters were assembled, complete with boron nitride, stainless steel and ceramic barriers. Experimental trials were extremely successful and no visible corro-sion was observed. The ceramic barriers were then removed from the smaller anode diameter and tests repeated. No anodic corrosion was observed.
The invention is illustrated by the following Examples, wherein the results of experiments carried out in an experimental apparatus to produce phospho-rous acid are described.
This Example describes details of the apparatus used to carry out the process in accordance with the present invention.
An experimental reactor having the arrangement generally seen in the drawing (Figure 1) was con-structed comprising a carbon steel cylinder with an outside diameter of 66 cm and a height of 122 cm. The inside surface was insulated with 15.3 cm of insula-tion comprising 5.1 cm of Cerlite lOOCTM next to the shell and 10 cm of Emerald GVMTM vibratable plastic on the inner surface, having an inside diameter of 30.5 cm. The exterior of the reactor was insulated using - ~ . .
207~4~
- 1'1-2.5 cm of CerwoolTM, which was covered with an aluminum sheet.
The roof of the reactor was made of carbon steel with an opening in the centre, onto which was fitted a copper roof designed to hold the plasma torch and protect it from the heat load rising from the reactor. Two quenches were! positioned at the centre line of the reactor, pointed in the direction of gas flow and ports in the wall of the cylinder were located for thermocouple placement and gas sampling.
At the bottom of the reactor was a conical sec-tion made of carbon steel, 30.5 cm in height with a 5.1 cm diameter side exhaust port for the exit gas. A
second 10.2 cm side gas exhaust port was located at the bottom of the reactor. At the base of the cone was a liquid seal of 10.2 cm i.d. and 25.4 cm in height. A catch pot was attached to collect any unre-acted phosphorus. A liquid sampling port was locatedin the downspout of the liquid to permit representa-tive samples to be withdrawn. The product acid passed through the seal to collection tanks.
2~ The exit gas was passed through a water-cooled gas scrubber before being vented to atmosphere. The scrubber consisted of a stainless steel cylinder of 25.4 cm o.d. and 7~.2 cm in height with a cooling coil positioned in the interior. The scrubbing solution, used to remove any phosphine present, was a mixture of sodium bicarbonate and sodium hypochlorite.
The plasma torch was a modified Norton Model AA61 DCT~ having two gas inlets and a small diameter ~ . .
~7~9 anode. The torch was powered by a 60 kW rectifier (Miller Welder Model SRS-1500F7~M) and was initiated by a high frequency starter (Miller Welder Model HF-2000TUI) .
The Example illustrates a material balance inaccordance with the present invention.
A material balance ~Eor phosphorus reactant and products was determined for two experiments carried out in the experimental reactor of Example 1 and the data is presented in Table I below:
Table I
Experiment No. _ 2 _ Mole P Mole H2 Mole P Moie H2 Input - P (gas) 27.5 18.3 Output (liquid) - H3P2 0.01 0 0.12 0 - H3P03 16.8 25.2 8.3512.5 H3PO4 1.01 2.52 0.77 1.9 - PH3 0.05 0 0.04 0 Total P 17.87 9.28 Difference 9.02 (P4OX vented)9.63 ~ P4O6 (as P)9.14 13.71 8.2412.4 :~ ~ P4Olo (as P) 0.55 1.370.75 1.8 - Calculated 42.81 28.6 - Found 46.25 26.1 - Mass BalanCe ~2 108% 92%
2~7~9 As may be seen Erom this data, the quantity of hydrolyzed oxides accounts for between 50 (expt. 2) and 77~ (expt. 1) of the phosphorus fed to the reac-tor. Assuming the vented oxides have the same concen-tration as the liquid, the proportions of each werecalculated and, from this, the quantity of hydrogen that would be expected to be observed. This value was compared with the actual amount of hydrogen observed.
The differences in the hydrogen balance arises from the time lag between gas samples leaving the reactor and entering the gas chromatograph for analysis. No unreacted phosphorus was observed in either experi-ment.
This Example sets forth the results of a series of experiments.
A series of experiments was carried out in the experimental apparatus described in Example 1 in which the ratio of steam to phosphorus was varied and the effect of this variation on purity of phosphorous acid produced was observed. The results obtained are set forth in the following Table II:
, - ;
;
207~
Table II
H2O/P4 ~ H3PO3 H3PO4 Expt. No. Molar Production Rate Purity ratio Mole/Min . -- . .. .,.. _............. .. .. I .
la 9.40.075 0.028 73%
b 4.30.214 0.046 82~
2a 9.820.064 0.042 61%
b 5.550.100 0.057 76%
c 3.270.206 0.049 81%
d 2.240.536 0.125 81%
3a 1.75 0.679 0.067 91%
b 1.64 0.828 0.073 92%
c 1.56 0.836 0.068 93%
d 1.12 0.723 0.056 93%
4 0.83 1 0.850 0.051 94%
The stoichiometric requirement of the reaction to produce H3PO3 is H2O:P4 of 1.5:1 while that for S H3PO4 is 2.5:1. As may be seen from the results in Table II, the purity of product phosphorous acid increases with decreasing steam : P feed mole ratios.
It was also observed that the purity of the product also is dependent on the feed rates of the reactants.
In each of these experiments, no unreacted phosphorus was observed, with the exception of the 1~ experiment 4, in which unreacted phosphorus was pre-sent.
,-, . . ~
: : , : . ~.. ~. . , ,., :, 2~70949 While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skillecl in the art. Accordingly, S the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.
~ ~, ` " . ' ``"'' , -~ , - . , , -.
Claims (4)
1. A process for the production of phosphorus chemicals, which comprises:
forming a hot gas plasma in an enclosed reac-tion zone, introducing gaseous phosphorus and steam water into said gas plasma in said enclosed reaction zone such as to react said gaseous phosphorus with steam water in said gas plasma at a temperature of about 1500° to about 2500°K, so as to effect substantially complete conversion of phosphorus to phosphorus oxides which are at least about 90% P203, contacting said phosphorus oxides at a tempera-ture above about 1500°K in said enclosed reaction zone with a quench medium selected from water and an inert quenching medium to quench said phosphorus oxides to a temperature below about 1100°K sufficiently rapidly to prevent substantially decomposition of said phosphorus oxides from occurring, whereby to form from said phos-phorus oxides, in the case of water being the quench medium, phosphorous acid having a purity of at least about 90% wherein the major impurity in said phospho-rous acid is phosphoric acid, and, in the case of an inert quenching medium being the quench medium, stable P203 having a purity of at least about 90% wherein the major impurity is P205, said phosphorous acid and stable P203 being substantially uncontaminated with unreacted phosphorus, and recovering said phosphorous acid or stable P203 from said enclosed reaction zone.
forming a hot gas plasma in an enclosed reac-tion zone, introducing gaseous phosphorus and steam water into said gas plasma in said enclosed reaction zone such as to react said gaseous phosphorus with steam water in said gas plasma at a temperature of about 1500° to about 2500°K, so as to effect substantially complete conversion of phosphorus to phosphorus oxides which are at least about 90% P203, contacting said phosphorus oxides at a tempera-ture above about 1500°K in said enclosed reaction zone with a quench medium selected from water and an inert quenching medium to quench said phosphorus oxides to a temperature below about 1100°K sufficiently rapidly to prevent substantially decomposition of said phosphorus oxides from occurring, whereby to form from said phos-phorus oxides, in the case of water being the quench medium, phosphorous acid having a purity of at least about 90% wherein the major impurity in said phospho-rous acid is phosphoric acid, and, in the case of an inert quenching medium being the quench medium, stable P203 having a purity of at least about 90% wherein the major impurity is P205, said phosphorous acid and stable P203 being substantially uncontaminated with unreacted phosphorus, and recovering said phosphorous acid or stable P203 from said enclosed reaction zone.
2. The process of claim 1, wherein said reaction temperature is about 1500° to about 2000°K.
3. The process of claim 2, wherein said reaction temperature is about 1700° to about 1800°K.
4. The process of claim 1, wherein the plasma has a plasma arc and an anode having interior and exterior surfaces and wherein said plasma arc is attached onto said anode interior surface.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2070949 CA2070949A1 (en) | 1992-06-10 | 1992-06-10 | Production of phosphorous acid using gas plasma |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2070949 CA2070949A1 (en) | 1992-06-10 | 1992-06-10 | Production of phosphorous acid using gas plasma |
Publications (1)
| Publication Number | Publication Date |
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| CA2070949A1 true CA2070949A1 (en) | 1993-12-11 |
Family
ID=4150002
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2070949 Abandoned CA2070949A1 (en) | 1992-06-10 | 1992-06-10 | Production of phosphorous acid using gas plasma |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2112156A1 (en) | 2008-04-25 | 2009-10-28 | Thermphos International B.V. | Method for the Manufacture of Aminoalkylene Phosphonic Acid |
| EP2113483A1 (en) | 2008-04-25 | 2009-11-04 | Thermphos International B.V. | Method for the manufacture of concentrated phosphorous acid |
| WO2010136566A1 (en) | 2009-05-28 | 2010-12-02 | Straitmark Holding Ag | Method for the manufacture of amino alkylene phosphonic acids |
| US8884053B2 (en) | 2008-04-25 | 2014-11-11 | Straitmark Holding Ag | Method for the manufacture of aminoalkylene phosphonic acid |
| CN115490218A (en) * | 2022-09-26 | 2022-12-20 | 临沂市春明化工有限公司 | Temperature control system for preparing phosphorous acid |
-
1992
- 1992-06-10 CA CA 2070949 patent/CA2070949A1/en not_active Abandoned
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2112156A1 (en) | 2008-04-25 | 2009-10-28 | Thermphos International B.V. | Method for the Manufacture of Aminoalkylene Phosphonic Acid |
| EP2113483A1 (en) | 2008-04-25 | 2009-11-04 | Thermphos International B.V. | Method for the manufacture of concentrated phosphorous acid |
| US8884053B2 (en) | 2008-04-25 | 2014-11-11 | Straitmark Holding Ag | Method for the manufacture of aminoalkylene phosphonic acid |
| CN104386658A (en) * | 2008-04-25 | 2015-03-04 | 斯特瑞马克控股公司 | Method for the manufacture of concentrated phosphorus acid |
| WO2010136566A1 (en) | 2009-05-28 | 2010-12-02 | Straitmark Holding Ag | Method for the manufacture of amino alkylene phosphonic acids |
| CN115490218A (en) * | 2022-09-26 | 2022-12-20 | 临沂市春明化工有限公司 | Temperature control system for preparing phosphorous acid |
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