DE1145148B - Process for the production of alkali phosphates and carbon dioxide - Google Patents

Description

GERMAN

PATENT OFFICE

F 32673 IVa / 12i

REGISTRATION DATE: DECEMBER 1, 1960

NOTICE THE REGISTRATION XJND ISSUE OF EDITORIAL: MARCH 14, 1963

The invention relates to an improved method for reacting alkali carbonates with phosphoric acid with the formation of alkali phosphates and carbon dioxide of the highest purity as valuable By-product.

The reaction of various sodium carbonates with phosphoric acid is used on a large scale for production of monosodium and disodium phosphates, isolated and applied as such or by further chemical conversion into trisodium phosphate or by heat treatment be converted to tetrasodium pyrophosphate, sodium tripolyphosphate, sodium metaphosphate, etc. can. Other alkali metal phosphates can be or can be obtained by reacting the corresponding carbonates be made with phosphoric acid.

A by-product of the conversion of alkali carbonates and phosphoric acid is carbon dioxide. It is a valuable intermediate chemical compound and is of value for various other purposes as well after conversion into liquid or solid form. For any use it is desirable that it is formed at a constant rate and with a high degree of purity. It used to be common wasted, in part because it was not formed at a steady rate and as it contained air and other impurities.

The evolution of carbon dioxide during the reaction of alkali carbonates with phosphoric acid leads to serious foam problems. These problems become particularly acute when certain Sodium carbonates are used, which contain traces of foam-inducing impurities. Because of these foam problems it was necessary to carry out the reaction batchwise with occasional Interrupt the addition of the alkali carbonate to reduce the foaming guarantee.

It has been found that less equipment is used in a continuous process could be that the devices and measures could be reduced and that a Carbon dioxide of high purity could be formed at a steady rate. The size of the apparatus is of considerable importance in the production of phosphates from phosphoric acid and alkali, since the apparatus is made of a corrosion-resistant material, such as. B. stainless steel have to be.

The term alkali carbonate used in the description and in the claims includes all compounds which are produced by reaction of alkali processes
of alkali phosphates and carbon dioxide

Applicant:

FWC Corporation,

New York, N.Y. (V. St. A.)

Representative: Dr. F. Zumstein,

Dipl.-Chem. Dr. rer. nat. E. Assmann

and Dipl.-Chem. Dr. R. Koenigsberger,

Patent Attorneys, Munich 2, Bräuhausstr. 4th

William E. Yates, Lawrence, Kan.,

James Wilding, South Charleston, W. Va.,

and John Lester Morrow, Severna Park, Md.

(V. St. A.),
have been named as inventors

carbonated hydroxides can be obtained. The term thus includes normal carbonates, acidic Carbonates, sesquicarbonates, etc., which can be anhydrous or hydrated.

According to the invention, an alkali phosphate solution and carbon dioxide are prepared by adding phosphoric acid, an alkali carbonate and water continuously into one end of a tubular reactor be given in which the mentioned acid and the carbonate are mixed, with them partially react with each other, and by removing the partially reacted mixture from the other end of the reactor is withdrawn by the mixture mentioned continuously in a tank reactor with a stirrer in which there is a further reaction and in which there is gaseous carbon dioxide separates from the liquid phase without substantial foaming by removing the carbon dioxide is continuously withdrawn from the top of the mentioned tank reactor with stirrer and by continuously using the alkali phosphate solution from the lower part of the mentioned tank reactor Stirring device is withdrawn.

A third reactor can be used, which is also a tank reactor and preferably

309 539/354

larger than the first can be by substantially one to ensure complete separation of the carbon dioxide from the liquid.

The term "tubular reaction vessel" means an extensive reaction space, e.g. B. a pipe into which the ReaMonsteemann continuously are felt at one end and continuously removed from the other end without the Reactants are substantially mixed with previously introduced material. If two If currents are sensed, the substance in one steom mixes with the one introduced at the same time Substance in the other stream, but mixing with before or after imported substance in one stream or another not to a significant extent. One can say that the substance flows through the reactor in an approximately laminar flow.

In contrast, a tank reactor with a stirrer is a. such, whose dimensions are rather the of a tank than that of a pipe and in which the introduced substance with previously introduced Substance is mixed. The reactor is provided with a stirrer or other device, the mixing of the newly introduced substance with the substance already present in the tank guaranteed.

In the method according to the invention, the first part of the reaction in a minimum volume of substance, as the alkali carbonate and the phosphoric acid first be introduced into a tubular reactor, with a dilution beforehand imported substance is avoided. This causes a great reaction speed, since the Reactant concentration is high. Another effect is that of the volume of the Liquid from which the carbon dioxide formed during the reaction must be separated is reduced to a minimum.

Although the ease with which the carbon dioxide is removed from the liquid of the discharge from the tubular reactor separates, can not be fully explained, it is assumed that they with the small volume of liquid in relation to the volume of carbon dioxide.

The proportion of the reaction that takes place in the tank reactors with a stirrer varies with the Throughput rate, however, is preferably less than half of the total reaction. The speed and the other conditions are controlled so that the volume of the in the tank reactors formed gas is sufficiently small that it can be easily separated without significant foaming can.

One embodiment of the method is illustrated in the drawing. A sodium carbonate solution or slurry and phosphoric acid are each passed through lines 1 and 2 into a first reactor 3, a tubular reactor. The reactor 3 is designed in such a way that it is emptied through the opening 4 into a reactor 6, which is a tank reactor with a stirring device. A baffle 5 at the opening 4 to divert the incoming flow away from the exit 8 of the reactor forms a plate which is placed over the end of the reactor 3 and a semicircular section cut out of the tube just above the plate. The cross section of the opening 4 is preferably at least as large as the cross section of the reactor 3, so that no pressure arises in the reactor.

The reactor 6 is provided with a stirrer 7, with an outlet 8 for carbon dioxide and water vapor, an outlet 9 for removing the solution and preferably with a steam coil (not shown) for heating. The outlet 9 is of such a size that it does not act as a siphon when the solution passes through.

ίο Both output 8 and output 9 are combined into one second, larger tank reactor 10 emptied. Carbon dioxide and water vapor leave the system Exit 12 and the phosphate solution is removed through exit 13. The reactor 10 also contains a steam coil (not shown).

In a preferred mode of making sodium phosphate, a sodium carbonate slurry is used pumped through line 1 into reactor 3. The use of a slurry more than one solution reduces the amount of water added to the system. This is desirable because all of the added water must be separated from the product at the end. The slurry can be made by adding one or even more parts by weight of sodium carbonate gives water to every part. When mixing equal parts by weight of water and sodium carbonate (50% slurry) and heating to a temperature near the boiling point approximately half of the sodium carbonate is dissolved and the residue is in suspension. It can Slurries at concentrations of about 63% can be used.

The reactor 3 is advantageously made of a tube with a diameter of several centimeters built, with actual size varying with throughput. For a large-scale operation the diameter can be 15.24 to 20.32 cm. The diameter should be small enough to be enough to ensure high liquid velocity, so that a settling of alkali carbonate is avoided when the latter is applied in the form of a slurry.

The length of the reactor 3 should be chosen so that the reaction in it is at least 50% complete will. A length of 0.91 to 1.22 m is sufficient in most cases, but a greater length can be applied. The inlet pipes in the reactor 3 should be created so that the Phosphoric acid and the alkali metal carbonate are mixed together on entering the reactor. Usually adequate mixing of the two streams is ensured if the inlet openings are narrow are adjacent. Mixing is caused by the formation of a large volume of carbon dioxide Reaction supported.

A large capacity is not required for the reactor 6. Usually a capacity of 380 to 7601 are sufficient. The reactor 10 could also be relatively small, but is a considerable one Capacity desirable to both the reaction and the separation of the carbon dioxide from the Enable solution with 100%.

For the production of sodium phosphates, sodium carbonate, Sodium bicarbonate or sodium sesquicarbonate can be used. To other alkali carbonates, that can be applied belong

Potassium carbonate, potassium bicarbonate, lithium carbonate, Lithium bicarbonate, etc. The carbonates can be in solution or in slurry or in dry Form can be added. However, the dry form is not preferred because it is difficult to introduce to avoid small amounts of air, which contaminate the carbon dioxide at the same time as the carbonate would, and because of the reaction, because of the time required for all of the carbonate to dissolve is, runs less quickly.

A 75% phosphoric acid is preferred, but a stronger or weaker one can also be used Acid can be applied. Concentrations below 50% should generally be avoided as they

The ratio of reactants was such that a mixture of disodium phosphate and monosodium phosphate was formed in a molar ratio of 2: 1. Such a mixture is valuable for manufacture of sodium tripolyphosphate.

The reaction mixture was passed from the first reactor into a second reactor, the out a 454-1 tank fitted with a stirrer. The temperature of the reaction mixture was raised to about 88 ° C with the aid of steam to achieve a more complete reaction. The reaction of the mixture entering the second reactor was about 72% and that of these Mixture leaving the reactor to about 90%

was equipped with a stirrer and closed steam coils to increase the Temperature of the solution to about 100 ° C were applied. There was another in this tank Reaction, the completeness of the reaction being increased to 99% or more. The phosphate solution was withdrawn from the bottom of the tank for further processing and the carbon dioxide from the

lead to relatively dilute solutions of the product. 15 constantly.
The temperature of the phosphoric acid is not critical. The liquid ran through the second reactor

and can run from normal temperature up to 100 ° C or an overflow pipe into a third reactor, which is made from vary even higher. a tank with a diameter of 3.66 m and

As mentioned, it is advantageous to have the alkali carbonate at a height of 3.66 m and to add the carbon diamine in the form of a slurry. The tem- perature was passed through a ceiling pipe at the temperature of the slurry should preferably be in the gas space of the same tank. The third reactor should be close to the boiling point so that a high reaction rate is ensured in the tubular reactor. However, lower
Temperatures are applied.

In general, the acid and the concentrations of the slurry are chosen so that one
concentrated solution of the product is formed, but without any precipitation of the product
during the reaction comes. If necessary, can tip 30. After cooling to condense the water, the concentration of the solution of the product varies, the carbon dioxide had a purity of or by supplying a separate water stream above 99% and was used to make dry in the first reactor or in one of the later ice.

Reactors are regulated. In other approaches in the same device

If necessary, other substances can be added together with the alkali carbonate and phosphoric acid at rates of about 10,200 kg per hour, in reactor 3 or in any of the later ones
Reactors are given, provided that such added substances the foaming tendency of the
Do not increase liquid. For example, an un- 40
pure product are added in reactor 3 and
to form a substance of standard quality
be reworked.

Essentially the same pressure is maintained in each of the reactors. This pressure is given, with the tank being filled up to 0.61 m, preferably about atmospheric pressure, although countered and the stirrer was started. Then were at the same time Sodium carbonate and phosphoric acid are added in such amounts that a mixture of disodium phosphate and monosodium phosphate was formed in corresponding amounts of 2: 1. The mixture was held at about 100 ° C.

When the tank was half full with liquid, the foam had reached the top of the tank and it became necessary to pass the addition rate of 8 inches which was placed horizontally. 55 Reactants Reduce To Allow Settling The reaction mixture was made from the opposite foam. The intermittent end of the tube through an opening,
whose cross-section corresponded to that of the pipe, into a
second reactor emptied. The sodium carbonate slurry was made by mixing about 60
60 parts by weight of anhydrous sodium carbonate with

Comparative example 1 to example 1

A batch reaction was carried out in a 3.66 X 3.66 meter tank similar to that in the previous example was similar to the tank used as the third reactor. Water and approximate 1810 kg of dry sodium carbonate were added

if necessary, lower or higher pressures can be used.

example

A sodium carbonate slurry and phosphoric acid were added to one end of a first Pumped reactor, which consists of a 1.06 m long stainless steel pipe with a diameter of

if the respondent continued so quickly as the foam formation allowed, until a total of 10,700 kg of sodium carbonate had been added.

The time required for addition was 6 hours, with the average addition rate was 2450 kg per hour.

Taking into account the time required to empty the tank and start a new batch

40 parts of water made and at a temperature of 95 ° C and a speed of 5440 kg
Sodium carbonate fed per hour. The 75%
Phosphoric acid was at a temperature of 65 that was, the average addition was -40 ⁰ C and at a speed of 6000kg speed in the entire cycle 1360 kg per hour, compared with a maximum of

10200kg per hour in the system of example 1.

g g

Phosphoric acid fed per hour. The temperature in the first reactor was about 78 ° C. The Ver-

At your diskcMÄuieriicheta procedure, occurred during the interruption in the addition of sodium carbonate air into the tank, and this reduced the Purity of the isolated carbon dioxide and made it unsuitable for transfer to dry ice.

Comparative example 2 to example 1

The procedure of Example 1 was carried out without using the first and second reactors, Sodium carbonate and phosphoric acid were added continuously and the product continuously removed from the large tank. The maximal Rate at which the sodium carbonate was added could be was about 2720 kg per hour and the foam layer was about 1.52 m.

The volume of the first and the second reactor does not work together with respect to the third reactor, however, if you put the first and the second reactor in front of the large reactor, the Capacity of the latter increased to about four times or even more.

Although the process is illustrated by a system in which two tank reactors are connected to the tubular reactor, the main advantages of the process using only one tank reactor in addition to the tubular reactor will. However, in order to achieve the maximum capacity per unit of the total volume of the system, two or more tank reactors should be connected to the tubular reactor.

Claims (6)

PATENT CLAIMS: 1. A method for preparing an alkali metal phosphate solution and carbon dioxide by reacting phosphoric acid with an alkali metal carbonate, characterized in that phosphoric acid, an alkali metal carbonate and water are continuously introduced into one end of a tubular reactor so that the acid and the carbonate are mixed and partially react with one another that the partially.! converted mixture is withdrawn from the other end of the reactor, that the mixture is continuously passed into a tank reactor with a stirrer, in which a further reaction takes place and see gaseous carbon dioxide separates from the liquid phase without significant foaming, that the Carbon dioxide is continuously withdrawn from the top of the agitated tank reactor and that the alkali phosphate solution is continuously withdrawn from the lower end of the agitated tank reactor. 2. The method according to claim 1, characterized in that the alkali carbonate is sodium carbonate is applied. 3. The method according to claim 1, characterized in that the alkali carbonate as an aqueous Solution is introduced. 4. The method according to claim 1, characterized in that the alkali carbonate as an aqueous Slurry is introduced. 5. The method according to claim 1, characterized in that that the carbon dioxide from the top of the tank reactor with stirring device continuously into the gas space of a second TankreaktoTS with stirrer is passed that the solution from the lower part of the tank reactor is continuously passed into the second tank reactor that the carbon dioxide is continuous withdrawn from the top of the second tank reactor and that the alkali phosphate solution is continuously withdrawn from the lower end of the second tank reactor. 6. The method according to claim 5, characterized in that the temperature of the reaction mixture in the first tank reactor to about 90 ° C is increased and that the temperature of the reaction mixture in the second tank reactor is increased to about 100 ° C. Documents considered: German Auslegeschrift No. 1086 678. 1 sheet of drawings © 309 539 / 35-3.63