DE2109754A1 - Process for the continuous production of aminoplast solutions - Google Patents

Description

21st

Badische Anilin- & Soda-Fabrik AG

Our mark .: O.Z. 27 571 Hp / Fe / Wil 6700 Ludwigshafen, I March 1971

Process for the continuous production of aminoplast solutions

The invention relates to a process for continuous production of aminoplast solutions from formaldehyde and aminoplast formers, in particular urea, in at least three in a row switched stirred kettles at elevated temperature and with repeated changes in the molar ratio of the reaction components to each other.

In the known discontinuous processes for the production of aminoplast solutions, the reaction is carried out in individual reaction vessels or stirred kettles in which the reactants Formaldehyde and z. B. Urea In aqueous. Solution first in alkaline reaction medium and then after acidification in acidic Reaction medium are condensed to a resin solution. As a rule, the pH in the is increased after the condensation neutral or weakly basic range by adding lye.

For the known continuous production process, tubular reactors are usually used, in which the condensation without Backmixing, d. H. runs in a largely laminar flowing medium, used. In fact, it is claimed in the literature that In order to produce a technically usable end product, a sufficient reaction time without backmixing must be observed must be. It is essential that the pH of the reaction mixture is maintained during this supposedly decisive condensation phase gradually, d. H. largely linearly from a higher value to a value several units lower. Simultaneously can be different discrete by appropriate heating in successive sections of the tube system Temperature levels are maintained.

Another continuous process is the reactants initially separated, heated and then simultaneously treated with an acidic or alkaline catalyst in an injection chamber

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agree; the outgoing here first partial Kondensa ⁴ ion is terminated in another vessel.

The known continuous processes have several disadvantages. When using tubular reaction vessels without backmixing easily occurs crust formation or clogging of the reactors, so that often a time-consuming and costly mechanical cleaning is required. Another disadvantage is the difficulty of failing to adapt to different ones Throughput speeds. Has a particularly serious effect the sudden failure of the energy supply or of a reaction component in these systems, as this causes large quantities reactive liquids are blocked, whereby the production of the whole plant can come to a standstill.

The task was therefore to develop a method in which aminoplast solutions can be produced in a simple manner without the disadvantages described occurring.

This object was achieved according to the invention with a process for the continuous production of aminoplast solutions by condensation of aminoplast formers with formaldehyde in the presence of a catalyst mixture of amine and acid in homogeneous aqueous solution at or near the boiling point the solution dissolved in stirred kettles, the reaction taking place in a sequence of at least three stirred kettles with backmixing the solution is carried out, and the amounts of the catalyst mixture to be added and the amount of aminoplast former, its main part after mixing with the formaldehyde solution in the first stirred tank is introduced and the remaining, required amount in at least one further portion the following stirred tank is metered in so that a molar ratio of formaldehyde to aminoplast former is added in the first stirred tank from 2.1 to 3 and a pH of 5 * 5 to 7 * 5 * iro second stirred kettle a molar ratio of formaldehyde to aminoplast former of 1.8 to 2.1 and a pH of 4 to 5 and in the third stirred tank a molar ratio of formaldehyde to aminoplast former of 1.4 to 1.9 and a pH of 5 * 5 to 7 * 5 is maintained.

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; costume. Man

The main aminoplast former is urea, but dicyandiamide or melamine or mixtures of these can also be used Use substances with urea.

The urea is usually available in 50 to 90% aqueous solutions Solutions applied. It is advantageous to use an aqueous solution as it occurs during urea synthesis. Man but can also be a solution of urea or another aminoplast former in aqueous formaldehyde solution of neutral or use weakly acidic pH.

The formaldehyde is used in the form of the commercially available J50 bis 45 $ solutions. However, one can also use aqueous solutions a precondensate of formaldehyde and z. B. urea, which contains an excess of formaldehyde and by absorption obtained from formaldehyde gas in aqueous urea solution can be, or a precondensate of urea and formaldehyde go out.

Ammonia or amines or mixtures of both are used as the basic component in the catalyst solution, although Ammonia is preferred. Low molecular weight mono- and polyvalent alkylamines and hydroxyalkylamines are suitable as amines. In detail his mentioned: methylamine, ethylamine, mono-, di- or triethanolamine or ethylenediamine.

The acids used are inorganic or organic acids with a pK value of less than 4.0, such as hydrochloric acid, sulfuric acid, Nitric acid, phosphoric acid, acetic acid, chloroacetic acid, oxalic acid, maleic acid and especially formic acid or their acidic salts.

The mixture of base and acid is preferably used in the form of an aqueous solution, with a considerable excess of amine is used, which depends on the molar ratio of the main reaction component and the average residence time in the tank cascade in the range of VaI amine: VaI acid between 10 and 150, preferably between 15 and 100 is selected.

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The reaction occurs at or near the boiling point the solution executed, d. do between about 90 and 105 ° C.

For the stirred kettle cascade, conventional stirred kettles are used. It is advisable to use stirred kettles of the same size, but individual kettles, in particular the second stirred tank can be chosen to be larger. It is technically advantageous if you can do the second in this case The stirred kettle is divided into two stirred kettles, so that the cascade preferably consists of four stirred kettles or a particularly preferred one Embodiment consists of five identical stirred kettles.

The stirred kettles are expediently switched one after the other in stages, so that from one overflow the solution overflows by gravity from the first boiler into the second and so on, It has proven to be particularly advantageous if the overflow into the next boiler takes place via a pipe that immersed deeply in this boiler so that a complete and even back-mixing with the boiler contents occurs.

In detail, one proceeds in the reaction according to the invention in such a way that aqueous solutions of the reactants formaldehyde and z. B- urea in one. Mixing zone mixed with a catalyst solution and then immediately into the first reactor of the Introduces stirred tank cascade. By preheating the individual solutions to about 50 to 6o ° C it is achieved that already in the first reaction kettle sets a temperature of about 95 ° C, so that in the following stirred kettles as a result of the weak exothermic reaction, the boiling point can be reached and maintained without additional energy input.

The aminoplast former is metered into at least 2, preferably three or four, portions of different stirred tanks. The following molar ratios of formaldehyde and aminoplast former, in particular urea, should be adhered to with four stirred tanks will.

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Stirred tank 1: molar ratio PA: HA = stirred tank 2: molar ratio FA: HA = stirred tank J>: molar ratio FA t HA = stirred tank 4; Molar ratio FA; HA =

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2.1 to 3,

preferably 2.1 to 2.5;

1.8 to 2.6,
preferably 1.9 to 2.4;

1.6 to 2.4,
preferably 1.7 to 2.2;

1.4 to 2.2, preferably 1.5 to 2.1.

When using precondensate solutions of formaldehyde and urea, the specified molar ratio ranges the higher values are preferred, while the lower values are preferred when formaldehyde solutions are used.

In the process according to the invention, it is important that the specified graded pH ranges in the individual reaction vessels are maintained, so that in each subsequent stirred tank a significantly lower pH than in the previous one Stirred tank prevails. The reaction solution overflowing from one stirred tank to the next thus arrives as a result of the rapid Mixing practically immediately into a reaction medium with a lower pH value. Because the speed of the condensation reaction increases with the concentration of hydrogen ions, there will also be a sharp increase in the uniform crosslinking speed en set.

The pH range required for the condensation reaction can be set all at once by adding a suitable Catalyst solution together with the main components formaldehyde or formaldehyde-containing precondensate and aminoplast former happen in a mixing zone switched on immediately in front of the first stirred tank. It is also possible to use the specified pH ranges by adding the pH-regulating components to the individual stirred kettles. The choice of pH levels is determined by the number and size of the individual stirred kettles, i. H. by the mean residence time in the respective kettles as well as the amount and composition of the catalyst. The required pH value ranges can therefore be achieved through a suitable choice can be set by adding the catalyst once to the sludge zone in front of the first stirred tank.

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The dosage is handled in such a way that initially, d. H. in the mixing zone, at a lower temperature, a pH value in the alkaline range is established that in the first A neutral to weakly acidic reaction is present, and that in each of the following kettles one further in the acidic reaction Range lying pH level is reached. In a stirred tank cascade, which consists of five stirred tanks of the same size, the following levels can be selected:

Starting pH of the mixture: 7 * 3 to 8.3 pH in kettle 1: 6.0 to 7.0

pH in Kettle 2: 5.0 to 6.0

pH in Kettle 3: 4.5 to 5.0

pH in Kettle 4: 4.0 to 4.5

pH in kettle 5; 6.5 to 7.5.

In the process according to the invention, the residence time in the basic pH range in the mixing zone is generally between 5 and 25 seconds; in the remaining pH stages that follow, the residence time is approximately 5 to 15 minutes in each case.

With the method according to the invention, 30 to 60% glue solutions can be produced produce. The resin solutions produced by the new process are characterized by a particularly good storage stability the end. The process sequence is far less susceptible to failure than with previously known processes, since if the Energy or input materials, each individual stirred tank can be immediately neutralized and cooled. By backmixing operating times of up to 3,000 hours can be achieved with no shutdown required Elimination of crust formation can be achieved. The system can then be cleaned in a few hours. Further the throughput can be varied from one to three times while maintaining the type conformity of the product. It is noteworthy that the production of resin solutions described here in a stirred tank cascade is also low personnel costs possible. Two streets can be monitored and maintained by one man.

The solutions prepared in this way can be used under reduced pressure

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to concentrated resin solutions (approx. 60 to 75 ^ pesticide content) evaporated or in spray dryers to be dried into plague resin powder.

example 1

1400 parts by weight of aqueous formaldehyde solution (35 $ lg) are mixed hourly and continuously with 532 parts by weight Urea solution (80 $ ig) and 49.4 parts by weight of an aqueous Solution containing 10 parts by weight of ammonia and 0.25 parts by weight of formic acid in a mixing zone and directs the mixture after a dwell time of about 20 seconds in the first of four vessels of a reactor cascade. After a middle The solution reaches the following reaction vessel with a residence time of approx. 12 minutes.

Every hour 50 and in the fourth, 184 parts by weight of the urea solution every hour dosed.

The catalyst mixture used results in the following pH values, measured with a glass electrode (two-rod chain) at 20 ° C, a:

pH 8.0 in the mixing zone

pH 6.6 in the first reactor

in the second reactor pH 5 * 4

pH 4.5 in the third reactor.

In the fourth reactor, the pH is adjusted to 7.1 by adding dilute sodium hydroxide solution.

The temperature in the first reactor is 94 ⁰ C, in the second 101 ° C, the third 102 ⁰ C, in the fourth 100 ⁰ C. '

The resin solution obtained is continuously evaporated under reduced pressure to a concentration of resin of 65 wt.%.

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Example 2

Through continuous metering, 3835 parts by weight of an aqueous precondensate solution containing 1535 parts by weight of formaldehyde and 877 parts by weight of urea are produced per hour. 550 parts by weight of urea solution (90Joig) and 49 parts by weight an aqueous solution containing 9.8 parts by weight of ammonia and 1.4 parts by weight of formic acid, mixed in a mixing zone and immediately ("dwell time approx. 7 seconds) in the first of five vessels of a reactor cascade introduced. The mean residence time of the solution in each individual reactor is approx. 7 minutes.

In the second reactor 116 parts by weight, in the fourth 84.6 and in the fifth 503 parts by weight of the urea solution dosed.

Due to the mixture of catalyst used make the following pH values measured with a glass electrode (two-bar chain) tei 20 ⁰ C, a:

in the mixing zone pH 7.9

pH 6.5 in the first reactor

pH 4.8 in the second reactor

in the third reactor pH 4.3

in the fourth reactor pH 4.2.

In the fifth reactor, a pH of 7.0 to 7.3 is set by adding dilute lye.

The temperature in the first reactor is 97 ° C, in the second 100 ° C, the third 101 ° C, in the fourth 10O ⁰ C, in the fifth 100 ° C.

The resin solution obtained contains over 50 % solids. By evaporation in vacuo to a solids content of approx. 60 to 70 % , a resin solution is obtained which has very good properties.

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Example 3

By continuously metering in 1106 parts by weight of an aqueous precondensate solution of 70 ⁰ C, the 442 parts by weight of formaldehyde and 221 parts by weight of urea per hour containing 1060 parts by weight of formaldehyde, IO58 GewichtsteiIe urea solution (65%, 75 ° C) and 35 parts by weight of an aqueous solution containing Contains 15.9 parts by weight of methylamine and 0.5 parts by weight of sulfuric acid, mixed in a mixing zone and immediately placed in the first of five containers of a reactor cascade

The type and amount of the catalyst mixture cause the following pH values, - measured with glass electrode

In the mixing zone
in the first reactor
in the second reactor in the third reactor in the fourth reactor

In the fifth reactor, the pH of the solution is adjusted to approx. 7.2 by adding dilute sodium hydroxide solution.

The temperature in the first reactor is 95 ° C, in the second 101 ⁰ C, in the third 10 ^ ⁰ C, in the fourth and fifth 100 ⁰ C 100 ⁰ C.

at 20 ⁰ C: PH 7.6 pH 6.7 pH 5.4 pH 4.6 pH 4.4.

The condensate solution obtained shows phase separation ^{at 26 °} C. when one part by volume is mixed with 5 parts by volume of water. After evaporation in vacuo to a solids content of approx. 65 % , it gives a glue resin with excellent performance properties and very good storage stability.

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Claims (5)

- ίο - ο. ζ.27 371 Claims /. Process for the continuous production of aminoplast solutions by condensation of aminoplast formers with formaldehyde in the presence of a catalyst mixture of ammonia or amine and acid or their acidic salts in homogeneous aqueous solution at the boiling point or near the boiling point of the solution in stirred tanks, characterized in that the reaction is carried out in a A sequence of at least three stirred kettles is carried out with back-mixing of the solution, the amounts of the catalyst mixture to be added and the amounts of aminoplast former, the main amount of which is introduced into the first stirred kettle after mixing with the formaldehyde solution, and the remaining amount required in at least one further portion of one of the following stirred kettles is metered, so that in the first stirred tank a molar ratio of formaldehyde to aminoplast former from 2.1 to 3> and a pH of 5 * 5 to 7.5, in the second stirred tank a molar ratio of formaldehyde to aminoplast from 1.8 to 2.1 and a pH value of 4.0 to 5.0, and in the α »ίίίτι riin> stirred tank a molar ratio of formaldehyde to aminoplast former of 1.4 to tr ^ · and a pH value of 5.5 to 7, 5 is complied with. 2. The method according to claim 1, characterized in that the reaction is carried out in four or five stirred kettles held one behind the other. 3. The method according to claim 1, characterized in that urea is used as the aminoplast former. 4. The method according to claim 1, characterized in that the catalyst mixture used is solutions which contain ammonia or amines and acids or their acidic salts with a pK less than 4.0, the molar ratio of ammonia or amine to acid being 10 to 150. 5. The method according to claim 1, characterized in that instead of pure formaldehyde solution, solutions of precondens 209838/0961 - Ii - ο.ζ. 27 371 seeds from formaldehyde and urea (with a molar ratio Formaldehyde to urea from. at least 1; 3 * 5) used. Badische Anilin- & Soda-Fabrik AG / S 209838/0961