DE2109754B2 - Process for the continuous Her position of aminoplast solutions - Google Patents

Description

The main aminoplast former is urea. However, one can also use dicyandiamide or use melamine or mixtures of these substances with urea.

The urea is usually 50 to 90% igen aqueous solutions applied. An aqueous solution is advantageously used immediately, as in the Urea synthesis occurs. But you can also use a solution of urea or another aminoplast former Use in aqueous formaldehyde solution of neutral or weakly acidic pH.

The formaldehyde is used in the form of commercially available 30 to 45% solutions. One can but also of aqueous solutions of a precondensate of formaldehyde and z. B. Urea, the one Contains excess formaldehyde and by absorbing formaldehyde gas in aqueous urea solution can be obtained, or go out from a precondensate of urea and formaldehyde.

Ammonia or amines or mixtures are used as the basic component in the catalyst solution of both, but ammonia is preferred. The amines are low molecular weight and polyvalent alkylamines and hydroxyalkylamines into consideration. In detail its named: 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 its acidic salts.

The mixture of base and acid is preferably used in the form of an aqueous solution, with uses a substantial excess of amine, depending on the molar ratio of the main reaction component and mean residence time in the boiler cascade in the range from VaI amine to VaI acid between 10 and 150, preferably between 15 and 100, is selected.

The reaction is carried out at or near the boiling point of the solution; H. between approximately 90 and 105 ° C.

For the stirred kettle cascade, conventional stirred kettles are used. Appropriately be Stirring vessels of the same size are used, but individual vessels, in particular, can be used to increase the residence time the second stirred tank can be chosen larger. It is technically beneficial to go into this case divides the second stirred kettle into two stirred kettles, so that the cascade preferably consists of four stirred kettles or in a particularly preferred embodiment consists of five identical stirred kettles.

The stirred kettles are expediently switched one after the other so that there is an overflow the solution overflows by gravity from the first kettle into the second and so on. It has proved to be particularly advantageous when the overflow into the next boiler via a pipe happens that is deeply immersed in this boiler, so that a complete and even backmixing enters with the contents of the boiler.

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 mixed in a mixing zone with a catalyst solution and then immediately introduced into the first reactor of the stirred tank cascade. By preheating the individual solutions to about 50 to 60 ° C is achieved that a temperature of about 95 ⁰ C is established in the first reaction vessel, so that achieved in the following stirred vessels due to the weakly exothermic reaction without further supply of energy, the boiling point and maintained can.

The aminoplast former is used in at least 2, preferably 3 or 4, parts of different stirred kettles metered in. The following molar ratios of formaldehyde and should be used for four stirred tanks Aminoplast formers, especially urea, are observed.

Stirring tank 1: molar ratio FA to HA =
2.1 to 3, preferably 2.1 to 2.5;

Stirring kettle 2: molar ratio FA to HA =

1.8 to 2.6, preferably 1.9 to 2.4;

Stirring vessel 3: molar ratio FA to HA =

1.6 to 2.4, preferably J, 7 to 2.2;
Stirring kettle 4: molar ratio FA to HA =

1.4 to 2.2, preferably 1.5 to 2.1.

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

In the process according to the invention it is important that the specified in the individual reaction vessels graded pH ranges are maintained, so that in each subsequent stirred tank a clearly lower pH than prevails in the preceding stirred tank. The one from one stirred kettle to the next Overflowing reaction solution thus arrives practically immediately as a result of the rapid mixing in a reaction medium with a lower pH value. Since the speed of the condensation reaction with As the concentration of hydrogen ions increases, they are accordingly also leaps and bounds higher and more uniform Networking speeds set.

The pH range required for the condensation reaction can be set at once Addition of a suitable catalyst solution together with the main components formaldehyde or formaldehyde-containing Precondensate and aminoplast formers in one immediately in front of the first stirred tank activated mixing zone happen. It is also possible to increase the specified pH value ranges by adding

of the pH-regulating components in the individual stirred kettles. The choice of pH levels is made determined by the number and size of the individual stirred kettles, d. H. by the mean residence time in the respective Boilers as well as by quantity and combination

setting of the catalyst. By making a suitable choice, the required pH value ranges can therefore be set by adding the catalyst once to the mixing zone upstream of the first stirred tank.
The dosage is handled in such a way that

that initially, d. H. in the mixing zone, at a lower temperature there is one in the alkaline range pH adjusts that a neutral to weakly acidic reaction is present in the first stirred tank, and that in the following kettles one further in the acidic

Range lying pH level is reached. In a stirred tank cascade, five of the same size Stirred tanks, 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

The residence time in the process according to the invention is generally between 5 and 25 seconds in the basic pH range in the mixing zone; in the The residence time for the other subsequent pH stages is approximately 5 to 15 minutes in each case.

The process according to the invention can be used to produce 30 to 60% linseed solutions. The after Resin solutions produced by new processes are distinguished by a particularly good storage stability. Of the The process sequence is far less susceptible to failure than in previously known processes, because of the failure of energy or input materials, each individual stirred tank can be neutralized and cooled immediately. Through the Backmixing can lead to operating times of up to 3000 hours without having to be shut down for necessary removal the crust formation can be achieved. The system can then be cleaned in a few hours. Furthermore, the throughput can be one to three times with complete preservation of the type conformity of the product can be varied. Noteworthy is the preparation of resin solutions described here in a stirred tank cascade also possible with little personnel expenditure. It can be two streets from to be monitored and serviced by a man.

The solutions prepared in this way can be concentrated under reduced pressure in a manner known per se Resin solutions (about 60 to 75% solids content) evaporated or in spray dryers to solid resin powder to be dried.

example 1

Every hour, 1400 parts by weight of aqueous formaldehyde solution (35%) are mixed in continuously 532 parts by weight of urea solution (80%) and 49.4 parts by weight of an aqueous solution containing 10 parts by weight Ammonia and 0.25 parts by weight of formic acid in a mixing zone and directs the Mixing after a dwell time of about 20 seconds in the first of four vessels of a reactor cascade a. After an average residence time of about 12 minutes, the solution passes into the following one Reaction vessel.

50 parts by weight of the urea solution are metered into the second and third containers every hour and 184 parts by weight each hour into the fourth.

The catalyst mixture used produces the following pH values, measured with a glass electrode (Two-bar chain) at 20 ° C, one:

In the mixing zone pH 8.0

In the first reactor pH 6.6

In the second reactor pH 5.4

In the third reactor pH 4.5

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 ° C, in the second 101 ⁰ C, the third 102 ° C, in the fourth to 100 ° C.

The obtained resin solution is continuously reduced to a concentration of resin under reduced pressure evaporated from 65 percent by weight.

Example 2

Through continuous metering, 3835 parts by weight of an aqueous precondensate solution, which contains 1535 parts by weight of formaldehyde and 877 parts by weight of urea, 550 parts by weight Urea solution (90%) and 49 parts by weight of an aqueous solution containing 9.8 parts by weight of ammonia and Contains 1.4 parts by weight of formic acid, mixed in a mixing zone and immediately (dwell time approx. 7 seconds) placed in the first of five vessels of a reactor cascade. The mean residence time of the solution in each individual reactor takes about 7 minutes.

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

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

In the mixing zone pH 7.9

In the first reactor pH 6.5

In the second reactor pH 4.8

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 ⁰ C, in the fourth to 100 ° C, in the fifth 100 ° C.

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

Example 3

By continuously metering in 1106 parts by weight of an aqueous precondensate solution of 7O 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, 1058 parts by weight of urea solution (65%, 75 ° C) and 35 parts by weight of an aqueous solution containing 15 , Contains 9 parts by weight of methylamine and 0.5 parts by weight of sulfuric acid, mixed in a mixing zone and immediately introduced into the first of five vessels of a reactor cascade. The mean residence time of the mixture is calculated to be about 10 minutes for each of the reactors of the same size.
The type and amount of the catalyst mixture result in

The following pH values, measured with a glass electrode at 20 ° C:

In the mixing zone pH 7.6

In the first reactor pH 6.7

In the second reactor pH 5.4

In the third reactor pH 4.6

In the fourth reactor pH 4.4

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

The temperature in the first reactor is 95 ° C, in the second 101 ° C, the third 103 ⁰ C, in the fourth and fifth 100 ⁰ C 100 ° C.

The resulting condensate solution shows when one part by volume is mixed with 5 parts by volume of water phase separation at 26 ° C. After evaporation in a vacuum to a solids content of about 65% a glue resin with excellent properties and very good storage stability.

Claims (4)

after the condensation, an increase in the pH in the claims: neutral or weakly basic range by adding lye. 1. Process for continuous production For the known continuous production of Aminoplast solutions by condensation of 5 are mostly tubular reactors, in Aminoplast formers with formaldehyde on the other hand, condensation without back-mixing, d. H. wait for a catalyst mixture of ammonia or a largely laminar flowing medium to run off, Amine and acid or their acidic salts are used in homo-. In fact, it is claimed in the literature that gener aqueous solution at boiling point or to produce a technically useful end pronahe the boiling point of the solution in stirred kerosene ducts necessarily a sufficient reaction time without be, characterized in that back-mixing must be observed. Essential man the reaction in a sequence of at least borrowed that the pH of the Reaktijnsmidrei Stirring kettles with back-mixing of the schung during this supposedly decisive one Carries out solution, gradually adding the condensation phase, d. H. largely Amounts of the catalyst mixture and the amounts 15 linearly from a higher value to a plurality Aminoplast former, the main amount of which drops after Mi- units which are lower in value. Simultaneously Mixing with the formaldehyde solution in the first can be done by appropriate heating in a stirred tank is introduced and the remaining successive sections of the pipe system Required amount is complied with in at least one other different discrete temperature levels Share to be metered into one of the following stirred kettles ao. is chosen so that in the first stirred tank a mol- After another continuous process ratio of formaldehyde to aminoplast former, the reactants are first determined separately 2.1 to 3 and a pH value of 5.5 to 7.5, in two- warms and then at the same time with acidic or alkaline th stirred tank a molar ratio of formaldehyde to Shem catalyst combined in an injection chamber; Aminoplast formers from 1.8 to 2.1 and a pH of »5, the initially partial condensation that takes place here Value from 4.0 to 5.0, and in the last stirred tank is finished in another vessel, The known continuous processes have a molar ratio of formaldehyde to aminoplast Formers from 1.4 to 2.2 and a pH of various disadvantages. When using tubular 5.5 to 7.5 is observed. Small reaction vessels without backmixing occur easily 2. The method according to claim 1, characterized in that crust formation or clogging of the reactors indicates that one implementation in four or so is often time consuming and costly five stirred kettles connected in series - mechanical cleaning is required. Another leads. The disadvantage is the difficulty of the inadequate adaptation 3. The method according to claim 1, characterized by different throughput speeds, draws that urea 35 is used as an aminoplast former. These systems have a particularly serious effect used. the sudden failure of the power supply or 4. The method according to claim 1, characterized in that a reaction component is made because it is large draws that as a catalyst mixture Lö- quantities of reactive liquids are blocked, with solutions used, the ammonia or amines the production of the whole plant to a standstill and acids or their acidic salts with a pK 4 ° can come. contain less than 4.0, the molar ratio of 10 to 150 was therefore the object of a process for demoniac or amine to acid. winding, in which in a simple manner aminoplast-S.Verfahren according to claim 1, characterized marked solutions can be produced without the sign that one occurs instead of the purely formal-described disadvantages,
dehyde solution solutions of precondensates from 45. This object was used according to the invention with a formaldehyde and urea (with a Molver process for the continuous production of the amino ratio of formaldehyde to urea from at least plastic solutions by condensation of aminoplast 1: 3.5). pictures with formaldehyde in the presence of a kata analyzer mixture of amine and acid in a homogeneous 50 aqueous solution at boiling point or near the The boiling temperature of the solution dissolved in stirred kettles, the reaction taking place in a sequence of at least three stirred kettles with back-mixing of the solution The invention relates to a process that is carried out continuously, and the amount of amino formaldehyde and aminoplast formers, in particular plastic formers, the main portion of which after mixing with urea in at least three formaldehyde solutions in a row is added to the production of aminoplast solutions from the catalyst mixture the first stirred kettle einteten stirred kettles at elevated temperature and below and the remaining, required amount in multiple changes in the molar ratio of the at least one further portion of one of the following reaction components to each other. ^6o stirred tank is metered in so that in the first In the known discontinuous process stirred kettle a molar ratio of formaldehyde to amino for the production of aminoplast solutions, the plastic former is 2.1 to 3 and a pH of 5.5 conversion in individual reaction vessels or stirred up to 7.5, in the second stirred kettle a molar ratio kettles running in which the reactants formaldehyde to aminoplast formers from 1.8 to 2.1 formaldehyde and z. B. urea in aqueous solution ⁶ 5 and a pH of 4 to 5 and in the last stirred tank first in an alkaline reaction medium and then a molar ratio of formaldehyde to aminoplast former after acidification in an acidic reaction medium to 1.4 to 2.2 and a pH -Value from 5/5 to 7.5 a resin solution to be condensed. Usually done is held.