DE1205071C2 - Process for the production of aqueous formaldehyde solutions which are stable in a temperature range from í¬ 20 to + 60íµ - Google Patents

Description

R-C

C-NH,

NH,

in which R is an aryl, aralkyl, a fully or partially hydrogenated aryl group, also an aniline alkyl, N-alkyl-substituted aniline alkyl radical and in which the hydrogen atoms of the 2- and 4-position amino groups wholly or partially by an alkyl, aryl, wholly or partially hydrogenated aryl group and the sulfates of these compounds are added to the formaldehyde solution will.

2. The method according to claim 1, characterized in that the stabilizing agents in one Amount of 0.01 to 5 parts by weight per 100 parts by weight of formaldehyde solution are added.

3. The method according to claim 1, characterized in that the method at a pH between 3.0 and 5.0, at temperatures between 20 and 100 ⁰ C, preferably between 40 and 70 ⁰ C, for a period of 10 minutes up to 10 hours.

4. The method according to claim 1, characterized in that the stabilizing agent or agents fed to the solution directly in the column for absorption of the formaldehyde in water.

can be and the aqueous formaldehyde solutions over longer periods of time also at lower Making temperatures storable.

Our own experiments showed that aqueous formaldehyde solutions can be stabilized in such a way that they ^{can be stored in the temperature range between -10 and + 50 °} C. if 1.5 to 5% melamine or 3 to 6% urea or 3 to 10% phenol can be used as a stabilizer. The percentage of stabilizer depends on the formaldehyde concentration of the solutions.

Urea, melamine and phenol partially eliminate the disadvantages of methanol, but they have to as before used in such amounts that they have versatile use of the commercial ones Prevent formaldehyde solutions. You can only produce urea or formaldehyde Melamine-formaldehyde resins are used.

It is also known to concentrate formaldehyde solutions by adding a colloid, especially from certain cellulose derivatives or melamine. Solutions containing such stabilizers included, but are not stable if kept at low temperature. Rather, they will pastes that have to be carefully heated to turn them back into a precipitate-free liquid to transform.

The aim of the invention is to eliminate said disadvantages. The invention accordingly provides a process for the preparation of aqueous formaldehyde solutions in a temperature range from -20 to + 6O ⁰ C is resistant. The process is characterized in that one or more stabilizers of the general formula

R-C

C-NH ₂

NH,

The invention relates to a process for the preparation of aqueous formaldehyde solutions, which are stable in a temperature range between -20 and +60 ⁰ C.

Ice is known to have aqueous formaldehyde solutions with a concentration above 30% at low levels Temperatures are hardly storable and due to the formation of formaldehyde polymers the tendency to cloudiness / own.

To avoid these difficulties, methanol is often added to the solutions; the commercial one 37% formaldehyde solution generally contains 7 to 14 weight percent methanol. This brings with it certain economic and technological There are disadvantages because, for example, methanol increases in the further processing of the formaldehyde solution Resins interfere by reducing the kinetics of the condensation reactions. Methanol must also be in high percentages are used and is also poisonous.

For these reasons, various studies dealt with the use of other stabilizers, like urea, melamine and phenol, which are used in smaller proportions compared to methanol

45 in which R denotes an aryl, aralkyl, a completely or partially hydrogenated aryl group, also an aniline alkyl, N-alkyl-substituted aniline alkyl radical and in which the hydrogen atoms of the amino groups in the 2- and 4-position are wholly or partially replaced by an alkyl , Aryl fully or partially hydrogenated aryl group and the sulfates of these compounds are added to the formaldehyde solution.
Notably, it is the stabilizing agent at pH values between 3 and 5, temperatures between 20 and 100 ⁰ C, in particular between 40 and 70 ° C, with reaction times between 10 minutes and 10 hours.

The proportion of stabilizing agents used depends on the formaldehyde concentration in the Solutions. Amounts from 0.01 to 5 parts by weight per 100 parts by weight of solution are used. These new stabilizers are very easy to use. You can refer to that of the formaldehyde solution coming from the manufacturing plant, which is heated and possibly in the storage tanks is kept moving, or they can be added continuously to the absorption columns

fed pastures, in which gaseous formaldehyde with that calculated for the industrial cycle Amount of water is absorbed.

If the specified conditions are used, aqueous formaldehyde solutions are obtained. B. -1O ⁰ C, for several days at high temperatures, for. B. + 50 ° C, are stable for a few months.

The temperature of -10 ^° C. was chosen as the “standard low temperature” in the stability tests.

The tests carried out showed the special stabilizing effect of the benzoguanamines and of various compounds belonging to the aforementioned formula such as:

1. Phenylacetoguanamine

N
- /
-C

NH ₂
2. Tetrahydrobenzoguanamine

H ₂ NC

CH ₇ -CH,

C-CH

CH

CH ₇ -CH

NH ₂
3. n-Methylanilino-propioguanamine

/ \
H ₂ NC C-CH ₂ -CH

The treated with the stabilizing agents formaldehyde solutions are stable within a temperature range of -20 to +60 ⁰ C and can be used without any restriction in all Anw.endungsgebieten where usually not inhibited aqueous formaldehyde solutions are used.

However, storage tests were also carried out at lower temperatures for various periods of time, and the solutions treated in this way also had very good storage properties ^:
found.

A commercial solution containing 36 percent by weight formaldehyde and 14% methanol, is stable at a temperature of -1O ⁰ C only 4 to 6 days.

The shelf life of the solutions was dependent on the different storage temperatures of time by observing the appearance of the solutions and controlling the changes certain properties, such as viscosity, density and pH value.

A solution is said to be stable as long as

when their appearance remains clear and free of precipitation and the other properties on values that do not differ much from the initial values.

The invention is illustrated by the following examples explained. Unless otherwise stated, the percentages are percentages by weight.

Example 1 1

2000 g of a 36% aqueous formaldehyde solution was poured into one with a stirrer, a thermometer and a 3-1 flask equipped with a reflux condenser was filled. The solution is at pH of about 3.5 kept moving and gradually heated to a temperature of 50 ° C.

Maintaining the above-mentioned working conditions for 2 hours were thereafter

NH 1.6 g of benzoguanamine crystals were added. The stable

lized solution was then emptied and, after CH ₃ measurement of its viscosity, density and pH value, poured into a thermostat cell to determine its stability over time.

The stability of the solution is shown in the table below:

Look

clear

36% CH ₂ O solution stabilized with 0.08% benzoguanamine; Changes in density, viscosity and pH value after storage at - 10 ⁰ C.

Properties at the beginning

viscosity

at 20 ° C

cP

2.45

density

at
20 C
g / cm ³

1.1050

PH value
at 2t) C

3.7

salary

35.9

The solution can be stored for a few days at a temperature of -10 ^{° C. and for a few months at higher temperatures.}

The formaldehyde solution containing benzoguanamine is suitable for the production of urea-formaldehyde, melamine-formaldehyde or phenol-formaldehyde resins. The goodness of these resins is the same in properties
after 10 days of storage at -10 ° C

Look

clear

viscosity

at 20 "C

cP

2.47

density
at

20 ° C
g / cm ³

1.1054

pH value
at 20 C

3.7

CH, O

salary

35.8

65

as when using non-inhibited formaldehyde solution.

B e i s ρ i e 1 2

It was carried out with the experimental set-up given in Example 1 under the working conditions of Example 1 worked. The concentration of the water

The formaldehyde solution was 43%. It was either taken directly from the manufacturing facility taken or prepared by concentration of the 36% aqueous solution in the laboratory.

2000 g of the 43% solution were added with stirring and while keeping the pH constant at 3.5 heated to 70 ° C.

When this temperature was reached, 6.0 g of benzoguanamine crystals were added and the used ones Maintain process conditions for 3 hours. The stabilized solution was then added emptied and after measuring its viscosity, density and pH value in a thermostat cell for Observation of their temporal stability given.

At -10 ⁰ C the solution can be stored for 8 days and at higher temperatures for more than 2 months.

This solution is also used for the production of urea, melamine and phenol-formaldehyde resins suitable.

Example 3

The working conditions of Example 1 were repeated on an industrial scale.

30 t of a 36% strength aqueous CH ₂ O solution directly from the production plant were ^{poured into a 35 m 3} tank and kept in circulation by means of a pump. The solution was maintained at a pH of 3.5 and gradually heated to 50 ⁰ C.

24 kg of benzoguanamine crystals were then added and the above-mentioned conditions during a few hours.

The solution which had the same stability properties as the solution of Example 2 is without changing the usual procedure for the production of urea, melamine and phenol-formaldehyde resins suitable. These resins showed analytical and application properties, which were identical to those obtained from non-inhibited 36% formaldehyde solution Resins.

Example 4

The stabilization of the aqueous formaldehyde solution was carried out on an industrial scale, the benzoguanamine being introduced directly into the formaldehyde production plant together with the amount of water used in the work process. The working conditions and the proportion of benzoguanamine were as in Example 3.

In fact, a sample of the solution, which was kept at a temperature of −10 ^° C., remained unchanged in appearance and with regard to its initial properties for 10 to 12 days.

At 0 ⁰ C and at +20 ⁰ C, the solution can be kept for more than 2 months . The stabilized solution obtained in this way can be stored in the specified temperature range and is suitable for the production of urea, melamine and phenol-formaldehyde resins. These resins show analytical and application properties which are identical to those of the products made from uninhibited CH ₂ O.

Example 5

It is used the apparatus described in Example. 1 2000 g of a 36% strength aqueous formaldehyde solution are heated ^{to 60 ° C. with stirring at a pH of about 3.4.} At this temperature, 2.30 g of Ν, Ν'-dimethylbenzoguanamine crystals are added and the aforementioned conditions are maintained for about 10 hours.

The solution is then emptied and, after measuring its density, viscosity and pH value, is brought into the thermostat cells to determine its stability over time. At a temperature of - 10 ⁰ C ίο the solution is stable for 8 to 10 days, at +20 ⁰ C for more than 2 months.

Example 6

The device described in Example 1 is used. 2000 g of a 36% strength aqueous formaldehyde solution are heated ^{to the temperature of 50 ° C. at a pH of 3.3 with stirring.} At this temperature 2.50 g of benzoguanamine sulfate crystals are added and the aforementioned conditions are maintained for 16 hours. The solution is then emptied and, after measuring its density, viscosity and pH value, is brought into the thermostat cells to determine its stability over time.

At a temperature of −10 ^° C. the solution is stable for 12 days, at 0 ^° C. for more than 1 month and at + 20 ^° C. for more than 2 months.

Example 7

The device described in Example 1 is used. 2000 g of a 36% strength aqueous formaldehyde solution are heated to a temperature of 60 ° C. with stirring at a pH of about 3.2. At this temperature, 8.0 g of phenylacetoguanamine crystals are added and the aforementioned Maintain conditions for one hour. The solution was then drained and after Measurement of their density, viscosity and their pH value in the thermostat cells for determination their temporal stability brought.

At the temperature of - 10 ⁰ C, the solution for 4 days was, however, more stable at +20 ⁰ C over 2 months.

Example 8

The device described in Example 1 is used

.used. 2000 g of a 36% strength aqueous formaldehyde solution were heated to a ^{temperature of 50 ° C. with stirring at a pH of about 3.2.}

At this temperature 8.0 g of tetrahydrobenzoguanamine were added, reducing the pH rose to about 3.6. The working conditions used were maintained for about 16 hours, the solution is then emptied and, after measuring its density, viscosity and pH value, into the thermostat cells to determine their temporal stability.

At the temperature of - 10 ⁰ C is the solution for 8 to 10 days, however, more stable at +20 ⁰ C over 2 months.

B ice ρ i e 1 9

The device described in Example 1 is used. 2000 g of a 36% strength aqueous formaldehyde solution are at a pH of about

3.3 heated to a temperature of 80 ^{° C. with stirring.}

Be; this temperature is 4.0 g of methylanilinopropioguanamine crystals added and the aforementioned conditions maintained for 30 minutes.

The solution is then emptied and, after measuring its density, viscosity and pH value, is brought into the thermostat cells to determine its stability over time. At the temperature of - 10 ⁰ C is the solution for 6 to 7 days, however, more stable at + 20 ° C over 2 months.

Example 10

Six samples, each consisting of 1000 g of an aqueous formaldehyde solution with a CH ₂ O concentration of 35, 40, 45, 50, 55 and 60% and a methanol content of less than 1%, are each 0.5, 1, 2, 5, 10, 20 and 25 g of benzoguanamine added.

The solution is kept at a temperature of 55 to 65 ° C for 2 hours until the benzoguanamine is completely dissolved. '

The solutions are then cooled to room temperature (16 to 22 ^° C.) and then observed whether they become cloudy and a precipitate forms.

The results are shown in the following table :

Weight percentage Weight percentage stability A 1 » clear formaldehyde Benzoguanamine bti 16 to
22 ⁰ C Out
see clear % % Ta ₈ . clear 35 0.05 30th slightly cloudy 40 0.10 30th slightly cloudy 45 0.25 30th cloudy 50 1.00 15 to 30 55 2.00 2 to 4 60 2.50 not stable

• 5.73 309620 / 4-48

Claims (1)

Patent claims: 1. Process for the preparation of aqueous formaldehyde solutions which ^{are stable in a temperature range from -20 to +60 0} C, characterized in that one or more stabilizers of the general formula