SU451251A3 - Method for continuous preparation of urea formaldehyde resin solutions - Google Patents

Description

The invention relates to methods for producing solutions of urea resins, which are successfully used for gluing various wood products. A continuous process is known for preparing urea formaldehyde resin solutions by condensing urea or forcondensates from formaldehyde and urea with formaldehyde at 94-102 ° C, first in alkaline and then in acidic medium, carried out in successive feed reactants. However, this method is relatively long and the resulting solution contains a significant amount (1.0-1.2%) of free formaldehyde. The aim of the invention is to intensify the process and reduce the free formaldehyde content in the resin solution. This goal is achieved by adjusting the pH of the reaction mixture with a mixture of ammonia or an amine with an acid or acid salt and carrying out condensation while maintaining the molar ratio of formaldehyde and leuchine 2.1-3: 1 in the first reactor and a pH value of 5.5-7.5, all intermediate reactors have a molar ratio of 1.6-2.6: 1, preferably 1.8-2.1: 1, and a pH of 4.0-5.0 and in the last reactor, a molar ratio of 1.4-1. , 9:: 1 and pH 5.5-7.5. Example 1. By continuous dosing, the mixing zone is mixed with 770 wt. hours / hour of a solution of form.aldehyde (35%), 92.6 wt. hours / hour of urea solution (80%) and 27.2 wt. hours / hour of an aqueous solution containing 5 wt. amnak and 0.25 wt. including formic acid. From this zone, the mixture after an average residence time of approximately 25 seconds is fed to the first of the four vessels of the reactor cascade. After about 15 minutes (average residence time), the solution enters the next reactor. Additionally, 27.5 wt. hours / hour and in the fourth 101 weight. hours / hour of urea solution, and in the fifth - small amounts of sodium liquor. Using a measuring cell from a glass measuring electrode and a calomel electrode, the following pH values were determined for comparison: In the mixing zone of 7.6 In the first reactor, 5.8 in the second, 5.2 in the third, 5.05 in the fourth, 1.1.

3

The temperature in the first reactor is approximately 97 ° C, in the second and third 100 ° C, and in the fourth 98 ° C.

The degree of condensation of the obtained resin solution can be approximately determined by clouding the mixture of 5 vol. including water and 1, vol. including hot resin solution. Turbidity occurs at 19 ° C.

The concentration of the resin solution can be brought to 65% by treatment under vacuum.

Example 2. 3835 weight. hours / hour of an aqueous solution of forcondensate with a content of 877 weight. including urea and 1535 weight. h. formaldehyde in the mixing zone is continuously mixed with 619 wt. hours / hour 80% solution of urea and 40 weight. hours / hour of an aqueous solution containing 7.5 wt. ammonia and 1 wt. including formic acid, and for about 21 hours, it is introduced into the first of five reactors arranged in a cascade. In the second reactor serves 130.5 wt. hours / hour, in the fourth 95.2 weight. h / h n in fifth fifth 565,9 weight. hours / hour 80% urea solution. The total residence time of the solution in the reactor cascade is 45 minutes; for each individual reactor, an average residence time of 9 minutes is obtained.

The introduction of this mixture of catalysts allows the following pH values to be measured, measured at 20 ° C with a double rod chain consisting of measuring glass and calomel electrodes:

In the mixing zone 7.5

In the reactor

first5.8

second 5.3

third5.15

fourth 5.0.

In the fifth reactor, the pH of the solution is adjusted to 7.0 with diluted liquor.

The temperature in the first reactor is 98 ° C, in the second and third reactors 101 ° C, in the fourth 99 ° C and in the fifth 97 ° C.

The resulting 50% resin solution can be applied as glue, or by vacuum treatment, the coceptration of the solution can be increased to 60-70%.

Example 3. In the mixing zone, 1430 wt. hours / hour of an aqueous solution of formaldehyde (35%), 525 weight. hours / hour of urea solution (80%) and 47.0 weight. hours / hour of an aqueous solution containing 9 wt. am ammonia and 0.19 weight. h. formic acid. After 20 minutes the mixture is fed to the first of four reactors. After about 12 mip, the solution goes to the next reactor.

In the second reactor doses of 55 wt. hours / hour of urea solution, in the third 102.5 wt. hours / hour of urea solution, and in the fourth reactor 75 weight. hours / hour of urea solution.

The introduction of this mixture of catalysts permits the following

four

pH, measured with a glass electrode {double rod) at 20 ° C:

In the zone of displacement 8.0 In the reactor

first6,6

second 5.5

third4,4.

In the fourth reactor, a pH of 7.1 is established by the addition of diluted sodium hydroxide.

The temperature in the first reactor is 94 ° C, in the second 1.01 ° C, in the third 102 ° C, and in the fourth 100 ° C.

The obtained resin solution under the pony; the continuous pressure is continuously evaporated to co-graft weight. %

Example 4. Continuously serving in the zone of displacement, mix 1072 weight. hours / hour having a temperature of 70 ° C. an aqueous solution of horkodepatsat containing 420 weight. including formaldehyde p 210 weight. including urea, 1000 wt. hours / hour formaldehyde (40%), 707 weight. hours / hour of urea solution (65%, 75 ° C) and 30 weight. hours / hour of an aqueous solution containing 15.0 weight. including sickle acid, after which the mixture is immediately fed to the first of five reactors.

453 wt. hours / hour 65% solution of urea. The average residence time of the mixture in each of the equally large reactors is approximately 10 minutes.

The primer mixture of catalysts allows the following RP values to be set: In the mixing zone 7.6

In the reactor

first 6,7

second5.4

third4,5

fourth4,3.

In the fifth reactor, adding dilute sodium liquor, an RP solution of about 7.2 is installed.

The temperature in the nerve reactor is 95 ° C, 101 ° C in the second, 102 ° C in the third, 100 ° C in the fourth, and 99 ° C in the fifth.

The first solution is treated under vacuum and a solution of the resin is obtained - 65% conceptual.

The obtained solutions contain minor amounts of free formaldehyde -0.40% (66% solution), they are stable when stored for 6-8 weeks at 20 ° C and 3-4 weeks at 30 ° C.

The solutions have been successfully used for the manufacture of particle board.

Subject invention

The method of continuous preparation of urea-formaldehyde resin solutions by condensation of urea or forcondensates from formaldehyde and urea with formaldehyde at 94-102 ° C, first in alkaline, then in 5 acidic medium, carried out in a continuous supply of initial reagents, characterized in that intensifying the process and reducing the free for 5 maldehyde content in the resin solution; adjusting the pH of the reaction mixture is carried out with a mixture of ammonia or an amine with an acid or acid 6 salt and cond Sation is carried out by maintaining a molar ratio of formaldehyde and urea in the first reactor of 2.1–3: 1 and a pH value of 5.5–7.5; in all intermediate reactors, a molar ratio of 1.6–2.6: 1 , preferably 1.8-2.1: 1, and a pH of 4.0-5.0, and in the last reactor a molar ratio of 1.4-1.9: 1 EH5.5-7.5.