CS227901B1 - Process for the production of urea-formaldehyde condensates - Google Patents

Abstract

Production of slightly water-soluble and/or insoluble urea-formaldehyde condensates by the action of formaldehyde on urea under catalysis by mineral acids. The most preferred molar ratio of urea to formaldehyde is 0.90 to 1.51. The products can serve as components for the preparation of fertilizers, rubber chemicals and other products of chemical technology.

Description

The present invention relates to the production of low and / or poorly soluble urea-formaldehyde condensates in water. The process is carried out by the action of formeldehyde on urea at a molar ratio of urea to formeldehyde preferably of 0.90 to 1.51 and under catalysis with mineral acids.

Urea-formaldehyde condensates are widely used as adhesives, coatings, dressings in the textile and paper industries, as a soluble nitrogen fertilizer, are part of some cosmetics and nutritional ingredients. The monomeric form applied in the above-mentioned articles is mostly a precondensate with an initial molar ratio of urea to formaldehyde of less than 0.66, i.e. predominantly di- and trimethylolurea.

For application in some cosmetic preparations, the monomeric form is mostly monomethylolurea. The molar ratios of urea to formaldehyde of 0.55 to 6.40 are applied in the melt-soluble fertilizers and the process is mostly carried out with precondensation in an alkaline medium as the first stage of the synthesis.

The preparation of polymethylolureas involves the action of formaldehyde on an aqueous urea solution at 4 ° C to the boiling point of the reaction mixture, for one hour to several days and at a pH of mostly 8 to 11. The resulting products readily polycondensate at higher temperatures or under acidic conditions. in the case of monomethylol- and dimethylolurea to tri- to heptamers (Gavat et al., Rev. Roum. Chim. 1968, 13, 599j JI de Jong sJ.de Jonge: Rec. Trav, Chim, 1953, 72, 1027); cyclic structures (G. Walter: Trans. Faraday Soc. 1936, 32, 377;

Η. B. Yuska and E. Fishkin; Am, Chem. Soc., Div. Org. Coat. Plastic. Chem., Pop. 1973. 33.

308).

The cause of the reactivity of the mono- and dimethylolureas in an acidic environment is the formation of N-carbamoyl-carbenium-iminium ion, which then attacks a structurally suitable nucleophilic substance (H. Petersen: Textil-Rundschau 1961, £ 6, 646); these N-Mannich polycondensations are the principle of adhesive and finishing applications of precondensates.

The great practical importance of the reaction of formaldehyde with urea in an alkaline environment corresponds to the relatively high publication activity. In contrast, the literature contains considerably less data on the condensation of formaldehyde 8 by urea in an acidic environment.

One of the first specified products of the reaction of formaldehyde with urea in an acidic environment was methylene urea, obtained by treatment with 1 mole of formaldehyde for 1.33 mole of urea for several days (Dlxon: J. Chem. Soc. 1918, 113, 233). Kadowaki: Bull. Chem. Soc. Japan 1936, 11 248) or more recently 3.32 moles of formaldehyde in the form of a 40% aqueous solution per 20 moles of urea (FB Slezák et al .: J. Org. Chem. 1960, 25, 1). 672; U.S. Patent No. 3,035,055), in all cases at normal temperature.

Methylene urea and formaldehyde in acidic environments resulted in trimethylene tetra and pentamethylene hexemureas at normal temperature (H. Kadowaki: Bull. Chem. Soc. Japan 1936, 11,248). Mixtures of methylenedi-, trimethylenetetra-, tetramethylenepenta-, pentamethylenehexa- and hexamethyleneheptamurea resulted from the study of acid catalyzed condensation of formaldehyde with urea (JI de Jong and J. de Jonge: Rec. Trav. Chim. 1953, 72. 1 027): applied here aqueous solutions of formaldehyde at a concentration of 2 to 7.5 moles of substance in liter and aqueous solutions of urea at a concentration of 2 to 5 moles of substance in liter, at initial molar ratios of urea to formaldehyde of 1.00 and 0.66, at reaction temperatures of 25 to 76 ° C and pH of the reaction mixture 1.7 to 6.6. However, the reaction time is unclear in the cited work.

Linear polycondensates were detected by NMR-spectroscopy in reaction mixtures with an initial molar ratio of urea to formaldehyde of 0.77 to 0.50 at a pH of the reaction mixture of 4.5 to 8.5 (Slonin I.J. et al .: High Molecular Soil, Ser. A, 1977, 2, 776).

The cyclic dimer, namely 2-keto-5-carbamoyl-1,3,5-perhydrotriazine, has been shown by NMR spectroscopy to be an acid catalyzed condensation of monomethylolurea under mild reaction conditions (B. B. Yuska et E. Pishkin: Am. Chem. Soc. Plastic Div.

Chem., Pap. 1973, gg., 308.).

More recent work is of interest in the preparation of condensate for fertilizer use, based on a molar ratio of urea to formaldehyde of 1.30 to 1.45, and the reaction being conducted in the presence of a catalytic amount of acetate, šlavelalan, citrate or urea tartrate. 570 579 - Derwent No. 51103A / 28).

It follows from the above that the preparation of trimethylenetetra to hexamethylaneheptamuras, respectively. The cyclic structures, i.e. the sparingly water-insoluble and insoluble condensates, can be realized via polymethylolureas (especially mono- and dimethylolureas) and directly by the action of formaldehyde on urea under catalysis with substances of an acidic nature.

The second method of synthesis is technically and economically more acceptable mainly because the relatively lengthy preparation of the precondensate is omitted.

The cited works on acid-catalyzed condensation of formaldehyde with urea show that dilute reactant solutions are used, the reaction time is unclear, and if necessary, catalysts may be used which may be detrimental to the further use of the condensate.

The present invention solves the preparation of sparingly water-insoluble and insoluble condensates resulting from the starting molar ratios of urea to formaldehyde, preferably 0.90 to 1.51. The amount of water present in the reaction mixture is, compared to the cited works, mixed to 6 to 16 moles of water per mole into the reaction of bromine urea, which makes it possible to recover the product more efficiently in terms of energy (drying reaction) and ecological (returning mother liquors to the process) .

The preparation of the urea-formaldehyde condensates according to the invention consists of three stages:

- in the first step, urea is treated with fopmaldehyde in the presence of 0.001 to 0.010 mol of mineral acid per mole of urea at temperatures up to 105 ° C;

- in the second step, after completion of the reaction, the pH of the mixture is adjusted to a value of 4 to 8 by means of an alkaline reacting substance (e.g. dilute sodium hydroxide solution);

- in a third step, the condensate is recovered from the reaction mixture by either filtering, centrifuging or drying the reaction mixture in a spray drier;

For some purposes, the condensates can be obtained by a process in which the second stage is omitted. The entire process can be conducted discontinuously or continuously.

During filtration or centrifugation of the reaction mixture, the mother liquor is eliminated, which can be returned to the process, for example as a urea solvent.

The products resulting from the process of the present invention can be applied in specialty fields of chemical technology, such as in the production of fertilizers, rubber chemicals and elsewhere.

Example 1 wt. parts of urea (i.e. 0.666 mol of urea) was dissolved in 50 parts by volume of water and 40 parts by volume of 40.08% by weight of water were added to the 12 ° C solution. formaldehyde (i.e. 0.587 mol of formaldehyde and 1.463 mol of water). While stirring, the mixture was acidified with 1.2 parts by volume of 20.3% nitric acid (i.e. 0.004 mol of nitric acid).

After five minutes of reaction, the mixture reached a maximum temperature of 59.5 ° C and then cooled to 26 ° C. After adjusting the pH of the reaction mixture with about 20% aqueous sodium hydroxide solution to a value of 7, the product was isolated by filtration on a vacuum pad.

80 masses resulted. parts by filtration cake which, by drying in a thin layer for 2 hours at a temperature of 95 to 100 ° C, gave 40.2 wt. parts of dry matter. 29 volumes of mother liquors were removed from the product insulation.

Using differential thermal analysis (DTA), working with sample weights of about 0.1 g and a linear rate of rise of 6 ° C per minute, the product found the onset of the first solid phase endothermic change at 119.7 ° C, its peak at 133, 2 ° C, and the onset of endothermic solid phase decomposition at 221.4 ° C with a peak at 245.5 ° C.

Example 2 wt. parts of urea (0.666 mol of urea) was dissolved in 50 parts by volume of water (i.e., 2.775 mol of water) and to this solution, 13 ° C warm, was added 50 parts by volume of 40.08% formaldehyde (i.e. 0.734 mol of formaldehyde and 1.829 moles) mol of water). While stirring, 1.2 volumes of 20.3% nitric acid (i.e. 0.004 mol of nitric acid) were added to the reaction mixture.

After nine minutes of reaction, the mixture reached a maximum temperature of 62 ° C and was then cooled to 25 ° C. The pH of the mixture was adjusted to pH 7 with about 20% aqueous sodium hydroxide solution and then filtered on a vacuum pad. 80 masses resulted. parts by weight of the filter cake which, as in Example 1, gave 48.1 wt. parts of dry matter.

Using DTA as in Example 1, the beginning of the first solid phase endothermic change at 117 ° C and its peak at 126.5 ° C and the solid phase endothermic decomposition at 235.6 ° C and its peak at 251, Low: 14 ° C.

Example3

800 wt. parts of urea (13.320 mol of urea) was dissolved in 1,800 parts by volume of water (99.911 mol of water). To this solution, 7 ° C warm, was added 900 parts by volume of formaldehyde containing 407 wt. parts of the substance in 1000 parts by volume of the solution (i.e. 12.198 mol of formaldehyde and 34.369 mol of water). 1

To this mixture was added 25 volumes of 20.3% nitric acid (0.072 mol nitric acid). The maximum temperature of the mixture reached after 18 minutes of reaction was 68 ° C. After cooling the mixture to 50 ° C, its pH was adjusted to 4.5 by adding 15 parts by volume of 20% sodium hydroxide solution. The neutralized reaction mixture was fed to a spray dryer with an inlet temperature of 180 ° cf; dosing of the mixture was effected at a rate such that the temperature of the outlet gases was 85-95 ° C. 920 g of the product was obtained in the form of a fine powder and an additional 25 g was collected from the effluent stream.

Using DTA as in Example 1, the onset of the first solid phase endothermic change at 114.4 ° C and its peak at 25.0 ° C and the solid phase endothermic decomposition at 240.0 ° C with peak were found in this condensate. at 253.9 ° C,

Example 4

The reaction was conducted as in Example 3 except that after the addition of half the total amount of formaldehyde the mixture was heated to 60 ° C, then nitric acid was charged as in Example 3 to obtain a pH of 6.5. After the cloudiness of the reaction mixture was formed, the other half of the amount of formaldehyde was added. The maximum reaction temperature was 94 ° C. After 20 minutes of interaction of the components, the mixture was cooled to 63 ° C, neutralized by the addition of 16 volumes of about 20% aqueous sodium hydroxide solution and filtered on a suction cup. There were 2,135 masses. parts of filter cake containing 896 wt. parts of dry matter.

Using DTA as in Example 1, the condensate found the beginning of the first small solid endothermic change at 104.5 ° C and its peak at 109.0 ° C, the second, less pronounced and elongated solid phase endothermic change at 115.8 ° C and its peak at 142.8 ° C and finally the onset of solid phase endothermic decomposition at 243.1 ° C.

Example 5, 800 wt. parts of urea (D3.320 mol of urea) was dissolved in 2,560 parts by volume

11.99% aqueous formaldehyde solution (10.571 mol formaldehyde and 129.304 mol water). The solution temperature was adjusted to 34 ° C and then 20 volumes of 20.3% nitric acid (0.057 mol of nitric acid) was added.

The maximum temperature, i.e. 71 ° C, was reached after 11 minutes of reaction. The mixture was then fed to a spray drier operating at an inlet temperature of 230 ° C and an outlet gas temperature of 70-75 ° C. 898 g of the product were obtained in the form of a fine powder and 20 g of condensate were collected from the off-gases.

Using DTA as in Example 1, it was found that the onset of the first, less pronounced solid endothermic change is at 104.4 ° C and its peak at 110.0 ° C, the onset of the second, less pronounced and elongated solid phase endothermic change is at 115.5 ° C and its peak at 124.6 ° C and the onset of solid phase decomposition is at 234.5 ° C.

Example 6

The reaction was conducted as in Example 5 except that 8.809 mol of formaldehyde (as an 11.99% aqueous solution) was taken into 13.320 mol of urea, the initial temperature of the mixture of solutions was 26.5 ° C and the maximum temperature, i.e. 60.5 ° C, after 12 minutes of reaction.

Drying was carried out as in Example 5, except that the inlet of the reaction mixture into the spray dryer was controlled so that the outlet gases had a temperature of 80-85 ° C. The product was clearly coarser than Example 5.

Example 7

Solution 312.5 wt. parts of urea (5.203 moles of urea) in 1000 parts by volume of 11.99% formaldehyde (4.129 moles of formaldehyde and 50.509 moles of water) were acidified by adjusting its temperature to 30 ° C by adding 0.85 parts by volume of 94.6% sulfuric acid (0.015 parts). mol of sulfuric acid).

The maximum temperature, i.e. 69 ° C, was reached in 19 minutes of reaction. After adjusting the temperature of the reaction mixture to 35 ° C and its pH to 6 (about 20% sodium hydroxide solution), centrifugation was performed. 671.6 parts by weight of the filter cake were obtained with a content of 49.43% by weight. humidity. The product isolation resulted in 660 parts by volume of mother liquors.

Example

312.5 wt. parts of urea (5.203 mol of urea) were dissolved in 660 parts by volume of the inert liquids of Example 7. The resulting solution, heated to 25 ° C, was mixed with 351.6 parts by volume of formaldehyde solution containing 407 wt. parts of the substance in 1000 parts by volume of the solution (i.e. it was mixed with 4.765 mol of formaldehyde and 13.427 mol of water).

The solutions were acidified by the addition of 0.94 parts by volume of 94.6% sulfuric acid (0.016 mol of sulfuric acid). After 14 minutes, the reaction mixture reached a maximum temperature of 64 ° C. After adjusting the pH of the mixture to 6 and cooling to 20 ° C, the product was isolated by centrifugation. There were 615.7 masses. % of filter cake containing 41.6 wt. humidity is 97.2% compared to theory. 725 parts by volume of mother liquors were removed from the product isolation.

Example 9

The stirred reactor was held for 10 minutes at a working temperature of 52-55 ° C and charged with 1000 parts by volume of a 30.77% urea solution of 6 to 8 ° C hot (5.550 moles of urea per hour) and containing 1.45 parts by weight of urea. nitric acid (0.023 mol of nitric acid).

At the same time, 325 parts by volume of a 37.17% formaldehyde solution (4.405 mol of formaldehyde) of 6-15 ° C warm are fed into the reactor.

The contents of the reactor are then continuously fed into a spray drier with an inlet temperature of 230 ° C and an outlet gas temperature of 90 to 95 ° C. This results in 369 masses. parts of product per hour in the form of fine flour. 10 to 20 wt. parts per hour.

Claims (3)

SUBJECT OF THE INVENTION Process for the production of urea-formaldehyde condensates, characterized in that it consists of three stages, wherein in the first stage urea is treated with a 10 to 41% aqueous formaldehyde solution in an aqueous medium, preferably with from 11.99 to 40.08% aqueous urea. formaldehyde solution, with an initial molar ratio of urea to formaldehyde of 0.80 to 1.80, preferably with an initial molar ratio of urea to formaldehyde of 0.90 to 1.51, and an initial molar ratio of water in the reaction mixture to urea of 6 to 16, preferably at an initial molar ratio of water in the reaction mixture to urea of 6.36 to 10.08, in the presence of 0.001 to 0.010 mol of mineral acid per mole of urea, preferably in the presence of 0.003 to 0.006 mol of mineral acid per mole of urea, at temperatures 0 to 105 ° C, preferably at temperatures of 6 to 94 ° C, for a period of time 3 to 60 minutes, preferably 5 to 20 minutes, in the second step, the pH of the reaction mixture is adjusted to a pH of 4 to 8, preferably adjusted to a pH of 4 by means of a basic reacting substance, such as aqueous sodium hydroxide solution 5 to 7.0, and in the third step, isolation of the condensates is performed by filtration, centrifugation or drying of the reaction mixture in a spray drier. 2. A process for the production of urea-formaldehyde condensates according to claim 1, characterized in that the filtrate after the condensate isolation in the third step is also used to form the aqueous medium in the first stage. .3. A process for producing urea-formaldehyde condensates according to Claims 1 and 2, characterized in that the process is conducted batchwise or continuously.