RU2331654C1 - Method of obtaining carbamide-formaldehyde concentrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention pertains to the method of obtaining carbamide-formaldehyde concentrate, used as raw material in the production of high quality low toxic resins, used for gluing wood, when making wood chipboards, hardboards and medium density fibre boards with formaldehyde emission class E-1, as well as a free flowing additive to carbamide. The method involves chemosorption of formaldehyde, formed during oxidative dehydrogenation of methanol on an iron-molybdenum catalyst in pipe shaped or flange type reactor, 50-65% water solution of carbamide in a neutral or weakly alkaline medium in a sectional column with simultaneous concentration. Removal of water is done by a stream of formaldehyde containing gas from the upper column, and regulation of the buffer capacity of carbamide-formaldehyde concentrate is done by supplying a solution of an alkaline agent to the lower and dish-shaped section and to the still of the absorption column.

EFFECT: obtaining carbamide-formaldehyde concentrate with overall concentration of carbamide and formaldehyde near to 85 mass % and lower buffer capacity.

2 tbl, 3 ex

Description

The invention relates to methods for producing a urea-formaldehyde concentrate (CPK) with an improved fractional composition used as a raw material in the production of high-quality low-toxic resins used for gluing wood, in the production of particleboard, fiberboard and MDF emission class E-1 on formaldehyde, as well as an anti-caking additive to urea and other purposes.

Today, requirements for environmental protection at wood processing enterprises producing urea-formaldehyde resins have substantially increased. For this reason, the most promising are technological processes involving the use of urea-formaldehyde concentrate with a total content of urea and formaldehyde of more than 80 wt.% (KFK-85). This allows you to completely eliminate the formation of highly toxic tar tar wastewater during the synthesis of adhesive compositions, the volume of which in the woodworking industry exceeds 100 thousand tons per year.

It should also be borne in mind that urea-formaldehyde concentrate is widely used as an anti-caking additive to granular urea, and the product with over 15% by weight of uronic and triazinone derivatives has the best properties.

Known [GB 1517366, Cl. C08G 12/12, C07G 45/24, 47/04] a method for producing a urea-formaldehyde concentrate, which includes four stages of chemisorption of formaldehyde-containing gases obtained on a silver catalyst with an aqueous solution of urea.

In its implementation, a different molar ratio of formaldehyde: urea in the absorbers is maintained.

The process under consideration involves the use of urea-formaldehyde concentrate from different columns at the first stage of chemisorption.

The disadvantages of this cascade method for the synthesis of urea-formaldehyde concentrate include the difficulty in maintaining the necessary molar ratios of formaldehyde and urea in the absorbers, which does not guarantee the stability of the quality of the product produced. Moreover, due to the low pH values in the first three columns of the cascade, methylene ureas of different structure, which are responsible for its increased viscosity, are formed in the urea-formaldehyde concentrate in the first three columns of the cascade.

On the other hand, the use of a silver catalyst for the oxidative dehydrogenation of methanol to formaldehyde leads to a significant increase in the concentration of methyl alcohol in the commercial product. This reduces the reactivity of urea-formaldehyde resins based on it and contributes to the gas contamination of the premises at the stage of pressing wood boards.

Known [RU No. 2142964, cl. C08G 12/12] a method for producing a urea-formaldehyde concentrate, comprising the oxidative dehydrogenation of methanol on an iron-molybdenum catalyst in a tubular or shelf type reactor and the stage of chemisorption of formaldehyde-containing gas in a three-section column with a 50-65% aqueous urea solution with an addition of 0.05-2.0 wt. .% of the amine fed to one of the plates of the absorption column simultaneously with an alkali solution of 12-24% concentration and maintaining the molar ratio of formaldehyde: urea of 4.2-6.2 and 2 on the lower and middle sections of the column 2-4.4 and pH 7.5-9.3 and 7.4-9.4, respectively.

Variation of the content of uronic and triazinone derivatives in the finished product is achieved by changing the pH of the medium, the content of the amine component in the urea solution on the lower and middle sections of the absorption column.

The disadvantages of this method can be attributed to significant fluctuations in pH in sections of the column, due to changes in the activity and selectivity of the iron-molybdenum catalyst, the modes of the absorption process, the instability of the quality of the used urea in the buffer tank.

The closest in technical essence can be considered a method of producing a urea-formaldehyde concentrate of a certain composition [RU No. 2196147, cl. C08G 12/12] by chemisorption of formaldehyde-containing gases obtained by oxidative dehydrogenation of methanol on an iron-molybdenum catalyst, with a 50-65% aqueous urea solution containing 0.05-2.0 wt.% Ammonia per 100 wt.% Urea, in a three-section column ( absorber) to obtain a urea-formaldehyde concentrate with a controlled content of uronic and triazinone derivatives, which is achieved by varying the concentration of ammonia in the urea solution, the molar ratio of formaldehyde and urea in the middle and lower sections of the columns They are, moreover, the pH values at a predetermined level are supported by the introduction of 0.05-0.5 wt.% buffer additive per 100 wt.% urea into the urea solution.

The disadvantages of this method include the low total concentration of urea and formaldehyde in the produced CPK (less than 80 wt.%) And its increased buffer capacity (more than 20) due to the use of a buffer additive at the chemisorption stage. The latter circumstance negatively affects the reactivity of CPK in the synthesis of urea-formaldehyde resins.

An object of the invention is to optimize the synthesis of urea-formaldehyde concentrate with improved performance and, above all, with a total concentration of urea and formaldehyde close to 85 wt.% And a reduced buffer capacity.

The problem is achieved in that the known method provides concentrated CPK, that is, the removal of part of the water from the top of the absorption column with a stream of formaldehyde-containing gas supplied to the lower section, and the sodium formate formed as a result of the Cannizzaro-Tishchenko reaction at the lower and the middle sections and in the cube of the absorption column catalyzed by alkali metal hydroxides (NaOH, KOH) and Ca (OH) ₂ .

2CH ₂ O + H ₂ O → CH ₃ OH + HCOOH

NSOOH + MeOH → MeOSON + H ₂ O

The essence of the proposed technical solution is a method for producing a urea-formaldehyde concentrate, including chemisorption of formaldehyde formed during the oxidative dehydrogenation of methanol on an iron-molybdenum catalyst in a tubular or shelf type reactor, with a 50-65% aqueous urea solution in a neutral or slightly alkaline medium in a sectional column with simultaneous achieved removal of water by the flow of formaldehyde-containing gas from the top of the column, and regulation of the buffer capacity of the carba midoformaldehyde concentrate is carried out by feeding a solution of an alkaline agent in the lower and plate sections and in the cube of the absorption column.

The proposed technical solution differs from the known ones in that chemisorption is carried out simultaneously with the concentration of urea-formaldehyde concentrate by a stream of formaldehyde-containing gas passing through sections of the absorption column.

The latter is achieved by the fact that water vapor with a small amount of methanol and formaldehyde is discharged in the form of condensate from the upper section (sanitary zone) of the column to the urea solution preparation unit. Non-condensed gases are mixed off-column with a methanol-air mixture and sent to an oxidative dehydrogenation reactor.

The difference of the proposed solution lies in the fact that in order to achieve a given buffer capacity of commercial CPC, an alkaline agent is supplied to the cube of the column in order to establish a certain pH value.

The invention is illustrated by the following examples.

As the absorption column used a vertical apparatus of cylindrical mud, having a cubic part, lower and middle sections, a dish-shaped part and an upper (sanitary) section. In order to increase the efficiency of mass transfer, the lower, middle and upper sections are filled with stainless steel Raschig rings.

The formaldehyde-containing gas supplied to the chemisorption from the oxidative dehydrogenation reactor of methanol had a composition, vol.%:

Methanol 0,065 Dimethyl ether 0,110 With 1,000 CO ₂ 0,101 Formaldehyde 7,864 H ₂ O 8,400 Oxygen 7,316 Nitrogen 75,140 Formic acid 0.004

The carbamide used met the requirements of GOST 2081 grade B, the biuret content in it did not exceed 1.0 wt.%.

The urea buffer capacity, estimated by the volume of a 0.5 N HCl solution, which went into titration with 75 cm ^{3 of a} 1% aqueous urea solution, varied from 1.7 to 2.0.

Comparative characteristics of urea-formaldehyde concentrates made according to examples of the proposed method and the known method are presented in tables 1 and 2.

EXAMPLE 1

Formaldehyde-containing gas with a temperature of 185 ° C obtained in a methanol oxidative dehydrogenation reactor is continuously fed into the lower section of the absorption column in an amount of 419 kg / h based on formaldehyde, and 264 kg / h of a 60% aqueous urea solution with temperature 58-60 ° C.

At the same time, an 8% sodium hydroxide solution in quantities of 4.6, 9.4 and 8.2 kg / h, respectively, is metered into the cube, lower section and the dish-shaped zone of the column. The supply of aqueous solutions of urea and alkali is regulated so that the molar ratio and pH in the bottom part, lower and middle sections of the column are maintained at the levels shown in table 1.

EXAMPLE 2

The conditions are similar to example 1.

The amounts of dosed caustic soda per cubic meter, the lower section and the plate part of the absorption column were 6.2, 11.5 and 9.3 kg / h, respectively.

EXAMPLE 3

Formaldehyde-containing gas with a temperature of 185 ° C is continuously supplied to the lower section of the absorption column in an amount of 432 kg / h based on formaldehyde, and 278.7 kg / h of a 62% aqueous urea solution in the tray portion.

The supply of 10% caustic soda to the cube, the lower section and the plate section of the column were 5.5 8.0 and 6.1 kg / h, respectively.

From the description of the invention and the tables it can be seen that according to the claimed technical solution, it is possible to obtain a urea-formaldehyde concentrate with a total content of urea and formaldehyde of at least 84 wt.% (KFK-85), as well as lower the buffer capacity.

Table 1 Chemisorption conditions upon receipt of urea-formaldehyde concentrates by the proposed method. Indicator The value of the indicator for examples control ^x) one 2 3 The supply of components to the plate part of the column, kg / h formaldehyde 418-425 419 419 432 carbamide (concentration,%) 260-265 (50-65) 264 (60) 264 (60) 278.7 (62) caustic soda solution 13.2-14.0 8.2 9.3 6.1 (concentration,%) (10.0-18) (8.0) (8.0) (10) The filing of a solution of caustic soda in the cube and column sections, kg / h: cube - 4.6 6.2 5.5 lower section 13.2-14.0 (10.0-18) 9,4 11.5 8.0 Buffer Additive there is absent The amount of condensate to be removed from the upper section of the column, kg / h. - 53 57 45 pH in column sections: cube - 7.9 8.1 8.2 lower 8.3-9.0 8.0 8.2 8.1 average 8.1-8.6 8.0 8.1 7.9 ^x) Received by a known method.

table 2 Properties of urea-formaldehyde concentrates obtained by the proposed method. Indicator The value of the indicator for examples control ^x) one 2 3 The formaldehyde content, wt.% 57.0-57.4 59,4 59.2 59.8 The total content of urea and formaldehyde, wt.% 79.4-79.9 84.1 84.0 84.7 The molar ratio of formaldehyde: urea. 5.0-5.2 4.8 4.8 4.8 The content of uronic derivatives, wt.% 2.0-22.0 0 2 0 The content of triazinone derivatives, wt.% 0-4.0 are absent The content of methylol groups, wt.% 24.0-27.0 26.0 26.1 27,2 The methanol content, 5 wt.% - 0.1 0.1 0.1 The solids content after calcination at 105 ° C - 0.3 0.35 0.3 Buffer capacity 20.0-22.0 fourteen fifteen 12 pH after 24 hours storage at 25 ° C 8.3-8.7 7.7 7.8 8.0 Color on the Arna scale, units - less than 10 ^x) Received by a known method.

Claims (1)

A method of producing a urea-formaldehyde concentrate, including chemisorption of formaldehyde formed during the oxidative dehydrogenation of methanol on an iron-molybdenum catalyst in a tubular or shelf type reactor, with a 50-65% aqueous urea solution in a neutral or slightly alkaline medium in a section column with simultaneous concentration, characterized in that water is achieved by the flow of formaldehyde-containing gas from the top of the column, and the regulation of the buffer capacity of urea-formaldehyde concentrate suschestvlyaetsya feed solution of an alkali agent and a dished bottom section and a cube absorption column.