RU2204569C2 - Urea-formaldehyde resin production process - Google Patents

Abstract

FIELD: polymer production. SUBSTANCE: resin is obtained by condensation of urea-formaldehyde concentrate with first and second urea portions in presence of, as buffer additive, vat residue originated from monoethanolamine purification in ammonia production process, said additive being introduced in alkaline stage before charging first urea portion. EFFECT: optimized conditions of synthesis of low-molecular high- viscosity urea-formaldehyde resins and improved their quality. 1 tbl, 3 ex

Description

 The invention relates to methods for producing urea-formaldehyde resins used as binders and adhesives for gluing wood, in the manufacture of chipboard, fiberboard and MDF and other purposes.

 Due to the increased requirements for formaldehyde emissions from wood products obtained using urea-formaldehyde resins, the so-called low-molar resins, characterized by a minimal ratio of formaldehyde to urea, are widely used in the timber industry enterprises.

 In the case of their synthesis using formalin technology, the significant disadvantages of resins are reduced quality indicators, low storage stability and low curing reactivity, a significant amount of highly toxic tar resin, and increased formaldehyde emission from resin compositions.

A known method of producing urea-formaldehyde resin [Doronin Yu.G., Svitkina MM, Miroshnichenko S.N. Synthetic resins in woodworking. M .: Forest industry, 1970. P. 41-49], which includes four main stages: obtaining methylol derivatives of urea (precondensate) in a slightly alkaline or neutral medium at a temperature of 80-100 ^o With a duration of 30-60 minutes and a molar ratio of urea and formaldehyde 1: (1.97-2.0), condensation of gummy products in an acidic environment at pH = 4.0-5.5 for 20-60 minutes, concentration of the resin under vacuum at pH = 6.0 7.5 and a temperature of 65-70 ^o C, dokondensatsiyu reaction mixture with an additional portion of urea at 60-65 ^o C, pH = 6.5 to 7.5 for 30 min to konechnog the molar ratio of urea to formaldehyde of 1: (1,3-1,66). In the process of post-condensation or cooling of the finished resin, it is stabilized with ammonia water, diethylene glycol, trisodium phosphate, sodium tetraborate.

 The disadvantage of this method is its multi-stage and duration, which reduces the productivity of technological equipment, as well as a low degree of formaldehyde conversion, since tar water at the resin concentration stage contains up to 5-8 percent of unreacted formaldehyde.

 Resins obtained by this method are quite soluble in water, they have a high concentration of methanol, which prevents the production of environmentally friendly wood products.

A known method of producing urea-formaldehyde resin from urea-formaldehyde concentrate containing 55% of the "total" formaldehyde and 21% of the "total" urea [RU 2059663, cl. C 08 G 12/12, 1996]. It is based on adding the first portion of urea to the urea-formaldehyde concentrate in order to establish the molar ratio of formaldehyde: urea (Ф: К) = 2.0, heating the reaction mixture at 40 ^o С for two hours, introducing a 10% solution of acetic acid to reduce the pH of the mixture is up to 5.2 and acid condensation is carried out at 90 ^o C until a viscosity of 1000 MPa • s is reached. After that, the pH of the reaction mixture is set at 7.5, a second portion of urea is introduced and the pre-condensation process is completed for one hour at 60 ^{° C.}

 The disadvantages of this method include the increased viscosity of the urea-formaldehyde resin at the stage of acid condensation, the reduced reactivity of the finished urea-formaldehyde binder, characterized by the parameter "gelation time", the difficulty of controlling the process of resin synthesis.

где R₁ и R₂ = H, CH₂OH,
и 1-5% триазинов общей формулы

где R₁ и R₂ = H, CH₂OH, R₃ = H, CH₃.The closest in technical essence can be considered a method of producing a urea-formaldehyde resin by condensation of a urea-formaldehyde concentrate with urea in several stages in a solution with variable acidity using a buffer additive only at the last stage of the process [RU 2136703, cl. C 08 G 12/12, 12/40 // C 08 L 61/24; 09/10/1999]. At the same time, a product containing 54.7% of "total" formaldehyde, 23.6% of "total" urea and 21.7% of water, modified 1-15% by weight of the general formula was taken as a urea-formaldehyde concentrate

where R ₁ and R ₂ = H, CH ₂ OH,
and 1-5% triazines of the general formula

where R ₁ and R ₂ = H, CH ₂ OH, R ₃ = H, CH ₃ .

The synthesis of urea-formaldehyde resin is carried out by condensation of a urea-formaldehyde concentrate with the first portion of urea in the presence of a viscosity regulator - the addition of demineralized water or a 5% aqueous solution of methanol with pH = 7.5-9.0 for 10 min at 90 ^o C with pH = 7 , 6-8.8 to achieve a molar ratio of formaldehyde: urea = 2.0. Upon completion of the alkaline stage, the reaction mixture is rapidly cooled to (80 ± 2) ^o С, an acidic agent is introduced to lower the pH to 5.0 or less, acid condensation is carried out at (81 ± 2) ^o С before the resin coagulation begins, alkalization and the simultaneous introduction of a second portion of urea and borax or a similar compound and the completion of the condensation at (66 ± 2) ^o C for 30 minutes

 The disadvantage of this technical solution is that the urea-formaldehyde concentrate used, with a low content of impurities (methanol, sodium formate, etc.), has increased reactivity, especially at the stage of acid condensation, which makes it difficult to control the process of obtaining highly viscous resin at low pH values.

 The aim of the invention is to optimize the synthesis of low-molecular-weight high-viscosity urea-formaldehyde resins while improving their quality.

 This is achieved by the fact that in the known method, in order to reduce pH fluctuations and increase the viscosity of the finished urea-formaldehyde binder, the synthesis of the resin during the whole process is carried out in the presence of a stabilizing buffer additive, introduced into the urea-formaldehyde concentrate at the alkaline stage before loading the first portion of urea, and as a buffer additive at the alkaline stage, the bottom residue of the monoethanolamine purification of ammonia production is taken (the bottom residue of the MEA purification).

The essence of the proposed solution is the synthesis of urea-formaldehyde resins by condensation of a urea-formaldehyde concentrate containing 0.02-0.3% buffer additive with the first portion of urea in the presence of a viscosity regulator - demineralized water or an aqueous solution of methanol with pH = 7.5-9.0, for 10 minutes at (88 ± 3) ^o С and pH = 7.6-9.0 until the molar ratio Ф: К = 2 is reached. Upon completion of the alkaline stage, the reaction mass is rapidly cooled to (80 ± 2) ^o С, administered sour agent to reduce the pH to 4-5, holding at (80 ± 3) ^o C to acidic ndensatsii for 20-50 min prior to coagulation of the resin is introduced a second portion of urea and completion dokondensatsii at (65 ± 2) ^o C for 30 min.

 If necessary, long-term storage of the resin in the reaction mixture at the stage of pre-condensation is introduced borax, trisodium phosphate or similar in purpose compounds in an amount of 0.02-0.20 wt.% Based on 100 wt.% Urea-formaldehyde concentrate.

 Unlike the bottom residue of monoethanolamine purification of ammonia production, introduced at the alkaline stage of condensation and regulating the working properties of the resin, the additive at the stage of pre-condensation of borax, trisodium phosphate or other compounds affects only the shelf life of the urea-formaldehyde resin and cannot be considered as a significant factor.

 The proposed solution differs from the known ones in that the process of producing a urea-formaldehyde resin throughout, starting from the stage of alkaline condensation, is carried out in the presence of a buffer additive that regulates the reactivity of the system, increases the viscosity of the resin and avoids the undesirable transition of the reaction mass to a solid state when acidic agent (ammonium chloride, formic acid, etc.).

 A distinctive feature of the proposed technical solution is that as a buffer additive, the bottom residue of monoethanolamine purification of ammonia production is used.

 The invention is illustrated by the following examples: urea-formaldehyde concentrate is used in the form of an aqueous composition containing (41.5-59.0)% of "total" formaldehyde and (21.0-26.0)% of "total" urea. The molar ratio of urea: formaldehyde is 1: (3.2-5.4).

 The bottoms of the MEA-purification is an industrial waste of ammonia production, which includes (55 ± 5)% monoethanolamine, (8-10)% imidazolidone derivatives and (30-35)% water.

 To neutralize and acidify the reaction mixture, aqueous solutions of sodium hydroxide, formic acid, ammonium chloride and other bases and acids are used.

 Comparative characteristics of resins made according to examples of the proposed method and the prototype are presented in the table.

 EXAMPLE 1

4650 kg of urea-formaldehyde concentrate containing 55.4% of "total" formaldehyde, 22.7% of "total" urea and 21.9% water (molar formaldehyde: urea molar ratio is 4.88) are charged into a 10 m ³ reactor. 1080 kg of demineralized water and 4.65 kg of cubic residue of monoethanolamine purification of ammonia production are added to it. The contents of the reactor are heated to 30-40 ^o C, the pH of the reaction mixture should be 8.3 ± 0.3. If the pH does not match this value, it is brought to the required level by the addition of a small amount of a 10% sodium hydroxide solution.

After that, the first portion of urea is fed into the reactor until the molar ratio urea: formaldehyde = 1.0: 2.0 is reached. The condensation solution is heated to 90 ^{° C.} with vigorous stirring and held for 10 minutes.

Upon completion of alkaline condensation, the temperature of the reaction mixture is reduced to (80 ± 2) ^o C and 35 kg of 10% ammonium chloride are introduced into the reactor from the measuring unit in order to lower the pH.

The end of the polycondensation is determined by the technological sample: in a beaker with 50 cm ^{3 of} water, cooled to 12-14 ^o C, add 3 cm ^{3 of the} reaction mass. Condensation is stopped after the appearance of stable turbidity or small coagulation. Its duration depends on temperature and steady-state pH.

 Upon completion of the acidic stage of polycondensation, the contents of the reactor are neutralized with a 10% sodium hydroxide solution to pH = 7.3-7.8, adding it from a measuring device in an amount of 34 kg, and a second portion of urea is introduced to achieve a molar ratio Ф: К = 1, 15, as well as 2.3 kg of bottoms of MEA-purification of ammonia production.

The temperature of the reaction mixture spontaneously decreases to (66 ± 2) ^o С and is maintained at this level for 30 minutes. The finished resin is cooled to 20-25 ^o C and pumped into a container for storage.

 EXAMPLE 2

 The conditions for producing the resin according to Example 1. At the alkaline condensation stage, 7.0 kg of the bottom residue of monoethanolamine purification of ammonia production were introduced, and after the condensation together with the second portion of urea, 2.3 kg of borax.

 EXAMPLE 3

 The condensation conditions in Example 1. As a urea-formaldehyde concentrate, a product was used containing 26% of the "total" urea, 41.6% of the "total" formaldehyde and 32.4% of water (molar ratio Ф: К = 3.2).

 At the stage of alkaline condensation, 120 kg of water were introduced into the reactor.

 From the description of the invention and the table it can be seen that according to the claimed technical solution, it is possible to control the duration of the acidic condensation stage and thereby obtain high-quality urea-formaldehyde resins with the necessary set of working properties: viscosity, miscibility with water, gelatinization time, free formaldehyde content.

Claims (1)

 A method of producing a urea-formaldehyde resin by condensing a urea-formaldehyde concentrate with a first portion of urea in the presence of a viscosity regulator and a buffer additive and heating in an aqueous solution with variable acidity, followed by condensation of the resulting product with additional urea at an initial and final molar ratio of urea and formaldehyde of 1: (1, 9-2.1) and 1: (1.0-1.7), respectively, and cooling the finished resin, characterized in that the condensation of urea-formaldehyde concentration This and urea throughout the process are carried out in the presence of a buffer additive - the bottom residue of monoethanolamine purification of ammonia production, introduced at the alkaline stage before loading the first portion of urea in an amount of 0.02-0.30 wt. % based on 100 wt. % urea-formaldehyde concentrate.

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