RU2418008C1 - Method of producing carbamide-formaldehyde concentrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves oxidative dehydrogenation of methanol to formaldehyde on an iron-molybdenum catalyst in one or more flow- or deck-type reactors, as well as chemisorption and absorption of formaldehyde-containing gas in two successively lying towers. During chemisorption in the first tower, the absorbent used is 50-65% aqueous solution of carbamide and carbamide-formaldehyde concentrate is obtained during chemisorption. Non-absorbed gas coming out of the chemisorption column is divided into two parts. The smaller part is taken for catalytic burning and the larger part is fed into the lower section of the absorber. Demineralised water is used during absorption in the second tower and the methylene glycol solution formed is fed into the upper section of the first tower.

EFFECT: avoiding formation of methane-containing waste water.

1 cl, 1 ex, 1 dwg

Description

The invention relates to methods for producing a urea-formaldehyde concentrate with improved properties and 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 [see V.P. Makhlai, S.V. Afanasyev. Chemistry and technology of urea-formaldehyde concentrate. Samara Ed. Itself. Scientific Center of the Russian Academy of Sciences. 2007. - 234 p.].

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.

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 in turn does not guarantee the stability of the quality of the produced product. Moreover, due to the low pH values in the first three columns of the cascade, methylene ureas differing in structure, responsible for its increased viscosity, are formed in the first three columns of the cascade along with urea-formaldehyde concentrate.

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-particle and fiber boards.

Known [RU 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 step 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 on the lower and middle sections of the column a molar ratio of formaldehyde: urea of 4.2-6.2 and 2, 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 pH fluctuations in the 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 is the method of producing urea-formaldehyde concentrate described in [RU 2331654, cl. C08G 12/12]. It includes chemisorption of formaldehyde with a 50-65% aqueous urea solution in a neutral or slightly alkaline medium in a sectional column, concentration of the product with a stream of formaldehyde-containing gas, and regulation of the buffer capacity of the urea-formaldehyde concentrate by feeding an alkaline agent to the lower and plate sections and to the cube of the absorption column.

Its disadvantages include the formation of condensate contaminated with methanol.

An object of the invention is to optimize the scheme for producing urea-formaldehyde concentrate in order to improve product quality and improve environmental performance.

The problem is achieved in that in the known method, the chemisorption and absorption of formaldehyde-containing gas is carried out in two successive column devices, first with a 50-65% aqueous urea solution, and then with demineralized water, with the resulting methylene glycol solution being fed into the upper section of the first column device.

The essence of the proposed technical solution is a method for producing a urea-formaldehyde concentrate, including the oxidative dehydrogenation of methanol to formaldehyde on an iron-molybdenum catalyst in one or more tubular or shelf-type reactors, as well as chemisorption and absorption of formaldehyde-containing gas in two successive column apparatuses, the first as an absorbent, a 50-65% aqueous urea solution is used, with the preparation of chemo orbtsii urea formaldehyde concentrate, and unabsorbed gas is discharged from the chemisorption of the column is divided into two parts, the smaller is directed to a catalytic afterburning, and large - in the lower section of the absorber; during absorption, demineralized water is used in the second column apparatus to supply the resulting methylene glycol solution to the upper section of the first column apparatus.

The proposed technical solution differs from the known ones in that the chemisorption of formaldehyde-containing gas is carried out in two successively arranged column apparatuses, in the first - with a urea solution to obtain a urea-formaldehyde concentrate composition, wt.%:

mass fraction of total urea 24.5-25.5 mass fraction of total formaldehyde 59.5-60.5 water and impurities rest

and in the second, with demineralized water, feeding the resulting methylene glycol solution into the upper section of the first absorber.

In the urea-formaldehyde concentrate produced, urea is in a bound state, mainly in the form of a mixture of mono-, di- and trimethylolureas.

The invention is illustrated by the following example (see drawing).

Example

Methanol is continuously fed into two successive evaporators 3.1 and 3.2, which turns into a vapor state, mixes with air and gas, and is sent to tubular reactors 1.2 and 2.2 in the form of an air-air mixture.

The receipt of the components of the air-alcohol mixture to each of the two reactors is supported at the following level, kg / h:

nitrogen 38610-42900 oxygen 5526-6140 carbon monoxide 432-480 methanol 5769-6410 dimethyl ether 171-190 formaldehyde 6-7 water 738-820

The heat of exothermic reactions is removed by a dauther circulating in the annular space of apparatuses 1.2 and 2.2, and is used to produce steam with a pressure of 1.2 MPa in waste heat boilers 1.1 and 2.1.

The reaction gases leaving the reactors are cooled in the evaporators 3.1 and 3.2 to the required temperature and in the form of a combined stream enter the chemisorption column 4, kg / h:

nitrogen 77220-85800 oxygen 5256-5840 carbon monoxide 1260-1405 methanol 171-190 dimethyl ether 510-570 formaldehyde 10000-11130 water 8060-8960

At the same time, a 50.2% aqueous urea solution in the amount of 8300-9220 kg / h is fed into the upper section of this column apparatus. The temperature in the sections of the chemisorber is maintained at the required levels due to the circulation of liquids by pumps 5 and 6 and the inclusion of a heat exchanger 7 in the technological scheme.

The non-absorbed gas leaving the chemisorption column is divided into two parts in a ratio of 1: 4. The smaller one is sent to the catalytic afterburning, and the larger one is sent to the lower section of the absorber 8. It is an all-welded body with 6-12-cap plates placed in it, a liquid flow distributor and a nozzle section, and the necessary temperature regime in the column is provided by a circulation pump 9, a cube heater 10, a plate heat exchanger of the middle part of the column and cooling elements installed between the plate caps (not shown).

Upon contact of formaldehyde with water, methylene glycol is formed, which is confirmed by NMR spectroscopy.

The gas from the absorber 8 is mixed with air and is used to obtain a spirit-air mixture.

In order to irrigate the cap plates, the supply of demineralized water with a temperature of not more than 25 ° C in the amount of 270-305 kg / h is provided.

To obtain a urea-formaldehyde concentrate, carbamide was used that meets the requirements of GOST 2081 grade B with a biuret content of not more than 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.

The resulting urea-formaldehyde concentrate was characterized by the following quality indicators:

mass fraction of total urea, wt.% 25.0 mass fraction of total formaldehyde, wt.% 60.1 mass fraction of methanol, wt.% 0.1 mass fraction of methylol groups, wt.% 30,0 pH 8.0

During its synthesis, waste water is not formed.

Thus, it can be seen from the description and claims 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 about 85 wt.% (KFK-85), and also to eliminate the formation of methanol-containing wastewater.

Claims (1)

A method of producing a urea-formaldehyde concentrate, including the oxidative dehydrogenation of methanol to formaldehyde on an iron-molybdenum catalyst in one or more tubular or shelf-type reactors, as well as chemisorption and absorption of formaldehyde-containing gas in two successive column apparatuses, characterized in that when chemically adsorbed in the first 50-65% aqueous urea solution is used in the absorbent to produce urea-formaldehyde concentration during chemisorption non-absorbed gas leaving the chemisorption column is divided into two parts, the smaller is sent to the catalytic afterburning, and the larger is sent to the lower section of the absorber; during absorption, demineralized water is used in the second column apparatus to supply the resulting methylene glycol solution to the upper section of the first column apparatus.

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