RU1773257C - Method of modified carbamide synthesis - Google Patents

Abstract

The invention relates to the technology of mineral fertilizers, in particular to methods for producing modified high-strength urea. The method is carried out by introducing into the carbide melt a modifying additive - a pre-demethanol-free 45-70% aqueous solution of low molecular weight monomethylol - or dimethylolmethylene carbamide compounds, taken in an amount of 0.2-0.5 wt.% In terms of dry matter in the finished product.

Description

The invention relates to a technology for producing mineral fertilizers, in particular to a method for producing modified urea.

A known method for producing modified urea by introducing into the urea melt a urea-formaldehyde solution prepared by reacting urea with formaldehyde, a portion of formalin (12-15% of the total) is pre-acidified with concentrated sulfuric acid to a pH of 0.8, and the rest is introduced urea to a molar ratio between urea and formaldehyde of 1.3-1.8: 1, a 40% solution of sodium hydroxide or gaseous ammonia is dosed to a pH of 9.5-10.0 and the melt is sent to granulation. The mass fraction of the additive, calculated on the dry matter of the finished product, is 0.4-1.0%.

With the introduction of 0.4 and 0.7 wt.% Of the additive, the static strength of the granules (LNG) is 430 and 437 g / granule, and the friability after six months of storage in bulk is 75-80 and 80-85%, respectively.

However, the known method does not provide a noticeable increase in the strength of urea granules and their complete friability during storage and transportation, and the presence of methanol in the additive solution makes the process of obtaining modified urea fire and explosion hazardous and toxic.

The purpose of the invention is to prevent caking of the finished product during long-term storage and transportation, as well as increasing its strength.

The goal is achieved in that in the method for producing modified urea by introducing an additive based on urea-formaldehyde compounds (CBS) into the urea melt, a pre-desaturated 45-70% aqueous solution of urea monomethylol or dimethylolmethylene compounds with molecular mass 140-170, taken in

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the amount of 0.2-0.5 wt.% in terms of the dry matter of the finished product.

A method for producing a modified urea is as follows. A carbamide melt is introduced into a thermostated vessel with a stirrer, into which a 45-70% aqueous solution of urea monomethylol or dimethylolmethylene compounds with a molecular weight of 140-170 is added in an amount of 0.2-0. 5 wt.%, Calculated on the dry matter of the finished product, is kept at a residual pressure of 5.0-6.5 kPa and a temperature of 136 ° C until a melt concentration of 99.8% is reached, after which it is granulated in a known manner. LNG 650-780 g / granule (hereinafter, the granule size is 2 mm}.

The aqueous solution of urea monomethylol or dimethylolmethylene compounds used as a modifying additive is prepared as follows.

1. Formalin containing 5-11 wt.% Methanol is loaded into a thermostated stirred reactor, a 10-40% sodium or potassium hydroxide solution pH 7.0-7.5 is added and crystalline urea or 50-70% is added urea solution to a molar ratio between formaldehyde and urea 1: 1 The urea formaldehyde solution is intensively outweighed for 30 min at 35-40 ° С, then polycondensation is carried out at 80-90 ° С in a slightly alkaline medium (pH 7.5-8 , 0) with distillation of methanol to obtain urea monomethylmethylene compounds with a molecular weight of 140-170. To maintain pH, a 10-40% sodium or potassium hydroxide solution is added. A mixture of water vapor and methanol is condensed in the refrigerator.

The resulting aqueous solution of methanol-free urea monomethyl methylene compounds has a concentration of 45-70%, pH 7.2-7.5, contains 0.3-0.5 wt.% Free formaldehyde.

(2) Similarly, but at a molar ratio of Int / formaldehyde and urea of 2: 1, after stirring at 35-40 ° C for 60 minutes and polycondensation, urea-formalzdehyde oligomers are obtained consisting of dimethylolmethylene carbamide compounds with a molecular weight of 140-170.

The resulting aqueous solution of methanol-free dimethyl methylene compounds of urea has a concentration of 45-70%, pH 7.2-7.5, contains 0.5 wt.% Free formaldehyde.

Example 1. In a thermostatic container with a stirrer at a temperature of 136 ° C, 300 g of urea are melted, 1.8 g of a 50% solution of monomethylol methylene compounds are introduced

carbamide with a molecular weight of 140 and maintained at a working pressure of 5.0-6.5 kPa and a temperature of 136 ° C until a melt concentration of 99.8% is reached. Granulation by spraying from a height

20 m under pressure through 1.0 mm holes. The finished product contains 0.3 wt.% Modifying additives. LNG 650 g / granule.

In examples 2-4, proceed as in example 1.

Example 2. With the introduction of 2.1 g of a 70% solution of carbamide monomethyl methylmethylene compounds with a molecular weight of 170, the finished product contains 0.5 wt.% Of a modifying additive. LNG 720 g / grapule.

Example 3. Using 1.3 g of a 45% solution of carbamide dimethylolmethylene compounds with a molecular weight of 150, a product is obtained containing 0.2 wt.% Mrdification additive. LNG 670 g / granule. Example 4. When 2.5 g of a 60% solution of carbamide dimethylolmethylene compounds with a molecular weight of 170 are supplied, the finished product contains 0.5 wt.% Of a modifying additive. LNG 760 g / granule

Example 5. The technological process for the production of modified urea at the Chirchik Production Association Electrochemprom includes the main stages of the preparation of aqueous solutions of low molecular weight urea-formaldehyde oligomers at the experimental KFS plant in the ASG workshop and the introduction of additives into the urea melt

current production of nitrogen fertilizer.

Obtaining dimethylolmethylene compounds of urea consists of the stages of preparation of formlin by neutralization

with a 40% sodium hydroxide solution to pH 7.5, obtaining a urea-formaldehyde solution in a stirred reactor with a molar ratio between formaldehyde and urea of 2: 1, pH 8.0 and

at a temperature of 40 ° C for 60 min, to obtain a 50% solution of methanol-free dimethylmethylene compounds of urea with a molecular weight of 170 at 80 ° C in a reactor with a stirrer equipped with steam

jacket, condensation of the steam-methanol mixture in a water tube cooler, followed by disposal of a 10% methanol solution.

Cooked non-methanol

50% dimethylolmethylene solution

urea compounds are fed to a mobile tank and then to the urea workshop. When the productivity of the urea shop for the finished product is 30 t / h and the concentration of the introduced modifying additive is 0.3 May. % from the receiving tank by means of a centrifugal pump, 0.2 t / h of a 50% solution of carbamide dimethyl methylene compounds are fed to the metering tank, which through a cassette filter and flow meter enters the separator 11 of the evaporation stage into the carbamide cloak. With a residual pressure in the separator of 5, 0-6.5 kPa and a melt temperature of 13 ° C, a melt concentration of 99.8% by weight is achieved. Granulation of urea melt containing 0.3 wt.% Additives is carried out in a granulation tower 70 m high using a centrifugal granulator. In the lower part of the tower, urea granules in a fluidized bed are cooled to 25-40 ° C and fed to a conveyor for loading in bulk to railway cars.

LNG 780 g / granule

Example 6. Analogously to example 5, but 0.25 t / h of a 50% solution of urea monomethyl methylmethylene compounds with a molecular weight of 160 are fed into the urea melt entering the separator AND the evaporation stage. The finished product contains 0.4 wt.% Modifying additives. SLH 750 g / granule.

Claims (1)

As can be seen from the obtained LNG data of carbamide modified by the proposed method, 1.7-1.8 times higher than that of carbamide modified in a known manner. In this case, 100% is ensured — for the friability of the product when stored for six months in bulk, while in the known method the urea dispersibility is reduced to 70-85%, which makes it difficult to store, fill in bulk cars, and transport. During transportation of urea modified by the proposed method, the particle size distribution of the product, its 100% friability and LNG at the level of 700-750 g / granule are preserved in bulk in railway wagons, which allows for bulk transportation. SUMMARY OF THE INVENTION A method for producing a modified urea, comprising introducing an additive based on low molecular weight urea-formaldehyde compounds into the urea melt, granulation, characterized in that, in order to prevent caking of the finished product during long-term storage and transportation, as well as to increase its strength , as an additive, a 45-70% aqueous solution of urea monomethylol or dimethylmeshlene compounds with a molecular weight of 140-170, obtained by polycondensation at 80-90 ° C carb, is used mido- formaldegidnogs solution in a weakly alkaline medium in an amount of 0.2-0.5 wt.% on dry substance of the final product.