IE50427B1

IE50427B1 - Process for the extraction of urea grains with improved properties

Info

Publication number: IE50427B1
Application number: IE1134/80A
Authority: IE
Original assignee: Sueddeutsche Kalkstickstoff
Priority date: 1979-06-01
Filing date: 1980-05-30
Publication date: 1986-04-16
Also published as: ATE1095T1; EP0019881A1; PH16338A; JPS565452A; AU534680B2; EP0019881B1; BR8003414A; AU5864980A; IE801134L; DE2922436A1; CA1146973A; IN153885B

Abstract

1. Urea particles, characterised by a content of 0,1 to 3,5 wt.% of dicyandiamide.

Description

The invention concerns urea grains with improved properties and a process for their production from a concentrated urea solution or from a molten urea by the addition of from 0.1 to 3.5% by weight of dicyand iaraide to the urea before it is converted into grains.

Urea is used either per se or mixed with other nitrogenous compounds, e.g. diammonium phosphate or dicyandiamide or its salts(DE-PS 1 592 768,DE-OS 2 531 962) on a large scale for fertilizers.However the urea has the disadvantage that the grains which are made from it, e.g. prills, possess poor storage properties due to their relatively small hardness and to the resultant abrasion during transport and loading or unloading, and above all they tend to cake together in a humid atmosphere.

Numerous proposals have been made to improve their storage properties. Thus apart from additives, which are applied to the urea grains,it is also recommended that such additives be applied to the molten ureas or to aqueous urea solutions. A known process is the improvement of the urea grains by the addition of agueous formaldehyde solution or of aqueous formaldehyde-urea condensates such as di- and trimethylol urea(DE-OS 2 139 278, DE-OS 2 825 039).But it has been shown that the resulting improvement of the grain hardness is only minor.In addition, processes based on formaldehyde are unsatisfactory; for the small amounts of methanol which are always present in formaldehyde solutions are concentrated during the urea process, so that after a relatively short time the operation comes to a standstill. Moreover the addition of aqueous solutions is generally regarded as unfavorable, since to produce the urea grains, water has to be removed completely.For the same reason, the other proposed additives such as polyvinyl alcohol, dissolved in water(DE-OS 1 916 089),or aqueous glue, starch and cellulose solutions(DP 949 238,DP 530 449) should be regarded as disadvantageous.

S0427 -3Surprisingly it has now been found that urea grains· with improved properties can be produced if 0.1 to 3.5% by weight of dicyandiamide is added to the nolten urea or melt or to a concentrated urea solution. Owing to the stated relatively small amounts of dicyandiamide, already at the lower limit of the cited range a big increase in the hardness of the urea grains extracted from such a melt is attained.

This also substantially reduces abrasion during transport and storage processes.

Whereas during the fracture of pure urea grains, break up into numerous little fragments takes place, increasing the hygroscopy of the urea and thereby the danger of caking, with the urea grains obtained from the invention, which for example fragment during transportation, fracture results in only a few large fragments. The urea grains thus remain free flowing even if stored for long periods. In general, additions of 0.1 to 1.5% by weight are adequate to ensure a major increase of the stability of the urea grains. Additions of more than 3.5% by weight of dicyandiamide do not in fact lead to any further substantial increase in hardness of the urea grains, but are beneficial for many uses, e.g. for applications in agriculture. Dicyandiamide also has the advantage that it is a substance benefiting plants,and its nitrogen content has fertiliing effects. Dicyandiamide can with advantage be added directly to molten urea, and simultaneously other conventional additives, such as e.g. small amounts of acids, can be supplied. But dicyandiamide can be added, advantageously in aqueous solution, also to a concentrated aqueous urea solution, though this has the drawback that the water then has to be removed again. The dicyandiamide additive is specially suitable for improving the abrasion resistance and breaking strength of urea prills. The urea grains according to the invention §0427 -4can have the same sizes as were previously known for urea grains. An average diameter between 0.1 and 15 mm is preferred, while special preference is given to between 0.5 and 6 mm. The invention will be more closely described in the following examples: Example 1 0.5¾ by weight of dicyandiamide was continuously added by a dosing device to a urea melt such as is conventionally used in the prill device at the top of a prill10 tower. From the prills extracted from the melt in the usual manner, a screen fraction of from 1.6 - 1.8 mm was screened out and was tested for breaking strength (proportion of fracture on collision with a wall at a speed of 13 m/sec.) and also for compression strength (loading capacity to fracture in g).

Result: % by weight Working Fracture Load in g Urea without additive 4.4 620 Urea with 0.5% by weight of dicyandiamide 0.7 890 Example 2 In analogy with example 1, urea prills with an additive of 3% by weight of dicyandiamide were prepared and tested.

Result: Urea without additive Urea with 3% by weight of dicyandiamide % by weight Working Load Fracture_in g 4.3 605 0.4 950 Example 3 An aqueous solution of dicyandiamide was continuously added to a 75% aqueous urea solution in such an amount that the percentage share by weight of dicyandiamide was % by weight.

The urea solution was processed in the conventional manner, - forming crystals. The latter showed the following properties: Working Load in g % by weight Fracture Urea without additive 4.0 Urea with 1 % by weight of dicyandiamide 0.5 580 905 Example 4 To crystalline urea 0,2 % by weight of dicyandiamide are added and thoroughly mixed. The mixture so obtained was prilled in the conventional manner by melting and cooling of the melted droplets. The prills were tested for strength as follows: grs. prills were filled into a vertical drop tube and loaded 10 times with a drop weight of 500 grs. and a drop distance of 25 cm (10 inches). The prills are then sieved over a 0,2 mm sieve. The percent mechanical abrasion under dynamic stress is calculated by multiplication of the weight of the <0,2 mm fraction by the factor 5. The measured mechanical abrasion was 7,5 % corresponding to an increase in strenght of 8 % compared with pure urea.

Claims

CLAIMS:

1. Urea grains having a content of from 0.1 to 3.5% by weight of dicyandiamide, based on the total amount of urea and of dicyandiamide.

2. 5 2. A process for the production of urea grains which comprises adding 0.1 to 3.5% by weight of dicyandiamide, based on the total amount of urea and of dicyandiamide, to a concentrated urea solution or molten urea and converting the urea solution or molten urea into grains.

3. 10 3. A process according to claim 2, wherein a molten urea, which contains 0.1 to 3.5% of dicyandiamide, is prilled.