JPH02229710A - Method for preventing caking of ammonium nitrate-based chilling agent freezing mixture - Google Patents

Abstract

PURPOSE:To improve the caking preventing property of an ammonium nitrate- based freezing mixture by adding potassium pyrophosphate to the freezing mixture. CONSTITUTION:About 80wt.% ammonium nitrate is mixed with about 20wt.% urea, ammonium sulfate, ammonium chloride or other inorg. salt for ensuring easy handleability to obtain the freezing mixture. About 1-5wt.% potassium pyrophosphate is added to the freezing mixture and mixed in a mixer such as a rotating cylinder. During this mixing, moisture absorption from the air is prevented with dried air, etc. The caking of the freezing mixture can be prevented without adversely affecting the freezing performance.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for preventing caking of a cryogen.

More specifically, the present invention relates to a method for preventing caking of a cooling agent whose main component is ammonium nitrate, which is dissolved in water or a gel-like substance to generate cooling.

Conventional technology> Ammonium nitrate (hereinafter referred to as ammonium nitrate) is a hygroscopic inorganic salt, and moreover, it undergoes a volume change at 32.3°C.
Because of the phase transition, they tend to solidify due to changes in temperature, often making handling difficult. Caking also occurs in mixtures of ammonium nitrate and other inorganic salts.

In particular, cryogens containing ammonium nitrate as a main component are used in MM where the temperature is high despite being used in a closed system, so even if there is no moisture absorption from the outside, at 32.2℃ ■←→■
The volume changes due to phase transition, and at this time, the contained water is repeatedly dehumidified and absorbed, resulting in powdering and solidification.

Conventional caking prevention methods include (1) diatomaceous earth, talc,
A method in which fine powders such as bentonite, acid clay, magnesium carbonate, and magnesium hydroxide are added as a buffer between particles of ammonium nitrate; (2) a method in which various surfactants are added as a crystal habit converter; (4) Method of adding fatty acid amide and fatty acid amine (Japanese Patent Publication No. 53-8668)
) etc. are known.

(Problem to be solved by the invention) Most of the conventional anti-caking agents are poorly soluble or insoluble in water, and are not used in cooling agents that attempt to obtain cold temperatures by rapidly dissolving ammonium nitrate in water. In this case, dissolution of ammonium nitrate in water is significantly inhibited because the anti-caking agent is hydrophobic or hydrophobic, which is not preferable.

In addition, a method of adding a surface hydrophobizing agent such as liquid paraffin or wax, or a method of adding fatty acid amide and fatty acid amine is a method of preventing particle adhesion by covering the surface of ammonium nitrate, or a method of preventing adhesion of particles to each other by covering the surface of ammonium nitrate. Although it is effective as a method to prevent moisture,
Ammonium nitrate containing some moisture at 32.2℃■←→
- It cannot be applied as an anti-caking agent for cryogens whose main ingredient is ammonium nitrate, which undergoes repeated phase transitions and undergoes volume changes, resulting in powdering, dehumidification, and moisture absorption, which solidify.

In view of this situation, the present inventor conducted various studies regarding the prevention of caking of cryogens whose main component is ammonium nitrate, and found that by adding potassium birophosphate to a cryogen whose main component is ammonium nitrate, excellent caking prevention was achieved. The present inventors have found that the present invention is effective and does not have any adverse effect on the performance of the cryogen, leading to the completion of the present invention.

<Means for Solving the Problems> That is, the present invention is a method for preventing caking, which is characterized by adding 1 to 5% of potassium pyrophosphate to a cryogen containing ammonium nitrate as a main component.

In the present invention, the cryogen may include ammonium nitrate mixed with about 20% of an inorganic salt such as urea, ammonium sulfate, or ammonium chloride. The content of ammonium nitrate, which has high cold performance, may be 100% or about 50 to 60%, and is not particularly limited, but a material containing about 80% ammonium nitrate is often used for ease of handling.

Potassium pyrophosphate used as an anti-caking agent in the present invention does not need to be pure, and any commercially available one for industrial use may suffice.

If the amount of potassium birophosphate added is too small, the anti-caking effect will be insufficient, and if the amount added is too large, the anti-caking effect cannot be expected to increase commensurately, which is not only economically disadvantageous. Since the proportion of anti-caking agent in the cryogen increases, which is disadvantageous in terms of cooling performance, it is usually used in an amount of about 1 to 5% by weight based on the cryogen whose main component is ammonium nitrate.

The method of adding potassium pyrophosphate is not particularly limited and may be carried out by conventional means. However, it is not preferable to allow potassium pyrophosphate to come into contact with the atmosphere and absorb moisture.

Generally, using a device such as a rotating cylinder or rotating plate,
A method is adopted in which potassium pyrophosphate is added and mixed with a cryogen whose main component is ammonium nitrate. At this time, it is preferable to use dry air, dry nitrogen, etc. in the container part of the mixing device to remove atmospheric moisture during the mixing operation. prevent it from absorbing moisture.

Although the mechanism for preventing caking according to the present invention is not clear, 32
．． When ammonium nitrate undergoes a phase transition at 2°C, potassium pyrophosphate absorbs the water released and forms a hydrate of potassium bikurate, so a cryogen whose main ingredient is ammonium nitrate gradually reduces water content. The temperature eventually reached 32.2 degrees Celsius.
It is presumed that this is because a metastable transition occurs in which no phase transition occurs. In addition, since the permanent product of potassium birophosphate is a stable non-caking substance, it is presumed that these effects are combined to exhibit an excellent anti-caking effect.

EXAMPLES> The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Crystalline ammonium chloride (hereinafter referred to as ammonium chloride) (water content: 0.04% by weight, pure Minutes: 99.5% by weight of industrial commercial product) 20% by weight of potassium birophosphate (water-soluble phosphoric acid:
41.74%, water-soluble potassium: 55.22% industrial commercial product) and mixed for 5 minutes at room temperature in a polyethylene bag to produce a cryogen to which potassium pyrophosphate was added.

A caking test was conducted on this cryogen. The solidification test method was to charge 80g of cryogen into a vinyl chloride cylinder (diameter 50L, height 75mm), apply a load with a 2kg lead rod, heat it in a hot air thermostatic oven at 40℃ for 3 hours, and then heat it at 27℃ for 3 hours. The cryogen was subjected to four 3 hour temperature cycles at °C. Next, the cryogen was taken out from the cylinder, and the crushing load was measured using a hydraulic strength tester. The results are shown in Table 1.

Comparative Examples 1-2 The same procedure as Example 1 was carried out except that potassium pyrophosphate was not added and diatomaceous earth was used instead of potassium pyrophosphate. The results are shown in Table 1.

Although the same level of effectiveness was observed in terms of cooling performance in Table 1, the cold performance described below was not as good.

Example 2, Comparative Example 3 A cryogen in which potassium birophosphate was added to the same cryogen bulk as in Example 1, and a cryogen in which powdered anhydrous sodium acetate (grade 1 reagent) was added. Consolidation tests were conducted.

Consolidation tests were conducted as in Example 1 except that the cryogen was subjected to five temperature cycles of 2 hours at 40°C and then 12 hours at 25°C.

As shown in Table 2 and Table 1, potassium birophosphate exhibited an excellent anti-caking effect. As shown in Table 2, the well-known diatomaceous earth does not have a sufficient anti-caking effect with anhydrous sodium acetate, which is thought to have the same anti-caking mechanism. On the other hand, potassium pyrophosphate was found to have an excellent anti-caking effect.

Example 3, Comparative Examples 4 to 5 A cryogen containing 2% by weight of potassium birophosphate as an anti-caking agent obtained in the same manner as in Example 1, and a cryogen containing 2% by weight of diatomaceous earth to prevent caking. The cooling performance of the cryogen without added agent was measured.

A rotor of a magnetic stirrer was placed at the bottom of a glass container, and a 24-mesh wire mesh was placed 10 am above the bottom. 60 g of water was poured into this container, and the rotor was rotated at 80 times/min to stir the water. 60 g of the above-mentioned cryogen was added to this, and the degree of drop in water temperature was measured every minute using a thermometer. Note that the water temperature before adding the cryogen was 19°C.

The results are shown in Figure 1.

Effects of the Invention By adding potassium pyrophosphate to a cryogen whose main component is ammonium nitrate, it is possible to easily prevent the cryogen from caking without any adverse effect on the performance of the cryogen.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the results of measuring the cooling performance of anti-caking agents.

Claims (1)

[Claims] (1) A method for preventing caking, which comprises adding 1 to 5% by weight of potassium pyrophosphate to a cryogen containing ammonium nitrate as a main component.