JPS60166208A - Production of condensed phosphoric acid - Google Patents

Abstract

PURPOSE:To prevent effectively the coloring of condensed phosphoric acid, by adding hydrogen peroxide to a reaction system for dissolving phosphoric acid anhydride in phosphoric acid manufactured by the wet process to produce the condensed phosphoric acid. CONSTITUTION:Phosphoric acid manufactured by the wet process is introduced into a reaction tank, and phosphoric acid anhydride is then mixed therewith. The temperature is increased by the heat of reaction, but kept at 120 deg.C or below in a water bath. Condensed phosphoric acid is produced while adding 0.005- 0.05pts.wt., expressed in terms of hydrogen peroxide based on 100pts.wt. H3PO4, hydrogen peroxide to the resultant mixture at the same time. Thus, colored materials due to a very small amount of organic materials in the phosphoric acid manufactured by the wet process and lower phosphoric acid in the phosphoric acid anhydride are decomposed by the hydrogen peroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates more specifically to the decolorization of condensed phosphorus.

Condensed phosphoric acid is phosphoric acid containing a concentration of 100% by weight or more in terms of HaPQs.
In the chemical formula of n+1, n = 1. 2. 5... is a mixture of various phosphoric acids.

Because condensed phosphoric acid has a dehydrating effect, it is used as a reagent for organic synthesis in various polymerization, cyclization, and rearrangement reactions, and has other uses such as chemical polishing agents for steel, electrolytes for fuel cells, and soil conditioners. There is.

Methods for producing condensed phosphoric acid are broadly divided into two methods, depending on the starting materials: a thermal dehydration method of lyorthophosphoric acid and a method of dissolving phosphoric anhydride (N. phosphoric acid). However, the thermal dehydration method of orthophosphoric acid requires a high temperature of about 200 to 350° C. even if it is concentrated under vacuum, so it has not been carried out because there is no industrially inexpensive corrosion-resistant material. The industrially practiced production method is the latter, which involves burning yellow phosphorus in air to produce phosphoric anhydride and adjusting the water to be absorbed at the same time, or dissolving phosphoric anhydride in hydrated orthophosphoric acid. be.

Both phosphoric anhydride and orthophosphoric acid have been conventionally produced by a so-called "dry process" using yellow phosphorus as a starting material.

In recent years, due to changes in the energy situation, methods for producing orthophosphoric acid have changed, in addition to the "dry process phosphoric acid", by refining crude phosphoric acid obtained by decomposing phosphate rock with sulfuric acid and extracting it with organic solvents, oxidizing agents, activated carbon, etc. "Wet process phosphoric acid", which is obtained by removing organic matter using an adsorbent, is also produced with comparable quality. Particularly in Western Europe and Japan, soaring electricity prices are promoting a shift in purchasing practices.

The present inventors considered dissolving phosphoric acid anhydride in the above-mentioned wet process phosphoric acid to produce condensed phosphoric acid, and as a result of repeated experiments, they found that the wet process phosphoric acid has a higher yield than the dry process phosphoric acid. It was discovered that condensed phosphoric acid takes on a brown color when exposed to water. As a result of various studies on the causes that affect this phenomenon, we hypothesized that trace amounts of organic matter in wet phosphoric acid and lower phosphoric oxides derived from phosphoric anhydride interact in a complex manner to promote coloration. The present invention was completed by successfully decomposing a substance with hydrogen peroxide.

That is, in the present invention, phosphoric anhydride is dissolved in wet phosphoric acid, and hydrogen peroxide is added when producing condensed phosphoric acid.

The present invention will be explained in more detail below.

The phosphoric acid liquid obtained by refining the crude phosphoric acid obtained by decomposing phosphate rock with sulfuric acid using an extraction method using various organic solvents such as alcohols, ketones, ethers, and phosphate esters can be used for phosphate rock, auxiliary raw materials, and equipment. Due to the presence of organic substances derived from the material, phosphoric acid becomes colored during concentration heating. Therefore, methods such as calcining phosphate rock, decolorizing it with an oxidizing agent such as sodium chlorate, calcium hypochlorite, or hydrogen peroxide, adsorbing it with an adsorbent such as activated carbon, or a combination of these operations are used. However, if organic substances are not substantially completely removed, the quality is comparable to that of dry phosphoric acid in terms of appearance and chromaticity (AP) when heated (color grade measurement using IA chromaticity standard solution). I can't do it.

However, even if organic substances are removed in this way, trace amounts of organic substances in wet process phosphoric acid undergo a dehydration reaction accompanying the dissolution of phosphoric anhydride during the process of producing condensed phosphoric acid, resulting in further local reaction heat. This gives it a distinct brown color. Observing the progress of coloring, the coloring increases not only during the initial reaction period in which phosphoric anhydride generates white dew, but also as the dissolution operation is performed successively.

Although the cause of this coloring could not be fully investigated, it is assumed that it is due to a complex reaction between the organic matter in the wet phosphoric acid and the lower phosphoric oxides derived from the phosphoric anhydride. That is,
Even if we measure the chromaticity (APHA) of wet method phosphoric acid and phosphoric anhydride (dissolved in pure water to make orthophosphoric acid) when heated in the range of 100 to 250°C, the chromaticity is compared to that of condensed phosphoric acid. However, the higher chromaticity of condensed phosphoric acid is due to the addition rate of phosphoric anhydride and the H8 of bound phosphoric acid.
This is because it is also affected by the Po4 conversion value and the rotation speed of the stirrer.

As a result of intensive research into using an oxidizing agent to decompose the colored substances generated during the production of condensed phosphoric acid using such a complex mechanism, the present inventor found that hydrogen peroxide is extremely effective, and it has been found that hydrogen peroxide is extremely effective. We have obtained the knowledge that the chromaticity of the color is also 5 or less.

The conditions for dissolving phosphoric anhydride in wet method phosphoric acid are as follows:
Since the dissolution rate is faster at higher temperatures, it is possible to conduct the reaction in a shorter time. However, taking into account the material of the equipment, during the initial intense reaction, the addition rate of phosphoric anhydride and the amount of cooling water in the reactor may be adjusted to reduce the temperature.
In order to keep the temperature below 0°C and further dissolve the phosphoric anhydride, the temperature is kept below 150°C for about 2.5 hours.

Some of the organic substances remain, and even if the chromaticity is good in appearance, the chromaticity during heating becomes a practical problem. This tendency is particularly strong in the case of hydrogen peroxide, so the consumption of hydrogen peroxide must be increased. For this purpose, in Japanese Patent Application Laid-open No. 58-56910, hydrogen peroxide was divided and a long reaction was carried out.
-109805 publication, it is carried out in the presence of a catalyst,
In each case, the amount used is 0.07 to 3 parts by weight based on 100 parts by weight of PQ.

In the present invention, although the reason is not clear, the anhydrous phosphoric acid dissolved during the production of synthetic phosphoric acid acts on the organic matter in the wet phosphoric acid and becomes a substance rich in chromophore groups, thereby removing hydrogen peroxide. Since it is thought that H and P are easily attacked by oxygen during the nascent stage, the temperature should be maintained at 120°C or higher, and H, P
0.005 as KOz per 100 parts by weight of O4 equivalent value
When used in an amount of ~0.05 part by weight, not only the appearance but also the chromaticity upon heating becomes good.

The concentration of commercially available hydrogen peroxide is 30-60% by weight.
Either is fine, but since the amount added is small, 30 to 3
5% by weight is preferred. Hydrogen peroxide may be added at any time during the dissolution of the phosphoric anhydride or after the completion of dissolution, but the latter time is preferred because the coloring is stronger and the decolorizing effect is higher.

In addition, the reaction time is α5 to 1 hour, and excess hydrogen peroxide is self-decomposed and the product is not contaminated.

The present invention will be explained below using specific examples.

"%" and rpmJ in the examples are by weight. Further, the chromaticity during heating was measured by heating the sample to 250° C., cooling it, and using an APHA chromaticity standard solution.

Example 1 Crude phosphoric acid obtained from Moroccan phosphate ore was purified by a solvent extraction method using n-butanol, and treated with sodium chlorate and activated carbon to obtain wet process phosphoric acid having the following composition.

4 pq, 85.4% 804 12 ppm Fe 1 ppm Chromaticity (appearance) 5 or less Chromaticity (when heated) 10 2,000 g of this wet method phosphoric acid was introduced into a glass stirrer and reaction tank, and a commercially available Phosphoric anhydride 945Q was added over 10 minutes. At this time, since the temperature of the liquid rose due to the heat of reaction, a water bath was used to adjust the temperature so that it did not exceed 120°C. Then, use an electric heater to raise the liquid temperature to 140-150℃.
Add the remaining phosphoric anhydride 1 over 1 hour and 40 minutes while adjusting the
．． 8909 was dissolved to produce condensed phosphoric acid with an H3PO4 equivalent value of 116%. Color (appearance) of this condensed phosphoric acid
was 50, and the chromaticity upon heating was 140, giving it a brown color.

This condensed phosphoric acid 8009 was introduced into a similar apparatus, the liquid temperature was maintained at 140°C, commercially available 55% hydrogen peroxide α49 was added over 2 minutes, and the mixture was heated and stirred for 40 minutes. As a result, the chromaticity (appearance) of condensed phosphoric acid was 5 or less, the chromaticity when heated was also 5 or less, and it was colorless and transparent. Similarly, 85% orthophosphoric acid was produced using commercially available phosphoric anhydride.
The chromaticity upon heating was measured and found to be 30.

Example 2 Condensed phosphor wrinkles were produced in the same manner as in Example 1, but the addition rate of phosphoric anhydride was twice as fast as in Example 1, so the chromaticity (appearance) was 110 and brown. The coloration increased further.

Nevertheless, the amount of hydrogen peroxide added in Example 1
, a similar quality of synthesized phosphoric acid was obtained.

Claims (2)

[Claims] (1) Wet method A method for producing condensed phosphoric acid, which is characterized in that hydrogen peroxide is added when producing condensed phosphoric acid by dissolving phosphoric anhydride in phosphoric acid. (2) The temperature of the condensed phosphoric acid is maintained at 120° C. or higher, and hydrogen peroxide is added in an amount of aoos to 0.05 parts by weight per 100 parts by weight of bird P. The method for producing condensed phosphoric acid as described in (1).