JPS5867679A - Manufacture of cyanuric acid by trimerizing isocyanic acid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of cyanuric acid by trimerization of isocyanic acid.

Conventional industrial processes for the production of cyanuric acid involve heat treatment of urea. When heated, urea first melts and then solidifies, but further heating is required to convert it to cyanuric acid.

However, when performing this heating, the transfer of heat in the solid substance is poor and the temperature t becomes too high, resulting in a decrease in yield, and it is difficult to remove the solid product adhering to the Have difficulty. The resulting product is often highly 1llI
Because it contains impurities of &.

Further purification steps are required.

The object of the invention is a process for the production of sialic acid from incyanic acid, in which the selectivity achieved in the conversion to cyanuric acid is the highest and the formation of rigid products, in particular siamelide, is therefore minimized. The aim is to provide a method to achieve this goal.

According to the invention, incyanic acid Fi is brought into contact with a liquid organic solvent that absorbs isocyanic acid but can readily precipitate cyanuric acid.

Once this trilobated anti-hysocyanic acid is absorbed, the reaction proceeds rapidly, and the resulting insoluble cyanuric acid precipitates. Separation of this solid product is carried out by precipitation and P separation.

This is readily accomplished by centrifugation or any suitable means of separating liquids and solids. Thiamelide.

Urea and other solid by-products 4h also precipitate and are separated from the liquid reaction medium together with the cyanuric acid formed.

This complicates the purification of cyanuric acid. The present method doubles the conversion to cyanuric acid, not only to obtain the highest yield of product, but also to simplify the purification of the product and eliminate the need for 2PT. VC111 is concerned with maximizing the selection rate of VC111.

In the prior art, cyanic acid or isocyanic acid v trimerization ti, slow 4P, Klaaon l co(F) reaction 2J, Praet, C4am, (Z
) 8 B, 116-182. Klason is anhydrous cyanogen lIg
! proposed that it polymerizes to form cyamelide, while cyanic acid polymerizes in solution to form cyanuric acid.

For the purpose of describing the present invention, we will use the term isocyanic acid and HNCOl- to include any of the isomers, cyanic acid or isocyanic acid, or mixtures thereof. In most cases, the feed mixture will actually contain an equilibrium mixture of the two isomers. The present invention provides the best yields when both the feed and liquid solvent are anhydrous.

Unirnar (Wmrnar) and 7x7*n (Fe@r
o%) ij,, 1920 VcJosrn, Chum,
Son, 11th.

1356 to show that the conversion to cyanuric acid increases with increasing VC temperature from 0°C to 20°C.
The results of polymerizing liquid cyanic acid at several temperatures in °C were reported.

Makronol, W. Kern et al.
Cham.

14.146-155 (1954) by pouring into cyanzene in several flHlji at 15° C. in benzene. The proportion of siamelide in the product mixture ranged from F120 to 5096 and increased as the conversion percentage increased.

In contrast to prior art trimerization methods, according to one embodiment of the present invention, cyanel fIR1-90 is purified to cyanuric acid with purities as high as 98-99 and in some embodiments as high as about 98-99. According to the high conversion rate of 1, it can be produced with a conversion rate greater than iI〇-.

Our results differ from those obtained by Cologne in several respects. Cologne mixed isocyanic acid liquid with benzene at low current, gradually raised the temperature to 15°C, and in the presence of an accelerator, e.g.
Polymerization of liquid cyanic acid in benzene occurs violently at 15° C. When promoters are used in the process of the invention - the reaction is not violent, the polymerization is rapid and exothermic, but But it can be easily controlled.

Cologne obtained a higher conversion percentage to silimelide as the total conversion percentage of cyanic acid increased.

We are able to obtain very high conversion rates by maintaining selectivity for conversion to cyanuric acid above 1i90.

Although the present invention can be carried out using a number of organic solvents as the liquid medium for the polymerization, we believe that some organic solvents are superior to others in obtaining high conversion selectivities. discovered.

That is, it is preferable to use all polar solvents.

A certain relationship exists between the dielectric constant of the solvent and the purity of the nine cyanuric acid produced. In the Examples below, the increase in product purity observed when using several solvents with increasing t''4 is described.

Purities above 90- were consistently obtained using several polar solvents containing dielectric constants above about 16.

V over 5! When all the solutions with electric constant are used, it is always 8.
A purity of 0- or higher was obtained. It is preferable that there is no water in the isocyanic acid raw material or liquid solvent used in the invention.

The currently most preferred liquid solvent appears to be a7tonitrile. However, it is preferable to use all liquids with higher boiling points to minimize losses due to evaporation during gas-liquid contact.

The present invention is conveniently carried out at normal room temperature. Since the trimerization reaction is exothermic and it heats up the liquid solvent, it is desirable to cool the solvent to some extent. does not require elevated temperatures; however, the present invention is not limited to any particular temperature, with the upper limit being the boiling point of the liquid solvent selected.

In a most preferred embodiment of the invention, a feed gas containing a gaseous cap of insian M' is contacted with a liquid solvent. The step of absorbing isocyanate gas can be carried out in any gas-liquid contacting apparatus suitable for this use; one obtains the advantages of the present invention; no sophisticated equipment is required for this absorption.

It can be carried out in a punch reaction by simply blowing the gas into the solvent. Since this trimerization reaction is rapid and the product precipitates, the injection of feed gas can be continued until the desired amount of product is obtained, and when the desired amount of product is obtained, the gas is supplied again. is stopped and all solid product is separated. The method of the invention is easily adapted for use in continuous manufacturing equipment.

The liquid solvent is circulated through a gas-liquid contact absorption column, preferably countercurrently with a gaseous feed stream containing cyanate gas. The solvent removed from the absorber contains a total of product solids in the form of a slurry, which can be divided by 11 fft by %P. This solvent is then recycled to the absorber. The circulating liquid may be cooled if necessary. This rate of absorption is so rapid that practically complete absorption can easily be achieved in a single pass when an absorber of sufficient absorption capacity is used.

The present invention' is preferably carried out in a liquid solvent using a good trimerization catalyst (promoter), only a catalytic amount is required, and about 1 wt. of triptylamine is used in the liquid phase. It is found that it is convenient to carry out the process when the selected compound is a tertiary amine or a pyridine, and it can perform both functions.

A preferred type of catalyst is a tertiary amine, and #l is also a preferred catalyst, hatriptylamin. Other catalysts that may be useful in variations of this invention are sodium hydroxide, sodium methoxide, sodium acetate, lithium hydroxide, sodium formate, sodium carbonate, sodium benzoate.

Sodium boron hydroxide, potassium tart-butoxide, calcium acetate, lead oleate, metal naphthanates, titanium tetrabutyrate, Friedel-Krach catalyst, 7-oxalic acid, pyridine, triethylphosphine, chloride salts.

A convenient source of gaseous isocyanic acid for use in the process of the present invention is to synthesize HCN with oxygen (
An example is the product gas stream obtained from an air catalytic oxidation process. Catalytic oxidation of HCN was covered by the first German patent.
．． No. 040.521 and No. 1.05alO1. By choosing the reaction conditions that are most favorable for the selectivity of cyanic acid, the conversion of HCN is ~100%.
, a selectivity of conversion to isocyanic acid of about 80% can be obtained. The product stream from this HCN oxidation reactor consists primarily of isocyanic acid and by-products as well as unreacted feed gases, i.e., cyanogen, CO, COI% HCN, O,
This is a mixed gas flow consisting of Hlo, etc.

You can use incyanic acid from other sources instead. 5cIENcE in the appropriate mixture.

VOI, 202, ps25 (November 1978), a nitric acid-containing product from nitric oxide. See U.S. Patent No. 4174,37γ.

Japanese Patent Application No. 7000 of 1972 describes isosifalt of 99-purity from the thermal decomposition of urea.

Although some impurities in the feed gas stream are soluble in the solvent used to absorb the isocyanate, all impurities in the feed gas are effectively removed by absorption and trimerization of the cyanate component. In order to be separated, the VC must not have any impurities appreciably reactive with If, and in particular must not form insoluble products. Although pure isocyanate can be used as feed to the absorber in the process of the invention, it is preferable to use all isocyanic acid together with a diluent gas that does not form a precipitate, e.g.
, O, or argon are advantageous for cooling the liquid, removing the heat of reaction, and controlling the temperature Vt. Also the diluent gas in the feedstock. For more even absorption, there is a desirable kernel to help disperse the isocyanate into the altl-liquid.

The invention can be carried out in an absorber essentially at atmospheric pressure. Reduce losses due to solvent evaporation or absorber [f
The absorber may be operated under pressure to increase
This is unnecessary and unnecessary in our most preferred implementation.

An embodiment of the present invention 1, including the presently most preferred method of application, is as follows.

Example 1 In an example of trimerization carried out in a laboratory, a gas having approximately the following composition was continuously supplied to a gas-liquid contactor.

HNCO1 5 Volume Chi N* 82.5 1 0, α21 HCN (L7 # COas y COl 2.6
#(C#), (LO1#) The overall gas flow rate is about 1!18G?・mol/hour, which is good.

The gas was fed in a single pass to a glass column approximately 18'" high and 1# in diameter and flowed upwards. Tributylamine2.
A solution of 5f and acetonitrile 21Sf was circulated downward through the column. As this liquid leaves the bottom of the column, it is recirculated to the top of the liquid tube column by a centrifugal pump, and a portion of this recirculated solution is passed through a strained stainless steel filter before being reintroduced into the absorption reactor. can be passed. A few minutes after starting this system, there is a white solid in the % recirculated liquid? I could see it. & After nitrogen, started passing some of the liquid through the filter. This continued for 60 minutes after starting, and then the source gas was stopped.

The filter cake was scraped off the filter and dried. Pure [921G cyanuric*t-containing dry solid &1
Example 2 The same recirculation system as described in Example 1 is used, but
In another experiment, but without filtration, a liquid solution of 99f nitrile and 1f tributylamine was circulated for 7 t, a gas stream of the same composition as in Example IK. Glass column VC11 was fed for 5 minutes at a slightly different rate from Example 1. Next generated slur lJ? Separated by F. What is the weight of the solid product after drying? 1.4t, cyanuric acid? 9
It contained 9%.

The yield of the solid fed in this experiment, based on fl-HNCOf, was 97-9.

Example 3 In a separate experiment, another HNCO-containing waste stream of the same composition as described in Example 1 was treated with O-dichlorobenzene 20
0 and tributylamine 8f' into the stirred liquid solution in the flask. 3G'CK
After 30 minutes of absorption and reaction, the slurry was filtered and the solid product was dried.
Yield of solid ZnO based on lNCOt.

Example 4 In one trimerization in the laboratory, a gas having approximately the following composition was continuously fed into the apparatus.

HNCO9,9 volume- N, 81. 'rl Q, LO# HCN　　　　　　　&8　z co a, osz QQ, 1.9 # (CN), zO# The overall gas flow rate was approximately &1 F.mol/hour.

The gas was bubbled into a stirred liquid solution of acetonitrile lOO21 and tributylamine 2t in a flask, the temperature of the liquid being maintained at 20°C. After several minutes, a solid could be seen in the liquid. After 45 minutes, the raw material gas was stopped, the slurry was separated, and the solid product was dried.

Cyanur s! 93*t - Contains 7.2 f dry solids
was recovered (73% solid yield based on the supplied HNCOll). It is expected that improving the gas-liquid contact will improve the solid yield.

Example 5 In another experiment, the good gas composition of the supplied gas was HNCO14
Trimerization was carried out exactly as in Example 4, except that the volume was N* 8L3# O3α6N HCN 521 Co Q, l I c6Il zl # (CN), 13 *.

Overall gas flow is about t! It was Llt Saki Lua time.

7.4 ft of dry solid containing 92% of cyanuric acid was recovered (yield of solids 78% based on HNCOl supplied).
).

Table 1 lists several liquid organic solvents t, in order of decreasing value of -['4 (shown in the middle column). Right column [1-!,
The purity of the solid product separated from the liquid solvent is demonstrated in an experimental procedure such as that described in Example 2 and IK, which conveniently utilizes several indicated solvents as liquid solvents. Where several values are shown, each represents an individual experiment performed using the indicated solvent. In this table, results marked with a box indicate that no catalyst was used.

Table 1 (25-40℃, triptylene catalyst 19! All used)
Acetonitrile 39 97.99,97.
99 amyl acetate 25 94%93.
94 Cyclohexanone 18 95.98%9
4 Acetophenone 17 95.94 Pyridine IL3 80 O-dichlorobenzene 10 8 Fujimethoxyethane
7.2 97 Chlorobenzene 6 89.
83 Vinegar #n-Butyl 5 570-Chlorotoluene 45 67 Diethyl ether
Table 3 56 xylene (mixed)! 4 6
1 toluene 2,4 59,6B tributyl ane in about 2.2 561 cyclohexane 10 3 tones Example 6 In another experiment, a gas mixture containing 113% by volume (volume) HNCO and 1,S by volume % No. After absorption and reaction for 30 minutes at 9° and 30° C., the slurry was separated and the solid The product was dried. A dry solid I Lljj containing 9.% sialic acid was recovered.

Example 7 Japanese Patent Application No. 7000 (1974)
A gaseous effluent containing cyanic acid was produced by decomposition of urea using the technique described in .

Bubble into a stirred flask containing a 1% solution of tributylamine in acetonitrile. Ciasuric acid with a purity of 99% or more was produced in a yield of 99%.

In all the above examples, the isocyanic acid was brought into contact with the liquid reaction medium in gaseous form. We are here, Isocyan II! In a liquid state, the liquid raw material was brought into contact with an organic liquid solvent medium that was constantly stirred by stirring or the like by slowly adding the liquid raw material. The results obtained under these circumstances are.

The results were approximately the same as those obtained when inocyanic acid is contacted in the gaseous state with a liquid solvent.

Claims (1)

[Claims] 1. In addition to a liquid organic solvent for isocyanic acid and isocyanic acid, in the solvent, to the incyanic eIt. When absorbed and absorbed, a trimerization reaction occurs to produce cyanuric acid, and this cyanuric s! A method for producing cyanuric acid, characterized in that the liquid organic solvent is a polar solvent with an electric coefficient of 5 or more. 2. The method of claim 1, wherein the isocyanic acid is added by contacting a gas containing gaseous incyanic acid with a defined liquid organic solvent. 1. The method according to claim @1m, wherein the polar solvent has a monoelectric constant t- of 15 or more. 4. Is the gas containing isocyanic acid further an inert gas diluent? A method according to claim 2 containing.翫 The method according to claim 1, wherein the specified organic solvent is acetonitrile. The method according to claim 2, wherein the contacting is carried out in a continuous gas-liquid contacting device while circulating the liquid solvent countercurrently with a continuous flow of the gas containing isocyanic acid in the device. 7. The method of claim 2 further comprising the step of separating the solid product containing cyanuric acid from the organic solvent. 8. The method of claim 7, wherein the solid product comprises at least 90 wt. sialic acid. 9. The method of claim 1, wherein the liquid organic solvent contains a catalyst for the trimerization of isocyanic acid. 11. The method according to claim 9, wherein the specified catalyst is tributylazane.