CS205668B1 - Method for stabilizing formaldehyde in solutions - Google Patents

Abstract

The invention solves the method of stabilizing formaldehyde in solutions at temperatures above 100 °C, especially during pressure distillation or rectification of formaldehyde from solutions from the production of diols to polyols. Stabilization of formaldehyde is carried out by adding ea to the formaldehyde solution. at a temperature range of 100 to 300 °C, it is treated at least once with oxygen or ozone, which is supplied pure or mixed with an inert gas in an amount of at least 1 dm3 per 1 kg of formaldehyde.

Description

The invention provides a method for stabilizing formaldehyde in solutions at temperatures above 100 ° C, in particular under pressure distillation, or rectifying formaldehyde from diol to polyol solution solutions.

For thermal stresses of formaldehyde solutions at temperatures above 100 ° C, which may be considered, in particular, for formaldehyde reactants at elevated temperatures above 100 ° C, e.g. in the manufacture of acrolein from acetaldehyde and formaldehyde, optionally in its pressure rectification from aqueous solutions to encapsulate formaldehyde, or to remove it from aqueous solutions to isolate the main product, e.g. In the production of D1 to Polylols, formaldehyde is lost by the formation of condensates from formaldehyde forms.

Since, from an industrial viewpoint, formaldehyde is most often separated from reaction solutions of polyols, this case is discussed in more detail.

Di- to polyols are industrially advantageously prepared by condensation of formaldehyde with another aldehyde and / or ketone in a basic medium. Reakoia is general in the sense that in this way all aldehydes or ketones having at least one hydrogen on the X-carbon can be condensed with respect to the carbonyl group.

The hydrogens are gradually replaced by a methyl group from formaldehyde, after complete hydrogen substitution, the reaction is terminated by reduction of the carboxyl group by a mixed Ca < 2 > pizza reaction, while formaldehyde oxidation to formic acid. In this way, pentaerythritol, 1,1-trimethylolethane, isobutyraldehyde neopentyl glycol, cyclohexanone Z, 2,6,6-tetramethylolcyclohexanol, and the like are prepared from formaldehyde and from acetaldehyde. / E. Berlou, R.H. Barth, J.E. Snowt The Pentaerythritols, Reinhold Publ. Co., New York 1958, J. F. Wallkeri Formaldehyde, Am. Chem. Soo. Monograph Series, New York 1953 / In order to maximize the yield of the desired product, it is preferred to work with excess formaldehyde. The excess is 30 to 250%, relative to the theoretical amount. With this high molar excess of formaldehyde, it would be uneconomical to remove excess iformaldehyde chemically or thermally, and therefore this neutralization reaction solution is generally obtained by pressure distillation / Brit. pat.

757,564 /. Pressure distillation, i.e. distillation above 100 ° C, is necessary because of the formaldehyde-methylene glycol-water equilibrium, as a result of which the distillate is not enriched in formaldehyde to 100 ° C, but water.

When the heat of the eyes is increased, the formaldehyde reacts with alcohols in an acidic environment, in particular at a pH of less than 4, and conversely in a basic environment! of formaldehyde to syrups. While the suppression of the formation of formalities from di- to polyols removes the method according to MS. AO č. 193 858, the suppression of the formation of syrups from formaldehyde at elevated temperatures above 100 ° C has not yet been described. For the reasons given above, formaldehyde separation was solved by compromise, using temperatures as low as possible, respectively. very short residence times in the column. However, these measures place increased demands on the design of the rectification column and adversely affect the efficiency of the rectification column.

X

205 B68

These disadvantages are discouraged by the use of the process according to the invention, wherein the process is to stabilize formaldehyde in solutions at temperatures above 100 ° C, in particular by pressure distillation, or to rectify formaldehyde from diol to polyol solutions by converting the formaldehyde solution into a solution. the temperature of 100 to 300 ° C is at least disposable with oxygen or ozone, which is supplied pure or mixed with an inert gas or liquid in an amount of at least 1 dm per kg of formaldehyde, preferably in the form of air and / or oxygen-producing compounds releases at elevated temperature. with

It is an advantage of the process according to the invention that the presence of oxygen during distillation, rectification or inhibits respectively during thermal stress of the solution. retarding the formation of condensates from formaldehyde · Thus, in comparison with the foregoing antifoams, it can be prone to high temperatures or higher temperatures. for a longer period of time, S0 is advantageous in terms of formaldehyde separation and, in turn, means lower losses of the formaldehyde obtained or higher yields thereof. the presence of * oxygen thus ensures higher yields of formaldehyde, on the one hand, because it prevents the formation of airups from formaldehyde, it makes it possible to obtain a product of higher quality indicators, respectively. in greater amounts to reduce losses during purification of the crude product. The process is relatively simple, since it does not need the addition of other substances which, on the one hand, can affect the properties of the product and increase the cost of its purchase.

The formaldehyde solution to be treated at elevated temperature may be weakly acidic to neutral, preferably pH 4 to 7 ·

In the case where the thermal stress is carried out in an autoclave, it is sufficient to pressurize the air after the addition of the formaldehyde solution so that its pressure is> 100 kPa to prevent syrup formation. Syrup formation is particularly pronounced in the presence of weak acid salts, such as in the production of polyols. In addition, the pressure will also depend on the molar ratio of formaldehyde to oxygen. The experiments were carried out in a 1.5 L stainless steel autoclave using 200 ml formaldehyde solution from the polyol production as feeds. In this case, it was sufficient to pressurize the autoclave to 303 kPa by air and within 24 hours at 150 ° C no formaldehyde syrups were formed and the product was water-soluble. When at this temperature, only atmospheric pressure at atmospheric pressure at the start of heating the autoclave during 3 hours, syrups were formed from formaldehyde and the solution was dark brown with a syrupy caramel smell.

When pure oxygen was used, a pressure of 100 kPa was sufficient to achieve the same effect. The presence of ozone or perozdols also made the pressure lower.

In case the thermal stress of the formaldehyde solution was carried out during its rectification on the rectification column, air was introduced into the reboiler at a rate of 1 l / h at the bed.

300 ml of solution / h at rectification at 500 kPa.

In this way, 95-98% of the injected formaldehyde was recovered by rectification, and the boiling solution was clear, watered, possibly only slightly yellowish.

This method guarantees the stability of formaldehyde regardless of the temperatures and thermal stresses used, thereby substantially reducing formaldehyde consumption standards per tonne of product205668 here.

In the example, only the method of stabilizing formaldehyde in polyol solutions is mentioned. 4, it is evident that the method will be applied in various formaldehyde solutions exposed to thermal stress at temperatures above 100 ° C.

Example 1>

Measurement of the thermal stability of formaldehyde is carried out in a 1.5 L stainless steel autoclave. The autoclave is equipped with a magnetic anchor stirrer, a thermometer, a pressure gauge and court valves for sampling liquid and gaseous impacts.

The stirrer speed is controlled by a speed stabilizer.

The heating of the autoclave is by circulating the silicone oil through a thermostat through the casing of the autoclave. ¹

The reaction mixture is sucked into the cold autoclave under vacuum, whereby the silicone oil is circulated after heating to the desired temperature by switching on the circulation pump.

The results of the experiments are included in Table 1.

As can be seen from the results shown in Table 1, various syrups are formed from formaldehyde depending on the reaction temperature. Experiments 1 to 4 eu made Standard without add.

t '. . .

The second group consisted of experiments that by adding oxygen, either in the form of air, with pure oxygen or ozone, achieved a high irritating and retarding effect on the formation of syrups from formaldehyde.

Here, with an increase in initial air pressure of 2.7 to 300 kPa, the amount of syrups from formaldehyde decreases, with no more than 7 kPa at more than 200 kPa. No syrups are produced for 12 hours.

The same effect is achieved with the addition of oxygen of 100‘kPa resp. 75 kPa of ozone.

Table.1

Influence of reaction temperature on ‘formation of syrups from formaldehyde. The reaction solution from the preparation of pentaerythritil with a molar ratio of formaldehyde - acetaldehyde of 11: 1 in a concentration of 15.0% by weight was used as the raw material. % formaldehyde, 0.16 wt. syrups, 7.65 wt. % monopentaerythritol, 0.08% dipentaerythritol and 8.0 wt. calcium formate. Handle 500 g.

205 008

attempt number The reaction at (° c) Reaction time ^(h) The addition kind of pressure Formation of formaldehyde condensates (% by weight) 1 100 6.0 0 0 0 2 120 6.0 0 0 5 3 140 3 '° 0 0 50.0 4 l60 0.5 0 0 40.0 5 i4o 3.0 vzduoh 2.7 kPa 56.0 6 i4o 3.5 vzduoh 100 kPa 50.0 7 i4o 4.0 vzduoh 200 kPa 42.0 8 140 7.0 vzduoh 300 kPa 0.0 9 140 12.0 vzduoh 400 kPa 0.0 10 140 10.0 oxygen 100, kPa 0.0 11 i4o 10.0 ozone 75 kPa 0.0

Example 2 (

The rectification of formaldehyde in the reaction solution from the manufacturing pentaerythritol e makes a length of 5 m on a 30-storey Rashig-packed column. and a diameter of 80 mm, and a spray of 10 l / h of solution at 150 ° C. While the bottom product of the column was brown in normal rectification, with continuous introduction of air into the column digester, the digestion did not turn brown, was cloudy, and there was no increment of syrups between feed and product withdrawal.

The reaction solution from the preparation of tetramethyloloyclohexanol is rectified on the column in the same manner. The solution contains 3 wt. formaldehyde. After rectification on the column, the main product is obtained with a content of 10% by weight. % formaldehyde and a toasted product with less than 0.1% by weight formaldehyde. The product in the presence of air is clear, free of formaldehyde syrups. While in the presence of oxygen, formaldehyde syrups are not formed and the product is water-clear, oxygen-free, the product is lived to brownish and contains 10 to 15% by weight of formaldehyde syrups. from a metered amount of formaldehyde.

Example 3.

250 ml of 10% formaldehyde containing 1% formic acid are metered into an iron autoclave ea. By thermal stressing the solution at 180 ° C for 60 minutes, 30% of the formaldehyde condensates are formed. If air is introduced into the autoclave at the beginning of the heating of the autoclave, no formaldehyde syrups are formed.

Claims (1)

OBJECT OF THE INVENTION A method of stabilizing formaldehyde in solutions at temperatures above 100 ° C, in particular by distilling off, or rectifying formaldehyde from solutions from the production of diols to polyols, and by aa to a solution of formaldehyde at a temperature of 100 to 300 ° C, at least disposable with cyan or ozone, and added to the filter or mixed in a mixture of at least 1 dm / 1 formaldehyde.