CS208628B1 - Method for removing formaldehyde from aqueous solutions - Google Patents

Abstract

The invention relates to the field of organic chemistry, including the removal of exhalates from chemical production to improve ecology. It solves the removal of formaldehyde from waste water of chemical production, primarily from the production of urea-formaldehyde resins, phenol-formaldehyde resins as well as pentaerythritol. The essence of the invention is the use of alkali metal salts and alkaline earth metal salts as formaldehyde decomposition catalysts.

Description

208 621

The present invention provides a process for the removal of formaldehyde from aqueous solutions, in particular from the production of urea formaldehyde and phenol formaldehyde nutrients as well as pentaerythritol. In various organic products in which formaldehyde is used as one of the raw materials, there is a problem of removing formaldehyde from the waste leaders as well as from the byproducts of the product. low, below 1 wt. and waste water also contains other impurities, formaldehyde recovery is not economical and even simple recirculation is not possible, Formaldehyde conduits are waste. In this case, it is necessary to remove formaldehyde from the waste leaders, as it consumes oxygen in the waterman, on the other hand it is poisonous for the living organism. The maximum permissible concentration in the ambient air is 2 mg. m J / Hommel: Handbuohder gef & Verlag Springer, Berlin, 1973, 1974.

Removal of formaldehyde by chemical reactions, whether by reaction with ammonia urotropin, Cannizzar reaction in alkali to formic acid, alkaline formate and methanol atS. reaks are known, but require stoichiometric amounts of substances, whereby practitioners increase the amounts of organic and inorganic substances in the effluents, as well as show SalSie chemical degradation / J. F. Walker: Form-aldéhyde, Ám. Chem. Soo. Monograph Series, New York (1953). Formaldehyde can also be disposed of thermally at temperatures above 300 ° C / F. P. Snowden, D.W., G. Style! Trans, Fara-day Soc., 35, 426 (1939)] · The lining is carried out on hydrogen and carbon monoxide. At 510 DEG -607 DEG C., condensation reaction products are also formed in addition to hydrogen and carbon monoxide. J. M. Pletcher: Why. Roy. Soc. (London) A 129, 284 (1993). The decomposition can be accelerated by the catalytic effect of the finely ground platinum, already at 150 ° C, or at 500 ° C.

These disadvantages, i.e. the use of stoichiometric amounts of chemical agents, respectively. catalysts based on precious metals, respectively. the use of high temperatures eliminates the process of this invention in which the removal of formaldehyde from aqueous solutions, in particular from the production of urea-formaldehyde and phenol-formaldehyde resins, as well as from the production diols to polyols, is carried out by the formaldehyde is treated with alkali metal and / or earth compounds in an amount of 0.1 to 20% by weight at a temperature of 100 to 250 ° C, preferably 140 to 180 ° C. An advantage of the process of the present invention is that only the catalytic amount of substances is added to the reaction, the substances available, many times directly present in the solution, from which the formaldehyde itself is removed, relatively low reaction temperatures are used, and the removal of formaldehyde is quantitative; it is possible, if necessary, to obtain a solution of the solution by boiling, with respect to different temperatures, boiling with water.

Various alkali metal and / or alkaline earth compounds can be used as catalyst. For reasons of availability, the use of anodium and calcium compounds is most appropriate.

It is possible to use, for example, formates, oxides or hydroxides, sulphates, phosphates of 208 828 oS, and the acids are preferably used which have a pK a of at least one degree at 25 ° C higher than 3 and these less acidic hydrogens are also metal.

For example, while sodium dihydrate has at least catalytic properties, disodium hydrophosphate has a stronger and trisodium phosphate the strongest catalytic effect.

Particularly suitable are the use of formic acid compounds, which in many cases are directly formed by formaldehyde reactions. So. for example, in the synthesis of polyols from formaldehyde and aldehyde and / or ketone addition in addition to the desired polyol product, sodium but calcium formate is produced by Cannizzaro reacto, depending on the type of alkaline reagent used. also sodium hydroxide, respectively. calcium. A Cannizzar oxidation-reduction reaction is known at a temperature of 20 to 50 ° C with a stoichiometric amount of base, and 0.5 mol equivalent of base is consumed for 1 mol of formaldehyde. In the case of the use of small amounts of base, the base is consumed in heating to form the formate, while the formate formed exhibits a formaldehyde conversion effect at higher temperatures above 100 ° C.

While at a temperature of 100 ° C or 8 hours, the consumption of formaldehyde is not observable in the presence of formates, and at higher temperatures of about 140 ° C to 180 ° C, it is already a reaconductor so that it can be used in an industrial raster.

The use of said method is suitable for removing formaldehyde from residues after separation of the desired product, e.g. from pentaerythritol, mother liquors or syrups, but from aqueous solutions resulting in the concentration of solutions containing formaldehyde as well as from all solutions containing formaldehyde. Other advantages of the process, as well as the particular embodiment, can be seen from the examples which, however, do not exhaust all combinations of use. Example 1 In a 1.5 L autoclave, the formaldehyde solution was thermally stressed at 10 ° C. The aqueous solution contains 7.6 $ hni. pentaerythritol and 15.0 wt. formaldehyde.

The conversion of formaldehyde depending on the presence of calcium formate is shown in Table 1 ·

Table 1. Effect of reaction time and calcium formate content on formaldehyde conversion at 16 ° C, pentaerythritol content 7.6%, formaldehyde content 15.0% by weight. 208 628

Calcium Formate Content Reaction Time Formaldehyde / wt. / / min / /% / 0.0 140 16 3.0 140 100 5.0 75 100 10.0 50 100 15.0 45 100

The product, in addition to the catalyst, contains 6.5 wt. methanol and 0.1 wt. formic acid and 2 $ formaldehyde syrups. In the event that the product does not contain formaldehyde syrups in addition to the presence of air, the reaction time is clear with 5 wt. calcium formate is extended for 6 h at 100 $ conversion! formaldehyde. When 8 wt. calcium acetate, the conversion after 6 h is 43 wt.%. In the presence of 8 wt. sodium propionate conversion for 6 h is 27.8 $ by weight. In the presence of sodium chloride and calcium the conversion of formaldehyde is 14 to 16 ¢. For the presence of trisodium phosphate in 6 h the conversion is 96%, with hydrophosphate dibasic 86% and with dihydrate sodium 15% · Example 2 In a 1.5 L stainless steel autoclave, 250 g of an aqueous solution of formaldehyde was charged at 140 ° C for 6 hours. 15 S solution. the formaldehyde is monitored in the presence of a multiplicity of sodium and calcium formate. The results are summarized in Table 2.

Table 2. Effect of the amount of catalyst at 140 ° C on the conversion of formaldehyde. Naf - sodium formate

Caf - calcium formate

Formate content Reaction time Formaldehyde conversion / 5% w / w / Λ / 0.0 6.0 12.0 5.0 Naf 6.0 60.0 10.0 Naf 1.2 100.0 15.0 Naf 1.0 100.0 3.0 Caf 6.0 50.0 15.0 Caf 3.0 100.0 The product contains 6 wt. methanol and 0.2 µl formic acid and 2 wt. syrups from formaldehyde.

Claims (1)

208 828 Example 3 Waste liquors from the pentaerythritol production plant are detected at a temperature of 150 ° C. of formaldehyde, 7.0 wt%, pentaerythritol, 10 wt%, calcium formate and 20 wt% formaldehyde syrups. After the transfer of the steam snake with a residence time of 1 h, the conversion of formaldehyde is about 100% by weight. and the formaldehyde content is less than 0.05% by weight. / sensitivity of analytical method /. EXAMPLE 4 Residues of a pressure rectifying column after separation of fortualdehyde from the reaction solution from a pentaerythltol production plant contain 13 wt. pentaerythritol, 0.8 wt. fomnaldehyde and 5 wt. calcium formate. After 1 hour at 180 ° C in the presence of oxygen, the formaldehyde content drops below 0.05% by weight. Condensate after concentrating the solution to 25% by weight. of pentaerythritol at 90 ° C contains less than 0.05 wt. formaldehyde, while the heat-free thickening was 0.65 wt. EXAMPLE 5 Waste water from the urea-formaldehyde-based adhesives encapsulates 3.2 [mu] l of formaldehyde. potassium phosphate, at 180 ° C, during 70 ml, the formaldehyde content drops below 0.1% by weight. Formaldehyde removal solution is used to prepare liquid fertilizers for agriculture. METHODS OF THE INVENTION The process for removing formaldehyde from aqueous solutions is particularly desirable from the production of formaldehyde and phenol formaldehyde nutrients, as well as from production to polyols. the formaldehyde solutions act with alkaline and / or alkaline earth compounds in an amount of 0.1 to 20% by weight. at a temperature of 100 to 250 ° C, preferably 140 to 180 ° C.