CS272982B1 - Method of pentaerythritol's reaction solutions treatment - Google Patents

Abstract

The invention concerns treatment of reaction solutions by the reaction of formaldehyde with acetaldehyde in the presence of alkalis, particularly in an environment of calcium hydroxide. The method is significant in that the action of the alkalis, preferably calcium hydroxide, significantly reduces the content of formaldehyde in the solution after rectifying separation in the reaction of un-reacted formaldehyde. Calcium hydroxide is removed from the solution by the action of carbon dioxide with subsequent filtration of the mixture of calcium carbonate, indissoluble organic compounds and foreign matter from the calcium hydroxide. The result of the process is reduction of the loss of pentaerythritol and improvement in the quality of calcium formate and pentaerythritol.

Description

The present invention provides a process for treating pentaerythritol reaction solutions obtained from formaldehyde and acetaldehyde in the presence of alkaline reagents.

For the production of pentaerythritol from formaldehyde and acetaldehyde in an alkali environment such as calcium hydroxide, the molar ratio of formaldehyde to acetaldehyde in the range of 4.2 to 10: 1 is used in the reaction stage of the technology. in terms of mono and dipentaerythritol content and specific raw material consumption and energy. The unreacted formaldehyde, depending on the rolled ratio of the two aldehydes, is separated by physicochemical methods, on an industrial scale, almost exclusively by rectification of the reaction solutions or by a chemical reaction, most often by a formation reaction. pentaširupy. It is a mixture of C ₂ to C 8 hydroxy compounds, especially hydroxyaldehydes and hydroxyketones, but also other reaction products of formaldehyde itself, acetaldehyde itself, and their reaction products with each other.

However, modern pentaerythritol production technology is needed because of the need to obtain a product with a monopentaerythritol content of more than 95 wt. and, in order to obtain low specific feedstock consumption in the reaction stage, they operate at a molar ratio of formaldehyde to acetaldehyde above 5.5: 1, followed by removal of the alkalinity of the reaction medium and rectification separation of unreacted formaldehyde.

The formaldehyde present in the reaction solution increases the solubility of pentaerythritol through formation of pentaerythritol formalities and semi-formalities, causes a decrease in the pentaerythritol separation efficiency and negatively affects the crystallization process of calcium formate and pentaerythritol from aqueous solution. The presence of formaldehyde in the solutions after rectification of the reaction solutions results in losses of pentaerythritol in the separation process stages and inferior quality of the final product.

In the rectification separation of unreacted formaldehyde, the technological conditions are chosen such that the solution after rectification contains not more than 0.1% by weight. formaldehyde. If calcium hydroxide is used as the condensation agent, maintaining the said concentration of formaldehyde without causing the formation reaction is very difficult, especially at pH values of the reaction medium higher than 5.5. Pentaerythritol forms are increased at pH values below 5.5. On an industrial scale, the concentration of residual formaldehyde ranges from 0 to 0.3% by weight. These values indicate that the solution is or is reacted and is dark brown in color or difficult to process at higher formaldehyde concentrations.

For this reason, various processes have been proposed for removing residual formaldehyde from a solution obtained by rectifying a reaction solution of pentaerythritol containing more than 1% by weight. formaldehyde. It is known to remove formaldehyde from solution after rectification of the reaction mixture by treatment with ammonia, a salt thereof and organic compounds (NSR Pat.

262,154 and 2,262,196, Jap. pat. 73 29672). The formaldehyde adsorption method on the ion exchanger in the SOg H cycle is also used to purify formaldehyde-containing solutions at low concentrations. However, this process is not sufficiently effective and requires solutions without solid impurities, which are mainly insoluble polypentaerythritols and impurities present in calcium hydrate. On an industrial scale, for example in the USSR pentaerythritol production technologies, contacting the reaction solution with an aqueous sodium bisulfite solution is used to remove formaldehyde. (Jap. Pat., 74-08466). The whole formaldehyde removal process utilizes its reaction with urea in an acid medium (MS AO 234 590). However, this process is not used in pentaerythritol production technology because the reaction progress is sufficiently rapid up to an ambient pH of 4, with the risk of the formation of water-soluble methylureas which enter the separation process and may cause deterioration in the color of the final product.

CS 272 982 Bl

Another serious problem of processing the pentaerythritol solution after rectifying the separation of formaldehyde is the negative effect of insoluble, very fine particles on the separation process of pentaerythritol and calcium formate. As mentioned above, these products are the condensation products of formaldehyde and acetaldehyde, mainly polypentaerythritols and unwanted impurities in the alkaline reagent (gel silicates). These are introduced into the reaction solution after distilling off the formaldehyde in the mixed salts obtained by treating the mother liquors from the crystallization of the crude pentaerythritol. The presence of these substances and impurities worsens the crystallization process of pentaerythritol and calcium formate and their saturated solutions and causes poor filterability of the respective suspensions. The result is a deterioration in the quality of pentaerythritol and calcium formate, in particular of a granulometric composition, and a decrease in the specific consumption of formaldehyde, acetaldehyde and calcium hydroxide. The disadvantages of the processes for treating reaction solutions of pentaerythritol are avoided by the process of the present invention.

It is an object of the present invention to provide a process for treating reaction solutions of pentaerythritol, which are obtained by reacting formaldehyde with acetaldehyde in the presence of an alkaline reaction. agents. Preferably, the reagent is calcium hydroxide. The process is characterized in that to the reaction solution having a pH of 4 to 7 and from which the unreacted formaldehyde has been separated by distillation, most preferably by rectification, is added in the form of a suspension in the form of a suspension to obtain a pH of 7.5 to 13, preferably 4.5 to 10.5, which are necessary for the condensation and / or Cannizzar reaction of formaldehyde to proceed. After the addition of calcium hydroxide, the reaction mixture is stirred at 25 to 85 ° C, preferably at 55 to 65 ° C, for 2 to 50 minutes. The reaction time is determined by the desired concentration of residual formaldehyde in the reaction solution. In view of the effect of formaldehyde on the solubility of pentaerythritol and the course of the crystallization process of both formaldehyde and acetaldehyde reaction products, the reaction mixture is allowed to react to a formaldehyde concentration of less than 3.3. 10 kmol per 1 m ^{3 of} solution.

After the formaldehyde concentration has been reduced to the desired value, carbon dioxide is added to the reaction mixture in an amount to remove calcium hydroxide from the solution. The precipitated calcium carbonate together with the insoluble reaction products which enter the solution in the recycled mixed salts from the step of treating the mother liquors from the crystallization process is known as " of crude pentaerythritol, separated by filtration.

According to the process of the invention, a solution of pentaerythritol and calcium formate was obtained from which insoluble gels were removed and the formaldehyde content was reduced. Both factors significantly affect the separation efficiency of pentaerythritol and calcium formate.

A higher effect of the present invention over the prior art processes for treating pentaerythritol reaction solutions prior to processing is to improve the crystallization process of pentaerythritol and calcium formate, reduce the solubility of pentaerythritol and thereby reduce pentaerythritol losses in mother liquors. The overall result of the invention is to increase the separation efficiency of both reaction products and improve the quality of pentaerythritol. The following examples illustrate the advantages of the invention:

Example 1 (comparative)

To the reaction solution after the distillation of formaldehyde in an amount of 10,000 m ³ / h containing 0.2 wt. formaldehyde is added 1000 kg of so-called. mixed salts from the mother liquor treatment from the crystallization of crude pentaerythritol and the resulting mixture is processed by fractional crystallization to calcium formate and a pentaerythritol solution. The solubility of pentaerythritol in the mother liquor from crystallization is 9.1% by weight, the obtained calcium formate contains 4% by weight. % of organic compounds over the required 3 wt.

CS 272 982 Bl

Example 2

To 12 m ³ / h of a solution of pentaerythritol and calcium formate containing 0.25 wt. Formaldehyde obtained by pressure rectification of the reaction solution is dosed with 1 m ³ / h of 8.9% calcium hydroxide suspension. The resulting solution having a pH of 10.2 was stirred at 65 ° C for 10 minutes. The content of forraaldehyde is reduced from 0.25% by weight. to 0.08 wt. After the formaldehyde content was reduced, the solution was neutralized with 1.6 kmol / h of carbon dioxide. The precipitated calcium carbonate together with insoluble impurities is filtered on a FPAKM-25 pressure filter.

A clear solution is obtained, which is subjected to fractional crystallization to give pentaerythritol and calcium formate. Commercial calcium formate contains 2.5 wt. ingredients. The solubility of pentaerythritol and calcium formate in the mother liquor from the crystallization of crude pentaerythritol is reduced from 9.2 to 7.1 wt%, thereby reducing losses by 90 kg / h.

Claims (2)

OBJECT OF THE INVENTION Process for treating reaction solutions of pentaerythritol obtained by reacting formaldehyde with acetaldehyde in the presence of alkaline reagents, preferably in a calcium hydroxide medium, characterized in that calcium hydroxide is metered into the reaction solution at pH 4-7 after separation of formaldehyde, preferably by rectification. pH of the reaction medium 7.5 to 13, preferably 9.5 to 10.5, the resulting mixture is stirred at 25 to 85 ° C, preferably at 55 to 85 ° C, for 2 to 50 minutes, preferably to concentrations below 3.3. 10 ³ kmol / m ^{3 of} formaldehyde, followed by 1.35. 10 ³ to · 5. The 10-1 moles / m ³ carbon dioxide solution and the precipitated calcium carbonate are separated from the solution preferably by filtration.