CS211642B1 - Process for purifying pentaerythritol - Google Patents

Abstract

The aim of the invention is to improve the quality of raw pentaerythritol by reducing the content of alkali metal formate and syrups while simultaneously reducing the losses of raw pentaerythritol during its processing into technical pentaerythritol. The above effects are achieved by converting mother liquors from the recrystallization of raw pentaerythritol into raw pentaerythritol, while the raw pentaerythritol with higher purity is processed into technical pentaerythritol and the filtrate is recycled to the separation stages of the production process.

Description

The invention provides a method for purifying crude pentaerythritol obtained by crystallization of a concentrated reaction solution followed by filtration of crystallized pentaerythritol.

Crude pentaerythritol, obtained by crystallization of pentaerythritol solutions, prepared by thickening solution solutions optionally enriched with pentaerythritol and / or alkali metal formate, which are returned / recycled / reacted in the form of mixed salts or aqueous solutions, contains according to a method of processing various amounts of impurities that need to be removed to achieve the final product of desired quality. The quality of the product is determined largely by the content of monopentaerythritol, the content of the hydroxyl groups, the melting point of the product, the ash content, and the Color Test value. Inorganic impurities / sodium cations and calcium (which cause clouding of alkyd resins / Mtiller H: Fette Seizen - Anstrichmittel 58, 1174 (1956)) have a negative impact on the quality of the technical pentaerythritol coating to the lacquers. Gourley S., Dunlop W., Journal of the Oil, color chemists association 40, 40 (1957). Formic ions cause heating to quench the degradation of pentaerythritol. Acidite may also cause turbidity - opalescence of cancers. The undesirable result of technical pentaerythritol is bis-pentaerythritol monoformal / Salkind M., Ahern H. F, Albert A. A. Ind. Chem., 50, 1108 (1958); U.S. Pat. 2,464,430, NSR Pat. 1,034,811.

The melting point of pentaerythritol is adversely affected by the content of penta-trentol, tripentaerythritol, the most important but alkali metal formates. The formaldehyde condensation internal condensation products have a very detrimental effect on the dyeing of pentaerythritol.

The above-mentioned additives, negatively affecting the quality of technical pentaerythritol, remain in the crude pentaerythritol PartialSp in the crystalline state, e.g., alkaline formates, or in the form of moisture in the cake of crude pentaerythritol. · '/

The most important way of purifying crude pentaerythritol is to recrystallize it in de-ionic water, most often carried out by dissolving crude pentaerythritol in the condensate or unsaturated pentaerythritol solution at temperatures of 80-110 ° C from which adsorption by solid adsorbents, e.g. on pumice, bleaching earth, activated carbon, molecular sieves, they remove the products of the condensation reaction of formaldehyde alone, acetaldehyde itself, the products of their reaction, the reaction products of the reaction intermediates and other organic impurities. The alkali metal and / or earth formate cations are most commonly removed on cation exchangers (Cs. 100 891], a process for the removal of formate by electrodialysis is also known (US Pat. No. 3,779,883) and methods for removing the calcium cation by transferring phosphoric acid and oxalic acid. Reduction of the crystalline sodium or calcium formate contained in the crude pentaerythritol cake is achieved by washing the cake with deionic water, or reducing the concentration of crystalline formate in the crude pentaerythritol suspension.

In particular, the purification of crude pentaerythritol is used to prepare very pure pentaerythritol, the most important of which is the process of its recrystallization from alcohols / NSRpat. 922 771, Jap. pat. 63-20557) and dimethylformamide / Fr. pat. .1 255 983 /.

An indirect process for refining crude pentaerythritol is by purifying the reaction solutions of peneterythritol which can be enriched with pentaerythritol and / or an alkali metal formate recycled from the separation part of the production of pentaerythritol by combining disodium sulphate, activated carbon and zinc dust. 2,806,069), by providing ozone, hydrogen peroxide, and filtering insoluble organic impurities. pat. 218 638, NSR Pat. 948 658, Brit. pat.732 015, Svajč. pat. 223 701 /. Another method of purifying crude pentaerythritol is by irradiated saturated pentaerythritol solutions by infrared, ultraviolet rays / NSR pat. 922 771 /. It is also known to refine such solutions on polymeric resins / Can. pat. 955,603]. From the processes described above for purifying crude pentaerythritol, the most widely used is the washing of the crude pentaerythritol cake with deionium water, most often condensate from the production of pentaerythritol. The wash solution is recycled into the pentaerythritol production vaporization stage, since the cake is washed away from formate. of the alkali metal and sulfides also dissolve a portion of the pentaerythritol. “T

The disadvantage of this refining process is the increase in the amount of recycled solutions and thereby the efficiency of the separation of pentaerythritol and the energy efficiency of the process.

It is an object of the present invention to provide a process for purifying pentaerythritol obtained from the reaction solutions of pentaerythritol, respectively. from reaction solutions enriched in pentaerythritol and alkali metal formate from recycled pentaerythritol production streams, characterized in that the reduction of undesirable impurities is achieved by peeling crude crystalline pentaerythritol-leaching liquor from the recrystallization of crude pentaerythritol, wherein the washing filtrate is returned to the crystallization of crude pentaerythritol and / or to the evaporation stages of the process of producing pentaerythritol. By adding the mother liquors used to wash the crude pentaerythritol cake to the crystallization of crude pentaerythritol, a significant reduction in the concentration of alkali metal formate and the so-called formaldehyde syrups in the crude pentaerythritol suspension is achieved, thereby reducing the content of these ingredients in the pentaerythritol cake . The treatment of the scrubbing solution in the evaporation stages of the production process is advantageous to add the solution to the stage in which the reaction solution evaporates. a reaction solution enriched in streams that are recycled from the pentaerythritol separation portion. In the case of simultaneous addition of the washing solution to the crystallization of the crude pentaerythritol and to the stage in which the reaction solution evaporates, the quality and quantity of the crude and thus pure technical pentaerythritol can be influenced by the ratio of the washing filtrate added to the crystallization and evaporation of the reaction solution. . By increasing the amount of the washing solution, withdrawn from the step of evaporating the reaction solution, an increase in the production of crude pentaerythritol can be achieved. Increasing the amount of washing filtrate added to the crystallization of the crude pentaerythritol is. Pentaerythritol of improved quality can be obtained. The ratio of the amounts of wash solution drawn to the indicated steps of pentaerythritol production is determined by the compromise of quality and economy of production of technical pentaerythritol.

In contrast to the prior art process of pentaerythritol refining, the process of purifying crude pentaerythritol according to the invention is characterized by the advantages of which are: improving the quality of raw pentaerythritol by reducing the content of alkali metal formate and formaldehyde syrups without in purification, there was a reduction in the amount of ascuric pentaerythritol that occurs when the filter cake of the crude pentaerythritol was washed with deionic water. In the case of washing the crude pentaerythritol with deionic water, the sieving increases the energy consumption of the process because the added water needs to evaporate in the production process. - increasing the production of pentaerythritol in the same raw material loading of the reaction portion if the washing filtrate is added to the stage in which the reaction solution is evaporated. - increasing the production and improving the quality of pentaerythritol if the washing solution is added to the crystallization of crude pentaerythritol and the degree of evaporation of the reaction solution. reducing the consumption of solid adsorbents used to remove formaldehyde syrups as a result of reducing the pentaerythritol feed syrup content. - Expansion of the working cycle of the cation exchangers, thus reducing the consumption of regeneration and ampic acid and deionic water. '. The advantages of the purification process of crude pentaerythritol according to the invention are illustrated by the following examples:

Claims (1)

EXAMPLE 1 [Comparative] Mother liquor from recrystallization of pentaerythritol with no calcium content of 3000 kg / h. using a wash of 1200 kg / h of crude pentaerythritol containing 0.376% calcium and 0.83% formaldehyde syrups. Crude pentaerythritol is obtained with a content of 0.0179% calcium and 0.042% of syrups. Recrystallization, filtration and drying afforded the technical pentaerythriol with a color fusion / APHA test / 200 and a melting point of 235 ° C. The wash liquors are treated together with the mother liquor from the crystallization of the crude pentaerythritol. EXAMPLE 2 3,000 kg / h of mother liquors from recrystallization of pentaerythritol are used to wash 200 kg / h of crude pentaerythritol with the same calcium and syrup content as in Example 1a, after washing the crude pentaerythritol is added to the crystallization. Upon reaching steady state in the pentaerythritol separation part, 1,200 kg / h of crude pentaerythritol is obtained with a content of 0.010 of calcium and 0.0237 of syrups. Recrystallization of the crude pentaerythritol thus produced yields a final product with a color test of 50-100 and a melting point of 238-240 ° C. Example 3 The same amount of recrystallization liquors is used to wash the same amount of urea pentaerythritol with the same calcium and syrup content as in the comparative example, except that the wash liquors are fed to the evaporation stage in which the reaction solution is concentrated. Upon reaching a steady state in the separation section, 1,263 kg / h of crude pentaerythritol is obtained by recrystallization, which yields 45 kg / h of technical product more than the comparative example, to achieve the same quality parameters. EXAMPLE 4 The same amount of recrystallization liquor is used to wash 1200 kg / h of crude pentaerythritol as in the comparative example, with 1000 kg / h of washing liquor being recycled to the crystallization of crude pentaerythritol and 3,000 kg / h to the evaporation stage, in which thickens the reaction solution. Crystallization and filtration yielded 1,242 kg / h of crude pentaerythritol containing 0.0127 of calcium and 0.032 of syrups upon steady state. Recrystallization yielded 30 kg / h of technical product as compared to the comparative example. The final product is characterized by a color test of 150 and a melting point of 237 ° C. DISCLOSURE OF THE INVENTION A process for purifying pentaerythritol obtained by crystallization of a concentrated reaction solution and filtering crystalline pentaerythritol characterized in that the mother liquor from the recovery of pentaerythritol in an amount of 200 to 4,000 kg of recrystallization liquors per 1,000 kg of pentaerythritol, preferably 2,000 kg of recrystallization liquor per 1,000 kg of crude pentaerythritol is fed to a crude pentaerythritol cake and the obtained filtrate is recycled to the crystallization of crude pentaerythritol and / or to the evaporation stages of the pentaerythritol process. Severoprafia. n. p-race 7. Moet