CS267084B1 - A method of producing pentaerythritol with the desired content of monopentaerythritol - Google Patents

Abstract

The essence of the solution is to regulate the content of dipentaerythritol in the technical product, under unchanged temperature and pressure conditions, while obtaining a product with the desired content of dipentaerythritol or monopentaerythritol. The content of dipentaerythritol is regulated according to the formaldehyde content in the solution of the reaction part of the production before its separation or removal from the solution. When the desired concentration of dipentaerythritol is achieved, the amount of formaldehyde in the solution is maintained at a constant level, while the content of condensates of formaldehyde itself must be less than 6 g.dm"3, preferably less than 2 g.dm"^ and the content of the alkaline catalyst before neutralization of the reaction solution must be higher than 0.3 g.dm"3, preferably 2 to 3 g.dm"3.

Description

The invention relates to a process for the production of pentaerythritol with the desired content of monopentaerythritol and dipentaerythritol, in particular by a continuous process.

Various alkaline condensing agents can be used in the production of pentaerythritol, but sodium hydroxide or calcium hydroxide are almost exclusively used in existing plants. Recently, there have been isolated references to the use of anion exchangers (E. Berlow, RH Barth, JE Snow: The Pentaerythritols Reinbold Publ. Corp. New York 1958, S. Trybula, K. Terelak, (3. Kesicka, J. Jurkiewicz: Przemysl Chemiczny 61, 309 (1982) Due to the use of pentaerythritol as well as the desired properties of the final products, different types of pentaerythritol are produced which differ from each other by melting point or -OH group content, ie different monopentaerythritol and dipentaerythritol content.

Obtaining the final pentaerythritol with a strong content of dipentaerythritol, resp. Tripentaerythritol is most often made by recrystallization of technical grade pentaerythritol on the basis of the varying solubility of the mono- and diderivatives in water. Another method is the separation of mono- and diderivatives by sieving the product based on the size of the crystals, the fine fraction being enriched in dipentaerythritol. In addition to physical methods for the separation of technical pentaerythritol, methods are known which lead to the enrichment of the technical product with monopentaerythritol.

It is known that at low molar ratios of formaldehyde and acetaldehyde (3) the product contains a maximum amount of dipentaerythritol, while using molar ratios of 5 to 10 yields a product containing 98 to 99% monopentaerythritol (E. Berlow, RH Barth, JE Snow: The Pentaerythritols). , Reinhold P. Corp. New York 1958). It has also been published (DI Belkin: Ž. Prikl. Chimii 52, 237 (1979), M. Lichvář, J. Sabadoš, L. Komora, V. Macho: Chern, industry 34, 305 (1984); 36, 57 (1986) /) that at the same molar ratios of formaldehyde-acetaldehyde, it is possible to reduce the dipentaerythritol content of the product from 11% to 1.8% by reducing the reaction temperature from 70 to 10 ° C. Furthermore, it is known that using a weaker base (calcium hydroxide) and under the same technological conditions, less dipentaerythritol is formed, based on monopentaerythritol. In modern technologies working in continuous processes not only in the isolation but also in the reaction part, the problem is to achieve the same composition of the final product and in technical pentaerythritol the content of dipentaerythritol varies in the range of 8 to 15% by weight. As a result, it is necessary either to place a homogenizer of the final product in the production plant, or to change the recipes of the pentaerythritol processor. The situation is complicated by the fact that when working with higher molar ratios of formaldehyde to acetaldehyde, formaldehyde is obtained from the reaction solution by pressure rectification and, after separation of the lower boiling products, is recycled back to the production plant. Due to the different concentration of formaldehyde in the reaction solution, the technological conditions and thus the composition of the product change. In order to maintain the same technological conditions, it is then necessary to analyze the composition of the regenerated formaldehyde and, based on the composition, to correct the concentration and amount of fresh formaldehyde. In this way, it is possible to produce pentaerythritol with a low dipentaerythritol content.

In the production of technical pentaerythritol with a content of 12 + 3% dipentaerythritol, the procedure is usually carried out in such a way that in continuous and discontinuous processes e.g. using calcium hydroxide as condensing agent, the process is carried out at temperatures up to 40 ° C, respectively with the addition of inhibitors of the actual condensation of formaldehyde (MS AO 170 614, AO 170 615 and AO 177 651). to a temperature of 50 to 60 ° C in a basic environment. This produces glycoldehyde, tetrosis, pentoses and hexoses from formaldehyde.

In batchwise reaction synthesis processes, it is possible to suppress these fluctuations with the sizes of the stockpiles of the returnable product. In the case of continuous production, constant conditions can be achieved by the control computer.

In order not to have to isolate dipentaerythritol from the technical product by a physical process and thus produce a product with a high monopentaerythritol content on the same equipment, we have found a simple process which is possible under unchanged temperature, pressure conditions.

CS 267 084 B1 to produce a product with the desired content of dipentaerythritol, resp. monopentaerythritol in the range of 80 to 99% by weight, without reducing the productivity of the device.

The process for producing pentaerythritol with the desired monopentaerythritol content, in particular by a continuous process by reacting fresh and regenerated formaldehyde with acetaldehyde in an alkaline medium, according to the invention is controlled by the dipentaerythritol content of the product. unchanged dosage of regenerated formaldehyde, wherein before the regeneration of formaldehyde from the reaction solution the content of condensates - 3 - 3 of formaldehyde alone in the solution is lower than 6 g.dm, preferably lower than 2 g.dm, and the content of alkaline catalyst before neutralization of the reaction solution is higher than 0. , 3 g.dm, preferably 2 to 3 g.dm.

The advantage of the process according to the invention is that it is possible to produce the commercial product pentaerythritol with different dipentaerythritol content on existing plants without any accessories according to the requirements of the customer and the method of its use. In this case, for example, when working in the technology of separating formaldehyde by distillation, it is not necessary to control the content and concentration of the return formalin under the assumption of continuous circulation without interrupting its entire separated amount back into the reaction. The desired concentration at the outlet of the solution from the reaction system can be controlled by the amount of fresh formaldehyde feed.

This quantity is also the same for the desired type of product when working on the same technological equipment as well as the same technological conditions.

In processes with a discontinuous reaction moiety at a given temperature and time regime, it is also possible to use said process, provided that the reaction solution is analyzed after stabilizing the decrease in formaldehyde concentrations per unit time before its physical removal, resp. by a chemical process from the reaction solution. The determination is preferably made by taking a sample into the suspended acid so that the final product has a pH below 7. Such a sample can be analyzed by various methods, whether gas or preferably liquid chromatography, polarographic method or volumetric methods, e.g. fluororglucin, resp. by dragonfly methods (dimedon).

In this case, it is advisable to use a selective method for formaldehyde so that any unreacted intermediates do not affect the determination. On the other hand, the control can also be carried out on the basis of the relative value of the formaldehyde content and the determined ratio of pentaerythritol, resp. dipentaerythritol in the same solution, resp. the product is preferably by liquid chromatography. In the continuous process of synthesis, there are different variants of the arrangement of the reaction system. It is either a flow-through reaction system with a piston flow, a system with stirred reactors, but systems are not rare, where the feed of raw materials is made to the mixing zone of the reactor and the reaction is done in a flow-through piston reactor, resp. system of several reactors. Surprisingly, we found that it is possible to control: the composition of the product in all the above systems, regardless of the use of the catalyst, i.e. sodium hydroxide, resp. of calcium hydroxide, provided that the concentration of the basic catalyst at said sampling point, i. j. after completion of the reactions, but before formaldehyde removal and neutralization

-3 -3 solution is higher than 0.3 g.dm, optimally 2 to 3.g.dm.

This is because such a concentration of the basic catalyst is necessary for the pentaerythritol formation reaction to take place. Below this concentration, the composition of pentaerythritol no longer depends on the formaldehyde content.

Higher than optimal amounts also guarantee the achievement of the desired effect, but are not advantageous in that they increase the consumption of acid used to neutralize the reaction solution before it is concentrated, resp. by removing unreacted formaldehyde.

CS 267 084 Bl

It is necessary to analyze the reaction solutions before removing the formaldehyde from the solution, most preferably according to the work-up procedure. In the solution heat treatment procedure, in the samples before the solution is fed to the formaldehyde thermal removal node, i.e. when the concentration of the condensation products of the formaldehyde itself is in the solution (determined e.g.

iodistane method for vicinal hydroxyl groups) to 6

The determination of formaldehyde in the samples can be done in the whole reaction system in the mixture starting from the dosing of formaldehyde, resp. dosing of acetaldehyde, provided that the collection is done at the same place, respectively. in the same time period starting from the formaldehyde dosing. However, since in these cases the loss of formaldehyde per unit time is still very large, so that considerable differences could occur during sampling and neutralization due to non-preservation of time periods, it is preferable to take sampling at a time when pentaerythritol formation is complete.

E.g. in a continuous reaction system with a cascade of stirred reactors using calcium hydroxide as catalyst, at an initial acetaldehyde concentration of about 3.3% by weight, before converting formaldehyde to syrups, it is necessary to obtain a technical product containing 85 + 2% monopentaerythritol and 12 + 3% dipentaerythritol work with formaldehyde content at the end of the reaction system 9 to 12 g.dm. In the same system, if we wanted to achieve a monopentaerythritol content of more than 96% by weight, with a content of 2 to 3% by weight of dipentaerythritol, it is necessary to keep the formaldehyde content of more than 4.6% by weight before neutralizing the solution, with a calcium hydroxide content of more than 0% by weight. , 5 g.dm $ and the content of -3 condensates of formaldehyde determined by the iodistane method 1.0 to 3 g.dm.

In this process, it is more convenient to remove formaldehyde from the solution by distillation, resp. rectification and not thermally disposal - condense in an alkaline environment to tetrose to hexose.

The advantage of this process is that with the same pentaerythritol production technology e.g. with a pressure rectification column included, it is possible to produce a product with a vigorous composition without having to change the thermal conditions in the reaction or insulating part without additional accessories.

Furthermore, such an arrangement also reduces the consumption standards of raw materials, especially formaldehyde, compared to the process of thermal removal of formaldehyde, eliminates the time losses caused by the transition from thermal disposal of formaldehyde to pressure rectification, necessary to remove condensates of formaldehyde itself to below 3 g.dm.

Exemplary embodiments supplementing the explanation of performing reactions according to customer requirements are given below.

Example 1. 3

In a cascade of stirred reactors consisting of 6 1 dm reactors, formaldehyde, 50% total acetaldehyde, aqueous calcium hydroxide suspension and aqueous sodium tetraborate solution were fed to the first reactor at 35 ° C so that the calculated formaldehyde concentration before the reaction in the first reactor was 9.2 wt%, and the solution flow rate was 3 -1 dm .h. 30% acetaldehyde was fed to the second reactor, 10% of the whole amount to 10 and 4 reactors each. The formaldehyde content in the solution after leaving the reaction cascade -3 ~ 3 was 4.6% by weight, the syrup content 2 g.dm, the calcium hydroxide content 1.0 to 3.0 g.dm, the pentaerythritol content 3.9% by weight. , dipentaerythritol content 0.09% by weight, bispentaerythritol monoform content 0.16% by weight, achieved selectivity of acetaldehyde to technical grade pentaerythritol 93.4%.

CS 267 084 Bl

If we increased the total acetaldehyde feed while maintaining the division into individual members so that the formaldehyde content after leaving the cascade was 2.8 wt%, the monopentaerythritol content rose to 6.0 wt%, the dipentaerythritol content to 0.42 wt%. ., bispentaerythritol monoformal content 0.21% by weight.

With a further increase in the total amount of acetaldehyde, the formaldehyde content at the outlet of the cascade decreased to 0.9% by weight, the monopentaerythritol content increased to 6.3% by weight, the dipentaerythritol content to 1.0% by weight, the bispentaerythritol monoform content was 0.25% by weight. . In the first case after isolation of pentaerythritol the product contained 96.5% monopentaerythritol and 1.7% dipentaerythritol, in the second case 92% monopentaerythritol and 6% dipentaerythritol and in the third case 85% monopentaerythritol and 12% dipentaerythritol when the solution was treated in the same way.

Example 2

A mixture of formaldehyde, calcium hydroxide, water, borax and acetaldehyde was fed to the reactor cascade, with acetaldehyde fed to the first three reactors, the other 3 -1 components to the first reactor. The amount of reaction mixture was 15 dm / h, the reactor size was 2 dm 2, the first four reactors, the fifth 6 dm 2. The first four reactors were stirred with external cooling through a circulating heat exchanger, the fifth reactor was a piston reactor with a ratio of a ratio of 1:10, the flow of suspension in the reactor from the bottom of the mountain. After the fifth reactor, the reaction solution was passed to a neutralizer, where the pH was adjusted to pH 5.5 to 6.0 by the addition of formic acid. At a formaldehyde concentration of 12.5% by weight, (calculated on the feed to the first reactor), and a formaldehyde-3 ”3 -3 du concentration from the neutralizer of 33.6 mg.cm, syrups 2.08 mg.cm of calcium hydroxide 2.1 mg.cm before the neutralizer, the concentration of monopentaerythritol was 6.5 g.100 ml, dipentaerythritol 0.3 g.100 ml and bispentaerythritol monoformal 0.4 g.100 ml. After isolation of pentaerythritol, the product contained 95% by weight, monopentaerythritol and 4% by weight. dipentaerythritol.

After increasing the concentration of formaldehyde in the neutralizer to 56 mg.cm, the content of monopentaerythritol in the product increased above 97% by weight, the content of dipentaerythritol was 1.1% by weight. After reducing the formaldehyde content in the neutralizer to 26 mg.dm, the monopentaerythritol content decreased to 90% by weight, and the dipentaerythritol content increased to 9% by weight. After further reducing the formaldehyde-3 content to 13 mg / cm 2, the monopentaerythritol content decreased to 85% and the dipentaerythritol content increased to 12.5%.

The regulation of the formaldehyde content in the neutralizer was done on the basis of its analysis by increasing resp. by destroying the feed of fresh formaldehyde into the first reactor and metering all of the formaldehyde obtained by rectification at 155 ° C and the corresponding pressure from the neutralized solution after distilling off the methanol.

In case we exchanged the condensing agent calcium hydroxide for sodium hydroxide in order to achieve the same content of monopentaerythritol in the product it was necessary to work with -3 concentrations of formaldehyde at the outlet 25 to 30 mg.cm higher.

Claims (3)

In case the total acetaldehyde feed was increased by maintaining the distribution of the individual members so that the formaldehyde content after exiting the cascade was 2.8 wt%. the content of monopentaerythritol increased to 6.0% by weight, the content of dipentaerythritol to 0.42% by weight, the content of bispentaerythritol monoformal was 0.21% by weight. Further increasing the sum of acetaldehyde, the formaldehyde content from the cascade dropped to 0.9% by weight, the content of inopentaerythritol increased to 6.3% by weight, the content of dipentaerythritol to 1.0% by weight, the bispentaerythritol monoformal content was 0.25% by weight. In the first case, after isolation of pentaerythritol, the product contained 96.5% of inonenta-pentaterythritol and 1.7% of dipentaerythritol, in the latter case, 92% of inonenta-penttritol and 6% of dipentaerythritol, and in the third case 85% of monopentaerythritol and 12% of dipentaerythritol in the same solution. Example 2 A mixture of formaldehyde, calcium hydroxide, water, borax and acetaldehyde was metered into the reactor cascade, with acetaldehyde being fed into the first three reactors, the other three components into the first reactor. Reaction mixture amount was 15 dm, reactor size 2 dm, first four reactors, fifth 6 dm Reactor temperature was kept at 40 + 1 ° C. For the first time, four reactors were mixed with external cooling through a circulation heat exchanger, a fifth reactor was a piston with a ratio of 1:10 to the ratio of the suspension, and the flow rate of the slurry in the bottom reactor. After the fifth reactor, the reaction solution was fed to the neutralizer where it was adjusted to pH 5.5-6.0 by the addition of formic acid. At a formaldehyde concentration of 12.5 wt. (calculated on the feed into the first reactor), and the outlet concentration of formaldehyde -3 -3-3 du from the neutralizer 33.6 mg.cm, syrups 2.08 mg.cm calcium hydroxide 2.1 mg.cm before the neutralizer was the concentration of monopentaerythritol 6.5 g.100 ml, dipentaerythritol 0.3 g.100 ml 1 and bispentaerythritol monoformal 0.4 g 100 ml After isolation of pentaerythritol, the product contained 95 wt. % monopentaerythritol and 4 wt. dipentaerythritol. After increasing the concentration of formaldehyde in the neutralizer to 56 mg.cm the content of monopentaerythritol in the product increased over 97% by weight, the content of dipentaerythritol was 1.1% by weight. After reducing the formaldehyde content in the neutralizer to 26 mg.dm, the monopentaerythritol content decreased to 90% by weight. and the dipentaerythritol content increased to 9% by weight. After Salda the reduction of formaldehyde-3 hydu content to 13 mg.cm, the content of monopentaerythritol decreased to 85% and the dipentaerythritol content increased to 12.5%. The regulation of formaldehyde content in the neutralizer was done by analyzing it by increasing or decreasing it. by reducing the feed of fresh formaldehyde to the first reactor and dosing the total amount of formaldehyde obtained by rectification at 155 ° C and the corresponding pressure from the neutralized solution after distilling off the methanol. If we exchanged the calcium hydroxide to sodium hydroxide condensation reagent to achieve the same monopentaerythritol content in the product, it was necessary to work -3 with formaldehyde concentrations at the outlet of 25 to 30 mg.cm higher. SUBJECT OF THE INVENTION A process for the production of pentaerythritol with the desired monopentaerythritol content by a continuous process of reacting fresh and recovered formaldehyde with acetaldehyde in an alkaline medium, wherein the dipentaerythritol content of the product is controlled by the formaldehyde content of the reaction solution prior to its separation from the solution. changing the amount of fresh formaldehyde with unchanged dosing of recovered formaldehyde, wherein prior to regenerating formaldehyde from the reaction solution, the condensate content of the -3-3 formaldehyde alone in solution is less than 6 g.dm, preferably less than 2 g.dm, and the alkaline content of 6 CS 267 084 B1 of -3 of the catalyst before neutralizing the reaction solution is greater than 0.3 g.dm, preferably 2-3 g.dm. 2. A process for producing pentaerythritol according to claim 1, wherein, when the condensate content rises above 2 g.dm-, the reaction temperature is reduced, preferably by increased cooling water feed or by increased dosage of condensate inhibitors. 3. A process for producing pentaerythritol according to claim 1 or 2, characterized in that when the alkaline catalyst concentration is less than 0.5 g.dm, its dosage is increased to the pentaerythritol production stage.