CS195087B1 - Method for the continuous preparation of pentaerythritol - Google Patents

Description

The invention describes a process for separating raw materials in the production of PE from formaldehyde and acetaldehyde in the presence of alkali.

In order to achieve the desired yield of pentaerythritol in its industrial preparation, various reaction conditions are chosen, which depend on the molar ratio of formaldehyde to acetaldehyde used, whichever is used, as well as the reaction system used.

Another important factor affecting the overall economy of the process is the use of the optimum aldehyde concentration in the reaction system, which can be influenced by the amount of dilution water added in the reaction. The higher formaldehyde concentrations used and its excesses give a medium quality product and adversely affect the effort to obtain the highest possible PE concentration in the reaction. On the other hand, too dilute solutions in the reaction deteriorate the economics of PE production, since virtually all of the dilution water needs to be evaporated during the PE isolation process. % to 20.25 wt. This concentration is mainly dependent on the molar ratio of formaldehyde to acetaldehyde used. When using a molar ratio of formaldehyde to acetaldehyde less than 5: 1, increasing the concentration of formaldehyde adversely affects both the quality and the amount of PE produced. In the continuous production of PE, three feed metering methods are known. The first method is to introduce formaldehyde, acetaldehyde and the alkali used at the same time into the reactor or the reactor. to the first stage of the multistage reaction system.

Such a dosing method requires the use of high molar ratios of formaldehyde to acetaldehyde and a very intense reaction heat removal, but a relatively simple reaction system.

The second method is to feed the entire amount of formaldehyde and the alkali used into the first stage of the multistage reaction system, and the acetaldehyde dosing is divided into 2-7 parts which are metered into the first and subsequent stages of the reaction system.

This method allows the use of lower starting molar ratios of formaldehyde to acetaldehyde and hence a lower energy requirement for distillation of the feed water or excess formaldehyde during the treatment of the reaction solution.

In a third dosing method using not only acetaldehyde but also an aqueous alkali solution using a multistage reaction system, the dosing of these raw materials need not be maintained in an equivalent ratio. In the patent literature, as well as in the published articles dealing with the preparation of PE, we did not encounter the separation of formaldehyde into the individual stages of the reaction system.

SUMMARY OF THE INVENTION The present invention provides a novel feed method for the continuous production of PE from formaldehyde and acetaldehyde in an alkaline environment, characterized in that in addition to acetaldehyde, formaldehyde is also divided into 2-4 portions which are individually dosed into the first 2-4 members of the multistage reaction system. . The required amount of alkali is either fed to the first reactor or is possible to feed to multiple reactors / max.

4), while maintaining the alkali concentration in excess of the equimolar concentration of the resulting pentaerythrose. Thus, according to the present invention, the total amount of formaldehyde injected is divided into a plurality of portions and these are fed into a plurality of first members of the reaction system, as opposed to the previously used method of injecting the entire amount of formaldehyde into a single reactor. When feeding formaldehyde to individual reactors, both the feed and the acetaldehyde are required in at least as much as formaldehyde, as the high molar ratio of formaldehyde to acetaldehyde maintained in such a manner allows a high yield of pentaerythriol to be achieved. At a dosage of 50-80 wt. of formaldehyde from its total amount to the first reactor, a considerable reduction or elimination of the need for dilution water is achieved while maintaining the same initial concentration of the aqueous-alkaline formaldehyde solution. At the same time, a substantial increase in the PE concentration in the treatment reactor of the solution is achieved, which also makes it possible to increase the performance of the process equipment.

The most important advantage of the proposed dosing method is the great energy savings (steam), since a much smaller amount of water (about 30-40%) is needed to evaporate the reaction solution.

Thus, the addition of formaldehyde in several batches to a multistage reaction system has the following advantages: *

1. An increase in PE yield which is achieved by maintaining the overall high Fd concentration at a substantially lower initial Fd concentration. Maintaining a constant concentration of Fd in the reactors to which acetaldehyde is fed can be significantly influenced to increase the PE recovery.

2. Reduce the process energy consumption of the reaction solutions by reducing the need for dilution water.

3. Improving the performance of production equipment.

Example # 1 - comparative

The first reactor of the reaction cascade consisting of six reactors

Claims (3)

195087 4), while concentrating excess concentrations in excess of the equimolar concentration of the resulting pentaerythrose. Thus, according to the present invention, the total amount of formaldehyde injected is divided into multiple portions and these are fed to a plurality of first members of the reaction system, the difference of the previously used form of formaldehyde injection into a single reactor. When dispensing formaldehyde into the individual reactors, an acacetaldehyde dispenser is required, at least in many cases, such as formaldehyde, since such a high molecular weight acetaldehyde formaldehyde molar ratio allows for high yield of pentaerythiol. With 50-80 wt. The formaldehyde from its total amount to the first reactor has a remarkable reduction or elimination of the need for dilution water while maintaining the same initial concentration of water-alkaline solution of formaldehyde. At the same time, a more substantial increase in the PE concentration is achieved by the treatment of the solution, which makes it possible to increase the performance of the process equipment. The most important advantage of the proposed method of dosing is the high energy / steam savings, since it is necessary to evaporate a much smaller amount of water (ca. 30-40 ° C) when treating the reaction solution. Thus, the dosing of formaldehyde in multiple portions into a multi-stage reaction system has the following advantages: An increase in PE yield that is achieved by reacting to substantially lower initial Fd concentrations while maintaining a total high Fd concentration. In order to increase the yield of PE, the maintenance of the constant concentration of Fd in the reactors into which the acetaldehyde, which can be achieved by these processes, also has a significant effect. 2. Reducing the energy consumption of the process by treating the reaction solutions by reducing the need for dilution water. 3. Increasing the performance of the plant and. Example. 1 - Comparative Into the first reactor of the reaction reactor, the remaining six reactors are dosed with P-RED-ET A process for the continuous preparation of pentaerythritol from formaldehyde and acetaldehyde in an alkaline medium characterized in that the reaction system, consisting of three to three. Seventh step is formaldehyde / or acetaldehyde dosed in two, three or four steps, an aqueous solution of alkaline to two steps, with 30-100% formaldehyde, preferably 40-60%, by weight of the total amount of formaldehyde, 20-70% acetaldehyde, to the first step preferably 30% by weight of the total amount of acetaldehyde, 50-100% of the aqueous solution of alkali, preferably 80% by weight of the total amount of the aqueous alkali solution, the second stage being 0-60% formaldehyde 3,850 kg / h 34, 6% aqueous formaldehyde solution, 5.460 kg / h 8.4% calcium hydroxide solution, 4.900 kg / h water and 208 kg / acetaldehyde. 141 kg / h of acetaldehyde are metered into the second reactor of the reaction vessel, 104 kg / h of acetaldehyde into the third reactor. 14,663 kg / h of reaction solution emerged from the reaction cascade, which contained 7.45% of teakerythritol at the outlet of the sixth reactor cascade, i.e., 1,092 kg / h. This amount represents 78% by weight. pentaerythritol extract on acetaldehyde feed. The reaction solution is worked up in a known manner. Example £. In the first reactor of the cascade reaction cascade of Example 1, 2310 kg / h of 36.4% formaldehyde, 5460 kg / h8.4% calcium hydroxide solution, 664 kg / well and 208 kg / h are dosed. h acetaldehyde. 1540 kg / hformaldehyde and 141 kg / h acetaldehyde, a 104 kg / h acetaldehyde reactor, are charged to the second reactor of the reaction cascade. A 10,427 kg / reaction solution containing 11.29% pentaerythritol, i.e. 1177 kg / h, emerges from the reaction cascade. This amount represents an 84% yield of pentaerythritol, calculated on the acetaldehyde feed. The solution thus prepared is processed by a known method. Example 3 In the first reactor of the reaction cascade, with the cascade of Example 1, 2117.5 kg / h of 36.4% formaldehyde, 5460 kg / h of 8.4% Ca / OH solution is dosed. 125.5 kg / acetaldehyde. 1155 kg / h of 36.4% formaldehyde and 138.3 kg / h of acetaldehyde are metered into the second reactor of the reaction vessel. To the third reactor of the reaction cascade was added 577.5 kg / h of 36.4% formaldehyde and 125 kg / hacetaldehyde. 64.1 kg / h of acetaldehyde are metered into the fourth reactor of the reaction vessel. 9763 kg / h of a reaction solution containing 12.15% pentaerythritol, i.e. 1185.8 kg / h, were recovered from the reaction column. This amount represents a 84.7% yield of pentaerythritol, calculated on the acetaldehyde feed. The solution thus prepared is worked up in a known manner. OF THE INVENTION The hydu, preferably 30-40% by weight, of the total amount of formaldehyde, 10-60% acetaldehyde, preferably 30% by weight of the total amount of acetaldehyde, 0-50% aqueous alkali, preferably 20% in the third step, 0-40% formaldehyde, preferably 15-20% by weight of the total amount of formaldehyde, 0-50% acetaldehyde, preferably 25% by weight of the total amount of acetaldehyde, is added to the fourth step is dosed with 0-30% formaldehyde, preferably 10% by weight of the total amount of formaldehyde, 0-30% acetaldehyde, preferably 15% by weight of the total amount of acetaldehyde metered. Sí'verngr «íia. n. p. race 7. Miwt