CS256742B1 - A method of recovering formaldehyde from a reaction mite in the production of pentaerythritol - Google Patents

Abstract

The new method solves the problem of regeneration of unreacted formaldehyde from the reaction solution in the production of pentaerythritol, neutralized with an organic acid, especially formic acid to form calcium formate. In this method, the pH of the reaction solution is maintained at a constant value in the range of 3.5 to 7.0 and then, after preheating to a temperature of 60 to 140 °C, preferably 80 to 95 °C, it is fed to rectification, where at a pressure of 0.3 to 0.6 MPa and a pressure drop of 0.01 to 0.08 MPa, a distillate containing 10 to 16 wt. % formaldehyde and 2.0 to 4.0 wt. % methanol is obtained, which, after separation of the methanol in a further rectification at reduced or atmospheric pressure, is returned as a regenerated aqueous solution of formaldehyde for reuse in the reaction system for the production of pentaerythritol.

Description

236742

The present invention relates to a novel process for the regeneration of unreacted formaldehyde from a reaction solution in the production of pentaerythritol, consisting in rectifying the reaction solution under elevated pressure and subsequently separating the methanol from the distillate to obtain an aqueous solution of formaldehyde-compliant properties.

Practically there is no more suitable route n, and recovery of formaldehyde from the reaction solution such as separation of unreacted form aldehyde from the reaction solution by recrystallization. However, formaldehyde rectification from sodium solutions is very difficult, and due to the formation of false azeotropic compositions, depending on working pressure and other technological conditions, but also due to the negative effects of reaction effluents, especially at higher temperatures that the rectification compartments formaldehyde is required.

Problems related to the formation of unfair azeotropes are known because they are extensively described in Walker J. F .: "Form-aldehyde", II. ed., New York 1953 in the section on rectification of formaldehyde solutions. The liquid-vapor balance of formaldehyde-water at elevated pressure is processed by a cell in Zurn. Prikl. Chim. 50 (1), 39.1977.

A second area of difficulty in separating the formaldehyde from the reaction solutions from the production of pentaerythritol is that the reaction solution is not subjected to high temperatures in the pressure rectification of formaldehyde. The negative effect of high temperature exposure, the reaction solution in the production of pentaerythritol, appears to have a great deal of impact despite the prior neutralization in the increased formation of formaldehyde substances, thereby naturally reducing the recovery yield. These problems are mainly acute in lime milk technology to achieve the desired alkaline environment in action.

The process of separating and recovering formaldehyde from the reaction solution while continuously producing pentaerythritol is also hampered by the high formaldehyde requirement of the solution leaving the rectification column for further processing. Taknapr. the formaldehyde content of this pentaerythritol production should not exceed 0.1% by weight, and therefore rectification must be carried out in such a way as to avoid the possibility of cross-linking formaldehyde to the rectification column and thus to the outgoing reaction solution. The higher formaldehyde content has a very adverse effect on the crystallization of peneterythritol because it increases its solubility by water. This not only reduces the yields of peneterythritol, but also increases the cost of purifying wastewater.

The problems mentioned do not only make it difficult to identify formaldehyde from the reaction solutions in the production of pentaerythritol, but under certain circumstances I can also lead to complete failure and long-term shutdown of the production node due to contamination of the rectification column.

However, it has been shown that the appropriate combination of process conditions and compliance with each other will eliminate these difficulties. The operation of rectifying the formaldehyde from the reaction solutions in the production of pentaerythritol is reliable under these technological conditions, not only the steady-state conditions in the production, but also the short-term normal operating conditions and the fluctuations in the operation of the previous reaction system production and preparation and feedstocks into the reaction system. At the same time, the desired economic effect of operating the production node is ensured in this way.

In a novel process for the recovery of formaldehyde from the reaction solution in the preparation of peneterythritol neutralized with an organic acid, in particular formic acid, the pH of the reaction solution is kept constant at 3.5 to 7.0, preferably 5.0 for the formation of calcium formate. to 6.0, and is then brought into rectification after preheating to a temperature in the range of 60 to 140 ° C, preferably 80 to 95 ° C, where at a pressure of 0.3 to 0.6 MPa and at a pressure drop of 0, A distillate is obtained containing from 10 to 16 wt. % of formaldehyde and 2.0 to 4.0 wt. methyl alcohol, which, after separating the methanol in a further rectification, is reduced or atmospheric pressure, as a recovered aqueous solution of formaldehyde for use in the reaction system for producing pentaerythritol.

The new formaldehyde regeneration process is particularly advantageous in the production of pentaerythritol-formaldehyde-acetaldehyde in aqueous alkaline environments, while the more beneficial extracts are obtained in a molar excess of formaldehyde in acetaldehyde over the stoichiometric amount of formaldehyde. However, such a process for the production of pentaerythritol is economically efficient only when the unreacted formaldehyde is regenerated with minimal losses and quality satisfactory for its use in the condensation reaction.

In this process of formaldehyde regeneration, clear aqueous solutions of pentaerythritol and calcium formate, containing no more than 0.1% by weight of formaldehyde, are obtained at the bottom of the column so that further processing of the solutions, e.g., by crystallization of pentaerythritol, occurs without difficulty. The content of syrups is low and does not increase in rectification, which is important for the process and economical efficiency of the process. This positive phenomenon may be to some extent related to the minimization of high temperature exposure to the high formaldehyde reaction solution and to the water vapor depressant effect of the bottom on the cold spray coating.

Claims (3)

258742 5 th. However, the explanation is not unambiguous because the improvement of rectification is the result of the complex influence of the optimum combination of multiple technological parameters interdependent. It is important to note that these technological conditions also provide for a higher operational stability of the rectification operations, whereby all unwanted substances are removed from the recovered formaldehyde to such an extent that they do not accumulate during the long-term continuous operations. The following are examples of a novel process for formaldehyde regeneration, illustrating the process conditions and the results obtained. Example 1 Formaldehyde in this example is recovered from the reaction solution in the production of pentaerythritol. This solution contains on average 5.0 wt. unreacted formaldehyde, 7.9 wt. % of pentaerythritol including diphenaphererythritol; dissolved calcium formate, 1.56 wt. % methyl alcohol, 0.3 wt. calcium hydroxide and 0.12 wt. syrupy substances. The farmhouse is water. This formic acid solution, pH 5.2, is preheated first in the heat exchanger with the effluent bottom solution and then in a 95 ° C steam pre-heater and fed to the rectification column at this temperature. The injection rate is an average of 14,500 kg.Tr. The rectification is carried out at a pressure of 0.55 MPa and a temperature at the bottom of the column at 15-5 ° C. The column head temperature is 149 ° C. A pressure gradient in the column of 0.04 MPa. The rectification under these conditions is such that the formaldehyde content of the distillate is 14.75% by weight. Under these conditions, a clear solution containing 0.05 wt. % free formaldehyde and 0.17 wt. syrupy liquor. The distillate, excluding formaldehyde, contains 3.3% by weight. methyl alcohol, which is separated from the free formaldehyde solution by an additional rectification column, operating at a vacuum and atmospheric pressure. This permits an aqueous formaldehyde solution containing on average 650 kg. h_1 of formaldehyde, which corresponds to 90% of the re-generation efficiency. Example The rectification is carried out under the same conditions as in Example 1 except that pre-heating increased the feed temperature to 135 ° C. At this temperature, the sulfur content of the effluent solution increased from below to about 0.4% by weight. and the amount of recovered formaldehyde was reduced to an average of 615 kg. h “1. Example 3 The conditions of regeneration are the same as in Example 1 except for the working pressure and temperature of the rectification column to separate formaldehyde. The pressure is 0.51 MPa, the temperature at the column is 150 ° C, the head of the column is 147 ° C. The pressure drop in the column is 0.03 MPa. The formaldehyde concentration in the distillate was reduced by 12% by weight. The amount of syrup in the solution leaving the bottom of the column is unchanged, the formaldehyde content being on average 0.07% by weight. After rectifying the methanol from the distillate, it is fed formaldehyde to the reaction portion of the product. PRED Μ ET A process for the recovery of formaldehyde from a reaction solution in the production of pentaerythritin neutralized with an organic acid, in particular formic acid, to form calcium formate, characterized in that the pH of the reaction solution is kept constant between 3.5 and 7 And, after being preheated to a temperature of 60 to 140 ° C, preferably 80 to 95 ° C, is brought to rectification, where at a pressure in the range of 0.3 to 0.6 MPa and at a pressure drop of 0.01 to 0.08 MPa, a distillate is obtained containing preferably 10 to 16 wt. % formaldehyde and 2.0 to 4.0 wt. methyl alcohol, which is recovered as a recovered aqueous formaldehyde solution upon purification of the pentaerythritol reaction system upon separation of the methyl alcohol in further reduction under reduced or atmospheric pressure.