CS202251B1 - Process for removing methanole from solutions of pentaerithritole - Google Patents

Description

The invention describes a method of removing methanol from solutions of pentaerythritol prepared by reaction of formaldehyde and acetaldehyde in an alkaline medium.

In the preparation of pentaerythritol from formaldehyde and acetaldehyde in an alkaline medium, in addition to the main reaction leading to the formation of pentaerythritol and the alkali metal formate, the internal Gannizzar formaldehyde reaction takes place simultaneously to form methanol and alkali metal form according to the equation »

CH ₂ O + MeOH-CH 2 OH + HCOO Me 'where Me is an alkali metal cation. The amount of methanol formed depends on the conditions maintained during the main reaction of the preparation of pentaerythritol. In addition to the methanol produced by the Gannizzar reaction of formaldehyde, a saler amount of methanol is fed into the reaction solution with formaldehyde, which already contains 0.5-6% methanol as a raw material feedstock. A further portion of the methanol may be fed from the extraction stage where the solvent streams in methanol are separated from the recycle stream of formate and pentaerythritol, while the wet filter cake is returned to the neutralized reaction solution.

202 251

The treatment of the above solutions is conditioned by the methanol content of the reaction solution. In the case of a negligible internal Oannizzar Reaction of formaldehyde with a low methanol content (below 1% by weight) in the formaldehyde feed and without the use of methanol syrup extraction, the amount of methanol leaving in the vapour is not economically advantageous? him. If the course of the internal Oannizzar reaction is more significant, or formaldehyde with a higher methanol content is used in the reaction. an extraction procedure for the isolation of syrups with methanol is used, the amount of methanol in the reaction solution is considerable and this is removed from the solution by vacuum or atmospheric rectification. This process requires a large amount of energy (steam), is characterized by the thermal stress of the solutions at elevated temperatures (above 80 ° C), during unwanted side reactions to produce isolation-difficult products, decreases the separation power and increases the color of the pentaerythritol solutions.

It is an object of the present invention to provide a method for removing methanol and pentaerythritol solutions without thermal stress on the solutions and without the formation of unwanted by-products. The neutralized and solids-free reaction solution contained 0.1-5.0% methanol, in addition to the first member of a three-member or multi-member evaporator operating under vacuum at 40-60 ° C, where a substantial amount of methanol was distilled off. The obtained aqueous methanol-salt solution can be concentrated in a rectification column and reused in the extraction stage of the process. A reaction solution which is substantially free of methanol in the first evaporator member is fed to the evaporator salts and concentrated. up to the degree of its saturation to pentaerythritol at temperatures of 70-90 ° C. The hitherto known methods of separating methanol from the reaction solution in a rectification column at temperatures above 80 ° C result in thermal degradation of the formaldehyde and acetaldehyde reaction products, resulting in reduced pentaerythritol recovery. deteriorating his quartz lity. An important advantage of the proposed process is to obtain methanol with reduced thermal stress on the entire amount of the reaction solution of pentaerythritol, which has a positive effect on the yield of pentaerythritol and its quality. The advantage of this process is to concentrate methanol from the aqueous methanolic solution in the rectification column in the absence of pentaerythritol, alkali metal formate and other syrupy substances present in the reaction solution. This advantage will have a positive effect. to reduce the investment costs needed for machinery and technology, and also significantly reduce energy consumption (steam and electricity).

Example 1 is comparative

The reaction solution prepared by the reaction of formaldehyde and acetaldehyde in an alkaline medium together with a return stream from the extraction of mixed salts, contains 9.2 wt. pentaerythritol and 2.0% methanol in 15,000 kg / h of solution are fed to a vacuum rectification column operating at 80 ° at the bottom of the column and a pressure of 34 kPa at the top of the column. A distillate of 270 kg / h with a concentration of 95% methanol is obtained. The methanol-free reaction solution from the fifth column at 14,700 kg / h contains 9.05% of pentaerythritol, passed through a three-member evaporator and worked up according to a known method.

The disadvantage of this process is the considerable energy consumption and loss of 50 kg / h of pentaerythritol, which reacts with by-products at 80 ° C.

ŽXÍtíM-2

A reaction solution prepared by reacting formaldehyde and acetaldehyde in an alkali medium, together with a return stream of mixed salt extraction, containing 9.2 wt. of pentaerythritol and 2.0% methanol in 15,000 kg / h of solution are fed to the first 3-member evaporator to obtain 3010 kg / h of distillate with a final methanol content of 7.5% at 50 ° C and 12.5 kPa. A solution devoid of substantial part of methanol in an amount of 11,990 kg / h containing 11.5% of pentaerythritol e is passed to the evaporator members. From the amount of the aqueous methanolic solution obtained, 230 kg / h of distillate having a methanol concentration of 98% are decracted in vacuo and used in the extraction stage of pentaerythritol separation.

This process has the advantage of negligible evaporation losses of pentaerythritol at 50 ° C, reduced colouration of the solutions, and a 30% lower energy consumption compared to the procedure given in Example 1. Because of the price relations of the unit amounts of pentaerythritol and methanol, the procedure given in Example 2 is clearly more advantageous.

Claims (2)

OBJECT OF THE INVENTION 1. A method for removing methanol from pentaerythritol solutions prepared by the reaction of formaldehyde and α-etaldehyde in an alkali environment, characterized in that the removal of methanol from the pentaerythritol solutions comprises 0.1-5% methanol by one-step distillation in a first member of two or more members. a multi-member vacuum evaporator at temperatures of 40-60 ° C, preferably 50 ° C; and a solution of pentaerythritol from which the methanol has been removed is further processed by a known method. 2. A method for treating the aqueous methanolic condensate obtained in accordance with claim 1, wherein the aqueous methanolic condensate obtained from the first evaporator member is concentrated in a rectification column to a minimum methanol content of 90%, the methanol obtained being used for further processing, preferably for syrup extraction. A more advanced stage of this process.