DE10237746A1 - Process for the distillative removal of formaldehyde from polyol-containing reaction mixtures with the addition of solvents - Google Patents

Abstract

Process for the distillative removal of formaldehyde from reaction solutions containing a methylolated alkanal which results from the reaction of formaldehyde with an alkanal which has at least one acidic hydrogen atom in the alpha position to the carbonyl function, or from the reaction of a 2-alkylacrolein or acrolein with water and Formaldehyde is obtained and this reaction is carried out in the presence of catalytic amounts of an organic amine, the low-boiling compounds obtained at the top of a distillation separator being condensed and the water-insoluble fraction of the condensate being separated off.

Description

To represent the type of invention is in the preamble of claim 1 of a known method in the sense of DE-A 199 63 445 assumed, in which formaldehyde is separated from the reaction solutions by distillation, the reaction solutions containing a methylolated alkanal which results from the reaction of formaldehyde with an alkanal which has at least one acidic hydrogen atom in the α-position to the carbonyl function, or from the reaction of a 2-alkylacrolein or acrolein is obtained with water and formaldehyde. This reaction takes place in the presence of catalytic amounts of an organic amine. For an effective removal of the formaldehyde, water is added to the reaction solutions before and / or during the distillation. However, intermediate products, so-called organic high boilers, are formed which are sparingly soluble in water and are therefore removed. However, these organic high boilers level up via the formaldehyde recycle, which means that the system has to be shut down and flushed at regular intervals in order to remove the organic high boilers.

A method is intended with the invention for the separation of formaldehyde from reaction mixtures containing polyol by distillation be created, which the safe discharge undesirable By-products guaranteed.

This task is performed by the in the indicator of the measures contained in claim 1 solved.

The separation of the formaldehyde the aldolization mixtures generally take place in a distillative Separating device, preferably in a distillation column 5 to 100 separation levels. The column is generally with operated at a temperature of 50 ° C to 160 ° C; the pressure is 0.2 bar to 5 bar, the reflux ratio approximately 10 to 0. Overall, it has proven to be expedient to separate what is Feed the reaction mixture at the top of the column and at the same time via the Column tray to supply water, generally water vapor.

By distillation low-boiling overhead product, essentially containing water, Ethyl acrolein, formaldehyde and trimethylamine and about 2% by weight organic high boilers, and a high-boiling bottom product. The bottom product is, for example, according to that in the German patent application 198 09 418 A1 hydrogenated process and then to pure processed according to specification trimethylolpropane (TMP).

The one at the head of the distillation separator Low-boiling compounds obtained (top product) are condensed according to the invention and the insoluble in water Part of the condensate separated. Virtually all are suitable for this known phase separators, in particular separators, which act as separating forces Gravity, centrifugal forces, inertia or electrical forces to use.

According to a further feature of the invention the insoluble in water Proportion of condensate in a phase separator with ordered separators separated. Grid-like structures and spacing arrangements come as separating elements from two or more sheets of webs and / or profiles or Packings made of sheet metal or fabric layers, as is usually the case in the distillation separation technique can be used. With such a phase separator orderly separating elements enable particularly high separating performance reach with little pressure loss of the distillate.

The invention is explained in more detail below with reference to the drawing using an exemplary embodiment. In this example an aldolization mixture was used, which was represented as follows:
An apparatus consisting of two heatable stirred tanks connected by overflow pipes with a total capacity of 72 l was filled with fresh, aqueous formaldehyde solution (4300 g / h of a 40% aqueous solution or n-butyraldehyde (1800 g / h) and with fresh trimethylamine as a catalyst (130 g / h) in the form of a 45% strength aqueous solution, the reactors were heated to 40 ° C. A low-methanol formaldehyde can be used, as described in the document DE 199 63 438 A1 is described.

The discharge was made directly via a Falling film evaporator with attached column (11 bar heating steam) passed and there at normal pressure into a low-boiling overhead product, essentially containing butyraldehyde, ethyl acrolein, formaldehyde, Water and trimethylamine and a high-boiling bottom product separated.

The top product became continuous condensed and returned to the reactors described above.

The high-boiling bottom product the evaporator (approx. 33.5 kg / h) was continuously supplied with fresh Trimethylamine catalyst (50 g / h in the form of a 45% aqueous solution Solution) added and into a heatable tubular reactor provided with packing guided with an empty volume of 12 l. The reactor was there to 40 ° C tempered.

The discharge of the post-reactor was continuous only in the upper part of another distillation unit ( 1 ), the formaldehyde removal, (11 bar heating steam) and distilled there into a low-boiling overhead product, essentially containing water, ethyl acrolein, formaldehyde, water and trimethylamine, about 2% by weight of organic high boilers, and a high-boiling bottom product. The low-boiling overhead product (27 kg / h) was continuously condensed and the phase separator ( 2 ) supplied, whereas the high-boiling bottom product was collected. In the bottom of the distillation unit at ( 3 ) 4.5 kg / h water vapor fed.

The bottom product thus obtained contained in addition to water essentially dimethylol butyraldehyde, formaldehyde and traces of monomethylol butyraldehyde.

The formaldehyde was separated off from the bottom product according to that in the document DE 199 63 455 A1 described method. A 70% aqueous discharge was obtained which contained 24% by weight of dimethylol butyraldehyde (DMB). The bottom product was then hydrogenated and worked up to pure specification-compliant TMP.

At the head of the distillation device ( 1 ) The low-boiling compounds obtained, essentially water, ethyl acrolein, formaldehyde and trimethylamine and the organic high boilers, were completely subjected to a phase separator ( 2 ) fed. The phase separator consisted of a metal container made of a DN 80 pipe and a length of 320 mm with two sight glasses at both ends.

about Head was discontinuously discharged organic phase. The discharge took place from 50% level, the over a sight glass was found; it ended at about 100% Stand aqueous phase. During the test period, one was removed approximately every 20 hours average flow of organic high boilers of approx. 30 g / h. These contained the following components: 20% by area ethyl acrolein, 30% Ethylhexenal, 20% dimeric ethyl acrolein, 1% formaldehyde and others "organic high boilers" which cannot be determined more precisely. The aqueous phase was continuously over Dumped and as before in the aldolization reactors recycled.

Claims (2)

Process for the separation of formaldehyde by distillation reaction solutions containing a methylolated alkanal resulting from the reaction of formaldehyde with an alkanal which has at least one acidic hydrogen atom in the α-position to the carbonyl function, or from the reaction of a 2-alkylacrolein or acrolein is obtained with water and formaldehyde and this Reaction in the presence of catalytic amounts of an organic amine carried out is characterized in that the head of a distillative Separating device obtained, low-boiling compounds condensed and the insoluble in water Portion of the condensate is separated. A method according to claim 1, characterized in that the insoluble in water Proportion of condensate in a phase separator with ordered separators is separated.