DD281183A5 - METHOD OF ISOLATING ALPHA-ETHYLACROLEINE - Google Patents

Abstract

The invention relates to a process for the isolation of alpha-ethylacrolein from crude products of thermal cleavage of organic byproducts of trimethylolpropane production. In a first distillation, a distillate is separated from the crude product, which practically contains the total amounts of methanol and butanal and a portion of the alpha-ethylacrolein, while the decomposing in two phases sump consists of the total amount of water and the residual amount of alpha-ethylacrolein. From the distillate of this first distillation, the methanol is separated in a second distillation step by extractive distillation with water and washed in the bottom. The distillate consists of a mixture of alpha-ethylacrolein and butanal, from which a small amount of water separates as the lower phase. By suitable combination of the obtained distillation cuts and phases and their distillation, the individual products are obtained in high purity. {Distillation; extractive distillation; Insulation; alpha-ethyl acrolein; butanal; methanol; Water; trimethylolpropane; By-products; thermal splitting}

Description

Field of application of the invention

The invention relates to the isolation of alpha-ethylacrolein from a crude product obtained by thermal cleavage of organic byproducts of trimethylolpropane production. Alpha-ethylacrolein is an important feedstock for dyes, pharmaceuticals, pesticides, solvents and polymers.

Characteristic of the known state of the art

The known process of the synthesis of alpha-ethylacrolein via the Mannich base and their decomposition leads to a crude product which is not comparable in its composition with the crude product to be processed according to the invention (DE 31061557).

The same applies to the production of alpha-ethylacrolein by reacting formaldehyde with butanol in the gas phase over a suitable catalyst (US Pat. No. 3,578,702). US 3701798 claims the gas phase reaction of butanol with methanolic formaldehyde at 34% conversion to alpha-Fthylacrolein. For the workup of the resulting synthesis mixture of methanol, butanol, water, alphü-ethylacrolein and formaldehyde, however, no evidence is given.

According to DD patent DD 77201 organic trimethylolpropane byproducts can be thermally cleaved to form a mixture of alpha-ethylacrolein, methanol, water, formaldehyde and butanal, which still contains small amounts of other unknown impurities. A technical process for the isolation and purification of alpha-ethylacrolein from this mixture is not known. In patent specification DD 77201, the drying of the cleavage product with calcium chloride is mentioned under preparative conditions in order to obtain a product which can be worked up by distillation. However, this is technically complex and uneconomical and does not meet modern demands of environmental protection.

The main constituents of the crude product to be worked up according to the invention are alpha-ethylacrolein (0.55 to 0.65 kg / kg), methanol (0.20 to 0.30 kg / kg), water (0.05 to 0.10 kg / kg), formaldehyde (0.01 to 0.02 kg / kg), butanol (to about 0.05 kg / kg) and various unknown components (to about 0.05 kg / kg).

The work-up of this crude product, in particular the isolation and purification of the alpha-ethylacroiein, are extremely complicated by the highly non-ideal distillative behavior of this component mixture, due to the occurrence of azeotropes. This already shows the following table of the boiling behavior:

Component or azeotrope

Kp. ( ⁰ C)

Composition in kg / kg

Methanol / alpha-ethylacrolein 63.6 0.762 / 0.238 methanol 64.6 1.00 Butanal / water 68 0.90 / 0.10 (heterogeneous) butanal 75.7 1.00 alpha-ethyl acrolein / water 78.7 0.877 / 0.123 (heterogeneous) alpha-ethylacrolein 92 1.00

Whether or not further azeotropes are present in this system is not yet known. According to Ogorodnikov, Lesteva and Kogan in "Azeotropic Mixtures" (Leningrad 1971), for example, an azeotrope methanol-butanal is denied, but our own investigations make such an azeotrope with a bp of 335K with a methanol content of otwa 0.37 kg / An example of a technical separation of the complex mixture described is not yet described, but due to its strong non-ideality, complexity and heterogeneity, this system is currently not yet available for forecasting or calculation.

Object of the invention

The aim of the invention is the development of a continuous process for the isolation and recovery of alpha-ethylacrolein from an alpha-ethyl-acrolein-containing crude product, obtained by thermal cleavage of organic by-products of trimethylolpropane production. At the same time there should be the possibility to recover further materials. Furthermore, the recovery of alpha-ethylaciolein should be possible in an economically favorable manner and meet the requirements of environmental protection.

Explanation of the essence of the invention

The object was to develop a continuous process for isolation and purification of alpha-ethylacrolein from an alpha-ethylacrolein-containing crude product obtained by thermal cleavage of organic trimethylolpropane byproducts. At the same time, the alpha-ethylacrolein contained in the crude product should be obtained largely completely and in an environmentally friendly manner with the least possible technical effort.

The object is achieved by a process for isolating alpha-ethylacrolein from a crude product which is essentially a. * alpha-ethylacrolein, methanol, butanal, water and formaldehyde and is obtained by thermal cleavage of organic hub products of trimethylolpropane generation, achieved by a combination of distillation steps according to the invention that this raw product initially in the temperature range ven 333 to 361K under atmospheric pressure i ι a first continuous distillation A having a theoretical separation number of 20 to 50 at a reflux ratio of 5 to 20, preferably 8 to 12, in a distillate A, consisting of the total amounts of methanol and Bi'tanal and a part of the alpha-ethylacroleins and a two-phase decomposing virtually methanol-free bottoms A, consisting of the total amount of water and the remaining alpha-ethylacrolein, is separated, that the distillate A in a second in the temperature range from 345 to 370K under normal pressure continuously operating distillation stage B with a theoretical separation step number fed from 20 to 50 and rising to the top of the column vapors by placing the 2 to 10 times, preferably 4 to 7 times the amount of water, based on the total mass of fed into the column B distillate A, at the top of the column B of an extractive distillation be subjected to that from the distillate B separating aqueous lower phase returned to the column B and consisting of the total amount of fed into the column B butanais and alpha-ethylacrolein and small amounts of water, practically methanol, formaldehyde and byproduct-free upper phase of Distillate B with the upper phase of the bottom A, as well as the entire amount of methanol containing bottom product of the distillation B with the lower phase of the bottom Avereinigt and the resulting mixtures are worked up in a conventional manner by distillation to pure alpha-ethylacrolein, pure butanal, methanol and pollution-free wastewater ,

The definition of the exact driving parameters of distillation A depends on the composition of the crude product used and the column dimensions. However, maintaining the column bottom temperature at from 348 to 361 K, preferably 352 to 358 K, and top temperatures from 333 to 343 K, preferably 335 to 338 K, proved to be advantageous under conditions of column A selected from the above, on the one hand a substantially anhydrous distillate A to obtain which contains the fed with the crude total amounts of methanol and butanal in addition to aliquots of alpha-ethylacrolein, and on the other hand, a virtually methanol and butanalfreien sump A, which fed from the larger Resimenge of alpha-ethylacrolein and the total amount of the crude product Water exists. The bottom product of the distillation, which decomposes in two phases, is continuously removed and separated into the phases in a decanter D. According to the mutual solubilities, the upper phase consists predominantly of alpha-ethylacrolein with formaldehyde, byproducts and some water and the lower phase mainly of water dissolved alpha-ethylacrolein.

In distillation B, the decomposition of the distillate Ad takes place by extractive distillation with water. The water is given up at the top of column B and trickles up against the head of distilling vapor. As a result of this extractive distillation one obtains a pristine methanol-free distillate B and a substantially aldehyde-free aqueous one

Bottom product B. The distillate B consists of the total amounts of alpha-ethylacrolein and butanal, which were fed to the distillate A in the distillation B, and some water, which separates as the lower phase from the distillate B due to their low mutual solubilities. This aldehyde-containing lower phase is expediently returned to the distillation B. This recycling takes place at the top of the column B, but could also be carried out together with the feed of the distillate A in the column. Bottom product B contains virtually all of the methanol fed into the workup with the crude product.

Also for the operation of the distillation B, the definition of the exact driving parameters depends on the current composition of the distillate A and the columns of sizing. For the illustrated distillation conditions, maintaining a bottom temperature of 360 to 370K, preferably 362 to 364 K, a head temperature of 345 to 355K, preferably 348 to 350 K, and an ExtraKtivwassertemperatur 340-345K, preferably 342 to 344 K, proved to be advantageous ,

The continuously withdrawn upper phases of the distillate B and the bottom product A white united and then worked up by known distillation processes, which in addition to pure alpha-ethylacrolein and pure butanal is recovered.

A small amount of the aldehydes, including the formaldehyde is lost by gumming in the form of Destiliationsrückstundes. A small amount of aqueous butanalhaltlger flow can be attributed to the separation process. Likewise, the bottom product of distillation Bund the lower phase of the bottom product of the distillation are Avreinigung and then recovered in a known per se therefrom by distillation of the methanol. The wastewater obtained in this case is virtually pollutant-free and meets the requirements of environmental protection. The major part of this waste water is recycled to the extractive distillation B, a smaller amount is centrifuged from the process a and discarded.

For the operation of the distillation A and the distillation B, other pressure conditions, e.g. Vacuum or overpressure, possible, without changing the illustrated separation behavior. To avoid additional expenses, however, the operation under normal pressure proves to be the most advantageous.

The separating behavior of the crude product used according to the invention is surprising. Thus, due to the boiling behavior of the individual components and of the binary systems described above, it was not to be expected that in distillation A a quantitative separation of the methanol and the butanais from a complex crude product would be possible in addition to a certain amount of alpha-ethylacrolein. It was also not expected that in the extractive distillation with water, the obtained in the distillation A methanol-butanal-alpha-ethylacrolein mixture can be decomposed so that compared to butanal and alpha-ethylacrolein and their azeotropes with water low-boiling methanol washed virtually completely in the bottom, while the low-boiling methanol-alpha-ethylacrolein Azeotro.o is destroyed and the higher-boiling components butanal and alpha-Ethylenacrolein can be obtained together with water, virtually free from other components, as a distillate.

Ausführungsbelsplel

In a continuous from about 3I) computed bottoms column A, 1000.0 parts by mass / h of the alpha-ethylacroleinhaltigon crude product of the following composition are fed between the lower and the middle third of the column column:

formaldehyde

methanol

water

butanal

alpha-ethylacrolein

unknown by-products

0.0144 kg / kg 0.2180 kg / kg 0.0755 kg / kg 0.0376 kg / kg 0.6270 kg / kg 0.0274 kg / kg

When maintaining a bottom temperature of 355 to 357 K, a top temperature of 334 to 337 K and a reflux ratio of 10 incurred 334.63 parts by mass / h of distillate of the following composition:

formaldehyde

methanol

water

butanal

alpha-ethylacrolein

unknown by-products

Traces 0.5524 kg / kg 0.0001 kg / kg 0.0952 kg / kg 0.3521 kg / kg traces

The bottoms of distillation A are 605.37 parts by mass / h, which are passed through a decanter D and here in a hydrous lower phase (62.14 parts by mass / h) and a predominantly of alpha-Ethylacrolein .sowie the low-volatility by-products existing upper phase ( 543.23 parts by mass / h) of the following composition (in kg / kg):

bottoms upper phase under phase -4- 281 183 (Average) 0.0238 0.0255 0.0091 formaldehyde traces traces traces methanol .1247 0.0273 .9763 water traces traces traces butanal .8062 .8967 0.0145 alpha-Ethylacrolf / in 0.0453 0.0505 traces unknown by-products

The distillate of the column A is fed into the column BN between the lower and middle thirds, the constructional conditions being identical to those of the column A. When maintaining a sump temperature of 362 to 364 Kund a head temperature of 348 to 3Ö0K 2170.47 parts by mass / h of water with a temperature of 343 K and the 18.74 parts by mass / h of lower phase, which are separated from the distillate at the top of the column given up. 200.62 parts by mass / h of distillate are obtained, which decomposes into 18.74 parts by mass / h of an aqueous lower phase and into 181.88 parts by mass / h of an alpha ethylacrolein-rich upper phase of the following composition (in kg / kg):

distillate upper phase Unterphfse (Average) formaldehyde traces Spuron traces methanol 0.0001 0.0001 traces water .1180 0.0290 .9815 butanal 0.1883 0.2068 0.0097 alpha-ethylacrolein .6936 .7641 0.0088 unknown by-products traces traces traces

The bottom product of column B is 2383.23 parts by mass / h of a virtually butanal and alpha ethyl acrolein-free product of the following composition:

formaldehyde traces methanol 0.0915 kg / kg water 0.9085 kg / kg butanal traces alpha-ethylacrolein 0.0004 kg / kg unknown by-products hurry

By combining the upper phase of the distillate O (r column B with the upper phase of the separated product in the decanter D bottom product of the column A 725.11 Massetei! E / h of an alpha-ethylacroleinreichen product having the following composition:

formaldehyde

methanol

water

butanal

alpha-ethylacrolein

raw ''. by-products

0.0191 kg / kg 0.00002 kci / kg 0.0277 kg / ton 0.0519 kg / kg 0.8635 irg / kg 0.0378 kg / kg

This product is now in a known manner by distillation to reir. worked up in butanal and pure alpha-ethylacrolein. It fin:

Water fraction (with 0,0303kg / kg Butanal) 20,73 via.-T / h

Butanal (0.9961 kg / kg) 33.40 Ma.-T / h

alpha-ethyl acrolein (0.99 kg / kg) 609.77 Ma.-T / h

distillation residue

(with 0.6167kg / kg predominantly polymeric aldehydes,

of which 0.3639kg / kg alpha-ethylacroic 61.21 Ma.-T / h

In the same way, the oil phase obtained from decanter D is combined with the bottoms product of column B to give 2445.37 parts by weight / h of a product of the following composition:

formaldehyde

methanol

water

butanal

alpha-ethylacrolein

unknown by-products

0.0002 <g / kg 0.0891 i <g / kg 0.9103 kg / kg Traces 0.0004 kg / k «Traces

From this product is also recovered without any problems by distillation, the methanol. In detail, dabp.i

Methanol alpha-ethyl acrolein (azeotrope) 3.80 Ma.-T / h Methanol (0.9848 kg / kg) 218.41 Ma.-T / h Waste water (practically free of pollutants) 2 223.1 β Ma. T / h

The biranal-containing water fraction from the A'jfarbeitung the upper phases and the small amount of methanol-alpha-ethylacrolein Azeütrop from the workup of the lower phases can be recycled at a suitable place in the process. The majority of the wastewater is reused in the column B for the extractive distillation, the remainder is discarded.

Claims (4)

claims: A process for the isolation of alpha-ethylacrolein from a crude product consisting essentially of alpha-ethylacrolein, methanol, butanal, water and formaldehyde obtained by thermal cleavage of trimethylolpropane byproduct organic by a combination of distillation steps characterized in that this crude product initially in the temperature range from 333 to 361 K under atmospheric pressure in a first continuous working distillation A with a theoretical separation stage number of 20 to 50 at a Rücklaufverhäitnis 5 to 20 in a distillate A, consisting of the total amounts of methanol and butanal and a portion of the alpha-ethylacroleins and a two-phase decomposing virtually methanol-free bottom product A, consisting of the total amount of water and the remaining alpha-ethylacrolein, is separated, that the distillate A in a second in the temperature range from 345 to 370K under atmospheric pressure continuously working distillation stage B with a theoretical separation stage number of 20 to 50 fed and rising to the top of the column vapors by giving 2 to 10 times the amount of water, based on the total mass of the fed into the column B distillate A, at the top of the column B of an extractive distillation be subjected to that from the distillate B separating aqueous lower phase returned to the column B and consisting of the total amount of fed into the column B butanais and alpha-ethylacrolein and small amounts of water, practically methanol, formaldehyde and byproduct-free upper phase of Distillates B with the upper phase of the bottom A, as well as the entire amount of methanol containing bottom product of the distillation B combined with the lower phase of the bottom A and worked up the resulting mixtures in a conventional manner by distillation to pure alpha-ethylacrolein, pure butanal, methanol and pollution-free wastewaterbecome. 2. The method according to claim 1, characterized in that the distillation A under atmospheric pressure at bottom temperatures of 348 to 361 K, preferably 352 to 358K, and head temperatures of 333 to 343K, preferably 335 to 338K, and the distillation B under atmospheric pressure at bottom temperatures of 360 to 370K, preferably 362 to 36-1! \, Head temperatures of 345 to 355 K, preferably 348 to 350K, and an extractive water temperature of 340 to J45K, preferably 342 to 344K, is performed. 3. The method according to claim 1, characterized in that the distillation A is carried out at a reflux ratio of 8 to 12. 4. The method according to claim 1, characterized in that at the top of the distillation stage B, the 4- to 7-fold amount of water, based on the total mass of the fed into the column B distillate A, is abandoned.