DE1044068B - Process for the production of acrylic acid nitrile - Google Patents

Description

Process for the production of acrylonitrile The production of acrylonitrile by reacting acrolein with ammonia and oxygen in the presence of a catalyst at elevated temperature in the gas state is known. In this implementation contains the gaseous reaction product leaving the reaction vessel in addition to acrylonitrile unreacted raw materials and other impurities can be caused by known Methods to be cleaned.

In these known processes, the majority of the impurities, like acrolein and hydrogen cyanide, from the gaseous reaction product Extraction of the acrylonitrile with a suitable solvent, e.g. B. water, preferably after the removal of any excess ammonia that may be present by washing with a dilute acid. The solution of acrylonitrile in the solvent can then be treated with an alkaline compound or by reacting the remaining acrolein and hydrogen cyanide with formation Purify a cyanohydrin, whereupon to remove the solvent and to Obtaining a concentrated acrylonitrile, the mixture is fractionally distilled.

This distillate will hereinafter be referred to as "acrylonitrile oil" will.

It has now been found that the resulting »acrylonitrile oil «Still contains traces of impurities and that these will be used during later manufacture of acrylonitrile polymers interfere. As is known, one of the types of use is of polyacrylic acid nitrile for the production of textile fibers.

For this purpose, the polymer is dissolved in a suitable solvent and then spun dry or nai by known methods. Polymers made from Acrylonitrileöl «were produced, however, are not always satisfactory Spider properties, and it may happen that the threads obtained are not can be processed into fibers with good tensile strength.

The purpose of the invention is now a process for the purification of »acrylonitrile oil «With a trace amount of impurities. This makes an acrylonitrile obtained, which results in a polymer with satisfactory spinning properties polymerisi. leaves, so that the threads made from it become fibers of excellent quality Texture can be processed.

The inventive method for obtaining acrylonitrile, from which the impurities adversely affecting fiber formation are removed and that by catalytic oxidation of acrolein in the presence of ammonia has been obtained, by cleaning is now characterized by net that you can Acrylonitrile pre-purified by fractional distillation, the small quantities Contains acrolein and hydrogen cyanide or other impurities in the presence of at least 12 percent by weight of water, based on the acrylonitrile, distilled.

You can mix the "acrylonitrile oil" with water in the distillation device on the floor and introduce the mixture either at atmospheric or at reduced pressure or at USer pressure distill. But you can also use the "acrylonitrile oil" either on its own or Introduce together with water into a distillation column, in which water upwards distilled, and the azeotropic mixture of acrylonitrile and water at the top of the Remove the column, while the traces of any high-boiling impurities in the bladder flow back. Another way of working is that one uses the "acrylonitrile oil" in a mixture with water passes into a kettle with a stirrer, from which the azeotropic Mixture of acrylonitrile and water removed by distillation and that in the kettle look back All or part of the water is withdrawn continuously or at intervals to prevent the accumulation of impurities.

It should consistently at least about 12% water, based on the acrylonitrile, be present in the bladder to form the azeotropic mixture. Can be beneficial excess water at the top of the column and acrylonitrile oil saturated with water «Between head and foot of the column in the Initiate device. The .. distillate separates into two layers, of which the upper, oily, the Acrylonitrile saturated with water and the lower the water with a low Contains dissolved acrylonitrile content. The lower layer will be beneficial returned to the distillation device, preferably at the top of the column.

After the extractive distillation with water you can get the obee out fractionally distill the existing layer with water-saturated acrylonitrile, causing one to polymerize. sufficient pure acrylonitrile is obtained ..-.

@@ It is known that you can acrylonitrile, which by addition obtained from acetylene on hydrogen cyanide. can be cleaned if you wash it with water extractive distilled. By this process, the in the addition reaction resulting by-products, especially vinylacetylene, divinylacetylene (and also the Acetonitrile and propionitrile, which are not so disturbing per se, are removed. It actually was to expect that an acrylonitrile, which by oxidation of a mixture of acrolein and ammonia has been kept, after a conventional work-up for spinning purposes should be sufficiently pure and other measures, such as extractive distillation, are not necessary. However, it has been shown that in this meadow Acrylonitrile still contains traces of impurities, if they do are not removed, interfere with the subsequent processing of the polyacrylonitrile. It was now due to the completely different structure of these impurities those formed in the manufacture of acrylic acid from acexylene and hydrogen cyanide By-products are not to be expected by an extractive distillation of the prepurified Acrylonitrile can be removed with water to remove these harmful impurities.

The following example illustrates the method of the invention. All parts and percentages relate to weight unless otherwise specified.

Example yin mixture of acrolein, ammonia and air was used for the preparation of acrylonitrile passed over a molybdenum oxide catalyst. That the conversion vessel Leaving gas mixture of acrylonitrile, acrolein, hydrogen cyanide and. ammonia was first used with dilute sulfuric acid to remove ammonia and then washed with water. The aqueous extract was in a stripper, which was provided with a settling device, distilled. That in the sitting device The crude acrylonitrile which precipitated contained t 82, 5 ° lo acrylonitrile, 9, 6% hydrogen cyanide, 0.40% acrolein, 0.20 / o acrolein cyanohydrin and about 7% water and was left to stand at 20 ° C until the acrolein concentration increased 0.04% decreased xvar. The resulting solution had a pN value of 5 and was continuously fractionated to add the cyan, hydrogen at the head of the device remove.

The main amount of acrylonitrile and cyanohydrin condensation product Entlraltende residue was then fed to a climbing film evaporator and at 53 ° C and a pressure of 160 mm Hg distilled, with the acrylonitrile at the top the device passed while the cyanohydrin condensation product as a residue remained in the device. The distillate contained 96.5% acrylonitrile, 0.1 m / o Hydrogen cyanide, 0.04% acrolein, 2% acetonitrile and less than 1% propiononitrile. This distillate that should be designated in the following with "A", that was " Acrylic acid nitrile oil «and was used as the starting material for the process according to the invention used.

The distillate xA «contained traces of an impurity, its composition was not fully cleared up. It appears to be a ketone compound with multiple conjugated double bonds whose presence was recognized by the absorption at 2850 Å. Such an absorption shows the distillate "A". but not the distillate "B".

The distillate "A" was in a distillation column with fifty Trays introduced at a height of two fifths above the base of the column, Whole the bladder with water in an amount equal to about 14 "/ o the weight of the nitrile present was filled. The azeotropic mixture of acrylonitrile and water. distilled over at 71 ° C and separated into two layers. the Upper layer rich in acrylonitrile, which contains 95% acyl nitrile, 0.1% hydrogen cyanide, 0.04% acrolein, 2% acetonitrile, less than 1% propionic acid nitrile and about Containing 2% water was designated as distillate "B", while the lower, aqueous Layer with a low content of acrylonitrile after adding 10% water back into the bladder. was returned. The bubble residue, which is about 3% of the used Corresponding amount of the "acrylonitrile oil" was deducted to make up a collection to prevent high-boiling substances.

The distillate "B" became in one with the untreated distillate "A". Comparison of the polymerization test carried out as follows.

Parts of the distillate "A" and "B" were used in separate experiments in the. a vessel provided with a stirrer passed, which is air-free with 247 parts distilled water, 0.233 parts of ammonium persulfate and 0.466 parts of sodium bisulfite was filled.

The air present in the reaction vessel was previously through nitrogen been suppressed. The mixture was poured in a stream of nitrogen with constant stirring on the walnut cooler. Polymerized at a temperature of 60 ° C. for 2 hours. The resulting Polymers. would be nitrided off, the residue thoroughly first with water and then with Washed methyl alcohol and afterwards in a vacuum cabinet at one temperature dried below 40 ° C and weighed. The limiting viscosity number # of the polymer was determined by measuring the viscosity of the solution in dimethylformamide at 20.degree an OstwaId viscometer according to the regulations of the »British Standard Specification 186, 1937 «determined. The specific viscosity was determined by the quotient: outflow time of the solution minus the outflow time of the solvent divided by the outflow time of the solvent, and the intrinsic viscosity of the polymer by the specific Viscosity of the solution divided by its concentration in grams per 100 ccm of solution, calculated.

The spinning solutions were made by dissolving 1-9 parts of polymer in 100 parts by volume Dimethylformamide prepared and spun at 115 ° C in the head of a vertical tower, through which a stream of hot air was blown. The temperature in the Turtn was adjusted so that they are immediately below the spinneret 180 ° C, in the middle of the tower was 250 ° C and at its foot 160 ° C. The threads were after leaving of the tower wound at a speed of 670 m per minute. During the Spinning: was any tendency for the thread to break off on the way from the spinneret to the take-up reel recorded. A tear is apparent due to the presence of extremely small gel particles, which by the Filters in front of the spinner had not been removed.

The strands of the threads produced were then at 100 ° for 30 minutes C steamed to drive off the last traces of solvent.

The steamed strands of thread were then left in the air for 10 minutes Heated 170 ° C and then at this temperature between clamps at one speed stretched by 20 cm per minute. The highest allowable elongation was determined by the maximum value of the ratio of the stretched length divided by the unstretched length, at which one to Decreasing number of broken threads in the strand was present, was calculated.

The stretched strands are then cut into fibers of 12 cm and weighed them.

The tensile strength in grams per denier of the drawn one was then determined Multiple thread determined with a tensile strength meter.

The table below shows that the filaments of the polymer produced from distillate "B" have a lower tendency to tear, better drawing and greater tensile strength during spinning, without the polymer showing any significant differences in yield or actual viscosity. M mpfp Polymeres Grenz-Hodistes Tear Strength Distillate Yield Viscosity Number Fractions During Spinning Extension-in grams Distillate 71 ratio per denier 13A «95 2, 0 numerous fractions; 7: 1 4, 15 it is difficult to walk more than 100 m to wind up coherently »Bvr 95 2, 15 very few fractions; 9: 1 4, 73 a permanent winding is possible The results show that distillate "A" is unsuitable for industrial spinning and drawing, while distillate "B" is satisfactory.

The used as starting material for the process according to the invention "Acrylic acid nitrile oil" is produced by. Acrolein in the gas state with ammonia and oxygen over a catalyst at elevated temperatures the process of German Patent 897 560 and the resulting gaseous Purifies reaction mixture according to the method of patent 949 053. This pre-cleaning is necessary because in the presence of the impurities the production of a pure Acrylonitrile fraction by fractional distillation as a result of the formation of g of condensation products in the still fails. The cleaning can through this. take place that the reaction mixture with an alkaline compound treated to completely neutralize the hydrogen cyanide, or that the unreacted aldehyde completely polymerized, depending on the alkaline compound used. On the other hand, you can also use the unreacted aldehyde and hydrogen cyanide condense with each other in such a way that one of the participants in the conversion is completely converted will. The resulting condensation product can then be added to the reaction mixture removed.

By means of these measures, either the unreacted aldehyde can be removed or separate the hydrogen cyanide from the reaction product. It is only necessary to completely remove one of the two impurities in order to prevent the formation of condensation products, such as cyanohydrin, during the fractional distillation of the reaction mixture, which can then be carried out without difficulty.

The "acrylonitrile oil" can be obtained from the gaseous reaction mixture after leaving the reaction vessel by extraction with water and distillation the aqueous solution can be obtained as crude nitrile oil. This is done at low temperature left to stand, whereby the hydrogen cyanide reacts with the acrolein. This The condensation product is then separated off from the acrylonitrile.

This separation can be done in various ways, for example by distillation under suitable conditions or by extraction with a suitable one Solvent. The separation must be carried out under such conditions that no decomposition of the volatile cyanohydrin condensation product occurs. The separation can be achieved by simple distillation at a suitable low level Temperature, e.g. B. below 100 ° C and preferably, e below 70 ° C, perform. In this way the crude unsaturated nitrile distills off and the cyanohydrin condensation product remains as a residue.

A particularly suitable measure for separating the cyanohydrin from unsaturated nitrile is short-path distillation, preferably in a climbing film evaporator. In this process, the reaction mixture is only elevated in temperature for a very short time exposed to temperatures.

PATENT CLAIMS Process for the production of acrylonitrile from from which the impurities adversely affecting fiber formation are removed and obtained by the catalytic oxidation of acrolein in the presence of ammonia has been, by purification, characterized in that it is fractionated by Distillation of pre-purified acrylonitrile, the small amounts of acrolein and hydrogen cyanide or contains other impurities, in the presence of at least 12 percent by weight Water, based on the acrylic acid ritrile, distilled.

Claims (1)

Considered publications: German Patent Specifications No. 849839, 732562, 850 888; U.S. Patent Nos. 2,324,854, 2,409,124; french U.S. Patent No. 914,167; Angewandte Chemie, Vol. 61, 1949, p. 230.