DD282818A7 - METHOD DISTILLATIVE AND OXIDATIVELY PREPARED TECHNICAL ACETONITRILS - Google Patents

Abstract

The invention relates in terms of apparatus, energy and material economy an improved process for acetonitrile cleaning of a pretreated technical acetonitrile, the impurities water and propionitrile, in the trace range, the oxidation products of substances such as oxazole, blue, methacrylonitrile, acrylonitrile, allyl alcohol and acrolein and as catalytic decomposition products of the acetonitrile contains ammonium compounds. After decantation of the undissolved potassium permanganate and its reduction products, the acetonitrile is subsequently dried by stripping off the azeotrope and simultaneously pre-stripped by inert gas. With further Strippgaszufuehrung for desorption of acetonitrile impurities takes place at atmospheric pressure, temperatures of 345 to 355 K at a Rücklaufverhaeltnis 15 to 20: 1, the fine distillation, the two-stage condensate system, consisting of partial condenser and downstream post-condenser, at temperatures of 330 to 340 K or 320 to 330 K are operated. The method gives the highest purity of the acetonitrile with the standard values of a spectroscopically pure end product. In addition, a complete purification of the acetonitrile is achieved with a simplified cleaning technology and an improved analgesic effectiveness. Fig. 1 {acetonitrile; precision cleaning; Process coupling; Decanting; Distillation; stripping; desorption; two-stage condensation; Batch distillation column}

Description

The oxidative decomposition products of acetonitrile could be characterized in the prior art only by increased time and manual effort at gf linger system efficiency, u.a. by high acetonitrile losses, are separated in an existing plant to obtain an acetonitrile required purity.

Object of the invention

The invention has the aim of removing from a distillative and oxidatively pretreated acetonitrile interfering impurities, such as the oxidation products of these impurities, water, propionitrile and inorganic and organic ammonium compounds, by low energy and equipment expense of existing plants so far that the for the purest representation the acetonitrile required purity while increasing the efficiency of the system is achieved.

Explanation of the essence of the invention

The object of the invention is to remove by process-specific coupling of processes of decantation, distillation, stripping, special condensation and desorption of a distillatively and oxidatively pretreated acetonitrile, the oxidation products of acetonitrile, water, propionitrile and inorganic and organic ammonium compounds and with the process design for simplicity the ultrafine cleaning technology and to increase the effectiveness of existing plants.

The object is achieved in that d.is acetonitrile after a known per se oxidative treatment with potassium permanganate, a decantation to separate the excess undissolved potassium permanganate and its reduction products is made to subject it to a distillation with downstream two-stage selective condensation for distillative purification. With the separation of the undissolved potassium permanganate and its reduction products from the acetonitrile in the decantation of the formation of undesirable ammonium compounds is limited and further discharged the undissolved potassium permanganate as a potential water-forming agent. During the subsequent fine distillation, the acetonitrile is subsequently dried in a process stage by stripping off the water-acetonitrile azeotrope and at the same time pre-stripped by inert gas through the bubble distillation column of adhering oxidation products.

With the two-stage selective condensation and the defined operating parameters on the partial condenser and subsequently arranged after-condenser is in addition to the production of a pure acetonitrile required purity by the targeted return of the condensed vapors from the partial condenser in the technical acetonitrile, given its recycling, the condensed vapor phase for the desorption of acetonitrile impurities is subjected to a targeted Inertgasbesprudelung in Nachkondonsator. The return of the condensed vapor phase of the postcondensation takes place i.a. into the storage tanks for technical acetonitrile, which does not meet the qualitative suitability test as EinsatzprodL'kt for the production of spectroscopically pure acetonitrile. As a suitability test method for the quality of the feedstock and for the quality of the condensed vapor phase of the postcondensation, ultraviolet spectroscopy is used.

With the inventive method, consisting of the process steps, distillation, stripping, desorption and two-stage selective condensation, water and hydrogen cyanide, the oxidation products of the present in the trace range acetonitrile impurities and the organic and inorganic ammonium compounds can be removed from the acetonitrile, while propionitrile, acetanide and z , B. ammonium acetate aufkonzeniriercn in the bottom of the column in the distillation and discharged from there after the fine cleaning.

The process according to the invention is expediently carried out in such a way that a technical acetonitrile is used to prepare a spectroscopically pure acetonitrile which has no aromatic impurities, since these aromatic impurities are only obtained by a high expenditure in terms of apparatus and time owing to the same boiling position as the acetonitrile Remove from the end product at low product yield. These aromatic impurities can be detected by dips in the absorption spectrum of the wavelength range 250-270nm. For ultrafine cleaning, the acetonitrile pretreated by distillation and catalytic oxidation in the trace range after acetonitrile impurities oxidative post-treatment in a stirred at 310 to 335 K with the addition of potassium permanganate and separated in the subsequent running at ambient temperature decantation the undissolved potassium permanganate and its reduction products from the acetonitrile ,

After drying the acetonitrile, which takes place at 335-345K without external reflux with simultaneous pre-stripping of the acetonitrile from the adhering oxidation products of acetonitrile impurities is at atmospheric pressure, 345-355 K and a reflux ratio of 15 to 20: 1 with further Strippgaszuspeisung in the Blasendestationskolonns and in the post-condenser for the desorption of the acetonitrile impurities continued with the film distillation. By a defined TemperaturregimeführL'ng the two-stage condensation system with temperatures at the sub-condenser of 330-340K or 320 to 330 Kam post-condenser, the crystallization u. a. Ammoniumcarbamat, -bonbonate and Ammoniumhydrcgencarbonat prevented as accumulating ammonium compounds and thus simultaneously avoided the displacement of this part of the plant. While a spectroscopically pure acetonitrile of the required quality can be withdrawn at the partial condenser, the vapor phase of the partial condenser is fed to a postcondensation and desorption by means of stripping gas, which effects the material utilization of the acetonitrile condensate, inter alia. with its return to the storage tanks for technical acetonitrile, without reducing the quality of the technical acetonitrile.

jsführungsbelspiel

The invention will be explained in more detail with reference to an embodiment. Figure 1 shows the schematic representation of the method according to the invention. For the production of spectroscopically pure acetonitrile a technical acetonitrile without aromatic impurities from storage tank 1 was used according to the suitability test method. The acetonitrile which had been pre-purified by distillation according to DD-WP 229274, 225C92 and 230529, by distillation and catalytically, still had the following impurities before its ultrafine purification:

Allyl alcohol 35ppm acrylonitrile 80ppm acrolein 163ppm propionitrile 330ppm water 0.14 parts by weight oxazoles 10ppm methacrylonitrile <10ppm hydrocyanic acid 10ppm

Through potassium permanganate feed 2 in a stirred tank 3, the oxidative aftertreatment of the acetonitrile impurities present in the trace range and in the downstream decanter vessel 4 at ambient temperature the separation of the undissolved potassium permanganate and its reduction products from the acetonitrile took place at 325K. During the subsequent fine distillation, the acetonitrile present with 0.1 wt .-% water was further dried in a bubble distillation column 5 at 339 K without external reflux by stripping the acetonitrile-water azeotrope and pre-stripped with adhering acetonitrile impurities in the distillation column while inert gas 8. At atmospheric pressure, 350 K and a reflux ratio of 18: 1 was carried out with further inert gas 8 in the bubble distillation column 5 and the post-condenser 7, the further purification process by distillation. The temperature at the partial condenser 6 was 334K, while the inert gas applied to the post-condenser 7 was operated at 326 K. By the Inertgaszuführung 8 at the post-condenser 7 and the defined temperature control on the two-stage selective condensation system, the solubility of entrained acetonitrile impurities including the crystallization of undesirable ammonium compounds is prevented and promoted using the desorption of nitrogen as inert gas, the expulsion of these impurities from the purification process via the Inertgasabführung 10. While in the bottom of the bubble distillation column 5 concentrated propionitrile, ammonium acetate and acetamide was discharged, compared with the prior art agents, characterized by Vorlaufwegnahme and repeatedly repeating distillation processes, with the inventive method after a distillation process on the partial condenser 6, a high purity acetonitrile with the deducted for the intended use purities required in the absorption spectrum. The water content of the ultrapure acetonitrile was 190 ppm. The yield of spectroscopically pure acetonitrile could be increased by the method according to the invention from values: S50 parts by weight in% to values of 65-75 parts by mass in% compared with the prior art agents. With the two-stage selective condensation was the recycling of the condensed vapor phase from the partial condenser 6, as impurities

Propionitrile <10 ppm

Water 0.32 mass% in%

and

Sputters of ammonium compounds

showed, wherein the return of this acetonitrile was carried out in the not suitable for the production of a pure acetonitrile storage tank 1.

Claims (1)

A process for the fine-graining of a distillation and oxidative pretreating technical acetonitrile obtained as a byproduct in the ammoxidation of propene and subjected to an oxidative aftertreatment with potassium permanganate at 310 to 335 K, then in a bubble distillation column under inert gas by dripping a water-acetonitrile azeotrope and dried adhering Aceionitrilverunreinigungen was largely freed by subsequent fine distillation in a bubble distillation column at 335 to 355 K under atmospheric pressure, characterized in that the fine distillation under further Strippgaszuführung at a reflux ratio of 15 to 20: 1 and the output of a two-stage selective condensation, consisting of partial condensation at 330 to 340 K in a partial condenser (6) and postcondensation at 320 to 330K under inert gas in a post-condenser (7) is subjected. For this 1 page drawing Field of application of the invention The invention relates to a process for the ultrafine purification of an oxidatively and by distillation prepurified acetonitrile, which has as impurities ammonium compounds and in the trace range as impurities hydrocyanic acid and the oxidation products of the substances oxazole, methacrylonitrile, acrylonitrile, allyl alcohol and acrolein. Characteristic of the known state of the art The technically pure acetonitrile produced as a by-product in the ammoxidation of propene and prepared by azeotropic distillation and subsequent dehydrative purification still contains a number of impurities which are followed by purification of the technically pure acetonitrile for use in ultraviolet spectral analysis, chromatography or as a sorption agent in technical Verfahi s required. For post-purification of the technically pure acetonitrile several methods are known in the art. However, these methods relate mainly to the DE-OS 3011391 and Japanese Patent Nos. 35416/72 and 4531/77 on the removal of selected impurities, sometimes coming as in US Patent 4,119,497 to load a complex regeneration system foreign drag and solvent used , In DD-PS 229274 a process for the oxidative removal of unsaturated compounds from a pretreated acetonitrile is described, which is obtained by catalytic oxidation, subsequent oxidation with a solid inorganic oxygen-donating compound and final rectification required for the intended use purity of the acetonitrile. For the fine cleaning of destiliativ prepurified acetonitrile while the feedstock of a catalytically oxidative treatment for the conversion of the distillatively vcirgereinigt acetonitrile contained unsaturated organic compounds according to DD-PS 225692 subjected and after the subsequent multi-stage fine cleaning, for. nachoxidiert after DD-PS 230529 with fractional partial condensation and subsequent quenching with a solid anoiganischen oxygen donating compound. As a solid oxidizing agent for the post-oxidation of the unsaturated acetonitrile impurities present in the trace range, potassium permanganate was used for economic reasons. It has already been proposed that the oxidatively and doratively pretreated acetonitrile z. Example, a blown distillation column with downstream partial condenser and subjected by process-specific coupling of the process steps distillation, stripping, condensation and desorption of a discontinuous fine cleaning to remove the present in the trace range oxidation products of acetonitrile, water and propionitrile. In this case, the acetonitrile is dried by stripping the azeotrope and stripped in the subsequent fine distillation, the acetonitrile by an inertization of adhering acetonitrile impurities. The final product is an acetonitrile having a purity required for the intended use. Although in the post-oxidation of the acetonitrile by Kaliumpermanganatzugabe resulting Oxio'ationsprodukte the acetonitrile impurities can be generally separated by separation by stripping and desorption in the distillative fine cleaning. However, as a result of the potassium permanganate treatment during the oxidative degradation of acetonitrile contaminants present in the trace range formed decomposition products of the acetonitrile influence by the release of these products bound by the brownstone under distillation conditions, the fine cleaning of the acetonitrile and require a lot of effort with repetitive multiple distillation operations despite Vorlaufwegnahmo and Sumpfdestillatausschusung in the first distillation operation, to obtain a final product of required purity. With the Kaliumpermanganatzugabe due to the oxidative action of potassium permanganate, the formation of these undesirable decomposition products of the acetonitrile is promoted, wherein the acetonitrile ^M nd its oxidation products are hydrolyzed under catalytic composed of manganese dioxide and the organic and inorganic ammonium compounds with simultaneous increase of the already contained in Acetonitrileinsatzprodukt or in incurred by the preceding process stages reaction water. Increases the formation of these oxidative decomposition products by higher Kaliumperrr anganatverbräuche due to increased Totaloxi organization and lower degradation rates of the unwanted organic acetonitrile by SelektiviU.s- and activity losses of the catalyst in catalytically oxidative acetonitrile according to DD-PS 225692.