CN1151123C - Acetonitrile refining and recovering process - Google Patents

Abstract

The present invention relates to a method for refining and recovering acetonitrile, which is mainly characterized in that a decyanation tower uses negative pressure operation, and the middle and lower part of a dehydrating tower is filled with extraction water. The method of the present invention can reduce the partial pressure in a vapor phase at the tower top of the decyanation tower and the concentration in reflux liquid, avoid the polymerization of acidum hydrocyanicum and improve the content of acetonitrile. The lower part of the dehydrating tower is filled with extraction water to remove propionitrile and high-boiling-point heavy component impurities generated in the reaction by an extractive distillation method. Thus, the refining and recovery of acetonitrile is realized, and the purity of an acetonitrile product can reach 99.9%.

Description

A kind of acetonitrile refining and recovering process

Technical field

The invention belongs to propylene ammmoxidation process and produce the vinyl cyanide technology, more particularly, is a kind of method for refining and reclaiming by the acetonitrile by product that generates in the propylene ammmoxidation process acrylonitrile production process.

Background technology

Acetonitrile is the by product that generates in the propylene ammmoxidation process acrylonitrile production process, it is the very complicated aqueous mixture of a kind of component, its main component is water and acetonitrile, also contain trace impurities such as vinyl cyanide, propionitrile, prussic acid, acetaldehyde, acetone, ammonia, copper, iron simultaneously, by weight, it generally consists of: water 40%-60%; Acetonitrile 55%-35%; Other impurity 5%.

At present, both at home and abroad the main production of acetonitrile device is: (1) under 1 or 1 above normal atmosphere, in the distillation zone, distill crude acetonitrile, remove most of prussic acid and heavy constituent.(2) azeotrope is passed through digestor, handle, remove remaining prussic acid (USP4328075,3201451) with the aqueous solution of alkali and formaldehyde.(3) carry out after-fractionating under 1 normal atmosphere being lower than, this azeotrope is separated into rich aqueous bottoms and is rich in second azeotrope of the ＂ acetonitrile/water ＂ of acetonitrile.(4) carry out after-fractionating being higher than under 1 the atmospheric distillation pressure, make as the acetonitrile purification that sides stream.Prussic acid content in the easy polymerization of acetonitrile refining method ubiquity decyanation tower both domestic and external, the reactor discharging is difficult to control, heavy constituent foreign matter content height such as propionitrile are difficult to continuous, steady, the macrocyclic purity of producing up to 99.9% high quality acetonitrile product.

Summary of the invention

The objective of the invention is to overcome the deficiency of prior art, the acetonitrile refining and recovering process that a kind of on-stream time is short, reach 99.9% high quality acetonitrile product by refined raw output purity is provided.

Realize the main technical schemes of the object of the invention: the decyanation tower adopts negative-pressure operation, adds extracting water in the dehydration tower middle and lower part.

Concrete grammar of the present invention may further comprise the steps:

(1) byproduct that from propylene ammmoxidation process acrylonitrile production process, produces---ethane nitrile wastewater solution, enter the middle and upper part of decyanation tower, in tower, distill, light constituents such as the prussic acid more than 95% in the acetonitrile solution, vinyl cyanide, acetone, propenal are separated from cat head, heavy constituent and other impurity are discharged at the bottom of tower, and first azeotrope enters reactor in the middle and lower part of tower.Described decyanation tower is to operate under negative pressure, and tower top pressure is that 0.07-0.09MPa (absolute pressure), temperature are 60-70 ℃;

(2) second azeotrope behind reactor reaction enters the dehydration tower middle and lower part, and the while adds extracting water in a tower tray place on second azeotrope inlet, obtain removing second azeotrope of 85% above water at cat head, a part is (2.2-2.6)/1 as its reflux ratio of trim the top of column, a part is as the charging of finishing column, described dehydration tower is operated under negative pressure, and tower top pressure is 0.015-0.045MPa (absolute pressure), and described extracting water add-on is the 10-20% of the second azeotrope weight.Described reflux ratio is quantity of reflux/cat head extraction amount.

Advantage of the present invention and effect:

The decyanation tower is to operate under negative pressure in the inventive method, both can reduce the dividing potential drop of prussic acid in the cat head vapour phase and the concentration of phegma, prevents the prussic acid polymerization, and the prussic acid content of side line discharging is reduced, and improves ethane nitrile content; The present invention utilizes propionitrile boiling point height, and the characteristics of Yi Rongshui from the middle and lower part adding extracting water of dehydration tower, are removed propionitrile with the extracting rectificating method.The easy polymerization of decyanation tower in the technology before improving, propose ＂ water is sent into distillation tower (being the decyanation tower) ＂ from the top that crude acetonitrile enters the point of distillation tower as the CN1231282A patent application, cause tower still and tower middle portion temperature difference excessive, influence steaming of prussic acid, cause this tower polymerization.Must clean one time the decyanation tower about the average every three months of old technology, its attached pipeline is often polymerization especially, bring difficulty to continuous production, and acetonitrile purity only is 99.4%, quality is difficult to satisfy user's requirement, and the improvement technology that the present invention adopts the decompression of aforesaid ＂ double tower, dehydration tower to add extracting water ＂ is rationally solved two problems that remove prussic acid and remove the propionitrile heavy constituent, once make with extra care and production purity to reach 99.9% high-quality nitrile product, and improve the yield of device.

Embodiment

Also further specify characteristics of the present invention in conjunction with the accompanying drawings below by specific examples.

Embodiment

Fig. 1 is a process flow sheet of the present invention, and all equipment all is known among the figure.

By shown in Figure 1, the acetonitrile solution by the acrylonitrile workshop is sent here enters decyanation tower 2 from pipeline 1 continuously The middle and upper part. This tower operates under negative pressure, and the cat head operating pressure is 65 ℃ of 0.086MPa (absolute pressure), temperature. Part light component in the raw material pushes up through pipeline 3 to condenser 4 condensations from tower 2, is back in the tower. Not cold The solidifying gas that contains HCN is pumped waste gas absorption tower 6 by vacuum jet pump 5 and is absorbed after separating. Gained Contain acetonitrile about 80% the 1st azeotropic mixtures from the tower lateral line withdrawal function, through pipeline 7 inflow reactors 8. At the tower reactor collection In contain most of H₂The waste water of O and organic heavy component is delivered to incinerator and is burned at the bottom of tower; By reactor 8 The material that comes out enters dehydrating tower 10 middle and lower parts through pipeline 9, carries out rectification under vacuum in tower, the control of dehydration cat head Pressing pressure is that the high concentration acetonitrile that 0.035MPa (absolute pressure), cat head steam is the 2nd azeotropic mixture (90% acetonitrile With 10% H₂A condensate liquid part of O) getting off through overhead condenser 11 condensations is as overhead reflux, one one The lease making heat exchange enters finishing column 13 middle and upper parts as the finishing column charging by pipeline 12; Extracting water is through pipeline 14 Enter the middle and lower part of tower 10 and on the top of charging aperture, the addition of extracting water is for being come out by reactor 8 13% of the 2nd azeotropic mixture amount is utilized propionitrile boiling point height, and the characteristics of Yi Rongshui are removed with the method for extracting rectification Propionitrile and the higher boiling heavy component impurity that generates in reaction reach refining purpose. Final products are through pipe Line 15 removes finished pot 16.

The present invention compares with the product that improves front explained hereafter, and the purity of acetonitrile only is 99.4% before improving, and produces The product quality is difficult to satisfy user's requirement, and tower 2 part pipelines are easy to polymerization, an average every three months left side Right tower 2 will polymerization, has to clean, and its attached pipeline is often polymerization especially, gives to produce continuously and brings very Big difficulty. Acetonitrile purity can reach 99.9% after improving, and tower 2 is as long as annual the cleaning once is attached Belong to also big leap ahead of pipeline polymerization interval.

Claims (1)

1. acetonitrile refining and recovering process is characterized in that may further comprise the steps:

(1) the byproduct ethane nitrile wastewater solution that comes from the propylene ammmoxidation process acrylonitrile production, enter the middle and upper part of decyanation tower, in tower, distill, this tower is operated under negative pressure, the 95% above light constituent that comprises prussic acid, vinyl cyanide, acetone, propenal in the ethane nitrile wastewater solution is separated from cat head, heavy constituent and other impurity are discharged at the bottom of tower, and first azeotrope enters reactor in the middle and lower part of tower, and described decyanation column overhead pressure is that 0.07-0.09MPa absolute pressure, temperature are 60-70 ℃;

(2) second azeotrope enters the dehydration tower middle and lower part behind reactor reaction, and the while adds extracting water in a tower tray place on second azeotrope inlet, obtain removing second azeotrope of 85% above water at cat head, a part is as trim the top of column, reflux ratio (2.2-2.6)/1, a part is as the finishing column charging, and described dehydration tower is operated under negative pressure, tower top pressure is 0.015-0.045MPa (absolute pressure), and the add-on of described extracting water is the 10-20% of the second azeotrope weight.