Preparation and purification of acetonitrile

Acetonitrile is the simplest organic nitrile,also known as cyanomethane and methylnitrile.It is a colorless transparent liquid at room temperature,which is highly volatile,has a special smell similar to ether is flammable,and is accompanied by a bright flame when burning.It is miscible with water, methanol,carbon tetrachloride,methyl acetate,ethyl acetate,dichloroethane and many unsaturated hydrocarbon solvents.It is toxic and can be metabolized into hydrogen cyanide and thiocyanate.Acetonitrile is an important organic intermediate with excellent solvent properties.It is widely used as polar aprotic solvent.The biggest use of acetonitrile is as a solvent, which can be used to synthesize vitamin A,cortisone,carboamine drugs and their intermediates,as well as active medium solvent for manufacturing vitamin B1 and amino acids.It can replace chlorinated solvent.It is used in vinyl coatings, as extractant of fatty acids, alcohol denaturant,butadiene extractant and solvent of acrylonitrile synthetic fibers,and also has many uses in fabric dyeing,lighting industry,perfume manufacturing and light-sensitive material manufacturing. 

Production method of acetonitrile

There are many production methods of acetonitrile,among which the industrial production mainly includes acetic acid ammoniation, acetylene ammoniation and propylene ammoxidation by-product.

1. Acetic acid ammoniation method takes acetic acid and ammonia as raw materials,reacts with aluminum oxide catalyst at 360-420 ℃ to synthesize acetonitrile in one step,and the finished product is obtained by absorbing water and rectifying the reaction solution. Raw material consumption quota: acetic acid (98%) 1763kg/t,liquid ammonia (99.5%) 691kg/t.

2. Acetylene ammoniation method uses acetylene and ammonia as raw materials,aluminum oxide as catalyst,and under the temperature of 500-600 ℃,one-step reaction to synthesize acetonitrile.Raw material consumption quota:10231m3 acetylene,1007kg/t liquid ammonia (99.4%).

3. In the propylene ammoxidation by-product method,propylene,ammonia and air are used as raw materials to synthesize acrylonitrile through catalyst,and acetonitrile is also by-product.Each ton of acrylonitrile can produce 25-100kg acetonitrile.

4. It is obtained by dehydration of acetamide and phosphorus pentoxide.

5. It is obtained by the reaction of dimethyl sulfate and sodium cyanide.

Purification method of acetonitrile

In industry,acetonitrile is a by-product from the reaction of propylene and ammonia to produce acrylonitrile,so there are often impurities such as water,acrylonitrile,ether,ammonia,and even hydrolysis products such as acetic acid and ammonia in acetonitrile. 

 The purification methods are as follows:

1. Add phosphorus pentoxide (10-20g/L) into acetonitrile,heat and return to colorless,which can remove most of the water.Avoid adding excessive phosphorus pentoxide,or orange polymer may be generated.Add a small amount of potassium carbonate into the distilled acetonitrile and then distill it to remove excessive phosphorus pentoxide,and finally fractionate it with fractionating column.

2. 1L ordinary anhydrous acetonitrile is evaporated after refluxing with 36 grams of ground potassium permanganate and 28 grams of potassium carbonate for 5 hours,then adding 10g of phosphorus pentoxide into the evaporated solvent,refluxing for 5 hours,refining, keeping the temperature unchanged,and taking 81 ℃ fraction.

3. Add silica gel or 4A molecular sieve and shake it to remove most of the water in acetonitrile. Then, mix it with calcium hydroxide until hydrogen is no longer released. Fractionate it. In this way, acetonitrile containing only a small amount of water but no acetic acid can also be achieved.

4. Acetonitrile can also be dried by azeotropic distillation with dichloromethane,benzene and trichloroethylene.