GB2322856A

GB2322856A - Purification of Acetonitrile

Info

Publication number: GB2322856A
Application number: GB9704816A
Authority: GB
Inventors: Gerard Kenny
Original assignee: G K ANALYTICAL SCIENCES LIMITE
Current assignee: G K ANALYTICAL SCIENCES LIMITE
Priority date: 1997-03-03
Filing date: 1997-03-07
Publication date: 1998-09-09
Anticipated expiration: 2017-03-07
Also published as: IES73196B2; GB2322856B; GB9704816D0

Abstract

An acetonitrile purification process comprises adding phosphorous pentoxide to a crude mixture in an amount of 0.125 to 0.625% by weight. Water is added to the mixture in an amount of at least 0.005% by volume. The mixture is distilled and purified acetonitrile is recovered.

Description

"Solvent Purification" The invention relates to a purification process for purifying acetonitrile containing impurities such as allyl alcohol, acetone, water, oxazole, acrylonitrile, methacrylonitrile and/or propionitrile.

Acetonitrile was first produced commercially in 1952. It is widely used in liquid-liquid extraction, selective recrystallisation and extractive distillation. Because of its favourable dialectric, solvent and optical properties it is also widely used in analytical chemistry, particularly in high performance liquid chromatography (HPLC), DNA and peptide synthesis, residue analysis and in W and DR spectroscopy.

In our UK-A-2249308 we have described a process for producing acetonitrile having a high level of purity in a cost efficient manner.

As modern chemical and biological process techniques become ever more sophisticated and new techniques are developed there is a need to provide an improved cost efficient process for producing acetonitrile with high levels of purity, especially with very low levels of water as impurity.

This invention is directed towards providing such an improved acetonitrile purification process.

According to the invention there is provided an acetonitrile purification process for the purification of an acetonitrile mixture containing impurities to produce purified acetonitrile, the process comprising the steps of: adding phosphorus pentoxide to the mixture in an amount of from 0.125% to 0.625% by weight of the mixture; adding water to the mixture in an amount of at least 0.005% by volume of the mixture; distilling the mixture in a distillation column; recovering purified acetonitrile from the distillation column; and producing a first residue containing impurities and phosphorus pentoxide.

In one embodiment of the invention phosphorus pentoxide is added to the mixture in an amount of from 0.25% to 0.5% by weight of the mixture, especially approximately 0.375% by weight of the mixture.

In a preferred embodiment of the invention water is added to the mixture in an amount of at least 0.01% by volume of the mixture, especially in an amount of approximately 0.015% by volume of the mixture.

In one embodiment of the invention the process includes the step of adding an oxidising agent to the mixture prior to distillation. Preferably the oxidising agent is potassium permanganate which is preferably added in an amount of from 0.00625% to 0.0125% by weight of the mixture, especially approximately 0.00875% by weight of the mixture.

In a particularly preferred embodiment of the invention the process includes the steps of: adding further acetonitrile containing impurities to the first mixture; adding further phosphorus pentoxide and water to the mixture; distilling the mixture; recovering purified acetonitrile, and producing a second residue containing impurities and phosphorus pentoxide.

Preferably the process further includes the steps of: adding further acetonitrile containing impurities to the second residue; adding further phosphorus pentoxide to the mixture; distilling the mixture; recovering purified acetonitrile; producing a third residue containing impurities and phosphorus pentoxide; and removing the third residue.

The invention also provides purified acetonitrile when produced by the purification process of the invention.

The invention will be more clearly understood from the following description thereof given by way of example only with reference to accompanying drawing which is a schematic diagram of a distillation apparatus used in the process of the invention.

Referring to the drawing there is illustrated a distillation apparatus used in the acetonitrile purification process of the invention. The apparatus comprises a distillation column 1 having a packing of raschig rings with from 30 to 40 theoretical plates. Feed acetonitrile containing impurities is added along an inlet line 2 to a reboiler 3 having a steam heating coil 4. The feed acetonitrile is then delivered into a boiling vessel 5. Vapour from the distillation column 1 is condensed by passing cooling water through a coil 7 in a condenser 8.

Reflux is returned to the column through a reflux line 9.

When the desired purity level of acetonitrile is reached the purified acetonitrile is delivered along an outlet line 10 through a molecular sieve 12 [?] to a collection vessel 13. Purified acetonitrile from the vessel 13 or residue from the boiling vessel 5 may be taken off along a delivery line 15.

EXAMPLE 1 Acetonitrile containing impurities is added to the boiling vessel 5. Water is added to the acetonitrile in an amount of approximately l5ml per 100 litres of acetonitrile.

Phosphorus pentoxide is then added to the acetonitrile in an amount of approximately 300g per 100 litres of acetonitrile. The mixture is gently heated to reflux and refluxed for from 15 minutes to 30 minutes. Distillation is continued and the purified acetonitrile is delivered into the receiving vessel 13 and bottled. A first residue containing impurities and phosphorus pentoxide is produced.

Further acetonitrile containing impurities is introduced into the boiling vessel 5 and water in an amount of approximately 15m1 per 100 litres of acetonitrile is added. Additional phosphorus pentoxide in an amount of approximately 250g per 100 litres of acetonitrile is added. The distillation process is repeated as above producing purified acetonitrile and a second residue which may be retained in the system.

Further acetonitrile containing impurities is introduced into the boiling vessel 5 and water in an amount of approximately l5ml per 100 litres of acetonitrile is added. Additional phosphorus pentoxide in an amount of approximately 200g per 100 litres of acetonitrile is added. The distillation process is repeated as above producing purified acetonitrile and a third residue which is cleaned from the system.

We have surprisingly found that very high purity levels, especially with regard to water, can be achieved using phosphorus pentoxide in the defined amounts in combination with water. In particular, the process may be operated to maximise the production of purified acetonitrile with minimum downtime required for cleaning out impurity residue products.

EXAMPLE 2 Example 1 above was repeated except that in this case in each stage an amount of approximately 7g per 100 litres of potassium permanganate is added to the mixture.

This further enhances the purity levels of the acetonitrile produced.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims

1. An acetonitrile purification process for the purification of an acetonitrile mixture containing impurities to produce purified acetonitrile, the process comprising the steps of: adding phosphorus pentoxide to the mixture in an amount of from 0.125% to 0.6258 by weight of the mixture; adding water to the mixture in an amount of at least 0.005% by volume of the mixture; distilling the mixture in a distillation column; recovering purified acetonitrile from the distillation column; and producing a first residue containing impurities and phosphorus pentoxide.

2. An acetonitrile purification process as claimed in claim 1 wherein phosphorus pentoxide is added to the mixture in an amount of from 0.0258 to 0.5% by weight of the mixture.

3. An acetonitrile purification process as claimed in claim 1 or 2 wherein the phosphorus pentoxide is added to the mixture in an amount of approximately 0.375% by weight of the mixture.

4. An acetonitrile purification process as claimed in any preceding claim wherein water is added to the mixture in an amount of at least 0.01% by volume of the mixture.

5. An acetonitrile purification process as claimed in any preceding claim wherein water is added to the mixture in an amount of approximately 0.015% by volume of the mixture.

6. An acetonitrile purification process as claimed in any preceding claim including the step of adding an oxidising agent to the mixture prior to distillation.

7. An acetonitrile purification process as claimed in claim 6 wherein the oxidising agent is potassium permanganate.

8. An acetonitrile purification process as claimed in claim 7 wherein potassium permanganate is added in an amount of from 0.00625% to 0.0125% by weight of the mixture.

9. An acetonitrile purification process as claimed in claim 7 or 8 wherein potassium permanganate is added in an amount of approximately 0.00875% by weight of the mixture.

10. An acetonitrile purification process as claimed in any preceding claim including the stages of: adding further acetonitrile containing impurities to the first mixture; adding further phosphorus pentoxide and water to the mixture; distilling the mixture; recovering purified acetonitrile, and producing a second residue containing impurities and phosphorus pentoxide.

11. An acetonitrile purification process as claimed in claim 10 including the steps of: adding further acetonitrile containing impurities to the second residue; adding further phosphorus pentoxide to the mixture; distilling the mixture; recovering purified acetonitrile; producing a third residue containing impurities and phosphorus pentoxide; and removing the third residue.

12. An acetonitrile purification process substantially as hereinbefore described with reference to the examples.

13. Purified acetonitrile whenever purified by a process as claimed in any preceding claim.