IE80800B1 - Solvent purification - Google Patents

Abstract

A purification process for purifying a solvent, especially methanol comprises introducing feedstock solvent into a boiling vessel. The feedstock is refluxed for a period of at least 5 minutes, distilling the methanol and delivering the purified solvent into a first purified solvent receiver. Further feedstock is drip fed into the boiling vessel. The delivery of purified solvent is directed to a second receiver while the purified solvent in the first receiver is bottled. Sodium borohydride is added to the boiling vessel in an amount of approximately 0.025% by weight of the methanol.

Description

The invention relates to solvent purification, in particular to a process for purifying all alcohol, especially Methanol containing impurities such as Acetone, Methyl Ethyl Ketone, Water, Formic Acid, Formaldehyde, Acetic Acid and Methyl Esters and the like.

Methanol is widely used in selective recrystallisation and extractive distillation. Because of its favourable dielectric, solvent, and optical properties it is also widely used in analytical chemistry, particularly in high performance liquid chromatography (hplc), organic synthesis, pesticide residue analysis, UV and IR spectroscopy, purge and trap analysis, and DNA and peptide synthesis .

As analytical chemistry techniques and analytical machines become ever more sophisticated there is a need to develop processes for producing Methanol to a very high level of purity for use as a standard in such equipment.

This invention is therefore directed towards providing a process for producing Methanol having a very high level of purity in a cost efficient manner.

According to the invention there is provided a purification process for purifying solvent containing impurities to produce purified solvent, the process comprising the steps of:25 introducing feedstock solvent containing impurities into a boiling vessel; refluxing the feedstock solvent in the boiling vessel for a period of at least 5 minutes; distilling the solvent by passing the solvent through a distillation column; delivering the purified solvent thus produced into a first purified solvent receiver; drip feeding further feedstock solvent containing impurities into the boiling vessel; closing off delivery of purified solvent to the first receiver; opening delivery of the purified solvent to a second receiver; bottling purified solvent from the first receiver while purified solvent is delivered to the second receiver; on completion of bottling from the first receiver and filling of the second receiver closing off delivery to the second receiver and re-opening delivery to the first receiver; and bottling purified solvent from the second receiver while delivery of purified solvent from the distillation column to the first receiver is continued.

Preferably the solvent purification process includes the step of adding a reducing agent, preferably sodium borohydride, to the solvent in the boiling vessel, and producing a first residue containing impurities and reducing agent.

In a particularly preferred embodiment of the invention the process includes the steps of:3 adding further feedstock solvent containing impurities to the boiling vessel; adding further reducing agent to the mixture; distilling the mixture; recovering purified solvent; and producing a second residue containing impurities and reducing agent.

Preferably the process includes the steps of:adding further feedstock solvent containing impurities to the second residue; adding further reducing agent to the mixture; distilling the mixture; recovering purified solvent; producing a third residue containing impurities and reducing agent; and removing the third residue.

In a preferred embodiment of the invention the sodium borohydride is added in an amount of from 0.0125% to 0.0375% by weight of the solvent containing impurities.

Preferably the solvent is an alcohol, especially methanol.

The invention also provides purified solvent whenever purified by the 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 the accompanying drawing which is a schematic diagram of a customer designed distillation apparatus used in the process of the invention.

Referring to the drawing, there is illustrated a distillation apparatus used in the process of the invention comprising a distillation column 1 of packed raschig rings having from 30 to 40 theoretical plates. Feed solvent from a raw material vessel 20 is added into a boiling vessel 2 through an inlet value 3. The feed material is heated by passing through a reboiler 5 having a steam heated coil 6. Vapour from the distillation column 1 is condensed by passing cooing water through a coil 7 in a condenser 8. Reflux material is returned to the column 1 through a reflux line 9. When the desired purity level has been reached the material is fed through an outlet line 10 to a first collection vessel 12, on opening a first delivery valve 13 and closing a second delivery valve 14. Alternatively, as explained in more detail below, on closing of the first delivery valve 13 and opening of the second delivery valve 14 the purified solvent may be directed to a second collection vessel 15. The purified solvent is bottled using an automatic filling machine 16. The purified solvent may be passed through a secondary condenser 11 prior to delivery to the collection vessels 12, 15.

Feedstock solvent is delivered from the feedstock solvent vessel 20 in accordance with the level of solvent in the boiling vessel 2 as determined by a level controller 21 which operates a control valve 22 on the feedstock solvent feed line.

Purified solvent may be recycled from the first collection vessel 12 along a recycling line 25 on opening of a recycle valve 26.

Residue may be removed through a residue discharge line 27 on opening a residue discharge valve 28.

EXAMPLE Feedstock methanol is introduced into the boiling vessel 2. Sodium borohydride in an amount of approximately 20g per 100 litres of solvent is added to the solvent in the boiling vessel 2. The feedstock solvent mixture is refluxed for from 15 to 30 minutes with steam. When the required purity level is achieved the purified solvent is delivered into the first receiving vessel 12. When the first vessel 12 is filled to the required level the inlet valve 13 to the first vessel 12 is closed and the inlet valve 14 to the second receiving vessel 15 is opened. Feedstock methanol is drip-fed from the supply vessel 20 into the reboiler 5. The level of feedstock methanol is monitored at all times by the automatic level controller 21 and associated control valve 22. The optimum delivery of feedstock methanol is determined by sampling of the purified solvent delivered into the receiving vessel 15.

When the second receiving vessel 15 is almost full the distilled solvent is switched back to the first receiving vessel 12 by closing the valve 14 and opening valve 13. Purified solvent from the second receiving vessel 15 is bottled. Distillation is continued to the first receiving vessel 12 while purified solvent from the second receiving vessel 15 is bottled. When the first receiving vessel 12 has been filled with solvent the distillation delivery is switched back to the second receiving vessel 15.

During the distillation process for methanol sodium borohydride is added to the feedstock solvent in the boiling vessel in an amount of 20g per 100 litres of methanol. A first residue containing impurities and sodium borohydride is produced. Further feedstock methanol containing impurities is introduced into the boiling vessel and additional sodium borohydride in an amount of approximately 15g per 100 litres of methanol is added. The process produces a second residue containing impurities and sodium borohydride. Further feedstock methanol containing impurities is introduced into the boiling vessel and additional sodium borohydride in an amount of approximately lOg per 100 litres of methanol is added. The process produces a third residue which may be removed or a further amount of feedstock methanol and lOg of sodium borohydride per 100 ml of solvent may be added.

In this way very high purity levels can be achieved while operating the process to maximise production of purified solvent with minimum downtime required for cleaning out impurity residue products.

The continuous distillation process of the invention offers considerable manufacturing advantages as there are substantial reductions in down-time required for cleaning, bottling and re-charging. In addition, the amount of treatment chemicals required is optimised. The process removes substantially all impurities, including halogenated, aromatic and carbonyl compounds and a ultra pure high quality solvent is produced which is suitable for a very wide range of applications.

The high grade purified Methanol is used in HPLC analysis and has a wide range of application including applications in organic synthesis and in residue analyses, purge and trap analysis and IV-IR Spectroscopy.

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

Claims (6)

1. A solvent purification process for purifying solvent containing impurities to produce purified solvent, the process comprising the steps of:introducing feedstock solvent containing impurities into a boiling vessel; refluxing the feedstock solvent in the boiling vessel for a period of at least 5 minutes; distilling the solvent by passing the solvent through a distillation column; delivering the purified solvent thus produced into a first purified solvent receiver; drip feeding further feedstock solvent containing impurities into the boiling vessel; closing off delivery of purified solvent to the first receiver; opening delivery of the purified solvent to a second receiver; bottling purified solvent from the first receiver while purified solvent is delivered to the second receiver; on completion of bottling from the first receiver and filling of the second receiver closing off delivery to the second receiver and re-opening delivery to the first receiver; and bottling purified solvent from the second receiver while delivery of purified solvent from the distillation column to the first receiver is continued.

2. A solvent purification process as claimed in claim 1 including the step of adding a reducing agent to the solvent in the boiling vessel and producing a first residue containing impurities and reducing agent.

3. A solvent purification process as claimed in claim 2 including the steps of:adding further feedstock solvent containing impurities to the boiling vessel; adding further reducing agent to the mixture; distilling the mixture; recovering purified solvent; and producing a second residue containing impurities and reducing agent.

4. A solvent purification process as claimed in claim 3 including the steps of:adding further feedstock solvent containing impurities to the second residue; adding further reducing agent to the mixture;

5.

6. 8. 9. 10. 11. distilling the mixture; recovering purified solvent; producing a third residue containing impurities and reducing agent; and removing the third residue. A solvent purification process as claimed in an of claims 2 to 4 wherein the reducing agent is sodium borohydride. A solvent purification process as claimed in claim 5 wherein the sodium borohydride is added in an amount of from 0.0125% to 0.0375% by weight of the solvent containing impurities. A solvent purification process as claimed in claim 6 wherein the sodium borohydride is added in an amount of approximately 0.025% by weight of the solvent containing impurities. A solvent purification process as claimed in any preceding claim wherein the solvent is an alcohol. A solvent purification process as claimed in claim 8 wherein the solvent is methanol. A solvent purification process substantiaily as hereinbefore described with reference to the drawing and example. Solvent whenever purified by a process as claimed in any preceding claim.