FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - "Pyridine recovery process"
2. Applicant(s)
(a) NAME: Alembic Ltd.
(b) NATIONALITY : An Indian Company
(c) ADDRESS : Alembic Campus, Alembic Road, Vadodara-390 003, Gujarat, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

Field of invention
The present invention relates to recovery of the Pyridine from feed mixture obtained after any reaction in which Pyridine is used as one of the reagent.
The structural formula of Pyridine is represented by formula (I) as given below.

Background of the invention
Pyridine is a nitrogenous base which is from the class of nitrogen containing heterocyclic compounds. It is widely used in organic synthesis either as a base, catalyst, complexing agent with other reagent. It is the most important reagent especially for pharmaceutical industries. It is chemically known as azabenzene having formula C5H5N and molecular weight 79.10. It is flammable liquid.
Pyridine is used as a solvent in paint and rubber preparation and in research laboratories for functions such as extracting plant hormones. Approximately half the Pyridine produced is used as an intermediate in making insecticides and herbicides for agricultural applications and denaturing alcohols. It is used in different products such as medicines, vitamins, food flavorings, pesticides, paints, dyes, rubber products, adhesives, and water proofing for fabrics.
Pyridine is a solvent which is widely used in the fine chemical and pharmaceutical industries. After use it is frequently rejected from the process in the form of an aqueous solution from which it is economically attractive to recover the Pyridine. Unfortunately, conventional distillation cannot achieve recovery of a high-strength Pyridine product because it has an azeotrope with water.
Pyridine is hazardous chemical and is classified in the class 3 category. It causes severe eye and skin irritation with burns. It causes respiratory tract irritation and is
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harmful if swallowed, inhaled, or absorbed through the skin. It may cause central nervous system depression. Since Pyridine is not biodegradable, it is harmful to the environment. Pyridine is regulated by the Resource Conservation and Recovery Act, and the Comprehensive Environmental Response, Compensation and Liability Act Pyridine releases into the air are regulated by the Occupational Safety and Health Administration (OSHA); The Food and Drug Administration (FDA) regulates Pyridine as a food additive, or synthetic flavoring substance component of polycarbonate, and as a resin, or indirect food additive. Therefore it is very important to remove Pyridine from the effluent before it is drained.
Pyridine is used in the process for prepration of pharmaceutical products such as Sucralose, Irbesartan and many other drug intermediates. Moreover, Pyridine is costly chemical so its recovery is very important to any pharmaceutical industry to minimize the overall cost of any production.
Techno force solution provides a process for Pyridine recovery which is as illustrated in the schematic diagram as shown in Fig. 2.
In this process, water and Pyridine, which form an azeotrope are separated by passing the mixture into a Distillation Column, followed by a Liquid-liquid Extractor (LLE) and another Column which gives almost 99.5% pure Pyridine at the bottom and an azeotropic mixture of Pyridine-water at the top which is recycled back to the LLE. In this process, different kinds of column and liquid-liquid extractor are used. This process requires special kind of equipment and expertise for handling it.
Another process is disclosed by De Dietrich for the recovery of the Pyridine. The schematic diagram is as shown in Fig. 3.
In this process, in the mixer-settlers, the aqueous Pyridine solution is intimately contacted with the chlorinated solvent and then the two phases settled out.
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Because Pyridine is much more soluble in the chlorinated solvent than in water, in each mixer-settler progressively more of the Pyridine passes into the solvent. The products rejected from the extractors are therefore a chlorinated solvent stream rich in Pyridine (the 'Extract') and an aqueous stream stripped of Pyridine but containing some dissolved solvent (the 'Raffinate'). Further process steps are provided to treat these streams. In this process chlorinated solvent is required to extract the Pyridine from aqueous solution to chlorinated solvent phase. Moreover, the production assembly is complex and requires special kind of apparatus.
GB657567 disclose a continuous process for recovering Pyridine by continuous neutralizing acid salt of Pyridine where liberated Pyridine is steam distilled and the distillate is saturated with salt readily soluble in water whereupon Pyridine is separated.
JP2193967 disclose a process for recovering Pyridine from a waste liquid containing at least Pyridine acetic acid or acetic anhydride, organic silicon compound and inert organic solvent by neutralizing the mass, azeotropic distilling the mass and separating organic toluene-Pyridine layer and aqueous-Pyridine layer; aqueous-Pyridine layer is salted so as to separate Pyridine which is again distilled to get pure Pyridine.
However, in above two processes a very large quantity of salt is required to saturate the solution. Moreover, these processes also needed with requirement of specialized equipment which makes it operationally difficult.CN13 70770 disclose a process for recovering Pyridine from waste liquid from cortical hormone production whichcomprise distilling the mass to give the distillate 20-25% concentrate with respect to Pyridine which is concentrated to 40% through secondary distillation and then basified with NaOH flakes to give 90% concentration which is further treated to reach industrial quality standard.
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However, this process requires repeated distillation to get maximum Pyridine reached solution. Repeated distillation makes it a commercially costly process.
It is therefore, a need to develop a process for recovery of Pyridine which is simple, easy to handle and feasible at industrial scale.
Surprisingly the present inventors found an efficient process for the recovery of Pyridine from an effluent obtained from any synthetic reaction after workup procedure. The present inventors have directed their research work towards developing a process which provides a method which is easy, simple and cost effective and which provide Pyridine with high purity.
Object of the invention
A primary object of the present invention is to provide a process for recovery of Pyridine from an effluent containing Pyridine and other components.
Another object of the present invention is to provide a process for recovery of highly pure Pyridine having purity of 99.5%.
Yet another object of the present invention is to provide a process for recovery of Pyridine, which is simple, easy to handle and feasible at commercial scale.
Summary of the invention
Accordingly, present invention provides a process for recovery of Pyridine of
formula (I).
A schematic flow diagram of Pyridine recovery process is shown in Fig. 1.
A process comprising steps of
(i) azeotropic distillation of basic aqueous solution of effluent containing
Pyridine and other components (ii) addition of alkali metal hydroxide to the distillate obtained from step (i) (iii) separation of Pyridine phase from aqueous phase
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optionally drying the Pyridine layer obtained in step (iii).
The aqueous phase obtained from step (iii) is optionally recycled to neutralization
step prior to distillation step (i).
Wherein "other components" comprise unreacted compounds of the reaction, byproducts formed during reaction, organic or inorganic impurities, inorganic salt, water and trace amount of organic solvent
Brief description of the drawings
Fig. 1 depicts a flow diagram of the operations performed in the process for
recovery of Pyridine.
Fig. 2 depicts a flow diagram of process for recovery of Pyridine given by Techno
force solution.
Fig. 3 depicts a flow diagram of process for recovery of Pyridine given by De
Dietrich.
Detailed description of the invention
A process for recovery of Pyridine comprising steps of
(i) azeotropic distillation of basic aqueous solution of effluent containing
Pyridine and other components (ii) addition of alkali metal hydroxide to the distillate obtained from step (i) (iii) separation of Pyridine phase from aqueous phase optionally drying the Pyridine layer obtained in step (iii).
The aqueous phase obtained from step (iii) is optionally recycled to neutralization step prior to distillation step (i).
Wherein "other components" comprise unreacted compounds of the reaction, byproducts formed during reaction, organic or inorganic impurities, inorganic salt, base, water and trace amount of organic solvent
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The acidic aqueous effluent containing Pyridine (1-25% Pyridine in the mass; and pH~3) and other component is basified using base up to pH 11-12. This base is selected from the group comprising alkali or alkaline earth metal hydroxide, oxide, carbonate or bicarbonate. The example of base as mentioned hereinabove includes but not limited to NaOH, KOH, LiOH, Mg(OH)2, NaHC03, KHCO3, LiHCO3, Na2C03, K2CO3, Li2C03, CaC03, MgC03, CaO, NH3 and the like or mixture thereof. The preferred base is lye i.e 50% NaOH.
This neutral mass is taken for azeotropic distillation. The azeotropic distillation is carried out at temperature ranging from about 92°C to about 98°C for period of time sufficient. The distillate is colourless and containing about 50% Pyridine and free from any solid impurities. To this distillate alkali metal hydroxide such as NaOH or KOH flakes are added and stirred gently. This mass is allowed to settle and Pyridine is separated from aqueous phase. The Pyridine is optionally dried on column or molecular sieve or any other conventional method to give highly pure Pyridine. The aqueous phase obtained can be optionally used for the neutralization of acidic aqueous effluent prior to step (i).
Pyridine obtained by the process of present invention is highly pure and having HPLC purity of 99.5%.
The process of the present invention is described by the following examples, which are illustrative only and should not be construed so as to limit the scope of the invention in any manner.
Example
Recovery of Pyridine
An aqueous acidic solution of Pyridine (150.0L; having 20-25% Pyridine content; having pH~3) was basified with caustic lye (46-48% NaOH in 70.0L water) up to pH~11-12. The solution was distilled at 94-98°C at atmospheric pressure. The distillate (70L) was collected containing Pyridine approximately 50% in
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concentration. This distillate was saturated with NaOH flakes (20-22Kg). The solution was allowed to settle and Pyridine layer was separated and was further dried on molecular sieves. The recovered quantity of Pyridine is 30-35L having purity 99.5% (by HPLC)
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We claim
1. A process for recovery of Pyridine comprising steps of
(i) azeotropic distillation of basic aqueous solution of effluent containing
Pyridine and other components (ii) addition of alkali metal hydroxide to the distillate obtained from step (i) (iii) separation of Pyridine phase from aqueous phase or
optionally drying the Pyridine layer obtained in step (iii)
2. The process as claimed in claim 1, wherein alkali metal is selected from NaOH, KOH, or mixture thereof.
3. The process as claimed in claim 1, further comprise optionally recycling of the aqueous phase obtained from step (iii) for basification step prior to distillation step (i).
4. The process as claimed in claim 1, in which basic aqueous solution is obtained by basifying acidic aqueous effluent containing Pyridine and other component with base.
5. The process as claimed in claim 4, wherein base is selected from the group comprising alkali or alkaline earth metal hydroxide, oxide, carbonate or bicarbonate; or ammonia or mixture thereof.
6. The process as claimed in claim 5, wherein base is selected from NaOH, KOH, LiOH, Mg(OH)2, NaHC03, KHC03, LiHC03, Na2C03, K2C03, Li2CO3, CaC03, MgC03, CaO, NH3 or mixture thereof.
Dated this 25th Day of August 2006
Sonali Bhokarikar OfS.Majumdar&Co. Applicant's agent
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Abstract
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The present invention relates to a process for recovery of Pyridine of formula (I)