AU594491B2

AU594491B2 - Method for the purification of trifluralin

Info

Publication number: AU594491B2
Application number: AU76665/87A
Authority: AU
Inventors: Guido Ravetta
Original assignee: I Pi Ci SpA
Current assignee: I Pi Ci SpA
Priority date: 1986-08-12
Filing date: 1987-08-07
Publication date: 1990-03-08
Anticipated expiration: 2007-08-07
Also published as: DE3726698A1; AR243153A1; IL83485A0; BR8704581A; IT8667656A0; AU7666587A; IT1195822B; DE3726698C2

Description

1"t !)944 9 1 AUTSTRAIA Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int,, Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: This document contains the anmdmt mts raad-e cU Sc c!.$ot 49 ar.-d k~ LorrcL i\ r Nam~s)of APPLICANT' S REFERENCE: E017161 BEN-PR/lab Nams of Applicant(s): I.Pi.Ci. S.p.A.

Address(es) of Applicant(s): Via Beltrami 11, 20026 Novate Milanese, Milano,

ITALY.

0 404 Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUCTRALIA Compl.ote Specification for the invention ent~itled: METHOD FOR THE PURIFICATION OF TRIFLURALIN Our R~ef 63225 POF Code: 1249/72766 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6003cq/1-1 I 0 00 00 0 000 00 0 0 00 a a.

o 0 0 0 o 0 0 aQO o 000o 0 0 0 oo 0 00 0 0 o o 0 0 oo0 *0 a0 000 A The present invention relates to a method for the purification of trifluralin in ord&r to reduce its nitrosamine content.

The need to provide for the removal or destruction of nitrosamines in crude trifluralin has constituted a particularly pressing technical problem since the confirmation of the carcinogenic action of nitrosamines in animals. A further problem lies in the necessity of avoiding, as far as possible, the recrudescence of nitrosamines in trifluralin which has already been purified.

It is therefore highly desirable to have available a method for the purification of trifluralin which enables the nitrosamine content to be reduced to extremely low levels and which also eliminates from the trifluralin, not only the nitrosamines but also their precursors in order to stabilise the trifluralin against the said phenomenon of recrudescence.

In view of tie above object, the subject of th6 present invention is a method characterised in that it comprises the operation of bringing a liquid flow of triflura-' at a temperature of from 70 to 120 0 C into contact with a counterflow of saturated or superheated steam in a liquid-gas contact apparatus, and recovering the purified trifluralin leaving the contact apparatus.

Further characteristics of the method according to the invention will become apparent from the detailed description which follows with reference to the appended drawing which illustrates diagrammatically, by way of non-limiting example, the relative apparatus.

2 With reference to the drawing, a flow 2 of trifluralin is supplied from a storage tank 4 provided with a heating jacket to the head of a liquid-gas contact apparatus 6, preferably constituted by a column with s i e v e or va 1 v e plates. The liquid trifluralin flow 2 may consist of crude trifluralin in the fused state, or possibly dissolved in an organic solvent. The preferred solvent is a polar organic solvent with a low boiling point, such as methyl ethyl ketone (MEK). The trifluralin may be dissolved previously in the solvent or the latter may be supplied through 8 directly to the head of the contact column.

The crude trifluralin flow from the synthesising So° process generally has an active principal content of o approximately 95-96% by weight and is preferably o 0 subjected to washing with water before being supplied 00 0 oo to the contact column 6 in order to eliminate any salts o in it which could cause corrosion in the column.

However, whether or not the prior washing is carried 9'o out does not affect the results in terms of removal of o ooo o 0o the nitrosamines.

0 9 0 Q 00 o0o, A flow of saturated or superheated steam 10 is supplied to the foot of the column 6, generally at a temperature of from 90 to 120 C. The V/L ratio between the mass °o flow rates of the steam supplied and of the trifluralin supplied is generally between 0.3 and 1.

The pressure within the column 6 is preferably kept below atmospheric pressure with the aid of a vacuum pump 26.

A gaseous flow 12 of exhausted steam is extracted from the head of the column 6 and includes the stripped 3 nitrosamines and other organic impurities, together i with a certain quantity of trifluralin. The flow 12 Scondensed at subatmospheric pressure and a temperature above 40 0 C in a condenser 14.

The flow of condensate is then subjected to phase separation in a Florentine flask 16 so that the organic phase can be separated from the aqueous phase by decantation.

The organic phase is preferably recycled, at least in part, in a flow 18 to the head of the contact column.

In this case, it is preferable to supply a flow 20 of organic solvent, preferably methyl ethyl ketone, into the flow of condensate before the phase separation to encourage the nitrosamines to pass from the organic phase into the aqueous phase. Naturally, it is not necessary to provide the flow 20 when the trifluralin is supplied to the column 6 in solution in an organic solvent.

So oo Alternatively, the organic phase can be disposed of by combustion, or subjected to solvent extraction with 0 °0 solvents such as methylene chloride to extract the o 00 nitrosamines. The solvent, including the nitrosamines, is then evaporated or burnt and the refined product may °o optionally be recycled to the contact apparatus.

0 0 0 A flow 22 is also withdrawn from the Florentine flask 16 and consists of the aqueous phase, rich in nitrosamines and possibly including the organic solvent supplied at 20. The flow 22 can be subjected to a biological treatment to degrade its nitrosamine content, or it can be sent to an activated-carbon adsorption column.

I

i 4 A flow 24 of purified trifluralin is extracted from the foot of the contact column Typically, the purified trifluralin has an active' principal content of more than 98% by weight for a supply having a 95-96% content as specified above. The examples which follow give data illustrative of the nitrosamine content found in the flow of purified trifluralin extracted from the contact column and of the recrudescence of the nitrosamines.

The analyses for determining the nitrosamine contents were carried out in all cases with a mass spectrograph on eluates resulting 2rom their chromatographic separation and subsequent concentration in Kuderna-Danish apparatus.

Example 1 Laboratory apparatus consisting of a glass column, 62mm in diameter and 1m high, filled with 6mm x 6mm Raschig rings was used. The column was provided with a therinostatic system for maintaining an internal o° temperature of approximately 80°C with a pressure of 200mm Hg at the head of the column. The tests were S0 oo carried out without recycling of the organic phase separated by condensation of the gaseous flow extracted from the head of the column.

o 0 0 0 0 A flow of 1.25 kg/h of crude trifluralin with a nitroso-di-n-propylamine (NDPA) content of 127 ppm was supplied to the head of the column. A flow of 4.5 kg/h of superheated steam was supplied to the foot of the column. The trifluralin flow extracted from the foot of the column had an NDPA Content of 0.21 ppm.

5 Example 2 A glass column 62mm in diameter and 1 meter high provided with 23 perforated plates and a thermostatic system was used. The tests were also carried out in this case without recycling of the organic phase separated from the gaseous flow. A flow of 2.7 kg/h of crude trifluralin with an NDPA content of 127 ppm was supplied to the head of the column. A flow of 4.65 kg/h of superheated steam was supplied to the foot of the column. The temperatura of the column was approximately 85 C with a pressure at the head of 230mm Hg.

The trifluralin flow collected from the foot of the column had an NDPA content of 0.08ppm.

Example 3 A pilot plant of the type described with reference to the appended drawing was used. A column with a 2 0. transverse surface area of 0.0475 m provided with perforated plates was used. A flow of 25 kg/h of crude O oo trifluralin with a pure trifluralin content of 97.15% and an NDPA content of 60 ppm was supplied to the head of the column. A flow of 40 kg/h of superheated steam was supplied to the foot of the column.

o o0 The tests were carried out without recycling of the organic phase.

The temperature of the column was 85°C and the pressure at the head was 110 mm Sg.

The trifluralin collected from the foot of the column had a pure trifluralin content of 98.1% and an NDPA content of less than 0.02 ppm.

L _N_ 6 Example 4 The column of Example 3 was supplied at the head with kg/h of crude trifluralin having a pure trifluralin content of 97.15% and an NDPA content of 60 ppm, and at the foot with 40 kg/h of superheated steam.

The temperature of the column was 100 C and the pressure at the head was 110 mm. Hg.

The trifluralin collected from the foot of the column had a pure trifluralin content of 98.7% and an NDPA content of less than 0.05 ppm.

o 00 0 0 0 0 0 o Example 0 0 o A flow of 50 kg/h of crude trifluralin with an NDPA 0 o 0 a 0 .a content of 24 ppm was supplied to the head of the 0 o.o column described with reference to Example 3, and a flow of 40 kg/h of superheated steam was supplied to j the foot.

0 0 0oo°° The temperature of the column was 110 C and the o pressure at the head was 110mm Hg.

0 00 The head vapours were condensed and the organic phase oo separated from the condensed water was recycled to the 0 oo head of the column.

After the test had been running for 60 hours, a sample of trifluralin taken from the foot of the column had an NDPA content of less than 0.05 ppm.

In order to determine the stability of the trifluralin purified by means of the method according to the o 0 0 I oo o 0 o o o O 0 0 o oo 0 000 -7 invention against recrudescence of nitrosamines, tests consisting of the heating of- the purified trifluralin to a temperature of approximately 90°C were carried out. It is, in fact, known that such heat treatment, to which the trifluralin is subjected during the formulation of herbicidal compositions, can result in a substantial increase in its nitrosamine content.

Example 6 In order to carry out the above determination, a sample of trifluralin, purified as described in Example 3, that is, having a nitrosamine content of less than 0.02 ppm, was put in a glass flask and kept for 24 hours at o 90 C. Analysis carried out after 24 hours showed an NDPA content which was still less than 0.02 ppm.

Example 7 The test of example 6 was repeated with the introduction of a test strip of metal sheet into the glass flask. Ct is, in fact, known that an increase in the nitrosamine c:ontent is favoured by heating in the presence of iron. The NDPA content analysed after 24 hours at 90 0 C was 0.1 ppm., denoting that although a slight formation of nitrosamines had occured, it was not, however, sufficient to prejudice the purity of the trifluralin.

Example 8 The test of Example 7 was repeated with the use of trifluralin purified by the method described in Example 2, with an NDPA content of 0.08 ppm, the trifluralin being kept for approximately 150 hours at 110°C in 0 0 o 6 o 0 0 0 O 00 0 0 0 000 0 000o 8 contact with an iron test strip.

The analysis carried out gave an NDPA content of 0.2 ppm.

o O 0o o0o 00 o o a 0 00 00 0-0

Claims

1. A method for the purification of trifluralin by the reduction of its nitrosamine content, including the operation of bringing a liquid flow of trifluralin at a temperature of from 70 C to 120 C into contact with a counterflow of saturated or superheated steam in a liquid-gas contact apparatus and recovering the purified trifluralin leaving the contact apparatus.

2. A method as claimed in Claim 1, in which the contact apparatus is arranged vertically with the trifluralin being fed in at the head and the steam being fed in at the foot; a gaseous flow is extracted from the head of the contact apparatus including steam, 0 trifluralin and organic impurities which is condensed o at a temperature higher than 40°C and subjected to .0o separation of the aqueous phase from the organic phase, and in which the organic phase is at least partly recycled to the head of the contact apparatus. o 0 o o 3. A method as claimed in Claim 1, in which the liquid flow of trifluralin consists of fused trifluralin. o 0 0

4. A method as claimed in Claim 1, in which the liquid flow of trifluralin consists of trifluralin dissolved in an organic solvent. f 000 A method as claimed in Claim 2 or Claim 3, in which a flow of organic solvent with a 'ow boiling point is supplied to the flow of condensate before the phase separation.

6. A method as claimed in Claim 5, in which the organic solvent is methyl ethyl ketone.

7. A method as claimed in any one of Claims 1 to 6 in which the ratio between the mass flow rates of the flow of steam and the flow of trifluralin supplied to the contact apparatus is from 0.3 to 1.

8. A method, as claimed in claim 1, substantially as hereinbefore described with reference to any one of the examples. DATED: 21 December, 1989 PHILLIPS ORMONDE FITZPATRICK Attorneys for: I.Pi.Ci. S.p.A. 2 eg^ a*C 1 t L 0 OO 0 00 0 0 0 000 0 00 0 0 0 0000 0 00 0 0 00 0 0 0 000 0 00 0 00 00 0 0 00 00 0 0 0 WDP 3028N 7)T