US2412650A

US2412650A - Process of separating j-picoline

Info

Publication number: US2412650A
Authority: US
Publication date: 1946-12-17
Anticipated expiration: 1963-12-17

Description

Patented cc. 1?, 1946 PROCESS OF SEPARATING 3-PICOLINE, 4-PICOLINE, AND 2,6-LUTIDINE George Riethof, Mount Lebanon. Pa.

No Drawing. Application June 15, 1945, Serial No. 599,766

7 Claims. 1

This invention relates to a separation process; and more particularly it relates to the separation of 3-picoline, -picoline, and 2,6-luticline from one another.

One of the principal sources of these three compounds, 3-picoline, 4-picoline, and 2,6-lutidine is the basic coal tar oils in which they commonly occur associated with one another. These basic coal tar oils may be practically fractionated to produce certain cuts composed predominately of a mixture of 3-picoline, -picoline and 2,6- lutidine. Hence, these materials are generally commercially obtained as a basic oil mixture boiling about 140-145" C. Since these compounds boil so closely together, it is not commercially feasible to fractionate such basic oil mixtures into their separate components.

In my co-pending application, Serial No. 535,397, filed May 12, 1944, now Patent 2,383,016, granted August 21, 1945, I have disclosed that such bases may be separated from each other and recovered by azeotropic distillation utilizing a maximum boiling azeotrope and the process is carried out by admixing a suitable quantity of phenol with the basic oils.

I have now discovered that formic acid may be employed to recover such bases by a process of azeotropic distillation utilizing a maximum boiling point azeotrope. The use of such acid has certain advantages over phenol.

The azeotrope formed with formic acid boils between 155 and 165 C. but by using these high temperatures, the formic acid decomposes rapidly and therefore is not useable. I have found that formic acid becomes useable if the distillation is carried out under a sufficiently reduced pressure, e. g., 100 mm. to 200 mm. of mercury to thereby lower the temperature of the maximum azeotrope so far, that none or very little decomposition of formic acid occurs. Moreover, and quite unexpectedly there is obtained a new result. That is, I find in all other maximum azeotropes such as those produced with phenol, acetic, propionic and isobutyric acids, the order of distilling over of the different picolines is first, 2-6 lutidine, 2nd, beta picoline and 3rd, gamma picoline. On the other hand, the formic acid azeotrope distills over in a different order namely, first beta-picoline, 2nd, gamma picoline, and 3rd, 2-6 lutidine. Thus, the lowest boiling maximum azeotrope in the case of the phenol and the allphatic acids becomes the highest boiling azeotrope by using formic acid. Since the most valuable component of the basic oils is the beta picoin that the beta picoline can be obtained substantlally pure and in a much simpler operation. There is no separation to be carried out before the beta picoline comes over, as the fractional distillation of the maximum azeotrope has only to separate the beta picoline from the gamma by an operation which in effect is similar to a first containing oils into their separate components which can be easily operated with close control so as to yield commercially pure products.

It is a still further object to provide a new separation process which employs the use or" maximum boiling azeoptropic mixtures.

Additional objects and the entire applicability of the present process will become more apparent from the description of the invention given hereinafter.

The objects are accomplished according to the process of my invention by admixing the indicated basic oils with a suitable quantity of formic acid and distilling from this mass the maximum boiling azeotropes of the basic components of the oil with the acid and separately collecting the various fractions,

The process of this invention is more fully illustrated in the following example, in which all parts are by weight unless otherwise specified.

Example A commercial mixture of 300 parts of a basic coal tar oil containing approximately 2,6.- lutidine, 3-picoline and 35% 4-picoline is charged into the still pot of a rather high eficiency fractionating column. To this basic oil is added 450 parts of formic acid concentration) a ratio of acid to basic oil of about 4 to 3. The acid/basic oil mixture is then subjected to fractional distillation through the column under a pressure of about 200 mm. of mercury and a temperature of about 110 to 125 C. or a pressure of about mm. of mercury and a temperature of about 98 to C. A forerun of approximately 100 cc. of the total mixture, mostly of aqueous formic acid, is collected after which the maximum boiling azeotropes of B-plcoline, s -picoline and 2.6-lutidine distill over and are collected in that order.

In order to obtain 3-picoline of even higher purity the first cut or 3-picoline/acid azeotrope is again fractionated through a similar column and a fraction of 80% to 90% is collected. This middle fraction is then treated with an excess of sodium hydroxide solution and the 3-picoline is distilled off.

The 2,6-lutidine and the 4-picoline fractions are treated in a similar fashion in order to obtain the substantially pure compounds.

The temperature range as given above as Well as the pressure ranges may of course be varied but pressures and temperatures are utilized of an order which is effective to prevent decomposition of the formic acid and assure that the fractions will distill over in the manner above described with the beta picoline constituting the first cut.

The ratio of formic acid to basic oils as illustrated in the above example may be varied but preferably more acid by weight is employed than the weight of the oil and it has been found best to employ an amount of the acid effective to form an azcotrope with all of the basic oil present, plus allowance for some decomposition of formic acid.

The composition of the basic oil being treated may be varied. However, this process is principally applicable to those basic oils which are composed predominately of 3-picoline, 4-picoline and 2,6-lutidine. The ratio by weight of these latter materials may be varied relative to one another.

Iclaim:

l. The process of separating a mixture predominately containing at least two of the bases B-picoline, -picoline, and 2,6-lutidine which comprises including in the mixture formic acid and fractionaiiy distilling the mass under reduced pressure.

2. The process-of claim 1 wherein the distillates are acid azeotropes of said bases.

3. The process of claim 1 wherein the distillate fractions boiling in the range between substantially 98-125 C. under a pressure of about 200 to 100 mm. of mercury are separately collected.

4. The process of claim 1 wherein the distillate fractions boiling in the range between substantially 98-125 C. under a pressure of about 200 to 100 mmv of mercury separately collected and redistilled.

5. The process of claim 1 wherein the distillate fractions boiling in the range between substantially 98-125" C. under a pressure of about 200 to 100 mm. of mercury are separately collected and redistilled and wherein the redistilled fractions are treated to recover the substantially pure base contained therein.

6. The process of separating a mixture containing at least two of the bases S-picoline, -plcoline and 2,6-lutidine which comprises including in the mixture formic acid, fractionally distilling the mass, and thereafter recovering from the fractions the substantially pure case contained therein, the fractional distillation being under reduced pressure and at a temperature effective to susbtantially prevent decomposition of the formic acid,

'7. The process of separating a mixture predominately containing at least two of the bases 3-picoline, l-picoline, and 2,6-lutidine which comprises including in the mixture formic acid and fractionally distilling the mass under re duced pressure, the fractions distilling over as 3-picoline, 4-picoline and 2,6-lutidine in the order named.

GEORGE RIETHOF'.