FRACTIONNEMENT D'UN MELANGE AZEOTROPE PAR DISTILLATION DANS UNE COLONNE, SELON UNE METHODE SEMBLABLE A LA DISTILLATION EXTRACTIVE

SEPARATION OF AN AZEOTROPIC MIXTURE BY DISTILLATION IN A DISTILLATION COLUMN BY A PROCEDURE SIMILAR TO EXTRACTIVE DISTILLATION

Abrégé anglais

Abstract of the Disclosure: A mixture which is azeo-
tropic or which behaves almost azeotropically and is
difficult to separate by distillation, is separated into
two pure or substantially pure fractions by distillation,
by adding a further component, using a procedure which is
similar to extractive distillation and is carried out in a
distillation column, a section of which is divided into a
feed part and a take off part by means of a separating
unit which is effective in the longitudinal direction and
completely or partially prevents cross-mixing of liquid
streams and/or vapor streams. In this process, the azeo-
tropic mixture is fed as bleed streams to the feed part
and to the take off part, in each case at or near the top,
and one of the two pure or substantially pure fractions is
removed as a top product from the distillation column
while the other is removed as a side product from the take
off part.

Revendications

The embodiments of the invention in which an ex-
clusive property or privilege is claimed are defined as follows:
1. A process for separating by distillation a
mixture which is azeotropic or behaves almost azeotropically
and is difficult to separate by distillation into two pure
or substantially pure fractions, wherein:
a) use is made of a single distilation column
having a section divided into a feed part and a take off
part by means of a separating unit which is effective in the
longitudinal direction and prevents cross-mixing of liquid
stream, vapor stream or both of them;
b) a further component in which one of the two
fractions to be separated is readily soluble, is added as
an extraction agent into the mixture;
c) the mixture to be separated is fed as a bleed
stream to the feed part of the distillation column, at or
near the top of said feed part;
d) the fraction readily soluble in the further
component added to the mixture is removed as a side product
from the take-off part of the column, and
e) the other fraction sparingly soluble in the
further component is removed as a top product from the
column.
2. The process of claim 1, wherein:
- the column has an undivided section located
above the divided section;
- the take-off part of the divided section of the
column has its top sealed off tightly from the undivided
upper sections; and
- the top of said take-off part is equipped with
a condenser for partial or total condensation of the readily
soluble fraction of the mixture, which is removed from said
take-off part.

3. The process of claim 2, wherein:
- the further component used as an extraction
agent is removed from the bottom of the column up and
recycled up to the undivided upper section of said column.
4. The process of claim 1, wherein the mixture to
be separated is also fed as a bleed stream to the take-
off part of the distillation column, at or near the top of
said take-off part.
5. The process of claim 4, wherein:
- the column has an undivided section located
above the divided section;
- the take-off part of the divided section of the
column has its top designed to allow the vapors to pass
therethrough but to prevent the liquids from doing so; and
- the mixture fed as a bleed stream at or near the
top of said take-off part is introduced in an amount corres-
ponding to the amount of liquid required for mass transfer
within said take-off part.
6. The process of claim 5, wherein:
- the mixture fed as a bleed stream at or near
the top of the take-off of the column is in liquid form and at a
very low temperature.
7. The process of claim 6, wherein:
- the further component used as an extraction agent
is removed from the bottom of the column up and recycled up
to the undivided upper section of said column.

Description

;n a d;stillation column by a Droeedure sim;Lar
to extrartive distillation
~.
The present inven~ion rel3tes to a process for
separating a mixture which is azeotrop;c or behaves
almost azeotrop;cally and ;s d;ff;cult to separate
~~ by d;stillat;on~ into two pure or substant;a~ly pure
fractions by dist;llation, by adding a further compo-
nent, using a procedure wh;ch is similar to extract;ve
d;stillation and is carr;ed out in a d;st;llation column,
a section of wh;ch is divided into a feed part and a take
o~f part by means of a separating unit ~h;ch is effective
in the longitudinal direction and completely or partially
prevents cross-m;x;ng of liquid streams and/or vapor
streams.
It is known that a two-component azeotropic
mixture can be separated into its individual components
by means of various distillation methodc~ These are
essentiaLly t~o~pressure distillation9 azeotropic dis-
ZO tillation and extractive d;st;llation~ These three dis-
tillation rnethods are descr;bed in detail by R. 8illet
in Distillation Industrielle, 1972, pages 223-231.
All three distillation methods have the disad-
vantage that two or more distiLlat;on columns are re-
quired for separating the two-component azeotrop;c mix-
ture, enta;l;ng high costs in terms of apparatus and ;n-
strumentation.
It is an object of the present invention to sim-
plify the separation by distillat;on of two-component azeo-
tropic mixtures ;e. to carry out the procedure in a single-
stage d;st;llation process us;ng one distillation columnN
It has been found that this object is achieved, in
accordance with the invention, if the azeotropic mixture
is fed as bleed streams to the feed part and to the take
off part, in each case at or near the top, and one of
the two pure or substantially pure fractions is removed
as a top product from the distillation column while the
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-- 2
other is removed as a side product from the take off part.
More particularly, the present invention proposes
a process for separating by distillation a mixture which is
a~eotropic or behaves almost azeotropically and is difficult
to separate by distillation into two pure or substantially
pure fractions, wherein:
a) use is made of a single distilation column
having a section divided into a feed part and a take off
part by means of a separating unit which is effective in the
longitudinal direction and prevents cross-mixing of liquid
stream, vapor stream or both of them;
b) a further component in which one of the two
fractions to be separated is readily soluble, is added as
an extraction agent into the mixture;
c) the mixture to be separated is fed as a bleed
stream to the feed part of the distillation column, at or
near the top of said feed part;
d) the fraction readily soluble in the further
component added to the mixture is removed as a side product
from the take-off part of the column, and
e) the other fraction sparingly soluble in the
further component is removed as a top product from the
column.
In accordance with a first ~referred embodiment of
the invention:
- the column has an undivided section located
above the divided section;
- the take-off part of the divided section of the
column has its top sealed off tightly from the undivided
upper sections; and
- the top of said take-off part is equipped with
a condenser for partial or total condensation of the readily
soluble fraction of the mixture, which is removed from said
take-off part.
In accordance with another preferred embodiment of

L7
- 2a -
the invention, the mixture to be separated is also fed as a
bleed stream to the take-off part of the distillation column,
at or near the top of said take-off part.
These two preferred embodiments of the invention
are illustrated in the accompanying drawing, and are described
in detail below.
Figure 1 shows a process flowchart for a distilla-
tion column in which the two-component azeotropic mixture
is fed as bleed streams to the feed part and to the take
oEf part, in each case at the top.
Figure 2 shows a process flowchart for a distilla-
tion column in which the two-component azeotropic mixture is
fed exclusively to the feed part.
In Figure 1, a distillation column 1 (referred to
below as column 1) is divided into a feed part 3 and a
take off part 4 by means of a separating unit 2 which is
effective in the longitudinal direction. The take off part
4 is closed at the upper end of the separatin~ unit 2 by
means of a liquid collector 5 of conventional construction,
so thatthe liquid flowing downward from the undivided upper
section 6 of column 1 is conducted completely into the feed
part 3 of the column, with the result that the further
component E ~extraction agent) cannot pass from the undivided
upper section 6 into the take off part 4. The two-component
azeotropic mixture A, B is fed as bleed streams to the top
of the feed part 3, which is open at the top, and the top
of the take off part 4, which allows the vapor to pass
through the top but prevents liquid from doing so. The
bleed stream is fed in at the top of the take off part 4
in an amount corresponding to the amount of liquid required
for mass transfer within the take off part 4. Because it
has this function, this feed is preferably introduced in
liquid form and at a very low temperature, in order to keep
,;
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- 2b _ ~ 2 ~ 71 7
the amount very small. Accordingly, in Figure 1, the two-
component azeotropic mixture A, B is fed as bleed streams
to the feed part and to the take off part, in each case
at or near the top, while that component, A, of the said
mixture which is sparingly soluble in the
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lZ227~L~
- 3 - OOZ. 0~50/36670
further component E is distilled off via the top of the
column in a conventional manner, and that component, B,
of the stated mixture which is readily soluble in the
further component E is removed from t~e take off part,
in the form of vapor or liquid. As in the conventional
extractive distillation, the further component E is fed
;nto the upper, und;vided section of the column, and is
removed as a bottom product, either in pure form or
containing small residual amounts of the read;ly soluble
component B, and, if required, is recycled to the
column.
In Figure 2, the top of the take off part 4 is
sealed off tightly from the undivided upper section 6.
Furthermore, the top of the take off part 4 is equipped
with a condenser 7 for partial or total condensation of
the readily soluble component ~ of the two-component
mixture, which is to be removed from the take off part
4. In this case, ~he take off part 4 corresponds to the
downstream rect;fication column in the convent;onal ex-
tractive distillation, for separatin~ the componentwh;ch is readily soluble in the further component from
this component ~extraction agent).
In contrast to s;mple distillations ln columns
divided lengthwise, in the novel procedure for extractive
d;st;llation the side fract;on removed from the take off
part passes from the feed part ;nto the take off part
only at the lower end of the long;tudinal partition.
Apart from the special case where the vapor rising ;n the
take off part undergoes total condensation at the upper
end of the longitudinal partit;on, ;t ;s even possible
for flow to take place in the oppos;te direct;on, ie.
some of the fract;on to be removed as a s;de str~am
passes, at the upper end of the long;tud;nal part;tion,
from the take off part back into the upper, common column
sect;on or ;nto the feed part.
The decisive advantage of the novel process is
that the separat;on of a two-component azPotrop;c mix-

17
4 ~ture ;nto ;ts ;nd;v;dual components can be carr;ed out
by means of one d;st;llat;on column.