Improvements in the Manufacture of Acetic Acid.
Year: 1897

page_text: Date of Application, 25th May, 1897
Improvements in the Manufacture of Acetic Acid.
I, ERNEST GEORGE SCOTT, of 67, Lord Street, Liverpool, in the County of
Lancaster, Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to the manufacture of acetic acid. Hitherto it has been
the practice to distil wood destructively to obtain crude acetic acid (wood acid)
then to neutralize this acid with lime thereby forming a solution of acetate of lime,
then to evaporate this solution to dryness, giving impure acetate of lime which
evaporation is a costly operation and then to distil this acetate mixed with hydro-
chloric acid to obtain commercial acetic acid.
The object of my invention is to simplify the manufacture by avoiding the use
of lime, the evaporation and the admixture of mineral acid, all of which have for:
their object the removal of the tar and the strengthening of the acid by removal
of water.
According to my invention I put the crude acid (containing about 10% acetic
acid) into a still, heated by steam coils, and heat it to about 100 C. in a vacuum.
The effect of this moderate heat, is that the acid and water distil the tar, at the
low temperature, remaining behind.
I effect the strengthening of the acid by the removal of the water as follows:-
The mixed vapours of acid and water coming over from the still enter a vessel con-
taining a coil, in which vessel a portion of the vapours is condensed either by
radiation from the vessel or by cold water run through the coil. Or if radiation
produces too much cooling steam may be put through the coil to retard condensa-
tion. The vapours uncondensed in the first vessel enter a second vessel where
a further condensation takes place and so on, the vapours passing through a series
of vessels. The last vessel is kept cold so that everything not previously condensed
condenses there before reaching the vacuum pump. The vapour passing from
one vessel to another bubbles through the liquid of condensation the effect of
which bubbling is that more acid is condensed than steam and so the first vessel
gets strong with acid and the second weaker and so on until the last one which
contains practically only water. When the liquid in the first vessel is strong
enough; (say 25%), for use, it is removed and the contents of the second vessel are
put into the first and so on.
If greater strength and purity are required, the operation is repeated.

page_text: I, ERNEST GEORGE SCOTT, of 67, Lord Street, Liverpool, in the County of
Lancaster, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement:-
This invention relates to the manufacture of acetic acid. Hitherto it has been
the practice to distil wood destructively to obtain crude acetic acid (wood acid)
then to neutralize this acid with lime thereby forming a solution of acetate of lime,
then to evaporate this solution to dryness, giving impure acetate of lime (which
evaporation is a costly operation) and then to distil this acetate mixed with hydro-
chloric acid to obtain commercial acetic acid.
The object of my invention is to simplify the manufacture by avoiding the use
of lime, the evaporation and the admixture of minéral acid, all of which have for
their object the removal of the tar and the strengthening of the acid by removal
of water.
According to my invention I put the crude acid into a steam heated still and
heat it to about 100° C. in a vacuum. The effect of this moderate heat, is that
the acid and water distil, the tar, at the low temperature used, remaining behind.
I effect the strengthening of the acid by the removal of the water as follows:-
The mixed vapours of acid and water coming over from the still enter a vessel con-
taining a coil, in which vessel a portion of the vapours is condensed either by
radiation from the vessel or by cold water run through the coil. Or, if radiation
produces too much cooling, steam may be put through the coil to retard condensa-
tion. The vapours uncondensed in the first vessel enter a second vessel where
a further condensation takes place and so on, the vapours passing through a series
of vessels. The last vessel is kept cold so that everything not previously condensed
condenses there before reaching the vacuum pump.
The vapour passing from one vessel to another bubbles through the liquid of con-
densation, the effect of which bubbling is that more acid is condensed than steam and
so the first vessel gets strong with acid whilst the second is slightly weaker and so on
until the last one which contains practically only water. When the liquid in
the first vessel is strong enough for use, it is removed and the contents of the
second vessel are put into the first and so on.
When desired, instead of keeping the last vessel cold, the weak acid and steam
are allowed to go into another vessel (termed the neutralizer) where they enter
through a perforated pipe a hot strong solution of carbonate of soda or caustic
soda or other alkali. The effect of this is that the acetic acid combines with the
alkali forming acetate of soda or potash etc., and the steam. passes on alone to be
condensed and withdrawn by the vacuum pump. Moreover the chemical heat of
combination between the acid and alkali induces more evaporation and so there
is very little water to be removed from the acetate before crystallization.
If desired the whole of the acetic acid may be converted into acetate in this
way, this being a most economical way of converting acetic acid into acetates.
A suitable arrangement of apparatus for carrying out my invention is shewn
in elevation in the accompanying drawing in which a indicates the still which is
advantageously provided with a jacket through which steam is passed and which
has within it a steam heating coil b, c¹, c².
c10 indicate a series
of condensers of which in the drawing I have only shewn three but of which any
desirable number for instance, say 10, may be used, each of the said condensers

page_text: having arranged in conjunction with it a pipe'd through which the vapour enters
the condenser, the said pipe d passing nearly to the bottom of the said condenser
and being connected with the top of the preceding vessel, the pipe d of the first.
condenser c¹ of the series being connected with the top of the still.
Each of the condensers c¹, c
clo is also provided with an internal
coil e through which steam or a cooling medium such as water may be passed as
required. The top of the last condenser 10 of the series is connected by a pipe f
to the neutralizing vessel g connected with which by a pipe h is a jet condenser i;
is a pump for maintaining a vacuum throughout the apparatus.
In using this apparatus the wood acid is put into the still a and a vacuum is
produced throughout the whole plant by the pump j. Steam is then turned on
through the coil b, and, if necessary, through the jacket (if used), to cause the acid
and water contained in the still to vaporize at a low temperature so that very
little tarry matter is carried over. The mixture of acid and steam produced in
the still a passes through the pipe d into the first condenser c¹ which contains at
the bottom a small quantity of weak acid (into which the pipe d dips) as also do
all the cther condensers of the series. The steam and acid entering the condenser c¹
bubble through the acid in the bottom thereof so that a proportion of the steam
and acid is condensed, this proportion being capable of regulation by more or
less heating or cooling the contents of the condenser by passing a heating or cooling
medium through the coil e. The uncondensed vapours pass on through the next
condenser of the series and so on from condenser to condenser until they reach the
condenser c¹0. From the top of the last condenser, the vapour passes through the
pipe to the bottom of the neutralizer g which contains a solution of alkali or
alkaline carbonate. As the vapour enters this neutralizer, the acid combines with
the alkali whilst the steam passes on through the pipe h to the jet condenser i
where it is finally condensed.
When the acid in the charge originally placed in the still a is vapourised the
contents of the condenser or condensers nearest the still if sufficiently strengthened,
are removed and the contents of the other condensers are allowed to flow
successively into the condensers nearest the still and so on, connecting pipes k¹, k
being arranged between the various condensers to allow the liquid to flow from one
to the ether. If after one charge of the still a is finished, the contents of the
condenser are not sufficiently strong, they may be subjected to the treatment
during the evaporation of a further charge in the still or until the desired strength
is attained.
It will thus be understood that a fractional condensation is constantly taking
place, the contents of the condenser nearest the still being the strongest and
gradually becoming weaker in the condensers more remote from the still."
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. In the manufacture of acetic acid the process consisting in subjecting the
crude acid to distillation in a vacuum, substantially as described.
2. In the manufacture of acetic acid the process consisting in subjecting the
vapours evolved in the still to fractional condensation in vacuo, in a series of con-
densers through which the acid is allowed to flow from time to time towards the
vessel nearest the still whereby it is gradually increased in strength, substantially
as described.
3. In apparatus for the manufacture of acetic acid wherein the vapour from a
still is subjected to fractional condensation, the combination of a series of con-
densers connected together in series and each provided with an independent coil
whereby its contents may be heated or cooled, substantially as described.
4. The process of manufacturing acetic acid consisting in subjecting the crude
acid to vapourisation in a still and passing the vapour evolved through a series

page_text: of condensers in which fractional condensation takes place the vapour escaping
from the last condenser of the series being neutralized with an alkali or alkaline
carbonate, substantially as described.
Dated the 23rd day of Fahmuam 1000
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.