Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITION COMPRISING CHOLINE HYDROXIDE AND PROCESS FOR
PREPARING THE SAME
The present invention relates to a composition comprising choline hydroxide, a
stabilizer, and a solvent, to a process to prepare the composition, and to the
use thereof.
Choline hydroxide, also known as choline base or (2-hydroxyethyl) trimethyl-
ammonium hydroxide, is a well-known organic base suitable for many uses.
However, compositions of choline hydroxide, especially in water, are subject
to
a gradual decomposition process. The main reason for this decomposition is
thought to be the tendency of choline base to attack itself, as a result of
which
the products of this decomposition are reacted further. The underlying
chemistry
of this degradation is quite complex and not fully understood yet, but it
results in
choline base solutions turning brown to black during longer storage and
developing precipitates.
To avoid this decomposititin it is known to add a stabilizer to aqueous
compositions of choline hydroxide, which allows longer storage of the choline
base solution as a clear solution.
US 4,294,911 discloses the addition of a stabilizing concentration of a
sulfite to
an aqueous choline hydroxide composition. Sulfite is normally added as the
inexpensive and readily available sodium sulfite salt. A disadvantage of using
sodium sulfite is that concentrated choline base solutions still darken in a
relatively short period of time, which is believed to be due to a low
solubility of
the sodium sulfite in concentrated choline base solutions. For example, in a
45
wt% aqueous choline base solution less than 0.5 wt% sodium sulfite is soluble.
More soluble sulfites exist, but these are much more expensive and/or not
readily available.
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US 4,686,002 discloses the addition of a stabilizing concentration of
formaldehyde to an aqueous choline hydroxide composition. Formaldehydes
are banned from many applications due to environmental issues.
The object of the present invention is to provide a stabilized composition of
choline hydroxide free of the above drawbacks.
This object is achieved by providing a composition comprising choline
hydroxide, a solvent, and one or more stabilizers selected from the group
consisting of a hydride and choline sulfite.
The stabilizer used in the composition of the present invention causes the
composition to retain its white colour for a longer period of time compared to
sodium sulfite. The stabilizers of the present invention further have the
advantage that they generally introduce less salt into the composition; a
lower
amount of the hydride is generally required to prevent darkening of the
composition as compared to conventional compositions comprising sodium
sulfite salt, and choline sulfite does not introduce any salt into the
composition.
;1- - ,Wl
It should be noted that in US 6,065,424 an aqueous composition comprising a
choline hydroxide or a borohydride salt is discussed. However, this
publication
does not disclose compositions of a choline hydroxide and a borohydride salt.
Neither does this publication relate to stabilizing choline hydroxide
solutions, or
even acknowledge the fact that borohydride salts can stabilize choline
hydroxide.
In a preferred embodiment of the composition according to the present
invention, the solvent is water or an alcohol, more preferred is water or
methanol, most preferred is water. However, also a mixture of these solvents
can be used.
In a further preferred embodiment the invention relates to a composition
comprising choline hydroxide and a borohydride compound wherein the amount
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of borohydride compound is smaller than the amount of choline hydroxide on a
weight basis.
In another preferred embodiment the composition according to the invention
comprises 10 to 60 wt% choline hydroxide, based on the total weight of the
composition. In a more preferred embodiment the composition comprises 20 to
55 wt% choline hydroxide, based on the total weight of the composition, and in
a most preferred embodiment it comprises 30 to 50 wt%.
In yet another preferred embodiment the composition according to the invention
comprises a hydride as stabilizer in an amount of 1 ppm to 1,000 ppm,
preferably 10 ppm to 500 ppm, and most preferably 50 ppm to 200 ppm.
If the stabilizer is choline sulfite, the composition according to the
invention
comprises 0.1 to 19 wt%, based on the total weight of the composition,
preferably 0.2 to 5 wt%, and most preferably 0.5 to 1 wt% of choline sulfite.
Compositions comprising these amounts of stabilizer reveal a higher colour
stability than conventional choline base compositions containing sodium
sulfite
as stabilizer.
The present invention further pertains to a masterbatch comprising 10 to 60
wt% of choline hydroxide, 5 to 20 wt% of one or more stabilizers selected from
the group consisting of a hydride and choline sulfite, with the remaining part
being solvent, based on the total weight of choline hydroxide, stabilizer, and
solvent. Such a masterbatch, which typically comprises a large quantity of
stabilizer, can be added to a choline hydroxide solution in the desired amount
in
order to stabilize the solution. Such masterbatches preferably comprise 8 to
15
wt% of stabilizer and most preferably between 10 and 12 wt%, based on the
total weight of the masterbatch.
The stabilizer of the present invention is selected from the group consisting
of
hydrides and choline sulfite. The hydride generally is a strong reducing agent
and can be any hydride known to the man skilled in the art. Suitable examples
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of hydrides are lithium hydrides, aluminium hydrides, and borohydrides. The
preferred hydrides are borohydrides. In this application the term
"borohydride"
refers to any compound, or mixture of compounds, comprising a molecule of
boron and hydrogen, also known as hydroborons, with the formula B,Hy, x and y
being integers >0, such as B2H6 (boroethane), B4Hjo (borobutane), B5H9, and
B10H14 (borodecane), and anions derived therefrom such as BH4. Gaseous
borohydrides are less preferred, as they are difficult to handle and may
impose
safety risks. Preferred borohydrides comprise one or more anions derived from
borohydride. The preferred borohydride is a BH4 salt and particularly
preferred
are alkali metal borohydride salts. A preferred alkali metal borohydride salt
because of its commercial availability and the fact that it is relatively safe
to
make, handle, and use is sodium borohydride (NaBH4).
In an alternative preferred embodiment according to the invention, the
composition comprises a hydride, and in particular a borohydride compound,
which is fixed to a polymer carrier. The use of such a (boro)hydride compound
has the advantage that the (boro)hydride stabilizer may be easily removed from
the choline base solution when desired., for example when the choline base
solution is used in an application where the (boro)hydride or the inorganic
counterion has a detrimental effect.
In another preferred embodiment the composition comprises one or more
additional stabilizing compounds. Suitable examples of such stabilizing
compounds include sulfites, formaldehyde, hydroxylamines, derivatives and
mixtures thereof. Preferably, the second stabilizing compound is a sulfite or
a
sulfite derivative. Sulfite derivatives include for example dithionites. In a
more
preferred embodiment the sulfite is sodium sulfite. In another more preferred
embodiment two or more additional stabilizing compounds are used.
Advantages of the stabilizer, and in particular of the borohydrides, are their
reducing power and their compatibility with the choline base production
process.
Because of their reducing power the choline base solution is clear and paper
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white. The hydrides, and in particular the borohydride compounds, can even be
added to a choline base mixture that is already yellowed and still provide a
clear
and white solution.
5 Another advantage of the stabilizers of the invention is that they are
stable
under strongly alkaline conditions. This means that the concentration of the
stabilizer in choline base can be increased to amounts sufficiently high to
combine the desired properties of both choline hydroxide and stabilizer. This
is
particularly advantageous when borohydrides are used as stabilizer.
The process further pertains to a process for preparing the composition
according to any one of claims 1-5 by combining one or more stabilizers
selected from the group consisting of a hydride and choline sulfite with a
choline
hydroxide solution.
The fact that the stabilizer of the invention is compatible with the
production
process of choline base makes it possible to add the stabilizer to the
starting
materials and/or the a;rreaction mixture in the process of producing choline
hydroxide.
Therefore, the current invention also relates to a process for preparing the
composition of the invention comprising the steps of reacting ethylene oxide
with trimethylamine in the presence of one or more stabilizers selected from
the
group consisting of a hydride and choline sulfite, said stabilizer being added
to
the ethylene oxide, the trimethyl amine and/or the reaction mixture. This
process for preparing choline base is generally carried out by reacting
ethylene
oxide with trimethyl amine in an inert atmosphere at a temperature of 0 to 70
C.
If choline sulfite is used as the stabilizer, it is also envisaged to prepare
the
choline sulfite in situ by subjecting the choline hydroxide solution produced
by
reacting ethylene oxide and trimethyl amine to sulfur dioxide. The resulting
amount of choline sulfite in the chlorine hydroxide solution will depend on
the
period of time the choline hydroxide solution is subjected to the sulfur
dioxide.
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By subjecting the chlorine hydroxide solution to sulfur dioxide for a certain
period of time, the resulting amount of choline sulfite can be set as desired.
In a preferred embodiment of the process to prepare choline base the
stabilizer,
in particular a borohydride, is used in an amount such that 1-1,000 ppm,
preferably 10-500 ppm, more preferably 50-200 ppm of borohydride is present
on the total weight of the final product solution.
In the event that one wishes to prepare a masterbatch according to the
invention with the above processes, the stabilizer is used in an amount such
that 5 to 20 wt%, preferably 8-15 wt%, and most preferably 10-12 wt% is
present on the total weight of the final product solution.
In an alternative preferred embodiment of the process the choline base is
prepared at a temperature between 10 and 50 C and an inert atmosphere is
created by flushing the reactor and the solution with an inert gas, while a
safety
pressure of the inert gas - normally nitrogen - is maintained during the
reaction
step. In a more preferred embodiment of the process the-temperature is
between 15 and 45 C, most preferred is a temperature of about room
temperature.
The compositions according to the present invention are suitable for many
applications. As already indicated above, as the amount of stabilizer in a
choline
base can be relatively high, the compositions can also be used in applications
where the stabilizer is active as well. In this respect, the stabilizers of
the
invention, and in particular borohydride, are particularly suitable for use in
the
production and bleaching of paper.
Accordingly, a method to bleach paper pulp is also covered by the present
application. In this method paper pulp is contacted with the compositions
according to the present invention.
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Aqueous compositions comprising a borohydride salt are known for bleaching
paper and are disclosed, e.g., in WO 88/10334. However, aqueous
compositions comprising choline hydroxide and a borohydride salt for bleaching
paper are not disclosed for this use. Besides, borohydride solutions known to
be
used in applications where borohydride is active often are solutions of
borohydride in caustic, which often makes them less suitable for applications
that are not compatible with a caustic solution, such as the production of
paper.
The present invention will now be further illustrated by the following
examples:
Preparation Example A
A solution of choline base in water is prepared in a 1-litre pressure
autoclave by
reacting 116 g of ethylene oxide with a solution of 150 g of trimethylamine in
417 g of water. By using a cooling jacket the temperature during the reaction
is
kept between 15 and 45 C. Before starting the reactor is flushed with nitrogen
and a safety pressure of 2-3 bar nitrogen is maintained during the
ethoxylation
step..,
The resulting solution of 45 wt% of choline base in water is used in Examples
1
- 3 below.
Preparation Example B
A solution of choline suifite is prepared by adding gaseous sulfur dioxide in
a
stoichiometric amount to the 45 wt% aqueous choline base solution of Prep.
Example A. The resulting 53 wt% solution of choline sulfite is used in
Examples
1, 2, 5, and 6 below.
Preparation Example C
A solution of sodium borohydride in choline base is prepared by adding solid
sodium borohydride to a 45 wt% aqueous choline base solution of Prep.
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Example A until a concentration of 12 wt% borohydride is reached. The
resulting aqueous composition is used in Preparation Example D below.
Preparation Example D
A solution of choline base in water is made in a 1-litre pressure autoclave by
reacting 116 g ethylene oxide and 150 g of trimethylamine in 417 g of water.
By
using a cooling jacket the temperature during the reaction is kept between 15
and 45 C. Before starting the reactor is flushed with nitrogen and a safety
pressure of 2-3 bar of nitrogen is maintained during the ethoxylation step.
Before starting the reaction 0.85g of the borohydride solution described in
Example C is added. The resulting aqueous composition is used in Examples 4
and 5 below.
Comparative Example 1
Two samples of 110 g of the choline base solution of Prep. Example A were
drawn into 100 ml sample bottles under flushing with n,itrogen. Choline
sulfite
solution of preparation example B was added till the total concentration of
choline sulfite in the sample was 0.2 wt%. The sample bottles were closed and
stored under ambient conditions. After 4 months the solutions were slightly
yellow but still clear (i.e. free of precipitates).
Comparative Example 2
Two samples of 110 g of the choline base solution of Prep. Example A were
drawn into 100 mi sample bottles under flushing with nitrogen. Choline sulfite
solution of preparation Example B was added till the total concentration of
choline sulfite in the sample was 0.4 wt%. The sample bottles were closed and
stored under ambient conditions. After 4 months the solutions were slightly
yellow but still clear.
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Comparative Example 3
Two samples of 110 g of the choline base solution of Prep. Example A were
drawn into 100 mi sample botties under flushing with nitrogen.
Paraformaldehyde was added till the total concentration of paraformaldehyde in
the sample was 0.4 wt%. The sample botties were closed and stored under
ambient conditions. After 4 months the solutions were darkened and a layer of
brown precipitates had formed on the bottom of the sample botties
Example 4
Two samples of 110 g of the choline base solution of Prep. Example D were
drawn into 100 ml sample bottles under flushing with nitrogen. The sample
bottles were closed and stored under ambient conditions. After 4 months the
solutions were still clear and paper white.
Example 5
Two samples of 110 g of the choline base solution of Prep. Example D were
drawn into 100 mi sample bottles under flushing with nitrogen. Choline sulfite
solution of preparation Example B was added till the total concentration of
choline sulfite in both samples was 0.4 wt%. The sample bottles were closed
and stored under ambient conditions. After 4 months the solutions were still
clear and paper white.
Example 6
Two samples of 110 g of the choline base solution of Prep. Example D were
drawn into 100 ml sample bottles under flushing with nitrogen. Choline sulfite
solution of preparation Example B was added till the total concentration of
choline sulfite in both samples was 2.6 wt%. The sample bottles were closed
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and stored under ambient conditions. After 4 months the solutions were still
clear and paper white.
Example 7
5
Two samples of 110 g of the choline base solution of Prep. Example D were
drawn into 100 mi sample bottles under flushing with nitrogen. Sodium sulfite
was added till the total concentration of sodium sulfite in both samples was
0.5
wt%. The sample bottles were closed and stored under ambient conditions.
10 After 4 months the solutions were still clear and paper white, but a white
layer of
unsolved sodium sulfite had formed on the bottom of the sample bottle.
