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 decomposition 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. 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.

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 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 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 BxHy, x and y being integers >0, such as B2H6 (boroethane), B4H10 (borobutane), B5Hg, 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 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.

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 ..reaction 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 700C.

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. 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 5O0C 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. 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 450C. 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 sulfite 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. 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 15O g of trimethylamine in 417 g of water. By using a cooling jacket the temperature during the reaction is kept between 15 and 450C. 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 nitrogen. 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 ml 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. Comparative Example 3

Two samples of 110 g of the choline base solution of Prep. Example A were drawn into 100 ml sample bottles under flushing with nitrogen. Paraformaldehyde was added till the total concentration of paraformaldehyde in the sample was 0.4 wt%. The sample bottles 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 bottles

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 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 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 and stored under ambient conditions. After 4 months the solutions were still clear and paper white.

Example 7

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. 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. 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.