Using Novel Amines to Stabilize Quaternary Trialkylalkanolamines

Abstract

New stabilizers for solutions of choline hydroxide and related quaternary trialkylalkanolamines are disclosed. The stabilizers are alkyl hydroxylamines, hydrazines, hydrazides, or derivates thereof, including compounds containing more than one such functionality. The new stabilizers are effective at concentrations less than about 1000 ppm, and choline hydroxide solutions stabilized with the compounds described herein typically have Gardner Color change less than about 2.0 after six months at reasonable temperatures.

Claims

1. A composition comprising a quaternary trialkylalkanolamine in a water-containing solvent at a concentration between about 0.1 wt % and about 80 wt % with a stabilizer selected from the group consisting of an alkyl hydroxylamine, a hydrazide, a hydrazine, and a mixture thereof.

2. A composition comprising a quaternary trialkylalkanolamine and a stabilizer selected from the group consisting of an alkyl hydroxylamine, a hydrazide, a hydrazine, and a mixture thereof.

3. The composition of claim 2, wherein the quaternary trialkylalkanolamine is choline hydroxide.

4. The composition of claim 2, wherein the stabilizer is DEHA.

5. The composition of claim 2, wherein the stabilizer is carbodihydrazide.

6. The composition of claim 2, wherein the stabilizer is hydrazine.

7. The composition of claim 2, wherein a concentration of the stabilizer in the composition is not more than about 1 wt %.

8. The composition of claim 7, wherein the concentration of the stabilizer in the composition is not more than about 500 ppm.

9. The composition of claim 7, wherein the concentration of the stabilizer in the composition is not more than about 300 ppm.

10. The composition of claim 2, wherein the composition has a Gardner Color change less than about 2.0 after 6 months.

11. A method of stabilizing a quaternary trialkanolamine solution comprising: providing a liquid stabilizer comprising a dialkylhydroxylamine, a hydrazide, a hydrazine, or a derivative thereof; and blending the liquid stabilizer with the quaternary trialkanolamine solution to form a stabilized solution.

12. The method of claim 11, wherein the liquid stabilizer comprises DEHA.

13. The method of claim 11, wherein the liquid stabilizer comprises carbodihydrazide.

14. The method of claim 11, wherein the liquid stabilizer comprises hydrazine.

15. The method of claim 11, wherein the quaternary trialkylalkanolamine solution is formed from a reaction mixture comprising a trialkylamine and an alkylene oxide, and the liquid stabilizer is blended with the reaction mixture before forming the quaternary trialkylalkanolamine.

16. The method of claim 11, wherein the liquid stabilizer comprises more than one stabilizer from the group of a dialkylhydroxylamine, a hydrazide, a hydrazine, and derivatives thereof.

17. The method of claim 11, wherein the liquid stabilizer is DEHA.

18. The method of claim 11, wherein the liquid stabilizer is carbodihydrazide.

19. The method of claim 11, wherein the liquid stabilizer is hydrazine.

20. The method of claim 11, wherein the stabilizer is present in the stabilized solution at a concentration less than about 1000 ppm.

21. A method of forming a stabilized quaternary trialkylethanolamine solution, comprising blending a quaternary trialkylethanolamine solution with an aldehyde scavenger stabilizer in an amount such that the stabilized quaternary trialkylethanolamine solution has a concentration of the stabilizer that is less than about 1000 ppm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION

[0011] The inventors have discovered new ways to stabilize aqueous choline hydroxide solutions, and variants thereof, using nitrogen compounds. Choline hydroxide may be formed by reacting aqueous trimethylamine with ethylene oxide.

(CH.sub.3).sub.3N(aq)+C.sub.2H.sub.4O->[(CH.sub.3).sub.3NC.sub.2H.sub.4OH].sup.+[OH].sup.

Choline hydroxide is a quaternary ethanolamine compound, derivatives of which may be formed by using amine precursors other than trimethylamine. Use of alkylene oxides other than ethylene oxide may also yield variant quaternary trialkylalkanolamines. Exemplary variants that may be stabilized according to the methods and compositions herein include, but are not limited to, trimethylpropanolamine, triethylethanolamine, dimethylethylethanolamine, diethylmethylethanolamine, dimethylethylpropanolamine, diethylmethylpropanolamine, triethylpropanolamine. In general, a quaternary trialkylalkanolamine that may benefit from the methods and compositions described herein has the formula [R.sup.1R.sup.2R.sup.3NR.sup.4OH].sup.+[OH].sup., wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is each a lower alkyl group such as methyl, ethyl, or propyl. Choline hydroxide is a molecule according to the above formula where R.sup.1, R.sup.2, and R.sup.3 is each a methyl group and R.sup.4 is an ethyl group. For purposes of explanation, the following discussion describes methods and compositions for stabilizing choline hydroxide solutions, but such methods and compositions are also applicable to the foregoing variants and other related, but not named, variants.

[0012] Choline hydroxide solutions in water tend to develop color, and precipitate solids, over time. It is believed that choline hydroxide decomposes mainly into its constituents, trimethylamine and ethylene glycol, but that small amounts of acetaldehyde are also formed as the bonding electrons between carbon and nitrogen migrate along the axis of the carbon chain to form a carbon oxygen double bond rather than cross directly to the oxygen atom. It is believed that acetaldehyde imparts color to the solution over time, and may polymerize to varying degrees to form solids. Trimethylamine may also impart color to the solution over time.

[0013] Aldehyde scavenger compounds can be used to prevent the acetaldehyde from polymerizing and reduce coloration by reacting with the acetaldehyde to form a non-chromophore before the acetaldehyde can polymerize. In general, amine derivatives may react as nucleophiles with aldehydes to form imines, oximes, enamines, and the like. Hydroxylamines, in particular, react with aldehydes to form oximes. Hydrazine and derivatives thereof may similarly react with aldehydes to form hydrazones. Compounds having higher nucleophilic strength will typically be better aldehyde scavengers, and will stabilize a choline hydroxide solution at lower usage levels. For example, a solution of about 45 wt % choline hydroxide is effectively stabilized by diethylhydroxylamine (DEHA) at a concentration of about 500 ppm, and by carbohydrazide (also known as carbodihydrazide) at a concentration as low as 250 ppm. In one example, a choline hydroxide solution stabilized with 250 ppm carbodihydrazide has Gardner Color change less than about 2.0 after 6 months shelf life at nominal temperatures. Solutions that have higher concentrations of stabilizer, or that use more effective stabilizers, may show Gardner Color change less than 1.5 or less than 1.0 after 6 months at nominal temperatures.

[0014] Effective stabilizers for choline hydroxide solutions must themselves be stable in a high pH environment. Citric acid, which is otherwise an excellent stabilizer, reacts with choline hydroxide to form a salt. It is theorized that the sodium sulfites have limited utility for this reason. It is also theorized that ammonium bisulfite and ammonium bisulfate have better utility than sodium sulfites for this reason. Generally, stabilizers useful for choline hydroxide must be able to withstand a pH of 12-14 without hydrolyzing.

[0015] A composition comprising a quaternary trialkylalkanolamine in a water-containing solvent at a concentration between about 0.1 wt % and about 80 wt % may be stabilized using an alkyl hydroxylamine, a hydrazide, a hydrazine, or a mixture thereof. In general, alkyl hydroxylamines, hydrazines, and hydrazides are effective to stabilize strong aqueous choline hydroxide solutions at levels below about 0.2 wt % stabilizer based on total weight of the solution. Choline hydroxide is commonly used in 45% aqueous solutions that are very basic, having pH generally between 12 and 14. Such conditions favor strong nucleophilic attack on aldehydes to make derivative compounds that do not impart color. The more effective stabilizers will stabilize an aqueous 45% choline hydroxide solution at concentrations of 1000 ppm or less, for example 750 ppm stabilizer concentration. The most effective stabilizers are effective at concentrations of 500 ppm or less, for example at 300 ppm or 250 ppm.

[0016] The alkyl groups of the alkyl hydroxylamine stabilizer may be any alkyl group that does not overly hinder the nucleophilic nitrogen atom or substantially reduce the nucleophilicity of the unpaired nitrogen electrons, which form the basis of amine nucleophilicity. Mono- or dialkyl hydroxylamines are both effective, but dialkyl hydroxylamines are generally more effective as stabilizers. The alkyl groups may be the same, as in DEHA, or different, and may be linear, branched, or cyclic. In some cases, one or more conjugated alkyl groups may be used, if desired, including aromatic groups. Alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, and isobutyl are examples of alkyl groups that may appear in alkyl hydroxylamines usable as choline hydroxide stabilizers.

[0017] Hydrazine, substituted hydrazines and hydrazides may also be used effectively as stabilizers for solutions of choline hydroxide and it variants, reacting with acetaldehyde decomposition products to produce hydrazones. Hydrazine itself is effective, although hydrazine is often difficult to use. Molecules having dual or multiple functionality, such as hydroxylamines having hydrazine or hydrazide derived substituents or hydrazines/hydrazides with hydroxylamino substituents, for example a compound having the general formula

##STR00001##

where R, R, R, and R each independently represents hydrogen or any desired alkyl group, including carbonyl groups, may also be used as a stabilizer for choline hydroxide solutions or their derivatives. Such stabilizers are essentially grafted mixtures of the hydroxylamine, hydrazine, and/or hydrazide stabilizers described above.

[0018] Variants of choline hydroxide in which one or more of the methyl groups is replaced by an oxygen or nitrogen containing functional group may also benefit, to varying degrees, from the stabilization described herein. If the functional group is an oxygen or nitrogen containing group, propensity for forming acetaldehyde or other chromophores by decomposition is expected to decline because the electron density around the hydroxyl oxygen is reduced by the shift in overall electron density toward the additional electronegative functional groups. Such compounds would be expected to require less stabilizer. If the functional group contains aromaticity, delocalization of electrons around the aromatic center will also improve stability for similar reasons. Under sufficiently hydrolyzing conditions, however, such compounds may nonetheless benefit from similar stabilization.

[0019] The stabilizers described herein may be added to a choline hydroxide, or variant, solution as a solid or a liquid, and may be dissolved in water or another solvent miscible with water prior to mixing with the choline hydroxide solution. For example, DEHA is a liquid at room temperature and is commonly used as an 85% solution in water. Such a solution may be mixed with a 45% choline hydroxide solution in water to form a stabilized choline hydroxide solution. The mixing may be performed in-line, for example using an in-line or static mixer, as the choline hydroxide solution is formed, or the stabilizer may be mixed in a mixing tank or a transportation vehicle or package, such as a bottle, tank, truck, or railcar.

[0020] While choline hydroxide is normally used as an aqueous solution, other solvents may be used to carry choline hydroxide along with the stabilizers described herein. Polar solvents such as alcohols, for example methanol, ethers, sulfoxides, and the like may be used. Carbonyl-containing solvents are typically not used with the stabilizers described herein, because solvents that may react with the stabilizer are avoided. In some cases, the choline hydroxide, or other quaternary trialkylalkanolamine, forming reaction may be performed in the presence of a non-aqueous polar solvent, and the stabilizer added afterward. Further, a stabilizer may be blended into the reaction mixture before the quaternary trialkylalkanolamine is formed. In other embodiments, a variant of choline hydroxide may be formed by reacting a hydroxylamine such as DEHA with ethylene oxide, or another alkylene oxide, and excess DEHA may be used to stabilize the resulting compound.

[0021] FIG. 1 is a graph showing the choline hydroxide stabilizing performance of DEHA and carbodihydrazide in a number of examples. The data show the evolution of Gardner Color in a 45% aqueous choline hydroxide solution maintained in an oven at 40 C. at various durations. Axis 100 shows the examples as 110, 120, 130, 140, and 150. Axis 102 is Gardner Color index. Each bar of an example represents a different duration in the oven. Each bar 111 is the initial Gardner Color (i.e. color after zero days). Each bar 112 is Gardner Color after 5 days. Each bar 113 is Gardner Color after 15 days. Each bar 114 is Gardner Color after 25 days. Each bar 115 is Gardner Color after 40 days.

[0022] Each of the examples 110, 120, 130, 140, and 150 was prepared from a stock aqueous 45% choline hydroxide solution made from an aqueous solution of trimethylamine and ethylene oxide. Example 110 was prepared by putting 100 g of the stock solution into a glass vessel equipped with suitable stopper and adding 1000 ppm by weight of DEHA. Example 120 was prepared by putting 100 g of the stock solution into a glass vessel equipped with suitable stopper and adding 500 ppm by weight of DEHA. Example 130 was prepared by putting 100 g of the stock solution into a glass vessel equipped with suitable stopper and adding 500 ppm by weight of carbodihydrazide. Example 140 was prepared by putting 100 g of the stock solution into a glass vessel equipped with suitable stopper and adding 250 ppm by weight of carbodihydrazide. Finally, example 150 was prepared by putting 100 g of the stock solution into a glass vessel equipped with a suitable stopper without adding a stabilizer. Example 150 thus serves as a reference.

[0023] The data of FIG. 1 show Gardner Color growth of the stabilized examples 110, 120, 130, and 140 generally half that of the unstabilized example 150, or less. Examples 110 and 120 showed generally similar performance. Examples 130 and 140 showed higher color growth than examples 110 and 120, but still evidence effective stabilization of the overall solution. The data also show that the stabilized solutions generally exhibited Gardner Color growth less than about 2.0 over the 40 day test period, while the unstabilized solution showed Gardner Color growth of approximately 4.0 over the same period at the same conditions.

[0024] It should be noted that a stabilized quaternary trialkylalkanolamine composition may be used in any convenient form. Besides a direct aqueous solution, the composition may be emulsified or otherwise dispersed in an immiscible medium, if desired, or used as a dispersion medium to carry an immiscible or insoluble material that is not reactive with any component of the composition.

[0025] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.