WO2002070458A1

WO2002070458A1 - Low colour nitrogen-containing surfactants

Info

Publication number: WO2002070458A1
Application number: PCT/EP2002/002179
Authority: WO
Inventors: Hendrick Petrus Frick; Ajit Kumar
Original assignee: Huntsman International Llc A Limited Liability Company Formed Under The Laws Of Delaware, Usa
Priority date: 2001-03-01
Filing date: 2002-02-28
Publication date: 2002-09-12
Also published as: GB0105046D0

Abstract

A method reducing the imine content of surfactants contamined with imines, such as amphoteric surfactants, which comprises converting the imines to oxoazeridines by reaction with an oxidising agent, such as hydrogen peroxide, and converting the oxoayeridines to gem diols by reaction with a nucleophile, such as sodium bisulphite.

Description

LOW COLOUR NITROGEN-CONTAINING SURFACTANTS

The invention relates to the production of low colour nitrogen-containing surfactants and in particular, of products which exhibit improved colour stability at neutral pH. As normally manufactured many surfactants that contain amine or amido groups, such as amphoteric and cationic surfactants are obtained as 30 to 40% solutions in water, and contain 5 to 10% sodium chloride as a major impurity. In addition there are smaller amounts of organic impurities. Common trace impurities of, e.g., amphoteric surfactants include imines, which are highly coloured. Even in very low concentrations, imines can give the product a yellowish or off-white tinge.

When amphoteric surfactants are purified by removal or substantial reduction of the gross impurities, such as sodium chloride and water, the concentration of imines is proportionately increased. The purified amphoteric surfactant may therefore appear, paradoxically, less pure due to intensified colouration.

It is known to oxidise the imines to oxoazeridines, which are colourless. This can be effected using oxidising agents such as hydrogen peroxide, the bleaching being most efficient at high pH, e.g. above 10, however products treated in this way exhibit poor colour stability unless they are maintained at elevated pH. We believe that at lower pH the oxoazeridines are converted back into imines. For many purposes it is desired to supply amphoteric surfactants at a pH substantially below 10. We have now discovered that colour stability of amphoteric, or other imine-contaminated surfactants, is improved if the oxoazeridines are reacted with a nucleophile, which converts them to gemdiols.

Off R CH -N -R ^ RCH-NR

^{\ /} I I

O OH OH Our invention therefore provides a method of reducing the imine content of surfactants contaminated with imines, which comprises converting the imines to oxoazeridines by reaction with an oxidising agent, and converting the oxoazeridines to gem diols by reaction with a nucleophile.

The surfactant preferably has at least one amino or amido group, e.g. an amphoteric or zwitterionic surfactant, especially a betaine, such as an alkyl or amidopropyl betaine, or an amphoacetate, or a cationic surfactant or an alkanolamide or ethoxy alkanolamide. Other potentially imine contaminated surfactants include amine ethoxylates.

According to a preferred embodiment, aqueous surfactants, such as betaines, amidobetaines or amphoacetates, are reacted consecutively with the oxidising agent, e.g. hydrogen peroxide, and the nucleophile, e.g. bisulphite, at elevated pH and temperature.

The preferred oxidising agent for use according to the invention is hydrogen peroxide, but other peroxides may be used, such as inorganic peroxysalts or organic peroxides including peracetic, perbenzoic and other percarboxylic acids. The invention will be described specifically with respect to hydrogen peroxide but the following comments apply mutatis mutandis to any other effective oxidising agent. Oxidation is effected at an elevated pH, above 9, desirably above 9.1, preferably above 9.5 e.g. 10 to 12. pH values above 12 are not recommended. For maximum yield and to avoid unduly long reaction times the oxidation may be carried out at elevated temperatures e.g.above 40°C, preferably 45 to 70°C, especially 50 to 69,e.g. 55 to 65°C. Temperatures above 69°C, or, more preferably, above 65°C, are preferably avoided because the reaction at such temperatures is very rapid and is followed by reversion of the colour, unless the nucleophile is applied immediately the reaction is complete. It would, however, be possible in theory to carry out the reaction at higher temperatures, e.g.up to 80, 90, or even boiling, if it could be controlled sufficiently. The oxidation reaction is continued until the colour has been reduced to acceptable levels, e.g. less than 100 Hazen, preferably less than 75 Hazen, especially less than 50 Hazen, more especially less than 40 Hazen. The proportion of hydrogen peroxide is typically between 0.1 and 1% based on weight active matter, e.g. 0.25 to 0.75%. The reaction is usually substantially complete in from 30 minutes to 4 hours e.g. 1 to 3 hours.

We prefer that the pH be maintained above 9, preferably above 9.5, e.g. above 10, during the nucleophilic reaction. It is preferred to reduce the free peroxide levels below 70ppm and more preferably below 50ppm prior to addition of the nucleophile. The preferred nucleophile is a bisulphite, typically an alkali metal bisulphite, e.g. sodium metabisuphite. However other strong nucleophiles, such as alkali metal alkoxides, e.g. sodium ethoxide, hydroxylamine, acid anhydrides, e.g. acetic anhydride, sodium borohydride or Grignard reagents, are also effective.

The gem diols are stable at both acid and alkaline pH and the amphoteric surfactant remains substantially colourless, even when the pH is lowered. It is generally preferred that the pH of the product be adjusted below 10, preferably below 9, e.g. below 8, especially between 5 and 7.5.

The proportion of nucleophile is sufficient to prevent or inhibit colour reversion. Typically this requires between 0.03 and 0.7% based on the weight of active matter. Where sodium bisulphite has been used as the nucleophile it is preferred to heat the product sufficiently to reduce residual bisulphite levels below 50ppm, preferably below 20ppm. This normally requires heating at 40 to 80°C e.g. 50 to 70°C.

The proportion of reagents and duration of the foregoing steps will depend on the initial colour intensity and purity of the amphoteric product.

The procedures described above are normally applied to an unpurified amphoteric surfactant, e.g. an aqueous solution having a concentration between 20 and 40% active matter and 5 to 10%) sodium chloride, but may alternatively be applied to desalted and/or partially concentrated products provided that they are sufficiently stirrable and have a continuous aqueous phase. We particularly prefer to apply the process of the invention to surfactants prepared from substantially single homologue feedstocks, e.g. from feedstocks containing more than 80%), more preferably more than 90%>, especially more than 95%> by weight of a single homologue. In particular we prefer to decolourise surfactants having a substituent with more than 14, especially more than 16, carbon atoms. Such substantially single homologue surfactants, when purified sufficiently to reduce their inorganic salt content below 10%, preferably below 5%, more preferably below 2%, especially below 1%, based on the weight of surfactant, can be dried to solid, non- hygroscopic hydrates, containing from 2 to 10, more usually 5 to 8%> by weight water. The advantages of the invention are especially marked in such dried products. Reduction of the salt content, when required, can be achieved using, for example, membrane filtration or electro osmosis.

The invention is applicable to the purification of betaines, amidobetaines, amphoacetates, sulphobetaines and phosphobetaines. The betaines may be prepared by reacting a tertiary amine with chloracetic acid. Typically the tertiary amines comprise one long chain (e.g. 8 to 23 carbon) aliphatic group which may be a straight or branched chain, saturated or unsaturated aliphatic group, and two short chain e.g. C_t to alkyl or hydroxyalkyl groups. Amido betaines typically derive from mono (long chain aliphatic amidopropyl, amidoethyl or amidobutyl) di-(short chain aliphatic) tertiary amines. Amphoacetates are typically prepared from secondary amidoamines. The amphoteric surfactants may optionally have two long chain aliphatic groups as in fabric conditioners.

The invention is illustrated by the following example in which, unless stated to the contrary, all percentages are by weight based on the total weight of surface-active matter.

EXAMPLE I

A 20,000 Kg batch of a 30%> aqueous solution of C12-14 amidopropyl dimethyl betaines at pH 11.8 and having a colour intensity in excess of 100 Hazen was charged to a stirred reactor and heated to 60°C. 60Kg of 30% hydrogen peroxide solution was added over a period of 20 minutes, and the mixture stirred, with cooling when required to maintain the exothermic reaction at 60°C, for a further 20 minutes. 40Kg of 30%) hydrogen peroxide was added over 13.5 minutes and the mixture stirred at

60°C for 1.5 hours until peroxide level has reduced below 50ppm

The stirring and temperature were maintained while 3Kg sodium bisulphite were added, and until the bisulphite concentration had fallen below lOppm. The reaction mixture was cooled and the pH adjusted to 5 with hydrochloric acid.

The product had a colour intensity of 30 Hazen, which remained stable on storage.

EXAMPLE II

The process of Example I was repeated with a desalted lauryl amidopropyl betaine. The product was dried at 60°C to a moisture content of 6%. A dry, white, free-flowing powder was obtained. A similar product prepared omitting the steps of Example I was orangey yellow.

Similar results are obtained using sodium ethoxide, sodium borohydride, acetic anhydride, or hydroxylamine instead of sodium bisulphite.

EXAMPLE III

The process of Example I was successfully used to decolourise coconut monoethanolamide, stearyl dimethylammonium chloride, lauryl amphoacetate and an ethoxylated coconut monoethanolamide.

Claims

1. A method of reducing the imine content of surfactants contaminated with imines, which comprises converting the imines to oxoazeridines by reaction with an oxidising agent and converting the oxoazeridines to gem diols by reaction with a nucleophile.

2. A method according to claim 1, wherein said surfactant comprises an amino or amido group.

3. A method according to claim 2, wherein said surfactant is an amphoteric, zwitterionic or cationic surfactant or an alkanolamide, ethoxylated alkanolamide or amine ethoxylate.

4. A method according to claim 3, wherein said surfactant is an alkyl betaine, alkyl amidopropyl betaine, sulphobetaine or amphoacetate.

5. A method according to any foregoing claim, wherein said oxidising agent is a peroxide.

6. A method according to claim 5, wherein said peroxide is hydrogen peroxide.

7. A method according to any foregoing claim, wherein said nucleophile is a sulphite, alkoxide, acid anhydride, borohydride or Grignard reagent.

8. A method according to claim 7, wherein said nucleophile is sodium metabisulphate.

9. A method according to any foregoing claim, wherein an aqueous solution of said surfactant is reacted successively with said oxidising agent and said nucleophile at elevated pH and temperature.

10. A method according to claim 9, wherein said elevated pH is above 10.

11. A method according to either of claims 9 and 10, wherein said temperature is between 50 and 65°C.

12. A method according to any foregoing claim, wherein said surfactant consists of a substantially single homologue comprising a substituent with more than 14 carbon atoms and wherein, either before or after said reactions, at least any excess of inorganic salt over 5% by weight of said surfactant is removed, and said surfactant is finally dried at a temperature below its softening point to a moisture content of from 2 to 10%.

13. A method of decolourising an amine- or amide- containing surfactant, which comprises reacting said surfactant in aqueous solution with hydrogen peroxide at a pH of 10 tol2 and a temperature of 50 to69°C, adding to the reaction mixture, at said pH and temperature, sufficient nucleophile to inhibit any colour reversion and lowering the pH below 10.