WO2012135463A2

WO2012135463A2 - Surfactant compositions and methods of manufacture

Info

Publication number: WO2012135463A2
Application number: PCT/US2012/031158
Authority: WO
Inventors: Paul Theodore SHARKO; Julian Richard Barnes; Elizabeth Elaine ENDLER
Original assignee: Shell Internationale Research Maatschappij BV; Shell Oil Co
Current assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2011-03-31
Filing date: 2012-03-29
Publication date: 2012-10-04
Anticipated expiration: 2013-09-30
Also published as: WO2012135463A3

Abstract

Surfactant blends that are useful in detergent composition are described herein, particularly, surfactant blends comprising alcohol ethoxylates, alcohol ethoxysulfates and less than 20 wt% water. Further, methods of manufacturing these surfactant blends are described herein.

Description

SURFACTANT COMPOSITIONS AND METHODS OF MANUFACTURE

Field of Invention

This invention relates to surfactant compositions for use in detergent applications and methods for manufacture of those compositions.

Background

There has been considerable recent activity to produce liquid detergents with increasing concentrations of active ingredients, including surfactants. However, since high surfactant levels are prone to generate gel phases that present challenges during formulation, dosing, and washing, formulation strategies are needed to address the technical challenges of concentrated liquids while optimizing the balance between cost and performance. These gel phases present significant challenges in handling the surfactant component of a detergent. Historically, solvents such as low-molecular-weight alcohols were used to inhibit the formation of gel regions in alcohol ethoxysulfates. Such alcohols tend to be flammable and volatile, and alternatives for keeping surfactants fluid during the preparation of detergents are needed.

US 5,209,874 describes a liquid surface active composition which comprises an alcohol ethoxylate, a salt of an alcohol ethoxysulfate and water. This composition is useful in a variety of detergent applications. This patent is hereby incorporated by reference.

Summary

The invention provides a composition comprising an alcohol ethoxylate having a formula R¹-0-(CH₂CH₂0)_m-H where R¹ is one or more substantially straight-chain alkyl groups having Y carbon atoms; a salt of an alcohol ethoxysulfate having a formula R²-0- (CH₂CH₂0)_n-S0₃X where R² is one or more substantially straight-chain alkyl groups having Z carbon atoms, X is a cation selected from an alkali metal ion, an ammonium ion, and mixtures thereof; and less than 20 wt% water wherein Z is at least 9, Y may be less than, greater than, or equal to Z, and m is greater than or equal to n.

The invention further provides a method of preparing a surfactant blend comprising reacting an alcohol ethoxylate of the formula R¹-0-(CH₂CH₂0)_m-H with gaseous S0₃ to produce the acid form of an alcohol ethoxysulfate; and neutralizing the acid form of the ethoxysulfate with an alkaline solution of alcohol ethoxylate of the formula R²-0-(CH₂CH₂0)_n-H where R¹ is one or more substantially straight-chain alkyl groups, R² is one or more substantially straight-chain alkyl groups, m is less than or equal to n, and n is at least 4.

The invention further provides a method of preparing a surfactant blend comprising reacting an alcohol ethoxylate of the formula R¹-0-(CH2CH₂0)_m-H with gaseous S0₃ at a mole ratio of S0₃ to alcohol ethoxylate of less than 1 to produce the acid form of an alcohol ethoxysulfate in a solution of unreacted alcohol ethoxylate; and neutralizing the acid/unreacted ethoxylate mixture with an alkaline aqueous solution where R¹ is one or more substantially straight-chain alkyl groups, and m is at least 4. Brief Description of the Drawings

Figure 1 depicts the chemical reactions involved in two embodiments of the manufacture of the surfactant compositions.

Figures 2a-2b depict the viscosity of various surfactant blends.

Figure 3 depicts the gel regions of surfactant blends formed using different neutralization agents.

Figure 4 depicts the solution time of surfactant blends.

Figure 5 depicts the detergency performance as determined by reflectance detergency of surfactant blends in combination with selected detergent components.

Figure 6 depicts the detergency performance as determined by radiotracer detergency of surfactant blends in combination with selected detergent components.

Figure 7 depicts the detergency performance as determined by reflectance detergency of surfactant blends in combination with selected detergent components.

Figure 8 depicts the detergency performance as determined by reflectance detergency of surfactant blends in combination with selected detergent components.

Figure 9 depicts the detergency performance as determined by a soil titration method of surfactant blends. Detailed Description

Liquid product formulations have increased in popularity as consumer cleaning products have evolved. Compact formulas have gained acceptance as a means to produce more sustainable formulations, as packaging and transportation footprints are reduced. Also, as washing temperatures have declined globally, the improved dissolution of liquids in low temperature wash water has become an attractive attribute compared to less soluble powders.

As the primary components of cleaning formulation, surfactants are selected for their performance and handling characteristics. For household laundry, a blend of anionic and nonionic surfactants is typically most effective against a wide variety of soils. In liquid formulations, alcohol ethoxysulfate (AEOS) surfactants are often used as the anionic surfactants, while alcohol ethoxylates (AE) are used as the nonionic surfactants. The properties of AEOS in liquid detergents include relatively high-foaming, low sensitivity to water hardness, and excellent enzyme stability relative to linear alkylbenzene sulfonate (LAS). Mixed surfactant systems have been used for a number of years, since these systems often exhibit synergism or antagonism.

This invention provides surfactant blends of alcohol ethoxylates and alcohol ethoxysulfates that provide excellent performance and demonstrate excellent handling characteristics. Surfactants provide the primary soil removal capability of a detergent, with enzymes, builders, and antiredeposition agents often added to the detergent formulation to assist with soil removal. Additionally, a surface is often judged to be clean through visual inspection, and optical brighteners may be added to a detergent to improve the appearance of fabrics. Further, detergent compositions may also be designed to impart a secondary benefit, such as antimicrobial activity or skin

moisturization for dish detergents, fabric softening for laundry detergents, or fragrance (both dish and laundry detergents). Viscosity and shelf-life are important to detergent production, handling and storage. Therefore, rheology modifiers, pH adjustment materials, preservatives are often used in detergents.

The surfactant blends described by the invention may be used to prepare liquid detergents that may be used for cleaning a variety of surfaces. A detergent formulation containing the surfactant composition described in the invention may also contain water, additional surfactants, enzymes, antiredeposition agents, optical brighteners, builders, foam boosters or reducers, rheology modifiers, pH adjustment materials, preservatives, antimicrobial agents, skin conditioners, or fragrances.

The nomenclature to be used herein for the alcohol ethoxylates is depicted in Table 1 along with the pour points of the respective alcohol ethoxylates. The name with a "S" designation indicates an alcohol ethoxysulfate formed by sulfating the alcohol ethoxylate, e.g., AE 91-8S.

Table 1

Name Hydrophobe Average EO Length Pour Point (°C)

AE 91-8 Cg,Cio,Cn 8 16

AE 23-2 2 0

AE 23-6.5 6.5 15

AE 25-7 Cl2,Ci3,Ci₄,Ci5 7 20

AE 45-7 C_l4,Ci5 7 24

The surfactant blends comprise an alcohol ethoxylate component, an alcohol ethoxysulfate component and less than 20 wt% of water. The composition is preferably free of organic solvents, particularly low molecular weight organic solvents, such as, lower alcohols having from 1 to 5 carbon atoms.

The general class of alcohol ethoxylates suitable for use in the surfactant blends described herein is characterized by the chemical formula

wherein R¹ is a straight-chain or branched-chain alkyl group having in the range of from about 8 to about 18 carbon atoms, preferably 9 to 15 carbon atoms, and m represents the average number of oxyethylene groups per molecule and is in the range of from about 1 to about 12. Ethoxylates within this class are conventionally prepared by the sequential addition of ethylene oxide to the corresponding alcohol (R¹OH) in the presence of a catalyst. The general class of alcohol ethoxysulfates suitable for use in the surfactant blends described herein is characterized by the chemical formula

R²-0-(CH₂CH₂0)_n-S0₃X

wherein R² is a straight-chain or branched-chain alkyl group having in the range of from about 8 to about 18 carbon atoms, n represents the average number of oxyethylene groups per molecule and is in the range of from about 1 to about 12, and X is a cation selected from an alkali metal ion, an ammonium ion, and mixtures thereof.

Ethoxysulfates within this class are typically prepared by one of two methods, which are depicted in Figure 1.

The first method for producing the surfactant blends is termed "neutralization". In this method, an alcohol ethoxylate, generally containing an average of three or fewer EO groups, is fed to a falling-film sulfation reactor and reacted with gaseous S0₃ at a mole ratio of about 0.98 - 1.02 to produce the acid form of an alcohol ethoxysulfate. Upon exiting the column, this acid is then immediately neutralized in an alkaline solution of nonionic surfactant, generally an alcohol ethoxylate which generally contains an average of four or more EO groups. The alcohol groups are designated Ri and R₂ in the figure, where R may be selected from C₈ to Ci₈. Sodium hydroxide (NaOH) or triethanolamine (TEA) is typically combined with the nonionic surfactant to produce a solution that is used for neutralization of the alcohol ethoxysulfate acid.

The second method that may be used is applied when the same alcohol as the feed alcohol is used to dilute the AEOS (e.g. Ri = R₂). In practice this is carried out by "undersulfation". In this method, an alcohol ethoxylate, generally containing an average of four or more EO groups, is fed to a falling-film sulfation reactor, reacted with gaseous S0₃ at a mole ratio significantly under 1 to produce an acid form of an alcohol

ethoxysulfate in a solution of unreacted alcohol ethoxylate. This acid/unreacted ethoxylate solution is then immediately neutralized with a solution of aqueous base upon exiting the column, usually a solution of NaOH or TEA. This process yields a final ethoxysulfate/ethoxylate blend product that is similar to the first process described above.

Both methods can be used to produce surfactant blends with total active surfactant content (AEOS and AE) greater than 70%, preferably greater than 85%, and more preferably greater than 90%. The high active products are typically transparent and fluid at reasonably low temperatures.

The following examples show the performance and handling characteristics of embodiments of the surfactant blends described herein.

Examples

The more important handling characteristics such as viscosity, solution time, gel formation, ability to reduce surface tension and critical micelle concentration (CMC) were studied for various surfactant blends.

Viscosities of surfactants and surfactant blends were measured using a temperature-controlled Brookfield viscometer. Solution times were determined by preparing 50 mL of deionized water at 25°C in a flat bottom pour point tube stirred at 500 rpm with a 1.5 x 0.5 cm magnetic stir bar and adding 0.20 mL of ethoxylate below the water line. The solution time was judged as the time at which the ethoxylate was completely dissolved. Gel curves were obtained for selected systems by studying desired ratios of surfactant concentrate and deionized water in test tubes. The samples were heated to approximately 70°C and thoroughly mixed manually. After observation at the maximum test temperature, the solutions were cooled in 10°C intervals and observed under polarized light at each temperature.

Figures 2a-2b illustrate viscosity data for different surfactant blends measured at

25°C and 40°C. As expected, the viscosity of the surfactant blends decreases with increasing temperature. Alcohol molecular weight also significantly impacted viscosity, with AE 91-8S/AE 91-8 demonstrating a lower viscosity than AE 23-2S based blends. Changing the counter ion from sodium (NaOH as the neutralization agent) to amine (TEA as the neutralization agent) also had a significant impact on viscosity, with a measured reduction of almost one order of magnitude. High observed viscosities are often due to the onset of gel regions, and smaller gel regions are seen for samples neutralized with TEA, as in Figure 3. The term gel is used here to indicate the collection of micelle structures that do not flow, such as hexagonal and bicontinuous phases. Adding co- solvents, such as propylene glycol, can also help narrow the gel regions. Figure 4 also helps demonstrate how alcohol ethoxylates based on alcohols of lighter molecular weight improve fluidity and rate of dissolution in water. The latter is important to insure good cleaning performance in a wash cycle. AE 91-8 and AE 23-6.5 are shown for reference relative to the surfactant blends. The dissolution test (a spinning stir bar in a volume of liquid) is rather mild and solution times will likely be long relative to solution times achieved through high shear mixing. Solution times of <5 minutes are considered acceptable, since more rigorous mixing conditions would likely be used during the preparation of a formulation.

The surface tension of deionized water is 72 dynes/cm. At surfactant

concentrations well beyond the critical micelle concentration, the surfactant blends generally reduce the surface tension of water to values of 28-32 dynes/cm, behavior which is consistent with data for single component alcohol ethoxylates. An exception to this trend is the single component alcohol ethoxysulfate AE 91-8S, which only reduces surface tension to 39 dynes/cm. Therefore, it is likely that alcohol ethoxysulfates based on AE 91-8 are highly soluble in water and are not as active at the air-water interface as are alcohol ethoxysulfates based on higher molecular weight alcohols.

Micelle formation impacts detergency and solubilization. Additionally, the reduction of surface tension by a surfactant is key to good performance in a variety of applications. Tables 2a-d illustrate critical micelle concentration (CMC) data for selected alcohol ethoxylates and surfactant blends as measured at 25°C in deionized water.

Generally, lower CMC values are considered desirable, as a surfactant with a low CMC value is regarded as efficient at reducing surface tension. Table 2a shows that AE 91-8 has a CMC approximately one order of magnitude higher than AE 23-6.5 or AE 25-7. This difference is most likely due to the lighter molecular-weight alcohol used as the surfactant hydrophobe. The data in Table 2b compare the CMCs for surfactant blends containing different anionic: nonionic surfactant ratios, as well as different counter ions used for neutralization.

In Table 2c, samples based on AE 23-2S show slightly higher CMC values than samples based on 25-3S; however, this difference is likely to have minimal impact on detergency performance. The samples described in Tables 2a-2c were prepared through neutralization, while the samples described in Table 2d were prepared by undersulfation. There are little differences between previous data and the CMC values for blends based on undersulfated AE 23-6.5 and AE 25-7. However, the CMC values of the AE 91-8S based material are somewhat higher than the other blends, suggesting that some formulations based on light alcohol ethoxylates may have different cleaning performance than the other samples.

Table 2a

Sample CMC (%wt)

AE 91-8 0.027

AE 23-6.5 0.0017

AE 25-7 0.0009

Table 2b

Anionic Nonionic Counter Anionic: Synthesis CMC

Surfactant Surfactant Ion Nonionic (wt %) Method (%wt)

AE 25-3S AE 91-8 NaOH 2:1 Neutralization 0.0020

AE 25-3S AE 91-8 TEA 2:1 Neutralization 0.0021

AE 25-3S AE 91-8 ill! 1 1 Neutralization 0.0028

AE 25-3S AE 91-8 TEA 1:1 Neutralization 0.0031

Table 2c

Anionic Nonionic Counter Anionic : Synthesis CMC (%wt) Surfactant Surfactant Ion Nonionic (wt%) Method

AE 23~2S AE 91-8 NaOH 2:1 Neutralization 0.0030

AE 23-2S AE 91-8 TEA 2:1 Neutralization 0.0048 AE 91-8 NaOH 2:1 Neutralization 0.0020

AE 25-3S AE 91-8 TEA 2:1 Neutralization 0.0021 Table 2d

Anionic Nonionic Counter Anionic : Synthesis CMC Surfactant Surfactant Ion Nonionic (wt%) Method (%wt)

AE Z3-6.5S AE 23-6.5 NaOH 2:1 Undersulfation 0.0023

AE 25-7S AE 25-7 NaOH 2:1 Undersulfation 0.0021

AE 91-8S AE 91-8 NaOH 2:1 Undersulfation 0.10

Soil removal was measured by reflectance or by radiotracer methods, and the methods have previously been correlated. Soils, wash temperatures, and water hardness 5 were selected to match consumer-relevant conditions. No enzymes or optical brighteners were used. For reflectance measurements, pre-soiled swatches were washed in a Terg-o- tometer for a 10 minute wash cycle. The soil used exclusively in this method was a

synthetic multisebum.

In order for highly concentrated formulations to be accepted by consumers, the

10 detergent must provide effective cleaning. Figures 5-8 illustrate the performance of

surfactant blends in laundry applications, while Figure 9 highlights the use of blends in liquid dish applications.

The data in Figure 5 show effective dust sebum soil removal from polycotton fabric at low temperature conditions of 10^°C and 20^°C for prototype formulations using 15 AE 23-2S as the anionic. No significant difference at a 95% confidence level was seen

between AE 91-8 and AE 23-6.5 when used as the nonionic surfactant. Therefore, AE 23- 2S/AE 91-8 is a good candidate for detergent formulations, since it was previously shown to have promising physical properties.

AE 91-8S does not clean radiolabeled multisebum soil from polycotton fabric as

20 effectively as AE 23-2S, as shown in Figure 6. The formulations based on AE 23-2S remove

over 50% more soil compared to AE91-8S/AE 91-8. This difference is most likely due to the reduced surface activity and high CMC of AE91-8S/AE 91-8. Therefore, while samples based on AE 91-8S/AE91-8 have high fluidity, other surfactant blends provide a better balance between handling properties and performance. The potential impact of surfactant blends at short wash times was also

investigated. The results shown in Figure 7 suggest that undersulfation of an alcohol ethoxylate (i.e. using the same alcohol as the feed to dilute the AEOS formed) may provide a slight advantage. All tested formulations follow the same trend in which the most significant cleaning occurs in the first 3 minutes of the wash cycle, but does not level off until at least 10 minutes of cleaning.

Selection of the proper surfactant blend for a formulation is a function of desired performance, desired formulation appearance, and logistics and handling capacity. Figure 8 shows that a targeted level of cleaning performance can be achieved at similar total surfactant loading with different neutralization agents and different ratios of anionic: nonionic surfactant. Alcohol ethoxysulfates are the primary components of liquid dish formulations, and additional surfactants are commonly used to boost performance.

Figure 9 shows that an anionic: nonionic surfactant blend is nearly as effective at cleaning food soil as a standard blend of linear alkylbenzene sulfonate (LAS) and alcohol ethoxysulfate. As previously mentioned, the blend of AE 23-2S/AE 91-8 is relatively fluid at high concentrations and is a candidate for the concentration of liquid dish products.

Claims

C L A I M S

1. A composition comprising:

a. an alcohol ethoxylate having a formula R¹-0-(CH₂CH₂0)_m-H where R¹ is one or more substantially straight-chain alkyl groups having no more than Y carbon atoms;

b. a salt of an alcohol ethoxysulfate having a formula R²-0-(CH₂CH₂0)_n-S0₃X where R² is one or more substantially straight-chain alkyl groups having at least Z carbon atoms, X is a cation selected from an alkali metal ion, an ammonium ion, and mixtures thereof; and

c. less than 20 wt% water

wherein Z is at least 9, Y may be less than, greater than, or equal to Z, and m is greater than or equal to n.

2. A composition as claimed in claim 1 wherein Z is 12.

3. A composition as claimed in claim 1 wherein Y is 15.

4. A composition as claimed in claim 1 wherein R¹ is one or more substantially

straight-chain alkyl groups having 9, 10 or 11 carbon atoms.

5. A composition as claimed in claim 1 wherein R¹ is one or more substantially

straight-chain alkyl groups having 12, 13, 14 or 15 carbon atoms.

6. A composition as claimed in claim 1 wherein R² is one or more substantially

straight-chain alkyl groups having 12, 13, 14 or 15 carbon atoms.

7. A composition as claimed in claim 1 which comprises from about 15 to about 60 percent by weight alcohol ethoxylate and from about 30 to about 70 percent by weight alcohol ethoxysulfate.

8. A method of preparing a liquid detergent formulation which comprises mixing a liquid surface active composition comprising a) from about 15 percent by weight to about 60 percent by weight alcohol ethoxylate, b) from about 30 to about 70 percent by weight alcohol ethoxysulfate with non-surfactant liquid detergent ingredients.

9. A method of preparing a surfactant blend comprising: a. reacting an alcohol ethoxylate of the formula R¹-0-(CH₂CH₂0)_m-H with gaseous S0₃ to produce the acid form of an alcohol ethoxysulfate; and b. neutralizing the acid form of the ethoxysulfate with an alkaline solution of alcohol ethoxylate of the formula R²-0-(CH₂CH₂0)n-H

where R¹ is one or more substantially straight-chain alkyl groups, R² is one or more substantially straight-chain alkyl groups, m is less than or equal to n, and n is at least 4.

10. A method of preparing a surfactant blend comprising:

a. reacting an alcohol ethoxylate of the formula R¹-0-(CH₂CH₂0)_m-H with gaseous S0₃ at a mole ratio of S0₃ to alcohol ethoxylate of less than 1 to produce the acid form of an alcohol ethoxysulfate in a solution of unreacted alcohol ethoxylate; and

b. neutralizing the acid/unreacted ethoxylate solution with a solution of sodium hydroxide or triethanolamine

where R¹ is one or more substantially straight-chain alkyl groups, and m is at least 4.

11. A method as claimed in claim 7 wherein the mole ratio of S0₃ to alcohol

ethoxylate is less than 0.9.

12. A method as claimed in claim 7 wherein the mole ratio of S0₃ to alcohol

ethoxylate is less than 0.8.

13. A liquid detergent composition comprising a surfactant composition produced as described in claim 9 and additional liquid detergent ingredients.

14. A liquid detergent composition comprising a surfactant composition produced as described in claim 10 and additional liquid detergent ingredients.

15. A liquid detergent composition comprising a surfactant composition produced as described in claim 11 and additional liquid detergent ingredients.

16. A liquid detergent composition comprising a surfactant composition produced as described in claim 12 and additional liquid detergent ingredients