Methyl Ester Sulfonate

C H A P T E R

9 Methyl Ester Sulfonate Norio Tobori*, Toshio Kakui† *

LION Specialty Chemicals Co., Ltd., Sumida-ku, Tokyo, Japan †LION Corporation, Sumida-ku, Tokyo, Japan

9.1 INTRODUCTION Fatty acid methyl ester sulfonates (MESs) are oleochemical-based anionic surfactants derived from palm or coconut oil through transesterification and subsequent sulfonation. Linear alkylbenzene sulfonates (LASs), alkyl sulfonates (ASs), and alpha olefin sulfonates (AOSs) are generally used as detergent surfactants. However, because of the two oil crises in the 1970s, detergent manufactures have been interested in natural fat- and oil-based surfactants, rather than those that are petroleum-based, and have considered MESs as a possible detergent ingredient. MESs have good surface-active properties (Stirton et  al., 1962; Boucher et  al., 1968) and excellent detergency performance as a laundry detergent main ingredient (Okumura et al., 1976; Stirton et  al., 1954; Schambli and Schwuger, 1990), as well as good biodegradability (Maurer et al., 1977; Steber and Wierich, 1989). MESs were shown to be scum dispersant in the 1960s, and thus, their sulfonation mechanism (Stirton, 1968; Weil et al., 1953), characteristics, application, and manufacturing process (Stein and Baumann, 1975; Kapur et al., 1978) have been extensively studied. They have only recently been found to be applicable as a main component of laundry detergent products, and their manufacture on a commercial basis is now possible. There are problems in manufacturing MESs because of (a) the dark color of the sulfonated product, (b) the generation of disodium salts through sulfonation as a by-product, and (c) the low active ingredient content for a detergent raw material. It is thus difficult to produce high-quality MESs suitable for laundry detergents. Due to hydrolysis, MESs may possibly undergo degradation into the disodium the disodium salt on contact with alkaline components (Yamane and Miyawaki, 1989). The technology became available for producing high-quality MESs on a commercial basis in the early 1990s through improvements such as sulfonation, bleaching, and neutralization. This new technology was introduced into Japan, and a new compact powder detergent was produced in 1991. Further compact products were subsequently developed using the improved MESs. In the United States, Stepan Company developed coco-based MES and promoted their usage during the same period (Drozd and Desai, 1991; Smith, 1989). To date, there are many suppliers of MES in the world. Major global producers of MES are tabulated in Table 9.1. Biobased Surfactants https://doi.org/10.1016/B978-0-12-812705-6.00009-5

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Copyright © 2019 AOCS Press. Published by Elsevier Inc. All rights reserved.

304

9.  Methyl Ester Sulfonate

TABLE 9.1  Global Major Producers of MES Companies

Location

Annual Capacity (MT)

Guangzhou Keylink Chemical Co.

China

40,000

Zhejiang Zanyu Technology Co., Ltd.

China

60,000

Stepan

United States

50,000

Dersa, Bogota

Colombia

15,000

KLK Oleo

Malaysia

100,000

Global Eco Chemicals Malaysia Sdn. Bhd

Malaysia

50,000

PT Global Eco Chemicals Indonesia

Indonesia

50,000

This chapter summarizes the application of MESs in laundry detergent formulations and their fundamental surfactant properties, solid structure, and biodegradability.

9.2  PHYSICAL AND CHEMICAL PROPERTIES OF METHYL ESTER SULFONATE MESs have the chemical structure shown in Fig. 9.1. The structure is that of a fatty acid methyl ester with a sulfonate group in the α-position. MESs are prepared by the direct sulfonation of fatty acid methyl esters from triglyceride through transesterification. The number of carbon atoms in MESs is generally 12–18 for detergent use.

9.2.1  Surfactant Properties 9.2.1.1  Basic Surfactant Properties (CMC, Krafft Point and Solubility) Fujiwara reported the basic properties of MESs and their water hardness tolerance (Fujiwara et  al., 1993). Solubility and the critical micellar concentration (CMC) curves as a function of temperature for C14-, C16-, and C18MES-Na are shown in Fig. 9.2 along with those of the corresponding calcium salts. The CMCs and Krafft points of MES-Na, MES-Ca, and AS-Na (sodium lauryl sulfate) are presented in Table 9.2. The solubility and the CMC were found to decrease with rising carbon number and a counterion change from Na to Ca. These features are characteristic of anionic surfactants (Hato and Shinoda, 1973). Table 9.2 shows that the increase in Krafft points of the MES compounds as a result of the counterion change is less than that for AS compounds (Hato and Shinoda, 1973; Shinoda et al., 1986).

FIG. 9.1  Chemical structures of MES and disodium salt. III.  BIOBASED SURFACTANTS



9.2  Physical and Chemical Properties of Methyl Ester Sulfonate

305

100 14 SFNa 16 SFNa 14 SFNa

10

Solubility (mM)

18 SFNa 1 16 SFCa

0.1

18 SFCa

0.01

0.001

0

10

20

30 40 Temp. (°C)

50

60

FIG. 9.2  Solubility and CMC curves of MES surfactants. Solubility for MES-Ca represents those of RCH(COOCH3)

SO3·1/2Ca. From Fujiwara, M., Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 782.

TABLE 9.2  Krafft Points and Critical Micellar Concentrations (CMCs) of Some Surfactants Surfactant

Krafft Point (°C)

CMC (mM)

Reference

C14MES-Na

6

2.8 (13°C)

Fujiwara et al. (1993)

C16MES-Na

17

0.73 (23°C)

Fujiwara et al. (1993)

C18MES-Na

30

0.18 (33°C)

Fujiwara et al. (1993)

28

0.66 (30°C)

Fujiwara et al. (1993)

C16MES-Ca

41

0.19 (45°C)

Fujiwara et al. (1993)

C18MES-Ca

49

0.042 (50°C)

Fujiwara et al. (1993)

C12AS-Na

9

8.1

Shinoda et al. (1986)

C14AS-Na

30

2.1

Shinoda et al. (1986)

C12AS-Ca

50

1.2

Hato and Shinoda (1973)

C14AS-Ca

71

0.68

Hato and Shinoda (1973)

From Fujiwara, M., Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 782.

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306

9.  Methyl Ester Sulfonate

0 AS-Na –2 MES-Na

In CMC (mol/L)

–4

MES-Ca

–6

–8

–10

–12

6

8

10

12

14

16

18

No. of C-atoms

FIG. 9.3  Relationship between the logarithm of the CMC and the number of carbon atoms in the hydrophobic chain. The number of carbon atoms was plotted according to the following structures: AS = CnH2n + 1OSO3M and SF = Cn − 1H2(n − 1) + 1CH(COOCH3)-SO3M. Key: AS-Na◇, MES-Na●, and MES-Ca○. From Fujiwara, M., Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 782.

The CMC of MES-Ca is approximately 25% of that corresponding to MES-Na. Using the method of Shinoda, the logarithm of CMC was plotted against hydrophobic chain length (Fig. 9.3) and the logarithm of counterion concentration (Shinoda, 1963). Good linearity for MES-Na and MES-Ca was demonstrated, suggesting micelle formation by MES-Na and MES-Ca following the equation:

{

}

ln ( CMC ) = −mω / kT + K g / Zi ln ( 2000πσ 2 / DNkT ) − ln C g + constant where m is the number of calcium atoms, ω is the cohesive energy change for transferring one methylene group from a hydrophobic environment to aqueous medium, Kg is an experimental constant related to the degree of counterion binding by micelles, Kg/Zi is determined from the slope of the CMC as a function of Zi valent counterion concentration, D is the dielectric constant of the solution, N is Avogadro’s number, σ is the charge density on the micelle surface, and Cg is the total concentration of the counterion per liter. The energy calculated for MES-Na and MES-Ca was 1.1 and 0.93kT, respectively, and those values are almost equal to that of a typical ionic surfactant (e.g., AS-Na, 1.1kT). III.  BIOBASED SURFACTANTS



9.2  Physical and Chemical Properties of Methyl Ester Sulfonate

307

TABLE 9.3  Micellar Weights, Aggregation Numbers, and Second Virial Coefficients (B2) of Some Surfactants Surfactant

Medium

Molecular Weight of Micelles (g/mol)

Aggregation Number

B2 (mL/g)

C14MES-Na

0.01 N NaNO3

28,000

81

7.30 × 10−3

0.1 N NaNO3

32,800

95

8.73 × 10−3

0.4 N NaNO3

41,000

119

3.05 × 10−4

C16MES-Na

0.01 N NaNO3

31,600

85

5.20 × 10−3

C18MES-Na

0.01 N NaNO3

42,500

106

2.18 × 10−3

C14MES-Ca

H2O

32,600

96

1.87 × 10−3

0.003 N Ca(NO3)2

45,100

132

7.78 × 10−4

0.01 N Ca(NO3)2

42,200

124

−2.39 × 10−4

From Fujiwara, M., Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 783.

The dissociation of counterion for MES-Na and MES-Ca micelles was determined and was found to be essentially the same as that of typical anionic surfactants. The aggregation number of micelles is important for expressing the physicochemical properties of surfactant solutions. The micelle weight, aggregation number, and second virial coefficient for MES-Na and MES-Ca are listed in Table 9.3. The aggregation number of C14 MES increased from 81 to 119, and the second virial coefficient decreased from 7.30 × 10−3 to 3.05 × 10−4 with increasing electrolyte concentration. This behavior corresponds to that of C12AS-Na reported by Hayashi and Ikeda (1980). The aggregation number of C14MES is basically the same as that of C16MES, whereas C18MES number slightly exceeds that of C16 in the 0.01 N NaNO3 solution. The aggregation number of MES-Ca is larger than that of MES-Na even in distilled water and increases with electrolyte addition. 9.2.1.2  Water Hardness Tolerance Fujiwara proposed a mechanism for the good hardness tolerance of MESs based on the precipitation phase boundary for MES-Ca salts (Fujiwara et  al., 1993). The boundaries for C12AS-Na, C14MES-Na, and C16MES-Na are shown in Fig.  9.4. The boundary lines were obtained after 10 min, 1 h, 1 day, and in the equilibrium state, since precipitation was time-­ dependent. The equilibrium phase boundary for C12AS-Na, which has poor tolerance to hardness, agreed with that reported previously (Steliner and Scamehom, 1989). The phase boundary at equilibrium was quite close to that at 10 min, indicating that precipitation occurs very rapidly and equilibrium is easily attained. In activity, washing this surfactant would precipitate within 10 min, and surface activity would be lost. Precipitation region concentrations for C14MES-Na at equilibrium are low and that for C16MES-Na is spread over the range 3–10°DH (DH is German hardness, 1°DH = 10 ppm CaO). If washing is under the control of the precipitate boundary at equilibrium, all MES would precipitate with the loss of solution activity. The precipitation region of C14MES-Na and C16MES-Na in an actual washing was much smaller than that of AS-Na. The reason for the hardness tolerance of MES-Na may be due to the extremely slow precipitation rate of Ca salts at low temperature. III.  BIOBASED SURFACTANTS

308

9.  Methyl Ester Sulfonate

10–1

10–1

10 min

1 day

–2

10

Ca(NO3)2 (moles•L–1)

10–1

10 min

Precipi tation region –2

10–2

–3

10–3

10 10 min

1h

10 °DH –3

10

10

3 °DH

eq. 10–4 eq. Monophasic

Monophasic

region

–5

10

10

–5

10

(A)

eq.

region

–4

10

–3

10

–2

10

–1

10

C12AS-Na (moles･L–1)

10–5

(B)

Monophasic

10–5

–5

25°C 10–6

10–6

1 day

10–4

10–4

25°C 10–6 10–4

10–3

10–2

C14MES-Na (moles･L–1)

10–1

10–5

(C)

region

30°C 10–4

10–3

10–2

10–1

C16MES-Na (moles･L–1)

FIG. 9.4  Precipitation phase boundary diagrams of C12AS-Na, C14MES-Na, and C16MES-Na. From Fujiwara, M.,

Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 784.

9.2.2  Solid State Properties Few studies have been carried out on the solid or crystalline state of anionic surfactants apart from the monocrystalline X-ray diffraction analysis of the hydrated solid of sodium dodecyl sulfate (Kekicheff et al., 1989). To extend this to detergent powders, the crystalline state must be understood since features such as powder caking and the quick dissolving rate of a powder particle in water are closely related to the surfactant solid properties. Fujiwara investigated the crystalline state of C16MES-Na with regard to hydration, phase transition, and adsorption/desorption of moisture using the C16MES-Na as a model substance (Fujiwara et al., 1997). The phase behavior of MES-Na was studied by differential scanning colorimetry (DSC) for several C16MES-Na solid samples with different moisture contents. The results for samples with 0%–8.9% moisture content are shown in Fig. 9.5. For nonhydrated MES-Na, a single endothermic peak was noted. The phase transition temperature (Tc) and enthalpy change (ΔH) were 112°C and 22.1 kJ/mol, respectively. With increasing moisture, the endothermic peal gradually shifted to lower temperature with a concomitant decrease in size. At the same time, a new peak appeared at 68°C, and the size of this peak increased at constant temperature. The spectrum at 8.9% moisture content showed an endothermic peak with Tc and ΔH of 7°C and 67.5 kJ, respectively, which may possibly have been due to the phase transition of MES-Na·2H2O crystals from solid to liquid form since the molar ratio of [H2O]/[MES-Na] was 2.0. The X-ray diffraction patterns for these MES-Na samples are presented in Fig.  9.6. The MES-Na solid at 0% and 8.9% moisture content gave one peak corresponding to spacing of 26.9 and 30.1 Å, respectively. At 1.6% and 5.6% moisture content, however, two peaks of 26.9 and 30.1 Å appeared simultaneously. The two different crystal structures thus appear to coexist independently in solid MES-Na with moisture content from 0% to 8.9%.

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309

9.2  Physical and Chemical Properties of Methyl Ester Sulfonate

Temperature (°C) 0

20

40

80

60

100

120

Moisture content (wt. %)

0 1.6 3.6 5.6

ENDO.

6.5 8.1 8.9

FIG. 9.5  DSC curves for C16MES-Na solids with moisture contents from 0 to 8.9 wt%. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3346.

45K

Intensity (cps)

45K

22.5

22.5

5

6 2q (°)

0

7

(B)

5

6 2q (°)

45K

26.9 Å

30.1 Å

22.5 30.1 Å

30.1 Å

0

(A)

45K

26.9 Å

26.9 Å

7

0

(C)

5

6 2q (°)

22.5

7

0

(D)

5

6 2q (°)

7

FIG. 9.6  X-ray diffraction patterns of C16MES-Na solids with moisture contents from 0 to 8.9 wt%: (A) 0 wt%, (B)

1.6 wt%, (C) 5.6 wt%, and (D) 8.9 wt%. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3346.

Fujiwara analyzed for the phase transition behavior quantitatively using the phase role and the Flory-Huggins-Scott equation (Wittman and Manley, 1977). C16MES-Na solids with 0%–8.9% moisture content were found to be a mixture of MES-Na crystals of anhydrate and 2 mol hydrate. C16MES-Na solids with greater moisture contents were also investigated. DSC of C16MES-Na solids at 8.9%–32.6% moisture content was carried out, and the results are shown in Fig. 9.7. Data similar to those in Fig. 9.6 were obtained, showing a shift of the endothermic peak corresponding to the phase transition of the MES-Na·2H2O to the lower-­ temperature side and the appearance of a new peak at 53°C. At 19.5% moisture content, a peak that apparently corresponds to the phase transition of the MES-Na·5H2O crystal

III.  BIOBASED SURFACTANTS

310

9.  Methyl Ester Sulfonate

0

20

Temperature (°C) 40 60 80

100

120

Moisture content (wt. %) 8.9 11.8 13.5 17.6

ENDO.

19.5 23.7 28.3 30.6 32.6

FIG. 9.7  DSC curves for C16MES-Na solids with moisture contents from 8.9 to 32.6 wt%. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3347.

was observed. At 19.5%–32.6% moisture content, a shift of the endothermic peak corresponding to the phase transition of the MES-Na·5H2O crystals to the lower-­temperature side occurred, accompanied by a peak at 42°C, which was assigned to the phase transition of MES-Na·10H2O crystals. The transition temperature change in this moisture content range in all cases was attributed to the mixture of MES-Na·5H2O and MES-Na·10H2O crystals. Based on these findings, an overall phase diagram of the C16MES-Na/water system is proposed in Fig. 9.8, in which four different hydrated crystals (anhydrate, 2 mol hydrate, 5 mol hydrate, and 10 mol hydrate), two liquid crystals (lamellar and hexagonal), a micelle solution, and a monomer solution are presented. MES-Na crystals have several different hydrations, and this can be studied in relation to the atmosphere. The moisture content and X-ray diffraction spectra of MES-Na solid samples with 40% initial moisture content were determined at a constant relative humidity of 10% and ambient temperature (Fig. 9.9). The moisture content initially decreased rapidly for 5 h and then remained constant at 32 wt% up to 20 h. There was then a gradual decrease from 20 to 50 h, reaching 9 wt%, corresponding to the phase transition of MES-Na·2H2O. The moisture content then fell to 7 wt% and remained constant. The X-ray diffraction patterns indicated essentially the same results at from 40 to 10 wt% moisture content, where two peaks of 4.1 and 4.2 Å appeared. Finally, at 7 wt% moisture content, a single peak of 4.25 Å was observed.

III.  BIOBASED SURFACTANTS



311

9.2  Physical and Chemical Properties of Methyl Ester Sulfonate 120 M1

Temperature (°C)

100

L1

80

H1

+

L1

H1

La

+ La

H1

S2H2O

+La

60

S2H2O + La

S5H2O +H1?

40 20

S10H2O

S2H2O

S5H2O

+

S5H2O

+

Sum2o + M1

+ S2H2O

S10H2O

0 0

20

40

60

80

100

Surfactant concentration (wt. %)

FIG. 9.8  Phase diagram of the C16MES-Na-water system. H1, hexagonal liquid crystalline phase; L1, micellar solu-

tion phase; Lα, lamellar liquid phase; M1, monomer solution phase; S0H2, anhydrous MES; S2H2O, MES·2H2O; S5H2O, MES·5H2O; S10H2O, MES·10H2O. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3345–3348.

Intensity (cps)

6K

3

Moisture content (wt. %)

40

20

6K

3

3 4.20 Å

0

30

6K

18

20

4.10 Å

22 2q (°)

4.10 Å 4.20 Å

4.10 Å 4.20 Å 24

26

0

18

20

22

2q (°)

24

26

0

18

20

6K

22 2q (°)

24

26

24

26

4.20 Å 4.25 Å

10H20

3 4.10 Å 0

5H20

18

20

6K

22

2q (°) 4.25 Å

10

0

3

2H20

50

100 Time (h)

150

0

60 days

18

20

22

24

26

2q (°)

FIG. 9.9  Time dependence of moisture content for the hydrated C16MES-Na solid. Conditions: initial moisture

content 40 wt%, 10% relative humidity, and room temperature. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3348.

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312

9.  Methyl Ester Sulfonate

Intensity (cps)

8.7K

8.7K 4.25 Å 4.25 Å 4.20 Å

4.35

4.10 Å 0 18

4.35

18

20

22 2q (°)

24

26

Intensity (cps)

8.7K

4.15 Å

4.35

22 2q (°)

24

0

26

18

20 22 2q (°)

24

26

8 4.20 Å 4.10 Å

0

20

Moisture content (wt. %)

Intensity (cps)

8.7K 4.25 Å

4.35

6

4

2

4.05 Å 0

18

20

22 2q (°)

24

26

0

10

20 Time (h)

30

40

120

FIG. 9.10  Time dependence of moisture content for the dry C16MES-Na solid. Conditions: initial moisture content

0.2 wt%, 80% relative humidity, and 50°C. From Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3348.

MES-Na crystals in the dry state were also studied in a humid atmosphere. MES-Na solids with initial 0.2 wt% moisture content were maintained under 80% relative humidity at 50°C. Phase changes are shown in Fig. 9.10. The moisture content gradually increased up to 20 h and then leveled off near 25 h, where it became 8.6 wt%, corresponding to MES-Na·2H2O crystals. X-ray diffraction showed two peaks of 4.1 and 4.2 Å at 0.2–4 wt% moisture content and then a single peak of 4.25 Å at a moisture content less than 6 wt%. Recently, the crystalline structure of hydrated solids in mixed system composed of MES-Na and other surfactants (Watanabe et al., 2016) and the effect of the crystalline structure of MES induced by temperature and humidity history on the brittleness of grains (Watanabe et al., 2018) were also reported.

9.2.3 Biodegradability The biodegradability of MES-Na has been reported (Miura, 1991). Masuda et al. reported studies that used a different examination method and proposed a pathway of MES biodegradation by micrograms (Masuda et al., 1993a,b). These studies involved a shaking culture method, river die-away test, and biochemical oxygen demand measurement (Japanese Ministry of International Trade and Industry (MITI) test). Biodegradation was monitored by methylene blue active substances (MBAS), dissolved organic carbon (DOC), and biochemical

III.  BIOBASED SURFACTANTS



313

9.2  Physical and Chemical Properties of Methyl Ester Sulfonate

oxygen demand (BOD). Results from the shaking culture method are given in Fig. 9.11. It can be seen that MES and AOS-Na (alpha olefin sulfonate) lose more than 90% of methylene blue (MB) activity in a day and 100% within 2 days. LAS-Na lost MB activity in 5 days, and more than 40% of the dissolved organic carbon still remained after 15 days. MES-Na is thus shown to be readily biodegradable substances from the viewpoint of both primary and ultimate degradation under shaking culture conditions. The river die-away test, a biodegradation test using actual river water, was conducted on four different surfactants. Fig. 9.12 shows that MES-Na and AOS-Na surfactants quickly and 100

100

LAS DOC residue (%)

MBAS residue (%)

LAS

50 MES AOS

0

0

5

50 MES AOS

0

10

0

5

Time (day)

10

15

Time (day)

FIG. 9.11  Biodegradation of surfactants by shaking culture method. AOS, C11–C15AOS-Na; LAS, C10–C14LAS-Na;

and MES, C12–14MES-Na. From Masuda, M., Odake, H., Miuram K., Oba, K., 1993. Biodegradation of 2-sulfonatofatty acid methyl ester. I. J. Jpn. Oil Chem. Soc. 42, 645. 100 Surfactants 5 mg/L

MBAS residue (%)

80 AOS

60

MES LAS

Soap

40 20 0

0

1

2

3

4

5

Time (day)

FIG.  9.12  Biodegradation of surfactants in river water (river die-away test) detected by MBAS. Surfactants, 5 mg/L. AOS, C11–C15AOS-Na; LAS, C10–C14LAS-Na; MES, C12–14MES-Na; and Soap, C11–17COO-Na. From Masuda, M., Odake, H., Miuram K., Oba, K., 1993. Biodegradation of 2-sulfonatofatty acid methyl ester. I. J. Jpn. Oil Chem. Soc. 42, 646.

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314

9.  Methyl Ester Sulfonate

100

100 mg/L

Surfactants Activated sludge

MES

30 mg/L

50

Biodegradability [(BOD/TOD)x100] (%)

LAS 0

0

10

20

30

100 MES 50

Surfactants Activated sludge

LAS 0

0

10

20

50 mg/L 30 mg/L

30

100 MES LAS

50

0

0

Surfactants Activated sludge

10

20

5 mg/L 10 mg/L

30

Time (day)

FIG. 9.13  Biodegradation of C12–14MES-Na and C10–C14LAS-Na detected by BOD in the MITI test. From Masuda, M., Odake, H., Miuram K., Oba, K., 1993. Biodegradation of 2-sulfonatofatty acid methyl ester. I. J. Jpn. Oil Chem. Soc. 42, 647.

easily undergo biodegradation, with total elimination of MB activity, within 3 days. For soap, 5 days were required for the loss of MB activity, suggesting that soap causes some kind of precipitation in river water whereby degradation is delayed. The results of the BOD/total oxygen demand (TOD) measurements in the MITI test are shown in Fig. 9.13. These results indicate that the biodegradation of MES-Na starts quickly and proceeds rapidly in the early stage at each surfactant concentration. For LAS-Na, degradation starts later and is in proportion to the increase in surfactant concentration. Results also indicate that both MES-Na and LAS-Na surfactants undergo ultimate biodegradation.

9.3  PRODUCTION OF METHYL ESTER SULFONATE The general MES-Na manufacturing process is shown in Fig. 9.14, and each stage is explained below (Itakura, 2004; Niikura et al., 2013):

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FIG. 9.14  MES-Na manufacturing process. ME refers to fatty acid methyl ester.

(1) A sulfonation stage, in which SO3 is chemisorbed by methyl ester (ME) to give an intermediate species. Generally, an SO3/ME molar ratio of 1.2 is used, and the reaction temperature is about 80°C. (2) An aging stage, in which the reaction mixture is kept at a high temperature in order to complete the reaction. Generally, it is performed at a minimum of 80°C. After aging, conversion of the initial ME is more than 98%. (3) An esterification stage, in which methanol is added to the reaction mixture, and the 1:2 adduct and disodium are converted into MES-H. The final yield of MES-H is generally over 90%. (4) A neutralization stage, in which aqueous sodium hydroxide is added to the esterified reaction mixture. (5) A bleaching stage, in which hydrogen peroxide is added to the neutralized reaction mixture. After bleaching, the color of the MES-Na product is generally less than 100. Acid bleaching prior neutralization is also established as an alternative to bleaching after neutralization.

9.4 APPLICATION 9.4.1  Powder Laundry Detergent The choice of surfactants for laundry detergents is based on factors such as performance, manufacturing technology, social considerations, and demands for feedstock. In Japan, in response to environmental concern in the 1970s, zeolite replaced polyphosphate as a detergent builder, and new surfactants from natural fats and oils attracted much attention. MESs, which appeared in 1991, were considered suitable for a compact detergent in Japan.

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FIG. 9.15  Relationship between detergency and concentration of surfactant. Conditions: Terg-O-Tometer, artificial soil (cotton), 25°C, water hardness 54 ppm (CaCO3), surfactant 270 ppm, sodium carbonate 135 ppm, and sodium silicate 135 ppm. Key: ◆C18MES-Na, ■C16MES-Na, *C14MES-Na, □C10–14LAS-Na, and ◇C12AS-Na.

The practical detergency and the surface activity of MESs are discussed in the following sections, along with formulations and the manufacturing process. 9.4.1.1 Detergency The detergency of MES-Na for different alkyl chain lengths has been evaluated for comparison with C10–14LAS-Na and C12AS-Na at low temperature and water hardness (Satsuki, 1992). Detergency was studied using the Terg-O-Tometer (US testing) and artificial soiled swatches as fabrics at 120 rpm, 25°C, and a 10 min wash plus two rinses of 3 min each. Sodium carbonate (135 ppm) and sodium silicate (35 ppm) were used in each washing test. Water hardness was controlled to 3°DH. Detergency was determined based on a swatch reflectance before and after washing and the Kubelka-Munk equation (Okumura et al., 1980). The swatches were prepared by soaking unsoiled swatches in an aqueous dispersion containing oil, protein, and mineral components, followed by drying in air. Detergency test results on three different surfactants as a function of concentration are shown in Fig.  9.15. C16MES-Na and C18MES-Na showed better detergency than LAS-Na or, in particular, AS-Na, and the best results were obtained at low surfactant concentrations. C16MES-Na gave the best detergency, followed by C18MES-Na and then C14MES-Na. Detergency followed the order C16MES-Na ≥ C18MES-Na > LAS-Na > AS-Na, C14MES-Na. The effects of temperature (Fig.  9.16) and cloth-to-liquor ratio (Fig.  9.17) on detergency have been evaluated (Satsuki, 1992). Detergency decreases with reduction in temperature, and results for MESs were best at low temperatures and low liquor ratio. The surface-active properties of the three surfactants were examined to determine in performance. Adsorption onto particle soil, dispersion of clay, emulsification of oily soil, and the zeta potential of oil droplets in the emulsion system were measured for C14–16MES-Na, LAS-Na, and AS-Na solution as a function of surfactant concentration. The MES-Na surfactants gave the best results in all cases as shown in Figs. 9.18 and 9.19 (adsorption and emulsification, respectively) (Satsuki, 1992). III.  BIOBASED SURFACTANTS



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FIG. 9.16  Effect of washing temperature on detergency. Conditions: Terg-O-Tometer, artificial soil, liquor ratio 30, water hardness 54 ppm (CaCO3), surfactant (AS, C12AS-Na; LAS, C10–14LAS-Na; and MES, C14–16MES-Na) 270 ppm, sodium carbonate 135 ppm, and sodium silicate 135 ppm.

FIG.  9.17  Effect of cloth-to-liquor ratio (w/w) on detergency. Conditions: Terg-O-Tometer, artificial soil, 25°C, water hardness 54 ppm (CaCO3), surfactant (AS, C12AS-Na; LAS, C10–14LAS-Na; and MES, C14–16MES-Na) 270 ppm, sodium carbonate 135 ppm, and sodium silicate 135 ppm. From Satsuki, T., Umehara, K., Yoneyama, Y., 1992. Performance and physicochemical properties of α-sulfo fatty acid methyl esters. J. Am. Oil Chem. Soc. 69, 675.

The adsorption of each surfactant on clay particles was determined for an aqueous dispersion prepared by agitating red-yellow diluvium for 3 h in the presence of each surfactant. In the emulsifying tests, emulsified oil was proportional to surfactant concentration. 9.4.1.2 Solubilization MES-Na has superior solubilization capacity, which is essential for characterizing surfactants. MES-Na was found to be highly capable of solubilizing oleic acid, which is usually present abundantly in natural soil. The solubilization capacity for LAS-Na, AS-Na, and C14–16MES-Na III.  BIOBASED SURFACTANTS

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FIG.  9.18  Adsorption of surfactants onto particle soil. Conditions: clay 0.4%, 25°C, and sodium carbonate 270 ppm. AS, C12AS-Na; LAS, C10–14LAS-Na; and MES, C14–16MES-Na. From Satsuki, T., Umehara, K., Yoneyama, Y., 1992. Performance and physicochemical properties of α-sulfo fatty acid methyl esters. J. Am. Oil Chem. Soc. 69, 676.

FIG. 9.19  Emulsification of oily soil by surfactants. Conditions: artificially oily soil 0.2%, 25°C, and sodium sulfate 270 ppm. AS, C12AS-Na; LAS, C10–14LAS-Na; and MES, C14–16MES-Na. From Satsuki, T., Umehara, K., Yoneyama, Y., 1992. Performance and physicochemical properties of α-sulfo fatty acid methyl esters. J. Am. Oil Chem. Soc. 69, 676.

was evaluated using oleic acid as a polar oil solubilizate and nonpolar n-­octane. Fujiwara investigated the solubilization of MES-Na and obtained the following results (Fujiwara et al., 1995). First, C14–16MES-Na had a larger solubilization capacity than LAS-Na. Second, capacity depended on the number of micelles and degree of solubilization per micelle. Third, micellar weight initially decreased for a small amount of solubilizate and then increased with increasing solubilizate amount. Fourth, the solubilization process was accompanied by the reconstitution of micelles.

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9.4.1.3  Enzyme Stability Enzymes are essential components of detergents. Surfactants have significant influence on enzyme activity in detergents. A stable enzyme and surfactant system is desirable for optimal enzyme functioning in washing. Nonionic surfactants have little effect on enzyme activity, whereas cationic surfactants have considerable effect. Anionic surfactants exert an intermediate effect, the extent depending on the surfactant. The effects on three anionic surfactants on enzyme activity were examined using protease as the detergent enzyme (Satsuki, 1992; Satsuki et al., 1999). Activity stability in a washing liquor was assessed at low temperature, low water hardness, and weak alkaline pH. The results are shown in Fig. 9.20. Enzyme activity decreased with time for all the surfactants. In MES-Na solution, only a slight decrease in activity was noted, whereas that for LAS-Na and AS-Na solutions, it was significant; residual activity for either solution was below 50% after standing for 2 h at 25°C. The inhibition of enzyme activity due to surfactants is thought to be caused by adsorption of the surfactant onto the enzyme, leading to denaturation of the enzyme protein. 9.4.1.4 Formulations The best feature of MESs is that its surfactant content can be reduced without compromising performance. Formulations containing MES-Na are listed in Table 9.4 (Satsuki, 1986). Compared with the popular formulation of LAS-Na/AS-Na or LAS-Na/AOS-Na, those of MESs allow for sufficient detergency with low surfactant content, with no need for additional sequestering or alkaline builders. Detergent powders containing MES-Na as the main component have various technical problems, such as a low dissolving rate in low-temperature water, possibly due to the high Krafft point and high crystallinity of MES-Na. Ester bonds in the MES-Na molecule may easily undergo hydrolysis with consequent formation of the disodium salt, which has low surface activity. The hydrolysis of MES-Na in detergent powder may occur on contact with alkaline components.

FIG. 9.20  Effect of surfactants on protease activity. Conditions: surfactant 300 ppm, protease 0.008 AU/L, pH 10.5, and 40°C. AS, C12AS-Na; LAS, C10–14LAS-Na; and MES, C14–16MES-Na.

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TABLE 9.4  Formulations of MES-Based Detergents Component

LAS-Based

MES-Based

MES-/LAS-Based

Surfactant

30–40

30–40

30–40

(LAS/AOS and LAS/AS) Builder

15–25

15–25

15–25

Alkali

15–25

15–25

15–25

Enzyme

+

+

+

FWA

+

+

+

AS, C12AS-Na; LAS, C10–14LAS-Na; MES, C14–16MES-Na; and FWA, fluorescent whitening agent.

FIG. 9.21  Krafft point of MES/LAS mixture. LAS, C10–14LAS-Na; MES, C14–16MES-Na.

A new surfactant system, which uses LAS-Na with MES-Na, has been established, and good results obtained from it, as shown in Table 9.4. This system not only eliminates the disadvantages of MES-Na but also enhances washing detergency at low temperatures. The surfactant properties of the MES-Na/LAS-Na blend were investigated physicochemically by Krafft points determined from the cross temperature point of the solubility line and the CMC lines against temperature (Fig. 9.21). The value of the Krafft point was determined with increasing LAS-Na content. The blend was also studied by DSC using a surfactant powder with 5% moisture content. MES-Na powder is a 2 mol hydrate, judging from moisture content. Fig. 9.22 shows the DSC pattern for C14–16MES-Na. An endothermic peak can be seen at 39°C, lower than that of C16MES-Na (see Fig. 9.5). For LAS-Na powder, no endothermic peak was observed. MES/ LAS in a one-to-one ratio clearly showed a smaller DSC peak, indicating that the MES-Na powder no longer had high crystallinity. DSC and Krafft point data suggest that MES-Na

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FIG. 9.22  DSC profiles of C14–16MES-Na/C10–14LAS-Na mixture. Sample: surfactant powder, water content 5%, and DSC condition 1°C/min.

FIG. 9.23  Detergency of C14–16MES-Na/C10–14LAS-Na mixture. Conditions: Terg-O-Tometer, artificial soil (cotton), water hardness 54 ppm (CaCO3), surfactant (MES + LAS) 200 ppm, sodium carbonate 200 ppm, and zeolite 150 ppm.

should be mixed with LAS-Na at a molecular level to reduce the DSC endothermic peak and falloff of the Krafft points. This mixing would also enhance detergency, which was assessed under the usual conditions using artificial swatches (Fig. 9.23). Detergency was found to increase with the ratio of MES-Na to LAS-Na at 25°C; the detergency was a maximum at oneto-one blend ratio.

9.4.2  Liquid Laundry Detergent 9.4.2.1  Detergency at Neutral pH Liquid detergent has several advantages over powder detergents. Liquid detergents readily and completely dissolve in water, even in cold water; thus, liquid detergent is less messy than powder detergents. In the form of liquids, problem such as caking upon storage is eliminated as often seen with powders when exposed to moisture. However, the challenges arise

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FIG. 9.24  Solubilization temperatures for a combination of C16–18MES and other surfactants. The total concentration of the surfactants is 20 wt%, and the pH is set at 7.5.

in formulating a stable liquid detergent from C16–18MES-Na because of high Krafft point and low solubility at low temperature (Zulina et al., 2017). Tobori et  al. reported the formulation to decrease the solubilization temperature of the C16–18MES-Na solution, along with the combined use of other surfactants (Tobori, 2017; Kubozono et al., 2015). Fig. 9.24 shows the solubilization temperatures for a combination of C16–18MES-Na and other surfactants. When a combination of appropriate surfactants such as alcohol ethoxylate with 7 mol ethylene oxide (C12AE (7EO)), alcohol ether sulfate (C12AES (2EO)-Na), and C10–14LAS-Na was used, the solution containing 5 wt% MES-Na remained clear below 0°C (Fig. 9.24). Moreover, the detergency of MES-Na for sebum was higher than that of AES-Na or LAS-Na under liquid detergent conditions. We confirmed that the solubility of MES-Na could be improved by enhancing the detergency of sebum secreted by the sebaceous gland in humans in a liquid laundry detergent system. Based on these observations, we conclude that MES-Na has great potential to be used as an ingredient in liquid detergents, even in low-temperature conditions.

9.5 CONCLUSION Methyl ester sulfonates are derived from renewable sources. They have excellent surfactant properties. They are easily incorporated into formulations that meet many different requirements, such as cold-water washing, and they provide the advantages of low cost, excellent surfactant properties, low aquatic toxicity, and rapid biodegradability. In addition, they are mild and safe for the human skin. The employment of MES in detergents is increasing, and certainly, this trend will continue in the future.

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323

References Boucher, E.A., Grinchuk, T.M., Zttlemoyer, A.C., 1968. Surface activity of sodium salts of alpha-sulfo fatty esters; the air-water interface. J. Am. Oil Chem. Soc. 45, 49–52. Drozd, J.C., Desai, D.D., 1991. Liquid laundry detergents based on soap and alpha-sulfo methyl esters. J. Am. Oil Chem. Soc. 68, 59–62. Fujiwara, M., Miyake, M., Abe, Y., 1993. Colloidal properties of alpha-sulfonated fatty acid methyl esters and their applicability in hard water. Colloid Polym. Sci. 271, 780–785. Fujiwara, M., Kaneko, Y., Oubu, K., 1995. Light scattering study on the micellar systems solubilizing a fatty acid. Colloid Polym. Sci. 273, 1055–1059. Fujiwara, M., Okano, T., Amano, H., Asano, H., Oubu, K., 1997. Phase diagram of alpha-sulfonated palmitic acid methyl esters sodium salt/water system. Langmuir 13, 3345–3348. Hato, M., Shinoda, K., 1973. The solubilities, critical micelle concentrations, and Krafft points of bivalent metal alkyl surfaces. Bull. Chem. Soc. Jpn. 46, 3889–3890. Hayashi, S., Ikeda, S., 1980. Micelle size and shape of sodium dodecyl sulfate in concentrated NaCl solution. J. Phys. Chem. 84, 744. Itakura, K., 2004. Powders, flakes, or pellets containing salts of alpha-sulfofatty acid alkyl esters in high concentrations, process for production thereof, granulated detergents, and process for production thereof, WO2004111166A1. Kapur, B.L., Solomon, J.M., Bluestein, B.R., 1978. Summary of the technology for the manufacture of higher a­ lpha-sulfo fatty acid esters. J. Am. Oil Chem. Soc. 55, 549–557. Kekicheff, P., Grabielle-Madelmont, C., Ollivon, M., 1989. Phase diagram of sodium dodecyl sulfate-water system: a calorimetric study. J. Colloid Interface Sci. 131 (1), 112–132. Kubozono, T., Morimoto, Y., Endo, C., Otsuka, S., Tobori, N., 2015. New features of methyl ester sulfonate (MES) for laundry detergent. In: Proceeding of the 10th World Surfactant Congress and Business Convention (CESIO), Istanbul, pp. 126–129. Masuda, M., Odake, H., Miuram, K., Oba, K., 1993a. Biodegradation of 2-sulfonatofatty acid methyl ester. I. J. Jpn. Oil Chem. Soc. 42, 643–647. Masuda, M., Odake, H., Miura, K., Ito, K., Yamada, K., Oba, K., 1993b. Biodegradation of 2-sulfonatofatty acid methyl ester. II. J. Jpn. Oil Chem. Soc. 42, 905–909. Maurer, E.W., Weil, J.K., Linfield, W.M., 1977. The biodegradation of esters of alpha-sulfo fatty acids. J. Am. Oil Chem. Soc. 54, 582–584. Miura, M., 1991. Performances of fatty acid alpha-sulfomethyl esters (3). Biodegradation. In: 3rd Annual Meeting of Home Economics. vol. 3, pp. 1099–1108. Niikura, F., Omine, M., Kimura, Y., Konta, H., Kageyama, M., Tobori, N., Araki, K., 2013. Coloration process in the sulfonation of fatty acid methyl ester with sulfur trioxide. J. Am. Oil Chem. Soc. 90 (6), 903–909. Okumura, O., Sakatani, T., Yamane, I., 1976. Mechanism of sulfonation of fatty acid esters with sulfur trioxide and properties of alpha-sulfo fatty acid esters. In: Proceedings of the 7th Committee International des Derives TensoActs. vol. 1. Mowcow, pp. 225–234. Okumura, O., Tokuyama, K., Sakatani, K., Tsuruta, T., 1980. J. Jpn. Oil Chem. Soc. 30, 432–441. Satsuki, T., 1986. Methyl ester sulfonates: a surfactant based on natural fats. In: Proceeding of the 3rd World Conference on Detergents, Monteux, pp. 135–140. Satsuki, T., 1992. Application of MES in detergents. Inform 3, 1099–1108. Satsuki, T., Tobe, S., Yoneyama, Y., Mukaiyama, K., 1999. Blending effect of different kind of surfactant on enzyme activity. Mater. Technol. 17, 119–125. Schambli, F., Schwuger, M.J., 1990. Physico-chemical properties of alpha-sulfo fatty acid methyl esters and alpha-sulfo fatty acid di-salts. Tenside Surfactant Deterg. 27 (6), 380–389. Shinoda, K., 1963. The formation of micelles. In: Colloidal Surfactants. Academic Press, New York, pp. 55–57. Shinoda, K., Maekawa, M., Shibata, M., 1986. Ionic surfactants soluble in hard water and hydrocarbons: behavior of organized surfactant solutions as a function of the hydrophilic-lipophilic balance. J. Phys. Chem. 90, 1228–1230. Smith, N.R., 1989. Alpha-sulfo methyl esters: a new alternative. Soap Cosmet. Chem. Spec 48–57. April. Steber, J., Wierich, D., 1989. The environmental fate of fatty acid alpha-sulfomethyl esters. Tenside Surfactant Deterg. 26, 406–411.

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Stein, W., Baumann, H., 1975. Alpha-sulfonated fatty acids and esters; manufacturing process, properties and applications. J. Am. Oil Chem. Soc. 52, 323–329. Steliner, K.L., Scamehom, J.F., 1989. Hardness tolerance of anionic surfactant solutions I. Anionic surfactant with added monovalent electrolyte. Langmuir 5, 70–74. Stirton, A.J., 1968. Alpha-sulfo fatty acids and derivatives; synthesis, properties and use. J. Am. Oil Chem. Soc. 39, 490–496. Stirton, A.J., Weil, J.K., Bistline Jr., R.G., 1954. Surface-active properties of salts of alpha-sulfo fatty acid methyl esters and alpha-sulfo fatty acid and esters. J. Am. Oil Chem. Soc. 31, 13–16. Stirton, A.J., Bistline Jr., R.G., Weil, J.K., Maurer, J., 1962. Sodium salts of alkyl esters of alpha-sulfo fatty acids; wetting, lime soap dispersion and related properties. J. Am. Oil Chem. Soc. 39, 128–131. Tobori, N., 2017. The Use of Palm Oil-based Detergents toward Sustainable Society. In: Proceeding of the MPOB International Palm Oil Congress & Exhibition (PIPOC 2017), Kuala Lumpur, OS2, pp. 16–20. Watanabe, H., Morigaki, A., Kaneko, Y., Tobori, N., Aramaki, K., 2016. Effect of temperature and humidity history on brittleness of α-sulfonated fatty acid methyl ester salt crystals. J. Oleo Sci. 65 (2), 143–150. Watanabe, H., Morigaki, A., Yuba, M., Yamada, K., Miyake, M., Tobori, N., Aramaki, K., 2018. Structural analyses of hydrated crystals in mixer green surfactant systems: α-sulfonated fatty acid methyl ester salt and fatty acid soap mixture. J. Surfactant Deterg. 21, 221–229. Weil, J.K., Bistline Jr., R.G., Stirton, A.J., 1953. Sodium salts of alkyl alpha-sulfo-palmitate and stearates. J. Am. Oil Chem. Soc. 75, 4859–4860. Wittman, J.C., Manley, R.S.J., 1977. Polymer-monomer binary mixture. I. Euretic and epitaxial crystallization in poly(e-caprolactone)-trioxane mixtures. J. Polym. Sci. B Polym. Phys. 15, 1089–1100. Yamane, I., Miyawaki, Y., 1989. Manufacturing process of alpha-sulfomethyl esters and their application to detergents. In: Proceedings of 1989 International Palm Oil Development Conference: Chemistry, Technology and Marketing, Malaysia, pp. 132–141. Zulina, A.M., Zainab, I., Razmah, G., 2017. Performance of palm-based C16/18 methyl ester sulphonate (MES) in liquid detergent formulation. J. Oleo Sci. 66 (7), 677–687.

Further Reading Satsuki, T., Umehara, K., Yoneyama, Y., 1992. Performance and physicochemical properties of α-sulfo fatty acid methyl esters. J. Am. Oil Chem. Soc. 69, 672–677.

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