MES – Myths, Mysteries and Perspectives on

Properties and Use

Jorge Aparicio*, Brian W. MacArthur, Wm. Brad Sheats and Burton J. Brooks,

The Chemithon Corporation, Seattle, WA 98053 USA (* Presenting author)

ABSTRACT:

During the last fifty years studies have appeared examining the properties of alpha-sulfonated
fatty acid methyl esters (MES) generally as the sodium mono-salt. The literature reports many
advantages of MES, but also frequently mentions certain properties that may be
disadvantageous. Thus, studies of pure component aqueous solutions report Krafft point
temperatures for MES that are higher than other common anionic surfactants, suggesting that
solubility of MES may be a limitation, especially in cold water washing. Further, they point to the
hydrolysis of MES as a limitation in comparison with other anionic surfactants. This paper will
review these issues and present ample evidence to show that in fact MES is a versatile
surfactant that can be formulated into a broad range of detergent products, including formulas
that are suitable for low temperature washing applications. Hydrolysis of MES can be
controlled and avoided and we’ll discuss how to do that. We will review product formulations
and show typical examples of heavy duty powder and liquid products and other products that
use MES as a primary surfactant.

KEYWORDS: MES, properties and use; Krafft point; hydrolysis

PROPERTIES OF MES REVIEWED:

For clarity we use the abbreviation “MES” to denote the sodium mono-salt of alpha-sulfonated
fatty acid methyl esters. Further, we will use the notation “65:35 C1618 MES”, for example, to
denote MES active that contains a ratio of 65% to 35% of C16 MES to C18 MES.

In the 1960s, early papers on methods for making fatty acid methyl esters and their derivatives
and also papers describing the properties of pure component MES began to appear [1,2].
During the 1970s further studies of the process for making light colored MES and their
properties were published [3, 4, 5 and 6]. These develop the basic chemistry in the process of
sulfonating fatty acid methyl ester using air-SO3 as the sulfonating agent. In the 1990s,
papers describing how to use MES in detergent applications began to appear [7, 8, and 9].
Significant commercial processes for making MES appear in patent literature, for example
patents from Lion Corporation [10, 11], Henkel KGaA [ 12,13], and The Chemithon
ICSD 2012, Shanghai, PRC – April 2012 1 © 2012 The Chemithon Corporation
Corporation[14,15,16]. Commercial plants have now been in production for many years, so that
it has become much easier to obtain fatty acid methyl ester feedstock, MES active and
commercial products for further studies. We find many papers that have published the
properties of MES and particularly the many advantages MES provides. A few highlights are
reproduced here as a review.

MES PERFORMANCE HIGHLIGHTS:

Satsuki [7] provides data on the properties of MES in comparison with other anionic surfactants.
He shows a comparison of pure homologs of MES in a medium-temperature washing test (25
and 40 °C) against LAS and AS, reproduced here as Figure 1. Note that the C16 and C18
actually outperform LAS in this test. Satsuki compares surfactant detergency as a function of
concentration, comparing MES with LAS and AS at 25°C in medium and 40 °C in high hardness
wash water. Figure 2 shows that MES (C1416 MES was used) easily outperforms the other
surfactants and can produce equal detergency at much lower concentrations.

Terg-O-Tometer, Artificial Soil (cotton), 25 ˚C or 40˚C

Liquor ratio 30, Water hardness 54 or 270 ppm (CaCO3)
Surfactant 270ppm, Na2CO3 135ppm, Silicate 135ppm

Figure 1. Effect of MES carbon chain length on detergency [7]

ICSD 2012, Shanghai, PRC – April 2012 2 © 2012 The Chemithon Corporation
 Terg-O-Tometer. Artificial soil, 25˚C, Water hardness 54 ppm (CaCO3)
Surfactant 0 to 400 ppm, Na2CO3 135 ppm, Silicate 135 ppm

Figure 2. Relationship of Detergency and Surfactant Concentration [7]

Satsuki also shows the effect of water hardness on detergency reproduced here as Figure 3.
The MES has better detergency over a wider range of hardness than other surfactants. Satsuki
also reports the effect different surfactants have on enzyme activity, shown here in Figure 4.
MES is seen to have the least impact on enzyme activity.

Figure 3. Effect of Water Hardness on Detergency (phosphate-built formulation) [7]

ICSD 2012, Shanghai, PRC – April 2012 3 © 2012 The Chemithon Corporation
 Surfactant 300 ppm, Protease 0.008AU/L, pH 10.5, 40˚C

Figure 4. Effect of Surfactants on Protease Activity [7]

Satsuki reports results of biodegradability tests comparing MES with LAS. He reports total
organic carbon and methylene blue active substances as a function of time, as reproduced here
in Figure 5a and 5b. MES degrades significantly faster than LAS, and is substantially degraded
in about one day.

Figure 5a. Biodegradation of Surfactant (TOC) [7]

ICSD 2012, Shanghai, PRC – April 2012 4 © 2012 The Chemithon Corporation
Figure 5b. Biodegradation of Surfactant (MBAS) [7]

Drozd [9] provides another overview of the properties, particularly focusing on middle chain
length MES in household cleaning products. Among the many advantages he cites are the
following human and environmental safety attributes:

 derived from renewable resources;

 mild to skin;
 not a human skin sensitizer;
 not a primary skin irritant;
 nontoxic orally;
 biodegradable;
 practically nontoxic to aquatic organisms; and
 contains no known by-products with safety issues.

Drozd discusses surfactant performance properties of MES and cites surface tension reduction
capability, foaming and wetting properties are very good, good solubility and good solubilizers
for other surfactants, work well in hard water, excellent lime soap dispersants and are
compatible with enzymes. Drozd presents detergency data in moderately hard water
comparing soil removal, ∆R, from a standardized washing test for detergent formulas based
MES of different carbon-chain lengths up to C18 in comparison with LAS (see Figure 6). This
shows that the longer chain MES exhibit better detergency than LAS and lower chain length
MES.

ICSD 2012, Shanghai, PRC – April 2012 5 © 2012 The Chemithon Corporation
Figure 6. Detergency of Methyl Ester Sulfonates in Moderately Hard Water [9]

Based on studies such as these it is not surprising that MES has attracted increased attention in
the detergent industry worldwide. MES has a lot to offer as a primary surfactant in detergent
products. In terms of cost, performance, safety for human use and for the environment MES is
superior to other types of surfactants. Nevertheless, there are a few properties of MES that are
often cited, and presented as relative disadvantages. For example, the longer hydrocarbon
chain MES, including C16 and C18 and presumably mixtures of C1618 MES, exhibit Krafft
points that are higher than other commonly used surfactants, such as LAS and AS. Authors
often mention this property which relates to solubility of the pure surfactant and state that this
will make it difficult to use in formulations for cold water washing applications. However, this is
not true at all. Similarly, some studies mention the hydrolytic stability of MES as a relative
disadvantage. Here again, this is generally not difficult to overcome. So we would like to turn
attention onto these myths and set the record straight.

ALLEGED DISADVANTAGES OF MES: Relatively Poor Solubility (Krafft point)

In most of the papers that delve into the properties of MES you can find a discussion of the
critical micelle concentration and Krafft point temperatures. These properties are fundamental
to the performance of any surfactant in a detergent application. Surfactants are unique in their
molecular structure, and possess a hydrophilic portion joined with a hydrophobic portion. A
typical example is an anionic surfactant possessing a sulfonated head group fixed to a long
hydrocarbon chain, such as LAS, AS or MES. The head group is the hydrophilic portion, and
the hydrocarbon chain is the hydrophobic portion. These structures force the surfactant
molecules into unique behaviors in aqueous solutions, and the property of detergency is one of
these. Note that oil solubility may be important in other applications, such as lube oils.

ICSD 2012, Shanghai, PRC – April 2012 6 © 2012 The Chemithon Corporation
SOLUBILITY OF SURFACTANTS:

In an aqueous solution at equilibrium we can imagine a mass of pure crystalline surfactant

covered with water and with an air-water interface. Molecules of surfactant will dissolve into the
bulk water until a saturation concentration is reached, and this concentration depends only on
the system temperature. If we start at a low temperature (say about 0 °C) we can plot the
concentration of surfactant in the bulk solution as a function of temperature. As we increase the
system temperature, the concentration of surfactant will increase typically in a linear manner
until a concentration is reached called the critical micelle concentration, CMC. At this
temperature the first micelles start to form. A micelle is an aggregation of surfactant molecules
oriented with the hydrophilic head groups on the outside and the hydrocarbon chains
overlapping on the inside. Micelles can form as spheres, ovals, cylinders, and even discs. At
the CMC, the slope of the concentration vs. temperature curve changes abruptly. At higher
temperatures, the surfactant is forming more and more micelles and the concentration in the
solution rises much more rapidly. The Krafft point temperature, TK, is the temperature
corresponding to the CMC on the solubility vs temperature curve. Various measurement
methods for the Krafft point have been devised, and as a consequence, the literature shows
some variability in Krafft point data.

The Krafft point is a useful indication of the relative solubility of a surfactant, because in typical
detergent washing applications, we want to have micelles. We want to have plenty of
surfactant molecules available and displacing and solubilizing the soil in the wash solution.
Therefore, the temperature at which we use the cleaning product must be considered, and we
want the surfactant to have a Krafft point below the washing temperature.

The Krafft point for pure component MES homologs have been reported [2, 17] and generally
increase with molecular weight or carbon chain length. The TK value for pure C16 MES is 28 +
1°C, and for pure C18 MES the TK value is 40 + 1°C. These data are the highest values we
could find for TK reported in the literature. TK values in other papers such as Satsuki [7] give
data that are significantly lower, and the discrepancy may be due to the analytical method or
sample purity or both. These values suggest that pure MES solutions would not make a very
effective detergent especially in a cold water washing application. The relatively high Krafft
point for MES is therefore often mentioned as a disadvantage, and this is the first issue that we
would like to discuss in more detail. Can we find a way to use MES in a cold water washing
application?

ICSD 2012, Shanghai, PRC – April 2012 7 © 2012 The Chemithon Corporation
MES IN COLD WATER WASHING:

Schambil [6] discusses the effect of mixing pure C16 and pure C18 MES, which has a beneficial
impact on the Krafft point. There is a eutectic depression of the Krafft point in mixtures of
C1618 MES, as shown in Figure 7, which is taken from Schambil. The Figure shows a
minimum TK at about 65:35 to 70:30 C1618 MES. The TK value in this region is about 15 °C.

Figure 7. Eutectic Depression of the Krafft Point in Mixtures of pure C16 MES and Pure
C18 MES [6]

It is important to note that natural palm stearin MES often has just about this mixture of C16 and
C18 MES. For this reason natural (distilled but not fractionated) palm stearin MES would be the
most soluble MES to employ in a detergent formulation intended for cold water washing
conditions.

It has long been known that mixtures of surfactants also can significantly depress the Krafft
point. In Yoneyama [8] the Krafft point of mixtures of LAS with MES are reported, and Figure 8
reproduces the data. You can see that an 80:20 mixture LAS:MES had a Krafft point of 0 °C.

ICSD 2012, Shanghai, PRC – April 2012 8 © 2012 The Chemithon Corporation
Figure 8. Krafft Point of MES/LAS Mixed Systems [8]

We point out that the pure MES Krafft point in this curve is about 25 ˚C, which indicates use of
C16 MES in this experiment. Use of a 65:35 C1618 MES would produce even more dramatic
reductions, allowing a greater proportion of MES to be used in the formulation.

Figure 9, also from Yoneyama, shows mixtures of MES with AE (nonionic surfactant), and the
Krafft point was 0+ °C for a mixture of 60+:40- AE:MES in this case.

Figure 9. Krafft Point of MES/AE Mixed Systems [8]

ICSD 2012, Shanghai, PRC – April 2012 9 © 2012 The Chemithon Corporation
These figures demonstrate that a mixture of surfactants in an aqueous solution behaves in a
unique manner, as the surfactants solubilize eachother, and mixed micelles form with a CMC
and Krafft point unique to the mixture. The mixture will perform like a new surfactant with a
combination of the properties of its constituents. Studies have shown that use of branched or
linear anionic or nonionic surfactants in binary or ternary or even more complex combinations
can have beneficial effects. So in fact detergent products are formulations that possess their
own unique properties, and one can use longer chain MES, which is superior in detergency, to
design a formulation for a particular application.

COLD WATER WASHING FORMULAS EMPLOYING MES:

If we consider cold water washing perhaps in relatively hard water at about 10 °C or less, we
can mix anionic surfactants or nonionic surfactants with MES or use combinations of branched
or linear surfactants, and obtain synergistic performance characteristics, such as a depression
of the Krafft point down to say 5 °C or less. With this enhanced solubility it is possible to
develop detergent formulas that will work in cold water washing conditions.

It is not surprising that patents have appeared that describe formulations using longer chain C16
and C1618 MES specifically for cold water washing conditions. Thus, in Hecht [18] we find
mixtures of MES with nonionic surfactant or a branched surfactant or with alkyl or alcohol sulfate
in various binary compositions. They also disclose compositions using LAS and MES with and
without a branched surfactant in binary and ternary surfactant systems. Still other examples
with four or five surfactants are disclosed. The patent also mentions that their Krafft point
temperatures were determined on a Phase Technology Phase Analyzer system, which
determines Krafft temperature by scanning diffusive light scattering in aqueous solutions
containing 1 wt% of total surfactant. Compositions with Krafft point temperatures below 5 °C
are disclosed, and examples are provided.

MES can of course be used for warm or hot water washing applications. It is an excellent
surfactant and should be considered for the many advantages that have been mentioned.

ALLEGED DISADVANTAGES OF MES: Limitations Due to Hydrolytic Stability:

The hydrolytic stability of MES is described in the chemistry for sulfonation of fatty acid methyl
esters, as has been disclosed in previous publications [19]. The process objective is to
maximize the yield of the desired mono-salt MES and to avoid production of disalt, which is
generally counted in the total active surfactant, but disalt has poor detergency and is therefore
considered a loss of yield. Disalt is therefore to be minimized.

ICSD 2012, Shanghai, PRC – April 2012 10 © 2012 The Chemithon Corporation
SOURCES OF DI-SALT IN MES SYNTHESIS:

Disalt can form during the sulfonation of methyl ester according to equation (1.), as a
consequence of a persistent intermediate (III), which is methyl ester sulfonic acid with an
adducted sulfur trioxide. Upon Neutralization this will directly form disalt (IV). Therefore, the
process must digest the sulfonic acid mixture at sufficient temperature for a sufficient time to
fully react the adducted sulfur trioxide and minimize the amount of (III).

O O
ΙΙ ΙΙ
R - CH - (C - OCH3):SO3 (III) + 3 NaOH → R - CH - C - ONa (IV) + 2 H2O + CH3OSO3Na (1)
Ι Ι
SO3H SO3Na

Furthermore, during Neutralization, and in subsequent use, the desired MES mono-salt (VI)
can hydrolyze if exposed to favorable conditions, according to equation (2). This hydrolysis will
produce both disalt and methanol.

O O
ΙΙ ΙΙ
R - CH - C - OCH3 (VI) + NaOH → R - CH - C - ONa (IV) + CH3OH
(2)
Ι Ι
SO3Na SO3Na

Therefore, minimizing the yield to disalt requires completion of the reaction of the intermediate
adduct to methyl ester sulfonic acid prior to neutralization, and precise control of the bleaching
and neutralization conditions to prevent conversion of MES to disalt and methanol.

Studies of the hydrolytic stability of MES typically show the rate of hydrolysis of MES in a
washing solution as a function of pH and a family of curves is shown for a range of
temperatures. A typical plot of this type is taken from Stein [3] shown here as Figure 10. At
moderate temperatures MES is stable up to a pH of about 9.5 or 10 and above that pH the rate
of hydrolysis increases. At higher temperatures such as 80 ˚C the curve shows rapid hydrolysis
below a pH of 3 and above a pH of about 9.5.

ICSD 2012, Shanghai, PRC – April 2012 11 © 2012 The Chemithon Corporation
Figure 10. Rate of Hydrolysis of Palm Kernel Methyl Ester Sulfonate. Concentration = 3.4
g/liter. [3]

The figure shows that MES needs to be maintained in a pH range where it is stable. It does not
like extreme high or extreme low pH conditions, and as the temperature rises above typical
ambient conditions, the rate of hydrolysis will increase. Note that use of a detergent product is
completed in a relatively short period of time, so that provided the pH of the wash media is
controlled, the MES active should be stable and present no problem.

The Chemithon Corporation has been sulfonating methylester feedstocks for 25 years in a pilot
plant that exactly duplicates Chemithon’s commercial process, and as a result of the studies we
have done, Chemithon has an inventory of MES product materials that has been stored for
various periods of time. The MES products were analyzed when they were freshly made. So
we thought it would be useful to check the analysis of some well-aged MES samples to see if
they had changed. A sample of pure C1618 MES flakes made in January of 2006 and now
aged some six years showed no change in %disalt/100% total active (MES + disalt). A pure
C16 MES flake sample made in February 2003 and now aged nine years also showed no sign
of hydrolysis as %disalt/100% active remained unchanged. We also checked a commercial
powder product that contained more than 20% C16 MES powder dry blended into the
formulation. This sample was manufactured in 2004 and has been stored indoors but left open
to the atmosphere for about eight years. Once again there was no change in the %disalt/100%
active, indicating that no appreciable hydrolysis had occurred. All of these samples have been
stored at typical ambient temperatures. This shows that hydrolysis can be avoided and in the
right conditions MES is stable for long periods of time.

CURRENT PRODUCTS THAT EMPLOY MES:

Product formulation US patents [20,21,22] have appeared that disclose formulas for detergent
products that contain MES. These include products specifically designed for cold water
washing based on longer chain MES. Liquid products are also described. The number of

ICSD 2012, Shanghai, PRC – April 2012 12 © 2012 The Chemithon Corporation
detergent products containing MES is growing quickly worldwide. Today you can find detergent
formulas for granules or powders, liquids and even in soap bars. MES products have long
been in use in Japan, and today more MES is being produced and products are being
introduced in many more countries. Certainly throughout Asia and the Pacific Rim, MES figures
to be a major surfactant as production in the region rises.

In the USA, Sun Products Corporation (formerly HUISH Detergents, Inc.) has been
manufacturing MES based products for more than ten years, using methyl ester sulfonates
derived from palm oil. They have their own methyl ester refining plant which may be the largest
one in North America. Sun Products has the largest methyl ester sulfonation plant in the world,
which started up in 2001. Figure 11 shows some examples of detergent powder products
branded by Sun Products Corporation, and used with their permission. Also, Figure 12 shows
examples of liquid products branded by Sun Products Corporation, and used with their
permission.

In Malaysia, the Malaysian Palm Oil Board (MPOB) is engaged in development of production
and use of palm oil and especially higher value derivatives. MPOB has installed a pilot
sulfonation plant (supplied by Chemithon Corporation) to enable research and development of
MES, and numerous studies have been published by them. MPOB has developed product
formulations using MES and palm oil derivatives, and some of these are shown in Figure 13,
and are used with their permission.

ICSD 2012, Shanghai, PRC – April 2012 13 © 2012 The Chemithon Corporation
Figure 11. Powder packages for detergents based on MES.
Used by permission of Sun Products Corporation, 2012.

ICSD 2012, Shanghai, PRC – April 2012 14 © 2012 The Chemithon Corporation
Figure 12. Liquid packages for detergents based on MES.
Used by permission of Sun Products Corporation, 2012.

ICSD 2012, Shanghai, PRC – April 2012 15 © 2012 The Chemithon Corporation
Figure 13. Products produced by the Malaysian Palm Oil Board (MPOB) using MES.
Used by permission of the Malaysian Palm Oil Board, 2012

CONCLUSIONS:

Published studies and patents highlight the recent advances in process technology for making
methyl ester sulfonates, as well as the advantageous properties of MES. They show that using
MES in detergent formulations makes sense. Methyl ester sulfonates are derived from
renewable sources, they have excellent surfactant properties, we can work them up in
formulations that meet many different requirements, such as cold water washing, and we get the
advantages of low cost, excellent surfactant properties, low aquatic toxicity and rapid
biodegradability, and they are mild and safe for human skin. We have shown that the often
cited Krafft point of pure component MES homologs is not a barrier to formulating products with
longer chain MES. In fact, 65:35 C1618 MES would seem to be the best choice. Similarly, we
can avoid hydrolysis of MES by controlling the pH and temperature in ranges where MES is
stable. More and more products are appearing that contain MES, and certainly this trend will
continue in the future. What the world needs now is more methyl ester sulfonates for use in its
cleaning products.

ICSD 2012, Shanghai, PRC – April 2012 16 © 2012 The Chemithon Corporation
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ICSD 2012, Shanghai, PRC – April 2012 17 © 2012 The Chemithon Corporation