SULFURIZED EP ADDITIVE SERIES PART II - LIGHT S-EP AND ITS BASIC APPLICATION

In previous part, I have given a basic introduction of S-EP classification, dark S-EP and its application. In this part, I am going to talk about light S-EP. Because I have no right to publish TDS and MSDS without permission of suppliers, I only can show you the light S-EP which I can find them in the Internet, and these documents must belong to the big market share S-EP (i.e., DIC, ELCO, LANXESS).

I. What Is Light S-EP?

There is not a specific definition as far as I know, but I will base on DIC has shown the graph below:

Figure 1: DAILUBE Product Line

Basing on the published product line of DIC Japan and the data I have, the product with ASTM D-1500 wit a color of 6 Dil (Dilution of 15% volume) can be called light color. However, I think the S-EP with color below 8 (ASTM D-1500) without dilution should be called light S-EP. Absolutely, the color less than 5 is the perfect light S-EP.

As dark S-EP, light S-EP can be classified by its chemical structures. There are 4 typical types: light S-Olefins, light S-triglycerides, light S-Esters, and light S-Fatty acid. In general chemistry, we know that color of organic compounds depends on its saturation. The structures with more double bonds, it will become dark and dark... Therefore, to make the light color S-EP, the important process is to reduce the double bonds and chromophoric groups in its chemical structures.

2. How To Prepare Light S-Olefins EP?

RAW MATERIALS:

There are many types of raw materials to make S-EP. It can be classified as followed:

- Vegetable Oil: soybean, palm oil, tall oil...

- Animal triglycerides: lard oil, fish oil, tallow oil...

- Fatty acids, TOFA...

- Olefins: isobutane, polyisobutene...

MERCAPTAN ROUTE:

There are several ways to synthesize S-olefins EP and I will give you the brief summary on Mercaptan Route. Other is using disulfur dichloride (S2Cl2) and sodium sulfide as raw materials (you can google it for further information)

First, the reaction between H2S and olefins forms mercaptans (R-CH2-CH(SH)-R) as intermediates under Lewis acid at a widen range of temperature from -20 deg. C to 90 deg. C. Reaction temperature depends on what kinds of Lewis acids is used. 

Second, the formed mercaptans are reacted with H2O2 to form dialkyldisulfides 

2R-CH2-CH(SH)-R + H2O2 ===> R-CH2-CHR-S-S-CHR-CH2-R (1)

or dialkyl-trisulfides / dialkyl-polysulfides are synthesized through reaction of mercaptans and Sx molecules (Sulfur molecule is a cyclic octatomic molecules = S8 ring)

2R-CH2-CH(SH)-R + S2 ===> R-CH2-CHR-S-S-S-CHR-CH2-R (Dialkyl-trisulfides) + H2S (2)

2R-CH2-CH(SH)-R + Sx ===> R-CH2-CHR-S-S(x-1)-S-CHR-CH2-R (Dialkyl-polysulfides) + H2S (3)

To control the color of the reaction, high-pressure and high-temperature equipments have been employed. The reactor muse be high-pressure resistance. The operating temperature is from 120 deg. C to 170 deg. C. Pressure can be up to 50-60 bar when the olefins have low boiling point (i.e., isobutene). With high boiling olefins (e.g., diisobutene), the reaction pressure is much lower ~ 2-15 bar. By using H2S as a reducing agent, it will reduce the double bonds which are known as chromophoric groups. As a result, there are a bit double bonds in chemical structures of final products ==> the light color S-Olefins are more oxidative stable in contrast to darker ones.

Figure 2: RC 2540, Active Dialkyl-pentasulfide, Light Color

The chemical structure of RC 2540 can be described:  R-CH2-CHR-S5-CHR-CH2-R. This possesses a very light color, just type 2.5 by ASTM D-1500. Because it contains S5 in the structures, it is called active S-EP. It means it corrodes Cu and yellow alloys. As shown by ASTM D-130, it is very active just at 2.5% in base oil 3h/100 deg. C... 3b-4c... 

3. Light Color Sulfurized EP Application - Especially Metalworking Fluids

There are many applications for light color S-EP. Normally, the big consumption for S-EP is Metalworking Fluid and Grease. Others are Gear Oil, Slide-way Oils, Hydraulic Oils, Agricultural Applications, Automotive Applications.

Figure 3: EP Performance of RC 2540

The traditional Gear Oils, which can find in the Gear Oil packages of AFTON CHEMICAL and LUBRIZOL with specific smell, are Sulfured Isobutylene (SIB). SIB is often applied in the close gear box, but it cannot be used in open gear box because of its distinct odor. Future formula will be made with long-carbon chain length to avoid the bad smell due to its high boiling point.

The choose of S-EP for Bentonite Grease should be selected carefully to avoid destroying Bentonite Grease structures. Ca and Li greases can be used S-EP, but we need to pay attention on Cu corrosion protection (ASTM D-130) at specific temperature. 

If looking at the EP performance of RC 2540, there is no big difference in Welding Load when adding 2 to 15 % RC 2540. However, the scar diameter increase with an increase of its treat-rate. This can be explained by its high active sulfur... ~ 90%. Because its high activity, it dramatically reacts with metal surface to form metal sulfides leading to higher wear. Therefore, the scar diameter is directly proportional to the S content in the oil as seen in Figure 3. RC 2540 can be used to replaced SIB in many applications. It also can be used in Metalworking fluids as Lanxess recommended.

4. S-EP Manufacturers

- Arkema, France

- DIC Corporation, Japan

- Elco, US.

- Lubrizol, US.

- Lanxess, Germany.

- Others (Indian, Chinese...)

Written by Steven Nguyen