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

SULFURIZED EP ADDITIVE SERIES PART I - DARK S-EP FOR METALWORKING FLUIDS

I. DIFFERENCE BETWEEN EP AND AW ADDITIVE

Extreme Pressure (EP) and Anti Wear (AW) additives are very common in metalworking fluids (MWF) industry. The classification of those additive are very confused for those who is just involved in this industry as I used to be 4 years ago. However, I will not talk about their lubricity mechanism, so I will distinguish them very short and easy to understand as follow.

- AW become effective at relatively low contact temperatures and become ineffective at moderate contact temperatures. Four-ball Test ASTM D 4172 (lubricating fluids) can be used to check the scar diameter at 1200 rpm in 60 mins with a force of ~ 40 Kg, 1/2 inch steel balls. Some products can be run up to 98 Kg, even more.

- EP additive remains its effective at relatively high contact temperatures. Four-ball Test ASTM D 2783, 1,770 rpm, RT, 10 sec, 1/2-inch steel balls. Welding load and Last Non-Seizure Load (LNSL) are the key important parameters in this test.

As you can see in the Fig. 1, A to B is "ball to ball" contact, B to C to D is "face to face" contact. 

- AW will affect B point, when formulators can accept metal shape change, they will expand the B point by adding more AW additive.

Figure 2: Real test data of ADEKA Additive for AW/EP test.

- EP additive will enhance the D point. If lubricant-makers want to continue machining even though the metal shape change happens.

II. SULFURIZED EP ADDITIVE

- There are 4 typical types of S-EP additive based on their chemical structure: S-olefin, S-triglyceride, S-ester, S-fatty acid. Some manufacturers can make a mixture containing more than 2 of those types to enhance the EP performance.

Figure 3: Sulfurized Olefin

Figure 4: Sulfurized Ester

Figure 5: Sulfurized Triglyceride (Dark Sulfur)

Figure 6: Sulfurized fatty oil/olefin mixture (light color).

- In term of their color, EP additive can be classified into 2 types: Dark and Light colors.

- Some people will pay attention to its activity, so there are Active and Inactive S-EP additives. Some manufacturers distinguish those 2 types based on the Sulfur chain in the chemical structure. Inactive is less than 3 Sulfur, and Active is from 4 to 5 Sulfur. Others will pay attention to the result of ASTM D-130 and ASTM D-1662.

Figure 7: Properties of S-EP additives

The very basic properties of S-EP can be shown in the Fig. 7. Those are just very basic information, the key important thing is how you formulate the oil for machining, and the majority of the blenders around the world are not afford to buy a four-ball machine. Therefore, you need to understand the machining process and chemical structures of additives to take advantage of the synergistic effect of them for the optimized products for real test in your customers workshops.

III. DARK SULFURIZED EP ADDITIVE AND ITS APPLICATION

In principle, the molecules contains many chromophoric functional groups will enhance the color intensity; therefore, the colors will be darker. As you can see in Fig. 5, Dark S-EP always contains the chromophoric groups in its chemical structure. These structure are not chemically stable since its activity is very high.

The S-EP is the cheapest ones in S-EP additive because of the available raw materials and its less complicated synthesis process. There are 3 types of dark S-EP: S-olefin, S-ester, and S-triglyceride (vegetable or lard oil). You can see the basic classification of DIC S-EP products in Figure 8.

Figure 8: Classification of DIC S-EP Additive

Dark S-EP additives normally are applied in the low-tier cutting and forming applications where the customers can accept its smell and dark colors with a reasonable price and medium performance. 

HERE ARE SOME BASIC PROPERTIES OF THE DARK S-EP:

- Anti-oxidant (AO): Dark S-EP has lower anti-oxidant performance because there are many unsaturated groups in the structure shown in Fig. 7. Light-colored products manufactured with high-pressure hydrogen sulfide processes or by mercaptan oxidation, so it does not maintained the unsaturated double bonds left in the structures ==> they show better oxidation stability.

- Lubricity: Please take a look at Fig. 7. Sulfurized triglyceride provide the best lubricity in both inactive and active type, the second one is ester, and the last one is S-olefin. Lubricity depends on its chemical type. There is nothing to deal with dark and light color. However, at the same chemical structure, the higher MW of dark S-EP may provide the better EP/AW performance.

- Polymerization: Triglyceride type (i.e., lard oil, soybean oil) do polymerize and form solid (e.g., rubberlike products). Because olefins consist of few double bonds and some process can reduce the structure to make only one double bond structure, the polymerization can be controlled. Esters are quite similar to olefins, but due to its natural chemical structure varying amounts of multiple unsaturated compounds, polymerization also can take place. Dark S-EP products will also resume polymerization after the production process is finished.

- Solubility and Polarity: The more polarity, the less solubility in oil. S-EP solubility > S-Ester > S-triglyceride.

- Storage stability: Depending on the raw materials, its chemical structures, and sulfurization process plus technique, some S-EP will continue to polymerize during storage, especially dark S-EP triglyceride type.

Watching Part II: https://phugiadaunhot.blogspot.com/2020/10/sulfurized-ep-additive-series-part-ii.html

Written by Steven Nguyen.