Ind. Eng. Chem. Res. 2008, 47, 8561–8565
8561
Synthesis of Environmentally Friendly Calcium Oleate Detergent Yonglei Wang,†,‡ Wumanjiang Eli,*,† Yuanfeng Liu,† and Laizao Long†,‡ Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Urumqi 830011, People’s Republic of China, and Graduate UniVersity of the Chinese Academy of Sciences, Beijing, People’s Republic of China
This article discusses a method for synthesizing an environmentally friendly calcium oleate detergent using vegetable oil instead of mineral oil as the raw material. Reaction conditions including the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, the molar ratio of Ca(OH)2 to CaO, the carbonation temperature, the amount of methanol, the molar ratio of water to CaO, the gas flow rate of CO2, and the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] were optimized. Using the optimized conditions, a high-alkali calcium oleate solution with a total base number (TBN) of 376 mg of KOH/g and an overbased calcium oleate solution with a value of TBN ) 420 mg of KOH/g could be obtained. In this study, a high-alkali calcium oleate solution and an overbased calcium oleate solution were synthesized.
Introduction Lubricating oils should maintain the necessary lubricating and protective properties under different working conditions and loads. However, in the course of operation, internal combustion in engines converts lubricating oil to acidic degradation products. Those acidic degradation products attack and corrode engine parts and catalyze the formation of sludge, thereby reducing lubrication and accelerating friction of moving parts in contact with the lubricating oil. It is therefore desirable to add basic substances to the lubricating oil that can neutralize acids as they are formed in the engine before they reach concentrations sufficient to cause corrosion or catalyze the sludge reaction. Colloidal carbonates of alkaline earth metals have been found to be well-suited for this purpose.1,2 So far, many traditional overbased detergents such calcium (or magnesium or barium) sulfonate (or phenate, salicylate, or phosphonate) have been developed. Recently, increasing attention to environmental issues has driven the lubricant industry to increase the ecological friendliness of its products. The use of synthetic, biodegradable, and environmentally friendly lubricants3-6 has increased over the past 15 years because of concerns over the potential hydrocarbon contamination of the environment by less-degradable mineraloil-based lubricants. At present, traditional lubricant detergents mainly use mineral oil as a raw material so that they are not environmentally friendly. Compared to traditional lubricant detergents, calcium oleate detergent has two advantages. First, calcium oleate detergent uses biodegradable base oils as raw materials, so it is biodegradable and environmentally friendly. Second, the raw material of calcium oleate detergent is oleic acid, which is a renewable resource, whereas most raw materials of traditional lubricant detergents are obtained from petroleum, which is a nonrenewable resource. Thus, calcium oleate detergent can better meet the requirements of sustainable development. * To whom correspondence should be addressed. Tel.: (086)09913662347. Fax: (086) 0991-3835229. E-mail:
[email protected]. † Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences. ‡ Graduate University of the Chinese Academy of Sciences.
Experimental Section Materials and Reagents. Oleic acid with a purity of >75 wt % was purchased commercially. Cottonseed oil was used as a diluent and was supplied by an oil refinery company. Xylene (technical grade), methanol (analytically pure), CaCl2 (analytically pure), Ca(OH)2 (analytically pure), CaO (analytically pure), and CO2 were received from an industrial air company. Test Methods. ASTM (American Society of Testing and Materials) and UOP (Universal Oil Products Company) test methods were applied. For total base number (TBN, in units of milligrams of KOHper gram) was determined according to method ASTM D664. Viscosity (in centistokes) was determined according to method ASTM D445. Mechanism. The following reaction mechanism describes the approach used to synthesize calcium oleate detergent. CaO + H2O f Ca(OH)2 2RCOOH + Ca(OH)2 f (RCOO)2Ca + 2H2O (RCOO)2Ca + nCa(OH)2 + nCO2 f (RCOO)2Ca · nCaCO3 + nH2O R ) CH3(CH2)7CHdCH(CH2)6CH2s (RCOO)2Ca · nCaCO3 is calcium oleate detergent, in which the calcium carbonate is dispersed in particles smaller than 100 nm. Procedure. Measured quantities of oleic acid and cottonseed oil were added to a three-neck, 250-mL flask fitted with a condenser, a thermometer, a gas dispersion tube, and a stirrer. CaCl2 was added to the flask to promote the calcium oxide hydration reaction, and then the participating solvents (xylene, methanol, and water) were added. The flask was heated to 50 °C, a mixture of CaO and Ca(OH)2 was added, and the reaction mixture was held at 50 °C for about 1.5 h. The mixture was then heated to 67 °C, and a quantity of gaseous CO2 was introduced into the reactor through the gas dispersion tube via a traditional flowmeter. Particles larger than 100 nm, which were not in the desired size range, were removed by filtration through a Buchner funnel containing filtration paper and 10 g of diatomite. Finally, the polar solvents (namely, xylene, methanol, and water) were evaporated to give the final product of environmentally friendly calcium oleate detergent.
10.1021/ie800679a CCC: $40.75 2008 American Chemical Society Published on Web 10/16/2008
8562 Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008
The feed for the synthesis of high-alkali calcium oleate solution was as follows: 7 g of oleic acid + 10 g of cottonseed oil + 0.1 g of CaCl2 + 18 g of total lime [Ca(OH)2 + CaO] + 1 g of water + 6 g of methanol + 8 g of CO2 + xylene. The final product of this synthesis had the following properties: TBN, 376 mg of KOH/g; viscosity, 32 cSt. The feed for the synthesis of overbased calcium oleate solution was as follows: 7 g of oleic acid + 10 g of cottonseed oil + 0.1 g of CaCl2 + 27 g of total lime [Ca(OH)2 + CaO] + 1.5 g of water + 6.5 g of methanol + 12 g of CO2 + xylene. The final product of this synthesis had the following properties: TBN, 420 mg of KOH/g; viscosity, 94 cSt. After optimization of the reaction conditions, namely, the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, the molar ratio of Ca(OH)2 to CaO, the carbonation temperature, the amount of methanol, the molar ratio of water to CaO, the gas flow rate of CO2, and the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], we could obtain a high-alkali calcium oleate solution with a value of TBN ) 376 mg of KOH/g and an overbased calcium oleate solution with a value of TBN ) 420 mg of KOH/g. Results and Discussion
Figure 1. Effects of the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid on both the TBN and viscosity of the calcium oleate detergent. Reaction conditions: molar ratio of Ca(OH)2 to CaO, 9:1; carbonation temperature, 341 K; amount of methanol, 8 mL; molar ratio of water to CaO, 2:1; gas flow rate of CO2, 40 mL/min; molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], 0.6:1.
Of all the properties of lubricant detergents, the total base number (TBN) and the viscosity of the product are the two primary concerns. The TBN is defined as the amount of potassium hydroxide that would be equivalent to 1 g of the material and is expressed in units of miligrams of KOH per gram. The degree of alkalinity of the product depends on the amount of CaCO3 it contains, which shows the capability of the product to neutralize acid. It is measured by the standard potentiometric titration method ASTM D664. The viscosity of the product determines whether the product is easy to handle and is measured by the standard method ASTM D445. The preparation of overbased detergent is difficult because the final product tends to be insoluble, to lack clarity, or to become too viscous to be readily handled. Therefore, the present process is directed toward improving the TBN and reducing the viscosity of the lubricant detergent product. Various synthetic routes to traditional overbased detergents have been described previously.2,7-10 Many studies have also been made to attempt to elucidate the acid neutralization mechanism1,11-14 and antifriction properties15-17 of overbased detergents. In this article, taking the TBN and viscosity of the product as the two main parameters, we discuss the effects of various factors in the preparation process to determine the best reaction conditions for the synthesis environmentally friendly calcium oleate detergent. Molar Ratio of Total Lime [Ca(OH)2 and CaO] to Oleic Acid. The appropriate molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid is essential to produce an overbased calcium oleate solution that is clear and has a low solids content. More total lime [Ca(OH)2 and CaO] is required in the process to increase the reaction Ca(OH)2 + CO2 f CaCO3 + H2O. The effects of the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid on both the TBN and viscosity of the calcium oleate detergent are shown in Figure 1. As shown in Figure 1, as the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid was increased, the TBN and the viscosity of the product increased gradually. Initially, the TBN of the product increased rapidly with increasing molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid. However, when the molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid was above 20, the TBN of the product did not increase
considerably, but the viscosity of the product increased rapidly. This is probably because the TBN increased only slightly with increasing molar ratio of the total lime [CaO and Ca(OH)2] to oleic acid in reaction when the calcium oleate detergent contained the maximum amount of amorphous CaCO3. However, excess amounts of amorphous CaCO3 can cause the formation of larger crystalline CaCO3 particles, which causes the viscosity of the final product to increase rapidly. Therefore, to increase the utilization ratio of total lime and obtain a product with a satisfactory alkali value, the optimal molar ratio of the total lime [CaO and Ca(OH)2] to oleic acid was found to be 10-15 in our experiments. Molar Ratio of Ca(OH)2 to CaO. Generally, a basic metal compound, which can be a hydroxide or oxide of the metal, is used to supply excess basicity to an overbased detergent. Overbased detergent solutions have been produced using calcium oxide, calcium hydroxide, and mixtures of calcium oxide and calcium hydroxide.1 When calcium oxide is used alone, it can suffer from the disadvantage that a crystalline dispersed carbonate phase is obtained. Calcium hydroxide, when used alone, can yield a great deal of solids in the crude reaction product. For these reasons, it is advantageous in industrial practice to use a mixture of calcium hydroxide and calcium oxide as the reserve alkalinity agent.18 The effects of the molar ratio of Ca(OH)2 to CaO on both the TBN and viscosity of the calcium oleate detergent are shown in Figure 2. As shown in Figure 2, as the molar ratio of Ca(OH)2 to CaO was increased, the TBN and the viscosity of the product initially increased and then decreased. When the molar ratio of Ca(OH)2 to CaO was above 9, the TBN and the viscosity of the product began to decrease gradually. In our experiments, the TBN of the product attained the highest value at a Ca(OH)2/CaO molar ratio of 9. Thus, according to these results, we selected a Ca(OH)2/CaO molar ratio of 9 for subsequent experiments. Carbonation Temperature. The effects of temperature during the carbonation process cannot be ignored. The results showed that, if the carbonation temperature was below 50 °C, the rate of formation of CaCO3 was slow. At carbonation temperatures above 85 °C, the conversion rate of the reaction Ca(OH)2 + CO2 f CaCO3 + H2O was high, but the amount of undesired CaCO3 particles with sizes larger than 100 nm
Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008 8563
Figure 2. Effects of the molar ratio of Ca(OH)2 to CaO in total lime on both the TBN and viscosity of calcium oleate detergent. Reaction conditions: molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, 10:1; carbonation temperature, 341 K; amount of methanol, 8 mL; molar ratio of water to CaO, 2:1; gas flow rate of CO2, 40 mL/min; molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], 0.6:1.
Figure 3. Effects of the amount of methanol on both the TBN and viscosity of the calcium oleate detergent. Reaction conditions: molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, 10:1; molar ratio of Ca(OH)2 to CaO, 9:1; carbonation temperature, 341 K; molar ratio of water to CaO, 2:1; gas flow rate of CO2, 40 mL/min; molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], 0.6:1.
increased so that the TBN of the product decreased. Therefore, an appropriate carbonation temperature of 67 °C was selected in our experiments. Amount of Methanol. Methanol are used as a promoter that functions as a solubilizing agent for the conversion of calcium oxide to calcium hydroxide and the conversion of calcium hydroxide to calcium carbonate and prevents excessive water formation during the reaction.2 The effects of the amount of methanol on both the TBN and viscosity of the calcium oleate detergent are shown in Figure 3. As shown in Figure 3, as the amount of methanol was increased, the viscosity of the product increased gradually, whereas the TBN of the product initially increased and then decreased. The TBN of the product attained the highest value at an amount of methanol of 8 mL. When the amount of methanol was insufficient, the reaction could not proceed fully, and the TBN of the product was low. Moreover, the complete
Figure 4. Effects of the molar ratio of water to CaO on both the TBN and viscosity of the calcium oleate detergent. Reaction conditions: molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, 15:1; molar ratio of Ca(OH)2 to CaO, 9:1; carbonation temperature, 341 K; amount of methanol, 8 mL; gas flow rate of CO2, 40 mL/min; molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], 0.6:1.
absence of methanol might cause the system to become too viscous, resulting in an unacceptable product. However, if the amount of methanol was excessive, the formation of an insoluble gel that is a characteristic of crystalline CaCO3 increased, which caused filtration to become very difficult and the TBN of the product decreased gradually. Thus, we chose 8 mL as the optimal amount of methanol. Molar Ratio of Water to CaO. Water is a necessary component in the process of preparing the calcium oleate detergent. It plays an important role in the reaction for two reasons. On one hand, it should be sufficient for the conversion of calcium oxide to calcium hydroxide, and on the other hand, it also is used as a promoter to improve the carbonation reaction. In our experiments, the effects of different molar ratios of water to CaO on both the TBN and viscosity of the calcium oleate detergent were investigated. The results obtained are shown in Figure 4. As shown in Figure 4, the TBN and the viscosity of the product decreased gradually with increasing molar ratio of water to CaO. Having less water or no water caused the formation of larger CaCO3 particles during carbonation, which caused filtration to become difficult and made the final product too viscous to be readily handled. However, excessive amounts of water caused the TBN of the product to decrease rapidly and the color of the product to gradually become turbid. The experimental results indicated that the molar ratio of water to CaO should be within certain limits. In our experiments, it was feasible to use water/CaO molar ratios of 1.5-3. Gas Flow Rate of CO2. The appropriate gas flow rate of CO2 is very important during carbonation. If the gas flow rate of CO2 is too high, the formation of an insoluble gel that is characteristic of crystalline CaCO3 occurs because of the high concentration of CO2 in the reactor. On the contrary, if the gas flow rate of CO2 is too low, the carbonation is inadequate, so that the time of carbonation must be extended to obtain a product with a satisfactory alkali value. The effects of the gas flow rate of CO2 on both the TBN and viscosity of the calcium oleate detergent are shown in Figure 5. As shown in Figure 5, for the same amount of CO2, the TBN and viscosity of the product first increased and then decreased with increasing flow rate of gaseous CO2. The TBN of the
8564 Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008
product increased rapidly. However, if the amount of injected CO2 was too high, the excess CO2 could cause the reaction CaCO3 + CO2 + H2Of Ca(HCO3)2 to occur, so as to gradually decrease the TBN of the product. The more serious situation is that extremely excessive CO2 could cause the phenomenon termed “overcarbonation”, which results in an unacceptable product. Reports in the literature1,13,19 also suggest that a stable system requires a certain amount of residual calcium hydroxide, which ensures that the inorganic core is amorphous. Therefore, the feasible range for the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] was found to be about 0.6-0.8. Conclusion
Figure 5. Effects of the gas flow rate of CO2 on both the TBN and viscosity of the calcium oleate detergent. Reaction conditions: molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, 10:1; molar ratio of Ca(OH)2 to CaO, 9:1; carbonation temperature, 341 K; amount of methanol, 8 mL; molar ratio of water to CaO, 2:1; molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO], 0.6:1.
In this study, a high-alkali calcium oleate solution and an overbased calcium oleate solution were synthesized using oleic acid as the biodegradable raw material, which can substitute for traditional lubricant detergents as an environmentally friendly detergent. Using the feed for the synthesis of a high-alkali calcium oleate solution and a gas flow rate of CO2 of 40 mL/ min, a high-alkali calcium oleate detergent with a TBN value of 376 mg of KOH/g was obtained. When a higher TBN value was required, an overbased calcium oleate solution with TBN ) 420 mg of KOH/g was obtained by using the feed for the synthesis of an overbased calcium oleate solution. Experiments indicated that the method for synthesizing an environmentally friendly calcium oleate detergent was feasible, so this method currently shows great potential for industrialization. Acknowledgment The authors thank Y. Chen and Y. L. Zhang for helpful discussions and also acknowledge the Testing Center of Xin Jiang University for their technical and instrument support. Literature Cited
Figure 6. Effects of the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] on both the TBN and viscosity of the calcium oleate detergent. Reaction conditions: molar ratio of total lime [Ca(OH)2 and CaO] to oleic acid, 10:1; molar ratio of Ca(OH)2 to CaO, 9:1; carbonation temperature, 341 K; amount of methanol, 8 mL; molar ratio of water to CaO, 2:1; gas flow rate of CO2, 40 mL/min.
product obtained the highest value at a gas flow rate of CO2 of 40 mL/min. Therefore, the optimal gas flow rate of CO2 was 40 mL/min. Molar Ratio of Injected CO2 to Total Lime [Ca(OH)2 and CaO]. The required amount of CO2 should be in accordance with the amount of total lime [Ca(OH)2 and CaO], which determines whether the TBN of the product is satisfactory. The effects of the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] on both the TBN and viscosity of the calcium oleate detergent are shown in Figure 6. As indicated in Figure 6, as the molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] was increased, the TBN of the product first increased and then decreased. The TBN of the product attained the highest value at a molar ratio of injected CO2 to total lime [Ca(OH)2 and CaO] of 0.6. If the amount of injected CO2 was insufficient, the TBN of the product was low. Then, with increasing amount of injected CO2, the TBN of the
(1) Galsworthy, J.; Hammond, S.; Hone, D. Oil-Soluble Colloidal Additives. Curr. Opin. Colloid Interface Sci. 2000, 5, 274. (2) Besu¨ergil, B.; Akın, A.; Celik, S. Determination of Synthesis Conditions of Medium, High, and Overbased Alkali Calcium Sulfonate. Ind. Eng. Chem. Res. 2007, 46, 1867. (3) Haigh, S. D. Fate and Effect of Synthetic Lubricants in Soil: Biodegradation and Effect on Crops in Field Studies. Sci. Total EnViron. 1995, 168, 71. (4) Erhan, S. Z.; Asadauskas, S. Lubricant Basestocks from Vegetable Oils. Ind. Crop Prod. 2000, 11, 277. (5) Wagner, H.; Luther, R.; Mang, T. Lubricant Base Fluids Based on Renewable Raw Materials: Their Catalytic Manufacture and Modification. Appl. Catal. A: Gen. 2001, 221. (6) Cermak, S. C.; Isbell, T. A. Physical Properties of Saturated Estolides and Their 2-Ethylhexyl Esters. Ind. Crop Prod. 2002, 16, 119. (7) Muir, R. J.; Eliades, T. I.; Matthews, L. High Viscosity Overbased Sulfonate Detergent and Marine Cylinder Oils Containing Same. U.S. Patent 6,444,625, 2002. (8) Ibrahim, T.; Cleverley, J. A.; Skinner, P. Overbased Metal Detergents. U.S. Patent 6,569,821, 2003. (9) Hammond, S.; Price, M. A.; Skinner, P. Overbased Detergent Additives. U.S. Patent 6,599,867, 2003. (10) Kocsis, J. A.; Baumann, A. F.; Karn, J. L. Process for Preparing an Overbased Detergent. U.S. Patent 7,238,651, 2007. (11) Hone, D. C.; Robinson, B. H.; Steytler, D. C. Mechanism of Acid Neutralization by Overbased Colloidal Additives in Hydrocarbon Media. Langmuir 2000, 16, 340. (12) Wu, R. C.; Campbell, C. B.; Papadopoulos, K. D. Acid-Neutralizing of Marine Cylinder Lubricants: Effects of Nonionic Surfactants. Ind. Eng. Chem. Res. 2000, 39, 3926. (13) Hudson, L. K.; Eastoe, J.; Dowding, P. J. Nanotechnology in Action: Overbased Nanodetergents as Lubricant Oil Additives. AdV. Colloid Interface Sci. 2006, 123, 425.
Ind. Eng. Chem. Res., Vol. 47, No. 22, 2008 8565 (14) Fu, J. Z.; Lu, Y. F.; Campbell, C. B.; Papadopoulos, K. D. Acid Neutralization by Marine Cylinder Lubricants Inside a Heating Capillary: Strong/Weak-Stick Collision Mechanisms. Ind. Eng. Chem. Res. 2006, 45, 5619. (15) Vipper, A.; Zadko, I.; Karaulov, A.; Ermolaev, M. Antifriction Action of Engine Oil Additives. Lubr. Sci. 2001, 14, 43. (16) Najman, M.; Kasrai, M.; Bancroft, G. M.; Davidson, R. Combination of Ashless Antiwear Additives with Metallic Detergents: Interactions with Neutral and Overbased Calcium Sulfonates. Tribol. Int. 2006, 39, 342–355. (17) Costello, M. T.; Urrego, R. A.; Kasrai, M. Study of Surface Films of Crystalline and Amorphous Overbased Sulfonates and Sulfu-
rized Olefins by X-ray Absorption near Edge Structure (XANES) Spectroscopy. Tribol. Lett. 2007, 26, 173. (18) Powers III, W. J.; Matthews, L. A.; Jao, T. C. Process for Preparing Overbased Calcium Sulfonates. U.S. Patent 4,929,373, 1990. (19) Bandyopadhyaya, R.; Kumar, R.; Gandhi, K. S. Modelling of CaCO3 Nanoparticle Formation During Overbasing of Lubricating Oil Additives. Langmuir 2001, 17, 1015.
ReceiVed for reView April 27, 2008 ReVised manuscript receiVed August 15, 2008 Accepted September 3, 2008 IE800679A
