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Ind. Eng. Chem. Res. 2010, 49, 8902–8907
Synthesis of Environmentally Friendly Overbased Magnesium Oleate Detergent and High Alkaline Dispersant/Magnesium Oleate Mixed Substrate Detergent Yonglei Wang†,‡ and Wumanjiang Eli*,† Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Urumqi 830011, China, and Graduate UniVersity of the Chinese Academy of Sciences, Beijing 100049, China
This article describes a method for synthesizing an environmentally friendly overbased magnesium oleate detergent using oleic acid and active-60 magnesium oxide as materials. Reaction conditions including solvent, molar ratio of active-60 magnesium oxide to oleic acid, molar ratio of methanol to active-60 magnesium oxide, molar ratio of ammonia to active-60 magnesium oxide, addition mode of ammonia, carbonation temperature, molar ratio of injected CO2 to active-60 magnesium oxide, and CO2 rate were optimized. Under the optimized conditions, the overbased magnesium oleate detergent with a total base number (TBN) of 402 mg of KOH/g could be obtained. To improve the dispersing capability and the stability of the magnesium oleate detergent, the different dispersant/magnesium oleate mixed substrate detergents were synthesized using Tuwen-80, poly-12-hydroxystearic acid-pentaerythritol (PTHSAP), and poly-12-hydroxystearic acidpolyethylene polyamine (PTHSAPP) as dispersants. 1. Introduction Modern machines all require lubricating oils to extend their time of usage. However, some acidic products1-3 are produced by the oxidative degradation of the base oil and the reaction of gases (SO2, NOx, etc.) with water in the environment. These acids attack metal surfaces leading to the corrosion of engine components. Therefore, some basic detergents need be added to lubricants to neutralize acids as they are formed in the engine.4-6 Recently, the use of environmentally friendly lubricant base oils7-10 increased, as did the necessity of studying their environmentally friendly additives. In our previous studies,11 we used oleic acid as the material to synthesize biodegradable, environmentally friendly calcium oleate detergent and acquired satisfactory products, and, to meet the demand of low-ash oil better, magnesium oleate detergent was also studied. Because of the weaker metallicity of magnesium than that of calcium and different physical-chemical properties of their compounds (MgO and CaO; Mg(OH)2 and Ca(OH)2; MgCO3 and CaCO3), the syntheses of high alkaline and overbased magnesium oleate detergent are much more complicated than that of calcium oleate detergent. Using magnesium oxide (Light) as material,12 the high alkaline magnesium oleate detergent with total base number (TBN) of 256 mg of KOH/g can be obtained, and higher alkalinity could not be reached. To improve the capability of neutralizing acid and reduce the residue ratio farther, the active60 magnesium oxide with higher activity and reactivity was used as material to synthesize the overbased magnesium oleate detergent with the TBN of 402 mg of KOH/g. Compared to that of magnesium oxide (Light), because of more micronized particles of active-60 magnesium oxide, its average particle size is generally less than 2 µm, which results in a larger proportion of the number of surface atoms and the number of bulk atoms, therefore the active-60 magnesium oxide has higher capacity * To whom correspondence should be addressed. Tel.: (086) 09913662347. Fax: (086) 0991-3835229. E-mail:
[email protected]. Address: Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Urumqi, Xinjang 830011, China. † Xinjiang Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences. ‡ Graduate University of the Chinese Academy of Sciences.
of chemical activity and physical adsorption. In addition, some dispersants also were used as mixed substrates to synthesize dispersant/magnesium oleate detergents in order to improve the dispersing capability and the stability of the magnesium oleate detergent. 2. Experimental Section 2.1. Materials. Methanol (analytical pure, Luoyang Chemical Co., Ltd.), ammonia (28%, analytical pure, Urumqi Tianyue Reagent Co., Ltd.), and active-60 magnesium oxide (technical grade, Shanghai Dunhuang chemical plant) were used. Oleic acid with a purity of 85 wt % and diluent oil (light lubricating oil) were technical grade and provided from Xinjiang Fine Chemical Engineering Center. Xylene and petroleum ether (90-120 °C) were analytically pure and were provided from Tianjin Zhiyuan Chemical Co., Ltd. Cyclohexane, heptane and Tween-80 all were analytically pure and were provided from Shanghai Shanpu Chemical Co., Ltd. CO2 was technical grade and was received from Urumqi Industrial Air Company. All other materials were obtained from commercial sources. 2.2. Analytical Methods. American Society of Testing and Materials (ASTM) test methods were applied. Total base number (TBN, mg of KOH/g) was determined according to ASTM D2896 and viscosity (cSt, 100 °C) was determined according to ASTM D445. 2.3. Synthesis of Overbased Magnesium Oleate Detergent. Measured quantities of oleic acid and diluent oil were dissolved in methanol and xylene. Then the active-60 magnesium oxide was added to the diluted mixture. The mixture was stirred for 1 h and then was heated to 60-65 °C. The ammonia was added to the mixture and gaseous CO2 was then introduced into the reactor via the gas flowmeter. Finally, the environmentally friendly magnesium oleate detergent was obtained by filtration and evaporation to remove residue and the solvent (such as xylene, methanol, and water, etc.). The synthesis mechanism of magnesium oleate detergent is shown in Scheme 1. The feed for the synthesis of overbased magnesium oleate solution was as follows: 7 g (0.025 mol) of oleic acid + 10 g of diluent oil + 10 g (0.25 mol) of active-60 magnesium oxide
10.1021/ie100377h 2010 American Chemical Society Published on Web 08/27/2010
Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010 Scheme 1. Synthesis Mechanism of Magnesium Oleate Detergent
Table 1. Performance of Different Solvents
2RCOOH + MgO f (RCOO)2Mg + H2O
solvent
MgO + H2O f Mg(OH)2
filterability TBN (mg KOH/g) viscosity (cSt, 100 °C)
(RCOO)2Mg + nMg(OH)2 + nCO2 f (RCOO)2Mg · nMgCO3 + nH2O R ) CH3(CH2)7CHdCH(CH2)6CH2+ 7 g (0.22 mol) of methanol + 4.5 g (0.13 mol) of ammonia + 13.2 g (0.30 mol) of CO2 + xylene. The final product of this synthesis had the following properties: TBN, 402 mg of KOH/ g; viscosity, 152 cSt. 2.4. Synthesis of Dispersant/Magnesium Oleate Mixed Substrate Detergent. The mixed substrate detergents are synthesized using a mixture of two or more substrates to react with the alkaline compounds. The method was that measured quantities of dispersant and oleic acid were added at one time, and the remainder of the steps were similar to that used for the synthesis of magnesium oleate detergent. The oil-soluble dispersants of Tween-80, poly-12-hydroxystearicacid-pentaerythritol (PTHSAP),13 and poly-12-hydroxystearic acid-polyethylene polyamine (PTHSAPP) were used as mixed substrates. Compared to that of the magnesium oleate detergent, the stability of the dispersant/magnesium oleate mixed substrate detergent was improved. The final product possessed excellent capability of neutralizing acid and dispersing wastes. The feed for the synthesis of high alkaline dispersant/ magnesium oleate detergent solution was as follows: 7 g of mixed substrate (dispersant: oleic acid/by weight, 1:20-1:5) + 10 g of diluent oil + 8 g (0.20 mol) of active-60 magnesium oxide + 5.8 g (0.18 mol) of methanol + 3.5 g (0.1 mol) of ammonia + 10.5 g (0.24 mol) of CO2 + xylene. The final product of this synthesis had the following properties: TBN, >300 mg of KOH/g; viscosity, 300 mg of KOH/g could be obtained. Acknowledgment
a Reaction conditions: oleic acid/dispersant (by weight), 10:1; solvent, xylene; molar ratio of active-60 magnesium oxide to mixed substrate, 8:1; molar ratio of methanol to active-60 magnesium oxide, 0.9:1; molar ratio of ammonia to active-60 magnesium oxide, 0.5:1; addition mode of ammonia, c; carbonation temperature, 60-65 °C; molar ratio of injected CO2 to active-60 magnesium oxide, 1.2:1; CO2 rate, 60 mL/min.
We thank Y. F. Liu, G. X. Cai, L. T. Zhang, H. L. Liu, F. Zhang, and P. Song for providing raw material and fruitful discussion, and we also appreciate the Analysis Center of Xinjiang Technical Institute of Physics and Chemistry for their technical and instrument support.
was low. Second, the too high CO2 rate resulted in high CO2 concentration in the reactor, which would cause the reaction CO2 + Mg(OH)2 f MgCO3 to be too rapid to be dispersed in oil timely, so that some MgCO3 particles aggregated into residue and the TBN of the product decreased. The TBN of magnesium oleate detergent attained the highest value at the CO2 rate of 60 mL/min; thus, 60 mL/min was chosen as optimal CO2 rate for our reaction system. 3.9. Dispersant/Magnesium Oleate Mixed Substrate Detergent. The Tween-80, poly-12-hydroxystearic acid-pentaerythritol (PTHSAP), and poly-12-hydroxystearic acid- polyethylene polyamine (PTHSAPP) were used as mixed substrate dispersants to synthesize multifunctional magnesium oleate detergent. In these oil-soluble dispersants, Tween-80 is a traditional dispersant, solubilizer, and lubricant. The PTHSAP as dispersant was applied in synthesizing calcium oleate detergent and obtained satisfactory product. The PTHSAP and the PTHSAPP have the same main organic chain (poly-12-hydroxy stearic acid), but their anchoring groups (PTHSAP, pentaerythritol; PTHSAPP, polyethylene polyamine) were different, so we selected them as mixed substrate dispersants to offset the weak dispersing capability of the magnesium oleate detergent and improve the stability of the product. Results are shown in Table 4. As shown in Table 4, compared to that of magnesium oleate detergent, although the TBN of the magnesium oleate/dispersant mixed substrate detergent cannot be increased obviously, the
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ReceiVed for reView February 19, 2010 ReVised manuscript receiVed August 15, 2010 Accepted August 16, 2010 IE100377H
