Wang Yonglei; Li Haiyun; Fang Hongxia; Ni Zhifei; Zhao Lele

(School of Chemistry and Chemical Engineering, Huangshan University, Huangshan, Anhui 245041)

Synthesis of Environmentally Friendly Magnesium Linoleate Detergent

Wang Yonglei; Li Haiyun; Fang Hongxia; Ni Zhifei; Zhao Lele

(School of Chemistry and Chemical Engineering, Huangshan University, Huangshan, Anhui 245041)

This paper mainly covers a method for preparing a highly alkaline magnesium linoleate solution with a total base number (TBN) value of 328 mg KOH/g using linoleic acid as the biodegradable raw material, which can substitute for traditional lubricant detergents as an environmentally friendly detergent. Reaction conditions, including the molar ratio of magnesium oxide to linoleic acid, the molar ratio of methanol to magnesium oxide, the carbonation temperature, the molar ratio of water to magnesium oxide, the flow rate of CO2gas and the duration for injection of CO2to magnesium oxide system, were optimized.

lubricant detergent; magnesium linoleate; high total base number; biodegradation

1 Introduction

Lubricating oils is an absolutely necessary material used in internal combustion engine. However, in the course of engine operation, the hot combustion gas blowby leaking through the piston ring into the lube oil system often oxidizes lubricating oil into acidic degradation products[1-3]. Those acidic degradation products can corrode engine parts and catalyze the formation of oil sludges, thereby reducing the oil lubricity and accelerating the wear of moving parts. It is desirable to add basic substances to neutralize acids as soon as they are formed in the engine. Colloidal carbonates of the alkaline earth metals have been found to be well suited to this purpose. Therefore, the most commonly used method was the addition of alkaline lubricant detergents[4-5].

Recently, more lubricant manufacturers enhanced the ecological friendliness of its products under the environmental pressure of mankind. In parallel with the development of some environmentally friendly lubricating oils[6-8], the environmentally friendly and biodegradable lubricant detergents also should be timely studied in order to adapt to the development requirements of lubricant products. At present, the high alkalinity lubricant detergents[9-12]mainly include phenates, sulphonates, salicylates and phosphonate. However, they are less degradable after using, so they are not environmental-friendly in nature. In our previous studies[13-15], the environmentally friendly calcium oleate detergent was synthesized and a product with satisfactory performance was obtained. To improve the biodegradability of the lubricant detergent further, the linoleic acid was used in this study as a biodegradable starting material for synthesizing the high alkalinity magnesium linoleate detergent with its advantages presented as follows. Firstly, the high alkalinity magnesium linoleate detergent can use biodegradable and reproducible vegetable oil as raw material, so it is biodegradable and environmentally friendly, which can better meet the requirements for sustainable development. Secondly, compared to the calcium salt detergent, the ash of magnesium linoleate detergent is lower, which can better meet the demand for low-ash oil.

2 Experimental

2.1 Materials

Linoleic acid with a purity of 85% and the diluent oil (biodegradable lubricating oil composed of trimethylolpropane triheptanoate[16]) were of technical grade and provided by the Xinjiang Fine Chemical Engineering Center. Xylene, methanol and ammonia were all of technical grade and obtained from the Xilong Chemical Co., Ltd. Active-60 magnesium oxide was of technical grade and wasobtained from the Shanghai Dunhuang Chemical Plant. CO2was of technical grade and was received from the Huangshan Industrial Air Company. All other materials were obtained from commercial sources.

2.2 Analytical methods

The total base number (TBN) of detergent samples was determined according to the ASTM standard method D2896-11. The viscosity (100 ℃) of detergent samples was determined according to the ASTM standard method D445-09. The turbidity (JTU) of detergent samples was determined according to the test method SH/T 0028. The biodegradability of lubricant detergent (in 21 days) was determined according to the test method CEC L-33-A-93.

2.3 Synthesis of the highly alkaline magnesium linoleate detergent

Measured quantities of linoleic acid, diluent oil, methanol and xylene were added to a three-necked distillation flask. After mixing was initiated, magnesium oxide was added into the flask. After neutralization reaction was completed, a definite quantity of water was added to the reactor and gaseous CO2was then introduced into the reactor through a gas flowmeter. Finally, the waste residue was removed by centrifugation and filtration, and the solvent (such as xylene, methanol, and water) was evaporated to obtain the environmentally friendly magnesium linoleate detergent. The mechanism for synthesis of magnesium linoleate detergent is shown in Scheme 1.

The dosage of materials for the synthesis of high alkalinity magnesium linoleate solution covered: 7.0 g of linoleic acid, 10 g of diluent oil, 9 g of magnesium oxide, 5.7 g of methanol, and 2.4 g of water along with CO2and xylene. The properties of final product obtained from this synthesis covered a TBN value of 328 mg KOH/g, a viscosity of 86 mm2/s, a turbidity of 78 JTU, and a biodegradability of 71%.

3 Results and Discussion

3.1 Molar ratio of magnesium oxide to linoleic acid

Sufficient magnesium oxide is necessary to produce a qualified detergent product. The effects of molar ratio of magnesium oxide to linoleic acid on both the TBN value and viscosity of the magnesium linoleate detergent were studied with the results shown in Figure 1.

Figure 1 shows that as the molar ratio of magnesium oxide to linoleic acid increased, the TBN and the viscosity of the product also increased gradually. Initially, the TBN of the product increased rapidly with an increasing molar ratio of magnesium oxide to linoleic acid. However, when the molar ratio of magnesium oxide to linoleic acid was above 10, the TBN of the product did not increase significantly. This was probably due to the fact that the TBN increased only slightly with an increasing molar ratio of magnesium oxide to linoleic acid, as soon as the magnesium linoleate detergent contained a maximum amount of amorphous MgCO3. In order to realize a satisfactory TBN and reduction of production cost, an optimal molar ratio of magnesium oxide to linoleic acid of 9 was feasible.

3.2 Molar ratio of methanol to magnesium oxide

Methanol was used as the promoter for the conversion of magnesium hydroxide to magnesium carbonate[3-4]. The effects of molar ratio of methanol to magnesium oxide on both the TBN value and viscosity of the magnesium linoleate detergent were studied, with the results shown in Figure 2.

Figure 2 Effects of the molar ratio of methanol to magnesium oxide on both the TBN and viscosity of the magnesium linoleate detergent

The results in Figure 2 demonstrated as the molar ratio of methanol to magnesium oxide was increased, the TBN of the product at first increased and then decreased gradually. This occurred because the amount of methanol was probably insuf ficient, and the conversion rate of magnesium linoleate and colloidal magnesium carbonate was slow, leading to a low TBN of the product along with an increased residue formed thereby. As the amount of methanol was increased, the TBN of the product also increased. However, excessive methanol might induce a too rapid formation of colloidal MgCO3to be dispersed timely, resulting in a rapid decrease of TBN value of the product. The product attained the highest TBN at a molar ratio of methanol to magnesium oxide equating to 0.8. Therefore, the optimal molar ratio of methanol to magnesium oxide was set at 0.8.

3.3 Carbonation temperature

Carbonation temperature has an important effect on the quality of the magnesium linoleate detergent, with the results presented in Table 1.

Table 1 shows that, as the carbonation temperature was increased, the TBN of the product at first increased rapidly and then decreased slightly. Meanwhile, the filterability and quality of the product also deteriorated gradually. When the carbonation temperature was above 70 ℃, the conversion of Mg(OH)2to MgCO3was too high, which would induce the formation of crystalline material in the final product. Therefore, a carbonation temperature of 60—65 ℃ was feasible.

Table 1 Effect of different carbonation temperature on detergent quality

3.4 Molar ratio of water to magnesium oxide

In the process of synthesizing lubricant detergent, water was a necessary material. The effects of molar ratio of water to magnesium oxide on both the TBN and viscosity of magnesium linoleate detergent are shown in Figure 3.

Figure 3 Effects of the molar ratio of water to magnesium oxide on both the TBN and viscosity of the magnesium linoleate detergent

Figure 3 shows the TBN and viscosity of the product that at first increased and then decreased as the molar ratio of water to magnesium oxide was increased. Less wateror absence of water might induce the formation of large MgCO3particles. Insufficient water would cause incomplete conversion of magnesium oxide to magnesium hydroxide and magnesium carbonate, resulting in wastage of magnesium oxide and lower TBN of the product. Then the TBN of the product increased with further increase of molar ratio of water to magnesium oxide. However, excessive amount of water also caused a rapid reduction of TBN of the product. This occurred probably owing to the fact[17-18]that excessive water might induce the deterioration of micellar system, leading to agglomeration and precipitation of colloidal particles in the micellar system. The TBN of the product attained the highest value at a molar ratio of water to magnesium oxide of 0.6. Thus, 0.6 was selected as the optimal molar ratio of water to magnesium oxide.

3.5 Gas flow rate of CO2

The flow rate of CO2gas has an important impact on the quality of the magnesium linoleate detergent. When the total volume flow of CO2was fixed, the effects of the flow rate of CO2on both the TBN and viscosity of the magnesium linoleate detergent are shown in Figure 4.

Figure 4 Effects of the gas flow rate of CO2on both the TBN and viscosity of the magnesium linoleate detergent

Test results in Figure 4 show that at a fixed total gas volume flow of CO2, when the gas flow rate of CO2was increased, the TBN and viscosity of the product at first increased and then decreased. When the gas flow rate of CO2was low, a detergent product with a high TBN needed much time for injection of CO2. Then the TBN of the product increased rapidly with an increasing flow rate of CO2. However, a too high flow rate of CO2might induce the formation of insoluble gel because of the high concentration of CO2in the reaction. Meanwhile, a too high flow rate of CO2could cause wastage of a great deal of CO2that had not enough time to react on Mg(OH)2so that the TBN of the product decreased. Generally, a high flow rate of CO2could increase the product alkalinity moderately and shorten the time of carbonation. The TBN of the product attained the highest value at a CO2gas flow rate of 90 mL/min. Therefore, the optimal flow rate of CO2was set at 90 mL/min.

3.6 Time required for injection of CO2

The amount of CO2should be specified in accordance with the amount of magnesium oxide in order to utilize magnesium oxide fully. When the CO2gas flow rate was fixed, the amount of CO2introduced was dependent on its injection time. The effects of the time required for injection of CO2on the TBN and viscosity of the magnesium linoleate detergent are shown in Figure 5.

Figure 5 Effects of the time required for injection of CO2on both the TBN and viscosity of magnesium linoleate detergent

Figure 5 demonstrates the TBN of the product which increased at first and then decreased as the time required for injection of CO2was increased. If the time required for injection of CO2was short, the amount of injected CO2was insufficient, which would result in an insufficient formation of colloidal magnesium carbonate to cause alow TBN in the product. Then the TBN of the product would rise with an increasing time needed for injection of CO2. However, a longer time required for injection of CO2would produce excess CO2, which could also cause the gradual drop in TBN of the product. The TBN of the product attained a highest value at a time required for injection of CO2equating to 60 min. Therefore, the optimal time required for injection of CO2was set at 60 min.

4 Conclusions

A biodegradable, environmental friendly and highly alkaline magnesium linoleate detergent was synthesized using linoleic acid as the biodegradable raw material. Under the suitable conditions covering an amount of linoleic acid of 7 g, a molar ratio of magnesium oxide to linoleic acid of 9:1, a molar ratio of methanol to magnesium oxide of 0.8:1, a carbonation temperature of 65 ℃ a molar ratio of water to magnesium oxide of 0.6:1 a CO2gas flow rate of, 90 mL/min and a duration for injection of CO2equating to 60 min, the magnesium linoleate detergent with a TBN of 328 mgKOH/g could be obtained. This method for synthesizing an environmentally friendly magnesium linoleate detergent currently has a great potential for commercialization.

Acknowledgement:This work was supported by the Natural Science Research Project of Anhui Educational Committee (No. KJ2013B273), the National Students’ Innovative Training Program (No. 201210375035) and the Scientific Research Foundation for Introduced Scholars, Huangshan University (No. 2013xkjq004 ).

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Recieved date: 2013-10-15; Accepted date: 2013-11-18.

Wang Yonglei, E-mail: wylei@hsu. edu.cn.