Ind. Eng. Chem. Res. 2009, 48, 3749–3754
3749
Synthesis and Characterization of Polyol Poly-12-Hydroxy Stearic Acid: Applications in Preparing Environmentally Friendly Overbased Calcium Oleate Detergent Yonglei Wang,†,‡ Wumanjiang Eli,*,† Ayixiamuguli Nueraimaiti,† and Yuanfeng Liu† 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 100049, People’s Republic of China
In this study, the poly-12-hydroxy stearic acid (PTHSA) was synthesized and then modified by esterification with pentaerythritol to obtain a polyol polymeric hyperdispersant (polyol-PTHSA). Under suitable reaction conditions (molar ratio pentaerythritol/PTHSA, 1.2:1; reaction temperature, 453 K; and reaction time, 4-8 h), the polyol-PTHSA with acid value of 3 mg of KOH/g can be obtained. The structures were confirmed by FT-IR analysis. The polyol-PTHSA was subsequently used as a hyperdispersant in the process of preparing environmentally friendly overbased calcium oleate detergent to increase the total base number of the product. Reaction conditions including the polymerization catalyst, the catalyst amount, the amount of xylene, the polymerization temperature, the polymerization time, the polyol-PTHSA amount, and the acid value of the PTHSA were optimized. 1. Introduction Polymeric hyperdispersants are specifically designed and synthesized polymeric additives.1-3 In their structures, they can be simply described as having two key components: anchoring groups (such as -NH2, -COOH, -SO3H, and -OH, etc.) that adsorb onto the particle surface and polymeric chains that provide the steric stabilization barrier around the particles and prevent agglomeration. Recently, the polymeric hyperdispersants have widely attracted attention for both academic studies and industrial applications4-9 because of their economic and technical advantages in surface coating industries.10-14 However, the current research and applications mainly focused on paint,15,16 ink,17,18 magnetic,19,20 and lubricant,21-23 ignoring nanocarbonate dispersion in lubricant detergent, which is another very important field. Using polymeric hyperdispersant in preparing lubricant detergent has three advantages. First, the polymeric hyperdispersant has more anchoring groups, which can disperse more nanocarbonate particle in oil medium so as to increase the total base number (TBN) of the lubricant detergent. Second, the organic chain of the polymeric hyperdispersant is long enough to have a high affinity for the oil medium, forming a thick steric barrier around the nanocarbonate particles and preventing agglomeration, which can improve the stability of lubricant detergent. Third, the polymeric hyperdispersant possesses very good ability to disperse combustion waste, so the lubricant detergent can better suspend contaminants and prevent deposit formation via addition of polymeric hyperdispersant in the process of preparation. In this work, poly-12-hydroxy stearic acid (PTHSA) was synthesized and then modified using pentaerythritol to obtain a polyol polymeric hyperdispersant (polyol-PTHSA), and the * To whom correspondence should be addressed. Tel.: (086) 09913836643. 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.
polyol-PTHSA was used as a hyperdispersant in the process of preparing environmentally friendly overbased calcium oleate detergent. 2. Experimental Section 2.1. Materials. 12-Hydroxy stearic acid (acid value, 182 mg of KOH/g; technical grade, Tongliao Tonghua Castor Chemical Co., Ltd.), pentaerythritol (technical grade, Puyang Yongan Chemical Co., Ltd.), and oleic acid with a purity of 85 wt % (technical grade, Xinjiang Fine Chemical Engineering Center) were used. Molecular sieves 5A (analytical pure, Country Medicine Reagent, Ltd.). Cation exchange resin-732, p-toluene sulfonic acid, and SnCl2 · 2H2O were all analytically pure and were obtained from Shanghai Shanpu Chemical Co., Ltd. Xylene, methanol, CaO, and Ca(OH)2 were all analytically pure and were obtained from Tianjin Chemical Technology, Ltd., and CO2 was received from Urumqi Industrial Air Company. All other materials were purchased from commercial sources. 2.2. Analytical Methods. American Society of Testing and Materials (ASTM) test methods were applied. Acid value (in units of milligrams of KOH per gram) was determined according to method ASTM D1639. TBN (in units of milligrams of KOH per gram) was determined according to method ASTM D664. The Fourier transform infrared (FT-IR) spectrometry of Avatar 370 was used in spectrum analysis. 2.3. Procedure. The PTHSA was synthesized in a nitrogenblanketed reactor fitted with a stirrer, thermocouple, temperaturecontrol instrument, and water separator (to remove the water during the formation of PTHSA). THSA (60 g) was refluxed with xylene under constant agitation in the presence of 0.5% SnCl2 · 2H2O as catalyst. The reaction mixture continued to be refluxed until the theoretical amount of water was collected, corresponding to the desired extent of reaction. The extent of reaction was also evaluated by testing the acid values of the reaction mixture. The polymerization was stopped by cooling the reaction mixture when the desired extent of reaction was reached. Then the measured quantity of pentaerythritol was added to the cooled
10.1021/ie8016016 CCC: $40.75 2009 American Chemical Society Published on Web 03/19/2009
3750 Ind. Eng. Chem. Res., Vol. 48, No. 8, 2009 Scheme 1. Synthesis Mechanism of the Polyol-PTHSA
Table 1. Catalytic Performance of Different Catalystsa catalyst
acid value (mg of KOH/g)
molecular sieves 5A cation exchange resin-732 p-toluene sulfonic acid SnCl2 · 2H2O
48 53 58 36
a Reaction conditions: Catalyst weight percentage, polymerization temperature, 463 K; polymerization time, 6 h.
0.5%;
Table 2. Effects of Catalyst Weight Percentage on the Acid Value of the PTHSAa acid value (mg of KOH/g) time (h)
6
10
catalyst (wt %) 0.3 0.5 1
46 36 34
39 28 27
a Reaction conditions: temperature, 463 K.
reaction mixture. The reaction mixture was further refluxed. When the acid value of the reaction mixture was about 3 mg of KOH/g, the reaction was stopped and the reaction mixture was washed with hot water to remove the catalyst and any unreacted pentaerythritol. The water and xylene were distilled off under reduced pressure to get the polyol-PTHSA. The synthesis mechanism of the polyol-PTHSA is shown in Scheme 1. 2.4. Application of the Polyol-PTHSA in Preparing Environmentally Friendly Overbased Calcium Oleate Detergent. The literature24 reported in detail the preparation of environmentally friendly calcium oleate detergent using oleic acid as the raw material. In this study, we mainly investigated the effects of the weight percentage of polyol-PTHSA to total materials (oleic acid and polyol-PTHSA) and the degree of polymerization of polyol-PTHSA (corresponding to the different acid value of PTHSA) on the TBN of the environmentally friendly overbased calcium oleate detergent. The method was as follows. The xylene solution of the oleic acid, polyol-PTHSA, and diluent oil was added to the three-necked distillation flask, and the mixing was initiated. The mixture of CaO and Ca(OH)2 was added to the flask followed by the addition of the methanol and then the water. The flask was held at 50 °C for about 1.5 h and then was heated to 67 °C. A quantity of gaseous CO2 was then introduced through the glass tube via the flowmeter. Finally, the particles that were not in the desired size range were removed by filtration, and the solvent (such as xylene, methanol, and water) was evaporated to give the final product of environmentally friendly calcium oleate detergent. 3. Results and Discussion Many studies of the polymeric hyperdispersants1-9 and the overbased detergents24-30 have been described previously. The conversions of THSA to PTHSA and PTHSA to polyol-PTHSA were all confirmed from the acid values of the reaction mixtures. In addition, the effects of the polyol-PTHSA on the TBN of the overbased calcium oleate detergent were also investigated. 3.1. Linear Polymerization and Cyclization. Though THSA possesses two functional groups with the trend of cyclization, only the linear polymerization can occur rather than cyclization because of the following reasons:
Catalyst,
SnCl2 · 2H2O;
polymerization
For HO(CH2)nCOOH, n is 1, by bimolecular condensation reaction, it tends to form a hexatomic ring. n is 2, it mainly forms acrylic acid by dehydration of hydroxyl. n is 3 or 4, it tends to form steady lactone with a pentatomic or hexatomic ring. n is 5 or above 5, it mainly forms a linear polyester. For THSA, n is 11, and thus it mainly forms a linear polyester.
3.2. Catalytic Performance of Different Catalysts. The catalytic performance of molecular sieves 5A, cation exchange resin-732, p-toluene sulfonic acid, and SnCl2 · 2H2O was evaluated in the process of synthesizing PTHSA. Results obtained are shown in Table 1. As shown in Table 1, in the same reaction conditions, compared to other catalysts, the acid value of the product using SnCl2 · 2H2O as catalyst was lowest, which demonstrated that the SnCl2 · 2H2O showed highest catalytic activity. Meanwhile, the colors of products using molecular sieves 5A, cation exchange resin-732, and SnCl2 · 2H2O as catalyst were all very good. However, using p-toluene sulfonic acid as catalyst, the color pollution was serious and the experimental reproducibility was poor at a high temperature. Therefore, we chose SnCl2 · 2H2O as optimal polymerization catalyst. 3.3. Catalyst Amount. Table 2 shows the effects of catalyst weight percentage on the acid value of the PTHSA. As shown in Table 2, along with the increase of the catalyst amount, the polymerization rate increased and the acid value of products decreased more rapidly. At 10 h, the acid values of the PTHSA with 0.3, 0.5, 1% (wt %) SnCl2 · 2H2O as catalyst were 39, 28, and 27 mg of KOH/g, respectively, which showed that the acid values of the PTHSA with 0.5 and 1% SnCl2 · 2H2O as catalyst were very small difference. Considering the appropriate polymerization rate and the reduction of catalyst cost, we chose the optimal weight percentage of SnCl2 · 2H2O as catalyst to be 0.5%. 3.4. Amount of Xylene. In our experiments, xylene was a reagent that removed water, the amount of which was very important. If the amount of xylene was insufficient, the water during the formation of PTHSA could not be removed in a timely manner so as to reduce the polymerization rate. More-
Ind. Eng. Chem. Res., Vol. 48, No. 8, 2009 3751
Figure 1. Effects of polymerization time on the acid value of the PTHSA. Reaction conditions: Catalyst, SnCl2 · 2H2O; catalyst weight percentage, 0.5%; polymerization temperature, 463 K. Table 3. Effects of Polymerization Temperature on the Acid Value of the PTHSAa acid value (mg of KOH/g) time (h)
6
8
10
12
temp (K) 433 448 463 478
56 47 36 34
48 41 31 30
42 36 28 26
37 32 25 24
a Reaction conditions: percentage, 0.5%.
Figure 2. Typical IR spectrums of (a) THSA, (b) PTHSA, and (c) polyolPTHSA.
over, the insufficient amount of xylene also may induce the color of the product to become dark. Contrarily, if the amount of xylene was excessive, the polymerization temperature could not be maintained at a steady set temperature because of its dramatic reflux. Experimental results showed that, when the water separator was filled with xylene, about 10-15 mL of xylene in reactor could maintain the stability of polymerization temperature and remove the water in a timely manner. In addition, the amount of xylene may reduce gradually because of its volatilization in the course of the reaction, so the timely addition of xylene to the reactor was necessary. Thus, it was feasible that the amount of xylene in the reactor was about 10-15 mL. 3.5. Polymerization Temperature. Temperature plays an important role in the process of polymerization for two reasons. On the one hand, it affects the generated rate of water in the reactor, and on the other hand, it also affects the removed rate of water from the reactor to the water separator. In our
Catalyst,
SnCl2 · 2H2O;
catalyst
weight
experiments, we studied the effects of 433, 448, 463, and 478 K on the acid value of the PTHSA. Results obtained are shown in Table 3. As shown in Table 3, with the rise of the polymerization temperature, the polymerization rate increased and the acid value of the product decreased more rapidly. On the whole, the polymerization rates of both 463 and 478 K were faster than that of both 433 and 448 K, and the acid values of both 463 and 478 K had a very small difference after 6 h. It is probably because the higher temperature can accelerate the polymerization and shorten the time of reaching the reaction balance, and then it can promote the polymerization to react forward better by removing less water during the formation of PTHSA in a more timely manner. However, after the reaction balance, a higher temperature cannot increase the degree of polymerization of the product significantly, and thus extending the polymerization time was necessary to obtain a product with a satisfactory degree of polymerization. Moreover, an extremely high temperature may increase the occurrence of a side reaction. Therefore, considering the appropriate polymerization rate and the avoidance of the side reaction, we chose 463 K as the optimal polymerization temperature. 3.6. Polymerization Time. Sufficient polymerization time was necessary to obtain a product with a satisfactory degree of polymerization. The effects of polymerization time on the acid value of the PTHSA are shown in Figure 1. As shown in Figure 1, along with the extension of polymerization time, the acid value of the product decreased gradually. Experimental results indicated that the removed rate of water
3752 Ind. Eng. Chem. Res., Vol. 48, No. 8, 2009
Figure 3. Effects of the amount of polyol-PTHSA on the TBN of the calcium oleate detergent. Reaction condition: Acid value of the PTHSA, 50 mg of KOH/g.
Figure 4. Effects of the acid value of PTHSA on the TBN of the calcium oleate detergent. Reaction condition: Polyol-PTHSA amount, 10%.
was very rapid during the initial two hours, then it became slow gradually, which corresponded to the change of the acid value of the product in Figure 1. This phenomenon demonstrated that the original reaction balance may have been reached during the initial two hours. On the whole, the acid value of the product decreased rapidly during the initial 12 hours, and after that it decreased slowly. After 16 hours, the acid value decreased less through extending the polymerization time. Therefore, an appropriate polymerization time was 16 hours in our experiments. 3.7. Modification of PTHSA Using Pentaerythritol. For PTHSA, to improve the ability of dispersing nanocarbonate, pentaerythritol was used to modify the PTHSA. In the process of modification, the amount of pentaerythritol was in excess slightly to ensure more hydroxyl in polyol-PTHSA, and the acid value of the final polyol-PTHSA was about 3 mg of KOH/g. The reaction conditions were as follows: the molar ratio
pentaerythritol/PTHSA, 1.2:1; the reaction temperature, 453 K; and reaction time, 4-8 h (for PTHSA with different acid values). 3.8. Infrared Spectrum Analysis. The infrared spectrum was used to analyze the chemical structures of the THSA, the PTHSA, and the polyol-PTHSA, and their typical infrared spectrums are shown in Figure 2. In Figure 2a (THSA), the broad adsorption peaks at 3000-3300 cm-1 were the characteristic adsorption peaks of association of carboxyl and hydroxyl. In Figure 2b (PTHSA), the adsorption peaks at 1732, 1178, and 1112 cm-1 were the characteristic adsorption peaks of the ester group; absence of an absorption peak at 3000-3300 cm-1 was evidence for the complete conversion of THSA. In Figure 2c (polyol-PTHSA), in addition to the characteristic adsorption peaks of the ester group at 1732, 1178, and 1112 cm-1, the adsorption peaks at
Ind. Eng. Chem. Res., Vol. 48, No. 8, 2009 3753 -1
3523 and 1058 cm were the characteristic adsorption peaks of the hydroxyl group, which confirmed the introduction of pentaerythritol. In addition, the adsorption peak of 723 cm-1 in both parts b (PTHSA) and c (polyol-PTHSA) were stronger than that in part a (THSA), which showed more methylene in parts b (PTHSA) and c (polyol-PTHSA) and also confirmed that parts b (PTHSA) and c (polyol-PTHSA) have a higher degree of polymerization. 3.9. Amount of Polyol-PTHSA. In our experiments, the polyol-PTHSA was used in the process of preparing environmentally friendly overbased calcium oleate detergent to increase the TBN of the product. The action of different weight percentages of the polyol-PTHSA to total materials (oleic acid and polyol-PTHSA) on the TBN of the calcium oleate detergent was investigated. Results obtained are shown in Figure 3. As shown in Figure 3, as the amount of polyol-PTHSA (wt %) was increased, the TBN of the product increased first and then decreased. The TBN of the product attained the highest value at the weight percentage of the polyol-PTHSA of 10%. Meanwhile, the viscosity of the product also increased gradually along with the increase of the amount of polyol-PTHSA. It is probably due to the high viscosity of polyol-PTHSA. In our experiments, the optimal weight percentage of the polyolPTHSA was 10%. 3.10. Acid Value of the PTHSA. In the process of preparing environmentally friendly overbased calcium oleate detergent, the degree of polymerization of the polyol-PTHSA also has some effects on the TBN of the product. Actually, the degree of polymerization of the polyol-PTHSA was that of the PTHSA, which decided the molecular weight of the polyol-PTHSA and corresponded to the acid value of the PTHSA. Therefore, we took the acid value of the PTHSA as a variable to study the effects of the degree of polymerization of the polyol-PTHSA on the TBN of the calcium oleate detergent. Results obtained are shown in Figure 4. For PTHSA, the acid value and the degree of polymerization had an inverse relationship. As shown in Figure 4, as the acid value of the PTHSA increased, the TBN of the product increased first and then decreased, which demonstrated that an appropriate range of acid value of the PTHSA was necessary to obtain a product with satisfactory TBN. The TBN of the product attained the highest value at the acid value of the PTHSA of 50 mg of KOH/g. Thus, the optimal acid value of the PTHSA was 50 mg of KOH/g selected for preparing environmentally friendly overbased calcium oleate detergent in our experiments. 4. Conclusions In this study, the poly-12-hydroxy stearic acid was synthesized by linear polycondensation and then modified by esterification with pentaerythritol to obtain a polyol polymeric hyperdispersant (polyol-PTHSA). The FT-IR characterization results showed that the polyol-PTHSA was an aliphatic high polymer containing hydroxyl and ester groups. Under suitable reaction conditions (catalyst, SnCl2 · 2H2O; catalyst weight percentage, 0.5%; polymerization temperature, 463 K; polymerization time, 12 h), the PTHSA with acid value of 25 mg of KOH/g can be obtained. For the modification of PTHSA using pentaerythritol, the optimal reaction conditions were as follows: molar ratio pentaerythritol/PTHSA, 1.2:1; reaction temperature, 453 K; and reaction time, 4-8 h. In the process of preparing environmentally friendly overbased calcium oleate detergent, the polyol-PTHSA was used as a hyperdispersant and the optimal reaction conditions were a weight percentage of the
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ReceiVed for reView October 22, 2008 ReVised manuscript receiVed January 9, 2009 Accepted February 20, 2009 IE8016016
