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9CHEMICAL SCIENCES
SYNTHETIC LUBRICATING OILS ON BASE OF COMPLEX ESTERS OF ALKENYLSUCCINIC ACIDS
Mammadyarov M.A.
Aliyeva F.Kh.
Mammadova F.A.
Y.H.Mammadaliyev Institute of Petrochemical Processes of Azerbaijan National Academy of Sciences,
Baku, Azerbaijan
ABSTRACT
The main purpose is the investigation of synthesis of complex esters of alkenylsuccinic acids and study of their viscous-temperature and exploitation properties depending on their chemical structure. Synthesized complex esters of alkenylsuccinic acids, by their properties, can be proposed as the bases and components of lubricating oils.
Keywords: anhydride, vicinal dicarboxylic acids, complex esters, esterification, lubricating properties, viscosity
Intensively developing modern technique puts very strict requirements to lubricants. There is an acute problem of ensuring the operation of equipment in conditions of extreme changes in temperature conditions.
For the first time the industrial production of esters of synthetic oils (on the base of sebacic acid) began at the end of the last century [1-3] and were dictated by need of developing aviation. Now, these oils found the use and in other branches of industry [4-7]. In currently produced on a commercial scale, not only petroleum oils, but also synthetic oils on the basis of ethers of pen-taerythritol and ethers of terminal dicarboxylic acids not completely meet requirements of the modern and perspective technique. An important theoretical and practical value, therefore, is the creation of new types of synthetic oils.
The available references in the field of essential synthetic oils generally cover ethers with a terminal arrangement of ester groups. Meanwhile, there are ethers with a heme and vicinal arrangement of ether groups. In view of this, the synthesis and testing of these esters as a basis of synthetic oils are of great scientific and practical interest.
It is well known that the properties of any chemical compound, first of all, are due to the nature of the chemical structure. The researches in the field of synthetic oils in this direction, unfortunately very little. Therefore, carrying out similar studies in the field of oils, especially in the field of synthetic oils, is of great theoretical and practical importance.
In the laboratory of synthetic oils of the Institute of Petrochemical Processes of Azerbaijan National Academy of Sciences the technology of preparation of new types of synthetic oils on the base of esters of alkenylsuccinic acids has been developed. These types of synthetic oils on its exploitation characteristics do not yield in, and on some properties exceed industrial
esters of synthetic oils [8]. In addition, the opening of anhydride ring in molecule of initial alkenylsuccinic anhydride allows to synthesize the multifunctional esters and to investigate more deeply the structural correlation of the prepared compounds.
Anhydrides of alkenylsuccinic acids were prepared by ene synthesis of maleic anhydride and a-ole-fins. The process is carried out in autoclave. The optimal conditions: temperature 200-2200C, reaction time 10-12 hours, ratio maleic anhydride:a-olefins 1:3-4 were determined. For prevention of polymerization of a-olefins in reaction mixture was added 0.3-0.5% mass of hydroquinone. After atmosphere distillation of excess of a-olefins the condensate was distilled under vacuum. The yield of anhydrides of alkenylsuccinic acids was 69-75% from theoretical [9].
Anhydrides of alkenylsuccinic acids (C6, C8, C10) are liquids of light-yellow color. The structure of anhydrides of alkenylsuccinic acids was proved by data of IR- and PMR-spectroscopy.
Esterification reaction was carried out in flask equipped with mixer, thermometer and reverse cooler. Ceokar-2 was used as catalyst of esterification. The end of esterification reaction was determined on quantity of released reaction water.
Recently a great attention is also paid to the preparation of complex esters. Complex esters can be synthesized by using dicarboxylic acids, glycols and aliphatic fatty acids. With the aim of study of influence of structure of complex esters on viscous-temperature and other properties a number of complex esters on the base of anhydride of hexenylsuccinic acid, glycols have been synthesized. Fatty acids and aliphatic alcohols have been also used. For preparation of complex esters the esterification was carried out stage by stage (two or three stage).
In the first stage the esterification was carried out without catalyst. The end of reaction was determined with glycols in ratio of anhydride:glycol =1:1 or 1:2. on value of acidic number.
Considering that anhydride ring is opened in more mild
In the second stage ether I was etherified by ali-
conditions the first stage was carried out at 120-1300C phatic alcohol:
Fig. 1. Synthesis esters of aliphatic alcohols and monoethyleneglycols of ASA
No subjected reaction mass to treatment, the third The end of reaction was determined on quantity of isostage was carried out; the product with fatty acids was lated water. etherified. Acid was taken in ratio Ia:fatty acid 1:1-2.
Fig. 2. Synthesis complex ester containing 3 ester groups
After distillation in vacuum the purpose product Ether II was subjected to esterification with fatty
was isolated. acids.
Fig. 3. Synthesis complex ester containing 4 ester groups
Complex esters are oily liquids with high boiling temperature, physical-chemical properties of which are presented in Table 1.
Physical-chemical characteristics of complex esters of hexenylsuccinic acid
Table 1.
R1 R2 Yield, % B.p., 0C/mmHg Refraction index 20 n D , 20 d 2 Acidic number, mgKOH/g
CH2CH2OH C6H13 87.8 - 1.4636 1.0250 1.76
chochooc-chi 1 2 2II 5 11 o C6H13 46.5 213-215/2 1.4552 0.9678 5.75
CH2CH20H C8H17 81.17 - 1.4640 1.0148 3.15
ch ch oc-c h 2 2II 5 11 o C8H17 48.2 268-270/3 1.4556 0.9594 8.72
ch9ch9oc-ch11 2 2II 5 11 o C9H19 52.6 252-256/2 1.4560 0.9563 9.08
ch2choc-c5h,, 2i 11 5 11 Ch3 o C9H19 30.0 260-265/2 - 0.9530 10.42
(ch2ch2o)2c-c5hn o C9H19 89.3 - 1.4580 0.9928 neutr.
(c^c^o^c^hn o C9H19 99.2 - 1.5665 0.9829 2.53
CH2CH20H CH2CH20H - 96.38 1.4760 1.0811 neutr.
(ch2ch2o)2c-c5hii o (ch2ch2o)2c-c5hii o 242246/2 38.04 1.4576 1.0257 9.12
ch2choh Ch3 ch2choh Ch3 - 89.09 1.4732 1.0744 14.25
ch2choc-c5hi 1 2I II 5 11 Ch3 o ch2choc-c5h,, 2I II 5 11 Ch3 o - 52.24 - 1.0587 0.59
(ch2ch2o)2c-c5hii o (c^c^o^c^hH o - 58.12 1.4722 1.0872 1.37
ch3ch2ch2ch=chch2ch-c ^-qri
' Complex esters of HSA-
ch-c-qr2 2 ^
Complex esters containing in its composition glycol radicals, i.e. free hydroxyl groups, as expected, possess high viscosity at 1000C, high low-molecular fluidity and low viscosity index, in spite of satisfactorily values of freezing point. An availability of free OH-group sharply deteriorates low-temperature fluidity almost not affecting on level of freezing point. This once more proves that freezing point and low-temperature fluidity are not in direct dependence. The defining factor of low-temperature fluidity is the nature of substituent, in
this case - availability of OH-group. In the case of propylene glycol a branching of structure of glycol rather decreases freezing point but is not almost reflected on low-temperature fluidity.
By esterification of free OH-group the complete ethers more small-viscous at 1000C were prepared. These complex esters were differed with increase of viscosity index, the best low-temperature properties. Data are presented in Table 2.
Table 2.
Viscous-temperature properties of complex ethers of hexenylsuccinic acid
R1 R2 Viscosity, mm2/s Viscosity index Temperature, 0C
1000C 500C -400C cong. flash
CH2CH2OH C6H3 3.85 12,96 18133,5 108,5 -50 158
CH2 CH2OCC5Hn 2 2 II5 11 o C6H3 3.11 9.21 4798.9 131.1 -54 185
CH2CH20H C8H17 8.74 37.59 - 126.2 -42 238
CH2 CH2OCC5H1- 2 2 II5 11 o C8H17 3.28 9.47 4607.76 135.5 -58 225
CH2 CH2OCC5H1-2 2 15 11 o C9H19 3.31 9.93 3544.13 138.5 -64 234
choçhooccshi - k o C9H19 3.72 11.64 4735.22 130.0 -58 236
(ch2ch2o)2c-c5hn o C9H19 4.92 15.76 12350.5 157.3 -54 220
(ch2ch20 )3c-c5hn o C9H19 4.48 14.10 10836.77 151.6 -52 238
CH2CH20H CH2CH20H 13.09 94.09 - 61.2 -30 174
CH2 CH2OCC5H,- 2 2 II5 11 o CH2 CH2OCC5H,- 2 2 C o 3.54 11.49 19433.9 104.0 -60 208
CH2CHOH ch3 CH2CHOH ch3 27.23 342.35 - 8.2 -5 176
CH2CH2OCC5H11 ch3 o CH2CH2OCC5H1-1 ch3 o 18.71 130.1 - 90.6 -16 240
(ch2ch2o)2c-c5hn o (ch2ch2o)2c-c5hn o 12.75 59.86 - 123.0 -26 260
-O
ch3ch2ch2ch=chch2ch-c -ori
*Complex esters of HSA
It was known that the thermal stability of chemical compound is in direct dependence on structure of compound. For determination of character of similar dependence in a number of esters of hexenylsuccinic acid
the comparative derivatographic investigation of thermal stability of a series of esters containing different ester fragments in various quantities has been carried out. Data of these investigations are presented in Table 3.
Table 3
Data of thermogravimetric analysis of esters of alkenylsuccinic acid*
№ R1 R2 T10%, 0C T50%, 0C T90%,0C Decomposition time from 10 to 90%, in minutes
I C9H19- C9H19- 262 348 379 11.7
II CH3-C6H10- CH3-C6H10- 290 328 348 5.8
III C6H5CH2- C6H5CH2- 260 325 361 10.1
IV ch3 1 3 -ch2choc8h17 ch3 1 3 -ch2choc8h17 262 358 395 13.3
V -CH2CH2O H -CH 2CH2O H 300 390 441 14.1
VI O II -CH2CH2OCC5H11 O II -CH2CH2OCC5H11 348 400 445 9.7
VII C9H19- C6H11- 282 360 390 10.8
VIII CH3C6H10- C7H15- 286 335 362 7.6
IX CH2C6H5 C7H15- 280 345 370 9.0
X CH2CH2OH C8H17- 296 378 415 10.9
XI O II -CH2CH2OCC5H11 C8H17- 278 354 390 11.2
*Complex esters of HSA -
ch3ch2ch2ch=chch2ch-c ¿^ori
ch2-c-or2 °
It is seen in comparison of thermogarvimetric parameters of the prepared compounds that even an initial period of thermochemical conversions characterizing by parameter of T10% is differed depending on structure of molecule. As it is seen from Table 9 more stable compound is complex ester of hexenylsuccinic acid with four ester groups, as 10% mass loss occurs at temperature 3480C whereas in dinonyl ether this temperature corresponds to 2620C, but temperature at which 90% mass loss takes place - 4450C, and in dinonyl ether - 3790C.
It was known that cyclohexanols are secondary alcohols, thermal stability of which gives in esters of primary alcohols. This is confirmed on example of esters prepared by us. In spite of the fact that temperature at which it takes place 10% mass loss of dimethylcyclo-hexanol ether of hexenylsuccinic acid, corresponds to 2900C (higher than in dinonyl ether of hexenylsuccinic acid - 2620C), however at 3480C 90% mass loss takes place, whereas in dinonyl ether such mass loss takes place at temperature 3790C. Distortion of symmetry leads to improvement of thermal stability of esters. As it is seen from Table 3, complex esters possess the best thermal stability.
Thermooxidative stability of esters of hexenylsuccinic acid was determined on GOST (SS) 23797-79. The results of experiments are presented in Table 4.
For experiment of thermooxidative stability ethers with various structures were chosen. As it is seen from Table 4 the investigated ethers are sufficiently stable to oxidation. In all cases corrosion on plates of aluminum
alloy AK-4 is absent. The slight corrosion has been detected on steel of mark SHK-15.
Asymmetric esters of hexenylsuccinic acid possess the best thermooxidative properties than symmetric: distortion of symmetry leads to improvement of evaporation (1.66% against 3.83%), decrease of precipitation insoluble in isooctane. And cyclic ethers, in particular, dimethylcyclohexane ether of hexenylsuccinic acid possess worse thermooxidative properties than aliphatic ethers.
As already it was told, this has been connected with structure of alcohol radical which is secondary and therefore less stable than aliphatic primary alcohols which have been proved by thermographic analysis.
It was known that the availability of hydroxyl group in molecule of ether negatively influences on its thermooxidative stability which has been proved once more in the case of study of thermooxidative stability of complex ester containing free OH-group. This ester is differed with great quantity of precipitation insoluble in isooctane (1.08%), and corrosion on plates SHK-15 (ester IX). Complex esters not containing free OH-groups in molecule possess better thermooxidative properties (ester X).
One of determining factors of exploitation properties of synthetic lubricating oils are their lubricating properties which have been immediately connected with chemical structure of molecule. The availability of polar centers first of all and also spatial conformation of molecule shows noticeable influence on lubricating properties. Such polar center in molecules of esters of hexenylsuccinic acid is the polar ester group.
Table 4.
Data of thermooxidative stability of esters of HSA* __
№ R1 R2 Viscosity, mm2/s at 1000C After oxidation Corrosion, mg/cm2 Vaporability, % mass
Increase of viscosity, % Acidic number, mgKOH/g Precipitate insoluble in isooctane % mass
before oxid. after oxid. AK-4 SHK-15
I C8H17 C8H17 3.04 3.71 22,03 4.49 0.086 abs abs 3.83
II CH3-C6H10 CH3C6H10 5.42 7.33 35,28 16.46 0.84 abs 0.509 7.33
III C6H5CH2 C6H5CH2 3.53 3.95 11.89 9.09 1.16 abs 0.608 1.70
IV ch3 1 3 -ch2ch0c8h17 ch3 1 3 -chachoc8hi7 3.24 5.97 84.25 3.43 0.67 abs abs 10.3
VII C9H19 C5H11 3.13 3.93 25.5 4.80 0.01 abs 0.115 1.66
VIII CH3C6H10 C7H15 3.18 4.66 46.2 8.69 0.11 abs abs 5.66
IX C6H5CH2 C7H15 3.25 5.2 60.0 5.3 0.24 abs abs 2.70
X CH2CH20H C8H17 8.74 13.89 58.7 7.31 1.08 abs -0.542 4.66
XI O II -ch2ch20cc5h11 C8H17 4.92 7.10 44.3 neutr. 1.430 abs 0.098 3.00
.O
CH3CH2CH2CH=CHCH2CH-C^ORI CH-C^ORa
*Complex esters of HSA - O
_Lubricating properties of esters of hexenylsuccinic acid*
Table 5.
№ R1 R2 Rub index (Is) Critical load, (Pk) Weld load, (Pc) Wear index at load 40 kg/mm (J)
I n-C8H17 n-CgHn 26 56 135 0.95
II ch3^ >- CH30- 25 56 135 0.69
III o ch2- o ^>-ch2- 26 56 135 0.79
IV ch3 1 3 c8h17 ochch2 - ch3 i 3 c8h17 ochch2 " 26 56 137 0.73
V - CH2CH20H - CH2CH2ОH 30 71 141 0.75
VI -ch2 ch2occ5h1-1 2 2 ii 5 11 O -ch2 ch2occ5hf, 2 2 c 5 11 O 32 75 147 0.70
VII n-C8H17 n-C6Hlз 29 56 135 0.83
VIII n-C7H15 cO 25 56 135 0.85
IX n-C7H15 26 56 126 0.79
X n-C8H17 -CH2CH2ОH 29 71 141 0.70
XI n-C8H17 -CH2 CH^CC^ O 32 75 141 0.68
XII Di(2-ethylhexyl)sebacianate (DOS) - 50 - 0.69
XIII Ester of pentaerytrite and SZhK C5-C9 29 50 - 0.79
*Complex esters of HSA -
.O
ch3ch2ch2ch=chch2ch-c ^orj
CHjC^OR2
Molecule of symmetric diester of hexenylsuccinic acid possesses two ester groups. The comparison of properties of compounds I, II, III differing between itself with nature of alcohol radical shows that their main difference is in wear parameters. Ester with aliphatic normal alcohol radical has maximal wear (0.95 mm). Minimum wear (0.69 мм) - has been established in the case when cyclo-hexane ring is radical. Esters with aromatic alcohol radicals occupy intermediate position (0.79 mm). Distortion of symmetry in this case leads to improvement of lubricating properties.
In alkoxyisopropyl esters of HSA which besides ester groups have also two ether groups the polarity of molecule is increased and lubricating properties are correspondingly improved, in particular, parameter of weld loading (Pw) is increased and diameter of spot of wear is decreased.
Complex esters of HSA on its lubricating properties exceed not only other esters of HSA but also sebacic acid and pentaerythritol. Complex esters which contain in molecule three and four ester groups, i.e. possess a great number of polar centers, on all parameters exceed symmetric, asymmetric and also alkoxypropyl esters of HSA not having OH-group (ester XI) in its composition.
As it is seen from Table 5 all esters of HSA on data Рк exceed sebacic acid but complex esters on rub index (Рк), and also on diameter of spot of wear exceed not only diethers of HSA and also ebacic acid and ethers of pentae-rythritol. Probably, this has been connected with structural peculiarity and availability of 3-4 polar ester groups, as
with increase of number of carboxyl groups in composition of molecule their polarizability is increased.
CONCLUSION
1. New complex esters on the base of anhydrides of ASA, glycol and fatty acids have been synthesized and asymmetric, alkoxypropyl and complex esters have been also prepared.
2. The physical-chemical, viscous-temperature, thermal, thermooxidative properties and also lubricating properties of these compounds have been determined. On the base of study of correlation dependence between chemical structure and exploitation properties of these esters a number of regularities which give a possibility to carry out experiment purposefully and selectively has been established.
3. The synthesized complex esters can be proposed as bases and components of perspective lubricating oils.
This work was supported by the Science Development Foundation under the President of the Republic of Azerbaijan. Grant №. EIF-2014-9 (24) -KETPL-14/05/4.
References
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3. Patent 52024 Ukraine. 2003.
4. Patent 6649574 USA. 2004.
5. Patent 6818145 USA. 2007.
