Znd. Eng. Chem. Res. 1993,32, 3170-3173
3170
Synthesis of Basic and Overbasic Sulfonate Detergent Additives H. H. Abou El Naga, Wedad M. Abd El-Azim,' S. A. Bendary, and N. G. Awad Research Centre, Misr Petroleum Co., P.O. Box 228, Cairo,Egypt
Heavy alkylbenzene, which accumulates as a by-product from linear alkylbenzene synthesis, is evaluated as a starting material for preparation of basic and over basic sulfonate detergent additives. Chemical structure analysis showed that this by-product contains several components in different proportions. Most of these components, as traced via mass spectrometry, showed the presence of paraffinic side chains within the carbon range C11-C22. Accordingly, sulfonation conditions for it were adjusted to optimize the reaction yield and sulfonic quality. Neutralization of the sulfonic acid was carried out by adding CaO in the presence of methanol as a promoter. Preparation of over basic sulfonate was run via a carbonation process a t 55-60 "C. Evaluation of synthesized basic calcium sulfonate in comparison to a commercial additive is supported by its efficiency as a detergent additive. The synthesized product has a higher total base number and Ca content than those for the commercial one. On the other hand, evaluation of the synthesized overbasic calcium sulfonate compared with overbasic commercial additives with medium and high alkalinity indicated that the synthesized product can be classified as overbasic calcium sulfonate with medium alkalinity, good dispersive power, and detergent efficiency. 1. Introduction
Detergent and dispersant additives are essential in manufacturing lubricating oils for modern engines. Detergent additives are used to keep engines and especially their hottest parts in a proper state of cleanness. Dispersant additives are used to keep in fine suspension the solid impurities which accumulate in the lubricating oil during its use.l Extensive field testing has shown that the level of detergent alkalinity, also called basicity, has a direct effect on engine cleanness and durability. Total base number (TBN) is the numerical expression of alkalinity. Increased detergent alkalinity reduces deposits and wear effects which results in improved oil consumption and longer engine life.2 Sulfonates are one of the most important detergent additives, which are prepared by neutralizing sulfonicacids of the general formula R-SOsH, with a metallic base. Most sulfonate detergent additives are in the form of calcium and barium salts.3 It is important that the molecular weight of the corresponding hydrocarbon must be of the order of 350 or more. The overbasic sulfonate additives contain an excess of alkaline earth metals, i.e., over that amount required for completely neutralizing their sulfonic acid constituent^.^ Since the inception of the overbasing technique, different petroleum sulfonic acids have been used as starting materials in preparation of the overbasic products. There are different patents and procedures for producing the overbasic alkaline earth metal sulfonates. Benbury and Bray6 described a blend of petroleum lubricating oil (MW 400-600) and linear alkylbenzene (25-35 carbon atoms), which is sulfonated with oleum. Watson et a1.6 have found that preparation of oil-soluble alkaline earth sulfonates with high alkalinity can be improved by using an amine promoter during the carbonation of a mixture comprising neutral alkaline earth sulfonates. Koft' also described a process to prepare overbasic oilsoluble metal salts by reacting a mixture comprising an oil-soluble organic acid, an alcohol, and a diluent with sequential addition of a metal oxide and carbon dioxide in the presence of a halide. Norman et al.8 succeeded in preparation of oil-solublebasic metal salts of organic acids, such as sulfonic acids, carboxylic acids, and phosphorus
Table I. Analysis Results for HAB Sample test method specification ASTM-D sp gr at 15/4 O C 1298 color Saybolt 156 flash point (PM) OC, "C IP-35 445 kinet viscosity at 40 O C , cSt 445 kinet viscosity at 100 O C , cSt viscosity index 2270 97 pour point, "C TAN, mg of KOH/g of sample 664 Conradson carbon, wt % 874 95 water content, w t % refractive index (20 "C) 1218 average molecular weight 2502
HAB sample 1 0.8817 +50 200 41.63 5.85 74 -36 0.035 0.1 free 1.4887 400
acids. These salts are obtained by reacting acids with excess amounts of metal bases in the presence of an acidic gas, e.g., carbondioxide, anda promoter, such as analcohol, under substantially anhydrous conditions. A published patent9 is based on using alkylaromatic hydrocarbons with an alkyl chain, from CISto c36, as raw material for synthesizing overbasic alkylaromatic sulfonates. Some other authorslo stated that synthetic sulfonates are an important outlet for heavy alkylbenzene byproducts. Abou El Naga et a1.l1J2 previously studied the possibility to upgrade by-products of linear alkylbenzene and dodecylbenzene. Effective surface-active agents were synthesized through proper sulfonation of their byproducts. The present work is aimed at producing basic and overbasic sulfonate detergent additives by using the local available heavy alkylbenzene. A developed sulfonation technique is proposed. Synthesized sulfonate salts are comparatively evaluated with commercial additives. 2. Experimental Section
In this study a sample of heavy alkylbenzene (HAB), as a by-product accumulated from locally produced linear alkylbenzene, was used. Analysis of this sample was carried out according to the standard ASTM routine methods as listed in Table I. The fine chemical structure for this sample was traced via gas chromatography and mass spectrometry (GC/MS). (GC/MS analysis was
QSS8-58S5/93/2632-317Q~Q4.QQJQ0 1993 American Chemical Society
Ind. Eng. Chem. Res., Vol. 32, No. 12, 1993 3171 I
1
T I C of DATAZZOHNY-AK.D
weight of sample, g sulfonation time, min sulfonation temp, "C flow rate of air, l/h oleum temperature, "C oleum weight, g yield, w t 7'% sludge formation
o 2.OEt5'
E 1.5€+5-
0
c l.OEt52 0.5EtL-
1
A
21.2
21.4
proposed condition 200-300 25-360 35-60 300-650 30-100 400-1200
optimum condition 250 200 55-60 550 100 900
>90 nil
234
I
L
Table 111. Proposed and Optimum Sulfonation Conditions for Tested Sample (HAB)
216
21.8
221)
225
Time (rnin.)
I
22k
I
Figure 1. Chromatogram of heavy alkylatedbenzene (HAI3)sample. HP model,MS 5988, column type, HP-1;rate of temperatureincrease, 8 "C/min;final temperature, 285 "C. Electron energy, 70 eV. Table 11. Some Existing Components in Heavy Alkylbenzene Sample mol base component name peak comDonent formula MW 1 232 1-butylheptylbenzene 105 91 2 246 1-pentylheptylbenzene 246 1-butyloctylbenzene 91 3 246 1-propylnonylbenzene 4 91 91 330 1-octyldecylbenzene 5 105 246 1-ethyldecylbenzene 6 91 260 1-pentyldecylbenzene 7 91 260 1-butylnonylbenzene 8 91 260 1-propyldecylbenzene 9 91 260 1-ethylundecylbenzene 10 260 1-methyldodecylbenzene 105 11 274 1-butyldecylbenzene 105 12 91 302 1-butyldodecylbenzene 13 91 330 1-butyltetradecylbenzene 14 91 386 1-butyloctadecylbenzene 15 ~~
carried out at Microanalytical Centre, Cairo University.) Figure 1 represents the obtained chromatogram, while Table I1 lists the MS results. Sulfonation was carried out with so3gas, in a glassware apparatus, which consists of an air pump, a flowmeter, an air dryer containing anhydrous CaC12 crystals, a hot plate to heat oleum, a reaction vessel which includes a heating device (water bath), a magnetic stirrer, a thermometer, and a water container. Different sulfonation conditions were applied in order to ascertain their suitability for the synthesis of oil-soluble sulfonates. The conditions were varied, e.g., reaction temperature (from 35 up to 55-60 "C), reaction time (from 25 min up to 6h); refer to Table 111. The optimum sulfonation conditions, i.e., those which give the maximum yield of sulfonated products, are listed in Table 111. The sulfonation process were carried by first heating 65 ~ 0 1 5 %oleum to around 100 "C. A dry air stream was then passed through the heated oleum. Evolved SO8 gas was transferred with the dry air stream to pass through the sulfonation vessel. Sulfonation was carried out under
stirring at 55-60 "Cfor 2.5-3 h; stirring was continued for a further 1 h. Neutralization for prepared sulfonic acid compound was carried out by adding calcium oxide in the presence of methanol as a promoter at 70 "C. The temperature was then raised to 100 "C. A sufficient amount of benzene was added to the neutralized sulfonate. Calcium sulfonate as a final product was obtained by stripping out the benzene under vacuum. The obtained neutral sulfonate was diluted with a suitable base oil. Preparation of overbasic calcium sulfonate was run via a carbonation process. This process was carried out as follows: 1. Nearly 1:l mole ratio of carbon dioxide gas to calcium oxide was introduced at a constant flow rate into the carbonation vessel. 2. A mixture of calcium sulfonate, calcium oxide, methanol, and toluene at mass ratio 1:0.25:1.50:2, respectively, was put in the carbonation vessel at 55 "C under vigorous stirring. 3. After complete reaction, methanol and toluene were stripped out, leaving a viscous solution. 4. A sufficient quantity of pure benzene was added to this viscous solution. The mixture was then centrifuged for 2 h at 1500 rpm. Overbasic calcium sulfonate was obtained by stripping out the benzene under vacuum. Physical and chemical properties of the synthesized neutral and overbasic calcium sulfonates were compared with commercial additives. Results are listed in Table IV. Two testa were carried out to evaluate the detergency and dispersency powers for the overbasic synthesized calcium sulfonate. Two commercial overbasic sulfonate additives with high and medium alkalinities were also tested as references for comparison with synthesized sample. Dispersive power was evaluated by applying a sedimentation test,13in which carbon black is added to additive and nonadditive oil samples under stirring. The mixtures are allowed to settle. The dispersive power is defined as the ratio of the time necessary for a certain quantity of carbon black to settle from additive oil to that time in the case of nonadditive oil. Detergency power was evaluated by applying the chromatography test,14 in which carbon black with two different percent weights (1 % and 2 % ) is dispersed in a detergency oil and then the mixture is filtered through a glass tube filled with layers of sand separated by filter papers. Detergency power is measured by the number of filter papers blackened by the eluated solution. Table V includes the obtained results for these evaluation tests. 3. Results and Discussion
The analysis results as listed in Table I, show that the heavy alkylbenzene (HAB) has acceptable properties for
3172 Ind. Eng. Chem. Res., Vol. 32,No. 12, 1993 Table IV. Analysis Results for Synthesized Basic and Overbasic Calcium Sulfonate Samples (SIand 8,) in Comparison with Commercial Detergent Additives concn of TBN,O mg of KOH/ Ca sulfated g of sample contentb, w t % ash: w t % sulfonate, wt % sulfonate samde
SI
basic (HAB) calcium sulfonate commercial basic calcium sulfonate, additive S2 overbasic (HAB) calcium sulfonate commercial overbasic sulfonate with medium alkalinity SM commercial overbasic sulfonate with high alkalinity SH a ASTM-D 664. b Atomic absorption. ASTM-D 874.
60
SN
Table V. Dispersive and Detergency Power for Synthesized Overbasic (HAB) Calcium Sulfonate
sample
dispersive powep
SH SM
11 6.6
s2
11
0
detergency powerb lwt% 2wt% 4 6 5
5 6 6
Sedimentation test. b Chromatography test.
use as a starting material in the synthesis of sulfonated detergent additive for lubricating oil blends, especially it has an average molecular weight around 400. 3.1. Heavy Alkylbenzene Molecular Structure. Separation of the heavy alkylbenzene into its chemical components is accomplished by GC. Figure 1represents the obtained chromatogram, which shows that this sample contains several components in different proportions. Only 15 of these components were traced via the applied GC mass spectrum technique. The separation was carried out to evaluate the fine chemical structure of heavy alkylbenzenecomponents. Table I1includes the molecular formula, molecular weight, component name, and base peak of each separated component. Examination of these results, as listed in Table I1 and represented in Figure 1, indicate the following: 1. This heavy alkylbenzene contains 15 components with different boiling ranges. 2. The 15 detected components have substitution with branched side chains (C11-C22) at the a-position to the benzene ring. Substituent groups include CH3, C2H5, C3H7, C4H9, CsHii, and CaHi7. 3. Most detected components give rise to base peaks with mle 91;four components only give a base peak with mle 105. This chromatogram also shows that other components, i.e., those which are not traced via the applied GCIMS technique, have side chains with more than (222. The measured average molecular weight for the heavy alkylbenzene indicates the presence of these components in addition to the detected 15 ones. 3.2. Synthesis of Basic Additive. Generally, sulfonation of the aromatic compounds with sulfur trioxide is an irreversible reaction,l5 which proceeds via the following rnechanism:'e
Several sulfonation trials on HAB sample were carried out to select the optimum sulfonation conditions, i.e., those which give the maximum yield (over 905% ) of sulfonic acids. Results of the proposed and optimum sulfonation conditions, as listed in Table 111,indicate that sulfonation of HAB, under the optimum sulfonation conditions, is not
60
43.5 24 200 170 400
3.43 2.35 8.3 7.4 15.5
11 8 26.05 24.8 52.7
accompanied by sludge formation, which occurs when sulfonated material contains undesirable components.17 Synthesized sulfonicacid was then neutralized with CaO. Obtained calcium sulfonate must be diluted with light base oil in order to maintain it in the liquid phase; otherwise it can be immediately changed to the solid phase. Synthesized neutral calcium sulfonate sample (SI)was analyzed to give results as listed in Table IV. 3.3. Synthesis of Overbased Additive. Carbonation processes were carried out on oil-soluble neutral calcium sulfonate. Results showed that calcium sulfonate of HAB (SIsample, Table IV) can be easily carbonized to overbasic calcium sulfonate in the presence of methanol as a promoter according to the following reaction: promoter (methanol)
RS03M + XMOH c neutral sulfonate metal hydroxide carbon dioxide RS03M-XMC03 + H 2 0 overbasic sulfonate water Synthesized overbased calcium sulfonate, sample S2, was analyzed to give results as listed in Table IV. 3.4. Evaluation of Synthesized Basic and Overbasic Additives. Table IV includes the analysis results for synthesized basic and overbasic samples (labeled S1 and SZ,respectively). Analysis results for the commercial additive samples are also included in this table. These commercial additives were given the labels SN for the basic calcium sulfonate sample,l8 SM for the medium alkalinity overbasic calcium sulfonate sample,lg and SH for the high alkalinity overbasic calcium sulfonate sample. Results of synthesized basic calcium sulfonate (sample SI)in comparison to those of commercial basic calcium sulfonate additive (sample SN) as listed in Table IV indicate that sample SI,at a concentration of 60 w t % ,has a higher TBN, Ca content, and sulfated ash than sample SN. These results support the suitability of sample SIas a detergent additive. Reducing of Ca content can let sample S1 have the same results as sample SN in TBN and sulfated ash. The results for synthesized overbasic calcium sulfonate (sample Sa) compared with those of the commercial overbasic calcium sulfonate additives with medium and high alkalinity, (samples SM and SH,respectively)indicate the following: 1. Sample S2 can be classified as an overbasic calcium sulfonate with medium alkalinity rather than with high alkalinity. This conclusion is based on its TBN, Ca content, and sulfated ash results. 2. Sample S2 has acceptable results, which can be attributed to the suitability of the heavy alkylbenzene sample toward sulfonation and consequently the suitability of S1 toward carbonation. Results for despersive and detergency powers for synthesized overbasic Ca sulfonate (sample S2) as listed in Table V, compared with those for commercial samples SH SM, indicate the following:
Ind. Eng. Chem.Res., Vol. 32, No. 12,1993 3173
1. Commercialoverbasiccalcium sulfonate (sample SH), with high alkalinity, has a better dispersive ability and lower detergent efficiencythan medium alkalinity calcium sulfonate (sample SM). 2. The synthesized overbasic calcium sulfonate (sample SZ)has a better dispersive ability than SM sample which can be attributed to its higher TBN and/or the chemical structure of HAB sample. 3. Synthesized overbasic calcium sulfonate (sample SZ) has the same detergent efficiency as sample SM in the presepce of 2 wt % carbon black oil contamination. A slight difference between their detergent efficiencies at 1 wt % carbon black oil contamination can be also observed. Accordingly, it is possible to conclude that sample SZ has good detergent efficiency in the presence of high contamination. Such detergent efficiency is similar to those of the commercial additives. Explanation of these results can be based on the chemical structure of the alkylbenzene, as previously illustrated. This product has long side chains with carbon number within the range C11 to >CZZ, which all are in the a-substitution positions. According to previous publications long side chains can improve the detergency power.z0
Conclusion Basic and overbasic calcium sulfonate detergent additives were synthesized via developed sulfonation, neutralization, and carbonation processes. Heavy alkylbenzene, which is accumulated as a by-product in the local linear alkylbenzene unit, is successfully used as a hydrocarbon sulfonatable fraction in these preparations. Optimum sulfonation conditions for this product require 5560 "C reaction temperature and 150-min digestion time. Both neutralization and carbonation processes must be carried out in the presence of methanol as a promoter. Dispersive and detergent powers for synthesized basic and overbasic calcium sulfonate of heavy alkylbenzene are very acceptable compared with commercial additives. Literature Cited (1) Industrial Lubricants Greases and Related Products; SBP Chemical Engineering Series 48; SBP Board of Consultants and Engineers: New Delhi, India, 1978. (2) Gergel, W. C. Detergents Alkalinity, the Key to Diesel Engine Performance. Fifth International Seminar on New Deuelopment
in Engine Oils, Industrial Oils, Fuels and Additives, Oct 14-17, 1985; Misr Pet. Co. Research Centre Chamra: Cairo, Egypt, 1985. (3) Laurent, R.;Tirtiaux, R. Overbased Sulfonates, Lubricating Oil Additives of Reduced Foaming Tendency. U.S. Patent 29997, assigned to Exxon Company, March 31,1981. (4) Ranney, M. W. Lubricant Additives; Chemical Technology Review 2; Noyes Data Corporation: Park Ridge, NJ, 1973. (5) Benbury, L. S.;Bray. U.S. Patent 3,591,498,assigned to Bray Oil Company, July 6,1971. (6) Watson, R. W.; Richardson, E. E.; Sabol, A. R. U.S. Patent 3,492,230, assigned to Standard Oil Company, Jan 27,1970. (7) Koft, E., Jr. U.S. Patent 3,544,463, assigned to Mobil Oil Corporation, Dec 1,1970. (8) Norman, G. R.;Le Suer, W. M. U.S. Patent 3,595,790,assigned to the Lubrizol Corporation, July 27,1971. (9) UR. Pat. 047126, 1984. (10) Adami, I.; Moretti, G. F.; Davidson, A. Proceeding of Second World Conference on Detergents;Montreux, Switzerland, Oct 5-10, 1986. (11) Abdel h i m , W. M.; Abou El Naga, H. H.; Sidaros, K. N. Upgrading of Linear Alkyl Benzene By-product. J. Chem. Technol. Biotechnol. 1990,47, 61-69. (12) Abou El Naga, H. H.; Abdel h i m , W. M.; Sidaroe, K. N. Evaluation of Sulfonated By-products of Dodecyl Benzene Production. J. Chem. Technol. Biotechnol. 1987,40,51-61. (13) Tolly, S. K.; Larsen, R.G. Lubricating Oil Detergency. Znd. Eng. Chem. (Anal. Ed.) 1943,15,91-95. (14) Macnab, J. G.; Winning, W. C.; Baldain, B. G.; Miller, F. L. Lubrication of Severe-Duty Engines (DIESELS). SAE J. (Tram.) 1941,39,309-3325. (15) Libidif, N. Chemistry and Technology in the Busic Organic Synthesis and Petrochemicals; USSR, MOSQUE, (1979); Part 2, Chapter 5. (16) Brand, J. C. P.; Jarive, A. W. P.; Homing, W. C. J. Chem. SOC. 1959,3844. (17) Polanina, V. A,; Marcheva, E. N.; Ponomareva, T. P.; Siryuk, A. G.; Fernamdes, M. M. Influence of Aromatic Hydrocarbon Groups in Lube Distillate on Properties of Sulfonate Additives; All-Union Scientific Research Institute for Petroleum, Processing (VNIINPO Translated from Khimiya, Tekhnologiya Topliv Masol (1981, (No. 71, 31-33). (18) Institut Francaia DuPetrole. Lubricating Oil Additiues;Data Sheets IP-L-200, D.S.lOB-01/86,1985. (19) Institut Francaia DuPetrole. Lubricating 0ilAdditiues;Data Sheets, IP-L-BOS, D.S.2A-01/85, 1985. (20) Both, H. S.; Everon, H. E. Znd. Eng. Chem. 1948,40,1491. Received for review Auguat 9, 1993 Accepted September 20, 1993.
* Abstract published in Advance ACS Abstracts, November 1, 1993.
