Composition Of Used Oil

CHEMICAL COMPOSITION V, A. L i t v i s h k o v a , A. V N e p o g o d ' e v ,

OF USED

M O T O R OILS U D C 665.521.5

A. I. B u k h t e r , a n d A. M. B e z h a n i d z e

Changes in oil composition during engine operation are caused by the accumulation of solid contaminants and by chemical conversion of the additives and the hydrocarbon base oil. For many years it was assumed that the chemical composition of the base oil remains essentially unchanged during operation and that the quality and properlies of additive-free oils can be completely restored by treatment to remove contaminants [1]. Some investigators have held the opposite opinion that the chemical composition of the oil undergoes considerable change during operation in an engine [2]. The need for a more critical study of changes in hydrocarbon base oils is dictated by the increasingly severe requirements placed on oil quality. Here we are presenting results from a study of four used-oil samples: (1) DS-11 without additives, used 40 h in an IKM-1 single-cylinder carburetor-engine unit; (2) AS-8 containing 3.5~ VNII NP-360 additive [barium alkylphenolate and zinc bis(alkylphenyl)dithiophos" phate] after a 5000-kin test run in a Volga automobile; (3) AS-8 consisting of the distillate fraction recovered from used oil (sample 2) by vacuum distillation, plus 16% freshresidual component, this blend having been operated 40 h in an IKM-1 unit; (4) mixture of used diesel oils after reclaiming.

TABLE I. Composition of New and Used Oils

Hydrocarbon group content (in %) Oil

Mixture of used diesel oils after reclaiming Reclaimed 98070H~SOa(3% by weight). 20~ N-a2co~ (5%'by.weight) DS-11 (i~ditlve-free) new used (40 b., IKM-1 unit) ..... AS-8 new (base oil) new plus 3.5% VNII NP-360 additive Used (GAZ-21 engine, 5000 km run) Reclaimed distillate plus 16% fresh residual component Used (40 h, IKM-1 unit)

paraffinic-- group naphthenic I

aromatic group II

group III

66, 7

13,0

2,8

8,4

69,0 62,7

13,9 13,4

5,0 3,2

54, 1 47,8

28,0 20,8

58,5 9 . 58,3

t total yield in resins separaIlion

residue oi silica gel and losses

5,3

96,2

3,8

8,8 8,2

3,1 3,4

100,0 90,6

0,0 9,4

16,4 :9,6

None None

0,6 14,6

99,1 92,8

0,9

11,9 11,2

18,3 18,6

9,8 9,9

1,5 1,8

100 99,8

0,0

I 47,3

I1,1

16,3

9,7

2,8

87,2

12,8

56,5 48,0

12,2

18,4 14,4

10,6 11,2

1,9 8,1

99,6 94,7

13,0

9

7,2

0,2

9

0,4 5,3

Note: No Group IV aromatic compounds were present in any of the oils. ROZ VNII NP. Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 12, pp. 50-53, December, 1974".

9 19 75 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher

for $15.oo.

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Fig. 1. Infrared spectra of new and used oil fractions: a) Group I hydrocarbons; b) OroupII; c) Groups III and IV; d) resins. Oils: 1) new; 2) used in IKM-1 unit; 3) mixture of used diesel oils. Fig. 2. Infrared spectra of oil fractions (see Fig. 1 for designations a, b, c, d). Oils: 1) new; 2) reclaimed with sulfuric acid; a) reclaimed with alkali. The operating conditions for the oil in the single-cylinder IKM-1 unit were quite severe. At the end of the test (40 h), the oil viscosity usually had increased by 40-70%. For purposes of comparison, the corresponding new oils were tested: DS-11, AS-8, and AS-8 plns 3.5% VNII NP-360 additive.

963

TABLE 2. Composition of Hydrocarbon Part of New and Used Oils Hydrocarbon group content .o .,~

Oil

aromatic ca,

o DS-11 (additive-free) 55,0 28,4 16,6

new

used (40 h, IKM-1 unit) AS-8 plus-3%VNII NP-360 additive new used (GAZ-21 engine, 5000-km run) reclaimed distillate plus 16% fresh residual c o m ponent

None

(1) Paraffinic-naphthenic (n}~ < 1.4900) (2) Aromatic

N one

Group I (n}~ = 1.4900-1.5300) 59,5 12,1 18,6

9,8

56,0 13,1 19,3

11,6

Group II (n]~ =1.5300-1.5500) Group III (n]~ = 1.5500-1.5900) Group IV (n]~ > 1.5900)

Used (40 h, IKM-1 unit)

57,8 12,5 18,0

10,9

55,5 15,0 16,6

12,9

Note: No Group IV a r o m a n c hydrocarbons were present in any of the oils. TABLE 3. Results of Thermal-Oxidative Stability Tests on Oils in IKM-1 Unit Increase in viscosi-

ty at 50"C (%) after Blend composition

2o h

40 h

50

70

56

80

55

79

73

ll0

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1800

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1700

Frequency, cm -1 Fig. 3. Infrared spectra of reclaimed oils: 1) Fresh; 2) mixture of components after vacuum distillation; 3) hydrotreated components; 4) components after contact-treating; 5) deasphalted distillation residue. 964

The used-oil samples were partitioned on Grade ASK silica gel. Insoluble compounds were first removed by disolving the oil in n-heptane in a 1/3 ratio, filtering the solution through "Blue Ribbon" filter paper, and distilling off the solvent, the oil sample remaining after this treatment being used for the adsorptive separation. The fractions obtained in the separation were combined on the basis of refractive index to make up cuts of the following hydrocarbon types:

(3) Resinous compounds (all hydrocarbons desorbed by a l c o h o l - benzene mixture). Each separation was performed twice, or three times if the yield was less than 92%. The deviations in parallel e x , periments were at most * 1% for the individual fractions and the total yield. We must note first of all that we were never successful in any of the used-oil experiments in achieving complete desorption of the products from the silica gel (Table 1). The silica gel remained dark after separation of the used oils. It is still not clear just what this residue is. We established only that treatment of the used oil with concentrated sulfuric acid removes these products, and treatment with sodium carbonate partially converts them to resins.* None the less, these products must be taken into account in the balance for the adsorptive separation of used oils. In the used oils, particularly those tested in the IKM-1 unit, decreases in resin content were observed, along with decreases in the content of paraffinic-napththenic hydrocarbons and in the Groups I and II aromatic hydrocarbons; the contents of Groups III and IV aromatic hydrocarbons were essentially unchanged. The drops in paraffinic-naphthenic hydrocarbon content can be explained in part by the fact that the used oils (in comparison with the fresh oils) contain such additional components as "undesorbed" resins. If the comparison is made on the basis of the hydrocarbon part of the used oil (total of paraffinic- naphthenic and aromatic fractions taken as 100%), the relative amounts of the groups are very close to those for the new oil (Table 2). 9As in Russian Original; statement does not agree with data in Table 1 -- Translator.

Only a slight decrease in the paraffinic-naphthenic part is observed for the used oil, and approximately the same increase in the Group Iii aromatic hydrocarbons. The total of Groups I and II aromatic hydrocarbons remains essentially unchanged. The hydrocarbon groups recovered by adsorplion from the new and used oils were examined in an IKS-14 infrared spectrophotometer in the frequency range of 1810-1550 c m "I to detect the presence of oxidation products and other products of aging (Fig. i). The paraffinic-- naphthenie fractions of the new and used oils are identical in this range of frequencies. The spectra of the Group I aromatic compounds show slight differences; greater amounts of carbonyl compounds are observed in the used-oil fractions (1750 cm'l). The spectra of the Group II aromatic compounds show that the used oil contains m u c h greater quantities of carbonyl compounds (1710 and 1690 cm'~). Also detected were compounds absorbing at 1630-1640 c m -I, possibly organic nitrates or unsaturated compounds [3]o The spectra of the Group III aromatic compounds show that the used oil also contains considerable amounts of oxidation products and products that absorb in the 1630-1640 c m "I region. The resins of the used oil contain three times the amount of oxidation products present in the resins of the new oil. Moreover, the used-oil resins contain compounds absorbing at 1680-1640 c m ' t . The content of oxygen in the aromatic fractions of the used oil can be estimated by the method of [4]: 0.1% for Group I, 0.2% for Group II, and 0 . 5 9 for Groups llI and IV aromatic hydrocarbons. This comparison of the new and used oils shows that the reIative amounts of hydrocarbon groups in the base oil change only slightly during engine operation, but the composition of the groups may change substantially. The oxygen-containing compounds are very difficult m remove from the aromatic fractions and resins of used oiI. Treatment with concentrated sulfuric acid or sodium carbonate does almost nothing (Fig. 2). It will be seen from the data of Fig. 3 that the oxygen-containing compounds al~0 persist when the used oil is vacuum-distilled, remaining in the distillate and residue even after treatment with liquid propane. We were not even successful in reducing the content of these compounds in the distillation components by contact treatment with bleaching clay. Complete removal of the oxygen-containing compounds was achieved only by hydrotreating (gage pressure 40 k g f / e m z, temperature a00~ A1-Co-Mo catalyst). Even after such treatment, the aromatic fractions were distinguished by higher contents of polyeyclic compounds than were observed in the fresh oil. In order to investigate the effect of oxygen-containing compounds on the properties of oils tested in the IKM-1 unit, blends were prepared from the overhead and residual products obtained by vacuum distillation of the used oil, after hydrotreating or contact-treating, with a Group "V" additive package in each of the blends. The blend had a viscosity of 1t eST at 100~ The test result showed that the oils containing components that had not been treated to remove oxygen-containing compounds were poorer in thermal-oxidative stability (Table 8). CONCLUSIONS I. During engine operation, lubricating oil accumulates not only insoluble eontaminanm, but also soluble products of aging such as "resins" and also heavier substances that cannot be desorbed from silica gel by alcohol-benzene or acetone--benzene mixtures. The relative content of hydrocarbon groups is thereby reduced, mainly through "dilution ~ of the oil by aging products. The ratio of components in the total paraffinic-naphthenic and aromatic fractions of the oil is changed only slightly by operation in the engine. 2. According to the infrared spectra, the paraffinlc-naphthenic fractions of new and used oils do not differ substantially from each other. 3. The aromatic fractions of the used oil, in contrast to the fractions of the new oil, contain oxygen groups that can be removed only by catalytic hydrotreating. 4. Oxygen groups in the aromatic fractions are den/mental to the thermal-oxidative stability of the oil. LITERATURE I. 2. 3. 4.

CITED

E.G. Semenido, Conference on Viscosity of Liquids and Colloidal Solutions [in Russian], Izd. Akad. Nauk SSSR, Moscow (1944), Part 2, pp. 21q-221. B.V. Losikov, N. G. Puchkov, and B. A. Englin, Principles of Application of Petroleum Products [in Russian], Gostoptekhizdat, Moscow (1959), p.. 401. L.I. Bellamy, The Infrared Spectra of Complex Molecules, Methuen, London, 1954. K . H . Rentrop, G. Kell, and H. Echardt, Schmierstoffe Schmierungstech., p. 16 (1967).

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