Atmospheric Oxidation and Antioxidants. Volume II

542 Pages·1993·11.93 MB·English

by  Gerald Scott (Auth.)

Atmospheric
Oxidation and
Antioxidants
VOLUME II
G. Scotty editor
Department of Chemical Engineering
and Applied Chemistry
Aston University
Aston Triangle
Birmingham B4 7ET
U.K.
ELSEVIER
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PREFACE
Oxidation by molecular oxygen is one of the most practically important of
all chemical processes. It is the basis of energy production in animals and,
at the same time, a major cause of irreversible deterioration and ultimate
death. Man uses oxygen positively in the production of energy by combus­
tion, and many important industrial processes in the petrochemical in­
dustry are based on the controlled oxidation of hydrocarbons. At the same
time, oxidation is the main cause of deterioration of foodstuffs and of many
industrial polymers.
It is clearly of great practical importance that the mechanisms of oxida­
tion and its prevention should be understood in order to utilise the reactions
of oxygen more effectively but, equally importantly, to control the adverse
effects of oxygen on man-made products and in biological systems. The three
volumes of this work are directed toward these objectives. Volume I reviews
current understanding of autoxidation, largely on the basis of the reactions
of oxygen with characterised chemicals. From this flows the modern mech­
anisms of antioxidant action and their application in stabilisation technol­
ogy. Volume II examines the oxidation chemistry of carbon-based materials
in more detail with emphasis on the technological phenomena that result
from the attack of oxygen and the practical procedures developed to prevent
them. Volume III addresses our present understanding of how oxidation is
involved both positively and negatively in life processes. This is a more
recent and rapidly developing aspect of oxidation chemistry and many of the
concepts still have to be proved by rigorous scientific investigation. Never­
theless, the mechanistic principles developed as a result of studies in vitro
over the years now provide the basis for understanding the complex oxida­
tion chemistry of life processes and its control by biological antioxidants.
The three volumes, although complementary to one another, form a single
whole and it is hoped that, by frequent cross-reference, the reader will be
enabled to utilise ideas and experience from other disciplines to enlighten
his own. The first edition of this work was published a quarter of a century
ago in a single volume. The increase in size of the second edition reflects the
growth of interest in the subject in the intervening period. Nevertheless, the
mechanisms outlined in the first edition still form the basis of our present
understanding of oxidation chemistry and there will therefore be frequent
reference to it in this edition.
GERALD SCOTT
XI
LIST OF AUTHORS
S. AL-MALAIKA (Volume I)
Department of Chemical Engineering and Applied Chemistry, Aston
University, Aston Triangle, Birmingham B4 7ET, U.K.
N.C. BILLINGHAM (Volume II)
School of Chemistry and Molecular Sciences, University of Sussex,
Brighton BN1 9QJ, U.K.
JOHN A. BLAIR (Volume III)
Pharmaceutical Sciences Institute, Aston University, Aston Triangle,
Birmingham B4 7ET, U.K.
E.B. BURLAKOVA (Volume III)
The Institute of Chemical Physics, Kosygin-str. 4, Moscow 117334,
Russia
G. CAMINO (Volume II)
Dipartimento di Chimica Inorganica, Università Degli Studi di Torino,
Via Pietro Giuria, 10125 Torino, Italy
D.J. CARLSSON (Volume II)
Division of Chemistry, National Research Council of Canada, Ottawa,
K1A 0R9, Canada
T. COLCLOUGH (Volume II)
Exxon Chemical Technology Centre, Abingdon, Oxon. 0X13 6BB, U.K.
NANCY E. DAVIDSON (Volume III)
Oncology Center, Johns Hopkins Medical Institutions, 615 N. Wolfe
Street, Baltimore, MD 21205, U.S.A.
H.H. DRAPER (Volume III)
Department of Nutritional Sciences, University of Guelph, Ontario,
Canada NIG 2W1
XU
H. BRIAN DUNFORD (Volume III)
Department of Chemistry, University of Alberta, Edmonton, Alberta,
Canada T6G 2G2
GILL FARRAR (Volume III)
Pharmaceutical Sciences Institute, Aston University, Aston Triangle,
Birmingham B4 7ET, U.K.
JOHN M.C. GUTTERIDGE (Volume III)
National Institute for Biological Standards and Control, Blanche Lane,
South Mimms, Potters Bar, Herts. EN6 3QG, U.K.
KATHRYN Z. GUYTON (Volume III)
Department of Environmental Health Sciences, Johns Hopkins
Medical Institutions, 615 N. Wolfe Street, Baltimore, MD 21205, U.S.A.
BARRY HALLIWELL (Volume III)
Department of Biochemistry, King's College (KQC), Strand Campus,
London WC2R 2LS, U.K.
THOMAS W. KENSLER (Volume III)
Department of Environmental Health Sciences and Department of
Pharmacology and Molecular Sciences, Johns Hopkins Medical
Institutions, 615 N. Wolfe Street, Baltimore, MD 21205, U.S.A.
S.P. KOCHHAR (Volume II)
SPK Consultancy Services, 48 Chiltern Crescent, Earley, Reading RG6
IAN, U.K
R.P. LATTIMER (Volume II)
The B.F. Goodrich Research and Development Center, Brecksville, OH
44141, U.S.A.
R.W. LAYER (Volume II)
The B.F. Goodrich Research and Development Center, Brecksville, OH
44141, U.S.A.
DIANA METODIEWA (Volume III)
Department of Chemistry, University of Alberta, Edmonton, Alberta,
Canada T6G 2G2
ETSUO NIKI (Volume III)
Department of Reaction Chemistry, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113, Japan
Xlll
Z. OSAWA (Volume II)
Faculty of Engineering, Gunma University, Kiryu, Gunma 376, Japan
D.G. POBEDIMSKY (Volume III)
Russian Academy of Technological Sciences, Leninsky Prospect 9,
Moscow 117049, Russia
GREGORY A. REED (Volume III)
Department of Pharmacology, Toxicology, and Therapeutics,
University of Kansas Medical Center, Kansas City, KS 66103, U.S.A.
C.K. RHEE (Volume II)
The Uniroyal Goodrich Tire Company, Brecksville, OH 44141, U.S.A.
TADEUSZ SARNA (Volume III)
Department of Biophysics, Institute of Molecular Biology, Jagiellonian
University, A. Mickiewicza 3, 21-120 Krakow, Poland
GERALD SCOTT (Volumes I, II and III)
Department of Chemical Engineering and Applied Chemistry, Aston
University, Aston Triangle, Birmingham B4 7ET, U.K.
HAROLD M. SWARTZ (Volume III)
University of Illinois, College of Medicine at Urbana-Champaign, 506
South Mathews, Urbana, IL 61801, U.S.A.
PAUL J. THORNALLEY (Volume III)
Department of Chemistry and Biological Chemistry, University of
Essex, Wivenhoe Park, Colchester C04 3SQ, Essex, U.K.
PETER WARDMAN (Volume III)
Cancer Research Campaign, Gray Laboratory, P.O. Box 100, Mount
Vernon Hospital, Northwood, Middlesex HA6 2JR, U.K.
Chapter 1
LUBRICATING OIL OXIDATION AND
STABILISATION
T. COLCLOUGH
1. INTRODUCTION
Lubricants can be broadly divided into two main categories, namely
engine and transmission lubricants for transport applications, and in­
dustrial oils, which include plant machinery oils, hydraulic fluids, gear
lubricants, metal-working lubricants and greases. This review is mainly
concerned with the first of these and in particular with the practical aspects
of the oxidation and stabilisation of automotive crankcase lubricants.
Modern crankcase lubricants are required to perform a number of func­
tions:
(i) to provide a thin film of oil between moving parts to prevent metal to
metal contact and so reduce wear and friction;
(ii) to cool parts of the engine;
(iii) to keep parts of the engine clean and protect against rust and
corrosion;
(iv) to seal combustion pressures in the piston ring zone and minimise
combustion chamber deposits.
Problems which arise from the oxidation of a lubricant include viscosity
increase due to sludge, deposits and the formation of acids with corrosion.
Factors which affect oxidation include the composition of the basestock and
fuel, driving conditions, engine design, and the nature of the lubricant
additives present. Modern motor oils are a combination of appropriate
basestocks and additives, formulated to provide satisfactory performance
over extended periods of motoring, which could involve up to 12,000 miles or
more between oil changes.
Automotive lubricants are being subjected to increasingly severe operat­
ing conditions, through the use of longer drain intervals and higher outputs
and speeds, which lead to higher engine and oil temperatures. Combustion
products play a major role in lubricant oxidation, and these are affected by
many factors which include fuel quality, blow-by rates, ignition timing,
air-fuel ratios, positive crankcase ventilation (P.C.V.) and exhaust gas
2 T.C0LCL0UGH
recirculation (E.G.R.) systems. Sludge problems, which were originally in­
vestigated in the 1950s, reappeared during the 1980s, due to the use of
engines with closed circulation systems, higher levels of oxides of nitrogen
(NO ) and low quality fuels.
x
Stricter emission controls have led to the use of catalytic converters which
can be poisoned by high levels of phosphorus in the oil. This in turn has led
to a reduction in some applications in the treat levels of zinc dialkyldithio-
phosphates (ZDDPs), which have been well established as the primary
antioxidants for automotive lubricants since about 1950. Phosphorus levels
of 0.1 to 0.2% were typical in passenger car motor oils up to about 1980, but
levels of 0.08-0.1% P then became common in Europe and the USA and
0.05% P in Japan.
A number of earlier reviews have appeared on lubricating oil oxidation
[1,2] and gasoline and diesel engine chemistry [3-6]. Since then, depletion
of best quality crude oil reserves has led to the use of lower quality base-
stocks and fuels. Also, environmental constraints and more severe operating
conditions have placed much greater stresses on lubricating oils, and this
trend is likely to continue in the future.
2. EFFECT OF BASESTOCK COMPOSITION ON OXIDATION STABILITY
Many factors, which include refining conditions, viscosity index (VI),
sulphur content, clay treatment, catalysis by metals and hydrocarbon struc­
ture, were all investigated in the 1940s and led to the development of
relationships between mineral oil composition and oxidisability [7-13].
Solvent extraction removes aromatic components and improves the VI and
the colour of oils and reduces the tendency to form sludge. Too severe
extraction gives white oils which are more susceptible to oxidation, but the
oxidation products are soluble. The more highly extracted oils were found to
be more responsive to antioxidants [9].
The effect of solvent refining on oxidation stability was studied by Davis
et al. (Table 1) [7]. The first extraction removed the more easily oxidised
materials, leaving the natural inhibitors, which were then removed by
further extractions. A similar order of ranking was found in the presence of
an iron catalyst but no correlation between oxidation stability and VI was
found.
Paraffinic oils oxidise more readily and autocatalytically whereas aro­
matic oils oxidise less readily, generally involving autoinhibition due to the
formation of antioxidants, but give rise to more insolubles and lacquer. Alkyl
aromatics containing reactive benzylic hydrogen atoms oxidise very readily,
whereas alkylated naphthalene and other polynuclear aromatics were
stable to oxidation due to the formation of inhibitors. It was found that an
aromatics content of about 5% was the optimum to provide maximum
oxidation stability [9].
LUBRICATING OIL OXIDATION AND STABILISATION
TABLE 1
Effect of solvent extraction on oxidation stability [7]
VI Induction Period mins (175°C)
1. Raw Oil 63 70
2. First Extraction 90 267
3. Second Extraction 96 146
4. Third Extraction 98 60
5. Fourth Extraction 107 37
6. White Oil 65 18
2.1 Composition of Lubricating Oils
Lubricating oils are generally defined as those fractions which are ob­
tained from crude oil by nondestructive distillation with boiling ranges from
300°C to over 500°C and molecular weights from 225 to over 700. Other
processes are then used to separate the vacuum distillate by chemical type,
and these include solvent extraction, hydrogen processing, acid refining and
clay treatment. The solvent extraction process separates out aromatic oils,
which are used in chemicals and rubber processing, from the paraffinic and
naphthenic components, which are called Raffinates or Solvent Neutral oils
[14].
TABLE 2
Composition of base oils [14]
ASTM method Paraffinic Naphthenic Aromatic
Viscosity Index D2270 100 -15 0 -185
Mol. Wt. D2503 440 320 330 246
Clay-Gel Analysis D2007
% Polars 0.2 2 3 8
% Aromatics 8.5 36 43 80
% Saturates 91.3 62 54 12
Carbon Atom Type D3238
% Aromatics (CA) 2 14 19 41
% Naphthenics (CN) 32 41 37 36
% Paraffins (Cp) 66 45 44 23
4 T. COLCLOUGH
The severity of the refining and solvent extraction process can be varied
to control the level of paraffinic, naphthenic or aromatic component. Physi­
cal properties of four representative oils are shown in Table 2.
The paraffinic basestocks, which are normally used in automotive lubri­
cant formulations, typically contain from 0-1% sulphur, depending on the
crude oil source and refining process. Synthetic poly-a-olefin (PAO) base-
stocks are also used in automotive lubricants primarily to control viscom-
etrics, are oligomers of decene-1 and contain no sulphur.
The composition of three 150 neutral basestocks reported by Murray et
al. are shown in Table 3 [15]. These data were obtained by Chromatographie
separation and mass spectrometric analysis and show how the composition
of 150 neutral basestocks can vary depending on the crude source.
The solvents normally used in solvent extraction are phenol, furfural or
JV-methylpyrrolidinone (NMP). The organic materials which are extracted
are rich in sulphur and aromatics have good antioxidant activity. Although
TABLE 3
Solvent 150 neutral basestock compositions [15]
Composition A B C
Saturates (%) 63.7 83.8 84.0
Paraffins 26.3 21.1 25.1
One-ring naphthenes 18.0 24.2 23.3
Two-ring naphthenes 10.3 15.9 14.0
Three-ring naphthenes 5.6 8.9 8.1
Four-ring naphthenes 2.9 8.2 9.0
Five-ring naphthenes 0.6 3.9 4.0
Six-ring naphthenes 0.0 1.6 0.5
Aromatics (%) 30.8 14.7 11.8
Alkyl benzenes 15.2 5.8 5.0
Naphthenes-aromatics 10.1 6.1 5.1
Bicyclic 4.7 2.5 1.5
Tricyclic 0.8 0.3 0.2
Other* (%) 5.5 1.5 4.2
Sulphur (ppm) 4500 190 900
Total Nitrogen (ppm) 38 4 35
Basic Nitrogen (ppm) 38 0 34
* Including tetracyclic and higher aromatics, sulphur and nitrogen heterocyclic com­
pounds.