Lubricating oil with improved diesel dispersancy

Alkenyl succinimide or borated alkenyl succinimide dispersants as exemplified by a polyisobutenyl succinic anhydride-alkylene polyamine reaction product are substantially improved in their dispersancy properties in diesel engines by treating such dispersants at elevated temperatures with an oil-soluble strong acid, such as an alkaryl sulfonic acid or a phosphoric acid, such as a dialkyl monoacid phosphate. The treated dispersants are included in conventional lubricating oil formulations.

This invention relate to lubricating oil compositions exhibiting improved 
dispersancy in diesel engines. More particularly, the invention relates to 
a method of improving conventional alkenyl succinimide and borated alkenyl 
succinimide and borated alkenyl succinimide dispersants through use of 
oil-soluble organic acids. 
It is widely recognized that lubricating oils for diesel engines are 
typically subjected to severe engine operating conditions and that 
providing a highly potent sludge dispersant is an important objective in 
the industry for diesel engine lubricating oil formulations. 
Dispersants based upon the reaction product of various polyamines with 
alkenyl hydrocarbon substituted succinic anhydrides or acids, as well as 
the borated derivatives thereof, are known in the art and are disclosed, 
for example, in U.S. Pat. No. 3,172,892, issued Mar. 9, 1965 to LeSuer et 
al. and U.S. Pat. No. 3,933,659, issued Jan. 20, 1976 to Lyle et al. The 
alkenyl portion of these dispersants is typically a polymer of a C.sub.2 
-C.sub.5 monoolefin, especially polyisobutylene. 
The present invention provides enhancement of the dispersant potency of 
these alkenyl succinimide and borated alkenyl succinimide dispersants and 
diesel engines through use of very minor amounts of certain organic acids. 
In accordance with the present invention, there are provided lubricating 
oil compositions exhibiting improved dispersancy in diesel engines 
comprising a lubricating oil and an acid-treated, oil-soluble alkenyl 
succinimide or borated alkenyl succinimide dispersant, said dispersant 
being acid-treated by having incorporated therein about 0.1 mole to 0.5 
mole, preferably 0.2 to 0.3 mole, per mole of dispersant, of an 
oil-soluble organic acid having a pK of about -10 to +5, pK being the 
dissociation constants of the acid in water. 
Oil-soluble alkenyl succinimide ashless dispersants are those formed by 
reacting a polyalkenyl succinic acid or anhydride with a 
polyalkyleneamine. The alkenyl group of the succinic acid or anhydride is 
derived from a polymer of a C.sub.2 to C.sub.5 monoolefin, especially a 
polyisobutylene wherein the polyisobutenyl group has a number average 
molecular weight (Mn) of about 700 to about 5,000, more preferably about 
900 to 1,500. While homopolymers of ethylene, propylene, butylene, 
isobutylene and pentene are preferred, copolymers of these mono-olefins 
are also suitable for providing the polyalkenyl succinic acid or 
anhydride. Preferred are the polyisobutenyl succinic anhydrides within the 
aforesaid molecular weight range. 
Suitable polyamines for reaction with the aforesaid succinic acid or 
anhydrides to provide the succinimide are those polyalkyleneamines 
represented by the formula NH.sub.2 (CH.sub.2).sub.n 
--(NH(CH.sub.2).sub.n).sub.m --NH.sub.2 wherein n is 2 to 3 and m is 0 to 
10. Illustrative are ethylene diamine, diethylene triamine, triethylene 
tetramine, tetraethylene pentamine, which is preferred, tetrapropylene 
pentamine, pentaethylene hexamine and the like, as well as the 
commercially available mixtures of such polyamines. These amines are 
reacted with the alkenyl succinic acid or anhydride in ratios of about 1:1 
to 10:1 moles of alkenyl succinic acid or anhydride to polyamine, and 
preferably in a ratio of about 2:1. 
The borated alkenyl succinimide dispersants are also well known in the art 
as disclosed in U.S. Pat. No. 3,254,025. These derivatives are provided by 
treating the alkenyl succinimide with a boron compound selected from the 
group consisting of boron oxides, boron halides, boron acids and esters 
thereof, in an amount to provide from about 0.1 atomic proportion of boron 
to about 10 atomic proportions of boron for each atomic proportion of 
nitrogen in the dispersant. The borated product will generally contain 
about 0.1 to 2.0, preferably 0.2 to 0.8, weight percent boron based upon 
the total weight of the borated dispersant. Boron is considered to be 
present as dehydrated boric acid polymers attaching as the metaborate salt 
of the imide. The boration reaction is readily carried out adding from 
about 1 to 3 weight percent based on the weight of dispersant, of said 
boron compound, preferably boric acid, to the dispersant as a slurry in 
mineral oil and heating with stirring from about 135.degree. to 
165.degree. C. for about 1 to 5 hours followed by nitrogen stripping and 
filtration of the product. 
Such alkenyl succinimide ashless dispersants and borated derivatives 
thereof are used customarily in lubricating oil compositions in amounts 
ranging from 0.1 to 10 percent, preferably 0.5 to 5 percent by weight 
based upon the total weight of the finished compositions. The same amounts 
are applicable to the acid treated diesel oil dispersants of the present 
invention. 
The improved acid-treated alkenyl succinimide and borated alkenyl 
succinimide dispersants of the present invention are prepared by adding a 
suitable acid to a solution of dispersant in hydrocarbon lubricating oil 
base stock, preferably a concentrated solution of about 40 to 60 wt. % 
dispersant, preferably about 50 wt. %, is used. The same lubricating oil 
base stock used in formulating the finished oil is a convenient vehicle 
for providing the solution. Preferred base stocks are paraffin mineral 
oils having a viscosity of about 20 to 100 cS min. (100.degree. F.) and 
blends of such oils. The acid treatment is effected by heating the 
solution of dispersant to about 80.degree. to 200.degree. C., preferably 
to about 100.degree. to 175.degree. C., such as 150.degree. C., and adding 
thereto 0.1 to 0.5 mole of a suitable organic acid per mole of dispersant. 
The preferable range of addition is about 0.2 to 0.3 mole per mole of 
polyalkenyl succinimide or borated polyalkenyl succinimide dispersant. The 
mixture is stirred at this temperature for about 15 minutes to 3 hours 
until the acid reacts into the system. While not wishing to be bound by 
this theory, it is believed that at this relatively elevated temperature, 
a capping reaction occurs whereby an amide is formed between unreacted 
amino moieties and the organic acid additive. A convenient method of 
conducting this acid treatment is to add the organic acid as the final 
step in the dispersant preparation process, i.e., after boration or after 
reaction of the polyalkenyl succinic anhydride with the alkylene 
polyamine. Subsequent to this, conventional lubricating oil blending 
techniques are followed to provide finished lube oils exhibiting improved 
dispersancy in diesel engines. 
The oil-soluble organic acid can be used in accordance with this invention 
and may be generally classified as those acids containing a hydrogen 
dissociating moiety which has a pK of -10 to about +5.0. The term pK can 
be defined as the negative logarithm to the base 10 of the equilibrium 
constant for the dissociation of the oil-soluble organic acid. 
As used herein, oil-soluble is defined as those organic acids which 
themselves are substantially soluble in mineral oil at 20.degree. C. to at 
least 50 weight percent. 
Representative classes of the strong organic acids containing 
oil-solubilizing groups are the hydrocarbyl substituted maleic acids, 
malonic acids, phosphoric acids, thiophosphoric acids, phosphonic acids, 
thiophosphonic acids, phosphinic acids, thiophosphinic acid, sulfonic 
acid, sulfuric acid, and alpha-substituted or nitrilocarboxylic acids 
wherein the oil-solubilizing group or groups are hydrocarbyl and 
containing from 8 to 70 or more, preferably from 20 to 40, optimally 25 to 
35, total carbon atoms. These ranges are considered to approximate 
oil-solubility for the general classes of organic acids suitable herein. 
A preferred category of organic acids for use in this invention are the 
oil-soluble sulfonic acids which are typically alkaryl sulfonic acids. 
These sulfonic acids are typically obtained by the sulfonation of alkyl 
substituted aromatic hydrocarbons such as those obtained from the 
fractionation of petroleum by distillation and/or extraction or by the 
alkylation of aromatic hydrocarbons as, for example, those obtained by 
alkylating benzene, toluene, xylene, naphthalene, diphenyl and the halogen 
derivatives such as chlorobenzene, chlorotoluene and chloronaphthalene. 
The alkylation may be carried out using known processes in the presence of 
a catalyst such as ACl.sub.3 or BF.sub.3 with alkylating agents having 
from 9 to about 70 carbon atoms, such as, haloparaffins, olefins that may 
be obtained by dehydrogenation of paraffins, polyolefins from ethylene, 
propylene, etc. Preferred sulfonic acids are those obtained by the 
sulfonation of hydrocarbons prepared by the alkylation of benzene or 
toluene with tri-, tetra- or pentapropylene fractions obtained by the 
polymerization of propylene. The alkaryl sulfonic acids contain from 9 to 
70, preferably from 18 to 34, optimally from 22 to 30, carbon atoms per 
alkyl substituent in the aryl group and these groups may be monoalkylated 
or polyalkylated aryl moieties. 
Particularly preferred is an alkylated benzene sulfonic acid having a 
molecular weight (Mn) of from 475 to 600 wherein the alkyl substituent 
groups contain about 18 to 34 carbons. 
The oil soluble phosphorous-containing acids are a second preferred 
category useful in the present invention can be described as hydrocarbyl 
substituted derivatives of phosphoric acid, H.sub.3 PO.sub.4, phosphonic 
acid HP(0)(OH).sub.2 or phosphinic acid H.sub.2 P(0)(OH) which have at 
least one free acidic hydrogen and one or two hydrogens are replaced by 
one or two C.sub.8 -C.sub.70 hydrocarbyl radicals such as alkyl, aryl, 
alkaryl, aralkyl and alicyclic hydrocarbon radicals to provide the 
required oil solubility. C.sub.9 to C.sub.30 mono- or di-alkyl (mono- or 
di-acid phosphates) derivatives of a H.sub.3 PO.sub.4 are a particularly 
preferred sub-category of acids for use in improving diesel dispersancy 
and tridecyl mono/dihydrogen phosphonic acid is a preferred embodiment. 
Suitable acids include also the corresponding C.sub.9 -C.sub.70 
hydrocarbyl mono or di-substituted thiophosphoric, thiophosphinic or 
thiophosphonic acids. 
The acids are usually prepared by reacting P.sub.2 O.sub.5 or P.sub.2 
S.sub.5 with the desired alcohol or thiol to obtain the substituted 
phosphoric acids. 
The desired hydroxy or thiol compound should contain hydrocarbyl groups of 
from about 8 to about 70 carbon atoms with preferably about 15 total 
carbon atoms average to provide oil solubility to the product. Examples of 
suitable compounds are hexyl alcohol, 2-ethylhexyl alcohol, nonyl alcohol, 
dodecyl alcohol, stearyl alcohol, amylphenol, octylphenol, nonylphenol, 
methylcyclohexanol, alkylated naphthol, etc., and their corresponding thio 
analogues; and mixtures of alcohols and/or phenols such as isobutyl 
alcohol and nonyl alcohol; orthocresol and nonylphenol; etc., and mixtures 
of their corresponding thio analogues. 
In the preparation of the hydrocarbyl substituted thiophosphoric acids, any 
conventional method can be used, such as, the preparation described in 
U.S. Pat. Nos. 2,552,570, 2,579,038 and 2,689,220. By way of illustration, 
a dialkaryl substituted dithiophosphoric acid is prepared by the reaction 
of about 2 moles of P.sub.2 S.sub.5 with about 8 moles of a selected 
alkylated phenyl, e.g., a mixture of C.sub.8 -C.sub.12 alkyl substituted 
phenols, i.e., nonyl phenol, at a temperature of from 50.degree. C. to 
125.degree. C. for about 4 hours. In the preparation of hydrocarbyl 
substituted thiophosphinic acids, as conventionally known, a disubstituted 
phosphine is oxidized to give disubstituted thiophosphinic acids (see F. 
C. Witmore's Organic Chemistry", published by Dover Publications, New 
York, NY (1961) page 848). 
Particularly preferred for preparation of oil-soluble phosphoric, 
phosphonic and phosphinic acids useful in the process of the invention are 
mixed aliphatic alcohols obtained by the reaction of olefins of carbon 
monoxide and hydrogen and substituted hydrogenation of the resultant 
aldehydes which are commonly known as "Oxo" alcohols, which Oxo alcohols 
for optimum use according to this invention will contain an average of 
about 13 carbon atoms, such as a di-C.sub.13 Oxo phosphoric acid. The 
oil-soluble phosphorous-containing acids are readily prepared from these 
alcohols by reaction with P.sub.2 O.sub.5 as is well known in the art. 
Another class of useful strong organic acids are oil-soluble hydrocarbyl 
substituted maleic acids of the general formula: 
##STR1## 
wherein R" is an oil-solubilizing, hydrocarbyl group containing from about 
9 to 70 carbons. Representative of these oil-soluble maleic acid 
derivatives are pentadecylmaleic acid, hexadecylmaleic acid, eicosylmaleic 
acid, triacontanylmaleic acid and polymers of C.sub.2 -C.sub.5 monoolefins 
having from 15 to 70 or more carbons substituted onto said maleic acid. 
Additional suitable strong acids are those oil-soluble C.sub.9 -C.sub.70 
hydrocarbyl-containing substituted malonic acids of the general formula: 
EQU R"CH(COOH).sub.2 
wherein R" has the meaning set forth above as an oil-solubilizing 
hydrocarbyl group which is illustrated by the following representative 
compounds which include the malonic acid counterparts of the 
above-referenced hydrocarbyl substituted maleic acids, i.e., 
pentadecylmalonic acid, hexadecyl malonic acid, etc. 
Another class of useful acids are oil-soluble C.sub.9 -C.sub.70 hydrocarbyl 
substituted sulfuric acids of the general formula R"HSO.sub.4 wherein R" 
is the hydrocarbyl oil-solubilizing group as exemplified by 
pentadecylsulfuric acid, hexadecylsulfuric acid, eicosylsulfuric acid, 
triacontanylsulfuric acid, etc. 
A further group of acids which can be used in accordance with this 
invention are oil-soluble mono- and di-alpha-substituted hydrocarbyl 
carboxylic acids having the general formula: 
##STR2## 
wherein R" is a C.sub.9 -C.sub.70 hydrocarbyl, oil-solubilizing group as 
referenced above and X refers to hydrogen, nitrilo, nitro, halo, such as 
chloro, or a cyano group or groups. These materials are represented by the 
following: alpha-nitro and alpha-di-nitro, substituted acids, such as 
dodecanoic, pentadecanoic, octadecanoic, docosanoic, octacosanoic, 
tricontanoic, tetracontanoic and the like.

The invention is further illustrated by the following examples which are 
not to be considered as limitative of its scope. 
EXAMPLE 1 
A paraffinic mineral oil solution was prepared containing 49 wt. % of a 
polyisobutylene succinic anhydride polyamine dispersant (Mn=980; 2.2 moles 
of succinic anhydride per mole of polyamine). The polyamine was a mixture 
of alkylene polyamines approximating tetraethylene pentamine available 
under the trade name "DOW E-100" from Dow Chemical Co., Midland, Michigan. 
This dispersant has been borated by reaction with a slurry of 1.4 moles of 
boric acid in mineral oil and the final product contained 1.5 wt. % 
nitrogen and 0.5 wt. % boron. 
Three acid treated dispersant materials in accordance with this invention 
were provided by: 
(1) Incorporating into a 50 wt. % solution of dispersant in the mineral oil 
1.2 wt. % of tridecyl mono- di- acid phosphate by adding in the phosphate 
and stirring the mixture at about 150.degree. C. for 30 minutes. 
(2) Incorporating into the dispersant solution 2.5 wt. % (0.2 molar 
equivalents) of an alkyl benzene sulfonic acid having an Mn=530 by adding 
in the acid to a 50 wt. % solution of dispersant in the mineral oil at 
150.degree. C. 
(3) Incorporating into the dispersant solution 1.0 wt. % (0.08 molar 
equivalents) of the same sulfonic acid as in subparagraph 2 above using 
the same blending technique. 
Lubricating oil formulations were prepared containing the standard borated 
dispersant before acid modification, noted below as Base Formulation and 
formulations containing each of the three acid modified borated 
dispersants, and noted corresponding below as Formulations 1, 2, and 3. 
Each formulation was an SAE 10W30 quality crankcase oil which also 
contained conventional amounts of an olefin copolymer V.I. improver, a 
rust inhibitor, a metal detergent and a zinc dialkyldithiophosphate in a 
mineral oil base. These formulated oils were each subjected to engine 
testing in the "Caterpillar 1H-2" test which is an industry and government 
accepted test for the dispersancy and overall effectiveness of diesel oil 
lubricants. The results and explanation of the test are given below: 
______________________________________ 
240 Hour Caterpillar 1H-2 Test 
Formulation TGF.sup.2 WTD.sup.3 
______________________________________ 
Base.sup.1 16.6% 189.1 
No. 1 0.5% 55.2 
No. 2 6.0% 37.0 
No. 3 1.0% 106 
______________________________________ 
.sup.1 Base this result is an average data base used for comparison in 
evaluating new diesel formulations and is an average of 25 engine tests. 
.sup.2 TGF top groove fill, % deposits in groove 
.sup.3 WTD weighted total demerits 
The Caterpillar 1H-2 test is also a U.S. Federal Test Method 791-346 and is 
used to meet military specifications, such as MIC-C-21260B and industry 
specifications, such as SAE 183 and General Moters GM 6146M. The purpose 
of the test is to determine the effect of an oil on ring sticking, wear 
and accumulation of deposits. The test uses a single cylinder Caterpillar 
diesel 51/8".times.61/2". 
For the 1H-2 test WTD (Weighted Total Demerits) is the principal value and 
for a 240 hour test, the target specification is a value below the 75-80 
range. This is derived from the published specification target of WTD 140 
for a 480 hour test. WTD is a cumulative rating based on observation of 
deposits in the groove and land areas of the piston and lacquer on piston 
skirts with all these specific evalations being weighted according to 
their relative importance and the final WTD value being calculated in 
accordance with the test procedure.