The present invention relates generally to polyalkenyl succinic anhydrides or acids and in particular to polyalkenyl bis (succinic anhydrides or acids), hereinafter to be referred to as PABSA, compositions containing PABSA, processes for producing PABSA, the conversion of PABSA into derivatives thereof and the use of the derivatives in lubricating oil compositions.

The reaction of maleic anhydride or maleic acid with a mono- olefin polymer to produce a polyalkenyl succinic anhydride or acid is well-known. Thus polyisobutene succinic anhydride, hereinafter to be referred to as PIBSA, which is extensively used in the form of its ester or imide as a dispersant in lubricating oil applications, is produced by reacting polyisobutene with maleic anhydride. The reaction may be represented by the following equation:

polyisobu ene maleic PIBSA anhydride

It is also known from USP 4012438 that there can be produced alkyl or cycloalkyl tetracarboxylic acid compounds of the formula:

B

wherein A and C are monovalent succinic acid groups having attachment to B at either of the two carbon atoms of A or C having unsatisfied valences and a hydrogen atom attached to the other unsatisfied carbon atom; and wherein B is a connecting alkane or cycloalkane group of 4 to 30 carbon atoms having 2 of the above-described monovalent groups A and C, which may be the same or different, attached at carbon atoms 1 and 2 or at carbon atoms 1 and 3; and optionally having carbon atom 1 and carbon a cm 4 connected by a 1-8 carbon methylene bridge; the remainder of the unsatisfied carbon valences of said bivalent hydrocarbon group being attached to hydrogen atoms; and wherein R is H and

2 3

R and R are H or the same or different hydrocarbyl groups- X and

Y together are -0- or X and Y are the same or different groups having the structure: -OR, in which R is H or the same or different alkyl or cycloalkyl groups having from 1 to 8 carbon atoms each. The alkyl or cycloalkyl tetracarboxylic acid compound of the a oresaid formula is produced by hydrogenation of the corresponding compound in which-B is an alkenyl group of 4 to 30 carbon atoms.

Theoretically it should be possible to produce a polyalkenyl bis (succinic acid or anhydride) by reacting the mono (succinic acid or anhydride) , as produced by the reaction of maleic anhydride and PIBSA, with further maleic anhydride, as represented by the following equation :-

CH„ C CHH--,,

II 2 1 3 CH - CO

° _n <OC - C1H - CH. ² , - C - CH2„ - C -CH,

₁ n 3 If >

CH - CO

OC - CH- CH,

2 polyisobutene mono (succinic ianh ^~ ydride) maleic anhydride

_Λ . _^ 0C - CH - CH„ - C - CH„ - CH - O^ ° ₁ 2 || 2

OC - CH„ CH CH - CO'"' 2 I

H„C - C - CH.,

3 3 I CH 1 1 3

(H-C- C —)-- 2 1 nn--ϊ CH. l 3

CH. polyisobutene bis (succinic anhydride)

_

However, no such polyalkenyl bis-(succinic acid or anhydride) has been reported and in practice it has not been found possible even to produce the mono-(succinic acid or anhydride) at 100% conversion of the olefin polymer. For example, the reaction of 1 mole of polyisobutene of mean average molecular weight 1000, i.e. the average molecular weight for 1 mole of olefin as determined by measurement of the bromine number, with 1 mole of maleic anhydride should theoretically produce polyisobutene mono-(succinic anhydride) having a PIBSA Number of about 102, (the PIBSA Number being the number of milligrams of potassium hydroxide required to neutralise one gram of sample). In practice it has not been found possible to exceed a PIBSA Number of about 90 in uncatalysed maleinisations, which figure corresponds to approximately 85% molar conversion of the polyisobutene. One of the reasons for this is believed to be that the polyisobutene contains about 15% of unreactive impurities.

We have now surprisingly found that polyalkenyl bis—(succinic acid or anhydride) in which the polyalkenyl group is derived from a polyolefin having a number average molecular weight (Mn) in the range from 500 to 2100 can be produced by modification of the process conditions and in particular by the use of a nickel salt as catalyst. Accordingly, the present invention provides a polyalkenyl bis-(succinic acid) or a polyalkenyl bis-(succinic anhydride) in which the polyalkenyl group is derived from a polyolefin having an Mn in the range from 500 to 2100. In another aspect the invention provides a composition comprising a polyalkenyl mono-(succinic acid or anhydride) and a polyalkenyl bis-(succinic acid or anhydride) in which the polyalkenyl groups are derived from a polyolefin having an Mn in the range from 500 to 2100. The polyalkenyl groups may suitably be derived from a polyolefin such as polyethylene, polypropylene and polybutylene or an olefin copolymer. Preferably the polyalkenyl group is derived from poly¬ isobutene.

According to another aspect of the present invention there is provided a process for the production of a composition as hereinbefore described which process comprises reacting a polyolefin having an Mn

in the range frcm 500 to 2100 with a greater than equimolar amount of maleic acid or maleic anhydride at elevated temperature and either at sub-atmospheric, atmospheric or super-atmospheric pressure whilst passing a stream of gas through the reactants or at sub-atmospheric pressure in the absence of a stream of gas either for the duration or a part of the reaction.

Preferably the maleic acid or anhydride is reacted with the polyalkylene in a molar proportion in the range 1:1 to 3:1. Although all the maleic acid or maleic anhydride may be added in one portion at the beginning of the reaction, it is preferred to add it either intermittently or continuously throughout the course of the reaction.

Suitably the elevated temperature may be greater than 150°C and is preferably in the range from 200 to 260°C. Even more prefer¬ ably the reaction is carried out with a programmed temperature increase over the temperature range 230 to 250°C.

The pressure at which the process is operated depends on whether or not a stream of gas is passed through the reactants. Thus the pressure may be atmospheric, sub-atmospheric or super-atmospheric when a stream of gas is passed through the reactants. The gas may be an inert gas such as nitrogen or an entrainer gas such as carbon dioxide or a lower hydrocarbon. In the absence of a gas stream the pressure must be sub-atmospheric either for the duration or part of the reaction. Although the reaction may be carried out wholly at sub-atmospheric pressure, it is preferred to carry out the early stages of the reaction at super-atmospheric pressure and reduce the pressure to sub-atmospheric at some point during the reaction, preferably during the later stages of the reaction.

It is thought that the passage of a stream of gas or the use of sub-atmospheric pressure facilitates the removal of volatile impurities. The use of a stream of inert gas is preferred in plant scale operation of the process because of the long operating times required to achieve significant pressure change.

The reaction time may suitably be at least 4 hours and is preferably from 6 to 12 hours. The process may be operated in the presence or absence of a catalyst, preferably in the presence of a catalyst.

With regard to the catalyst we have found that nickel salts and in particular nickel iodide are active catalysts for the production of polyalkenyl bis-(succinic acid or anhydride), regard¬ less of the alkenyl substituent. Accordingly the present invention also provides a process for the production of a polyalkenyl bis-(succinic acid or anhydride) which process comprises reacting a polyolefin with a greater than equimolar amount of maleic acid or maleic anhydride at elevated temperature and in the presence of a catalyst comprising a nickel salt.

The nature of the polyalkylene, the molar proportions of reactants, the reaction temperature and the reaction time may suitably be the same as those described hereinbefore. It is also preferred to operate the process at atmospheric, sub-atmospheric or super-atmospheric pressure whilst passing a stream of gas through the reactants or to operate at sub-atmospheric pressure in the absence of a gas stream either for the duration or a part of the reaction.

Both processes produce, in addition to PABSA, the polyalkenyl mono-(succinic acid or anhydride) and therefore afford a convenient method for producing the compositions of the present invention. In the absence of a catalyst it is possible to convert polyisobutene of number average molecular weight 1000 to PABSA-containing compositions having a PIBSA Number in the range 90 to 115. In the presence of nickel iodide as catalyst it is possible to increase the PIBSA Number to at least 12Q; corresponding to about 40% conversion to PABSA.

The PABSA or the composition of the invention may suitably be converted to an ester or an ester composition by reaction with an alcohol under known esterification conditions or it may be converted to an imide or an imide composition, suitably by reaction with an amine of the formula:

H N(CH CHNH)xH ¹ in which x is an integer and R is a C to C alkyl radical or hydrogen by, for example, the process described in British Patent

Specification No. 922831. Both the ester and the imide may be used in lubricating oil compositions. It has been found that less succinimide derived from the PABSA-containing composition of the invention is necessary to produce the same functional group concentration than when succinimides derived from the corresponding mono-(succinic acid or anhydride) are used, without any apparent loss in dispersancy properties. Practically this results in a decrease in the viscosity of lubricating oil formulations incorporating succinimides prepared from the PABSA-containing compositions of the present invention.

Accordingly there is provided a lubricating oil composition which comprises a lubricating base oil and an imide or ester dispersant derived from either PABSA or the PABSA-cont-aining composition as hereinbefore described. In addition to the succinimide or ester dispersant the lubricat¬ ing oil composition may also contain one or more conventional lubricating oil additives.

The invention will now be illustrated by reference to the following Examples. Preparation of polyisobutene bis-(succinic anhydride) Example 1

Polyisobutene (400 g of Mn 1000), maleic anhydride (64 g) and nickel iodide (0.64 g) were added to a stainless steel Magnedrive autoclave ( 1 capacity) and the mixture was heated under stirring to 230°C under an applied pressure of 30 psig of nitrogen. The reaction mixture was also sparged continuously with nitrogen using

_. a flow rate of ca. 3 1 h . The reaction temperature was gradually increased from 230° to 240°C over a period of two hours. A further addition of maleic anhydride (33 g) was made over a 2 hour period at 240°C to 250°C/30 psig and subsequently the reaction mixture was heated for a further 4 hours at 250° to 260°C/30 psig. The reaction product (484 g) was cooled to 150°C and then discharged from the autoclave. The reaction product comprises 1.1% w/w of unconverted maleic anhydride, 30% w/w of unconverted pol isobutenes and the remainder was polyisobutene succinic anhydride. This product gave

_1 a total PIBSA number of 120 mg KOH equiv. g , after correcting for

its maleic anhydride content. This high PIBSA number indicated that a substantial amount of bis succinic anhydride) substitution of the polyisobutene had occurred. Example 2 Polyisobutene (400 g of Mn 1000) was added to a stainless steel Magnedrive autoclave (11 capacity) and was heated to 230°C under .1 stirring and nitrogen sparging (gas rate ca. 3 1 h ) under an applied pressure of 40-44 psig of nitrogen. Maleic anhydride

(63 g) was then pumped into the reactor over a 2 hour period while the temperature of the reaction mixture was increased from 230° to 240°C. Additional maleic anhydride (32 g) was pumped into the reaction mixture over 2 hours at 240°C/40-44 psig and subsequently the temperature of the reactants was increased from 240° to 250°C over a further 4 hour period. The reaction mixture was then cooled to 150°C and discharged from the reactor. The product was flash- distilled up to 215°C/100 mbar to remove unconverted maleic anhydride as an overhead product. The distillate residue was then filtered to remove resin derived from the maleic anhydride and

-1 the filtrate product gave a total PIBSA number of 115 mg KOH equiv.g . Preparation of succinimide dispersant from polyisobutene bis-(succinic anhydride)

Example 3

PIBSA reaction product having a PIBSA Number of 120 from

Example 1 (220 g) was mixed with an equal weight of lube oil and heated.to 19 ^' 0°C/1 bar. Triethylene tetramine (15.78 g) was then added with stirring over 15 minutes and the mixture was subsequently heated for 3 hours at 190°C. The PIBSA imide product contained

1.37% w/w nitrogen, 0.52% w/w basic nitrogen and gave a viscosity of 76.3 cSt at 100°C. A PIBSA imide derived from conventional PIBSA having a total

PIBSA Number of 95 mg KOH equiv. g typically contains 1.4% w/w nitrogen, 0.58% w/w basic nitrogen and gives a viscosity of 495 cSt at 100°C.

The imide derived from the polyisobutenyl bis-(succinic anhydride) composition has a lower viscosity (76.3 cSt) than the imide derived from the polyisobutenyl mono-(succinic anhydride)

(495 cSt).

OMPI

Engine Test Example 4

A Petter AV.l engine test was carried out on a standard formulation in which a smaller amount than usual of the imide

95 product of Example 3 (viz. jjcf ^usual addition) was used to give the same concentration of imide functional groups in the test mixture and this gave the same good engine test rating (as determined by measurement of the extent of carbonisation of the piston surfaces) as that obtained from the conventional formulation containing imide derived from polyisobutenyl mono-

(succinic anhydride). Effect of Pressure

Example 5

Polyisobutene (1 mole of Mn 1000), and maleic anhydride (1.6 moles) were added to a stainless steel Magnedrive autoclave ( 1 capacity) and the mixture was heated under stirring to 238°C under an applied pressure of 10 psig of nitrogen. After 2 hours under these conditions the total PIBSA No. was determined. The pressure was reduced to atmospheric for a further 2 hours and the PIBSA No. again determined. Finally the pressure was reduced to -10 psig for 4 hours and the PIBSA No. was determined at the end of this period. The results are given in the accompanying Table. Comparison Test 1

The procedure of Example 5 was repeated except that the pressure ■was maintained at 10 psig throughout and measurement of the PIBSA No. were made after 4 and 8 hours. Comparison Test 2

The procedure of Comparison Test 1 was repeated except that the pressure was maintained at 20 psig throughout and the PI3SA No. was measured after 4 hours only.

Comparison Tests 1 and 2 are not examples according to the invention and are included only for the purpose of comparison. Example 6

Example 5 was repeated except that the pressure was maintained at 20 psig throughout and the reactants were sparged with nitrogen at a rate of 4 volumes nitrogen per volume of reaction mixture per hour. The total PIBSA No. was measrued after 6 hours.

TABLE

REED RATIO UNCONVERTED MA

Total

Example Pressure Temp Duration PIBSA NO. IN REACTION No. (psig) (°C) PIB MA (hours) PRODUCT mg. KOH/g. (Moles) (Moles) (% w/w)

(a) Comparison 1.6 Test 1 10 238° 4 85 8 85 3.4

Example 5 (10 238° 1.6 0 - 2 85 atmospheric 238° 2 - 4 87 3.2

(-10 238° 4 - 8 95 1.7

Comparison Test 2 20 238 ^c 1.6 89 3.2

Example 6 20 238 ^c 1.6 96 4.1

10

The results presented in the Table demonstrate that in Comparison Test 1 a PIBSA No. of 85 was obtained within 4 hours at 238°C/10 psig and that this did not increase after a further 4 hours reaction. In Example 5 equilibration was achieved within 2 hours at 238°C/25 psig but further reaction occurred following a reduction in pressure from 25 to 15 psig absolute to give a PIBSA number of 87 which was further increased to 95 by reducing the pressure to 5 psig absolute. In Example 6 a similar PIBSA number was achieved by isobaric pressure operation, simply by sparging the reaction mixture with a stream of nitrogen.