EP3967739A1

EP3967739A1 - Use of isosorbide diester as a deposit control agent

Info

Publication number: EP3967739A1
Application number: EP20305997.7A
Authority: EP
Inventors: Karima ZITOUNI; Micky-Lee FU-XIANG
Original assignee: Oleon NV; Oleon Sdn Bhd
Current assignee: Oleon NV
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2022-03-16
Anticipated expiration: 2040-09-09
Also published as: EP3967739B1

Abstract

The present invention relates to the use of isosorbide diesters as a deposit control agent and optionally additive solubilizing agent. It also concerns lubricant compositions comprising it, and methods for reducing/preventing deposits and optionally improving solubilizing property of base oils.

Description

The present invention relates to the use of at least one diester as a deposit control agent.
A deposit control agent prevents or reduces agglomerates formation and their deposits. In particular, the deposit control agent reduces the formation of sludge, varnish or lacquer and their deposits.
Sludge, varnish and lacquer are different formats of deposit composed of residues of oxidized base oil formed when a lubricant composition is exposed to high temperature conditions in the presence of oxygen, nitrogen oxides and oxidation-derived hydroperoxides, resulting in the oxidation of the base oil comprised in the lubricant composition.
Varnish and lacquer forms when resin (polymeric compounds from oxygenates) deposits on the hot surface and subsequently dehydrated to form a firm film. In general, lacquer occurs in lubricant composition in the case of diesel engine pistons while varnish is the normally fuel-derived. Sludge occurs at a cooler place (<200°C). It can be watery or hard depending on the dehydration extent (Bouman, C.A. Properties of Lubricating Oils and Engine Deposits. London, U.K.: MacMillan and Co., 1950, pp. 69-92.)
In the field of lubricants, agglomerates and deposits in lubricant compositions are unwanted. Indeed, besides the facts that these deposits interfere with the lubricating properties, there also leads to others issues with the systems, such as unwanted oil consumption, ring sticking, and corrosion and wear to the moving components within engine.
A lubricant composition typically comprises a base oil, usually the major constituent (the constituent whose content is the highest), and one or more additive(s).
An additive is used to enhance one or more intrinsic property(ies) of the base oil and / or provide it with one or more additional property(ies).
The American Petroleum Institute (API) has categorized base oils into five groups:

The first three groups are mineral oils refined from petroleum crude oil:
- Group I base oils have a saturated hydrocarbon content of less than 90 % by weight, an aromatic hydrocarbon content of more than 1.7 % by weight, a sulphur content of more than 0.03 % by weight, and a viscosity index between 80 and 120;
- Group II base oils have a saturated hydrocarbon content of more than 90 % by weight, an aromatic hydrocarbon content of less than 1.7 % by weight, a sulphur content of less than 0.03 % by weight, and a viscosity index between 80 and 120;
- Group III base oils have a saturated hydrocarbon content of more than 90 % by weight, an aromatic hydrocarbon content of less than 1.7 % by weight, a sulphur content of less than 0.03 % by weight, and a viscosity index greater than 120;

Group IV base oils are synthetic oils, such as polyalphaolefins.
Group V is for all other base oils not included in any of Groups I to IV.

For years, main base oils used in lubricant compositions in various industries, such as in engine oils, hydraulic fluids (oils), gear oils, metalworking fluids (oils) or compressor oil were of Group I for their attractive properties, especially for their viscosity and their ease in solubilizing additives due to the presence of aromatics.
However, new specifications and new regulations have pushed formulators to interchange Group I base oils by Group II and III base oils with lower sulphur contents and lower aromatic contents.
But those Group II and Group III base oils present a lower solvent power, meaning it is more difficult for them to dissolve some additives and to compatibilize the residues of oxidized base oil within the bulk solution. These residues agglomerate and further lead to to the formation of sludge, varnish and lacquer.
Furthermore, Group V base oils are generally not used as base oils themselves, but as co-base oils to improve the solubility of additives. Thus, adipates, trimethylolpropane esters and alkylated naphtalenes are used for this purpose with mineral oils from Group II and III and PAO, and besides their aid in solubilizing additives, they can also improve one or more property(ies) of the base oil, in particular they can contribute to reduce the formation of sludge, varnish or lacquer. But a solubilizer is not necessarily a deposit control agent.
Thus, to maintain performance of lubricant compositions and systems using them longer, it is necessary to prevent or reduce those sludge, varnish and/or lacquer formation. This is possible by using a deposit control agent.
A deposit control agent is an agent that has deposit control property i.e. it prevents or reduces the formation of sludge, varnish and/or lacquer.
Typical examples of deposit control agent is sulfonates, phenates, salicylates, polymeric compounds derived from polyisobutylene with polar moiety.
However, there is still a need for a new alternative solution.
It has been surprisingly found that specific diesters present a better deposit control property than other Group V base oils.
The present invention therefore relates to the use of one or a mixture of isosorbide diester(s) of formula I,
wherein R¹ and R², identical or different, each represents a linear, straight or branched, saturated or unsaturated, hydrocarbon chain comprising from 3 to 17 carbon atoms; as a deposit control agent, wherein the isosorbide diester has a pour point of at most 15°C.
Preferably, the hydrocarbon chain R¹ and R² independently comprise from 5 to 17 carbon atoms.
The pour point refers to the lowest temperature at which a liquid remains pourable. Thus, isosorbide diesters with a pour point of at most 15°C are liquid and they can be more easily used.
The pour point can be determined according to method described in ASTM D97.
Preferably, the pour point of the isosorbide diesters is of at most 10°C.
As shown in Example 2, isosorbide diesters of formula I present good deposit control property. In particular, they reduced the sludge formation.
In a first embodiment, R¹ and R² are identical.
In a first particular embodiment of the first embodiment, each hydrocarbon chain R¹ and R² comprises from 3 to 9 carbon atoms.
In a second particular embodiment of the first embodiment, hydrocarbon chain R¹ and R² are unsaturated and comprise 17 carbon atoms.
In a second embodiment, R¹ and R² are different.
Preferably, at least R¹ or R² is a saturated hydrocarbon chain comprising from 3 to 9 carbon atoms or an unsaturated hydrocarbon chain comprising 17 carbon atoms.
Preferably, hydrocarbon chains R¹ and R² comprise independently from 7 to 15 carbon atoms, more preferably from 7 to 9 carbon atoms.
More particularly, hydrocarbon chains R¹ and R² comprise 7 or 9 carbon atoms, preferably in a weight ratio hydrocarbon chains comprising 7 carbon atoms / hydrocarbon chains comprising 9 carbon atoms, comprised between 1 and 2, more preferably between 1.05 and 1.85.
Advantageously, a mixture of isosorbide diesters of formula I is used.
The mixture of isosorbide diesters may comprise at least two isosorbide diesters of formula I. For example, the mixture may comprise at least two isosorbide diesters, at least one isosorbide diester of formula I comprising identical R¹ and R² but said R¹ and/or R² being able to be different from the first isorsorbide diester to the other one.
More particularly:

the mixture of isosorbide diesters may comprise at least two isosorbide diesters of formula I, each comprising identical R¹ and R² but R¹ and R² being different from each other diester; and/or
the mixture of isosorbide diesters may comprise at least one isosorbide diester of formula I with identical R¹ and R² and at least an isosorbide diester of formula I with R¹ and R² different.

Preferably, in the mixture of isosorbide diesters of formula I, hydrocarbon chains R¹ and R² comprise independently from 7 to 15 carbon atoms.
As an example, isosorbide diester may be prepared from at least two different fatty acids, such as caprylic acid and capric acid. Thus, it is possible to obtain a mixture of isosorbide diesters: one isosorbide diester with R¹ and R² comprising 7 carbon atoms, one isosorbide diester with R¹ and R² comprising 9 carbon atoms and one isosorbide diester with R¹ and R² comprising respectively 7 and 9 carbon atoms.
In addition to the deposit control property, isosorbide diesters of formula I present other properties, such as lubricant additives solubilizer.
As shown in Example 3, isosorbide diesters of formula I are effective in the solubilization of additives usually used in the field of lubricants.
Advantageously, at least 30% by weight of hydrocarbon chains R¹ and R² comprise 7 carbon atoms and at least 30% by weight of hydrocarbon chains R¹ and R² comprise 9 carbon atoms, weight percent being based on the weight of all hydrocarbon chains R¹ and R² of isosorbide diester(s).
Preferably, at least 50% by weight of hydrocarbon chains R¹ and R² comprise 7 carbon atoms, based on the weight of all hydrocarbon chains R1 and R2 of isosorbide diester(s).
Advantageously, the weight ratio hydrocarbon chains comprising 7 carbon atoms / hydrocarbon chains comprising 9 carbon atoms, is comprised between 1 and 2.
Preferably, the weight ration hydrocarbon chains comprising 7 carbon atoms / hydrocarbon chains comprising 9 carbon atoms is comprised between 1.05 and 1.85.
More particularly, in the one or the mixture of isosorbide diester(s) of formula I with R¹ and R² different, hydrocarbon chains R¹ and R² comprise 7 or 9 carbon atoms.
Such advantageous isosorbide diesters can solubilize even more easily different types of additives in different base oils.
Advantageously, in the use according to the invention, the isosorbide diester is further used to solubilize an additive used in the field of lubricants.
A person skilled in the art knows how to select the most suitable additive(s) used in the fields of lubricants depending on the lubricating application. By way of example, reference may be made to the following manuals: "Fuels and Lubricants Handbook : technology, properties performance and testing", by George E. Totten, 2003 and "Handbook of lubrification and tribology, vol II : Theory and Design", by Robert W. Bruce, 2012.
The additive(s) is/are preferably chosen from the group constituted by:

friction reducers;
anti-wears;
detergents;
antioxydants;
viscosity index improvers;
pour point depressants;
anti-foaming agents;
de-emulsifiers;
anti-corrosion (or anti-rust) agents;
thickening agents;
metal deactivators.

In addition of the deposit control property and the similar or even better solvent power, isosorbide diesters of formula I present good thermal-oxidative stability and a good hydrolytic stability.
The isosorbide diesters of formula I are obtainable by a process comprising a step of esterification reactions of isosorbide with at least one linear carboxylic acid, straight or branched, saturated or unsaturated, comprising from 4 to 18 carbon atoms. More particularly, the linear carboxylic acid, straight or branched, saturated or unsaturated, comprising from 4 to 18 carbon atoms is a fatty acid.
All the advantageous features and preferred embodiments mentioned above also apply to the process, in particular, those relating to the hydrocarbon chain, which correspond to those of the carboxylic or fatty acid.
The invention also relates to a lubricant composition comprising a base oil selected from Group II to Group IV, and a deposit control agent which is an isosorbide diester or a mixture of isosorbide diesters of formula I.
Isosorbide diesters of formula I are as described above, including preferential and advantageous features.
In the lubricant composition, the base oil content is of at least 50% by weight, based on the weight of the lubricant composition, preferably of at least 75% by weight, based on the weight of the lubricant composition.
Preferably, the quantity of isosorbide diester(s) is comprised between 0.1 and 35% by weight, more preferably between 0.1 and 20% by weight, based on the weight of the lubricant composition.
The lubricant composition may further comprise an additive used in the field of lubricants.
The additive used in the field of lubricants is as described above.
The total quantity of additional additives is preferably comprised between 5 and 25% by weight, more preferably between 5 and 20% by weight, base on the total weight of the lubricant composition.
The lubricant composition is preferably an engine oil, a hydraulic oil, a gear oil, a transmission oil, a metalworking oil, compressor oil.
Finally, the invention further relates to a method for reducing deposits in a lubricant composition, by adding into the lubricant composition at least 0.1% by weight of an isosorbide diester of formula I, weight percentage being based on the weight of the lubricant composition.
More particularly, the deposits are sludge, varnish or lacquer.
Advantageously, the method according to the invention can be also performed for further improving solubility of additive(s) used in lubricants field, in a Group II to IV base oil.
The base oil is preferably chosen among mineral oils from Group II or III, or polyalphaolefins from Group IV.
Additive(s) used in the fields of lubricants are preferably as described above.
In methods according to the invention, the isosorbide diester of formula I is as described above, including preferential and advantageous features.
The invention is further described in the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples.

Example 1: Preparation of isosorbide diesters

1.1. Chemicals used

isosorbide (diluted at 80 wt% in water, POLYSORB^® LPB - ISOSORBIDE EXP from Roquette Frères);
fatty acids:
- ∘ caprylic acid (IFFCO (Malaysia) Sdn. Bhd);
- ∘ capric acid (POFAC 1099, Southern Acids Industries Sdn. Bhd);
- ∘ iso-nonanoic acid (I-Nonanoic acid, BASF SE);
- ∘ oleic acid (Materia Hnos. S.A.C.I.F);

1.2. Preparation of isosorbide diesters

Isosorbide and 1.9 weight equivalents of fatty acid(s) were introduced in a reaction vessel. The esterification was carried out at elevated temperature (from 180 to 230°C) and stopped when acid value was less than 5 mg KOH/g.
Distillation was then carried out under vacuum (<40 mbar) at a temperature of 180°C-230°C and stopped once the acid value was below 1.0 mg KOH/g.
The acid values were measured according to standard AOCS Cd 3d-63.
Three isosorbide diesters were prepared according to this method:

Isosorbide di-caprylate/caprate (ISD1) prepared from a mixture of fatty acids comprising 60 wt% of caprylic acid and 40 wt% of capric acid, wt% being based on the weight of fatty acids.
Isosorbide diisononanoate (ISD2)
Isosorbide dioleate (ISD3)

Kinematic viscosity has been measured according to ASTM D445.
Their characteristics are described in Table 1 bellow: Table 1: Characteristics of isosorbide diesters of formula I

Acid value (KOH/g) Kinematic viscosity at 40°C (m²/s) Kinematic viscosity at 100°C (m²/s) Pour point (°C)

ISD1 0.47 25.50 4.8 -12

ISD2 0.43 66.96 7.38 -24

ISD3 0.21 53.79 9.67 6

Example 2: Evidence of properties of isosorbide diesters

2.1 Deposit control property

2.1.1 Chemicals used

Isosorbide diesters prepared at Example 1
Comparative Group V base oils with sludge or varnish control property:
- ∘ diisotridecyl adipate (DITA), Plasthall DTDA from Hallstar
- ∘ alkylated naphthalene (AN), NA-LUBE KR-008 from King Industries
- ∘ trimethylolpropane tricaprylate/caprate (TMP C8-C10), Radialube 7368 from Oleon
Base oil: mineral oil from Group II (GII): Tudalen 10F (Kinematic viscosity at 40°C = 29cSt, Sulfur = 0.004%) from Hansen & Rosenthal Group.

2.1.2 Method

Oxygen-induced degradation (modified Rotating Pressurized Vessel Oxidation Test, RPVOT) was used to evaluate the sludge formation in mineral oils with and without the use of isosorbide diester or other known products with deposit control property. RPVOT is a test that utilizes an oxygen-pressured vessel to evaluate the oxidation stability of new and in-service turbine oils.
The usual RPVOT setup has been slightly amended as follows: the conditions will be as follows:
Different mixtures comprising 10 wt% of each isosorbide diester or other comparative Group V base oils were diluted in 90 wt% of the mineral oil GII, weight percentages being based on the weight of the mixture. 50 g of each mixture (without water and without copper) were then subjected to 90 Psi oxygen and heated at 150°C for 150 min.
After the heating, the mixtures were filtered through Milipore MF membrane filter (0.8 um) using 50 ml of hexane to ease the filtration and for rinsing purpose.
50 g of mineral oil GII (without any additional chemical) were also submitted to the same conditions.

Each 50 g sample was tested three times, and the quantities of sludge retained on filter for each sample, described in Table 2 below, are the average of quantities of the three tests.

Table 2: Contents of additive packages 1-8 according to the invention

	GII + 10wt% of
	-	ISD1	ISD2	ISD3	DITA	AN	TMP C8-C10
Sludge retained on filter (mg)	120.0	49.3	47.6	48.1	58.5	80.7	59.1
Reduction of sludge formation (%)	-	59.0	60.3	59.9	51.2	32.8	50.7

*based on the weight of the additive package

2.2 Additives solubilizing improving property

To evaluate how isosorbide diesters can help solubilizing additives in base oils, isosorbide diesters were added into mixtures comprising Group III and IV base oils and one additive known to be not soluble in those base oils.

2.2.1 Chemicals used

Base oils
- ∘ mineral oil from Group III (GIII), PX 20 from Pertamina;
- ∘ polyalphaolefin from Group IV, (PAO4), SpectraSyn 4 from ExxonMobil;
- ∘ metallocene polyalphaolefin from Group IV (mPAO150), SpectraSyn Elite 150 from ExxonMobil;
Additives:
- ∘ friction modifiers:
  - ▪ ethylene glycol dimerate (EGD), Radialube 7660 from Oleon;
  - ▪ sorbitan monolaurate (SML), Radiasurf 7125 from Oleon;
- ∘ antiwear:
  ▪ molydenum dithiocarbamate (MoDTC), SAKURA-LUBE 165 from Adeka;
- ∘ detergent:
  ▪ calcium dinonylnaphthalene sulfonate (CaDNNS), CA 6500 from Additiv-Chemie Luers;
Isosorbide diesters prepared at Example 1
Comparative Group V base oils:
- ∘ diisotridecyl adipate (DITA), Plasthall DTDA from Hallstar
- ∘ diisodecyl adipate (DIDA) from Fisher Scientific
- ∘ trimethylolpropane tricaprylate/caprate (TMP C8-C10), Radialube 7368 from Oleon.
- ∘ alkylated naphthalene (AN), NA-LUBE KR-008 from King Industries

2.2.2 Method

Different mixtures comprising a base oil and an additive were prepared.
First, 0.5 wt % or 3 wt% of an additive was placed into a vial.
A base oil was added until the mixture correspond to 80 wt%, letting 20wt% left for the addition of isosorbide diester or Comparative Group V base oils. Example, when 0.5 wt% of additive was added, 79.5 wt% of base oil was added, left 20 wt% allowance for isosorbide diester or Comparative Group V base oils to be added. 20 wt% was determined as the maximum allowed isosorbide diester or Comparative Group V base oils to be used.
Isosorbide diester or Comparative Group V base oils was thus added to the mixture, starting from 1 wt% and the resulting mixture was stirred via vortex mixer for 20 seconds before evaluating the solubility. If the solubility is insufficient, more isosorbide diester or Comparative Group V base oils was added.The evaluation of solubility of additives was determined with the help of a visual aid (line background). The additive was considered soluble when the line appeared as clear as in the case of only base oil (control) was used.
If the mixture appeared cloudy, additional isosorbide diesters or Comparative Group V base oils was added and stirred, and a novel evaluation of solubility was repeated, until 20% of isosorbide diesters or Comparative Group V base oils were used.
If less than 20% of co-base oil were used, the remaining weight was topped up with the base oil.
The confirmation of the solubility of the additive was determined when the resulting mixture appeared at least as clear as no cloudiness or sediment could be observed, after 1 day at room temperature.

Quantities of isosorbide diesters or Comparative Group V base oils that were needed to solubilize each additive are indicated in Table 3 below:

Table 3: Quantities of isosorbide diesters or Comparative Group V base oils to solubilize additives

Additive	Base oil	Isosorbide diesters or Comparative Group V base oils
		ISD1	ISD2	ISD3	DITA	DIDA	AN	TMP C8-C10
control	GIII
0.5wt%* EGD	not soluble	+++	--	-	-	not soluble	not soluble	--
control	mPAO150
0.5wt%* MoDTC	not soluble	+++	--	+++	not soluble	+++	--	-
3wt%* CaDNNS	not soluble	+++	+++	+++	++	+++	++	+++

"+++" less or equal to 10 wt%; "++" between 10 and 15 wt%; "-" more or equal to 15 wt%;
"--" more or equal to 20 wt%, based on the weight of the resulting mixture

Isosorbide diesters solubilize EGD in mineral oil of Group III and MoDTC and CaDNNS in PAO 150. In particular, ISD1 exhibits better performances, since lower quantities are needed to solubilize additives. Therefore, IDS1 helps solubilizing all those additives in different base oils with better performances than Comparative Group V base oils, as shown by results gathered in Table 4.

Table 4: Quantities of IDS1 or Comparative Group V base oils to solubilize additives

Additive	Base oil	Isosorbide diester or Comparative Group V base oils (wt%*)
		ISD1	DITA	AN	TMP C8-C10
	GIII
0.5wt%* SML	not soluble	+++	not soluble	++	-
	PAO4
0.5wt%* EGD	not soluble	-	not soluble	not soluble	-

*based on the weight of the resulting mixture

Claims

Use of one or a mixture of isosorbide diester(s) of formula I,

wherein R¹ and R², identical or different, each represents a linear, straight or branched, saturated or unsaturated, hydrocarbon chain comprising from 3 to 17 carbon atoms;

as a deposit control agent, wherein the isosorbide diester has a pour point of at most 15°C.
Use of one isosorbide diester of formula I according to claim 1, wherein R¹ and R² are identical.
Use of one isosorbide diester of formula I according to claim 1, wherein R¹ and R² are different.
Use according to any of claims 1 to 3, wherein a mixture of isosorbide diesters of formula I is used.
Use according to any of claims 1, 3 or 4, wherein at least 30% by weight of hydrocarbon chains R¹ and R² comprise 7 carbon atoms and at least 30% by weight of hydrocarbon chains R¹ and R² comprise 9 carbon atoms, weight percent being based on the weight of all hydrocarbon chains R¹ and R² of isosorbide diester(s).
Use according to any of claims 1 or 3 to 5, wherein the weight ratio hydrocarbon chains comprising 7 carbon atoms / hydrocarbon chains comprising 9 carbon atoms, is comprised between 1 and 2.
Use according to any of claims 1 to 6, wherein the isosorbide diester is further used to solubilize an additive used in the field of lubricants.
Lubricant composition comprising a base oil selected from Group II to Group IV, and a deposit control agent, which is an isosorbide diester or a mixture of isosorbide diesters of formula I.
Method for reducing deposits in a lubricant composition, by adding into the lubricant composition at least 0.1% by weight of an isosorbide diester of formula I, weight percentage being based on the weight of the lubricant composition.
Method according to claim 9, for further improving solubility of additive(s) used in lubricants field, in a Group II to IV base oil.