Process for in-situ synthesis of dispersion ZnO—TiO2 nanoparticles in oil

Abstract

The present invention provides a process for in situ synthesis of dispersion of ZnO and TiO.sub.2 nanoparticles in an oil medium, wherein the process comprises: (a) providing layered basic zinc hydroxide (LBZ) in an oil medium, containing a dispersant, (b) providing a titanium precursor in the oil medium to obtain a mixture, (c) hydrolyzing the mixture to obtain a suspension, and (d) decomposing the suspension to obtain a dispersion of mixture of ZnO and TiO.sub.2 nanoparticles. The present invention also provides an oil dispersion comprising dispersant stabilized mixture of zinc oxide and titanium dioxide nanoparticles were synthesized through this process. The dispersion contains up to 2.5 Wt % metals loading balanced with dispersant and base oil or dispersant alone. Addition of this dispersion to oil of lubricating viscosity improves the anti-wear property and resulting a low SAPS formulation.

Claims

1. A process for in situ synthesis of dispersion of ZnO and TiO.sub.2 nanoparticles in an oil medium, wherein the process comprises: (a) providing layered basic zinc hydroxide (LBZ) in an oil medium, containing a dispersant, (b) providing a titanium precursor in the oil medium to obtain a mixture, (c) hydrolyzing the mixture to obtain a suspension, and (d) decomposing the suspension to obtain a dispersion of mixture of ZnO and TiO.sub.2 nanoparticles.

2. The process of claim 1, wherein the titanium precursor is a titanium tetra alkoxide precursor having formula Ti(OR).sub.4, wherein R is C1 to C4 alkyl group and the titanium tetra alkoxide precursors is selected from the group comprising of titanium tetra isopropoxide, titanium tetrabutoxide, titanium tetra ethoxide, and titanium tetra methoxide.

3. The process of claim 1, wherein the hydrolysis is achieved by the water existing in the form of hydrate within LBZ and the hydrolysis of mixture comprises refluxing the mixture of step (b) to hydrolyze titanium precursor to obtain a colloidal suspension containing titanium hydrous oxide in oil containing LBZ and dispersant.

4. The process of claim 1, wherein the decomposition comprises heating to 120-150 C. to obtain a dispersion of mixture of ZnO and TiO.sub.2 nanoparticles, along with dispersant and residual anions.

5. The process of claim 1, wherein the in situ prepared nanoparticles of ZnO and TiO.sub.2 are stabilized by dispersant in the oil medium, wherein the dispersant is ashless dispersant.

6. The process of claim 1, wherein the dispersant is present in the concentration range of 50-75 wt % or 50-65 wt % and the dispersant is oil soluble and free from phosphorus and sulfur.

7. The process of claim 4, wherein the dispersant is nitrogen substituted long chain alkenyl succinimide dispersant and selected from the group consisting of Polyisobutylene Succinimides (PIBSI), oil soluble fatty acid, sorbitan ester, and oil soluble carboxylic acids.

8. The process of claim 1, wherein step (a) comprises dispersing LBZ in a C1-C3 alcohol and adding to oil medium containing 40-60% of dispersant.

9. The process of claim 1, wherein providing a titanium precursor in said oil medium to obtain a mixture comprises stirring the mixture of step (a) continuously at 200-1500 RPM and adding stoichiometric amount of titanium tetra alkoxide precursor resulting Ti content of 3% by weight.

10. The process of claim 1, wherein the step (c) comprises: (i) hydrolyzing the titanium tetra alkoxides precursor by the water molecules of layered basic zinc hydroxide (LBZ) in oil medium comprising dispersant to give a colloidal suspension comprising titanium hydrous oxide in oil containing LBZ and dispersant; and (ii) evacuating the colloidal suspension of step (i) and followed by heating to 120-150 C. for 45 to 90 minutes to trigger the LBZ decomposition to ZnO and TiO.sub.2 formation from titanium hydrous oxides to give a clear dispersion of ZnO nanoparticles in the oil medium along with nanoparticles of TiO.sub.2, dispersant and residual anions.

11. The process of claim 6, wherein the nanoparticles of TiO.sub.2 is prepared by the presence of 2 moles of H.sub.2O within LBZ and ZnO nanoparticles is prepared by the decomposition of LBZ within the oil medium containing stabilizing agents and nano TiO.sub.2.

12. The process of claim 6, wherein in the oil medium the nanoparticles of TiO.sub.2 and ZnO are stabilized by dispersant in the concentration range in weight percent 50-75% or 50-65%, wherein dispersant is ashless dispersant.

13. The process of claim 7, wherein the ashless dispersant is oil soluble compounds containing polymeric hydrocarbon structure and polar functional groups that stabilize nanoparticles.

14. The process of claim 7, wherein the ashless dispersant is nitrogen substituted long chain alkenyl succinimides dispersant and selected from the group consisting of Polyisobutylene Succinimides (PIBSI), oil soluble fatty acid, sorbitan ester or oil soluble carboxylic acids.

15. The process of claim 6, wherein in step (i) the LBZ is dispersed in a C1-C3 alcohol and added to oil containing 40-60 wt % of dispersant before adding the titanium tetra alkoxide precursor to obtain a mixture and then the mixture is refluxed and during refluxing period the moles of water molecule hydrolyze titanium tetra alkoxide to give a colloidal suspension containing titanium hydrous oxide in oil containing LBZ and dispersant.

16. The process of claim 6, wherein the oil is selected from the group comprising of base oil, process oil, mineral lubricating oils, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types, polyalphaolefins (PAOs) derived from monomers having from 4 to 30 carbon atoms having a viscosity in the range from 1.5 to 150 mm.sup.2/s (cSt) at 100 C., esters of dicarboxylic acids with a variety of alcohols, or a mixture thereof.

17. The process of claim 6, wherein LBZ having formula Zn.sub.5(OH).sub.8(X).sub.2.2H.sub.2O and X is anions and selected from a group comprising of Cl, NO.sub.3, Br, I, and CH.sub.3COO.sup..

18. The process of claim 6, wherein the layered base zinc (LBZ) is prepared by the process comprising: (a) dissolving a Zinc salt comprising of zinc acetate dihydrate in an alcoholic solvent and heating to 90-120 C. for 40 minutes to 24 hours to obtain a suspension; (b) centrifuging the suspension as obtained in step (a) and washing with deionized water to precipitate layered base zinc (LBZ) having 2 moles of water in the form of hydrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.

(2) The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.

(3) The terms comprises, comprising, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that one or more processes or composition/s or methods proceeded by comprises . . . a does not, without more constraints, preclude the existence of other processes, sub-processes, composition, sub-compositions, minor or major compositions or other elements or other structures or additional processes or compositions or additional elements or additional features or additional characteristics or additional attributes.

Definition

(4) For the purposes of this invention, the following terms will have the meaning as specified therein:

(5) Nanoparticle as used herein having the size of a particle spans in the range between 1 and 100 nm. Nanoparticles have different physical and chemical properties from bulk metals (e.g., higher specific surface areas, specific optical properties, mechanical strengths, etc.), properties that might prove attractive in various industrial applications.

(6) Layered basic zinc hydroxide (LBZ) used herein is an organic-inorganic hybrid of Zinc salt. This material is a precursor for controlled synthesis of Zinc based nanoparticles.

(7) Oil soluble organo zinc like ZDDP, Zn-DTC are known and similarly organo titanium like polytitanoxanes, alkyl titanium phosphates (Ti-DDP) are known and applied as antiwear additives. These are good antiwear additives; however, the presence of S and P in these additives would potentially hamper the performance of pollution controlling devices. In this art, Zn and Ti are stabilized in oil medium as nano metal oxide form incorporated in oil medium and tested for their influence on antiwear property in lube formulations.

(8) ##STR00001##

(9) Zinc compounds having stacked hydroxides layers held together by anions (Cl, NO.sub.3, Br, I, CH.sub.3COO) between the layers. It is well known that the decomposition of LBZ (structure mentioned above) yields flakes of porous nano ZnO as mentioned in reaction equation (2) [Journal of Colloid and Interface Science 272 (2004) 391-398]. In this invention, a two steps in situ approaches was followed to prepare metal oxide nanoparticles and it follow as (i) hydrolysis of titanium alkoxide precursor utilizing the water molecules of LBZ as mentioned in equation (1) and (ii) ZnO nanoparticles preparation in situ by the decomposition of layered basic zinc hydroxides (LBZ) as mentioned in equation (2) and both these steps executed within an oil medium containing stabilizing agents. The dispersants present in the oil medium stabilize the freshly formed nanoparticles oxides and thus were obtained a clear dispersion of ZnO and TiO.sub.2 in oil. The residual anions evolved during decomposition were removed through vacuum stripping.

(10) The additive is free from S and P and thus it is greener additive and could cater wherever the demand arises for low SAP formulations. The importance of low SAPS (sulfated ash, phosphorous, Sulfur) content lubricating oil has already been taught in WO 2014/033634. The ashing factor for different metal content in lubricating formulation is taken from website reference and detailed below (http://www.konnaris.com/search/calculations.htm).

(11) TABLE-US-00001 Element Ashing Factor Lithium 7.92 Magnesium 4.95 Calcium 3.40 Boron 3.22 Sodium 3.09 Potassium 2.33 Barium 1.70 Molybdenum 1.50 Zinc 1.50 Lead 1.464 Manganese 1.291 Copper 1.252

(12) It is prudent from the table that Zn has a moderate ashing factor and Titania is greener with nil contribution towards sulfated ash. ZDDP additive contains Zn along with S & P in the moiety and the contribution towards SAPS is very high. The low SAPS formulation is not only desired for better engine performance and extended oil life; it is also desired for low emission & higher fuel economy.

(13) Accordingly, the present invention provides a process for in situ synthesis of dispersion of ZnO and TiO.sub.2 nanoparticles in an oil medium, wherein the process comprises: (a) providing layered basic zinc hydroxide (LBZ) in an oil medium, containing a dispersant, (b) providing a titanium precursor in the oil medium to obtain a mixture, (c) hydrolyzing the mixture to obtain a suspension, and (d) decomposing the suspension to obtain a dispersion of mixture of ZnO and TiO.sub.2 nanoparticles.

(14) In an embodiment of the present invention, the LBZ is obtained by dissolving a Zinc salt in an alcoholic solvent and heating to 90-150 C. for a time period in the range of 40 minutes to 24 hours to obtain a white suspension, centrifuging and washing twice with deionized water to precipitate LBZ.

(15) In one of the embodiment of the present invention, the titanium precursor is a titanium tetra alkoxide.

(16) In another embodiment of the present invention, the hydrolysis is achieved by the water existing in the form of hydrate within LBZ.

(17) In still another embodiment of the present invention, the hydrolysis of mixture comprises refluxing the mixture of step (b) to hydrolyze titanium precursor to obtain a colloidal suspension containing titanium hydrous oxide in oil containing LBZ and dispersant.

(18) In still another embodiment of the present invention, the decomposition comprises heating to about 120-150 C. to obtain a dispersion of mixture of ZnO and TiO.sub.2 nanoparticles, along with dispersant and residual anions.

(19) In still another embodiment of the present invention, the heating is conducted for about 45 to 90 minutes.

(20) In yet another embodiment of the present invention, the process for in situ synthesis of dispersion of mixture of ZnO and TiO.sub.2 nanoparticles in an oil medium, further comprising decomposing and removing residual anions through vacuum stripping.

(21) In yet another embodiment of the present invention, the in situ prepared nanoparticles of ZnO and TiO.sub.2 are stabilized by dispersant in the oil medium, wherein the dispersant is ashless dispersant. The dispersant is present in the concentration range of 50-75 wt %. In one of the embodiment the dispersant is present in the concentration range of 50-65 wt %. The dispersant is oil soluble and free from phosphorus and sulfur. The dispersant is nitrogen substituted long chain alkenyl succinimide dispersant and selected from the group consisting of Polyisobutylene Succinimides (PIBSI), oil soluble fatty acid, sorbitan ester and oil soluble carboxylic acids.

(22) In yet another embodiment of the present invention, the step (a) of the process comprises dispersing LBZ in a C1-C3 alcohol and adding to oil medium containing 40-60% of dispersant.

(23) In one embodiment of the present invention the oil medium is base oil.

(24) In an another embodiment of the present invention, prior to decomposing the suspension, the suspension is evacuated at room temperature and heated to 80 C.-140 C. to remove alcohol solvent.

(25) In yet another embodiment of the present invention, providing a titanium precursor in said oil medium to obtain a mixture comprises stirring the mixture of step (a) continuously at about 200-1500 RPM and adding stoichiometric amount of titanium tetra alkoxide precursor resulting Ti content of 3% by weight.

(26) The present invention provides a process for in situ synthesis of dispersion of ZnOTiO.sub.2 nanoparticles, stabilized in oil soluble mixed metal-oxide nanoparticles dispersion comprising: (i) hydrolyzing the titanium tetra alkoxides precursor by the water molecules of layered basic zinc hydroxide (LBZ) in oil medium comprising dispersant to give a colloidal suspension comprising titanium hydrous oxide in oil containing LBZ and dispersant; and (ii) evacuating the colloidal suspension of step (i) and followed by heating to 120-150 C. for 45 to 90 minutes to trigger the LBZ decomposition to ZnO and TiO.sub.2 formation from titanium hydrous oxides to give a clear dispersion of ZnO nanoparticles in the oil/hydrocarbon medium along with nanoparticles of TiO.sub.2, dispersant and residual anions.

(27) In another embodiment of the present invention, the nanoparticles of TiO.sub.2 is prepared by the presence of 2 moles of H.sub.2O within LBZ and ZnO nanoparticles is prepared by the decomposition of LBZ within the oil medium containing stabilizing agents and nano TiO.sub.2.

(28) In one of the embodiment of the present invention, in the oil medium the nanoparticles of TiO.sub.2 and ZnO are stabilized by dispersant in the concentration range in 50-75 wt. %, wherein dispersant is ashless dispersant. In yet another embodiment of the present invention, in the oil medium the nanoparticles of TiO.sub.2 and ZnO are stabilized by dispersant in the concentration range in weight percent 50-65 wt. %, wherein dispersant is ashless dispersant.

(29) In yet another embodiment of the present invention, the ashless dispersant is oil soluble compounds containing polymeric hydrocarbon structure and polar functional groups that stabilize nanoparticles.

(30) In yet another embodiment of the present invention, the ashless dispersant is nitrogen substituted long chain alkenyl succinimides dispersant and selected from the group consisting of Polyisobutylene Succinimides (PIBSI), oil soluble fatty acid, sorbitan ester or oil soluble carboxylic acids.

(31) In an another embodiment of the present invention, in step (i) of the process for in situ synthesis of dispersion of ZnOTiO.sub.2 nanoparticles the LBZ is dispersed in a C1-C3 alcohol and added to oil containing 40-60 wt. % of dispersant before adding the titanium tetra alkoxide precursor to obtain a mixture and then the mixture is refluxed and during refluxing period the moles of water molecule hydrolyze titanium tetra alkoxide to give a colloidal suspension containing titanium hydrous oxide in oil containing LBZ and dispersant.

(32) In yet another embodiment of the present invention, the C1-C3 alcohol is selected from the group comprising of methanol, ethanol, isopropanol or combination thereof.

(33) In yet another embodiment of the present invention, the oil is selected from the group comprising of base oil, process oil, mineral lubricating oils, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types, polyalphaolefins (PAOs) derived from monomers having from about 4 to about 30 carbon atoms having a viscosity in the range from about 1.5 to about 150 mm.sup.2/s (cSt) at 100 C., esters of dicarboxylic acids with a variety of alcohols, or a mixture thereof.

(34) In yet another embodiment of the present invention, the titanium tetra alkoxides precursors having formula Ti(OR).sub.4, wherein R is C.sub.1 to C.sub.4 alkyl group and the titanium tetra alkoxide precursors is selected from a group comprising of titanium tetra isopropoxide, titanium tetrabutoxide, titanium tetra ethoxide, titanium tetra methoxide.

(35) In yet another embodiment of the present invention, the LBZ having formula Zn.sub.5(OH).sub.8(X).sub.2.2H.sub.2O and X is anions and selected from a group comprising of Cl, NO.sub.3, Br, I, and CH.sub.3COO.sup..

(36) In one of the embodiment of the present invention, the layered base zinc (LBZ) is prepared by the process comprising: (a) dissolving a Zinc salt in an alcoholic solvent and heating to 90-120 C. for 40 minutes to 24 hours to obtain a suspension; (b) centrifuging the suspension as obtained in step (a) and washing with deionized water to precipitate layered base zinc (LBZ) having 2 moles of water in the form of hydrate.

(37) In yet another embodiment of the present invention, the Zinc salt is selected from the group comprising of zinc acetate dihydrate.

(38) The present invention provides an oil dispersion comprising dispersion ZnOTiO.sub.2 nanoparticles stabilized in oil/hydrocarbon medium as obtained from the process, wherein the dispersion contains up to 2.5 wt % metals loading balanced with dispersant and base oil or dispersant alone. The oil dispersion of the present invention improves antiwear property.

(39) The following non-limiting examples illustrate in details about the invention. However, they are, not intended to be limiting the scope of present invention in any way.

Example 1

(40) About 100 ml of liquor solution of zinc acetate dihydrate (Zn(CH.sub.3COO).sub.2.2H.sub.2O) in the concentration 0.15 moles per cubic decimeter was charged in a round bottom flask fitted with a reflux condenser and heated at 140 C. for 24 h to give white precipitate. The precipitate was filtered and washed twice with deionized water to give fine white product layered basic zinc acetate (LBZA) of formula Zn.sub.5(OH).sub.8(CH.sub.3COO).sub.2.2H.sub.2O. The product was redispersed in isopropyl alcohol (25 ml) for further use/characterization.

Example 2

(41) To a 500 ml two neck round bottom flask containing 60 g polyisobutylene succinimides (PIBSI) dispersant and 16 g group II lubricating base oil added the iso propanol suspension prepared from the example 1 (LBZA) and then stoichiometric amount of titanium tetra isopropoxide (2.13 g) was added and heated to reflux for 90 minutes to give a colloidal suspension. The suspension was transferred to rotavapor flask and iso propanol was stripped under vacuum at 90 C. and then heated further to 140 C. under vacuum to remove decomposing acetates to give clear stable product containing 0.46% Ti and 1.45 Wt % of Zn (metal content) and confirmed by ICP-AES (Inductively coupled plasma-atomic emission spectrometry) analysis. The product could readily be mixed in any mineral oil (Group I/II/II/IV) of lubricating viscosity.

Example 3

(42) To a 750 ml high pressure reactor (Premex) added 300 ml isopropanol solution containing zinc acetate dihydrate (Zn(CH.sub.3COO).sub.2.2H.sub.2O) in the concentration 0.05 moles per cubic decimeter and heated at 95 C. for 24 h to give highly viscous colloidal white precipitate. The product was washed thoroughly by centrifuge with distilled water for three times before being mixed with 50 ml isopropyl alcohol to give a colloidal suspension for further use.

Example 4

(43) In another typical reaction run, 14 g of process oil and 53.6 g of PIBSI (M.W 800) was taken in a 250 ml reaction flask to this added the portion of suspension prepared from example 3 followed by 2.13 g titanium tetra isopropoxide. The mixture was heated to reflux for 90 minutes triggering hydrolysis of titanium precursor. After hydrolysis, the mixture was transferred to rotavapor flask and the solvent was removed under vacuum stripping at 90 C. The final mixture was heated further to 140 C. under vacuum for another 45 minutes to give clear product containing metals in the concentration range Ti-0.5 Wt % and Zn-2.0 Wt % and confirmed by ICP-AES. The product could readily be mixed in any mineral oil (Group I/II/II/IV) of lubricating viscosity.

Example 5

(44) The product obtained from Example 4 was diluted with Gr II base oil to get ppm (parts per million) level of TiZn concentration in final dispersion blends which were evaluated for anti-wear performance in four ball tester (Falex wear test machine) at 348K; 15 kg weight load (ASTM D4172). The tests were repeated two times (results with best precision were considered) and WSD results are summarized for neat base oil and blends in the below Table. The antiwear performance of the blends containing metal nanoparticles is comparable with the ZDDP containing blend.

(45) TABLE-US-00002 Metal Concentration (ppm) WSD Dispersant (Wt %) Ti (TiO.sub.2) Zn (ZnO) (mm) 0 0 0 0.65 1.55 0 0 0.70 1.55 116 (193) 380 (472) 0.35 1.55 98 (163) 400 (496) 0.35 1.55 100 (168) 390.sub.% (480) 0.34 1.55 0 500# (634) 0.35 #ZDDP blend .sub.%result of example 2

(46) Although in the current invention nano zinc oxide & nano titania combination gives equivalent performance to ZDDP, however effect of Zn in sulfated ash contribution may be significantly reduced by exchanging Zinc Oxide partially with Titania, which is more greener.