Iron oxide nanoparticle dispersions and fuel additives for soot combustion
View Patent ↗Aqueous and substantially crystalline iron oxide nanoparticle dispersions and processes for making them are disclosed. The nanoparticle size and size distribution width are advantageous for use in a fuel additive for catalytic reduction of soot combustion in diesel particulate filters. Nanoparticles of the aqueous colloid are transferred to a substantially non-polar liquid comprising a carboxylic acid and one or more low-polarity solvents. The transfer is achieved by mixing the aqueous and substantially non-polar materials, forming an emulsion, followed by a phase separation into a substantially metal-free remnant polar phase and a substantially non-polar organic colloid phase. A method for rapid and substantially complete transfer of non-agglomerated nanoparticles to the low polarity phase in the presence of an organic amine, and a rapid phase separation of the substantially non-polar colloid from a remnant aqueous phase, are provided.
1. A process for preparing a dispersion, comprising:
(a) forming an aqueous dispersion comprising iron-containing nanoparticles adjusted to a pH in the range of 4 to 5;
(b) adding and mixing to the aqueous dispersion of step (a), an immiscible carboxylic acid and a non-polar solvent to form an emulsion;
(c) allowing the Immiscible non-polar phase to separate from a remnant aqueous phase; and,
(d) physically separating the non-polar phase comprising a dispersion of iron-containing nanoparticles from the remnant aqueous phase.
2. The process of claim 1 , wherein said aqueous dispersion comprising iron-containing nanoparticles is adjusted to a pH in the range of 4.2 to 4.8.
3. The process of claim 1 , wherein the pH is adjusted by the addition of an alkaline material.
4. The process of claim 3 , wherein said alkaline material is an organic amine.
5. The process of claim 4 , wherein said organic amine is octylamine.
6. The process of claim 1 , wherein said immiscible carboxylic acid is comprised of 6 or more carbon atoms.
7. The process of claim 1 , wherein said immiscible carboxylic acid is octanoic acid or oleic acid.
8. The process of claim 1 , wherein said non-polar phase comprising a dispersion of iron-containing nanoparticles provides an ignition temperature for carbonaceous soot of less than 200° C. when burned as part of a fuel in a diesel engine.