Patent Application
20070160759
The present invention relates generally to coatings that facilitate inhibiting the formation and/or adhesion of deposits on surfaces that contact hydrocarbon fluids, and more specifically to methods and apparatus for coating a surface that contacts a hydrocarbon fuel to facilitate reducing deposition of carbonaceous deposits thereon.
Thermal instability, or in the case of fuels, fuel instability, generally refers to the formation of undesired deposits that occur when hydrocarbon fluids, for example fuels and lubricating oils, are at elevated temperatures, for example generally above about 105° C. In the case of fuels, there may be two distinct mechanisms occurring within two overlapping temperature ranges. In the first mechanism, sometimes referred to as “coking”, an increase in a formation rate of coke deposits may occur above temperatures of about 345° C. Coke formation can be caused by hydrocarbon pyrolysis, and may sometimes limit usefulness of the fuel. A second mechanism may occur at lower temperatures, generally in the range of about 105° C. to about 345° C., and can involve oxidation reactions that may lead to polymerization and/or carbonaceous gum deposits.
A layer of platinum, sometimes referred to as a platinum coke barrier coating (CBC), has been used on surfaces that are exposed to hydrocarbon fluids to facilitate reducing deposition of carbonaceous deposits. For example, see U.S. Pat. No. 6,808,816 (Mancini et al.). At least some known methods of depositing a layer of platinum may include coating a surface by evaporating platinum precursor materials, for example platinum acetyl acetone or platinum pentanedionate, and exposing the surface to the resulting vapors. However, such known deposition methods may be less efficient than desired, for example yielding only about 10% platinum from the precursor material. Moreover, such known deposition methods may utilize equipment, for example, a chemical vapor deposition (CVD) reactor, that evaporates the precursor materials and channels the resulting vapors into a chamber containing a part to be coated. The cost of acquiring, leasing, operating, and/or maintaining such equipment may increase a cost of depositing a platinum layer and therefore fabricating coated parts. Moreover, loading parts into and unloading coated parts from such equipment may increase a time of fabricating coated parts. Furthermore, such equipment may generally coat all exposed surfaces of a part. Accordingly, covering surfaces that are not desired to be coated may increase a time and/or cost of fabricating coated parts. Moreover, using such equipment may sometimes only be cost-effective if a batch of a plurality of parts are coated simultaneously.
In one aspect, a method is provided for at least partially coating a surface of an object with a layer of platinum. The method includes applying a platinum precursor material to the object surface, evaporating the platinum precursor material from the object surface such that a residue comprising platinum remains on the surface, and heating the object such that the residue evaporates and re-deposits on the object surface as a layer comprising platinum.
In another aspect, a method is provided for at least partially coating an object with a layer of platinum. The method includes applying a mixture of a platinum precursor material and a solvent to a surface of the object that will be exposed to a hydrocarbon fuel, evaporating the mixture of solvent and platinum precursor material from the object surface such that a residue comprising platinum remains on the surface, covering at least a portion of the object surface with a covering, and heating the object such that the residue evaporates and re-deposits on the object surface as a layer comprising platinum.
In the exemplary embodiment, a liquid hydrocarbon fluid (not shown) contacts and flows across wall surface 13 protected by coating system 14, such that heat transferred to the fluid from an external heat source must be conducted through the coating system 14. Accordingly, coating system 14 may facilitate protecting object wall 12, and more specifically may facilitate reducing or preventing the formation and/or adhesion of carbonaceous deposits from the hydrocarbon fluid that may be caused by elevated temperatures of object wall 12 and the hydrocarbon fluid. Object wall 12 may be fabricated from any suitable material such that wall 12 is capable of performing the functions described herein, such as, but not limited to, steel and/or corrosion-resistant alloys of nickel and/or chromium. In some known situations, alloys containing iron, chromium and/or nickel may facilitate the formation of fuel thermal decomposition products such as, but not limited to, gum and coke in the fluid hydrocarbon fluid.
Coating system 14 includes a layer 18 of platinum on object wall surface 13 and, in some embodiments, a diffusion barrier layer 16 on surface 13 that separates platinum layer 18 from object wall surface 13. Although only one diffusion barrier layer 16 is illustrated, system 14 may include any number of diffusion barrier layers 16. Although only one platinum layer 18 is illustrated, system 14 may include any number of platinum layers 18. Moreover, in some embodiments system 14 may not include a diffusion barrier layer 16, such that platinum layer 18 is directly coated on object wall surface 13. In the exemplary embodiment, coating system 14 is generally continuous and completely covers all of object wall surface 13 that would otherwise contact the hydrocarbon fluid.
In the exemplary embodiment, platinum layer 18 may be generally reactive with the hydrocarbon fluid at elevated temperatures and may exhibit low emissivity toward the hydrocarbon fluid. For example, although platinum layer 18 may have other incident radiant energies, in some embodiments platinum layer 18 has an incident radiant energy of between about 500 and about 4,500 btu per square foot hour within a wavelength band of between about 2 and about 9 micrometers. Moreover, and for example, although platinum layer 18 may exhibit other reflectivities and emissivities, in some embodiments platinum layer 18 exhibits a reflectivity of between about 60% and about 100% and an emissivity of about 0.2 or less within a wavelength band of between about 2 and about 6 micrometers. Accordingly, platinum layer 18 may facilitate reducing radiation heat transfer to the hydrocarbon fluid from object wall 12. As such, the temperature of the hydrocarbon fluid, and therefore the tendency for the fluid to form carbonaceous deposits, may be reduced. Although platinum layer 18 may generally facilitate deposition of carbonaceous deposits at other rates, in some embodiment, and for example, platinum layer 18 may facilitate deposition at a rate of between about 0 and about 10 mg/cm3 cm. For example, in some embodiments platinum layer 18 may facilitate deposition of less than about 5 mg/cm3 cm. In some embodiments, and for example, although platinum layer 18 may have other surface roughnesses, to facilitate reducing emissivity, in some embodiments platinum layer 18 includes a surface roughness of about 1.0 micrometer or less. A surface roughness of about 1.0 micrometers or less may facilitate reducing a surface reaction time and/or concentration of deposit precursors (radicals and atoms) that may facilitate polymer growth.
In some embodiments, coating system 14, and more specifically platinum layer 18, may facilitate catalyzing the hydrocarbon fluid that eventually becomes sufficiently hot to form carbonaceous gum deposits to facilitate rapid formation of gum substances. As such, it is believed that platinum layer 18 may facilitate catalyzing the formation of carbonaceous gum substances in a hydrocarbon fluid to the extent that, in a flowing fluid system, the gum substances grow too quickly to allow them to adhere to object wall 12. Rather, gum substances may be found in the form of very fine particulate within the fluid.
Platinum layer 18 may include any suitable thickness capable of performing the functions described herein, which may depend, for example, on a surface roughness of object wall surface 13. Although platinum layer 18 may include other thicknesses, in some embodiments, and for example, platinum layer 18 includes a thickness of between about 50 and about 500 nanometers. For example, in some embodiments platinum layer 18 includes a thickness of between about 200 and about 350 nanometers. In the exemplary embodiment, platinum layer 18 is generally continuous and completely covers all of object wall surface 13 that would otherwise contact the hydrocarbon fluid.
Diffusion barrier layer 16 may facilitate preventing or reducing interdiffusion between platinum layer 18 and object wall 12, which in some situations may occur at elevated temperatures, for example above about 105° C. Diffusion barrier layer 16 may also facilitate protecting object wall 12 from chemical attack from contaminants in the hydrocarbon fluid, such as, but not limited to, sulfur and/or water that would form sulfuric acid and possibly pit object wall surface 13. Accordingly, diffusion barrier layer 16 may facilitate preventing or inhibiting reactions between constituents of the hydrocarbon fluid and object wall 12. Diffusion barrier layer 16 may include any suitable material such that layer 16 is capable of performing the functions described herein. For example, and although diffusion barrier layer 16 may include other materials, in some embodiments layer 16 includes ceramics such as, but not limited to, silica, alumina, yttria, hafnia, tantala, mullite, and/or complex chemical combinations of silica with boron, phosphorous, and/or alumina. Diffusion barrier layer 16 may include any suitable thickness capable of performing the functions described herein. Although diffusion barrier layer 16 may include other thicknesses, in some embodiments, and for example, diffusion barrier layer 16 includes a thickness of between about 500 and about 1500 nanometers. For example, in some embodiments diffusion barrier layer 16 includes a thickness of between about 700 and about 1300 nanometers. In the exemplary embodiment, diffusion barrier layer 16 is generally continuous and completely covers all of object wall surface 13 that would otherwise contact the hydrocarbon fluid. Diffusion barrier layer 16 may be deposited, or applied, on object wall surface 13 using any suitable process, method, structure, and means.
Method 50 also includes evaporating 56 the platinum precursor material and/or the mixture containing the platinum precursor material from object wall surface 13 such that a residue including platinum remains on surface 13. The platinum precursor material and/or the mixture containing the platinum precursor material may be evaporated 56 at any suitable temperature, pressure, and in any suitable medium. For example, and although the platinum precursor material and/or the mixture containing the platinum precursor material may be evaporated 56 at other temperatures, pressures, and in other mediums, in some embodiments evaporation 56 is performed in air at a temperature between about 18° C. and about 26° C. and at about atmospheric pressure. For example, in some embodiments evaporation 56 is performed at a temperature between about 21° C. and about 23° C. After partial or complete evaporation 56, object wall surface 13 is at least partially covered 58 with a covering (not shown), such as, but not limited to, a metallic covering, such as but not limited to, aluminum, steel, nickel, and/or cobalt-based sheet materials.
Method 50 includes heating 60 the at least partially covered object 10 such that the residue evaporates and re-deposits on object wall surface 13 as platinum layer 18 (shown in
Some of the residue may be deposited on the covering as platinum, and/or some of the platinum precursor material may be lost during evaporation 56 and/or heating 60. For example, in some embodiments greater than about 20% of the platinum precursor material applied 52 to surface 13 is deposited on object wall surface 13 as platinum. For example, in some embodiments greater than about 80% of the platinum precursor material applied 52 to surface 13 is deposited on object wall surface 13 as platinum, and in other embodiments greater than about 90% of the platinum precursor material applied 52 to surface 13 is deposited on object wall surface 13 as platinum. Accordingly, method 50 may facilitate improving a deposition efficiency of the coating of platinum layer 18 on object 10 as compared with at least some other known methods of coating object 10 with platinum layer 18. Moreover, because method 50 may not require equipment such as, but not limited to, chemical vapor deposition (CVD) reactors, method 50 may facilitate reducing an overall cost of coating object 10 with platinum layer 18 by facilitating reducing or eliminating the associated costs of acquiring, leasing, operating, and/or maintaining such equipment. Furthermore, method 50 may facilitate reducing a time of coating object 10 with platinum layer 18 by facilitating reducing the associated time of loading and unloading object 10 into such equipment. As such, method 50 may facilitate more cost-effective coating of a fewer number of objects 10 simultaneously as compared with at least some known methods. Even further, method 50 may facilitate coating of only one or a select number of surfaces of object 12, because such surfaces are coated by the application 52 step(s) described and/or illustrated herein rather than using known chemical vapor deposition, and method 50 may therefore facilitate reducing a time and/or cost of coating object 10 with layer 18.
Exemplary embodiments of methods are described and/or illustrated herein in detail. The methods are not limited to the specific embodiments described herein, but rather, steps of each method may be utilized independently and separately from other steps described herein. Each method step can also be used in combination with other method steps.
When introducing elements/components/etc. of the methods described and/or illustrated herein, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
