Patent Application
20120000817
This invention relates to a process for reducing the color level of middle distillate fuels, such as diesel fuel and kerosene.
Color, sulfur level and cloud point are important product specifications for diesel fuel and kerosene. For example, changes in the U.S. regulatory system in 2006 reduced the maximum sulfur levels in diesel fuels from 500 wppm (S500) to 15 wppm (S15). Similarly, the color specification required for most refinery diesel pools is less than 2.5 ASTM color units, which means that many refineries limit the color for desulfurized diesel to less than about 2.0 ASTM color units. In addition, depending on season and geography, diesel fuels and kerosene may be required to have a cloud point of less than −27° C.
Generally, a multi-stage hydrotreating process is used to reduce the sulfur and color levels of diesel fuel to the required values. For example, U.S. Pat. No. 6,103,104 discloses a process in which a middle distillate petroleum stream is hydroprocessed in two or more first temperature stages operated at a temperature from about 360° C. to about 450° C. The reaction product of the first temperature stage(s) is(are) then quenched to a temperature from about 260° C. to about 350° C., stripped of H2S, NH3 and other dissolved gases, then sent to the second temperature stage which is operated at the quenched temperature range, whereby color bodies produced in the higher temperature first stage are hydrogenated in the second stage.
Chinese Published Patent Application No. CN 1824736 discloses a method for preparing diesel oil with improved color property and ultra-low sulfur content by deep hydrodesulfurization and hydrotreating comprising (1) carrying out deep hydrodesulfurization to produce a hydrocarbon oil with a boiling point of 200-400° C. in the presence of a catalyst (including CoMo as active metal) at 330-380° C. under 40-48 kg/cm2 with a liquid hourly space velocity (LHSV) of 0.1-2.0 hr−1, and (2) hydrotreating in the presence of catalyst (including NiMo as active metal) at 230-320° C. under 40-80 kg/cm2 with a LHSV of 4-10 hr−1. The resultant diesel oil has a sulfur content not more than 10 ppm and a Saybolt color index not less than 10.
U.S. Pat. No. 6,652,735 discloses a process for isomerization dewaxing of a hydrocarbon feed, such as a diesel oil, which includes contacting the hydrocarbon feed with a large pore size, small crystal size, crystalline molecular sieve, such as zeolite beta, and an intermediate pore size, small crystal size, crystalline molecular sieve, such as ZSM-23 or ZSM-48, to produce a dewaxed product with a reduced pour point and a reduced cloud point.
To date, the chemistry involved in the formation of color bodies in diesel fuels has not been well understood, although it is known to be generally related to prior desulfurization and/or isomerization at high temperature. As a result, the maximum operating temperature for many desulfurization and isomerization units is limited by the color specification of the product rather than by catalyst activity, thereby limiting cycle length.
It has been discovered that the color of diesel fuel and kerosene can be specifically dependent on the 3+ ring aromatic content of the fuel. Based on this knowledge, a new process for producing low color fuels has been developed in which an additional catalyst bed can be added to the desulfurization/isomerization reactor for color control or the last bed in the desulfurization/isomerization reactor is converted for color control. This final bed can be operated at a temperature close to, but lower than, that of the preceding catalyst beds in the reactor. Either a recycle gas or the liquid diesel product can be used to quench the effluent from the desulfurization/isomerization bed, so that the color control bed can be operated at the lower temperature. This color control catalyst bed can re-saturate at least some of the 3+ ring aromatics generated by the desulfurization/isomerization catalyst beds. With such an arrangement, the main desulfurization/isomerization bed(s) can be operated over a broader temperature range as the catalyst ages, thereby prolonging the catalyst cycle length while simultaneously meeting the color specification.
One aspect of the invention relates to a process for producing a diesel and/or kerosene fuel of low color, the process comprising: (a) supplying a middle distillate feed having a first cloud point and hydrogen to a reactor having at least one first catalyst bed containing a first desulfurization and/or isomerization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and containing a decolorization catalyst; (b) reacting the feed with the hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 290° C. to about 430° C. to produce a first liquid effluent having a second cloud point; (c) cooling the first liquid effluent by about 10° C. to about 40° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature of about 280° C. to about 415° C. to produce a second effluent having an ASTM color of less than 2.5 and a third cloud point.
Another aspect of the invention relates to a process for producing a low color and low sulfur diesel and/or kerosene fuel, the process comprising: (a) supplying a hydrogen and middle distillate feed having a first cloud point and containing at least 0.03 wt % sulfur to a reactor having at least one first catalyst bed comprising a first desulfurization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and comprising a decolorization catalyst; (b) reacting the feed with hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 315° C. to about 430° C. to produce a first liquid effluent comprising 15 wppm or less sulfur and having a second cloud point; (c) cooling the first liquid effluent by about 15° C. to about 35° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature from about 300° C. to about 415° C. to produce a second effluent comprising 15 wppm or less sulfur, having a third cloud point, and having an ASTM color of less than 2.5.
Still another aspect of the invention relates to a process for producing a low color diesel and/or kerosene fuel having a low cloud point, the process comprising: (a) supplying a middle distillate feed having a first cloud point and hydrogen to a reactor having at least one first catalyst bed comprising a first isomerization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and comprising a decolorization catalyst; (b) reacting the feed with hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 285° C. to about 420° C. to produce a first liquid effluent having a second cloud point that is at least 10° C. less than that of the first cloud point; (c) cooling the first liquid effluent by about 10° C. to about 20° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature from about 275° C. to about 400° C. to produce a second effluent having a third cloud point that is at least 10° C. less than that of the first cloud point and having an ASTM color of less than 2.5.
Described herein is a simplified process for lowering the sulfur content and/or the cloud point of a middle distillate feed and for simultaneously removing color components produced in the desulfurization and/or isomerization step. The product can be a fuel composition having a boiling range in the diesel and/or kerosene temperature range, and which fuel composition can exhibit a low sulfur content and/or a low cloud point and can exhibit a low color value. As used herein, the term “low color” refers to a (diesel and/or kerosene) fuel product having a color value of less than 2.5, for example less than 2, as measured according to ASTM D-6045. Also as used herein, the term “low sulfur” refers to a (diesel and/or kerosene) fuel product containing less than 15 wppm sulfur, as measured according to ASTM D-5453. Further as used herein, the term “low cloud point” refers to a (diesel and/or kerosene) fuel product having a cloud point of less than 10° C., as measured according to ASTM D-2500.
The middle distillate feed suitable for use in the present processes can include any refinery hydrocarbon feedstream boiling in the range from about 300° F. (about 149° C.) to about 775° F. (about 413° C.), for example from about 350° F. (about 177° C.) to about 750° F. (about 399° C.), from about 400° F. (about 204° C.) to about 700° F. (about 371° C.), or from about 450° F. (about 232° C.) to about 650° F. (about 343° C.). Such middle distillate feeds can include hydrotreated feedstreams, feedstreams that have not previously been hydrotreated, and combinations thereof.
The middle distillate feeds employed herein can generally contain significant quantities of nitrogen and sulfur impurities, in which case the process can be employed to lower the nitrogen and/or sulfur level of the feed to that required for the final (diesel and/or kerosene) fuel. The feeds according to the invention can contain nitrogen-containing compounds, abbreviated as “nitrogen”, “nitrogen level”, or “nitrogen content”, and/or sulfur-containing compounds, abbreviated as “sulfur”, “sulfur level”, or “sulfur content”. Typically, the nitrogen content of such feeds can be from about 50 wppm to about 6000 wppm, preferably from about 50 wppm to about 2000 wppm, for example from about 50 wppm to about 1500 wppm, from about 50 wppm to about 1000 wppm, from about 75 wppm to about 1000 wppm, from about 75 wppm to about 800 wppm, or from about 100 wppm to about 500 wppm. The nitrogen may be present as both basic nitrogen and/or non-basic nitrogen species. Non-limiting examples of basic nitrogen species can include quinolines and substituted quinolines, and non-limiting examples of non-basic nitrogen species may include carbazoles and substituted carbazoles. Additionally or alternately, the sulfur content of such feeds can be from about 50 wppm to about 40000 wppm, for example from about 50 wppm to about 15000 wppm, from about 100 wppm to about 30000 wppm, from about 100 wppm to about 10000 wppm, from about 200 wppm to about 20000 wppm, from about 200 wppm to about 10000 wppm, from about 200 wppm to about 5000 wppm, from about 500 wppm to about 5000 wppm, or from about 350 wppm to about 2500 wppm sulfur. The sulfur can typically be present as organically bound sulfur, e.g., including simple aliphatic, naphthenic, and aromatic mercaptans, sulfides, di- and poly-sulfides, and the like, and combinations thereof. Other organically bound sulfur compounds can include thiophenes, tetrahydrothiophenes, benzothiophenes, and their higher homologs and analogs, as well as combinations thereof
Further additionally or alternately, the total aromatic content of such feeds can be between about 5 vol % and about 30 vol %, with the 3+ ring aromatic content generally ranging from about 0.5 wt % to about 5 wt %. Still further additionally or alternately, the middle distillate feeds may contain significant quantities of straight chain and/or lightly branched paraffins that can solidify at relatively high temperatures.
In such circumstances, the present process can be employed to hydroisomerize those materials into more highly branched paraffins, e.g., thereby reducing the cloud point and/or pour point of the feed.
In the present process the middle distillate feed and hydrogen can be supplied to a reactor comprising one or more first catalyst beds, each containing a first catalyst effective to desulfurize and/or isomerize the feed, and at least one second catalyst bed downstream of the first catalyst bed(s) and containing a second catalyst effective to remove color components in the feed. Depending on the composition of the feed, the first catalyst bed can be operated at a temperature from about 290° C. to about 430° C., for example from about 315° C. to about 400° C., such that the feed can react with the hydrogen in the presence of the first catalyst to produce a first liquid effluent having a lower sulfur content and/or a lower cloud point than the feed.
On exiting the first catalyst bed(s), the first liquid effluent can be cooled by about 10° C. to about 40° C., for example about 15° C. to about 35° C., with a quench medium, and then the entire cooled first liquid effluent can be cascaded to the at least one second catalyst bed. The second catalyst bed can be operated at a temperature from about 280° C. to about 415° C., for example from about 300° C. to about 400° C., such that the first effluent can react with the hydrogen in the presence of the second catalyst to remove color components produced in the first catalyst bed(s) and can produce a second liquid effluent having an ASTM color of less than 2.5, for example less than 2.0. As indicated above, without being bound by theory, it is believed that the color in the first liquid effluent can be the result of 3+ ring aromatics present in the feed and/or generated during the desulfurization and/or isomerization step. Such 3+ ring aromatics can be at least partially saturated (in this context, “saturated” is meant chemically by hydrogen, not having hydrogen physically dissolved therein) during the decolorization reaction such that the second liquid effluent can advantageously contain less than 3 vol %, for example less than 2.0 vol %, of 3+ring aromatic compounds. The term “3+ ring aromatic compounds” as used herein means a compound that has at least 3 aromatic rings in its structure.
Generally, the quench medium used to cool the first liquid effluent can be the second effluent and/or unreacted hydrogen gas from the decolorization reaction, though one or more other refinery streams can be additionally or alternately used. Typically, the hydrogen partial pressure in either or both of the first and second catalyst beds (and/or in a reactor containing same) can be between about 400 psig (about 2.8 MPag) and about 1500 psig (about 10.3 MPag), for example between about 500 psig (about 3.5 MPag) and about 1300 psig (about 9.0 MPag).
In a first embodiment, in which the sulfur level of the feed is at least 0.03 wt %, for example at least 0.05 wt % or at least 0.5 wt %, the/each first catalyst bed can contain a desulfurization catalyst. Suitable desulfurization catalysts can comprise at least one metal/compound from Groups 8-10 of the Periodic Table of the Elements (such as iron, cobalt, and/or nickel, preferably cobalt and/or nickel) and at least one metal/compound from Group 6 (such as molybdenum and/or tungsten, preferably including molybdenum), optionally but preferably on a high surface area support material (such as alumina, silica, alumina-silica, titania, zirconia, or a combination thereof). Typically, the reactor can contain a plurality, for example from 2 to 5, of the first catalyst beds, which can be operated at a temperature from about 315° C. to about 430° C. and at an LHSV from about 0.3 hr−1 to about 1.5 hr−1 to produce a first liquid effluent containing 15 wppm sulfur or less, for example 10 wppm sulfur or less.
In the first embodiment, the quenching step can be controlled to lower the temperature of the first liquid effluent by about 17° C. to about 40° C., and the entire cooled first liquid effluent can be cascaded to a decolorization catalyst, which can optionally but preferably be the same as the desulfurization catalyst The second catalyst bed can typically be operated at a temperature from about 300° C. to about 415° C. and at an LHSV from about 4 hr−1 to about 10 hr−1 to produce a second effluent having an ASTM color of less than 2.5, preferably less than 2.0, in addition to a sulfur content of 15 wppm or less.
In a modification to the first embodiment, in which the feed can have a cloud point of at least 5° C. in addition to a sulfur level of at least 0.03 wt %, the reactor can include a plurality of first catalyst beds connected in series, and the final first catalyst bed in the series can contain an isomerization catalyst. Suitable isomerization catalysts for use in this modification can include, but are not limited to, shape selective zeolites selected from zeolite beta, ZSM-23, ZSM-48, and mixtures thereof The isomerization catalyst bed can typically be operated at a temperature from about 343° C. to about 430° C. and at an LHSV from about 1 hr−1 to about 4 hr−1 to produce a first liquid effluent containing 15 wppm sulfur or less and typically having a cloud point from about 10° C. to about 30° C. less the feed. The quenching step can then be arranged to lower the temperature of the first liquid effluent by about 10° C. to about 28° C., and the entire cooled first liquid effluent can be cascaded to a decolorization catalyst, which can optionally but preferably be the same as the isomerization catalyst. The second catalyst bed can typically be operated at a temperature from about 300° C. to about 421° C. and at an LHSV from about 4 hr−1 to about 10 hr−1 to produce a second effluent having a relatively low color (e.g., an ASTM color of less than 2.5, preferably less than 2.0), a relatively low sulfur content (e.g., 15 wppm or less, such as 10 wppm or less) and a lower cloud point than the feed.
In another embodiment, the sulfur level of the feed can be less than 0.03 wt %, but the cloud point of the feed can be in excess of 0° C. In this embodiment, the/each first catalyst bed can contain an isomerization catalyst, typically at least one shape selective zeolite, e.g., selected from zeolite beta, ZSM-23, ZSM-48, and mixtures thereof. Generally, the reactor can contain a plurality, for example from 2 to 5, of the first catalyst beds, which can be operated at a temperature from about 285° C. to about 420° C. and at an LHSV from about 1 hr−1 to about 4 hr−1 to produce a first liquid effluent having a cloud point at least 10° C., for example from about 10° C. to about 30° C., less than that of the feed.
Additionally or alternately in such an embodiment, the quenching step can be controlled to lower the temperature of the first liquid effluent by about 10° C. to about 22° C., and the entire cooled first liquid effluent can be cascaded to a second catalyst bed containing a decolorization catalyst. Suitable decolorization catalyst can include, but are not limited to, (a) a noble metal (e.g., platinum, palladium, rhodium, or the like, or a combination thereof, preferably containing platinum) with MCM-41, and/or (b) at least one Group 8-10 metal or metal compound (e.g., cobalt and/or nickel) and at least one Group 6 metal or metal compound (e.g., molybdenum and/or tungsten) on a relatively high surface area support material (e.g., having a BET surface area of at least 60 m2/g, at least 75 m2/g, at least 90 m2/g, at least 100 m2/g, or at least 110 m2/g), such as alumina, silica, alumina-silica, titania, zirconia, or a combination thereof, for example comprising alumina. In one preferred embodiment, the decolorization catalyst can be the same as the isomerization catalyst. The second catalyst bed can typically be operated at a temperature from about 275° C. to about 400° C. and at an LHSV from about 5 hr−1 to about 15 hr−1 to produce a second effluent having a cloud point at least 10° C. less than that of the feed and an ASTM color of less than 2.5.
Additionally or alternately, the present invention can include one or more of the following embodiments.
Embodiment 1. A process for producing a diesel and/or kerosene fuel of low color, the process comprising: (a) supplying a middle distillate feed having a first cloud point and hydrogen to a reactor having at least one first catalyst bed containing a first desulfurization and/or isomerization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and containing a decolorization catalyst; (b) reacting the feed with the hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 290° C. to about 430° C. to produce a first liquid effluent having a second cloud point; (c) cooling the first liquid effluent by about 10° C. to about 40° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature of about 280° C. to about 415° C. to produce a second effluent having an ASTM color of less than 2.5 and a third cloud point.
Embodiment 2. A process for producing a low color and low sulfur diesel and/or kerosene fuel, the process comprising: (a) supplying a hydrogen and middle distillate feed having a first cloud point and containing at least 0.03 wt % sulfur to a reactor having at least one first catalyst bed comprising a first desulfurization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and comprising a decolorization catalyst; (b) reacting the feed with hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 315° C. to about 430° C. to produce a first liquid effluent comprising 15 wppm or less sulfur and having a second cloud point; (c) cooling the first liquid effluent by about 15° C. to about 35° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature from about 300° C. to about 415° C. to produce a second effluent comprising 15 wppm or less sulfur, having a third cloud point, and having an ASTM color of less than 2.5.
Embodiment 2a. The process of Embodiment 1 for producing a low color and low sulfur diesel and/or kerosene fuel, wherein the process further comprises: in step (a) the middle distillate feed contains at least 0.03 wt % sulfur; in step (b) the first catalyst bed is operated at a temperature from about 315° C. to about 430° C. thereby producing the first liquid effluent comprising 15 wppm or less sulfur; in step (c) the first liquid effluent is cooled by about 15° C. to about 35° C. with the quench medium; and in step (e) the cooled first liquid effluent is contacted with hydrogen in the presence of said decolorization catalyst at a temperature from about 300° C. to about 415° C. to produce a second effluent having 15 wppm or less sulfur and having an ASTM color of less than 2.5.
Embodiment 3. A process for producing a low color diesel and/or kerosene fuel having a low cloud point, the process comprising: (a) supplying a middle distillate feed having a first cloud point and hydrogen to a reactor having at least one first catalyst bed comprising a first isomerization catalyst and at least one second catalyst bed downstream of the first catalyst bed(s) and comprising a decolorization catalyst; (b) reacting the feed with hydrogen in the presence of the first catalyst in said at least one first catalyst bed at a temperature from about 285° C. to about 420° C. to produce a first liquid effluent having a second cloud point that is at least 10° C. less than that of the first cloud point; (c) cooling the first liquid effluent by about 10° C. to about 20° C. with a quench medium; (d) cascading the entire cooled first liquid effluent to said at least one second catalyst bed; and (e) contacting the cooled first liquid effluent with hydrogen in the presence of said decolorization catalyst at a temperature from about 275° C. to about 400° C. to produce a second effluent having a third cloud point that is at least 10° C. less than that of the first cloud point and having an ASTM color of less than 2.5.
Embodiment 3a. The process of Embodiment 1 for producing a low color diesel and/or kerosene fuel having a low cloud point, wherein the process further comprises: in step (a) the middle distillate has a first cloud point; in step (b) the first liquid effluent has a second cloud point that is at least 10° C. less than that of the first cloud point; in step (c) the first liquid effluent is cooled by about 10° C. to about 20° C. with the quench medium; and in step (e) the second effluent is produced having a third cloud point that is at least 10° C. less than that of the first cloud point and has an ASTM color of less than 2.5.
Embodiment 4. The process of any one of the previous embodiments, wherein said reacting step (b) is conducted at a temperature from about 315° C. to about 400° C. and/or wherein said contacting step (e) is conducted at a temperature from about 300° C. to about 400° C.
Embodiment 5. The process of any one of the previous embodiments, wherein the hydrogen partial pressure in the reactor is between about 400 psig (about 2.8 MPag) and about 1500 psig (about 10.3 MPag).
Embodiment 6. The process of any one of the previous embodiments, wherein the first liquid effluent is cooled in step (c) by about 15° C. to about 35° C., and/or wherein the quench medium is the second effluent and/or unreacted hydrogen gas from said contacting step (e).
Embodiment 7. The process of any one of the previous embodiments, wherein said second effluent has an ASTM color of less than 2.0 and/or comprises less than 2 vol % of 3+ ring aromatic compounds.
Embodiment 8. The process of any one of the previous embodiments, wherein the desulfurization catalyst, the decolorization catalyst, or both comprises nickel and molybdenum.
Embodiment 9. The process of any one of the previous embodiments, wherein the reactor includes a plurality of first catalyst beds, and wherein at least one of said first catalyst beds comprises an isomerization catalyst, such as selected from zeolite beta, ZSM-23, ZSM-48, and mixtures thereof
Embodiment 10. The process of any one of the previous embodiments, wherein said reacting step (b) is conducted at an LHSV from about 0.3 hr−1 to about 1.5 hr−1 or from about 1 hr−1 to about 4 hr−1, and/or wherein said contacting step (e) is conducted at an LHSV from about 5 hr−1 to about 15 hr−1 or from about 4 hr−1 to about 10 hr−1.
Embodiment 11. The process of any one of the previous embodiments, wherein the decolorization catalyst comprises a noble metal, such as platinum, and MCM-41.
Embodiment 12. The process of any one of the previous embodiments, wherein the second cloud point is about 10° C. to about 30° C. less than the first cloud point.
The invention will now be more particularly described with reference to the following non-limiting Examples and the accompanying drawings.
Example 1 was based on pilot plant data which simulated the operation of a ˜30,000 barrel/day reactor with a total of 3 catalyst beds in series in the case of “without color control” operation. For the “color control” operation, a 4th bed can be added to the reactor as the “color control” bed.
A conventional NiMo/Al2O3 desulfurization catalyst was employed in each of the first three catalyst beds using the conditions summarized in Table 2. The same catalyst was employed in the 4th bed in each of the runs (Runs 6 to 10 in Table 2) with color control operation. In each of the color control runs, the effluent from the third desulfurization bed was quenched by about 63° F. (about 35° C.) before entering the inlet of the color control bed. For these simulations, recycled hydrogen gas was used to quench the color control bed.
The feed used for the simulation in this Example had the properties listed in Table 1 below.
The results of the simulation were provided in Table 2 and
The same feed shown in Table 1 and the same reactor employed in Example 1 were used for the pilot plant simulations of Example 2. However, the desulfurization catalyst in Bed-3 was replaced by an isomerization catalyst comprising a Pt-promoted ZSM-48/Al2O3 catalyst that had a relatively high isomerization activity for converting normal paraffins to branched paraffins, such that a reduced cloud point of the diesel fuels resulted. The simulations were based on a cloud point reduction of about 32° F. (about 18° C.) between the feed and the diesel product.
The results are summarized in Table 3 and
In this example, in the pilot plant simulations, the properties of the feed used in this Example are shown in Table 4. For the conditions without color control, the reactor had only one bed filled with the same isomerization catalyst as used in Example 2. For the color control conditions, the reactor had two catalyst beds, namely an isomerization bed and a color control bed, both filled with the same isomerization catalyst used in Example 2.
The results are summarized in Table 5 and
While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.
This application claims the benefit of U.S. Provisional Application No. 61/360,637 filed Jul. 1, 2010.
| Number | Date | Country | |
|---|---|---|---|
| 61360637 | Jul 2010 | US |
