Coating processes – Coating by vapor – gas – or smoke – Metal coating
Reexamination Certificate
1997-01-10
2002-07-16
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Metal coating
C427S253000, C427S383700, C208S047000, C208S049000, C208S0520CT, C502S035000, C502S516000
Reexamination Certificate
active
06419986
ABSTRACT:
FIELD OF INVENTION
The invention is a method of removing reactive metal from at least a portion of a metal-coated hydrocarbon conversion reactor system, so that the reactive metal does not deactivate the hydrocarbon conversion catalyst. It is especially applicable to catalytic reforming processes using halided catalysts.
BACKGROUND AND RELEVANT REFERENCES
Platinum L-zeolite catalysts for low-sulfur reforming were invented in the early 1980's. After about 10 years of intensive effort, and much research, low sulfur reforming was commercialized in the early 1990's. Progress toward commercialization required many discoveries. Two key discoveries were the criticality of ultra-low sulfur levels in the feed, and the impact of these ultra-low sulfur levels on reactor metallurgy, i.e., the discovery of the need to prevent coking, carburization and metal dusting. A preferred way to prevent coking, carburization and metal dusting utilizes a metal protective layer, especially one comprising tin.
While commercialization of ultra-low sulfur reforming was being pursued, a second generation of sulfur-sensitive platinum L-zeolite catalysts were being developed. These new catalysts are halided. They allow operations at higher severity, tolerate a wide range of hydrocarbon feeds, have high activity and long life.
Recent attempts to utilize this second generation of catalysts for ultra-low sulfur reforming resulted in an unexpected and undesired reduction in catalyst activity. After much research and experimentation, it was discovered that the catalyst had been partially poisoned by the metal of the protective layer specifically by tin; which had been used to prevent carburization and metal dusting of the reactor system surfaces. Somehow, some of this tin had migrated and deposited on the catalyst. In contrast, when conventional platinum L-zeolite catalysts are used for ultra-low sulfur reforming in a tin-coated reactor system, neither tin migration nor catalyst deactivation due to tin migration are observed. The cause of these problems has now been traced to low levels of volatile hydrogen halides that, under certain conditions, evolve from the catalysts themselves. These halides interact with reactive tin and can deactivate the catalyst.
Therefore, one object of the present invention is to reduce catalyst deactivation by metal derived from a metal-coated reactor system. Another object of the invention is to reduce catalyst contamination from a freshly metal-coated reactor system which would otherwise result in catalyst deactivation. This new process will also improve the reproducibility of catalytic operations, since catalyst activity and life can be better predicted.
The use of metal coatings and metal protective layers, especially tin protective layers, in hydrocarbon conversion processes is known. These layers provide improved resistance to coking, carburization and metal dusting, especially under ultra-low sulfur conditions. For example, Heyse et al., in WO 92/1856 coat steel reactor systems to be used for platinum L-zeolite reforming with metal coatings, including tin. See also U.S. Pat. Nos. 5,405,525 and 5,413,700 to Heyse et al. Metal-coated reactor systems are also known for preventing carburization, coking and metal dusting in dehydrogenation and hydrodealkylation processes conducted under low sulfur conditions; see Heyse et al., in U.S. Pat. No. 5,406,014 and WO 94/15896. In the '014 patent, Example 3 shows the interaction of a stannided coupon with hydrocarbons, methyl chloride and hydrogen at 1000 and 1200° F. The coupon was stable to methyl chloride concentrations of 1000 ppm at 1000° F., showing that the tin coating is stable to halogens at reforming temperatures.
The use of catalysts treated with halogen-containing compounds for catalytic reforming is also known. See, for example U.S. Pat. No. 5,091,351 to Murakawa et al. Murakawa prepares a Pt L-zeolite catalyst and then treats it with a halogen-containing compound. The resulting catalyst has a desirable long catalyst has a desirable long catalyst life and is useful for preparing aromatic hydrocarbons such as benzene, toluene and xylenes from C
6
-C
8
aliphatic hydrocarbons in high yield. Other patents that disclose halided L-zeolite catalysts include U.S. Pat. Nos. 4,681,865, 4,761,512 and 5,073,652 to Katsuno et al.; U.S. Pat. Nos. 5,196,631 and 5,260,238 to Murakawa et al.; and EP 498,182 (A).
None of these patents or patent applications disclose any problems associated with the metal-coated reactor systems. They neither teach the desirability nor the need for removing metal from the reactor system, especially not prior to catalyst loading or prior to hydrocarbon processing.
Indeed, the art teaches the advantages of combining one of the preferred coating metals—tin—with a reforming catalyst, specifically with a platinum L-zeolite catalyst. U.S. Pat. No. 5,279,998 to Mulaskey et al., teaches that activity and fouling rate improvements are associated with treating the exterior of the platinum L-zeolite catalyst with metallic tin particles having an average particle size of between 1 and 5 microns (tin dust). For example, Table I of the Mulaskey patent shows improved catalyst performance when metallic tin dust is combined with a platinum L-zeolite catalyst that has been treated with fluoride according to the process of U.S. Pat. No. 4,681,865.
In light of the above teachings, we were surprised to find a decrease in catalyst activity upon reforming in a freshly tin-coated reactor system using a halided platinum L-zeolite catalyst. (See Example 5 below.)
Tin-coated steels are known to be useful for a variety of purposes. For example, surface coating compositions, known as stop-offs or resists, are temporarily applied to portions of a steel tool surface to shield them during case hardening. For example, in U.S. Pat. No. 5,110,854 to Ratliff the stop-off is a water-based alkyd resin containing tin and titanium dioxide.
It is also known that reacting tin with steel at elevated temperatures results in coated steels having surface iron stannides. Aside from hydrocarbon processing, as discussed above, coated steels have been used in applications where steels with hard and/or corrosion resistant surfaces are desired. For example, Caubert in U.S. Pat. No. 3,890,686 describes preparing mechanical parts having coatings consisting of three iron stannides to increase the resistance of these parts to seizing and surface wearing. In Example 2, a piece of coated steel is prepared by heating the steel of 1060° F. in the presence of tin chloride (SnCl
2
) and hydrogenated nitrogen for 1.5 hours.
It is also known to treat tin-coated steels to further modify their properties. For example, Galland et al., in U.S. Pat. No. 4,105,950 teach that hot dipping stainless steel into molten tin results in two intermetallic stannide layers, an outer FeSn layer and inner layer which comprises a mixture of Fe (Cr,Ni,Sn) and FeSn
2
. The inner layer has a greater hardness. They teach that the outer layer can be removed by grinding, by reacting with 35% nitric acid containing a polyamine, or by electrochemical means, leaving behind the harder and more corrosion resistant inner layer.
Another example where tin-coated steel is modified in Carey II, et al., in U.S. Pat. No. 5,397,652. Here, tin-coated stainless steels are taught as roofing meterials and siding, especially for use in marine or saline environments. Carey II, et al. teach that hot-dipping stainless steel into molten tin results in a bonded tin coating and an underlying intermetallic alloy of chromium-iron-tin. They teach treating the coated steel with an oxidizing solution (aqueous nitric acid) to obtain a uniformly colored stainless steel. The nitric acid preferentially reacts with the bonded tin coating leaving behind the uniformly colored intermetallic alloy. None of these patents on coated steels are concerned with hydrocarbon conversion processing.
None of the art described above is concerned with the problems associated with reactive metals derived from metal coatings, such as ti
Chen Hong Chiu
Hagewiesche Daniel P.
Holtermann Dennis L.
Wilson Charles R.
Wolpert Richard M
Chen Bret
Chevron Phillips Chemical Company IP
Meeks Timothy
Pennie & Edmonds LLP
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