Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1998-06-03
2001-07-31
Geist, Gary (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C502S330000, C502S170000, C204S157410
Reexamination Certificate
active
06268522
ABSTRACT:
The present invention relates to a process for producing a catalyst by UV photoreduction of metal salts on a support, to the catalyst produced in this way and to its use for preparing vinyl acetate.
It is known that vinyl acetate can be prepared in the gas phase from ethylene, acetic acid and oxygen. The supported catalysts used for this synthesis comprise Pd and an alkali metal, preferably K. Further additives used are Cd, Au or Ba. The metal salts can be applied to the support by steeping, spraying on, vapor deposition, impregnation, dipping or precipitation.
In the case of the Pd/Au/K catalysts it has been found to be advantageous to apply the two noble metals in the form of a shell on the support, i.e. the noble metals are distributed only in a zone close to the surface while the regions lying further inside the shaped supported body are virtually free of noble metal. The thickness of these catalytically active shells is generally about 0.1-2 mm. Shell catalysts make it possible to carry out the process more selectively than in the case of catalysts in which the support particles are impregnated through to the core (“fully impregnated”) or make it possible to increase the capacity. Here, the reaction conditions can be kept unchanged compared to the fully impregnated catalysts and more vinyl acetate can be produced for a given reactor volume and time. This makes the work-up of the crude vinyl acetate obtained easier, since the vinyl acetate content of the gas leaving the reactor is higher, which leads to an energy saving in the work-up section. Suitable work-ups are described, for example, in U.S. Pat. No. 5,066,365, DE-34 22 575, DE-34 08 239, DE-29 45 913, DE-26 10 624 and U.S. Pat. No. 3,840,590. On the other hand, if the plant capacity is kept constant, the reaction temperature can be lowered and the reaction can thus be carried out more selectively at the same total output, resulting in raw material savings. This also reduces the amount of the carbon dioxide which is formed as by-product and therefore has to be discharged and consequently reduces the loss of entrained ethylene associated with this discharge. In addition, this method of operation leads to a lengthening of the operating life of the catalyst.
Many documents disclose catalysts and processes for preparing vinyl acetate and processes for their production. These are fully impregnated catalysts or shell catalysts which are generally subjected to a chemical reduction of the noble metal compounds applied to the support to deposit the noble metals on the catalyst support. It has surprisingly been found that the catalytically active metals can also be deposited on the support by photoreduction.
The deposition of a metal on the surface of a support can be carried out from a gas, a liquid or an adsorbed surface layer. Such processes are described for many metals (including Ni, Ag, Au, Pd, Pt, Os and Ir) in the publications “Laser Processing and Chemistry” (Springer-Verlag, Berlin-Heidelberg-N.Y., 1996) and “Chemical Processing with Lasers” (Springer-Verlag, Berlin-Heidelberg-N.Y., 1986) by D. Bäuerle.
In terms of the process of the invention, the deposition of catalytically active metals from adsorbed surface layers is of particular interest.
W. Kräuter, D. Bäuerle, F. Fimberger, Appl. Phys. A 31, 13 (1983) describe the laser-induced deposition of Ni from the gas phase (Ni(CO)
4
) using a krypton ion laser having wavelengths of from 476 to 647 nm. The substrate used was glass or Si. It is pointed out that the commencement of the deposition is attributable to the photoreduction of an adsorbed Ni(CO)
4
layer. This photoreduction is significantly more efficient when ultraviolet (UV) light is used than when visible light is used.
Y. -F. Lu, M. Takai, S. Nagatomo, K. Kato and S. Namba, Appl. Phys. A 54, 51-56 (1992) describe the deposition of Ag from an adsorbed silver acetate layer on a manganese-zinc ferrite substrate. An argon ion laser having a wavelength of 514.5 nm was used for the irradiation.
R. C. Sausa, A. Gupta and J. R. White, J. Electrochem. Soc. 134, 2707-2713 (1987) describe the deposition of Pt onto quartz from an organometallic layer, likewise by irradiation using an argon ion laser. The layer was produced by evaporation of the solvent from a solution containing the organometallic compound (Bright Platinum-05X, Engelhard Corporation) plus varnish-like binders and solvents. The deposited Pt was used as nucleating layer for electroless deposition of copper.
H. Esrom, J. Demmy and U. Kogelschatz, Chemtronics 4, 202-208 (1989) report the use of an Xe
2
* excimer lamp (wavelength 172 nm) for depositing Pd nuclei on aluminum oxide substrates for the electroless deposition of copper. The adsorbed layer used was palladium acetate.
Y. Zhang and M. Stuke, Chemtronics 4, 212-215 (1989) also describe the deposition of Pd from a palladium acetate layer on aluminum oxide ceramics, quartz substrates and silicon wafers. The synchrotron radiation having a wavelength range of 40-400 nm from an electron synchrotron was used for irradiation.
H. Esrom and G. Wahl, Chemtronics 4, 216-223 (1989) describe the photoreduction of palladium acetate by irradiation with light from an ArF excimer laser (wavelength 193 nm) and a KrF excimer laser (wavelength 248 nm). This process was used to deposit Pd nuclei for the electroless deposition of copper on quartz and aluminum oxide ceramics.
A. G. Schrott, B. Braren and R. Saraaf, Appl. Phys. Lett. 64, 1582-1584 (1994) report the photoreduction of PdSO
4
to metallic Pd using an excimer laser. Here too, it could be shown that nucleated substrates (SiO
2
) could be used for electroless deposition of copper.
P. B. Comita, E. Kay, R. Zhang and W. Jacob, Appl. Surf. Sci. 79/80,196-202 (1994) describe the laser-induced coalescence of gold clusters in a thin fluorocarbon layer which has been produced by plasma polymerization. During the production of this layer, gold was embedded by ion sputtering. The polymer matrix was broken up and vaporized by irradiation with an argon ion laser to leave coherent gold structures.
None of these publications discloses a process for producing catalysts.
The photoinduced deposition of noble metals from adsorbed surface layers has been carried out using both UV light sources and light sources which emit visible light. Since the absorption coefficients of the materials used in the process of the invention are significantly higher in the ultraviolet spectral region than in the visible spectral region, correspondingly lower power densities can be employed if UV light sources are used. Since a significantly higher throughput is achieved in this way, the use of UV light sources is preferred. The sources having the shortest wavelengths generally display the highest efficiency and their use is therefore particularly preferred.
The UV radiation sources used for the photoreduction are prior art. They are lamps, lasers or other radiation sources such as synchrotrons or plasma discharger. Lamps which can be used are, in particular, Hg vapor lamps (with strong emission lines at wavelengths of 185 nm and 254 nm) and narrow-spectrum excimer lamps in which the UV radiation arises from the disintegration of excimers or exciplexes such as Kr
2
* (wavelength 146 nm), Xe
2
* (172 nm), KrCl* (222 nm) or XeCl* (308 nm). As high-power UV lasers, use is made of pulse excimer lasers. Here too, the light arises from the disintegration of excimers or exciplexes such as F
2
* (157 nm), ArF* (193 nm), KrF* (248 nm), XeCl* (308 nm) and XeF* (351 nm). It is also possible to use frequency-multiplied Nd-YAG lasers (wavelength 1064 nm
; n=3, 4, 5, . . . ). Further sources of UV radiation are synchrotrons which produce broad-band radiation extending into the X-ray region and the light of a plasma discharge at low pressure.
It is an object of the present invention to provide a process for producing shell catalysts which comprise noble metals, which process does not use chemical reducing agents and allows the shell thickness to be adjusted in a simple way. It is a further object of the pr
Bauerle Dieter
Dingerdissen Uwe
Hagemeyer Alfred
Heitz Johannes
Kuhlein Klaus
Celanese GmbH
Deemie Robert W.
Frommer & Lawrence & Haug LLP
Geist Gary
LandOfFree
Catalyst, process for its production and its use for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst, process for its production and its use for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst, process for its production and its use for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2463193