Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Gas or vapor treating
Reexamination Certificate
2000-01-13
2002-04-30
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Gas or vapor treating
C502S038000, C502S052000, C502S056000, C502S022000, C502S029000
Reexamination Certificate
active
06380119
ABSTRACT:
The present invention relates to a process for regenerating a zeolite catalyst, in particular a zeolite catalyst which was used in the epoxidation of olefins with a hydroperoxide, in particular of propylene with hydrogen peroxide. The regeneration is carried out by controlled combustion of the predominantly organic coatings responsible for the deactivation in an inert gas atmosphere which contains exactly defined amounts of oxygen or oxygen-donating substances.
When carrying out reactions in the presence of catalysts, in particular in the presence of catalysts which have micropores, such as titanium silicalite having, for example, the MFI structure or titanium-containing zeolites having, for example, the BEA structure, the catalysts may be deactivated by, in particular, organic coatings. The major part of these organic coatings can be removed by calcination of the catalyst or by washing with solvents (M. G. Clerici, G. Bellussi and U. Romano, J. Catal 129 (1991), 159-167).
Furthermore, EP-A 0 743 094 describes the regeneration of a titanium-containing molecular sieve which was used in the catalysis of an oxidation reaction, for example the epoxidation of an olefin with hydrogen peroxide or with another active oxygen compound. According to his publication, the regeneration of the deactivated catalysts which is described there is carried out by combustion by means of calcination of the organic coatings present thereon using molecular oxygen, a calcination temperature of more than 150° C. and less than 400° C. being used.
Moreover, JP-A 0 31 14 536 describes the regeneration of a titanium silicalite epoxidation catalyst by combustion of the coatings at from 400 to 500° C. or by washing of the catalysts at temperatures above the epoxidation temperature. The solvents stated there are water, alcohols, ketones, aliphatic and aromatic hydrocarbons, halogen-containing hydrocarbons, esters, nitriles or acids.
Furthermore, DE-A 44 25 672 mentions the regeneration of a catalyst used for epoxidation, in particular of propylene, by combustion thereof in an oxygen-containing atmosphere at elevated temperatures.
However, the prior art regeneration processes have some aspects which are undesired in practice, in particular where catalysts containing micropores, for example the titanium silicalites used in particular in epoxidation, are to be regenerated.
Some of the catalysts preferably used for epoxidations, for example a titanium silicalite having the MFI structure or a titanium silicalite having the BEA structure, have micropores with diameters of from about 0.5 to about 0.6 nm of from about 0.6 to about 0.7 nm. In both cases, however, it is impossible completely to remove oligomeric or even polymeric byproducts of the reactions catalyzed by these catalysts, in particular of the epoxidation, merely by washing with solvents at elevated temperatures.
The above statements are applicable in particular to catalysts having micropores but, depending on the molecular weight and on the dimensions of the oligomeric or polymeric byproducts forming during the reaction, are also applicable to catalysts having mesopores and/or macropores.
However, if it is intended to remove these organic coatings completely, this is possible only by combustion thereof with oxygen or with oxygen-donating substances. The regeneration of a highly selective zeolite catalyst having a specific structure by combustion at elevated temperatures is however difficult, since complete or local overheating of the catalyst may lead to loss of selectivity as a result of the partial or, in extreme cases, complete destruction of the structure inherent in the zeolite catalysts, which destruction occurs with such overheating. If, in order to avoid such overheating, the combustion is carried out at below 400° C., the coatings are not completely removed during relatively short calcination times. Complete removal of the coatings by very long calcination at below 400° C. is however of no commercial interest.
It is an object of the present invention to provide a process for regenerating a zeolite catalyst at elevated temperatures, which ensures complete removal of the organic coatings even during relatively short calcination times. The calcination should take place in a controlled manner so that local overheating and hence irreversible damage to the catalyst, which leads to loss of selectivity, to increased formation of byproducts and hence to substantially more rapid deactivation of the regenerated catalyst when used again, is avoided.
We have found that this object is achieved by the novel process.
The present invention therefore relates to a process for regenerating a zeolite catalyst which comprises the following stages (I) and (II):
(I) Heating a partially or completely deactivated catalyst to 250-600° C. in an atmosphere which contains less than 2% by volume of oxygen and
(II) treating the catalyst at from 250 to 800° C., preferably from 350 to 600° C., with a gas stream which contains from 0.1 to 4% by volume of an oxygen-donating substance or of oxygen or of a mixture of two or more thereof.
Preferably, the novel process comprises a further stage (III):
(III) Treating the catalyst at from 250 to 800° C., preferably from 350 to 600° C., with a gas stream which contains from more than 4 to 100% by volume of an oxygen-donating substance or of oxygen or of a mixture of two or more thereof.
There are no particular restrictions with regard to the zeolite catalysts regenerated in the present process.
Zeolites are known to be crystalline aluminosilicates having ordered channel and cage structures which possess micropores which are preferably smaller than about 0.9 nm. The network of such zeolites is composed of SiO
4
and AlO
4
tetrahedra which are linked by common oxygen bridges. An overview of the known structures is given, for example, in W. M. Meier, D. H. Olson and Ch. Baerlocher, Atlas of Zeolite Structure Types, Elsevier, 4th Edition, London 1996.
Zeolites which contain no aluminum and in which some of the Si(IV) in the silicate framework has been replaced by titanium as Ti(IV) are also known. These titanium zeolites, in particular those having a crystal structure of the MFI type, and possibilities for their preparation are described, for example in EP-A 0 311 983 or EP-A 405 978. In addition to silicon and titanium, such materials may also contain additional elements, for example aluminum, zirconium, tin, iron, cobalt, nickel, gallium, boron or small amounts of fluorine. In the zeolite catalysts preferably regenerated by the novel process, some or all of the titanium of the zeolite may be replaced by vanadium, zirconium, chromium or niobium or a mixture of two or more thereof. The molar ratio of titanium and/or vanadium, zirconium, chromium or niobium to the sum of silicon and titanium and/or vanadium and/or zirconium and/or chromium and/or niobium is as a rule from 0.01:1 to 0.1:1.
It is known that titanium zeolites having the MFI structure can be identified by particular X-ray diffraction patterns and additionally by an infrared (IR) skeletal vibration band at about 960 cm
−1
and thus differ from alkali metal titanates or crystalline and amorphous TiO
2
phases.
Preferably Ti, V, Cr, Nb and Zr zeolites, particularly preferably Ti zeolites, and especially Ti zeolites as used in particular for the epoxidation of olefins, are regenerated by the novel process.
Specific examples are Ti, V, Cr, Nb or Zr zeolites having the pentasil zeolite structure, in particular the types allocated by X-ray analysis to the BEA, MOR, TON, MTW, FER, MFI, MEL, CHA, ERI, RHO, GIS, BOG, NON, EMT, HEU, KFI, FAU, DDR, MTT, RUT, LTL, MAZ, GME, NES, OFF, SGT, EUO, MFS, MCM-22 or MFI/MEL mixed structure and ITQ-4, those having the MFI structure, BEA structure, MEL structure, ITQ-4 or MFI/MEL mixed structure being regarded as particularly preferred. Zeolites of this type are described, for example, in the above-mentioned publication by W. M. Meier et al.
Particularly preferred catalysts are specifically the Ti-containing catalysts, which are referred to in g
Grosch Georg Heinrich
Harder Wolfgang
Möller Ulrich
Rieber Norbert
Walch Andreas
Griffin Steven P.
Ildebrando Christina
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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