Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – From nonhydrocarbon feed
Reexamination Certificate
2000-07-25
2002-06-04
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
From nonhydrocarbon feed
C585S638000, C585S640000
Reexamination Certificate
active
06399844
ABSTRACT:
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for converting methoxy compounds, like methanol or dimethyl ether, into olefins, preferably ethylene, by contacting such methoxy compounds over a series of fixed catalyst beds.
2. Description of the Related Art
A new family of molecular sieve catalysts has been developed by Union Carbide workers. See U.S. Pat. No. 4,499,327. These silico alumino phosphate molecular sieve catalysts have demonstrated a high activity for converting methoxy compounds like methanol and/or dimethyl ether into olefin mixtures. Unlike earlier ZSM-5 catalysts which convert methoxy compounds to liquid grade hydrocarbons of a gasoline range (methanol to gasoline; or MTG), these new molecular sieve catalysts for conversion of methanol to olefins are more selective to the conversion of methanol to C
2-4
olefins (MTO) and produce a lower concentration of higher carbon number alkylate and aromatic by-products. Based upon the carbon content of the feedstock, these new methanol to olefin (MTO) catalysts produced high yields of C
2-4
olefinic materials.
Even so, with the new (MTO) catalysts, the formation of aromatics (C
6+
) is not completely suppressed. Because of the molecular size of aromatic by-products, once formed, they can not readily pass through the pore structure of the Zeolite catalyst. Such aromatics as are formed, which are thus effectively trapped against further free passage through the catalyst pores, are believed to undergo further reactions to ultimately yield coke. Hence, even with the new (MTO) catalyst, if used in a fixed bed operation, such catalyst has a very short active life before regeneration of the catalyst becomes necessary. Time on stream (TOS) of a fixed bed of MTO catalyst was initially measured in hours only. Such a short operational time on stream, obviously, is not acceptable as a basis for a commercial operation; because of the need to regenerate the catalyst after its activity has deteriorated. For safety reasons, when a catalyst reaction vessel is taken out of service for regeneration of the catalyst therein, the process shutdown period must be much longer than the few hours needed to simply regenerate the catalyst.
Many factors have been considered in an attempt to prolong the useful catalyst life of the new MTO catalyst for use in a fixed bed operation. Lowering of the partial pressure of the methoxy compound in contact with the MTO catalyst was examined as one possible means of prolonging the useful active catalyst life. Although lowering the partial pressure of methanol over the MTO catalyst was found to prolong the period of time for which the MTO catalyst was active, it was also discovered that the rate at which methoxy compound converted over the MTO catalyst was also reduced as a function of reducing partial pressure of the methoxy compound in essentially an inverse relationship to the period of time by which the MTO catalyst activity was prolonged. The end result of this inverse relationship is that the total amount of olefin product make during the increased TOS (time on stream) of the catalyst remained essentially unchanged. That is, the total quantity of olefin product made between catalyst regenerations (the TOS period) remains essentially the same whether the time on stream (TOS) was short because of a high initial partial pressure of the methanol feed or long because of a low initial partial pressure of the methanol feed. In other words, the degree to which the methanol feed to a one pass single fixed bed of MTO catalyst was diluted by a non-reactive component, such as steam or a non-reactive hydrocarbon, was found to be an ineffective parameter by which to increase or control the final yield of olefin product during the on steam operational time of the MTO catalyst.
While market conditions may vary at any particular point in time, on average ethylene is a much more valuable product than other higher olefins like propylene or butylene. Hence, it is of a long run concern that the yield of ethylene as based upon carbon feed input is maximizable compared to that input carbon which is diverted into higher olefins like propylene or butylene. With the new MTO catalyst, it has been demonstrated that ethylene is the product olefin first made upon initial contact of methoxy compound with the catalyst, but that on further contact of the ethylene make with the catalyst, the ethylene initially made is converted into other olefins like propylene and/or butylene. In a one pass process, wherein methoxy compound is passed only one time over a fixed catalyst bed at a high conversion rate of the methanol, the by-reactions which deplete the initial ethylene make by conversion of same to other higher olefins become most pronounced at high methanol conversion levels; that is when methanol conversion exceeds about 90%.
Given the so demonstrated short TOS of the new MTO catalyst at high conversion rates that equate to acceptable olefin yield rates, when considered for fixed bed operations, an inclination would be to use a high MTO catalyst inventory—much more than the minimum quantity of MTO catalyst required for an acceptable methanol conversion—so that upon aging of the MTO catalyst mass from the inlet to outlet side of the reaction vessel there will remain a MTO catalyst zone of sufficient activity to continue operation at acceptable conversion rates of the feed MeOH. That is, the mass-volume of the MTO catalyst inventory undergoes a progressive volume zone aging which proceeds from the feed input, wherein methoxy compound partial pressure is at its highest level, and thus coking is at its highest rate, to that point within the catalyst mass volume inventory at which there is essentially no methoxy compound partial pressure because of its essentially complete conversion at this point within the catalyst mass (about 90% of methanol conversion), after which no significant coking occurs in the catalyst mass after this point. This zone of aging catalyst moves progressive through the fixed catalyst bed and as the leading edge of this zone becomes catalytically inactive due to its high coking level, until such time as that zone of catalyst closest to the product outlet side of the reactor has, through the width of its mass of this zone, undergone such aging/coking as to reduce its activity below acceptable levels. At this point in time, a fixed bed reactor of the MTO catalyst would be taken out of operation and its entire inventory of MTO catalysts would have to be regenerated to restore its activity. This, today, is the only expedient for utilizing the new MTO catalyst in a fixed bed operation such that the reactor could possibly operate for an acceptable period of time at practical olefin production rates. However, as one will readily appreciate, there is a high capital cost involved in this expedient for extending TOS. Further, in this single bed-one pass-high conversion-mode of operation there is no capability for controlling the degree of methanol conversion—the degree of conversion will always by high, ≧95%, and typically about 99%. As previously noted, at such high degrees of methanol conversion significant amounts of the ethylene make is diverted by side reactions into production of propylene and/or butylene.
Further, with fresh, or freshly regenerated catalysts, as would be the case with the regeneration of that mass of MTO catalyst within a one pass single fixed bed, the initial ethylene production of the regenerated MTO catalyst is very low. It was found that as a reasonable amount of coke is deposited on the catalyst, the ethylene yield is actually increased substantially. A. N. Rene Bos et al. Conversion of Methanol to Lower Olefins,
Ind. Engl. Chem. Res
., 1995 Vol. 34, pp. 3808-3816. The coke formed at high temperature on such MTO catalysts is most likely due to the formation of small amounts of aromatics which, becoming entrapped in the s
Akin Gump Strauss Hauer & Feld L.L.P.
Griffin Walter D.
Van Dijk Technologies, Inc.
LandOfFree
Fixed bed process for conversion of methanol with silico... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fixed bed process for conversion of methanol with silico..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fixed bed process for conversion of methanol with silico... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2960473