Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – From nonhydrocarbon feed
Reexamination Certificate
1999-10-15
2002-04-16
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
From nonhydrocarbon feed
C585S640000, C585S715000
Reexamination Certificate
active
06372949
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a single stage process for converting oxygenates such as methanol to gasoline and distillate, or olefins, in the presence of unidimensional ten member ring zeolites such as ZSM-22, ZSM-23 and ZSM-48.
BACKGROUND OF THE INVENTION
In order to provide an adequate supply of liquid hydrocarbons for use as synfuels or chemical feedstocks, various processes have been developed for converting coal and natural gas to gasoline, distillate and lubricants. A substantial body of technology has grown to provide oxygenated intermediates, especially methanol. Large scale plants can convert methanol or similar aliphatic oxygenates to liquid fuels, especially gasoline. However, the demand for heavier hydrocarbons has led to the development of processes for increasing the yield of gasoline and diesel fuel by multi-stage techniques.
Methanol is converted to gasoline employing Mobil Oil Corporation's MTG (methanol to gasoline) process. The MTG process is disclosed in the patent art, including, for example, U.S. Pat. Nos. 3,894,103; 3,894,104; 3,894,107; 4,035,430 and 4,058,576. U.S. Pat. No. 3,894,102 discloses the conversion of synthesis gas to gasoline. MTO processes provide a simple means of converting syngas to high-quality gasoline. The ZSM-5 catalyst used is highly selective to gasoline under methanol conversion conditions, and is not known to produce distillate range fuels, because the C
10
+ olefin precursors of the desired distillate are rapidly converted via hydrogen transfer to heavy polymethylaromatics and C
4
to C
8
isoparaffins under methanol conversion conditions.
In order to make diesel fuel using ZSM-5 the MTO process was integrated with the MOGD process. Because the conversion of methanol to diesel with zeolites requires two steps, the Fischer Tropsch process is generally reported to be preferred for the conversion of syngas to distillates.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks, for producing C
5
+ gasoline, diesel fuel, etc. In addition to the basic work derived from ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of a new industrial process, known as Mobil Olefins to Gasoline/Distillate (“MOGD”). This process has significance as a safe, environmentally acceptable technique for utilizing feedstocks that contain lower olefins, especially C
2
to C
5
alkenes.
In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C
2
to C
5
olefins alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. Garwood et al have also contributed improved processing techniques to the MOGD system, as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of lower olefins, especially propene and butenes, over ZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C
5
+ aliphatic and aromatic hydrocarbons. Olefinic gasoline is produced in good yield by the MOGD process and may be recovered as a product or recycled to the reactor system for further conversion to distillate-range products. Operating details for typical MOGD units are disclosed in U.S. Pat. Nos. 4,445,031, 4,456,779, Owen et al, and U.S. Pat. No. 4,433,185, Tabak, incorporated herein by reference.
In addition to their use as shape selective oligomerization catalysts, the medium pore ZSM-5 type catalysts are useful for converting methanol and other lower aliphatic alcohols or corresponding ethers to olefins. Particular interest has been directed to a catalytic process (MTO) for converting low cost methanol to valuable hydrocarbons rich in ethene and C
3
+ alkenes. Various processes are described in U.S. Pat. No. 3,894,107 (Batter et al), U.S. Pat. No. 3,928,483 (Chang et al), U.S. Pat. No. 4,025,571 (Lago), U.S. Pat. No. 4,423,274 (Daviduk et al) and U.S. Pat. No. 4,433,189 (Young), incorporated herein by reference. It is generally known that the MTO process can be optimized to produce a major fraction of C
2
to C
4
olefins. Prior process proposals have included a separation section to recover ethene and other gases from by-product water and C
5
+ hydrocarbon liquids. The oligomerization process conditions which favor the production of C
10
to C
20
and higher aliphatics tend to convert only a small portion of ethene as compared to C
3
+ olefins.
The Gould et al U.S. Pat. No. 4,579,999 discloses an integrated process for the conversion of methanol to gasoline and distillate. In a primary catalytic stage (MTO) methanol is contacted with zeolite catalyst to produce C
2
to C
4
olefins and C
5
+ hydrocarbons. In a secondary catalytic stage (MOGD) containing an oligomerization catalyst comprising medium-pore shape selective acidic zeolite at increased pressure, a C
3
+ olefins stream from the primary stage is converted to gasoline and/or distillate liquids.
The Harandi et al U.S. Pat. No. 4,899,002 discloses a process for the increased production of olefinic gasoline conversion under moderate severity conditions. The product of the olefins to gasoline conversion is passed to an olefin to gasoline and distillate (MOGD) conversion zone for distillate production.
The methanol to olefin process (MTO) operates at high temperature and near 30 psig in order to obtain efficient conversion of the methanol to olefins. These process conditions, however, produce an undesirable amount of aromatics and C
2
olefins and require a large investment in plant equipment.
The olefins to gasoline and distillate process (MOGD) operates at moderate temperatures and elevated pressures to produce olefinic gasoline and distillate products. When the conventional MTO process effluent is used as a feed to the MOGD process, the aromatic hydrocarbons produced in the MTO unit are desirably separated and a relatively large volume of MTO product effluent has to be cooled and treated to separate a C
2
− light gas stream, which is unreactive, except for ethene which is reactive to only a small degree, in the MOGD reactor, and the remaining hydrocarbon stream has to be pressurized to the substantially higher pressure used in the MOGD reactor.
U.S. Pat. No. 5,177,279 to Harandi discloses converting methanol, dimethyl ether (DME) or the like to gasoline and distillate, in a continuous process with integration between major process units. The methanol feed is split between two major process units, with a first portion of the methanol feed being fed to the methanol to olefins unit reactor (MTO) and a second portion of the methanol feed being fed to an olefin to gasoline and distillate unit reactor (MOGD) to produce gasoline or distillate. The process uses shape-selective zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38 and MCM-22. The same zeolite may be used in both process units.
Gasoline and distillate are currently the transportation fuels of choice and are currently manufactured by refining oil. Should the supply of crude oil fail to meet the demand for these transportation fuels, there will be a need to produce them from the more abundant supplies of coal and natural gas. It has long been known that these alternate feedstocks can be gasified and converted to methanol and then to gasoline over acidic, zeolite catalysts. However, a need has remained to directly convert methanol to gasoline and distillate using a zeolite catalyst. The process of the invention is first to demonstrate that such a direct conversion is possible. The ability to produce distillates directly may allow zeolite-based processes to compete better with Fischer-Tropsch for the conversion of coal and methane to synthetic distillate. It is also desirable to find a means to convert methanol directly to high yields of C
4
to C
12
olefins.
SUMMARY OF THE INVENTION
The present invent
Brown Stephen H.
Levin Doron
Shinnar Reuel
Weber William A.
Griffin Walter D.
Hughes G. J.
Mobil Oil Corporation
Nguyen Tam M.
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