Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1997-12-12
1999-06-01
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568698, 518700, C07C 4100, C07C 2700
Patent
active
059089636
DESCRIPTION:
BRIEF SUMMARY
This invention is directed to the preparation of dimethyl ether (DME). The invention concerns in particular a process for the production of fuel grade DME containing small amounts of methanol and water from a H.sub.2 /CO/CO.sub.2 comprising synthesis gas.
Presently, DME is used in the industry for the manufacture of synthetic gasoline. Further industrial applications comprise the use of DME as aerosol propellant and more recently as intermediate in the production of acetic acid.
The major route in the production of DME on industrial scale comprises dehydration of methanol by use of a dehydration catalyst in a fixed bed reactor, and rectification of the product to recover a DME product with high purity as required by the aerosol industry.
From the literature, a number of alternative preparation methods are known including direct synthesis of DME from hydrogen and carbon oxides. Preparation of DME directly from H.sub.2 /CO/CO.sub.2 synthesis gas in a fixed bed reactor of a combined methanol catalyst and dehydration catalyst is disclosed in DD 291,937, U.S. Pat. No. 5,254,596, EP 164,156, U.S. Pat. No. 4,417,000, U.S. Pat. No. 4,177,167, U.S. Pat. No. 4,375,424, GB 2,093,365, GB 2,097,382, U.S. Pat. No. 4,098,809, EP 409,086, GB 2,099,327, DE 3,220,547, DE 3,201,155, DE 3,118,620, DE 2,757,788, DE 2,362,944, DK 6031/87 and DK 2169/89.
The above prior art is mainly directed to preparation and utilization of catalyst compositions being active in preparation of methanol from synthesis gas and dehydration of methanol to DME by the following reaction scheme:
Formation of methanol and DME is, by the above reaction scheme, limited by chemical equilibrium.
The effluent stream from the DME reactor is thus a mixed product stream of DME, methanol and water together with unreacted synthesis gas. A recycle stream of unreacted synthesis is separated from the product stream and recycled to the reactor. Because of a high partial pressure of DME in the product stream, part of produced DME will be removed together with the recycle stream.
To obtain reasonable conversion rates, it is necessary to remove DME from the recycle stream prior to recycling of the stream during direct DME synthesis. DME separation is thereby usually performed by a recycle gas wash.
DE 4,222,655 discloses a DME preparation process, wherein DME in a recycle gas stream from a high pressure separator is separated by washing the gas stream with methanol in a gas washing unit. The washed bottom stream from the washing unit contains DME and CO.sub.2 and is later recombined with the product stream from the high pressure liquid separator. The combined product stream is subsequently washed in a second washing unit with methanol or water for the removal of CO.sub.2 from the product stream
The washed product stream containing DME and methanol in substantially equal amounts is finally subjected to a number of rectification stages to provide a DME product of high purity.
Recent investigations have shown that DME products containing up to 20% by mass methanol and up to 20% by mass water are efficient as fuel in compression ignition engines (Fleisch T., McCarthy C., Basu A., Udovich C., Charbonneau P., Slodowske W., Mikkelsen S. E., McCandless D., A New Clean Diesel Technology, Int. Congr. & Expos., Detroit, Mich., Feb. 27-Mar. 2, 1995).
As used herein above and in the following description, the term "fuel grade DME" refers to DME products with the above composition being useful as fuel in compression ignition engines and gas turbines.
By the known synthesis processes, the amount of methanol and water contained in DME raw product does not meet the specification of fuel grade DME. Excess of methanol in DME raw product produced represents a major drawback in the preparation of fuel grade DME by the known processes. Methanol has in the known processes either to be supplied from process external sources or excess of methanol removed and recycled to the process, which reduces the process efficiency towards the production of DME.
SUMMARY OF THE INVENTION
The main object
REFERENCES:
patent: 5218003 (1993-06-01), Lewnard et al.
Hansen John Bogild
Joensen Finn
Voss Bodil
Holdor Topsoe A/S
Killos Paul J.
Parsa Jafar
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