Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-11-09
2002-12-31
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C502S064000
Reexamination Certificate
active
06500992
ABSTRACT:
BACKGROUND OF THE INVENTION
It is well known that ethers may be prepared by reacting an alcohol with an olefin to form the desired product. The reaction mixture containing catalysts and/or condensing components may be separated and further treated to permit attainment of the desired product specification.
MTBE is being used as a blending component in high-octane gasoline, as the gasoline additives based on lead and manganese have been phased out. Currently, all commercial processes for the manufacture of MTBE are based upon the liquid phase reaction of isobutene and methanol catalyzed by cationic ion-exchange resin (see: Izquierdo, J. F., Cunill, F., Vila M., Tejero J. and Tborra M. Equilibrium constants for methyl tertiary butyl ether liquid-phase synthesis. Journal of Chemical and Engineering Data, 1992, vol. 37, p. 339.; Brockwell, H. L., Sarathy P. R. and Trotta R. Synthesize ethers. Hydrocarbon Processing, 1991, vol. 70, No. 9, p. 133.; Chemical Economics Handbook, Gasoline Octane Improvers. CEH Marketing Report, 1986, p. 543, Stanford Research Institute, SRI International, Menlo Park, Calif.). The isobutene is obtained by the fluid catalytic cracking process, from the isomerization of n-butene and dehydrogenation of isobutane. The methanol is produced from syngas (a mixture of carbon monoxide and hydrogen) obtained from the steam reforming of natural gas. The cationic ion-exchange resins used in MTBE synthesis normally have the sulfonic acid functionality (see: Tejero, J. Journal of Molecular Catalysis, 1987, vol. 42, p. 257; Subraminium and Bhatia, Canadian Journal of Chemical Engineering, 1987, vol. 65, p. 613).
(CH
3
)
2
C═CH
2
+CH
3
OH→(CH
3
)
3
C—O—CH
3
These cationic ion-exchange resins are generally based on polystyrene-divinylbenzene backbone and have a very limited stability range with regard to operating temperatures, with temperatures above 100° C., normally leading to irreversible destruction of the resin and loss of catalytic activity. The catalyst life in commercial operation is about two years. The MTBE synthesis reaction is exothermic, yielding −37.7 kJ mol
−1
of energy.
The detrimental effects of instability of the resin catalyst used in the preparation of MTBE have been discussed in a patent by Takezono and Fujiwara [U.S. Pat. No. 4,182,913]. According to the findings of this study, at higher temperatures, a large quantity of acids is effused from the strongly acidic cation-exchange resin and the deterioration of the catalyst resin is accelerated. Even when the temperature is low, a small quantity of the strong acidic substance is effused into the reaction mixture. When such a reaction mixture containing the acid substance is fed into the succeeding step of unreacted gas separation, so as to separate the unreacted gas by distillation, the decomposition or reverse reaction of the main product is caused to occur, which reduces the yield. In addition, various portions of the apparatus are corroded by the strong acids released. In this reaction, diisobutene and tertiary butyl alcohol (TBA) are the by-products of dimerization of isobutene and reaction of water with isobutene respectively. The amount of diisobutene formed increases with rise in temperature [Chu and Kohl, Industrial and Engineering Chemistry Research, 1987, vol 26, p. 365]. TBA formation is insignificant as long as the feedstocks are thoroughly dried. According to LeChatlier's principle, the reaction equilibrium for MTBE formation is more favorable at lower temperatures, but reaction rate is decreased considerably. Thus current operation temperatures appear to be limited by three factors: (i). resin catalyst instability at temperature above 100° C.; (ii). poor selectivity due to dimerization above 100° C.; and (iii). equilibrium conversion limitation. It is also pointed out that the progress of the reaction over cationic ion-exchange resin is usually complicated by various adsorption and diffusion factors, by swelling phenomenon, and by the variable distribution of the components between the solution and cationic exchanger phase.
The zeolites have a porous structure and are represented by the following general formula;
M
2
O.
x
Al
2
O
3
.y
SiO
2
.z
H
2
O
Where M is an alkali metal or alkaline earth metal cation or organic base cation, n is the valence of the cation and x and y are variables.
In U.S. Pat. No. 5,157,162 to Knifton there is disclosed a process for one-step synthesis of MTBE using tertiary butanol and methanol over a catalyst comprising fluorosulfonic acid modified montmorillonite clay at temperature of about 20° C. to about 250° C.
In U.S. Pat. No. 5,220,078, a process is disclosed for producing MTBE using tertiary butanol and methanol over a catalyst comprising of fluorophosphoric acid modified Y-type zeolite at temperature of about 20° C. to about 250° C.
U.S. Pat. No. 5,300,697 discloses a process for producing MTBE using tertiary butanol and methanol over a catalyst comprising of hydrogen fluoride modified Y-type zeolite at temperature of about 20° C. to about 250° C. All of these processes are limited by the fact that the conversion is low and the selectivity of the reaction for MTBE is quite small.
It would be a substantial improvement in the art if MTBE could be selectively synthesized from isobutene and methanol using a catalyst which allows for rapid conversion of isobutene. In our invention, aluminum fluoride-modified zeolite can be used as an improved and novel catalyst for the selective synthesis of MTBE from isobutene and methanol with high conversion. The accompanying examples demonstrate good yields of MTBE when using the modified zeolites of the instant invention for such a reaction.
SUMMARY OF THE INVENTION
In accordance with certain of its aspects, the novel method of this invention for preparing MTBE from methanol and isobutene comprises reacting methanol and isobutene in the presence of a catalyst comprising an aluminum fluoride-modified zeolite containing at least one metal from Group IIIA of the periodic table. Examples demonstrate particularly the effectiveness of an aluminum fluoride-modified MFI-type zeolite. MFI is the structure type code (allocated by the Structure Commission of the International Zeolite Association) to a number of zeolites having similar topology such as ZSM-5 and silicalite.
DESCRIPTION OF THE INVENTION
Preparation of the product using this invention may be carried out typically by reacting methanol and isobutene in the presence of an etherification catalyst. The etherification is carried out in one-step and the catalyst preferably comprises MFI-type zeolite modified hydrothermally with aluminum fluoride. This important reaction does not restrict the scope of the invention.
The reaction of isobutene and methanol can be represented by the following equation:
Generally the methanol and isobutene coreactants may be mixed in any proportion in order to generate the desired MTBE, but preferably the molar ratio of methanol to isobutene in the reaction mixture should be about 0.1 to 10. In order to achieve maximum selectivity to MTBE and optimum conversion per hour, an excess of methanol in the reaction mixture is desirable. The most preferred methanol-to-isobutene molar ratio is from 1:1 to 5:1.
The synthesis of MTBE according to the reaction given above can also be conducted where the isobutene and methanol reactants are mixed with other C
4
aliphatic and olefinic hydrocarbons such as isobutane, n-butane and n-butene.
The same etherification process may also be applied for the preparation of other alkyl tertiary ethers. For example, the said etherification process may be applied to the reaction of a C
1
-C
4
primary alcohol such as methanol, ethanol, n-propanol and n-butanol with a C
4
-C
6
tertiary olefin, such as for example, tertiary amyl olefin. Reaction of methanol with tertiary amyl olefin would then yield methyl tertiary amyl methyl ether (TAME). Similarly, reactions of ethanol with isobutene would then yield ethyl tertiary butyl ether (ETBE).
Good results were realized usin
Dennison, Schultz & Dougherty
Keys Rosalynd
King Fahd University of Petroleum & Minerals
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