Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-10-12
2002-12-03
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C525S291000, C525S242000
Reexamination Certificate
active
06489516
ABSTRACT:
The present invention relates to the preparation of ethers. The invention relates in particular to the etherification process for the etherification of an olefinic hydrocarbon feed, according to which process the olefin or mixture of olefins is reacted with an alcohol or mixture of alcohols in the presence of a catalyst, characterized in that a catalyst is used which comprises a grafted polymer fiber, there being functional groups attached to the grafted polymer fiber.
According to such a process, the olefins of an olefinic hydrocarbon precursor, in particular C
8
. . . C
2
olefins, are reacted with a suitable alcohol in the presence of a catalyst in order to produce corresponding ethers. The reactions can be carried out in a stirred reactor, a fixed-bed reactor, a fluid-bed reactor, a tubular reactor or a catalytic distillation column. These ethers are recovered, and they are treated further when necessary in order to prepare engine fuel components.
The invention also relates to the use of the fiber catalyst as an etherification catalyst, which has been grafted and to which grafted polymer fiber there are attached functional groups, as an etherification catalyst.
Tertiary ethers are compounds used as components in gasoline, having many properties which improve the quality of gasoline. Being oxygen-containing compounds they enhance the combustion of the fuel and thus reduce emissions from traffic. Owing to their high octane number they replace in gasoline lead and aromates, which have previously been used for increasing the octane number. By means of etherification it is also possible to decrease the concentration of olefin in gasoline. It is expected that in the future the use of ethers as gasoline components will increase along with emission restrictions and legislation concerning the environment. Methyl-tert-buty ether MTBE and tert-amyl-methyl ether TAME are the most commonly used gasoline ethers, but continuous research is also being carried out into new tertiary ether molecules. It is also expected that in the future new ethers, having molecule sizes greater than have conventional ethers, will gain a foothold on the market.
In the preparation of tertiary ethers there have been used as catalysts, for example, zeolites, heteropolyacids and their salts, silicates and clays modified in different ways, and homogenous acid catalysts. In commercial applications, however, strongly acid cationic ion exchange resins are used almost without exception.
Ion exchange resins are by their basic structure styrene and divinyl benzene copolymers sulfonated with sulfuric acids. The active sites of the catalyst are made up precisely of these hydrogen ions of the acid. The catalyst particles are spherical in shape, and their diameters range typically from 0.3 to 1.0 mm. The sulfonic acid groups are evenly distributed over the entire catalyst particle, and in order for the reaction to take place, the starting materials of the reaction must pass to the active sites of the catalyst.
In ion exchange resin catalyst particles the components must thus first pass from the bulk solution to the catalyst particle. Thereafter the components must further pass under the effect of diffusion to the catalyst's active sites, where the reaction occurs. Also, the reaction products must pass, under the effect of diffusion, out of the pores of the catalyst particle, and further back into the bulk solution.
In spherical porous particles the distances become large. The tertiary olefins used as the precursors in the etherification reaction, as well as the product components, ethers, are by structure branched products. The larger and the more branched the molecules which are being etherified, the more difficult and slower is the passage of the component in the pores of the catalyst particle. In fact, a situation is approached in which the total rate of reaction is determined by the mass transfer, i.e. the rate of diffusion, and no longer by the rate of the chemical reaction.
Also cross-linking, which is an important variable for resin particles in terms of the structure, stiffens the structure of the resin and thereby renders the diffusion of the components in the pores of the catalyst particle more difficult. Resin catalysts are indeed quite complicated in structure. Changes in the conditions easily cause changes in the catalyst structure. Furthermore, the ion exchange resin matrix swells under the effect of polar substances. For example, methanol, which is often used as a starting material in etherification, is strongly polar. The effect of swelling on the number and quality of the active sites in a catalyst is not precisely known, but as the matrix swells the concentration of the polar component increases and the mass transfer of the other components in the pores of the catalyst is probably slowed down further.
Publication EP-A-629 441 describes the preparation of a fibrous polyethylene or polypropylene catalyst. The said catalysts were packed in a net-like fabric before they were used. The publication reports that the object is to prepare a catalyst the active sites of which are easily accessible, but does not discuss in detail the potential uses of the catalyst except that they can be used in organic syntheses.
The object of the present invention is to eliminate the problems of the prior art and to provide an entirely novel process for the preparation of ethers.
The invention is based on the idea that olefins, in particular branched C
8
-C
2
olefins, are reacted with alcohol in the presence of a fibrous catalyst. The catalyst is based on a polyolefin backbone to which a compound which contains reactive groups is grafted, whereafter a functional group is introduced into the fibrous structure. Surprisingly, the catalyst according to the invention has been found to be highly reactive, in particular in the etherification reaction of heavier olefins and methanol. The use of the fiber improves the rate of the reaction as compared with known catalysts, in particular when the molecule size of the ether being produced increases, whereupon the difference from conventional etherification catalysts is considerable.
More precisely, the process according to the invention is characterized by the etherification of an olefinic hydrocarbon feed, according to which process the olefin or mixture of olefins is reacted with an alcohol or mixture of alcohols in the presence of a catalyst, characterized in that a catalyst is used which comprises a grafted polymer fiber, there being functional groups attached to the grafted polymer fiber.
The catalytic properties of the catalyst according to the invention are highly similar to those of conventional ion exchange resins, but owing to its structure its mass transfer properties differ from those of ion exchange resins. The active sites of the catalyst are on the catalyst surface, and mass transfer to the fiber surface is significantly easier than into the pores of a spherical catalyst particle. On the other hand, the catalytically active sulfonic acid groups are located in a side chain of the polymer, and the side chains of the polymer are not cross-linked in the catalyst according to the invention. Thus the mobility of the side chains is greater than in ion exchange resin particles, and the diffusion resistance to the passage of components is, even on account of this fact, less than in ion exchange resins.
When, according to the invention, a fiber catalyst is used in etherification, higher rates of reaction are achieved and thus shorter residence times in the reactors are made possible. Thus it is possible to speed up the etherification process and thereby to increase production. The advantages of the invention are especially prominent when there are produced ethers having more than 6 carbon atoms, and in particular when there are 9-10 carbon atoms. According to the invention, the catalyst can also be used in the reaction in the form of a slurry, since the good filterability of the fibers ensures that the fibers are easily separated from the reaction solution. Even in other respect
Karinen Reetta
Krause Outi
Fortum Oil and Gas Oy
Keys Rosalynd
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