Abstract:
A process for converting an olefin, or a mixture of olefins, to an ether, or a mixture of ethers, which comprises reacting said olefin, or said mixture of olefins, with an alkanol in contact with silicatungstic acid.

Description:
This application is a continuation-in-part application of our Application Ser. No. 000,141, filed Jan. 2, 1979, now abandoned, entitled Novel Etherification Process, which in turn, was a continuation-in-part application of our Application Ser. No. 916,969, filed June 19, 1978, now U.S. Pat. No. 4,175,210, entitled Novel Etherification Process. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a new and useful process for converting an olefin, or a mixture of olefins, to an ether, or a mixture of ethers, which comprises reacting said olefin, or said mixture of olefins, with an alkanol, or a mixture of alkanols, in contact with silicatungstic acid. 
     2. Description of the Prior Art 
     Present commercial methods for reacting an olefin with an alkanol to obtain an ether involve the use of a mineral acid catalyst, such as, for example, sulfuric acid. Unfortunately, such methods have a number of disadvantages. These can include, for example, severe corrosion, acid-handling difficulties, high loss of acid, and the costly step of reconcentrating a diluted acid. More significantly, these methods, being used primarily to convert branched olefins to ethers, do not readily convert a mixture of olefins and, in particular, the unbranched and cyclic olefins to ethers. Consequently, a need exists for a simple, economical process for converting all classes of olefins, or a mixture of olefins, to ethers. Accordingly, the present invention provides a process for converting an olefin, or a mixture of olefins, to an ether, or a mixture of ethers, which comprises reacting said olefin, or said mixture of olefins, with an alkanol in contact with silicatungstic acid. 
     SUMMARY OF THE INVENTION 
     We have discovered a novel process for converting a specific branched olefin, a specific diolefin or mixtures of said specific branched olefins and/or specific diolefins to an ether or a mixture of ethers which comprises reacting said olefin, or said mixture of olefins, with an alkanol, or a mixture of alcohols, in contact with silicatungstic acid. 
     DETAILED DESCRIPTION OF THE PROCESS 
     The branched olefins or diolefins that can be employed herein can be defined by the following structure: ##STR1## wherein R 1  is hydrogen, alkyl or alkenyl; but when R 1  is alkenyl R 2  and R 3  are hydrogen or alkyl; and when R 1  is hydrogen or alkyl, R 2  and R 3  are alkyls; said alkyls and alkenyls having from one to 12 carbon atoms, preferably from one to eight carbon atoms. Especially suitable branched olefins and diolefins that can be used will have from four to 14 carbon atoms, preferably from four to ten carbon atoms. Branched olefins suitable for use herein can include, for example, isobutylene, 2-methylpentene-2, 2-methylbutene-2 and 2,3-dimethyloctene-2. Diolefins suitable for use herein can include, for example, 1,3-pentadiene (piperylene) and 2-methylbutadiene (isoprene). 
     The alkanol that can be reacted with the branched olefins or diolefins defined above can be methanol, ethanol, isopropanol, normal propanol or mixtures thereof. In a preferred embodiment the alkanol is methanol. 
     The ethers produced as a result of the claimed reaction herein can be defined by the following structure: ##STR2## wherein R 1 , R 2  and R 3  are as defined above and n is an integer from 1 to 3, preferably 1. Specific ethers that can be obtained from the claimed reaction include the following: 2-methoxy-2-methylbutane, methyl, t-butyl ether, ethyl t-butyl ether, isopropyl t-butyl ether, 2-methoxy-2-methyloctane, 2-methoxy-2,3-dimethyloctane, 3-methoxy-2,3-dimethyloctane, 3-methoxycyclopentene, 4-ethoxy-pentene-1, 4-propoxyl-pentene-1, 3-methyl-3-methoxy-butene-1, and methyl, sec-pentyl ether. 
     The alkanol can be mixed with the olefin in the present invention in any molar ratio. In general, the molar ratio of alkanol-to-olefin ranges from about 1:1 to about 15:1, preferably from about 2:1 to about 5:1. 
     The silicatungstic acid used as a catalyst herein is old and well-known and can be defined by the formula SiO 2 .12WO 3 . A description of a typical preparation of silicatungstic acid is set forth, for example, in U.S. Pat. No. 3,361,518. The preparation of the deposition of silicatungstic acid on a silica is described, for example, in U.S. Pat. No. 2,982,799. In general, the weight percentage of silicatungstic acid relative to silica in the catalyst is about five to 100 percent, preferably about 30 to about 100 percent. The weight of catalyst per weight of reaction solution can be in the range of about 1:100 to about 1:1, preferably about 1:4 to about 1:40. 
     The present invention is carried out in batch form, that is, in a reactor with all the components therein. The temperature of the process of the present invention is not critical. In general, the temperature ranges from about 50° to about 200° C., preferably from about 80° to about 120° C. In the present invention the preferred pressure is atmospheric pressure (ambient pressure), but the pressure can range from about 0.1 to about 10 atmospheres, (9.646 to about 964.6 kPa) or even higher. The reaction time is also not critical and can be, for example, from about one minute to about 12 hours or even longer, but preferably from about one-half to about four hours. 
     In general, this product is a mixture of unreacted alcohol, unreacted olefin, the desired ether, and, depending on the alkanol used, dimethyl ether, diethyl ether or dipropyl ether. The liquid product is removed from the solid catalyst by filtration or by percolation. The desired ether is separated from the remaining product by any suitable procedure, but preferably by distillation at ambient pressure. Unreacted alcohol and olefin are recovered by distillation and can be recycled. The ether, or mixtures of ethers, obtained herein can be incorporated in gasoline to increase its octane rating. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will be further described with reference to the experimental data. 
     The supported catalyst used in the experiments was prepared as follows: 
     Silicatungstic acid, purchased from Fisher Scientific, was dissolved in water to provide 422.9 grams of solution containing 21.82 percent SiO 2 .12WO 3 . The support was 215.3 grams of Davison silica gel, SiO 2 , grade 70, 10-20 mesh which had been calcined at 538° C. for 10 hours. The support and solution were mixed to give 638.2 grams, net weight, of powder and this was dried at 121° C. for 24 hours to give 310 grams of dry product. This product was calcined at 400° C. for 16 hours to give the catalyst 30 percent silicatungstic acid on silica gel. 
     Several runs were carried out wherein a branched olefin or a diolefin and methanol were combined with 30 percent SiO 2 .12WO 3  on silica (6.2 grams per 61.6 grams of solution) in a liquid phase batch reactor and agitated during the reaction period. The product obtained in each run was distilled to obtain the desired ether, which was analyzed by gas chromotography using a 10-foot 20 percent silicone (fluoro) QF-1 (FS-1265) column programmed from 50° to 195° C. The data obtained are summarized below in Table I. 
     
                                           TABLE I__________________________________________________________________________                                                     Mol                                                     Per                                 Product Analysis,   Cent   Alcohol/                      Weight Per Cent     Conver-   Olefin              Temper-                            Pressure,  Unre- Unre-   sionRun     Molar           Time,                       ature,                            kPa        acted acted   toNo.   Olefin   Ratio        Catalyst   hr. ° C.                            (psig)                                 CH.sub.3 OCH.sub.3                                       CH.sub.3 OCH.sub.3                                             Olefin                                                 Ether                                                     Ether__________________________________________________________________________1  2-methyl-   butene-2   2.5  30% SiO.sub.2 . 12WO.sub.3                   1.0 113  275.6(40)                                 1.2   54.5  18.2                                                 26.1*                                                     50        (6.2 grams per        61.6 grams of        solution)2  1,3-penta-   3.2  unsupported                   1.0 85-92                            275.6(40)                                 2.7   69.9  16.7                                                 6.9**                                                     22   diene     SiO.sub.2 . 12WO.sub.3 . 26H.sub.2 O        (12.3 grams per        66 grams of solu-        tion)3  1,3-penta-   3.2  unsupported                   1.0 67-71                            275.6(40)                                 1.1   67    25  3.0**                                                      8   diene     SiO.sub.2  . 12WO.sub.3 . 26H.sub.2 O                   1.0 90-93                            275.6(40)                                 1.7   65.3  5.1 8.5**                                                     23        (6.0 grams per        60 grams of        solution)__________________________________________________________________________ *2-methoxy-2-methylbutane **methyl secpentenyl ether 
    
     Referring to Table I, Run No. 1 shows that a branched olefin having a double bond and reacted with supported silicatungstic acid had a mol percent conversion of 50. Run No. 2 shows that a diolefin, 1,3-pentadiene, with pure, unsupported silicatungstic acid and an alcohol to olefin molar ratio of 3.2 had an acceptable mol percent conversion of 22. Run No. 3 shows that using a diolefin, 1,3-pentadiene, with silicatungstic acid in a batch system that there was a 8 mol percent conversion after 1 hour at 67°-71° C., but heating an additional hour at 90°-93° C. brought the conversion level to 23 mol percent. 
     Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.