GB2082177A - Process for the Preparation of Octane Boosting Branched Aliphatic Ethers using Solid Super-acid Catalysts - Google Patents

Abstract

A process for the preparation of aliphatic ethers by reacting the corresponding alcohol and/or olefin over a solid superacidic catalyst, for example a perfluoroalkane sulphonic acid or a perfluorinated polymeric sulfonic acid.

Description

SPECIFICATION Process for the Preparation of Octane Boosting Branched Aliphatic Ethers using Solid Superacid Catalysts The invention relates to a process for the preparation of aliphatic ethers by reacting the corresponding alcohol and/or olefin over a superacid catalyst.

Gasoline additives, such as methyl tert-butyl ether (MTBE) have gained significance in recent years. They help to boost octane ratings of gasoline without the use of organometallic or other environmentally unacceptable additives such as carcinogenic aromatics.

Standard methods for the preparation of ethers include dehydration of alcohols (with sulfuric acid or other acid catalysts, such as p-toluenesulfonic acid), reaction of sodium or potassium aicoholates with alkyl (aryl) halides (the so-called Williamson synthesis), or in the case of reactive halides (such as triphenylmethyl chloride), their reaction with alcohols in the presence of pyridine or other bases.

The present invention relates to the discovery of an efficient new process for the preparation of aliphatic ethers, particularly those containing branched chains, as well as mixtures thereof, suitable as gasoline additives providing significantly increased octane ratings.

The process involves the reaction of alcohols alone or in admixture with different alcohols and/or with an olefin over a superacid catalyst to obtain the corresponding ethers or mixed ethers. The invention further includes the reaction of an olefin and water over a superacid catalyst to obtain the corresponding ether.

According to the present invention there is provided a process for producing aliphatic ethers which comprises reacting an alcohol corresponding to the desired ether over a solid superacidic catalyst, or which comprises reacting an olefin and water over the said solid superacid catalyst.

In the case of preparing symmetrical ethers, the reaction of the corresponding alcohol is carried out over a solid superacidic catalyst, such as, for example, a C,0 to C18 perfluorinated alkanesulfonic acid such as perfluorodecanesulfonic acid or perfluorododecanesulfonic acid; a polymeric perfluorinated sulfonic acid such as polymeric trifluoroethylenesulfonic acid; a copolymer of tetrafluoroethylene and trifluoroethylene-sulfonic acid; the acid form of commerciallv available DuPont Nafion resins; or copolymers of perfluorinated ethers and perfluoroalkenesulfonic acids. The process can be carried out batch-wise or in a continuous operation removing ether and water formed in the reaction. By reacting, over the same catalyst, the corresponding alcohols together with olefins mixed ethers are obtained.The process is exemplified by the following reaction scheme showing the preparation of diisopropyl ether or isopropyl terbutyl ether.

When carrying out the latter reaction with tert-butyl alcohol and propylene, a single ether is obtained, whereas reacting isopropyl alcohol with isobutylene, besides the mixed isopropyl tert-butyl ether, diisopropyl ether, the dehydration product of isopropyl alcohol is formed as the predominant product.

When reacting together tert-butyl alcohol and isopropyl alcohol a mixture of tert-butyl isopropyl ether and diisopropyl ether is obtained, but no di-tert-butyl ether. As both ethers have high octane numbers, but differ in their boiling points (see Table below), the use of mixtures of ethers can be also advantageous. On the other hand, as shown in the preparation from tertiary alcohols, the reaction with olefins can be directed to give single products. Further, propylene and isobutylene also form low molecular weight oligomers (dimers, trimers, tetramers) as by-products, which, however, due to their branched nature may be advantageous in mixtures to be used as gasoline additives.

Comparison of the Boiling Range of Gasoline Additive Branched Alkyl Ethers bpOC CH3OC(CH3)3 53-56 CH3CH2OC(CH3)3 73 CH3CH2OCH(CH3)2 63-64 [(CH3)2CH]20 68-69 CH3OC(CH3)2CH2CH3 86 (CH3)3COCH(CH3)2 91-94 The temperature of the process can also be used to control product compositions: Methyl alcohol and isobutylene at 900C give 95% yield of methyl tertbutyl ether (MTBE).

In contrast when reacting at higher temperatures, such as 170--2000, dimethyl ether is formed preferentially.

Ethyl tert-butyl ether is similarly obtained in nearly quantitative yield from tert-butyl alcohol and ethylene.

and is also obtained from ethyl alcohol and isobutylene.

As ethyl alcohol is of increasing significance as a motor fuel, ethyl tert-butyl ether is of significance as an additive readily obtainable from the alcohol and isobutylene.

A further significant aspect of the present invention relates to the discovery that over the superacidic solid catalysts it is possible to react olefins with a limited amount of water (from 0.5 to 1.0 equivalent) to give branched chain ethers directly. An example is the preparation of diisopropyl ether in 50% yield and 95% selectivity from propylene, the balance being isopropyl alcohol.

H20,120 CH3CH=CH2 [(CH3)2CH]2O+(CH3)2CHOH RFSO3H 95% 5% The invention is applicable to the reaction of oleins and alcohols in general but is particularly applicable to the lower olefins and alcohols containing up to six carbon atoms.

The perfluorinated alkanesulfonic acids can be prepared by known methods, such as by the use of electrofluorination in the preparation of perfluorinated alkane-sulfonyl fluorides, which can be hydralyzed to alkane-sulfonic acids, according to the J. Chem. Soc. (London) (1947) pages 2640- 2645, or by the reaction of perfluorinated alkyl iodides (RFI) through their Grignard reaction with sulfur dioxide or addition of sulfonyl halides to perfluorinated olefins.

Trifluoroethylenesulfonic acid polymers can be prepared by known methods, including hydrolysis with water and a strong base of trifluoroethylenesulfonyl fluoride polymers, according to U.S.

3,041,31 7. The hydrolysis results in the formation of the alkali salts of the polymeric sulfonic acid, from which the active acid form is liberated by treatment with HNO3 or H2SO4. Tetrafluoroethyienetrifluoroethylenesulfonic acid co-polymers can be similarly prepared according to U.K. Patent No.

1,184,321.

Commercial DuPont Nafion brand ion membrane resins, such as Nafion 501 are perfluorinated polymers having sulfonic acid groups in the amount of about 0.01 to 5 mequiv/gram catalyst. The polymer is the potassium salt. Such polymers can be prepared as disclosed in Conolly et al. U.S. Patent No. 3,282,875 and Cavanaugh et al. U.S. Patent No. 3,882,093 by polymerizing perfluorinated vinyl compounds, or by copolymerizing the corresponding perfluorinated vinyl ethers with perfluoroethylene and/or perfluoro-alpha-olefins (U.S. Patent No. 4,401,090). The commercial Nafion resins can be converted into their acid form by repeated treatment with aqueous strong acids, such as nitric or sulfonic acid.

A superacid is an acid having an Ho value on the Hammett scale in excess of -1 such as -25.

Thus weaker acids such as sulfuric acid (Ho of-li) and HF (Ho of -10) are excluded.

The branched chain aliphatic ethers obtainable by the described new processes disclosed in this invention are of significant practical use as efficient and inexpensive additives to gasoline or alcohol fuels providing significant increase of octane number.

The present invention is illustrated by the foilowing Examples, which are not to be considered to limit the scope of the invention in any manner.

Example 1 1 0g of perfluorododecanesulfonic acid (C12F2sSO3H) was deposited onto 90g of porous alumina.

20g of this catalyst was changed into a glass tube reactor of 1 80mmx 1 Omm dimension and 20g/hr isopropyl alcohol was reacted over the catalyst at 1 1 OOC. A 21 % conversion to disopropyl ether with 90% selectivity was obtained.

Example 2 50g of commercial Nafion-K resin (potassium salt of the DuPont Company's ion-membrane material) was refluxed in 250ml of deionized water for two hours. After filtering, the resin was treated with 100ml of 20% to 25% nitric acid for 5 hours at room temperature. Filtering was followed by a three times repeat of the nitric acid treatment. Finally, the resin (Nafion-H) was washed to neutrality with deionized water and dried in a vacuum drying over at 1050C for 24 hours.

1 5 g of the above activated Nafion-H catalyst was reacted with 20 grams/hr of isopropyl alcohol under the conditions of Example 1 giving diisopropyl ether with 26% conversion and 92% selectivity.

Example 3 A reaction was carried out as described in Example 2 but reacting a mixture of 1 5g/hr of tertbutyl alcohol and 8g/hr propylene at 1100. A 1 6% conversion to tert-butyl isopropyl ether was obtained.

Example 4 A reaction was carried out as described in Example 1, but with a mixture of 1 6g/hr of methyl alcohol and 20g/hr isobutylene at 900. Methyl tert-butyl ether was obtained with 62% conversion and 81 % selectivity.

Example 5 A reaction was carried out as in Example 4, but in a batch-wise fashion in a stainless steel pressure autoclave with a reaction time of 2 hours. 95% conversion to methyl tert-butyl ether was obtained with 90% selectivity.

Example 6 1 0g of perfluorodecanesulfonic acid (CloF21SO3H) was deposited on 75g of porous chromosorb (Registered Trade Mark). 1 0g of this catalyst was charged into a stainless steel reactor together with 21 g (0.1 5mol) propylene and 4.5g water and reacted at 120 C for 24 hours. A 42% conversion to diisopropyl ether was obtained with 91% selectivity.

Example 7 A reaction was carried out as under Example 6, but with the use of Nafion-H catalyst. A 50% conversion to diisopropyl ether with 95% selectivity was obtained.

Example 8 A fixed bed stainless steel catalytic tube reactor of 1 50x 1 Omm dimension was charged with 1 Og of polymeric trifluoroethylenesulfonic acid catalyst. Propylene 1 Og/hr and water 2g/hr were passed over the catalyst at 500 psig and 1000C. Diisopropyl ether was obtained with 16% propylene conversion and 81% selectivity.

Example 9 A reaction was carried out as in Example 8, but using tetrafluoroethylenetrifluoroethylenesulfonic acid polymer as the catalyst. Diisopropyl ether was obtained with 13% propylene conversion and 80% selectivity.

Claims (8)

Claims

1. A process for producing aliphatic ethers which comprises reacting an alcohol corresponding to the desired ether over a solid superacidic catalyst, or which comprises reacting an olefin and water over the said solid superacid catalyst.

2. A process according to Claim 1, in which an olefin is reacted over the catalyst together with the alcohol.

3. A process according to Claim 1 or 2, in which the alcohol is a lower alcohol.

4. A process according to Claim 1,2 or 3, in which the olefin is a lower olefin.

5. A process according to any one of the preceding claims, in which the solid superacid is a perfluoro-alkanesulfonic acid or a perfluorinated polymeric sulfonic free acid.

6. A process according to any one of the preceding claims, in which the amount of water is between about 0.5 and 1 equivalents.

7. A process according to Claim 1 substantially as hereinbefore described in any one of the foregoing Examples 1 to 9.

8. An aliphatic ether whenever prepared by a process as claimed in any one of the preceding claims,