Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1998-03-23
2001-04-17
Reamer, James H. (Department: 1614)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06218583
ABSTRACT:
The present invention relates to a process for the selective production of ethers from alcohols with the use of liquid acid catalysts and more specifically the production of di-alkyl ethers from the corresponding alcohols.
Di-alkyl ethers form, among other things, interesting products with a high cetane number which can contribute to the formulation of diesel gasoils with better performances and reduced emissions.
Whereas various process alternatives are available for improving the quality of gasolines, as far as gas oil is concerned, which is a notably less developed product than gasoline, there seem to be two main ways of obtaining a good quality refinery product: either the crude oil is of a high quality, and the gas oil obtained by distillation is therefore of an excellent quality (necessitating only quite a bland hydrotreatment) or recourse must be made to forced hydrotreatment and Hydrocracking processes on the various fractions.
A third solution is to synthesize, or obtain from other sources, synthetic fuels or fuels of a natural origin which can form high-quality components for reformulated gas oils: examples of the first category are Fischer-Tropsch gas oils (by means of the SMDS process; Tijm P. J. A., ACS August (1994), 1146) and an example of the second category is “bio-diesel” deriving from seed oils (Staat F., Valley E., Chemistry & Industry (1994) 863).
Another particularly interesting group of compounds consists of linear ethers, with a total number of atoms of ≧9, which have a blending cetane number which is more than double the specific value of present gas oils and with extremely advantageous properties at cold temperatures (Pecci G. C., Clerici M. G., Giavazzi F., Ancillotti F., Marchionna M., Patrini R., IX Int. Symp. Alcohols Fuels, (1991), 1, 321; Giavazzi F., Terna D., Patrini R., Ancillotti F., Pecci G. C., Trere R., Benelli M., IX Int. Symp. Alcohols Fuels, (1991)1,327).
In Europe the future specifications on fuel seem to be directed towards diesel with an ever increasing cetane number (especially if regulations are introduced for regulating cold emissions), at the same time reducing the content of sulfur and polyaromatic hydrocarbons.
As linear ethers radically improve the cetane number and properties at cold, they therefore represent very promising additives from the point of view of performance and environment (Marchionna M., Patrini R., Giavazzi F., Pecci G. C., Preprints 212th Nat. Meet. Am. Chem. Soc., Div. Petr. Chem, (1996),41, 585).
In addition to this possible use, alkyl ethers already have a wide variety of industrial uses such as both reaction and extraction solvents, and are also widely applied in the fields of dyes, paints, rubbers, resins and lubricants.
Ethers are generally produced by means of three main synthesis groups:
a) Williamson Synthesis
RX+R′ONa→R′OR+NaX (X=Br, I, . . . )
b) Sum of alcohol based on alkene
ROH+R′CH=CH
2
→ROCH(CH
3
)R′
c) Dehydration of alcohol (bimolecular)
2ROH→ROR+H
2
O
Reactions b) and c) both take place with acid catalysis and are the most widely used syntheses in industrial applications; the sum b) of alcohol with olefin is only possible when the double olefin bond is substituted so as to give a secondary or tertiary carbocation and has found great industrial development for the synthesis of MTBE, ETBE and TAME, all additives with a high octane number for gasoline.
The bimolecular dehydration reaction c) of alcohol on the other hand is particularly useful for obtaining symmetrical ethers from primary alcohols, even if it can also be advantageously used for secondary alcohols; in the latter case it is difficult however to obtain high selectivities to ethers with respect to the olefinic by-product, obtained by monomolecular dehydration
ROH→olefins+H
2
O
Higher selectivities have recently been obtained, in the case of secondary alcohols, by the use of suitable reactors and catalysts (Brown S. H., U.S. Pat. No. 5,444,168, (1995)).
In addition the olefins produced can subsequently be added to the alcohol to give branched ethers with a different structure from the ether produced by bimolecular dehydration; therefore if high selectivities into the above ether are desired, it is necessary to reduce the production of olefins to the minimum.
So far in industrial practice the dehydration of alcohols has been catalyzed with sulfuric acid; this catalyst generally offers quite high selectivities to ether (>80-85%) but has various problems: it is generally used in high concentrations, it is corrosive and in addition, whereas the selectivity to olefins is rather low, heavy products are generally formed (alkyl sulfates, etc.) which tend to blacken the product and complicate the recovery of the acid catalyst.
To overcome these problems, the use of acid cationic resins was proposed in the past (Karpov O. N., Bystrova R. M., Fedoysuk L. G., Zh. Prikl. Khim., 40(1967)219); these catalysts are quite active and selective (yields to di-n-pentylether, DNPE, of about 80% starting from n-pentanol) but there are considerable problems of stability at the reaction temperature: with alcohols and ethers with a boiling point of >120° C. (from n-butanol to higher products), the catalyst is rapidly deactivated.
It is known that also other acid catalysts of the sulfonic type (toluene-sulfonic, fluoro-sulfonic, triflic, etc.) are used in this type of reaction. Their use has also been cited in recent patents but little information has been given on their performance and above all there is no information on the separation and recycling process of the catalyst (Bohlander R., Ridinger R., DE-4438581, (1996); Daute P., Fies, M., DE-19511668, (1996)); in some cases the acid is neutralized by means of treatment with a base.
It has now been found that by operating with a particular process using liquid acid catalysts and using an apparatus for the azeotropic removal of the water (mixed with the alcohol) from the reaction environment, almost total yields to ethers are obtained starting from the corresponding alcohols, also allowing a simple and functional recovery of the catalyst from the reaction product and its recycling to the reaction environment.
The process of the present invention for the production of ethers starting from the corresponding alcohols, in the presence of liquid acid catalysts, essentially comprises the following steps:
a) sending a stream containing C
4
-C
10
alcohols to a reaction zone obtaining a product essentially consisting of ethers and the acid catalyst;
b) feeding the product essentially consisting of ethers and the acid catalyst to an extraction zone with C
4
-C
10
alcohols in order to obtain a stream essentially consisting of ethers and a stream containing said alcohols and said catalyst;
c) sending the non-reacted alcohols and the water formed by the reaction zone to a distillation zone from which an azeotropic alcohol/water stream is obtained together with the residual stream which is sent to the reaction zone;
d) sending the azeotropic alcohol/water stream to a separation zone to separate the alcohol, which is recycled to the reaction zone, from the aqueous stream.
The product consisting of the ethers and acid catalyst, before being sent to the extraction zone (b), is optionally sent to a further extraction zone in which at least part of the aqueous stream separated in (d) is fed in countercurrent.
The C
4
-C
10
alcohols used are alicyclic primary alcohols and can contain cyclic and aromatic groups; aliphatic alcohols however are those particularly preferred.
The alcohols used can also be mixed with each other.
In fact the process claimed is particularly suitable when streams are used coming from hydroformylation processes which contain n-butanol and 2-methylpropanol and/or n-pentanol and 2-methyl-butanol:
When only one aliphatic alcohol is subjected to reaction, symmetrical dialkylethers are obtained with a high selectivity; when, on the other hand mixtures of aliphatic alcohols are treated, mixed ethers are also obtaine
Marchionna Mario
Patrini Renata
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Reamer James H.
Snamprogetti S.p.A.
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