Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-07-26
2001-10-09
Lambkin, Deborah C. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06300506
ABSTRACT:
The present invention relates to a continuous process for the preparation of epoxides.
More specifically, the present invention relates to a continuous process for the preparation of propylene oxide by direct epoxidation of propylene with hydrogen peroxide, or compounds capable of producing hydrogen peroxide under the reaction conditions, in a solvent medium, in the presence of a catalytic system consisting of a zeolite containing titanium and a buffer system with a pH controlled within values of 5.5 to 8.0, consisting of a nitrogenated base and a salt thereof with an organic or inorganic acid.
Epoxides, or olefin oxides, are intermediates useful for the preparation of a wide variety of compounds. For example epoxides can be used for the production of glycols, condensation polymers such as polyesters, or for the preparation of intermediates useful in the synthesis of polyurethane foams, elastomers, seals and similar products.
The use of zeolitic compounds with an MFI structure containing titanium atoms (TS-1) as catalysts in the direct epoxidation reactions of olefin compounds with hydrogen peroxide, is known in literature (EP-100,119).
However, the acidity which characterizes these catalysts contributes, together with the possible acidity present in the homogeneous phase, to catalyzing consecutive solvolitic reactions on the epoxide with the opening of the ring. This leads to an increase in production costs for both the decrease in yield to epoxide and for the separation of the by-products formed.
To overcome these disadvantages, processes have been proposed in the art for improving the catalytic performances of these zeolitic compounds by appropriate activation treatment.
For example, the patent EP-230,949 describes an epoxidation process which uses, as catalyst, a titanium silicalite treated, before or during the epoxidation reaction, with a neutralizing agent selected from organic derivatives of silicon of the type X—Si(R)
3
or hydrosoluble substances deriving from cations of group I and II with a different base strength.
The patent EP-712,852 relates to an epoxidation process of olefins in the presence of titanium-silicalite which uses as neutralizing agent a non base salt selected from lithium chloride, sodium nitrate, potassium sulfate and ammonium phosphate. Under these conditions the maximum selectivity obtained is in the order of 93%.
The patent U.S. Pat. No. 5,675,026 describes an epoxidation process which uses as catalyst a titanium-silicalite treated, before or during the reaction, with a neutral or acid salt, selected from Na
2
SO
4
, (NH
4
)
2
SO
4
, NH
4
NO
3
or NaH
2
PO
4
.
Operating according to these known processes, propylene oxide is obtained with a good yield and selectivity.
These processes, however, have disadvantages deriving from the fact that these catalytic systems have a short duration of the catalytic cycle and consequently require frequent regeneration.
This creates considerable problems from both a technical and economic point of view, above all when the epoxidation process is carried out in continuous.
In fact, a lowering in the production yield of the epoxide and a reduction in the catalytic activity during the subsequent regeneration phases, have been observed.
It has now been found that it is possible to overcome the disadvantages of the known art described above by means of the process of the present invention, which is based on the use of a buffer system with a pH controlled within the values of 5.5 and 8.0 and which is such that the pH of the reaction system ranges within the above values.
The use of this buffer system has substantial advantages, and in particular:
(i) it allows the catalytic activity to be kept stable over period of time, reducing the frequency of the regeneration cycles of the catalyst to the minimum; and
(ii) it allows the preparation of epoxides with high yields and selectivities.
In accordance with this, the present invention relates to a continuous process for the preparation of epoxides by direct oxidation of an olefin with hydrogen peroxide, or compounds capable of producing hydrogen peroxide under the reaction conditions, in a solvent medium, in the presence of a catalytic system consisting of a synthetic zeolite containing titanium atoms and a buffer system with a pH controlled within the values of 5.5 and 8.0, consisting of a nitrogenated base and a salt thereof with an organic or inorganic acid.
The nitrogenated base is selected from compounds having general formula (I)
wherein: R, R
1
and R
2
, the same or different, can be H, an alkyl group with C
1
-C
10
carbon atoms, a —COR
3
group wherein R
3
is an alkyl group with C
1
-C
10
carbon atoms or NH
2
, or a
group wherein n is a number from 1 to 10 and R
4
and R
5
are H or C
1
-C
10
alkyl groups.
Preferred compounds having formula (I) are: ammonia, methylamine, ethylamine, diethylamine, trimethylamine, ethanolamine, diethanolamine, triethanolamine, n-proplylamine.
Organic acids which can be used for the purposes of the present invention can be selected from carboxylic acids, such as acetic acid, formic acid, propionic or butyric acid and their derivatives, such as for example oxyacids such as glycol acid and &agr;-lactic acid.
The inorganic acids are selected from sulfuric and phosphoric acid.
Sulfuric acid, acetic acid and formic acid are particularly preferred for the purposes of the present invention.
The olefin compounds which can be used in the process of the present invention can be selected from organic compounds having at least one double bond and can be linear or branched aliphatic, aromatic, alkylaromatic and cyclic. They are preferably olefin hydrocarbons having from 2 to 30 carbon atoms in the molecule and containing at least one double bond.
Examples of olefins suitable for the purposes of the present invention are selected from those having general formula (II)
wherein: R
1
, R
2
, R
3
and R
4
, the same or different, can be H, an alkyl radical with from 1 to 20 carbon atoms, an aryl radical, an alkylaryl radical with from 7 to 20 carbon atoms, a cycloalkyl radical with from 6 to 10 carbon atoms, an alkylcycloalkyl radical with from 7 to 20 carbon atoms. The radicals R
1
, R
2
, R
3
and R
4
, can form, in pairs, saturated or unsaturated rings. These radicals may additionally contain halogen atoms, nitro, nitrile, sulfonic groups and relative esters, carbonyl, hydroxyl, carboxyl, thiol, amine and ether groups.
Examples of olefins which can be epoxidated with the process of the present invention are: ethylene, propylene, allyl chloride, allyl alcohol, butenes, pentenes, hexenes, octeneheptenes-1, 1-tridecene, mesityl oxide, isoprene, cyclo-octane, cyclohexene or bicyclic compounds such as norbornenes, pinenes, etc. The olefins can carry the above substituents both on the unsaturated carbon atoms and on different positions.
The oxidizing agent used in the process of the present invention is hydrogen peroxide (H
2
O
2
) or a compound which is capable of generating H
2
O
2
under the epoxidation conditions.
An aqueous solution of hydrogen peroxide is preferably used, at a minimum concentration of 1% by weight, preferably with a titer greater than or equal to 35% by weight.
The quantity of hydrogen peroxide with respect to the olefin is not critical, but a molar ratio olefin/H
2
O
2
ranging from 10:1 to 1:10, preferably from 6:1 to 1:2, is preferably used.
The epoxidation reaction can be carried out in one or more solvents liquid at the epoxidation temperatures. Solvents of a polar nature are typically used, such as alcohols (methanol, ethanol, isopropyl alcohol, t-butyl alcohol, cyclohexanol), hydro-alcohol mixtures, ketones (for example acetone, methyl ethyl ketone, acetophenone), ethers (tetrahydrofuran, butyl ether), aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, esters.
Methanol and, among the ketones, acetone, are preferably used. A mixture of methanol/water with a weight ratio ranging from 50/50 to 99/1, is particularly preferred.
The catalyst which can be used in the process of the present invention is selected f
Forlin Anna
Paparatto Giuseppe
Tegon Paolo
Enichem S.p.A.
Lambkin Deborah C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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