Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-10-11
2003-04-29
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S399000, C568S881000, C568S884000, C568S885000, C568S910000, C568S470000, C502S155000, C502S162000, C502S166000, C585S639000, C585S640000, C585S649000
Reexamination Certificate
active
06555715
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for reacting C
2
to C
6
alkanes with oxygen in the presence of a catalyst comprising an imide promoter and a metal co-catalyst to provide an oxygenated product. The oxygenated product can be further reacted with hydrogen to form the corresponding alcohol and the alcohol can be dehydrated to provide the corresponding olefin.
BACKGROUND OF THE INVENTION
Organic compounds containing an oxygen in the structure have various industrial uses either in and of themselves or as precursors to more valuable materials. These oxygenated organic compounds are usually prepared by processes which convert hydrocarbons to the oxygen containing organic compounds. Although saturated hydrocarbons such as paraffins and naphthenes are the lowest cost and most readily available hydrocarbons, they are also very stable and thus not very chemically reactive. In particular, linear paraffinic compounds are the hardest to oxygenate. It would be very desirable to easily convert paraffins (and especially linear paraffins) to oxygenates.
There are a number of reports in the literature of various ways to oxidize hydrocarbons to the corresponding aldehyde or ketone. One reference is U.S. Pat. No. 5,958,821 B1 which discloses oxidizing various hydrocarbons such as cycloalkanes, aromatic hydrocarbons, etc. with oxygen in the presence of an oxidation catalyst comprising an imide compounds such N-hydroxyphthalimide and a metal compound co-catalyst such as cobalt or manganese acetyl acetonate. The patentee of the '821 reference enumerates virtually every class of known hydrocarbons and virtually every metal in the periodic table. Other references which have addressed the oxygenation of alkanes include Shun-Ichi Murahashi et al. in
J. Chem. Soc., Chem. Commun
., 139-140 (1993) in which the authors present results for the oxidation of alkanes and alkenes with oxygen in the presence of aldehydes and using a copper compound catalyst. Their results showed that linear alkanes such as N-decane had extremely low conversion. In
Catalysis Letters
8 (1991), 45-52 the same authors have shown that isobutane can react with oxygen in the presence of an iron perhaloporphyrin complex to give mostly tert-butyl alcohol. Shun-Ichi Murahashi et al. have reported in
Tetrahedron Letters
, vol. 34, no. 8 pp. 1299-1302, 1993 the ruthinium catalyzed oxidation of alkanes with alkyl hydroperoxide. Specifically, they reacted n-heptane and n-decane to provide ketones and alcohols., G. P. Khirnova et al. in
Petrol. Chem. U.S.R.R
. vol. 21, no. 1, pp. 49-52, 1981 have reported the liquid phase oxidation of isobutane using a heterogeneous catalyst containing cobalt and molybdenum borides or molybdenum carbides. The main products of this reaction were tert-butyl hydroperoxides, tert-butyl alcohol and acetone. It has also been shown in U.S Pat. No. 5,395,980 B1 that isobutane can be converted to tert-butyl hydroperoxide at elevated temperatures (about 140° C.) by reacting it with oxygen in the presence of tert-butyl alcohol and di (tert-butyl) peroxide.
There are also reports of the oxidation of alkanes with oxygen using N-hydroxyphthalimide (NHPI) as a catalyst and a metal compound co-catalyst. For example, Y. Ishii et al. in Catalysis Surveys
from Japan
3 (1999 27-35) report the oxidation of various alkanes including isobutane. The isobutane gave tert-butyl alcohol and acetone and tert-butyl hydroperoxide. The other alkanes which were tested were all branched alkanes. No results are presented for the oxidation of n-butane using NHPI as the catalyst. Ishii et al. in
J. Org. Chem
. 1996, 61, 4520-4526 present results of the oxidation of various cycloalkanes using NHPI and Co(acac)
n
. Results are also presented for the oxidation n-octane to give octanols and octanones.
The above references show that branched alkanes can be oxidized using various catalytic systems, whereas light normal paraffins (C
2
-C
6
) require very strong oxidants such as hydrogen peroxide or organic peroxides. The references by Ishii et al. indicate that only branched low molecular weight alkanes, e.g. isobutane, and longer chain alkanes e.g. octane, can be converted to alcohols or ketones using NHPI and a metal co-catalyst.
Despite the reports in the literature as to the unreactivity of linear light paraffins, applicants have surprisingly found that C
2
to C
6
linear alkanes can be converted to ketones or alcohols using a catalyst comprising NHPI (and its derivatives) in combination with a metal co-catalyst. In particular, applicants have found that propane and n-butane can be converted to acetone and methyl ethyl ketone respectively at a selectivity of greater than 90% by reacting the alkanes with an 8% oxygen
itrogen gas at 70° C. using a catalyst comprising NHPI and a cobalt (acac) co-catalyst in acetic acid.
SUMMARY OF THE INVENTION
As stated, this invention relates to a process for converting light paraffins to the corresponding oxygenated compounds and optionally then proceeding to convert the oxygenated compounds to the corresponding olefins. Accordingly, one embodiment of the invention is a process for converting light paraffins to an oxygenated compound, comprising reacting light paraffins selected from C
2
to C
6
linear alkanes, with oxygen, in the presence of a catalyst comprising at least one imide promoter and a co-catalyst at oxidation conditions to provide an oxygenated compound, the imide having the formula:
where R
1
and R
2
are independently selected from the group consisting of hydrogen, halogens, alkyl groups, cycloalkyl groups, aryl groups, hydroxyl group, alkoxy groups, carboxyl group, alkoxycarbonyl groups and acyl groups or R
1
and R
2
may bind to form a double bond, an aromatic ring or a non-aromatic ring; X is oxygen or a hydroxyl group and n=1 and the co-catalyst comprising at least one metal selected from the group consisting of Groups IVB, VB, VIB, VIIB, VIII elements of the Periodic Table of Elements to provide an oxygenated compound.
Another embodiment of the invention is to take the oxygenated compound of the previous paragraph and react it with hydrogen in the presence of a hydrogenation catalyst at hydrogenation conditions to provide alcohols and then optionally contacting the alcohols with a dehydration catalyst to provide olefins.
These and other objects and embodiments will become clearer after a detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As stated the present invention relates to a process for converting light paraffins, i.e., alkanes to oxygenated compounds and optionally converting the oxygenated compounds to olefins. The light alkanes which are within the scope of the invention are the linear alkanes having from 2-6 carbon atoms, especially C
2
to C
4
linear alkanes and more particularly propane and n-butane. Although a feedstream comprising single alkane is preferred to be used in the present process, the feedstream to the process will usually contain a mixture of two or more alkanes, with one alkane being the major component. The process generally involves reacting the alkanes with oxygen in the presence of a catalyst comprising an imide promoter and a metal co-catalyst. Accordingly, one essential element of the catalyst of the present invention is an imide promoter. The imide promoter is represented by the general formula (1):
where R
1
and R
2
are independently selected from the group consisting of hydrogen, halogens, alkyl groups, cycloalkyl groups, aryl groups, hydroxyl group, alkoxy groups, carboxyl group, alkoxy-carbonyl groups and acyl groups or R
1
and R
2
may bind to form a double bond, an aromatic ring or a non-aromatic ring; X is oxygen or a hydroxyl group and n=1.
In the imide compound shown by formula 1, when R
1
and/or R
2
represent halogens, these include iodine, bromine, chlorine and fluorine. Alkyl groups include without limitations, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, heptyl, or other straight chains or branched chain alkyl groups having 1 to 10 carbon atoms
Bricker Jeffery C.
Frame Robert R.
Kocal Joseph A.
Kumar Shailendra
Molinaro Frank S.
Tolomei John G.
UOP LLC
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