Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1998-02-04
2001-05-01
Kight, John (Department: 1612)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S326000, C549S508000, C502S022000, C502S153000, C502S183000, C502S325000, C502S339000
Reexamination Certificate
active
06225477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention:
This invention relates to a method of improving the catalytic performance (i.e., sustaining and/or regenerating catalytic activity) of a carbon-supported, rhenium-containing catalyst and, in particular, a hydrogenation catalyst comprising a composite of palladium or ruthenium in combination with rhenium on a support of activated carbon. More specifically but not by way of limitation, this invention pertains to depositing and/or replenishing rhenium metal on bimetallic palladium and rhenium or ruthenium and rhenium on carbon support (i.e., Pd,Re/C or Ru,Re/C, respectively) catalysts or catalyst precursor by depositing fresh fmely divided rhenium metal on these catalysts during hydrogenation of maleic acid to tetrahydrofuran and/or 1,4-butanediol.
2. Description of the related art:
Supported rhenium containing catalysts are well known in the art and are useful in a number of important processes. Such catalysts include: palladium, rhenium/carbon catalysts and ruthenium, rhenium/carbon catalysts used in the hydrogenation of maleic acid to tetrahydrofuran; platinum; rhenium/alumina catalysts used in reforming of oil to gasoline; and rhenium on alumina catalyst used in olefin metathesis. During use of such catalysts, the catalytic activity of the catalyst can decrease over time as the rhenium component of the catalyst assumes a catalytically less active form.
There are many patents relating to the art of converting maleic acid or maleic anhydride or a variety of hydrogenatable precursors such as fumaric acid, succinic acid (SAC), maleic acid (MAC), dimethyl succinate, gamma-butyrolactone (GBL) or mixtures thereof to tetrahydrofuran (THF) and 1,4-butanediol (BDO) by catalytic hydrogenation. Of particular importance, U.S. Pat. No. 4,609,636 describes the preparation and use of a catalyst composite comprising palladium and rhenium on a carbon support for manufacture of THF, BDO or mixtures thereof from a variety of hydrogenatable precursors. This patent also cites patents that attempt to maximize product yields. Similarly, U.S. Pat. No. 5,418,952 describes the preparation and use of a catalyst composite comprising ruthenium and rhenium on a carbon support for the same use.
The catalysts of U.S. Pat. No. 4,609,636 and U.S. Pat. No. 4,550,185 are composites of palladium and rhenium on a carbon support, the composite comprising about 0.5% to 10% palladium and about 1% to 10% of rhenium by total weight, the palladium being present in the form of crystallites having an average size of about 10 nm to 25 nm and the rhenium being in the form of a highly dispersed phase of crystallites having an average size of less than about 2.5 nm. These catalysts are closely related to the catalyst of the present invention .
Also pertinent is a report by H. Smith Broadbent reported in Annals of the New York Academy of Sciences, 145 (1) (1967) (pages 68 through 71), which is a comprehensive study of “Rhenium and Its Compounds as Hydrogenation Catalysts”. Broadbent teaches (page 62, last paragraph) in-situ preparation of an insoluble rhenium black by addition of rhenium heptoxide to a reducible organic substrate, with or without added solvent, followed by a hydrogenation step. Broadbent indicates the rhenium black is some form of Re(II), probably a hydrated monoxide. This catalyst, although less active than nickel or platinum metal hydrogenation catalysts for hydrogenation of most compounds, was judged superior to all other catalysts except, perhaps, other oxides of rhenium, for hydrogenation of carboxylic acids.
BRIEF SUMMARY OF THE INVENTION
It has now been found that the loss of catalytic activity in a Pd, Re/C catalyst and Ru, Re/C catalyst used in hydrogenation of maleic acid to tetrahydrofuran and/or 1,4-butanediol is mechanistically associated with agglomeration of the rhenium component of the catalyst as well as the direct loss of rhenium by dissolution. One object of the invention is thus to treat the catalyst in a manner which deposits fresh rhenium in a catalytically active form.
The catalytic activity of a rhenium-containing supported catalyst, most preferably either a Pd, Re/carbon or Ru, Re/carbon-supported hydrogenation catalyst, is enhanced by treatment of the catalyst with a water-soluble perrhenate (such as perrhenic acid, HReO
4
), followed by further treatment of the catalyst in a reducing atmosphere at elevated temperature and pressure prior to or while in use. This process has been found to enhance the activity of freshly-prepared, carbon-supported Pd, Re catalysts in the hydrogenation of maleic acid to THF/BDO, and to increase the activity of used or deactivated catalysts.
Treatment with soluble perrhenate as disclosed may be carried out after a fresh catalyst has been prepared, or after the catalyst has been used. The catalytic activity of the fresh or used-but-still-active catalyst is enhanced, the activity of the deactivated catalyst can be either restored to its fresh state (i.e., the activity it exhibited after initial startup) or enhanced further. The extent of the desired boost in catalytic performance will determine the amount of HReO
4
to be added. We have found in the hydrogenation of maleic acid that the performance is boosted 70 to 100 STY units per weight % Re added in favorable cases.
Space time yield, STY, for purposes of this invention is defined as follows:
STY={g/hr THF liq+g/hr THF gas}/kilogram of catalyst
Selectivity is defined as follows:
Selectivity={moles/hr product}/{moles/hr product and byproduct}
or
Selectivity={moles/hr THF gas+THF liq+GBL liq+BDO liq}/{moles/hr THF gas+THF liq+GBL liq+BDO liq+PrOH liq+BuOH liq+alkane gas}
where GBL is gamma-butyrolactone, BDO is 1,4-butanediol, PrOH is n-propyl alcohol, BuOH is n-butyl alcohol, and alkane is methane, ethane, propane, and butane. NOTE: Only insignificant amounts of GBL and BDO are present in the gas phase. Mass balance expressed as a percentage is defined for purposes of this invention as 100 times the millimoles per hour of products recovered divided by the millimoles per hour of MAC being fed.
The added HReO
4
is then reduced by treatment with hydrogen at elevated temperature and pressure and deposited onto the support material in a highly dispersed, catalytically active form. The treatment with hydrogen at elevated temperature and pressure can be performed immediately prior to introduction of the substrate (maleic acid) feed or, alternatively, under true working conditions; i.e. concurrently while the maleic acid substrate is being fed and hydrogenated to THF.
Another embodiment of the invention is related to the finding that exposure of fresh Pd, Re/C catalyst-HReO
4
—H
2
O slurry to flowing hydrogen at 2,000 psig (1.38×10
7
Pa) and ambient temperatures for approximately 8 hours (low temperature activation) prior to elevating the temperature (as above) provides additional performance enhancement.
Surprising features of this invention in light of the art are that:
1) Fresh catalysts prepared by rhenium deposition in water perform as well as palladium, rhenium-on-carbon catalysts prepared before introduction into the reactor, thus eliminating the usual rhenium impregnation, drying, and reduction steps. Those skilled in the art will appreciate that this offers advantages to the catalyst user of flexibility in catalyst choice (a large variety of “off-the-shelf” Pd/C catalysts are commercially available) as well as potential savings compared to buying a pre-fabricated Pd, Re/C catalyst from a catalyst vendor
2) Catalysts deactivated during the process of hydrogenation of maleic acid to tetrahydrofuran and 1,4-butanediol can be regenerated by deposition of fresh rhenium onto the damaged catalyst under working conditions and the concentration of unreduced substrate and intermediates in the reactor ranging from near zero to working concentration. Removal from the reactor is not required. Also, the process can proceed without inter
Campos Daniel
Ernst Richard Edward
Michel John Byrne
Covington Raymond
E. I. Du Pont de Nemours and Company
Kight John
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