Catalyst and process for preparing 2-buten-1-ol compounds

Details Catalyst and process for preparing 2-buten-1-ol compounds Catalyst and process for preparing 2-buten-1-ol compounds

2001-01-16

2001-08-21

Shippen, Michael L. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C560S113000, C560S261000, C568S450000, C568S675000, C568S687000, C568S825000, C568S838000, C568S857000, C568S875000

Reexamination Certificate

active

06278031

ABSTRACT:

The present invention relates to a fixed-bed catalyst and a continuous process for preparing 2-buten-1-ol compounds.
J. Am. Chem. Soc., 85 (1963), pages 1549 to 1550 discloses the isomerization of an unsaturated alcohol using a carbonyl compound of a metal from group VIII of the Periodic Table of Elements as catalyst. This process gives numerous by-products and secondary products, for example the corresponding aldehydes.
Can. Journ. of Chem., 46 (1968), 2225 to 2232 discloses the thermal isomerization of unsaturated alcohols in the absence of a catalyst. At the high temperatures required, the starting compounds are partly converted to resin.
DE-C-19 01 709 describes a process for preparing buten-2-ol-4 compounds in which buten-1-ol-4 compounds are reacted in the presence of palladium or palladium compounds, for example palladium/carbon, and hydrogen.
However, when using pure palladium in the presence of hydrogen, significant hydrogenation of the double bond of the compounds occurs and a saturated product is formed. In addition, low-boiling compounds such as hydrocarbons and aldehydes are formed as by-products, for example by hydrogenolysis and isomerization. The hydrogenation of the double bond is undesired since in the case of some butenols there are only small boiling point differences between unreacted starting material and hydrogenation product. Thus, the boiling point of 3-methyl-3-buten-1-ol, for example at 1020 mbar, is 131.5° C. while the boiling point of the corresponding hydrogenation product 3-methyl-1-butanol is 130.9° C. This makes it difficult to separate hydrogenation product and starting material by distillation.
DE-C-27 25 965 discloses a process for preparing a 2-alken-1-ol in which a 3-alken-1-ol is converted into the boric ester of the alkenol, the isomerization is subsequently carried out in the presence of a palladium catalyst, e.g. palladium on activated carbon, and hydrogen and the resulting reaction mixture is subjected to solvolysis. Fewer by-products are formed as a result of the hydroxyl group of the 3-alken-1-ol being protected by esterification. However, additional process steps are necessary.
DE-A-27 51 766 discloses a process for isomerizing 3-buten-1-ol compounds to give the corresponding 2-buten-1-ol compounds, with the isomerization being carried out in the presence of palladium and selenium or tellurium as catalyst and hydrogen. The catalyst used is palladium and selenium on activated carbon. As further usable supports, mention is made of barium sulfate, silica gel, aluminum oxide and zeolites. The catalysts can also be used without supports. Relatively high proportions of low boilers such as isoprene and methylbutenes are formed.
The known catalytic isomerizations are carried out batchwise, for example in a stirred reactor using the suspension method.
However, since the double-bond isomerization of substituted butenols is an equilibrium reaction, complete conversions are not obtained but part of the starting material always remains and for further use has to be separated from by-products formed. To carry out the isomerization in a more economical way, the reaction should be able to be carried out continuously and lead to a minimum proportion of hydrogenation products or low boilers.
It is an object of the present invention to provide a catalyst and a process for the continuous preparation of 2-buten-1-ol compounds by isomerization of 3-buten-1-ol compounds such that the proportion of hydrogenation products and low boilers obtained is very low.
We have found that this object is achieved by a fixed-bed catalyst which comprises palladium and selenium or tellurium or a mixture of selenium and tellurium on a silicon dioxide support and has a BET surface area of from 80 to 380 m
2
/g and a pore volume of from 0.6 to 0.95 cm
3
/g in the pore diameter range from 3 nm to 300 &mgr;m, with from 80 to 95% of the pore volume being in the pore diameter range from 10 to 100 nm.
The object is also achieved by use of the catalyst as an isomerization catalyst and by a process for preparing 2-buten-1-ol compounds of the formula (I)
H
2
R
1
C—R
2
C═CR
3
—CR
4
R
5
—OR
6
  (I)
where the individual radicals R
1
, R
2
, R
3
, R
4
, R
5
and R
6
can be identical or different and are each hydrogen or an aliphatic radical which may be unsubstituted or substituted by OH, OR where R is aliphatic, halogen or carboxyl, furthermore R
2
can also be the radical —CHO, R
2
and R
5
together with the carbon atoms located between them can also be parts of an alicyclic ring, and R
6
can also be a cycloaliphatic, araliphatic, aromatic radical or the radical —C(═O)—R
7
, where R
7
is an aliphatic, cycloaliphatic, araliphatic or aromatic radical, by isomerizing 3-buten-1-ol compounds of the formula (II)
HR
1
C═CR
2
—CHR
3
—CR
4
R
5
—OR
6
  (II)
where R
1
, R
2
, R
3
, R
4
, R
5
and R
6
are as defined above, in the presence of hydrogen and a catalyst, wherein the process is carried out continuously over the fixed-bed catalyst described above.
The catalyst preferably contains from 0.1 to 2.0% by weight of palladium and from 0.01 to 0.2% by weight of selenium, tellurium or a mixture of selenium and tellurium, based on the total weight of the catalyst.
The BET surface area is preferably from 100 to 150 m
2
/g, in particular from 110 to 130 m
2
/g. The BET surface area is determined by N
2
adsorption in accordance with DIN 66131.
The pore volume in the pore diameter range from 3 nm to 300 &mgr;m is preferably from 0.8 to 0.9 cm
3
/g, in particular from 0.8 to 0.85 cm
3
/g. From 80 to 95%, preferably from 85 to 93%, of this pore volume are in the pore diameter range from 10 to 100 nm. The pore volume is determined by Hg porosimetry.
The catalyst preferably contains from 0.2 to 0.8% by weight, in particular from 0.4 to 0.6% by weight, of palladium. The catalyst preferably contains from 0.02 to 0.08% by weight, in particular from 0.04 to 0.06% by weight, of selenium, tellurium or a mixture of selenium and tellurium, preferably selenium.
Apart from the active components mentioned, further metals may be present on the catalysts in small amounts. Preferably, only palladium, selenium and/or tellurium, in particular only palladium and selenium, are present on the silicon dioxide support.
The catalysts of the present invention can be prepared by any suitable methods. They are preferably prepared by impregnation of a silicon dioxide support with a solution of a palladium compound and a selenium compound or tellurium compound or a mixture of a selenium compound and a tellurium compound. It is here possible to use one or more palladium compounds, selenium compounds and/or tellurium compounds. Preference is given to using the compounds in the form of aqueous solutions. In such solutions, palladium is preferably used in the form of salts such as palladium nitrate or complexes. Selenium and/or tellurium are used, for example, in oxidic form. Further suitable palladium, selenium and tellurium compounds are described in DE-A-27 51 766. The silicon dioxide support can be impregnated in succession with solutions of the individual compounds in any order, with the catalyst support being able to be dried between the individual impregnation steps. However, the catalyst support can also be impregnated with a solution in which the compounds of the active substances are present in an appropriate desired ratio. The concentration of the solutions can be selected such that the desired amount of palladium and selenium and/or tellurium can be applied to the catalyst by means of a single impregnation. However, application by multiple impregnation is also possible.
The catalyst support is preferably agitated in the solution of the active substances, and the impregnated catalyst is then dried at about 120° C. and subsequently heat treated at about 200° C. Before or during use of the catalyst in the isomerization, the active substances, ie. palladium and selenium and/or tellurium, are reduced in the presence of hydrogen.
The catalyst support is preferably prepared by precipitat

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