Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-02-17
2001-10-02
Padmanabhan, Sreem (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S861000, C568S881000
Reexamination Certificate
active
06297409
ABSTRACT:
The present invention relates to a continuous process for the preparation of a high-purity hydrogenated ose by catalytic hydrogenation of the corresponding ose in falling film reactors.
More particularly, the invention relates to a continuous process for the preparation of a high-purity hydrogenated ose by catalytic hydrogenation of the corresponding ose in a series of fixed beds of ruthenium catalyst arranged in two reaction zones, a first zone consisting of at least one fixed bed of ruthenium catalyst and a second zone consisting of at least one fixed bed of ruthenium catalyst containing a promoter, the whole operating in such a way as to give the hydrogenated ose with a high purity, a high degree of conversion and a high selectivity at the outlet of said second hydrogenation zone.
“Ose” is understood as meaning a carbohydrate comprising n carbon atoms and containing n-1 alcohol groups and one carbonyl group. When the carbonyl group is an aldehyde group, the ose is an aldose; when the carbonyl group is a ketone group, the ose is a ketose.
In terms of the invention, the ose has a carbon skeleton comprising n carbon atoms, n being between 3 and 7 and preferably between 4 and 6.
The ose can also belong to either the D series or the L series.
The ose can be selected especially from the group comprising aldotetroses, such as erythrose and threose, and aldopentoses or aldohexoses, such as glucose, mannose, galactose, ribose, arabinose, xylose and lyxose. The ose is preferably selected from aldoses and in particular is D-glucose.
Processes for the catalytic hydrogenation of oses are conventionally batch processes in which a pulverulent hydrogenation catalyst consisting of Raney nickel is used in suspension in the ose solution.
However, these batch processes have the disadvantage of a very low productivity and require large and expensive reactors.
Moreover, although the Raney nickel catalyst can be filtered off and re-used, a high proportion has to be replaced with fresh catalyst.
Finally, such processes remain high energy consumers.
To mitigate these disadvantages, it was proposed to carry out continuous hydrogenation processes using a plurality of cascade reactors containing pulverulent catalysts consisting of Raney nickel in suspension.
However, the activation, circulation and selective separation of said pulveruilent catalysts generally result in further substantial catalyst consumption.
Continuous processes in fixed beds of nickel/copper catalyst on an inert support were then described, but these have to be carried out under high pressure conditions and at a low surface flow velocity.
The high temperatures also used lead to isomerization and cracking reactions and to caramelization of the oses to the extent that, in the case of the hydrogenation of D-glucose, the sorbitol produced contains in particular an appreciable amount of mannitol.
One of the first continuous hydrogenation processes using one or more reactors containing nickel catalysts in a series of fixed beds is described in patent U.S. Pat No. 2,650,941.
However, the temperature and pressure conditions are still high, these conditions being necessary for attaining a degree of conversion of glucose to sorbitol in the order of 98.8%.
Other processes have been described which make it possible to increase this degree of conversion, but the formation of acids derived from oses which is inherent in the use of nickel is the main cause of catalyst deactivation and of the drop in selectivity in terms of hydrogenated reaction products.
Thus, under these conditions, gluconic acid is produced in the process for the hydrogenation of glucose, causing leaching of the metallic nickel and especially contamination, by the nickel, of the sorbitol produced.
A number of other group VIII metals, such as palladium, ruthenium and platinum, have been tested as alternative catalysts.
Thus it has been shown that palladium, ruthenium and platinum catalysis consumes less metal than nickel catalysis for a hydrogenation reaction carried out under similar temperature and pressure conditions. Ruthenium is the most efficient catalyst.
It actually affords more effective conversions, including at temperatures below 160° C. and pressure conditions in the order of 100 bar. Furthermore, it is remarkably stable under acid conditions and makes it possible, for example, to hydrogenate the gluconic acid produced during the hydrogenation reaction of glucose.
U.S. Pat. No. 2,868,847 thus describes the use of ruthenium catalysts supported on charcoal, alumina, silica or kieselguhr for the hydrogenation of carbohydrates to polyols by a batch process.
However, although this hydrogenation of glucose to sorbitol with a ruthenium catalyst makes it possible to avoid caramelization reactions and at the same time the spurious production of gluconic acid, the productivity is still too low to be economically satisfactory.
U.S. Pat. No.4,380,679, U.S. Pat No. 4,380,680 and U.S. Pat. No. 4,487,980 describe continuous hydrogenation processes using fixed beds of ruthenium catalyst supported on charcoal, alumina or titanium dioxide, respectively, and allow the hydrogenation to be carried out under good conditions.
However, although the degrees of conversion reach 99%, the selectivities are relatively low and do not exceed 96%.
U.S. Pat. No. 3,963,789 describes the use of series of beds of ruthenium catalyst, but this process necessitates several operating cycles with acid regeneration of the catalyst and, moreover, also leads to the production of substantial amounts of isomerization products, i.e. mainly mannitol, with the sorbitol.
U.S. Pat. No. 4,476,331 also describes a multistage continuous process, the first stage consisting of a ruthenium catalyst in fixed beds and the second stage consisting of ruthenium catalysts treated with sulfur.
However, the object of this configuration is to produce sugar alcohols in the first stage and crack them in the second. For example, said patent describes the hydrogenation of hexoses to hexitols in the first stage and the cracking of said hexitols to sugar alcohols comprising 3 or 4 carbon atoms, using higher temperature conditions, in the second stage.
Patents EP 300.018, U.S. Pat. No. 4,626,604 and EP 319.208 describe multistage continuous hydrogenation processes under adiabatic conditions, using fixed beds of a group VIII catalyst, which afford degrees of conversion of aldehydes to their corresponding hydrogenated products in the order of 100%. However, it is necessary to re-introduce hydrogen at the inlet of each falling film reactor, either by itself or with fresh amounts of aldehydes to be hydrogenated. Moreover, these aldehydes are preferably compounds comprising from 7 to 17 carbon atoms of the oxoaldehyde type.
It is therefore clearly apparent in the state of the art that continuous processes for the hydrogenation of oses do not make it possible to obtain their corresponding hydrogenated products with a high purity and a high selectivity for a high degree of conversion.
In particular, these processes obligatorily involve thorough purification of the hydrogenated ose obtained in order to eliminate all traces off co-products. In the case of the hydrogenation of D-glucose to sorbitol, these co-products will be especially mannitol, arabitol and iditol.
This requirement therefore generates additional purification costs.
The aim of the invention is therefore to rectify this situation and to propose a means whereby the various practical constraints can be better satisfied and whereby, in particular, a good compromise can be reached between purity, degree of conversion and selectivity.
After numerous researches, the Applicant found that such a means could consist of a special continuous catalytic hydrogenation process in falling film reactors.
Surprisingly and unexpectedly, the Applicant found that the choice of a special ruthenium catalyst, i.e. one containing a promoter, under special conditions, i.e. in the constitution of the second hydrogenation zone, made it possible to obtain a hydrogenated ose with a high purity, a high degree of
Choque Jean-Christophe
Fleche Guy
Merchant & Gould P.C.
Padmanabhan Sreem
Roquette Freres
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