Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-03-02
2001-10-02
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S852000
Reexamination Certificate
active
06297408
ABSTRACT:
BACKGROUND
This invention relates to an improved process for the production of 1,3-propanediol by catalytic hydrogenation of 3-hydroxypropanal.
1,3-Propanediol is used as a monomer unit for polyesters and polyurethanes and as a starting material for synthesizing cyclic compounds.
Various processes are known for the production of 1,3-propanediol via 3-hydroxypropanal (HPA) which start either from C
2
and C
1
structural units or from a C
3
structural unit, such as, for example, acrolein. When acrolein is used, it is first hydrated in aqueous phase in the presence of an acidic catalyst to form HPA. After removing the unreacted acrolein, the aqueous reaction mixture formed during hydration still contains, in addition to 85 wt % based on total organics of 3-hydroxypropanal, approximately 8 wt % 4-oxaheptane-1,7-dial and further organic components in smaller proportions by weight. This reaction mixture is hydrogenated in the presence of hydrogenation catalysts to produce 1,3-propanediol. The 1,3-propanediol is recovered from the reaction mixture by distillation and/or extraction based methods known to those skilled in the art.
U.S. Pat. No. 5,334,778 discloses a two stage process for hydrogenating 3-hydroxypropanal which yields 1,3-propanediol having a residual carbonyl content, expressed as propionaldehyde, of below 500 ppm. The hydrogenation is carried out at 30° C. to 80° C. to a 3-hydroxypropanal conversion of 50 to 95% and then is continued at 100° C. to 180° C. to a 3-hydroxypropanal conversion of substantially 100%. Suitable hydrogenation catalysts therein include Raney nickel suspension catalysts, and supported catalysts based on platinum or ruthenium on activated carbon, Al
2
O
3
, SiO
2
, or TiO
2
as well as nickel on oxide- or silicate-containing supports.
According to U.S. Pat. No. 5,015,789, very active nickel catalysts exhibit inadequate long-term stability, with a rapid drop in hydrogenation conversion and reaction speed upon repeated use of the catalyst. This results in frequent replacement of the entire catalyst packing, which is associated with known problems in the disposal and working up of compounds containing nickel. In addition, soluble nickel compounds can form and are released into the product stream, requiring further steps to separate the resulting contaminants.
Hydrogenation processes may be characterized by the conversions, selectivities, and space-time yields achievable therewith. Percent conversion of 3-hydroxypropanal is defined by:
X
=
%
Conversion
of
HPA
=
moles
of
HPA
converted
moles
of
HPA
supplied
×
100
Selectivity of the hydrogenation process is a measure of the amount of converted 3-hydroxypropanal which is converted into the desired product:
%
Selectivity
=
moles
of
1
,
3
-
propanediol
moles
of
HPA
converted
×
100
The space-time yield is another important characteristic for continuous hydrogenation processes, stating the achievable quantity of product per unit time and reaction volume.
When hydrogenating 3-hydroxypropanal to 1,3-propanediol on a large industrial scale, it is vital, with regard to the economic viability of the hydrogenation process and the quality of the product, for conversion and selectivity to be as close as possible to 100%. The 1,3-propanediol may be separated from the water as well as remaining 3-hydroxypropanal and secondary products contained in the product stream by distillation after the hydrogenation. However, this distillative separation is rendered very difficult by residual 3-hydroxypropanal and secondary products and may even become impossible due to reactions between the residual 3-hydroxypropanal and 1,3-propanediol to yield acetals such as 2-(2′-hydroxyethyl)-1,3-dioxane (HED), which have a boiling point close to the boiling point of 1,3-propanediol. Thus, the lower the conversion and selectivity, the poorer the achievable product quality.
In order to produce 1,3-propanediol economically, it is also important for the catalyst to exhibit high activity for the hydrogenation of 3-hydroxypropanal. The objective should thus be to find a process in which the smallest possible quantity of catalyst is necessary for the production of 1,3-propanediol; i.e., it should be possible to achieve the greatest possible conversion of 3-hydroxypropanal to 1,3-propanediol with a small volume of catalyst.
Another important quality criterion for hydrogenation catalysts is their operational service life. Good catalysts should ensure high conversion and selectivity in the hydrogenation of 3-hydroxypropanal to 1,3-propanediol over the course of their service life.
SUMMARY OF THE INVENTION
The present invention provides an improved two-stage process for the production of 1,3-propanediol which comprises hydrogenating an aqueous solution of 3-hydroxypropanal using an oxide-supported metal hydrogenation catalyst in a first, low temperature, stage and continuing hydrogenation in a second, high temperature, stage using an activated carbon-supported (i.e., charcoal supported) metal hydrogenation catalyst. More specifically, the process of the present invention comprises hydrogenating an aqueous 3-hydroxypropanal solution at a temperature of between about 30° C. to 80° C., preferably about 40° C. to 80° C., to a conversion of greater than about 70% in the presence of a first hydrogenation catalyst, which comprises a metal supported on an oxide phase, followed by a second hydrogenation stage in which the reaction mixture from the first stage is further hydrogenated to a conversion of up to 100% at a temperature of between about 80° C. to 180° C., preferably about 100° C. to 150° C., in the presence of an activated carbon-supported metal hydrogenation catalyst. The temperature in the second hydrogenation stage is greater than the temperature in the first hydrogenation stage. Preferably, the temperature of the second hydrogenation stage is about 10° C. to 100° C., preferably about 20° C. to 60° C., higher than the temperature in the first hydrogenation stage.
The process of the current invention avoids the high-temperature leaching problems of certain oxide support materials, such as SiO
2
, as well as the deactivation problems of the activated carbon-supported catalysts in the first, low temperature, hydrogenation stage. In addition, the benefit of increased selectivity to 1,3-propanediol is realized by the use of activated carbon-supported catalysts in the second, high-temperature, hydrogenation stage. In a preferred embodiment, the oxide-supported catalyst comprises ruthenium on SiO
2
or TiO
2
and the activated carbon-supported catalyst comprises ruthenium or palladium on activated carbon.
DETAILED DESCRIPTION OF THE INVENTION
The process of the current invention comprises an improved two-stage process for the hydrogenation of 3-hydroxypropanal. In the first, low temperature, stage, an aqueous HPA solution is hydrogenated in the presence of an oxide-supported metal hydrogenation catalyst at a temperature of between about 30° C. to 80° C., preferably about 40° C. to 80° C. and more preferably about 40° C. to 70° C., until a conversion of greater than about 70% is achieved. Preferably, the conversion in the first stage is at least 90%, more preferably at least 95%. The reaction product from the first hydrogenation stage is heated and further hydrogenated in a second, high temperature, stage at a temperature between about 80° C. to 180° C., preferably about 100° C. to 150° C. and more preferably about 100° C. to 130° C. in the presence of an activated carbon-supported metal hydrogenation catalyst to a conversion of substantially 100%. The temperature in the second hydrogenation stage is greater than the temperature in the first hydrogenation stage. Preferably, the temperature of the second hydrogenation stage is about 10° C. to 100° C. preferably about 20° C.
Haas Thomas
Hofen Willi
Jaeger Bernd
Sauer Joerg
Vanheertum Rudolf
Barts Samuel
E. I. Du Pont de Nemours and Company
Price Elvis O.
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