Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-10-11
2001-11-06
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S861000, C568S852000, C568S868000, C560S191000
Reexamination Certificate
active
06313358
ABSTRACT:
The present invention relates to a process for the preparation of 1,6-hexanediol by hydrogenating adipic esters or ester mixtures which contain these and which contain organic halogen compounds as an impurity, the starting material being passed over a copper catalyst to remove the halogen compounds before the hydrogenation.
WO 97/31 882 describes a process for the preparation of 1,6-hexanediol in which a carboxylic acid mixture which contains essentially adipic acid and 6-hydroxycaproic acid and is obtained as a byproduct of the oxidation of cyclohexanone/cyclohexanol with oxygen or oxygen-containing gases and by water extraction of the reaction mixture is esterified with a low molecular weight alcohol to give the corresponding carboxylic esters, and the esterification mixture obtained is freed from excess alcohol and low boilers in a first distillation stage, the separation of the bottom product into an ester fraction essentially free of 1,4-cyclohexanediols and a fraction containing at least the major part of the 1,4-cyclohexanediols being carried out in a second distillation stage and the ester fraction essentially free of 1,4-cyclohexanediols being catalytically hydrogenated.
It has now been found that the activity of the hydrogenation catalyst decreases in the course of time, and it is presumed that this deactivation is attributable to the content of organic halogen compounds in the starting material.
It is an object of the present invention to remove these organic halogen compounds completely or virtually completely, i.e. to a residual content of less than 0.5 ppm, preferably less than 0.1 ppm.
The removal of organic halogen impurities from another substrate is known. For example, U.S. Pat. No. 5,614,644 describes the removal of organic halogen compounds from furan and hydrogenated furan using copper-containing catalysts. There, however, it is possible only to reduce the content of the impurity from 50-2000 ppm to less than 15 ppm, preferably to less than 5 ppm.
We have found that this object is achieved and that surprisingly, in a process for the preparation of hexanediol by hydrogenating dialkyl adipates or mixtures which contain a dialkyl adipate as the essential component and organic halogen compounds as impurities, it is possible to reduce the content of organic halogen compounds to extremely low values, for example less then 0.5 ppm, preferably less than 0.1 ppm, and hence greatly to increase the time on stream of the hydrogenation catalyst if, before the hydrogenation, the dialkyl adipates or the mixtures containing dialkyl adipates are passed, preferably in the liquid phase, at from 50 to 250° C. and from 1 to 100 bar over copper catalysts which have a copper content, calculated as CuO, of from 0.5 to 80% by weight, a surface area of from 5 to 1500 m
2
/g, a porosity of from 0.05 to 1.5 cm
3
/g and a copper surface area of from 0.1 to 20 m
2
/g (in each case per g of catalyst), in order to remove the organic halogen compounds.
With the copper catalysts to be used according to the invention, not only is it possible virtually completely to remove the halogen compounds but they are furthermore distinguished by the fact that they are chemically stable with respect to the ester mixture, i.e. no catalyst components can be detected in the ester mixture freed from the halogen-containing impurities and, apart from the removal of the halogen-containing impurities, they do not change the ester mixture chemically in its composition.
It is assumed that, in the treatment of the starting material stream with the copper catalysts, cleavage of the organic halogen compounds occurs and the copper catalysts simultaneously serve as absorbents for the liberated halogens. The terms catalyst and absorbent are therefore used synonymously below.
Both unsupported and supported copper catalysts can be used as copper-containing halogen absorbents.
On the one hand, supported copper catalysts in which the copper component is present in finely divided form on an inert carrier are preferably used. Examples of suitable carriers are active carbons, silicon carbide, alumina, silica, titanium dioxide, zirconium dioxide, zink oxide, magnesium oxide, calcium oxide, barium sulfate or mixtures thereof, preferably active carbons and zirconium dioxide. The carriers can be used, for example, in the form of extrudates, pellets, tablets or granules.
On the other hand, unsupported copper catalysts which contain, for example, TiO
2
, Al
2
O
3
, ZrO
2
or mixtures of these compounds, among these preferably TiO
2
, as further components in addition to copper are preferably used.
The catalysts to be used according to the invention have a copper content, calculated as CuO, of 0.5-80, preferably 2-60, % by weight, a surface area of 5-1500, preferably 10-1000, m
2
/g and a porosity of 0.05-1.5, preferably 0.1-0.8, cm
3
/g.
Particularly preferably used supported catalysts are on the one hand ZrO
2
-supported copper catalysts which have a copper content, calculated as CuO, of 2-8% by weight, a surface area of 50-150 m
2
/g, a porosity of 0.2-0.4 cm
3
/g and a copper surface area of 1.0-3.0 m
2
/g and, on the other hand, active carbon-supported copper catalysts which have a copper content, calculated as CuO, of 2-8% by weight, a surface area of 500-1000 m
2
/g, a porosity of 0.5-0.8 cm
3
/g and a copper surface area of 1.0-5.0 m
2
/g.
Particularly preferably used unsupported catalysts are unsupported copper catalysts which contain TiO
2
as a further component in addition to copper and have a copper content, calculated as CuO, of 20-60% by weight, a surface area of 10-150 m
2
/g, a porosity of 0.1-0.5 cm
3
/g and a specific surface area of 0.5-3.0 m
2
/g.
The catalysts to be used according to the process are distinguished in particular by a large copper surface area of 0.1-20.0, preferably 0.5-10.0, particularly preferably 1.0-5.0, m
2
/g of catalyst. A large copper surface area is important for efficient removal of the halogen-containing impurities from the ester mixture and for a high absorption capacity of the copper-containing absorbent for the halogens eliminated. The specific copper surface area specified according to the claim is determined with the aid of N
2
O pulse chemisorption explained in more detail below.
Apparatus:
PulseChemiSorb 2705 from Micromeritics.
Sample Pretreatment:
About 0.3 g of reduced catalyst is placed in a quartz U-tube reactor with a broad sample part (d
a
-11 mm). The sample is heated in a stream of 5% H
2
/Ar (30 ml/min) at a heating rate of 5 K/min to 240° C. This is followed by reduction with hydrogen at 240° C. for two hours. The sample is then eluted for 30 minutes in a helium stream of 30 ml/min and cooled to 70° C. under this gas.
Carrying out the Measurement:
To measure the reactive N
2
O chemisorption, N
2
O pulses are metered into a helium stream of 30 ml/min by means of a metering loop (volume 1000 &mgr;l) and passed through the sample at 70° C. The pulsing is continued until four equal pulses (the same amount of N
2
O in each case) are detected in succession. The analysis of the amount of N
2
O consumed or of the N
2
formed is carried out on a short chromatographic separation column downstream of the reactor and containing Porapale-N® by means of a thermal conductivity detector.
Evaluation of the Measurement:
1. A mean value of the pulse area (MPA) in arbitrary units [a.U.] is determined from the constancy of four pulses each having the area content PA
i
. With a total of n pulses, i.e.
MPA
=
∑
i
=
n
-
3
n
PA
i
/
4
(
1
)
From this MPA value, it is possible to convert the pulse areas into &mgr;l with the aid of the reference volume RV.
xMPA [a.U. ]=yRV [&mgr;l] (2)
2. The amount of adsorbed gas AdG is calculated from the area content of the n individual pulses PF
i
as follows:
AdG
[
w
.
E
.
]
=
n
*
MPA
-
∑
i
=
1
n
PA
i
=
(
n
-
4
)
*
MPA
-
∑
i
=
1
n
-
4
PA
i
(
3
)
3. The amount of adsorbed gas AdG in &mgr;l is calculated with the aid of (2).
4. The amo
Breitscheidel Boris
Pinkos Rolf
Stein Frank
Barts Samuel
BASF - Aktiengesellschaft
Keil & Weinkauf
Price Elvis O.
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