Process for the production of ethylene glycol and/or glycollic acid esters, and catalyst therefor

In a process for producing ethylene glycol and/or a glycollic acid ester by the vapor phase catalytic hydrogenation of an oxalic acid diester in the presence of a catalyst and hydrogen gas, the improvement wherein the catalyst has the following composition formula EQU CuMo.sub.k Ba.sub.p O.sub.q wherein k, p and q represent gram-atoms of Mo, Ba and O, respectively, per gram-atom of Cu, k is a number of from 0 to 3, p is a number of from 0 to 6, and q is a number determined depending upon the atomic valence and gram-atoms of Cu, Mo and Ba, provided that k and p are not zero at the same time; and the aforesaid catalyst.

This invention relates to an improved process for producing ethylene glycol 
and/or a glycollic acid ester by the vapor (or gaseous) phase catalytic 
hydrogenation of an oxalic acid diester in the presence of a catalyst and 
hydrogen gas, and to a catalyst for use in the process. The catalyst has 
excellent performance comparable to that of conventional copper chromite 
type catalysts, and the process of this invention is free from the 
troubles associated with the treatment of the conventional 
chromium-containing catalysts after use, especially the toxic hazard of 
chromium. Furthermore, the process can give either ethylene glycol or 
glycollic acid esters selectively depending upon the reaction conditions 
employed. 
More specifically, this invention pertains, in a process for producing 
ethylene glycol and/or a glycollic acid ester by the vapor phase catalytic 
hydrogenation of an oxalic acid diester in the presence of a catalyst and 
hydrogen gas, to the improvement wherein the catalyst has the following 
composition formula 
EQU CuMo.sub.k Ba.sub.p O.sub.q ( 1) 
wherein k, p and q represent gram-atoms of Mo, Ba and O, respectively, per 
gram-atom of Cu, k is a number of from 0 to 3, p is a number of from 0 to 
6 and q is a number determined depending upon the atomic valences and 
gram-atoms of Cu, Mo and Ba, provided that k and p are not zero at the 
same time. The invention also relates to the aforesaid catalyst. 
A process for the production of ethylene glycol and glycollic acid esters 
by vapor phase catalytic hydrogenation of oxalate esters, such as dibutyl 
oxalate, at an elevated temperature in the presence of a hydrogenation 
catalyst, such as a copper chromite type catalyst, and hydrogen gas is 
known, for example, from U.S. Pat. No. 4,112,245 (corresponding to 
Japanese Patent Publication No. 42971/80), and German Pat. No. 459,603. 
The U.S. Patent states that in the process disclosed therein, 
hydrogenation catalysts containing copper either in the elementary form or 
combined with oxygen, as well as other hydrogenating metal oxides employed 
in conjunction with copper, supported or unsupported, may generally be 
used, and that especially preferred catalysts are the copper zinc chromite 
or copper chromite catalysts which may be promoted with barium or sodium 
hydroxide and which have been reduced in hydrogen. The working examples of 
this U.S. Patent disclose the use of copper zinc chromite, barium-promoted 
copper chromite, sodium hydroxide-promoted copper chromite and copper 
chromite catalysts. 
These previously recommended copper chromite-type catalysts have excellent 
catalytic performance, but since they cause troubles in industrial 
operations, their practical value is extremely reduced. Specifically, 
chromium is an essential ingredient of catalysts of the above type, but it 
is extremely difficult to recover chromium completely from spent catalysts 
with good efficiency. As is well known, chromium even in trace amounts 
shows strong toxicity to humans, and the discarding of the spent catalysts 
containing chromium causes serious environmental pollution. 
On the other hand, various general hydrogenation catalysts other than those 
of the copper chromite type are known. Examples include metal catalysts 
such as Raney nickel, cobalt, copper, iron, platinum, and palladium, and 
the oxides and sulfides of these metals. It is well known however that 
these general hydrogenation catalysts do not always show practical utility 
in all catalytic hydrogenation reactions, and unless a catalyst is 
selected which conforms to many different factors such as the mode and 
mechanism of a given reaction, the reaction conditions, etc., the desired 
reaction cannot be carried out with good efficiency, and moreover that 
there is no established guideline for the selection of such a catalyst. 
The present inventors have worked extensively in order to provide a 
catalyst free from the troubles of the aforesaid copper chromite-type 
catalysts in the production of ethylene glycol and/or a glycollic acid 
ester by the vapor phase catalytic hydrogenation reaction of an oxalic 
acid diester. As a result, they found that a novel catalyst substantially 
free from chromium and having the composition formula (1) given 
hereinabove has excellent catalytic performance comparable to that of the 
copper chromite type catalytes in the aforesaid particular reaction, and 
does not require treatment after use unlike the copper chromite type 
catalysts, and that the use of this novel catalyst makes it possible to 
form either ethylene glycol or glycollic acid esters selectively depending 
upon the reaction conditions used. 
It is an object of this invention therefore to provide an improved process 
for producing ethylene glycol and/or a glycollic acid ester by the 
vapor-phase catalytic hydrogenation of an oxalic acid diester. 
Another object of this invention is to provide a novel catalyst for the 
vapor phase catalytic hydrogenation of an oxalic acid diester. 
The above and other objects and advantages of this invention will become 
apparent from the following description. 
The catalyst in accordance with this invention has the following 
composition formula 
EQU CuMo.sub.k Ba.sub.p O.sub.q ( 1) 
wherein k, p and q represent gram-atoms of Mo, Ba and O, respectively, per 
gram-atom of Cu, k is a number of from 0 to 3, p is a number of from 0 to 
6, and q is a number determined depending upon the atomic valences and 
gram-atoms of Cu, Mo and Ba, provided that k and p are not zero at the 
same time. 
The catalyst of this invention having the composition formula (1) above can 
be prepared, for example, by the following procedure. 
A water-soluble copper compound such as cupric nitrate is dissolved in 
water to form an aqueous solution containing a copper ion, and the aqueous 
solution is added to an aqueous solution of an alkalizing agent such as an 
aqueous solution of sodium hydroxide to form a precipitate. The 
precipitate is collected by a suitable solid-liquid separating means such 
as filtration, and washed fully with water. The above operation of 
precipitate formation can be carried out at room temperature, and cooling 
or heating is not particularly required. For example, it may be carried 
out at a temperature of about 30.degree. to about 90.degree. C. The 
resulting cake-like solid is admixed with the desired calculated amounts 
of a molybdenum compound such as molybdic acid and/or a barium compound 
such as barium hydroxide. If desired, a small amount of water is further 
added. These are mixed and milled for a period of, for example, about 2 
hours to about 20 hours. The treated product is dried for a period of 
about 10 to about 20 hours. The resulting catalyst may be used in the 
vapor phase catalytic hydrogenation of an oxalic acid diester according to 
this invention after it is subjected to reducing treatment. The reducing 
treatment can be carried out, for example, in a hydrogen stream at a 
temperature of, for example, about 160.degree. to 250.degree. C., for a 
period of, for example, about 0.5 to about 5 hours. 
The copper compound (including copper salts) used in the catalyst 
preparation may be any water-soluble copper compound. Examples include 
copper nitrate, copper sulfate, copper chloride, copper oxalate and copper 
acetate. Cupric nitrate is especially preferred. The aqueous solution 
containing an alkalizing agent is, for example, an aqueous solution of an 
alkali such as sodium hydroxide, potassium hydroxide, and sodium 
carbonate, but is not limited thereto. Preferably, the alkalizing agent is 
used in an amount sufficient to precipitate a copper ion substantially 
completely. 
Sources of molybdenum and barium which are used in the above catalyst 
preparation may include molybdic acid (H.sub.2 MoO.sub.4), barium 
hydroxide [Ba(OH).sub.2 ], ammonium molybdate, molybdenum oxide, barium 
oxide, and barium molybdate which contains both Mo and Ba. These specific 
names of compounds are given only for the purpose of illustration. 
According to the process of this invention, an oxalic acid diester is 
catalytically hydrogenated in the vapor phase in the presence of the 
aforesaid catalyst. 
Preferred examples of the starting oxalate are di(C.sub.1 -C.sub.8)-alkyl 
esters of oxalic acid, specifically dimethyl oxalate, diethyl oxalate, 
dibutyl oxalate, diamyl oxalate, etc. 
The known reaction conditions disclosed, for example, in the above cited 
U.S. Pat. No. 4,112,245 (corresponding to Japanese Patent Publication No. 
42971/1980), German Pat. No. 459,603, and British Pat. No. 2,031,883 
(corresponding to Japanese Laid-Open Patent Publication No. 40685/1980) 
can be properly selected for the practice of the process of the present 
invention. The preferred reaction conditions for the vapor phase catalytic 
hydrogenation in the presence of the catalyst of this invention are as 
follows: 
Temperature: about 120.degree. to about 300.degree. C., preferably about 
150.degree. to about 240.degree. C. 
Contact time: about 0.01 to about 20 seconds, preferably about 0.2 to about 
6 seconds 
pressure: about 0.1 to about 200 atmospheres, preferably about 0.5 to about 
50 atmospheres, 
Hydrogen/oxalate mole ratio: at least about 2, preferably about 10 to about 
500 
Generally, both ethylene glycol and a glycollic acid ester can be formed by 
the vapor phase catalytic hydrogenation of an oxalic acid diester in the 
presence of the catalyst having the composition formula (1). Ethylene 
glycol is formed at a high selectivity when k+p is not more than 2 and the 
ratio of k to p is within the range of from 0.5 to 2 in the catalyst 
(namely when the total gram-atoms of molybdenum and barium atoms in the 
catalyst are not more than two times the gram-atoms of copper and the 
ratio of the gram-atoms of the molybdenum atom to the gram-atoms of the 
barium atom is from 0.5 to 2). This tendency becomes especially remarkable 
when k+p is 1.5 or below and the k/p ratio is about 1, for example 0.8 to 
1.2. 
When the reaction pressure in the vapor phase catalytic hydrogenation in 
the presence of the catalyst of this invention is present at a relatively 
low value (for example, at 0.5 to 3 atmospheres), the glycollate tends to 
be formed in a relatively large amount. Conversely, when it is prescribed 
at a higher value (for example, more than 3 atmospheres), ethylene glycol 
tends to be formed in a relatively large amount. 
The ratio between ethylene glycol and the glycollate in the reaction 
product obtained by the hydrogenation reaction of the oxalate in the 
presence of the catalyst of this invention shows the aforesaid tendency 
according to the proportions of the catalyst ingredients and the reaction 
pressure. Hence, the ratio between the components of the reaction product 
can be varied as desired by properly selecting and presetting these 
conditions. Furthermore, it is possible to obtain substantially only one 
of ethylene glycol and glycollate selectively.

The following examples illustrate the present invention more specifically. 
EXAMPLE 1 
One hundred grams of cupric nitrate trihydrate [Cu(NO.sub.3).sub.2.3H.sub.2 
O] was dissolved in 400 ml of water. The aqueous solution was added to 300 
ml of an aqueous solution of sodium hydroxide at about 80.degree. C. 
(prepared by dissolving 35 g of sodium hydroxide in 300 ml of water) to 
form a precipitate at about 80.degree. C. Th precipitate was collected by 
filtration, and fully washed with water to form a cake-like solid. 
Molybdic acid (0.83 g) and 1.7 g of barium hydroxide were added to the 
solid, and then a small amount of water was added. They were fully mixed 
and milled for 16 hours. The resulting mixture was dried at about 
140.degree. C. for 12 hours. In the resulting catalyst, the Cu:Mo:Ba 
atomic ratio was 1:0.01:0.01. 
1.0 g of the resulting catalyst was taken, and filled in a stainless steel 
reaction tube (4 mm in inside diameter). While the catalyst in the 
reaction tube was heated at 200.degree. C., hydrogen gas was passed 
through the catalyst for 4 hours to reduce the catalyst. Diethyl oxalate 
was hydrogenated in the reaction tube at each of the temperatures shown in 
Table 1 under atmospheric pressure with a contact time of 1.5 g.second/ml. 
The hydrogen/diethyl oxalate mole rate in the feed was set at 200. The 
results are shown in Table 1. 
TABLE 1 
______________________________________ 
Conversion 
Reaction of diethyl Selectivity to 
Selectivity to 
temperature 
oxalate ethylene ethyl glycol- 
(.degree.C.) 
(%) glycol (%) late (%) 
______________________________________ 
190 100 89.9 0.7 
180 100 86.7 3.0 
______________________________________ 
EXAMPLE 2 
A catalyst in which the Cu:Mo:Ba ratio atomic ratio was 1:0.06:0.06 was 
prepared in the same way as in Example 1 except that the amounts of 
molybdic acid and barium hydroxide were changed. Diethyl oxalate was 
hydrogenated under the same conditions as in Example 1 except that the 
resulting catalyst was used, and the reaction temperature was varied as 
shown in Table 2. The results are shown in Table 2. 
TABLE 2 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl glycol- 
(.degree.C.) 
oxalate (%) glycol (%) late (%) 
______________________________________ 
193 100 93.4 1.0 
175 99.5 87.2 7.8 
______________________________________ 
EXAMPLE 3 
A catalyst in which the atomic ratio of Cu:Mo:Ba was 1:0.1:0.1 was prepared 
in the same way as in Example 1 except that the amounts of molybdic acid 
and barium hydroxide were changed. Diethyl oxalate was hydrogenated under 
the same conditions as in Example 1 except that the resulting catalyst was 
used, and the reaction temperature was changed as shown in Table 3. 
TABLE 3 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl glycol- 
(.degree.C.) 
oxalate (%) glycol (%) late (%) 
______________________________________ 
180 100 91.1 0.8 
170 100 75.4 21.3 
______________________________________ 
EXAMPLE 4 
A catalyst in which the atomic ratio of Cu:Mo:Ba was 1:0.2:0.2 was prepared 
in the same way as in Example 1 except that the amounts of molybdic acid 
and barium hydroxide were changed. Diethyl oxalate was hydrogenated under 
the samd conditions as in Example 1 except that the resulting catalyst was 
used and the reaction temperature was changed as shown in Table 4. The 
results are shown in Table 4. 
TABLE 4 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl 
(.degree.C.) 
oxalate (%) glycol (%) glycollate (%) 
______________________________________ 
190 100 87.0 0 
185 100 93.9 0 
177 100 97.7 1.2 
______________________________________ 
EXAMPLE 5 
A catalyst in which the Cu:Mo:Ba atomic ratio was 1:0.5:0.5 was prepared in 
the same way as in Example 1 except that the amounts of molybdic acid and 
barium hydroxide were changed. Diethyl oxalate was hydrogenated under the 
same conditions as in Example 1 except that the resulting catalyst was 
used and the reaction temperature was changed as shown in Table 5. The 
results are shown in Table 5. 
TABLE 5 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl 
(.degree.C.) 
oxalate (%) glycol (%) glycollate (%) 
______________________________________ 
200 98.3 47.5 50.6 
210 100 74.1 20.9 
220 100 73.9 6.1 
210* 100 80.1 1.9 
200* 100 63.2 26.8 
______________________________________ 
The reactions at the asterisked temperatures were carried out with a 
contact time of 3.0 g.sec/ml. 
EXAMPLE 6 
A catalyst in which the Cu:Mo:Ba atomic ratio was 1:2:2 was prepared in the 
same way as in Example 1 except that the amounts of molybdic acid and 
barium hydroxide were changed. Diethyl oxalate was hydrogenated under the 
same conditions as in Example 1 except that the resulting catalyst was 
used and the reaction temperature was changed as shown in Table 6. The 
results are shown in Table 6. 
TABLE 6 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl 
(.degree.C.) 
oxalate (%) glycol (%) glycollate (%) 
______________________________________ 
210 46.4 0 88.1 
220* 53.6 0 83.2 
240* 81.4 0 75.6 
______________________________________ 
The reactions at the asterisked temperatures were carried out with a 
contact time of 3.0 g.sec/ml. 
EXAMPLE 7 
A catalyst in which the Cu:Mo:Ba atomic ratio was 1:0.2:0.01 was prepared 
in the same way as in Example 1 except that the amounts of molybdic acid 
and barium hydroxide were changed. Diethyl oxalate was hydrogenated under 
the same conditions as in Example 1 except that the resulting catalyst was 
used and the reaction temperature was changed as shown in Table 7. The 
results are shown in Table 7. 
TABLE 7 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl 
(.degree.C.) 
oxalate (%) glycol (%) glycollate (%) 
______________________________________ 
190 96.3 0 77.1 
185 85.3 0 80.3 
______________________________________ 
EXAMPLE 8 
A catalyst in which the Cu:Mo:Ba atomic ratio of 1:0.01:0.2 was prepared in 
the same way as in Example 1 except that the amounts of molybdic acid and 
barium hydroxide were changed. Diethyl oxalate was hydrogenated under the 
same conditions as in Example 1 except that the resulting catalyst was 
used and the reaction temperature was changed to 193.degree. C. 
Analysis of the products in the early stage of the reaction showed a 
diethyl oxalate conversion of 99.6%, an ethylene glycol selectivity of 
85.9%, and an ethyl glycollate selectively of 16.2%. 
EXAMPLE 9 
A catalyst in which the Cu:Mo atomic ratio was 1:0.2 was prepared in the 
same way as in Example 1 except that the amount of molybdic acid was 
changed and barium hydroxide was not added. Diethyl oxalate was 
hydrogenated under the same conditions as in Example 1 except that the 
resulting catalyst was used and the reaction temperature was changed as 
shown in Table 8. The results are shown in Table 8. 
TABLE 8 
______________________________________ 
Reaction Conversion of 
Selectivity to 
Selectivity to 
temperature 
diethyl ethylene ethyl 
(.degree.C.) 
oxalate (%) glycol (%) glycollate (%) 
______________________________________ 
200 54.4 0 91.3 
210 84.4 0 86.2 
218 94.6 0 81.7 
______________________________________ 
EXAMPLE 10 
A catalyst in which the atomic ratio of Cu:Ba was 1:0.2 was prepared in the 
same way as in Example 1 except that the amount of barium hydroxide was 
changed and molybdic acid was not added. 
Diethyl oxalate was hydrogenated under the same conditions as in Example 1 
except that the resulting catalyst was used and the reaction temperature 
was changed to 190.degree. C. 
Analysis of the reaction poducts in the early stage of the reaction showed 
a diethyl oxalate conversion of 73.6%, an ethylene glycol selectivity of 
53.7%, and an ethyl glycollate selectivity of 31.2%. 
EXAMPLES 11 TO 14 
Ten milliliters (12.1 g) of the catalyst prepared in Example 4 was taken, 
and filled in a stainless steel reaction tube (10 mm in inside diameter). 
The catalyst was then subjected to a reducing treatment under the same 
conditions as set forth in Example 1. Diethyl oxalate was hydrogenated in 
the reaction tube under the various reaction conditions shown in Table 9. 
TABLE 9 
__________________________________________________________________________ 
Reaction conditions Results 
Mole ratio 
Conversion 
Selectivity 
Selectivity 
Temper- of hydrogen/ 
of diethyl 
to ethylene 
to ethyl 
ature 
Pressure LHSV diethyl 
oxalate 
glycol 
glycollate 
Example 
(.degree.C.) 
(kg/cm.sup.2 .multidot. G) 
SV (hr.sup.-1) 
(g/ml .multidot. hr) 
oxalate 
(%) (%) (%) 
__________________________________________________________________________ 
11 225 0 (atmospheric) 
5300 0.11 315 100 62.7 37.0 
12 195 3 1400 0.024 383 100 87.0 0 
13 210 3 5550 0.083 435 100 95.9 0 
14 225 3 5810 0.198 213 100 85.4 11.3 
__________________________________________________________________________ 
The above examples demonstrate that when the hydrogenation catalyst of this 
invention is used in the hydrogenation of the oxalate, the oxalate reacts 
at a high conversion and the selectivities to ethylene glycol and the 
glycollate are high.