Method of producing carbonic acid diester

A carbonic acid diester is produced, at a high reaction rate with a high selectivity and stability, by catalytically reacting carbon monoxide with a nitrous acid ester, preferably in a gas phase, in the presence of a solid catalyst composed of a solid carrier and a catalytic solid material deposited on the carrier and comprising: (1) a first catalyst component comprising at least one member selected from the group consisting of platinum group metals and compounds thereof; (2) a second catalyst component comprising at least one member selected from the group consisting of lanthanide group metals and compounds thereof; and collecting the resultant carbonic acid diester from a reaction mixture discharged from the catalytic reaction step.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of producing a carbonic acid 
diester. 
More particularly, the present invention relates to a process of 
continuously producing a carbonic acid diester from carbon monoxide and a 
nitrous acid ester by using a new type of catalyst having a high 
selectivity, at a high reaction rate with a high selectivity and stability 
over a long period of time. 
The carbonic acid diester is very useful as a starting material of 
medicines and pesticides, and as an intermediate compound of a 
polycarbonate and urethane. 
2. Description of the Related Art 
A conventional method of producing a carbonic acid diester by a reaction of 
phosgene with an alcohol is well known, and has been practiced for some 
time. Nevertheless, this conventional method is disadvantageous in that 
phosgene has an extremely strong toxicity, and thus, is not preferable as 
a starting material in view of environmental and health considerations. 
Also, the reaction of phosgene with an alcohol produces hydrochloric acid 
as a by-product, which corrodes the reaction device. 
Therefore, there is a strong demand for a new method of producing a 
carbonic acid diester without using phosgene. 
In response to this demand, various attempts have been made to produce a 
carbonic acid diester from an alcohol and carbon monoxide, as disclosed 
in, for example, Japanese Unexamined Patent Publication (Kokai, JP-A) No. 
60-75,447, and 63-72,650, and Japanese Examined Patent Publication 
(Kokoku, JP-B) 63-38,018. 
In those methods, the carbonic acid diester is produced by a catalytic 
oxygen-oxidizing reaction of carbon monoxide with an alcohol in a liquid 
phase, in the presence of a catalyst consisting of a copper halide or 
palladium halide. 
These methods are disadvantageous in that, in the catalytic 
oxygen-oxidizing reaction, carbon dioxide is produced as a by-product, and 
thus the production of the carbonic acid diester is effected with a low 
selectivity based on the amount of carbon monoxide supplied to the 
reaction system. Also, the catalytic oxygen-oxidizing reaction produces 
water (H.sub.2 O) as another by-product, and thus the resultant carbonic 
acid diester must be isolated from the water by a difficult refining 
procedure. Also, the above-mentioned methods are further disadvantageous 
in that since the reaction is carried out in a liquid phase, the resultant 
carbonic acid diester must be separated from the catalyst in the reaction 
system. 
Accordingly, the above-mentioned methods are not satisfactory for 
industrial use. 
There have been attempts made to eliminate the above-mentioned 
disadvantages, and as one such attempt.sub., Japanese Unexamined Patent 
Publication No. 60-181,051 discloses a method of producing carbonic acid 
diester by a catalytic oxidizing reaction of a nitrous acid ester with 
carbon monoxide, in a gas phase, in the presence of a catalyst composed of 
a solid platinum group metal or compound thereof carried on a solid 
carrier and an oxidant in an amount of 10 molar % in terms of O.sub.2, per 
mole of carbon monoxide present in the reaction mixture. 
In this method, the oxidant in the above-mentioned specific amount based on 
the carbon monoxide effectively inhibits a production of oxalic acid 
diester as a by-product, but the addition of the oxidant in the 
above-mentioned specific acid based on the amount of the carbon monoxide 
cannot completely inhibit the production of the oxalic acid diester, and 
therefore, the desired carbonic acid diester is produced with an 
unsatisfactorily low selectivity. Also the reaction rate and the 
durability of the catalyst are unsatisfactory. 
Further, the above-mentioned method is further disadvantageous in that the 
proportion of nitrous acid ester in a reaction mixed gas comprising the 
nitrous acid ester, carbon monoxide, alcohol and oxygen is higher than an 
explosion (flammable) limit of the mixed gas, and thus this reaction mixed 
gas is not preferable in view of the safety of the procedure. 
Accordingly this method is not satisfactory for practical use. 
Japanese Unexamined Patent Publication Nos. 3-141,243 and 4-139,152 
disclose a method of producing dimethyl carbonate by a catalytic reaction 
of carbon monoxide with methyl nitrite in a gas phase by using a catalyst 
comprising a carrier, for example, activated carbon, and a catalytic 
member selected from compounds of platinum group metals, for example, 
palladium chloride and palladium sulfate, and compounds of metals selected 
from iron, copper, bismuth, cobalt, nickel and tin, and carried on the 
carrier. This method is unsatisfactory in catalytic activity and 
durability of the catalyst for practical use. 
Japanese Unexamined Patent Publication No. 4-89,458 discloses a method of 
producing dimethyl carbonate by a catalytic reaction of carbon monoxide 
with methyl nitrite in a gas phase, in the presence of a catalyst 
comprising a carrier consisting of, for example, activated carbon, and a 
catalytic member selected from compounds of platinum group metals, for 
example, palladium chloride and palladium sulfate, and compounds of 
specific metals selected from iron, copper, bismuth, cobalt, nickel and 
tin, and further in the presence of a small amount of hydrogen chloride, 
while maintaining the catalytic activity of the catalyst at a high level 
over a long period of time. However, the practical life span of the 
catalyst is not always satisfactory, and thus there is a demand for an 
improved method satisfactory for practical use. 
As mentioned above, the conventional methods of producing carbonic acid 
diester from nitrous acid ester and carbon monoxide are unsatisfactory in 
the durability of the catalyst and are not always satisfactory in reaction 
rate and selectivity. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method of producing a 
carbonic acid diester from a nitrous acid ester and carbon monoxide by a 
catalytic reaction procedure, by which the resultant carbonic acid diester 
can be easily isolated and recovered. 
Another object of the present invention is to provide a method of producing 
a carbonic acid diester from a nitrous acid ester and carbon monoxide in 
the presence of a catalyst having a high resistance to deterioration and 
deactivation and thus usable stably over a long period of time. 
Still another object of the present invention is to provide a method of 
producing a carbonic acid diester by a catalytic reaction of a nitrous 
acid ester with carbon monoxide under moderate and safe reaction 
conditions, at a high reaction rate with a high selectivity and stability. 
The above-mentioned objects can be attained by the method of the present 
invention for producing a carbonic acid diester, which comprises the steps 
of: 
(A) catalytically reacting carbon monoxide with a nitrous acid ester in the 
presence of a solid catalyst composed of a solid carrier and a catalytic 
solid material carried on the carrier and comprising: 
(1) a first catalyst component comprising at least one member selected from 
the group consisting of platinum group metals and compounds thereof; 
(2) a second catalyst component comprising at least one member selected 
from the group consisting of lanthanide group metals and compounds 
thereof; and 
(B) collecting the resultant carbonic acid diester from a reaction mixture 
discharged from the catalytic reaction step (A). 
In the method of the present invention, the catalytic solid material 
optionally further comprises at least one additional component selected 
from the group consisting of iron, copper, bismuth, cobalt, nickel, tin, 
vanadium, molybdenum and tungsten, and compounds of the above-mentioned 
metals. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the method of the present invention, a nitrous acid ester is reacted 
with carbon monoxide in the presence of a specific solid catalyst to 
produce a carbon acid diester at a high reaction rate with a high 
selectivity and stability. Preferably, the catalytic reaction is carried 
out in a gas phase. 
The nitrous acid ester usable for the method of the present invention is 
preferably selected from the group consisting of nitrites of lower 
aliphatic monohydric alcohols having 1 to 4 carbon atoms, for example, 
methyl nitrite, ethyl nitrite, n-propyl nitrite, isopropyl nitrite, 
n-butyl nitrite, isobutyl nitrite and sec-butyl nitrite; nitrites of 
cycloaliphatic monohydric alcohols, for example, cyclohexyl nitrite; and 
nitrites of aralkyl monohydric alcohols, for example, benzyl nitrite and 
phenylethyl nitrite. 
Among the above-mentioned nitrous acid esters, the nitrites of aliphatic 
monohydric alcohols having 1 to 4 carbon atoms are preferable for the 
present invention, and the most preferable nitrous acid esters for the 
present invention are methyl nitrite and ethyl nitrite. 
The solid catalyst usable for the present invention comprises a solid 
carrier and a catalytically active solid material carried on the solid 
carrier. 
The catalytic solid material comprises: 
(1) a first catalyst component consisting of at least one member selected 
from the group consisting of platinum group metals, for example, 
palladium, platinum, iridium, ruthenium and rhodium, and compounds of the 
platinum group metals, preferably platinum group metal compounds; and 
(2) a second catalyst component consisting of at least one member selected 
from the group consisting of lanthanide group metals and compounds 
thereof. 
The platinum group metal compounds usable for the first catalyst component 
include halides, for example, chlorides, bromides, iodides and fluorides, 
inorganic acid salts, for example, nitrates, sulfates, and phosphates, and 
organic acid salts, for example, acetates, and benzoates of the platinum 
group metals. 
The platinum group compounds preferably selected from the group consisting 
of halides, for example, palladium chloride, palladium bromide, palladium 
iodide, palladium fluoride, lithium tetrachloropalladate, sodium 
tetrachloropalladate, potassium tetrachloropalladate, platinum chloride, 
iridium chloride, ruthenium chloride, ruthenium bromide, rhodium chloride, 
rhodium bromide, ,and rhodium iodide; inorganic acid salts, for example, 
palladium nitrate, palladium sulfate, palladium phosphate, rhodium nitrate 
and rhodium sulfate; and organic acid salts, for example, palladium 
acetate, palladium benzoate and rhodium acetate. 
Among the above-mentioned compounds, the halides and sulfates of palladium, 
ruthenium and rhodium are particularly preferable for the present 
invention, but the most preferable compound for the first catalyst 
component is palladium chloride. 
The chlorides of the platinum group metals usable for the present invention 
are not limited to those as mentioned above. The substances usable for the 
first catalyst component may be platinum group metals or the compound of 
the metals, which are capable of producing complexes contributory to the 
reaction of the above-mentioned chlorides or chlorine in the presence of 
hydrogen chloride. 
In the second catalyst component (2) of the present invention the 
lanthanide group metal is selected from the group consisting of lanthanum, 
cerium, praseodymium, neodymium, promethium, samarium, europium, 
gadolinium terbium dysprosium, holmium, erbium, thulium, ytterbium, and 
lutetium. 
Also, the lanthanide group metal compound is selected from the group 
consisting of oxides, halides, and inorganic and organic salts of the 
lanthanide group metals. 
Preferably, the lanthanide group metal compound is selected from oxides, 
chlorides and nitrates of the lanthaide group metal. 
Optionally, the catalytic solid material usable for the present invention 
further comprises at least one additional component selected from the 
group consisting of iron, copper, bismuth, cobalt, nickel, tin, vanadium, 
molybdenum, tungsten, and compounds of the above-mentioned metals. 
The compounds of iron, copper, bismuth, cobalt, nickel, and tin are 
halides, for example, chlorides, bromides iodides and fluorides inorganic 
acid salts, for example, nitrates, sulfates and phosphates, and organic 
acid salts, for example, acetates, of the above-mentioned metals. 
Preferably, the metal compounds usable for the additional catalyst 
component are selected from iron, copper, bismuth, cobalt, nickel, tin, 
halides and sulfates of the above-mentioned metals. 
The compounds of vanadium, molybdenum, and tungsten are oxides, metal 
acids, metal salts of the metal acids and ammonium salts of the metal 
acids of the above-mentioned metals. 
The vanadium, molybdenum and tungsten compounds usable for the additional 
catalyst components may be selected from metal oxides, namely vanadium 
oxide, molybdenum oxide, and tungsten oxide; and metal acid ammonium 
salts, for example, ammonium vanadate, ammonium molybdate and ammonium 
tungstate. 
The solid carrier usable for the method of the present invention preferably 
comprises at least one member selected from the group consisting of 
diatomaceous earth, activated carbon, silicon carbide, titania, zeolite, 
alumina, for example, .gamma.-alumina, and silica-alumina. The activated 
carbon, zeolite, alumina, and silica-alumina are the most preferable 
materials for the solid carrier. 
The catalytically active solid material can be carried on the solid 
deposited by a conventional application method, for example, an 
impregnating immersion-absorption method in which the solid carrier is 
immersed in a dispersion of the catalytic solid material in the form of 
fine particles, so that the catalytic solid material particles are allowed 
to be adsorbed by the solid carrier, a mix-kneading method in which a 
mixture of grains of the solid carrier and fine particles of the catalytic 
solid material is kneaded so that the catalytic solid material particles 
are adhered to the solid carrier grains, a deposition method in which fine 
particles of the catalytic solid particles are deposited on the solid 
carrier grains, an evaporate-drying method in which a dispersion of the 
catalytic solid material in a volatile solvent is applied to solid carrier 
grains and then the resultant product is dried by evaporating away the 
volatile solvent, or a co-precipitation method in which the solid carrier 
and the catalytic solid material are co-precipitated from a solution 
thereof so that the precipitated catalytic solid material in the form of 
fine particles is carried on the precipitated solid carrier in the form of 
grains or particles. 
Preferably, in the preparation of the solid catalyst of the present 
invention, the impregnating method and the evaporate-drying method are 
utilized, because these methods are simple and easy. 
These methods are carried out by using a solvent. The solvent is preferably 
selected from for example, aqueous hydrochloric acid solution, aqueous 
ammonia solution and alcohols, which are capable of dissolving uniformly 
the above-mentioned catalyst components. 
In the preparation of the solid catalyst, the catalyst components may be 
carried at one time or successively stepwise. 
In the solid catalyst of the present invention, the first catalyst 
component is preferably present in an amount, in terms of the platinum 
group metal as used, of 0.1% to 10% by weight, more preferably 0.5% to 2% 
by weight, based on the weight of the solid carrier. 
Also, the second catalyst component (lanthanide group metals or compounds 
thereof) preferably present in an amount, in terms of the lanthanide group 
metal as used, of 0.1 to 50 gram atom equivalents, more preferably to 10 
gram atom equivalents, per gram atom equivalent of the first catalyst 
component in terms of the platinum group metal contained therein. 
Further, the additional catalyst component comprising at least one member 
selected from iron, copper, bismuth, cobalt, nickel, tin and compounds 
thereof is preferably present in an amount, in terms of the metal as used, 
of 0.1 to 50 gram atom equivalents, more preferably 1 to 10 gram atom 
equivalents, per gram atom equivalent of the first catalyst component in 
terms of the platinum group metal contained therein. 
Furthermore, the additional catalyst component comprising at least one 
member selected from vanadium, molybdenum, tungsten and compounds thereof 
is preferably present in an amount, in terms of the metal as used, of 0.1 
to 20 gram atom equivalent, more preferably 0.5 to 10 gram atom 
equivalent, per gram atom equivalent of the first catalyst component in 
terms of the platinum group metal contained therein. 
Usually, the solid catalyst usable for the present invention is in the form 
of fine particles, coarse particles, grains or other shapes. There is no 
limitation of the size of the solid catalyst. 
Preferably, the solid catalyst in the form of fine particles has a size of 
from 20 to 100 .mu.m. 
Also, the solid catalyst in the form of coarse particles preferably has a 
mesh size of from 4 to 200. 
Further, the solid catalyst in the form of grains or shaped articles 
preferably has a size of 0.5 to 10 mm. 
The catalytic reaction step of the nitrous acid ester with carbon monoxide 
can be carried out in a batch system or a continuous reaction system in a 
gas phase or a liquid phase. The continuous reaction system in a gas phase 
is advantageous for an industrial production of the carbonic acid diester. 
In any reaction system, the solid catalyst of the present invention may be 
placed in a fixed catalyst bed or a fluidized catalyst bed of a reactor. 
When the specific solid catalyst of the present invention is employed, the 
catalytic reaction of a nitrous acid ester with carbon monoxide can be 
effectively conducted even under moderate conditions. For example, the 
catalytic reaction in the method of the present invention can be effected 
at a temperature of from 0.degree. C. to 200.degree. C., preferably from 
50.degree. C. to 140.degree. C. under the ambient atmospheric pressure. Of 
course, the catalytic reaction of the present invention can be effected 
under pressurized conditions, without difficulty. For example, the 
catalytic reaction of the present invention can be carried out at a 
temperature of 50.degree. to 150.degree. C. under a pressure of 1.degree. 
to 20 kg/cm.sup.2 G. 
The nitrous acid ester usable as a starting substance for the method of the 
present invention can be easily prepared, for example, by decomposing 
sodium nitrite in an aqueous solution in the presence of nitric acid or 
sulfuric acid to generate a mixed gas of nitrogen monoxide (NO) and 
nitrogen dioxide (NO.sub.2), oxidizing a portion of the nitrogen monoxide 
(NO) in the mixed gas with molecular oxygen to convert same to nitrogen 
dioxide (NO.sub.2) and to provide a NOx gas having a molar ratio of 
nitrogen monoxide to nitrogen dioxide, NO/NO.sub.2, of 1/1, and bringing 
the NOx gas into contact with an alcohol. 
In another method, after the catalytic reaction is completed, a reaction 
gas is discharged from the reactor, nitrogen monoxide (NO) generated from 
the nitrous acid ester is separated from the discharged reaction gas, and 
then reacted with oxygen and the corresponding alcohol to re-produce a 
nitrous acid ester. 
In the above-mentioned methods, the nitrous acid ester-preparation step and 
the carbon monoxide-nitrous acid ester reaction step are preferably 
carried out in a slightly pressurized system, for example, under a 
pressure of about 2 to 3 kg/cm.sup.2. 
The nitrous acid ester-containing gas prepared by the above-mentioned 
methods, contains, in addition to the nitrous acid ester, unreacted 
alcohol, nitrogen oxides (particularly NO), and occasionally a small 
amount of water and/or oxygen. This type of nitrous acid ester-containing 
gas can be employed as a nitrous acid ester source and a good result can 
be obtained. 
In the method of the present invention, the starting materials, i.e., 
carbon monoxide and a nitrous acid ester, are fed in a gas phase into a 
reactor. In this feed gas, the starting materials are preferably diluted 
with an inert gas, for example, a nitrogen, argon or carbon dioxide gas. 
The feed gas for the catalytical reaction step need not have a specific 
composition, but from the viewpoint of safety, the feed gas preferably has 
a content of the nitrous acid ester of 20% by volume or less, more 
preferably, 5 to 20% by volume. Also, from the viewpoint of economy, the 
content of carbon monoxide in the feed gas is from 5% to 20% by volume. 
When the nitrous acid ester is diluted with carbon monoxide in place of the 
inert gas, and the resultant feed gas is fed into a reactor, the content 
of carbon monoxide in the feed gas is allowed to be raised up to 80% by 
volume. Nevertheless, in an industrial production process, it is 
preferable that the feed gas to be subjected to the reaction be returned 
to the reaction step for reuse by discharging a portion of the returned 
gas to the outside of the reaction system. Also, usually, carbon monoxide 
is consumed at a conversion of about 20% to 30% by volume per one pass 
through the reaction system. Therefore, a content of carbon monoxide of 
more than 20% by volume in the feed gas does not bring any advantage but 
results in an increased loss thereof. 
Also, a content of carbon monoxide of less than 5% by volume brings an 
unsatisfactory productivity of a carbonic acid diester. Accordingly, from 
the view point of economy, the content of carbon monoxide in the feed gas 
is preferably in the range of from 5% to 20% by volume. 
In the method of the present invention, the feed gas preferably contains 
carbon monoxide in a molar ratio to a nitrous acid ester of 0.1/1 to 10/1, 
more preferably 0.25/1 to 1/1. Also, the feed gas is preferably fed into a 
catalytic reaction step (reactor) at a space velocity of 500 to 20,000 
hr.sup.-1, more preferably 2,000 to 15,000 hr.sup.-1. 
In the method of the present invention, it is preferable that a reduction 
in catalytic activity of the catalyst be prevented by carrying out the 
catalytic reaction of carbon monoxide with a nitrous acid ester in the 
presence of a catalytic activity reduction-inhibiting agent comprising at 
least one member selected from the group consisting of hydrogen chloride 
and chloroformic acid esters. 
In this method, hydrogen chloride is preferably anhydrous, and the 
chloroformic acid esters are preferably selected from the group consisting 
of esters of chloroformic acid with a lower aliphatic monohydric alcohols, 
for example, methyl chloroformate, ethyl chloroformate, n-propyl 
chloroformate, isopropyl chloroformate, n-butyl chloroformate, isobutyl 
chloroformate and sec-butyl chloroformate; esters of chloroformic acid 
with cycloaliphatic alcohols, for example, cyclohexyl chloroformate, and 
esters of chloroformic acid with aralkyl alcohols, for example, 
phenylethyl chloroformate. Usually, a chloroformic acid ester having the 
same alkoxyl group as in the nitrous acid ester used is preferably 
employed. 
There is no restriction to a manner in which hydrogen chloride or a 
chloroformic acid ester is incorporated into the reaction system. For 
example, a small amount of hydrogen chloride or a chloroformic acid ester 
is continuously added to the reaction system in the following manner. 
When hydrogen chloride is continuously added, if the amount of hydrogen 
chloride is too large, the hydrogen chloride is adsorbed by the catalyst 
and the catalytic reaction is hindered. Therefore, the amount of hydrogen 
chloride to be added to the reaction system is preferably controlled to a 
specific level of 1 to 50 molar %, more preferably 5 to 20 molar %, based 
on the molar amount of the platinum group metal in the catalyst, per unit 
time. Particularly, where the catalytic reaction is carried out in a fixed 
bed type reactor at a gas phase space velocity (GHSV) of 3,000 hr.sup.-1, 
hydrogen chloride is preferably added in an amount of 5 to 500 ppm by 
volume, more preferably 10 to 100 ppm by volume into the feed gas and the 
hydrogen chloride-containing feed gas is continuously fed into the 
reactor. 
When a chloroformic acid ester is continuously added to the reaction 
system, there is no upper limit to the amount of the chloroformic acid 
ester. However, the use of chloroformic acid ester in a too large an 
amount is economically disadvantageous. It is preferable that the 
chloroformic acid ester be added in an amount of 1% by volume or less, 
more preferably 1000 ppm by volume or less to the feed gas, and the 
chloroformic acid ester-containing feed gas be fed continuously into the 
reactor. 
The addition of the chloroformic acid ester to the feed gas can be carried 
out in one of the following manners. 
In one manner, a nitrogen gas flows on a surface of a heated chloroformic 
acid ester to allow a vapor generated from the heated chloroformic acid 
ester to be incorporated into the nitrogen gas stream. 
In another manner, a reactor equipped with an inlet conduit for feeding a 
feed gas and another inlet conduit for feeding a chloroformic acid 
ester-containing gas is used. The chloroformic acid ester is evaporated in 
an evaporator arranged outside of the reactor, and the resultant 
chloroformic acid ester vapor is fed together with a carrier gas 
consisting of, for example, nitrogen gas, into the reactor through the 
above-mentioned other inlet conduit. 
Other manners usable for industrial procedures can be utilized for this 
purpose. 
When the catalytic reaction is completed, a resultant reaction gas 
(mixture) is discharged from the reactor. The resultant reaction gas 
comprises, in addition to the desired carbonic acid diester corresponding 
to the nitrous acid ester used, by-products, for example, oxalic acid 
diester, unreacted carbon monoxide and nitrous acid ester, another 
by-products, for example, nitrogen monoxide and carbon dioxide. 
The discharged reaction mixture is subjected to a cool-condensing 
procedure, a non-condensed gas fraction comprising carbon monoxide, 
nitrous acid ester, nitrogen monoxide and carbon dioxide is purged from 
the reaction mixture, and returned to the reactor. The resultant carbonic 
acid diester is easily separated from the reaction mixture and collected 
by a customary method, for example, distillation. 
The carbonic acid diesters capable of being produced by the method of the 
present invention include dialkyl carbonates, for example, dimethyl 
carbonate, diethyl carbonate, and di-n-propyl carbonate; dicycloalkyl 
carbonates, for example, dicyclohexyl carbonate; and diaralkyl carbonates, 
for example, dibenzyl carbonate. Preferably, the method of the present 
invention is utilized to produce di-lower alkyl carbonates, for example, 
dimethyl carbonate.

The present invention will be further illustrated by way of specific 
examples which are merely representative and do not restrict the scope of 
the present invention in any way. 
In the examples, the space time yield (STY) in g/liter.multidot.hr of the 
resultant product was calculated in accordance with the following equation 
(I): 
EQU STY (g/liter.multidot.hr)=a(b.times..theta.) (I) 
wherein .theta. represents a catalytic reaction time in hours of carbon 
monoxide with a nitrous acid ester in a reaction tube, a represents a 
weight in grams of the resultant carbonic acid diester during the 
catalytic reaction time .theta., and b represents a volume in liters of a 
solid catalyst present in the reaction tube. 
Also, in the examples, the selectivity X of the carbonic acid diester (for 
example, dimethyl carbonate) based on carbon monoxide, and the electivity 
Y of the carboxylic acid diester based on a nitrous acid ester were 
calculated in accordance with the following equations (II) and (III): 
EQU X(%)={C/(c+2.times.d+e)}.times.100 (II) 
EQU and 
EQU Y(%)={C/(c+d+f+g)}.times.100 (III) 
wherein X and Y are as defined above, c, d, e, f, and g respectively 
represent the amounts in moles of a carbonic acid diester, an oxalic acid 
diester, carbon dioxide, formic acid ester and dialkylformal (for example, 
methylal), each produced within the reaction time 8 in hours, under the 
given reaction conditions. 
c . . . carbonic acid diester 
d . . . oxalic acid diester 
e . . . carbon dioxide 
f . . . formic acid ester 
g . . . dialkylformal 
Example 1 
Preparation of Catalyst 
A catalyst component solution containing Pd, Cu and Ce was prepared by 
heat-dissolving 0.178 g (1 millimole) of palladium chloride (PdCl.sub.2), 
0.340 g (2 millimoles) of cupric chloride (CuCl.sub.2.2H.sub.2 O) and 
0.746 g (2 millimoles) of cerium chloride hexahydrate (CeCl.sub.3.6H.sub.2 
O) in 40 ml of methyl alcohol at a temperature of 40.degree. C. to 
50.degree. C. 
Granular activated carbon in an amount of 10 g was immersed in the 
solution, and the resultant mixture was stirred at room temperature for 
one hour. Then, methyl alcohol was evaporated away from the mixture at a 
temperature of 50.degree. C. under a reduced pressure. The resultant 
mixture was dried in a nitrogen gas atmosphere at a temperature of 
200.degree. C, to provide a solid catalyst. In the resultant catalyst, a 
mixture of PdCl.sub.2, CuCl.sub.2 and CeCl.sub.3 was carried on a carrier 
consisting of the activated carbon. The total content of the metal 
compound in terms of metallic palladium was 1.0% by weight based on the 
weight of the carrier, and the atomic ratio of Pd, Cu and Ce in the 
catalyst was Pd:Cu:Ce=1:2:2. 
Production of a Carbonic Acid Diester 
The above-mentioned solid catalyst in an amount of 1.5 ml was placed in a 
gas phase reaction tube having an inside diameter of 20 mm and equipped 
with an outside heating jacket. The reaction tube filled by the solid 
catalyst was fixed vertically and a heating medium consisting of a 
silicone oil was made to flow through the outside heating jacket to 
maintain the inside temperature of the reaction tube at a level of 
120.degree. C. 
A mixed gas consisting of 8% by volume of methyl nitrite, 8% by volume of 
carbon monoxide, 3% by volume of nitrogen monoxide, 10% by volume of 
methyl alcohol and 71% by volume of nitrogen was fed into the reaction 
tube through a top inlet thereof at a space velocity (GHSV) of 8,000 
hr.sup.-1 under the ambient atmospheric pressure. The methyl nitrite was 
produced from nitrogen monoxide, oxygen and methyl alcohol. 
In the reaction tube, the methyl nitrite reacted with carbon monoxide at a 
temperature of 120.degree. C. in the presence of the solid catalyst. 
The resultant reaction mixture discharged from the reaction tube through a 
bottom thereof was made to flow through methyl alcohol cooled with ice, to 
collect the resultant reaction product. The collected reaction product was 
subjected to gas chromatography, and it was confirmed that at 4 hours 
after the start of the reaction procedure, the space time yield (STY) of 
dimethyl carbonate was 475 g/liter.multidot.hr. 
The selectivities (X and Y) of dimethyl carbonate based on carbon monoxide 
and on methyl nitrite were 95% and 97%, respectively. 
Comparative Example 1 
Preparation of Catalyst 
A catalyst was prepared by the same procedures as in Example 1, except that 
no cerium chloride hexahydrate (CeCl.sub.3.6H.sub.2 O) was used. In the 
resultant catalyst, a catalyst solid mixture of PdCl.sub.2 and CuCl.sub.2 
was carried on a carrier consisting of the activated carbon, the total 
amount of the metal compounds was 1% by weight in terms of metallic Pd, 
based on the weight of the carrier and the atomic ratio of Pd to Cu was 
Pd:Cu=1:2. 
Preparation of Dimethyl Carbonate 
Dimethyl carbonate was produced by the same procedures as in Example 1 
except that the above-mentioned catalyst was employed for the catalyst of 
Example 1. As a result, it was confirmed that the STY of dimethyl 
carbonate was 494 g/liter.multidot.hr and the selectivities X and Y of 
dimethyl carbonate based on carbon monoxide and on methyl nitrite were 88% 
and 89%, respectively. 
Examples 2 to 17 and Comparative Example 2 
Preparation of Catalyst 
In each of Examples 2 to 17 and Comparative Example 2, a catalyst was 
produced by the same procedures as in Example 1, except that the catalyst 
was prepared from the platinum group metal compound, lanthanide group 
metal compound and at least one member selected from iron, copper, 
bismuth, cobalt, nickel, tin, vanadium, molybdenum and tungsten compounds, 
in the composition, atomic ratio and amount as shown in Table 1. 
Preparation of Dimethyl Carbonate 
Dimethyl carbonate was prepared by the same procedures as in Example 1, 
except that the above-mentioned catalyst was employed in place of the 
catalyst of Example 1. The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Item 
Selectivity of 
dimethyl 
carbonate 
(%) 
Space Based on 
time yield 
Based 
methyl 
Example 
Composition of catalyst (STY) on CO 
nitrite 
No. Metal compounds/carrier(*).sub.1 
Metal atomic ratio 
(g/liter .multidot. hr) 
[X] [Y] 
__________________________________________________________________________ 
Example 1 
PdCl.sub.2 --CeCl.sub.3 --CuCl.sub.2 /C 
Pd/Ce/Cu = 1:2:2 
475 95 97 
Comparative 
PdCl.sub.2 --CuCl.sub.2 /C 
Pd/Cu = 1:2 
494 88 89 
Example 1 
Example 
2 PdCl.sub.2 --LaCl.sub.3 --CuCl.sub.2 /C 
Pd/La/Cu = 1:2:2 
447 95 97 
3 PdCl.sub.2 --PrCl.sub.3 --CuCl.sub.2 /C 
Pd/Pr/Cu = 1:2:2 
471 95 97 
4 PdCl.sub.2 --NdCl.sub.3 --CuCl.sub.2 /C 
Pd/Nd/Cu = 1:2:2 
436 93 96 
5 PdCl.sub.2 --SmCl.sub.3 --CuCl.sub.2 /C 
Pd/Sm/Cu = 1:2:2 
475 93 96 
6 PdCl.sub.2 --EuCl.sub.3 --CuCl.sub.2 /C 
Pd/Eu/Cu = 1:2:2 
422 91 95 
7 PdCl.sub.2 --GdCl.sub.3 --CuCl.sub.2 /C 
Pd/Gd/Cu = 1:2:2 
431 94 97 
8 PdCl.sub.2 --TbCl.sub.3 --CuCl.sub.2 /C 
Pd/Tb/Cu = 1:2:2 
447 92 95 
9 PdCl.sub.2 --DyCl.sub.3 --CuCl.sub.2 /C 
Pd/Dy/Cu = 1:2:2 
413 94 97 
10 PdCl.sub.2 --HoCl.sub.3 --CuCl.sub.2 /C 
Pd/Ho/Cu = 1:2:2 
438 90 94 
11 PdCl.sub.2 --ErCl.sub.3 --CuCl.sub.2 /C 
Pd/Er/Cu = 1:2:2 
359 94 97 
12 PdCl.sub.2 --TmCl.sub.3 --CuCl.sub.2 /C 
Pd/Tm/Cu = 1:2:2 
396 90 95 
13 PdCl.sub.2 --LaNO.sub.3 --CuCl.sub.2 /C 
Pd/La/Cu = 1:2:4 
532 92 93 
14 PdCl.sub.2 --CeCl.sub.3 /C 
Pd/Ce = 1:2 
338 98 96 
15 PdCl.sub.2 --PrCl.sub.3 /C 
Pd/Pr = 1:2 
302 91 92 
16 PdCl.sub.2 --EuCl.sub.3 /C 
Pd/Eu = 1:2 
282 93 93 
17 PdCl.sub.2 --GdCl.sub.3 /C 
Pd/Gd = 1:2 
308 92 91 
Comparative 
PdCl.sub.2 --CuCl.sub.2 --(NH.sub.4).sub.10 Mo.sub.7 O.sub.24 
Pd/Cu/Mo =1:2:2.1 
485 88 85 
Example 2 
__________________________________________________________________________ 
Note: 
(*).sub.1 . . . C = activated carbon carrier 
Example 18 
Production of Dimethyl Carbonate 
The same solid catalyst as in Example 2 in an amount of 5 ml was place in a 
gas phase reaction tube having an inside diameter of 17 mm and equipped 
with an outside heating jacket. The reaction tube filled by the solid 
catalyst was fixed vertically and a heating medium consisting of a 
silicone oil was made to flow through the outside heating jacket to 
maintain the inside temperature of the reaction tube at a level of 
120.degree. C. 
A mixed gas consisting of 10% by volume of methyl nitrite, 10% by volume of 
carbon monoxide, 20% by volume of nitrogen monoxide, 9% by volume of 
methyl alcohol, 20 ppm by volume of hydrogen chloride and 57% by volume of 
nitrogen was fed into the reaction tube at a space velocity (GHSV) of 
4,000 hr.sup.-1. 
In the reaction tube, the methyl nitrite reacted with carbon monoxide at a 
temperature of 120.degree. C. under a pressure of 3 kg/cm.sup.2 G in the 
presence of the solid catalyst. 
The resultant reaction mixture was subjected to gas chromatographic 
analysis, and it was confirmed that at 4 hours after the start of the 
reaction procedure, the space time yield (STY) of dimethyl carbonate was 
600 g/liter.multidot.hr, and at 10 hours after of the start of the 
reaction procedure, the space time yield (STY) was reduced to a level of 
500 g/liter.multidot.hr. However, thereafter, the space time yield of 
dimethyl carbonate was maintained at the level of 500 g/liter.multidot.hr 
until the completion of the reaction, namely 100 hours after the start of 
the reaction. The selectivities (X and Y) of dimethyl carbonate based on 
carbon monoxide and on methyl nitrite were 97% and 98%, respectively, at 4 
hours after the start of the reaction, and 95% and 96% at 10 hours after 
the start of the reaction, and thereafter, were maintained constant at the 
levels mentioned above. 
Comparative Example 3 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 18 were carried out except that the same catalyst as in 
Comparative Example 1 was employed in an amount of 5 ml. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 500 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction, and reduced to a level of 400 g/liter.multidot.hr 
at the stage of 10 hours after the start of the reaction. Thereafter, the 
space time yield (STY) was maintained constant at the level of 400 
g/liter.multidot.hr. 
The selectivities of dimethyl carbonate were 88% based on carbon monoxide 
and 90% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, 83% based on carbon monoxide and 85% based on methyl nitrite 
at the stage of 10 hours after the start of the reaction, and thereafter 
were maintained constant at the above-mentioned levels, until the 
completion of the reaction. 
Comparative Example 4 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 18 were carried out except that the same catalyst as in 
Comparative Example 1 was employed in an amount of 5 ml and no hydrogen 
chloride was employed. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 500 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction, and reduced to a level of 350 g/liter.multidot.hr 
at the stage of 10 hours after the start of the reaction, to 250 
g/liter.multidot.hr at the stage of 20 hours after the start of the 
reaction, to a level of 150 g/liter.multidot.hr at the stage of 30 hours 
after the start of the reaction, and then to a level of 75 
g/liter.multidot.hr at the stage of 50 hours after the start of the 
reaction. 
The selectivities of dimethyl carbonate were 88% based on carbon monoxide 
and 89% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, 82% based on carbon monoxide and 84% based on methyl nitrite 
at the stage of 10 hours after the start of the reaction, 76% based on 
carbon monoxide and 78% based on methyl nitrite at the stage of 20 hours 
after the start of the reaction and then 60% based on carbon monoxide and 
63% based on methyl nitrite at the stage of 50 hours after the start of 
the reaction. 
Example 19 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 18 were carried out excepts that the same catalyst as in Example 
14 was employed in an amount of 5 ml. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 450 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction, and reduced to a level of 350 g/liter.multidot.hr 
at the stage of 10 hours after the start of the reaction. Thereafter, the 
space time yield (STY) was maintained constant at the level of 350 
g/liter.multidot.hr. 
The selectivities of dimethyl carbonate were 98% based on carbon monoxide 
and 98% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, and 96% based on carbon monoxide and 96% based on methyl 
nitrite at the stage of 10 hours after the start of the reaction, and 
thereafter were maintained approximately constant at the above-mentioned 
levels, until the completion of the reaction. 
Example 20 
preparation of Catalyst 
A catalyst was prepared by the same procedures as in Example 14 except that 
the granular activated carbon used as a carrier in Example 14 was replaced 
by y-alumina having a BET surface area of 190 m.sup.2 /g. 
The composition of the resultant catalyst was PdCl.sub.2 CeCl.sub.3 
/Al.sub.2 O.sub.3, the total amount of the metal compounds used as the 
catalyst components was 1.5% by weight in terms of metallic Pd, based on 
the weight of the carrier, and the atomic ratio of Pd to Ce was Pd:Ce=1:2. 
Production of Dimethyl Carbonate 
The above-mentioned solid catalyst in an amount of 2.5 ml was placed in a 
gas phase reaction tube having an inside diameter of 10 mm and equipped 
with an outside heating jacket. The reaction tube filled by the solid 
catalyst was fixed vertically and a heating medium consisting of a 
silicone oil was made to flow through the outside heating jacket to 
maintain the inside temperature of the reaction tube at a level of 
100.degree. C. 
A mixed gas consisting of 25% by volume of methyl nitrite, 25% by volume of 
carbon monoxide, 2% by volume of nitrogen monoxide, 8% by volume of methyl 
alcohol 500 ppm by volume of hydrogen chloride and 40% by volume of 
nitrogen was fed into the reaction tube at a space velocity (GHSV) of 
8,000 hr.sup.-1 under the ambient atmospheric pressure. 
In the reaction tube, the methyl nitrite reacted with carbon monoxide at a 
temperature of 100.degree. C. under the ambient atmospheric pressure in 
the presence of the solid catalyst. 
The resultant reaction mixture was subjected to gas chromatographic 
analysis, and it was confirmed that at the stage of 4 hours after the 
start of the reaction procedure, the space time yield (STY) of dimethyl 
carbonate was 880 g/liter.multidot.hr. This space time yield (STY) of 880 
g/liter.multidot.hr was maintained unchanged until the stage of 50 hours 
after the start of the reaction, at which stage, the reaction was 
completed. 
The selectivities (X and Y) of dimethyl carbonate was 98% based on carbon 
monoxide and 96% based on methyl nitrite at the stage of 4 hours after the 
start of the reaction, and were maintained approximately constant until 
the completion of the reaction. 
Example 21 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 18 were carried out except that hydrogen chloride used in Example 
18 was replaced by 100 ppm by volume of methyl chloroformate. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 550 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction. Thereafter, this space time yield (STY) of 550 
g/liter.multidot.hr was maintained constant until the completion of the 
reaction, namely 100 hours after the start of the reaction. 
Thee selectivities of dimethyl carbonate were 97% based on carbon monoxide 
and 98% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, and thereafter were maintained constant at the 
above-mentioned levels, until the completion of the reaction. 
Comparative Example 5 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 21 were carried out except that the same catalyst as in 
Comparative Example 1 was employed in an amount of 5 ml. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 500 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction, and maintained constant at the level of 500 
g/liter.multidot.hr until the completion of the reaction, namely 100 hours 
after the start of the reaction. 
The selectivities of dimethyl carbonate were 88% based on carbon monoxide 
and 89% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, and thereafter were maintained approximately constant at the 
above-mentioned levels, until the completion of the reaction. 
Example 22 
preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 19 were carried out except that hydrogen chloride used in Example 
19 was replaced by 100 ppm by volume of methyl chloroformate. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 450 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction, and thereafter was maintained constant at the level 
of 450 g/liter.multidot.hr until the completion of the reaction, namely 
100 hours after the start of the reaction. 
The selectivities of dimethyl carbonate were 98% based on carbon monoxide 
and 98% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, and thereafter were maintained approximately constant at the 
above-mentioned levels, until the completion of the reaction. 
Example 23 
Preparation of Dimethyl Carbonate 
The same preparation procedures and analysis for dimethyl carbonate as in 
Example 20 were carried out except that hydrogen chloride used in Example 
20 was replace by 500 ppm by volume of methyl chloroformate, and the 
reaction temperature was changed to 90.degree. C. 
It was confirmed that the space time yield (STY) of dimethyl carbonate was 
at a level of 880 g/liter.multidot.hr at the stage of 4 hours after the 
start of the reaction. Thereafter, the space time yield (STY) was 
maintained unchanged at the level of 880 g/liter.multidot.hr until the 
completion of the reaction, namely 50 hours after the start of the 
reaction. 
The selectivities of dimethyl carbonate were 98% based on carbon monoxide 
and 96% based on methyl nitrite at the stage of 4 hours after the start of 
the reaction, and thereafter were maintained approximately constant at the 
above-mentioned levels, until the completion of the reaction. 
The test results of Examples 18 to 23 and Comparative Examples 3 to 5 are 
shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Item 
Composition of Reaction time (hr) 
catalyst Catalytic 
4 10 50 100 
4 10 
50 
100 
4 10 
50 
100 
Catalyst activity 
Space time Selectivity (%) of dimethyl 
carbonate 
Example 
components/ reduction- 
yield (STY) Based on 
No. carrier inhibiting agent 
(g/liter .multidot. hr) 
Based on CO 
methyl 
__________________________________________________________________________ 
nitrite 
Example 
18 PdCl.sub.2 --LaCl.sub.3 --CuCl.sub.2 /C 
HCl 600 
500 
-- 500 
97 
95 
-- 
95 98 
96 
-- 
96 
19 PdCl.sub.2 --CeCl.sub.3 /C 
HCl 450 
350 
-- 350 
98 
96 
-- 
96 98 
96 
-- 
96 
20 PdCl.sub.2 --CeCl.sub.3 /Al.sub.2 O.sub.3 
HCl 880 
-- 880 
-- 98 
-- 
98 
-- 96 
-- 
96 
-- 
21 PdCl.sub.2 --LaCl.sub. 3 --CuCl.sub.2 /C 
Methyl chloro- 
550 
-- -- 550 
97 
-- 
-- 
97 98 
-- 
-- 
98 
formate 
22 PdCl.sub.2 --CeCl.sub.3 /C 
Methyl chloro- 
450 
-- -- 450 
98 
-- 
-- 
98 98 
-- 
-- 
98 
formate 
23 PdCl.sub.2 --CeCl.sub.3 /Al.sub.2 O.sub.3 
Methyl chloro- 
880 
-- 880 
-- 98 
-- 
98 
-- 96 
-- 
96 
-- 
formate 
Comparative 
Example 
3 PdCl.sub.2 --CuCl.sub.2 /C 
HCl 500 
400 
-- 400 
88 
83 
-- 
83 90 
85 
-- 
85 
4 PdCl.sub.2 --CuCl.sub.2 /C 
-- 500 
350 
75 
-- 88 
82 
60 
-- 89 
84 
63 
-- 
5 PdCl.sub.2 --CuCl.sub.2 /C 
Methyl chloro- 
500 
-- -- 500 
88 
-- 
-- 
88 89 
-- 
-- 
89 
formate 
__________________________________________________________________________ 
Tables 1 and 2 clearly show that the method of the present invention in 
which a catalytic reaction of carbon monoxide with a nitrous acid ester is 
carried out in the presence of a specific catalyst containing 
catalytically active components, namely, platinum group metals or compound 
thereof and lanthanide group metals or compounds thereof, effectively 
eliminates the disadvantages of the conventional methods such that the 
reaction rate and selectivity of the desired compound are not always 
satisfactory and the conventional catalysts exhibit an unsatisfactory 
durability (catalyst life) for industrial use, and therefore a carbonic 
acid ester can be produced by the method of the present invention at a 
very high reaction rate with excellent selectivity and stability over a 
long period of time.