Process for cosynthesis of ethylene glycol and dimethyl carbonate

A process is disclosed for the cosynthesis of ethylene glycol and dimethyl carbonate by reacting methanol and ethylene carbonate in the presence of a catalyst selected from the group consisting of zirconium, titanium and tin.

This invention concerns a process for cosynthesis of ethylene glycol and 
dimethyl carbonate by the transesterification reaction of ethylene 
carbonate and methanol in the presence of homogeneous and heterogeneous 
catalysts from the group consisting of zirconium, titanium, tin oxides, 
salts and complexes. In addition to the fact that substantially fewer 
moles of methanol are needed in the methanol-ethylene carbonate feedstock 
per mole of dimethyl carbonate produced, this invention is advantageous in 
that the catalysts are in many cases found to perform better than sodium 
carbonate, which has been used in the art. 
BACKGROUND OF THE INVENTION 
Generally the prior art reports that the transesterification of aliphatic 
hydroxy compounds with carbonic acid, aliphatic diesters and aromatic 
diesters occurs readily in the presence of a basic catalyst and is a 
convenient method of synthesis of higher carbonates. 
Several references deal with the transesterification of glycol carbonates 
using an aliphatic alcohol. Most demonstrate the use of methanol and 
ethylene carbonate. 
U.S. Pat. No. 4,307,032 discloses a process for the preparation of a 
dialkyl carbonate by contacting a glycol carbonate of a 1,2-diol 
containing 2 to 4 carbon atoms with a selected alcohol to form the 
corresponding carbonate of said alcohol at a temperature of between 50 and 
250.degree. C, in the presence of an improved catalyst which is a thallium 
compound, allowing the reaction to take place under milder conditions. 
Thallium is however expensive and very toxic. 
In another process disclosed in U.S. Pat. No. 4,181,676 there is taught a 
method for preparation of dialkyl carbonate by contacting a glycol 
carbonate of a 1,2-diol having 2 to 4 carbon atoms with a selected group 
of alcohols at an elevated temperature in the presence of an alkali metal 
or alkali metal compound wherein the improvement comprises employing less 
than 0.01 percent by weight of alkali metal or alkali metal compound based 
on the weight of the reaction mixture. 
It is known that alkyl carbonates of the type ROCOOR can be obtained from 
alcohols and cyclic carbonates corresponding to the above formula through 
a transesterification reaction in the presence of alkali alcoholates or 
hydrates; however, moderate amounts of inorganic compounds are produced by 
these reactions and must be removed by methods which may unfavorably 
affect the general economy of the process. 
In U.S. Pat. No. 4,062,884 this problem was addressed and it was found that 
dialkyl carbonates can be prepared by reacting alcohols with cyclic 
carbonates in the presence of organic bases, which makes it unnecessary to 
remove inorganic compounds and allows the catalyst to be totally recovered 
by means of simple distillation. The preferred organic base is a tertiary 
aliphatic amine. 
U.S. Pat. No. 4,349,486 teaches a monocarbonate transesterification process 
comprising contacting a beta-fluoroaliphatic carbonate, a compound 
selected from the class of monohydroxy aliphatic alcohols, monohydroxy 
phenols and ortho-positioned dihydroxy aromatic compounds in the presence 
of a base. This invention claims to greatly reduce undesirable side 
reactions and only small amounts of carbonic acid-aliphaticaromatic mixed 
diester are associated with the isolated aromatic monocarbonate reaction. 
The Gilpin and Emmons Patent, referred to above, discusses problems 
associated with the separation of the methanol, dimethyl carbonate 
azeotrope and teaches one solution, wherein dimethyl carbonate is isolated 
from the azeotrope by a combination of low temperature crystallization and 
fractional distillation. 
In another article in the J. Org. Chem. 49(b) 1122-1125 (1984) Cella and 
Bacon discuss the results of their work. Among other things, they found 
that the alkylation of alkali metal bicarbonate and carbonate salts with 
alkyl halides in dipolar aprotic solvents and phase-transfer catalysts 
produces alkyl carbonates in good yields. The major limitation of this 
method is the failure of activated aryl halides or electronegatively 
substituted alkyl halides to produce carbonates due to the facility with 
which the intermediate alkoxy carbonate salts decompose. 
Disadvantages of the methods discussed above include in many cases the fact 
that it is necessary to use a large amount of methanol feedstock relative 
to the amount of dimethyl carbonate produced. Also, in many cases, alkali 
metal halides are coproduced and these halides present disposal problems. 
It would be a substantial advance in the art to devise an efficient process 
for co-producing dimethyl carbonate and ethylene glycol, which was 
homogenous and did not necessitate difficult product-catalyst separations. 
The dimethyl carbonate produced by this novel process can be used as a 
gasoline extender. 
SUMMARY OF THE INVENTION 
This invention concerns a process for the cosynthesis of ethylene glycol 
and dimethyl carbonate from ethylene carbonate and methanol by reacting 
ethylene carbonate and methanol in the presence of a homogeneous or 
heterogeneous catalyst selected from the group consisting of zirconium, 
titanium and tin oxides, salts or complexes thereof, at a temperature of 
from 20.degree. C. to 200.degree. C. and an operative pressure of zero to 
5000 psig, until the desired products are formed. 
A particular advantage of these systems over the prior art is the high 
selectivities to dimethyl carbonate (DMC) and ethylene glycol (EG)-basis 
the ethylene carbonate (EC) and methanol (MeOH) charged. These 
selectivities are illustrated in the accompanying Example I for the 
zirconium acetylacetonate catalyst and Example X for the zirconium 
diperchlorate oxide catalyst precursor. 
DETAILED DESCRIPTION OF THE INVENTION 
In the narrower and more preferred practice of this invention dimethyl 
carbonate and ethylene glycol are prepared simultaneously by a 
transesterification process which comprises reacting ethylene carbonate 
and methanol in the presence of a homogeneous zirconium, titanium or tin 
catalyst, at a temperature of between 50.degree. C and 150.degree. C, and 
a pressure of at least 50 psig, until the desired products are formed. 
Starting materials employed in the process are an aliphatic alcohol and an 
aliphatic carbonate. Alcohols which work in the process of this invention 
include the monohydric alcohols containing one to 14 carbon atoms, 
including methanol, ethanol, isopropanol and isobutanol. Methanol is the 
preferred alcohol. Alkylene carbonates which will work in the process of 
this invention include the carbonate derivatives of 1,2-diols containing 
two to 10 carbon atoms per molecule, including ethylene carbonate, 
1,2-propylene carbonate and 1,2-butanediol carbonate. Ethylene carbonate 
is the preferred alkylene carbonate feedstock for this process. The 
preferred starting materials are illustrated in the accompanying examples. 
Recovery of the desired ethylene glycol and dimethyl carbonate can 
generally be carried out by distillation and crystallization. 
More specifically, methanol and ethylene carbonate are pumped into a 
tubular reactor upflow at a flow rate of 0.1 to 100 liquid hourly space 
velocity (LHSV). The reactor temperature is held at between 20.degree. and 
200.degree. C. and a back pressure of zero to 5000 psi is maintained 
thorughout the experiment. 
The homogeneous catalyst systems suitable for the practice of this 
invention generally comprise a zirconium, titanium or tin compound. The 
compound can be in the form of a salt or complex. 
The zirconium-containing catalyst compound comprises a salt of zirconium or 
a complex. Suitable examples include zirconium salts of strong (mineral) 
acids, such as zirconium tetrachloride, ZrCl.sub.4, zirconium bromide, 
ZrBr.sub.4, zirconium fluoride, zirconium nitrate, zirconium sulfate, 
Zr(SO.sub.4).sub.2.4H.sub.2 O, zirconium mixed halides and zirconium 
tetraiodide, zirconium alkoxides such as zirconium methoxide, zirconium 
ethoxide and zirconium isopropoxide, zirconium salts of weak acids such as 
zirconium acetate and zirconium acetylacetonate, Zr(O.sub.2 C.sub.5 
H.sub.7).sub.4, as well as zirconium compounds containing the zirconyl 
moiety, as for example, zirconium diperchlorate oxide, 
ZrO(CLO.sub.4).sub.2.8H.sub.2 O and zirconium oxide nitrate, 
ZrO(NO.sub.3).sub.2.X H.sub.2 O. 
The preferred zirconium catalyst precursors are zirconium acetylacetonate 
and zirconium diperchlorate oxide. 
The titanium-containing catalyst compound may likewise comprise a salt of 
titanium or a complex. Suitable examples include titanium methoxide; other 
titanium alkoxides such as titanium isopropoxide, titanium acetate and 
titanium acetylacetonate also work. The preferred titanium compound is 
titanium isopropoxide. 
Suitable tin-containing catalyst precursors for EC/MeOH transesterification 
include compounds such as tin(II) 2-ethylhexanoate, tin methoxide, 
dimethyltin salts, dibutyltin acetate and tributyltin chloride. The 
preferred tin compound is tin(II) 2-ethylhexanoate. 
Also in some cases, the analogous zirconium, titanium and tin heterogeneous 
catalyst precursors may also be effective. Examples of suitable 
heterogeneous catalysts for the desired ethylene carbonate-methanol 
transesterification include zirconium oxide, ZrO.sub.2, and titanium 
oxide. Said heterogeneous zirconium or titanium catalysts may be in the 
form of pellets, extrudates, granules or powders. Also effective may be 
zirconium carbide, zirconium nitride and zirconium silicate. 
A particularly effective catalyst for the cosynthesis of dimethyl carbonate 
and ethylene glycol is a solution of zirconium diperchlorate oxide 
dissolved in the ethylene carbonate-methanol feed mix. This reaction 
solution is illustrated in accompanying Example X. 
During the cosynthesis of ethylene glycol and dimethyl carbonate by the 
reaction of ethylene carbonate with methanol, a large excess of methanol 
is normally employed in the prior art. Usually the initial molar ratio of 
methanol to ethylene carbonate is in the range of 5 or greater, and 
preferably at least 10. This preferred ratio range is illustrated by U. S. 
Pat. No. 3,803,201 (1974). In the practice of this invention, by contrast, 
the initial weight ratio of ethylene carbonate to methanol is preferably 2 
to 5. Such a range of weight ratios is illustrated by the accompanying 
examples. 
Potential advantages to operating at this ethylene carbonate-to-methanol 
weight ratio include: 
(a) More efficient transesterification. 
(b) Lower levels of methanol required to be recycled after the 
transesterification step. 
Ethylene glycol-dimethyl carbonate synthesis using the homogeneous catalyst 
described SUPRA can be conducted at reaction temperatures in the range 
from 20.degree. to 200.degree. C. The preferred operating temperature 
range is 50.degree.-150.degree. C. 
The reaction can be conducted under atmospheric pressure. A pressure 
reactor is nevertheless required in the case of low-boiling point 
components if the reaction is to be carried out in the upper temperature 
range and in the liquid phase. The pressure is not critical. In general 
the reaction is allowed to proceed under the autogenous pressure of the 
reactants. However, the reaction can also be carried out under elevated 
pressure, for example, under an inert atmosphere. A pressure of zero to 
5000 psig is appropriate here. An operating pressure of greater than 50 
psig is suitable and the preferred pressure was in the range of 50 to 150 
psi. 
The residence time for the ethylene carbonate and methanol reactants in the 
tubular reactor may vary over a wide range according to the temperature of 
reaction, the molar ratios of carbonate/alcohol feedstocks, etc. Using the 
homogeneous catalysts of this invention, the necessary residence time in 
the reactor may range from 0.01 hours to 10 hours, although it may be 
extended beyond 10 hours without danger of additional by-products being 
formed. The preferred residence time is in the range of 0.1 to 5 hours. 
The desired products of this process according to the invention are 
ethylene glycol and dimethyl carbonate. By-products include diethylene 
glycol, 1,1-dimethoxyethane, 1,2-dimethoxyethane, methyl 1,3-dioxolane, 
glycol monomethyl ether and dimethyl ether. 
Products have been identified in this work by gas chromatography (gc), NMR, 
IR and gc-IR or a combination of these techniques. Zirconium and titanium 
analyses were by atomic absorption (AA). All liquid product analyses have, 
for the most part, been by gc; all temperatures are in degrees centigrade 
and all pressures in pounds per square inch gauge.

The following examples illustrate the novel process of this invention. The 
examples are only for illustrating the invention and are not considered to 
be limiting: 
EXAMPLE I 
This example illustrates the cosynthesis of dimethyl carbonate and ethylene 
glycol from ethylene carbonate plus methanol, in good selectivity, using a 
homogeneous zirconium catalyst derived from zirconium acetylacetonate 
dissolved in the EC/MeOH feed mix. The weight ratio of ethylene carbonate 
to methanol is 2:3. 
To a 1 kg mixture of ethylene carbonate (EC) and methanol (typical 
composition: 59.0% MeOH, 41.0% EC) was added 50 g of zirconium 
acetylacetonate. The mixture was stirred to dissolve the zirconium salt, 
cooled in wet ice and the clear solution pumped through a 50 cc capacity, 
stainless steel, tubular reactor upflow at a rate of 25 cc/hr. The reactor 
temperature was held at 130.degree. C and a back-pressure of 100 psi was 
maintained throughout the experiment. After feeding the ethylene 
carbonate-methanol mix for several (3-8) hours, the liquid effluent was 
sampled at regular time intervals and analyzed by gas-liquid 
chromatography. 
Typically, this liquid effluent had the following composition: 
10.8 wt % dimethyl carbonate (DMC) 
6.9 wt % ethylene glycol (EG) 
30.4 wt % ethylene carbonate (EC) 
50.1 wt % methanol (MeOH). 
Estimated molar selectivity to DMC, basic EC converted= 
##EQU1## 
Estimated molar selectively to DMC, basic MeOH converted= 
##EQU2## 
EG selectivity basis EC converted: 
##EQU3## 
EG selectivity basis MeOH converted: 
##EQU4## 
where DMC, FW=90.0; EC, FW=88.0; EG, FW=62.0; MeOH, FW=32.0. 
EXAMPLES II to IX 
Table 1 shows the cosynthesis of dimethyl carbonate and ethylene glycol 
from ethylene carbonate plus methanol using a variety of homogeneous 
zirconium, titanium and tin catalyst systems. Here the most effective 
catalyst precursors are: 
zirconium acetylacetonate 
tin(II) 2-ethylhexanoate 
titanium isopropoxide. 
TABLE 1 
__________________________________________________________________________ 
DIMETHYL CARBONATE/ETHYLENE GLYCOL COSYNTHESIS.sup.a 
Reactor 
Feed 
Temp. 
Rate 
Liquid Product (wt %) 
Example 
Catalyst (.degree.C.) 
cc/hr 
DMC EG EC MeOH 
__________________________________________________________________________ 
II Zirconium tetrachloride 
130 25 5.6 3.6 
41.2 
46.0 
" 150 25 8.7 5.0 
31.6 
47.4 
III Zirconium iso- 
100 100 2.1 1.8 
38.0 
54.0 
propoxide.sup.b 
IV Zirconium acetyl- 
110 100 5.5 4.0 
36.9 
51.8 
acetonate.sup.b 
150 25 11.4 
7.6 
31.8 
47.0 
V Titanium isopro- 
100 100 4.7 1.8 
30.4 
52.9 
poxide.sup.b 
VI Titanium acetylacetonate.sup.b,d 
110 25 0.1 0.1 
52.5 
46.1 
" 130 25 0.3 0.2 
55.5 
42.9 
" 150 25 1.0 0.6 
49.4 
47.8 
VII Tin(II) 2-ethyl- 
100 100 5.8 2.2 
35.1 
55.8 
hexanoate.sup.c 
VIII Dibutyltin acetate 
100 100 1.5 0.4 
40.1 
56.9 
IX Tributyltin chloride 
100 100 0.2 40.6 
57.6 
__________________________________________________________________________ 
.sup.a Run in continuous, 50 cc capacity, tubular reactor, upflow at 25 
cc/hr. liquid flow rate, 100 psi pressure, feed composition: 59% MeOH, 41 
EC. 
.sup.b Solution in EC/MeOH was filtered prior to use. 
.sup.c Some catalyst precipitation during run. 
.sup.d Feed composition: 52.5% MeOH, 47.5% EC. 
EXAMPLE X 
This example illustrates the cosynthesis of dimethyl carbonate and ethylene 
glycol from ethylene carbonate plus methanol, in good selectivity, using a 
homogeneous zirconium diperchlorate oxide catalyst precursor. 
To a 1 kg mixture of ethylene carbonate and methanol (66.6% MeOH, 33.3 %EC) 
was added 50 g of zirconium diperchlorate oxide, ZrO(ClO.sub.4)2.8H.sub.2 
O. The mixture was stirred to dissolve the zirconyl salt (1.3% Zr), cooled 
in wet ice, and fed to the 50 cc tubular reactor at a rate of 25 cc/hr. 
using the procedures of Example I. The reactor temperature was held at 
100.degree. C, and a back pressure of 100 psi was maintained throughout 
the experiment. 
Typical liquid effluent showed the following composition 
10.4 wt % dimethyl carbonate 
9.0 wt % ethylene glycol 
24.2 wt % ethylene carbonate 
54.2 wt % methanol. 
The reactor temperature was then raised to 130.degree. C. Typical liquid 
product now showed the following composition: 
14.8 wt % dimethyl carbonate 
9.0 wt % ethylene glycol 
14.9 wt % ethylene carbonate 
53.1 wt % methanol 
In the latter experiment: 
Estimated molar selectivity to DMC, basis EC converted=89%. 
Estimated molar selectivity to DMC, basis MeOH converted=76%. 
Estimated molar selectivity to EG, basis EC converted=&gt;98%. 
Estimated molar selectivity to EG, basis MeOH converted=95%. 
EXAMPLE XI 
This example also illustrates dimethyl carbonate/ethylene glycol 
cosynthesis, but uses a homogeneous zirconyl nitrate catalyst precursor. 
To a 1 kg mixture of ethylene carbonate and methanol (57.0% MeOH, 38.5% EC) 
was added 50 g of zirconium dinitrate oxide, ZrO(NO.sub.3).sub.2 X H.sub.2 
O). The mixture was stirred to dissolve the zirconyl salt (1.5% Zr), 
cooled in wet ice, and fed to the 50 cc reactor at a rate of 25 cc/hr., as 
in Example I. The reactor temperature was held at 130.degree. C, and a 
back pressure of 100 psi was maintained throughout the experiment. 
Typical liquid effluent showed the following composition: 
4.8 wt % dimethyl carbonate 
8.3 wt % ethylene glycol 
27.3 wt % ethylene carbonate 
56.0 wt % methanol. 
The reactor temperature was then raised to 150.degree. C. Under these 
conditions the liquid product showed the following composition: 
6.8 wt % carbonate 
14.0 wt % ethylene glycol 
24.1 wt % ethylene carbonate 
52.5 wt % methanol. 
EXAMPLE XII 
This example illustrates the cosynthesis of dimethyl carbonate and ethylene 
glycol from ethylene carbonate plus methanol, in good selectivity, using a 
hetergeneous zirconium oxide catalyst. 
To the 50 cc tubular reactor of Example I, packed with 3.2 mm pellets of 
zirconium oxide (98% ZrO.sub.2), is pumped a solution of ethylene 
carbonate plus methanol (67.6% MeOH, 31.9% EC) at a rate of 50 cc/hr. 
Reactor temperature was held at 130.degree. C, the back pressure was 100 
psi. Typical liquid effluent showed the following composition. 
3.8 wt % dimethyl carbonate 
2.7 wt % ethylene glycol 
29.9 wt % ethylene carbonate 
63 1 wt % methanol. 
The reactor temperature was then raised to 160.degree. C. Typical liquid 
product under equillibrium conditions, using this higher reactor 
temperature were as follows: 
7.9 wt % dimethyl carbonate 
5.2 wt % ethylene glycol 
25.2 wt % ethylene carbonate 
60.8 wt % methanol. 
No zirconium could be detected in the product liquid, basis atomic 
absorption analyses (AA).