Catalyst for conversion of methane to ethylene, preparation thereof, and process for manufacturing ethylene using said catalyst

The present invention relates to a new catalyst for converting methane into ethane, preparation thereof, and process for manufacturing ethylene using said catalyst. The conversion reaction catalyst in the present invention is employed in converting directly methane or methane-containing gas in the presence of the above catalyst with the following general formula (1). EQU Ma.Pc.D/S (1) Where, PA1 M is a metal cluster or metal complex compound selected from the group of VIII, VII and VI series; PA1 S is an inorganic carrier; PA1 P is a promoter of phosphorus compound; PA1 D is a cobalt compound. And "a" is weight percentage of metal cluster or metal complex compound in catalyst, having a value of 0.01 to 10, "c" is weight percentage of promoter in catalyst, ranging from 1.0 to 35.0.

FIELD OF THE INVENTION 
The present invention relates to supported catalyst for converting methane 
into ethylene, preparation thereof, and process for manufacturing ethylene 
using said catalyst. More particularly, the present invention relates to a 
new catalyst which is expressed in the following general formula (1) for 
conversion reaction, preparation thereof, and process for preparation of 
ethylene by converting directly methane or methane-containing gas in the 
presence of the above catalyst. 
EQU M.sub.a P.sub.c D/S (1) 
Where, 
M is a metal cluster or metal complex compound selected from the group of 
VIII, VII and VI elements; 
S is an inorganic carrier such as SiO.sub.2 ; 
P is a promoter of phosphorus compound; 
D is a cobalt compound such as CoCl.sub.2 ; 
"a" is weight percentage of metal cluster or metal complex compound in 
catalyst, having a value of 0.01 to 10; "c" is weight percentage of 
promoter in catalyst, ranging from 1.0 to 35.0. 
BACKGROUND OF THE INVENTION 
In general, ethylene has been widely used as one of the basic reaction 
chemicals in the field of petrochemical industry and fine chemical 
industry. It is well known that synthesis of ethylene from methane by 
dehydrogenation is conducted at relatively high temperature of about 
1500.degree. to 1550.degree. C. through thermal or electric cracking 
reaction process. 
However, this method causes some problems such as loss of an enormous 
amount of thermal energy and necessity of using high temperature 
equipment, and particularly severe corrosion of the reactor owing to high 
temperature. 
As prior art describing synthesis of hydrocarbons by oxidative coupling and 
dehydrogenation in order to prepare lower hydrocarbons such as ethylene 
having a double bond by direct conversion of 5118654, Canadian Patent No. 
2016675 and Japanese Patent Nos. 04352730, 04368342. 
Above-referenced processes have more or less settled some disadvantages 
since the reaction is conducted at relatively lower temperature of about 
700.degree. to 800.degree. C. However, since the reaction is conducted 
with oxygen, helium, nitrogen and N.sub.2 O as oxidation or dilution gas, 
variety of reactants and a large amount of by-proudcts such as CO.sub.2 
are ensuing. Moreover, there are much difficulties in separating or 
purifying the reactants, let alone the inability to conduct a continuous 
process and the causation of a severe environmental pollution problem. 
In the meantime, natural gas contains impurities such as carbon dioxide, 
H.sub.2 S and moisture other than methane as the major ingredient. These 
impurities may affect catalytic activity, if they are not purified and the 
reaction cannot proceed properly. 
SUMMARY OF THE INVENTION 
In order to be free of said disadvantages associated with the 
above-referenced processes, it is therefore an object of the present 
invention to provide a method for preparation of high-yield ethylene with 
an available continuous process at relatively lower temperature in the 
presence of the catalyst, without generation of by-products such as carbon 
dioxide. Another object of the present invention is to provide a direct 
and continuous conversion method of methane containing some impurities, 
such as natural gas, to ethylene. A further object of the present 
invention is to provide a new catalyst used in said process and 
preparation thereof. 
To fulfill said object, an intensive study has been made by the inventor 
and it is found that the conversion catalyst may be made available through 
the following process: 
By the operation of converting methane or methane-containing gas directly 
in the presence of the catalyst expressed as said general formula (1) at a 
temperature of 350.degree. to 1050.degree. C., ethylene with high yield 
may be obtained without by-products such as carbon dioxide. Also, by the 
operation of adding solvent to the components of said general formula (1), 
suspended, agitated in reflux at a temperature of about 20.degree. to 
200.degree. C., evaporated residues by distillation under reduced pressure 
and dried in a vacuum drier, said catalyst can be obtained. 
In other words, the catalyst for conversion of the present invention is 
employed in converting methane or methane-containing gas into ethylene, 
and is characterized by expressing as general formula (1). The process for 
manufacturing the catalyst for conversion of the present invention is 
characterized by the following operation, wherein the components of said 
general formula (1) are added with solvent, suspended, agitated in reflux 
at a temperature of about 20.degree. to 200.degree. C., evaporated 
residues by distillation under reduced pressure and dried in vacuum drier. 
The process for manufacturing ethylene of the present invention is 
characterized by the direct conversion of methane or methane-containing 
gas into ethylene at a temperature of 350.degree. to 1050.degree. C. under 
1 to 10 atm in the presence of said catalyst. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be described in more detail as follows: 
The catalyst in the present invention is expressed by said general formula 
(1). In said formula (1), M is a metal cluster or metal complex compound 
such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt in VIII series, Mn, Re in VII 
series and Mo, W in VI series. 
For example, the metal compound includes RuCl.sub.2 (PPh.sub.3).sub.3, 
RuCl.sub.2 (CO).sub.2 (PPh.sub.3).sub.2, Ru.sub.3 (CO).sub.12, 
RuCl(CO)(PPh.sub.3).sub.2, IrCl(CO)(PPh.sub.3).sub.2, Pd(PPh.sub.3).sub.4, 
Pt(PPh.sub.3).sub.4, RuCl.sub.3.xH.sub.2 O, RhCl.sub.3.H.sub.2 O, 
IrCl.sub.3.xH.sub.2 O, H.sub.2 PtCl.sub.6.xH.sub.2 O, and PdCl.sub.2. 
Among them, the most preferable metal compounds are the Ru and Rh series. 
S is an inorganic carrier such as .alpha.-Al.sub.2 O.sub.3, 
.gamma.-Al.sub.2 O.sub.3, SiO.sub.2, SiO.sub.2 --Al.sub.2 O.sub.3, 
Y-zeolite, ZSM-5, zeolite, MgO, and TiO.sub.2. Among them, the most 
preferable compounds are .alpha.-Al.sub.2 O.sub.3 and MgO. P is a promoter 
of phosphorous compound such as PPh.sub.3, P(OCH.sub.3).sub.3, P(OC.sub.2 
H.sub.5).sub.3, and P(O)(OC.sub.2 H.sub.5).sub.3. D is cobalt compound 
such as CoCl.sub.2.xH.sub.2 O, Co(NO.sub.3).sub.2.xH.sub.2 O, and 
Co(CH.sub.3 COO).sub.2.xH.sub.2 O. 
In a case where the methane contains some impurities, a cobalt compound is 
used to prevent the lowering of catalytic activity and also to prevent the 
reduction of yield even in the absence of dilution gas such as N.sub.2. 
Its optimum use should be preferably in the range of below 0.3 wt %. If 
this range is exceeded, bonding interference among catalysts occurs and 
this may lead to reduction of catalytic activity. 
And "a" is weight percentage of metal cluster or metal complex compound in 
catalyst, having a value of 0.01 to 10, "c" is weight percentage of 
promoter in catalyst, ranging from 1.0 to 35.0. If "a" exceeds the above 
value, it may be associated with reduction of yield and if "c" exceeds the 
above level, the inlet or outlet of reactor may be blocked. 
The catalyst for conversion of the present invention is obtained by the 
following steps; 
(i) Adding said M, P, D and S to solvent such as dichloromethane or acetone 
at a temperature of 20.degree. to 200.degree. C. 
(ii) Mixing and suspending by refluxing. 
(iii) Drying by distillation under reduced pressure. 
Reaction conditions of direct converting of methane or methane-containing 
gas into ethylene in the presence of said catalyst according to the 
present invention are as follows: 
Reaction temperature is 350.degree. to 1050.degree. C., preferably in the 
range of 650.degree. to 950.degree. C. 
Reaction pressure is 1 to 10 atm, preferably in the range of 1 to 5 atm and 
more preferably normal pressure. 
Concentration of catalyst is below 5.0 wt %, preferably 1.0 to 3.0 wt %. 
Flow rate of source gas is 150 to 12000 cc/hr, preferably in the range of 
600 to 4800 cc/hr. 
Through the above process of the present invention, the rate of conversion 
of methane to ethylene is about 15 to 20%, which is lower than that of 
above-referenced processes to prepare ethylene based upon oxidative 
coupling and dehydrogenation reaction, showing 50 to 60%. 
However, in the present invention, the productivity is improved further 
because the continuous conversion reaction can be effectively carried out 
without generating by-products such as carbon dioxide. 
Even in the case when the methane for conversion contains some impurities, 
the catalytic activity may not be affected in the present invention. So 
there is great advantage to directly convert natural gas into ethylene 
without purifying. 
Normally weight percentage of carbon dioxide in natural gas is 0 to 5% in 
average. In case of using the catalyst for conversion of the present 
invention, a stable methane conversion rate of 8.2 to 10.1% is attainable 
with the range of carbon dioxide content being 0.2 to 1.0%. And normally 
weight percentage of H.sub.2 S in natural gas is below 1%. In case of 
using the catalyst of the present invention, about 14% of stable methane 
conversion rate is attainable, even if 1% of H.sub.2 S is contained. 
In addition to that, a small amount of water may be contained in natural 
gas. In case of using the catalyst of the present invention, 8 to 12% of 
stable conversion rate is attainable even if water is contained. In other 
words, if the catalyst of the present invention is used, a stable 
conversion rate is attainable of more than 10% regardless of the presence 
of any impurities. Also unconverted methane, passed through the reactor, 
can be used in the conversion reaction without purification.

EXAMPLES 
The examples of the present invention are as follows and the definitions 
for conversion rate, yield and selectivity are defined below. 
EQU Conversion rate (mol %)=(mol Nos. of methane reacted/mol Nos. of methane 
supplied).times.100 
EQU Yield (mol %)=(mol Nos. of lower hydrocarbon produced/mol Nos. of methane 
supplied).times.100 
EQU Selectivity (mol %)=(mol Nos. of lower hydrocarbon produced/mol Nos. of 
methane reacted).times.100 
PREATION EXAMPLE 1 
Preparation of Ru-series Catalyst 
5.16 g of .alpha.-Al.sub.2 O3, 1.00 g (1.04 mmol) of RuCl.sub.2 
(PPh.sub.3).sub.3, 1.09 g (4.16 mmol) of PPh.sub.3 and 0.01 g of 
CoCl.sub.2.xH.sub.2 O were added to mixed solvent consisting of 20 ml of 
dichloromethane and 10 ml of acetone, and stirred for about 30 minutes at 
a temperature of around 40.degree. to 60.degree. C. 
This suspension obtained by above procedure was evaporated by distillation 
under reduced pressure, then dried in a vacuum drier for about 20 hours to 
prepare RuCl.sub.2 (PPh.sub.3).sub.3.PPh.sub.3 /.alpha.-Al.sub.2 O.sub.3 
(2 wt % Ru) catalyst. 
PREATION EXAMPLE 2 
Preparation of Ru-series Catalyst Containing Moisture 
1.0 g of RuCl.sub.2 (PPh.sub.3).sub.3.PPh.sub.3 /.alpha.-Al.sub.2 O.sub.3 
(2 wt % Ru) catalyst, which was prepared in PREATION EXAMPLE 1, was 
dipped into 2 ml of distilled water for a few minutes and then, dried in a 
vacuum drier for 20 hours to prepare RuCl.sub.2 
(PPh.sub.3).sub.3.PPh.sub.3.H.sub.2 O/.alpha.-Al.sub.2 O.sub.3 (2 wt % Ru) 
catalyst containing moisture. 
PREATION EXAMPLE 3 
Preparation of Ir-series Catalyst 
This catalyst was prepared in the same manner as in PREATION EXAMPLE 1, 
except for substituting 0.78 g of IrCl(CO)(PPh.sub.3).sub.2 for 1.00 g of 
RuCl.sub.2 (PPh.sub.3).sub.3. 
PREATION EXAMPLE 4 
Preparation of Rh-series Catalyst 
This catalyst was prepared in the same manner as in PREATION EXAMPLE 1, 
except for substituting 0.69 g of RhCl(CO)(PPh.sub.3).sub.2 for 1.00 g of 
RuCl.sub.2 (PPh.sub.3).sub.3. 
PREATION EXAMPLE 5 
Preparation of Pd-series Catalyst 
This catalyst was prepared in the same manner as in PREATION EXAMPLE 1, 
except for substituting 1.16 g of Pd(PPh.sub.3).sub.4 for 1.00 g of 
RuCl.sub.2 (PPh.sub.3).sub.3. 
PREATION EXAMPLE 6 
Preparation of Pt-series Catalyst 
This catalyst was prepared in the same manner as in PREATION EXAMPLE 1, 
except for substituting 1.24 g of Pt(PPh.sub.3).sub.4 for 1.00 g of 
RuCl.sub.2 (PPh.sub.3).sub.3. 
EXAMPLE 1 
Methane without dilution gas was introduced at 600 to 2400 cc/hr of flow 
rate into continuous stationary phase flow reactor (inner diameter: 0.70 
cm, length: 40 cm, stuff: stainless steel 316) in the presence of the 
catalyst prepared in PREATION EXAMPLE 1. 
Products obtained by continuous reaction under 1 atm at the temperature of 
810.degree. C. were analyzed by gas chromatography and the catalytic 
activity was as shown in the following Table 1. 
TABLE 1 
______________________________________ 
Comparison of catalytic activity according to flow rate 
Flow rate 
Conversion Yield (%) Selectivity (%) 
(cc/hr) rate (%) Ethylene Ethane 
Ethylene 
Ethane 
______________________________________ 
600 17.1 15.5 1.6 90.6 9.4 
900 15.9 14.5 1.4 91.2 8.8 
1200 15.5 14.3 1.2 92.3 7.7 
2400 14.1 12.8 1.3 90.8 9.2 
______________________________________ 
EXAMPLE 2 
In order to verify differences of using dilution gas and not using dilution 
gas, and effect of carbon dioxide contained as impurity in natural gas on 
catalytic activity, the reaction conducted in the same manner as in 
EXAMPLE 1 by supplying source gas mixing each of methane, nitrogen and 
carbon dioxide in the presence of the catalyst obtained in PREATION 
EXAMPLE 1. The results were as shown in following Table 2. 
TABLE 2 
______________________________________ 
Comparison of conversion rate in case of containing 
nitrogen and carbon dioxide 
Mixing ratio 
(cc/min) Conversion 
Yield (%) Selectivity (%) 
CH.sub.4 :N.sub.2 :CO.sub.2 
rate (%) Ethylene Ethane 
Ethylene 
Ethane 
______________________________________ 
10:10:0 12.1 11.0 1.1 90.9 9.1 
10:5:0 14.4 13.2 1.2 91.7 8.3 
10:0:0 17.1 15.5 1.6 90.6 9.4 
10:0:1 8.2 5.8 2.4 70.7 29.3 
10:0:0.2 10.1 8.0 2.1 79.2 20.8 
______________________________________ 
EXAMPLE 3 
Effect of moisture contained in natural gas on catalytic activity was 
measured as shown in the following Table 3, at the result of the reaction 
conducted in the same manner as in EXAMPLE 1 in the presence of the 
catalyst obtained in PREATION EXAMPLE 2. 
TABLE 3 
______________________________________ 
Effect of moisture on catalytic activity 
Mixing Re- Con- 
ratio action version 
(cc/min) 
time rate Yield (%) Selectivity (%) 
CH.sub.4 :N.sub.2 
(hr) (%) Ethylene 
Ethane 
Ethylene 
Ethane 
______________________________________ 
10:10 3 6.9 6.3 0.6 91.3 8.7 
10:10 14 11.2 10.3 0.9 92.0 8.0 
10:0 3 11.6 9.4 2.2 81.0 19.0 
______________________________________ 
EXAMPLE 4 
In order to verify the effect of sulfur compound contained in natural gas 
on catalytic activity, the reaction conducted in the same manner as in 
EXAMPLE 1 in the presence of the catalyst obtained in PREATION EXAMPLE 
1. The result was as shown in following Table 4. 
TABLE 4 
______________________________________ 
Effect of sulfur on catalytic activity 
Reaction 
Conversion Yield (%) Selectivity (%) 
time (hr) 
rate (%) Ethylene Ethane Ethylene 
Ethane 
______________________________________ 
2 8.3 5.5 2.8 66.3 33.7 
30 14.0 11.9 2.1 85.0 15.0 
______________________________________ 
EXAMPLE 5 
Effects of each catalyst obtained in PREATION EXAMPLE 3 to 7 on 
catalytic activity were measured as shown in the following Table 5, at the 
result of the reaction conducted in the same manner as in EXAMPLE 1 at a 
flow rate of 1200 cc/hr. 
TABLE 5 
______________________________________ 
Comparison of catalytic activity according to each catalyst 
Conversion 
Yield (%) Selectivity (%) 
Catalyst rate (%) Ethylene Ethane 
Ethylene 
Ethane 
______________________________________ 
PREPA. 12.2 11.1 1.1 91.0 9.0 
EXAMPLE 3 
PREPA. 15.2 14.0 1.2 92.1 7.9 
EXAMPLE 4 
PREPA. 12.0 11.0 1.0 91.7 8.3 
EXAMPLE 5 
PREPA. 12.1 11.0 1.0 90.9 9.1 
EXAMPLE 6 
______________________________________