Method for producing synthesis gas

Details Method for producing synthesis gas Method for producing synthesis gas

1998-05-08

2001-01-16

Killos, Paul J. (Department: 1621)

Compositions

Gaseous compositions

Carbon-oxide and hydrogen containing

C123S203000, C123S241000

Reexamination Certificate

active

06174460

ABSTRACT:

AREA OF THE INVENTION
This invention relates to the technology of hydrocarbon processing and more particularly to the production of synthesis gas from gaseous hydrocarbon raw material.
DESCRIPTION OF THE PRIOR ART
The method for producing synthesis gas from hydrocarbon raw material, which involves mixing the raw mixture with an oxidizer, oxygen or oxygen-containing gas, or water vapor, feeding the mixture to the reaction zone at a temperature, which is 93° C. no less than the self-ignition point of the mixture, at a rate of the turbulent flow exceeding the rate of flame flash-back, and conversion of the mixture in the presence of monolytic catalyst, is disclosed in RF Pat. 1,831,468, to Danster, M. And Kornchak, D. Method of producing synthesis gas from hydrocarbon raw, Byul. Izobret., 1993, no. 28, Int. Cl.: CO1B3/38.
The above method needs creation of a special catalytic reactor and the usage of a selective catalyst.
Other methods of incomplete oxidation of hydrocarbon raw material used, for example, to produce synthesis gas are known:
CH
4
+0.5O
2
=CO+2H
2
The most similar to the present invention is the method for producing synthesis gas disclosed in (Kazarnovskii, Ya. S., Derevyanko, I. G., Stezhinskii., A. I., and Kobozev, N. I., Explosive methane conversion. Trudy of State Research Institute of Nitrogen Industry, Moscow, 1957, vol. VIII, pp. 89-104). The said method comprises combustion of a gas mixture composed of hydrocarbon raw material and oxygen-enriched air at &agr;=0.5-0.8 or air not enriched with oxygen at &agr;=0.827-1.2, explosive partial oxidation of hydrocarbons in the cylinder of an internal combustion engine, expansion and cooling the products when the piston of the engine moves to the bottom dead center, output of the products containing the synthesis gas from the reactive volume when the piston moves to the top dead center, and input of a new portion of the working mixture when the piston moves to the bottom dead center. Enriched gas from coke production is usually used as the hydrocarbon raw material, which predominantly contains carbon oxide and methane and ethylene fractions. The mixture of said raw material and air is supplied into the cylinders of the internal combustion engine, and the explosive partial oxidation is preceded by the forced ignition of the mixture. The specific productivity of the process with respect to the hydrocarbon raw material is about 700 kg/m
3
h.
The production of synthesis gas is combined with electric power production.
The use of the enriched gas of coke production, the product of natural gas processing, rather than the natural gas itself makes the synthesis gas production tied to the coke production facilities.
In addition, when this method uses air not enriched with oxygen at &agr;=0.827-1.2, the content of CO
2
is 1.5-2 times higher than that of CO, and the content of hydrogen does not satisfy the synthesis demands, while, at &agr;>1, hydrogen is absent at all. Thus, for not enriched air at &agr;=0.827, the ratio H
2
/CO is 0.76 and, in any example, does not reach the value of 2.0 generally accepted in methanol synthesis.
When the method is realized with oxygen-enriched air at &agr;=0.5-0.8 (the content of oxygen is 29 and 50%, respectively, for the values of &agr; indicated above) the ratio H
2
/CO does not satisfy the demands of catalytic synthesis (in some examples, this ratio is less than unity). At &agr;=0.8, the contents of CO
2
and CO are equal.
DISCLOSURE OF THE INVENTION
The object of this invention is to provide the method for producing synthesis gas useful in catalytic processing.
This method allows production of synthesis gas in commercial slightly modified internal combustion engines. This invention utilizes compression self-ignition and external mixture preparation.
The use of methane, ethane, and other gaseous hydrocarbons as raw materials, including the broad fraction of light hydrocarbons from the associated gases makes it possible to improve the ecological situation in the regions of oil production and processing. The specific productivity of this method is 2.5-3 times higher than in the method referred to above, and the volume ratios H
2
/CO=1-2, depending on the process regime and composition of raw material. This is of particular importance, because the efficiency of synthesis gas production is known to affect significantly the economy of synthetic motor fuel production (Lykov, O. P., Chemistry and Technology of Fuels and Oils. 1996, no. 3, pp. 15-24).
The object of the present invention is to provide an improved process, which includes combustion of the mixture of raw hydrocarbons with air and oxidation of hydrocarbons upon the compression stroke of the piston in the cylinders of the modified internal combustion engine, expansion and cooling of the products during the piston stroke to the bottom dead center, output of the products containing synthesis gas from the reaction volume upon the piston stroke to the top dead center, inlet of a new portion of the working mixture upon the piston stroke to the bottom dead center, wherein the mixture of raw hydrocarbons with air at &agr;=0.5-0.8 preheated to 200-450° C. is fed into the cylinders of the modified internal combustion engine, and the mixture is compressed until self-ignition takes place and a temperature of 1300-2300° C. is maintained over a 10
−2
-10
−3
s period, and the cycle is repeated with a frequency exceeding 350 min
−1
.
When the mixture of air and hydrocarbon raw material is preheated to the temperature lower than 200° C., no self-ignition takes place in the cylinder of the modified internal combustion engine. The choice of the upper temperature limit for preheating the mixture (450° C.) is based on safety considerations relating to the possible self-ignition of the mixture before it reaches the reaction volume.
When the content of air in its mixture with hydrocarbon corresponds to &agr;<0.5, the intense carbon black formation takes place and, thus, the synthesis gas quality gets worse. At the content of air corresponding to &agr;>0.8, the share of CO
2
in the exhaust gases becomes greater than that of CO. This also deteriorates the synthesis gas quality (Kazamovskii, Ya. S., Derevyanko, I. G., Stezhinskii., A. I., and Kobozev, N. I., Explosive methane conversion. Trudy of State Research Institute of Nitrogen Industry, Moscow, 1957, vol. VIII, pp. 89-104).
The lower temperature limit (1300° C.) is selected so as to ensure high conversion in the partial oxidation of the hydrocarbon raw material. The upper temperature limit (2300° C.) is selected so as to eliminate the black carbon formation at the low values of &agr; claimed and to provide survivability of the outlet valves.
The cycle frequency should exceed 350 min
−1
because no self-ignition takes place with slow compression.
When the partial oxidation is accomplished at temperatures referred to above over a period >10
−2
s, the yield of the target product decreases.
The partial oxidation accomplished at temperatures referred to above over a period <10
−3
s requires such an increase in the engine rotation speed that the inertial loads rise to the levels higher than allowable ones with respect to the strength considerations.
The method is accomplished as follows:
1. The raw hydrocarbon material is premixed with air to achieve &agr;=0.5-0.8.
2. The prepared mixture is heated to a temperature of 200-450° C.
3. The preheated mixture is drawn into the cylinder of the modified internal combustion engine type during the motion of the piston to the bottom dead center.
4. The partial oxidation of hydrocarbons is accomplished by compression of the mixture in the cylinder by means of the piston stroke to the upper dead center until self-ignition of the mixture takes place and a temperature of 1200-2300° C. is maintained over the period of 10
−2
-10
−3
s.
5. The products are cooled by expansion during the piston stroke to the bottom dead center.
6. The

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