Process and system for converting biogas to liquid fuels
A method of producing a hydrocarbon fuel from a hydrocarbon-containing gas is disclosed and described. A hydrocarbon-containing gas is produced ( 10 ) containing from about 25% to about 50% carbon dioxide and can be reformed ( 12 ) with a steam gas to form a mixture of hydrogen, carbon monoxide and carbon dioxide. The reforming can be a composite dry-wet reforming or a tri-reforming step. The mixture of hydrogen, carbon monoxide and carbon dioxide can be at least partially converted ( 14 ) to a methanol product. The methanol product can be converted to the hydrocarbon fuel ( 18 ), optionally via UME synthesis ( 16 ). The method allows for effective fuel production with low catalyst fouling rates and for operation in an unmanned, self-contained unit at the source of the hydrocarbon-producing gas.
1. A method of producing a liquid hydrocarbon fuel, comprising:
obtaining a biogas comprising 50-95 vol % methane and 25-50 vol % carbon dioxide;
in a first reactor, steam reforming the biogas with a steam gas to form a synthesis gas having a ratio of approximately 6:3:1 of hydrogen, carbon monoxide and carbon dioxide;
in a second reactor, converting the synthesis gas, in the presence of a methanol-synthesis catalyst and a DME catalyst, at least partially to a mixture of methanol and dimethyl ether; and
in a third reactor, converting the mixture of methanol and dimethyl ether, in the presence of a ZSM catalyst, to a gasoline mixture comprising aliphatic hydrocarbons and aromatic hydrocarbons.
2. The method of claim 1 , wherein the biogas is obtained by anaerobic digestion.
3. The method of claim 1 , further comprising scrubbing the biogas sufficient to remove substantially all H 2 S.
4. The method of claim 1 , wherein the biogas has a majority of methane and 30% to less than 50% carbon dioxide.
5. The method of claim 1 , wherein the steam gas further includes air such that the steam reforming is a tri-reforming process including simultaneous dry reforming, wet reforming and partial oxidation.
6. The method of claim 1 , wherein the mixture has a modulus of about 1 to 3, where the modulus is defined in terms of molar concentrations as:
[
H
2
]
-
[
CO
2
]
[
CO
]
-
[
CO
2
]
.
7. The method of claim 6 , wherein the modulus is 1.5 to 2.5.
8. The method of claim 1 , wherein the steam reforming is performed at about less than 150 psi.
9. The method of claim 1 , wherein the steam reforming is accomplished using a packed bed reactor including a supported catalyst.
10. The method of claim 9 , wherein the supported catalyst is a Ni—Ir catalyst.
11. The method of claim 10 , wherein the Ni—Ir catalyst has 2.5 wt % Ni and 0.5 wt % Ir with about 0.25 wt % variation for each of Ni and Ir.
12. The method of claim 1 , wherein the converting the synthesis gas is a catalytic reaction which includes a Cu—Zn-Alumina as a catalyst in a fixed bed reactor.
13. The method of claim 1 , wherein the converting the mixture of methanol and dimethyl ether includes a DME catalyst consisting essentially of y-alumina and Cu—Zn-alumina catalyst particles.
14. The method of claim 1 , wherein the aliphatic hydrocarbons comprise C5 to C12 chains and the aromatic hydrocarbons comprise xylenes and toluenes.
15. The method of claim 1 , wherein the converting the mixture of methanol and dimethyl ether occurs within one mile of a formation source of the biogas.