Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing organic compound
Reexamination Certificate
2000-04-07
2001-09-25
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing organic compound
C205S462000
Reexamination Certificate
active
06294068
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for producing C-2 and higher hydrocarbons from lower hydrocarbons, and particularly, direct gas phase electrocatalytic polymerization of lower hydrocarbons, such as methane, to produce higher hydrocarbons, e.g. ethane and gasoline range hydrocarbons.
There remains an interest in the energy industry to produce gasoline range hydrocarbons from natural gas or methane. A series of patents for this purpose where granted to George Olah, i.e. U.S. Pat. Nos. 4,433,192, 4,513,164, 4,465,893 and 4,467,130.
Krist et al. U.S. Pat. No. 5,064,733 describes the electrochemical conversion of CO
2
and CH
4
to C-2 hydrocarbons using a single electrochemical cell. This was accomplished by means of a cell divided by way of a solid electrolyte with methane-containing gas being introduced into one side of the cell and carbon dioxide into the other side of the cell. The process of that patent is primarily concerned with proton conductors used to dimerize methane. The process is operated at quite high temperatures in the order of 600 to 1000 °C. and no H
2
can be produced.
Another process for electrochemically converting methane to C
2
hydrocarbons is described in Hamakawa et al. “Electrochemical Methane Coupling Using Protonic Conductors”,
J. Electrochem. Soc
., Vol. 140, No. 2, February 1993, pp 459-462. This describes the low-level coupling of methane in a cell that includes an electrochemical hydrogen pump. This cell necessarily uses a high temperature proton conductor, SrCe
0.95
Yb
0.05
O
3
, as a solid electrolyte, operating at 1173K (900° C.). With this system the evolution of hydrogen and current density were both low. Under an applied potential, the current density was only 1% to fuel conversion and the conversion of CH
4
to high hydrocarbons was less than 1%.
It is the object of the present invention to polymerize and dimerize lower hydrocarbons in order to produce higher hydrocarbons, including unsaturated hydrocarbons.
SUMMARY OF THE INVENTION
One embodiment of this invention comprises a process for gas phase electrocatalytic polymerization of methane, ethane or methanol to produce higher hydrocarbons and hydrogen. This is done using an electrolysis cell having an anode chamber on one side of a solid electrolyte and a cathode chamber on the other of the solid electrolyte. According to this process, methane-, ethane- or methanol-containing gas is passed through the anode chamber to contact a catalytic anode which is connected to one side of the solid electrolyte, this solid electrolyte comprising a solid proton conducting membrane. An inert gas or oxygen is passed through the cathode chamber to contact a catalytic cathode which is connected to the other side of the proton conducting membrane. The membrane is designed so that H
+
is capable of passing through the membrane from the anode chamber to the cathode chamber. As a consequence, when methane is used as feedstock C-2 and higher hydrocarbons are formed in the anode chamber and hydrogen or water is formed in the cathode chamber.
A further embodiment of this invention is an electrochemical cell for gas phase electrocatalytic polymerization of methane, ethane or methanol to produce higher hydrocarbons and hydrogen. This cell comprises an anode chamber on one side of the solid electrolyte and a cathode chamber on the other side of the electrolyte. The solid electrolyte comprises a solid proton conducting membrane separating the anode chamber from the cathode chamber. A catalytic anode is connected to one side of the proton conducting membrane and a cathode is connected to the other side of the membrane. Means are provided for passing methane, ethane or methanol in contact with the catalytic anode and means are also provided for passing an inert gas or oxygen in contact with the cathode. Finally, means are included for withdrawing higher hydrocarbons from the anode chamber and for withdrawing hydrogen or water from the cathode chamber.
The membrane capable of transferring the H
+
from the anode chamber to the cathode chamber may be made from a variety of materials, e.g. perfluorosulfonic acid or polybenzimidazole. Perfluorosulfonic acid polymer is available under the trademark NAFION. The anode and cathode may also be formed from a variety of different materials, such as compressed carbon powder loaded with metal catalyst, carbon cloths supporting metal catalyst, nickel mesh impregnated with metal catalyst, etc. Among particularly useful catalysts, there may be mentioned noble metals, such as Pt, Pd, Ru, etc. The body of the electrolysis cell may also be formed from a variety of materials such as TEFLON™, a carbon block, metal, etc., with metal being preferred.
By forming the membrane from polybenzimidazole or perfluorosulfonic acid, the invention has the important advantage of providing excellent conversion of methane to electrical energy and higher hydrocarbons at quite moderate temperatures of less than 300° C. Thus, the electrochemical conversion is typically conducted at temperatures in the range of about 60 to 300° C., preferably about 65 to 225° C. When an untreated perfluorosulfonic acid polymer is used as membrane, the conversion must be conducted at a temperature below 120° C. In this case a methane activation catalyst is also required for the methane coupling reaction. When the perfluorosulfonic acid polymer membrane is treated with phosphoric acid, the working temperature can be increased to as high as 210° C., preferably about 180 to 210° C. The polybenzimidazole membrane (PBI) when treated with phosphoric acid can be operated at temperatures up to 300° C., preferably about 60 to 300° C. For the polybenzimidazole, a more preferred temperature is in the range of about 130 to 225° C., with a range of about 180 to 225° C. being particularly preferred.
REFERENCES:
patent: 5051156 (1991-09-01), Scharifker et al.
patent: 5064733 (1991-11-01), Krist et al.
patent: 5976721 (1999-11-01), Limaye
Hamakawa et al., “Electrochemical Methane Coupling Using Protonic Conductors”, J. Electrochem. Soc., vol. 140, No. 2, pp. 459-462. Feb. 1993.
Donini John C.
Donini Oreola
Petrovic Slobodan
Sanger Alan Rodney
Thind Surjit Singh
Donini Oreola
Natural Resources - Canada
Wong Edna
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