Carbon dioxide from methane oxidation

S. Sridhar, B. Smitha, M. Ramakrishna, and T. M. Aminabhavi. Modified poly(phenylene oxide) membranes for tbe separation of carbon dioxide from methane. J. Membr. Set, 280(l-2) 202-209, September 2006. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Acetic acid, CH3COOH(l), could be produced from (a) the reaction of methanol with carbon monoxide (b) the oxidation of ethanol (c) the reaction of carbon dioxide with methane. Write balanced equations for each process. Carry out a thermodynamic analysis of the three possibilities and decide which you would expect to be the easiest to accomplish. 

The basic elements of a SOFC are (1) a cathode, typically a rare earth transition metal perovskite oxide, where oxygen from air is reduced to oxide ions, which then migrate through a solid electrolyte (2) into the anode, (3) where they combine electrochemically with to produce water if hydrogen is the fuel or water and carbon dioxide if methane is used. Carbon monoxide may also be used as a fuel. The solid electrolyte is typically a yttrium or calcium stabilized zirconia fast oxide ion conductor. However, in order to achieve acceptable anion mobility, the cell must be operated at about 1000 °C. This requirement is the main drawback to SOFCs. The standard anode is a Nickel-Zirconia cermet. 

The values for the organism yield constants are assumed to be somewhat higher than for acetic acid since they are expressed on a molar basis and more than one species may participate in the reaction. The yield constants for carbon dioxide and methane are developed from the oxidation-reduction balances. 

The oxidation of 2 mol butyric acid to 4 mol acetic acid is coupled with the reduction of 1 mol of carbon dioxide to methane. Tracer experiments showed that 98% of the methane is derived from carbon dioxide. In these examples of methane fermentation involving carbon dioxide reduction, no carbon dioxide is formed in the oxidation of the substrate. The fermentation of propionic acid by M. propionicum is more complicated because it involves both carbon dioxide formation and consumption (Stadtman and Barker, 1951) ... 

The nano-grained nickel catalysts supported on zdrconia or zirconia-rare earth element oxides are prepared by the oxidation-reduction pretreatment of amorphous Ni-Zr-rare earth element alloys. The conversion of carbon dioxide to methane on the catalyst prepared from amorphous Ni-40Zr alloy is improved by the addition of 5 at% or more rare earth elements (Y, Ce and Sm). 

By mixing a solid absorbent for carbon dioxide with the reforming catalyst, it is possible to combine the steam reforming of methane [reaction (2.1)] and its subsequent shift reaction [reaction (2.5)] into a single step and, at the same time, reduce the temperature of the former from about 900 to 400—500 °C. Removal of the carbon dioxide from the reaction zone causes a shift in the equilibrium of the combined reaction so that the production of hydrogen is enhanced, while the carbon monoxide is oxidized to carbon dioxide. A typical product gas is composed of 90% hydrogen and about 10% unreacted methane, with a small percentage of carbon dioxide and a trace of carbon monoxide. 

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