Syngas methane yield

Figure 7.3 Suggestion for variable combination (graphite, 1 bar) (a) temperature and carbon conversion, (b) cold gas efficiency and dry methane yield, (c) syngas yield and H2/CO ratio, (d) selectivity of CO/C and CHVC.

Partial methane oxidation comprises very high rates so that high space-time yields can be achieved (see original citations in [3]). Residence times are in the range of a few milliseconds. Based on this and other information, it is believed that syngas facilities can be far smaller and less costly in investment than reforming plants. Industrial partial oxidation plants are on the market, as e.g. provided by the Syntroleum Corporation (Tulsa, OK, USA). Requirements for such processes are operation at elevated pressure, to meet the downstream process requirements, and autothermal operation. 

Metal oxide-mediated oxidation of methane using air as a primary oxidant is an alternative way to produce N2-free syngas. The concept is based on the oxidation of methane by transition metal oxides in high-oxidation state yielding syngas and corresponding metal oxide in a low-oxidation state ... 

These adducts are more active than the iron ones in the conversion of syngas. At 250°C, a higher yield of methane is observed (Table U) and carbon dioxide is produced in smaller amounts. Inspection of Table 5 summarizing the influence of the H2/CO ratio on products selectivity also indicates a higher production of saturated hydrocarbons. This behavior is typical for cobalt catalysts in F-T synthesis (j2,25). The chain-length distribution is similar to that observed for catalysts derived... 

MRG [Methane rich gas] A catalytic steam-reforming system, similar to the classic syngas reaction of steam with a hydrocarbon mixture, but yielding hydrogen, methane, and carbon monoxide in different proportions. The system is thermodynamically balanced,... 

Partial oxidation of methane (or hydrocarbons) is another option to produce syngas [4], This process, which runs without a catalyst, needs high temperatures for high CH4 conversion and to suppress soot formation. The process can handle other feedstocks, such as heavy oil factions and biomass, and yields syngas with a H2/CO ratio of about 2. The process is eminently suitable for large-scale production of syngas (e.g. for gas-to-liquids [GTL] plants). 

Syngas composition, most importantly the H2/CO ratio, varies as a function of production technology and feedstock. Steam methane reforming yields H2/CO ratios of three to one whereas coal and biomass gasification yields ratios closer to unity or lower. Conversely, the required properties of the syngas are a function of the synthesis process. Fewer moles of product almost always occur when H2 and CO are converted to fuels and chemicals. Consequently, syngas conversion processes are more thermodynamically favorable at higher H2 and CO partial pressures. The optimum pressures depend on the specific synthesis process. 

H2) where a complex network, involving secondary reactions of CO2 and H2O with CH4, enhance the yield of H2 and CO so that thermodynamic equilibrium can be reached easily [27]. It can be inferred that, like the oxidation of methane to syngas, the partial oxidation of methanol with a CH3OH/O2 ratio near to the stoichiometric value (ca. 2/1) operating with an optimum residence time and temperature can reach very high yields also approaching thermodynamic equilibrium. 

The steam reforming of methane to produce syngas includes nine basic reactions. The global equilibrium yield (GEY) and the potential maximal equilibrium yield (PMEY) can be calculated by a new method proposed by this paper. The optimal reaction assemblage (ORA) can be constructed by an optimization method. Where hydrogen is the desired product, the ORA is composed of reactions (1) and (2) in the nine-reaction system. The observed peak yield (OPY) of hydrogen equals 2.410 (mole fraction), its PMEY and GEY equal 3.341 (mole fraction). If carbon monoxide is the desired product, the ORA includes only reaction (1) in the nine-reaction system and the OPY, GEY and PMEY of carbon monoxide equal 0.344, 0.2767 and 0.9789 (mole fraction) respectively. Construction of the ORA is the key and fundamental way to improve the yield of a desired product. In this paper, the method of constructing the ORA is developed. 

---