Methane energy efficiency

Methane. As our most abundant hydrocarbon, methane offers an attractive source of raw material for organic chemicals (see Hydrocarbons). Successful commercial processes of the 1990s are all based on the intermediate conversion to synthesis gas. An alternative one-step oxidation is potentially very attractive on the basis of simplicity and greater energy efficiency. However, such processes are not yet commercially viable (100). 

Micro-arc formation between excited methane and excited C02 increased the conversions of CH4 and C02 and favored the production of CO. The energy efficiency of the reaction reached a maximum at CH4/C02 = 1. 

On the one hand, the current petrochemical route would continue to provide the world with the chemicals consumers require. To satisfy the need for a more sustainable development, the petrochemical industry would continue its drive toward a continuous improvement in energy efficiency (see Figure 10.3). This drive will primarily include the continuous improvement of the current crude-oil-based processes while stranded methane or CO2 would be utilized as complementary feedstock. 

Typically, ATR reactions are considered to be thermally self-sustaining and therefore do not produce or consume external thermal energy. In fact, since ATR consists of the combination of an exothermic reaction (CPO) which produces heat, with an endothermic reaction (CSR) where heat must be externally generated to the reformer, the balance of the specific heat for each reaction becomes a very distinctive characteristic of this process. This makes the whole process relatively more energy efficient since the heat produced from CPO can transfer directly to be used by CSR. However, other exothermic reactions may simultaneously occur, such as WGS and methanation reactions. 

Also, steam-methane reforming is about 65 to 75 percent energy efficient, which is considered a high percentage. 

Figure 5.1.6 Comparison of the energy efficiencies and current densities for C02 reduction to formic acid, syngas, and hydrocarbons (methane and ethylene) reported in the literature with those of water electrolyzers. Efficiencies of electrolyzers are total system efficiencies, while the CO2 conversion efficiencies only include cathode losses and neglect anode and system losses. Adapted from [17],...

Figure 5.1.6 evidences that electrochemical conversion of CO2 shows moderate efficiencies and reasonably high current densities, although not at the same time. While researchers have reported high faradaic efficiency for many products (typically >90% for formic acid and carbon monoxide, and 65-70% for methane and ethylene), high overpotentials are a major hindrance to improving energy efficiency. 

Methane is the simplest, most abundant, and geographically most widely distributed hydrocarbon. It therefore receives constantly increasing attention as an alternate energy source to coal and petroleum from both the world fuels industry and from the science and engineering community to broaden its utility and enhance its transportability by energy-efficient conversion to liquid hydrocarbons and functional chemical raw materials. 

These partial oxidation reactions are exothermic and, thus, reformers are expected to be energy efficient and compact compared to the steam reforming. The partial oxidation of methane can be carried out by Ni, Co, Rh, and Pt group metals for the temperature range of 700-1000°C, while that of methanol has been studied over Cu-based catalysts in the temperature range of 200-300° C. Autothermal reforming of... 

A number of patents have been issued claiming various methods for the operation of this process. Kraucli80 states that it is possible by this method to convert methane almost completely into acetylene with an energy efficiency of 35 to 40 per cent. 

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