The principle of fuel cells was first recognized by Sir William Grove during the early 1800s, but their practical use was only recently developed. The basis of most fuel cell technologies is still based on Grove's principle - that is, hydrogen and oxygen (air) are combined in an electrochemical cell-like device, producing water and electricity.
The process is clean, giving only water as a byproduct, but hydrogen itself must be first produced in an energy-consuming process, using (at present) mainly fossil fuels. The handling of hydrogen gas itself is not only technically difficult, but also dangerous. Nonetheless, the use of fuel cells is gaining application in static installations or in specific cases, such as space vehicles. Currently, hydrogen gas is produced mainly from still-available hydrocarbon (fossil fuel) sources using reformers, which converts them to a mixture of hydrogen and carbon monoxide. These two gases are then separated. Although this process relies on our diminishing fossil fuel sources, electrolysis or other processes to cleave water can also provide hydrogen without any reliance on fossil fuels. Hydrogen-burning fuel cells, by necessity, are still limited in their applicability. In contrast, a new approach (discussed in Chapter 11) uses directly liquid methanol (or its derivatives) in a fuel cell without first converting it to hydrogen. The direct oxidation liquid-fed methanol fuel cell (DMFC) has been developed in a cooperative effort between the University of Southern California and Caltech-Jet Propulsion Laboratory of NASA (who for a long time worked on fuel cells for the US space programs). In such a fuel cell, methanol reacts with oxygen of the air over a suitable metal catalyst, producing electricity while forming CO2 and H2O:
More recently, it was found that the process could be reversed. Methanol (and related oxygenates) can be made from CO2 via aqueous electrocatalytic reduction without prior electrolysis of water to produce hydrogen in what is termed a "regenerative fuel cell". This process can convert CO2 and H2O electrocatalytically into oxygenated fuels (i.e., formic acid, formaldehyde and methyl alcohol), depending on the electrode potential used in the fuel cell in its reverse operation.
The reductive conversion of CO2 to methanol can also be carried out by catalytic hydrogenation using hydrogen. Hydrogen can be obtained by electrolysis of water (using all kinds of energy sources such as atomic, solar, wind, geothermal, etc.) or other means of cleavage (photolytic, enzymatic, etc.). Methanol is a convenient medium to store energy, and is an excellent transportation fuel. It is a liquid (with a boiling point of 64.6 °C) that can be easily transported using the existing infrastructure. Methanol can also be readily converted to dimethyl ether. Di-methylether has a relatively higher calorific value and is an excellent diesel substitute.
Methanol produced directly from methane (natural gas) without going to syngas or by recycling of CO2 into CH3OH or dimethyl ether can subsequently also be used to produce ethylene as well as propylene. These are the building blocks in the petrochemical industry for the ready preparation of synthetic alipha tic and aromatic hydrocarbons, and for the wide variety of derived products and materials, obtained presently from oil and gas, on which we rely so much in our everyday life.
Synthetic hydrocarbons and their products
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Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.