Carbon dioxide reforming (also known as dry reforming) is a method of producing synthesis gas (mixtures of hydrogen and carbon monoxide) from the reaction of carbon dioxide with hydrocarbons such as methane. This chapter introduces the recent progress in production of H2-rich synthesis gas via dry reforming of hydrocarbons (methane, ethane, propane, and n-octane) and oxygenates mainly on the basis of papers published after 2004. This process is attractive from the environmental and economical viewpoint because of the potential utilization of greenhouse gases as resources, but dry reforming of hydrocarbons is highly energy consuming. Dry reforming of methane is the largest and the most economical way to produce hydrogen. Dry (CO2) reforming of hydrocarbons, ethanol, and DME is a promising way to produce H2-rich synthesis gas. Several research papers on dry reforming of methane have been published, and great achievements are in progress. But there are still two main drawbacks that hinder the commercialization and application in large scale. One is that all these reforming reactions are endothermic, and the calculated enthalpy (ΔH) increases with the number of carbon atoms in hydrocarbons. Another is that the carbon deposition occurs easily even on the surface of noble metals, and the deposited carbon would cause deactivation. And yet many commercial operations include CO2 in the feed to their reformers to adjust syngas composition.

This chapter provides a brief overview of fuel cell technology. It briefly discusses the basic principle of fuel cells. Fuel cells are electrochemical devices that convert the chemical energy of a chemical reaction directly into electrical energy and heat. In principle, a fuel cell operates like a battery, but does not run down or require recharging like a battery as long as fuel and oxidant are supplied. Fuel cells are energy conversion systems that efficiently generate electricity for stationary or transportation applications from fuels such as coal and petroleum or from biomass residues and human wastes. The basic physical structure or building block of most fuel cells consists of an electrolyte layer in contact with porous anode and cathode electrodes on either side. In the dual chamber fuel cell, a fuel enters the anode and an oxidant enters the cathode. These are separated by a selectively conductive electrolyte. Conduction through the electrolyte can occur in either direction, i.e., anode to cathode or cathode to anode, depending on the fuel cell. Fuel cells can be operated in a variety of modes, including constant fuel utilization, constant fuel flow rate, constant voltage, constant current, etc. The study concludes with a mention of the various types of fuel cells, such as direct carbon fuel cell, polymer electrolyte fuel cell, alkaline fuel cell, phosphoric acid fuel cell, molten carbonate fuel cell, and solid oxide fuel cell.

Components that constitute the balance of plant for a fuel cell power generator include sensors, controls, burners, heat exchangers, start-up power sources, power conditioners, sulfur cleanup, water recovery systems, steam generators, and fuel and air filters. This chapter provides an overview of fuel, air, water, and thermal management components. Fuel pumps can be of various types, including diaphragm, gear, piston, vane, and centrifugal. They must be controllable and compatible with the target fuel. Water pumps must also be controllable and compatible with water, which has minimal lubricity. As far as air pumps are concerned, positive displacement of air can be done via pumps or blowers. This includes air pressure required for fuel/air/steam mixing. Furthermore, a fuel cell power generator is a combination of multiple unit operations. Managing the interplay between these operations, both during steady state and transient operations, is a vital aspect of viable fuel cell generator designs. Proper thermal management, consequently, is a key design characteristic. Finally, a key element for successful commercial implementation of all these systems requires a well-conceived balance of plant integration of the various unit operations. These require use of dedicated pumps, blowers, sensors, and controls especially suited for fuel cell use. Investment in fuel cell technology has been primarily limited to government funding since commercial revenues are not imminent. This makes the development challenges particularly daunting.

This chapter explores aspects of oxidative steam reforming (OSR) chemistry that are important in a fuel-reforming process. In this method, steam and oxygen are fed together as oxidants to reform the hydrocarbon fuel into a H2-rich fuel stream suitable for fuel cells. OSR is generally considered as a combination of partial oxidation and steam reforming. Feeding air and steam together utilizes the heat generated from exothermic oxidation of the fuel to promote the endothermic steam-reforming reactions. OSR has been an established technology for H2 generation since the late 1950s. It is capable of producing H2 efficiently at high throughputs, which generally makes it the preferred method for industrial use in petrochemical production. However, using OSR for such applications requires a separation plant to remove N2 from air to reduce process gas volumes. Oxygen separation is very capital intensive (almost 40% of total cost) and generally precludes the use of OSR for large-scale applications. However, OSR does have some disadvantages. Using steam requires a water storage and supply system, which adds weight, complexity, and cost to the process. Also, as with any system that uses water, appropriate insulation is needed for applications in colder climates, and added space would be required for a reservoir in an already confined area (assuming for transportation use). Attempts to mitigate storage problems have looked into recycling the fuel cell exhaust to provide the necessary water requirements to maintain reforming capabilities under OSR conditions.

Fuel cells can efficiently produce electricity using hydrogen and syngas obtained by reforming/gasification of conventional gaseous, liquid, and solid fuels. However, these fuels contain sulfur as impurity that must be nearly completely removed to prevent poisoning of the fuel cell anode catalyst with H2S. Depending on the sulfur content of the fuel, deep desulfurization of gaseous and liquid fuels can be carried out either upstream of the catalytic reformer or syngas desulfurization can be carried out downstream of the reformer. This chapter deals with desulfurization for fuel cells. A number of promising sorbents continue to be developed for desulfurization of natural gas and LPG at room temperature and low pressure. Desulfurization of gasoline can also be carried out in the gas phase by reactive adsorption or passive adsorption. The concept of removal of sulfur compounds from gasoline, jet fuel, and diesel using sorbents in the liquid phase, especially at room temperature, is attractive because of its simplicity. Although there is significant research activity to develop such sorbents, it is not clear if a viable liquid-phase desulfurization process can be developed for compact fuel processors. Further research and development are needed to measure and validate liquid phase sorbent capacities with fuels meeting current sulfur regulations and to develop liquid phase sorbents that can be simply prepared and scaled up, easily regenerated offsite or onsite, and safely disposed of.

This chapter presents several methods for reforming of hydrocarbons or oxygenated hydrocarbons to syngas. It provides information on decomposition of hydrocarbons, supercritical reforming, non-catalytic thermal reforming in porous media, radio frequency (RF)-assisted reforming, and pre-reforming. Supercritical water oxidation technique for H2 production is gaining great attention because of unique properties of supercritical water that may change the fuel reactivity, thermodynamic equilibrium, and the reaction pathway. The properties of supercritical water such as solubility, density, and viscosity are significantly different than liquid or vaporized water. Non-catalytic thermal reforming using porous media combustion is gaining momentum for H2 production from hydrocarbon reforming. This non-catalytic approach involves combustion of a hydrocarbon fuel in a catalytically inert porous media at fuel rich conditions. The basic principle is the internal heat transfer from the product gases to the entering feed through solid conduction and solid-to-solid radiation characteristics of the porous media. Furthermore, RF-induced catalytic fuel reforming has been shown to be effective in enhancing the performance of reforming catalysts by reducing carbon formation. The observed effects of RF-fields on catalysis are increased catalyst activity and selectivity, reduced carbon formation, and reduced reactor heating. However, it is not known yet what mechanism (improved heating, excited surface states, or other mechanism) causes the improved catalyst performance. Finally, pre-reforming can be used to convert higher gaseous hydrocarbons (>C1) into smaller molecules (CO, H2, CH4, etc.).

This chapter deals with catalytic partial oxidation. Catalytic partial oxidation (CPOX) is an attractive option to produce H2 and CO from hydrocarbon fuels for fuel cell applications. It is suitable for compact or mobile fuel-processing systems integrated with solid oxide fuel cells due to similarity of operating conditions and the utilization of currently available infrastructure fuels. Following this, the study presents the reaction mechanisms and kinetics of CPOX, discussing two mechanisms for the CPOX of methane: direct and indirect. Under this, it analyzes several factors that impact the reaction. Higher hydrocarbons generally exhibit the indirect mechanism. It also provides a brief discussion of the reaction mechanism for oxygenates, analyzing several kinetic studies for methane. It also illustrates examples to demonstrate some of the approaches that have been taken and to highlight a few issues that must be considered when developing a mechanistic and kinetic model. Furthermore, it deals with hydrocarbons. In this regard, it discusses the CPOX of light hydrocarbons for many catalyst and support systems. It also examines base metal, and noble metal catalysts for hydrocarbon conversion and selectivity to H2 and CO (syngas). The effects of several support systems are analyzed, and the effect of different promoters is evaluated. The role of the support structure on enhancing catalytic performance is also investigated, and the bimetallic catalyst approach is considered. Finally, it shed light on some future development and applications for CPOX.

This chapter focuses on the processing technologies required to allow operation of polymer electrolyte membrane (PEM) fuel cells fuelled by reformate, including the final cleanup steps (PrOX, SMET), which are uniquely required for PEM. Selective methanation (SMET) of CO is a viable approach for the removal of CO from hydrogen-rich gas streams to be used with PEM fuel cells. Ru- and Ni-based catalysts are among the most extensively investigated and have shown the most promising performance. The key criteria for good performance include high activity, which allows operation at lower temperatures, and high selectivity, reflecting low activity for CO2 methanation and reverse water gas shift. Catalysts based on these metals tend to be the most selective at the lower operating temperature ranges, generally because CO adsorption predominates and adsorption of CO2 (hence reaction) is minimized. However, in order to obtain full CO conversion, higher temperatures may be required with subsequent loss of selectivity. The performance of these catalysts is strongly dependent on the support, preparation method, metal loading, metal particle size, promoter, and the operating conditions. Finally, some promising SMET strategies have been proposed and demonstrated that show viability for both performances, with CO concentrations below 10 ppmv being achieved, and durability, in which stability has been demonstrated for as long as 800 h on stream.

This chapter provides a thorough analysis of the important aspects of fuel-processing technology. Fuel cells are essentially continuously operating batteries, which generate electricity from a fuel, such as hydrogen, and an oxidant, such as air. Each type of fuel cell is designed to meet a different application. The proton exchange membrane fuel cell is being pursued by a number of companies because of its low operating temperature, response to transients, and compact size, which make it desirable for a number of residential, commercial, and military applications. Solid oxide fuel cells are being developed for small-scale stationary power applications, auxiliary power units for vehicles, and mobile generators for civilian as well as military applications. The purpose of a fuel processor is to convert a commonly available fuel, such as gasoline, diesel, or natural gas, into a gas stream containing primarily, or only, the compound(s) required by the fuel cell. The fuel to power the fuel cells can, in principle, be a wide range of oxidizable compounds, such as hydrogen, CO, CH4, and methanol. Because each type of fuel cell requires a different fuel, the fuel processor must be designed to match the fuel cell. There are three predominant modes of catalytic reforming: partial oxidation, steam reforming, and oxidative steam reforming. All three involve oxidation of the hydrocarbon fuel to produce a hydrogen-rich synthesis gas.

This chapter deals with various types of liquid fuels and the relevant chemical and physical properties of these fuels as a means of comparison to the fuels of the future. It gives an overview of the manufacture and properties of the common fuels as well as a description of various biofuels. A fuel mixture usually contains a wide range of organic compounds (usually hydrocarbons). The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, density, viscosity, and a host of other properties. Depending on the application (stationary, central power, remote, auxiliary, transportation, military, etc.), there are a wide range of conventional fuels, such as natural gas, liquefied petroleum gas, light distillates, methanol, ethanol, dimethyl ether, naphtha, gasoline, kerosene, jet fuels, diesel, and biodiesel, that could be used in reforming processes to produce hydrogen (or hydrogen-rich synthesis gas) to power fuel cells. Fossils fuels include gaseous fuels, gasoline, kerosene, diesel fuel, and jet fuels. Gaseous fuels include natural gas and liquefied petroleum gas. Types of gasoline include automotive gasoline, aviation gasoline, and gasohol. Some additives added into gasoline are antioxidants, corrosion inhibitors, demulsifiers, anti-icing, dyes and markers, drag reducers, and oxygenates.