5.4 Synthesis Gas to Hydrogen, Methanol, and Synthetic Fuels Jan van de Loosdrecht and J. W. (Hans) Niemantsverdriet 5.4.1 Introduction Synthesis gas, or syngas, is a mixture of carbon monoxide, carbon dioxide, and hydrogen. Syngas can be produced from many sources, including natural gas, coal, biomass, or virtually any hydrocarbon feedstock, by gasifying it with an oxi- dant such as O 2 or steam. Syngas is a versatile intermediate for the production of hydrogen, ammonia, methanol, and in Fischer-Tropsch synthesis (FTS), the produc- tion of synthetic hydrocarbon fuels. As such, syngas is also a key component in present and future sustainable energy technology. Figure 5.4.1 summarizes the con- versions. In this chapter, we describe how syngas can be produced and how it is converted into substances that are in essence storage media for chemical forms of energy. 5.4.2 Production of Synthesis Gas [1] The reaction between methane (or other hydrocarbons) and steam to syngas is en- dothermic and requires high temperatures. In addition, it competes with other reac- tions. Table 5.4.1 lists the important reactions that play a role. Indeed, only at temperatures above 700°C does the steam methane reforming (SMR) become ther- modynamically favored over the water-gas shift (WGS) and the carbon formation reactions in Table 5.4.1. Figure 5.4.2 summarizes the production processes for syngas production from nat- ural gas. SMR is generally carried out in tubular reactors that are externally heated by burners to achieve the necessary high temperatures. The catalyst is a supported nickel catalyst on a special support that has been designed to cope with the harsh con- ditions of high temperatures and high-pressure steam. The waste heat from the oven section is used to preheat gases and to produce steam. This plant is often used for oper- ation at moderate scale, such as relatively small methanol synthesis plants or H 2 production. It produces syngas with H 2 /CO ratios in the range of 3–4 [1]. Avoiding carbon deposition on the catalyst is a major challenge [2, 3]. Carbon can be present as graphite-like coke and in the form of whiskers, or carbon nanofibers. The latter lead to detachment of the nickel crystallites from the support and breaking of the catalyst pellets. This may cause blockage of the reformer reactor tubes and the formation of hot spots. Higher hydrocarbons exhibit a larger tendency to form Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 3/21/16 5:46 AM