Methanol from steam reforming, advantages

Advantages and Recent Advances in Methanol from Steam Reforming. Since the ICI LP methanol plant was first introduced in 1967, the design has been modified to enhance energy recovery as it became more economic to do so, due to increasing energy costs. Figure 4 shows this trend. 

Ethanol can be derived from biomass by means of acidic/enzymatic hydrolysis or also by thermochemical conversion and subsequent enzymatic ethanol formation. Likewise for methanol, hydrogen can be produced from ethanol with the ease of storage/transportation and an additional advantage of its nontoxicity. Apart from thermodynamic studies on hydrogen from ethanol steam reforming,117-119 catalytic reaction studies were also performed on this reaction using Ni-Cu-Cr catalysts,120 Ni-Cu-K alumina-supported catalysts,121 Cu-Zn alumina-supported catalysts,122,123 Ca-Zn alumina-supported catalysts,122 and Ni-Cu silica-supported catalysts.123... 

Methanol is unquestionably the easiest of the potential fuels to convert to hydrogen for vehicle use. Methanol disassociates to carbon monoxide and hydrogen at temperatures below 400°C and can be catalytically steam reformed at 250°C or less. This provides a quick start advantage. Methanol can be converted to hydrogen with efficiencies of >90 %. But methanol is produced primarily from natural gas requiring energy and it is less attractive than gasoline on a well-to-wheels efficiency (2). 

Logistic fuels, such as jet and diesel fuels, are readily available, but a compact and effective way to remove sulfur from these fuels is needed for portable hydrogen production. Consequently, for most portable applications, it is likely that sulfur-free fuels, such as methanol, will be used. An additional advantage of methanol is that it is easier to activate at low temperatures than other hydrocarbons. Therefore, a portable hydrogen production unit based on methanol steam reforming would be simpler and less costly than other alternatives. Methanol can also be considered an energy carrier as an alternative to liquefied natural gas... 

In addition to the direct use of ethanol as a fuel, its use as a source of H2 to be used with high efficiency in fuel cells has been thoroughly investigated. H2 production from ethanol has advantages compared vdth other H2 production techniques, including steam reforming of hydrocarbons and methanol. Unlike hydrocarbons, ethanol is easier to reform and is also free of sulfur, which is a well-known catalyst poison. Furthermore, unlike methanol, ethanol is completely renewable and has lower toxicity. 

Three different routes, or combinations of these, can be used to produce synthesis gas from methane. These are steam reforming, CO2 reforming and partial oxidation. Each has its advantages and likewise has drawbacks. Steam reforming, which is a common industrial method of synthesis gas production, is very endothermic, as seen in the equations below. It also produces an H2/CO ratio of about 3/1, which is good for hydrogen production, but is too high for fuel synthesis. Methanol and Fischer-Tropsch synthesis use a H2/CO ratio of about 2/1. 

The classical route of methane to methanol conversion involves oxidation of methane using various conditions. However, until recently, no satisfactory method had been devised to control the oxidation sufficiently to stop the reaction at methanol. Instead, oxidation tended to proceed beyond methanol to produce unwanted carbon dioxide. The conventional steam reforming process, which produces the intermediate syngas (a mixture of hydrogen gas and carbon monoxide, from which methanol can be synthesized), comprises 60—70% of the capital costs of methane to methanol conversion. Thus, a low temperature catalytic process that avoids syngas production would be highly advantageous from an economic perspective. 

Methanol can be easily produced from natural gas and has the significant advantage of being able to steam reform over suitable catalysis at temperatures as low as 200 °C. Peppley et al. (2003) have reviewed the methods used to convert methanol to hydrogen external to the fuel cell. As mentioned above, methanol is considered to be a promising fuel for use in low-temperature fuel cells where its high energy density as a liquid is considered particularly attractive for portable apphcations. 

The synthesis loop consists of a recycle compressor, feed/effluent exchanger, methanol reactor, final cooler and crude methanol separator. Krupp Uhde s methanol reactor is an isothermal tubular reactor with a copper catalyst contained in vertical tubes and boiling water on the shell side. The heat of methanol reaction is removed by partial evaporation of the boiler feedwater, thus generating 1—1.4 tons of MP steam per ton of methanol. Advantages of this reactor type are low byproduct formation due to almost isothermal reaction conditions, high heat of reaction recovery, and easy temperature control by regulating steam pressure. Tb avoid inert buildup in the loop, a purge is withdrawn from the recycle gas and is used as fuel for the reformer. 

---