Partial Oxidation Reforming

In contrast to steam reforming, partial oxidation (POX) uses air instead of steam and, as its name implies, burns the fuel in restricted amounts of air so that it generates partially combusted products, including hydrogen. POX generates heat and can, therefore, potentially respond faster than a steam reformer. This is beneficial for load-following applications (c.g., transportation). 

The preparation of synthesis gas from natural gas, which is the most important step in the gas-to-liquid transformation, has attracted increasing attention in the last decade. Steam reforming, partial oxidation, and C02 reforming are the three major processes that can be employed to prepare synthesis gas. Because steam reforming was reviewed recently in this series [Adv. Catal. 47 (2002) 65], this chapter deals only with the latter two processes. 

Today, different processes (steam reforming, autothermal reforming, partial oxidation, gasification) are available and commercially mature for hydrogen production from natural gas or coal. These processes would have to be combined with technologies for C02 capture and storage (CCS), to keep the emissions profile low. A power plant that combines electricity and hydrogen production can be more efficient than retrofitted C02 separation systems for conventional power plants. 

Equation 9-4 and related heats of reaction can be manipulated to show that the maximum efficiency is a state point function, regardless of path (steam reforming, partial oxidation, or autothermal reforming), and is achieved at the thermoneutral point. In practice, x is set slightly higher than the thermoneutral point so that additional heat is generated to offset heat losses from the reformer. Table 9-1 presents efficiencies at the thermoneutral point for various hydrocarbon fuels. 

A POX reformer also can be used for converting gaseous fuels, but does not produce as much hydrogen as the steam reformers. For example, a methane-fed POX reformer would produce only about 75% of the hydrogen (after shifting) that was produced by an SR. Therefore, partial oxidation reformers are typically used only on liquid fuels that are not well suited for steam reformers. Partial oxidation reformers rank second after steam reformers with respect to their hydrogen yield. For illustration, the overall POX reaction (exothermic) for methane is... 

Hydrogen production from carbonaceous feedstocks requires multiple catalytic reaction steps For the production of high-purity hydrogen, the reforming of fuels is followed by two water-gas shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. Steam reforming, partial oxidation and autothermal reforming of methane are well-developed processes for the production of hydro-... 

Small reformers R D areas include compact and low cost reformers (1-5 kW) to convert fossil fuels (natural gas, gasoline) or biomass fuels (ethanol) to hydrogen via different processes (steam reforming, partial oxidation, auto-thermal, non catalytic hybrid steam reforming). Improvements in reformer efficiency, capacities and response times, and integration of purification unit are also being studied. Examples of projects include ... 

Methanol as Source ofSNG. Methanol can be produced from a large range of feedstocks by a variety of processes. Natural gas. liquefied petroleum gas (LPG), naphthas, residua] oils, asphalt, oil shale, and coal are in the forefront as feedstocks to produce methanol, with wood and waste products from farms and municipalities possible additional feedstock sources, hi order to synthesize methanol, the main feedstocks are converted to a mixture of hydrogen and carbon oxides (synthesis gas) by steam reforming, partial oxidation, or gasification. The hydrogen and carbon oxides are then converted to methanol over a catalyst. 

Table 6) indicate that the fuel-processing efficiencies decrease in the order of steam reforming > autothermal reforming > partial oxidation for both gasoline and diesel fuels. 

Synthesis Gas. There are three principal routes to synthesis gas steam reforming, partial oxidation, and coal gasifica-... 

NGK Insulators of Japan were issued US. Patent 5,741,474 in 1998 for a Process for Production of High Purity Hydrogen. This process is a combination of reforming, partial oxidation and membrane separation. 

Process Steam Reforming Partial Oxidation Koppers-Totzek Steam-Iron Electrolysis Current Electrolysis SPE... 

Process Steam Reforming Partial Oxidation Gasification Steam-Iron Electrolysis (Current) Electrolysis (New Technology)... 

PROCESS TABLE 5. ESTIMATED AMMONIA PRODUCTION COSTS 1150 STPD CAPACITY STEAM REFORMING PARTIAL OXIDATION ... 

Fig. 7.13. The catalytic synthesis of hydrogen from natural gas for ammonia synthesis using hydrodesulfurization, steam reforming, partial oxidation, water gas shift, methanation, and C02 scrubbing.

JVoccss Steam reforming Steam reforming Partial oxidation Gasification ... 

The selective oxidation or preferential oxidation of CO in hydrogen-rich stream is another important object for ceria based catalysts. The gas mixture from steam reforming/partial oxidation of alcohols or hydrocarbons, followed by the WGS reaction contains mainly FI2, CO2 and a small portion of CO, H2O, and N2. When such gaseous stream would be taken as input for hydrogen fuel cells, the CO has to be removed to avoid poisoning of the anode electrocatalysts. Ceria based nanomaterials, such as ceria/gold, ceria/copper oxide catalysts exhibit suitable catalytic activities and selectivities for CO PROX process. 

As discussed above in the reforming of hydrocarbon fuels, H2 can be produced from alcohol fuels by at least three major catalytic processes, namely steam reforming, partial oxidation and ATR or oxidative steam reforming. The chemistry, thermodynamics, and recent developments in catalysis of methanol and ethanol reforming with steam for H2 production will be discussed in this section. 

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