Steam reforming, carbon oxide

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-... 

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. 

Primary steam reforming Secondary steam reforming Carbon monoxide conversion Carbon monoxide methanation Ammonia synthesis Sulfuric acid synthesis Methanol synthesis Oxo synthesis Ethylene oxide Ethylene dichloride Vinylacetate Butadiene Maleic anhydride Phthalic anhydride Cyclohexane Styrene Hydrodealkylation Catalytic reforming Isomerization Polymerization (Hydro)desulfurization Hydrocracking... 

CO2 reforming of methane can be used to adjust the H/CO ratio and provide the correct H2/CO ratio for Fischer-Tropsch synthesis and could potentially be used to reduce CO2 emissions from other processes however, it is even more endothermic than steam reforming. Partial oxidation is exothermic and has the correct H2/CO ratio for methanol synthesis, but requires a pure oxygen source, adding to the cost. In addition to the individual drawbacks, all of these processes must be run with 0/C ratios of greater than 1 to prevent coking of the catalyst. This makes the processes more expensive in practice than would be expected under optimized conditions for the stoichiometric reactions. The propensity of these processes to form carbon at low 0/C ratios is even more pronounced at... 

Steam reforming or oxidation of feedstock to form hydrogen and carbon oxides... 

Unlike steam reforming, partial oxidation is an exothermic process. Essentially, it is a combustion, but with a less-than-stoichiometric amount of oxygen, so that the products are carbon monoxide and hydrogen (instead of carbon dioxide and water vapor produced in full combustion). Similar to steam reforming, the reformate gas must go through shift reaction to... 

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

Synthesis gas, a mixture of CO and o known as syngas, is produced for the oxo process by partial oxidation (eq. 2) or steam reforming (eq. 3) of a carbonaceous feedstock, typically methane or naphtha. The ratio of CO to may be adjusted by cofeeding carbon dioxide (qv), CO2, as illustrated in equation 4, the water gas shift reaction. 

HTS catalyst consists mainly of magnetite crystals stabilized using chromium oxide. Phosphoms, arsenic, and sulfur are poisons to the catalyst. Low reformer steam to carbon ratios give rise to conditions favoring the formation of iron carbides which catalyze the synthesis of hydrocarbons by the Fisher-Tropsch reaction. Modified iron and iron-free HTS catalysts have been developed to avoid these problems (49,50) and allow operation at steam to carbon ratios as low as 2.7. Kinetic and equiUbrium data for the water gas shift reaction are available in reference 51. 

Steam Reforming Processes. In the steam reforming process, light hydrocarbon feedstocks (qv), such as natural gas, Hquefied petroleum gas, and naphtha, or in some cases heavier distillate oils are purified of sulfur compounds (see Sulfurremoval and recovery). These then react with steam in the presence of a nickel-containing catalyst to produce a mixture of hydrogen, methane, and carbon oxides. Essentially total decomposition of compounds containing more than one carbon atom per molecule is obtained (see Ammonia Hydrogen Petroleum). 

Steam reforming is the reaction of steam with hydrocarbons to make town gas or hydrogen. The first stage is at 700 to 830°C (1,292 to 1,532°F) and 15-40 atm (221 to 588 psih A representative catalyst composition contains 13 percent Ni supported on Ot-alumina with 0.3 percent potassium oxide to minimize carbon formation. The catalyst is poisoned by sulfur. A subsequent shift reaction converts CO to CO9 and more H2, at 190 to 260°C (374 to 500°F) with copper metal on a support of zinc oxide which protects the catalyst from poisoning by traces of sulfur. 

The operation of a large synthetic ammonia plant based on natural gas involves a delicately balanced sequence of reactions. The gas is first desulfurized to remove compounds which will poison the metal catalysts, then compressed to 30 atm and reacted with steam over a nickel catalyst at 750°C in the primary steam reformer to produce H2 and oxides of carbon ... 

The surface analyses of the Co/MgO catalyst for the steam reforming of naphthalene as a model compound of biomass tar were performed by TEM-EDS and XPS measurements. From TEM-EDS analysis, it was found that Co was supported on MgO not as particles but covering its surface in the case of 12 wt.% Co/MgO calcined at 873 K followed by reduction. XPS analysis results showed the existence of cobalt oxide on reduced catalyst, indicating that the reduction of Co/MgO by H2 was incomplete. In the steam reforming of naphthalene, film-like carbon and pyrolytic carbon were found to be deposited on the surface of catalyst by means of TPO and TEM-EDS analyses. 

The TEM images of deposits observed on Catalyst I used for the steam reforming of naphthalene are shown in Fig. 5. Two types of deposits were observed and they were proved to be composed of mainly carbon by EDS elemental analysis. One of them is film-like deposit over catalysts as shown in Fig. 5(a). This type of coke seems to consist of a polymer of C H, radicals. The other is pyrolytic carbon, which gives image of graphite-like layer as shown in Fig. 5(b). Pyrolytic carbon seems to be produced in dehydrogenation of naphthalene. TPO profile is shown in Fig. 6. The peaks around 600 K and 1000 K are attributable to the oxidation of film-like carbon and pyrolytic carbon, respectively [11-13]. These results coincide with TEM observations. 

The steam reforming catalyst is very robust but is threatened by carbon deposition. As indicated in Fig. 8.1, several reactions may lead to carbon (graphite), which accumulates on the catalyst. In general the probability of carbon formation increases with decreasing oxidation potential, i.e. lower steam content (which may be desirable for economic reasons). The electron micrograph in Fig. 8.4 dramatically illustrates how carbon formation may disintegrate a catalyst and cause plugging of a reactor bed. 

The objective of plasma-assisted decomposition of hydrocarbons is to produce hydrogen and carbon in an oxidant-free environment (as opposed to plasma-assisted POx and steam reforming that produce hydrogen and C02), according to the following generic reaction ... 

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