Light autothermic reforming

CAR [Combined autothermal reforming] A "reforming process for making "syngas from light hydrocarbons, in which the heat is provided by partial oxidation in a section of the reactor. Developed by Uhde and commercialized at an oil refinery at Strazske, Slovakia, in 1991. 

Qi et al. [32] tested autothermal reforming of n-octane over a ruthenium catalyst, which was composed of 0.5 wt.% ruthenium stabilized by ceria and potassium on y-alumina. It showed full conversion of n-octane for 800 h. However, the selectivity moved from carbon dioxide and methane toward carbon monoxide and light hydrocarbons, which has to be regarded as an indication of catalyst degradation during long-term tests despite the fact that full conversion was achieved. After 800 h the catalyst consequently showed incomplete conversion. Tests performed on the spent catalyst revealed losses of specific surface area and of 33 wt.% of the noble metal. 

For autothermal reforming of higher hydrocarbons, the main hydrocarbon byproduct usually observed is methane. The formation of light alkenes is favoured over alkanes in the case of incomplete conversion towards carbon oxides and methane [10, 72, 73]. 

Flytzani-Stephanopoulos and Voecks found that for autothermal reforming of n-tetradecane and benzene, the aromatic feed produced only methane, whereas aliphatic feed also produced light olefins and paraffins as shown in Figure 3.15 [74]. Ethylene was only an intermediate product in benzene reforming. 

Ferrandon and Krause investigated the effect of the catalyst support on the performance of rhodium catalysts wash-coated onto cordierite monoliths for autothermal reforming of gasoline [245]. The samples contained 2 wt.% rhodium on gadolinium/ceria, and lanthanum-stabilised alumina [245]. The latter sample showed higher activity and superior selectivity. Only 30 ppm of light hydrocarbons (C > 1) were detected. However, the sample also had higher surface area and rhodium dispersion. Both samples showed stable performance for more than 50-h test duration. 

Cheekatamarla and Lane ]257] found higher hydrogen yield and a lower content of light hydrocarbons for autothermal reforming of synthetic diesel fuel over bimetallic platinum/palladium and platinum/nickel catalysts compared with the monometallic samples. The catalysts showed medium-term stability for 50-h test duration in the presence of sulfur in the feed ]258]. 

Aicher et al. [72] developed an autothermal reformer for diesel fuel dedicated to supplying a molten carbonate fuel cell system from Ansaldo Fuel Cells S.p.A., Italy. The diesel fuel (which contained less than 10 ppm sulfur for the pilot plant application) was injected into the steam and air flows, which were pre-heated by a diesel burner to 3 50 °C. The reactor itself was operated at 4 bar, a S/C ratio of 1.5 and high O/C ratio of 0.98, which makes the reactor into a steam supported partial oxidation device. Consequently, the dry hydrogen content of the reformate was rather low with less than 35 vol.%. The operating temperature of the honeycomb had to be kept well above 800 °C to prevent coke formation and the presence of light hydrocarbons such as ethylene and propylene in the reformate. The reactor was operated for 300 h, which led to a slight deterioration in the catalyst performance. 

From natural gas and light hydrocarbons by steam reforming, catalytic autothermal reforming, or partial oxidation. 

Steam Reforming. When relatively light feedstocks, eg, naphthas having ca 180°C end boiling point and limited aromatic content, are available, high nickel content catalysts can be used to simultaneously conduct a variety of near-autothermic reactions. This results in the essentiaHy complete conversions of the feedstocks to methane ... 

Synthesis gas can be produced by the steam reforming process or by the autothermal process. Hydrocarbons are catalytically cracked in the presence of steam and applied heat in the steam reforming process. Hydrocarbons from methane up to the C4-C7 fractions of light petroleum can be used as raw materials. In contrast, the energy required for cracking is obtained by the partial combustion of the hydrocarbons themselves in the autothermal process. This latter process works without catalysts using steam-oxygen mixtures and hydrocarbons from methane to heavy fuel oils. 

Borup et al. [193] demonstrated that it is possible to heat up an autothermal methanol reformer equipped with a precious metal based catalyst from room temperature, when the O/C ratio of the feed exceeds 1.45. The S/C ratio was set to 1.0 for these investigations. The exothermic oxidation reactions clearly started even at ambient temperature and caused light-off of the reformer. 

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