Cracking autothermal

The transformation of straw and agrofood residues with high sulfur and ash content requires the development of materials for sulfur abatement at high temperature, tar cracking and as monolith for syngas production by exothermic or autothermal processes thanks to catalysts supported on materials with a high thermal conductivity. 

The reactor impregnated with nickel showed inferior performance again. Deactivation was observed, which was assumed to originate from coking, sintering, oxidation of the nickel or even losses of volatile nickel species. With increasing temperature, enhanced formation of by-products, namely methane and ethane, was observed in the reformate both under partial oxidation conditions and in the autothermal mode, which was attributed to thermal cracking. 

With the autothermal cracking process, heat for the thermal cracking is supplied by partial combustion of the feed. Water is used and carbon dioxide (CO2) may be recycled to attain a desired CO/H2 ratio. 

Carbon-based catalysts and in particular their kinetics have been intensively studied [41 3], because they should reduce the disadvantages related to metal-based catalysts. Carbon materials are more available, have the potential of cost reduction, do not require periodic regeneration because it is not necessary to separate the carbon-product from the catalyst. The fluidised bed reactor technology represents the optimal choice for this kind of hydrocarbon cracking process as it can withdraw the carbon particles evermore, permitting a reliable storage of produced carbon for further use [44 46]. A novel technological solution aimed to improve activity and stability of carbon catalysts has been recently proposed [47]. The presence of small amount of O2 in an autothermal approach seems to be the best solution to minimize CO2 emissions in the overall process. 

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. 

Finally, BASF have also developed a submerged flame autothermal cracking process for crude oil. Partial combustion raises the temperature locally, to the point at which cracking to both ethylene and acetylene occur. A typical off-gas composition comprises approximately Imol acetylene, M5mol ethylene, 7-5 mol carbon monoxide and 4 5 mol hydrogen, with minor amounts of C3 and higher products. 

The S/C ratio of the cracking reactors, which were regenerated by carbon gasification with steam, amounted to 3.0 [442]. Calculations revealed that the lowest efficiency was achieved with the autothermal reformer coupled to the adiabatic medium temperature water-gas shift reactor. The fuel cracker was best in terms of efficiency, water management, volume and weight, but lowest in terms of controllability, cost, emissions, dynamics and operability [442]. 

A catalytic cracking unit is operated in an autothermal way. The heat required to vaporize and crack the feed is provided by the heat content of the catalyst returning from the regenerator. The average residence time of the catalyst in the reactor has to be such that the coke content suffices to satisfy this condition. 

The Advanced Cracking Reactor (ACR) is an autothermal reactor where hydrocarbon feed and diluent are mixed with oxygen in order to partially oxidize the hydrocarbons and provide the heat for the pyrolysis reaction. High temperatures and very short contact times are achieved before a rapid direct quench by oil injection (Kearns et al., 1979). 

SBA-HT [Societe Beige de I Azote-Haldor Topsoe] A process for converting LPG to syngas rich in hydrogen. Two cracking processes are conducted in two zones of one reactor. In the first zone, the LPG is autothermally cracked with steam and oxygen. In the second, the products from the first are catalyticaUy cracked. It was... 

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