Thermal partial oxidation

The preceding discussion of thermal partial oxidation encompasses work in empty reactors and in fixed and fluid beds of inert materials, such as quartz or sand. A new type of reactor has been developed by Fenske and his associates (31), which they call a raining reactor. Inert solids are permitted to rain down through a reaction zone. Tests in the range 600°-1050°F were run that showed that solids rate was a critical variable, and the results of a major process variable study were presented. Residence times were varied from 0.02-0.5 minute, pressure from 1-8 atm, and propane to oxygen mole ratios from 2-20. 

In the following sections, the applications for synthesis gas will be summarized, the chemistry and thermodynamics related to the production of synthesis gas will be described and after which the various industrial processes for the manufacture of synthesis gas will be highlighted. The emphasis will be on catalytic routes, but thermal (partial oxidation) routes will be briefly described as well. Carbon capture and sequestration (CCS) is added, as this is an increasingly important issue for the use of synthesis gas as a source for hydrogen as an energy vector. 

Thermal partial oxidation with water injection HC... 

Thermal partial oxidation combined with steam reforming HC... 

Thermal partial oxidation (TPOX) requires high operating temperatures, between 1250-1500 °C and pressures of between 3-12 MPa, which means that a catalyst is not required. Due to the exothermic nature of the process additional heat is not required, as the heat produced is sufficient to maintain the operating conditions within the reactor. However, unlike SMR the process produces soot, which means that an additional cleaning process is necessary to remove solid particulates from the gas (Gupta, 2008 Holladay et al., 2009). 

At low temperatures, typical of barrier-discharge conditions, reaction of methoxy radical CH3O with methane, the main channel for the formation of methanol at higher temperatures, has a very low rate constant. Therefore, the mechanism of methanol formation under these conditions is likely to differ from the mechanism of its formation in the thermal partial oxidation of methane. This is evidenced by a significantly higher ( 15%) oxygen concentration at which the maximum selectivity to methanol is achieved (Figs 9.14 and 9.15). Therefore,... 

Two processes, partial oxidation and thermal decomposition, are used for the production of carbon blacks. The partial oxidation process can be represented by the foUowiag reaction ... 

Similar approaches are applicable in the chemical industry. For example, maleic anhydride is manufactured by partial oxidation of benzene in a fixed catalyst bed tubular reactor. There is a potential for extremely high temperatures due to thermal runaway if feed ratios are not maintained within safe limits. Catalyst geometry, heat capacity, and partial catalyst deactivation have been used to create a self-regulatory mechanism to prevent excessive temperature (Raghaven, 1992). 

In conventional cycles, combustion is the major source of irreversibility, leading to reduction in thermal efficiency. Some novel plants involve partial oxidation (PO) of the fuel in two or more stages, with the temperature increased before each stage of combustion, and the combustion irreversibility consequently reduced. In other plants full oxidation is employed which makes CO2 removal easier. 

Several of the gas turbine cycle options discussed m this section (intercooling, recuperation, and reheat) are illustrated in Figure 4. These cycle options can be applied singly or in various combinations with other cycles to improve thermal efficiency. Other possible cycle concepts that are discussed include thermochemical recuperation, partial oxidation, use of a humid air turbine, and use of fuel cells. 

As mentioned in Chapter 2, methane is a one-carhon paraffinic hydrocarbon that is not very reactive under normal conditions. Only a few chemicals can he produced directly from methane under relatively severe conditions. Chlorination of methane is only possible by thermal or photochemical initiation. Methane can be partially oxidized with a limited amount of oxygen or in presence of steam to a synthesis gas mixture. Many chemicals can be produced from methane via the more reactive synthesis gas mixture. Synthesis gas is the precursor for two major chemicals, ammonia and methanol. Both compounds are the hosts for many important petrochemical products. Figure 5-1 shows the important chemicals based on methane, synthesis gas, methanol, and ammonia. ... 

Techniques for the chemical recycling of plastics into monomers and petrochemical feedstocks are described, including chemical and thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification and partial oxidation. BRITISH PETROLEUM CO.PLC... 

This paper discusses in depth advanced technologies for recycled materials from solid waste streams. Chemical depolymerisation, thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification, partial oxidation, and feedstock compatibility are all explained. The economic feasibility of the methods are considered. 

The present work demonstrates that the mixed oxide catalyst with inhomogeneous nanocrystalline MosOu-type oxide with minor amount of M0O3- and Mo02-type material. Thermal treatment of the catalyst shows a better performance in the formation of the crystals and the catalytic activity. The structural analysis suggests that the catalytic performance of the MoVW- mixed oxide catalyst in the partial oxidation of methanol is related to the formation of the M05O14 t3 e mixed oxide. 

Two different methods were used to produce Iron oxide (Fe203) particles on Grafoll. One method was a simple Impregnation-calcination based on the method of Bartholomew and Boudart (20). The exact method used 1s described elsewhere (27). The second method used was a two step process. First, metallic iron particles were produced on the Grafoll surface via the thermal decomposition of Iron pentacarbonyl. This process Is also described in detail elsewhere (25). Next, the particles were exposed to air at room atmosphere and thus partially oxidized to 2 3 Following the production of Iron oxide particles (by... 

SMR—steam methane reformer ATR—auto thermal reformer POX—partial oxidation PSA—pressure swing adsorption... 

Gasification coupled with water-gas shift is the most widely practiced process route for biomass to hydrogen. Thermal, steam, and partial oxidation gasification technologies are under development. Feedstocks include both dedicated crops and agricultural and forest product residues of hardwood, softwood, and herbaceous species. 

In summary, major challenges in the partial oxidation of methane are (1) designs to avoid excessive thermal gradients (hot spots) in the catalyst bed (2) reduction of the cost of O2 separation and (3) elucidation of the reaction pathways as a step toward improved catalyst design. 

Recently, such a temperature oscillation was also observed by Zhang et al (27,28) with nickel foils. Furthermore, Basile et al (29) used IR thermography to monitor the surface temperature of the nickel foil during the methane partial oxidation reaction by following its changes with the residence time and reactant concentration. Their results demonstrate that the surface temperature profile was strongly dependent on the catalyst composition and the tendency of nickel to be oxidized. Simulations of the kinetics (30) indicated that the effective thermal conductivity of the catalyst bed influences the hot-spot temperature. 

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

The resulting radicals are not usually observed, but thermal desorption products indicate the nature of the surface intermediates. Molybdenum(V) dispersed on silica also gives rise to 0 and O2 ions when exposed to N2O and O29 respectively. The 0 ion on this surface may be used to activate methane and ethane in a catalytic cycle which leads to their partial oxidation. 

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