Indirect partial oxidation

The two mechanisms proposed to account for the partial oxidation of methane to syngas may be dedgnated as the IPO (Indirect Partial Oxidation) mechanism and the DPO (Direct Partial Oxidation) mechanism. The IPO mechanism was proposed by Prette et al [16] and Lunsford et al [12]. They think CO and H2 are the products of indirect reaction, the overall reaction of the POM reaction is composed of three different reactions... 

Jaglayan, B.S., iLSEN Onsan, Z., and Erhan Aksoylu, A. Production of hydrogen over bimetallic Pt—Ni/S-Al203 II. Indirect partial oxidation of LPG. Catalysis Letters, 2005,102 (1), 63. 

Caglayan BS, Onsan ZI, Aksoylu AE (2005) Production of hydrogen over bimetallic Pt-Ni/i5-Al2O3 II. Indirect partial oxidation of EPG. Catal Eett 102(l-2) 63-67 Otsuka K, Sunada YWE, Yamanaka I (1998) Direct partial oxidation of methane to synthesis gas by cerium oxide. J Catal 175 152-160... 

Indirect partial oxidation of methane in a catalytic tubular reactor... 

Combination of SR and TOX is known as indirect partial oxidation (IPOX). Due to the fast nature of TOX, it occurs earlier than SR and elevates the reactor temperature via exothermic heat release. In IPOX, oxygen is always used as the limiting reactant, and once it is completely consumed, the remaining methane is converted to hydrogen via Reaction 11.32. While SR and TOX are the main reactions, product distribution is strongly affected by the water-gas shift (WGS) ... 

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

A simplified scheme of the dual pathway electrochemical methanol oxidation on Pt resulting from recent advances in the understanding of the reaction mechanism [Cao et al., 2005 Housmans et al, 2006] is shown in Fig. 15.10. The term dual pathway encompasses two reaction routes one ( indirect ) occurring via the intermediate formation of COads. and the other ( direct ) proceeding through partial oxidation products such as formaldehyde. 

Recently, Germain et al. have also shown that the indirect anodic oxidation in fluorosulfuric add of fluorocarbon derivatives of the type RfCF2X (X — H, COOH, S03H, CH2OH, Br), which are not directly oxidizable, leads to fluorosulfates of the type FSG3CF3Rf (Eqs. 18 and 19) [37, 38], in these reactions, the peroxide (FS03)2, partially dissociated in its free radicals, is the in-situ electrochemically produced reactive intermediate as shown in Scheme 5.1. 

Much recent research (7-5) has been devoted to converting methane to products that are more easily transported and more valuable. Such more valuable products include higher hydrocarbons and the partial oxidation products of methane which are formed by either direct routes such as oxidative coupling reactions or indirect methods via synthesis gas as an intermediate. The topic of syngas formation by oxidation of CH4 has been considered primarily from an engineering perspective (7-5). Most fundamental studies of the direct oxidation of CH4 have dealt with the CH4 + O2 reaction system in excess O2 and at lower temperatures (6-10). 

The main aspects of the reactor design are temperature homogeneity and homogeneous gas flow for all 96 reactor positions. In Figs. 2.8 and 2.9, homogeneities of temperature and gas distribution are indirectly verified by an IR-thermo-gram and a product distribution of a partial oxidation reaction, measured over all 96 catalyst samples. 

Indirect processes for converting natural gas to alcohols and higher hydrocarbons require the initial conversion of methane to synthesis gas (CO/H2). This is a difficult and expensive step normally carried out by steam reforming and partial oxidation (6). Subsequent synthesis gas conversion steps, such as FT synthesis and related processes (1,2), must occur with high selectivity to desired products in order to minimize extensive recycle of undesired products to the initial synthesis gas generation step. C5+ paraffins, low- and intermediate-molecular-weight olefins, and C20+ linear hydrocarbons provide useful feeds in downstream processes leading to fuels and petrochemicals. 

The partial oxidation of methane has also been studied between 550 and 750°C over Ru/Ti02 (762). The importance of the indirect route has been shown at 550°C by an appropriate steady-state tracing experiment. 

Anodic oxidation of glucose gives mainly the glucono-(5-lactone (XCI) or gluconic acid (XCII) [Eq. (55)] [133-135]. Formation of aldonic acids from aldoses is the most commonly observed process in other cases [126]. Additional work has been done in the area of indirect anodic oxidation of partially protected carbohydrates at a nickel hydroxide anode [136]. 

At relatively low temperatures (< 800 °C), over most catalysts investigated, the catalytic partial oxidation of methane to synthesis gas is thought to follow the so-called indirect scheme, according to which initially methane is combusted until all... 

An indirectly heated rotary drum was developed by the firm Kiener in Goldshofe. The process was evaluated by Prof. Tabasaran of the T.U. of Stuttgart. The tar laden pyrolysis gas is partially oxidized and cracked on a bed of glowing coke, the temperature of which is controlled by suitable addition of combustion air. [16,11,18,12]. 

A significant component of acute inflammation is OS (Nonas et al., 2006). One aspect of OS is the production of oxidants and proinflammatory cytokines. It is defined as an imbalance of antioxidant/oxidant ratio, which has a consequent effect on gene expression. The maintenance of the antioxidant/oxidant ratio in the nonstressed cell would be termed redox homeostasis. Thiol groups that are part of intracellular proteins and glutathione (GSH) are critical for the maintenance of redox homeostasis. The vesicants as a class are either oxidants themselves, or they indirectly produce oxidants. Oxidants can be water soluble and fat soluble therefore, they can arise in any compartment of the cell. They are able to attack any cellular structure, rendering them partially or completely dysfunctional. 

Of the different reactions which employ methane as a reactant, those that lead to formation of syngas by steam or dry reforming and partial oxidation should be mentioned, and these can be considered as indirect methods for... 

Table 1 provides a synopsis of the Phase I pilot-scale testing carried out. Several runs with composted municipal solid waste (MSW) were carried out with a pipe reactor in the absence of oxidant, i.e., they were indirectly heated and did not utilize partial oxidation. The pipe reactor had an ID of 0.815 inches and a length of about 90 feet. 

---