Carbon Dioxide Acceptor Process

Spent acceptor leaving the gasifier is calcined in a regenerator vessel at approximately 1010°C (1850 ], at which temperature the carbon dioxide acceptor reaction is reversed the calcined acceptor is then returned to the gasifier. 

Both the product gas from the gasifier and the flue gas from the regenerator are quenched and purified. The flue gas is either recycled to the regenerator or flared whereas the product gas is sent to the methanation section. 

The methanation facilities, which convert the low-heat-content synthesis gas into a high-heat-content product, include a shift converter, carbon dioxide absorber, hydrodesulfurizer, zinc oxide sulfur guard, and a packed-tube methanator. 

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In the carbon dioxide acceptor process (Curran et al., 1969 Nowacki, 1980) (Figure 21.14), coal is first crushed to 8 x 100 mesh in hot-gas-swept impact mills in which the moisture content is reduced from ca. 38% w/w to ca. 16% w/w. The coal is further dried to 0.5% w/w moisture in... 

Photogenerated cofactors can be employed to drive biocatalytic enzyme cascades including the photosynthetic carbon dioxide fixation process [184] (Figure 35). Photogenerated NADPH provides a two-electron relay for the insertion of CO2 into a-ketoglutaric acid (23) and pyruvic acid (21) in the presence of isocitrate dehydrogenase (IcitDH) and malic enzyme (MalE), respectively. In these photosystems, Ru(bpy)3 " acts as a photosensitizer, as a primary electron acceptor... 

This reaction is the basis of Consolidation Coal Co/s carbon dioxide acceptor gasification process (13,17,18), which eliminates need for oxygen to provide heat to the steam-carbon reaction. The process could be modified for recovering elemental sulfur by incorporating a step using Reaction 1. 

It was proposed 8) that there was a cyclic process involved in regenerating the carbon dioxide acceptor according to the following scheme ... 

The second type of biological process is a direct treatment process, in which bacteria oxidize the sulfur species. This oxidative desulfurization reaction is carried out in the presence of an electron acceptor (such as nitrate, NOs ), a source of carbon (such as carbon dioxide or I ICO, ), and a source of reduced nitrogen (such as ammonia). The... 

C02 Acceptor A fluidized bed coal gasification process in which the heat is provided by the exothermic reaction of carbon dioxide with calcium oxide. Developed by the Conoco Coal Development Company in the 1970s. 

Concerning the reduction step of the redox reaction, the heterotrophic microorganisms may use different electron acceptors. If oxygen is available, it is the terminal electron acceptor, and the process proceeds under aerobic conditions. In the absence of oxygen, and if nitrates are available, nitrate becomes the electron acceptor. The redox process then takes place under anoxic conditions. If neither oxygen nor nitrates are available, strictly anaerobic conditions occur, and sulfates or carbon dioxide (methane formation) are potential electron acceptors. Table 1.1 gives an overview of these process conditions related to sewer systems. 

The radical-anions from from alkenes with electron withdrawing substituents will add to carbon dioxide [28]. This process involves the alkene radical-anion, which transfers an electron to carbon dioxide for which E° = -2.21 V vs. see [29]. Further reaction then occurs by combination of carbon dioxide and alkene radcal-anions [30]. The carbanion centre formed in this union may either be protonated or react with another molecule of carbon dioxide. If there is a suitable Michael acceptor group present, this carbanion undergoes an intramolecular addition reaction... 

The good electron acceptor property of carbon dioxide can be used for the hydrodimerization to oxalic acid 4. Electrolysis is performed in an undivided cell using zinc as sacrificial electrode material. The reported electrolysis data are 6 mA/cm2 with 12 mM NBu4+BF4 in DMF. The current efficiency for the formation of oxalic acid is stated to be 60%. Unfortunately, no further details are currently available about this particular process (Lehmann and Dunach, 2009, personal communication). 

BIOPLUME III is a public domain transport code that is based on the MOC (and, therefore, is 2-D). The code was developed to simulate the natural attenuation of a hydrocarbon contaminant under both aerobic and anaerobic conditions. Hydrocarbon degradation is assumed due to biologically mediated redox reactions, with the hydrocarbon as the electron donor, and oxygen, nitrate, ferric iron, sulfate, and carbon dioxide, sequentially, as the electron acceptors. Biodegradation kinetics can be modeled as either a first-order, instantaneous, or Monod process. Like the MOC upon which it is based, BIOPLUME III also models advection, dispersion, and linear equilibrium sorption [67]. 

Several heterofermentative LAB belonging to the genera Lactobacillus, Leu-conostoc, and Oenococcus can produce mannitol from fructose effectively (Saha, 2003). In addition to mannitol, these bacteria may produce lactic acid, acetic acid, carbon dioxide, and ethanol. The process is based on the ability of the LAB to use fructose as an electron acceptor and reduce it to mannitol with the participation of the enzyme mannitol 2-dehydrogenase (EC 1.1.1.38). 

In the absence of dioxygen, organic materials can be mineralized to carbon dioxide, although this is a less efficient process than that of aerobic respiration. Anaerobic biodegradation requires alternative electron acceptors, the use of which depends on their availability. The degree of easiness for biodegradation follows a sequence in order of decreasing affinity for electrons (i.e., nitrate > iron > sulfate > carbonate). 

Formic acid also reduces stable iminium functionalities (but not in general carbonyl groups). Acridi-nium ions are also readily reduced. This process bears some outward resemblance to the enzymatic transformation of formate to carbon dioxide by formate dehydrogenase, although a molybdenum/sulfur cluster is probably the hydride acceptor in the enzyme. ... 

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