Carbonization Stage

The raw coal (10% or lower surface water content, 5-50 mm particle size) is preliminarily dried in a rotary dryer. The gas exhausted from the dryer passes through a multi-cyclone to remove the dust before venting the gas to the atmosphere. The most efficient process for carbonizing semicoke and one that retains approximately 20% of the volatile matter in the semicoke is the internal-heating, low-temperature fluidized-bed carbonization furnace (Chapter 16). 

The preliminarily dried raw coal is charged to the middle section of furnace, and is subjected to fluidization carbonization. The semicoke is discharged from the top of the furnace together with the carbonization gas. The semicoke separated from carbonization gas by the primary cyclone and the secondary cyclone. 

After cooled, the sanicoke is transferred to a stockyard, and the carbonization gas is supplied to the refractory-Uned combustion furnace, where the carbonization gas is mixed with air to combust. The generated hot gas is injected into the raw coal dryer and to the succeeding briquette dryer to use as the drying heat source for the preliminary heating the raw coal and the drying heat source of the formed oval briquettes. 

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If we mix f-BuOH and HBr in an NMR tube and let the reaction run inside the NMR machine, we see no signals belonging to the cation. This proves nothing. We would not expect a reactive intermediate to be present in any significant concentration. There is a simple reason for this. If the cation is unstable, it will react very quickly with any nucleophile around and there will never be any appreciable amount of cation in solution. Its rate of formation will be less, much less, than its rate of reaction. We need only annotate the mechanism you have already seen, the SnI mechanism for nucleophilic substitution at saturated carbon stage 1 formation of the carbocation... 

Isoniazid interferes with mycolic acid synthesis by inhibiting an enoyl reductase (InhA) which forms part of the fatty acid synthase system in mycobacteria. Mycolic acids are produced by a diversion of the normal fatty acid synthetic pathway in which short-chain (16 carbon) and long-chain (24 carbon) fatty acids are produced by addition of 7 or 11 malonate extension units from malonyl coenzyme A to acetyl coenzyme A. InhA inserts a double bond into the extending fatty acid chain at the 24 carbon stage. The long-chain fatty acids are further extended and condensed to produce the 60-90 carbon (3-hydroxymycolic acids which are important components of the mycobacterial cell wall. Isoniazid is converted inside the mycobacteria to a free radical species by a catalase peroxidase enzyme, KatG. The active free radicals then attack and inhibit the enoyl reductase, InhA, by covalent attachment to the active site. 

The proper sequence will be governed by characteristics of the system as viewed both in its entirety and on the function of each individual stage. The proper sequence may be quite apparent, as for example in an application in which peroxide was added to the process liquor to make the impurity more adsorbable. Here it is obvious that the addition of peroxide should precede the carbon stage, but many situations are less clearly defined and can be resolved only by cut-and-try. 

At one time the process of oxidation seemed to be nothing but a preferential oxidation of hydrocarbons that had been deposited on the surface during the carbonization stage. According to this theory, the removal of the hydrocarbons was supposed to leave the carbon surface free to attract and adsorb other substances. There can be little doubt that some such process does play a part, perhaps an important part, and explains much of the general improvement in adsorptive power however, it does not explain differences in specific adsorptive powers. Why, for example, does oxidation with steam at 800° C provide specific adsorptive powers unlike those produced by activation with air at 400° C Or, to use another illustration, why should the type of adsorptive power produced by activation with steam at 800° C depend upon the previous treatment of the carbon, e.g., on whether the carbonization was conducted in the presence or absence of certain salts 71... 

EXAMPLE 11.16 Is the overall flux of carbon atoms through glycolysis markedly influenced by the three-carbon stages of the pathway ... 

A soft template route involves an organic compound, such as polymers or surfactants, which is used as a direct mold in order to obtain a structured carbon precursor. Then, the soft template is eliminated during the carbonization stage. Nowadays, there are a large number of preparation methods reporting materials with a wide variety of structures and pore size distributions. In general, these methods are more versatile and cheaper than nanocasting ones. Moreover, the... 

Fig. 6.5 Pore size distributions of fresh and cycled (87 cycles) materials (solid line) calcined stage (square) carbonated stage and (dashed line) model predictions for the carbonated material. Adapted with the permission from Ref. [16]. Copyright 2005, American Chemical Society...

Aromatic hydrocarbons occur as by-products only in fixed-bed processes, since the coal does not undergo a carbonization stage in fluidized or entrained bed gasification processes. As a result of the high reaction temperatures, all volatile hydrocarbons are rapidly converted to gas. 

After the oxidation stage, there no tension was needed in any subsequent carbonization stages. 

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