Carbon consumption

The total activated carbon consumption for Hquid-phase appHcations in the United States in 1987 was estimated to be about 76,700 t, which accounted for nearly 80% of the total activated carbon use. The consumption by appHcation is summarized in Table 5 (74). 

Table 5. Liquid-Phase Activated Carbon Consumption, 10 t...

Chemical Processing. Activated carbon consumption in a variety of chemical processing appHcations is about 8% of the total (74). The activated carbon removes impurities to achieve high quaHty. For example, organic contaminants are removed from solution in the production of alum, soda ash, and potassium hydroxide (82). Other apphcations include the manufacture of dyestuffs, glycols, amines, organic acids, urea, hydrochloric acid, and phosphoric acid (83). 

Pharmaceuticals. Pharmaceuticals account for 6% of the Hquid-phase activated carbon consumption (74). Many antibiotics, vitarnins, and steroids are isolated from fermentation broths by adsorption onto carbon foUowed by solvent extraction and distillation (82). Other uses in pharmaceutical production include process water purification and removal of impurities from intravenous solutions prior to packaging (83). 

Table 2. Liquid phase activated carbon consumption [11,16]. copyright 1992 John Willey Sons, Inc., with permission.

Table 3. Gas phase activated carbon consumption. Reprinted from [11], copyright 1992...

The main factors in the design of an adsorption system are the (1) Carbon consumption - The amount of earbon required to treat the liquid or gas, normally expressed per unit of the fluid treated and (2) Contact time - For a fixed flow rate, the contact time is directly proportional to the volume of carbon and is the main factor influencing the size of the adsorption system and capital cost. 

However, if the transition time of organic matter particles from one layer to another is short compared with Ds, then it is better to take H%iy = AjCa(, H e,i = A4C/,jI. In addition to these fluxes we should take into account the fluxes of detritus decomposition, solution of bottom sediments, and carbon consumption in the process of photosynthesis ... 

Carbon is used in lithium-ion cells for different functions conductive carbon black and/or graphite additives are applied in both the negative and the positive electrode to improve the electronic conductivity of the electrodes. These conductive additives constitute a fraction of up to about 10% of the total carbon consumption. The major fraction is represented by the active carbon materials which are electrochemically reduced and oxidized in the negative electrode during the battery charge and discharge process, respectively. 

For this reason the consumable anodes must be replaced periodically. The cathode consists of a molten aluminum layer on the bottom of the cell, and the anode-cathode distance is 4-5 cm. Alumina is periodically added to the cell in the proportion that it is consumed by electrolysis. The electrode processes during aluminum electrolysis are very complex [141] and a proper understanding of these processes is important because of the economic implications energy and carbon consumption, cell control, pollution of the environment, etc. 

Reaction (89) requires twice as much carbon as reaction (88) for the same quantity of electricity. One might then expect that the problem of the primary anode product could be easily solved by determining the gas composition and the carbon consumption. 

Data from industrial cells show that the exit gas contains 90-60% C02 and 10-40% CO. The carbon consumption usually ranges from 400 to 550 kg/ton Al, while the theoretical amount at 95% current efficiency is 350 kg/ton A1 for reaction (88) and 700 kg/ton Al for reaction (89). The question is then whether the extra consumption, compared to the theoretical value for reaction (88), is due to simultaneous primary formation of C02 and CO or if it is due to the Boudouard reaction between gaseous C02 and the sides and the interior parts of the anode [141], or carbon dust [200] dispersed in the electrolyte, or air burning of the anode. In any case, it is known [200,201] that in the laboratory a high content of CO is formed at low cds (<0.05 A cnr2) and almost pure C02 is formed at 1 A cm-2. 

It is the purpose of this paper to review the important factors which affect anode carbon usage in the aluminum industry, Consideration is given to the entire chain of events affecting carbon consumption, from the properties of the precursors for filler cokes and binder pitches, through production of these raw materials and their fabrication into anode carbon, and concluding with anode performance evaluation in full-size prebake and Soderberg cells of different designs. 

The third mechanism of carbon consumption is airburn of prebake anode tops and the bottom edges of Soderberg anodes during cell operation. This mechanism typically accounts for about 17% of total prebake carbon consumption, but can vary (for different cell designs) from less than 10% to about 40% during severe airburn problems. The following equation represents such airburn reactions ... 

In addition to oxidation losses-by the above four mechanisms, mechanical carbon loss (dusting) also occurs due to uneven oxidation of the anode surface. Furthermore, a variety of other factors, related to anode fabrication and use, can affect carbon consumption. The most important of these factors are (1) raw material quality,... 

Anode porosity is important because it affects the extent of oxidant-accessible surface. This surface is influenced both by coke microstructure and the fabrication process for converting the raw materials into baked carbon. The prime requirement for good anode carbon is minimum oxidant-accessible surface. It is also desirable that this surface have a low, uniform specific reactivity. Anode surface with pores having diameters in the 1-10 micron range are accessible to oxidation unless blocked in some manner. Submicron porosity, such as that produced by thermal desulfurization of coke, is oxidant diffusion-limited and will not affect carbon consumption significantly. Increasing anode carbon density will usually increase anode performance because the oxidant-accessible surface is reduced. 

In this case, anode carbon using such a filler-coke blend exhibited 15% higher carbon consumption than that carbon made with the anisotropic filler alone. 

The estimation of bacterial growth efficiency from the variation of bacterial biomass and organic carbon consumption could be underestimated due to continual recycling of organic matter by successive bacterial lysis and consumption of this lysed organic matter in our bioassays. In both Fe conditions, the increase of bacterial abundance is controlled by mortality processes. No protozoa were observed by microscopy. Mortality by protozoan grazing can thus be excluded. 

The treatment with a flow containing SO2+H2O+O2 gives an amount of 400 mg of sulphuric acid. Heating up this sample, sulphuric acid is removed from the surface by reduction that leads to carbon consumption. This mild gasification can produce either an opening of the microporosity to mesoporosity and/or the creation of new microporosity. This can be followed by the increase of pore volume calculated by Horvath-Kawazoe (HK, for micropores) and Barret-Joyner-Halenda (BJH, for mesopores) methods. 

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