Carbon liquefaction

Because of their extensive use in industrial activities, phenolic compounds are abundant in many wastewaters. They are present in oil refining, petrochemical, plastic, pesticide, carbon liquefaction, and food processing industrial wastewaters. In addition, phenol-like structures are part of the macromolecular natural humic substances present in water humics are known precursors of trihalomethane compounds in drinking water chlorination [176,177], These compounds are refractory to conventional processes such as biological oxidation because of their toxicity for microorganisms [178]. 

Methods of Liquefaction and Solidification. Carbon dioxide may be Hquefted at any temperature between its triple poiat (216.6 K) and its critical poiat (304 K) by compressing it to the corresponding Hquefaction pressure, and removing the heat of condensation. There are two Hquefaction processes. In the first, the carbon dioxide is Hquefted near the critical temperature water is used for cooling. This process requires compression of the carbon dioxide gas to pressures of about 7600 kPa (75 atm). The gas from the final compression stage is cooled to about 305 K and then filtered to remove water and entrained lubricating oil. The filtered carbon dioxide gas is then Hquefted ia a water-cooled condenser. 

Temperature The level of the temperature measurement (4 K, 20 K, 77 K, or higher) is the first issue to be considered. The second issue is the range needed (e.g., a few degrees around 90 K or 1 to 400 K). If the temperature level is that of air separation or liquefact-ing of natural gas (LNG), then the favorite choice is the platinum resistance thermometer (PRT). Platinum, as with all pure metals, has an electrical resistance that goes to zero as the absolute temperature decreases to zero. Accordingly, the lower useful limit of platinum is about 20 K, or liquid hydrogen temperatures. Below 20 K, semiconductor thermometers (germanium-, carbon-, or silicon-based) are preferred. Semiconductors have just the opposite resistance-temperature dependence of metals—their resistance increases as the temperature is lowered, as fewer valence electrons can be promoted into the conduction band at lower temperatures. Thus, semiconductors are usually chosen for temperatures from about 1 to 20 K. 

Kohlensaure-messer, m. instrument or apparatus for measuring carbon dioxide, an-thracometer, carbonometer. -saJz, n, carbonate. -schnee, m. carbon dioxide snow, dry ice. -Strom, m. stream or current of carbon dioxide, -verflussigung, /. liquefaction of carbon dioxide, -verlust, m. loss (or escape) of carbon dioxide, -wasche,/, carbon dioxide washer, -wasser, n, carbonated water, soda water. 

During the liquefaction process, usually much of the oxygen, carbon dioxide, sulfur compounds and water are removed so that liquefied natural gas (LNG) IS nearly 100 percent methane. LNG takes up one-six-hundredth the volume of natural gas, with a density less than half that of water. 

Liquefaction of coal involves the extraction of carbon by solvents at high pressures and at temperatures up to about 500 C, followed by separation of the extract, which is then hydrogenated in the presence of a catalyst to yield hydrocarbon oils. The corrosion conditions are not regarded as severe. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

In most cases, the inert materials are merely held together by matrices of the internally generated solids. It is important to recognize that there are two very distinct types of material generated by coal liquefaction namely carbonaceous (coke-like) solids and carbonates. 

A recent study in these laboratories (75) on calcium carbonate precipitation from Wyodak coal has confirmed the relationship between ion-exchangeable calcium and the appearance of calcium carbonates during liquefaction. These experiments were performed on samples of the subbituminous coal which had been demineralized, to ensure that all carboxylic acid groups were in the acidic form, and subsequently exchanged with varying amounts of calcium ions. 

At the Coal Research Establishment of the National Coal Board, methods for the liquefaction of coals to produce transport fuels, feedstocks for the chemical industry and high purity carbons suitable for electrode manufacture are being developed. 

The results are shown in Fig. 2, where the QI yield was adopted as a measure of liquefaction extent. Because the solubility of decacyclene in quinoline was rather limitted, the QI contained a considerable amount of decacyclene. Liquefaction of this coal proceeded scarcely below 420°C of the softening temperature with this solvent as well as pyrene. Above this temperature, the QI yield decreased sharply with the increasing liquefaction temperature until the resolidification temperature of the coal. The maximum LY observed at this temperature was estimated 67%, decacyclene being assumed uncharged under the conditions. Above the resolidification temperature, the QI yield increased sharply. The carbonization may start. Decacyclene was known unreacted at 470°C in its single heat-treatment (10), and in its cocarbonization with some coals(11), although it is fusible. Cocarbonization of fusible... 

The fusible coals can give a high liquefaction yield if the high fluidity during the liquefaction is maintained by the liquefaction solvent to prevent the carbonization. The properties of the solvent required for the high yield with this kind of coal are miscibility, low viscosity, radical quenching reactivity and thermal stability not to be carbonized at the liquefaction temperature as reported in literatures (12). 

Transalkylation might be expected another kind of the solvolitic reaction. However, the present results suggest low probability with alkylated pyrenes as suggested by the NMR analyses. Instead, the increased polarity by alkyl group or the enhanced reactivity of the carbonization precursor from alkylpyrene, especially ethylpyrene, may be responsible for a considerable liquefaction yield. The recovery of the solvent becomes difficult by its latter conversion as observed in the present study. 

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