Carbon yield from

In the case of oak wood used to manufacture charcoal in Missouri kilns, pyrolysis at 1.0 MPa increases the fixed-carbon yield from <24 wt% in an externally heated retort (or the Missouri kiln) to 29.9 wt% in the pressure vessel. The time requirement is reduced from =10,000 min for the Missouri kiln to about 70 min in the pressure vessel. 

The carbon yield from pitches can be understood by studying the yields of the generic components of pitch using the method of corbett (1,2). The amounts of saturates, napthene-aromatics, polar aromatics asphalentenes can be determined for different pitches for various... 

Pitch as a precursor material is cheaper than PAN as a precursor fiber, but the conversion of pitch into mesophase pitch and subsequent fiber formation is complex and costly. When a pitch is not transformed into a mesophase and is spun as an isotropic liquid, the resulting carbon fibers have extremely poor mechanical properties. These considerations explain why more than 90% of today s carbon fibers are fabricated from PAN based precursors. Processes for fabricating carbon fibers from PAN or pitch based precursor fibers differ in important aspects, but also share important commonalties (Figure 2). Finally, the carbon yield from PAN based precursor fibers is 50%, that from mesophase pitch is 70-80%, and that from rayon is 25%. 

Figure 14.13 Effect of carbonization pressure on carbon yield from petroleum pitch. Source Reprinted with permission from Lachmann WL, Crawford SA, McAllister LE, Proc Int Conf on Composite Mats, Met Soc of AIME, New York, 1978. Copyright 1978, The Metallurgical Society of AMIE, now TMS (The Minerals, Metals and Materials Society).

The controlled decomposition of phenolic resins, in an inert atmosphere, is a method used to make carbon-carhon composites. In this case the resin is combined with other forms of carbon, such as carbon fibers, coke, and ssmthetic graphite, and cured imder heat and pressure. Further heating to about 900°C converts the resin to a glassy form of carbon that can serve as a binder for the other carbon forms. The carbon yield from the phenolic resins can be in the range of 60-70% of the initial weight (see under Carbon-Carbon Composites). 

Japan. Shindo recognized the importance of an oxidative heat treatment step prior to carbonization in reducing the processing time and improving the carbon yield from PAN. He demonstrated good tensile strengths and moduli over 20 million psl, about three times those available from rayon precursor carbon fibers of that time. Shlndo s work was quickly taken up... 

Figure 1.1 illustrates the diversity of products derived from petroleum classified according to their distillation ranges and number of carbon atoms. From one crude to another, the proportions of the recovered fractions vary widely. A good illustration is the gasoline fraction (one of the most economically attractive) a crude from Qatar gives about 37 per cent by volume whereas a Boscan crude oil only yields 4.5%. 

Di-n-amyl ether. Use 50 g. (61 5 ml.) of n-amyl alcohol (b.p. 136-137°) and 7 g. (4 ml.) of concentrated sulphuric acid. The calculated volume of water (5 ml.) is collected when the temperature inside the flask rises to 157° (after 90 minutes). Steam distil the reaction mixture, separate the upper layer of the distillate and dry it with anhydrous potassium carbonate. Distil from a 50 ml. Claisen flask and collect the fractions of boiling point (i) 145-175° (13 g.), (ii) 175-185° (8 g.) and (iii) 185-190° (largely 185-185-5°) (13 g.). Combine fractions (i) and (u), reflux for 1 hour in a small flask with 3 g. of sodium, and distil from the sodium amyloxide and excess of sodium this yields 9 5 g. of fairly pure n-amyl ether (iv). The total yield is therefore 22 - 5 g. A perfectly pure product, b.p. 184 185°, is obtained by further distillation from a Little sodium. 

Unsaturated nitriles are formed by the reaction of ethylene or propylene with Pd(CN)2[252]. The synthesis of unsaturated nitriles by a gas-phase reaction of alkenes. HCN, and oxygen was carried out by use of a Pd catalyst supported on active carbon. Acrylonitrile is formed from ethylene. Methacrylonitrile and crotononitrile are obtained from propylene[253]. Vinyl chloride is obtained in a high yield from ethylene and PdCl2 using highly polar solvents such as DMF. The reaction can be made catalytic by the use of chloranil[254]. 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

Alkali metal xanthates are prepared in high yield from reaction of amyl alcohols with alkah metal hydroxide and carbon disulfide (39—42). The xanthates are useful as collectors in the flotation of minerals and have minor uses in vulcani2ation of mbber and as herbicides (39,41). 

A high yield chemical pulp, eg, 52—53% bleached yield from softwoods, can be obtained, but strength properties ate inferior to those obtained from the kraft process. If a protector, eg, potassium iodide, is added, an additional 2—3% yield is obtained, as is an improvement in all strength properties. The gas penetration problem can be minimized if ftbetization is accompHshed before treatment with oxygen. Oxygen treatment of virtually all types of semichemical and mechanical pulps has been explored (55). Caustic, sodium bicarbonate, and sodium carbonate have been used as the source of base (56,57). In all cases, the replacement of the kraft by these other processes has not been justified over the alternative of pollution abatement procedures. 

Cychc carbonates result from polyols by transesterification using organic carbonates (115). Thus sorbitol and diphenylcarbonate in the presence of dibutyl tin oxide at 140—150°C form sorbitol tricarbonate in quantitative yield (116). 

In operations similar to the E. ashbjii procedures, the closely related fungus Jishbjagossjpii gave similar yields. Thus, a yield of 7.3 g/L was obtained with a lyoptulked culture in a medium containing fat, leather glue, and com extracts (50), and 6.420 g/L with bone or hide fat, alone or in a mixture with other plant or animal fats as the carbon source (51). The yield from immersed cultures ofM. gossjpii was increased to 6.93—7.20 g/L by use of waste fats or technical cod-Hver oil (52). 

Synthetic Resins. Various polymers and resins are utilized to produce some specialty carbon products such as glassy carbon or carbon foam and as treatments for carbon products. Typical resins include phenoHcs, furan-based polymers, and polyurethanes. These materials give good yields of carbon on pyrolysis and generally carbonize directly from the thermoset polymer state. Because they form Httle or no mesophase, the ultimate carbon end product is nongraphitizing. 

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