BTX’s

That coal-derived liquids consist largely of aromatic and cyclic structures suggests that, with appropriate hydroprocessing, high yields of benzene, toluene, and xylenes (BTX s) should be obtained. If the by-products of that BTX production could be directed toward linear... 

Because the action of a presynaptic toxin, P-btx, is to start the initial burst of acetylcholine followed by the stop of acetylcholine release, it eventually causes paralysis of the muscle. The mechanism does not involve the hydrolysis of acetylcholine therefore, it is reasonable that anticholinesterase does not overcome p-btx s effect. 

Large-scale recovery of light oil was commercialized in England, Germany, and the United States toward the end of the nineteenth century (151). Industrial coal-tar production dates from the earliest operation of coal-gas faciUties. The principal bulk commodities derived from coal tar are wood-preserving oils, road tars, industrial pitches, and coke. Naphthalene is obtained from tar oils by crystallization, tar acids are derived by extraction of tar oils with caustic, and tar bases by extraction with sulfuric acid. Coal tars generally contain less than 1% benzene and toluene, and may contain up to 1% xylene. The total U.S. production of BTX from coke-oven operations is insignificant compared to petroleum product consumptions. 

A completely new approach for BTX production has emerged in recent years. It converts to paraffins into aromatics using a modified ZSM-5 zeoHte catalyst which contains gallium (19). An example of this approach, the Cyclar process, has been in commercial operation by British Petroleum at Grangemouth, Scotiand since August 1990 (20). It uses C —feed and employs UOP s CCR technology to compensate for rapid catalyst coking. 

Because of the importance of the petroleum-based processes discussed previously, only about 1% of the U.S. supply of BTX currentiy comes from coal pyrolysis (21). 

After the cmde BTX is formed, by reforming in this case, a heart cut is sent to extraction. Actually, the xylenes and heavier components are often sent to downstream processes without extraction. The toluene produced is converted to ben2ene, a more valuable petrochemical, by mnning it through a hydrodealkylation unit. This catalytic unit operates at 540—810°C with an excess of hydrogen. Another option is to disproportionate toluene or toluene plus aromatics to a mixture of ben2ene and xylenes using a process such as UOP s Tatoray or Mobil s Selective Toluene Disproportionation Process (STDP) (36). 

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

The petrochemical products from olefins plants are ethylene, propylene, C4 s (butanes, butylenes, and butadiene) and a stream containing the BTXs, Refinery cat.crackers produce propylene and C4S. They produce some ethylene, but often it is not recovered. 

Clonidine can be useful in treating the behavioral and attentional problems in Tourette s syndrome but is only 25% to 35% effective in controlling tics (Feck-man et ah, 1991). Two recent open trials found botu-linum toxin A (BTX) injections effective and well tolerated for treating tics in Tourette s syndrome (Awaad, 1999 Kwak et al., 2000). With no trials of any of these agents in subjects with MR, the clinician has no choice but to extrapolate from studies with typically developing children, while taking a very data-based approach to ensure that any treatments used are, in fact, effective. 

Lou and Lee (1995) oxidized BTX in a batch reactor using Fenton s reagent for simulating hydrocarbon-contaminated groundwater from a spill site. Changes in BTX concentration over time the effects of pFl, H202, and Fe2+ concentration on BTX destruction the optimum ratio of H202 BTX Fe2+ and the rate expression of BTX have been reported (Lon and Lee, 1995). Results were obtained in terms of destruction efficiency (DRE) of BTX, which is expressed as follows ... 

Unhydrogenated Coal-Derived Materials - Preliminary experiments on cracking the vapor from coal extract (B) at 1133°K for 0.7-8 s showed that the BTX yield peaked at 2 s whereas, ethylene was favored by shorter residence times. 

Figure 2 shows the effect of cracking temperature at 2 s vapor residence time on the yields of BTX, benzene, and ethylene from Linby coal (A), coal extract (B), and anthracene oil (C). 

Yields of BTX and benzene peaked at about 1273°K whereas, the maximum ethylene yields were obtained at about 1100°K. The mass balances and yields of the gaseous and liquid products at one condition, 1273°K for 2 s, are given in Table 2. 

Natural Gas Condensate - To compare the yields from coal-derived materials with those from a petroleum material, a full range, North Seal gas condensate (F) was cracked at 1158°K for 0.4 s. Its analysis is given in Table 1, and the yields obtained are listed in Table 2. More ethylene (30%) but less BTX (16%) were produced than from the highly hydrogenated coal materials ... 

Model Compounds - Four model compounds (mesitylene for aromatics, tetraline for hydroaromatics, decaline for naphthenes, and n-undecane for paraffins) were cracked singly and as mixtures at 1133°K for 1 s. The yields of BTX, ethylene, butadiene, and methane are shown as a bar chart in Figure 4. Decalin gave the highest BTX yield, 25%, compared with less than 7% from n-undecane. Mesitylene gave only 8% BTX. 

Figure 3. Effect of cracking temperature on yields from further hydrogenated extracts D1 (top) and El (bottom) (X) BTX, (A) ethylene, (O) benzene vapor residence time, 0.4 s nitrogen diluent...

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