Nitration grade xylene

Due to a relatively high content of the m- isomer xylene derived from coal or xylene from Borneo oil is the most convenient starting material for the preparation of nitration grade xylene. 

Recent German specifications for nitration grade xylene require determination of the freezing point of m- xylene, which should not be lower than -52°C. 100% of the xylene should distil within 1-2°C. 

ASTM D 843-97. Standard specification for nitration grade xylene. 

Group 1 Benzene, all ASTM grades Toluene, all ASTM grades Xylene, nitration grade Xylene, 5° Xylene, 10° Any other more highly refined products 96 15... 

Nitration grade xylene conforming to Specification D843. 

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

Mixed xylenes are commercially available in nitration grades that have tolerances of 3 and 10°F, depending on the specified amount of the hydrocarbon present. Purities of the ortho-, meta-, and para-xylenes are more often than not a matter of negotiation between buyer and seller. 

The historical development of aromatics production from petroleum is outlined, and the methods employed during World War II for the production of nitration grade toluene are described. Included is a discussion of methods of synthesizing and purifying benzene, xylenes, and aromatics of higher molecular weight both as mixtures and as pure compounds. Data are presented on the composition of the aromatic hydrocarbons available from typical hydroformates. Aromatics and mixtures thereof currently available from petroleum are listed. Some of the problems facing the industry in the field of aromatics production are discussed and the probable trend of future research is indicated. 

Information regarding the physical and chemical properties of benzene is shown in Table 3-2. The major impurities found in commercial products are toluene, xylene, phenol, thiophene, carbon disulfide, acetylnitrile and pyridine (NIOSH 1974). Commercial refined benzene-535 is free of hydrogen sulfide and sulfur dioxide, but contains a maximum of 1 ppm thiophene and a maximum of 0.15% nonaromatics. Refined nitration-grade benzene is free of hydrogen sulfide and sulfur dioxide. Benzene is also commercially available as thiophene-free, 99 mole%, 99.94 mole% and nanograde quality (HSDB 1996). 

Materials. Because of the large quantities required, the reagents had to be purchctsed in commercial quantities. The best commercicilly available grades were employed. The toluene was industrial nitration grade. GLC emalysis showed it to contain 0.21 wt.% paraffins but no detectable benzene or xylenes. The acids analysed as follows ... 

Xylene (Warning—See Note 6) nitration grade, conforming to the requirements of Specification D 843. 

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