Hydrogenation, temperature gradients

Newer coal-based methods of acetylene manufacture under development include the AVCO process, based on the reaction of coal in a hydrogen plasma. Finely divided coal is passed through a hydrogen plasma arc generating temperature gradients of up to 15,000 K. About 67% of the coal is consumed, yielding char and acetylene in concentrations up to 16%. An energy requirement of 9.5 kW h/kg acetylene has been reported (33). 

The work of Thiele (1939) and Zeldovich (1939) called attention to the fact that reaction rates can be influenced by diffusion in the pores of particulate catalysts. For industrial, high-performance catalysts, where reaction rates are high, the pore diffusion limitation can reduce both productivity and selectivity. The latter problem emerges because 80% of the processes for the production of basic intermediates are oxidations and hydrogenations. In these processes the reactive intermediates are the valuable products, but because of their reactivity are subject to secondary degradations. In addition both oxidations and hydrogenation are exothermic processes and inside temperature gradients further complicate secondary processes inside the pores. 

EfiBdent hydrogen supply iiom decalin was only accomplished by the si terheated liquid-film-type catalysis under reactive distillation conditions at modaate heating tempaatures of 210-240°C. Caibcm-supported nano-size platinum-based catalysts in the si ietheated liquid-film states accelerated product desorption fixjm file catalyst surface due to its temperature gradient under boiling conditions, so that both hi reaction rates and conversions were obtained simultaneously. 

Temperature gradients and local temperature fluctuations usually parameterized by t2 (Peimbert 1967) lead to a systematic bias when the electron temperature determined conventionally from [O m] X 4363/a 5007 is substituted into the expressions for effective recombination coefficients of hydrogen and helium. 

Exarchou, V. et al., Do strong intramolecular hydrogen bonds persist in aqueous solution Variable temperature gradient IH, 1H-13C GE-HSQC and GE-HMBC NMR studies of flavonols and flavones in organic and aqueous mixtures. Tetrahedron, 58, 7423, 2002. 

A stoichiometric mixture of 3.478 g. (15 mmoles) of tungsten-(VI) oxide and 11.897 g. (30 mmoles) of tungsten(VI) chloride is placed in the reaction tube, and an excess of 1 mg. of tungsten(VI) chloride per milliliter of tube volume is added. The tube is sealed under vacuum and heated in a temperature gradient of 200/175°C. with the reaction mixture placed in the hotter part of the furnace (Fig. 14). After about 10 hours the reaction is complete, and 15 g. of tungsten(VI) tetrachloride oxide are obtained (98% yield). The analyses of the sublimed product by the H-tube method are somewhat inaccurate, because of the extreme moisture sensitivity of this substance (loss of hydrogen chloride by hydrolysis). Anal. Calcd. for W0C14 W, 53.82 Cl, 41.50 O, 4.68. Found W, 54.20 Q, 41.40 O, 4.46. 

Hanika et al. (62) and Germain et al. (63) observed multiple steady states in the trickle-bed reactors for the hydrogenation of cyklohexane and hydrogenation of a-methylstyrene, respectively. One possible explanation of this effect is an abrupt increase of the reaction rate arising from temperature gradients within the bed and in the gas film surrounding the... 

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