Hydrodechlorination dichloroethane

WGSR conditions were found useful for hydrodechlorination of 1,2-dichloroethane [369], The primaiy product of the reaction is ethene (Scheme 3.62) which is reduced further to ethane in a separate catalytic cycle. 

The decomposition of dilute mixtures of NH3 in a PBMR using Pd-alloy membranes was studied by Collins and Way [2.322], and by Gobina et aL [2.323]. This application is of potential interest in the treatment of coal gasification streams, and the laboratory results showed promise. It would be interesting to see, whether the same membranes prove robust in the real coal-gas environment. The use of a PBMR to study the hydrodechlorination of dichloroethane was reported by Chang et al. [2.324]. The reported potential advantage of the membrane would be in preferentially removing the by-product HCl, which deactivates the catalyst. The authors attribute the observed improved performance, however, to a dilution effect. 

After drying and reduction, the Pd-Ag/C catalysts are composed of bimetallic Eilloy nanoparticles ( 3 nm). CO chemisorption coupled to TEM and XRD analysis showed that that, for catalysts 1.5% wt. in each metal, the bulk composition of the alloy is close to 50% in each metal, whereas the surface is 90% in Ag and 10% in Pd [9]. Mass transfer limitations can be detected by testing the same catalyst with various pellet sizes [18]. Indeed, if the reactants diffusion is slow due to small pore sizes, the longer the distance between the pellet surface and the metal particle, the larger the influence of the difiusion rate on the apparent reaction rate. Pd-Ag catalysts with various pellet sizes were thus tested in hydrodechlorination of 1,2-dichloroethane. Results were compared to those obtained with a Pd-Ag/activated charcoal catalyst. Fig. 4 shows the evolution of the effectiveness factor of the catalysts, i.e. the ratio between the apparent reaction rate and the intrinsic reaction rate, as a function of the pellet size. The intrinsic reaction rate was considered equal to the reaction rate obtained with the smallest pellet size. When rf = 1, no diffusional limitations occur, and the catalyst works in chemical regime. When j < 1, the observed reaction rate is lower than the intrinsic reaction rate due to a slow diffusion of the reactants and products and the catalyst works in diffusional regime [18]. 

A support with small mesopores ( 10 nm) leads to diffusional limitations, whatever the temperature chosen, as soon as the pellet size is larger than 250 pm. Indeed, 1,2-dichloroethane conversion, ethylene selectivity and reaction rate were found to decrease when the pellet size increases. Fig. 3 shows that the effectiveness factor decreases when the pellet size increases. The conversion and reaction rate are lower when the pellet size is larger due to diffusional limitations in the pore texture of the support. The selectivity decrease can be explained by the fact that the hydrodechlorination of 1,2-dichloroethane into ethylene may be followed by hydrogenation of ethylene into ethane [13]. This last reaction is favoured when diffusional limitations prevent ethylene from... 

Fig. 5(a) Reaction rate and selectivity for hydrodechlorination of 1,2-dichloroethane into ethylene at 350°C of all bead samples and reference sample and (b) photograph of CuBRAd beads. 

Pd-Ag bimetallic catalysts supported on carbon xerogels have been used in the hydrodechlorination reaction of 1,2-dichloroethane [103,104], Pd and Ag were deposited by co-impregnation using a solution of palladium and silver nitrates. Metal particle size ranged from 2 to 5 nm in Pd catalysts but had a wider distribution (4 to 20 mn) in Ag catalysts. Bimetallic Pd-Ag catalysts showed small particle alloys of 3 to 4 nm. The bulk Ag content in this alloy was limited to about 50 wt%, which fixed the minimum Pd surface content of the alloy at about 10 wt%. Pd catalysts produced mainly ethane, whereas bimetallic Pd-Ag catalysts were selective for the production of ethylene. The ethylene selectivity increased with silver fraction at the alloy surface. 

B. Heinrichs, P. Delhez, J.-P. Schoebrechts, and J.-P. Pirard, Palladium-Silver Sol-Gel Catalysts for Selective Hydrodechlorination of 1,2-Dichloroethane into Ethylene 1. Synthesis and Characterization, J. Catal., 172, pp. 322-35, 1997. 

S. Lambert, J.-F. Polard, J.-P Pirard, and B. Heinrichs, Improvement of Metal Dispersion in Pd/SiOj CogeUed Xerogel Catalysts for 1,2-Dichloroethane Hydrodechlorination, Appl. Catal. B, 50, pp. 127-40, 2004. 

Job J, Heinrichs B, Lambert S et al (2006) Carbon Xerogels as Catalyst Supports Study of Mass Transfer. American Institute of Chemical Engineers Fluid Mechanics and Transport Phenomena 52 2663-2676 Job N, Heinrichs B, Ferauche F et al (2005) Hydrodechlorination of 1,2-dichloroethane on Pd-Ag catalysts supported on tailored texture carbon xerogels. Catalysis Today 102 234—241... 

Harada M., Ono K., Tsuiki H., Ueno A., Mizushima T., Udagawa Y. Preparation offineFe-Ni alloy particles dispersed in silica. Chem. Lett. 1986 1569-1572 Heinrichs B., Delhez P., Schoebrechts J.P., Pirard J.P. Palladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene 1 synthesis and characterization. J. Catal. 1997 172 322-335... 

Heinrichs B., Schoebrechts J.P., Pirard J.P. Palladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene 3 kinetics and reaction mechanism. J. Catal. 2001 200 309-320... 

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