Browsing by Author "Mubofu, Egid Biatus"

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    Preparation of palladium carbon catalysts for hydrogenation of cardinal
    (University of Dar es Salaam, 1997) Mubofu, Egid Biatus
    Platinum group metals present good behavior as hydrogenation catalysts when supported on a highly porous material such as activated carbon sepiolite etc. in this study, a series of hydrogenation palladium catalysts supported on activated carbons from coconut shells (CONS) and bituminous coal (BCO) have impregnation from solutions of palladium chloride. Catalysts with palladium content between 0.02 to 1.08%wt were obtained after an over night oven drying at between 390-393K. The activated carboas were prepared by carbonization and activation at 1200K in CO2 gas to give products with percentage carbon burn-off (%CBO) ranging from 7 to 79. The adsorption capacity of palladium on the CONS and BCO based activated carbons showed dependence on the type of source material and the level of carbon burn-off of the carbons. The equilibrium adsorption data were correlated well by Langmuir and Freundlich isotherm equations. The Langmuir based adsorption capacities ranged from 22.16 to 86.55 mg paralladium per g carbon. The adsorption kinetics of palladium for both CONS and BCO supports had similar patterns in that the rates were very fast in the first hour and then decreased slowly as the adsorption approached equilibrium. The data were best described by Larders et al. model over the entire time span of the experiment but only in the first hour by the first order kinetic model. The evaluated “first order kinetic model” reaction rate constants ranged from 1.26 to 1.61x10-2 min -1. Generally, the rate constants for BCO based activated carbon increased with increase in percentage carbon burn-off (%CBO). The BET surface areas of the carbons/ catalysts were texturally characterized by a static volumetric technique, and the surface areas ranged from207 to 867 m2 g-1. The CONS based carbon had larger surface area due to microporosity than BCO based carbons which possess in addition to microspores some wider pores. Evaluation of the ash content of the carbons showed percentage ash values ranging from 0.61 to 30.20. The BCO based carbons had larger values of ash content that ranged from 11 to 30.20% and increased with the increase in the %CBO for CONS based carbons the ash constant ranged from 0.61 to 4.5%. Generally BCO had larger ash content than CONS based carbons of comparable %CBO. The cardinal for hydrogenations was obtained by double vacuum distillation of cashew nut shell liquid and fractions of cardinal distilled at between 501 to 508 K. when the low loaded palladium catalysts (0.02-1.08Pd/C) were checked for their activity towards hydrogenations of cardinot and cinnamic acid at room temperature and atmospheric pressure there was no detectable activity. The inactivity may have been caused by the inaccessibility of the microspores to the substrates. on the other hand 5%Pd/C catalyst focus Koch light laboratories showed activity towards hydrogenation under the same experimental condition.