The kinetics of nickel oxide reduction by hydrogen; measurements in a fluidized bed and in a gravimetric apparatus

Abstract

The suitability of a batch fluidized bed laboratory reactor for measuring the rates of gas-solid reactions was investigated. Experiments were carried out on the reduction of Falconbridge nickel oxide by hydrogen in a batch fluidized bed reactor within the tem-perature range 550 K to 650 K using particles in the range of 60 to 100 mesh. The reactor was operated at approximately atmospheric pressure and gas flow rates were in the range of two to four times the minimum fluidization velocity at temperature. The results showed internal consistency and rough agreement with the results of previous workers. The re-sults were interpreted and correlated by means of a structural model for gas-solid reac-tions. As a check on the fluidized bed measurements, experiments were also carried out using the conventional gravimetric technique to measure the rate of reduction of compac-ted pellets of nickel oxide by hydrogen. When due allowance was made for the change of surface area of the oxide during compaction, the results were in close agreement with the fluidized bed results. Rate measurements using hydrogen-nitrogen mixtures revealed that the reaction is not first order with respect to hydrogen, as usually assumed, but is ap-proximately of order two-thirds at one atmosphere hydrogen partial pressure.