Absorption of four valent nitrogen oxides into aqueous sodium hydroxide solutions in a packed tower

Author

Douglas Bruce Crawford

Date of Award

12-1990

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

R. M. Counce

Committee Members

Wayne T. Davis, George C. Frazier, Joseph J. Perona, Jack S. Watson

Abstract

The scrubbing of low partial pressures of nitrogen dioxide - nitrogen tetroxide mixtures is important to several industries. In this study a gas stream with N(IV) (NO₂ + 2 N₂O₄) partial pressures of 3 x 10^-4 atm to 5 X 10^-3 atm in air at atmospheric pressure is contacted with water and 0.3, 0.6, and 1.0 N NaOH aqueous solutions in a tower packed with high efficiency structured packing. Experimental temperatures are 23°C to 27°C. N(IV) scrubbing efficiencies range from 24% to 62%. The hydroxide concentration only slightly affects the scrubbing efficiencies. An analysis of literature data and the experimental results is used to produce an enhancement factor modifier for the concentration dependent effect of sodium hydroxide on the interfacial flux of N(IV). A review of the literature indicates that NO₂ and N₂O₄ are in equilibrium in the gas and liquid phases, that a film theory, fast reaction-regime model, referred to as a combined flux model, is available but untested for the interfacial combined flux of NO₂ and N₂O₄ and that a technique is available for comparing most previous experimental results in order to choose appropriate solubilities and rate constants for the reactive dissolution of N(IV). A hydrolysis reaction mechanism is proposed. The mechanism is consistent with the available literature. A reaction number, the square of the Hatta number, is derived for the combined flux model and tested against a general combined flux model which does not include the fast reaction regime assumption. The N(IV) reaction number is consistent with previously derived reaction numbers for first and second order reactions. The scrubbing experiments are conducted in the fast reaction regime. Based on the comparison of literature values and the results of the scrubbing experiments, a pseudo-second order rate constant for the hydrolysis of NO₂, 4.5 X 10⁷ m³/kgmol-s, a Henry's Law constant for N₂O₄, 0.93 kgmol/m³-atm, and a Henry's Law constant for NO₂, 0.0099 kgmol/m³-atm are recommended for use with the combined flux model to predict the performance of caustic N(IV) scrubbers at low N(IV) partial pressures near 25°C.

Recommended Citation

Crawford, Douglas Bruce, "Absorption of four valent nitrogen oxides into aqueous sodium hydroxide solutions in a packed tower. " PhD diss., University of Tennessee, 1990.
https://trace.tennessee.edu/utk_graddiss/11286