Catalytic wet air oxidation of spent kraft pulping liquors

Kraft recovery boiler capacity limitations can be alleviated by using wet air oxidation (WAO) to treat excess kraft black liquor. The WAO process can be described as the liquid phase oxidation of organic and oxidizable inorganic components at elevated temperatures (125°C to 320°C) and pressures (0.5 MPa to 20.0 MPa) using a gaseous source of oxygen.; In an attempt to improve the degree of oxidation of kraft black liquor, the use of different heterogeneous metal oxide catalysts was investigated. Experiments were carried out in a stainless steel batch reactor using pure oxygen. Screening experiments showed that cupric oxide (CuO) considerably improved the overall degree of oxidation. When using this catalyst a 71.6% reduction in the chemical oxygen demand occurred compared to a 45.9% reduction when no catalyst was used. Further experiments were performed to study the effect of oxygen charging pressure, temperature, and reaction time.