Catalytic wet air oxidation of pulp and paper mills effluent

Treatment of pulp and paper mills effluent using Wet Air Oxidation (WAO) and Catalytic Wet Air Oxidation (CWAO) was investigated. In particular, this thesis focused on: synthesis of innovative catalysts and studies on catalytic activity and stability at relatively mild temperatures. <br><br>Three different classes of catalysts were investigated: (1) homogeneous, (2) conventional alumina and kaolin supported single and mixed metal oxides and (3) advanced nano catalysts. WAO and CWAO studies were conducted using a model organic compound, ferulic acid, and actual pulp and paper mill effluent.<br><br>Chapter 1 reviews the literature relevant to this project, followed by the experimental details in chapter 2. <br><br>In chapter 3, nine homogeneous catalysts were tested for CWAO of ferulic acid. Based on the results of these catalysts, nine alumina and kaolin supported single metal and multi metal copper oxide based catalysts were prepared. Of the catalysts tested, Cu-Ni-Ce-Al2O3 was observed to be the most active with a reasonable stability. The Cu-Mn-Al2O3 catalyst was the most stable catalyst and second best in terms of activity. The catalytic mechanism studies confirmed that CWAO using these catalysts was mainly dominated by heterogeneous catalysis and not due to leached metal ions. Also an adsorption/ desorption/ oxidative mechanism was studied. Catalyst recycling studies (up to four cycles) were also performed. For catalysts stability, it was observed that solution pH had a significant effect. Also, catalyst composition and structure have shown substantial effects on catalyst stability. <br><br>In chapter 4, novel routes for synthesis of supported copper nano catalysts were investigated using galvanic replacement reactions. The prepared catalysts were characterised using TEM, SEM, Auger Imaging and XRD. It was confirmed that the deposited copper was in nano form and mostly as copper oxide. The synthesized catalysts were used for CWAO of ferulic acid and faster kinetic’s were observed compared to the conventional catalysts. A relationship between the structure of the nano catalysts and catalyst stability was also observed. Catalysts prepared over four hours, which had perforated ball like structure, had the highest amount of copper loading (as compared to catalysts prepared over ½ , 1, 2, and 8 hours) whilst also having the highest level of resistance to copper leaching. Catalyst re-cycling studies was also performed. <br><br>In chapter 5, selected catalysts from the previous chapters were used for CWAO of pulp and paper mill effluent. None of the catalysts showed any significant activity under the conditions used (190 °C, initial pH-13.1). Also, the CWAO tests conducted using a lower initial solution pH of 5.0 showed little improvements over the WAO test, whilst high leaching of the catalyst was also observed in the CWAO systems. Hence, it was concluded that the developed catalysts would not be suitable for CWAO of this particular wastewater.<br><br>In chapter 6, a conceptual process design for the treatment of pulp and paper mill effluent is proposed which consists of two major steps: pH pre-adjustment, followed by WAO at 190 °C. A Hazard and Operability study was performed for the proposed design.<br>