Higee Process Intensification And Application In Treatment Of O-Phenylenediamine By Ozone-Based Oxidation Processes

Higee, which is an abbreviation for high-gravity, is an innovative process intensification technology that was originally introduced in 1971 for separation processes. The technology is achieved by use of multiphase reactors ?Higee devices? capable of generating a high gravity condition of several orders of magnitude greater than the Earth's gravitational field. As a result, fluid and aqueous reactants flowing through such reactors is broken and split into fine liquid elements and very thin film layers. Also, for gas-liquid reactions, there is increased turbulence in the gas and liquid streams as well as fast renewal of gas-liquid interface. All of these can significantly enhance mixing and mass transfer performances.The treatment of organic effluents is a major challenge to many chemical industries especially those dealing in dyes, pharmaceuticals, paint, fertilizers, etc since they generate large volumes of effluents heavily laden with complex organics that are not only resistant to bio-degradation but also highly toxic and therefore pose a serious threat to the environment.This study focused on the application of Higee process intensification technology to treat o-phenylenediamine ?o-PDA?, an aromatic amine which is a major constituent of effluents originating from such chemical industries. The study supposes that chemical oxidation by ozone ?03 process? is a feasible approach to treat effluents containing o-PDA. Since ozone oxidation process in an aqueous solution is limited by ozone-liquid mass transfer rate as a result of rapid consumption of ozone, Higee technology achieved through a novel rotor stator-reactor ?RSR? was employed in an attempt to enhance ozone-liquid mass transfer rate and consequently improve degradation efficiency of o-PDA ?77?. Also, owing to the selective nature of ozone in reaction in addition to its low solubility in water,other ozone-based oxidation processes including simultaneous use of ozone and hydrogen peroxide ?O₃/H₂O₂ process?, ozonation in the presence of ferrous ion(O₃/Fe²⁺ process) and catalytic ozonation with persulfate ion activated by ferrous ion (O₃/Fe²⁺/PS process) were explored as possible approaches to enhance ozonation performance and consequently improve degradation efficiency of o-PDA. The effects of various operating parameters on ? under each of the oxidation approaches were systematically investigated in an attempt to establish the optimal working conditions. Chemical oxygen demand ?COD? reduction rate as well as the overall gas-phase volumetric mass transfer coefficient ?KGa? were also determined.Additionally, the intermediate products of degradation were identified to further evaluate the extent of o-PDA degradation. A separate experiment was also performed in a stirred tank reactor ?STR? for comparison. The following conclusions were drawn from this study:In the O₃ process, higher initial pH and inlet ozone concentration ?Ci?favored ? whereas higher liquid volumetric flow rate ?L? at a particular ozone dosage led to reduction in degradation efficiency. On the other hand, ? increased up to a maximum with an increase in temperature ?T? and rotation speed ?N?. The optimal operating conditions were thus determined as pH = 6.5 andN= 1000 rpm.The degradation efficiency and COD reduction rate ?CODR?achieved in the RSR were 109.0 and 114.0% respectively higher than those achieved in the STR.In the 03/H₂O₂ process, both ? and the overall gas-phase volumetric mass transfer coefficient ?KGa? were separately determined as a function of various operating parameters. Higher initial o-PDA concentration ?CAO? favored KGa while? decreased. Both ? and KGa increased with increase in N while they only increased up to peak values with increase in T. On the other hand, ? only increased up to a maximum with increase in H₂O₂ concentration ?CH₂O₂? while KGa generally increased throughout. Comparison results show that ?, KGa and CODR achieved by O₃/H₂O₂ process were 24.4, 31.6 and 25.2% respectively higher than those of the O₃ process. Analyses of the intermediate products further reveal that the degradation process was more enhanced in the 03/H₂O₂ process than in the O₃ process.In the O₃/Fe²⁺/PS process, higher PS concentration ?CPs? and N favored ?whereas it only increased up to a maximum with increase in T, initial pH and Fe²⁺concentration (CFe²⁺)· Degradation efficiency and CODR reached 98.7 and 82.6%respectively and 84.4 and 68.3% respectively in the 03/Fe2 /PS process and O₃/Fe²⁺ process under similar operating conditions.The work generally provides a feasible intensification means for the ozonation of o-PDA as well as other recalcitrant organic compounds.