Heterogeneous Photocatalytic Treatment of Wastewater from Amine-based Carbon Capture Plants

Abstract

Amine-based Carbon Capture (ABCC) is the advanced, cost-effective technology used to control climate change by capturing CO! emissions. Although it has been demonstrated commercially, amine degradation poses a significant threat to humans and aquatic life. Amine degradation produces a wide variety of complex products. Some of them are carcinogenic and mutagenic such as nitrosamines and some organic acids that have demonstrated acute toxicity for laboratory animals. In order to mitigate the adverse impact of these compounds on human health and aquatic life, heterogenous photocatalysis, an advanced oxidation process, which can degrade a wide variety of chemical species with the potent reactive hydroxyl radicals, was considered for the degradation of these compounds. The photocatalytic degradation of N-Nitrosodiethylamine (NDEA), acetic acid and formic acid were tested using various metal impregnated TiO2 such as Fe, Co, Ni and Cu. The operational parameters for the photocatalytic degradation process were chosen as solution pH, catalyst dose and metal impregnation percentage (imp %). Various techniques were used for the catalyst characterization such as Thermogravimetric Analysis (TGA), X-Ray Fluorescence Spectrometer (XRF), Brunauer-Emmett-Teller (BET), UV–visible spectrophotometer (UV-Vis), Scanning electron microscope (SEM), and X-ray diffraction (XRD). Designing the experiments, optimization, and impact of the parameters on the photocatalytic degradation of NDEA, acetic acid, and formic acid were analyzed using a Facecentered- central composite design (FC-CCD) in Response Surface Methodology (RSM) by Statease Design expert software. Various regression models were tested using ANOVA to fit between the responses (NDEA, acetic acid, and formic acid) of FC-CCD experimental runs and the independent variables. The quadratic model was analyzed as the best fit for all the responses and

the independent variables by eliminating insignificant factors. This model was best demonstrated for all the catalysts such as Fe, Co, Ni, and Cu impregnated TiO2. The interaction between the three variables and the responses were studied and presented in three-dimensional graphical representation. pH was found as an important factor for all three responses. The optimum conditions for the degradation of NDEA, acetic acid and formic acid using Fe-TiO2 catalyst were found as 3.65, 1.5 g/l, and 4.46. Whereas for the Co-TiO2 catalyst the optimum conditions were pH 3.77, catalyst dose of 0.95 g/l, and a metal impregnation percentage of 5. For the Ni-TiO2 the optimum conditions were pH-5.89, dose-0.5 g/l, and imp % of 3.18. A pH of 4.71, dose of 1.5 g/l and imp % of 4.66 were found as optimum conditions for Cu-TiO2. The optimum conditions of the parameters for the photocatalytic degradation of NDEA, acetic acid, and formic acid were determined using RSM and the average degradation efficiency of all the compounds reached 93.1% for Fe-TiO2, 92.08% for Co-TiO2. 89.09% for Ni-TiO2, 88.81% for Cu-TiO2, and 86.3% for TiO2 at the optimum conditions.