Highly ACTIVE Heterogeneous Catalyst M-Al2O3/SiO2 (M = Cu, Fe and Ni) Derived from POWER Plant Fly-ASH for the Degradation of Acrylonitrile an Emerging Pollutant

ARVIND KUMAR^1, *, BASHESWAR PRASAD¹

¹Department of Chemical Engineering, Indian Institute of Technology Roorkee,

Roorkee-247667 (Uttarakhand) India

*Corresponding Author: Arvind Kumar (akumar6@ch.iitr.ac.in)

Keywords: Catalytic peroxidation, Acrylonitrile, Fe-Al₂O₃/SiO₂ catalyst

Introduction

Acrylonitrile is one of the major toxic and refractory pollutant that widely used in the synthesis of nitrile rubber, ABS resins, plastic and acrylic fiber. United States Environmental Protection Agency (USEPA) classified as a 3^rd priority pollutant in the list of 129 priority pollutants. The chronic exposure of acrylonitrile leads to detrimental impacts on human bodies viz., asphyxia, inflation in respiratory system, mild jaundice, eye irritation, vomiting, headache etc. Therefore, it is urgently needed to treated acrylonitrile containing wastewater. A highly active heterogeneous catalyst M-Al₂O₃/SiO₂ (M = Cu, Fe and Ni) was derived from power plant fly-ash and further used to treat acrylonitrile. Fly-ash is a byproduct of power plant and a major source of water and air pollution. It pollutes the atmosphere and threaten the human health if it is not treated and directly discharge from power plant chimneys into atmosphere. Therefore, fly ash was used as a supporting material in M-Al₂O₃/SiO₂ heterogeneous catalyst.

Methodology

In the present investigation, acrylonitrile was removed from aqueous solution by catalytic peroxidation process. The catalyst was synthesized by wet impregnation method with various metals (Cu, Fe and Ni) and denoted by Cu-A/S, Fe-A/S and Ni-A/S, respectively. Synthesized catalysts were further characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Brunner-Emmitt-Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). The effects of various parameters on acrylonitrile degradation were evaluated through central composite design in response surface methodology (RSM) tool and optimized the operating parameters within their ranges viz., catalyst dose (100-1000 mg/L); stoichiometric molar ratio of H₂O₂/acrylonitrile (0.5-5); pH (2-10); temperature (28-80 ºC) and initial acrylonitrile concentration (100-1000 mg/L).

Results and conclusions

Some preliminary experiments were conducted and observed that only i.e., 32.62%, 36.15%, and 24.12% of acrylonitrile degraded with catalysts, Cu-A/S, Fe-A/S and Ni-A/S, respectively in the presence of H₂O₂ and only 18% of acrylonitrile removed without using any catalyst in the presence of H₂O₂ as shown in figure 1. The plausible reaction mechanism for acrylonitrile degradation at optimum operating conditions were proposed according to intermediates detected by GC-MS analysis. The hydroxyl radical generated mechanism is shown in Figure 1.

Two-step degradation kinetic study was performed at various temperatures and well fitted by first order and n^th order models. In-situ generated reactive oxygen species (ROS), e.g., hydroxyl radicals (^•OH), superoxide radicals (O₂^•־) and singlet oxygen (¹O₂) were treated with their respective quenchers as, tert-butyl alcohol (TBA) was used as hydroxyl radical scavenger, p-benzoquinone (p-BQ) was used as superoxide radical scavenger and sodium azide (SA) was used as a singlet oxygen scavenger. To assess the economic viability of catalyst reusability study was performed and remarkable results were obtained over the 5 cycles of experiments for acrylonitrile degradation at optimum operating conditions.

Figure 1. Preliminary study for acrylonitrile degradation and free radical generation mechanism.

Key Conclusions

The present study reveals that catalyst Fe-Al₂O₃/SiO₂ show best catalytic activity for acrylonitrile degradation by catalytic peroxidation process. The reusability study of catalyst shows that catalyst Fe-Al₂O₃/SiO₂ is very stable and maintained the satisfactory performance after fifth cycle. Scavenger study demonstrate that generated hydroxyl radicals play significant role for the degradation of acrylonitrile.