Catalytic destruction of lindane using a nano iron oxide catalyst

Date of Award

2011

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Sukh S. Sidhu

Abstract

Lindane, also known as gamma hexachlorocyclohexane, is toxic in nature. The objective of this work was to develop an economically viable technology for destruction of lindane into products that are nontoxic in nature. A catalytic approach was chosen for destructing lindane because thermal processes are expensive and can generate toxic products like dioxins. Initially, a set of exploratory experiments (Phase I) were performed using a micro iron oxide particle loaded catalyst (7 cm bed length and 0.92 g Fe2O3 loading). The iron oxide catalyst was chosen because results from a previous study done by our group had shown that iron oxide was effective in destroying chlorinated compounds. In phase I, lindane was passed over the catalyst for a period of ten minutes as a lindane-acetone (25 g / 80 ml) mixture at 1.44 g/hr. The results showed that the micro iron oxide catalyst was able to destruct only ̃80% of the lindane fed into the reactor. Changes in catalyst loading and space velocity failed to increase the destruction efficiency of the catalyst. It was decided that perhaps the destruction efficiency will increase if the micro iron oxide catalyst was replaced with a nano iron oxide catalyst. The second phase of the experiments was performed with a nano iron oxide catalyst (7 cm in bed length and 3% Fe2O3 loading). Same amount of lindane-acetone mixture, as in the first phase of experiments, was fed over the catalyst. The results showed that the nano iron oxide catalyst destroyed over 99% of lindane. Once the high destruction efficiency was achieved it was decided to conduct the next set of experiments (Phase III) at a larger scale with the lindane directly fed into the reactor without acetone. This required the design and construction of a solid feed system and a vaporizer that will vaporize lindane into gas phase before it passed over the catalyst. In the third phase, a total of two hundred grams of lindane at a feed rate of 0.2±0.03 g/min in gas phase was passed through two fixed bed catalytic reactors in series that housed nano iron oxides catalysts (catalyst 1 of 7 cm bed length and 7% Fe2O3 loading, catalyst 2 of 7 cm bed length and 3.5% Fe2O3 loading). The destruction efficiency of the catalyst was found to be 100% for the initial set of experiments. However, as more lindane was passed over the catalyst it was found that the chlorine from lindane was deactivating the catalyst. Chlorine deactivates the catalyst by forming iron chloride on the active sites of the catalyst resulting in a decrease in destruction efficiency. A restoration process was found to activate the catalyst in which water along with air was fed over the catalyst while maintaining the reactor temperature at 650°C. During this process, moisture is adsorbed on the surface of iron chloride and forms the complex (FeCl(OH)) which further reacts with moisture to form ferrous hydroxide. Ferrous hydroxide is then oxidized in the presence of oxygen to form iron oxide. The regenerated iron oxide catalyst was once again effective in destructing lindane. A preliminary cost estimate indicates that if the catalyst can be regenerated five times based on the amount of lindane destroyed during this study, the process will be economical compared to the other techniques available for lindane destruction and can be implemented at a larger scale. To avoid a separate process to regenerate the catalyst, experiments should be conducted by passing water along with lindane over the catalyst. In doing so, the destruction of lindane and the regeneration of the catalyst occur simultaneously. This technique will prolong the life of the catalyst.

Keywords

Chemicals Purification, Lindane, Ferric oxide, Iron catalysts

Rights Statement

Copyright © 2011, author

Link to Full Text

Share

COinS