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Catalytic Reduction of Nitrate in Groundwater Over Pd-Cu/AC Catalyst

Author: LiuMiaoMiao
Tutor: WangKunPing
School: Chongqing University
Course: Environmental Engineering
Keywords: Palladium Copper Active Carbon Catalyst Nitrate
CLC: X523
Type: Master's thesis
Year: 2011
Downloads: 67
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Abstract

With the development of industry and agriculture, nitrate pollution of groundwater constitutes an important environmental problem. The nitrate is reduced into nitrogen with hydrogen, which is a new water treatment technology. Catalytic reduction method is known to have great potential for rapid reaction, high selectivity of generating nitrogen, low energy consumption and easy operation. Catalytic nitrate reduction is one of the most promising methods.Pd-Cu/AC catalyst was prepared by wet impregnation method by using activated carbon as the carrier, and catalytic reduction of nitrate in drinking water has been studied. Pd-Cu/AC catalyst was prepared by wet impregnation method can be effectively removed of nitrate from water by catalytic reduction reaction. Single metal Pd/AC catalyst made the catalytic reduction of nitrate very slow. The concentration of the remaining nitrate was 70.33 mg·L^-1 in 2 hours for the 100mg·L^-1 nitrate solution when using the Pd/AC catalyst. Bimetallic catalysts for catalytic reduction of nitrate is essential. The conversion of nitrate was over 96%, and the production rate of ammonium was 22% in 2 hours for the 100mg·L^-1 nitrate solution when we using semi-continuous experiments and the dosage of the bimetallic catalyst is 2g.The reaction of nitrate removal from water demonstrated that the catalyst had the best metal loading conditions when the Pd/Cu ratio was 1:1,the bimetallic loading were 1.92wt% and the loading order of Pd and Cu was in the same time.The catalytic reaction can achieve the best results when the hydrogen flow is 100 ml·min^-1. Hydrogen flow rate is too low will slow down the process of catalytic reaction, when hydrogen flow rate was 50 ml·min^-1 when the reaction rate constant is only 100 ml·min^-1 the reaction rate constant of 61.89%; The reaction rate constant when hydrogen flow rate was 50 ml·min^-1 is only 61.89% of the reaction rate constant when hydrogen flow rate was 100 ml·min^-1. Hrogen flow rate is too high will have no benefit for the selectivity, for the ammonia nitrogen production rate was higher when hydrogen flow rate was 300 ml·min^-1 than the hydrogen flow rate was 100 ml·min^-1. The appropriate range of pH was 4.5-5.5, while too high or too low pH value resulted in the low catalytic activity and selectivity . When the pH value is 3.5-4.0, the percent conversion of nitrate is of 95.6% when the pH value is 4.5-5.5; the ammonia nitrogen production rate was higher when the pH value was 5.5-7.0 than the pH value was 4.5-5.5.Kinetic models of catalytic reduction of nitrate by Pd-Cu/AC catalyst were established, the physical meaning of the relevant model paremeters were also defined. The characteristics and laws of the rate constants, platfrom steady-state value and other model paremeters’influences from Pd/Cu ratio, Pd-Cu loading, hydrogen flow, pHvalue and the consumption of catalyst were disclosured.Use Pd-Cu/AC catalyst to remove the nitrate frome water is effective,and it can overcome the conventional physical-chemical methods and biological treatment technology disadvantages. The conversion of nitrate was over 96%, and the production rate of ammonium was 22% in 2 hours for the 100mg·L^-1 nitrate solution when we using semi-continuous experiments. For the scattered small-scale urban and rural and open country drinking water supply, the catalytic reduction is now regarded as the most promising approaches for removal of nitrate.

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CLC: > Environmental science, safety science > Environmental pollution and its prevention > Water pollution and its control > Groundwater
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