Hydrodechlorination of dichlorobiphenyls over Ni-Mo/Al2O3 catalysts prepared by spray-drying method.
The hydrodechlorination (HDCl) process of 2,3-, 2,4- and 2,5-dichlorobiphenyls was studied over a sulphided Ni-Mo/Al(2)O(3) catalyst in a stirred autoclave at a hydrogen pressure of 3 MPa. The catalysts were prepared by spray-drying. They were characterized by N(2) adsorption, thermogravimetry and scanning electron microscopy with X-ray microanalysis. The reaction temperature of the catalytic HDCl process was varied in the range of 230-290 degrees C. Polychlorinated biphenyls (PCBs) free transformer oil was used as reaction medium. The HDCl degree of dichlorobiphenyl isomers was in the range of 82-93%. The efficiency in the chlorine removal was found to be related to the position of the substituted chlorine atom and decreased as follows 2,4-dichlorobiphenyl approximately 2,5-dichlorobiphenyl>2,3-dichlorobiphenyl. For comparison, the HDCl process of 2,3-dichlorobiphenyl (2,3-PCB) without catalyst was also studied. The chlorine removal was 85% for the catalytic HDCl of 2,3-PCB whereas non-catalytic process led only to 16% of dechlorination in the same operating conditions, i.e. at 290 degrees C after 120 min. Monodichlorobiphenyls were not detected in the reaction products. The data for both catalytic and non-catalytic conversion of 2,3-PCB fit to a first-order model. Kinetic constants and the activation energy of the overall HDCl reaction of 2,3-PCB to biphenyl were evaluated. Compared to non-catalytic process, a nearly threefold decrease in the activation energy was observed in the presence of Ni-Mo/Al(2)O(3) catalyst prepared by spray-drying (48 kJ mol(-1) vs. 124 kJ mol(-1)).
Gryglewicz
G
G
Institute of Chemistry and Technology of Petroleum and Coal, Department of Chemistry, Wrocław University of Technology, ul. Gdańska 7/9, 50-344 Wrocław, Poland. grazyna.gryglewicz@pwr.wroc.pl
Stolarski
M
M
Gryglewicz
S
S
Klijanienko
A
A
Piechocki
W
W
Hoste
S
S
Van Driessche
I
I
Carleer
R
R
Yperman
J
J
D000537:Aluminum Oxide / Q000737:chemistry*; D002384:Catalysis; D004785:Environmental Pollutants / Q000032:analysis*; D007700:Kinetics; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D010316:Particle Size; D011078:Polychlorinated Biphenyls / Q000032:analysis* / Q000737:chemistry; D016062:Porosity; D013499:Surface Properties; D014865:Waste Disposal, Fluid / Q000379:methods*
D004785:Environmental Pollutants; C035197:nickel nitrate; D009532:Nickel; D008982:Molybdenum; D011078:Polychlorinated Biphenyls; D000537:Aluminum Oxide; C022175:ammonium molybdate