Catalytic steam reforming of chlorocarbons: polychlorinated biphenyls (PCBs)

Experiments with commercial askarals (Aroclors 1221, 1248 and 1254) have confirmed the feasibility of catalytic steam reforming as a method for destroying polychlorinated biphenyls (PCBs). Rhodium, platinum and nickel supported on γ-Al2O3 were used as catalysts. Process conditions were GHSV=10 000–17 000 h−1; H2O/C=10; and temperature=400–700°C. The Ni catalyst was the most active, giving conversions of 0.9999+ and stable operation at temperatures as low as 400°C. A slight amount of deactivation due to carbon formation was apparent at longer process times. This increased with the degree of chlorination of the PCBs. Carbon monoxide was the dominant carbon product, increasing with time due to poisoning of the water gas shift reaction by chloride species. Platinum achieved essentially the same results, except that higher temperatures (600°C) were necessary and deactivation occurred sooner. Examination of trace amounts of unconverted PCBs indicated a progressive dechlorination of the biphenyl ring.