Enhancement of N2 Formation from the Nitrogen in Carbon and Coal by Calcium

The effects of Ca catalysts on nitrogen release during heat treatment of polyacrylonitrile-derived carbon and pyrolysis of low rank coals have been studied with a fixed bed quartz reactor in a stream of high purity He. In the temperature-programmed treatment at 10 °C/min of the carbon with 3 wt % Ca, the Ca promotes N 2 formation at 850−1000 °C and the catalytic effect is larger at a higher temperature. When a low rank coal, after demineralization and subsequent addition of 3 wt % Ca, is pyrolyzed in the same manner as above, the Ca enhances the rate of N 2 formation at 850−1100 °C at largest by a factor of 15. In the fast heating pyrolysis at 400 °C/min of the demineralized samples, the Ca at loading of 1−3 wt % also increases N 2 yields at 1200−1350 °C irrespective of type of coal. These observations and nitrogen distribution indicate that the N 2 increased by Ca addition arises mainly from solid-phase reactions of heterocyclic nitrogen forms. The X-ray diffraction measurements after heat treatment and pyrolysis reveal that catalyst particles are too fine on the carbon to be detected and as small as 45−65 nm in size on the chars. The catalysis of N 2 formation at solid phase by the Ca is discussed in terms of the mobility of CaO particles, their agglomeration, and sulfur poisoning.