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Show refined top (T3) and bottom (B4) fractions were filtered onto 47 m m diameter 0.2 u m pore polycarbonate membranes, dried, and the filter cakes recovered and placed in glass vials for storage. The collected alcohol was filtered and recycled for use in additional separations. Carbon Characterization A Cambridge Instruments S240 scanning electron microscope (SEM) was used to examine particle morphology. Samples of the soot and char fractions were suspended in ethyl alcohol, serially diluted, and filtered onto 47 m m polycarbonate membranes which were cut, mounted, and gold coated for examination. The reactivity of the refined soot and char were determined using a Perkin Elmer T G A 7 thermogravimetric analyzer (TGA). Samples were heated at a rate of 40 °C per minute from ambient to 800 °C using a 1 0% oxygen atmosphere. These methods were selected to allow comparison to previous studies of char reactivity in the same laboratory. [22] The T GA analyzer output text file was loaded into a spreadsheet for calculations and plotting. The first derivative of the sample weight vs. time data was calculated numerically. Various averaging algorithms were tested and a five-point derivative provided a balance between filtering out noise and still resolving intermediate peaks in the reaction rate. Surface area was determined by the BET nitrogen adsorption method using a Quantachrome analyzer following the manufacturer's procedures for calibration and operation. The samples were weighed, outgassed for at least 30 minutes, then analyzed three times to verify reproducibility of the adsorption and desorption readings. Results Figure 3 shows the carbon in the total filter ash vs. the exit NOx concentration for a range of combustion conditions in the laboratory furnace. The previously published data[16] have been supplemented by the addition of data for a lignite and for a second bituminous coal. Trends of N O x vs. unburned carbon for the U T and IL bituminous coals are similar, and the lower carbon concentration for IL is partially due to the higher Char and Soot 8 September 4, 1998 |
