OCR Text |
Show normalized mass fractions (sum = 1.0), and the mass balance were determined. The "soot carbon" was defined as the fraction of carbon measured in the top product times the normalized mass of the top product. As discussed in the results, quality assurance criteria were set for both mass balance and carbon balance closure. Procedure variations such as changing the agitation and settling times, using a centrifuge in place of gravity settling, and using water or isopropyl alcohol instead of ethyl alcohol as the liquid phase were also tested as part of the separation method development. Experiments were also conducted to study the spontaneous coagulation of the soot particles and to study the causes of the observed systematic differences between measured and expected values. Preparation of Refined Fractions The quantitative separation method was designed so that all material ideally ended up in either the top or bottom fraction. This did not produce purified materials, and sample mass was limited. A separate procedure was developed to produce the larger masses of purified soot and char necessary for chemical and physical characterization of the fractions. The procedure for preparing the refined fractions is shown in Figure 2. Compared to the quantitative separation procedure, larger starting quantities of fly ash and alcohol were used to increase the product mass, times were adjusted to favor purity over yield, the intermediate fractions were discarded rather than being reprocessed, and solids were recovered by filtering. A 100-150 m g sample of fly ash was placed in a 600 ml beaker and suspended in 500 ml of ethyl alcohol using 10 minutes of ultrasonic agitation. This suspension was decanted after 30 minutes of gravity settling. The top fraction was resuspended, settled for 60 minutes and decanted twice to produce a refined top product. All solids which settled during the second and third processing of the top fraction were discarded. The bottom fraction from the first settling was resuspended in ethyl alcohol, gravity settled for 5 minutes and decanted three more times to produce a refined bottom fraction. The top suspension decanted from the second to fourth washing of the bottom fraction was also discarded. The Char and Soot 7 September 4, 1998 |