Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 microns in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 microns in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM2.5 samples than in the PM2.5+ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO4, while most of the V spectra closely resembled that of vanadyl sulfate (VO.SO4.xH2O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsenate (As+5). X-ray diffraction patterns of the PM2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+ fraction. Based on 13C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.
Diethyl carbonate (DEC) has been produced by the oxidative carbonylation of ethanol in the
gas phase over a heterogeneous CuCl2/PdCl2 catalyst supported on activated carbon. Yields of
DEC with this catalyst are approximately 10 wt % with the byproducts diethoxymethane, ethyl
formate, and acetaldehyde also formed in significantly lower yields. Treatment of the catalyst
immediately after preparation with potassium hydroxide enhances the production of DEC almost
2-fold without increasing the amount of byproducts formed. The reactions that form DEC and
the byproducts occur in a parallel, rather than a sequential, manner indicating that it should be
possible to identify a catalyst which is more selective for DEC.
The thermal decomposition of white birch wood and
filter pulp was studied in water and methanol
vapor at 2 MPa pressure in a flow-through reactor. The abundance
of the volatile products was
monitored by on-line GC/MS using repetitive sampling in combination
with fast separation on
a short capillary column. The reactor was heated to 400 °C at 20
°C/min and the intensity
profile of the product ions within the 30−200 amu range recorded.
The system was capable of
separating the profiles of typical hemicellulose products evolved at
lower temperature from the
characteristic cellulose and lignin products detected from wood.
Char yields in methanol were
similar to those in an inert gas atmosphere; however, the presence of
water markedly increased
the amount of char produced. The product distribution of cellulose
was strongly affected by the
solvents. In methanol, pyran derivatives dominate besides
levoglucosan and glycolaldehyde,
whereas the relative abundance of 2-furaldehyde and
5-(hydroxymethyl)-2-furaldehyde increased
in the presence of water. Water catalysis was also indicated by
lowering the decomposition
temperatures of cellulose. High-pressure (6.5 MPa)
thermogravimetric experiments in helium
or hydrogen atmospheres were also found to lower the reaction
temperature of wood. This
observation can be explained by the catalytic effect of reaction water
released during the thermal
decomposition of wood.
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