P.L. Walker Jr’s research while affiliated with Pennsylvania State University and other places

The coking of liquid phenanthrene in a batch reactor was followed by measuring the formation of pyridine insolubles as a function of time over the temperature range 510–570°C. Following an induction period, the disappearance of pyridine solubles is first order, with the rate constants having an activation energy of 65 kcal/mole. This is significantly higher than the activation energy (46 ) associated with the rate constants describing the carbonization of the isomer, anthracene. As the rate of carbonization increases, the low-temperature cokes produced decrease in their subsequent graphitizabilities. Further, the reactivity to air of the graphitized carbons is increased.

The effect of substitution of nitrogen into the 9 position and 9,10 positions of anthracene in place of C-H groups on the kinetics of carbonization to yield pyridine insolubles (PI) and the properties of the cokes and graphites produced have been studied. Acridine and phenazine exhibit higher carbonization rates than does anthracene. Carbonization of each of these heterocyclics leads to lowtemperature cokes exhibiting large flow domain, isochromatic regions and good graphitizability. However, the elimination of nitrogen from the low-temperature cokes upon their calcination does result in the production of cokes and graphites of lower particle densities and higher surface areas. The result is that these carbons have higher reactivities to air and they probably will lead to the production of artifacts of inferior mechanical properties.

The coking of liquid anthracene in a batch tubular reactor was followed by measuring the formation of pyridine insolubles and the disappearance of anthracene as a function of time over the temperature range 465–525°C. Conditions, that can affect coking behavior and rates, like partition of the feed between liquid and vapor, agitation of the reactor, and whether the gas pressure in the reactor is autogeneous or imposed are considered. Carbonization primarily involves hydrogen-transfer reactions and condensation (polymerization) of free radicals into larger molecular weight species. Cleavage (cracking) of hydroaromatic species, giving smaller liquid and gas phase molecules, is at a minimum under the conditions used in this study.

Differential scanning calorimetry (d.s.c.) and thermogravimetric analysis (TGA) were used to follow oxygen chemisorption on a series of coal chars when exposed to 0.1 MPa of O2 at 373 K. Elovich plots correlated heat release and weight of oxygen chemisorbed as a function of reaction time. Rates of both heat release and weight increase generally decreased with increasing rank of original coal. Rates of heat release upon oxygen chemisorption also generally increased as rates of gasification of the chars at higher temperatures in air increased. Enthalpies of oxygen chemisorption, as a function of reaction time, were calculated for selected chars.

We have talked about the large variability of coal as a precursor for carbons as we go from anthracite to bituminous to lignite. We can produce carbons of large variability in properties, like microporosity, by pretreating the coal and changing the nature of the precursor with which we start. We can produce a wide variety of carbons which, today, have important commercial applications. For tomorrow, there is great promise of producing new carbons of still greater commercial applications.

The influence of carbon active sites on the pyrolysis of propylene was studied in the temperature range 873–1073 K at a starting pressure of 1.6 Pa. Graphon, a graphitized carbon black, was used as a substrate for pyrolysis and subsequent carbon deposition. Pyrolysis was carried out in a static reactor at low pressures where secondary products were less likely to form and complicate the system. The pyrolysis of propylene over the Graphon substrate may be described by the expression d (ASA) moles/sec where ASA is the active surface area (cm2) of the carbon measured by propylene chemisorption at 573 K, (C3H6) is the concentration of propylene in moles/cm3, and k is the specific reaction rate constant having a value of 109.62 exp (−57 kcal/mole/RT) cm/sec. The carbon active surface greatly enhanced the rate of cracking of hydro-carbons to elemental carbon which was deposited directly on the surface. The carbon was found to deposit on the active sites and become new active sites. Thus, the carbon deposit replicated the active surface area and was autocatalytic.

Structural changes occurring during the hydrogen-assisted pyrite-pyrrhotite transition are characterized over the temperature range 400–600 °C. Newly developed pressure-temperature microscopy gave in-situ observations of pyrite decomposition at elevated temperatures and gas pressures. Composition of pyrrhotites was measured by X-ray diffraction and correlated with krypton surface areas. Surface areas increased with an increase in pyrite reduction due to a decrease in molar volume accompanied by the development of porosity. Increases in specific surface area are inversely proportional to the reduction temperature. Heats of adsorption of krypton on pyrite increase linearly with increases in the relative amount of the (100) crystallographic faces.