John W. Larsen

Mechanism of the carbon catalyzed reduction of nitrobenzene by hydrazine

The reduction of nitroaromatics to anilines by hydrazine is catalyzed by carbons. The carbon serves as an adsorbent and electrical conductor to enable the reaction to occur. Hydrazine is a two-electron reducing agent as shown by trapping the diimide intermediate with norbornene. The nitrobenzene reduction is a four-electron process proceeding first to phenylhydroxylamine which was observed in low concentrations in the reacting system by NMR. Phenylhydroxylamine is reduced to aniline in a second step. The two-electron intermediate, nitrosobenzene, gave different products than nitrobenzene under the reaction conditions and could not be trapped, supporting the expected four-electron pathway. By serving as an adsorbent and collecting hydrazine on their surfaces, carbons make it possible to execute a four-electron reduction using a two-electron reducing agent. This role of carbon was confirmed by successfully operating an emf cell using graphite or carbon paste electrodes immersed in solutions of hydrazine and nitrobenzene. The initial rates of reduction of substituted nitrobenzenes showed only a tiny substituent effect and proceed at nearly the same rate as the carbon-catalyzed decomposition of hydrazine leading to the conclusion that hydrazine reaction at the carbon surface is the rate determining step.

Temperature dependence of crosslinking processes in pyrolysing coals

Changes in the macromolecular structure of a lignite and a bituminous coal during rapid pyrolysis in the temperature range 300–1200 K are described. Solvent swelling techniques have clearly demonstrated that crosslinking occurs in lignites at somewhat lower pyrolysis temperatures than it does in bituminous coals. The onset of the crosslinking processes in bituminous coals coincides with the end of the tar formation period. In lignites, crosslinking occurs very early in the pyrolysis process, coinciding with low temperature release of CO2. The presence of natural moisture in the lignite appears to have a significant effect on pyrolysis chemistry, increasing the amount of crosslinking observed at any temperature.

An initial comparison of the interactions of Type I and III kerogens with organic liquids

The swelling of a pair of Type I (Green River and Rundle) kerogens and a Type III (Pittsburgh No. 8 coal) kerogen in a set of organic solvents is compared. Their behavior shows a regular trend with a low O/C Type I kerogen showing no specific interactions, and Type III dominated by specific kerogen-solvent interactions. The less polar low O/C Type I kerogen (Green River) follows regular solution theory and there appear to be no specific intermolecular interactions serving as non-covalent cross-links. The more polar higher O/C Type I kerogen comes close to regular solution behavior, but the data for polar and non-polar liquids are more scattered. There is evidence for specific interactions with hydrogen bonding solvents. The magnitude of the specific interactions is not large. The typical bituminous coal shows good regular solution behavior with non-polar solvents. All other solvents have specific interactions which can strongly enhance swelling. Good hydrogen bond acceptors show large effects. Only solvents which interact specifically can lead to significant swelling of untreated coal.

Multiple mechanisms for the loss of coking properties caused by mild air oxidation

Abstract Evidence is presented for the existence of at least three different mechanisms by which low temperature oxidation (weathering) destroys coals coking properties. Lithium aluminium hydride reduction of Bruceton coal oxidized for 28 days restores the FSI to its initial value of 8 from a value of 3. After 220 days oxidation, reduction raises the FSI from 0.5 to 2. Clearly, two different processes are responsible for the FSI decrease. The pyridine solvent swelling change during this time is quite small, much smaller than observed by Liotta. Thus the oxidative increase in cross-link density observed by Liotta is a third mechanism of thermoplasticity loss. The initial FSI decrease, that reversible by reduction, is tentatively ascribed to oxidative loss of readily donatable hydrogen from the coal. The second mechanism remains uncharacterized.

Coal macromolecular structure and reactivity

Abstract The macromolecular structure of coals will affect their reactivity in liquefaction reactions through the number of bonds which must be broken to achieve a given molecular weight reduction and through mass transport processes. Two criticisms of the macromolecular structure model, one based on solvent swelling and the other based on alkylation reactions, are shown to be unfounded. Coals undergo ready reaction with maleic anhydride at rates which are diffusion controlled. The absence of any effect of solvent swelling on these diffusion rates in two coals is discussed without resolution and data are presented on the activation energy for diffusion and the effect of reagent size. Solvent swelling measurements have been used to follow changes in cross-link density due to pyrolysis. A lignite rapidly forms new cross links concomitant with pyrolytic decomposition while cross link formation in a bituminous coal only occurs after a significant amount of tar formation.

Steric requirements for coal swelling by amine bases

Abstract A set of six coals ranging in rank from lignite to hvA bituminous was swollen with a series of alkyl-substituted pyridines and a smaller set of 4-alkylanilines. The size and branching of the alkyl groups was varied and the effect of this variation on the dissolution of the amines in the coal and the resulting coal swelling was measured volumetrically. In a few cases, substituents which hindered the amine nitrogen were studied. The lignite and subbituminous coal have a much higher tolerance to branched, bulky groups than do the bituminous coals. The presence of tertiary groups in a solute strongly inhibits their dissolution in bituminous coals. Bituminous coals behave as if extensive parallel packing of structures occurs. Often, they can accept very large planar groups but have a low capacity for branched groups.

Changes in the cross-link density of Paris Basin Toarcian kerogen during maturation

The volumetric swelling of three Paris Basin Toarcian kerogens by a set of 20 organic solvents was measured. There is no evidence of specific interactions (e.g. hydrogen bonds) between the kerogens and the liquids. Their interaction thermodynamics is described reasonably well by Regular Solution Theory. The cross-link density of the three kerogens is too high to permit accurate calculation of the number average molecular weight between cross links. Qualitatively, the swelling data demonstrate that the cross-link density increases with increasing maturation. Surprisingly, the solubility parameter (δ) of the kerogen is constant for the three samples of different maturity. Kerogen extractabilites have been measured and parallel the magnitude of solvent swelling, as expected.

Macromolecular structure and coal pyrolysis

Abstract A molecular level explanation for the dilatometric behavior of an hvAb coal is sought. The macromolecular network structure of bituminous coals is described with emphasis on the non-covalent interactions responsible for coals being glasses at room temperature. The existence of a glass to rubber transition in coals at 600 K detected by both DSC and NMR is described and related to the initial softening and contraction observed in the dilatometer. The relationship between the phase transition and the pyrolysis chemistry simultaneously occurring is discussed and it is concluded that it is not known whether covalent bond cleavage is a cause of the phase transition. Covalent bond cleavages are not necessary for the transition to occur. In coking coals, thermally induced cross linking begins at temperatures well above Tg and after most tars have been released from the coal. The high degree of structural anisotropy of all coals is revealed by solvent swelling. Its role in coke forming processes is unknown.

Carbon-catalyzed decompositions of hydrazine and hydroxylamine

Carbons catalyze the decomposition of hydrazine and of N H → N 1 4NH (3) 2 4 2 3 hydroxylamine. We wish to provide some details about both reactions. The reaction mechanisms have not been 3N H → 2N 1 3H 1 2NH (4) 2 4 2 2 3 studied in detail but some information has been produced. The hydrazine decomposition involves the formation of the We first encountered the carbon-catalyzed decomposidiazine (or diimide, HN5NH) intermediate. The hydroxyltion of hydrazine during our study of the carbon-catalyzed amine decomposition probably involves nitroxyl (HNO) as reduction of nitroaromatics by hydrazine [7]. Fig. 1 shows an intermediate. Three reviews provide lists of other plots of volume (at 1 at pressure) of gas evolved vs. time carbon-catalyzed reactions [1–3]. for refluxing solutions of hydrazine hydrate or monohyBeginning with the hydrazine decomposition, catalysis drate in isopropanol to which the indicated carbon had of this reaction by metals has been thoroughly studied been added. In the absence of the added carbon, hydrazine because of hydrazine’s use as a monopropellant, and an is stable under these conditions. The production of gas exhaustive review is available [4]. Four possible hydrazine upon addition of carbons to otherwise stable hydrazine decomposition pathways are shown in Eqs. (1)–(4). Resolutions demonstrates carbon-catalyzed decomposition. actions 2, 3, and 4 have all been catalyzed by various The carbons were used as received. There is no correlation metal-based catalysts, the most effective being those with between the rates or amounts of gas produced and either incomplete d shells [4]. The mechanism proposed by Sayer the metals content or the surface area of the carbons. is relevant [5] He proposed that an adsorbed hydrazine The first step in characterizing these reactions was a (denoted here by *) transfers two hydrogens to another search for hydrogen as a decomposition product. Using GC hydrazine to cleave the N–N bond and form two molecules techniques that were demonstrated to have a detection limit of ammonia and an adsorbed cis diazine (HN5NH, also of 0.5% yield of H , no H in the product gases was 2 2 known as diimide). The diazine then disproportionates to observed. Only one of the known hydrazine decomposition give N and hydrazine or decomposes to N and H . The pathways does not produce H (Eq. (3)), so it appears that 2 2 2 2 diazine disproportionation is well established and is a significant complication in the use of diazine to reduce double bonds [6]. Sayer’s mechanism is outlined in Scheme 1.

Changes in the cross-link density of Goynuk oil shale (Turkey) on pyrolysis

Abstract The effect of temperature and heating rate on the cross-link density of char samples obtained by pyrolysing Goynuk oil shale was investigated using the volumetric solvent swelling technique. The cross-link density decreases slightly with increasing pyrolysis temperature. The heating rate and thus the pyrolysis time had at most a small effect on the cross-link density. Char–solvent interactions do not follow regular solution theory. The demineralized kerogen swells more than does the native kerogen (16% ash).