Virgil I. Stenberg

Hydrocracking of diphenylmethane

Abstract This study presents the role of H 2 S other than H-transfer catalyst in the hydrocracking of diphenylmethane with H 2 –H 2 S-pyrrhotite. The results indicate that the partial pressure of H 2 S controls the conversion of pyrrhotite to FeS and FeS 2 , which in turn is closely related to the promotional activity of pyrrhotite on the diphenylmethane conversion. Under higher H 2 S overpressures, pyrite bands appear in the Mossbauer spectra providing proof of the reversibility of pyrite decomposition under liquefaction conditions. With lower H 2 S pressures, low activity troilite forms from the pyrrhotite. An enhanced activity was observed for a partial pressure of H 2 S, sufficient for the maintenance of a high iron deficient surface on the pyrrhotite particles. When the partial pressure was increased too much, the formation of FeS 2 was observed with a slight decrease in activity. FeS did not show as great an activity as the non-stoichiometric pyrrhotite.

Mechanisms leading to process improvements in lignite liquefaction using CO and H2S

Abstract Optimum distillate yields from US lignites can be as high on a dry, ash-free basis as those obtained from bituminous coals, but only if the vacuum bottoms are recycled. Lignites are more readily liquefied if the reducing gas contains some carbon monoxide and water, which together with bottoms recycle has proven to yield the highest conversions and the best bench-unit operability. The recycle solvent in the reported tests consisted of unseparated product slurry, including coal mineral constituents. Variability in coal minerals among nine widely representative US low-rank coals did not appear to correlate with liquefaction behaviour. Addition of iron pyrite did, however, improve yields and product quality, as measured by hydrogen-to-carbon ratio. Future improvements in liquefaction processes for lignite must maintain high liquid yields at reduced levels of temperature, pressure, and reaction time whilst using less reductant, preferably in the form of synthesis gas ( CO + H 2 ) and water instead of the more expensive pure hydrogen. Understanding the process chemistry of carbon monoxide and sulphur (including H 2 S) during lignite liquefaction is a key factor in accomplishing these improvements. This Paper reviews proposed mechanisms for such reactions from the viewpoint of their relative importance in affecting process improvements. The alkali formate mechanism first proposed to explain the reduction by CO does not adequately explain its role in lignite liquefaction. Other possible mechanisms include an isoformate intermediate, a formic acid intermediate, a carbon monoxide radical anion, direct reaction with lignite, and the activation of CO by alkali and alkaline earth cations and by hydrogen sulphide. Hydrogen sulphide reacts with model compounds which represent key bond types in low-rank coal in the following ways: (1) hydrocracking; (2) hydrogen donor; (3) insertion reactions in aromatic rings; (4) hydrogen abstraction, with elemental sulphur as a reaction intermediate; and (5) catalysis of the water-gas shift reaction. It appears that all of these reaction pathways may be operative when catalytic amounts of H 2 S are added during liquefaction of lignite. In bench recycle tests, the addition of H 2 S as a homogeneous catalyst reduced reductant consumption as much as three-fold whilst maintaining high yield levels when the reaction temperature was reduced by 60°C. Attainment of the high distillate yield at 400°C was accompanied by a marked decrease in the production of hydrocarbon gases, which normally is a major cause of unproductive hydrogen consumption and solvent degradation via hydrocracking. Processing with synthesis gas and inherent coal moisture using bottoms recycle and H 2 S as a catalyst appears to be the most promising alternative combination of conditions for producing liquids from lignite at reduced cost.

Mechanism of the hydrogen-sulphidepromoted cleavage of the coal model compounds: diphenyl ether, diphenylmethane and bibenzyl

Hydrogen sulphide is shown to cleave the model coal compounds: diphenyl ether, diphenylmethane and bibenzyl with the major products being phenol and thiophenol, toluene and thiophenol, and toluene, respectively. These reactions were determined to be radical in nature. The sulphur which incorporated into diphenyl ether and diphenylmethane forming thiophenol was determined to reside ultimately at the ipso position. The cleavage of all three model compounds was inhibited by the presence of 316 stainless steel. The nature of the iron sulphides produced and the amount of H2S reacted were determined. It is concluded that 316 stainless steel and tetralin act as sulphur radical scavengers. In the absence of steel or tetralin, the conversions of the model compounds occur by radical chain mechanisms in which H2S acts as a reagent.

Hydrocracking of diphenylmethane: Roles of H2S and pyrrhotite

To define the roles of H2S and pyrrhotite in high temperatures employed for normal coal liquefaction, diphenylmethane hydrocracking with H2 and H2-H2S was carried out with and without pyrrhotite. H2S promotes diphenylmethane hydrocracking with H2 both in the presence and absence of pyrrhotite, and the reaction is dependent upon the H2S pressure in both instances. It is also dependent on the H2 pressure when pyrrhotite is present. The results are interpreted in terms of H2S acting as a hydrogen transfer catalyst.

Thermal analysis of coals using differential scanning calorimetry and thermogravimetry

Abstract Differential scanning calorimetry, thermogravimetry and differential thermogravimetry studies have been performed on 10 different coals: four lignite, four subbituminous and two bituminous coals. Both the d.s.c. and TG thermograms are coal-specific. Upon heating the coals in an inert atmosphere up to 500 °C, 30.8 to 43.7 % weight loss occurs. The two temperature regions of increased chemical reactivity, one at 75–118 °C and the second at 375–415 °C are evident in the samples. Indian Head lignite and its char react with hydrogen above 400 °C with greater mass loss.

Carbon-13 Nuclear Magnetic Resonance Spectrum of Colchicine

Abstract 13C NMR chemical shifts of tropolone, tropolone methyl ether and colchicine are reported. The various carbon resonances have been assigned on the basis of substituent effects on benzene shifts, intensities, multiplicities generated in SFORD spectra and the comparison with structurally related compounds like tropolone and tropolone methyl ether.

PHOTOCHEMICAL OXIDATIONS—IV. THE PHOTOOXIDATION OF CYCLOHEXANE WITH OXYGEN

Abstract— –For the photooxidation of cyclohexane, data on the rates of formation of cyclohexanol (I), cyclohexanone (II), and cyclohexylhydroperoxide (III) are presented. There are induction periods for the formation of I and II but not for III. The alcohol (I) is not the precursor of II in this reaction. The photooxidation does not occur when optical filters eliminate wavelengths of 260 nm or less from the incident light, and therefore the contact charge transfer absorption is responsible for the initiation of the reaction. Ozone is not involved to any significant extent in this reaction. The photodecomposition of III produces I and II, and this decomposition is first order during the initial stages. An overall 11 step mechanism is suggested for the photooxidation.

Radicals in coals during pyrolysis in relation to liquefaction conversion

Abstract The increase in radical concentration as measured by e.s.r. on pyrolysis of nine lignites, two subbituminous coals and one bituminous coal was studied. No correlation was found between the net quantity of radicals produced on thermolysis and the percentage conversion to THF-soluble material using either a hydrogen donor solvent or a non-hydrogen donor solvent. Decker lignite produced a high steady state radical concentration at all temperatures used (150–450 °C). Wyodak subbituminous coal and Martin Lake lignite gave large steady state radical concentrations at lower reaction temperatures and low to modest levels at the higher temperatures. Zap, San Mighel and Gascoyne lignites exhibited reduced levels of steady state radical concentrations at the lower temperatures and increasing levels at the higher temperatures.

H2S optimization for lignite liquefaction

Abstract Two lignite samples, Beulah No. 3 and Big Brown No. 1, were liquefied at 420 °C using H 2 and synthesis gas to determine the optimum beneficial amount of H 2 S in the batch autoclave reactor. Under the conditions employed, 50–100 psi partial pressure of H 2 S, nominally 4–10 wt% of daf lignite, was optimum for both samples. Synthesis gas outperformed H 2 with and without H 2 S for the liquefaction of the two coals.

Carbon-13 Nuclear Magnetic Resonance Spectrum of Quinacrine

Abstract The natural abundance carbon-13 nuclear magnetic resonance spectrum of quinacrine was determined using the pulse Fourier transform technique. The chemical shift of various carbon resonances have been assigned on the basis of the substituent effects on benzene shifts, multiplicities generated in SFORD spectrum and comparison with structurally related compounds.