Solvent effects during reactions in supercritical water

Townsend, Susan H.; Abraham, Martín; Huppert, Gilbert L.; Klein, Michael T.; Paspek, Stephen C.

doi:10.1021/ie00073a026

Cited by 194 publications

(152 citation statements)

References 7 publications

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“…hydrogen and hydroxyl radicals, H 2 , H 2 O 2 , hydrous electrons (e aq -), and H - (Lin et al, 2005). Hydrogen radicals can also be produced by reaction of water with hydrocarbons and nitrogencontaining heterocycles (e.g., Townsend et al, 1988;Moriya and Enomoto, 2001;Yuan et al, 2006) and with fluids (e.g., via gas shift reaction; Sato et al, 2004). Aided by high temperatures, some of these highly reactive species may provide sufficiently large activation energies for abstracting structurally accessible organic nitrogen atoms from ultramicroporous carbonaceous matter during metamorphism.…”

Section: The Role Of H O-containing Hot Fluids During Transformationmentioning

confidence: 99%

Organic nitrogen chemistry during low-grade metamorphism

Boudou

Schimmelmann

Ader

et al. 2008

Geochimica et Cosmochimica Acta

136

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-Most of the organic nitrogen (N org ) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil N org within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of N org and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of N org a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of N org speciation, transformation and elimination before and during metamorphism and advocates the use of XRay Photoelectron Spectroscopy (XPS) to monitor changes in N org speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset N org is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much N org is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for N org elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate N org along a progressing reaction front, without causing nitrogen isotope fractionation in the residual N org in the unreacted core of the carbonaceous matrix. Before the reaction front can reach the core, an increasing part of core N org chemically stabilizes in the form of nitrogen atoms substituting for carbon in condensed, partially aromatic systems forming graphite-like structural domains with delocalized π-electron systems (nitrogen atoms substituting for "graphitic" carbon in natural metamorphic organic matter). Thus, this nitrogen species with a conservative isotopic composition is the dominant form of residual nitrogen at higher metamorphic grade.

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Section: The Role Of H O-containing Hot Fluids During Transformationmentioning

confidence: 99%

Organic nitrogen chemistry during low-grade metamorphism

Boudou

Schimmelmann

Ader

et al. 2008

Geochimica et Cosmochimica Acta

136

View full text Add to dashboard Cite

show abstract

“…Moreover, kinetics are also sometimes correlated simply with l/e, which is linearly related to ( E -1)/(2 E + 1). Several investigafors have correlated rate constants for reactions in SCFs with the solvent dielectric constant (Johnston and Haynes, 1987;Townsend et al, 1988).…”

Section: Reactions In Solution (Solvent Effects)mentioning

confidence: 99%

“…Klein's group at the University of Delaware studied the reaction pathways, kinetics, and mechanisms of solvolysis and pyrolysis of coal model compounds in SC water and other SCFs (Lawson and Klein, 1985;Townsend and Klein, 1985;Klein, 1985, 1987;Townsend et al, 1988;Abraham et al, 1988;Huppert et al, 1989;Wu et al, 1989Wu et al, , 1991aKlein et al, 1990Torry et al, 1992;Boock et al, 1992). They examined the effects of temperature, solvent density, phase behavior, and added salts, and used transition-state theory to interpret their results.…”

Section: Aiche Journalmentioning

confidence: 99%

Reactions at supercritical conditions: Applications and fundamentals

et al. 1995

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“…Streit (1988, 1989) included elementary reaction steps that involved water as a reactant in their detailed kinetic models of methane oxidation in SCW. Additionally, several pyrolysis studies in SCW revealed that water was an active participant in the reaction and not merely an inert solvent (Lawson and Klein, 1985;Townsend and Klein, 1985;Townsend et al, 1988;Huppert et al, 1989;Houser et al, 1986).…”

Section: Effect Of Pressurementioning

confidence: 99%