Quantum-chemical study of the nonclassical carbonium ion-like transition states in isobutane cracking on zeolites

The ''ab initio'' quantum chemical calculations at MP2/6- 31++G**//HF/6-31G* level were performed for some elementary steps of isobutane cracking on zeolites. The results demonstrated that adsorbed carbonium ions represent not the observable reaction intermediates, but the high-energy transition states of the corresponding elementary reactions. Calculated activation energies are in reasonable agreement with experimental dat

Rapid Mineral Precipitation During Shear Fracturing of Carbonate‐Rich Shales

Target subsurface reservoirs for emerging low‐carbon energy technologies and geologic carbon sequestration typically have low permeability and thus rely heavily on fluid transport through natural and induced fracture networks. Sustainable development of these systems requires deeper understanding of how geochemically mediated deformation impacts fracture microstructure and permeability evolution, particularly with respect to geochemical reactions between pore fluids and the host rock. In this work, a series of triaxial direct shear experiments was designed to evaluate how fractures generated at subsurface conditions respond to penetration of reactive fluids with a focus on the role of mineral precipitation. Calcite‐rich shale cores were directly sheared under 3.5 MPa confining pressure using BaCl2‐rich solutions as a working fluid. Experiments were conducted within an X‐ray computed tomography (xCT) scanner to capture 4‐D evolution of fracture geometry and precipitate growth. Three shear tests evidenced nonuniform precipitation of barium carbonates (BaCO3) along through‐going fractures, where the extent of precipitation increased with increasing calcite content. Precipitates were strongly localized within fracture networks due to mineral, geochemical, and structural heterogeneities and generally concentrated in smaller apertures where rock:water ratios were highest. The combination of elevated fluid saturation and reactive surface area created in freshly activated fractures drove near‐immediate mineral precipitation that led to an 80% permeability reduction and significant flow obstruction in the most reactive core. While most previous studies have focused on mixing‐induced precipitation, this work demonstrates that fluid–rock interactions can trigger precipitation‐induced permeability alterations that can initiate or mitigate risks associated with subsurface energy systems.Key PointsBarium carbonates precipitate near‐immediately with injection of BaCl2‐rich fluid into freshly sheared calcite‐rich shalesPrecipitation reactions are strongly localized, favoring narrow apertures and zones of extensive fragmentationFluid–rock interactions can promote significant precipitation‐induced permeability alterations that remain challenging to predictPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/1/jgrb54184_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/2/jgrb54184-sup-0001-2019JB018864-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/3/jgrb54184.pd

Prevention of benzene-induced myelotoxicity by nonsteroidal anti-inflammatory drugs.

Benzene affects hematopoietic progenitor cells leading to bone marrow depression and genotoxic effects such as micronucleus formation. Progenitor cell proliferation and differentiation are inhibited by prostaglandins produced by macrophages. Administration of benzene to DBA/2 or C57BL/6 mice caused a dose-dependent bone marrow depression and a significant increase in marrow prostaglandin E level and both were prevented by the coadministration of indomethacin and other inhibitors of the cyclooxygenase component of prostaglandin H synthase. Levels of benzene that decreased bone marrow cellularity also caused genotoxic effects measured as increased micronucleated polychromatic erythrocytes in peripheral blood, which was also prevented by the coadministration of indomethacin. These results suggest a possible role for prostaglandin synthase in benzene myelotoxicity; a mechanism by which this might occur is presented