Methane Activation and Oxidation in Sulfuric Acid

Abstract

In a versatile modular scaffold system, gradient nonwovens of in situ crosslinked gelatin nanofibers (CGN), fabricated by reactive electrospinning, are laminated with perforated layers and nonwovens of thermoplastic non‐crosslinked biodegradable polyesters. The addition of glyoxal to a gelatin solution in a non‐toxic solvent mixture consisting of acetic acid, ethyl acetate, and water (5:3:2 w/w/w) enables the in situ crosslinking of gelatin nanofibers during electrospinning. The use of this fluorine‐free crosslinking system eliminates the need of post‐treatment crosslinking and purification steps typical for conventional CGN scaffolds. The slowly progressing crosslinking of the dissolved gelatin in the presence of glyoxal increases the viscosity of the gelatin solution during electrospinning so that the average diameter of the crosslinked gelatin nanofibers gradually increases from 90 to 680 nm. During the subsequent lamination process, alternating layers of CGN and polycaprolactone (PCL) nonwovens, produced by 3D microextrusion of micrometer‐sized PCL fibers, are bonded together upon heating above the PCL melting temperature. In contrast to the water‐soluble gelatin nanofibers and the comparatively weak CGN, the CGN/PCL/CGN layered biocomposites are water‐resistant and very robust. In such modular scaffold systems, strength, biodegradation rate, and biological functions can be controlled by varying the type, composition, fiber diameter, porosity, number, and sequence of the individual layers. The CGN/PCL multilayer biocomposites can be cut into any desired scaffold shape and attached to tissue by surgical sutures in order to suit the needs of individual patients.

Hydrolysis of bamboo fiber cellulose in formic acid

“…Formic acid is a flat organic molecule, the average length of O5C-O-H bonds is 0.171 nm, the length of O5C-C-H bonds are 0.224 nm (Stein and Sauer, 1997;Goeppert et al, 2002;Jarvis, 2003). The bond length of hydrochloric acid is 0.128 nm.…”

H/D isotope exchange between methane and magic acid (HSO3F–SbF5): an in situ NMR study

“…H/D exchange was observed when methane was recirculated in D 2 SO 4 at temperatures of 250 C and above and an apparent activation energy of 176 kJ mol À1 was measured. 18 In the strongest superacid, HF-SbF 5 , we experimentally determined that the secondary kinetic isotopic effect for the H/D exchange, k(CH 4 )/k(CH 3 D), is very close to unity; 19 moreover, high level computational studies using H 2 F þ , more or less solvated by excess HF as the superacid species, suggested that CH 5 þ was not an intermediate in the exchange reaction but acted rather as a part of the activated complex strongly solvated by (HF) x . 19 The apparent activation energy of 75 kJ mol À1 measured by Hogeveen and Gaasbeek 9 shows the large difference of stability of this activated complex between strong acidic media and superacid media.…”

Direct and Remarkably Efficient Conversion of Methane into Acetic Acid Catalyzed by Amavadine and Related Vanadium Complexes. A Synthetic and a Theoretical DFT Mechanistic Study

“…Theoretical calculations are also performed to assist in the establishment of possible mechanisms for the carboxylation of methane, an approach that had not yet been previously addressed in detail for such a type of system. Although a number of mechanistic proposals have been recently considered for alkane hydroxylation, halogenation, and dehydrogenation reactions, of methane oxidation in sulfuric acid and on an Fe-exchanged zeolite, of activation of C−H bonds of alkanes by platinum, titanium, and lanthanide complexes, by dirhodium tetracarboxylate, by unsaturated aluminum ions, by Sc + cation, by metal oxides, etc., to our knowledge, there are only a few publications where possible mechanisms of alkane carboxylation were proposed ,,,,, and only one case with detailed theoretical calculations 34b that has been reported and in a system different from ours.…”