Byproduct Formation (byproduct + formation)

Distribution by Scientific Domains

Selected Abstracts

Photocatalytic oxidation of methanol using silica-titania composites in a packed-bed reactor

Jennifer M. Stokke
Abstract The processing of forest products into pulp, paper, paperboard, and other wood products results in the generation of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). This work focused on the development of a photocatalytic packed-bed reactor for the oxidation of methanol, which is the primary constituent in high volume low concentration gases emitted from pulp and paper mills. Bench-scale studies using an annular reactor packed with silica-titania composite (STC) pellets were conducted to maximize methanol removal and minimize the formation of byproducts, such as formaldehyde. Parameters such as STC pore size (ca. 40, 120, and 260 ) and UV wavelength (UVA and UVC) were varied. In the dark, the STC pellets removed methanol via adsorption and had a finite adsorption capacity dependent on the surface area of the composite. When irradiated with UV light, the STC pellets adsorbed and oxidized methanol simultaneously. At the bench-scale, 40 STC pellets irradiated with UVC light achieved the greatest methanol removal (ca. 90%) with minimal byproduct formation (i.e., effluent formaldehyde concentration was <1 ppmv). Based on these results, a 40 acfm pilot reactor was fabricated and achieved methanol removal rates up to 66% 7% with <1 ppmv formaldehyde production at steady state. 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source]

Palladium Nanowire from Precursor Nanowire: Crystal-to-Crystal Transformation via In,Situ Reduction by Polymer Matrix,

S. Porel
Abstract Precursor nanowires of potassium palladium(II) chloride crystallized inside a poly(vinyl alcohol) film are reduced to palladium nanowires by the polymer itself under mild thermal annealing. The chemical reaction occurring in situ inside the polymer film, including byproduct formation, is investigated through electronic absorption and X-ray photoelectron spectroscopy together with atomic force and electron microscopy. The overall process can be described as a novel case of crystal-to-crystal transformation at the nanoscopic level. Optical limiting characteristics of the nanowire-embedded polymer film are explored. The fabrication procedure developed, involving chemistry inside a polymer matrix mediated by the polymer, opens up a convenient route to the fabrication of free-standing metal nanowire-embedded thin films. [source]

Materials Issues Related to Catalysts for Treatment of Diesel Exhaust

Chaitanya K. Narula
The driver for lean NOx treatment is the need to meet regulatory standards for diesel engines and gasoline direct injection spark-ignited engines that offer better fuel economy. Efforts over the last decade have been focused toward finding an active lean NOx catalyst that can reduce NOx under oxidizing conditions or strategies such as selective catalytic reduction (SCR), plasma-catalysis, plasma catalyst SCR, and lean NOx traps with varying degrees of success. At present, it appears that SCR with urea and lean NOx traps are the leading contender technologies for commercial deployment. Key issues that remain to be resolved for these two technologies include byproduct formation, dosing control, and durability. In this review, we summarize material-related issues that are unique to each of these technologies, and point out the improvements necessary to facilitate their deployment. [source]

Novel Hemoglobins to Enhance Microaerobic Growth and Substrate Utilization in Escherichiacoli,

Christian J. T. Bollinger
Limited oxygen availability is a prevalent problem in microbial biotechnology. Recombinant Escherichia coli expressing the hemoglobin from Vitreoscilla (VHb) or the flavohemoglobin from Ralstonia eutropha (formerly Alcaligenes eutrophus) (FHP) demonstrate significantly increased cell growth and productivity under microaerobic conditions. We identify novel bacterial hemoglobin-like proteins and examine if these novel bacterial hemoglobins can elicit positive effects similar to VHb and FHP and if these hemoglobins alleviate oxygen limitation under microaerobic conditions when expressed in E. coli. Several finished and unfinished bacterial genomes were screened using R. eutropha FHP as a query sequence for genes (hmp) encoding hemoglobin-like proteins. Novel hmp genes were identified in Pseudomonas aeruginosa, Salmonella typhi, Klebsiellapneumoniae, Deinococcus radiodurans, and Campylobacter jejuni. Previously characterized hmp genes from E. coli and Bacillus subtilis and the novel hmpgenes from P. aeruginosa, S. typhi, C. jejuni, K.pneumoniae, and D. radiodurans were PCR amplified and introduced into a plasmid for expression in E. coli. Biochemically active hemoproteins were expressed in all constructs, as judged by the ability to abduct carbon monoxide. Growth behavior and byproduct formation of E. coli K-12 MG1655 cells expressing various hemoglobins were analyzed in microaerobic fed-batch cultivations and compared to plasmid-bearing control and to E. coli cells expressing VHb. The clones expressing hemoglobins from E. coli, D. radiodurans, P.aeruginosa, and S. typhi reached approximately 10%, 27%, 23%, and 36% higher final optical density values, respectively, relative to the plasmid bearing E. coli control (A600 5.5). E. coli cells expressing hemoproteins from P. aeruginosa, S. typhi, and D. radiodurans grew to similar final cell densities as did the strain expressing VHb (A600 7.5), although none of the novel constructs was able to outgrow the VHb-expressing E. coli strain. Additionally, increased yield of biomass on glucose was measured for all recombinant strains, and an approximately 2-fold yield enhancement was obtained with D.radiodurans hemoprotein-expressing E. colirelative to the E. coli control carrying the parental plasmid without any hemoglobin gene. [source]