Process intensification of nitrous gas absorption

The absorption of nitrogen oxides in water has important applications in nitric acid manufacture and pollution control. The design for optimum absorption efficiency and air pollution control has made necessary the installation of large reaction chambers and absorption towers for the adequate oxidation and absorption of nitrous gases. The worldwide production of weak acid has seen the progression of the process from the use of low through medium- to high-pressure technology in the efforts of achieving a more compact construction and avoiding the need for catalytic tail-gas treatment in plants with ever increasing capacities. Even at high pressures (8 bar), absorption columns employing sieve plates can reach up to 40 m in height for large-tonnage plants, and the relatively large pressure drop across the plates at these pressures leads to high power consumption and increased costs. As the dimensions of the absorption tower are typically governed by the conditions required for NO oxidation and thermal design, intensification of the process via miniaturisation can address the issues above through the high surface area to volume ratio offered by microreactor technology. The substantial improvement in heat and mass transfer due to the increase in effective exchange surface leads to an acceleration of the slow NO oxidation reaction and the enhancement of absorption rates. In addition to the development of such novel equipment for process intensification, the flow of the process can also be structured to improve process efficiency. An interesting method would be the replacement of the nitrogen ballast typically used in industry with steam, as the concentration of the gases upon condensation can lead to improved gas phase reaction rates. Furthermore, the provision of increased residence times due to the decrease in gas velocity upon condensation also makes the process more efficient. In this way, the size of the absorber can be significantly reduced and the high capital and operating costs associated with the employment of compressors in high pressure plants can be reduced. The objective of this thesis is to gain a fundamental understanding of the complex behaviour of nitric acid production in microchannels and obtain data for the development of a model used for process design and optimisation. Experiments on the oxidation and absorption of xviii nitrogen oxides have been conducted for a wide range of nominal residence times (0.03 – 1.4 s), gas compositions (5 – 10% NO, 5 – 49% O2, 46 – 82% H2O, balance argon), system pressures (2 – 10 bar absolute), mass fluxes (1.5 – 30 kg m-2 s-1), coolant mass fluxes (66 kg m-2 s-1 and 341 kg m-2 s-1), and coolant temperatures (23 – 51ºC) in circular tubes with internal diameters of 1.4 and 3.9 mm. Absorption efficiencies of up to 99% have been achieved without the use of counter-current flow typically employed in conventional nitric acid plants. The use high steam fractions was shown to cause significant improvements in gas phase reaction rates such that the usual industrial practice of applying high system pressures to enhance the NO oxidation reaction becomes unnecessary. Absorption efficiency can also be increased by increasing system pressures, but there are certain limits to which this can be done; a decline in performance may result when pressures are increased sufficiently high such that mass transfer becomes limiting. In addition to decreasing the tube diameter, increasing both the NO concentration and cooling duty also led to improved nitric acid yields. A simple model of condensing two-phase shear-driven annular flows, in which both laminar and turbulent regimes are valid and the vapour-liquid interface is assumed to be smooth, have been constructed and compared against experimental data. The model qualitatively captures most of the effects observed, but the presence of uncertainties in model parameters and the use of particular assumptions on the flow pattern and structure of the interface had to be compensated for through the use of a model fitted parameter iAθ. Larger corrections to the model were required in cases where the fluid was tending towards slug or plug flow, such as systems employing high H2O/NO ratios, since the interfacial area between vapour and liquid would be larger than that obtained if annular flow was assumed to occur under the same conditions. Higher values of iAθwere also found to give better fit to the experimental data at short nominal residence times (< 0.10 s) for absorption carried out under high system pressures, high oxygen partial pressures or high NO partial pressures, presumably due to incorrect representation of the overall heat and mass transfer flux under these conditions, among other things such as the parameter uncertainties, the presence of interfacial waves and the possibility of a flow regime transition from annular to intermittent flow. On the other hand, interfacial area multipliers less than unity were better suited to larger xix channels due to the possibility of flow stratification which acts to decrease the interfacial area and hence the nitric acid yield. The predictions of the model were subsequently used to determine the operating conditions optimal for the production of nitric acid in microreactors on a larger scale. In most of the cases considered, the pressure drop across the absorber length was found to be relatively small, hence much smaller channels can be utilised for increased absorption efficiency without considerable loss in pressure. It was also shown that most of the heat liberated near the inlet of the absorber stems from the release of latent heat of condensation, while chemical reactions account for most of the heat released downstream of the reactor. The absorption volume required for the commercial production of nitric acid in microchannels was compared against that typically employed by current industrial absorbers. The volume of the microreactor system was found to be about 2 orders of magnitude smaller than its larger counterpart. Although additional volume may be required for distillation of the weaker acid produced from the smaller system, substantial reduction in plant size can still be achieved since the volume of the cooler-condenser was excluded from the industrial plant calculations while the physical and chemical reactions involved in the cooler-condenser are already inherent in the microreactor system. In summary, the results of the experiments and model simulations have demonstrated that the absorption of nitrous gases in microchannels with the use of a steam ballast and close-to-stoichiometric quantities of oxygen can lead to intensification of the process, thus presenting an opportunity for a paradigm shift in nitric acid production

On a conjecture of Huang--Lian--Yau--Yu

We verify a formula on the solution rank of the tautological system arising from ample complete intersections in a projective homogeneous space of a semisimple group conjectured by Huang--Lian--Yau--Yu arXiv:1801.01194. As an application, we prove the existence of the rank one point for such a system, where mirror symmetry is expected.Comment: 8 pages. Comments are welcom

Considerable MHC Diversity Suggests That the Functional Extinction of Baiji Is Not Related to Population Genetic Collapse

To further extend our understanding of the mechanism causing the current nearly extinct status of the baiji (Lipotes vexillifer), one of the most critically endangered species in the world, genetic diversity at the major histocompatibility complex (MHC) class II DRB locus was investigated in the baiji. Nine highly divergent DRB alleles were identified in 17 samples, with an average of 28.4 (13.2%) nucleotide difference and 16.7 (23.5%) amino acid difference between alleles. The unexpectedly high levels of DRB allelic diversity in the baiji may partly be attributable to its evolutionary adaptations to the freshwater environment which is regarded to have a higher parasite diversity compared to the marine environment. In addition, balancing selection was found to be the main mechanisms in generating sequence diversity at baiji DRB gene. Considerable sequence variation at the adaptive MHC genes despite of significant loss of neutral genetic variation in baiji genome might suggest that intense selection has overpowered random genetic drift as the main evolutionary forces, which further suggested that the critically endangered or nearly extinct status of the baiji is not an outcome of genetic collapse

Prognostic implications of plasma fibrinogen and serum Creactive protein levels in non-small cell lung cancer resection and survival

Purpose: To investigate the prognostic implications of plasma fibrinogen and serum C-reactive protein (CRP) levels in tumour resection and survival following successful tumour resection in patients with nonsmall cell lung cancer (NSCLC).Methods: One hundred and fifty-three NSCLC patients who underwent surgical resection at a tertiary care hospital from January 2006 through December 2010 were enrolled. Pre-operative serum CRP and plasma fibrinogen levels were  measured. The levels of these biomarkers correlated with tumour size and pathologic TNM stage. The possibility of complete resection and associated findings are reported.Results: Plasma fibrinogen (r = 0.381, p = 0.002) and serum CRP (r = 0.471, p &lt; 0.001) levels were positively associated with tumour diameter. Increased levels of these biomarkers were significantly associated with sex, smoking status, histological type, tumour stage, and clinical stage. Partial tumour resection occurred in 28 % (27/95) of patients with an increased plasma fibrinogen level compared to 10 % (6/58) with a normal fibrinogen level (p = 0.008), and in 30 % (29/97) of patients with an increased serum CRP level compared to 11 % (6/56) with a normal CRP level (p = 0.006). Patients with elevated CRP and fibrinogen concentrations demonstrated higher susceptibility to disease advancement andsurvival compared to patients with normal fibrinogen and CRP levels.Conclusion: Pre-operative functional concentrations of serum CRP and plasma fibrinogen could serve as indicators of tumour resectability wherein a high tumour resection rate is possible in patients with favourable pre-operative levels of these biomarkers. Increased concentrations of serum CRP and plasma fibrinogen are associated with poor overall survival and progression-free survival.Key words: Plasma fibrinogen, serum C-reactive protein, biomarker, non-small cell lung cance

Genetic structure of glyphosate-resistant ( R ) and glyphosate-susceptible ( S ) populations of Eleusine indica (L.) Gaertn from Peninsular Malaysia

Glyphosate is the world’s most widely used herbicide, accounting for 11 % of worldwide herbicide sales (Powles et al., 1997). As a nonselective herbicide with no soil activity (Grossbard & Atkinson 1985), it is an ideal herbicide to control a broad range of weed species. In Malaysia, glyphosate is used to control various weed species growing in oil palm and rubber plantations. In some instances, multiple treatments have been carried out continuously for several years

Allele Size Miscalling due to the Pull-Up Effect Influencing Size Standard Calibration in Capillary Electrophoresis: A Case Study Using HEX Fluorescent Dye in Microsatellites

Microsatellites are important genetic markers and have been broadly employed in many genetic studies. Currently, polymorphisms in microsatellites are often detected by an automated system of capillary electrophoresis with fluorescent dyes. In this situation, different dye combinations may cause pull-up/bleed-through problems, which introduce noise signals from one dye channel into another, causing genotyping errors. Here, we report the detection of such a problem at two microsatellite loci that used the HEX dye. Using three datasets, we tested for noise effects in four allele-scoring programmes: Genemapper, Genemarker, Gelquest and Fragman. We found that, because some allele sizes were identical or close to the size of one of the internal size standards, all four programmes gave allele size calling errors due to wrongly identifying pull-up signals as the internal size standard. In addition, because allele miscalling in this study was caused by the fluorescent dye that the microsatellites used introducing noise of the same colour as the internal size standard used, the pull-up correction function in Genemapper, Genemarker and Fragman failed to deal with this. Considering that pull-up peak scoring errors can occur with any dye colour, the phenomenon is not limited to the current HEX dye. Using different software and visual scoring of each result will allow accurate sizing of microsatellite alleles

Application of semiochemical releasers and intercropping to control aphid and related virus in east China

Peer reviewe

Transcriptome profiling of the fifth-stage larvae of Angiostrongylus cantonensis by next-generation sequencing

Angiostrongylus cantonensis is an important zoonotic nematode. It is the causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. However, information of this parasite at the genomic level is very limited. In the present study, the transcriptomic profiles of the fifth-stage larvae (L5) of A. cantonensis were investigated by next-generation sequencing (NGS). In the NGS database established from the larvae isolated from the brain of Sprague–Dawley rats, 31,487 unique genes with a mean length of 617 nucleotides were assembled. These genes were found to have a 46.08 % significant similarity to Caenorhabditis elegans by BLASTx. They were then compared with the expressed sequence tags of 18 other nematodes, and significant matches of 36.09–59.12 % were found. Among these genes, 3,338 were found to participate in 124 Kyoto Encyclopedia of Genes and Genomes pathways. These pathways included 1,514 metabolisms, 846 genetic information processing, 358 environmental information processing, 264 cellular processes, and 91 organismal systems. Analysis of 30,816 sequences with the gene ontology database indicated that their annotations included 5,656 biological processes (3,364 cellular processes, 3,061 developmental processes, and 3,191 multicellular organismal processes), 7,218 molecular functions (4,597 binding and 3,084 catalytic activities), and 4,719 cellular components (4,459 cell parts and 4,466 cells). Moreover, stress-related genes (112 heat stress and 33 oxidation stress) and genes for proteases (159) were not uncommon. This study is the first NGS-based study to set up a transcriptomic database of A. cantonensis L5. The results provide new insights into the survival, development, and host–parasite interactions of this blood-feeding nematode. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00436-013-3495-z) contains supplementary material, which is available to authorized users