This research was to evaluate the treatment efficiency of a chlorinated hydrocarbons contaminated site by combined technologies of electrokinetic processing-Fenton process-catalytic iron wall. The L9 orthogonal arrays were utilized to investigate the effects of four experimental factors (i.e., H2O2 concentration, size fraction of iron particles, mass of iron particles and elapsed time) on the treatment efficiency. The experimental results were further subjected to the analysis of variance (ANOVA) and regular analysis. According to the ANOVA of results of nine experiments conducted under an electric gradient of 1 V/cm, the H2O2 concentration, mass of iron particles and elapsed time were determined to be very significant parameters for the destruction and removal efficiency (DRE) of 1,1,2,2-tetrachloroethane (TeCA) . In this system, the optimal conditions with respect to the DRE of TeCA would be 2¢MH2O2, 50-100 mesh iron, 0.2 wt% iron and 20-day treatment time. Under this optimal conditions, it was able to obtain a DRE of 69.56% and the corresponding operating cost would be 672.9 NT$/m3. Aside from the constant voltage operation, the constant current operation also was employed in this study. The latter was found to be superior to the former in terms of electroosmotic flow quantity and DRE. Experimental results of soil column tests showed that TeCA was transformed to trichloroethylene (TCE). TCE could be regarded as a daughter product of TeCA degradation. Results of Tests 17 and 18 showed that destruction dominated the DRE of TeCA, whereas removal played a much more important role in the DRE of Test 19. Regarding the treatment efficiency of a 9-day pilot test using the same combined treatment technologies, it was found to be very satisfactory. DREs of vinyl chloride, dichloroethane, and TCE were found to be >96%, >96%, and >94%, respectively in the anode and cathode wells. The concentrations of TCE in both anode and cathode wells were found to be lower than the regulatory threshold (i.e., 2£gg/L) and the operating cost was determined to be about NT$57.5/m3.

In this work, the steady-state performance of zeolite-based Cu-ZSM-5, vanadium based honeycomb monolith catalysts (V), vanadium-titanium based pillared inter layered clay catalyst (V-Ti PLIC) and vanadium-titanium-tungsten-based honeycomb monolith catalysts (V-Ti-W) was investigated in the selective catalytic reduction process (SCR) for NO removal using NH3 in presence of oxygen. The objective is to obtain the expression that would predict the conversion performance of the catalysts for different values of the SCR process parameters, namely temperature, inlet oxygen concentration and inlet ammonia concentration. The NOx emission, its formation and control methods are discussed briefly and then the fundamentals of the SCR process are described. Heat transfer based and chemical kinetics based SCR process models are discussed and widely used rate order based model are reviewed. Based on the experimental data, regression analysis was performed that gives an expression for predicting the SCR rate for the complete temperature range and the rate order with respect to inlet oxygen and ammonia concentration. The average activation energy for the SCR process was calculated and optimum operating conditions were determined for each of the catalyst. The applicable operating range for the catalyst depends on the NO conversion as well as on the ammonia slip and the N2O and NO2 emission. The regression analysis was repeated for the applicable range and an expression was obtained that can be used to estimate the catalyst performance. For the Cu-ZSM-5, the best performance was observed for 400oC, 660 ppm inlet ammonia concentration and 0.1% inlet oxygen concentration. For the V based honeycomb monolith catalyst, the best performance was observed for 300oC, 264 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti based PLIC catalyst, the best performance was observed for 350oC, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti-W based honeycomb monolith catalyst, the best performance was observed for 300oC, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. The conversion performance of all of these catalysts is satisfactory for the industrial application. At the operating conditions listed above, the N2O emission is less than 20 ppm and the NO2 emission is less than 10 ppm. The results were validated by comparing the findings with the similar work by other research groups. The mechanism of SCR process is discussed for each of the catalyst. The probable reactions are listed and adsorption and desorption process are studied. The various mechanisms proposed by the researchers are discussed briefly. It is concluded that V-Ti-W and Cu-ZSM-5 catalyst are very promising for SCR of NOx. The expressions can be used to estimate the conversion performance and can be utilized for optimal design and operation. The expressions relate the SCR rate to the input parameters such as temperature and inlet oxygen and ammonia concentration hence by controlling these parameters desired NOx reduction can be achieved with minimal cost and emission.

No description available.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 72-81).

In recent years, the need for high performance power sources has increased dramatically with the proliferation of ultra-compact electronic systems for mobile communication, man-portable and versatile military equipment, and electric vehicles. Volume- and mass- based power density are two of the most important performance metrics for portable power sources, including hydrogen generating fuel reforming systems (onboard) for hydrogen fuel cells. Two innovative multifunctional reactor concepts, CO2/H2 Active Membrane Piston (CHAMP) and Direct Droplet Impingement Reactor (DDIR), are combined for the purpose of hydrogen generating fuel reforming system (onboard) for fuel cells. In CHAMP-DDIR, a liquid fuel mixture is pulse-injected onto the heated catalyst surface for rapid flash volatilization and on-the-spot reaction, and a hydrogen selective membrane is collocated with the catalyst to reduce the diffusion distance for hydrogen transport from the reaction zone to the separation site. CHAMP-DDIR allows dynamic variation of the reactor volume to optimally control the residence time and reactor conditions, such as pressure and temperature, thus improving both the reaction and separation processes. A comprehensive CHAMP-DDIR model, which couples key physical processes including 1) catalytic chemical reactions, 2) hydrogen separation/permeation at membrane, 3) liquid fuel evaporation, and 4) heat and mass transport, has been developed to investigate the behavior of this novel reactor system, aiming at maximizing the volumetric power density of hydrogen generation from methanol/water liquid fuel. The relationships between system design parameters and the rate-limiting process(es), i.e., reaction, permeation, and transport, which govern reactor output, have identified. Experimental characterization of the prototype reactor has been performed for laboratory demonstration of the concept and model validation. Both model predictions and experiments successfully demonstrate the unique practical performance improvements of CHAMP-DDIR through combining time-modulated fuel introduction and the active change of reactor volume/pressure. This work has led to a number of fundamental insights and development of engineering guidelines for design and operation of CHAMP-DDIR class of reactors, which can be extended to a broad range of fuels and diverse practical applications.

Mobile group II introns are retroelements that insert site-specifically into double-stranded DNA sites by a process called retrohoming. Retrohoming activity rests in a ribonucleoprotein (RNP) complex that contains an intron-encoded protein (IEP) and the excised intron RNA. The intron RNA uses its ribozyme activity to reverse splice into the top strand of the DNA target site, while the IEP cleaves the bottom DNA strand and reverse transcribes the inserted intron. My dissertation focuses on the Lactococcus lactis Ll.LtrB group II intron and its IEP, denoted LtrA. First, I investigated the ability of microinjected Ll.LtrB RNPs to retrohome into plasmid target sites in Drosophila melanogaster precellular blastoderm stage embryos. I found that injection of extra Mg2+ into the embryo was crucial for efficient retrohoming. Next, I compared retrohoming of linear and lariat forms of the intron RNP. Unlike lariat RNPs, retrohoming products of linear intron RNPs displayed heterogeneity at the 5’-intron insertion junction, including 5’-exon resection, intron truncation, and/or repair at regions of microhomology. To investigate whether these junctions result from cDNA ligation by non-homologous end-joining (NHEJ), I analyzed retrohoming of linear and lariat intron RNPs in D. melanogaster embryos with null mutations in the NHEJ genes lig4 and ku70, as well as the DNA repair polymerase polQ. I found that null mutations in each gene decreased retrohoming of linear compared to lariat intron RNPs. To determine whether novel activities of the LtrA protein contributed to the linear intron retrohoming 5’ junctions, I assayed the polymerase, non-templated nucleotide addition and template-switching activities of LtrA on oligonucleotide substrates mimicking the 5’-intron insertion junction in vitro. Although LtrA efficiently template switched to 5’-exon DNA substrates, the junctions produced differed from those observed in vivo, indicating that template switching is not a significant alternative to NHEJ in vivo. Finally, I designed and constructed retargeted Ll.LtrB RNPs to site-specifically insert into endogenous chromosomal DNA sites in D. melanogaster. I obtained intron integration efficiencies into chromosomal targets up to 0.4% in embryos and 0.021% in adult flies. These studies expand the utility of group II intron RNPs as gene targeting tools in model eukaryotic organisms. / text

Vanadium and molybdenum oxide catalysts have been prepared on different Ti02 supports by a variety of methods. Solutions of VOC13, VO(O'Bu)3 and MoOC14 were used to graft VOX and MoOX monolayers onto the supports in a single treatment. The other methods were intended to produce more than one monolayer (i. e. aqueous impregnation and multiple treatments of VOC13 and VO(O1Bu)3 ). TPR and Raman spectroscopy showed the formation above the monolayer of a phase denoted as disordered vanadium oxide, which has the same reducibility as the monolayer species but which has a band in the Raman spectrum at 995 cm-l. Raman spectroscopy also showed the formation of a disordered molybdenum oxide phase. With supports which contained phosphorus and potassium as impurities, TPR and Raman spectoscopy indicated a potassium-containing vanadium oxide, which was difficult to reduce and which showed no band at 995 cm-1. "Paracrystalline" V205 and MoO3 are formed when the oxide content exceeds four monolayers. XPS measurements confirm the dispersion of MOX species (M = V, Mo) on the surface of the support in the monolayer region; they also show that disordered and paracrystalline oxide phases occupy a limited area of the monolayer surface, but could not distinguish between them. ESR results showed 95% of the supported vanadium in the oxidation state +5. Phosphorus and potassium impurities in (or on) the TiO2 support influence the structure and catalytic properties of the VOX monolayer phase. In the case of catalysts made on supports with low impurities, activities in butadiene oxidation and isopropanol decomposition are principally due to the monolayer species and little contribution is made by the disordered or paracrystalli ne V205, while in the catalysts made on the supports with relatively high level of impurities, the activities in both reactions increase with V205 content in the region of one to four monolayers. MoOX catalysts showed low activities and selectivities in butadiene oxidation.

Στo πρώτο κεφάλαιο της εργασίας αυτής περιγράφεται η τεχνολογία που έχει αναπτυχθεί για την αντιμετώπιση των εκπομπών των αυτοκινήτων. Κατόπιν γίνεται μια ανασκόπηση των τεχνολογιών που εφαρμόζονται για τον έλεγχο των στάσιμων πηγών ρύπων, όπου η ποικιλία και η ποσότητα των εκπομπών είναι πολύ μεγάλη. Περιγράφονται επίσης οι φυσικές και χημικές αρχές στις οποίες βασίζεται μια διαδικασία καταλυτικού μετατροπέα. Οι καταλυτικοί μετατροπείς σχεδιάζονται με στόχο την ελαχιστοποίηση της συγκέντρωσης των ρυπογόνων αερίων, όπως αυτή καταγράφεται σε μια προκαθορισμένη θέση, κατά μήκος της συσκευής. Στο δεύτερο κεφάλαιο διατυπώνεται το σύστημα Μερικών Διαφορικών Εξισώσεων (Μ.Δ.Ε.) του βασικού προτύπου και εξετάζεται το πρόβλημα βέλτιστου ελέγχου που ελαχιστοποιεί την συνάρτηση κόστους J(S) με την επιλογή της βέλτιστης συνάρτησης ελέγχου S(t). Ο βέλτιστος έλεγχος είναι αυτός που ελαχιστοποιεί την παραγωγή των επικίνδυνων αερίων μέσω του καταλυτικού μετατροπέα. Το μαθηματικό πρότυπο προσεγγίζεται μέσω αναγωγής του στο πρόβλημα αρχικών και συνοριακών τιμών της εξίσωσης θερμότητας τόσο σε ημιάπειρο όσο και σε πεπερασμένο διάστημα, χρησιμοποιώντας τις κατάλληλες μεθόδους. Στη συνέχεια, στο Κεφάλαιο 3, που αποτελεί και το κεντρικό μέρος της παρούσας διατριβής, επιλύουμε το βασικό μοντέλο εξέλιξης της θερμοκρασίας του καταλυτικού μετατροπέα, μελετώντας την ομογενή εξίσωση θερμότητας σε μία διάσταση, με μη ομογενή αρχική συνθήκη και μη ομογενή συνοριακή συνθήκη. Αναφερόμαστε σε μεθόδους επίλυσης διαφορετικών περιπτώσεων, μέσω της μεθόδου Μετασχηματισμού Fourier Ημιτόνου και Μετασχηματισμού Fourier Συνημιτόνου και της μεθόδου του Μετασχηματισμού Laplace, διαφωτίζοντας κάθε μία με παραδείγματα που καταδεικνύουν τα προτερήματα και μειονεκτήματά τους. Μελετάμε κατόπιν μέσω της μεθόδου Χωριζομένων Μεταβλητών την μη ομογενή εξίσωση της θερμότητας σε πεπερασμένο διάστημα 0<x<L. Κατόπιν, χρησιμοποιώντας στοιχεία από την όλη θεωρία που περιγράφηκε, επιλύουμε αναλυτικά, στο τέλος του Κεφαλαίου 3, το γραμμικοποιημένο μοντέλο του καταλυτικού μετατροπέα, κοντά σε μια κατάσταση ισορροπίας του και συζητάμε τη σημασία της λύσης του για την μελέτη της λειτουργίας του καταλύτη. Αναγνωρίζοντας ότι η πλήρης αναλυτική λύση του μοντέλου δίνεται μέσω μαθηματικών εκφράσεων που είναι δύσκολο να υπολογισθούν απ’ευθείας, αναφερόμαστε στο Κεφάλαιο 4 σε ορισμένες πολύ σημαντικές αριθμητικές μεθόδους για την επίλυση της εξίσωσης της θερμότητας υπό διαφορετικές αρχικές και συνοριακές συνθήκες. Οι τεχνικές αυτές, που είναι γνωστές και ως μέθοδοι πεπερασμένων διαφορών, είναι επιτυχείς μόνο αν χαρακτηρίζονται από τις ιδιότητες της σύγκλισης (σε μοναδική λύση) και της ευστάθειας. Κλείνοντας το κεφάλαιο 4 παρουσιάζουμε το κριτήριο von Neumann μέσω του οποίου μπορεί να εξασφαλισθεί στα προβλήματα αυτά η ευστάθεια και επομένως και η σύγκλιση των εν λόγω αριθμητικών μεθόδων. Τέλος, τα συμπεράσματά μας παρουσιάζονται στο Κεφάλαιο 5. / Catalytic converters are designed with the goal of minimizing the concentration of the polluting gases emitted by automobiles. The developed catalytic converter technologies are described and a mathematical model for optimizing their function is presented. The mathematical model is based on the problem of initial and boundary conditions of the heat equation at the semi-infinite and finite space using the appropriate methods. Methods for solving different cases of the heat equation are sinus and cosine Fourier transform, Laplace transform and the method of divided variables. Using the theory described, we solve in detail the linear model of catalytic converter, close to a condition of balance. The meaning of its solution is studied for the function of the catalytic converter. Finally some very important arithmetic methods for the solution of the heat equation under different initial and boundary conditions are described. These methods are known as “methods of finite differences” and are successful only under the conditions of stability and convergence. The Von Neumann criterion is presented. Using this criterion the stability can be ensured, thus the convergence.

Biogas as a fuel is attractive from a greenhouse standpoint, since biogas is carbon neutral. To be used as such, increasingly stringent emission standards must be met. Current low-emission technologies meet said standards by precisely controlling the air-fuel ratio. Biogas composition can vary substantially, making air-fuel ratio control difficult. This research was conducted as part of a larger project to develop a sensor that accurately measures biogas composition. Biogas was simulated by fuel mixtures consisting of natural gas and CO2; the effects that fuel composition has on emissions and catalyst performance were investigated. Engine-out THC and NOx increased and decreased, respectively, with increasing CO2 in the fuel mixture. Doubling the catalyst residence time doubled the conversion of THC and CO emissions. The effectiveness of the catalyst at converting THC emissions was found to be dependent on the relative proportions of engine-out THC, NOx and CO emissions.

No description available.