A comprehensive study on carbon dioxide reforming of methane over Ni/gamma-Al2O3 catalysts

Carbon dioxide reforming of methane into syngas over Ni/gamma-Al2O3 catalysts was systematically studied. Effects of reaction parameters on catalytic activity and carbon deposition over Ni/gamma-Al2O3 catalysts were investigated. It is found that reduced NiA1204, metal nickel, and active species of carbon deposited were the active sites for this reaction. Carbon deposition on Ni/gamma Al2O3 varied depending on the nickel loading and reaction temperature and is the major cause of catalyst deactivation. Higher nickel loading produced more coke on the catalysts, resulting in rapid deactivation and plugging of the reactor. At 5 wt % Ni/gamma-Al2O3 catalyst exhibited high activity and much lesser magnitude of deactivation in 140 h. Characterization of carbon deposits on the catalyst surface revealed that there are two kinds of carbon species (oxidized and -C-C-) formed during the reaction and they showed different reactivities toward hydrogenation and oxidation. Kinetic studies showed that the activation energy for CO production in this reaction amounted to 80 kJ/mol and the rate of CO production could be described by a Langmuir-Hinshelwood model.

Gas-phase photocatalytic oxidation of volatile organic compounds

Substances emitted into the atmosphere by human activities in urban and industrial areas cause environmental problems such as air quality degradation, respiratory diseases, climate change, global warming, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air pollutants, emitted largely by industry, transportation and households. Many VOCs are toxic, and some are considered to be carcinogenic, mutagenic, or teratogenic. A wide spectrum of VOCs is readily oxidized photocatalytically. Photocatalytic oxidation (PCO) over titanium dioxide may present a potential alternative to air treatment strategies currently in use, such as adsorption and thermal treatment, due to its advantageous activity under ambient conditions, although higher but still mild temperatures may also be applied. The objective of the present research was to disclose routes of chemical reactions, estimate the kinetics and the sensitivity of gas-phase PCO to reaction conditions in respect of air pollutants containing heteroatoms in their molecules. Deactivation of the photocatalyst and restoration of its activity was also taken under consideration to assess the practical possibility of the application of PCO to the treatment of air polluted with VOCs. UV-irradiated titanium dioxide was selected as a photocatalyst for its chemical inertness, non-toxic character and low cost. In the present work Degussa P25 TiO2 photocatalyst was mostly used. In transient studies platinized TiO2 was also studied. The experimental research into PCO of following VOCs was undertaken: - methyl tert-butyl ether (MTBE) as the basic oxygenated motor fuel additive and, thus, a major non-biodegradable pollutant of groundwater; - tert-butyl alcohol (TBA) as the primary product of MTBE hydrolysis and PCO; - ethyl mercaptan (ethanethiol) as one of the reduced sulphur pungent air pollutants in the pulp-and-paper industry; - methylamine (MA) and dimethylamine (DMA) as the amino compounds often emitted by various industries. The PCO of VOCs was studied using a continuous-flow mode. The PCO of MTBE and TBA was also studied by transient mode, in which carbon dioxide, water, and acetone were identified as the main gas-phase products. The volatile products of thermal catalytic oxidation (TCO) of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Continuous PCO of 4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both LH and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

Hydrogenation of L-arabinose, D-galactose, D-maltose and L-rhamnose

Under de senaste åren har intresset för utnyttjandet av förnybara resurser kraftigt ökat. I samband med detta utgör kolhydrater en viktig del av den tillgängliga förnybara biomassan och den har därefter blivit föremål för ett stort intresse inom hållbar kemi. Sockeralkoholer är en särskilt viktig grupp av molekyler som vanligtvis erhålls ur kolhydrater och som har mångsidiga tillämpningar som t.ex. lågkalorihaltiga sötningsmedel. Forskningen i doktorsarbetet omfattar hydreringen av naturligt förekommande sockerarter L-arabinos, D-galaktos, D-maltos och L-ramnos till respektive sockeralkoholer. Dessa sockeralkoholer kan användas bl.a. som hälsosamma sötningsmedel på samma sätt som xylitol. Grunden för detta arbete består av hydreringsexperiment som utfördes på en dispergerad ruteniumkatalysator i syfte att studera bildningskinetiken av de motsvarande sockeralkoholerna. Reaktionerna genomfördes vid temperaturer mellan 90 och 130 °C och vätetryck mellan 40 och 60 bar. Under dessa betingelser var det möjligt att åstadkomma sockeromvandlingar upp till 100 %. Reaktionshastigheterna modellerades matematiskt. Konkurrerande kinetiska modeller som baserades på Langmuir-Hinshelwood-konceptet föreslogs för att beskriva reaktionerna. Parametrar i hastighetsekvationerna bestämdes därefter genom icke-linjär regression. Dessa modeller kunde väl förutsäga hydreringsreaktionernas förlopp och de kan följaktligen användas för design av industriella anläggningar. Ytterligare hydreringsexperiment med sockerblandningar genomfördes för att fördjupa kunskaper i kinetik och reaktionsmekanismer av sockerhydreringen. Studierna genomfördes med syntetiska sockerblandningar av L-arabinos och D-galaktos (de viktigaste komponenterna i hemicellulosan arabinogalaktan). Fullständig omsättning uppnåddes med utmärkta selektiviteter som överskred 95 % och dessutom inverkade varken temperatur eller vätetryck på reaktionens förlopp på något oväntat sätt. Antagandet av konkurrerande adsorption för en samtidig reduktion av båda sockermolekylerna gav en kinetisk modell som noggrant beskrev de experimentella resultaten. Idén om att utforska potentiella sätt att påskynda bildningen av sockeralkoholer ledde till utföringen av hydreringsexperiment med L-arabinos och D-galaktos i närvaro av ultraljud. Det visade sig att ultraljudets inverkan var oberoende av sockerhalten och vätetrycket och att bestrålningen gynnade hydreringen av D-galaktos trots att den inte förhindrade Ru/C-katalysatorns deaktivering överhuvudtaget. En kinetisk modell som beaktade deaktiveringen utvecklades. Kontinuerlig hydrering av L-arabinos genomfördes med tre olika Ru-katalysatorer på tre olika bärare: tyg av aktivt kol, kolnanorör på svampliknande metalliska strukturer samt krossade partiklar av en kommersiell Ru/C-katalysator. Det visade sig att det var möjligt att omvandla L-arabinos till arabitol med höga selektiviteter med hjälp av Ru/koltyg-katalysatorn. Dessa experiment demonstrerade att hydreringen av de valda sockerarterna är en helt genomförbar rutt till framställning av fin- och specialkemikalier, som kan förverkligas i större skala.

Photocatalytic degradation of humic acid in saline waters. Part 1. Artificial seawater: influence of TiO2, temperature, pH, and air-flow

We report the first systematic study on the photocatalytic oxidation of humic acid (HA) in artificial seawater (ASW). TiO2 (Degussa P25) dispersions were used as the catalyst with irradiation from a medium-pressure mercury lamp. The optimum quantity of catalyst was found to be between 2 and 2.5 g l(-1); whiled the decomposition was fastest at low pH values (pH 4.5 in the range examined), and the optimum air-flow, using an immersion well reactor with a capacity of 400 ml, was 850 ml min(-1). Reactivity increased with air-flow up to this figure, above which foaming prevented operation of the reactor. Using pure. oxygen, an optimal flow rate was observed at 300 nil min(-1), above which reactivity remains essentially constant. Following treatment for 1 h, low-salinity water (2700 mg l(-1)) was completely mineralised, whereas ASW (46000 mg l(-1)) had traces of HA remaining. These effects are interpreted and kinetic data presented. To avoid problems of precipitation due to change of ionic strength humic substances were prepared directly in ASW, and the effects of ASW on catalyst suspension and precipitation have been taken into account. The Langmuir-Hinshelwood kinetic model has been shown to be followed only approximately for the catalytic oxidation of HA in ASW. The activation energy for the reaction derived from an Arrhenius treatment was 17 ( +/-0.6) kJ mol(-1). (C) 2003 Elsevier Science Ltd. All rights reserved.

The impact of water concentration on the catalytic oxidation of ethanol on platinum electrode in concentrated phosphoric acid

The electro-oxidation of ethanol on platinum in phosphoric acid opens the door to promote the oxidation reaction at higher temperatures. However, the effect of the presence of water is not well understood. In this work, the electro-oxidation of ethanol on platinum was studied in concentrated phosphoric acid containing different concentrations of water at room temperature. The results show that effect of bulk water on the rate electro-oxidation is highest at 0.60 V and decreases for increasing potentials. This was suggested as due to the increasing formation of oxygenated species on the electrode surface with potential, which in turn is more efficient than the increase of water content in the electrolyte. Altogether, these results were interpreted as an evidence of a Langmuir-Hinshelwood step involving oxygenated species as one of the adsorbed partners. (C) 2009 Elsevier B.V. All rights reserved.

TiO(2)-PHOTOCATALYZED DEGRADATION OF PHENOL IN SALINE MEDIA IN AN ANNULAR REACTOR: HYDRODYNAMICS, LUMPED KINETICS, INTERMEDIATES, AND ACUTE TOXICITY

The photocatalytic degradation of phenol in aqueous suspensions of TiO(2) under different salt concentrations in an annular reactor has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. The reactor operational parameters were optimized and its hydrodynamics characterized in order to couple mass balance equations with kinetic ones. The photodegradation of the organics followed a Langmuir-Hinshelwood-Hougen- Watson lumped kinetics. From GC/MS analyses, several intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 3-phenyl-2-propenal, in this order. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity was determined by using Artemia sp. as the test organism, which indicated that intermediate products were all less toxic than phenol and a significant abatement of the overall toxicity was accomplished, regardless of the salt concentration.

Avaliação de catalisadores a base de carbeto e nitreto de molibdênio na obtenção de lactitol via hidrogenação da lactose

Seeking a greater appreciation of cheese whey was developed to process the hydrogenation of lactose for the production of lactitol, a polyol with high added value, using the catalyst Ni / activated carbon (15% and 20% nickel), the nitride Mo2N, the bimetallic carbide Ni-Mo/ activated carbon and carbide Mo2C. After synthesis, the prepared catalysts were analyzed by MEV, XRD, laser granulometry and B.E.T. The reactor used in catalytic hydrogenation of lactose was the type of bed mud with a pressure (68 atm), temperature (120 oC) and stirring speed (500 rpm) remained constant during the experiments. The system operated in batch mode for the solid and liquid and semi-continuous to gas. Besides the nature of the catalyst, we studied the influence of pH of reaction medium for Mo2C carbide as well as evaluating the character of the protein inhibitor and chloride ions on the activity of catalysts Ni (20%)/Activated Carbon and bimetallic carbide Ni-Mo/Activated Carbon. The decrease in protein levels was performed by coagulation with chitosan and adsorption of chloride ions was performed by ion exchange resins. In the process of protein adsorption and chloride ions, the maximum percentage extracted was about 74% and 79% respectively. The micrographs of the powders of Mo2C and Mo2N presented in the form of homogeneous clusters, whereas for the catalysts supported on activated carbon, microporous structure proved impregnated with small particles indicating the presence of metal. The results showed high conversion of lactose to lactitol 90% for the catalyst Ni (20%)/Activated Carbon at pH 6 and 46% for the carbide Mo2C pH 8 (after addition of NH4OH) using the commercial lactose. Monitoring the evolution of the constituents present in the reaction medium was made by liquid chromatography. A kinetic model of heterogeneous Langmuir Hinshelwood type was developed which showed that the estimated constants based catalysts promoted carbide and nitride with a certain speed the adsorption, desorption and production of lactitol

Studies on the adsorption and kinetics of photodegradation of a model compound for heterogeneous photocatalysis onto TiO2

An investigation was made on the adsorption and kinetics of photodegradation of potassium hydrogenphthalate in an aqueous suspension of TiO2. Two models, Langmuir and Freundlich, were used to describe the adsorption process and the model proposed by Langmuir-Hinshelwood (L-H) was employed to describe the kinetics of the photodecomposition reactions of hydrogenphthalate. The results of the adsorptions were fitted to the models proposed by Langmuir and Freundlich. Adsorption was found to be a function of the temperature, with adsorption capacity increasing from 2.4 to 4.5 mg/g when the temperature rose from 20 to 30 degrees C. The kinetic model indicates that the rate constant, k, of the first order reaction, is high in the 10.0 to 100 mg/l interval, which is coherent with the low value of the adsorption constant, K. The results fitted to the L-H model led to an equation that, within the range of concentrations studied here, theoretically allows one to evaluate the photodegradation rate. (c) 2005 Elsevier Ltd. All rights reserved.

Aspetti fondamentali per l'analisi cinetica di reazioni fotocatalitiche.

La conoscenza e la determinazione dell’equazione cinetica è indispensabile per lo studio, la progettazione e l’ottimizzazione di qualsiasi reattore chimico. Normalmente l’analisi cinetica viene eseguita con reattori che operano in maniera quanto più prossima a condizioni ideali in modo da rendere più facile e meno affetta da errori l’interpretazione dei risultati sperimentali. In fotocatalisi è invece di fatto impossibile realizzare, anche in presenza di una perfetta miscelazione, un sistema ideale in cui si abbia un’uniforme distribuzione di tutti i parametri che influenzano la velocità di reazione. Infatti in un reattore fotocatalitico il campo di radiazione è intrinsecamente non uniforme poiché l’assorbimento della radiazione e quindi la sua attenuazione sono necessari per l’attivazione della reazione. Pertanto l’impossibilità di realizzare un sistema fotocatalitico che operi in condizioni quanto più possibile prossime all’idealità e l’incapacità di misurare sperimentalmente i valori locali di velocità di reazione e di velocità di assorbimento dei fotoni possono rendere complessa una corretta analisi cinetica. In questo lavoro vengono studiate le modalità con cui condurre comunque una rigorosa analisi cinetica di un sistema fotocatalitico slurry, nel quale il fotocalizzatore è disperso come polvere fine in sospensione nella soluzione reagente. La reazione studiata è quella di mineralizzazione dell’acido formico. Sono stati impiegati due reattori con geometrie ed illuminazioni differenti: un reattore piano illuminato con luci LED ed un reattore anulare con lampada lineare fluorescente blacklight. È stata verificata la validità di una particolare equazione cinetica, che tiene conto dell’effetto non lineare della velocità specifica (cioè per unità di massa di catalizzatore) di assorbimento dei fotoni e delle concentrazioni del reagente, dell’ossigeno e del fotocatalizzatore. Sono state inoltre determinate le condizioni critiche che possono portare ad errori nell’analisi cinetica ed è stata dimostrata l’utilità di un modello matematico che tiene conto dei bilanci di energia raggiante, di materia nonché del campo di moto. Il modello matematico, in cui compare un solo parametro aggiustabile (il tempo caratteristico di reazione od equivalentemente la costante cinetica), è in grado di riprodurre molto soddisfacentemente i risultati sperimentali in tutte le diverse condizioni operative: diversa geometria di reattore, diversa illuminazione, differente spessore ottico, diverse contrazioni di substrato e di fotocatalizzatore. Infine è stato mostrato come l’equazione cinetica ad una sola costante cinetica, che è stata adottata, descriva meglio la cinetica della reazione fotocatalitica in esame di altre equazioni a due o più costanti cinetiche spesso utilizzate in fotocatalisi e basate sulla teoria di Langmuir-Hinshelwood, a dimostrazione di un diverso meccanismo di reazione.

Proceedings of the Fifth Biochemical Engineering Symposium

This report presents the proceedings of the Biochemical Engineering Symposium held at Kansas State University, April 26, 1975. Since a number of the contributions will be published in detail elsewhere, only brief summaries of each contribution are included here. Requests for additional information on projects conducted at Iowa State University should be directed to Dr. Peter J. Reilly, and those at Kansas State University to the editors. Contents"Enzymatic Breakdown of Hemicellulose," Alfred R. Fratzke, Iowa State University "Biochemical Aspects of Hydrocarbon Uptake in Hydrocarbon Fermentations," Tadaatsu Nakahara, Kansas State University "Optimal Concentration Profiles for Bifunctional Catalysts with Langmuir-Hinshelwood Kinetics and Varying Effectiveness Factors," Ho Nam Chang, Iowa State University "Single Cell Protein Production from Hydrocarbons in Tower Systems," J. R. Gutierrez, Kansas State University "Effect of Temperature and pH on the Stability and Activity of Immobilized Glucoamylase and Glucose Isomerase," Gene K. Lee, Iowa State University "Oxygen Transfer in a Tower System with Two Liquid Phases," G. T. MacLean, Kansas State University "Continuous Production of Glucose from Dextrin by Glucoamylase Immlobilized on Porous Silica," Douglas D. Lee, Iowa State University

Photocatalytic decomposition of organophosphonates and fluorophenols in irradiated titanium dioxide suspensions

Dimethyl methyl phosphonate (DMMP), diethyl methyl phosphonate (DEMP), and fluorophenols undergo rapid decomposition upon TiO$\sb2$ catalyzed photooxidation in air saturated aqueous solution. The degradation rates of DMMP were determined over a range of temperatures, under solar and artificial irradiation with and without simultaneous sonication. Solar illumination is effective for the degradation and the use of low energy of sonication increases the rate of mineralization. The surface area and the type of TiO$\sb2$ dramatically affect the photoactivity of the catalyst. A number of intermediate products are formed and ultimately oxidized to phosphate and carbon dioxide. Possible reaction mechanisms and pathways for DMMP and DEMP are proposed. The Langmuir-Hinshelwood kinetic parameters for the photocatalysis of fluorophenols suggest modestly different reactivity for each isomer. The adsorption constant is largest for the ortho isomer consistent with the adsorption onto TiO$\sb2$ through both hydroxyl and fluoride groups to form a chelated type structure. ^

Photocatalytic decomposition of organophosphonates fluorophenols in irradiated titanium dioxide suspensions

Dimethyl methyl phosphonate (DMMP), diethyl methyl phosphonate (DEMP), and fluorophenols undergo rapid decomposition upon TiO2 catalyzed photooxidation in air saturated aqueous solution. The degradation rates of DMMP were determined over a range of temperatures, under solar and artificial irradiation with and without simultaneous sonication. Solar illumination is effective for the degradation and the use of low energy of sonication increases the rate of mineralization. The surface area and the type of TiO2 dramatically affect the photoactivity of the catalyst. A number of intermediate products are formed and ultimately oxidized to phosphate and carbon dioxide. Possible reaction mechanisms and pathways for DMMP and DEMP are proposed. The Langmuir- Hinshelwood kinetic parameters for the photocatalysis of fluorophenols suggest modestly different reactivity for each isomer. The adsorption constant is largest for the ortho isomer consistent with the adsorption onto TiO2 through both hydroxyl and fluoride groups to form a chelated type structure.

Estudo cinético do branqueamento do óleo da carpa (Cyprinus carpio L)

O óleo de pescado é caracterizado por ser uma fonte rica de ácidos graxos poliinsaturados ω-3, desde modo a sua oxidação lipídica se torna mais favorável quando comparado com outros óleos de origem vegetal. O objetivo do presente trabalho foi a otimização da etapa de branqueamento através da metodologia de superfície de resposta, sendo utilizado misturas de carvão ativado e terra ativada (Tonsil) para a remoção da cor e dos produtos de oxidação, procurando-se preservar o conteúdo total de carotenóides no óleo de carpa. O óleo bruto de carpa (Cyprinus carpio L.) para a realização do trabalho foi obtido a partir da realização de ensilagem ácida, passando posteriormente pelas etapas de refino: degomagem, neutralização, lavagem, secagem e branqueamento. A otimização da etapa de branqueamento foi realizada através de um planejamento fatorial composto central, com os fatores de estudo: a quantidade de adsorvente (Ads) e a quantidade de carvão ativado (Ca), sendo consideradas como respostas o conteúdo total de carotenóides e o valor de TBA. Na melhor condição do branqueamento do óleo de carpa foi realizado um estudo cinético, e para o cálculo das constantes cinéticas foram utilizados os modelos de Brimberg modificado e de Langmuir-Hinshelwood, A condição ótima do branqueamento foi com 2% de adsorvente e 10% de carvão ativado, onde ocorreram menores perdas de carotenóides (44,40%), com redução da cor escura presente no óleo de (85,62%) e redução do valor de TBA (73,10%), obtendo-se um óleo branqueado de carpa com qualidade oxidativa e melhor aspecto em relação à cor. Os dois modelos cinéticos representaram de forma satisfatória os dados experimentais do branqueamento do óleo de carpa, pelos altos coeficientes de determinação e baixos erros médios relativos apresentados. Foi possível observar que ocorreu uma rápida adsorção dos pigmentos carotenóides, e após 30 min a adsorção foi menos eficiente. Nos óleos bruto e branqueado de vísceras de carpa não foi identificada diferença significativa entre as concentrações de ácidos graxos, demonstrando que as etapas de refino utilizadas não alteraram o perfil de ácidos graxos do óleo bruto.

Alignment of hexatic langmuir monolayers under shear

We have studied the structural changes that fatty acid monolayers in the Ov phase undergo when a simple shear flow is imposed. A strong coupling is revealed by the changes in domain structure that are observable using Brewster angle microscopy, suggesting the possibility of shear alignment. The dependence of the alignment on the molecular polar tilt proves that the mechanism is different than in nematic liquid crystals. We argue that the degenerate lattice symmetry lines of the underlying pseudohexagonal lattice align in the flow direction, and we explain the observed alignment angle using geometrical arguments.