Effect of Nitrate and Sulfate Contamination on Degradation of Diuron via Electrochemical Advanced Oxidation in a Microreactor

The degradation of diuron, which is a toxic herbicide that causes a serious environmental problem in many countries, was performed using electrochemical advanced oxidation process (EAOP) in a microreactor. The influence of nitrate and sulfate contamination on the degradation was investigated. The experimental results clearly indicate that both nitrate and sulfate ions retard diuron degradation. Under the applied current of 1 mA, about 91% of diuron in deionized water is degraded within 100 s of residence time, while the degradation achieved is 79% and 76% when nitrate and sulfate ions are presented in the solution at concentration of 50 mM, respectively. Both ions behave as a scavenger for the reactive hydroxyl radical, although other mechanisms might also involve causing this retarding effect. Nitrate ion participates in diuron degradation causing new reaction pathways, while sulfate does not interfere with the diuron degradation pathway. The presence of ion in the solution also shifts the degradation route from one route to another

Dependence of Catalyst Surface in Photocatalytic Degradation of Phenyl Urea Herbicides

Photocatalytic degradations of various contaminants using in-house synthesized catalysts have been generally reported, but the degradation intermediates formed are normally inconsistent. This issue is particularly important for the degradation of toxic compounds which may form intermediates with increased toxicity. This work resolves this issue by systematically investigating adsorption and photocatalytic degradation of diuron, linuron, and 3,4-dichloroaniline (DCA) on two forms of zinc oxide (ZnO), i.e., conventional particles with zinc- and oxygen-terminated polar surfaces, and nanorods with mixed-terminated non-polar surfaces. Experimental results indicate that both rate of degradation and degradation pathway depend upon the adsorption configuration of the compound undergoing the degradation onto the surface of the catalyst. The adsorption configuration is surface dependent. On polar surfaces, both aliphatic and aromatic sides of diuron and linuron molecules adsorb on the surface, allowing the attack of hydroxyl radicals on both ends. On the other hand, on non-polar surface, only the aliphatic chain adsorbs onto the surface, resulting in the hydroxyl radicals attack only on the aliphatic side. The structure of the catalyst is therefore a crucial factor determining the dominant degradation pathway

Physical and numerical approximations of reactive distillation dynamics

Two approaches to reduce computational requirements for solving reactive distillation problems have been studied: simplification of the model using physical assumptions and numerical approximation using an orthogonal collocation technique. The results of a full-order model with time dependent stage molar holdups was compared to published steady-state experimental data and was found to be more accurate than previously published methods. Two example problems concerning reactive distillation columns with different number of stages were investigated in order to find limitations of the order-reduction technique. The steady-state results obtained in both cases were remarkably accurate, even though the reduced-order model contained only 40 percent of the number of equations. However, step and pulse responses indicated that very low order models did not provide good approximations in the dynamic behavior of a column which contained 29 stages. Modeling errors introduced by either physical or numerical approximations were compared for several example problems. The results showed that the reduced-order models with time-dependent holdups provided better steady-state and dynamic results than models using the physical approximation of constant molar holdups in almost every case. The only case in which the reduced-order model failed was when the 40% order-reduction model was used to approximate dynamic responses of a column with a significant pressure drop across each tray. The effects of plate and weir geometries were also studied. The results obtained indicated that the volume holdup on the plate was the dominant parameter: columns with plates of different sizes but the same steady-state holdup behaved similarly

Effect of Type of Metals on Site Selective Dehydrogenation of Stearic Acid

Short-chain fatty acids (SCFAs) have been used as raw materials in wide range of chemical and medical applications. One technique to produce SCFAs is oxidative cleavage of long-chain fatty acids (LCFAs). However, unless the LCFAs are unsaturated, the yield of SCFAs is often very low because the carboxylic group of the fatty acid is more active than other part of the molecule. This work explores the idea of introducing a double bond into saturated LCFA, i.e., stearic acid, via selective dehydrogenation using commercial heterogeneous catalysts. However, cracking of the LCFA is also catalysed. Different type of metals was therefore investigated to study the effect of metals on the cracking and dehydrogenation. The experiments were conducted in an autoclave reactor under inert atmosphere. The temperature was in the range of 250–350°C. The products were analysed by gas chromatography equipped with mass spectroscopy (GC/MS). The results reveal that the introduction of double bond in the aliphatic chain of the stearic acid is possible although the yields of the unsaturated LCFAs are low. Effects of various parameters, such as temperature, pressure, and reaction time, were also investigated and reported

Selective Oxidative Cleavage of Oleic Acid on Alumina Supported Metal Catalyst

Short-chain fatty acids (SCFAs) and medium-chain fatty acid (MCFAs) are valuable raw materials in wide range of chemical and medical applications. They can be converted to other derivatives by known chemical reactions. Unfortunately, both SCFAs MCFAs are not as abundant in nature as long-chain fatty acid (LCFAs). In this work, the oxidative cleavage of oleic acid, which is one of the most abundant unsaturated LCFAs in nature, was studied. The oxidation was induced by hydrogen peroxide catalyzed by a commercial alumina-supported metal catalyst. The products were analyzed by gas chromatography equipped with mass spectroscopy (GC/MS). The results revealed that MCFAs and SCFAs were detected in a product. In addition, aldehydes were also found. In this work, effects of catalyst loading, oleic acid-to-hydrogen peroxide ratio, reaction time were investigated and reported

Activity of nanosized titania synthesized from thermal decomposition of titanium (IV) n-butoxide for the photocatalytic degradation of diuron

Nanoparticles of anatase titania were synthesized by the thermal decomposition of titanium (IV) n-butoxide in 1,4-butanediol. The powder obtained was characterized by various characterization techniques, such as XRD, BET, SEM and TEM, to confirm that it was a collection of single crystal anatase with particle size smaller than 15 nm. The synthesized titania was employed as catalyst for the photodegradation of diuron, a herbicide belonging to the phenylurea family, which has been considered as a biologically active pollutant in soil and water. Although diuron is chemically stable, degradation of diuron by photocatalyzed oxidation was found possible. The conversions achieved by titania prepared were in the range of 70–80% within 6 h of reaction, using standard UV lamps, while over 99% conversion was achieved under solar irradiation. The photocatalytic activity was compared with that of the Japanese Reference Catalyst (JRC-TIO-1) titania from the Catalysis Society of Japan. The synthesized titania exhibited higher rate and efficiency in diuron degradation than reference catalyst. The results from the investigations by controlling various reaction parameters, such as oxygen dissolved in the solution, diuron concentration, as well as light source, suggested that the enhanced photocatalytic activity was the result from higher crystallinity of the synthesized titania