Diffusion and surface reaction in porous cubical catalyst: A mathematical approach

Background: Catalysts are the most vital part of any chemical industry. Catalyst is a substance that affects the rate of reaction, but the catalyst itself does not take part in the reaction. Catalysts offer different pathways of reaction by diffusing the reactant inside it to provide a large surface area within a small volume, thus, lowering the activation energy of molecules for reaction. Most of the catalytic reactions take place in liquid-solid or gas-solid interface where catalysts are mostly porous in nature. Spherical and cubic-shaped catalyst particles are commonly used in different industries. Methods: In the first phase of the present study, the physics behind the diffusion inside the catalyst pellet has been discussed. In the second part, governing differential equations have been established at a steady-state condition. For solving the differential equation, the equation is made dimensionless. Physical boundary conditions were used to solve the diffusion equation. The assumption of writing the differential equation of the reaction is elementary. Then the Thiele modulus is derived in terms of the reaction and geometrical parameter (Length) Results and Conclusion: In the third part, the differential equation is solved for first-order reaction with some constant values of the Thiele modulus and three-dimensional plots are obtained using numerical analysis. After that, the obtained Thiele modulus and effectiveness factor plot are compared to draw the conclusion of reaction rate limited and internal diffusion limited.

Photo-Fenton Oxidation of Methyl Orange Dye Using South African Ilmenite Sands as a Catalyst

In this study, the viability of South African ilmenite sands as a catalyst in the photo-Fenton-like degradation of methyl orange (MO) dye was investigated. The mineralogy and other properties of the material were characterized. Complete decolorization occurred under acidic conditions (pH < 4) in the presence of ilmenite and H2O2. Light irradiation accelerated the rate of reaction. Parameter optimization revealed that a pH of 2.5, UVB irradiation, 2 g/L catalyst loading, and a hydrogen peroxide concentration of 1.0 mM were required. Under these conditions, complete decolorization was observed after 45 min. Degradation kinetics were best described by the pseudo-first order (PFO) model. Rate constants of 0.095 and 0.034 min−1 were obtained for 5 and 20 mg/L MO concentrations, respectively. A 37% total organic carbon removal was observed after 60 min. This suggests a stepwise MO degradation pathway with intermediate formation rather than complete mineralization. Although iron leaching was detected, the mineralogy of the catalyst recovered after the reaction was similar to the fresh catalyst.

Kinetics Solvent Effect and Mechanism of Hydrolysis of Ethyl Caprylate Ester in Aqueous Organic Solvent Media

The specific rate constant of ethyl caprylate in alkali catalised hydrolysis in water-acetone mixture covering range of 30 to 70% (v/v) of acetone has been determined at temperature 20 to 400c. The rate of reaction decreases with increase in percentage of Acetone from 30 to 70% (v/v). The observed Activation energy decreases progressively with increase in acetone content of the medium. The effect of molar concentration of water and Dielectric constant on the reaction kinetic has also been studied. The thermodynamic parameters (DG*, DH* and DS*) has been determined which showed strong dependency on solvent composition.

Green synthesized Ag-TiO2 for degradation of organic dye through visible light driven photo-reactor and its kinetics

This study reports a green approach for the modification of titanium dioxide (TiO2) nanoparticles with immobilization of silver nanoparticles. One of the natural sources i.e., Mangifera indica leaf extract was utilized as reducing and capping agent for the fabrication of Ag-TiO2 nanocatalyst. Further, the surface morphology and band-gap energy of prepared Ag-TiO2 were analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and UV–Vis spectroscopy. Also, it was characterized by X-ray Powder Diffraction (XRD) which provides the information regarding the crystallinity of the Ag-TiO2. Subsequently, photo activity of Ag-TiO2 was investigated for the degradation of methylene blue (MB) dye wastewater through visible light driven photoreactor. The Ag-TiO2 provided highest (68%) of photo-degradation efficiency within 110 min for 7.81 × 10−5 mol/L initial MB concentration at pH 8 by using 0.19 g/L photocatalyst. Further, addition of 10 mM H2O2 boost up the MB photodegradation to 74%. The kinetic study confirmed the MB degradation followed first order rate of reaction.

The Effect of Titanium Tetra-Butoxide Catalyst on the Olefin Polymerization

The purpose of this study was to assess the ability of titanium Ti(IV) alkyloxy compounds supported by organic polymer polyvinyl chloride (PVC) to polymerize ethylene by feeding triethylaluminium (TEA) as a cocatalyst. Additionally, the impacts of the molar ratio of [Al]/[Ti] on the catalytic activities in ethylene’s polymerization and of the comonomer through utilization of diverse quantities of comonomers on a similar or identical activity were studied. The optimal molar ratio of [Al]/[Ti] was 773:1, and the prepared catalyst had an initial activity of up to 2.3 kg PE/mol Ti. h. when the copolymer was incorporated with 64 mmol of 1-octene. The average molecular weight (Mw) of the copolymer produced with the catalysts was between 97 kg/mol and 326 kg/mol. A significant decrease in the Mw was observed, and PDI broadened with increasing concentration of 1-hexene because of the comonomer’s stronger chain transfer capacity. The quick deactivation of titanium butoxide Ti(OBu)4 on the polymers was found to be associated with increasing oxidation when supported by the catalyst. The presence of Ti (III) after reduction with the aluminum alkyls cleaves the carbon-chlorine bonds of the polymer, producing an inactive polymeric Ti(IV) complex. The results show that synergistic effects play an important role in enhancing the observed rate of reaction, as illustrated by evidence from scanning electron microscopy (SEM). The diffusion of cocatalysts within catalytic precursor particles may also explain the progression of cobweb structures in the polymer particles.

Effect of sulfur solvent on the properties of lead sulfide quantum dots

Colloidal quantum dots (QDs) of lead sulfide have been synthesized and investigated using octadecene and white spirit as a solvent for sulfur, varying the concentration of precursors and the temperature of the process. A method has been proposed for the synthesis of these QDs using anhydrous white spirit as a solvent at a temperature of 200° C, which made it possible to obtain polygonal nanoparticles with an average diameter of 2 to 3.2 nm with a minimum spread in size (± 10%). Solvent white spirit, which has a low limiting solubility for sulfur and creates specific conditions for the reaction of the formation of lead sulfide at a high temperature (200° C), provides good synthesis kinetics in solution, a relatively low crystallization rate and creates conditions for the passage of all stages of the process from the formation of embryos before the maturation of the crystals. In this process, crystals of sufficiently stable sizes and shapes are steadily formed. It follows that the crystals are not spherical, but possibly somewhat rod-shaped, since their sizes differ in two directions. It is also seen that the sizes of QDs obtained using different concentrations of a sulfur solution in white spirit and varying the temperature differ insignificantly, since the confidence intervals are quite large and overlap. In one direction, the crystal size varies from 2 to 3.5 nm, and in the other from 3.5 to 5 nm. It has been found that at low temperatures the rate of reaction and crystal formation slows down. In this case, the anisotropic growth of crystals is pronounced, and the histogram curves are clearly divided into two regions. As a result, the transformation of the cubic structure of the crystal into a hexapod is noted. An increase in the concentration of lead in the reaction medium leads to a slight acceleration of the synthesis of nanoparticles.

Biodegradation of crude oil by immobilized Exiguobacterium sp. AO-11 and shelf life evaluation

Exiguobacterium sp. AO-11 was immobilized on bio-cord at 109 CFU g−1 carrier for the removal of crude oil from marine environments. To prepare a ready-to-use bioremediation product, the shelf life of the immobilized cells was calculated. Approximately 90% of 0.25% (v/v) crude oil removal was achieved within 9 days when the starved state of immobilized cells was used. The oil removal activity of the immobilized cells was maintained in the presence of oil dispersant (89%) and at pH values of 7–9. Meanwhile, pH, oil concentration and salinity affected the oil removal efficacy. The immobilized cells could be reused for at least 5 cycles. The Arrhenius equation describing the relationship between the rate of reaction and temperature was validated as a useful model of the kinetics of retention of activity by an immobilized biocatalyst. It was estimated that the immobilized cells could be stored in a non-vacuum bag containing phosphate buffer (pH 7.0) at 30 °C for 39 days to retain the cells at 107 CFU g−1 carrier and more than 50% degradation activity. These results indicated the potential of using bio-cord-immobilized crude oil-degrading Exiguobacterium sp. AO-11 as a bioremediation product in a marine environment.

Kinetic and Mechanism of Uncatalytic Oxidation of Dl-Threonine by Cerium (Iv) in Aqueous Acid Medium

Kinetic of uncatalyzed oxidation of DL-Threonine has been studied by Ce (IV) in acidic medium has been investigatigated by spectrophotometer technique. The rate of reaction determined at three different temperatures ranging from 298 K to 318 K at the interval of 10 K. The reaction has been found to be a first order reaction in presence or in absence of KCl, CTAB, and SDS. The rate constant, decreases with increasing the concentration of [HSO4-] and [H+] ion. The various thermodynamic parameters were calculated at 298 K, 308 K and 318 K. The proposed mechanism and results is discussed.

Stabilization of paper waste in bioreactor landfills using soybean peroxidase enzyme

One obvious way to reduce the amount of paper waste being discarded, and to conserve the forest resources, is to recycle more of the waste paper. But most common waste management technique for solid waste is the use of landfills. This study was aimed at decomposing the waste in aerobic condition before the anaerobic condition using soybean peroxidase enzyme (SBP). One bioreactor cell without enzyme was compared with two bioreactor cells, which contained different concentration of soybean peroxidase enzyme with hydrogen peroxide (H₂O₂). The rate of reaction was analyzed by performing COD, BOD₅, NH₃, TS and pH tests as well as monitoring the settlement. The findings showed that the bioreactors with enzyme had faster decomposition rate than the control one. Final COD concentration in control one was 62.6% higher than the bioreactor having higher concentrations of enzyme. Similarly, final BOD₅ concentration in control one was 70.7% higher than the bioreactor having higher concentration of enzyme. Furthermore, the results were compared with the previous study, the bioreactors having municipal solid waste (MSW) with biosolids. The results showed that the strength of leachate quality was much better in bioreactors having paper waste with enzyme than the bioreactor having MSW with biosolids. The COD reduction rate in case of enzyme was about more than double than the bioreactor having biosolids. Similarly, BOD₅ reduction rate in case of enzyme was 1.6 times higher than the biosolids and TS reduction rate was about 1.4 times higher than the bioreactor having biosolids.

Stabilization of paper waste in bioreactor landfills using soybean peroxidase enzyme

One obvious way to reduce the amount of paper waste being discarded, and to conserve the forest resources, is to recycle more of the waste paper. But most common waste management technique for solid waste is the use of landfills. This study was aimed at decomposing the waste in aerobic condition before the anaerobic condition using soybean peroxidase enzyme (SBP). One bioreactor cell without enzyme was compared with two bioreactor cells, which contained different concentration of soybean peroxidase enzyme with hydrogen peroxide (H₂O₂). The rate of reaction was analyzed by performing COD, BOD₅, NH₃, TS and pH tests as well as monitoring the settlement. The findings showed that the bioreactors with enzyme had faster decomposition rate than the control one. Final COD concentration in control one was 62.6% higher than the bioreactor having higher concentrations of enzyme. Similarly, final BOD₅ concentration in control one was 70.7% higher than the bioreactor having higher concentration of enzyme. Furthermore, the results were compared with the previous study, the bioreactors having municipal solid waste (MSW) with biosolids. The results showed that the strength of leachate quality was much better in bioreactors having paper waste with enzyme than the bioreactor having MSW with biosolids. The COD reduction rate in case of enzyme was about more than double than the bioreactor having biosolids. Similarly, BOD₅ reduction rate in case of enzyme was 1.6 times higher than the biosolids and TS reduction rate was about 1.4 times higher than the bioreactor having biosolids.