First-order Reaction Kinetic Model Research Articles

Enhanced photocatalytic performance of Bi2O3/H-ZSM-5 composite for rhodamine B degradation under UV light irradiation

Bi2O3/H-ZSM-5 composite photocatalysts were synthesized via a facile ion-exchange method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (DRS) were employed to study the phase structure, morphology and optical properties of the synthesized samples. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of rhodamine B (RhB) under UV light irradiation. The results showed that, at the optimal loading with 18wt.% Bi2O3, the Bi2O3/H-ZSM-5 composite photocatalyst acquires the highest photocatalytic activity. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. The increased photocatalytic performance could be attributed to the synergistic effect between Bi2O3 and H-ZSM-5. The special structure of H-ZSM-5 increases the number of the active sites to adsorb more dye and photodegrade it on Bi2O3 photocatalyst.

Drying and Denaturation Kinetics of Whey Protein Isolate (WPI) During Convective Air Drying Process

The denaturation and drying kinetics of whey protein isolate (WPI) in a convective drying (CD) environment was measured using single droplet drying experiments. The moisture content and temperature histories during drying of WPI droplets were predicted using reaction kinetics–based models. The denaturation kinetics of WPI in the CD process was predicted using first-order reaction kinetics considering the denaturation rate constant to be moisture content and temperature dependent. Single droplets of WPI (10% [w/v], 2.0 ± 0.1 mm initial diameter) were used throughout these experiments. The drying experiments were carried out at two temperatures (65 and 80°C) at a constant air velocity (0.5 m/s) for 600 s. The extent and nature of the denaturation of WPI during the CD was compared with those in isothermal heat treatments (IHT) at the same medium temperatures. The denaturation of WPI was 68.31% in convective air drying at 65°C and 600 s and it was 10.79% in the IHT at the same temperature and time. The stress due to dehydration and the exposure time were found to be responsible for the denaturation of WPI in the CD process and long exposure time was found to be responsible for its denaturation in the IHT process. At the media temperature of 80°C, the denaturation loss of WPI was 90.00 and 68.73% in IHT and CD processes, respectively. Both the thermal (moist heat) and dehydration stresses were found to be responsible for denaturation of WPI during CD process and very high thermal stress was found to be responsible for denaturation of WPI during the IHT. There was good agreement between the experimental and reaction engineering approach (REA)-predicted moisture content and temperature histories. The experimental moisture content and temperature histories were followed by the respective REA predictions within 6.5% (R 2 = 0.995) and 3% (R 2 = 0.981) errors, respectively. The denaturation kinetics of WPI during CD was predicted well (R 2 = 0.95 – 0.98; average error = 6.5 ± 0.5%) by a first-order reaction kinetics model.

Lake Restoration of Arsenic Pollution by Manganese Ore

Using manganese ore coated with small stones to adsorb arsenic from the contaminated water samples of Yangzonghai Lake, and several factors that may have impacts on the arsenic removal efficiency are analyzed. The result shows that the new adsorbent material has a great effect on arsenic removal. Temperature's effect on arsenic removal efficiency is not obvious. The arsenic removal efficiency increased dramatically in accordance with residence time within 0-660s, and then stabilized. The adsorption process is better when conducted in acidic conditions, the maximum adsorption rate reached 83.0% with the pH of 3.0 and it reached the minimum value of 14.7% when pH is 10. Fe3+ and Ca2+ can slightly promote manganese ore's adsorption of arsenic, and with anions CO32-, SiO32- , efficiency was slightly reduced. When fitting the kinetics data of arsenic removal by coated manganese ore, the adsorption process is correspondent with first-order reaction kinetics model. The adsorption isotherm is more close to the Freundlich isotherm model.

Thermogravimetric Analysis and Kinetics on Reducing Low-Grade Manganese Dioxide Ore by Biomass

Nonisothermal thermogravimetric analysis (TGA) was applied to evaluate rice straw, sawdust, wheat stalk, maize straw, and bamboo to explore their potential for reduction of manganese dioxide ore. Results from the biomass pyrolysis experiments showed that wood-based biomass materials, such as sawdust and bamboo, could produce more reductive agents, while herb-based biomass materials, such as rice straw, wheat stalk, and maize straw, had lower reaction temperatures. The peak temperatures for biomass reduction tests were 20 K to 50 K (20 °C to 50 °C) higher compared with the pyrolysis tests, and a clear shoulder at around 523 K (250 °C) could be observed. The effects of heating rate, biomass/manganese dioxide ore ratio, and different components of biomass were also investigated. An independent parallel first-order reaction kinetic model was used to calculate the values of activation energy and frequency factor for biomass pyrolysis and reduction of manganese dioxide ore. For better understanding the reduction process, kinetic parameters of independent behavior of manganese dioxide ore were also calculated by simple mathematical treatment. Finally, the isokinetic temperature Ti and the rate constant k0 for reduction of manganese oxide ore by reductive volatiles of biomass were derived according to the Arrhenius equation, which were determined to be 603 K (330 °C) and 108.99 min−1, respectively.

Catalytic Purification of Raw Gas from Biomass Gasification on Mo–Ni–Co/Cordierite Monolithic Catalyst

This study presents the preparation of a 1Mo3Ni1Co/Cor catalyst by vacuum impregnation to obtain a clean biomass gasification product gas. The effects of the air equivalence ratio (ER) and catalytic temperature on tar cracking and gas reforming were investigated. The regeneration activity of the 1Mo3Ni1Co/Cor catalyst was also evaluated in biomass gasification. Results show that the choice of ER is highly important, and an increase in catalytic temperature is favorable for cleaning biomass gasification raw gas. When the ER and catalytic temperatures were 0.21 and 800 °C, the gas yield, tar conversion, and hydrogen yield reached 1.28 N m3/kg, 99.2%, and 49.3 g/kg, respectively. The regeneration activity of this catalyst is relatively stable and close to that of the fresh catalyst after a 4 h reaction; however, this activity is relatively lower than that of the fresh catalyst in the initial stage. This difference is caused by the formation of Mo2C in gas reforming. Finally, the activation energy and the pre-exponential factor of the catalyst calculated by first-order reaction kinetics model are 33.79 kJ/mol and 523 s–1, respectively.

Research on Reaction Kinetics of Photocatalytic Degradation of Methylene Blue in Water Solution with SrTiO<sub>3</sub> Nano Film

The nanostructured SrTiO3 film was prepared by sol-gel method and spin-coating process. The X ray diffraction (XRD) analysis shows that the SrTiO3 film is perovskite structure and has the average particle size 25.39nm. The photocatalytic degradation experiments were carried out in methylene blue solutions with the SrTiO3 film. The experimental results show that: the critical concentration of methylene blue solution is slightly higher than 3.289×10-5mol/L at which concentration the degradability of film can be most effectively exploited; when the molar concentration is less than the critical concentration, the photocatalytic degradation reaction can be expressed as the first-order reaction kinetics model and the reaction rate decreases with increasing initial concentration; when the concentration is higher than the critical concentration, the degradation reaction is more consistent with the zero-order reaction kinetics model, and the reaction rate remains almost constant with the varied concentration

Studies on Photodegradation Kinetics of Rhodamine B by Titanium Dioxide - Carbon Composite Materials

The composite materials were prepared with high-viscosity clay as carrier, activated carbon as adsorbent, and titanium dioxide as photocatalyst.Kinetic process of photocatalytic degradation of rhodamine B was investigated at different reaction conditions using the composite materials.The results shown that : rhodamine B was the maximum catalytic activity when the initial reaction solution concentration is 5mg/L,pH=6,and composite material dosing quantity is 5g/L.The kinetics of photocatalytic degradation reaction can be expressed by the first-order reaction kinetic model.

Degradation Characteristics of a Microbial Consortium on Direct Fast Scarlet 4BS

High-effective decolorization microbial consortium was isolated and selected by enrichment and optimizing combination decolorization experiments. The optimal microbial consortium consisting of a fungus P6 and a bacterium H5 could use Direct Fast Scarlet 4BS as sole source of carbon and energy. The microbial consortium showed a significant improvement on dye decolorization rate under shaking culture that might be attributed to the synergetic reaction of single strains. This study also examined the kinetics of 4BS decolorization by immobilized microbial consortium. The results demonstrated that the activity of microorganisms inside the immobilized beads can be increased remarkably and the dependence of specific decolorization rate on 4BS concentration could be described as a typical first-order reaction kinetic model. The changes of proliferation and distribution of microbial consortium in gel beads were microscopically observed, which could be used for analysis of decolorization mechanism of 4BS.

Adsorption Properties and Degradation Dynamics of Endocrine-Disrupting Chemical Levonorgestrel in Soils

Levonorgestrel, a synthetic progesterone used as an oral contraceptive or emergency contraceptive pill, has been shown to be an endocrine-disrupting chemical. To assess the environmental risk of levonorgestrel, batch experiments and laboratory microcosm studies were conducted to investigate the adsorption and degradation of levonorgestrel in five contrasting soils of China. Freundlich and Langmuir models were applied to sorption data to examine the affinity of levonorgestrel for soils with varying physical and chemical properties. The K(f) of levonorgestrel in the tested soils ranged from 10.79 to 60.92 mg(1-n) L(n) kg(-1) with N between 0.69 and 1.23, and the Q(m) ranged from 18.18 to 196.08 mg/kg. The multiple regression analysis was conducted between K(f) and soil properties. Results indicate that total organic carbon plays a dominant role in the adsorption process. Gibbs free energy values less than 40 kJ/mol demonstrate that levonorgestrel sorption on soils could be considered as a physical adsorption. The degradation of levonorgestrel in five soils was fitted by the first-order reaction kinetics model. The half-lives of levonorgestrel were between 4.32 and 11.55 days. The initial concentration and sterilization experiments illustrated that the degradation rate of levonorgestrel in soil was concentration-dependent and microbially mediated. The low mobility potential of levonorgestrel in soils was predicted by the groundwater ubiquity score (GUS) and retardation factor (R(f)).

Investigation of liquid plasma catalysis on Ti electrodes for the decolorization of a brilliant red B solution

Abstract This investigation is intended to determine the catalytic effect of liquid plasma on TiO2, generated in situ on Ti anodes submerged in Na2SO4 electrolyte solution by observing the efficiency of the reaction in decolorizing a brilliant red B solution under voltage-stabilized DC power. The orthogonal test was performed in order to obtain the optimal reaction conditions for the test device. When placed under a constant voltage of 550 V, and with an electrode depth of 2 mm, Na2SO4 concentration of 5 g/L, pH of 2, the maximum decolorization ratio of 100 mL brilliant red B solution with the concentration of 20 mg/L was 97.8% after 40 min. The reaction rate constant was about 0.102 min−1, conforming to the first-order reaction kinetic model. Comparative tests were conducted with: Al electrode under 450 V; Mo electrode under 550 V; and a mixture of the electrolyte and TiO2 powder. The results showed that liquid plasma – TiO2 on the electrode of the catalytic system naturally integrated on the discharge electrode, with an increase in reaction rate by 26.8% while utilizing the same energy consumption.

A brief study on the degradation kinetics of seven organophosphorus pesticides in skimmed milk cultured with Lactobacillus spp. at 42 °C

Seven organophosphorus pesticides (OPPs) including dimethoate, fenthion, malathion, methyl parathion, monocrotophos, phorate and trichlorphon were added to skimmed milk. The milk was inoculated with one strain of Lactobacillus spp. including L. bulgaricus, L. paracasei and L. plantarum, and cultured at 42°C for 24h to investigate their impacts on degradation kinetics of the OPPs. The residual OPPs in the milk were extracted by an extraction solvent and quantified in a gas chromatography after purification. Degradation rate constant and half live periods of the OPPs were calculated from a first-order reaction kinetics model. The result shows that the selected Lactobacillus spp. exhibited some acceleration on OPPs degradation totally. Dimethoate and methyl parathion were more stable but malathion was the most labile. Both L. bulgaricus and L. plantarum had stronger acceleration on the degradation of the OPPs studied.

Arsenic removal from real arsenic-bearing groundwater by adsorption on iron-oxide-coated natural rock (IOCNR)

This study used iron-oxide-coated natural rock (IOCNR) an adsorbent of arsenic from real arsenic-bearing groundwater collected from the Lanyang Plain, North Eastern Taiwan. SEM and EDX were applied to characterize the as-prepared adsorbent. Batch adsorption studies were conducted at 25 ± 2°C. A 15 g L − 1 dose of adsorbent removed ~ 75% of the total arsenic from the real sample when the initial arsenic concentration was 40 μg L − 1 and the pH was 7.5 (reduced to 10 μg L − 1 , the maximum contaminant level (MCL)). The contact time was 6 h and the agitation speed 180 rpm. Adsorption followed the Langmuir isotherm and the maximum adsorptive capacity of IOCNR was 0.36 mg g − 1 . The dimensionless parameter ( R L ) and Gibbs free energy ( ∆G o ) changes suggested that the process is favorable and spontaneous. The adsorption process followed the first-order reaction kinetic model better than the other three kinetic models, and film-diffusion was the rate-limiting step. Arsenic removal efficiency of the exhausted and NaOH-regenerated IOCNR decreased in the second-cycle operation. Arsenic removal efficiency of IOCNR was comparable to that of the commercially available patented adsorbent LEWATIT FO36.

Preparation and characterization of bifunctional, Fe3O4/ZnO nanocomposites and their use as photocatalysts

Bifunctional magnetic-optical Fe3O4/ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe3O4 nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe3O4 with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1h when the amount of catalyst was 0.51gL−1 and initial concentration of MO was 6×10−5molL−1 in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe3O4/ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.

Inactivation of polyphenol oxidase from Pacific white shrimp by dense phase carbon dioxide

The inactivation of polyphenol oxidase (PPO) from Pacific white shrimp exposed to dense phase carbon dioxide (DPCD) treatment was investigated. PPO activity showed a dramatic loss at 4–25 MPa and 37 °C. At the lower pressure (4–15 MPa), the experimental data of inactivation followed the first-order reaction kinetic model, the pressure sensitivity (ZP) of the kinetic parameters was 49.02 MPa and the activation volume (△ V≠) was − 120.88 cm3/mol. At the higher pressure (20 and 25 MPa), the experimental data of inactivation followed the biexponential kinetic model. The kinetic rate constant kF and kS of fast and stable fractions were 2.45 and 0.08 min− 1, respectively. The decimal reduction time DF and DS were 0.94 and 29.43 min at 25 MPa and 37 °C, respectively. After DPCD treatment, the loss activity of PPO had no restoration storing for 6 days at 4 °C. The results of SDS-PAGE and activity staining also showed that DPCD treatment had the obvious inhibitory effect on PPO from Pacific white shrimp. The PPO activity in vivo was easier to be inactivated than that in crude PPO extracts under the same DPCD treatment conditions.

Developing microencapsulated flaxseed oil containing shrimp ( Litopenaeus setiferus) astaxanthin using a pilot scale spray dryer

Shrimp byproducts are an excellent source of astaxanthin. The antioxidant-rich natural astaxanthin, dispersed in alpha-linolenic acid-rich flaxseed oil, may provide healthier functional food options for consumers. The goal was to develop astaxanthin dry powder using microencapsulation technology. Emulsions prepared with flaxseed oil (EF) and flaxseed oil containing shrimp astaxanthin (ESA) were spray-dried to produce microencapsulated powders using a pilot scale spray dryer. Energy required for spray drying EF and ESA and physicochemical properties of the powders were evaluated. The energy required to spray dry EF and ESA was 2.676 × 104 and 2.405 × 104 kJ kg−1 respectively. The measured production rate of microencapsulated flaxseed oil (MF) and flaxseed oil containing shrimp astaxanthin (MSA) was lower than the estimated production rate. The astaxanthin concentration of MSA was 16.08 μg g−1 powder. The lipid oxidation of MSA was lower than that of MF at 5, 25, and 40 °C during 26 days storage. Degradation of astaxanthin in MSA, fitted with first-order reaction kinetics model, showed that the degradation rate constant for MSA increased with increased storage temperature, which indicated that astaxanthin degraded faster at higher temperature than that at lower temperature. This study demonstrated that astaxanthin extracted from shrimp byproducts using flaxseed oil can be microencapsulated using spray drying technology.

Characterization of Adsorption and Degradation of Diuron in Carbonatic and Noncarbonatic Soils

The adsorption and degradation of the pesticide diuron in carbonatic and noncarbonatic soils were investigated to better understand the fate and transport of diuron in the environment. Batch adsorption experiments yielded isotherms that were well-described by the linear model. Adsorption coefficients normalized to soil organic carbon content (K(oc)) were lowest for carbonatic soils, averaging 259 +/- 48 (95% CI), 558 +/- 109, 973 +/- 156, and 2090 +/- 1054 for carbonatic soils, Histosols, Oxisols, and Spodosols, respectively. In addition, marl-carbonatic soils had much lower K(oc) values (197 +/- 27) than nonmarl-carbonatic soils. Diuron degradation data fit a first-order reaction kinetics model, yielding half-lives in soils ranging from 40 to 267 days. There was no significant difference between the average diuron degradation rate coefficients of each of the soil groups studied. Given the low adsorption capacity of carbonatic soils, it may be advisable to lower herbicide application rates in agricultural regions with carbonatic soils such as southern Florida to protect aquatic ecosystems and water quality.

Use of a Pressuremeter To Measure the Kinetics of Carbon Dioxide Evolution in Chemically Leavened Wheat Flour Dough

Among a number of impediments to a wider use of chemical leavening agents in bakery applications is the lack of standardized instrumentation capable of providing information on the rates of CO2 production from chemical leaveners in a format that is meaningful to both the technologist (i.e., the dough rate of reaction or DRR) and the researcher (e.g., in terms of fundamental unitskmol CO2 per kg of dough per s). This paper presents an original methodology to carry out the DRR test using a commercial pressuremeter, the Gassmart apparatus, and to model the kinetics of CO2 evolution of chemically leavened dough. Lean formula doughs were leavened at 27 and 39 degrees C with four chemical leavening systems containing sodium bicarbonate and one of four leavening acids, sodium acid pyrophosphate 40 (SAPP), adipic acid (ADA), potassium acid tartrate (KAT), and glucono-delta-lactone (GDL). Chemical kinetics theory was used to gain an insight into the reaction mechanisms responsible for the evolution of carbon dioxide from the leaveners. A first-order reaction kinetics model was found to be suitable for describing the neutralizing properties of GDL and ADA leavening systems, whereas a first-order reaction kinetics model for irreversible parallel reactions better described the leavening properties of the acidic salts KAT and SAPP.

Kinetics of salmon quality changes during thermal processing

The kinetics of reactions leading to changes in salmon quality during thermal processing were evaluated. Small samples (D 30 mm × H 6 mm) cut from pink salmon ( Oncorhynchus gorbuscha) fillets were sealed in aluminum containers (internal dimension: D 35 mm × H 6 mm) and heated in an oil bath at 100, 111.1, 121.1, and 131.1 °C for different time intervals up to 180, 150, 120, 90 min, respectively. A fractional conversion model was used to describe the increase in cook loss during heating; and a quadratic relationship to correlate cook loss with area shrinkage ratio. Color changes (CIE L ∗, b ∗ and Δ E) involved whitening and browning phases. In the browning phase, the changes of CIE L ∗, b ∗ and Δ E followed a zero-order reaction. The progressive change of texture with time as indicated by shear force during heating went through four different phases, and the second (rapid tenderizing) and third phases (slow toughening) were modeled using a first-order reaction kinetic model. The decay of thiamin during heating was modeled with two different relationships: a second-order reaction in which the temperature dependence of the rate constant followed an Arrhenius relationship; and a Weibull-log logistic model recently proposed.

New basis for adsorption of ionic pollutants onto modified zeolites

This work presents studies of ions uptake from aqueous solutions by natural zeolites showing and validating techniques using pre-treated, modified, saturated zeolites and in the form of floc, with polymeric flocculants. Powdered zeolites (from Chile) were pre-treated with Na + ions (NaCl) following modification (adsorption by ionic exchange) with Ba 2+ ions. Batch adsorption studies of sulphate ions were performed with this treated material in the flocculated and powdered forms. Zeolites samples (approximately 48% clinoptilolite and 30% mordenite) were prepared and characterized by their particle size distribution ( d p: 25.4 μm), moisture (2.5%), porosity (0.89), specific surface area (80 m 2 g −1), specific mass (2.2 g cm −3), zeta potential (pie = pH about 1.8), cation-exchange capacity (1.08 meq NH 4 + g −1), microstructure and mineralogical composition. Adsorption studies showed that this natural zeolite does not adsorb sulphate ions, but after the treatment (with Ba 2+ ions) the zeolite (now Ba–Z) was able to uptake the sulphate significantly. The adsorption capacity was not influenced by the medium pH showing that the mechanism involved appear to be proceeding as a chemisorption reaction. Hence, sulphate ions adsorption showed high process kinetic (0.24 min −1) followed by a first-order reaction kinetic model and the data fitted a Langmuir isotherm model; q m and K parameters of 1.3 meq g −1 and 0.1 L meq −1, respectively. An interesting feature was the reuse of the saturated adsorbent materials as new adsorbents. Thus, the BaSO 4–Z (Ba–Z, loaded with sulphate ions) uptakes Ba 2+ ions again and this Ba 2+ bearing zeolite (BaSO 4–Ba–Z) showed, again, a high capacity of sulphate ions adsorption ( q m : 1.1 meq g −1). Moreover flocs of Ba–Z formed with a conventional flocculant (ionic polyacrylamide) showed high sulphate adsorption capacity ( q m : 1.1 meq g −1) and the results were not affected by the flocculant. Again, the saturated flocs were reused as adsorbents for Ba 2+ ions and subsequently for sulphate ions (last stage studied) showing a high adsorption capacity ( q m : 1.2 meq SO 4 g −1). It is believed that this new adsorption basis and reuse as pre-treated and modified zeolites, as powder or flocs form, broaden the applications in the area of adsorption of pollutants on natural zeolitic adsorbents.

Kinetic modelling of the thermal and pH inactivation of a thermostable β-galactosidase from Thermus sp. strain T2

β-Galactosidase from Thermus sp. strain T2 is a promising thermostable enzyme for the hydrolysis of lactose at temperatures from 60 to 70 °C. In this work, thermal and pH stability of such enzyme were investigated in a lacteous buffer containing 50 g L −1 lactose. Temperatures ranged from 60 to 110 °C while pH values cover the pH range for the potential application of the enzyme to hydrolyse lactose in dairy industry: from 3 to 4 of the acid whey to 6.5 of milk, as well as the basic pH used for immobilisation–stabilisation of the enzyme. Thermal inactivation kinetics followed two trends depending on the temperature range: from 60 to 90 °C an increase in the activity as the temperature rises was followed by its final decrease to a slightly active species; however, at higher temperatures follows a simple exponential trend with no residual activity. A kinetic model involving two consecutive first-order reactions with residual activity was chosen for the first temperature range, and a simple first-order reaction model was taken for the higher temperature range. With pH, again, two different tendencies were observed: a biphasic behaviour in the acidic range with final stabilisation of the activity depending on the pH value and a two-stage behaviour in the neutral-basic range, with a fast deactivation followed by a certain reactivation. As in the case of lower temperatures, a two first-order reaction kinetic model with residual activity fits deactivation data. The known presence of aggregates in initial enzyme preparations suggests inactivation routes where an initial disruption of aggregates leads to trimers, which are finally broken or reorganization of the aggregates.