Successive Regeneration Cycles Research Articles

Propane Dehydrogenation on Single-Site [PtZn4] Intermetallic Catalysts

Summary Propane dehydrogenation (PDH) is a commercial propylene production technology that has received much attention, but high reaction temperatures result in a decrease of propylene selectivity and catalyst stability. This paper describes a single-site [PtZn4] catalyst by assembling atomically ordered intermetallic alloy (IMA) as a selective and ultrastable PDH catalyst. The catalyst enables more than 95% of propylene selectivity from 520°C to 620°C. No obvious deactivation is observed within the 160-h test, superior to PtSn/Al2O3 and state-of-the-art Pt-based catalysts. Based on in situ X-ray absorption fine structure, X-ray photoelectron spectroscopy measurements, and density functional theory calculations, we reveal that the surface [PtZn4] ensembles in PtZn IMAs serve as the key active site structures, wherein the geometry-isolated and electron-rich Pt1 site in [PtZn4] ensembles readily promotes the first and second C–H cleavage of propane but inhibits further dehydrogenation of surface-bounded propylene. This significantly improves the selectivity and stability by prohibiting coke side reactions.

Fabrication of SiO2/CuFe2O4/polyaniline composite: A highly efficient adsorbent for heavy metals removal from aquatic environment

A novel multifunctional of SiO2/CuFe2O4/polyaniline composite was synthesized through the interaction between silica (SiO2), copper iron oxide (CuFe2O4), and polyaniline (PANI) as starting materials. SiO2/CuFe2O4/polyaniline composite was characterized for morphology, crystallinity, textural properties, and utilised for the removal of Fe(II), Mn(II), and Cu(II) from synthetic wastewater solutions. The roles of solution pH (2.0–6.0), interaction time (15–420 min), initial ion concentration (50–700 mg/L), and solution temperature (30–50 °C) in the adsorption process were investigated. The adsorption capacities of SiO2/CuFe2O4/PANI for the tested metal ions were high compared to SiO2, CuFe2O4, and polyaniline. Equilibrium studies indicated that Fe(II) and Mn(II) adsorption were compliant with the Langmuir model, while the Freundlich equation described the removal of Cu(II) ions. The maximum Langmuir capacities were up to 285.71, 416.67, and 454.55 mg/g for Cu(II), Fe(II), and Mn(II), respectively. The pseudo-first-order kinetic model fitted well the metal ions removal data. The rate-controlling step reflected the involvement of surface and inner pore diffusion (intraparticle) processes. Electrostatic attractions and chelation were mainly responsible for the binding of metals ions onto SiO2/CuFe2O4/PANI. The selectivity of the studied ions was governed mainly by the hydrated ionic radii and the composite adsorption active sites. SiO2/CuFe2O4/PANI can be easily reused with a slight decrease (around 2–3%) in metal removal efficiency after four successive regeneration cycles.

Desorption of chromium (VI) and lead (II) ions and regeneration of the exhausted adsorbent

The desorption characteristics of previously adsorbed hexavalent chromium [Cr(VI)] and divalent lead [Pb(II)] ions on groundnut husk were tested by various desorption eluents such as tap water, de-ionized water, NaOH, HCl and H2SO4. Among them, HCl and H2SO4 were chosen as the best desorbing agents for Cr(VI) and Pb(II) ions, respectively, due to their high desorption efficiency. The desorption efficiency of HCl and H2SO4 for Cr(VI) and Pb(II) ions was about 76.1% and 82.1%, respectively, at a concentration of 0.1 M for both elution agents. The exhausted groundnut husk was regenerated up to five cycles, and the removal efficiency of Cr(VI) and Pb(II) ions on the recycled groundnut husk could be maintained at 53.5% and 54.6%, respectively, in the third cycle. The successive regeneration cycles resulted in the reduction of the desorption efficiency by 20.0% and 26.7% for Cr(VI) and Pb(II) ions, respectively, after the third cycle. The results show that groundnut husk could be recycled when used to remove Cr(VI) and Pb(II) ions from Cr(VI) and Pb(II)-polluted water and wastewaters.

Mesoporous and high-surface-area activated carbon from defatted olive cake by-products of olive mills for the adsorption kinetics and isotherm of methylene blue and acid blue 29

Abstract The K2CO3 activation of defatted olive cake in N2 atmosphere was attempted for activated carbon (DOC-AC) preparation to test its ability for the adsorption of methylene blue (MB) and acid blue 29 (AB 29). The optimum conditions obtained by Box–Behnken design was 3.0 g/g impregnation ratio, 800 °C activation temperature, and 120 min activation time. These conditions led to 20.84 % carbon yield and 98.92 % MB, and 94.63 % AB 29 removal. The best DOC-AC showed a highly porous structure with 988.75 m2/g SBET and 0.53 cm3/g total pore volume. Batch mode adsorption was performed at different initial dye concentrations (25–400 mg/L), pH (3–11), temperature (30–50 °C), and contact time (0–26 h). The kinetic and equilibrium adsorption data of both dyes were fitted to pseudo-second-order and Langmuir models, respectively. Monolayer adsorption capacities were 359.38 mg/g for MB and 157.58 mg/g for AB 29. After six successive regeneration cycles, the adsorption efficiency for both dyes was > 70 %, indicating good potential of the DOC-AC for commercial applications.

A Highly Sensitive Impedimetric DNA Biosensor Based on Hollow Silica Microspheres for Label-Free Determination of E. coli.

A novel label-free electrochemical DNA biosensor was constructed for the determination of Escherichia coli bacteria in environmental water samples. The aminated DNA probe was immobilized onto hollow silica microspheres (HSMs) functionalized with 3-aminopropyltriethoxysilane and deposited onto a screen-printed electrode (SPE) carbon paste with supported gold nanoparticles (AuNPs). The biosensor was optimized for higher specificity and sensitivity. The label-free E. coli DNA biosensor exhibited a dynamic linear response range of 1 × 10−10 µM to 1 × 10−5 µM (R2 = 0.982), with a limit of detection at 1.95 × 10−15 µM, without a redox mediator. The sensitivity of the developed DNA biosensor was comparable to the non-complementary and single-base mismatched DNA. The DNA biosensor demonstrated a stable response up to 21 days of storage at 4 ℃ and pH 7. The DNA biosensor response was regenerable over three successive regeneration and rehybridization cycles.

Synthesis of a novel magnetic zeolite–hydroxyapatite adsorbent via microwave-assisted method for protein adsorption via magnetic solid-phase extraction

Proteins have a critical role in life, and their separation and detection are of high importance. In the present study, magnetic hydroxyapatite was reinforced with zeolite to become a novel adsorbent synthesized by microwave-assisted method to separate protein via magnetic solid-phase extraction. The synthesized procedure was optimized through the mass ratio of zeolite to hydroxyapatite and radiation time. The synthesized nanocomposite was characterized by techniques such as XRD, EDAX, FESEM, TEM, FTIR, VSM, and BET. Structural evaluation reveals that the magnetic zeolite as a core provides a bed for HAP spherical crystals formation and HAP crystals dispersed over the magnetic zeolites or as large grains located around it. The experimental data revealed the maximum separation was achieved at contact time 60 min, initial pH 2, protein concentration 1.2 mg/mL, and adsorbent dosage 50 mg without any salt in the solution. The maximum adsorption capacity was 82.62 mg/g. Desorption efficiency of 95% at initial pH 12 and separation efficiency more than 50% after 4 successive regeneration cycles are the advantages of the adsorbent. The adsorption studies showed that Freundlich and pseudo-second-order models were well fitted with the obtained experimental data.

Ash based nanocomposites for photocatalytic degradation of textile dye pollutants: A review

Ash is a highly available industrial and agricultural waste by-product. Giving insights into the huge generation of ash and environmental concern of disposal issue, aesthetic attention has been drawn on the sustainable utilization of ash as a renewable supporting material in the synthesis of photocatalytic nanocomposites. Coal fly ash, rice husk ash and volcanic ash are currently being investigated for their potential to be applied as an effective precursor material for photocatalyst preparation, owing to their advantages of high adsorption capability, high ion-exchange capacity, significant specific surface area and high reusability. The novelty of these studies is that prepared ash based photocatalysts could provide a synergistic effect of the adsorption capacity of ash and the photocatalytic activity of photocatalysts to enhance the overall degradation efficiency of dye. Exploring the possible usage of these abundant by-products not only solving the environmental problem but also highlighting its further economic value of utilization with the concept of “waste to wealth”. This paper presents a fundamental information pertaining to the basic principles of photocatalysis and semiconductor based photocatalysts. A brief overview of the role of ash based nanocomposites in terms of the preparation methods and conditions, morphologies, physiochemical properties and their photocatalytic performances on the degradation of dye pollutants is highlighted. The optimization, mechanism and stability study are also reviewed. The finding showed that the porous structure and the presence of aluminosilicate in the ash greatly enhance the adsorption capacity of the total composite in the dye degradation process. The photocatalytic performance was dependent on the calcination temperature, catalyst loading, solution pH, initial dye concentration and light source. However, reusability test indicated the high stability of the prepared ash based composites, with most of the dye degradation efficiency greater than 80% even after a few successive regeneration cycles.

Absorptive Hydrogen Scavenging for Enhanced Aromatics Yield During Non‐oxidative Methane Dehydroaromatization on Mo/H‐ZSM‐5 Catalysts

Addition of Zr metal particles to MoCx /ZSM-5 in interpellet mixtures (2:1 weight ratio) resulted in maximum single-pass methane conversion of 27 % for dehydroaromatization at 973 K (in significant excess of the equilibrium prescribed circa 10 % conversion at these conditions) and a concurrent 1.4-5.6-fold increase in aromatic product yields due to circumvention of thermodynamic equilibrium limitations by absorptive H2 removal by Zr while retaining cumulative aromatic product selectivity. The absorptive function of the polyfunctional catalyst formulation can be regenerated by thermal treatment in He flow at 973 K, yielding above-equilibrium methane conversion in successive regeneration cycles. H2 uptake experiments demonstrate formation of bulk ZrH1.75 on hydrogen absorption by Zr at 973 K. Cooperation between absorption and catalytic centers distinct in location and function enables circumvention of persistent thermodynamic challenges in non-oxidative methane dehydrogenation.

Absorptive Hydrogen Scavenging for Enhanced Aromatics Yield During Non‐oxidative Methane Dehydroaromatization on Mo/H‐ZSM‐5 Catalysts

AbstractAddition of Zr metal particles to MoCx/ZSM‐5 in interpellet mixtures (2:1 weight ratio) resulted in maximum single‐pass methane conversion of 27 % for dehydroaromatization at 973 K (in significant excess of the equilibrium prescribed circa 10 % conversion at these conditions) and a concurrent 1.4–5.6‐fold increase in aromatic product yields due to circumvention of thermodynamic equilibrium limitations by absorptive H2 removal by Zr while retaining cumulative aromatic product selectivity. The absorptive function of the polyfunctional catalyst formulation can be regenerated by thermal treatment in He flow at 973 K, yielding above‐equilibrium methane conversion in successive regeneration cycles. H2 uptake experiments demonstrate formation of bulk ZrH1.75 on hydrogen absorption by Zr at 973 K. Cooperation between absorption and catalytic centers distinct in location and function enables circumvention of persistent thermodynamic challenges in non‐oxidative methane dehydrogenation.

Excellent Performances of Dealuminated H-Beta Zeolites from Organotemplate-Free Synthesis in Conversion of Biomass-derived 2,5-Dimethylfuran to Renewable p-Xylene.

Direct synthesis of renewable p-xylene (PX) by cycloaddition of biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethylene was achieved over Al-rich H-beta zeolites synthesized by an organotemplate-free approach and their dealuminated counterparts with different Si/Al ratios. Among them, H-beta zeolite with an Si/Al ratio of 22, obtained from an Al-rich parent by dealumination, was found to be an excellent catalyst for the synthesis of PX. A PX yield of 97 % and 2,5-DMF conversion of 99 % were obtained under optimized conditions. These results are even better than those of a commercial H-beta zeolite prepared using a organotemplate synthesis with a similar Si/Al ratio of 19. The excellent performance of the H-beta zeolite with Si/Al ratio of 22 is closely related to its acidity and porous structure. A moderate Brønsted/Lewis acid ratio can improve the conversion of 2,5-DMF to as high as 99 %. Furthermore, dealuminated H-beta zeolite has a secondary pore system that facilitates product diffusion, which increases the selectivity to PX. In addition, this catalyst shows better regeneration. After five successive regeneration cycles, the yield of PX was still as high as 85 % without obvious dealumination. This work provides a deeper understanding of the more general Diels-Alder cycloaddition of furan-based feedstocks and olefins and significantly improves the potential for the synthesis of chemicals from lignocellulosic biomass.

Landfill leachate treatment by sorption in magnetic particles: preliminary study

Leachates are still an open issue in environmental protection. Many of the applied methods for their treatment present low efficiency and thus need to be used collectively. In practice reverse osmosis is mostly used, as it is the most effective option, regardless of its cost. Magnetic methods to treat effluents have been used for water and wastewater treatment by the use of magnetic particles together with magnetic separation for the removal of contaminants. However, large-scale applications are few or even non-existent when we deal with complex contaminated media such as landfill leachates, for which not even research studies at laboratorial scale with real samples have been done yet. In this work, we apply for the first time magnetic sorption for the treatment of leachates, and close the full cycle by studying the regeneration and re-use of the magnetic particles; we also study the influence of the concentration of magnetic particles, the use of several pre-treatment methodologies and the type of particle used in the process, in real landfill samples from the waste treatment plant of Salamanca (Spain), for the removal of COD, NO3−, NO2−, NH4+, Total-N, PO43−, SO42− and Cl−. Regeneration of the magnetic particles after being used in the sorption stage is also studied, as well as their efficiency regarding their re-use. It is also determined the optimum number of batches for complete desorption and for regeneration of the particles, the effect of successive regeneration and re-use cycles, the use of two different regeneration methods, the efficiency of the desorption, the effect of the quantity of solvent and the influence of the time of sorption. Due to its innovative character and the complexity of the media, this work represents a first preliminary approach and, although some promising results have been obtained, further studies are required to completely understand and evaluate the proposed treatment process.

Steam regenerative removal of hydrogen sulfide from hot syngas by a novel tin oxide and yttrium oxide sorbent

A novel H2S sorbent based on SnO2 and Y2O3 is developed by a co-precipitation method for steam regenerative removal of H2S from hot syngas at moderate temperatures (400–500 °C). SnO2-Y2O3 sorbent is stable in a reducing atmosphere (i.e. 500 °C, 50% H2) and achieves a 99.9% H2S removal during successive desulfurization and regeneration cycles. The addition of yttrium to SnO2 decreases the reduction property of SnO2 and no metallic Sn exists in the reducing atmosphere due to the formation of a pyrochlore-type compound, Y2Sn2O7. The SnO2-Y2O3 sorbent has a desulfurization performance deterioration with the increasing calcination temperature. The newly developed SnO2-Y2O3 sorbent can be regenerated by steam at 500 °C. In the eight successive desulfurization and regeneration cycles, SnO2-Y2O3 sorbent has a cyclic breakthrough sulfur capacity of 9 mg/g without significant sulfur capacity loss.

Regeneration of HDTMA-modified minerals after sorption with chromate anions

Surfactant-modified minerals have been widely used for the sorption of anionic and non-polar organic contaminants. This paper investigates the regeneration of various hexadecyltrimethylammonium bromide (HDTMA)-modified natural minerals saturated with chromate anions using different solutions for the extraction of chromates that has been sorbed at optimum conditions. The examined minerals include HDTMA-modified zeolite (clinoptilolite), exfoliated vermiculite, bentonite and attapulgite (palygorskite). Deionized water and sodium chloride, potassium chloride and sodium cyanide solutions at different concentrations (0.1–3 M) were employed as chromate desorption solutions. The HDTMA/Cr(VI)-mineral type, the desorbing solution type and its concentration and the mineral–solution contact time are key parameters that affect the process. From our results it was deduced that regeneration and reuse of HDTMA-modified minerals saturated with chromate is feasible. Bentonite exhibited greater stability than the other minerals studied in adsorption/desorption processes, maintaining 73% of its initial adsorption capacity after 14 successive regeneration cycles. The regeneration performance of the examined minerals follows the order: Bentonite > Attapulgite > Zeolite > Vermiculite. Kinetic study revealed that desorption was faster than adsorption, while the pseudo-second-order equation simulated better the experimental data.

Regeneration of Lyes for Cleaning-In-Place (CIP) Processes in Dairies: Comparison of Recycled Potash and Soda Solutions Cleaning Properties

The regeneration of lyes for their integration in the dairy CIP was investigated applying an original process combining adsorption/coagulation and flocculation operations. Solutions of potassium hydroxide (KOH) and caustic soda (NaOH) soiled with 1% (v/v) of whole milk were submitted up to twenty successive regeneration cycles. The multiple recycling of the regenerated solutions was found to modify their physicochemical characteristics that are an increase of the turbidity, total Chemical Oxygen Demand (CODt) and Total Nitrogen (TN) content simultaneously with a decrease of surface tension (I³) and equilibrium contact angle (I¸e). Along regeneration cycles, potash solutions exhibit quite a distinct trend from soda, especially a lower TN increase and a faster reduction of I³ leading to a significant lower value of the critical micelle concentration (32 Vs. 36 mN.m-1). These alterations can be correlated with the accumulation of surfactant molecules in the cleaning solutions derived from the saponification of fatty acids and the degradation of amino acids that can originate an improvement of the cleaning efficiency when re-used in CIP process.

Removal of Sr(II) from Aqueous Solutions by Aminosilane Functionalized MCM-48

In this research, NH2-MCM-48 adsorbent was synthesized by grafting of aminopropyl on the surface of MCM-48 mesoporous silica material. The synthesized adsorbent was characterized by FT-IR, XRD, thermogravimetric, and surface area techniques. The removal of Sr (II) by the synthesized adsorbent was studied and the effect of initial pH, contact time, cation concentration, and temperature on the Sr2+ adsorption was studied and optimized. Under optimized conditions, the removal capacity of 5.95 meq/g was obtained. The experimental data were analyzed using the Langmuir and Freundlich equations. Adsorption data was fitted with the Langmuir isotherm, indicating that the process was monolayer and chemical in nature. The calculated thermodynamic parameters, ΔH°, ΔS°, and ΔG° confirmed that the adsorption process was endothermic and spontaneous. The regeneration of the adsorbent was examined and it was found that 92% of the initial capacity was conserved after five successive regeneration cycles.

Removal of Dibenzothiophene from Organic Medium by Modified Zeolite

In this research, adsorption of dibenzothiophene (DBT) as a model of sulfur containing material has been studied by Pb exchanged Y-zeolite under different experimental conditions. The adsorption was kinetically fast and high adsorption capacity was obtained. The equilibrium adsorption data were analyzed using Langmuir and Freunlich isotherm models. The corresponding parameters and correlation coefficients of each model are reported and the data was well fitted by the Langmuir isotherm. Pseudo-first order, pseudo-second order and intra-particle diffusion models were evaluated to examine the kinetic of the adsorption process. It was concluded that removal of DBT was obeys the second-order model of kinetic. The adsorbent was tested for five successive regeneration cycles and the considerable capacity of the adsorbent was remained after regeneration.

Effect of shaking time, ionic strength, temperature and pH value on desorption of Cr(III) adsorbed onto GMZ bentonite

The Cr(III) desorption experiments of Gaomiaozi (GMZ) bentonite in aqueous solutions were performed. The variables affecting the desorption behaviors, such as contact time, concentration of the desorbent, pH value of the solution, temperature and desorption isotherms, were investigated by the batch experiments. The results show that the adsorbed Cr(III) on GMZ bentonite can be easily extracted by the desorbent. Kinetics examination shows that desorption is slower than adsorption, and the desorption rate increases with time and reaches the equilibrium after 3 h. The final desorption ratios of Cr(III) are 89.4%, 56.5% and 77.2% in the desorption solution with 0.1 mol/L HCl, 1 mol/L NaCl, and 1 mol/L CaCl2, respectively, and the concentration can promote the desorption progress. Furthermore, the results of successive regeneration cycles indicate that the bentonite has a good regeneration ability and reusability. The pH value is an important factor in the Cr(III) desorption from the GMZ bentonite. The results of adsorption and desorption isotherms show that both adsorption and desorption isotherms are consistent with the Freundlich equation. The comparison of adsorption and desorption isotherms implies that the adsorption/desorption hysteresis is negligible and the transport of Cr(III) in bentonite can be described by a reversible adsorption process.

Regeneration of activated carbon saturated with odors by non-thermal plasma

The dielectric barrier discharge (DBD) regeneration process of an activated carbon (AC) saturated with dimethyl sulfide was studied on a laboratory scale. The results showed sustainable high regeneration efficiency (RE) (>90%) in successive regeneration cycles (10 cycles). Energy density, humidity and oxygen content were key factors for DBD system, with optimum conditions of 761JL−1, 0–1vol% and 5%, respectively. The high efficiency was likely attributed to the improvement of structure and surface properties of AC by DBD. After the first regeneration, surface area, micropore volume and total pore volume of AC increased by 8%, 23% and 15% respectively, while average pore size decreased by 9.5%. The number of carboxylic groups doubled (from 0.22 to 0.48mmolg−1) while that of phenolic groups remarkably decreased (from 0.48 to 0.26mmolg−1) after successive regeneration cycles, which helped to maintain high RE. The results suggested DBD as a novel, efficient alternative process for odor-saturated AC regeneration.

Dearomatization of Normal Paraffin by Synthesized Nax Zeolite

Aromatic compounds produced in linear alkyl benzene (LAB) production process decrease the yield and quality of the product and enhance the deactivation rate of the catalysts. Therefore, the de-aromatization of different streams in LAB production complex is inevitable. In this research, the recycled paraffin from alkylation to dehydrogenation unit was de-aromatized by synthesized NaX zeolite. The effect of different parameters such as temperature, amount of the adsorbent, contact time and initial aromatic concentration was studied and optimized. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. It was concluded that the Langmuir model agreed very well with the experimental data. The calculated thermodynamic parameters of the adsorption showed that the adsorption process was spontaneous and exothermic. The reaction rate was estimated by the pseudo-second order kinetic model. To examine the re-generation ability of the adsorbent a fixed bed column was designed and the breakthrough curves were prepared for three successive regeneration cycles. The results indicated that the adsorbent capacity remained unchanged after three regeneration cycles.

Pairwise antibody footprinting using surface plasmon resonance technology to characterize human papillomavirus type 16 virus-like particles with direct anti-HPV antibody immobilization

This paper describes an approach to surface plasmon resonance (SPR) based epitope mapping, also referred to as pairwise antibody footprinting, involving the direct immobilization of an antigen-specific primary mAb to the surface of an SPR interface. This technique offers a more straightforward approach than indirect capture (e.g., via rabbit anti-mouse Fc) as it does not require additional steps to block the unoccupied immobilized anti-Fc to prevent non-specific antibody binding. This is also an alternative to the direct immobilization of an antigen of interest, which may cause conformational changes in the antigen or epitope degradation upon chemical immobilization, particularly in successive regeneration cycles. It is particularly suitable for highly multivalent targets such as virus-like particles (VLPs). Using this technique, we assessed a panel of eight monoclonal antibodies against HPV (human papilloma virus) L1 protein VLPs expressed by Saccharomyces cerevisiae. In the antibody epitope screening studies, HPV16 L1-directed conformational mAbs were clearly distinguished from the linear mAbs and consistent with known epitope information. Additional studies using a linear mAb and a conformational mAb demonstrate the practical application of this technique for characterizing the result of process changes and the consistency of recombinant HPV16 VLPs. The method is readily extensible to other VLPs and VLP-based vaccines.