Inert Support Material Research Articles

Unraveling of Tectona grandis reduced palladium nanoparticles decorated on Mg-Al layered double hydroxide as an efficient nanocatalyst for cross-coupling reactions and azo dye degradation

An eco-friendly approach for encapsulating active noble metal nanoparticles (NPs) onto inert support materials and utilizing these nanocatalysts with confined approaches is paving the way for betterment. This paper provides a brief explanation for implementing a biogenic protocol for fabricating palladium nanoparticles (Pd NPs) onto Mg-Al layered double hydroxide (Mg-Al-LDH) using Tectona grandis leaves extract (TGLE) as capping and reducing agents to develop Mg-Al-LDH@TGLE Pd nanocatalyst. The structural and chemical features of the developed nanocatalyst are well characterized by different spectroscopic and analytical techniques. Owing to the significance of Pd NPs in cross-coupling reactions, the Mg-Al-LDH@TGLE Pd nanocatalyst was examined for its catalytic performance in the Hiyama and denitrogenative cross-coupling reactions for the formation of biaryls. Further, the nanocatalyst demonstrated great proficiency in the degradation of the azo dye methyl orange (MO). The Mg-Al-LDH@TGLE Pd nanocatalyst gave pronounced results with good stability and selectivity for both reactions with recyclability up to four cycles. This study presents a greener approach avoiding complicated methodologies for support materials and their advances in catalytic reactions.

Miniaturized kapok fiber-supported liquid extraction for convenient extraction of pesticide residues in vegetable oils: Determination of organochlorine pesticides as a proof-of-concept study

In this paper, a miniaturized kapok fiber-supported liquid extraction (mini-KF-SLE) method was proposed for selective extraction of pesticide residues in vegetable oils. The natural kapok fiber was used as an inert oil support material based on its hydrophobic and lipophilic properties, and the extraction device was conveniently constructed by loading 15 mg of kapok fiber at the lower middle part of a 1-mL pipette tip. The vegetable oil sample (150 mg) without any pretreatment was directly loaded, followed by the addition of 150 μL of acetonitrile (ACN) as the extractant. After static extraction for 30 min, the extractant was pipetted out with a pipettor. As the proof of concept, it was applied for extracting eight organochlorine pesticides (OCPs) from vegetable oils and the eluate was analyzed by gas chromatography-electron capture detector (GC-ECD). Under optimized conditions, the extraction recoveries of OCPs were calculated to be in ranges of 35.8–79.5%. The satisfied quantitation ability was verified by the established method with coefficients of determination (R2) being greater than 0.99. The limits of detection (LODs) were in ranges of 2.0–50.0 ng/g. The relative recoveries were in ranges of 78.3–117.0% with the inter-/intra-day relative standard deviation (RSD) both being less than 13.3%. The potential of mini-KF-SLE to extract other kinds of pesticides was further verified by the successful extracting three triazole pesticides in vegetable oils with good extraction recoveries (>41.4%). The proposed mini-KF-SLE in combination with instrument detection techniques has the great potential in the low-cost and high-throughput determination of various pesticide residues in vegetable oils.

Role of an Inert Electrode Support in Plasmonic Electrocatalysis

Direct loading of plasmonic nanostructures onto catalytically inert conductive support materials leads to the Schottky barrier-free architecture of the photocatalytic system. Such systems have recently attracted the attention of the research community as they permit collection of hot carriers independent of their energy when additional charge separation strategies are used. However, a systematic mechanistic investigation and description of the contribution of an inert conductive support to plasmonic electrocatalysis is missing. Herein, we systematically investigated the effect of the supporting electrode material on the observed photoinduced enhancement by comparing the photoelectrocatalytic properties of AuNPs supported on highly oriented pyrolytic graphite (HOPG) and indium tin oxide (ITO) electrodes using electrocatalytic benzyl alcohol (BnOH) oxidation as a model system. Upon illumination, only ∼(3 ± 1)% enhancement in catalytic current was recorded on the AuNP/ITO electrodes in contrast to ∼(42 ± 6)% enhancement on AuNP/HOPG electrodes. Our results showed that the local heating due to light absorption by the electrode material itself independent of localized surface plasmon effects is the primary source of the observed significant photoinduced enhancement on the HOPG electrodes in comparison to the ITO electrodes. Moreover, we demonstrated that an increased interfacial charge transfer at elevated temperatures and not faster reactant diffusion as suggested previously is the main source of the thermal enhancement. This work highlights the importance of the systematic evaluation of contributions of all parts, even if they are catalytically inert, to the light-induced facilitation of catalytic reactions in plasmonic systems.

Sorption-enhanced steam gasification of woody biomass assisted by Ca/Na/FS (fine slag) composite sorbents

In this research, composite sorbents with high activity in promoting H2 production during sorption-enhanced steam gasification of pine sawdust (PS) were developed by doping coal gasification fine slag (FS) and NaOH into calcined conch shell (CS). The tests performed in a laboratory-scale fixed bed reactor demonstrated that the composite sorbents greatly improved H2 concentration and yield over that achieved with CHCS (CS after hydration and calcination), reaching 73.5% and 600.7 mL/g-PS, respectively. This promotion effect on H2 production was not influenced by the unburned carbon in FS. To obtain high H2 concentration and yield with as little NaOH and as much FS as possible, the optimum sorbent was found to be 3CS-2FS-0.32Na (in mass ratio of CS:FS:NaOH = 3:2:0.32). Under this condition, the H2 concentration and yield reached 74.3% and 572.3 mL/g-PS, respectively. In five cycles of experiment, although the H2 yield of 3CS-2FS-0.32Na decreased from 572.3 mL/g-PS to 416.6 mL/g-PS, it was always higher than with CHCS alone by at least 28%. The results in this study indicate that FS has potential to be an effective inert support material that endows CaO with high activity in H2 production during sorption-enhanced steam gasification. This might help to provide a new approach to minimizing the negative environmental impact of FS.

Transient Potassium Peroxide Species in Highly Selective Oxidative Coupling of Methane over an Unmolten K2WO4/SiO2 Catalyst Revealed by In Situ Characterization

The oxidative coupling of methane (OCM) over a K2WO4/SiO2 catalyst was investigated using a CH4–O2 flow system. The addition of H2O to the reactant stream caused an increase in the CH4 conversion rate and C2 selectivity, consistent with the kinetics associated with the equilibrated OH radical generation, followed by H-abstraction from CH4 with OH radicals. The C2+ (a sum of C2 and higher hydrocarbons) yield reaches a maximum of 24.7% (C2H4 yield 17.0%) at a CH4 conversion of 47.1%, comparable to those over the previously reported Na2WO4/SiO2 catalyst. In situ near ambient pressure X-ray photoelectron spectroscopy uncovered K2O2 and KO2 species at and above 560 °C in the presence of gas-phase O2. These K2O2/KO2 species are considered to catalyze H2O activation for OH radical generation. By in situ high-temperature X-ray diffraction, K2WO4 maintained a crystalline phase in the bulk during the OCM reaction at 850 °C in contrast to the molten state of Na2WO4 previously reported. This indicates that the melting of the supported component and the covering of support are not essential to achieve a high C2 yield in supported alkali metal tungstate catalysts as long as inert support materials are used toward OCM.

Preparation of CaO-SiO<sub>2</sub> Adsorbent for Potential CO<sub>2</sub> Capture via Dry Mixing Method

Calcium-looping technology is defined as one of the most desirable methods of carbon capture, utilization and storage (CCUS). However, because of sintering, rapid deactivation of CaO-sorbents is currently a major barrier to this technology. The stability of calcium based sorbent may be enhance by incorporating them with inert support materials such as MgO, Al2O2, ZrO2 and SiO2. For this study, calcium based sorbent has been incorporate with silica obtained from rice husk ash. CaO-SiO2 sorbents are prepared using physical dry mixing method which is much simpler compared to other available methods. The prepared CaO-SiO2 sorbents were then characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). New crystalline phase, larnite (Ca2SiO4) was detected in XRD patterns and this phase possess good chemical durability and may help to prevent sintering effect of calcium based sorbents and enhance their cyclic capability. CaO-SiO2 sorbent calcined at 700 oC with different grinding times have highest intensity of XRD peak at (104) with element of calcite. Sorbents with different weight composition of CaCO3-RHA were observed to have different surface morphology. SEM images of the sorbent (90wt% CaCO3-RHA) before calcination showed bigger particle size with irregular shape and more porosity. Then, SEM analysis was conducted for samples with different grinding times after calcination. CaO-SiO2 sorbents with 20minutes grinding time exhibited small size of particles with some porosity. Besides that, the particles are well distributed without agglomeration occured. The CaO-SiO2 sorbent calcined at 700 oC sorbents were tested for 20 consecutive carbonation and calcination cycles using Thermogravimetric Analysis (TGA). CaO-SiO2 sorbent treated with 700 oC calcination temperature and 20 minutes of grinding shows better cyclic CO2 sorption capacity.

Mass Transfer and Reaction in Hydrolysis of Coconut Husk Using Immobilized Enzyme on Chitosan Magnetic Nanoparticle

A more sustainable energy source is needed to fulfill the increasing demand for energy. In Indonesia, biomass waste utilization as biofuel source shows high potential. Coconut husk is a biomass comprised of cellulose and hemicellulose that can converted to reducing sugar through enzymatic hydrolysis and can be further converted into biofuel. However, enzymatic hydrolysis is expensive, as enzyme is soluble and cannot be separated after use. Immobilization is a technique where an enzyme is trapped onto an insoluble inert support material so that the enzyme can be recovered and reused. Chitosan magnetic nanoparticles (CMNP) are used in this experiment as the support as it is cheap and readily available. Since coconut husk is insoluble, mass transfer phenomena remains a major bottleneck in hydrolysis due to limitations in the substrate to enzyme accessibility, especially when the enzyme is immobilized on an insoluble material like CMNP. If only mass transfer resistance is accounted, hydrolysis only occurs on the enzyme particles’ surface. The mass transfer coefficients obtained are 0.0000723, 0.0368, 0.0295 in respect of A. niger cellulase, T. reesei cellulase, and T. longibrachiatum xilanase. Higher coefficients values contribute proportionally to higher yield. If the reaction is assumed to occur uniformly within the spherical immobilized enzyme, then the substrate will diffuse molecularly through the enzyme, where internal mass transfer is no longer negligible. Thiele’s Modulus obtained are 2.197, 0.0368, 0.0795 in respect of A. niger cellulase, T. reseei cellulase, and T. longibrachiatum xilanase. A smaller value in Thiele’s Modulus (ϕ ≤ 1) shows that diffusion occurs at a faster rate than the enzymatic reaction.

CuSO4/[Cu(NH3)4]SO4-Composite Thermochemical Energy Storage Materials.

The thermochemical energy-storage material couple CuSO4/[Cu(NH3)4]SO4 combines full reversibility, application in a medium temperature interval (<350 °C), and fast liberation of stored heat. During reaction with ammonia, a large change in the sulfate solid-state structure occurs, resulting in a 2.6-fold expansion of the bulk material due to NH3 uptake. In order to limit this volume work, as well as enhance the thermal conductivity of the solid material, several composites of anhydrous CuSO4 with inorganic inert support materials were prepared and characterized with regard to their energy storage density, reversibility of the storage reaction, thermal conductivity, and particle morphology. The best thermochemical energy storage properties were obtained for a 10:1 CuSO4-sepiolite composite, combining an attractive energy storage density with slightly improved thermal conductivity and decreased bulk volume work compared to the pure salt.

Chemical looping combustion with nanosize oxygen carrier: a review

This paper reports latest advancement on oxygen carriers (OCs) and effect of particle size from micro- to nanoscale in chemical looping combustion (CLC). CLC is basically a carbon capture and storage technology with the objective to reduce carbon dioxide emission from fossil fuel-based power plants, and it has the potential to reduce the global warming. Attention has been drawn toward utilization of nanosize-based oxygen carrier for bulk application. CLC is a novel technology for combustion of fossil fuels that avoids dilution of carbon dioxide (CO2) with flue gases. Performance of CLC system depends upon redox reactivity and stability of oxygen carrier particles at high operating temperature. Oxides of metals like nickel, iron, copper, and mixed metals have also been discussed. Tendency of discussed nano-OC to agglomerate and stability at high temperature can be addressed by the use of suitable inert support materials. Reactivity of oxygen carrier increases with decreasing particle sizes from micro- to nanosize. Recent developments in nanosized oxygen carriers can be exploited for application. The challenges associated with nanosize oxygen carriers are stabilization and agglomeration at temperature above 600 °C. Different techniques have been proposed and investigated to overcome challenges. Various metal/metal oxide pair has been evaluated for its oxygen bearing capacity, stability, and resistance to agglomeration. Stability and agglomeration of nanosize oxygen carrier at temperature above 700 °C is an open issue.

Two-Step Synthesis of Ca-Based MgO Hybrid Adsorbent for Potential CO&lt;sub&gt;2 &lt;/sub&gt;Capturing Application

Carbon capture and storage (CCS) is one of the method in reducing carbon dioxide (CO2) emissions into the atmosphere. CO2 capturing using calcium oxide (CaO) solid sorbents has been considered as an advanced concept for CO2 capture and recovery. However, the adsorption capacity of CaO decreases during repeated adsorption/desorption cycles. The stability of Ca-based sorbents during cyclic runs can be achieved via the incorporation of inert support materials. Among the available inert materials, MgO is most promising for CO2 due to high stability and a high Tammann temperature. Most of Ca- based MgO hybrid adsorbent synthesis methods sorbent come with its own limitations which are longer synthesis duration and complex or multistep methods. In this research, Ca-based MgO hybrid adsorbent was prepared via two-step method. Calcium acetate and magnesium nitrate as precursor had dissolved in water, follow by addition of ethanol. The mixture then became gelated and proceeded for calcination at 550°C and 650°C. The prepared sorbent was characterized by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and fourier transfer infrared spectroscopy (FTIR). The XRD analysis of the Ca-based MgO hybrid adsorbent showed the existence of MgO,CaO and CaCO3. FTIR analysis showed presence of Ca─O bond and Mg═O bond. The morphology of the hybrid adsorbent was found to be spherical to granular shape and agglomerated. The Ca- based MgO hybrid adsorbent structural and morphological shows great potential for CO2 capturing capacity over multiple carbonation cycles for CO2 capturing application.

Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand

Gold-Silver (Au-Ag) bimetallic alloy nanoparticles exhibit improved catalytic activity in comparison to the monometallic nanoparticles due to synergistic effect. In this work Au-Ag bimetallic alloy nanoparticles (BNPs) have been supported on alkali activated sand which acts as an inert support material, stabilizes the nanoparticles and prevents their agglomeration. In addition to providing high surface area for adsorption, sand is inexpensive and environmentally benign. Au-Ag alloy nanoparticles were prepared via co-reduction mechanism using polymer as a stabilising agent. Alkali activated sand was coated with the alloy nanoparticles using surface adsorption method. Efficient reduction of 4-Nitrophenol to 4-Aminophenol by NaBH4 in the presence of BNPs supported on alkali activated sand was investigated. Also, the heterogenous nature of the catalyst makes it highly reusable due to its effortless separation from the reaction medium.

Assessment of water treatment residuals as sorbent material in permeable reactive barriers: Application to a copper‐contaminated site

AbstractThe objective of this study is to design a pilot‐scale permeable reactive barrier (PRB) for the removal of copper from groundwater in Keweenaw Peninsula, Michigan. The reactive material selected for the barrier is drinking water treatment residuals (WTR)—the residuals of alum coagulants used in a local drinking water treatment plant. Physical and chemical properties of the WTR were determined. Synthetic precipitation leaching procedure tests indicated the concentrations of hazardous elements leached from the residuals do not exceed U.S. Environmental Protection Agency limits and, hence, can be safely recycled as PRB material. Batch reactor tests showed that equilibrium sorption of copper is high and fits a Langmuir‐type isotherm. Site characterization studies included groundwater flow direction, pore water velocity, and contaminant concentration to determine optimal dimensions and placement of the PRB. Permeameter tests were performed with various mixtures of the WTR and an inert support material (pea gravel) to determine the ideal mix to match the hydraulic conductivity of the field site. Kinetic and column experiments were conducted to understand the significance of chemical and physical mass transfer limitations. Based on the results, dimensions of a PRB to meet the Michigan Department of Environmental Quality target level of 0.031 milligrams per liter (mg/L) total Cu were calculated.

Effect of calcium precursors on pelletized property and cyclic CO2 capture performance

CaO is widely used for capturing CO2 in large scale application however the work on the manufacture of CaO based pellets for the application of CO2 capture is relatively limited. In this research investigated the effect of calcium precursors (Ca(OH)2, Ca(NO3)2 and Ca(CH3COO)2) and their synthesis method (sol-mixing and wet-mixing) on pelletization. Adsorbent synthesized from Ca(CH3COO)2 as a precursor using sol-mixing pelletize to porous spherical provide the best mechanical strength and CO2 adsorption capacity 0.51 and 0.41 g CO2/ g CaO at first cycle and tenth cycle respectively. The outstanding cyclic performance of Ca(CH3COO)2 sol-mixing can be ascribed to the presence of inert support material i.e. Ca9Al6O18 and Ca12Al14O33 with suitable pore volume to prevent sintering of CaO and structure collapsing at high temperature.

Sintering inhibition of flame-made Pd/CeO2 nanocatalyst for low-temperature methane combustion

Dispersed palladium on the high-surface-area ceria support is synthesized via one-step flame-assisted spray pyrolysis method, which applies a highly-quenched stagnation-point flame controlling catalyst sizes and structures. The X-ray photoelectron spectroscopy (XPS) spectra of Pd show a significantly high binding energy for flame-made Pd/CeO2 catalysts, possessing a value of 1.7eV larger than the reference value in literature. It suggests that the partial electron transfer occurs from metal Pd to their supports during the synthesis process, which creates Pd electron-deficient (cationic Pdδ+) and Ce electron-rich (anion Ceδ−), respectively. The catalytic activities of CH4 oxidation are performed over the temperatures ranging from 200°C to 600°C. In comparison with inert support materials, the synergistic effect is found between palladium and support ceria that leads to the enhanced catalytic activity. During the heating and cooling cycles of CH4 oxidation, Pd/CeO2 catalysts exhibit an exceptional inhibition effect against the sintering of Pd cluster and its dispersion decrement, which is related to strong electronic interaction of metal-support interfaces induced by the aforementioned partial electron transfer.

Trace Determination of Acesulfame-K Using Voltammetric Nanosensor and Evaluation of Kinetic Parameters

Because of widespread application in food industry, measurement of Acesulfame-K (AcK) is an important subject. This material is a synthetic and non-caloric sweetener that has been widely used instead of sugar in foodstuffs. Powerful analytical methods are needed for this growing market to assure quality control and the ingredients of the products. Till now, several analytical methods have been reported concerning the determination of AcK and other sweeteners including linear sweep voltammetry, solid-phase extraction and liquid chromatography–tandem mass spectrometry, liquid extraction and liquid chromatography-tandem mass spectrometry, square-wave voltammetry, differential pulse voltammetry, capillary electrophoresis, FT-Raman spectroscopy, Spectrophotometry, sinusoidal envelope voltammetry and potentiometry [1-5]. Consequently, the determination of AcK is regarded as an interesting issue for many researchers that work in the spectroscopic, chromatographic and electroanalytical methods of analytical chemistry. Electroanalytical literature survey shows not only the lack of mechanistic and kinetic information about AcK electrochemical behavior, but also absence of ultrasensitive AcK nanosensor. Thus, construction of nanoparticle-based AcK voltammetric sensor and evaluation of kinetic parameters of AcK can be considered as the novel aspects of this research that might differentiate this one from the previously reported ones, to the best of our knowledge. The cyclic voltammetric (CV), differential pulse voltammetric (DPV) and electrochemical impedance spectroscopic (EIS) measurements were performed with µAutolab FRA2 Potentiostat-Galvanostat. A three-electrode system was used with the Pt rod (2 mm/ 87 mm) or NPtAPE as working electrodes, glassy carbon electrode (GC rod 2mm/ 76mm) as the counter and an Ag/AgCl as the reference electrode (Autolab comp.). All tests were conducted under room temperature. A digital pH meter (Jenway 370) was applied for pH adjustment. The AcK voltammetric nanosensor (NPtAPE) was constructed by using nano Platinum (NPt) and Agar paste (AP) as electrocatalyst and inert support material, respectively. The NPt content of NPtAPE is an important factor that affects the obtained current intensity of this nanosensor. Using Nyquist manner plots, the EIS confirmed diminishing of charge transfer resistance (Rct) and enhancing electron transfer at the surface of NPtAPE. Various supporting electrolytes such as KCl, NaNO3 and KNO3 were tested to select the best of them in forthcoming experiments. Exact experimental calculations revealed the best pH and kinetic parameters of electrooxidation of AcK at the working electrode surface. After that, probable mechanism for this process was suggested which has three steps. NPtAPE showed linear dynamic ranges and extraordinary pM detection limit that made it a powerful device in sensing of AcK at trace level. In the final step of the work, NPtAPE was utilized for AcK quantitation in candy samples purchased from different companies successfully. In summary, NPtAPE is a new voltammetric nanosensor for ultrasensitive and rapid AcK determination in candy samples. Hence, it can be recommended for the routine quality control of AcK in food products. The proposed method was based on the oxidation of AcK by appropriate potential at the NPtAPE surface. The principal advantages of the proposed nanosensor are its excellent detection limit, wide linear dynamic ranges, simplicity, selectivity and rapidity. The heterogeneous rate constant confirms the catalytic role of NPt particles in enhancing S/N ratio in order to constructing ultrasensitive nanosensor. Keywords: Acesulfame-K; Nano Platinum; Cyclic voltammetry; Differential pulse voltammetry; Kinetic parameters

Dynamic Modelling of Biofilm Reactors with Immobilised Sulfate-Reducing Bacteria

This paper presents a simple, reliable and extensible dynamic biofilm model. The model simulates the case of Sulfate-Reducing Bacteria (SRB) grown as biofilm on the surface of an inert support material in a completely mixed bioreactor. The principles of microbial stoichiometry and thermodynamics combined with microbial kinetic equations and chemical reactions have been implemented in AQUASIM software. Simulation results predict the biofilm growth, the reactor bulk volume solute concentrations and their corresponding profiles in the biofilm layer. The interaction of metal ions with biogenic sulfide is also discussed as decontamination means for a wastewater stream containing high metal and sulfate concentrations.

Thermal hydrogen-atom transfer from methane: A mechanistic exercise

Hydrogen-atom transfer (HAT) constitutes a key process in a broad range of chemical transformations as it covers heterogeneous, homogeneous, and enzymatic reactions. While open-shell metal oxo species [MO] are no longer regarded as being involved in the heterogeneously catalyzed oxidative coupling of methane (2CH4+<O>→C2H6+H2O), these reagents are rather versatile in bringing about (gas-phase) hydrogen-atom transfer, even from methane at ambient conditions. In this mini-review, various mechanistic scenarios will be presented, and it will be demonstrated how these are affected by the composition of the metal-oxide cluster ions. Examples will be discussed, how ‘doping’ the clusters permits the control of the charge and spin situation at the active site and, thus, the course of the reaction. Also, the interplay between supposedly inert support material and the active site – the so-called ‘aristocratic atoms’ – of the gas-phase catalyst will be addressed. Finally, gas-phase HAT from methane will be analyzed in the broader context of thermal activation of inert CH bonds by metal-oxo species.

Development of extraction chromatographic adsorbent using alkylpyridinedicarboxyamides as extractant for separation of trivalent minor actinides from lanthanides – stability and separation ability against nitric acid exposure and gamma-ray irradiation

Toward the development of a practical separation method for trivalent actinides and lanthanides, we used extraction chromatography with alkylpyridinedicarboxyamides as the extractant. The results confirmed that the performance degradation of the adsorbent caused by contact with HNO3 and/or irradiation with gamma-rays would be very small during the operation of column chromatography. The optimal conditions for the column separation were also determined: eluent, 5 M HNO3; flow rate, 0.1 mL min−1. In addition, the change of average particle size of inert support material from 250–850 μm (XAD4) to 25–45 μm (Gelpack A040) brought about the improvement of separation between trivalent actinides and lanthanides.

Understanding the effect of inert support on the reactivity stabilization for synthetic calcium based sorbents

The decay of sorbent reactivity in multiple carbonation/calcination cycles is a critical problem for calcium looping. By introducing inert support materials into CaO particles, the cyclic reactivity of calcium based sorbent could be drastically improved. However, there is a lack of understanding of the interaction between the CaO grain and the support material; thus, much of studies of synthesizing calcium based sorbents are by trial-and-error. In order to understand the possible mechanism of synthetic calcium based sorbent, the widely accepted Zener pinning theory in the field of metallurgy was used here to describe the inhibition of CaO grain sintering due to the addition of inert support. A simple model of CaO grain growth for synthetic calcium-based sorbents was developed to analyze the effect of inert support on the stabilization of cyclic reactivity of CaO. The mechanism of sintering resistant in the synthetic calcium-based sorbents was the pinning force exerted by the dispersed support particles. The inhibition effect of inert support on CaO grain growth is related with the grain migration due to surface energy (γ), support size (r) and volume fraction (f), and the interaction (Finteract) between the support and CaO. The model was validated with the published data and can predict reasonably the experimental results, and the relative importance of some elementary steps was discussed. This study will provide a theoretical understanding for the further development and reactivity improvement of synthetic calcium-based sorbents.

고체발효에서 반응표면분석법을 이용한 구연산 생산 최적화

본 실험에서는 Aspergillus niger NRRL 567의 고체배양을 이용한 구연산 생산 시, 물리/화학적 발효 조건인 배양 온도, 배지 pH, 접종 농도 및 수분 함량이 구연산 생산에 미치는 영향을 단일변수(one-factor-at-a-time)와 반응표면 분석법(surface response methodology)을 이용하여 순차적 최적화를 수행하였다. 단일변수 최적화의 경우, A. niger에 의한 구연산 생산은 물리/화학적 발효 조건에 의해 영향을 받으며, 발효 온도 <TEX>$30^{\circ}C$</TEX>, 영양 배지 pH 7.1, 수분 함량 75%와 접종 농도 <TEX>$4.0{\times}10^6$</TEX> spores/ml에서 최대 구연산 생산인 98.2 g/kg DPM (dry peat moss)을 보였다. 단일변수 최적화에 근거하여 반응표면 분석법을 도입하여 2차 최적화를 수행했을 경우, 배지 pH와 수분 함량이 구연산 생산에 유의한 영향을 주었으며 온도 <TEX>$26.5^{\circ}C$</TEX>, 영양 배지 pH 9.9, 수분 함량 75.1%와 접종 농도 <TEX>$6.0{\times}10^6$</TEX> spores/ml에서 최대 구연산 생산인 118.8 g/kg DPM가 얻어졌다. 이는 최적화 이전의 대조군에 비해 구연산 생산이 1.6배 증가한 결과이다. In this present study, Aspergillus niger NRRL 567 was cultivated on an inert support material and the effects of various fermentation parameters including temperature, nutrient solution pH, inoculation level, and moisture content were observed and optimized by one-factor-at-a-time (OFAT) and response surface methodology (RSM), sequentially. It was found that the incubation temperature of <TEX>$30^{\circ}C$</TEX> with 75% moisture content, nutrient solution pH of 7.1 and inoculation level of <TEX>$4.0{\times}10^6$</TEX> spores/ml were the most favorable. Again, fermentation parameters were optimized using RSM. The determined optimum condition is <TEX>$26.5^{\circ}C$</TEX>, pH 9.9, 75.1%, and <TEX>$6.0{\times}10^6$</TEX> spores/ml. Under this optimized condition, A. niger NRRL 567 produced 118.8 g citric acid/kg dry peat moss at 72 hr. Maximum citric acid production of optimized condition by RSM represented a 1.6-fold increase compared to that obtained from control experiment.