Resin Beads Research Articles

NMR Relaxometry to Monitor InSitu the Loading of Amberlite IR120 and Dowex Marathon MSC Resins With Ni2+ and Cu2+ During a Column Experiment.

The removal of heavy metal ions from wastewater often necessitates the use of ion exchange resins. Current methods for assessing ion exchange efficiency are indirect and destructive. Some heavy metal ions, such as Cu2+ and Ni2+, are paramagnetic and influence the NMR relaxation times of water protons. NMR relaxometry can therefore be utilized to track the removal of these ions by ion exchange resins. In this study, we use relaxometry to monitor insitu the loading with Ni2+ and Cu2+ of Amberlite IR120 and Dowex Marathon MSC resins, with the resin column inserted into a low-field NMR device. The multiexponential transverse relaxation curves were fitted using a biexponential model. Before and during the loading of the resin, the water with the slowest relaxation corresponds to treated water (free of Ni2+ or Cu2+) flowing between the resin beads. After saturation, the slowest fraction corresponds to the untreated solution (containing Ni2+ or Cu2+) flowing between the resin beads saturated with paramagnetic ions. The evolution with time of the transverse relaxation rate and the amplitude of the slowly relaxing water fraction shows a clear transition, occurring later at the bottom of the resin bed compared with the middle and top. This is interpreted as an indication of the saturation of the studied zone with paramagnetic ions, confirmed by the quantification of Ni2+ or Cu2+ in the effluent using AES spectroscopy. This proof-of-concept study demonstrates that NMR relaxometry can be used insitu to monitor the loading of a resin bed with paramagnetic ions.

PH-induced morphological reversible transition from microparticles to vesicles for effective bacteria entrapment

Polymer particles with stimuli-responsive properties offer promising applications in healthcare, chemical reactors, development of artificial cells and organelles, as well as in the entrapment of bacteria. In this study, a novel biocompatible, biodegradable, and pH-responsive diblock copolymer based on polylactide (PLA) and poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) was synthesized via a metal-free one-pot/simultaneous ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) approach (ROP/RAFT). This copolymer was then employed to produce highly monodisperse microparticles using microfluidics droplet generation technique. Utilizing confocal microscopy imaging, a reversible pH-induced morphological transition from microparticles to vesicle-like structures was observed at pH 5.1. The reversible shift in morphology from microparticles to giant vesicles (Vs) in acidic environments is triggered by the protonation of amino groups of the PDPA block, rendering vesicle surfaces positively charged − an advantageous feature for attracting and engulfing negatively charged bacteria. Initial validation involved electrostatic interactions with negatively charged latex resin beads followed by assessing interaction capabilities with gram-negative bacteria, Escherichia coli (E. coli). Additionally, the reversible morphological transition of microparticles-to-vesicles was employed to study drug release at different pHs. This approach proven to be a promising strategy for targeted drug delivery and bacteria entrapment using smart pH-responsive microparticles.

Development of hybrid landing gear for OMOTENASHI surface probe

This study presents technologies of the triple hybrid landing gear for the OMOTENASHI(Outstanding Moon exploration Technologies demonstrated by Nano Semi-Hard Impactor) spacecraft, which consists of an airbag, a crushable material as a shock absorber, and an impact resistance structure. The inflated airbag has capability to possibly mitigate impact acceleration at the instant of landing and submergence into regolith that covers a planetary surface. The crushable material with lattice structures, manufactured by a metal 3D printer, serves a dual purpose: it dissipates kinetic energy and controls the impact acceleration at landing by compressing itself within a designed deceleration distance. Further, in the impact resistance structure, the protective object is filled with resin and hollow glass beads, and the impact resistance is improved while the weight reduction is maintained. This paper provides the technical details such as the required specification, verification test results, and assembly result of the surface probe as the smallest lander of the OMOTENASHI spacecraft.

Gold recovery from chloride leach solution of TCCA using D301 anion exchange resin and elution with thiourea

Trichloroisocyanuric acid (TCCA), which is used for gold leaching, is an alternative to cyanidation due to its lower toxicity and higher efficiency. This study investigated the gold recovery procedures from highly effective chloride leaching solution using the D301 resin. This approach prevented the inhibition of gold adsorption when using activated carbon. Herein, the optimal conditions for gold adsorption were discussed, including establishing adsorption kinetics and isotherms, and calculating adsorption activation energy. Additionally, SEM (Scanning Electron Microscope), FTIR (Fourier Transform Infrared Spectroscopy), and XPS (X-ray Photoelectron Spectroscopy) techniques were used to reveal the mechanism of gold adsorption using D301 resin. Under optimal conditions (pH 4.0, temperature 25 °C, time 120 min), an average adsorption percentage of 99.2% was achieved. Analysis of the adsorption data confirmed that gold adsorption followed the pseudo-second-order kinetic model and Freundlich adsorption isotherm. The calculated activation energy was 9.69 kJ mol−1, indicating a predominance of physical adsorption involving ion exchange reactions with protonated tertiary amine groups in the D301 resin beads. Furthermore, among various eluents tested in desorption experiments, a solution containing a mixture of thiourea and hydrochloric acid with 0.4 mol L−1 and 0.8 mol L−1, respectively, demonstrated superior efficiency, achieving a successful desorption percentage reaching 95.7 ± 0.3% within 80 min. After three cycles of resin regeneration, the regeneration efficiency reached 91.2% while maintaining an average adsorption percentage of 95.3%.

Transformation of Cu2O into Metallic Copper within Matrix of Carboxylic Cation Exchangers: Synthesis and Thermogravimetric Studies of Novel Composite Materials.

In order to systematize and expand knowledge about copper-containing composite materials as hybrid ion exchangers, in this study, fine metallic copper particles were dispersed within the matrix of a carboxyl cation exchanger (CCE) with a macroporous and gel-type structure thanks to the reduction of Cu2O particles precipitated within the matrix earlier. It was possible to introduce as much as 22.0 wt% Cu0 into a gel-type polymeric carrier (G/H#Cu) when an ascorbic acid solution was used to act as a reducer of Cu2O and a reagent transforming the functional groups from Na+ into the H+ form. The extremely high shrinkage of the porous skeleton containing -COOH groups (in a wet and also dry state) and its limited affinity for water protected the copper from oxidation without the use of special conditions. When macroporous CCE was used as a host material, the composite material (M/H#Cu) contained 18.5 wt% Cu, and copper particles were identified inside the resin beads, but not on their surface where Cu2+ ions appeared during drying. Thermal analysis in an air atmosphere and under N2 showed that dispersing metallic copper within the resin matrix accelerated its decomposition in both media, whereby M/H#Cu decomposed faster than G/H#Cu. It was found that G/H#Cu contained 6.0% bounded water, less than M/H#Cu (7.5%), and that the solid residue after combustion of G/H#Cu and M/H#Cu was CuO (26.28% and 22.80%), while after pyrolysis the solid residue (39.35% and 26.23%) was a mixture of carbon (50%) and metallic copper (50%). The presented composite materials thanks to the antimicrobial, catalytic, reducing, deoxygenating and hydrophobic properties of metallic copper can be used for point-of-use and column water/wastewater treatment systems.

Design of a continuous ion exchange process in battery metals recycling: From single column experiments towards a simulated moving bed configuration

In hydrometallurgical recovery of LIB metals, ion exchange (IX) has hitherto played only a minor role. Separation experiments were conducted in single laboratory-scale IX columns with the aim of laying the foundation for a continuously operated multicolumn IX process similar to a simulated moving bed (SMB) configuration. In this study, the initial process developed earlier was improved by reducing the number of process steps and external streams. The desorption step with oxalate solution was examined in single-column batch experiments to ensure complete desorption of iron in the proposed continuous multicolumn IX process. Additionally, the volume flowrates were adjusted to achieve acceptable switch times of 25 min in an SMB configuration. It was found that the bead size of the resin is a critical factor in IX recovery of battery metals. The raffinate purity for the case of processing 2.5 BV lithium-ion battery waste leachate (LIBWL) improved from 97.2 % to 99.8 % when the resin bead size was reduced from 0.55 ± 0.05 mm to 0.4 ± 0.04 mm and a narrower bead size distribution. The LIBWL feed concentration was varied to mimic the dilution of fresh feed in an SMB set-up. The percentage recovery of Co and Ni decreased from 93.7 % and 96.6 % to 80.8 % and 89.4 %, respectively, when the LIBWL was diluted. This was a result of the decrease in concentration of impurity metals in the feed. Less impurity metals were sorbed and consequently, more ion exchange sites were available for the sorption of the target metals, which enhanced the retention of Co and Ni. The results were used to develop an IX column operation strategy and to suggest an initial SMB design. The multicolumn configuration presented in this work offers great potential for continuous production of high-purity Li, Ni and Co-containing raffinate (> 99.5 %).

Bead-based spontaneous Raman codes for multiplex immunoassay

In the immunoassay process, for fulfilling the need to identify multiple analytes in a small amount of complex sample matrix, it is desirable to develop highly efficient and specific multiplex suspension array technology. Raman coding strategy offers an attractive solution to code the suspension arrays by simply combing narrow spectral bands with stable signal intensities through solid-phase synthesis on the resin beads. Based on this strategy, we report the bead-based spontaneous Raman codes for multiplex immunoassay. The study resulted in superior selectivity of the Raman-encoded beads for binding with single and multiple analytes, respectively. With the use of mixed types of Raman-encoded immunoassay beads, multiple targets in small amounts of samples were identified rapidly and accurately. By confirming the feasibility of bead-based spontaneous Raman codes for multiplex immunoassay, we anticipate this novel technology to be widely applied in the near future.

CaptureSelect FcXP affinity medium exhibits strong aggregate separation capability

Protein A affinity chromatography has been widely used for initial product capture in recombinant antibody/Fc-fusion purification. However, in general Protein A lacks the capability of separating aggregates (unless the aggregates are too large to enter the pores of resin beads or have their Protein A binding sites buried, in which case the aggregates do not bind). In the current work, we demonstrated that CaptureSelect FcXP affinity medium exhibited strong aggregate separation capability and effectively removed aggregates under pH or conductivity gradient elution in two bispecific antibody (bsAb) cases. For these two cases, aggregate contents were reduced from >16% and >22% (in the feed) to <1% and <5% (in the eluate) for the first and second bsAbs, respectively. While more case studies are required to further demonstrate FcXP's superiority in aggregate removal, findings from the current study suggest that FcXP can potentially be a better alternative than Protein A for product capture in cases where aggregate content is high.

A shape-predictive model for the spreading of photo-curable polymers in material extrusion additive manufacturing

Recently, there is a growing interest in material extrusion to print thermoset resins to manufacture large format and high-performance parts. However, the fidelity and mechanical integrity of the printed parts are limited by challenges such as uncontrolled spreading of individual beads (filament/droplet) after deposition and during cure. There is a considerable lack of experimental and theoretical studies on the spreading of reactive beads on solid substrates. In this work, we studied the simultaneous spreading and photo-curing of the photopolymerizable thermoset beads via experiment and numerical simulations. We used a novel experimental setup to track the spreading of droplets and filaments during photopolymerization and validate a moving mesh computational fluid dynamics (CFD) model. The CFD model was used to develop an approach (predictive model) to accurately predict the final spreading coefficient of cured resin beads without the need for full numerical simulations. The predictive model combines the generalized theory of a Newtonian spreading filament with a characteristic viscosity μave and time to gelation, τgel. Interestingly, μave is shown to be a material parameter that does not depend on processing conditions, but only on the material’s chemorheology. The predictive model is tested against a wide range of chemorheology and cure kinetic parameters and found to be in excellent agreement with the full numerical CFD simulations. This work will be very useful in estimating the final shape of beads during the material extrusion printing process, as well as a model to successfully parameterize extrusion-based 3D printers to control the shape of printed beads a-priori.

The effect of flame treatment on the compressive strength of composite sandwich panels made of pure epoxy resin H‐shaped structures and hollow glass bead/epoxy resin composite material

AbstractAt present, syntactic foam composites (HGB/EP) made of epoxy resin (EP) and hollow glass beads (HGBs) have received extensive attention in the research field of lightweight materials because of their high compression strength‐to‐density ratio. However, the deep‐sea environment has put forward higher requirements for the compressive properties of materials. The traditional sandwich structure with HGB/EP as the core has gradually failed to meet the requirements for the mechanical properties of equipment deeper in the ocean. This paper proposes a sandwich structure comprising a pure EP H‐shaped structural component as the rigid skeleton and an HGB/EP syntactic foam composite as the lightweight filling component. The pure EP H‐shaped structural component was subjected to flame treatment using a butane flame jet at different distances. The compression resistance of the resulting sandwich structure was tested, and the results showed varying degrees of improvement in compressive strength after flame treatment. The effects of flame treatment on the surface adhesion performance of the pure EP were characterized using compression‐shear tests, optical microscopy, contact angle tests, infrared spectroscopy, and flame temperature tests. The results demonstrated that flame treatment at a distance of 0 cm significantly increased the oxygen‐containing functional groups on the surface of the pure EP, improved the wettability of the pure EP surface, increased the adhesive strength between the pure EP H‐shaped structural component and HGB/EP, and enhanced the compressive strength of the sandwich structure. The shear strength of the shear test specimens improved by 33.0%, while the compressive strength of the sandwich structure specimens increased by 17.5%.Highlights The sandwich structure composed of pure epoxy resin H‐shaped structure and foam composite material was prepared. The distance of flame treatment affects the surface chemical groups of epoxy resin. Flame treatment significantly improved the surface wettability of epoxy resin.

Low-blank method for the offline batch analysis of the low concentration of dissolved lead in natural waters and its application to natural waters, including the tropical Northwest Pacific Ocean

In this study, Presep® PolyChelate resin was utilized for the offline batch extraction process and then combined with the isotope dilution method for the analysis of low concentrations of dissolved lead (Pb) in freshwater and seawater. The application of Presep® PolyChelate resin further lowered the procedural blank by reducing the amount of resin beads and buffer solution that were added with an 8-fold preconcentration. The adsorption and elution times were shortened to 2 d and 30 min, respectively, and > 85% recovery was achieved. The total procedural blank and detection limit were 0.2 ± 0.1 pmol/kg and 0.2 pmol/kg, respectively. The accuracy of this method was also verified using GEOTRACES intercalibration SAFe seawaters, with concentrations of 48.0 ± 0.5 pmol/kg (n = 3) and 27.0 ± 0.7 pmol/kg (n = 3) observed for SAFE S and D2, respectively. Full-depth profiles of dissolved Pb concentrations collected during the 2016 tropical Northwest Pacific Ocean cruise were analyzed. The dissolved Pb concentration increased from 30 pmol/kg at the surface to 50 pmol/kg at the subsurface and it then decreased to 8–9 pmol/kg in the bottom waters.

Enzymatic synthesis of tyrosol esters in organic solvents and ionic liquids: Correlation between enzyme activity and solvent properties

Tyrosol is a principle phenolic compound present in olive oil and wine with great pharmacological potentials due to its strong antioxidant property. Its application can be highly extended by increasing its lipophilicity through esterification. In this study, tyrosol esters were synthesized by enzymatic transesterification of tyrosol with vinyl esters, with a commercial lipase from Novozymes (Novozym 435, Candida antarctica lipase B (CALB) immobilized on macroporous acrylic resin beads) as the catalyst, both in organic solvents and in ionic liquids. Methyl tert-butyl ether (MTBE) was the best solvent, offering complete conversions towards the synthesis of tyrosol esters with varying chain lengths (C2-C18) within 1 h. Taking the enzymatic transesterification between tyrosol and vinyl acetate as the model reaction, 18 organic solvents and 24 ionic liquids were screened, and their solvent properties (i.e. hydrophobicity, polarity, viscosity, water activity, and partition coefficients of substrate and product) were correlated to the enzyme activity. Upon enzyme screening, four new lipases were found to be highly efficient, relative to the best-performed Novozym 435 and Lipozyme TLIM (Thermomyces lanuginosus lipase (TLL) immobilized on silica gel), in tyrosol ester synthesis. This work provides enzymatic methods of esterifying tyrosol that are much more efficient than those reported in literature, and will shed light on re-consideration of the roles of solvents in nonaqueous enzymology.

Improved mRNA affinity chromatography binding capacity and throughput using an oligo-dT immobilized electrospun polymer nanofiber adsorbent

Increased demand for mRNA-based therapeutics and improved in vitro transcription (IVT) yields have challenged the mRNA purification platform. Hybridization-affinity chromatography with an immobilized oligo-deoxythymidilic acid (oligodT) ligand is often used to capture mRNA through base pairing with the polyadenylated tail. Commercially available oligodT matrices include perfusive cross-linked poly(styrene-divinylbenzene) 50 µm POROS™ chromatography resin beads and convective polymethacrylate CIMmultus® monolithic columns consisting of 2 µm interconnected channels. POROS™ columns may be limited by poor mass transfer for larger mRNAs and slow flowrates, while monoliths can operate at higher flowrates but are limited by modest binding capacity. To enable both high flowrates and binding capacity for mRNA of all lengths, prototype chromatography media was developed by Cytiva using oligodT immobilized electrospun cellulose nanofibers (Fibro™) with a 0.3–0.4 µm pore size. In this work, four polyadenylated mRNAs ranging from ∼1900–4300 nucleotides were used to compare the dynamic binding capacity (DBC) of Fibro™, POROS® and CIMmultus® columns as a function of residence time and binding buffer compositions. Fibro™ improved the DBC ∼2–4-fold higher than CIMmultus® and ∼2–13-fold higher than POROS™ across all residence times, mRNA length, and binding matrix compositions tested. CIMmultus® DBC was least dependent on residence time and mRNA size, while both Fibro™ and POROS™ DBC increased at slower flowrates and with shorter mRNA. Surprisingly, inverse size exclusion (ISE) experiments showed that POROS™ was not limited by diffusion and POROS™ along with CIMmultus® demonstrate higher mRNA permeation however the Fibro™ prototype is not in the final configuration. Lastly, IVT reaction products were subjected to purification and oligodT elution product yield, quality, and purity were consistent across the three matrices investigated. These results highlight the benefits of high DBC and equivalent product profiles offered by the oligodT Fibro™ prototype compared to commercially available oligodT media.

Development of a solid-supported light-triggered nitric oxide donor

Nitric Oxide (NO) photocleavable donors are useful tools for interrogating nitric oxide signalling and have potential use in photopharmacological applications. There is currently intensive research into newer methods to improve NO release and kinetic profiles. Herein, we report the design and synthesis of a solid-supported photocleavable NO donor synthesized by ligating an N-nitroso photocleavable nitric oxide derivative to a TentaGel® polymer resin bead. Illumination with 365 nm light released nitric oxide that could be tracked via a turn-on fluorescence response (λex = 450 nm, λem = 545 nm) and measured using the Griess assay and diaminorhodamine derivatives. These beads were further shown to be compatible with living A549 cells and had the ability to deliver greater concentrations of nitric oxide to cells proximal to a bead versus cells at more distal locations within the same well.

High-Throughput Screening of pH-Dependent β-sheet Self-Assembling Peptide.

pH-dependent peptide biomaterials hold tremendous potential for cell delivery and tissue engineering. However, identification of responsive self-assembling sequences with specified secondary structure remains a challenge. In this work, An experimental procedure based on the one-bead one-compound (OBOC) combinatorial library is developed to rapidly screen self-assembling β-sheet peptides at neutral aqueous solution (pH 7.5) and disassemble at weak acidic condition (pH 6.5). Using the hydrophobic fluorescent molecule thioflavin T (ThT) as a probe, resin beads displaying self-assembling peptides show fluorescence under pH 7.5 due to the insertion of ThT into the hydrophobic domain, and are further cultured in pH 6.5 solution. The beads with extinguished fluorescence are selected. Three heptapeptides are identified that can self-assemble into nanofibers or nanoparticles at pH 7.5 and disassemble at pH 6.5. P1 (LVEFRHY) shows a rapid acid response and morphology transformation with pH modulation. Changes in the charges of histidine and hydrophobic phenyl motif of phenylalanine may play important roles in the formation of pH-responsive β-sheet nanofiber. This high-throughput screening method provides an efficient way to identify pH-dependent β-sheet self-assembling peptide and gain insights into structural design of such nanomaterials.

Enhanced adsorption performance of varying-length mRNA on Oligo dT affinity resins through optimal pore size and grafting

The enormous potential of mRNA-based therapeutics in vaccines and medicine has led to the consideration of various mRNA sizes, ranging from ∼1000 to 10,000 nucleotides (nt). However, the commonly used Oligo-deoxythymidine (Oligo dT) affinity resins are not initially designed for such a wide range of sizes, and present challenges in achieving optimal performance for the separation of a given mRNA. In this paper, two factors of the resin beads, pore size and grafting were focused. The effects of varying pore sizes, ranging from 150 to 850 nm, on both static and dynamic adsorption for varying-length mRNA (1000–8500 nt) were investigated. It was found that static adsorption capacity and uptake kinetics were correlated with the mRNA length. Interestingly, dynamic binding capacities (DBCs) showed an increase-then-decrease trend with increasing pore size. An optimal pore size of about 350 nm could lead to the highest DBCs for all tested mRNA. Additionally, the effects of polymer grafting on the adsorption performance were studied. The results revealed that polymer-grafted resin exhibited 24–55% higher DBCs than non-grafted resin. The enhanced DBCs could be attributed to the improved uptake rate facilitated by the polymer grafted. These investigations emphasize the importance of optimizing pore size and grafting for Oligo dT affinity resins, providing valuable guidance for selecting and designing new resins for different mRNA products.

Numerical analysis of the porous structure of spherical activated carbons obtained from ion-exchange resins

This paper presents the results of an analysis of the porous structure of spherical activated carbons obtained from cation-exchange resin beads subjected to ion exchange prior to activation. The study investigated the effects of the type of cation exchange resin, the concentration of potassium cations in the resin beads and the temperature of the activation process on the adsorption properties of the resulting spherical activated carbons. The numerical clustering-based adsorption analysis method and the quenched solid density functional theory were used to analyse the porous structure of spherical activated carbons. Based on original calculations and unique analyses, complex relationships between preparation conditions and the porous structure properties of the obtained spherical activated carbons were demonstrated. The results of the study indicated the need for simultaneous analyses using advanced methods for the analysis of porous structures, i.e., the numerical clustering-based adsorption analysis method and the quenched solid density functional theory. This approach allows a reliable and precise determination of the adsorption properties of the materials analysed, including, among other things, surface heterogeneities, and thus an appropriate selection of production conditions to obtain materials with the expected adsorption properties required for a given industrial process.

SEC-HPLC analysis of column load and flow-through provides critical understanding of low Protein A step yield

For a certain number of mAbs, bispecific antibodies (bsAbs) and Fc-fusion proteins that we worked on, the Protein A capture step experienced low yield (i.e., ∼80%). A previous case study suggested that non-binding aggregate formed in cell culture was the root cause of low Protein A step yield. In the current work, we selected five projects with the low Protein A yield issue to further illustrate this phenomenon. In all cases, existence of non-binding aggregates was confirmed by size-exclusion chromatography-high performance liquid chromatography (SEC-HPLC) analysis of Protein A load and flow-through. In addition, we demonstrated that aggregates failed to bind to Protein A resin mainly due to their large sizes, which prevented them from entering the resin beads. As the data suggested, SEC-HPLC analysis of Protein A load and flow-through, although not a standard procedure, can provide information that is critical for understanding the unexpected performance of Protein A chromatography in cases like those being presented here. Thus, SEC-HPLC analysis of Protein A load and flow-through is highly recommended for antibodies/Fc-fusions suffering from low Protein A yield.

Two-stage reaction rates in transesterification of palm oil with methanol catalysed by anion-exchange resin with tetrahydrofuran as a co-solvent

Several heterogeneous catalysts have been proposed as recoverable catalysts for transesterification in place of homogeneous hydroxide or methoxide. Anion-exchange resin is a potential recoverable and reusable catalyst but its industrial use is still barred by its low catalytic activity. Transesterification of refined palm oil with methanol catalysed by anion-exchange resin was studied. A phenomenon limiting the reaction rates was discovered and is presented. Two types of anion-exchange resins were used as the catalysts: dense IRA402 and macroporous A26. With IRA402, an oil conversion of only 6.1 % was obtained from 4 h transesterification at 60 °C with a methanol-to-oil molar ratio of 9.5:1 and 4 cm3 resin per 42 cm3 reaction mixture. Severe mass transfer resistance in this three-phase system appeared to be the limiting factor. Addition of tetrahydrofuran (THF) as a co-solvent helped form a single liquid phase. The oil conversion was improved to 19.3 %. The reaction between oil and adsorbed methoxide at resin’s ion-exchange sites seemed to be the rate-determining step. When A26 was used, the rate of FAME production was boosted due to the porous nature of the resin. Nevertheless, the reaction rate fell sharply after a while into a slower second stage. The formation of a secondary liquid phae in resin pores triggered by glycerol generation was proposed as the cause of this drop in the reaction rate. A higher oil conversion of 63.4 % was obtained. Diluting the reaction mixture with more THF eliminated the slower second stage and sustained the firststage’s faster reaction rate. An oil conversion of 84.7 % was achieved from 3 h transesterification. A finite-volume model was developed to simulate the reaction and internal mass transport in A26 resin beads. The proposed secondary liquid phase formation and a branching pore structure in resin beads were required in the model to reproduce experimental data. The findings suggested improvement directions for anion-exchange resin as a catalyst for transesterification.

Potential Errors in Cation Exchange Capacity Measurement in Soils Amended with Rock Dust: Two Case Studies

ABSTRACT The use of rock dust in agriculture has increased worldwide and particularly in Brazil since its regulation by Law 12.890 (2013). However, some inconsistent results in standard chemical analysis of soils amended with rock dust have drawn attention, and among them, cation exchange capacity (CEC). This paper evaluates the increase in sum of bases (SB) and CEC of two soils amended with commercial rock dust (magnesium silicate), measured by four methods: ion exchange resin, potassium chloride (KCl), compulsive exchange and cesium adsorption. The maximum possible increase of SB in the soil was estimated based on the total chemical analysis of the rock dust and compared to the measured CEC results. We concluded the resin method inflated the results, due to the dissolution of rock dust particles by the acid extraction used to recover the adsorbed cations in resin beads. These extra cations caused overestimation of the sum of bases and consequently, of the estimated CEC. Among the methods used, direct CEC methods were more appropriate, as well as the KCl, since it does not employ acid extractions at any step. In addition, calculations based on the total chemical analysis of the rock dust can help to identify some of the cases in which the routine analysis is inflated by the dissolution of rock dust.