Solid Calcium Research Articles

Solid Catalyzed Reaction of <i>Jatropha Curcas</i> Seed Oil with Methanol

Production of biodiesel by transesterification method from renewable feedstock has come to stay. Biodiesel usage in internal combustion engines is gradually gaining ground due to its ability to produce less carbon (iv) oxide gas than fossil diesel during combustion. The production of less carbon (iv) oxide fumes will help to reduce environmental pollution that causes climate change. Jatropha curcas seed oil is a viable renewable feedstock for biodiesel production. Transesterification of Jatropha curcas seed oil with methanol using solid calcium oxide as catalyst was carried out. The free fatty acid of the oil used was 1.4%, while the molar ratio of methanol to oil, reaction temperature and time were 8:1, 65 °C, and 1hour respectively. The biodiesel produced was analyzed with gas chromatography mass spectrophotometer and the methyl ester content was 87.25%. The fuel properties of the biodiesel produced in a reaction time of about 1 hour 30 minutes are within the range of the values given by ASTM D6751 standard.

Confining Iron Oxide Nanocubes inside Submicrometric Cavities as a Key Strategy To Preserve Magnetic Heat Losses in an Intracellular Environment.

The design of magnetic nanostructures whose magnetic heating efficiency remains unaffected at the tumor site is a fundamental requirement to further advance magnetic hyperthermia in the clinic. This work demonstrates that the confinement of magnetic nanoparticles (NPs) into a sub-micrometer cavity is a key strategy to enable a certain degree of nanoparticle motion and minimize aggregation effects, consequently preserving the magnetic heat loss of iron oxide nanocubes (IONCs) under different conditions, including intracellular environments. We fabricated magnetic layer-by-layer (LbL) self-assembled polyelectrolyte sub-micrometer capsules using three different approaches, and we studied their heating efficiency as obtained in aqueous dispersions and after internalization by tumor cells. First, IONCs were added to the hollow cavities of LbL submicrocapsules, allowing the IONCs to move to a certain extent in the capsule cavities. Second, IONCs were coencapsulated into solid calcium carbonate cores coated with LbL polymer shells. Third, IONCs were incorporated within the polymer layers of the LbL capsule walls. In aqueous solution, higher specific absorption rate (SAR) values were related to those of free IONCs, while lower SAR values were recorded for capsule/core assemblies. However, after uptake by cancer cell lines (SKOV-3 cells), the SAR values of the free IONCs were significantly lower than those observed for capsule/core assemblies, especially after prolonged incubation periods (24 and 48 h). These results show that IONCs packed into submicrocavities preserve the magnetic losses, as the SAR values remained almost invariable. Conversely, free IONCs without the protective capsule shell agglomerated and their magnetic losses were strongly reduced. Indeed, IONC-loaded capsules and free IONCs reside inside endosomal and lysosomal compartments after cellular uptake and show strongly reduced magnetic losses due to the immobilization and aggregation in centrosymmetrical structures in the intracellular vesicles. The confinement of IONCs into sub-micrometer cavities is a key strategy to provide a sustained and predictable heating dose inside biological matrices.

A New Route for Indirect Mineralization of Carbon Dioxide\u2013Sodium Oxalate as a Detergent Builder

Here, we bridge the gap between carbon mineralization and laundry detergent builder with sodium oxalate. Daily laundry can help mineralize carbon dioxide. First, we screen an environment-friendly process to produce sodium oxalate, using CO2 as a raw material. Then, we evaluate the properties of sodium oxalate as a detergent builder and prove the formation of calcium oxalate under laundry conditions. Our data suggest that sodium oxalate has excellent calcium-removing properties. Detergents based on sodium oxalate have good detergency. Furthermore, solid calcium oxalates (calcium oxalate monohydrate or calcium oxalate dihydrate, which has good stability in water and thermal stability), is obtained from washing waters. These results demonstrate the possibility of using sodium oxalate as detergent builder. The whole process can transform the greenhouse gas CO2 into commodity chemicals and can mineralize carbon.

Morphological transformation of calcium phenylphosphonate microspheres induced by micellization of γ-polyglutamic acid

The γ-polyglutamic acid (γ-PGA), an anionic homo-polyamide similar to naturally occurring polyaspartic acid in mollusk shells, is selected for morphosynthesis of calcium phenylphosphonates. It has been found that they exhibit a series of interesting morphological transformation with changing γ-PGA amount and initial pH. A rare, reversible transformation between solid and hollow microspheres, in particular, is observed. Systematic investigation suggests, for the first time, that γ-PGA exhibits the “schizophrenic” micellization behavior in response to structural and morphological changes caused by spontaneous hydrophobic modification with phenylphosphonic acids and calcium ions. The present work introduces a new paradigm for biomimetic synthesis. The results not only bring insight into the template mechanism of biomacromolecules from spontaneous hydrophobic modification, but also provide a universally applicable strategy for morphosynthesis of metal phosphonates containing hydrophobic groups. In addition, solid and hollow calcium phenylphosphonate microspheres with hierarchical structures are excellent adsorbents in the removal of aqueous lead ions. They consistently exhibit 100% Pb2+ removal efficiency when Pb2+ concentration is not more than 600 mg L−1 and even after four recycles, making them promising candidates as efficient and reusable adsorbents.

Increasing calcium solubility from whey mineral residues by combining gluconate and δ-gluconolactone

Insoluble milk mineral residues from whey processing, dominated by hydroxyapatite and calcium hydrogen phosphate, dissolved isothermally in aqueous gluconate/δ-gluconolactone, spontaneously forming solutions supersaturated in both calcium hydrogen phosphate and calcium gluconate. Calcium concentration of maximally supersaturated solutions was proportional to gluconate concentration, indicating gluconate assisted dissolution, while gluconolactone increased calcium available for dissolution and supersaturation. Precipitation of calcium gluconate, rather than of calcium hydrogen phosphate, was critical for supersaturation robustness. For calcium gluconate ionic product:solubility product of calcium gluconate ratios <12, the supersaturated solutions had a lag phase for precipitation of several weeks, which increased to several months by addition of solid calcium saccharate prior to dissolution of the mineral residues. Such supersaturated solutions with up to 7 g calcium L−1, corresponding to a factor of supersaturation of >100 times compared with equilibrium calcium hydrogen phosphate solubility, may be exploited for increasing calcium availability of whey mineral based functional foods.

Ultra-fast route to synthesizing biogenic carbonate hydroxyapatite: Consequence of a high-pressure solid-solid preparation technique

We employed a high-pressure solid–solid preparation technique in CO2 to synthesize carbonate hydroxyapatite (CHAp) powders from solid calcium and phosphate precursors. The synthesis parameters were investigated and optimized to determine the best precursor and optimal synthesis conditions. The results showed that the technique is green and that the biogenic calcium from eggshells in supercritical CO2 yielded B-type CHAp with desirable and recommended carbonate contents (4.1–5.1 wt %). The biogenic calcium source also yielded product with excellent surface area (212.4m2/g) and pore volume (0.65 cm3/g) compared to the synthetic calcium source, which exhibited high ibuprofen loading (270.0 mg/g) and enhanced dissolution (100% in 6 h) in simulated gastric fluid. These results indicate that the CHAp has potential for medical and other related applications. Mechanism study revealed that the procedure is a self-catalytic reaction triggered by water in the reactants with short time, which can overcome the disadvantages of existing techniques commendably.

Al2O3-Based Ceramic Composites with a High Brittle Fracture Resistance

We examine synthesis conditions of precursors to ZrO2–Al2O3–CeO2 powders modified with calcium cations. The precipitation procedure and the aging of reaction systems of precursors to the synthesized composites are shown to influence the morphology and particle size of the nanopowders and the evolution of the phase composition, microstructure, and mechanical characteristics of composites prepared from them. The composites offer a high brittle fracture resistance due to the combined effect of transformation and dispersion hardening owing to the presence of T-ZrO2-based solid solutions and calcium hexaaluminates (bending strength, up to 1000 MPa; fracture toughness KIc, up to 10.5 MPa m1/2).

CaCO3 supplementation of low-carbon wastewaters for the cultivation of Microalgae : a study with Desmodesmus multivariabilis

Microalgal biomass cultivated in wastewater has the potential for refining to energy products such as biodiesel and biohydrogen with the additional benefit of also treating the wastewater. As many species of microalgae can employ both Heterotrophic and Autotrophic modes of carbon synthesis, low-carbon waters benefit from the addition of inorganic carbon to the water. Capital and operational costs are a deterrent to using CO2 and other alternatives may be more attractive. NaHCO3 is a popular alternative but as a result of its solubility and alkalinity quickly raises the pH of the water which inhibits algal growth due the presence of free ammonia at high pH values. In this experiment, the growth of a South African strain of Desmodesmus multivariabilis was studied in the presence of solid calcium carbonate. Calcium carbonate was chosen for its low solubility, which would potentially allow for its dissolution to be driven by the inorganic carbon uptake in the media. The performance was compared to that of aerated wastewater and wastewater with solid CaSO4 as a non-carbon-containing substitute. It was found that there were significant differences in the growth and metabolism of all three experiments. Growth in the presence of solid calcium carbonate and calcium sulphate showed a preference for attached growth in the vicinity of solids, while suspended growth was preferred when just air was supplied. Furthermore, the experiment with air showed the highest growth rate, nitrogen uptake and a biomass yield that was more than an order of magnitude higher than with CaCO3. The experiment with CaSO4 showed low yields and growth rates, possibility indicating and inhibitory effect of the CaSO4. In the presence of CaCO3, a very high yield of extracellular organic metabolites was observed. The presence of these metabolites, as well as the stability of the pH and low growth, is a possible indication that the organism was controlling the pH as a defence mechanism. Despite not being a favourable substrate for growing D. multivariabilis, the high yield of extracellular metabolites may have a commercial potential, and the nature and use these metabolites deserve further investigation.

Oxygen generating biomaterial improves the function and efficacy of beta cells within a macroencapsulation device

Tissue-engineered devices have the potential to significantly improve human health. A major impediment to the success of clinically scaled transplants, however, is insufficient oxygen transport, which leads to extensive cell death and dysfunction. To provide in situ supplementation of oxygen within a cellular implant, we developed a hydrolytically reactive oxygen generating material in the form of polydimethylsiloxane (PDMS) encapsulated solid calcium peroxide, termed OxySite. Herein, we demonstrate, for the first time, the successful implementation of this in situ oxygen-generating biomaterial to support elevated cellular function and efficacy of macroencapsulation devices for the treatment of type 1 diabetes. Under extreme hypoxic conditions, devices supplemented with OxySite exhibited substantially elevated beta cell and islet viability and function. Furthermore, the inclusion of OxySite within implanted macrodevices resulted in the significant improvement of graft efficacy and insulin production in a diabetic rodent model. Translating to human islets at elevated loading densities further validated the advantages of this material. This simple biomaterial-based approach for delivering a localized and controllable oxygen supply provides a broad and impactful platform for improving the therapeutic efficacy of cell-based approaches.

Study on catalytic pyrolysis of vacuum residue and its eight group-fractions with solid acid-base mixed catalysts by Py-GC/MS

ZSM-5 zeolite was an excellent shape-selectivity catalyst, but its micropore structure, high hydrogen transfer activity and acid strength limited its application in the processing of heavy oil. This study put forward to adding solid base calcium aluminate into ZSM-5 to crack the large-molecule oil, while the ZSM-5 was used to convert the small-molecule gas-oil into light olefins. The experiments of catalytic pyrolysis of vacuum residue (VR) over calcium aluminate and ZSM-5 mixed catalysts were investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results showed that the maximum light olefin relative content of 26.99% obtained with 50% calcium aluminate/50% ZSM-5, which was higher than that obtained with pure ZSM-5. Besides, the calcium aluminate/ZSM-5 catalyst (acid-base mixed catalyst) was more favorable to the formation of olefins compared with FCC/ZSM-5 catalyst (acid-acid mixed catalyst). To further study the cracking of VR over acid-base mixed catalyst, the catalytic characteristics of its eight group-fractions were analyzed. The saturate fraction contributed to the formation of light olefins, while the highest relative content of aromatic compounds was obtained from light aromatic fraction. The various fractions showed different yields of hydrocarbons due to their different composition and structure and the interactions among them affected the product compositions of VR.

Oil majors invest in CO2 capture company

Venture investment arms of Chevron and Occidental Petroleum have invested an undisclosed sum in Carbon Engineering, a Canadian firm that is developing a chemical method of capturing CO2 from the atmosphere. In the process, CO2 reacts with calcium hydroxide to create a calcium carbonate solution. Carbonate pellets are formed, then decomposed into concentrated CO2 and solid calcium oxide. The CaO is then hydrated to regenerate the hydroxide. Carbon Engineering raised about $8 million in July.

Nitrous Oxide-Promoted Pauson-Khand Cycloadditions.

A Pauson-Khand cycladdition of alkynes, alkenes, and carbon monoxide, promoted by cobalt carbonyl and nitrous oxide to furnish cyclopentenones is described. Preliminary mechanistic experiments suggest that nitrous oxide functions in a similar manner to the N-oxide promoters typically employed in Pauson-Khand reactions. Only dinitrogen and carbon dioxide are produced as a consequence of the activation mechanism, thus avoiding high molecular weight reagents and the build up of basic byproducts. The chemistry is done using equimolar amounts of alkyne, alkene, and dicobalt octacarbonyl, and is performed directly from the acetylenic component without having to presynthesize a cobalt-alkyne complex. Terminal acetylenes were suitable substrates, as was solid calcium carbide, and the corresponding adducts were isolated in good yields. Furthermore, two sequential [4+3] and [2+2+1] cycloadditions were performed, generating funtionalized cyclopentenones in only two steps from readily available starting materials.

SOLID CaCO3 FORMATION IN WATERS OF CIRCULATING COOLING SYSTEMS OF POWER PLANTS UNDER THE CONDITIONS OF ELECTRIC LOAD CHANGE

The rate of solid calcium carbonate (Dve) formation in circulating water (CW) of circulating cooling systems (CCS) of power plants with cooler towers and the stability index of such water at changing electric load is analyzed. The relationship between streams of CCS, namely, feeding, evaporation and blow, which exist under the condition of constant CCS water volume and dependence of evaporation flow upon units load are the basis of analysis. Such dependence is based on the fact that the main channel of heat dissipation after steam turbine units is evaporation in cooling towers. The general expression has been obtained in quasiequilibrium approximation that establishes the relation between Dve and CW stability index. This dependence allows calculating CW stability degree for any models of CaCO 3 formation kinetics and to obtain corresponding Dve value. It has been shown that the rate of solid CaCO 3 formation is directly proportional to electrical load of power plant, Ca 2+ ion concentration in feed water and fraction of used heat dissipated by evaporation, antiproportional to stability index, inverse to CCS water volume and the average efficiency of power plant.

Modelling calcium leaching kinetics of cement asphalt paste

Calcium leaching is an important durability problem for cement asphalt (CA) mortar used in ballastless slab track which is under the coupled action of train-induced dynamic load and rainwater erosion. In this paper, a model based on the calcium mass conservation and the thermodynamic equilibrium of calcium was developed to describe the calcium leaching of CA paste in both deionized water and ammonium nitrate solution. In this model, the spatial–temporal distribution of solid calcium content in skeleton, porosity and diffusivity, which are directly or indirectly relevant to the calcium concentration in pore solution, were considered. Finite difference method was utilized to solve this model, and a three layer Crank–Nicolson differential scheme was applied to improve the stability. The model was experimentally verified using the Ca/Si molar ratio in solid and the calcium leaching rate characterized by SEM–EDX and potentiometric titration respectively. It was found that asphalt content does not change the spatial distribution of solid calcium in CA paste. Asphalt affects the leaching rate by reducing solid calcium concentration and changing the activation energy of micro-pore wall. Accelerating factors by ammonium nitrate solution were experimentally determined and predicted by the model.

Optimization of Biodiesel Production over Chicken Eggshell-Derived CaO Catalyst in a Continuous Centrifugal Contactor Separator

Solid calcium oxide (CaO) catalyst was prepared via the calcination of chicken eggshells as an environmentally friendly waste resource and incorporated in a continuous centrifugal contactor separator (CCCS) for intensified biodiesel synthesis. Biodiesel or fatty acid methyl esters (FAME) were produced via the transesterification of sunflower oil (containing 5 wt % tetrahydrofuran as a cosolvent) with methanol under 60 °C and separated from the glycerol and catalyst phases continuously in the CCCS. The influence of reaction parameters on biodiesel production was well modeled by response surface methodology. At an oil flow rate of 9 mL/min, an alcohol to oil molar ratio of 11:1, and a weight hourly space time (defined as the catalyst weight over the oil mass flow rate) of 0.050 h, an optimized FAME yield of 83.2% with a productivity of 638 kgFAME/(m3reactor·h) was achieved. CaO catalyst was reused without significant activity loss for at least four cycles.

Alkali Release from Aggregates in Long-Service Concrete Structures: Laboratory Test Evaluation and ASR Prediction.

This paper proposes a simple model for predicting the development of deleterious expansion from alkali-silica reaction (ASR) in long-service concrete structures. This model is based on some composition and reactivity parameters related to ASR, including the long-term alkali contribution by aggregates to concrete structures. This alkali contribution was estimated by means of a laboratory extraction test, appositely developed in this study in order to maximize the alkali extraction within relatively short testing times and with low leaching solution/aggregate ratios. The proposed test is a modification of the Italian Standard test method UNI 11417-2 (Ente Nazionale Italiano di Normazione) and it consists of subjecting an aggregate sample to leaching with saturated calcium hydroxide solution in a laboratory autoclave at 105 °C. Nine natural ASR-susceptible aggregates (seven sands and two coarse aggregates) were tested and the following optimized test conditions were found: leaching solution/aggregate weight ratio = 0.6; solid calcium hydroxide/aggregate weight ratio = 0.05; test duration = 120 h. The results of the optimized alkali extraction tests were used in the proposed model for predicting the potential development of long-term ASR expansion in concrete dams. ASR predictions congruent with both the field experience and the ASR prevention criteria recommended by European Committee for Standardization Technical Report CEN/TR 16349:2012 were found, thus indicating the suitability of the proposed model.

Role of Impurities in the Kinetic Persistence of Amorphous Calcium Carbonate: A Nanoscopic Dynamics View

Amorphous calcium carbonate is found in the early stages of biomineral formation. Its moldability and its kinetic persistence against crystallization make it of potential interest to the development of biomimetic materials. The presence of water and of inorganic impurities such as Mg2+ has been reported to increase its kinetic stability. Yet, the precise mechanisms of stabilization as well as the link between structural dynamics and crystallization kinetics are still missing. Here, we report the vibrational and diffusive dynamics of water and other atomic constituents in a series of Mg2+-doped solid amorphous calcium carbonates revealed using coherent X-ray and incoherent neutron scattering. This unique combination of techniques presents a novel view on the nanoscopic dynamic behavior of these amorphous materials: the presence of Mg2+ results in a higher frequency of structural rearrangements within the material. However, this increased dynamic behavior does not translate into a higher crystallization kin...

Hydrido Complexes of Calcium: A New Family of Molecular Alkaline-Earth-Metal Compounds.

The application of solid calcium hydride CaH2 has been mostly confined to its use as a desiccant, although its catalytic activity has long been known. Since the first isolation of a well-defined molecular calcium hydride in 2006, the past decade has witnessed a gradual emergence of this new family of compounds. Although the detrimental Schlenk equilibrium has kept the number of examples low, the novelty of their reactivity, especially in small-molecule activation, holds great promise. This Minireview gives an overview of the molecular calcium hydrides reported to date, highlighting their synthesis, structure, and reactivity.

On the solubility of whitlockite, Ca9Mg(HPO4)(PO4)6, in aqueous solution at 298.15 K

Whitlockite was assigned the ideal formula Ca9Mg(HPO4)(PO4)6, but the synthesis of a solid phase with this exact composition is very difficult. One of the reasons arises from the fact that there are no accurate values published for its solubility constant and/or other thermodynamic parameters. These could help to delineate a stability field in relation to the most common solid calcium and magnesium phosphates which normally co-occur with whitlockite. Calcium magnesium phosphates with the structure of whitlockite containing various nMg/nCa ratios were synthesized from aqueous solution of pH between 5.0 and 6.0, with the ratio of the concentrations of magnesium and calcium between 0.4 and 1.5, and excess of total calcium and magnesium over total phosphate. Those solids were used to determine the solubility of whitlockite with the ideal formula [lg Ks(whitlockite, solid, 298.15 K) = − 113.75 ± 2.18], which was used to determine its standard molar Gibbs energy of formation. This value, together with the previously published values for the standard molar Gibbs energy of formation of the relevant calcium and magnesium solid phosphates and other species at equilibrium, allowed the construction of a phase diagram containing all the relevant solid calcium and magnesium phosphates.

Study on reactions of gaseous P 2 O 5 with Ca 3 (PO 4 ) 2 and SiO 2 during a rotary kiln process for phosphoric acid production

Abstract In a rotary kiln process for phosphoric acid production, the reaction between gaseous phosphorus pentoxide (P 2 O 5 ) and phosphate ore and silica contained in feed balls (the so-called P 2 O 5 “absorption”) not only reduces phosphorous recovery but also generates a large amount of low melting-point side products. The products may give rise to formation of kiln ring, which interferes with kiln operation performance. In this study, the reactions of gaseous P 2 O 5 with solid calcium phosphate (Ca 3 (PO 4 ) 2 ), silica (SiO 2 ) and their mixture, respectively, were investigated via combined chemical analysis and various characterizations comprised of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis and differential scanning calorimeter (TG&DSC), and scanning electron microscopy and energy dispersive spectrometer (SEM&EDS). Attentions were focused on apparent morphology, phase transformation and thermal stability of the products of the P 2 O 5 “absorption” at different temperatures. The results show that the temperature significantly affected the “absorption”. The reaction between pure Ca 3 (PO 4 ) 2 and P 2 O 5 occurred at 500 °C. Calcium metaphosphate (Ca(PO 3 ) 2 ) was the primary product at the temperatures ≤ 900 °C with its melting point ≤ 900 °C while calcium pyrophosphate (Ca 2 P 2 O 7 ) was obtained over 1000 °C, which has a melting point ≤ 1200 °C. The “absorption” by pure SiO 2 started at 800 °C and the most significant reaction occurred at 1000 °C with formation of silicon pyrophosphate (SiP 2 O 7 ) product of melting point ≤ 1000 °C. Using mixed Ca 3 (PO 4 ) 2 and SiO 2 as raw material , the “absorption” by Ca 3 (PO 4 ) 2 was enhanced due to existence of silica. At 600–700 °C, silica was inert to P 2 O 5 and thus formed a porous structure in the raw material, which accelerated diffusion of gaseous P 2 O 5 inside the mixture. At higher temperatures, the combined “absorption” by calcium phosphate and reaction between silicon dioxide and the “absorption” product calcium pyrophosphate, reinforced the “absorption” by the mixture. Besides, it was found that both Ca(PO 3 ) 2 and SiP 2 O 7 were unstable at high temperatures and would decompose to Ca 2 P 2 O 7 and SiO 2 , respectively, at over 1000 °C and 1100 °C with the release of gaseous P 2 O 5 at the same time.