Confinement Effects in Lewis Acid-Catalyzed Sugar Conversion: Steering Toward Functional Polyester Building Blocks

We report the use of solid Lewis acid catalysts for the conversion of tetrose sugars to four-carbon α-hydroxy acid esters (C_4-AHA), which are useful as functional polyester building blocks. Sn-β was by far the most active and selective catalyst, yielding up to 80% methyl vinyl glycolate (MVG), methyl-4-methoxy-2-hydroxybutanoate (MMHB), and α-hydroxy-γ-butyrolactone (HBL) combined at 95% conversion. A very high turnover frequency (TOF) of 330 mol_(C4-AHA) mol_(Sn) h^(–1) was attained using Sn-β, a more than 6-fold increase compared with homogeneous SnCl_4·5H_2O. It is shown that, using different Sn-based catalysts with various pore sizes, the product distribution is strongly dependent on the size of the catalyst pores. Catalysts containing mainly mesopores, such as Sn-MCM-41 or Sn-SBA-15, prefer the production of the more bulky MMHB, whereas microporous catalysts such as Sn-β or Sn-MFI favor the production of MVG. This effect can be further enhanced by increasing the reaction temperature. At 363 K, only 20% MVG is attained using Sn-β, but at 433 K, this increases to 50%. Using a kinetic analysis, it was found that, in microporous catalysts, steric hindrance near the Sn active site in the catalyst pores plays a dominant role in favoring the reaction pathway toward MVG. Moreover, the selectivity toward both products is kinetically controlled

Valorization of fayalitic slag as pozzolanic material in blended cements

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Production of belite cement using boron and red mud wastes

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Valorization of Electric Arc Furnace Steel Slag as raw material in the production of low energy FA- belite cement

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Synthesis, characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material

This study investigated the use of 10 (M1), 17 (M2) and 27 wt.% (M3) electric arc furnace steel slag (EAFS) as a raw material in the production of calcium ferroaluminate belite cement clinker, after firing at 1320 C. The thermal behavior of the raw meals was studied by TG/DSC and XRD whereas for the analysis of the clinkers, XRD/QXRD, SEM/EDS and EPMA were employed. The resulting clinker was co-grinded with 5 and 20 wt.% Flue Gas Desulfurization (FGD) gypsum and the properties were determined by a series of tests in accordance to EN standards. The evolution of hydration was investigated by SEM and the development of compressive strength. The results revealed that the formed phases in the clinkers were C2S, C4AF and C 4A3Ŝ. The main hydration products were ettringite, AFm and hydrogarnet. The leached CrVI was below 1 ppm in M3. Compressive strength in cements with 5 wt.% FGD gypsum was (in MPa): 18.3 for M1, 14.3 for M2 and 7.8 for M3 at 28 days, whereas for 20 wt.% FGD gypsum, the values were almost doubled.© 2013 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Synthesis, characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material journaltitle: Cement and Concrete Composites articlelink: http://dx.doi.org/10.1016/j.cemconcomp.2013.08.002 content_type: article copyright: Copyright © 2013 Elsevier Ltd. All rights reserved.status: publishe

Utilization of EAF metallurgical slag in “green” belite cement

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Valorization of red mud as raw material in the production of belite cement clinkers

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Valorisation of electric arc furnace steel slag as raw material for low energy belite cements

In this paper, the valorisation of electric arc furnace steel slag (EAFS) in the production of low energy belite cements is studied. Three types of clinkers were prepared with 0 wt.% (BC), 5 wt.% (BC5) and 10 wt.% (BC10) EAFS, respectively. The design of the raw mixes was based on the compositional indices lime saturation factor (LSF), alumina ratio (AR) and silica ratio (SR). The clinkering temperature was studied for the range 1280–1400°C; firing was performed at 1380°C based on the results regarding free lime and the evolution of microstructure. In order to activate the belite, clinkers were cooled fast by blown air and concurrent crushing. The results demonstrate that the microstructure of the produced clinkers is dominated by belite and alite crystals, with tricalcium aluminate and tetracalcium-alumino-ferrite present as micro-crystalline interstitial phases. The prepared cements presented low early strength development as expected for belite-rich compositions; however the 28-day results were 47.5 MPa, 46.6 MPa and 42.8 MPa for BC, BC5 and BC10, respectively. These values are comparable with OPC CEMI 32.5 N (32.5–52.5 MPa) according to EN 197-1. A fast setting behaviour was also observed, particularly in the case of BC10, whereas soundness did not exceed 1 mm.status: publishe

Understanding the leaching behavior of inorganic polymers made of iron rich slags

This study investigates the leaching of main and trace elements from inorganic polymers made with an iron rich, fumed, > 90% amorphous slag. Different inorganic polymer binders were synthesized, varying the amount of the activating solution and the silica over sodium oxide ratio from 1.6, to 1.8, to 2.0, with constant water content of ±63%. Cascade and column leaching tests were performed in combination with geochemical speciation modeling (Visual MINTEQ) with the aim to understand the speciation of the elements in the inorganic polymer and their leaching behaviour as a function of pH. This would allow to identify the elements which would be the major issue with respect to leaching when the slag will be used in a construction material. The formed inorganic polymer was able to immobilize cationic elements such as barium, copper, magnesium, manganese, and zinc, in the pH range 7–12.5 due to adsorption. Elements such as antimony, arsenic, phosphorus, molybdenum, and vanadium were easily leached out in column and cascade leaching tests, because they most likely occurred as anions in the pore solution. Lead, chromium, and titanium were immobilized in the binder or in crystalline phases in the pH range 3.5–12.5. The study shows that there are multiple factors that affect leaching, the most important of which is shown to be the nature (cationic or anionic) of the elements and the morphology of the matrix. Anions that are present as trace elements (<0.1 wt%) can pose a potential threat in valorising these slags and actions should be taken, either at the metallurgical process itself or downstream, at the synthesis of the inorganic polymers. On the other hand, the results for the cationic species suggest that they are effectively immobilised in most of the cases and for a wide pH range.status: publishe

Low-carbon footprint cements incorporating high volumes of bauxite residue

The use of large quantities of bauxite residue (BR) to produce two types of low-carbon cement (ferrobelitic and aluminoferrite) was studied in this project. These types of cement are of great interest for the industry because of the lower energy demand and CO2 footprint as well as the higher possible incorporation of by-products, compared to ordinary Portland cement (OPC). To produce the clinkers, BR was combined with limestone, clays and reagent chemicals in order to achieve a suitable raw meal chemistry. The goal was to keep BR addition constant at 50 wt% in all mixtures. The mineralogical phase formation at different burning temperatures was estimatedby means of thermodynamic calculations. Clinkers were produced at different temperatures, 1200, 1250 and 1300 °C, followed by rapid cooling by air. The obtained clinkers were mineralogically quantified by the Rietveld method using X-Ray diffraction analysis. Additionally, microstructural characterisation was performed using SEM-EDS. Hydration kinetics were also studied by isothermal calorimetry. The results show that BR quantities as high as 50 wt% can be used to produce reactive, and environmental friendly cement clinkers.status: publishe