Temat: chromium reduction - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Reduction and Biosorption of Cr(VI) from Aqueous Solutions by Acid- -Modifi ed Guava Seeds: Kinetic and Equilibrium Studies
Autorzy:: Ortíz-Gutiérrez, Marel
Alfaro-Cuevas-Villanueva, Ruth
Martínez-Miranda, Verónica
Hernández-Cristóbal, Orlando
Cortés-Martínez, Raúl
Tematy:: Guava seeds
chromium reduction
biosorption
isotherms; Pokaż więcej
Wydawca:: Zachodniopomorski Uniwersytet Technologiczny w Szczecinie. Wydawnictwo Uczelniane ZUT w Szczecinie
Powiązania:: https://bibliotekanauki.pl/articles/778567.pdf Link otwiera się w nowym oknie
Opis:: The use of guava seeds (GS) and acid-modified guava seeds (MGS) for the removal of Cr(VI) from aqueous solutions was investigated. Batch-type experiments were performed with Cr(VI) aqueous solutions and biosorbents to determine the kinetic and equilibrium sorption parameters. Results indicated that GS and MGS were capable of reducing and remove Cr(VI) from solutions, but the reduction was only observed at some experimental conditions. Infrared analysis showed that several functional groups were involved in the reduction, and biosorption of Cr(VI), particularly alcohol, phenolic, carboxylic, and methoxymethyl structures. The mechanisms of reduction and biosorption depended upon the type of biosorbent, pH, and temperature of the system. The pseudo-second-order kinetic model describes the kinetic sorption data, and the Langmuir-Freundlich (L-F) model describes the isotherm data in most cases. Significantly high total chromium biosorption capacities were obtained. Acid modification of guava seeds improves chromium biosorption performance.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Sorption and reduction of chromiumion ions by the chelating ion exchanger Diaion CR20
Autorzy:: Wójcik, Grzegorz
Tematy:: chromium(III)
chromium(VI)
reduction
ion exchange
speciation
chelating resin; Pokaż więcej
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Powiązania:: https://bibliotekanauki.pl/articles/109632.pdf Link otwiera się w nowym oknie
Opis:: The chelating ion exchanger Diaion CR20 was applied for removal of chromium(VI) ions in the pH range from 1.5 to 10 and in the presence of 1 M H₂SO₄. The speciation analysis was used to predict the reduction process. Reduction of chromium(VI) to chromium (III) was observed during the chromium(VI) ions sorption. The kinetic parameters for the pseudo-first-order and pseudo-second-order, Elovich and intraparticle diffusion models were calculated. The most common three isotherm models: Freundlich, Langmuir and Dubinin-Radushkevich were used to describe chromium(VI) uptake. It was proved that the polyamine groups present in selected ion exchanger are able to sorb both chromium(VI) and (III) ions. The maximal sorption capacity towards chromium(VI) ions was estimated at pH 1.5 – 169.49 mg Cr(VI)/g and 159.31 mg Cr(VI)/g in 1 M H₂SO₄. Both static and column methods were used in the investigations.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Reduction of chromium(VI) ions from aqueous solutions by using the solvent impregnated resin
Autorzy:: Wójcik, G.
Hubicki, Z.
Tematy:: sorption of chromium(VI) ions
reduction; Pokaż więcej
Wydawca:: Fundacja na Rzecz Młodych Naukowców
Powiązania:: https://bibliotekanauki.pl/articles/115625.pdf Link otwiera się w nowym oknie
Opis:: The solvent impregnated resins enables effective recovery of microquantities of chromium(VI) ions from wastewaters. The solvent impregnated resin (SIR) Amberlite XAD 7 HP as polymer matrix has been prepared by the wet-impregnation technique. Aliquat 336 was employed as the extractant and acetone as the solvents for impregnation. Sorption of chromium(VI) was investigated in the batch process . Sorption of chromium(VI) was studied in the pH range from 1.5 to 7. It was stated that sorption of chromium(VI) ions depends on acidity of solution. The values of recovery factors of chromium(VI) are higher at low pH than in neutral solution. The speciation of chromium was investigated in the studied pH range. Reduction of chromium(VI) to chromium(III) under acidic conditions was observed. Chromium was determined by using the spectrophotometric and atomic absorption spectroscopy methods. Both methods permit to observe changing of valence of chromium(III) and (VI) oxidation states. The prepared SIR is a new sorbent used for recovery of chromium ions from wastewaters.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Preparation and characterization of SBA-1-supported chromium oxide catalysts for $CO_{2}$ assisted dehydrogenation of propane
Autorzy:: Ogonowski, Jan
Michorczyk, Piotr
Pietrzyk, Piotr
Opis:: A series of Crx/SBA-1 cubic mesoporous catalysts with 1, 3, 5, 7, 10, and 15 wt.% content of Cr (Crtotal) were obtained by incipient wetness impregnation of SBA-1. The obtained catalysts were characterized with various physicochemical techniques (chemical composition, low-temperature adsorption of N2, H2–TPR, XRD, UV–vis DRS, Raman, and EPR) and tested in dehydrogenation of propane to propene in the presence of CO2. Various chromium species including Cr6+, dispersed Cr5+, and crystalline Cr2O3 were found in the calcined Crx/SBA-1 samples. Cr6+ species were present mainly in the form of mono- and dichromates, despite the Cr loading. The presence of dispersed Cr5+ species and crystalline α-Cr2O3 in the calcined catalysts depended on the total Crtotal content. Cr5+ species were found in the samples containing below 7 wt.% of Crtotal, while particles of crystalline α-Cr2O3 were detected in the catalyst with Crtotal content above 5 wt.%. All of the Crx/SBA-1 catalysts exhibited excellent catalytic activity and high selectivity in the dehydrogenation of propane to propene in the presence of CO2 with the maximum propane conversion (37.7% at 550 °C) for ∼7 wt.% of Crtotal. For higher Cr contents the conversion of propane remained almost constant which was connected with the formation of crystalline Cr2O3 which was inactive in the test reaction. Operando UV–vis DRS measurements performed during the dehydrogenation of propane, both in the presence and absence of CO2 at 550 °C, indicated that the Cr6+ species (main redox sites) were reduced rapidly to Cr2+/Cr3+ species already at the beginning of the process. The dispersed Cr2+/Cr3+ ions were the main sites available to the reactants under the dehydrogenation conditions in all of the studied feed compositions.
Dostawca treści:: Repozytorium Uniwersytetu Jagiellońskiego

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Skocz do pozycji: 5.

Tytuł:: Ilościowa ocena i wydzielenie różnych form siarki w próbkach geologicznych wraz z zastosowaniem do badań pochodzenia związków siarki w systemach naftowych
Quantitative assessment and isolation of various sulphur forms in geological samples and its application in investigation of sulphur compounds origin in petroleum systems
Autorzy:: Wencel, Kinga
Bieleń, Wojciech
Tematy:: kerogen
siarka redukowana chromem
CRS
warstwy menilitowe
bakteryjna redukcja siarczanów
analiza elementarna
izotopy siarki
chromium-reduced sulfur
Menilite Beds
bacterial sulfate reduction
elemental analysis
sulfur isotopes; Pokaż więcej
Wydawca:: Instytut Nafty i Gazu - Państwowy Instytut Badawczy
Powiązania:: https://bibliotekanauki.pl/articles/31343902.pdf Link otwiera się w nowym oknie
Opis:: Siarka występuje w naturze w bogactwie form – jako siarka elementarna, siarczki, siarczany, organiczne związki siarki (OZS, ang. organic sulfur compounds, OSC). W pracy zbadano zależności pomiędzy występowaniem siarki w ropach i skałach macierzystych. Wydzielono siarkę pirytową, pierwiastkową, organiczną w kerogenie oraz OZS w bituminach. Do rozdzielenia siarki pirytowej pozostałej po izolacji kerogenu zastosowano metodę redukcji kwaśnym roztworem chlorku chromu (II) (ang. chromium reducible sulfur method, CRS), przeprowadzaną w inertnej atmosferze azotu w komorze rękawicowej. Zastosowanie CrCl2 w obecności HCl powoduje wydzielenie siarki pirytowej w postaci H2S. Siarkowodór jest następnie wprowadzany do roztworu AgNO3, gdzie zachodzi reakcja z wytrąceniem się czarnego osadu Ag2S. Ilość wytrąconej siarki była oznaczana wagowo, a kerogen i siarczek srebra (I) były poddawane badaniom izotopów siarki. Analiza elementarna badanego materiału przed usunięciem i po usunięciu siarki pirytowej oraz obliczenie stosunków atomowych H/C, O/C, N/C, S/C potwierdziły przydatność metody wykazanej w poprzednich badaniach i nie uwidoczniły istotnych zmian w badanym kerogenie. W pracy oddzielono siarkę pirytową od organicznej w kerogenie z wybranych próbek warstw menilitowych z zewnętrznych Karpat fliszowych oraz poddano obie formy tego pierwiastka badaniom izotopowym, a także skorelowano z danymi dotyczącymi innych form występowania siarki w skałach, bituminach i ropach. Co istotne, znaczną część siarki całkowitej w kerogenie stanowi siarka pirytowa, co implikuje konieczność rozdzielenia jej od siarki organicznej w celu sformułowania poprawnych wniosków dotyczących energii aktywacji kerogenu i tempa generacji węglowodorów. Badania izotopowe potwierdzają wcześniejsze interpretacje pochodzenia pirytu z procesu bakteryjnej redukcji siarczanów i euksynicznego środowiska depozycji oligoceńskich osadów w basenie Paratetydy.
Sulphur occurs in nature in a variety of forms: as elemental sulphur, sulphides, sulphates, and organic sulphur compounds (OSC). The work investigated the relationship between the presence of sulphur in crude oil and source rocks. Pyritic and organic sulphur was isolated in kerogen, while OSC and elemental sulphur was isolated in bitumens. The chromium reducible sulphur method (CRS) carried out in an inert nitrogen atmosphere in a glove box was used to separate pyritic sulphur remaining after kerogen isolation. The use of a CrCl2 solution in HCl results in the release of pyritic sulphur in the form of H2S. Hydrogen sulphide is later introduced into the AgNO3 solution, where reaction occurs resulting in precipitation of black Ag2S. The amount of precipitated sulphur was determined by weight, while kerogen remains and silver (I) sulphide underwent sulphur isotope testing. The elemental analysis of the tested material before and after the removal of pyritic sulphur and the calculation of the atomic H/C, O/C, N/C, S/C ratios confirmed the usefulness of the method demonstrated in previous studies and did not show any significant changes in the tested kerogen. In the work, pyritic sulphur was separated from organic sulphur in kerogen from selected samples of Menilite Beds from the Outer Carpathians and subjected to isotope tests, and correlated with data on other forms of sulphur occurrence in rocks, bitumens and crudes. A significant part of the total sulphur in kerogen is pyritic sulphur, which without determining the content of organic sulphur may lead to incorrect assumptions regarding the activation energy of kerogen and the rate of hydrocarbon generation. Isotopic studies confirm earlier interpretations of the origin of pyrite by bacterial reduction of sulphates and the euxinic environment of the deposition of Oligocene sediments in the Paratethys Basin.
Dostawca treści:: Biblioteka Nauki

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