Barbara Grzmil

Hydrolysis of titanium sulphate compounds

The influence of TiOSO4 and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO4 in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO4 dm−3, 216 g H2SO4 dm−3) and 92 % (300 g TiOSO4 dm−3, 216 g H2SO4 dm−3). The same relation was obtained when changing the concentration of free H2SO4 in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H2SO4 dm−3, 340 g TiOSO4 dm−3) and 96 % (136 g H2SO4 dm−3, 340 g TiOSO4 dm−3). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition.

Photodecomposition of dyes on Fe-C-TiO2 photocatalysts under UV radiation supported by photo-Fenton process.

Fe-C-TiO(2) photocatalysts were prepared by mechanical mixing of commercial anatase TiO(2) precursor with FeC(2)O(4) and heating at 500-800 degrees C under argon flow. These photocatalysts were tested for dyes decomposition: Methylene Blue (MB), Reactive Black (RB) and Acid Red (AR). The preliminary adsorption of dyes on the photocatalysts surface was performed. Modification of anatase by FeC(2)O(4) caused reducing of zeta potential of the photocatalyst surface from +12 to -7mV and decreasing of their adsorption ability towards RB and AR, which were negatively charged, -46.8 and -39.7, respectively. Therefore, unmodified TiO(2) showed the highest degree of RB and AR decompositions in the combination of dyes adsorption and UV irradiation. Methylene Blue, which had zeta potential of +4.3 in the aqueous solution was poorly adsorbed on all the tested photocatalysts and also slowly decomposed under UV irradiation. The high rate of dyes decomposition was noted on Fe-C-TiO(2) photocatalysts under UV irradiation with addition of H(2)O(2). It was observed, that at lower temperatures of heat treatment such as 500 degrees C higher content of carbon is remained in the sample, blocking the built in of iron into the TiO(2) lattice. This iron is reactive in the photo-Fenton process resulting in high production of OH radicals and also high activity of the photocatalyst. At higher temperatures of heat treatment, less active FeTiO(3) phase is formed, therefore Fe-C-TiO(2) sample prepared at 800 degrees C showed low photocatalytic activity for dyes decomposition. Fe-C-TiO(2) photocatalysts are active under visible light irradiation, however, the efficiency of a dye decomposition is lower than under UV light. In a dark Fenton process there is observed an insignificant generation of OH radicals and very little decomposition of a dye, what suggests the powerful of photo-Fenton process in the dyes decomposition.

Selective methane oxidation to formaldehyde using polymorphic T-, M-, and H-forms of niobium(V) oxide as catalysts

The investigations of selective methane oxidation to formaldehyde over T-Nb2O5, the mixture of M-Nb2O5 and H-Nb2O5 as well as H-Nb2O5 were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as the oxidizing agent. T-Nb2O5 samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h−1). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb2O5 displayed various formaldehyde and carbon dioxide yield. Using H-Nb2O5 and M-Nb2O5 phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb2O5 (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb2O5 supported on SiO2.

Formation of hydrated titanium dioxide from seeded titanyl sulphate solution

The paper analyses the influence of various kinds and amounts of titanium dioxide nuclei addition to a solution of titanyl sulphate on the conversion degree of TiOSO4 to hydrated titanium dioxide and sulphuric acid. An industrial solution of titanyl sulphate used to produce titanium white was used in the present investigations. It was found that the course of hydrolysis clearly depended on the investigated parameters. The anatase nuclei calcined at 373 K and 333 K and rutile nuclei increased the degree of titanyl sulphate hydrolysis as compared to non-nucleation hydrolysis. The final degree of hydrolysis was by 1–2 % higher than that achieved without any nuclei addition. The constant rates of both colloidal intermediate and final crystalline products formation were higher in the hydrolysis process with both anatase nuclei after heat treatment at lower temperature and rutile nuclei in comparison to the same processes conducted in the absence of these nuclei.

Production of potassium sulfate from potassium hydrosulfate solutions using alcohols

Potassium sulfate is used to produce multicomponent fertilizers, free of chlorides. The desalting out of potassium sulfate from an aqueous solution of potassium hydrosulfate was conducted using 40 mass %, 45 mass %, or 50 mass % aqueous solutions of either methanol or propan-2-ol. Composition of the resultant precipitate was analyzed using chemical methods and XRD analysis. The results of the XRD analysis revealed that the main precipitate phase is K2SO4. Small amounts of K5H3(SO4)4 were detected when the desalting out was carried out from 2.5 M KHSO4 solution using 40 mass % and 50 mass % methanol solution. When the amount of potassium bisulfate in the solution increased to 3.5 M and 3.8 M, the main phase consisted of K3H(SO4)2. Generally, the desalting out process using propan-2-ol caused the formation of K3H(SO4)2. Potassium sulfate was obtained only by desalting out the 2.5 M KHSO4 solution using 50 mass % aqueous propan-2-ol.