Biosynthesis of methanol from methane by <Emphasis Type="Italic">Methylosinus trichosporium</Emphasis> OB3b

Methanol has recently attracted significant interest in the energetic field. Current technology for the conversion of methane to methanol is based on energy intensive endothermic steam reforming followed by catalytic conversion into methanol. The one-step method performed at very low temperatures (35°C) is methane oxidation to methanol via bacteria. The aim of this work was to examine the role of copper in the one-step methane oxidation to methanol by utilizing whole cells of Methylosinus trichosporium OB3b bacteria. From the results obtained it was found that copper concentration in the medium influences the rate of bacterial biomass growth or methanol production during the process of methane oxidation to methanol. The presented results indicate that the process of methane oxidation to methanol by Methylosinus trichosporium OB3b bacteria is most efficient when the mineral medium contains 1.0 × 10⁻⁶ mol dm⁻³ of copper. Under these conditions, a satisfactory growth of biomass was also achieved. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

The inflection point of the variation of interionic distance between Sm3+ and Cl− in a methanol and water mixture

The stability constants, β₁, of the monochloride complex of Sm(III) have been determined in mixed system of methanol and water at 1.00 mol dm⁻³ ionic strength using a solvent extraction technique. The values of β₁ increase with an increase in the mole fraction of methanol (X _s ) in the mixed solvent system when 0≤X _s ≤0.351. The interionic distance of Sm³⁺−Cl⁻ (d _Sm−Cl) in the mixed solvent system was estimated by applying the Gibb's free energy derived from β₁ to a Born-type equation. It was determined that an inflection point of the variation in the estimatedd _Sm−Cl againstX _s was present in the vicinity ofX _s =0.054. The inflection point ofd _Sm−Cl shows a value ofX _s between those ofd _Eu−Cl andd _Nd−Cl previously obtained by us.     

Photocatalytic water purification: Destruction of resorcinol by irradiated titania

Ethanedial, butanoic acid anhydride and trihydroxybenzenes have been determined as intermediates of resorcinol photocatalytic oxidation. The photoreaction rate shows a 1st order dependence on resorcinol concentration. The calculated reaction rate constant is 2.1×10⁻⁸ mol dm⁻³ s⁻¹, which is similar to the rate constant of phenol photocatalytic oxidation on TiO₂ reported beore.     

Kinetics and the Mechanism of Iron(II) Reduction of cis-α-halogeno(cetylamine) (triethylenetetramine)cobalt(III) Complex Ion in Aqueous Acid Medium

The kinetics and mechanism of iron(II) reduction of cis- α-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co^III using an excess of the reductant under pseudo-first-order conditions: [Fe^II = 0.25 mol dm⁻³, [H⁺ = 0.1 mol dm⁻³, [μ = 1.0 mol dm⁻³ ionic strength in a nitrogen atmosphere at 303, 308 and 313 K. The reaction was found to be second order and showed acid independence in the range [H⁺ = 0.05−0.25 mol dm⁻³. The second order rate constant increased with Co^III concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe^II], [H⁺] and [ μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe²⁺(aq) with Co^III complex proceeds by an inner-sphere mechanism.     

Optimization of ammonium nitrate concentration in single-stage continuous cultures of Aspergillus niger with biomass retention

The effect of ammonium nitrate concentration in the citric acid biosynthesis by Aspergillus niger NC-12 in single-stage continuous cultures with biomass retention was investigated. Experiments were carried out in a BIOMER laboratory fermenter with 5 dm³ working volume. At the initial stage of each cultivation, the substrate in the bioreactor contained 1.5 g NH₄NO₃ dm⁻³. After 120 h onwards, the bioreactor was fed continuously at a constant dilution rate of 0.009 h⁻¹. NH₄NO₃ concentration in the feed was varied from one culture to another, ranging between 0.5 g dm⁻³ and 2.5 g dm⁻³. Promising results were obtained when NH₄NO₃ concentration of 1.5 g dm⁻³ was used. The observed concentration of citric acid (c _P) and yield of citric acid with respect to the introduced sucrose (Y _P/S) were 117.88 g dm⁻³ and 78.59 %, respectively. The efficiency coefficient of citric acid biosynthesis (K _ef) was very high, amounting to 83.38. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Profile distribution of As(III) and As(V) species in soil and groundwater in Bozanta area

The profile distribution of arsenic(III) and arsenic(V) species in soil and groundwater was investigated in the samples collected in 2005 from a hand-drilled well, in the Bozanta area, Baia Mare region, Romania. The total content of arsenic in the soil was in the range of 525–672 mg kg⁻¹ exceeding 21–27 times the action trigger level for sensitive soil. 0.9–11.3 % of the total content was soluble in water, 83.0–92.6 % in 10 mol dm⁻³ HCl and 2.6–13.3 % was the residual fraction. Arsenic(V) was the dominant arsenic species in the soil in the range of 405–580 mg kg⁻¹. The distribution and mobility of arsenic species was governed by soil pH and contents of Al, Fe, and Mn. The mobility of arsenic(V) decreased with depth, while that of arsenic(III) was high at the surface and in the proximity of groundwater. The total concentration of arsenic in groundwater was (43.40 ± 1.70) μg dm⁻³, which exceeded the maximum contaminant level of 10 μg dm⁻³. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Outer-Sphere electron-transfer and the effect of linkage isomerism in the titanium(III) reduction of nitro-pentacyanocobaltate(III) and nitro-, and nitrito-pentaamminecobalt(III) complexes in aqueous acidic media

The reductions of [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺, by Ti^III in aqueous acidic solution have been studied spectrophotometrically. Kinetic studies were carried out using conventional techniques at an ionic strength of 1.0 mol dm⁻³ (LiCl/HCl) at 25.0 ± 0.1 °C and acid concentrations between 0.015 and 0.100 mol dm⁻³. The second-order rate constant is inverse—acid dependent and is described by the limiting rate law:- k₂ ≈ k₀ + k[H⁺]⁻¹,where k=k′K_a and K_a is the hydrolytic equilibrium constant for [Ti(H₂O)₆]³⁺. Values of k₀ obtained for [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺ are (1.31 ± 0.05) × 10⁻² dm³ mol⁻¹ s⁻¹, (4.53 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ and (1.7 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ respectively, while the corresponding k′ values from reductions by TiOH²⁺ are 10.27 ± 0.45 dm³ mol⁻¹ s⁻¹, 14.99 ± 0.70 dm³ mol⁻¹ s⁻¹ and 17.93 ± 0.78 dm³ mol⁻¹ s⁻¹ respectively. Values of K _a obtained for the three complexes lie in the range (1–2) × 10⁻³ mol dm⁻³ which suggest an outer-sphere mechanism.     

Kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by periodate. Evidence for the inhibiting effect of copper(II)

A kinetic study of the oxidation of [Co(H₂L)(H₂O)₂]²⁺ (H₂L = N,N-bis (salicylaldehyde-1,2-diaminoethane) Schiff base) by periodate in aqueous solution was performed over pH (2.3–3.4) range, (0.1–0.5) mol dm⁻³ ionic strength and temperatures 20–35 °C for a range of periodate and complex concentrations. The reaction rate showed a first-order dependence on both reactants and increased with pH over the range studied. The effects of Cu(II) and Fe(II) on the reaction rate were investigated over the (1.0–9.0) × 10⁻⁵ mol dm⁻³ range. The reaction was inhibited as the concentration of Cu(II) increased, and it was independent on Fe(II) concentrations over the ranges studied. An inner-sphere mechanism is proposed for the oxidation pathways of both the protonated and deprotonated Co^II complex species.     

Solvent extraction of zirconium from hydrochloric acid solutions by sulphoxides and their mixtures

The solvent extraction of zirconium from HCl solutions by dipentyl sulphoxide (DPSO), dioctyl sulphoxide (DOSO), tributyl phosphate (TBP), and their mixtures in various solvents has been studied. At a given H⁺ strength, the extraction coefficient η of the metal increases with an increase in Cl⁻ activity whereas it is almost independent of H⁺ at constant Cl⁻. Under otherwise identical conditions, η increases with an increase in the extractant concentration but is virtually independent of the metal ion concentration over a wide range. The species extracted are ZrCl₄·DPSO, ZrCl₄·DOSO, and ZrCl₄·2TBP. In the case of mixtures, the slope of the log η−log M extractant plot for one component decreases with an increase in the concentration of the second component, the lines crossing at a common point. Extraction is favoured by solvents of low dielectric constant. It is possible to separate zirconium from thorium and uranium by solvent extraction with sulphoxides.     

Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

The kinetics of the reactions between azido-pentacyanocobaltate(III), Co(CN)₅N₃ ³⁻, and iron(II) polypyridyl complexes, Fe(LL)₃ ²⁺ (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm⁻³ NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL)₃ ²⁺ was kept constant, and the second-order rate constants obtained for the reactions at 35 °C were within the range of 0.156–0.219 dm³ mol⁻¹ s⁻¹ for LL = bipy and 0.090–0.118 dm³ mol⁻¹ s⁻¹ for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H⁺] = 0.001–0.008 mol dm⁻³. The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outer- and inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k ₅) is slower than through the outer-sphere path (k ₄). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Citric acid production from raw glycerol by acetate mutants of Yarrowia lipolytica

Three acetate mutants of the yeast species Yarrowia lipolytica were screened using batch cultivation. The strain Y. lipolytica 1.31 was found to be the most suitable for citric acid production from raw glycerol, a by-product of biodiesel production from rapeseed oil. At the initial concentration of glycerol of 200 g dm⁻³, the citric acid production of 124.5 g dm⁻³, yield of 0.62 g g⁻¹, and productivity of 0.88 g dm⁻³ h⁻¹ were achieved. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Kinetic, spectral and redox properties of the transients formed on one-electron reduction of 3, 3, 6, 6-tetramethyl-3, 4, 6, 7, 9-pentahydro-10-phenyl (1, 8) (2H, 5H) acridinedione in aqueous-organic mixed solvent system: A pulse radiolysis study

The phenyl substituted acridine-1,8-dione (AD) dye reacts with (CH₃)₂*COH radicals with a bimolecular rate constant of 0.6 × 10⁸ dm³ mol⁻¹ s⁻¹ in acidic aqueous-organic mixed solvent system. The transient optical absorption band (λ_max = 465 nm, ɛ = 6.8 × 10² dm³ mol⁻¹ cm⁻¹) is assigned to ADH* formed on protonation of the radical anion. In basic solutions, (CH₃)₂*COH radicals react with a bimolecular rate constant of 4.6 × 10⁸ dm³ mol⁻¹ s⁻¹ and the transient optical absorption band (λ_max = 490 nm, ɛ = 10.4 × 10³ dm³ mol⁻¹ cm⁻¹) is assigned to radical anion, AD*⁻, which has a pK_a value of 8.0. The reduction potential value of the AD/AD*⁻ couple is estimated to be between −0.99 and −1.15 V vs NHE by pulse radiolysis studies. The cyclic voltammetric studies showed the peak potential close to −1.2 V vs Ag/AgCl.     

Nature of the transient species formed in pulse radiolysis of n-allylthiourea in aqueous solutions

Reactions of e⁻_aq, OH radicals and H atoms were studied with n-allylthiourea (NATU) using pulse radiolysis. Hydrated electrons reacted with NATU (k = 2.8×10⁹ dm³ mol⁻¹ s⁻¹) giving a transient species which did not have any significant absorption above 300 nm. It was found to transfer electrons to methyl viologen. At pH 6.8, the reduction potential of NATU has been determined to be −0.527 V versus NHE. At pH 6.8, OH radicals were found to react with NATU, giving a transient species having absorption maxima at 400–410 nm and continuously increasing absorption below 290 nm. Absorption at 400–410 nm was found to increase with parent concentration, from which the equilibrium constant for dimer radical cation formation has been estimated to be 4.9×10³ dm³ mol⁻¹. H atoms were found to react with NATU with a rate constant of 5 × 10⁹ dm³ mol⁻¹ s⁻¹, giving a transient species having an absorption maximum at 310 nm, which has been assigned to H-atom addition to the double bond in the allyl group. Acetoneketyl radicals reacted with NATU at acidic pH values and the species formed underwent reaction with parent NATU molecule. Reaction of Cl^.−₂ radicals (k = 4.6 × 10⁹ dm³ mol⁻¹ s⁻¹) at pH 1 was found to give a transient species with λ_max at 400 nm. At the same pH, reaction of OH radicals also gave transient species, having a similar spectrum, but the yield was lower. This showed that OH radicals react with NATU by two mechanisms, viz., one-electron oxidation, as well as addition to the allylic double bond. From the absorbance values at 410 nm, it has been estimated that around 38% of the OH radicals abstract H atoms and the remaining 62% of the OH radicals add to the allylic double bond.     

Kinetics of oxidation of a 2-aminomethylpyridinechromium(III) complex by periodate

The oxidation kinetics of the 2-aminomethylpyridineCr^III complex with periodate in aqueous solution were studied and found to obey the rate law:Rate = [Cr^III]_T [IO₄ ^-]{k¹K² + k₂ K₁ K₃/[H⁺]}/{1+K₁/[H⁺] + k₂[IO₄ ^-]+K₁K₃/[H⁺][IO₄ ^-]} where K ₁, K ₂ and K ₃ are the deprotonation of [Cr(L)₂(H₂O)]³⁺ and pre-equilibrium formation constants for [(L)₂—Cr—OIO₃]²⁺ and [(L)₂—Cr—OH—OIO₃]⁺ precursor complexes respectively. An inner-sphere mechanism was proposed. The effect of Cu²⁺ on the oxidation rate was studied over the (1.0–9.0) × 10⁻⁵ mol dm⁻³ range. The reaction rate was found to be inversely proportional to the Cu²⁺ concentration over the range studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

An inflection point in the solvation number around Sm3+ in the mixed system of methanol and water

The stability constants (β₁) of the monofluoro complex of Sm(III) have been determined in mixed solvents of methanol and water at a 0.10 mol·dm⁻³ ionic strength using the solvent extraction technique. The values of lnβ₁ increase as the mole fraction of methanol (X _s) in the mixed solvent system increases. The variation in the stability constants can be correlated with both the large effect due to the solvation of F⁻ and the small effect due to both (1) the solvation of cations in connection with the complexation of SmF²⁺ and (2) the electrostatic attraction of Sm³⁺−F⁻. Based on the variation in the sum of (1) and (2) in H₂O and the mixed solvent solutions, it was determined that the coordination number (CN) of Sm(III) varied from a mixture of CN=9 and 8 to CN=8 for about a 0.06 mole fraction of methanol (X _s) in the mixed solvent. TheX _s value of the inflection point of the CN for Sm(III) is slightly higher thanX _s=0.03 for Eu(III) previously determined by us.     

Simultaneous production of citric acid and erythritol from crude glycerol by Yarrowia lipolytica Wratislavia K1

This study shows a possible microbial process for utilization of crude glycerol generated by the biodiesel industry for citric acid and erythritol production. Simultaneous production of citric acid and erythritol under nitrogen-limited conditions with glycerol as the carbon source was achieved with an acetate negative mutant of Y. lipolytica Wratislavia K1 in fed-batch cultivations. The effect of the initial glycerol concentration (from 30–180 g dm⁻³) on the citrate and erythritol production was investigated. As a result of the experiments, maximum citric acid production (110 g dm⁻³) and a very high amount of erythritol (81 g dm⁻³) were determined after 168 h of fed-batch cultivation with the initial glycerol concentration of 150 g dm⁻³ and the total glycerol concentration of 250 g dm⁻³. In addition, the citric acid to isocitric acid ratio of the products from this strain was 35.5:1. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Determination of metoprolol tartrate by capillary isotachophoresis

This paper describes two isotachophoretic methods of metoprolol tartrate (MT) determination in pure and dosage forms. The first method was used for direct analysis where the following electrolyte system was applied: 10 mmol dm⁻³ 3-morpholino-2-hydroxypropanesulfonic acid, 10 mmol dm⁻³ NaCl, 2 % hydroxyethylocelulose as leading (LE) and 10 mmol dm⁻³ glycyl-glycine as terminating (TE) electrolytes. The second method was used for indirect analysis of MT as tartrate ions. In this case, the leading electrolyte consisted of 10 mmol dm⁻³ HCl, β-alanine (BALA), pH 4-5, and the terminating one of 5 mmol dm⁻³ glutamic acid, 10 mmol dm⁻³ β-alanine. Calibration curves were calculated as follows: for system A: y = (0.52 ± 0.05)x − (0.9 ± 0.2) (LOD = 13.0 mg dm⁻³, LOQ = 31.7 mg dm⁻³); and for system B: y = (0.240 +- 0.001)x + (0.18 ± 0.06) (LOD = 1.8 mg dm⁻³, LOQ = 4.4 mg dm⁻³). The isotachophoretic method was compared with the pharmacopoeial one by statistical tests.     

Influence of biomass on hydrodynamics of an internal loop airlift reactor

The effect of the biomass presence on the overall circulation velocity, the linear velocities both in the riser and the downcomer and the overall gas hold-up was studied in a three-phase internal loop airlift reactor (ILALR). The measured data were compared with those obtained using a two-phase system (air—water). All experiments were carried out in a 40 dm³ ILALR at six different biomass concentrations (ranging from 0 g dm⁻³ to 7.5 g dm⁻³), at a temperature of 30°C, under atmospheric pressure. Air and water were used as the gas and liquid model media, respectively. Pellets of Aspergillus niger produced during the fermentation of glucose to gluconic acid in the ILALR were considered solid phase. In addition, liquid velocities were measured during the fermentation of glucose to gluconic acid using Aspergillus niger. All measurements were performed in a bubble circulation regime. At given experimental conditions the effect of the biomass on the circulation velocities in the ILALR was negligible. However, increasing of the biomass concentration led to lower values of the total gas hold-up. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Some applications of positron annihilation lifetime spectroscopy to complex formation and ion association studies

The rate constants for the reactions of positronium with halogen molecules and with halide ions in methanol (I₂, Br₂, Cl⁻, Br⁻) and in dimethylsulphoxide (I₂, Cl⁻) have been measured. The variations of the ortho-positronium lifetime in mixtures of these solutes have been used for quantitative determination of the formation constants of the corresponding polyhalides. These were found to be 2.9 and 5.4 M⁻¹, respectively, for I₂Cl⁻ and I₂Br⁻ in methanol and 2.0 M⁻¹ for I₂Cl⁻ in dimethylsulphoxide. Experiments on acidified AgClO₄ solutions confirmed the formation, at molar concentrations, of the Ag₂ ClO ₄ ⁺ species, very probably a triplet ion association.     

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. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.