Relationship between the density of supercritical CO<Subscript>2</Subscript> + ethanol binary system and its critical properties

The dependent relation between temperature and pressure of supercritical CO₂+ ethanol binary system under the pressure range from 5 to 10 MPa with the variety of densities and mole fractions of ethanol that range from 0 to 2% was investigated by the static visual method in a constant volume. The critical temperature and pressure were experimentally determined simultaneously. The PTρ figures at different ethanol contents were described based on the determined pressure and temperature data, from which pressure of supercritical CO₂ + ethanol binary system was found to increase linearly with the increasing temperature. P-T lines show certain convergent feature in a specific concentration of ethanol and the convergent points shift to the region of higher temperature and pressure with the increasing ethanol compositions. Furthermore, the effect of density and ethanol concentration on the critical point of CO₂ + ethanol binary system was discussed in details. Critical points increase linearly with the increasing mole fraction of ethanol in specific density and critical points change at different densities. The critical compressibility factors Z_c of supercritical CO₂ + ethanol binary systems at different compositions of ethanol were calculated and Z _c -ρ figure was obtained accordingly. It was found from Z _c -ρ figure that critical compressibility factors of supercritical CO₂ unitary or binary systems decline linearly with the increasing density, by which the critical point can be predicted precisely.     

Integration of Succinic Acid and Ethanol Production With Potential Application in a Corn or Barley Biorefinery

Production of succinic acid from glucose by Escherichia coli strain AFP184 was studied in a batch fermentor. The bases used for pH control included NaOH, KOH, NH₄OH, and Na₂CO₃. The yield of succinic acid without and with carbon dioxide supplied by an adjacent ethanol fermentor using either corn or barley as feedstock was examined. The carbon dioxide gas from the ethanol fermentor was sparged directly into the liquid media in the succinic acid fermentor without any pretreatment. Without the CO₂ supplement, the highest succinic acid yield was observed with Na₂CO₃, followed by NH₄OH, and lowest with the other two bases. When the CO₂ produced in the ethanol fermentation was sparged into the media in the succinic acid fermentor, no improvement of succinic acid yield was observed with Na₂CO₃. However, several-fold increases in succinic acid yield were observed with the other bases, with NH₄OH giving the highest yield increase. The yield of succinic acid with CO₂ supplement from the ethanol fermentor when NH₄OH was used for pH control was equal to that obtained when Na₂CO₃ was used, with or without CO₂ supplementation. The benefit of sparging CO₂ from ethanol fermentation on the yield of succinic acid demonstrated the feasibility of integration of succinic acid fermentation with ethanol fermentation in a biorefinery for production of fuels and industrial chemicals.     

Cyclic voltammetric studies of the redox behavior of iron(III)-vitamin B6 complex at carbon paste electrode

Electrochemical redox behavior of Fe-vit B₆ complex is investigated in HEPES buffer in the pH range 5.1–13.1 using cyclic voltammetry. Well-defined anodic and cathodic peaks are observed in the voltammograms at pH 13.1. At pH 8.0, only one cathodic peak and at pH 5.1, only one anodic peak are found. At all the pH values, the peak potential separation is much higher than that of a reversible electrochemical reaction. The peak current ratio (i _pa/i _pc) is less than unity and decreases with the scan rate. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 6, pp. 691–697. The text was submitted by the authors in English.     

Enantioselective separation of thalidomide on an immobilized α1-acid glycoprotein chiral stationary phaseglycoprotein chiral stationary phase

Summary An easy and rapid enantioselective separation for assay of racemic thalidomide on an immobilized α₁-acid glycoprotein chiral stationary phase (GPA CSP) is described. The effects of tetrahydrofuran (THF) as organic modifier, buffer concentration to control the ionic strenth, and mobile phase pH were studied. These variations have consequences in terms of chromatographic retention (k), resolution (R _s), selectivity (α), and peak asymmetry (USP tailing factor). The main condition affecting chromatographic retention was mobile phase pH. At pH 4.5, no separation of thalidomide enantiomers was achieved whereas at pH 7.9 chiral separation was optimum. Peak tailing was directly related to changes in pH and to addition of THF as mobile phase modifier. Results also indicated that the resolution factor is THF concentration-dependent, and that the separation factor (α) is the best parameter for evaluating enantioselectivity. The best mobile phase was pH 7.0, 30 mM ammonium acetate containing 0.3% THF. Under these conditions validation including linearity, recovery, and precision was performed. The suitability of this method has been successfully proved in a limited in-vivo study after intravenous administration of thalidomide to a New Zealand male rabbit.     

Facilitated Transport of Penicillin G by Bulk Liquid Membrane with TBP as Carrier

The facilitated transport of penicillin G from aqueous solutions to the stripping phase through bulk liquid membrane (BLM) containing TBP in 3% iso-octanol and n-butyl acetate was studied. Na₂CO₃ solution was used as the stripping phase. Experiments were performed as a function of stirring rate, TBP concentration and type of diluent in the liquid membrane phase, pH, and initial penicillin G concentration in the feed phase, Na₂CO₃ concentration in the stripping phase, etc. The results showed that the BLM process could carry out the simultaneous separation and concentration of penicillin G from dilute aqueous solutions, and arise “up-hill” effect due to the characteristic of non-equilibrium mass transfer. The diffusion of penicillin G complex in the liquid membrane phase played an important role in BLM process. The mass transfer mechanism of BLM for this system was also discussed.     

Optical sensor for carbon dioxide combining colorimetric change of a pH indicator and a reference luminescent dye

A new optical CO₂ sensor based on the luminescence intensity change of the europium(III) complex tris(thenoyltrifluoroacetonato) europium(III) dihydrate ([Eu(tta)₃]) caused by the absorption change of various pH indicators—thymol blue, phenol red, or cresol red—with CO₂ was developed and its CO₂ sensing properties were investigated. For all the CO₂ sensors using pH indicators the observed luminescence intensity from [Eu(tta)₃] at 613 nm increased with increasing CO₂ concentration. The linear calibration method based on the plot of (I₁₀₀–I₀)/(I–I₀) versus the inverse of CO₂ concentration was suggested, where I₀ and I₁₀₀ were luminescence intensities at 613 nm of the CO₂ sensor film in 100% nitrogen and 100% gaseous CO₂. In all cases the plots showed good linearity and the correlation factors of the plots, r², were 0.991 for thymol blue, 0.990 for phenol red, and 0.998 for cresol red. The slopes of the plots (A/B) for thymol blue, phenol red, and cresol red were 2.2, 5.2, and 9.0%, respectively. The response times of the CO₂ sensor film were 4.0 s for thymol blue, 4.4 s for phenol red, and 8.8 s for cresol red for switching from nitrogen to CO₂, and the recovery times of films were 36 s for thymol blue, 39.2 s for phenol red, and 56.6 s for cresol red for switching from CO₂ to nitrogen. The signal changes were fully reversible and hysteresis was not observed during the measurements. The highly sensitive CO₂ sensor was developed using thymol blue as an indicator for the CO₂-sensing probe.     

A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data

Adsorption separation of carbon dioxide from nitrogen (N₂, which represents air) was investigated by using H-ZSM-5 as the adsorbent with SiO₂/Al₂O₃ ratios of 30 and 280. Pure and binary isotherms at 40°C have been determined experimentally using concentration pulse chromatography.Presently available methods for determining binary isotherms from concentration pulse chromatography data have been reviewed and shown incapable of interpreting this particular binary system. A novel solution method is presented and shown to be superior to the other methods.The binary isotherms for the CO₂-N₂ system show an increase in CO₂ selectivity with increase in surface heterogeneity. The optimal separation factor for H-ZSM-5-30 was found to be 215 at 0.7% CO₂ in the feed, whereas, H-ZSM-5-280 has an optimal separation factor of 48 at 2.7% CO₂ in the feed.     

Nitrite formation in aerated aqueous azide solutions: A radiation chemical study

Gamma radiolysis of oxygenated 1–10 mM azide solutions was carried out at various pH values. In oxygenated 10 mM azide solutions, H₂O₂ and NO ₂ ⁻ were observed as radiolytic products while NH3 was not. The concentration of H₂O₂ reached its maximum level at a dose of 1 kGy, whereas NO ₂ ⁻ yield increased non-linearly beyond 2 kGy in this system. Both in aerated and oxygenated systems, G(NO ₂ ⁻ ) and G(H₂O₂) were found to vary with N ₃ ⁻ concentration. The yield of NO ₂ ⁻ was found to be dependent on both dose rate and pH. On pulse radiolysis, NO ₂ ⁻ was found as a radiolytic product in aerated 1 mM azide solution at pH 6.8. In this system the intermediate generated exhibits absorbance around 250 nm. The overall results obtained during the present study reveal that in presence of both reducing radical (mainly e _aq ⁻ ) and oxygen, N ₃ ⁻ produced an intermediate possibly NH₂O ₂ ^• radical, which is the prime source for NO ₂ ⁻ generation.     

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH?-CO2-HCO 3? -CO 32? -H2O System: A?Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol⋅kg⁻¹) in the presence of 0.01 mol⋅dm⁻³ KOH and KHCO₃ concentrations (0.001 to 0.826 mol⋅kg⁻¹) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO₃)₂²⁻ and Cr(OH)₄CO₃³⁻] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log ₁₀ K° values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g)⇌Cr(OH)(CO₃)₂²⁻+2H⁺} and {Cr(OH)₃(am) + OH⁻+CO₃²⁻ ⇌Cr(OH)₄CO₃³⁻}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.     

The effect of the physical properties of the liquid phase on the gas-liquid mass transfer coefficient in two- and three-phase agitated systems

The results of studies concerning two- and three-phase systems in an agitated vessel are presented. The aim of our research was to investigate the effect of the physical properties of the liquid phase on the value of the volumetric gas-liquid mass transfer coefficient in mechanically agitated gas-liquid and gas-solid-liquid systems. Our experimental studies were conducted in a vessel with an internal diameter of 0.288 m. The flat bottom vessel, equipped with four baffles, was filled with liquid up to a height equal to the inner diameter. The liquid volume was 0.02 m³. Three high-speed impellers of a diameter equal to 0.33 of the vessel diameter were used: Rushton turbine (RT), Smith turbine (CD 6), or A 315 impeller. The measurements were carried out in coalescing and non-coalescing systems. Distilled water and aqueous solutions of an electrolyte (sodium chloride) of two different concentrations were used as the liquid phase. The gas phase was air. In the three-phase system, particles of sea sand were used as solid phase. The measurements were conducted at five different gas-flow rates and three particle loadings. Volumetric gas-liquid mass transfer coefficients were measured using the dynamic method. The presence and concentration of an electrolyte strongly affected the value of the gas-liquid mass transfer coefficient in both two- and three-phase systems. For all agitators used, significantly higher k _l a coefficient values were obtained in the 0.4 kmol m⁻³ and 0.8 kmol m⁻³ aqueous NaCl solutions compared with the data for a coalescing system (with distilled water as the liquid phase). The k _l a coefficient did not exhibit a linear relationship with the electrolyte concentration. An increase in the sodium chloride concentration from 0.4 kmol m⁻³ to 0.8 kmol m⁻³ caused a considerable decrease in the volumetric mass transfer coefficient in both the two-phase and three-phase systems. It was concluded that the mass transfer processes improved at a certain concentration of ions; however, above this concentration no further increase in k _l a could be achieved.     

Production of succinic acid by anaerobiospirillum succiniciproducens

The effect of an external supply of carbon dioxide and pH on the production of succinic acid byAnaerobiospirillum succiniciproducens was studied. In a rich medium containing yeast extract and peptone, when the external carbon dioxide supply was provided by a 1.5M Na₂CO₃ solution that also was used to maintain the pH at 6.0, no additional carbon dioxide supply was needed. In fact, sparging CO₂ gas into the fermenter at 0.025 L/L-min or higher rates resulted in significant decreases in both production rate and yield of succinate. Under the same conditions, the production of the main by-product acetate was not affected by sparging CO₂ gas into the fermenter. The optimum pH (pH 6.0) for the production of succinic acid was found to be in agreement with results previously reported in the literature. Succinic acid production also was studied in an industrial-type inexpensive medium in which light steep water was the only source of organic nutrients. At pH 6.0 and with a CO₂ gas sparge rate of 0.08 L/L-min, succinate concentration reached a maximum of 32 g/L in 27 h with a yield of 0.99 g succinate/g glucose consumed.     

Succinic Acid Production from Cheese Whey using Actinobacillus succinogenes 130 Z

Actinobacillus succinogenes 130 Z was used to produce succinic acid from cheese whey in this study. At the presence of external CO₂ supply, the effects of initial cheese whey concentration, pH, and inoculum size on the succinic acid production were studied. The by-product formation during the fermentation process was also analyzed. The highest succinic acid yield of 0.57 was obtained at initial cheese whey concentration of 50 g/L, while the highest succinic acid productivity of 0.58 g h⁻¹ L⁻¹ was obtained at initial cheese whey concentration of 100 g/L. Increase in pH and inoculum size caused higher succinic acid yield and productivity. At the preferred fermentation condition of pH 6.8, inoculum size of 5% and initial cheese whey concentration of 50 g/L, succinic acid yield of 0.57, and productivity of 0.44 g h⁻¹ L⁻¹ were obtained. Acetic acid and formic acid were the main by-products throughout the fermentation run of 48 h. It is feasible to produce succinic acid using lactose from cheese whey as carbon resource by A. succinogenes 130 Z.     

Enthalpies of Absorption and Solubility of Carbon Dioxide in Aqueous Polyamine Solutions

The enthalpies of absorption and solubility at T=298.15 K of carbon dioxide in aqueous solutions of bis-(3-dimethylaminopropyl)amine (CAS RN: [6711-48-4]) are reported in this paper. It was observed that the saturation loading of the CO₂ is α=2.9 mol CO₂/mol TMBPA, which is close to the theoretical value, α⁰=3 mol CO₂/mol TMBPA. The molar heat of absorption of CO₂ is independent of the polyamine concentration of the solutions and the amount of CO₂ absorbed and was calculated to be Δ_abs H _m=–44 (±2) kJ mol^–1 CO₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of the behaviour of some new column materials in the chromatographic analysis ofCatharanthus alkaloids

Summary New column-packing materials specially designed for the HPLC analysis of basic compounds have been tested for the analysis ofCatharanthus alkaloids. Mobile phase optimization was performed for each column tested. The influence of mobile phase pH, nature and content of the organic modifier and salt concentration on retention, selectivity and resolution was studied. An important factor in the separation proved to be the pH of the eluent, because of the widely different pK _a values of the analytes. Complete separation was easily achieved on ODS columns, but polymeric materials also gave acceptable results. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Effect of pore expansion and amine functionalization of mesoporous silica on CO2 adsorption over a wide range of conditions

Adsorption of CO₂ was investigated over a wide range of conditions on a series of mesoporous silica adsorbents comprised of conventional MCM-41, pore-expanded MCM-41 silica (PE-MCM-41) and triamine surface-modified PE-MCM-41 (TRI-PE-MCM-41). The isosteric heat of adsorption, calculated from adsorption isotherms at different temperatures (298–328 K), showed a significant increase in CO₂–adsorbent interaction after amine functionnalization of PE-MCM-41, consistent with the high CO₂ uptake in the very low range of CO₂ concentration. The CO₂ adsorption isotherm and kinetics data showed the high potential of TRI-PE-MCM-41 material for CO₂ removal in gas purification and separation applications. With TRI-PE-MCM-41, the CO₂ selectivity over N₂ was drastically improved over a wide range of conditions compared to pure mesoporous silica. Moreover, the adsorption was reversible and fast, and the adsorbent was thermally stable and tolerant to moisture.     

Hydrogen Generation Through Indirect Biophotolysis in Batch Cultures of the Nonheterocystous Nitrogen-Fixing Cyanobacterium <Emphasis Type="Italic">Plectonema boryanum</Emphasis>

The nitrogen-fixing nonheterocystous cyanobacterium Plectonema boryanum was used as a model organism to study hydrogen generation by indirect biophotolysis in nitrogen-limited batch cultures that were continuously illuminated and sparged with argon/CO₂ to maintain anaerobiosis. The highest hydrogen-production rate (i.e., 0.18 mL/mg day or 7.3 μmol/mg day) was observed in cultures with an initial medium nitrate concentration of 1 mM at a light intensity of 100 μmol/m² s. The addition of photosystem II (PSII) inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) did not reduce hydrogen-production rates relative to unchallenged controls for 50 to 150 h, and intracellular glycogen concentrations decreased significantly during the hydrogen generation period. The insensitivity of the hydrogen-production process to DCMU is indicative of the fact that hydrogen was not derived from water splitting at PSII (i.e., direct biophotolysis) but rather from electrons provided by intracellular glycogen reserves (i.e., indirect biophotolysis). It was shown that hydrogen generation could be sustained for long time periods by subjecting the cultures to alternating cycles of aerobic, nitrogen-limited growth and anaerobic hydrogen production.     

Laccase of Coriolus zonatus

Laccase is one of the lignolytic enzymes found in liquid cultures of the fungus Coriolus zonatus in defined medium. The enzyme was isolated from culture liquid and characterized. Laccase from C. zonatus is a single-chain protein with a molecular mass of 60 kDa. Carbohydrate moiety of enzyme consisted of mannose, galactose and N-acetyl-glucosamine in a ratio of 6:2:0,6 respectively, and comprised 10% of the entiremolecule lsoelectric point was detected at pH 4.6. Laccase was found to have a pH optimum of 4.9 and temperature optimum of 55°C. Substrate specificity studies were conducted with catechol, K-ferrocyanide, hydroquinone, and sinapinic acid as substrates. The highest efficiency of catalysis was observed with sinapic acid as the substrate. The kinetic constants k _cat and K₂₈ of this reaction were 624 s⁻¹ and 7 μM, respectively.     

Apparent low surface areas in microporous SiO2-xerogels

Nitrogen adsorption at −195°C serves as routine method for the measurement of surface area of porous materials derived by sol-gel procedures. In a systematic study of the simultaneous effect of the pH and water-silane ratio of the starting solutions of preparation of SiO₂ xerogels on their surface areas, it was found that conditions of high acidity and low water/silane ratio result in microporous materials, the surface of which cannot be accessed by N₂ at −195°C, within a realistic time scale, but only by CO₂ at 0°C. In a typical result for TMOS/water/methanol = 1/2/3 at pH=1.0, the apparent N₂-area was zero, while the CO₂-area was 414 m²/gr. It is recommended to recheck apparent N₂-low surface areas of sol-gel materials by CO₂ adsorption. The behavior of pyrene-doped xerogels of this type is in agreement with the structural characterization by adsorption.     

The Effect of pH on Continuous Biohydrogen Production from Swine Wastewater Supplemented with Glucose

The effect of pH on hydrogen production from liquid swine manure supplemented with glucose by a mixed culture of fermentative bacteria in an anaerobic sequencing batch reactor was evaluated in this study. At 37 ± 1 °C, five pH values ranging from 4.7 to 5.9 at an increment of 0.3 were tested at a hydraulic retention time (HRT) of 16 h. The results showed that at this HRT, the optimal pH for hydrogen production was 5.0, under which the biogas comprised 33.57 ± 5.65% of hydrogen with a production rate of 8.88 ± 2.94 L-H₂/day and a yield of 1.48 ± 0.49 L-H₂/L liquid swine manure. The highest biomass concentration, highest butyric acid to acetic acid ratio, lowest propionic acid concentration, and the best stability were all found at pH 5.0, while the highest CH₄ productivity was found at pH 5.9. For efficient hydrogen production, oxygen content should be controlled under 2%, beyond which an inverse linear relationship (R ² = 0.986) was observed.     

Combined transformations of carbon dioxide and ethanol in the presence of the intermetallic compound TiFe0.95Zr0.03Mo0.02, Pd/SiO2, and Al2O3

The influence of the composition of catalytic systems and the method for H₂ feed into the reaction area on the degree of conversion of CO₂ during its joint transformations with ethanol and on the selectivity of formation of liquid organic products (ethyl acetate, acetaldehyde, and hydrocarbons) was studied atp=15 atm andT=573 K. A noticeable conversion of CO₂ and ethanol into ethyl acetate and acetaldehyde was observed in the presence of only the intermetallic compound, its composition with a palladium-containing catalyst, and the whole ternary catalytic system. The selectivity of the reaction changed when the binary catalytic composition consisting of the intermetallic and γ-Al₂O₃ was used. In this case, the fraction of C₉–C₁₄ alkenes and alkenes with normal and iso structures was mostly formed; its content was as high as 40%. The degree of conversion of CO₂ reached 30–36% and the selectivity to liquid products was 70–80% only when the hydrogen desorbed from the intermetallic was used. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1360–1364, July, 1998.