鼓泡浆态反应器中浸没表面的传热研究

在内径98mm的鼓泡浆态反应器内,考察了工艺参数对浸没表面与浆液间的传热系数的影响。浆态反应器轴向装有一个外径20mm,长120mm的测量传热膜系数用的铜制元件。为了模拟浆态FT合成反应系统,三相系统由N2、液体石蜡和石英砂（平均粒径53μm、110μm、180μm）或63μm以下的Fe2O3组成。工艺参数变化范围如下：表观气速0.005m/s～0.08m/s, 温度353K～453K, 压力0.1MPa～0.8MPa,固体的质量分数0～20%,初始液位高度625mm～1240mm。本研究使用单孔板、多孔板、烧结金属板三种气体分布器类型。结合实验数据,应用最小二乘法求得各个参数值,得到的无因次传热系数关联式为St=0.179(ReFr)－0.25Pr－0.66,相关指数0.98,最大偏差18％。该关联式可应用于气－液和粒径小于100μm的气－液－固体系。     

Degradation of paracetamol in a bubble column reactor with ozone generated in electrolyte-free water using a solid polymer electrolyte filter-press electrochemical reactor

A porous anode composed of β-PbO₂ was electrochemically deposited onto a carbon cloth substrate (e.g., CC/β-PbO₂) aiming for the electrochemical ozone production (EOP) in electrolyte-free water using a solid polymer electrolyte (SPE) filter-press reactor. Scanning electron microscopy (SEM) images revealed the presence of a three-dimensional oxide structure necessary to obtain a fluid-permeable anode. X-ray analysis showed the predominance of the β-PbO₂ phase. The maximum current efficiency for the EOP was 9.5% with an ozone production rate of 1.40 g h^?1. Using a constant ozone production rate of 0.5 g h^?1, the oxidative degradation of paracetamol (PCT) dissolved in water was accomplished as a function of the PCT concentration (20, 30, and 50 mg L^?1) and the pH (acid, natural (without adjustment), and alkaline). The UV-Vis spectrophotometric analysis showed that the degradation process is more pronounced in alkaline media with a strong reduction in the electrical energy per order (E _EO). A reduction of the chemical oxygen demand (COD) of up to 80% was observed. A linear correlation between data referring to COD and HPLC measurements with the UV absorbance measured at 243 nm (UV₂₄₃) was verified indicating that these different techniques can be complementary to each other. The nuclear magnetic resonance (NMR) study of the ozonation by-products revealed that the oxidation of PCT occurred through the rupture of the aromatic ring. The major part of phenol’s ring was oxidized to CO₃ ^2? while no reaction occurs in the acetamide group of paracetamol during the ozonation reaction.     

An outstanding catalyst for asymmetric transfer hydrogenation in aqueous solution and formic acid/triethylamine

A Rh/tetramethylcyclopentadienyl complex containing a tethered functionality has been demonstrated to give excellent results in the asymmetric transfer hydrogenation of ketones in both aqueous and formic acid/triethylamine media.     

Kinetics of the permanganate oxidation of formic acid in aqueous solution

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid at 30°C were examined by the spectrophotometric method. The chemical reaction 2MnO + 3HCOOH + 2H⁺ → 2MnO₂ + 3CO₂ + 4H₂O, appears to proceed via several parallel reactions. The overall rate equation has been obtained by using statistical multilinear regression analysis of the 660 cases studied, and the presence in the rate equation of two new terms in relation to previous studies shows that both permanganate autocatalytic effects and acid media inhibition must be taken into account when the reaction proceeds at constant ionic strength.     

Hydrothermal saccharification of cotton cellulose in dilute aqueous formic acid solution

Cotton cellulose subjected to a dilute aqueous formic acid solution, at acid concentrations up to 1% (w/w), under hydrothermal conditions in a semi-batch reactor was converted into glucose and oligomers with lower degrees of polymerizations (DP). After heating at 250 °C for 60 min in 0.1% (w/w) aqueous formic acid solution, yields of glucose and total sugar with DP = 1 to 9 were 36.6 and 83.8% (100 × gC/gC of initial cotton sample), respectively, and 5-hydroxymethylfurfural was almost as low as 1%. The yields of glucose and oligomers were significantly improved by adding the acid. The reaction was represented by first-order reaction kinetics with regard to (1 ?C x) where x is the conversion based on the total sugar or glucose yield. At 250 °C, the differences in the rate constants (k ? k _water) were proportional to the square root of formic acid concentration.     

Oxidative degradation of formic acid in aqueous solution upon dielectric-barrier discharge treatment

The kinetics of degradation of formic acid in an aqueous solution during its dielectric-barrier discharge treatment in oxygen was studied. It was shown that, the lower the initial concentration and the longer the time of contact of the solution and the gas with the discharge zone, the higher the degree of conversion of the acid, which can reach 99%. It was found that the main degradation products (～94% on carbon basis) are formaldehyde (～24%) and carbon dioxide (～70%).     

Interaction of silver nanoparticles with ozone in aqueous solution

The interaction between ozone and silver nanoparticles stabilized with sodium polyphosphate is studied in aqueous solutions. The process of ozone decomposition is established to have a chain character. The oxidation of one silver atom initiates the decomposition of about three ozone molecules. The stability of colloidal silver decreases upon the oxidation, which leads to its partial aggregation.     

Estimation of sodium bicarbonate crystal size distributions in a steady-state bubble column reactor

Sodium bicarbonate is a substance which is produced in the middle stages of the soda ash production process. In this precipitation process, carbon dioxide gas is continuously injected into the bubble column reactor, which contains carbonate and bicarbonate solutions. This work deals with the study of the gas?Cliquid mass transfer, coupled with chemical reactions, and the liquid?Csolid mass transfer, coupled with crystallization. In this mathematical model, a mole balance has been instituted on flows and components through the bubble column, which also utilized a nucleation and growth formula for the solid phase and the Danckwerts?? theory for mass transfer between the gas and liquid phases. The mathematical model can predict the effects of several parameters on the sodium bicarbonate crystal size distributions. We computed the mathematical simulation model results with the experimental results of the bubble column reactor of the Shiraz Petrochemical Complex for validating the model and investigated the effects of different parameters on the sodium bicarbonate crystal size distributions.     

Oxidative decomposition of oxalate ion with ozone in aqueous solution

The oxidation of oxalate ions with ozone in aqueous solution has been studied, and the effects of pH, temperature, and reactant concentrations on the reaction rate and efficiency have been estimated. The oxidative decomposition is most effective in alkaline medium (pH ≥ 10) at 50°C. Under these conditions, the consumption of ozone is 0.6±0.1 g per gram of oxalate or 1.1±0.1 mol per mole of oxalate, which corresponds to the stoichiometry (COO^–)₂ + O₃ + H₂O → 2CO₃^2– + O₂ + 2H⁺.     

Decomposition of sodium dodecyl sulfate with ozone in aqueous solution

Decomposition of sodium dodecyl sulfate with ozone in aqueous solution in the presence of high concentrations of sodium nitrate was studied. The factors affecting ozone interaction with a dissolved compound were determined.     

Numerical simulation of the kinetics of ozone decomposition in an aqueous solution

The kinetic scheme for ozone decomposition in an aqueous solution in a wide pH interval was proposed on the basis of the known literature data. The apparent first-order rate constant for ozone decomposition at pH 1–14 was calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1151–1156, June, 2008.     

Production of l-lactic acid byRhizopus oryzae in a bubble column fermenter

Two distinctive forms of growth (mycelial filamentous and mycelial pellets) ofRhizopus oryzae were obtained by manipulating the initial pH of the medium with the controlled addition of CaCO₃ in a bubble fermenter. In the presence of CaCO₃, diffused filamentous growth was obtained when the initial pH of the substrate was 5.5. In the absence of CaCO3, mycelial pellet growth was obtained when the initial pH was 2.0. The fermentation study indicated that the mycelial growth has a shorter lag period before the onset of acid formation. Both physical forms of growth ofRhizopus exhibited a high yield of L-lactic acid in the bubble fermenter when the initial glucose concentration exceeded 70 g/L. A final lactic acid concentration of 62 g/L was produced by the filamentous form ofRhizopus from 78 g/L glucose after 27 h. This showed a weight yield of 80% of glucose consumed, with an average specific productivity of 1.46 g/h/g. Similarly, the pellet form ofRhizopus produced a final lactic acid concentration of 66 g/L from 76 g/L glucose after 43 h, with a weight yield of 86% and an average specific productivity of 1.53 g/h/g.     

Specific features of chitosan-montmorillonite interaction in an aqueous acid solution and properties of related composite films

The rheological properties of chitosan solutions in a 2% aqueous solution of acetic acid with added montmorillonite nanoparticles and the mechanical properties and structural organization of chitosan-based composite films are studied. The interaction between the polymer functional groups and surface charges of nanoplatelets is confirmed by conductometric and potentiometric measurements. With the use of a X-ray diffraction analysis, it is shown that the nanoparticles in films are in the exfoliated and intercalated states. The incorporation of up to 10 wt % modified montmorillonite nanoparticles into the chitosan matrix results in a successive increase in rigidity and a decrease in the elongation at break.     

Chlorophyllide a/cyclodextrin interaction in aqueous solution

The interactions between Chlorophyllide a (Chlide), a pigment having the same structure of Chl a without the phytilic tail, and two CDs having the same moieties but different cavity size, the hydroxypropyl- β -cyclodextrin and the hydroxypropyl-γ-cyclodextrin, were studied in aqueous solutions by means of absorption, fluorescence spectroscopy, circular dichroism and isothermal titration calorimetry. The results obtained indicate that both cyclodextrins are able to modify the aggregation equilibrium of the pigment favouring the monomeric form. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction between a stationary mercury electrode and a hydrogen bubble in an aqueous sodium dodecyl sulphate solution

The stability and rupture of thin liquid films formed from an aqueous solution of Na₂SO₄ (0.05 mol dm⁻³) in the presence of 5 × 10⁻⁵ mol dm⁻³ sodium dodecyl sulphate between a stationary mercury electrode and a hydrogen bubble has been investigated as a function of electrode potential. The electrostatic component of disjoining pressure has been calculated using the results of capacity measurement for the mercury-solution interface. Special attention has been paid to films formed on positively charged mercury surfaces. In this case, despite the positive electrode polarization, the outer Helmholtz plane potential is found to be negative due to the high surface activity of the dodecyl sulphate anion. The van der Waals component of disjoining pressure has been calculated on the basis of a double sheath model of the two interacting surfaces, taking into consideration the orientation of the adsorbed surfactant layers at the interfaces. Calculations of the total disjoining pressure can explain film stability at negative mercury potentials, but do not explain film rupture when the polarization of the mercury is positive. The existence of a hydrophobic attractive interaction is postulated in the latter case.     

Phase equilibria in a system of aqueous arginine with an octane solution of sulfonic acid

The extraction of arginine (Arg) from aqueous salt (0.1 M NaCl) solutions with a sulfo extractant in a wide range of pH values and amino acid concentrations was studied. The 0.1 M solution of dinonylnaphthalenesulfonic acid (HD) in octane was used as an extractant. The degree of extraction was found to be high at pH 0.8–9.0. This can be explained by the effect of additional intermolecular interactions in the extractant phase involving the guanidine group of Arg.     

Study of the mass transfer kinetics in a monolithic column

The purpose of this work is to investigate the mass transfer kinetics of butylbenzoate on a monolithic RPLC column, with methanol-water (65:35, v/v) as the mobile phase. We used the perturbation method, measuring the height equivalent to a theoretical plate (HETP) of the peaks obtained as the response to small pulses of solute injected on a concentration plateau. The equilibrium isotherm of butylbenzoate was previously determined by frontal analysis. It is well accounted for by a liquid-solid extended multilayer BET isotherm model. The equilibrium data derived from the pulse method are in excellent agreement with those of frontal analysis in the accessible concentration range of 0 to 8 g/dm3. Plots of the HETP of small pulses. injected on eight different plateau concentrations, were acquired in a wide range of mobile phase flow velocities. The axial dispersion and the mass transfer kinetic coefficients were derived from these data. The validity of these measurements is discussed. The mass kinetics of butylbenzoate depends strongly on the plateau concentration. Processes involving adsorptive interactions between the solute and the stationary phase, e.g. surface diffusion and adsorption-desorption kinetics, combine in series to the external mass transfer kinetics and to effective pore diffusivity.     

Oxidation of formic acid by bromine in aqueous,strongly acid media

Spectrophotometric methods were used to investigate the rate of the reaction of Br₂ with HCOOH in aqueous, acidic media. The reaction products are Br^? and CO₂. The kinetics of this reaction are complicated by both the formation of Br₃^? as Br^? is formed and the dissociation of HCOOH into HCOO^? and H⁺. Previous work on this reaction was carried out at acidities lower than the highest used here and led to the conclusion that only HCOO^? reacts with Br₂. It is agreed that this is by far the principal reaction. However, at the highest acidity experiments, an added small component of reaction was found, and it is suggested that it results from the direct reaction of Br₂ with HCOOH itself. On this assumption, values of the rate constants for both reactions are derived here. The rate constant for the reaction of HCOO^? with Br₂ agrees with values previously reported, within a factor of 2 on the low side. The reaction involving HCOOH is more than 2000 times slower than the reaction involving HCOO^?, but it does contribute to the overall rate as [H⁺] approaches 1M. These derived rate constants are able to simulate quantitatively the authors' absorbance-versus-time data, demonstrating the validity of their data treatment methods, if not mechanistic assignments. Finally, activation parameters were determined for both rate constants. The values obtained are: ΔE^?(HCOOH + Br₂) = 13.3 ± 1.1 kcal/mol, ΔS^? (HCOOH + Br₂) = ?28 ± 3 cal/deg mol, ΔE^? (HCOO^? + Br₂) = 13.1 ± 0.9 kcal/mol, and ΔS^?(HCOO^? + Br₂) = ?12 ± 1 cal/deg mol. That the activation energies of the two reactions turn out to be essentially identical does not support the authors' suggestion that both HCOOH and HCOO^? react with Br₂.     

Cation-exchange behaviour of several elements in formic acid solution

The cation-exchange characteristics of 20 elements towards the strongly acidic cation-exchange resin Dowex 50 x 8 in media containing varying concentrations of formic acid and mixtures of formic acid with aqueous dioxan were investigated. Possible separations are indicated and discussed. Bismuth may be quantitatively separated from copper.