Simultaneous absorption of mercury and chlorine in sulfite solutions

Simultaneous absorption of mercury (Hg) and chlorine (Cl₂) into aqueous sulfite/bisulfite (0 to S(IV)) at pH 4.7 and 5.7 was measured in a wetted wall column. Experiments were performed at ambient temperature and pressure using 5- Cl₂ and 46 ppb Hg. Absorption was modeled using the theory of mass transfer with chemical reaction. At the gas/liquid interface, chlorine oxidizes the elemental Hg to a more soluble form. The rate constant for the reaction of mercury and chlorine was determined to be . Mercuric chloride and sodium hypochlorite also enhanced Hg absorption. The addition of sodium chloride did not affect the rate of Hg/Cl₂ absorption with S(IV). When no S(IV) was present, the chloride significantly enhanced Hg absorption. Possible reaction pathways are discussed. These results are relevant in the simultaneous removal of chlorine, sulfur dioxide, and elemental mercury from flue gas. A model was developed to predict the expected Hg removal in a limestone slurry scrubber. Mercury removal decreases as the S(IV) concentration increases. The process feasibility will depend on the SO₂/S(IV) concentration of the scrubber, the desired Hg removal, and the amount of Cl₂ which can be tolerated.     

Electrothermal fluidized bed chlorination of zircon

Zircon sand, ZrSiO₄, is chlorinated in an electrothermally-heated fluidized bed reactor using calcined petroleum coke as the reducing agent and chlorine as the chlorinating agent. The electrothermally-heated fluidized bed reactor proved to be versatile and effective for the chlorination of zircon sand. The rate of the reaction can be expressed by the formula The reaction was found to be of zero order with respect to the chlorine concentration, which suggests that chlorine is strongly adsorbed on the solid particles; as such, the concentration of chlorine in the gas phase has no effect on the reaction rate. The activation energy for the reaction was found to be 10.55 Kcal/gram mole which is indicative of control by the rate of a surface reaction or adsorption step.     

Simultaneous absorption of two gases accompanied by a complex chemical reaction: approximate solutions

Approximate solutions to the problem of simultaneous absorption of two gases in a liquid accompanied by a complex chemical reaction have been presented based on the film theory. Two approximate profiles, a nonlinear exponential profile and a trigonometric profile, for the concentration of each of the gaseous species in the film have been used in analysing the problem. The complex scheme considered is:

For the exponential case two approximations have been considered: [1] in which the higher order terms are included, and [2] in which the higher order terms are neglected.The results obtained using the two profiles have been compared with numerical solutions for the film theory in the range of

from 1 to 3. The results show that both the approximations yield solutions close to the numerical, in particular case [1] of the exponential approximation. Some special cases have then been considered followed by a discussion of an industrially important system: simultaneous absorption of ethylene and chlorine in water to give ethylene chlorohydrin.     

KINETICS OF ABSORPTION OF OXYGEN IN ALKALINE SOLUTIONS CONTAINING A QUINONE-TYPE COMPOUND

The rates of absorption of pure oxygen in alkaline aqueous solutions containing sodium salt of 1,4-naphthoquinone 2-sulfonic acid (NQS) as a catalyzer for the Takahax desulfurization process were measured at 25°C using a liquid jet column.

The kinetics of the absorption was examined based on the theory for gas absorption accompanied by an irreversible second order chemical reaction. The pH of the solution, that is, the concentration of hydroxyl ion plays an important role in a reaction of first order with respect to oxygen and to NQS. The reaction rate constant is directly proportional to pH in the range 9.8-11.5, for more alkaline solutions being found to be 4.5 × l0⁶L/mole ? s.     

Acceleration of the reaction of carbon dioxide into aqueous 2-amino-2-hydroxymethyl-1,3-propanediol solutions by piperazine addition

In this work, the kinetics of the reaction between CO₂ and piperazine-activated aqueous solutions of a sterically hindered alkanolamine, 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD) was studied in a wetted wall column contactor at 303.15, 313.15 and 323.15 K. The AHPD concentration in the aqueous solutions was kept at while the piperazine (PZ) concentration varied in the range . Under pseudo-first-order CO₂ absorption conditions, the overall pseudo-first-order rate constants were determined and reaction rate parameters were calculated with a non-linear regression from the overall reaction rate constant. The ratio of the diffusivity and Henry's law constant for CO₂ in solutions was estimated by applying the N₂O analogy and the Higbie penetration theory, using the physical absorption data of CO₂ and N₂O in water and of N₂O in amine solutions. Piperazine was found to be an effective activator in the aqueous AHPD solutions, as the addition of small amounts of PZ to these solutions has a significant effect on the enhancement of the CO₂ absorption rate for all studied temperatures.     

Application of an experimental design method to study the performance of electrochlorination cells

A study of the effects of some parameters on the active chlorine production from aqueous sodium chloride solutions in the hypochlorite electrochemical production cells was undertaken. These varying parameters included the anodic surface area (S_a), the ratio of anodic and cathodic surface areas () the inter-electrode gap, and the type of the cathode used. In addition, a study of the performance of some electrochemical cells that differ in the type of anodes (platinum-coated titanium, ruthenium-coated titanium, and graphite) was made. By means of the experimental design method employing a full factorial of2² the effects ofthe most influencing parameters, the set-up of optimum conditions, and the formation of optimal concentration of active chlorine were assessed. Under the following conditions, a concentration of as high as 65.67 g/L of active chlorine was gained: ruthenium-coated titanium anode (S_a = 24 cm²); titanium cathode, ; inter-electrode gap, 0.5 cm; current density, 35 A/dm² ; temperature, 20°C; concentration of NaCl aqueous solution, 3 M; time, 2 h.     

The kinetics and mechanism of the chloride-chlorate reaction

The kinetics of the reaction have been studied at 25°C. in strong acid solution; the effects of acidity, chloride, chlorate and chlorine are reported. A mechanism is postulated to interpret the peculiar features of this reaction as well as the stoichiometry and some of the kinetics of the parallel reaction The mechanism involves HClO₂ and HOCl as intermediates General rate expressions are derived for the formation of chlorine dioxide and chlorine, and the individual rate constants are calculated. An expression is obtained for the relationship between the ratio of chlorine dioxide to chlorine produced and the ratio of chlorate to chloride.     

High strength wastewater treatment in a jet loop membrane bioreactor: kinetics and performance evaluation

Treatment of wastewater containing high organic matter was investigated by means of a jet loop bioreactor combined with a membrane process. Volume of jet loop bioreactor and area of membrane filtration unit were 23 l and 155 cm² respectively. It was found that jet loop reactor had high mass transfer coefficient (K_La) varying from 58.8 to 486 h^-1 depending on the water flow rate (i.e. power input) and air flow rate. Oxygen transfer efficiency and oxygenation capacity of the reactor varied from 12 to 22.5% and from 0.2 to 1.8 , respectively. The efficiency of jet loop membrane bioreactor was found to be approximately 97% for a volumetric organic load of 2- over a period of 10 weeks. The reactor was not disturbed from the organic loads up to , but the treatment efficiency decreased to about 60% at higher organic loads. This decrease was due to insufficient oxygen transfer rate. The relationship between the effluent substrate concentration and the specific oxygen uptake rate (SOUR) values was determined. Applied food/microorganism (F/M) ratio was varied between 2.5 and . Critical sludge age of the system () was evaluated to be 7.2 h. Sludge with unsatisfactory settling characteristics formed at high F/M values under turbulent conditions. Therefore, membrane process was used for solid-liquid separation and effluent solid concentration was approximately zero. Specific cake resistances (α) changed with F/M ratio. It was found that permeate fluxes were significantly effected with F/M ratio much more than mixed liquor suspended solids (MLSS). Average flux was for pore sized cellulose acetate membrane. It was concluded that the jet loop membrane bioreactor has distinctive advantages such as the ability to treat high strength wastewater, low area requirements and easy operation.     

Kinetics of absorption of carbon dioxide in aqueous piperazine solutions

In the present work the absorption of carbon dioxide into aqueous piperazine (PZ) solutions has been studied in a stirred cell, at low to moderate temperatures, piperazine concentrations ranging from 0.6 to , and carbon dioxide pressures up to 500 mbar, respectively. The obtained experimental results were interpreted using the DeCoursey equation [DeCoursey, W., 1974. Absorption with chemical reaction: development of a new relation for the Danckwerts model. Chemical Engineering Science 29, 1867-1872] to extract the kinetics of the main reaction, 2PZ+CO₂→PZCOO^-+PZH⁺, which was assumed to be first order in both CO₂ and PZ. The second-order kinetic rate constant was found to be at a temperature of , with an activation temperature of . Also, the absorption rate of CO₂ into partially protonated piperazine solutions was experimentally investigated to identify the kinetics of the reaction . The results were interpreted using the Hogendoorn approach [Hogendoorn, J., Vas Bhat, R., Kuipers, J., Van Swaaij, W., Versteeg, G., 1997. Approximation for the enhancement factor applicable to reversible reactions of finite rate in chemically loaded solutions. Chemical Engineering Science 52, 4547-4559], which uses the explicit DeCoursey equation with an infinite enhancement factor which is corrected for reversibility. Also, this reaction was assumed to be first order in both reactants and the second-order rate constant for this reaction was found to be at 298.15 K.     

High-temperature chlorine corrosion of technical carbons Part II. Anodic corrosion in chloride melt

Medium (200 to 400°C) to high (600 to 800°C) temperature corrosion of technical carbons (Acheson graphites) have been investigated in alkali chloride melts at chlorine evolving anodes. At low temperature in chloride melts containing free Lewis acid (AlCl₃) no chlorine is evolved — even at high current densities — because chlorine, together with aluminium chloride, instantaneously form intercalation compounds with graphite and, as a consequence, the carbon desintegrates very rapidly. At 200°C carbon is consumed anodically in a C/Cl of molar ratio 70/1. With increasing temperature Scheson graphites become more stable so that at 700°C short term destruction cannot be observed in melts which contain free Lewis acid. Chlorine corrosion of carbon electrodes in purified basic alkali chloride melts, which are free of oxygen carriers and, in particular, free of water at temperatures between 600 and 800°C in basic chloride melts, is an electrochemical reaction proceeding at low current densities slower than anticipated from thermodynamic data for carbon chlorination equilibria. The anodic carbon corrosion reaction has an activation energy of only 50 kJ mol^–1 and its rate increases with increasing anode potential, or anodic current densities (rate: exp (i)). At a technical current density of 0.4 A cm^–2 at 700°C the corrosion rate is estimated to be of the order of centimeters per year, rendering carbon anodes dimensionally unstable. Most important is to note that apart from CCl₄, chlorinated carbon compounds (olefins and arenes) are generated as side-products which are noxious and ecologically dangerous and must not be released from processes which use carbon anodes for chlorine evolution from salt melts.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Kinetics of hydrogen peroxide bleaching of ALCELL® derived pulp

In this study, a kinetic model of the final bleaching stage with hydrogen peroxide in a totally chlorine free (TCF) bleaching sequence for ALCELL® processed pulp was developed. The model was based on the rate of chromophore destruction characterized by the decrease in the light absorption coefficient of bleached pulp at 457 nm, C_K. Based on the fact that the chromophore destruction proceeds rapidly in an initial phase followed by a much slower reaction during which a “floor-level” chromophore concentration is approached asymptotically, we propose that the hydrogen peroxide stage of the ALCELL® derived pulp in the studied TCF sequence consists of two distinct phases. The initial phase is a very fast reaction. The rate equation of the second phase was determined as: which is valid in a pH range of 10.5 to 11.5 and a temperature range of 60 to 92.5°C.     

Synthesis and characterization of low-temperature self-crosslinkable acrylic emulsion for PE film ink

A low-temperature self-crosslinkable acrylic emulsion was synthesized by semi-continuous emulsion polymerization technology using methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA) and diacetone acrylamide (DAAM) as monomers and adipic dihydrazide (ADH) as crosslinker. Transmission electron microscope (TEM) micrograph disclosed spherical emulsion particles possess core–shell structure. Fourier transform infrared (FTIR) spectrogram showed that crosslinking reaction between CO groups of DAAM and NHNH₂ groups of ADH can occur during coating film formation at low temperature, even at room temperature. Differential scanning calorimeter (DSC) analysis indicated that glass transition temperature (Tg) of the crosslinked film is increased by 5 °C. Thermogravimetric analysis (TGA) curves demonstrated that self-crosslinking reaction improves thermal stability of film. As DAAM content increased from 0% to 2%, water absorption ratio of film decreased from 26.2% to 7.4%, adhesion ratio on the PE thin film increased from 0% to 97%. While the n(ADH)/n(DAAM) ratio increased from 0:1 to 0.8:1, crosslinking density of films was increased from 0% to 88%, water absorption ratio decreased from 36.5% to 7.4% and adhesion ratio on the PE thin film increased from 0% to 97%. The optimal DAAM content and n(ADH)/n(DAAM) ratio was 2% and 0.8:1 in this experiment. The emulsion has good potential application in water-based ink for PE film.     

Quantification and prediction of jet macro-mixing times in static microwell plates

Automated experimentation in microwell plate formats is widely used in high throughput drug discovery. Such approaches are now being considered for the study of bioprocess unit operations in order to speed the delivery of new medicines to market. The generation of useful design data from microwell formats requires an understanding of the engineering environment within individual microwells. Rapid and efficient macro-mixing is crucial in this respect to ensure the generation of quantitative and reproducible data. In this study, we have developed a high-speed video technique for the accurate quantification of jet macro-mixing times in static microwell plates which also enables visualisation of jet formation and liquid flow patterns within wells. Mixing times have been determined using both the fixed and disposable tips of a Perkin Elmer MultiProbe II^TM liquid handling robot for a range of jet Reynolds numbers (Re_j=1000-3960) and liquid addition volumes . Three microwell geometries have been investigated; one that is identical to a single well from a standard 96-round well plate and two novel designs based upon theories of jet mixing (V_i=200 and ). For conditions where macro-mixing was complete within the lifespan of the jet, t₉₅ mixing times for the standard round well were in the range 0.033-0.121 s while for the larger of the two designed wells they were in the range 0.228-0.705 s. The rapid mixing times in the standard round well are a consequence of increased energy dissipation as the liquid jet impinges on the base of the well. For the two designed wells maximising the jet length to nozzle diameter ratio (X/d_i) is shown to promote the most efficient macro-mixing due to entrainment and circulation of the bulk liquid in the well. For low volume additions and short jet lifespans it is also shown that mixing times can be of the order of minutes. Finally, the t₉₅ results for each of the well geometries have been correlated to the conditions used for jet formation using a correlation of the form first proposed by Baldyga and co-workers [Baldyga, J., Bourne, J.R., Dubuis, B., Etchells, A.W., Gholap, R.V., Zimmermann, B., 1995. Jet reactor scale-up for mixing controlled reactions. Chemical Engineering Research & Design 73, 497-502]. This enables good prediction of the experimentally determined mixing times and estimation of the minimum liquid addition volume (V_Crit) that will ensure rapid and efficient macro-mixing. The correlation therefore enables automation users to optimise or control macro-mixing times in microwell experiments.     

1H-NMR/13C-NMR studies of branched structures in PVC obtained at atmospheric pressure

Summary The ¹H-NMR-spectra of raw poly (vinyl chloride) obtained at atmospheric pressure (U-PVC) have revealed the presence of high concentrations of branches. The content of labile chlorine was determined by reaction with phenole in order to estimate the branch points with tertiary chlorine. The branch length of reductively dehalogenated U-PVC by¹³C-NMR analysis have provided evidence for both short chain branches including chloromethyl groups and 2.4-dichloro-n-butyl groups and long chain branching. For a number of U-polymers the total amount of branching ranges from 7.5 to 13.5/1000 C. The ¹³C-NMR measurements point to a ratio of methyl/butyl branches of 1 1 and short chains/long chains of 6 1 .     

Electrochemical study of the diffusion at solid state. Gold—copper system

The time dependence of the potential of an alloy electrode during the electrolysis in a fused salt bath is used to determine the diffusion rate of the electroactive component. For a reversible electrochemical reaction the potential is related to the surface concentration by activity measurements. The analysis of this concentration change during electrolysis at constant current densities is done as well for anodic processes (oxydation of the less noble metal) as for cathodic processes (metal deposition). The evolution of the surface composition back to the equilibrium situation after the end of the electrolysis is also examined.This approach is illustrated on the experimental study of copper—gold systems using the cell:

When during the electrolysis the concentration changes are small the previous analysis leads to the determination of the intrinsic diffusion coefficients of copper atoms. These calculations are carried out for different alloy compositions (0 < X_Cu < 0.79, X_Cu = at. fraction of copper) in the temperature range 659–827 K. Moreover by using very different time scales (from 1 ms to 10 min) it is shown that the diffusion rate of copper near the interface is the same as in the bulk of the alloy.     

Kinetics and modeling of carbon dioxide absorption into aqueous solutions of piperazine

In this work, the kinetics of the reaction between CO₂ and aqueous piperazine (PZ) have been estimated over the temperature range of 298-313 K from the absorption data obtained in a wetted wall contactor. The absorption data are obtained for the PZ concentrations of 0.2- and for CO₂ partial pressures up to 5 kPa. A coupled mass transfer-kinetics-equilibrium mathematical model based on Higbie's penetration theory has been developed with the assumption that all reactions are reversible. The model is used to estimate the rate constants from the experimental data for absorption of CO₂ in aqueous PZ. The estimated rate constants of this study are in good agreement with those reported in the literature.     

An experimental and theoretical study of the nitrosation of ammonia and thiourea

The nitrosation reactions of both thiourea and ammonia have been investigated, owing to their interesting kinetic behaviour and their industrial importance in the sensitisation of emulsion explosives. Kinetic experiments were conducted using a well-mixed aqueous reactor, from which samples were periodically removed, quenched, and then analysed for nitrite concentration using ion chromatography. We derived a number of plausible rate equations for both the ammonia and thiourea gassing processes, which we subsequently tested against experimental results to determine the operating kinetic mechanism, under a range of conditions. The reaction between ammonia and nitrite was seen to proceed by way of the nitrosating agent dinitrogen trioxide. In the presence of thiocyanate, however, dinitrogen trioxide was replaced by the thermodynamically more powerful nitrosating agent nitrosyl thiocyanate. Both reaction mechanisms exhibited relatively similar temperature dependencies, with respective activation energies of 56 and , determined between 25 and 45 °C, indicating reaction-controlled regimes. The effects of pH, temperature and ammonium nitrate concentration on the rate of thiourea nitrosation were studied. The rate of reaction was independent of ammonium nitrate concentration, while decreasing the pH of the reaction medium resulted in significant increases in the rate of reaction. The activation energy was evaluated as being in the temperature range of 25 to 45 °C. Theoretical evidence at the G2MP2 level of theory supports a mechanism of thiourea nitrosation involving rapid deprotonation of S-nitrosothiourea, followed by rate-limiting S to N migration of the nitroso group.     

Carbothermic reduction of zinc sulfide in the presence of sodium carbonate

The carbothermic reduction of zinc sulfide in the presence of sodium carbonate has been studied using X-ray diffractometry (XRD), thermogravimetric analysis system (TGA), atomic absorption spectrometry (AAS), inductively coupled plasma-mass spectrometry (ICP-MS), elemental analyzer (EA) and scanning electron microscopy (SEM). Experimental results of AAS indicated that the reduction in the presence of sodium carbonate proceeded significantly faster than in the presence of calcium carbonate and its sulfur fixation efficiency was acceptable. The results of XRD revealed that zinc sulfide was first transformed from β-type to α-type, then reduced to zinc vapor. The sequence of the variation of sodium containing material was found to be . A reaction mechanism is proposed to interpret the overall reaction. Results of kinetic study indicated that the rate of reduction could be increased by increasing the reaction temperature, the initial molar ratio of C/ZnS, or the initial molar ratio of Na₂CO₃/ZnS. The rate was also found to be increased with a decrease in sample height, size of C aggregate, size of Na₂CO₃ aggregate or the initial bulk density. The reduction rate, however, was found not to be influenced by the argon flow rate. An empirical expression of the initial rate of zinc yield has been determined.