Sonochemical Destruction of CFC 11 and CFC 113 in Dilute Aqueous Solution

Hydrochlorofluorocarbon Adsorption by Granular and Extruded Activated Carbons

Experiments have been conducted to examine the adsorption/desorption characteristics of 1,1-dichloro-1-fluoroethane (HCFC-141b) by granular activated carbon (GAC) and extruded activated carbon. HCFC-141b is currently deemed an excellent replacement for CFC-11, a foaming agent widely used in the rigid polyurethane foam industries. Experimental results of adsorption and desorption were analyzed in terms of the equilibrium capacity, time to reach equilibrium and desorption efficiency of the adsorbent, and with the aim of assessing the viability of using both adsorbents for possible HCFC-141b recovery. The results have clearly revealed great potential for both adsorbents for this purpose.

Kinetics model for combined (alkaline+ultrasonic) sludge disintegration

Combined (alkaline+ultrasonic) technology could be applied as pretreatment to disintegrate sludge flocs and disrupt bacterial cells' walls. Influence factors were investigated, including ultrasonic density, ultrasonic intensity, sludge pH and sludge concentration. Based on the test data, kinetics model for sludge disintegration was established by applying multivariable linear regression method. It could be inferred from the kinetics model that sludge pH had the most significant effect on the sludge disintegration.

Effects of ultrasonic disintegration on sludge microbial activity and dewaterability

Ultrasonic treatment can disintegrate sludge, enhance microbial activity and improve sludge dewaterability at different energy inputs. To find their relationship, the three phenomena during ultrasonic treatment were investigated synchronously, and an experimental model was established to describe the process of ultrasonic sludge disintegration. Analysis results showed that the changes of sludge microbial activity and dewaterability were dependent on sludge disintegration degree during ultrasonic treatment. When sludge disintegration degree was lower than 20%, sludge flocs were disintegrated into micro-floc aggregates and the microbial activity increased over 20%. When sludge disintegration degree was over 40%, most cells were destroyed at different degree, and sludge activity decreased drastically. Only when sludge disintegration degree was 2-5%, sludge dewaterability was improved with the conditioning of FeCl(3). It was also found that the sonication with low density and long duration was more efficient than sonication with high density and short duration at the same energy input for sludge disintegration, and a transmutative power function model can be used to describe the process of ultrasonic disintegration.

Sonolysis of chlorinated compounds in aqueous solution

To examine the reaction rates of sonochemical degradation of aqueous phase carbon tetrachloride, trichloroethylene and 1,2,3-trichloropropane at various temperatures, power intensities, and saturating gases, the batch tests were carried out. The degradations of chlorinated hydrocarbons were analyzed as pseudo first order reactions and their reaction rate constants were in the range of 10(-1)-10(-3)/min. The reaction was fast at the low temperature with higher power intensity. Also, the reaction went fast with the saturating gas with high specific heat ratio, high solubility and low thermal conductivity. The main mechanism of destruction of chemicals was believed the thermal combustion in the bubble.

Comparison of enhancement of pentachlorophenol sonolysis at 20 kHz by dual-frequency sonication

The comparison of enhancement effect of pentachlorophenol sonolysis at 20 kHz by different dual-frequency ultrasonic irradiations has been investigated. Dual-frequency (20 kHz/40 kHz, 20 kHz/530 kHz, 20 kHz/800 kHz and 20 kHz/1040 kHz) ultrasounds have been used. It has been found that the rate of pentachlorophenol degradation at dual-frequency ultrasonic irradiation is the highest compared to mono-frequency ultrasonic systems. The combination of dual-frequency systems has synergistic effect and the enhancement effect of sonochemical degradation of pentachlorophenol at 20 kHz by dual-frequency systems appears to be remarkable frequency sensitive. The order of contribution to the enhancement effect of sonochemical degradation of pentachlorophenol at 20 kHz is as follows: 530 kHz > 800 kHz > 40 kHz > 1040 kHz.

Mechanisms and kinetics models for ultrasonic waste activated sludge disintegration

Ultrasonic energy can be applied as pre-treatment to disintegrate sludge flocs and disrupt bacterial cells' walls, and the hydrolysis can be improved, so that the rate of sludge digestion and methane production is improved. In this paper, by adding NaHCO3 to mask the oxidizing effect of OH, the mechanisms of disintegration are investigated. In addition, kinetics models for ultrasonic sludge disintegration are established by applying multi-variable linear regression method. It has been found that hydro-mechanical shear forces predominantly responsible for the disintegration, and the contribution of oxidizing effect of OH increases with the amount of the ultrasonic density and ultrasonic intensity. It has also been inferred from the kinetics model which dependent variable is SCOD+ that both sludge pH and sludge concentration significantly affect the disintegration.

Sonochemical removal of trihalomethanes from aqueous solutions

In this research, ultrasound irradiation was employed to degrade the trihalomethanes, THMs: CHCl3, CHBrCl2, CHBr2Cl, CHBr3, and CHI3. The kinetics reaction rates and removal efficiencies of the THMs compounds, as a sole component in the aqueous solutions, were studied. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and acoustic intensity of 3.75 W/cm2. The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of CHCl3 > CHBrCl2 > CHBr2Cl > CHBr3 > CHI3. Up to 100% of the CHCl3 was removed, while only 60% of the CHI3 was sonodegraded, after 180 min sonication. The THMs vapor pressure was found to be the most important parameter affecting the sonodegradation kinetics and efficiency, while the bond dissociation energy and hydrophilic/hydrophobic characteristics of the THMs compounds were found to be of secondary importance.

Sonochemical decomposition of volatile and non-volatile organic compounds--a comparative study

Sonochemical degradation which combines destruction of the target compounds by free radical reaction and thermal cleavage is one of the recent advanced oxidation processes (AOP) and proven to be effective for removing low concentration organic pollutants from aqueous streams. This work describes the degradation of several organic compounds of varying volatility in aqueous solution in two types of ultrasonic reactors. The process variables studied include initial concentration of the organics, temperature, and type of saturated gas. The effects of additional oxidant and electrolyte were also examined. A kinetic model was tested to determine its ability to predict the degradation rate constant of different volatile organic compounds at different initial conditions. A figure of merit for the electrical energy consumption for the two types of ultrasonic reactors is also presented.

Sonochemically induced decomposition of energetic materials in aqueous media

This study demonstrates that ultrasound rapidly degrades the energetic compounds RDX (cyclo-1,3,5-trinitramine-2,4,6-trimethylene) and ADN (ammonium dinitramide) in aqueous microheterogeneous media. The conditions for effective degradation of these nitramines, as monitored by UV absorption spectroscopy, were determined by varying sonication time, the heterogeneous phase and its suspension density, and the concentration of NaOH. In the presence of 5 mg/ml of aluminum powder and at pH approximately 12 (10 mM NaOH), 74% of the RDX and 86% of the ammonium dinitramide (ADN) in near-saturated solutions decompose within the first 20 min of sonication (20 kHz; 50 W; < or =5 degrees C). Sonication without Al powder and base yields minimal degradation of either RDX and ADN (approximately 5-10%) or the nitrite/nitrate ions that are expected byproducts during RDX and ADN degradation. Sonication at high pH in the presence of dispersed aluminosilicate zeolite, alumina, or titanium dioxide also yields minimal degradation. Preliminary electrochemical studies and product analyses indicate that in situ ultrasonic generation of metallic aluminum and/or aluminum hydride drives reductive denitration of the nitramines. Sonochemical treatment in the presence of a reductant offers an effective and rapid waste remediation option for energetic waste compounds.

Sonochemical degradation of chlorinated hydrocarbons using a batch and continuous flow system

The sonochemical degradation of chlorinated hydrocarbons such as 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene in aqueous solution was carried out in the batch and continuous flow systems at an ultrasonic frequency of 100kHz under an air atmosphere. In the batch experiment, the rate of degradation follows the order 1,1,1-trichloroethane>tetrachloroethylene>trichloroethylene, and the chlorinated hydrocarbon were readily degraded by ultrasonic irradiation. The experiments in the continuous flow system were performed in the range of volumetric flow rate from 7 to 30 x 10(-3)lmin(-1). The conversion of the chlorinated hydrocarbons at a steady-state of reactor depended on the volumetric flow rate. The yield of Cl(-) (as a measurement of mineralization of chlorinated hydrocarbons) was 70-90% of the chlorine atoms in the parent chlorinated hydrocarbon molecules. From the viewpoint of the scale-up process, the sonochemical degradation of trichloroethylene was simulated in a three stage reactor, and the conversion (>99%) in a third stage reactor was showed the good results that can be satisfied a desired water quality standard.

Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation.

Degradation of pentachlorophenol aqueous solutions using a continuous flow ultrasonic reactor: experimental performance and modelling

The degradation of aqueous solutions of pentachlorophenol (PCP) in a three-stage sonochemical reactor operating in the continuous flow mode has been investigated. The experimental reactor may be considered as a series of three high-frequency ultrasonic units. The influence of several parameters such as ultrasonic power, reactor volume and volumetric feed flow rate on the reactor performance is reported. Application of classical basic chemical engineering principles leads to a model that enables us to predict the PCP concentration within the reactor. In steady state, experimental conversion rates are shown to be in good agreement with model predictions.

Sonophotochemical destruction of aqueous solution of 2,4,6-trichlorophenol

The combination of ultrasound and photochemistry have been used to degrade an aqueous solution of 2,4,6-trichlorophenol. An ultrasonic probe of 22 kHz frequency and a UV tube of 15 W have been used. Anatase grade TiO2 was used as the semiconductor catalyst. The effect of parameters such as ultrasonic intensity, operating conditions, type of ultrasonic equipment, and mode of UV transmission have been studied. The sonophotochemical degradation has been found to be dependent on the intensity of sonication, temperature of the reaction, and the type of ultrasonic equipment used, but was independent of the mode of UV transmission. Enhancement in the degradation rate has been observed at a higher sonication intensity and temperature of the solution.

Sonication of aqueous solutions of chlorobenzene

Sonication at two frequencies (20 and 900 kHz) was carried out on dilute (220 ppm) aqueous solutions of chlorobenzene. The formation of chloride ions was followed using ion chromatography. The solutions became more colored with time; the absorbance maximum was around 270 nm. Some of the compounds remaining in the solution could be identified; they were chlorinated phenols, chloronaphthalene, mono and dichlorobiphenyls, etc. At the same acoustic power, the rate of chloride formation with 20 kHz ultrasound was greater when a probe with a larger tip area was used, but significantly less than the rate with 900 kHz. The use of ultrasound for conversion of chlorine in organic compounds in water to chloride can thus be performed more efficiently using a higher frequency and with a lower intensity (power per area). There is, however, a possibility that the toxicity of the aqueous solution is increased by such treatment.

Degradation of aqueous solution of potassium iodide and sodium cyanide in the presence of carbon tetrachloride

The degradation of potassium iodide, carbon tetrachloride and sodium cyanide has been studied using an ultrasounic probe of 20 kHz frequency. In the case of potassium iodide and sodium cyanide, the rate of degradation was much higher in presence of CCl4. The location of the ultrasonic horn showed a significant effect in the degradation of CCl4.

A few questions on the sonochemistry of solutions

Sonochemical reactions in solution have an underexploited synthetic potential. Most of the obstacles to expand this attractive domain come from unanswered questions on, for example, the importance of the radiomimetic effect, the implication of the solvent as a relay in the reaction mechanism, the existence of redox processes, and concerning cavitation, the structure of the bubble interface and the pressure effects associated to the collapse.