Effects of ultrasound on adsorption-desorption of p-chlorophenol on granular activated carbon

The aim of this work is the evaluation of the effects of ultrasound on p-chlorophenol adsorption-desorption on granular activated carbon. Adsorption equilibrium experiments and batch kinetics studies were carried out in the presence and the absence of ultrasound at 21 kHz. Results indicate that the adsorption of p-chlorophenol determined in the presence of ultrasound is lower than the adsorption observed in the absence of ultrasound. Desorption of p-chlorophenol from activated carbon with and without the application of ultrasound was studied. The desorption rates were favoured by increased ultrasound intensity. This rise is more noticeable as temperature increases. The addition of ethanol or NaOH to the system causes an enhancement of the amount of p-chlorophenol desorbed, especially in the presence of ultrasound. A synergetic enhancement of the desorption rate was observed when ultrasonic irradiation was coupled with ethanol chemical regeneration.     

Ultrasound-assisted regeneration of zeolite/water adsorption pair

The use of ultrasound to enhance the regeneration of zeolite 13X for efficient utilization of thermal energy was investigated as a substitute to conventional heating methods. The effects of ultrasonic power and frequency on the desorption of water from zeolite 13X were analyzed to optimize the desorption efficiency. To determine and justify the effectiveness of incorporating ultrasound from an energy-savings point of view, an approach of constant overall input power of 20 or 25 W was adopted. To measure the extent of the effectiveness of using ultrasound, the ultrasonic-power-to-total power ratios of 0.2, 0.25, 0.4 and 0.5 were investigated and the results compared with those of no-ultrasound (heat only) at the same total power. To analyze the effect of ultrasonic frequency, identical experiments were performed at three nominal ultrasonic frequencies of ~28, 40 and 80 kHz. The experimental results showed that using ultrasound enhances the regeneration of zeolite 13X at all the aforementioned power ratios and frequencies without increasing the total input power. With regard to energy consumption, the highest energy-savings power ratio (0.25) resulted in a 24% reduction in required input energy and with an increase in ultrasonic power, i.e. an increase in acoustic-to-total power ratio, the effectiveness of applying ultrasound decreased drastically. At a power ratio of 0.2, the time required for regeneration was reduced by 23.8% compared to the heat-only process under the same experimental conditions. In terms of ultrasonic frequency, lower frequencies resulted in higher efficiency and energy savings, and it was concluded that the effect of ultrasonic radiation becomes more significant at lower ultrasonic frequencies. The observed inverse proportionality between the frequency and ultrasound-assisted desorption enhancement suggests that acoustic dissipation is not a significant mechanism to enhance mass transfer, but rather other mechanisms must be considered.     

超声波在树脂再生中的应用

本文阐述了超声波用于树脂再生的最新技术，超声脱附以及它的原理一超声场聚能效应。该方法和传统的化学方法相比较：不仅具有操作简单，化学药品消耗少，排污量少等优点。而且还能增加树脂的脱附速率，减少脱附时间，增加解吸平衡物的浓度。本文综述了在这一领域的最近研究进展，各种不同频率和功率对树脂再生效果的影响，为该领域的研究工作提供参考。     

新型复合固体除湿材料的吸附和解吸性能研究

为实现固体除湿系统吸附材料的低温再生及提高吸附材料的除湿效率,制备了新型复合固体除湿材料。新型复合固体除湿材料是以陶瓷纤维为基质,运用MgCl2浸渍改性硅胶及CaCl2二次强化方法而形成的复合物,复合固体除湿材料中MgCl2和CaCl2浓度均为25%。通过恒温恒湿空调室实验研究温度、风速、湿度对MgCl2/CaCl2改性复合材料除湿性能及再生特性。实验表明:在温度20℃、湿度70%条件下,复合固体除湿材料除湿量可达161 mg/g,是未改性除湿材料的3.2倍,是单一改性除湿材料的1.3倍;当系统平衡时,其除湿速率分别是未改性除湿材料的6.1倍,是单一改性除湿材料的2.6倍。除湿材料的平衡吸附量和吸附速率均与相对湿度成正比,与温度成反比;且风速在0.5 m/s条件时具有最大的除湿量。同时,在约70℃较低的脱附温度,8 min可脱附≥90%的总吸附水量,每1 g吸附剂可脱附水量高达145 mg;脱附再生6次后,除湿量依然较高为138 mg/g,且基本不再变化。     

Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound

This work describes the results of investigations carried out to examine the adsorption kinetics of 4-chlorophenol (4-CP) from aqueous solution containing tert-butyl alcohol (10%, v/v) onto granular activated carbon (GAC) in the presence of ultrasound of different high frequencies (516, 800 and 1660 kHz) and acoustic powers (15.2, 21.5, 31.1 and 38.3 W). The main objective of this study is to describe the mechanism of ultrasound-assisted adsorption rather than the enhancement of adsorption capacity. Sonochemical degradation of 4-CP was studied in the absence and presence of tert-butyl alcohol. The sonolysis of 4-CP is effectively inhibited by the addition of tert-butyl alcohol (10%, v/v) and very little 4-CP degradation occurs, indicating that little or no pyrolysis of the compound occurs. Without addition of tert-butyl alcohol, after 300 min and at 1660 kHz, the removal of 4-CP in the presence of ultrasound for an acoustic power of 38.3 W was nearly total (99%), but in the conventional method only 60% was eliminated. In this case, the removal of 4-CP by GAC in the ultrasound-assisted technique is due to both adsorption and ultrasonic degradation, but the removal by simple stirring is only due to adsorption, which makes a direct comparison unacceptable. In order to distinguish sonochemical degradation and adsorption of 4-CP onto GAC and to make an exact and practical comparison of the adsorption in the absence and presence of ultrasound, kinetic adsorption experiments were conducted using aqueous solution containing 10% (v/v) tert-butyl alcohol. The obtained results show that both adsorption rate and adsorbed amount were significantly enhanced and improved in the presence of ultrasound for all the studied frequencies and powers. The enhancement of adsorption is favored by increasing ultrasonic power. Adsorption kinetic data were modeled using the liquid-film mass transfer equation and intraparticle diffusion model. The values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than that obtained in the absence of ultrasound. In the initial period of adsorption, where external mass transfer is assumed to predominate, liquid-film mass transfer coefficients significantly increased by the assistance of ultrasound. These results indicate that ultrasound enhances the mass transport in the pores as well as across the boundary layer. This effect increased with increasing ultrasonic power for the three studied frequencies. The average order for the studied ultrasonic waves according to the initial adsorption rate, the intraparticle diffusion coefficient and the liquid-film mass transfer coefficient is 516 kHz>800 kHz>1660 kHz.     

Desorption of a fixed-bed adsorber by ultrasound

Adsorption processes offer the possibility to remove trace impurities of liquid process streams. An important step in adsorption processes is the regeneration of the adsorbent as it does not only affect the adsorption-desorption cycle but also the expenses of the following process steps. In this study, various desorption experiments of a loaded polymeric resin have been conducted. They were performed with cold and hot water as well as with ultrasound at different frequencies and intensities. The results indicate, that an important factor of ultrasound enhanced desorption is the temperature rise due to ultrasonication. But as regeneration is more effective at higher frequencies even though temperatures inside the column are lower, another ultrasonic effect occurs during ultrasonic desorption.     

Sonolytic degradation of halogenated organic compounds in groundwater: mass transfer effects

Organic pollutants in liquid exposed to acoustic waves behave differently according to their physical and chemical properties. Laboratory batch experiments of sonication for the degradation of trichloroethylene (TCE) and ethylene dibromide (EDB) were carried out in groundwater at 20 kHz, and 12.5 and 35 W/cm(2). A theoretical model for the batch sonication system was derived to examine the mass transfer dependency of the ultrasonic degradation. Experimental results were supported with model predictions suggesting that both liquid phase diffusion coefficient and Henry's law constant are important parameters for the sonolytic degradation of the halogenated organic compounds in groundwater. When compared with the effect of the diffusion coefficient, Henry's constant exerts a greater influence on sonolytic degradation. When Henry's constant exceeds a value of 1 (volume/volume ratio), however, it no longer has much influence on the degradation process. The results also suggest that degradation is enhanced with an increase in ultrasonic power probably due to a greater bubble residence time and the formation of larger bubble at high-energy intensities.     

Comparison between the use of polyether ether ketone and stainless steel columns for ultrasonic-assisted extraction under various ultrasonic conditions

The ultrasound-assisted extraction (UAE) was conducted using the stainless steel (SS) and polyether ether ketone (PEEK) columns and analyzed with high-performance liquid chromatography (HPLC) to understand the mechanism of ultrasound-assisted chromatography (UAC). Empty SS and PEEK columns were used to extract dyes from a fabric under identical conditions with several parameters including the initial ultrasonic bath temperatures (30 °C and 40 °C), ultrasound power intensities (0, 20, 40, 60, 80, and 100 %), ultrasound operation modes (normal and sweep), and ultrasound frequencies (25 kHz, 40 kHz, and 132 kHz) to compare their extraction capabilities. After 30 min of extraction, the amount of extract was determined by HPLC. The PEEK material was significantly affected by ultrasonic radiation compared to the SS material, especially at a higher temperature (40 °C), power intensity (100 %), and frequency (132 kHz) with sweep mode. At a maximum power density of 45 W/L, the extraction effectiveness ratio of PEEK to SS was in the range of 1.8 - 3.9 depending on the specific frequency, initial temperature, and with or without temperature control. The most optimal ultrasound frequencies, in terms of enhancing extraction effectiveness, are in the order of 132 kHz, 40 kHz, and 25 kHz. Unlike the SS material, the PEEK material was more affected by temperature and acoustic effects under identical conditions, especially at 132 kHz ultrasound frequency. In contrast, at lower frequencies of 40 kHz and 25 kHz, no significant differences in the acoustic effects were observed between the PEEK and SS materials. The findings of this study contribute to elucidating the roles of column materials in UAE and UAC.     

Mass transfer enhancement in supercritical fluids extraction by means of power ultrasound

The use of high-intensity ultrasound represents an efficient manner of producing small scale agitation, enhancing mass transfer on supercritical fluids (SF) extraction processes. In this way, a supercritical CO(2) extraction of oil from particulate almonds using power ultrasound was studied. To examine the effect of the acoustic waves all experiments were performed with and without ultrasound. A power ultrasonic transducer for a working frequency of about 20 kHz was constructed and installed inside a high-pressure 5 l SF extractor. The experimental tests were carried out with CO(2) at 280 bar and 55 degrees C. Grounded almonds with an oil content of about 55%, in an amount of 1500 g were deposited inside the SF reactor where the solvent was introduced at a flow rate of 20 kg/h. The results show that the kinetics and the extraction yield of the oil were enhanced by 30% and 20% respectively, when a power of about 50 W was applied to the transducer. The average time of each extraction process was of about 8 h and 30 min. In addition, the transducer was also used as a sensitive probe capable to detect the phase behavior of supercritical fluids when it was driven with low power signals.     

Variation in the biological characteristics of BAC during ultrasonic regeneration

Ultrasonic treatment has been shown to have a favorable effect on the regeneration of spent biological activated carbon (BAC) from drinking water treatment plants. In this study, the use of ultrasound as a regeneration method had a significant effect on the recovery of spent BAC after 7.5 years of use; it effectively increased the iodine value from 300 mg/g to 600 mg/g and restored the specific surface area and pore volume of BAC. Ultrasound effectively changed the structure of the biofilm inside and on the surfaces of BAC particles, on the basis of confocal laser scanning microscopy (CLSM) images. The thickness of the surface biofilm attached to BAC reached an “active” level (about 100 μm) at the regeneration frequency of 40 kHz. The dehydrogenase activity significantly improved from 4.50 mg TF/g BAC to 9.13 mg TF/g BAC, and the content of adenosine-triphosphate (ATP) in regenerated BAC was maintained at a high level (2.501 × 10⁻⁶g ATP/g BAC), thus allowing the development of microbial growth. The production of soluble microbial products (SMPs) from regenerated BAC decreased during the reuse process. The removal efficiency of DOC, COD_Mn, NH₄⁺ and NO₃^– control increased by approximately 78%, 71%, 50% and 20%, respectively.     

液体材料超声处理过程中声场和流场的分布规律研究

针对合金熔体等液体材料的超声处理过程,选取水作为透明模型材料,采用数值模拟计算和示踪粒子实验方法,研究了20和490 kHz两种频率超声作用下水中的声场和流场分布.结果表明,增大变幅杆半径能够提高水中声压水平,扩大空化效应的发生区域.当超声频率为20 kHz时,水中声压最大值出现在超声变幅杆下端面处,且声压沿传播距离的增大而显著减小.如果超声频率增加至490 kHz,水中的声压级相比于20 kHz时明显提高,且声压沿着超声传播方向呈现出周期性振荡特征.两种频率超声作用下水中的流场呈现相似的分布特征,且平均流速均随着变幅杆半径增大表现出先升高后降低的趋势.变幅杆半径相同时,20 kHz频率超声作用下水中的平均流速高于490 kHz频率超声.采用示踪粒子图像测速技术实时观察和测定了水中的流速分布,发现其与计算结果基本一致.     

Dosimetry in sonochemistry: the use of aqueous terephthalate ion as a fluorescence monitor

The generation of HO radicals by acoustic cavitation in water was monitored by their reaction with terephthalic acid (TA) anion to produce fluorescent hydroxyterephthalate ions using a cleaning bath (38kHz) and a probe system (20, 40 and 60 kHz) as different sources of ultrasound. When using the ultrasonic bath as a source of energy for sonochemical studies, the shape of the reaction vessel is important. In the case of HO production from water (50 cm³), reaction in a conical flask (100 cm³) produces 2.75 times more radicals than a round-bottomed flask of the same capacity. The fluorescence yield (fluorescence intensity/ultrasound dosage) obtained using the conical flask and ultrasonic bath was similar to that for a probe operating at 40 kHz on the same volume of solution. For a probe system operating at 20, 40 and 60 kHz the greatest sonochemical efficiency was attained at the highest of these frequencies (60 kHz). For the probe system the fluorescence yield is directly proportional to power input and the concentration of TA. The fluorescence yield decreases as the temperature is increased.     

Fast and efficient removal of Reactive Black 5 from aqueous solution by a combined method of ultrasound and sorption process

Removal of Reactive Black 5 (RB5) from aqueous solutions was carried by the sorption process in the presence and in the absence of ultrasound. Sorption of the dye on the solid phase was investigated in a series of batch sorption experiments to determine the influence of different parameters such as contact time, amount of sorbent and concentration of pollutant on the removal efficiency of RB5 with and without ultrasound. The experimental data were fitted properly to the Freundlich model and the isotherm constants were 28.2 and 7.4 for k(f) and 0.13 and 0.38 for 1/n in the presence and in the absence of ultrasound (20 kHz) respectively. The data were analyzed with different sorption kinetic models and were better fitted with a pseudo-second-order kinetic model. Two ultrasonic generators at 20 and 500 kHz were used for sonication of the system. This investigation also reveals that RB5 can be removed by higher frequency apparatus (500 kHz) without sorbent in about 60 min sonication. The rate of removal was higher at the higher frequency than at the lower one.     

Ultrasonic frequency effects on the removal of Microcystis aeruginosa

Algae bloom in source water causes high chemical consumption and deteriorates water quality in waterworks. This paper studied the ultrasonic removal of Microcystis aeruginosa. The results showed that algae cells could be effectively removed by sonication and gas vesicle collapse was the main mechanism. The ultrasonic algae removal followed the first order reaction with a rate constant of 0.023 min(-1) (80 W, 80 kHz). Higher ultrasound frequency benefited algae removal; the algae removal rate constant was 0.114 min(-1) at 1320 kHz and 0.0224 min(-1) at 20 kHz (80 W). Higher ultrasound power also accelerated algae removal; the algae removal rate constant was 0.023 min(-1) at 80 W and 0.007 min(-1) at 32 W (80 kHz). However, high ultrasound power and long irradiation caused microcystins to increase. 80 W, 80 kHz sonication for 5 min increased the extracellular microcystins concentration from 0.87 microg/L to 3.11 microg/L. Sound frequency had little impact on the microcystins release. The chlorophyll a concentration initially decreased and then stabilized after 5 min of sonication.     

Ultrasound-assisted extraction of capsaicinoids from Capsicum frutescens on a lab- and pilot-plant scale

The influence of operating parameters (solvent type, powder to solvent ratio and temperature) on the ultrasonically assisted extraction of capsaicinoids from dried Capsicum frutescens (fruit) was studied. From the economic perspective, the suitable condition for capsaicinoid extraction by indirect sonication in an ultrasonic bath with a working frequency of 35 kHz was at a ratio of 1g of solid material: 5 ml of 95% (v/v) ethanol, 45 degrees C, where 85% of the capsaicinoids were removed from the raw material in 3h. In an experimental pilot study in 20-l extraction tank at the fixed ultrasonic frequency of 26 kHz and 70 kHz, the recovery of capsaicinoids was 76% and 70%, respectively. It was shown that the ultrasonic extraction produced a significant reduction in extraction time at a lower operational temperature than under a conventional industrial hot maceration process.     

双频超声交替强化超临界流体萃取装置的设计与应用

本文针对超临界流体萃取（SFE）系统设备的特点，设计丁可用于强化SFE过程的双频超声波交替强化装置。以香椿叶中黄酮类化合物为提取对象，对超声强化USFE过程的影响因素及强化效果进行了实验研究，结果表明；低频超声利于提取，频率为20kHz的超声强化的萃取率最大，38kHz的超声最小，两者交替的居于中间。     

Ultrasonic effects on titanium tanning of leather

The effects of ultrasound on titanium tanning of leather were investigated. Either 20 or 40 kHz ultrasound was applied to the titanium tanning of pigskins. Five different treatment conditions were carried out and the effects were examined, such as leather shrinkage temperature (T(s)), titanium content and titanium distribution in the leather. Overall heat loading was carefully controlled. Results showed that 20 kHz ultrasound effectively improves titanium agent penetration into the hide and increases the leather's shrinkage temperature. Doubling the frequency to 40 kHz produced negligible enhancements. An impressive 105.6 degrees C T(s) was achieved using 20 kHz ultrasound pretreatment of the tanning liquor followed by 20 kHz ultrasound in the tanning mixture (liquor plus pigskins) in a special salt-free medium. Finally, using a unique ultrasonic tanning drum with 26.5 kHz ultrasound, the T(s) reached a record level of 106.5 degrees C, a value not achieved in conventional (no ultrasound) titanium tanning. The ultrasonic effects on titanium tanning of leather are judged to make a superior mineral tanned leather.     

Investigation on the influence of ultrasonic pretreatment on color,quality and antioxidant attributes of microwave dried Inula viscosa (L.)

Impact of various ultrasound pretreatment and microwave drying parameters on the qualitative and antioxidant characteristics of Inula viscosa (L.) was investigated in this study. The leaves of Inula viscosa (L.) were sonicated for 10, 20, and 30 min in an ultrasonic bath (37 kHz, 150 Watts). Microwave drying was done at three distinct times (1, 3, and 5 min) and with three different microwave power levels (100, 180, and 300 Watts). Microwave dried samples were tested for color characteristics (L*, a*, b*), chlorophyll, carotenoid, total phenol, and antioxidant content. All dried samples were prepared by infusing them in hot water as tea, and the sensorial properties of teas including odor, color, aroma, and overall acceptability were evaluated by panelists. For 10, 20, and 30 min of ultrasound pretreatment, the L* values of leaves varied from 37.70 to 49.76, 34.97 to 46.25, and 27.88 to 43.34, respectively. The total carotenoid concentration ranged from 0.12 to 0.32 mg/g DW, while the total chlorophyll content was from 0.44 to 0.94 mg/g DW. The antioxidant activity of Inula viscosa (L.) leaves that were dried at 300 Watts for 5 min did not change significantly as a result of ultrasound pretreatment. There was a significant positive correlation between aroma and TPC, as well as between color and overall acceptability. The darkest-colored teas were deemed preferable by the panelists.     

Process intensification and kinetic studies of ultrasound-assisted extraction of flavonoids from peanut shells

In this work, extraction of flavonoids from peanut shells has been studied in the presence of ultrasound and the results are compared with Soxhlet and heat reflux extraction for establishing the process intensification benefits. The process optimization for understanding the effects of operating parameters, such as ethanol concentration, particle size, solvent to solid ratio, extraction temperature, ultrasonic power and ultrasonic frequency, on the extraction of flavonoids has been investigated in details. The highest extraction yield (9.263 mg/g) of flavonoids was achieved in 80 min at optimum operating parameters of particle size of 0.285 mm, solvent to solid ratio of 40 ml/g, extraction temperature of 55 °C, ultrasonic power of 120 W and ultrasonic frequency of 45 kHz with 70% ethanol as the solvent. Two kinetic models (i.e. phenomenological model and Peleg’s model) have been introduced to describe the extraction kinetic of flavonoids by fitting experimental data and predict kinetic parameters. Good performance with slight loss of goodness of fit of two models was found by comparing their coefficient of determination (R²), root mean square error (RMSE) and/or mean percentage error (MPE) values. This work would provide the reduction of degradation and the economic evaluation for the extraction processes of flavonoids from peanut shells, as well as give a better explanation for the mechanism of ultrasound.     

Intensification of leaching process by dual-frequency ultrasound

Ultrasound is gaining importance in metal extraction process. In the previous laboratory scale investigation the authors have established the positive influence of ultrasound on copper recovery from oxide ores of Malanjkhand, Madhya Pradesh, India in an ammonical media. The process parameters in a conventional agitation method were optimized and a maximum recovery of ≈32% in 20 min was obtained without sonication. The recovery was increased to ≈78% by the application of ultrasound over the same period with several advantages like decrease in leaching time and the reagent consumption. In the present study the leaching process is intensified by studying the metal recovery variation at different ultrasonic frequencies (20, 40, 43 and 720 kHz) and intensities (up to 8 W cm⁻²) with sonication time. The results show that sinusoidal ultrasound even at larger intensity has some limitations with single frequency. However, simultaneous application of dual frequency 20 and 40 kHz ultrasound enhanced extraction rates along with increased yield. While conventional single frequency exposure at either one of the two frequencies at the same acoustic power level did not yield similar results, application of two wave sources, as used in the study revealed that it is possible to save energy through lowering of time of operation process.