Effect of ultrasound on desorption kinetics of phenol from polymeric resin

This work mainly involves the study of desorption kinetics of phenol from polymeric resins under the influence of an ultrasound field. A new phase equilibrium-kinetics model (PEKM), for estimation of diffusion coefficient was proposed, kinetic experiments of phenol desorption on NKA-II resin in the presence and the absence of ultrasound were separately conducted, and diffusion coefficients of phenol within an adsorbent particle were estimated by means of proposed PEKM. Results showed that the use of ultrasound could enhance the diffusion of phenol within the resin. The diffusion coefficient of phenol in the resin in an ultrasonic field increased by an order of magnitude in comparison with the diffusion coefficient in the absence of ultrasound. The more intense the ultrasonic field the larger was the diffusion coefficient.     

Study of the energetic heterogeneity of the adsorption of phenol onto activated carbons by TPD under supercritical conditions

The Temperature Programmed Desorption (TPD) technique with liquid and supercritical water was used to study the heterogeneity of the adsorption of phenol onto different activated carbons. The presence of several desorption peaks in the spectra clearly indicated that phenol was adsorbed onto the activated carbon with different interaction energies. Calculation of the desorption activation energies revealed that most of the phenol was physisorbed, although a small part was always chemisorbed. The study of the textural characteristics of the carbons suggests that the width of the micropores governs the thermal desorption of the physisorbed phenol.     

Ultrasound-assisted adsorption/desorption for the enrichment and purification of flavonoids from baobab (Adansonia digitata) fruit pulp

This work described the purification and enrichment of flavonoids from baobab (Adansonia digitata) fruit pulp (BFP) by ultrasound-assisted adsorption/desorption procedure using macroporous resins. Four resins were tested and HPD-500 polar resin exhibited the best adsorption/desorption properties. Based on preliminary experiments and literature reports, the effects of various ultrasonic conditions including high power short time (HPST, 540 W for 5 min), medium power medium time (MPMT, 270 W for 15 min) and low power long time (LPLT, 45 W for 30 min) as well as different temperatures (T = 25–45 °C) on the adsorption of Total Flavonoids Content (TFC) were investigated in comparison with orbital shaking/no sonication (NS). Also, the effect of ultrasound on the desorption capacity and recovery of TFC was determined at different concentrations of ethanol (30–100%). Remarkably, ultrasonic treatment significantly increased the adsorption/desorption capacity and recovery and shortened the equilibrium time. The pseudo-second-order kinetic and Freundlich isotherm models better delineated the adsorption process under ultrasound. Moreover, the adsorption process was both spontaneous and thermodynamically favourable with physical adsorption and multilinear intraparticle diffusion being the predominant mechanisms of the whole process. HPST treatment at 25 °C with 80% ethanol as the desorption solvent most noticeably enhanced the adsorption/desorption of flavonoids and contributed to the highest recovery of TFC, Total Phenolic Content (TPC), and antioxidant capacity in addition to a 5–8-fold reduction in total sugar and acid contents when compared with NS treatment. Moreover, HPLC analysis revealed that the content of nine out of thirteen phenolic compounds from the HPST treatment was the highest, and the individual flavonoids content increased by 2–3-fold compared with the other treatments. Our analyses suggested that ultrasound can be employed as a practical approach to intensify the adsorption and desorption of functional compounds in BFP.     

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.     

外加阴离子吸附剂对复合污染黄土淋洗过程养分淋失的减缓机制(Ⅱ)

化学淋洗法是常用的污染场地修复方法,其经济性、简便性、安全性等指标较其他方法有较大优势。化学淋洗法存在的弊端之一是淋洗过程土壤伴存养分的同步淋失,若能在此瓶颈问题上有所突破,将会大大促进淋洗法场地修复的应用进程。本文研究的目标在于揭示合成秸秆基阴离子吸附剂对养分淋失的减缓机制,采用吸附平衡模式(等温线和动力学)与光谱分析技术(SEM和FT-IR)相结合,力图从微观层面验证宏观研究结果。Langmuir和准二级动力学方程能更好地描述硝酸根和磷酸根的吸附行为,由Langmuir方程计算得出q_m分别为7.507 5和4.194 6 mg·g-1,吸附反应为单层吸附和优惠吸附过程,主要控速步骤为化学吸附。阴离子吸附剂对硝酸根和磷酸根的吸附活化能(298 K)E_a分别为42.25和39.38 kJ·mol-1,吸附反应自发、吸热。纯净水和KOH能够实现阴离子吸附剂的再生,超声辅助和延长解吸时间对于解吸效果略有促进作用。吸附后阴离子吸附剂表面被点状分布的细微颗粒物覆盖,解吸后仅有少量枝状物零星分布。吸附前后FTIR图谱的主要波峰红移或蓝移,证实阴离子吸附剂表面及内部官能团通过静电作用与硝酸根和磷酸根结合。阴离子吸附剂对硝酸根和磷酸根的吸持固定是物理吸附和化学吸附共同作用的结果。     

原子吸收光谱法研究巯基改性膨润土对Pb2+的吸附解吸

通过红外光谱(FTIR)法和扫描电镜(SEM)对钙基和巯基改性膨润土的官能团和表面结构进行了比较分析,以火焰原子吸收光谱法(FAAS)为检测手段,研究了巯基改性膨润土对Pb2+吸附的影响因素并优化了吸附条件,讨论了模拟酸雨解吸Pb2+的条件。比较了钙基和巯基改性膨润土作为吸附剂对水溶液中Pb2+的吸附、固定能力。研究表明：25 ℃下,吸附时间为60 min、离子强度为0.1 mol·L-1的KNO₃、pH 6.0时,5.0 g·L-1巯基改性膨润土对100 mg·L-1的Pb2+的吸附率达到98%以上,平衡吸附量达到67.27 mg·g-1,吸附能力明显优于钙基膨润土(9.667 mg·g-1),吸附过程符合Langmuir和Freundlich等温线方程。用pH 3.50的极限酸度模拟酸雨进行解吸,解吸率为0。表明该巯基改性膨润土对Pb2+具有很强的吸附、固定能力,适于重金属铅污染土壤中铅的吸附固定修复之用。     

Regeneration of granular activated carbon using ultrasound

To evaluate the feasibility of ultrasonic regeneration of granular activated carbon (GAC), desorption of trichloroethylene (TCE) from GAC by ultrasound was investigated at 20 kHz. About 64% of TCE was desorbed from 5 g of GAC loaded with 6.5 mg TCE for 1 h in ultrasonic field and TCE desorbed to liquid phase were rapidly degraded by ultrasound. 34-43% of stoichiometrically calculated chloride, final degradation product of TCE, was observed in liquid phase during ultrasonic treatment. However, there was desorption limitation at 20 kHz ultrasound. Despite of prolonged ultrasonic irradiation, desorption efficiency of TCE did not exceed critical value. And also, the higher percentage of TCE was desorbed when a sample of 2 mg TCE/4 g GAC was treated ultrasonically than that of 2 mg TCE/g GAC under the same experimental conditions. These results indicate that desorption of TCE by 20 kHz ultrasound occurred mainly at a nearby surface of GAC. In conclusion, the ultrasonic regeneration showed a possibility as an alternative to chemical and thermal regenerations of GAC.     

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.     

Preparation of activated carbon from Enteromorpha prolifera and its use on cationic red X-GRL removal

Enteromorpha prolifera was pyrolyzed to prepare activated carbon using chemical activation by zinc chloride. The effect of activation parameters such as activation temperature, weight ratio (Enteromorpha prolifera to ZnCl₂), and activation time was investigated. The BET results showed that the surface area and pore volume of activated carbons were achieved as high as 1722 m²/g and 1.11 cm³/g, respectively, in the optimal activation conditions. Batch adsorption studies were carried out to study the adsorption properties of cationic red X-GRL onto activated carbon by varying the parameters like initial solution pH, contact time, and temperature. The kinetic studies showed that the adsorption data followed a pseudo second-order model. The isotherm analysis indicated that the adsorption data could be represented by the Langmuir isotherm model. The Langmuir monolayer adsorption capacity of cationic red X-GRL was estimated as 263.16 mg/g at pH 6.0.     

Intensified removal of copper from waste water using activated watermelon based biosorbent in the presence of ultrasound

Copper is one of the most toxic heavy metals having significant effects on the living organisms and hence effective removal of copper from waste water is crucial. The current work investigates the application of activated watermelon shell based biosorbent for the removal of copper from aqueous solution. The effect of activation using calcium hydroxide and citric acid as well as the effect of operating parameters like contact time, adsorbent dosage, temperature, pH, initial concentration and ultrasonic power on the extent of removal has been investigated. Experiments performed in the presence of ultrasound to investigate the degree of intensification as compared to the conventional agitation based treatment revealed that the adsorption rate significantly increases in the presence of ultrasound and also the time required for reaching the equilibrium reduces from 60 min in conventional approach to only 20 min in the presence of ultrasound. The extent of adsorption of Cu(II) on adsorbents was found to increase with an increase in the operating pH till an optimum value of 5. The extent of adsorption also increased with a decrease in the initial concentration and particle size as well as with an increase in ultrasonic power till an optimum. Kinetics and isotherm study revealed that all the experimental data was found to best fit the pseudo second order kinetics and Langmuir adsorption isotherm model respectively. Maximum adsorption capacity was found to be 31.25 mg/g for watermelon treated with calcium hydroxide and 27.027 mg/g for watermelon treated with citric acid. Overall present study established that activated watermelon is an environmentally friendly, low cost and highly efficient biosorbent that can be successfully applied for the removal of copper from aqueous solution with intensification benefits based on the ultrasound assisted approach.     

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.     

Experimental and predictive study on the performance and energy consumption characteristics for the regeneration of activated alumina assisted by ultrasound

Activated alumina used in dehumidification should be regenerated at more than 110 °C temperature, resulting in excessive energy consumption. Comparative experiments were conducted to study the feasibility and performance of ultrasonic assisted regeneration so as to lower the regeneration temperature and raise the efficiency. The mean regeneration speed, regeneration degree, and enhanced rate were used to evaluate the contribution of ultrasound in regeneration. The effective moisture diffusivity and desorption apparent activation energy were calculated by theoretical models, revealed the enhanced mechanism caused by ultrasound. Also, we proposed some specific indexes such as unit energy consumption and energy-saving ratio to assess the energy-saving characteristics of this process. The unit energy consumption was predicted by artificial neural network (ANN), and the recovered moisture adsorption of activated alumina was measured by the dynamic adsorption test. Our analysis illustrates that the introduction of power ultrasound in the process of regeneration can reduce the unit energy consumption and improve the recovered moisture adsorption, the unit energy consumption was decreased by 68.69% and the recovered moisture adsorption was improved by 16.7% under 180 W power ultrasound compared with non-ultrasonic assisted regeneration at 70 °C when initial moisture adsorption was 30%. Meanwhile, an optimal regeneration condition around the turning point could be obtained according to the predictive results of ANN, which can minimize the unit energy consumption. Moreover, it was found that a larger specific surface area of activated alumina induced by ultrasound contributed to a better recovered moisture adsorption.     

Heterogeneity of activated carbons with different surface chemistry in adsorption of phenol from aqueous solutions

The heterogeneity of activated carbons is investigated on the basis of adsorption isotherms of phenol from dilute aqueous solutions at different values of pH in the solution. The original carbon studied was prepared from polyethyleneterephtalate (PET). Its various oxygen surface functionalities were systematically changed by additional nitric acid and heat treatments. The Dubinin-Astakhov adsorption-isotherm equation was used to evaluate the parameters characterizing the adsorption of phenol from dilute water solutions on activated carbon surfaces. Adsorption energy distribution functions were calculated by the INTEG algorithm, based on a regularization method. Analysis of distribution functions for activated carbons provides significant comparative information about their energetic heterogeneity. Moreover, a comparison of the resulting energies obtained from the distributions can be made with enthalpic data.     

Effect of irradiation distance on degradation of phenol using indirect ultrasonic irradiation method

Ultrasound is used as degradation of hazardous organic compounds. In this study, indirect ultrasonic irradiation method was applied to the degradation process of phenol, the model hazardous organic compound, and the effects of irradiation distance on radical generation and ultrasonic power were investigated. The chemical effect estimated by KI oxidation dosimetry and ultrasonic power measured by calorimetry fluctuated for the irradiation distance, and there was a relationship between the period of the fluctuation of ultrasonic effect and the wavelength of ultrasound. The degradation of phenol was considered to progress in the zero-order kinetics, before the decomposition conversion was less than 25%. Therefore, the simple kinetic model on degradation of phenol was proposed, and there was a linear relation in the degradation rate constant of phenol and the ultrasonic power inside the reactor. In addition, the kinetic model proposed in this study was applied to the former study. There was a linear relation in the degradation rate constant of phenol and ultrasonic energy in the range of frequency of 20-30 kHz in spite of the difference of equipment and sample volume. On the other hand, the degradation rate constant in the range of frequency of 200-800 kHz was much larger than that of 20-30 kHz in the same ultrasonic energy, and this behaviour was agreed with the former investigation about the dependence of ultrasonic frequency on chemical effect.     

The impact of carbon surface chemical composition on the adsorption of phenol determined at the real oxic and anoxic conditions

The results of phenol adsorption-desorption isotherms (at 310 K) measured on the series of activated carbons (D43/1, NORIT RO 0.8, D55/2) are presented. The effect of carbon surface chemical composition on phenol adsorption determined at real oxic and anoxic conditions is discussed. To obtain the real anoxic conditions the two station controlled atmosphere chamber with two catalyst heater units (Plas Labs, Lansing, MI, USA) was applied. It is shown that the adsorption under oxic conditions is always larger than that determined for anoxic ones for all studied carbons. The analysis of those differences shows that in the range of micropore filling they decrease with the equilibrium phenol mole fraction in solution. Contrary they increase after micropores being filled. The average differences between the adsorption properties are the linear function of the concentration of surface acidic groups (assigned from the Boehm's method as “carboxylic”) calculated per the apparent BET surface area of studied carbons.     

The effect of ultrasound upon the oxidation of thiosulphate on stainless steel and platinum electrodes

Ultrasound was found to increase the oxidation peak current and hence the decomposition rate of thiosulphate 50-fold compared to silent conditions. The effects of the ultrasonic frequency (20 and 38 kHz) and power upon the electrochemical oxidation of thiosulphate in aqueous KCl (1 mol dm-3) at stationary stainless steel and platinum electrodes were studied chronoamperometrically and potentiostatically (at various scan rates). No sigmoidal-shaped voltammograms were observed for the redox couple S4O6(2-)/S2O3(2-) in the presence of ultrasound. However, application of ultrasound to this redox couple provided an increase in the oxidation peak current at the frequencies employed, the magnitude of which varied with concentration, scan rate and ultrasonic power. Under sonication at 20 and 38 kHz, the oxidation peak potential shifted anodically with increasing ultrasonic power. This anodic shift in potential may be due to the formation of hydroxyl radicals, changes in electrode surface composition and complex adsorption phenomena. The large increase in oxidation peak currents and the rates of decomposition of thiosulphate, in the presence of ultrasound, are explained in terms of enhanced mass transfer at the electrode due to cavitation and acoustic streaming together with microstreaming coupled with adsorption phenomena. It is also shown that changes in macroscopic temperature throughout the experiment are insufficient to cause the observed enhanced diffusion.     

Heterogeneity of activated carbons in adsorption of phenols from aqueous solutions—Comparison of experimental isotherm data and simulation predictions

Surface heterogeneity of activated carbons is usually characterized by adsorption energy distribution (AED) functions which can be estimated from the experimental adsorption isotherms by inverting integral equation. The experimental data of phenol adsorption from aqueous solution on activated carbons prepared from polyacrylonitrile (PAN) and polyethylene terephthalate (PET) have been taken from literature. AED functions for phenol adsorption, generated by application of regularization method have been verified. The Grand Canonical Monte Carlo (GCMC) simulation technique has been used as verification tool. The definitive stage of verification was comparison of experimental adsorption data and those obtained by utilization GCMC simulations. Necessary information for performing of simulations has been provided by parameters of AED functions calculated by regularization method.     

Effect of ultrasound in enantioselective hydrogenation of 1-phenyl-1,2-propanedione: comparison of catalyst activation, solvents and supports

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione was carried out over Pt/Al2O3, Pt/SiO2, Pt/SF (silica fiber), Pt/C catalysts modified with cinchonidine under ultrasonic irradiation. The initial rate, regioselectivity and enantioselectivity were investigated for different catalyst pretreatments, solvents and ultrasonic powers. The ultrasound effects were very catalyst dependent. The sonication significantly enhanced enantioselectivity and activity of the Pt/SF (silica fiber) catalyst. For the other Pt supported catalysts the reaction rate, enantioselectivity and regioselectivity increased moderately. The choice of solvent influenced the impact of ultrasound effect, namely in mesitylene, which has the lowest vapor pressure, the highest ultrasound enhancement was observed. The effect of sonication on catalysts surface was studied by transmission electron microscopy and scanning electron microscopy (SEM). No significant change in the metal particle size distribution due to sonication was observed. However, in the case of the Pt/SF catalyst, acoustic irradiation induced morphological changes on the catalyst particle surface (SEM), which might be the cause for enhancement of the initial reaction rate and enantioselectivity.     

Sonochemically enhanced adsorption and degradation of methyl orange with activated aluminas

Removal of Methyl orange (MO), as a model contaminants, in aqueous solution by the simultaneous application of ultrasound with the addition of porous adsorbent powders is reported. Activated alumina powders in acidic form were used as an adsorbent. Results showed that MO could be degraded by ultrasonic irradiation at 130 kHz with the first order rate constant of 8x10(-4) and 5x10(-4) sec(-1), in acidic and basic conditions, respectively, without adsorbents. Adsorption rates of MO by activated alumina mainly depended on the acidity of alumina, the pH of solution and the stirring speed. At pH=4.2 with mechanical stirring without ultrasonic radiation, acidic activated alumina (0.1 g/100 ml) removed MO at about two times more rapidly than ultrasonic irradiation. In the case of simultaneous application of ultrasound irradiation and activated alumina, MO was almost removed from the solution within 10 min, which corresponded to as a rate constant of 5x10(-3) sec(-1). This kind of synergistic enhancement of removal rate with ultrasound and adsorbents should be practically useful for the elimination of contaminants in the water treatment processes. In addition, the effects of pH and coexisting chemicals in the solution were examined for the processes. Although the adsorption process was effective in some selected conditions, ultrasonic degradation was more robust in wider range of pH and coexisting chemicals. Simultaneous application of the two processes can perform complementary.     

生物吸附剂ZL5-2对六价铬离子吸附作用的红外光谱分析

研究了Agrobacterium.sp产生的具有吸附作用的蛋白聚糖类物质ZL5-2对Cr(Ⅵ)的吸附作用,并对吸附Cr(Ⅵ)前后及解吸附后的ZL5-2进行了红外光谱分析。结果表明,ZL5-2对Cr(Ⅵ)吸附的最佳pH为0.5～1.5,随着pH增大,吸附作用减弱。60 min时吸附达到平衡,80 min后所有的Cr(Ⅵ)都被吸附。被吸附的Cr(Ⅵ)可以被解吸附,解吸率为13.6%～67.9%。通过红外光谱分析,发现吸附后ZL5-2在3 400 cm-1附近OH,NH伸缩振动峰强度减弱,并发生了约8 cm-1的位移,2 900 cm-1附近C—H伸缩振动减弱,1 600 cm-1处的酰胺Ⅰ带伸缩振动的相对强度减弱,并发生约13 cm-1的位移。解吸附后,OH,C—H伸缩振动又恢复到原来水平,而NH、酰胺Ⅰ带的伸缩振动未恢复到原来水平,推测该吸附过程存在可逆吸附和不可逆吸附,以可逆吸附为主。