Design Of Sonochemical Reactors Research Articles

Efficient sonochemical catalytic degradation of tetracycline using TiO2 fractured nanoshells

Overexposure to antibiotics originating in wastewater has profound environmental and health implications. Conventional treatment methods are not fully effective in removing certain antibiotics, such as the commonly used antibiotic, tetracycline, leading to its accumulation in water catchments. Alternative antibiotic removal strategies are garnering attention, including sonocatalytic oxidative processes. In this work, we investigated the degradation of tetracycline using a combination of TiO2 fractured nanoshells (TFNs) and an advanced sonochemical reactor design. The study encompassed an examination of multiple process parameters to understand their effects on the degradation of tetracycline. These included tetracycline adsorption on TFNs, reaction time, initial tetracycline concentration, solvent pH, acoustic pressure amplitude, number of acoustic cycles, catalyst dosage, TFNs' reusability, and the impact of adjuvants such as light and H2O2. Though TFNs adsorbed tetracycline, the addition of ultrasound was able to degrade tetracycline completely (with 100% degradation) within six minutes. Under the optimal operating conditions, the proposed sonocatalytic system consumed 80% less energy compared to the values reported in recently published sonocatalytic research. It also had the lowest CO2 footprint when compared to the other sono-/photo-based technologies. This study suggests that optimizing the reaction system and operating the reaction under low power and at a lower duty cycle are effective in achieving efficient cavitation for sonocatalytic reactions.

Enhancement of sonochemical production of hydroxyl radicals from pulsed cylindrically converging ultrasound waves

Sonochemistry is the use of ultrasound to generate highly reactive radical species through the inertial collapse of a gas/vapour cavity and is a green alternative for hydrogen production, wastewater treatment, and chemical synthesis and modifications. Yet, current sonochemical reactors often are limited by their design, resulting in low efficacy and yields with slow reaction kinetics. Here, we constructed a novel sonochemical reactor design that creates cylindrically converging ultrasound waves to create an intense localised region of high acoustic pressure amplitudes (15 MPaPKPK) capable of spontaneously nucleating cavitation. Using a novel dosimetry technique, we determined the effect of acoustic parameters on the yield of hydroxyl radicals (HO), HO production rate, and ultimately the sonochemical efficiency (SE) of our reactor. Our reactor design had a significantly higher HO production rate and SE compared to other conventional reactors and across literature.

Improving sonochemical efficiency by pulsing cylindrically converging acoustic waves

Sonochemistry is considered a green alternative for chemical synthesis, water treatment, and hydrogen production. There are several steps for sonochemical reactions. First, the nucleation of a bubble must occur through the application of an intense acoustic pressure field. After further ultrasonic irradiation, the bubble must grow to a diameter beyond a certain threshold so that it undergoes inertial collapse during the compressional phase of the acoustic field. Finally, this inertial collapse must achieve a quasi-adiabatic compression to cause pyrolysis of the gas or vapour molecules into radicals, which is the basis of sonochemical reactions. Conventional sonochemical reactors have sub-optimal acoustic fields and therefore require long reaction times to produce meaningful yields. We present a novel sonochemical reactor design that generates cylindrically converging waves into a reaction vessel. To determine the sonochemical efficiency (SE) of our design, we measured the hydroxyl radical yield under different operating conditions dosimetrically. We also compare the SE from an ultrasonic bath, immersed horn, and cup-horn reactor. These comparisons indicate that our reactor had a SE 200-fold, 3-fold, and 70-fold higher than the conventional reactors, respectively.

Numerical Simulation and Experimental Testing of Novel Sonochemical Reactor for Transesterification

Biodiesel is a powerful alternate fuel that has one of the best feedstock in the form of waste cooking oil (WCO). Producing biodiesel from WCO solves two major environmental and waste related issues. Firstly, biodiesel substantially reduces CO2 and Sulphur emissions and is capable of directly replacing petro-diesel in vehicles. Secondly, using WCO for biodiesel reduces the wastage of a potential fuel source and reduces problems such as sewer clogging which are caused by WCO draining. The biodiesel industry currently needs a continuous, compact, inexpensive and efficient reactor to make biodiesel lucrative and sonochemical reactors seems to be the best option. Hence, in this work a much needed task of a sonochemical reactor design development for biodiesel production is carried out through multiphysics simulations which account for ultrasound waves, cavitation attenuation, reactive flow and chemical kinetics. Numerical simulation is a coupled system of equations like Helmholtz equation, Navier–Stokes and species transport. Additionally, a full scale, closely resembling prototype of the reactor design is experimentally tested. In the prototype testing, piezo-electric hydrophone was carried for three cases to evaluate the acoustic pressure in the reactor. Experiments were performed with the reactor and the final biodiesel product was tested in a GC/MS analyzer. The numerical simulation showed several advantages of the design. The average conversion of biodiesel achievable at as low as 100 W ultrasonic power and was found to be 84%. The experimental testing also showed very high conversion of 91.23% for 100 W power and 12 l/h flow rate.

Optimizing Acoustic Energy for Better Transesterification: A Novel Sono-Chemical Reactor Design

Abstract Sono-chemical conversion is a process intensification technique increasingly being applied to several reactions due to its characteristic ability to reduce process time and increase production. Its application to the transesterification reaction (vegetable oil to biodiesel) has been widely studied and it is proven to give better results. Although this provides an advantage in processing time, the production volumes are still limited due to the existing inefficient reactor designs which are mostly batch type. In this work, we design a novel continuous flow sonochemical reactor with the aim to have higher biodiesel production. The uniqueness in the design comes from the shape and the addition of a static mixer. The variations in design (i.e. inclusion and exclusion of static mixer) is studied through numerical simulation of the acoustic wave, cavitation bubble temperature, reactive flow and chemical kinetics in a 2D axi-symmetric model of the reactor. Acoustic pressure, cavitation bubble temperature and biodiesel concentration are studied. It is noticed that the static mixer, which is made of a sound reflecting material, provides several physical advantages which positively affect the biodiesel formation. Due to the static mixer the peak acoustic pressure was higher (1.93 MPa) and also more regions of the reactor experienced acoustic pressure exceeding the blake. This enhanced the cavitation bubble temperatures and the biodiesel mole fractions.

Acoustic wave propagation in bubbly flow with gas, vapor or their mixtures

Presence of bubbles in liquids could significantly alter the acoustic waves in terms of wave speed and attenuation. In the present paper, acoustic wave propagation in bubbly flows with gas, vapor and gas/vapor mixtures is theoretically investigated in a wide range of parameters (including frequency, bubble radius, void fraction, and vapor mass fraction). Our finding reveals two types of wave propagation behavior depending on the vapor mass fraction. Furthermore, the minimum wave speed (required for the closure of cavitation modelling in the sonochemical reactor design) is analyzed and the influences of paramount parameters on it are quantitatively discussed.

Influences of non-uniform pressure field outside bubbles on the propagation of acoustic waves in dilute bubbly liquids

Predictions of the propagation of the acoustic waves in bubbly liquids is of great importance for bubble dynamics and related applications (e.g. sonochemistry, sonochemical reactor design, biomedical engineering). In the present paper, an approach for modeling the propagation of the acoustic waves in dilute bubbly liquids is proposed through considering the non-uniform pressure field outside the bubbles. This approach is validated through comparing with available experimental data in the literature. Comparing with the previous models, our approach mainly improves the predictions of the attenuation of acoustic waves in the regions with large kR0 (k is the wave number and R0 is the equilibrium bubble radius). Stability of the oscillating bubbles under acoustic excitation are also quantitatively discussed based on the analytical solution.

Study of Ultrasound Transmission through an Immersed Glass Plate in view of Sonochemical Reactor Design Optimisation

The purpose of this paper is to improve the design of an ultrasonic reactor for industrial applications in liquids, which consists of a double‐structured tank. This paper presents an experimental approach for studying ultrasonic transmission through an immersed glass plate. Several inclination angles, between 0 and 40∘, and several thicknesses have been investigated. Acoustic efficiency was determined using hydrophone measurements in different places in the reactor. A first reactor prototype was built and the optimised configuration defined was experimentally partially characterized and validated.

Some aspects of the design of sonochemical reactors

The magnitudes of collapse pressures and temperatures as well as the number of free radicals generated at the end of cavitation events are strongly dependent on the operating parameters of the equipment namely, intensity and frequency of irradiation along with the geometrical arrangement of the transducers and the liquid phase physicochemical properties, which affect the initial size of the nuclei and the nucleation process. In the present work, the effect of these parameters on the collapse pressure generated and the maximum size of the cavity during the cavitation phenomena have been studied using the bubble dynamics equation, which considers the compressibility of the medium and a single bubble in isolation. The different liquid phase properties considered include, liquid vapor pressure, viscosity, bulk liquid temperature, surface tension and nature of dissolved gases (polytropic constant of the gas). The theoretical predictions have been also compared with the experimental results observed in the literature qualitatively and some recommendations have been made for the selection of the operating parameters so as to achieve maximum benefits. The work presented here is novel in sense that no earlier studies have considered the compressibility of the liquid medium and tried to evaluate the effect of all the operating parameters on the cavitational activity.

Modeling of linear pressure fields in sonochemical reactors considering an inhomogeneous density distribution of cavitation bubbles

Although a lot of experimental work was done on the investigation of chemical effects of power ultrasound, only very few efforts were directed towards engineering aspects, like optimum design and scale-up of sonochemical reactors. This paper deals with the calculation of acoustic fields and energy density distributions in sonochemical reactors with an inhomogeneous distribution of cavitation bubbles, which are a basis for the design of sonochemical reactors of various geometrical shapes. The time-dependent wave equation applied to a damped wave propagation represents the basis of our theory. A new model is presented for the numerical calculation of three-dimensional pressure fields in liquids taking into account an inhomogeneous distribution of wave parameters due to the presence of the cavitation bubbles. Compared to a single-phase fluid, gas bubbles in a liquid lead to a heavy change of phase velocity and sound attenuation. These changes are calculated for every time step and volume element of the reactor. Employing this technique, one should be able to calculate the pressure field in a sonochemical reactor with a sufficient accuracy which serves to predict the spatial distribution of cavitation events.

Modeling of Sound Fields in Liquids with a Nonhomogeneous Distribution of Cavitation Bubbles as a Basis for the Design of Sonochemical Reactors

A new model is presented, which enables one to calculate the linear three-dimensional pressure field in any sonochemical reactor in a liquid with a nonhomogeneous density distribution of cavitation bubbles. The aim is to predict the local dependent sonochemical effects.