Ultrasound-assisted emerging technologies for chemical processes

Application and development of ultrasound in industrial crystallization

Crystallization is an important process that affects the properties of final products and is essential in nearly all chemical processing industries. In recent years, ultrasonic technology has received widespread attention due to its ability to enhance crystallization yield, improve crystal morphology and shape, and regulate the particle size and distribution of crystal products. It holds promising prospects for industrial crystallization. In this work, the ultrasonic cavitation effect and ultrasonic crystallization mechanism are described, and the influence of ultrasound on the crystallization effect of products is analysed and discussed. In addition, the application status of ultrasonic reactors and ultrasonic crystallization processes is introduced in detail, and the change trend from laboratory to industrialization is analyzed. Finally, the challenges and opportunities facing the industrialization of ultrasonic crystallization in future developments are discussed. The purpose of this work is to make the selective promotion or inhibition of ultrasound more helpful for industrial crystallization.

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

Facile room temperature synthesis of size-controlled spherical silica from silicon metal via simple sonochemical process

The waterglass or St o¨ ber method is commonly used to synthesize spherical colloidal silica; however, these methods have some disadvantages, such as complicated processes for the removal of sodium ions and expensive and energy-consuming raw materials such as tetraethoxysilane (TEOS). In this study, size-controlled spherical colloidal silica was synthesized from silicon metal at room temperature using an ultrasound process with hydrazine monohydrate as the solvent. Silicon metal dissolves easily in hydrazine monohydrate under ultrasound irradiation, and spherical colloidal silica can be synthesized by adding alcohol to this precursor solution. By changing the concentration or type of alcohol, size-controlled colloidal silica 20-200 nm in size could be easily obtained. In addition, finer and more monodisperse particles were produced by low-frequency ultrasound irradiation, which had a higher stirring effect at the particle formation stage. The present method is effective because size-controlled colloidal silica can be synthesized at room temperature using only silicon metal, hydrazine, and alcohol as raw materials, without complicated processes or expensive and energy-consuming raw materials such as TEOS or tetramethoxysilane (TMOS).

Ultrasound-assisted Peptide Nucleic Acids synthesis (US-PNAS)

Herein, we developed an innovative and easily accessible solid-phase synthetic protocol for Peptide Nucleic Acid (PNA) oligomers by systematically investigating the ultrasonication effects in all steps of the PNA synthesis (US-PNAS). When compared with standard protocols, the application of the so-obtained US-PNAS approach succeeded in improving the crude product purities and the isolated yields of different PNA, including small or medium-sized oligomers (5-mer and 9-mer), complex purine-rich sequences (like a 5-mer Guanine homoligomer and the telomeric sequence TEL-13) and longer oligomers (such as the 18-mer anti-IVS2-654 PNA and the 23-mer anti-mRNA 155 PNA). Noteworthy, our ultrasound-assisted strategy is compatible with the commercially available PNA monomers and well-established coupling reagents and only requires the use of an ultrasonic bath, which is a simple equipment generally available in most synthetic laboratories.

Ultrasonic cavitation: An effective cleaner and greener intensification technology in the extraction and surface modification of nanocellulose

With rising consumer demand for natural products, a greener and cleaner technology, i.e., ultrasound-assisted extraction, has received immense attention given its effective and rapid isolation for nanocellulose compared to conventional methods. Nevertheless, the application of ultrasound on a commercial scale is limited due to the challenges associated with process optimization, high energy requirement, difficulty in equipment design and process scale-up, safety and regulatory issues. This review aims to narrow the research gap by placing the current research activities into perspectives and highlighting the diversified applications, significant roles, and potentials of ultrasound to ease future developments. In recent years, enhancements have been reported with ultrasound assistance, including a reduction in extraction duration, minimization of the reliance on harmful chemicals, and, most importantly, improved yield and properties of nanocellulose. An extensive review of the strengths and weaknesses of ultrasound-assisted treatments has also been considered. Essentially, the cavitation phenomena enhance the extraction efficiency through an increased mass transfer rate between the substrate and solvent due to the implosion of microbubbles. Optimization of process parameters such as ultrasonic intensity, duration, and frequency have indicated their significance for improved efficiency.

Optimization of germination and ultrasonic-assisted extraction for the enhancement of γ-aminobutyric acid in pumpkin seed

Germination and ultrasonic-assisted extraction (UAE) are economical and effective methods to enhance bioactive compounds in plant seeds. We optimized the germination parameters and UAE parameters by using response surface methodology to maximize the recovery of γ-aminobutyric acid (GABA) in pumpkin seeds. The optimal germination conditions were as follows: soaking the seeds at 28°C for 6 h with 0.2% CaCl2, 3.8 mg/ml monosodium glutamate, and 4.0 mg/ml vitamin B6, then germination at 30°C for 61.6 h. The optimal conditions for UAE were as follows: 1:75 (w/v) material-to-solvent ratio, 220 W ultrasonic power, and ultrasonic treatment at 50°C for 14.4 min, which afforded an extraction yield of 2679 ± 10 mg/100 g. Moreover, the GABA-enhanced extract showed the potential of hypolipidemic effect in type 2 diabetes rats. These results confirmed that a combination of germination and UAE increased the GABA yield from pumpkin seeds and provided a basis for GABA-enhanced production to improve lifestyle-associated diseases.

Novel applications of ultrasonic atomization in the manufacturing of fine chemicals, pharmaceuticals, and medical devices

Liquid atomization as a fluid disintegration method has been used in many industrial applications such as spray drying, coating, incineration, preparation of emulsions, medical devices, etc. The usage of ultrasonic energy for atomizing liquid is gaining interest as a green and energy-efficient alternative to traditional mechanical atomizers. In the past two decades, efforts have been made to explore new applications of ultrasonic misting for downstream separation of chemicals, e.g., bioethanol, from their aqueous solutions. Downstream separation of a chemical from its aqueous solutions is known to be an energy-intensive process. Conventional distillation is featured by low energy efficiency and inability to separate azeotropic mixtures, and thus novel alternatives, such as ultrasonic separation have been explored to advance the separation technology. Ultrasonic misting has been reported to generate mist and vapor mixture in a gaseous phase that is enriched in solute (e.g., ethanol), under non-thermal, non-equilibrium, and phase change free conditions. This review article takes an in-depth look into the recent advancements in ultrasound-mediated separation of organic molecules, especially bioethanol, from their aqueous solutions. An effort was made to analyze and compare the experimental setups used, mist collection methods, droplet size distribution, and separation mechanism. In addition, the applications of ultrasonic atomization in the production of pharmaceuticals and medical devices are discussed.

Sonoprocessing: From Concepts to Large-Scale Reactors

Intensification of ultrasonic processes for diversified applications, including environmental remediation, extractions, food processes, and synthesis of materials, has received attention from the scientific community and industry. The mechanistic pathways involved in intensification of ultrasonic processes that include the ultrasonic generation of cavitation bubbles, radical formation upon their collapse, and the possibility of fine-tuning operating parameters for specific applications are all well documented in the literature. However, the scale-up of ultrasonic processes with large-scale sonochemical reactors for industrial applications remains a challenge. In this context, this review provides a complete overview of the current understanding of the role of operating parameters and reactor configuration on the sonochemical processes. Experimental and theoretical techniques to characterize the intensity and distribution of cavitation activity within sonoreactors are compared. Classes of laboratory and large-scale sonoreactors are reviewed, highlighting recent advances in batch and flow-through reactors. Finally, examples of large-scale sonoprocessing applications have been reviewed, discussing the major scale-up and sustainability challenges.

Ultrasound-assisted, low-solvent and acid/base-free synthesis of 5-substituted 1,3,4-oxadiazole-2-thiols as potent antimicrobial and antioxidant agents

One of the goals of green chemistry is to use environmentally friendly solvents or remove and reduce the volume of harmful spent solvents. In this study, a novel process for the synthesis of 5-substituted 1,3,4-oxadiazole-2-thiol derivatives was proposed via ultrasound-assisted reaction of aryl hydrazides with CS2 (1:1 molar ratio) in some drops of DMF in the absence of basic or acidic catalysts. They were produced in good to excellent yields under easy workup and purification conditions. In order to prove the usefulness of the prepared compounds, their antioxidant, antibacterial, and antifungal potentials were screened by DPPH free radical scavenging, serial twofold microdilution and streak plate methods. Acceptable to significant inhibitory activities were observed with synthesized heterocycles. The results showed that 5-(4-fluorophenyl)-1,3,4-oxadiazole-2-thiol (3c) is an broad-spectrum antimicrobial agent. Many of them displayed remarkable antioxidant properties comparable to standard controls (ascorbic acid and α-tocopherol). Synthesized 1,3,4-oxadiazoles are also potent candidates to treat cancer, Parkinson, inflammatory, and diabetes diseases. Eighteen 5-substituted 1,3,4-oxadiazole-2-thiol derivatives as potent antimicrobial and antioxidant agents were prepared via a new, efficient and green procedure.

Ultrasound-assisted biomass valorization to industrial interesting products: state-of-the-art, perspectives and challenges

Nowadays, the application of ultrasound (US) energy for assisting the lignocellulosic biomass and waste materials conversion into value-added products has dramatically increased. In this sense, this review covers theoretical aspects, promising applications, challenges and perspectives about US and its use for biomass treatment. The combination of US energy with a suitable reaction time, temperature and solvent contributes to the destruction of recalcitrant lignin structure, allowing the products to be used in thermochemical and biological process. The main mechanisms related to US propagation and impact on the fragmentation of lignocellulosic materials, selectivity, and yield of conversion treatments are discussed. Moreover, the synergistic effects between US and alternative green solvents with the perspective of industrial applications are investigated. The present survey analysed the last ten years of literature, studying challenges and perspectives of US application in biorefinery. We were aiming to highlight value-added products and some new areas of research.

Prospects and Challenges of Microwave-Combined Technology for Biodiesel and Biolubricant Production through a Transesterification: A Review

Biodiesels and biolubricants are synthetic esters produced mainly via a transesterification of other esters from bio-based resources, such as plant-based oils or animal fats. Microwave heating has been used to enhance transesterification reaction by converting an electrical energy into a radiation, becoming part of the internal energy acquired by reactant molecules. This method leads to major energy savings and reduces the reaction time by at least 60% compared to a conventional heating via conduction and convection. However, the application of microwave heating technology alone still suffers from non-homogeneous electromagnetic field distribution, thermally unstable rising temperatures, and insufficient depth of microwave penetration, which reduces the mass transfer efficiency. The strategy of integrating multiple technologies for biodiesel and biolubricant production has gained a great deal of interest in applied chemistry. This review presents an advanced transesterification process that combines microwave heating with other technologies, namely an acoustic cavitation, a vacuum, ionic solvent, and a supercritical/subcritical approach to solve the limitations of the stand-alone microwave-assisted transesterification. The combined technologies allow for the improvement in the overall product yield and energy efficiency. This review provides insights into the broader prospects of microwave heating in the production of bio-based products.

Process development and life cycle assessment of pomegranate biorefinery

According to the global survey, Iran, China, India, and USA are leading producers of pomegranate. Among them, India tops the chart as the highest producer of pomegranate, cultivating 1.14 million tons per annum. Peels cover 50% weight of whole pomegranate fruit and are mostly discarded as waste. This enormous peel waste has innumerable health benefits. Pomegranate peel (PP) constitutes various antioxidants, anthocyanins, and polyphenols such as ellagic acid, pectin, gallic acid, and many others which can be extracted. A detailed process for sequential extraction, with zero discharge, of such valuable chemicals from biorefinery point of view is developed in this study. Major products considered for extraction include ellagic acid (EA), lignin, and pectin. Also, the total phenolic content (TPC) and total reducing sugar (TRS) content are found in the intermediate stages. The percent yield of the products EA, lignin, and pectin is 10%, 13%, and 19% with respect to the weight of pomegranate peels (PP) processed. For the first time, a sequential extraction of products with its detailed process flow diagram, process inventory, and life cycle assessment (LCA) of PP biorefinery is presented. The global warming potential of the PP biorefinery is found to be 4505.8 kg CO₂ eq. per ton of PP processed. The intense hydrolysis step contributed majorly to the overall GWP indicator.

Recent Strategies for Hydrogen Peroxide Production by Metal-Free Carbon Nitride Photocatalysts

Hydrogen peroxide (H2O2) is a chemical which has gained wide importance in several industrial and research fields. Its mass production is mostly performed by the anthraquinone (AQ) oxidation reaction, leading to high energy consumption and significant generation of wastes. Other methods of synthesis found in the literature include the direct synthesis from oxygen and hydrogen. However, this H2O2 production process is prone to explosion hazard or undesirable by‑product generation. With the growing demand of H2O2, the development of cleaner and economically viable processes has been under intense investigation. Heterogeneous photocatalysis for H2O2 production has appeared as a promising alternative since it requires only an optical semiconductor, water, oxygen, and ideally solar light irradiation. Moreover, employing a metal-free semiconductor minimizes possible toxicity consequences and reinforces the sustainability of the process. The most studied metal‑free catalyst employed for H2O2 production is polymeric carbon nitride (CN). Several chemical and physical modifications over CN have been investigated together with the assessment of different sacrificial agents and light sources. This review shows the recent developments on CN materials design for enhancing the synthesis of H2O2, along with the proposed mechanisms of H2O2 production. Finally, the direct in situ generation of H2O2, when dealing with the photocatalytic synthesis of added-value organic compounds and water treatment, is discussed.

Mechanochemical Forces as a Synthetic Tool for Zero- and One-Dimensional Titanium Oxide-Based Nano-photocatalysts

A new field where the utilization of mechanochemistry can create new opportunities is materials chemistry, and, more interestingly, the synthesis of novel nanomaterials. Ball-milling procedures and ultrasonic techniques can be regarded as the most important mechanochemical synthetic tools, since they can act as attractive alternatives to the conventional methods. It is also feasible for the utilization of mechanochemical forces to act synergistically with the conventional synthesis (as a pre-treatment step, or simultaneously during the synthesis) in order to improve the synthetic process and/or the material's desired features. The usage of ultrasound irradiation or ball-milling treatment is found to play a crucial role in controlling and enhancing the structural, morphological, optical, and surface chemistry features that are important for heterogeneous photocatalytic practices. The focus of this article is to collect all the available examples in which the utilization of sonochemistry or ball milling had unique effects as a synthesis tool towards zero- or one-dimensional nanostructures of a semiconductor which is assumed as a benchmark in photocatalysis, titanium dioxide.

Lithium carbonate recovery from lithium-containing solution by ultrasound assisted precipitation

Lithium carbonate (Li₂CO₃), one of the most important lithium compounds, is usually prepared from lithium-containing solution. The lithium recovery rate and the purity of Li₂CO₃ are highly dependent on the lithium concentration. In order to get a high lithium recovery rate, high concentrated lithium-containing solution is required, while the purity of Li₂CO₃ can be low remaining a significant amount of impurities. Usually, it is not possible to obtain high purity Li₂CO₃ by single-step precipitation with a relatively high lithium recovery rate especially from a low concentrated lithium-containing solution. In this research, ultrasound is introduced to increase lithium recovery rate and prepare industrial grade Li₂CO₃. The research found that ultrasound can significantly reduce the polymerization of Li₂CO₃ crystal particles and promote dissociation of impurity ions. At the same time, ultrasound accelerates the nucleation process of Li₂CO₃ and boosts lithium recovery rate because of cavitation. The different parameters during the Li₂CO₃ precipitation process were systematically discussed. Under the optimized conditions, the lithium recovery rate can be increased by 12% with a global lithium recovery rate of 97.4%. Li₂CO₃ with a purity higher than industrial grade can be obtained by one-step precipitation. It demonstrates a potential pathway for effective lithium recovery from low concentrated lithium-containing solution and preparation of industrial grade Li₂CO₃.