Auswahl der wissenschaftlichen Literatur zum Thema „Sonochemical intensification“

Acoustic cavitation bubble dynamics has been extensively studied by physicists and mathematicians. Process intensification is primarily studied by chemical engineers. Chemists tend to focus on bubble dynamics in a multibubble field to optimize the physical and chemical forces generated during acoustic cavitation with an intention to maximise/intensify chemical processes. To achieve process intensification successfully a multidisciplinary approach is required. Our early work on multibubble cavitation unveiled various factors that contribute to process optimization. For example, while single bubble dynamics can estimate the maximum bubble temperatures, they may not be relevant to achieving higher chemical yield, which in turn depends on varus other factors such as average bubble temperatures, number of active cavitation bubbles, etc. Other factors critical for process intensification include the generation of a homogeneous cavitation field, control over mass transfer effects caused by bubble oscillations, reactor design, etc. The presentation will provide an overview on the relevance of single and multibubble bubble dynamics in ultrasonic/sonochemical processes.

The present work reports the use of sonochemical reactors for the degradation of phenol in the presence of additives with an objective of enhancing the rates of degradation at a pilot scale operation. Process intensification studies have been carried out using additives such as hydrogen peroxide (H2O2) (0.5–2.0 g/L), sodium chloride (0.5–1.5 g/L) and solid particles viz. cupric oxide (CuO) and titanium dioxide (TiO2) (0.5–2.5 g/L). Optimum concentration for H2O2 and sodium chloride has been observed beyond which no beneficial effects are obtained even with additional loadings. Maximum extent of degradation has been observed by using ultrasound/H2O2/CuO approach at a solid loading of 1.5 g/L followed by ultrasound/H2O2/TiO2 approach at a loading of 2.0 g/L. The obtained results at pilot scale operation in the current work are very important especially due to the fact that the majority of earlier studies are at laboratory scale which cannot provide the design related information for large scale operation as required scale up ratios are quite high adding a degree of uncertainty in the design. The novelty of the present work lies in the fact that it highlights successful application of sonochemical reactors for wastewater treatment at pilot scale operation.

Du fait de l'épuisement des ressources fossiles, l'intérêt de la lignine en tant qu'alternative durable est grandissant. Ainsi, le but principal de cette thèse était de mettre au point un procédé de clivage oxydant de la lignine par le dioxygène qui implique des voies non conventionnelles (sonochimie, ball-milling). Les catalyseurs utilisés sont des molybdovanadophosphates de KEGGIN. D'abord, nous avons optimisé les conditions opératoires (solvant, charge catalytique et taux de vanadium) pour le clivage, à pression atmosphérique de deux modèles, i. e. 2-phénoxyacétophénone (K1HH) et le 2-phénoxy-1-phenyléthanol (A1HH) en phénol, en benzaldéhyde et en acide benzoïque. Pour A1HH, des conditions plus dures se sont avérées être nécessaires (O2 5 bar, 120°C). Le catalyseur est synthétisé conventionnellement par la voie hydrothermale qui consiste à attaquer MoO3 et V2O5 dans l'eau à reflux en présence de H3PO4. Une longue durée de chauffage est souvent requise pour des rendements modérés. La synthèse par ball-milling a donc été envisagée. Elle consiste à préparer un oxyde mixte par broyage. L'attaque de ce dernier est alors plus courte, se déroule à plus faible température et donne lieu à des rendements en catalyseur plus élevés. Leur activité pour le clivage des modèles est similaire à celle de leurs homologues synthétisés par voie hydrothermale. Des tests préliminaires sur une lignine Organosolv issue de la paille de blé dans des conditions optimisées ont donné des faibles rendements en produits de clivage. L'assistance sonochimique a donc été testée montrant, dans le cas de A1HH, qu'une basse fréquence en conjonction avec un bullage de dioxygène constitue la meilleure option
Due to the depletion of fossil resources, the interest of lignin as a sustainable alternative to petroleum is growing. Thus, the main purpose of this thesis was to develop a process for oxidative cleavage of lignin by dioxygen that involves unconventional methodologies like sonochemistry and ball-milling. The catalysts used here were KEGGIN molybdovanadophosphates (PMoVx). First, the operating conditions (solvent, catalytic charge and vanadium content) were optimized to afford the cleavage of two models, 2-phenoxyacetophenone (K1HH) and 2-phenoxy-1-phenylethanol (A1HH), at atmospheric O2 pressure, into phenol, benzaldehyde and benzoic acid. For A1HH, harsher conditions were found to be necessary (O2 5 bar, 120°C). The catalysts were conventionally synthesized using a hydrothermal pathway, which consists in the H3PO4 attack of MoO3 and V2O5 in reflux water. A long heating period is often required to get moderate yields of PMoVx. Ball-milling synthesis was therefore considered. It consisted in preparing a mixed oxide by grinding MoO3 and V2O5. The latter's attack by H3PO4 was then shorter, took place at a lower temperature and resulted in higher yields of PMoVx. The activity of thus obtained PMoVx for model cleavage was similar to that of their hydrothermally synthesized counterparts. Preliminary tests on an Organosolv lignin from wheat straw under optimized conditions yielded low yields of cleavage products. Sonochemical assistance was therefore tested showing, in the case of A1HH, that a low frequency in conjunction with dioxygen bubbling was the best option

Biodiesel is an alternative to conventional fossil fuels. It has several advantages over conventional fuels. It is non-toxic, renewable, and biodegradable with no sulfur content. Researchers have used different techniques to produce biodiesel from various edible and non-edible oil sources in the last many years, but these technologies have several disadvantages. They are highly energy-intensive, have high operating costs, low volume throughput, and require high investment costs that make them uneconomical for large-scale operations. In recent years, sonochemical reactors such as ultrasonication or acoustic cavitation (AC) and hydrodynamic cavitation (HC) have been considered promising, efficient, and environmentally acceptable techniques for synthesizing biodiesel. These techniques work on the principle of generation, growth, and collapse of cavities due to pressure variation within the solution. The cavity collapse releases a tremendous amount of energy within a short period, typically within a microsecond at multiple locations within the solution. The release of such immense power generates local hot spots and highly disruptive pressure shock waves, which help in increasing the mass transfer rate and thereby causing improved transesterification reactions. This book chapter reviews the primary mechanism of intensified approaches using cavitation, fundamentals of acoustic and hydrodynamic cavitation reactors, basic designs, and operational guidelines for obtaining the maximum biodiesel yields. This chapter discusses the effect of various operating parameters of AC and HC on biodiesel yield. In the case of HC, details of different cavitating devices and the impact of geometrical and operating parameters that affect the cavitation conditions and biodiesel yield are discussed.