Intensification of esterification of acids for synthesis of biodiesel using acoustic and hydrodynamic cavitation

Response surface optimization of a single-step castor oil-based biodiesel production process using a stator-rotor hydrodynamic cavitation reactor

In order to combat environmental pollution and the depletion of non-renewable fuels, feasible, eco-friendly, and sustainable biodiesel production from non-edible oil crops must be augmented. This study is the first to intensify biodiesel production from castor oil using a self-manufactured cylindrical stator-rotor hydrodynamic cavitation reactor. In order to model and optimize the biodiesel yield, a response surface methodology based on a 1/2 fraction-three-level face center composite design of three levels and five experimental factors was used. The predicted ideal operating parameters were found to be 52.51°C, 1164.8 rpm rotor speed, 27.43 min, 8.4:1 methanol-to-oil molar ratio, and 0.89% KOH concentration. That yielded 95.51% biodiesel with a 99% fatty acid methyl ester content. It recorded a relatively low energy consumption and high cavitation yield of 6.09 × 105 J and 12 × 10-3 g/J, respectively. The generated biodiesel and bio-/petro-diesel blends had good fuel qualities that were on par with global norms and commercially available Egyptian petro-diesel. The preliminary cost analysis assured the feasibility of the applied process.

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging

Hydrodynamic cavitation is useful in many processing applications, for example, in chemical reactors, water treatment and biochemical engineering. An important type of hydrodynamic cavitation that occurs in a Venturi tube is vortex cavitation known to cause luminescence whose intensity is closely related to the size and number of cavitation events. However, the mechanistic origins of bubbles constituting vortex cavitation remains unclear, although it has been concluded that the pressure fields generated by the cavitation collapse strongly depends on the bubble geometry. The common view is that vortex cavitation consists of numerous small spherical bubbles. In the present paper, aspects of vortex cavitation arising in a Venturi tube were visualized using high-speed X-ray imaging at SPring-8 and European XFEL. It was discovered that vortex cavitation in a Venturi tube consisted of angulated rather than spherical bubbles. The tangential velocity of the surface of vortex cavitation was assessed considering the Rankine vortex model.

Characterization of homogenous acid catalyzed biodiesel production from palm oil: experimental investigation and numerical simulation

Biodiesel is a biological renewable source produced from the conversion of triglycerides to alkyl esters. Palm oil is one of the most used lipid feedstocks for biodiesel production. It becomes necessary to optimize the transesterification reaction parameters to reduce the cost and enhance the quality of biodiesel. This study focuses on the use of homogenous sulfuric acid as a catalyst for the transesterification of palm fatty acids to methyl esters in a batch-scale reactor. A novel examination of transesterification reaction input parameters using the technique for order performance by similarity to ideal solution optimization technique and the effect of these parameters on yield, viscosity, and density of palm biodiesel using 3D surface graphs is investigated in this research. The present optimization approach is implemented to find out the optimum ranking of biodiesel production. From the experimental and numerical simulation, optimum results were observed at the catalyst concentration of 6% (w/w), reaction temperature of 70 °C, the reaction time of 120 min, and alcohol to oil molar ratio of 30:1 at which yield of 95.35%, viscosity of 5.0 cSt, and density of 880 kg/m³ of palm biodiesel were obtained. The different physicochemical properties of produced palm methyl esters are obtained within standards set by international authorities. Selected optimized process parameters can be used for commercial-scale biodiesel production.

A novel design for biodiesel production from methanol + mutton bone fat mixture

Bioenergy plays a significant role in the green transition. In this work, the conversion of methanol and mutton bone fat oil (as a low-cost feedstock) for bioenergy production was studied. The five-level, three-factor response surface methodology (RSM) was used to optimize the transesterification reaction conditions for produced biodiesel. Twenty ultrasonic-assisted experiments at the frequency of 25 kHz were conducted to investigate the effects of methanol/oil molar ratio (M/O) and concentrations of KOH and NaOH as catalysts on biodiesel yield. A second-order polynomial equation was developed by fitting the RSM experimental data using Design-Expert software. Results showed that the optimum biodiesel yield of 90.087% could be achieved by the KOH catalyst with 2.5 wt% concentration and 15:1 M/O during 3 h of the reaction. Furthermore, the biofuel analyses showed that methanol and mutton bone fat oil can be used as a proper feedstock for biofuel production. In the following, a membrane filtration package system is proposed and modeled. The reaction kinetics was determined based on experimental data. The results of the mathematical modeling showed the reaction time appears to be 6 times shorter in a membrane setup (30 min). Consequently, membrane application is highly recommended for biodiesel production from mutton bone fat oil.

Cavitation based cleaner technologies for biodiesel production and processing of hydrocarbon streams: A perspective on key fundamentals, missing process data and economic feasibility - A review

The present review emphasizes the role of hydrodynamic cavitation (HC) and acoustic cavitation in clean and green technologies for selected fuels (of hydrocarbon origins such as gasoline, naphtha, diesel, heavy oil, and crude oil) processing applications including biodiesel production. Herein, the role of cavitation reactors, their geometrical parameters, physicochemical properties of liquid media, liquid oxidants, catalyst loading, reactive oxygen species, and different types of emulsification and formation of radicals, formation as well as extraction of formed by-products are systematically reviewed. Among all types of HC reactors, vortex diode and single hole orifices revealed more than 95 % desulfurization yield and a 20 % viscosity reduction in heavy oil upgrading, while multi-hole orifice (100 holes) and slit Venturi allowed obtaining the best biodiesel production processes in terms of high (%) yield, low cost of treatment, and short processing time (5 min; 99 % biodiesel; 4.80 USD/m³). On the other hand, the acoustic cavitation devices are likely to be the most effective in biodiesel production based on ultrasonic bath (90 min; 95 %; 6.7 $/m³) and desulfurization treatment based on ultrasonic transducers (15 min; 98.3 % desulfurization; 10.8 $/m³). The implementation of HC-based processes reveals to be the most cost-effective method over acoustic cavitation-based devices. Finally, by reviewing the ongoing applications and development works, the limitations and challenges for further research are addressed emphasizing the cleaner production and guidelines for future scientists to assure obtaining comprehensive data useful for the research community.

The effect of operating parameters of hydrodynamic cavitation – assisted alkaline catalyzed transesterification of sunflower oil with methanol on the degree of triglyceride conversion

The effect of operating parameters such as reaction mixture inlet pressure p 1 (101.3–1013.2 kPa), methanol to oil molar ratio M 1 (3–12), the concentration of catalyst C c (0.0–1.0 wt%), temperature T (25–50 °C) and the number of passes of the reaction mixture through the venturi type hydrodynamic cavitation reactor n (1–12) on alkali-catalyzed transesterification of sunflower oil with methanol assisted by hydrodynamic cavitation (ACTC) on the value of the degree of triglyceride conversion (DTC) was investigated. ACTC was performed by the venturi-type hydrodynamic cavitation reactor (VCR) of our construction. It was found that the values of DTC increase with the increase in p 1, M 1, C c, and n, and decrease with the increase in T. Cavitation yield (CY) values were calculated. The ACTC was proved to be the simplest, fastest, and most highly energy-efficient current technology for the production of biodiesel.

Novel strategies to enhance hydrodynamic cavitation in a circular venturi using RANS numerical simulations

Hydrodynamic cavitation is a popular advanced oxidation technique and it has received wide range of applications from waste water treatment to the nanoparticles synthesis in recent years. The enhancement of the intensity of the hydrodynamic cavitation is always been an emerging field of research. Within this framework, we have proposed and investigated three distinct strategies to enhance the intensity of cavitation in a circular venturi, namely, (1) by introducing the surface roughness on the wall (2) single or multiple circular hurdles in the diverging section (3) By modifying the diverging section from planer to the trumpet shape. RANS (Reynolds Averaged Navier-Stokes) based numerical simulations are carried out the over wide range of conditions: 2≤PR≤6 (pressure ratio), 6.2^∘≤β≤10^∘ (half divergent angle), 15^∘≤α≤20^∘ (half convergent angle), and 1≤l/d≤3 (throat length). An extensive numerical and experimental validation with the literature have been presented to ensure the reliability and accuracy of present work. Detailed results on velocity fields, local and average volume fraction, pressure loss coefficients, cavitation number, discharge coefficient and pressure distribution are reported as function of dimensionless parameters. Five designs of various combinations of surface roughness, circular hurdles, and trumpet diverging section have been compared. The effect of surface roughness on trumpet diverging wall has been observed to be more pronounced than the other designs. Trumpet diverging wall with surface roughness is found to be optimum for the practical applications.

Phytocannabinoids - An Overview of the Analytical Methodologies for Detection and Quantification of Therapeutically and Recreationally Relevant Cannabis Compounds

The legalization of the cultivation of low Δ9-tetrahydrocannabinol (Δ9-THC) and high cannabidiol (CBD) Cannabis Sativa plants is gaining momentum around the world due to increasing demand for CBD-containing products. In many countries where CBD oils, extracts and CBD-infused foods and beverages are being sold in health shops and supermarkets, appropriate testing of these products is a legal requirement. Normally this involves determining the total Δ9-THC and CBD and their precursor tetrahydrocannabinolic acids (THCA) and cannabidiolic acid (CBDA). As our knowledge of the other relevant cannabinoids expands, it is likely so too will the demand for them as additives in many consumer products ensuring a necessity for quantification methods and protocols for their identification. This paper discusses therapeutically relevant cannabinoids found in Cannabis plant, the applicability and efficiency of existing extraction and analytical techniques as well as the legal requirements for these analyses.

Hydrodynamic cavitation: A feasible approach to intensify the emulsion cross-linking process for chitosan nanoparticle synthesis

Chitosan nanoparticles (NPs) exhibit great potential in drug-controlled release systems. A controlled hydrodynamic cavitation (HC) technique was developed to intensify the emulsion crosslinking process for the synthesis of chitosan NPs. Experiments were performed using a circular venturi and under varying operating conditions, i.e., types of oil, addition mode of glutaraldehyde (Glu) solution, inlet pressure (P_in), and rheological properties of chitosan solution. Palm oil was more appropriate for use as the oil phase for the HC-intensified process than the other oil types. The addition mode of water-in-oil (W/O) emulsion containing Glu (with Span 80) was more favorable than the other modes for obtaining a narrow distribution of chitosan NPs. The minimum size of NPs with polydispersity index of 0.342 was 286.5 nm, and the maximum production yield (P_y) could reach 47.26%. A positive correlation was found between the size of NPs and the droplet size of W/O emulsion containing chitosan at increasing P_in. Particle size, size distribution, and the formation of NPs were greatly dependent on the rheological properties of the chitosan solution. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the molecular structure of palm oil was unaffected by HC-induced effects. Compared with ultrasonic horn, stirring-based, and conventional drop-by-drop processes, the application of HC to intensify the emulsion crosslinking process allowed the preparation of a finer and a narrower distribution of chitosan NPs in a more energy-efficient manner. The novel route developed in this work is a viable option for chitosan NP synthesis.

A review on recent advances in hydrogen energy, fuel cell, biofuel and fuel refining via ultrasound process intensification

Hydrogen energy is one of the most suitable green substitutes for harmful fossil fuels and has been investigated widely. This review extensively compiles and compares various methodologies used in the production, storage and usage of hydrogen. Sonochemistry is an emerging synthesis process and intensification technique adapted for the synthesis of novel materials. It manifests acoustic cavitation phenomena caused by ultrasound where higher rates of reactions occur locally. The review discusses the effectiveness of sonochemical routes in developing fuel cell catalysts, fuel refining, biofuel production, chemical processes for hydrogen production and the physical, chemical and electrochemical hydrogen storage techniques. The operational parameters and environmental conditions used during ultrasonication also influence the production rates, which have been elucidated in detail. Hence, this review's major focus addresses sonochemical methods that can contribute to the technical challenges involved in hydrogen usage for energy.

Investigating the Effects of Ultrasonic Frequency and Membrane Technology on Biodiesel Production from Chicken Waste

In this study, the experiments were carried out under different operating conditions to evaluate the effect of ultrasound waves on biodiesel production from chicken feet oil. A two-step esterification–transesterification mechanism was employed to improve the biodiesel quality. The continuous (methanol-to-oil molar ratio and KOH catalyst amount) and discrete (frequencies, 25 and 45 kHz) variables were investigated using the experimental design method. The five-level three-factor response surface method (RSM) was assisted to optimize the biodiesel synthesis variables. Applying RSM based on the central composite design (CCD), a polynomial equation was fitted to the experimental data with the aid of Design-Expert software. The model accuracy was checked by analysis of variance (ANOVA). The results showed the highest yield of 89.74% could be achieved by using an M/O molar ratio of 12, a KOH concentration of 1 wt%, and an ultrasound frequency of 45 kHz. Finally, a mathematical model of biodiesel production in a membrane system was developed. The reaction rate constant was calculated as a function of ultrasonic frequency. Compared with the conventional method, the membrane system has significantly improved chicken feet biodiesel production’s reaction rate. The membrane is more effective at higher frequencies than at lower ones.

Intensification of diesel oxidative desulfurization via hydrodynamic cavitation

A Hydrodynamic Cavitation Assisted Oxidative Desulfurization (HCAOD) process was applied for treatment of diesel fuel feedstock using hydrogen peroxide and formic acid as the oxidant and catalyst, respectively. Investigation on the effect of main process variables including pressure drop (3-6 bar), time of treatment (10-30 min) and formic acid to oxidant molar ratio (n_A/n_O) (1-5), was performed through applying Response Surface Methodology (RSM) based on Box-Behnken design. Single and interactive effects of the parameters were recognized. A remarkable 95% extent of desulfurization at optimum conditions with HC pressure drop of 4.2 bar, acid to oxidant ratio (n_A/n_O) of 3.2 at 29 min was achieved. The results were also compared to an oxidation system without the aid of hydrodynamic cavitation. Accordingly, HCAOD can be considered as a promising treatment scheme for intensification of diesel oxidative desulfurization.

Modeling & simulation studies on batch anaerobic digestion of hydrodynamically cavitated tannery waste effluent for higher biogas yield

This study describes the efficacy of the pretreatment method of tannery waste effluent (TWE) by hydrodynamic cavitation (HC) prior to anaerobic digestion (AD) using a slit venturi cavitating device operated at 5 bar pressure for 2 h. The HC effect caused faster disintegration and solubilization of larger organic molecules into smaller ones, so that it could be easily digested by the microbial cells resulting in higher degradation rates, lower acclimatization time, higher COD reduction of the TWE and higher biogas generation. The biogas yield and % COD reduction was almost twice higher in HC treated TWE compared to raw TWE. Biogas yield of 68.57 mL/g volatile solids with 43.17% COD reduction was obtained during AD of HC treated TWE in 2 L bioreactor with 10% seed dosage. 'AD' Simulator developed in MATLAB represented the AD performance for both raw and HC treated TWE feed and predicted for concentrations of organic polymers, monomers, VFA and biogas produced, in which model parameter optimization was done by validations using methane production data from bioreactors. The AD simulator estimated higher hydrolysis rate constants for HC treated TWE than for raw TWE as observed in the experiments. Biogas production increased up to 7.8 and 11.8 folds for raw and HC treated TWE samples respectively by adding food waste to TWE feed with organic loading rate of 48 h. Cost estimations proved that cost of excess biogas produced by anaerobic digestion of HC treated TWE mixed with food waste, recovers the extra cost of HC pretreatment when compared to raw TWE alone, establishing HC as an effective pre-treatment tool prior to AD.

Harnessing cavitational effects for green process intensification

The impressive chemico-physical effects observed in sonochemistry are a result of cavitation, as ultrasonic and hydrodynamic cavitation does not interact with matter at the atomic and molecular levels. Bubble collapse leads to the quasi-adiabatic heating of the vapour inside bubbles, giving rise to local hot spots in the fluid. Cavitation thus transforms a mechanical energy into high kinetic energy, which is released in very short bursts that are exploited for green process intensification. This paper reviews relevant applications of hydrodynamic and acoustic cavitation with the aim of highlighting the particular advantages that these phenomena offer to the intensification of green chemical processes. Emulsification, biodiesel preparation, wastewater decontamination, organic synthesis, enzymatic catalysis and extractions are discussed among others. As a comparison, hydrodynamic cavitation technique is more advantageous in dealing with process intensification at large-scale, as well as the enhancement of mass transfer and heat transfer, while ultrasonic cavitation technique is more convenient to operate, easier to control in the studies at lab-scale, and exhibits more efficient in producing active free radicals and inducing the cleavage of volatile compounds.

Ultrasonication-Assisted and Benzimidazolium-Based Brønsted Acid Ionic Liquid-Catalyzed Transesterification of Castor Oil

In this investigation, we report the synthesis of biodiesel using benzimidazolium-based brønsted acid ionic liquid (BBAIL) catalyst under the influence of ultrasonication. The prepared BBAIL catalyst was characterized by Fourier transform infrared and NMR spectroscopy techniques, and its acidity was determined by the Hammett method with 4-nitroaniline as the indicator. Ultrasonicator horn (22 kHz, 500 W) was used in this work with an on-off cycle of 50-20 s at 70% amplitude. The highest biodiesel yield of 96% was achieved by ultrasonication when 1:10 molar ratio of castor oil to methyl alcohol was used at 50 °C temperature with 9 mol % of the catalyst in just 90 min, which is about 10 times lesser than the process without ultrasonication. At similar conditions, 96% biodiesel yield was obtained in 14 h without ultrasonication. In summary, ultrasonication proved to be an efficient way to improve biodiesel synthesis in less time and BBAIL showed excellent activity toward the conversion of glycerides to synthesize biodiesel. Other important highlights are easy separation of the catalyst and recyclability up to three cycles with small decrease in its activity.

Intensified synthesis of medium chain triglycerides using ultrasonic reactors at a capacity of 4L

Lipids are considered as one of the most crucial nutrients for humans and among the various classes, medium chain triglycerides (MCTs) are considered as the most important functional foods and nutraceuticals. The present work deals with the intensification of synthesis of MCTs at a large capacity of 4L based on the use of ultrasonic bath and ultrasonic longitudinal horn. The effect of operating parameters like molar ratio of the reactants, type of catalyst and catalyst loading as well as the temperature on the extent of conversion has been investigated. The effect of molar ratio of lauric acid and glycerol was investigated over the range of 1:2 to 1:8 whereas the effect of loading of sulfuric acid was studied over the range of 4 ml/L-10 ml/L and zinc chloride loading over the range of 1 g/L-4 g/L. The effect of temperature was also studied using the conventional approach where it has been observed that 90 °C is an optimum temperature giving the extent of conversion as 72%. Also, the use of homogeneous catalyst as sulphuric acid was found to be more effective as compared to the solid catalyst as zinc chloride. It was observed that the maximum extent of conversion as 77.5% was obtained at 8 ml/L of sulfuric acid and molar ratio of 1:6 using ultrasonic longitudinal horn with US bath giving lower conversion as compared to US longitudinal horn but higher than the conventional approach under same operating conditions. The present work clearly established the intensification benefits in terms of reduction in time and higher conversion using cavitational reactors.

Microalgae as feedstock for biodiesel production under ultrasound treatment - A review

The application of ultrasound in biodiesel production has recently emerged as a novel technology. Ultrasound treatment enhances the mass transfer characteristics leading to the increased reaction rate with short reaction time and potentially reduces the production cost. In this review, application of ultrasound-assisted biodiesel production using acid, base and enzyme catalysts is presented. A critical assessment of the current status of ultrasound in biodiesel production was discussed with the emphasis on using ultrasound for efficient microalgae biodiesel production. The ultrasound in the biodiesel production enhances the emulsification of immiscible liquid reactant by microturbulence generated by cavitation bubbles. The major benefit of the ultrasound-assisted biodiesel production is a reduction in reaction time. Several different methods have been discussed to improve the biodiesel production. Overall, this review focuses on the current understanding of the application of ultrasound in biodiesel production from microalgae and to provide insights into future developments.

Ultrasonic-assisted continuous methanolysis of Jatropha curcas oil in the appearance of biodiesel used as an intermediate solvent

A environmental friendly system for fast transesterification of Jatropha curcas oil was developed for the production of biodiesel using an ultrasonic-assisted continuous tank reactor in the presence of fatty acid methyl ester (FAMEs) used as a green (intermediate) solvent with potassium hydroxide used as a catalyst. This research provide a new biodiesel production process, the optimal condition for the reaction were established: reaction temperature 25°C oil to methanol molar ratio was 1:5, catalyst concentration 0.75wt% of oil, solvent concentration 7.5%, flow rate 241.68±0.80ml/min, ultrasonic amplitude 60% and ultrasonic cycles 0.7s, transesterification was completed within 1.09min (residence time). The purity and conversion of biodiesel was 98.75±0.50% analyzed by the reverse phase HPLC method.

Intensification of biodiesel production from soybean oil and waste cooking oil in the presence of heterogeneous catalyst using high speed homogenizer

In the present work, high speed homogenizer has been used for the intensification of biodiesel synthesis from soybean oil and waste cooking oil (WCO) used as a sustainable feedstock. High acid value waste cooking oil (27mg of KOH/g of oil) was first esterified with methanol using sulphuric acid as catalyst in two stages to bring the acid value to desired value of 1.5mg of KOH/g of oil. Transesterification of soybean oil (directly due to lower acid value) and esterified waste cooking oil was performed in the presence of heterogeneous catalyst (CaO) for the production of biodiesel. Various experiments were performed for understanding the effect of operating parameters viz. molar ratio, catalyst loading, reaction temperature and speed of rotation of the homogenizer. For soybean oil, the maximum biodiesel yield as 84% was obtained with catalyst loading of 3wt% and molar ratio of oil to methanol of 1:10 at 50°C with 12,000rpm as the speed of rotation in 30min. Similarly biodiesel yield of 88% was obtained from waste cooking oil under identical operating conditions except for the catalyst loading which was 1wt%. Significant increase in the rate of biodiesel production with yields from soybean oil as 84% (in 30min) and from WCO as 88% (30min) was established due to the use of high speed homogenizer as compared to the conventional stirring method (requiring 2-3h for obtaining similar biodiesel yield). The observed intensification was attributed to the turbulence caused at microscale and generation of fine emulsions due to the cavitational effects. Overall it can be concluded from this study that high speed homogenizer can be used as an alternate cavitating device to efficiently produce biodiesel in the presence of heterogeneous catalysts.

Pilot scale intensification of rubber seed (Hevea brasiliensis) oil via chemical interesterification using hydrodynamic cavitation technology

Chemical interesterification of rubber seed oil has been investigated for four different designed orifice devices in a pilot scale hydrodynamic cavitation (HC) system. Upstream pressure within 1-3.5bar induced cavities to intensify the process. An optimal orifice plate geometry was considered as plate with 1mm dia hole having 21 holes at 3bar inlet pressure. The optimisation results of interesterification were revealed by response surface methodology; methyl acetate to oil molar ratio of 14:1, catalyst amount of 0.75wt.% and reaction time of 20min at 50°C. HC is compared to mechanical stirring (MS) at optimised values. The reaction rate constant and the frequency factor of HC were 3.4-fold shorter and 3.2-fold higher than MS. The interesterified product was characterised by following EN 14214 and ASTM D 6751 international standards.

Intensification of esterification of non edible oil as sustainable feedstock using cavitational reactors

Using sustainable feed stock such as non-edible oil for the biodiesel production can be one of the cost effective approaches considering the ever growing interest towards renewable energy and problems in existing approaches for production. However, due to the high free fatty acid content, non-edible oils require considerable preprocessing before the actual transesterification reaction for biodiesel production. The present work focuses on intensification of the esterification reaction used as preprocessing step based on acoustic and hydrodynamic cavitation also presenting the comparison with the conventional approach. Karanja oil with initial acid value as 14.15mg of KOH/g of oil has been used as a sustainable feedstock. Effect of operating parameters such as molar ratio, catalyst loading, temperature and type of catalyst (sulfuric acid and Amberlyst-15) on the acid value reduction has been investigated. The maximum reduction in the acid value (final acid value as 2.7mg of KOH/g of oil) was obtained using acoustic cavitation at optimum molar ratio of oil to methanol as 1:5 and 2% sulfuric acid loading at ambient temperature. In the case of hydrodynamic cavitation, acid value reduced upto 4.2mg of KOH under optimized conditions of first stage processing. In the second stage esterification using hydrodynamic cavitation and conventional approach, the final acid value was 3.6 and 3.8mg of KOH/g of oil respectively. Energy requirement analysis for ultrasound and conventional approaches clearly established the superiority of the ultrasound based approach. The present study clearly demonstrated that significant intensification benefits can be obtained in terms of the reduction in the molar ratio and operating temperature for the case of acoustic cavitation as compared to the conventional approach with somewhat lower effects for the hydrodynamic cavitation.

Hydrodynamic cavitation: an emerging technology for the intensification of various chemical and physical processes in a chemical process industry

Hydrodynamic cavitation (HC) has been explored by many researchers over the years after the first publication on hydrolysis of fatty oils using HC was published by Pandit and Joshi [Pandit AB, Joshi JB. Hydrolysis of fatty oils: effect of cavitation. Chem Eng Sci 1993; 48: 3440–3442]. Before this publication, most of the studies related to cavitation in hydraulic system were concentrated to avoid the generation of cavities/cavitating conditions. The fundamental concept was to harness the energy released by cavities in a positive way for various chemical and mechanical processes. In HC, cavitation is generated by a combination of flow constriction and pressure-velocity conditions, which are monitored in such a way that cavitating conditions will be reached in a flowing system and thus generate hot spots. It allows the entire process to operate at otherwise ambient conditions of temperature and pressure while generating the cavitating conditions locally. In this review paper, we have explained in detail various cavitating devices and the effect of geometrical and operating parameters that affect the cavitation conditions. The optimization of different cavitating devices is discussed, and some strategies have been suggested for designing these devices for different applications. Also, various applications of HC such as wastewater treatment, preparation of nanoemulsions, biodiesel synthesis, water disinfection, and nanoparticle synthesis were discussed in detail.

A Parametric Study of Biodiesel Production Under Ultrasounds

Biodiesel, a vegetable oil-derived fuel, can be used as a partial or complete substitute to diesel oil. The main argument for its usage in internal combustion engines is its net CO2 balance which is considerably reduced compared to diesel fuel of fossil origin. A systematic study of ultrasound continuous biodiesel production using canola oil was conducted in the presence of methanol and sodium methoxide as catalyst. Effects of various reaction parameters such as residence time, catalyst concentration, reaction temperature, ultrasounds amplitude and power, methanol/oil molar ratio were analyzed. Fatty acid methyl esters were produced rapidly by using ultrasound assisted transesterification. In typical conditions (35 °C) conversion to FAME higher than 80 % could be reached at residence time as low as 20 s. The parametric study allowed to establish that the effect of ultrasound wave on transesterification reaction rate is localized in a very small volume surrounding the sonotrode tip. This unprecedented conclusion has significant consequences for the design of the large scale continuous flow biodiesel production reactor.

Biodiesel production process intensification using a rotor-stator type generator of hydrodynamic cavitation

Triglyceride transesterification for biodiesel production is a model reaction which is used to compare the conversion efficiency, yield, reaction time, energy consumption, scalability and cost estimation of different reactor technology and energy source. This work describes an efficient, fast and cost-effective procedure for biodiesel preparation using a rotating generator of hydrodynamic cavitation (HC). The base-catalyzed transesterification (methanol/sodium hydroxide) has been carried out using refined and bleached palm oil and waste vegetable cooking oil. The novel HC unit is a continuous rotor-stator type reactor in which reagents are directly fed into the controlled cavitation chamber. The high-speed rotation of the reactor creates micron-sized droplets of the immiscible reacting mixture leading to outstanding mass and heat transfer and enhancing the kinetics of the transesterification reaction which completes much more quickly than traditional methods. All the biodiesel samples obtained respect the ASTM standard and present fatty acid methyl ester contents of >99% m/m in both feedstocks. The electrical energy consumption of the HC reactor is 0.030kWh per L of produced crude biodiesel, making this innovative technology really quite competitive. The reactor can be easily scaled-up, from producing a few hundred to thousands of liters of biodiesel per hour while avoiding the risk of orifices clogging with oil impurities, which may occur in conventional HC reactors. Furthermore it requires minimal installation space due to its compact design, which enhances overall security.

Optimisation on pretreatment of rubber seed (Hevea brasiliensis) oil via esterification reaction in a hydrodynamic cavitation reactor

Pretreatment of the high free fatty acid rubber seed oil (RSO) via esterification reaction has been investigated by using a pilot scale hydrodynamic cavitation (HC) reactor. Four newly designed orifice plate geometries are studied. Cavities are induced by assisted double diaphragm pump in the range of 1-3.5 bar inlet pressure. An optimised plate with 21 holes of 1mm diameter and inlet pressure of 3 bar resulted in RSO acid value reduction from 72.36 to 2.64 mg KOH/g within 30 min of reaction time. Reaction parameters have been optimised by using response surface methodology and found as methanol to oil ratio of 6:1, catalyst concentration of 8 wt%, reaction time of 30 min and reaction temperature of 55°C. The reaction time and esterified efficiency of HC was three fold shorter and four fold higher than mechanical stirring. This makes the HC process more environmental friendly.

Optimization of ultrasonic assisted continuous production of biodiesel using response surface methodology

This paper evaluates and optimizes the continuous production of biodiesel from waste cooking oil. In this research work, methanol and potassium hydroxide were used as catalyst engaging response surface methodology. For this purpose, the central composite experimental design (CCED), the effects of various factors such as irradiation distance, probe diameter, ultrasonic amplitude, vibration pulse and material flow into the reactor on reaction yield were studied to optimize the process. The results showed that all of the considered parameters affect the reaction efficiency significantly. The optimum combination of the findings include: irradiation distance which was 75 mm, probe diameter of 28 mm, ultrasonic amplitude of 56%, vibration pulse of 62% and flow rate of 50 ml/min that caused the reaction yield of 91.6% and energy consumption of 102.8 W. To verify this optimized combination, three tests were carried out. The results showed an average efficiency of 91.12% and 102.4 W power consumption which is well matched with the model's predictions.

Continuous lipase-catalyzed esterification of soybean fatty acids under ultrasound irradiation

This work investigates the continuous production of alkyl esters from soybean fatty acid (FA) charges using immobilized Novozym 435 as catalyst. The experiments were performed in a packed-bed bioreactor evaluating the effects of FA charge to alcohol (methanol and ethanol) molar ratio, from 1:1 to 1:6, substrate flow rate in the range of 0.5-2.5 mL/min and output irradiation power up to 154 W, at fixed temperature of 65 °C, on the reaction conversion. Results showed that almost complete conversions to fatty acids ethyl esters were achieved at mild ultrasonic power (61.6 W), FA to ethanol molar ratio of 1:6, operating temperature (65 °C) and remained nearly constant for long-term reactions without negligible enzyme activity losses.

Ultrasound assisted production of fatty acid methyl esters from transesterification of triglycerides with methanol in the presence of KOH catalyst: optimization, mechanism and kinetics

Ultrasound assisted transesterification of triglycerides (TG) with methanol in the presence of KOH catalyst was investigated, where the changes in the reactants and products (diglycerides (DG), monoglycerides (MG), fatty acid methyl esters (FAME) and glycerin (GL)) concentrations were discussed to understand the reaction mechanism and kinetics under ultrasound irradiation. The optimum reaction condition for the FAME production was the concentration of KOH 1.0 wt.%, molar ratio of TG to methanol of 1:6, and irradiation time of 25 min. The rate constants during the TG transesterification with methanol into GL and FAME were estimated by a curve fitting method with simulated curves to the obtained experimental results. The rate constants of [Formula: see text] were estimated to be 0.21, 0.008, 0.23, 0.005, 0.14 and 0.001 L mol(-1)min(-1), respectively. The rate determining step for the TG transesterification with methanol into GL and FAME was the reaction of MG with methanol into GL and FAME.

Mechanistic insight into sonochemical biodiesel synthesis using heterogeneous base catalyst

The beneficial effect of ultrasound on transesterification reaction is well known. Heterogeneous (or solid) catalysts for biodiesel synthesis have merit that they do not contaminate the byproduct of glycerol. In this paper, we have attempted to identify the mechanistic features of ultrasound-enhanced biodiesel synthesis with the base-catalyst of CaO. A statistical design of experiments (Box-Behnken) was used to identify the influence of temperature, alcohol to oil molar ratio and catalyst loading on transesterification yield. The optimum values of these parameters for the highest yield were identified through Response Surface Method (with a quadratic model) and ANOVA. These values are: temperature=62 °C, molar ratio=10:1 and catalyst loading=6 wt.%. The activation energy was determined as 82.3 kJ/mol, which is higher than that for homogeneous catalyzed system (for both acidic and basic catalyst). The experimental results have been analyzed vis-à-vis simulations of cavitation bubble dynamics. Due to 3-phase heterogeneity of the system, the yield was dominated by intrinsic kinetics, and the optimum temperature for the highest yield was close to boiling point of methanol. At this temperature, the influence of cavitation bubbles (in terms of both sonochemical and sonophysical effect) is negligible, and ultrasonic micro-streaming provided necessary convection in the system. The influence of all parameters on the reaction system was found to be strongly inter-dependent.