Ultrasound Technology for Fuel Processing

Ultrasound-assisted technique is well-known for process intensification via chemical and physical changes under the influence of acoustic cavitation. Acoustic cavitation is the phenomenon of nucleation, growth, and collapse of cavitation bubbles into a liquid medium that augments the reaction kinetics and the final process yield. This chapter provides a fundamental and detailed understanding of the acoustic cavitation phenomenon. It includes the history and origin of the acoustic wave and its formation, the concept of cavitation bubbles, bubble nucleation and growth mechanism, cavitation effects, and its types. Numerous process parameters, such as applied frequency, intensity, temperature, dissolved gas content, etc., also directly or indirectly influence the cavitation threshold are also highlighted. Further, the ultrasound's physical and chemical effects involving various chemical and biochemical processes to enhance the process yield are also reviewed. The mode of generation of ultrasound energy and its measurement technique are also briefly discussed. Finally, an overview of modeling and simulation of radial motion of single bubble growth, its oscillation in both ultrasound-assisted and conventional systems, and bubble growth rate under rectified diffusion are also discussed in detail. 

In the last two decades, the subject of hydrogen production by sonolysis (sono-hydrogen) has been widely investigated experimentally and theoretically. This chapter highlights the recent experimental and theoretical progress in the field of sonochemical production of hydrogen. The chapter will be divided into two parts: (i) literature review of the available experimental data (experimental conditions, production yields, influencing factors) and (ii) a numerical analysis of the treated subject, with emphasis on the impact of different energetic terms of the bubble energy balance on the sonochemical yields of hydrogen, all with relation to operational parameters (frequency, intensity of ultrasound, size of bubble population). The chapter will be closed with some perspectives on innovation and sustainability of the process.

The generation of energy from fossil fuels contributes significantly to global warming. This may be mitigated by the use of renewable (bio-based) feedstocks. Second generation biofuels made in biorefineries that utilize agricultural residues and other lignocellulosic wastes as feedstocks reduce the dependency on food crops such as sugar cane (for bioethanol) and oil seeds (for biodiesel). Pre-treatment of lignocellulosic feedstocks is key for ensuring process efficiency from the substrate to the product. There are many pre-treatment methods, and method selection is incumbent on the type of feedstock and the downstream processes required to generate the final product(s). Product yields can be increased by integrating two or three pre-treatment methods. For example, by combining physical and/or chemical pre-treatment with ultrasonication. The content of this chapter is focused on describing various pre-treatment methods that are used to break down and/or hydrolyse lignocellulosic biomass. The discussion extends to both conventional and novel ‘green’ methods and includes the advantages and disadvantages of each method type. Possible solutions for overcoming some of these disadvantages are included.

Generation of a tremendous amount of domestic sewage sludge pushes society to look for an alternate and viable option rather than its direct disposal. The organic-rich constituents of sludge make it an asset rather than waste. Sludge to energy conversion is a feasible option to combat the demand for renewable energy. Resource recovery from waste leads to socio-economic development by reducing fossil dependency with clean and green energy. This chapter mainly focuses on the potential of ultrasound-based techniques for the pretreatment of DSS to enhance bio-crude production. Thermochemical and biochemical treatment are two routes of sludge valorization with their advantages and limitations. Pyrolysis, gasification, combustion, and hydrothermal processing come under thermochemical treatment whereas, anaerobic digestion, aerobic digestion, and fermentation form the basis of biochemical treatment. Thermochemical routes demand energy, whereas biochemical routes are a time-consuming process. Pretreatment of sludge is a viable option to overcome these limitations. Ultrasound pretreatment increases COD solubilization, volatile suspended solids reduction, biogas production during AD, increases the yield and HHV of biocrude during thermochemical treatment, and favors lipid extraction for biodiesel production, and also promotes bioethanol production. Moreover, integrated ultrasound pretreatment positively affects the overall process by reducing the overall cost and increasing bio-crude production.

Increasing demand in terms of fuel and energy with limited fossil fuels forces researchers to develop renewable fuels in sustainable ways. Biodiesel, as an alternative to mineral diesel, has emerged as one of the potential renewable fuels. With an increasing demand for biodiesel, conventional and non-conventional sources of triglycerides were investigated. In terms of future demand, edible and non-edible sources are insufficient to fulfill the requirement and thus microbial oil will be one of the crucial feedstock for biodiesel production. The extraction of lipids from various biomass is one of the crucial steps in the synthesis of biodiesel, which controls the overall production cost. Over the last few years, conventional lipid extraction techniques such as solvent extraction, mechanical processes, and chemical treatments have been explored, however, all these have their own limitations. Moreover, in order to obtain high purity lipids in an economical way, the use of sonication has garnered much attention in extracting the lipids from the microbial biomass because of the shorter process time, the straightforwardness of the process, and the superior quality of products. It may also lead to reducing the use of solvents in the extraction process. The book chapter deals with the limitations of conventional extraction processes of lipids from microbial biomass and the role of ultrasound in efficient and economic operations. Moreover, to lower the production cost, the application of ultrasound in simultaneous extraction and transesterification has been explored.

The application of ultrasound has received immense research attentions in the past few years due to its application in various sectors including dye degradation, pretreatment process, fuel production, bioprocessing, etc. Recently, ultrasonication has been used as a novel bioprocessing tool for enhancing biofuel production from microbial and algal biomass during the fermentation process. Additionally, this technique is also used in many areas of downstream processing such as extraction of lipids from biomass, filtration, and crystallization. The usage of ultrasonication during the fermentation process can result in the enhancement of the transfer of oxygen for aerobic culture, homogenization of biomass for the reduction in clump formation, and faster substrate transfer to biomass which further results in enhanced microbial growth. In view of this, the present chapter mainly focuses on the role of ultrasonication in microbial and algal lipid production and its extraction process with an aim for liquid biofuel production. Additionally, the influence of various operating parameters (power intensity, frequency, duration, reactor design, and kinetics) over the growth, lipid production, and extraction process are also described in detail. 

Biodiesel synthesis from sustainable feedstock is gaining importance in depleting crude oil feedstock and addressing greenhouse emission challenges. A developing country like India has planned to reduce its 10% dependency on crude oil by 2022. Synthesis of biodiesel from sustainable edible feedstock has been a concern for energy vs. food issues. Non-edible feedstock such as Calophyllum innophyllum Linn, Karanja, Jatropha, Waste Cooking oil, waste engine oil, etc., is gaining importance. However, biodiesel synthesis from these feedstocks requires higher processing due to higher initial free fatty content. Intensified techniques can overcome the shortcoming of higher processing requirements. Spectacular effects associated with ultrasound and microwave are beneficial for enhancing the rate of processing. Individual results of microwave and ultrasound have certain limitations. The intensification of biodiesel synthesis is dependent on the removal of heat/mass barriers in the transesterification process. Microwave interaction with polar molecules present in the system enhances the temperature of the reaction at a very intense rate. Microemulsification and the high speed of micro-streaming velocities produced from the ultrasound during interaction with the aqueous phase are incredibly useful for reducing the mass transfer barrier in heterogeneous phases. The synergy of microwave and ultrasound may help enhance the processing rate on a multi-fold basis. The present chapter has presented an overview of microwave and ultrasound energy effects for biodiesel synthesis. Process economics has been discussed for future development in biodiesel synthesis.

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.

Crude oil is one of the prominent resources to fulfill the need of day-to-day life. With few reservoirs, the proper utilization and maximization of oil recovery from existing oil wells are one of the foremost objectives in today’s scenario. Conventionally, the inbuilt pressure and artificial pumping followed by water flooding could result in 30-50% of oil recovery. Thus, to produce the remaining residual crude oil, various enhanced oil recovery methods are adopted, including gas flooding, fire flooding, chemical EOR, etc. Still, oil recovery in large quantities persists to be a challenging task for engineers throughout the world. The major limitation for improving the oil recovery is the water enrichment of the reservoirs, which governs the oil displacement efficiency from the reservoir to the production platform. The application of sound waves in reservoir engineering is an established technology. In seismic surveys, sound waves of various frequencies have been used to predict oil and gas reserves. The advancement of the application of ultrasound irradiation on multiple sectors, including the enhancement of oil recovery from wells, has also been analyzed and tested. The idea behind applying cavitation technology is that the passage of ultrasound waves releases the energy in terms of transient cavitation and allows the formation of the fine emulsion of two immiscible phases. The emulsion enables the improvement of oil movability toward the production well without changing the porosity and permeability of rocks. Thus, the cavitation technique can be applied to estimate oil-water saturation in reservoirs and can further improve the oil recovery factor. This chapter emphasizes the fundamentals of enhanced oil recovery schemes, their mechanisms, and the application of ultrasound irradiation toward improved oil recovery. 

The increase in energy consumption throughout the globe with declining global light-oil reserves necessitates the utilization of heavy crude oil reservoirs to meet the demand. The processing of heavy crude oil in refineries creates extensive loads on thermal and catalytic processes to upgrade them as well as to meet market legislations. Heavy crude oil is rich in excess sulfur and other metals along with high molecular hydrocarbons such as resins, waxes, asphaltenes, heavy aromatics, etc. The separation of lighter hydrocarbon fractions is difficult as well as the processing of vacuum residue also needs attention. The thermal processes break the heavy hydrocarbons into smaller ones which later can be reformed or cracked using catalytic processes. The catalytic processes cannot be employed directly as the impurities will poison catalysts. Thermal processes such as vis-breaking, thermal cracking and coking are highly energy intensive processes and mainly progress through free radical mechanism. The application of ultrasound in the upgradation of heavy crude oil will help in the reduction of energy requirements and load on these thermal processes. The present chapter overviews ultrasound-assisted cavitation as an innovative method to intensify the cracking of asphaltenes and other heavy hydrocarbon molecules existing in the vacuum or atmospheric distillate residual.

In view of environmental concerns, the production of clean energy is one of the most critical issues in modern years to accommodate the growing energy needs of society (domestic usage), agriculture, and industry. Clean energy can be accomplished in several ways. A possible solution to this issue is to use renewable energy sources such as solar, wind, and nuclear power universally. The use of conventional techniques to produce energy by the combustion of fossil fuels has adverse effects on the environment due to the emission of greenhouse gas that contributes to global warming. The conventional method adopted by petroleum refinery industries has not been successful for profound desulphurization to achieve low sulphur contents. To overcome this, several new alternative chemicals, and physical and biological techniques have been developed to meet ultra-low sulphur fuel in the last two decades. Microbial desulphurization is one of the emerging alternative techniques that can remove the organo-sulphur compounds from fuels. The limitation of microbial desulphurization is the slow kinetics and it can be overcome by combining it with other desulphurization processes (hybrid system), such as the ultrasound-assisted processes. This chapter presents a critical account of research in different facets of ultrasound-assisted biodesulphurization. The microbial desulphurization process involves the use of free or immobilized microorganisms over the PU foams and the application of enzymes for desulphurization of DBT. The enzymes or proteins can act as catalysts to degrade sulphur compounds present in fuels. The present chapter also deals with the ultrasound-assisted microbial and enzymatic pathways. The concurrent analysis of experimental results on enzymatic biodesulphurizarion along with simulation results of cavitation bubble dynamics provides more insight into the actual mechanism of ultrasound on microbial and enzymatic desulphurization process.

The sulfur-containing hydrocarbons are the main source of SOx and CO2 gas emissions, which is a threat to the environment for sustainability development. According to the US environment protection agency, the sulfur content should be within the limit of 15 ppm and 30 ppm for diesel and gasoline, respectively. Also, a couple of advanced techniques have been developed so far for the removal of sulfur from fuels. Among these techniques, ultrasound-based advanced oxidation processes have been found to be more efficient and effective for sulfur removal. In this chapter, we have discussed the physical and chemical mechanism of ultrasound based advanced oxidation processes including the influences of process parameters such as pH, the concentration of sulfur, concentration of oxidant, presence of phase transfer catalyst, oxalate ions, etc. Also, several hybrid techniques are discussed with their advantages and disadvantages for obtaining ultra-low sulfur fuel.