A review on the microwave-assisted pyrolysis technique
Introduction
Energy is the most important necessity of humans existence on the earth. It is involved in most economic sectors, such as transportation, agriculture, industry and electricity generation, as well as food [1], [2]. Generally, there are three main categories of energy resources: fossil fuels, nuclear resources, and renewable resources [3]. There are several factors such as population growth and economic growth which affect the quality and quantity of energy use in the world. Recently, the world′s population has been increasing at an enormous rate. Although the growth rate for some nations is negative, the total world population is forecasted to increase by an average rate of 0.9% per year from 6.7 billion in 2008 to 8.5 billion in 2035, as illustrated in Table 1 [4]. Growth domestic product (GDP) affects the amount and type of energy use; the statistics show that GDP growth increases the demand for energy. The real GDP increased at an average rate of 2.4% annually from 2009 to 2011 [5]. Consequently, the total consumption and production of major sources of energy in the world such as liquid fuels, natural gas, and coal have increased in the past decades [6], [7]. On the other hand, fossil fuel consumption is known as the main reason for global warming and climate change. Carbon intensity of energy supplies and energy intensity of economic activities, which are the main factors that influence the carbon dioxide emission levels, are increasing day by day [8], [9]. The limited supply of fossil-based resources, yearly increases in the price of fossil fuels, increasing demand for energy due to rises in the population growth rate and GDP, and finally climate change, global warming, and the growing rate of carbon emission have stimulated interest in finding new alternative and cheaper energy resources. These alternative energy resources comprise renewable sources, such as geothermal energy [10], solar power [11], wind [12], hydropower [13], and biomass [14], [15].
Renewable technologies are considered clean sources of energy derived from natural processes and the optimal use of these resources minimizes environmental impacts and produces minimum secondary wastes; thus they are sustainable resources based on current and future economic and societal needs [16]. The limited supply of petroleum resources, global warming issues, increasing greenhouse gas emissions and increasing yearly prices of petroleum based fuels have motivated scientists to find new alternative and cheap energy resources [17]. One of the main strategies to decrease fossil fuel dependence is based on reducing energy consumption by applying energy saving programs focused on energy demand reduction, as well as using renewable energy sources, not only for large-scale energy production, but also for stand-alone systems as replacements for petroleum based fuels. Therefore, the use of renewable energies in the world will increase in order to have a more sustainable energy mix, reduce greenhouse gas emissions and a lower dependency from fossil fuels [18], [19].
About 14% of the total world energy demand is supplied by renewable energy sources, meaning that they still represent a small part of today′s global energy picture. Renewable energy resources include biomass, hydropower, geothermal, solar, wind and marine energies [16], [20], [21], [22]. Forest origins and wastes, agricultural crops and residues, and animal wastes are some potential natural energy sources of biomass. Three different phases of fuels can be produced from biomass: liquid-based, solid-based, and gas-based [23], [24], [25], [26]. Geothermal resources have been used to generate power in many countries around the world; some of these works related to geothermal power generations are discussed elsewhere [27], [28], [29], [30], [31], [32]. Solar energy has been utilized by many countries and has become more popular as a valuable energy source. It is one of the most important renewable resources with a high potential for solving the energy crisis in the world [33], [34], [35]. Wind energy is one of the greenest renewable resources for electricity generation, via mechanical power in windmills, and pumping water in wind pumps, and also sailing ships; in addition, it does not generate pollution or greenhouse gases [18], [36], [37].
Section snippets
Biomass resources
Biomass is known as living or recently living biological materials which can be used as a source of energy and seems to have a high potential for use as an energy source [38], [39]. Goran et al. believed that biomass has the potential to even be one of the main global primary energy sources during the next century [40]. It is one of the most promising alternative sources which can alleviate the energy crisis, reduce pollution and global warming, and it can contribute to sustainable development
Fundamentals of microwave heating
Von Hippel formulated the basic understanding of macroscopic microwave interactions with matter for the first time [61]. The application of microwave technology in the thermal treatment of biomass has increased from the mid-nineties. This technique not only reduces the energy consumption and processing time, but also enables the use of new chemistry (unique internal heating phenomenon associated with microwave energy). It can also enhance the overall production quality [62], [63].
Microwave
General overview and principles of pyrolysis process
It is essential to select the appropriate technology for the conversion of potential biomass resources into value-added products in order to moderate the energy crises and their consequent environmental degradation. Combustion or incineration (complete oxidation), gasification (partial oxidation), and pyrolysis (thermal degradation in the absence of oxygen) are the three main thermochemical conversion routes for the conversion of biomass resources into heat, electricity, fuels, chemicals, or
Variables affecting the microwave-assisted pyrolysis process
The yield and quality of produced value-added products are affected by some critical parameters in the microwave-assisted pyrolysis process. In order to obtain the highest quality and maximum conversion yield, these variables should be optimized. The most important variables in microwave-assisted pyrolysis reaction processes are listed below:
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Type and size of input biomass/materials
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Moisture and water content of input biomass/materials
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Reaction temperature
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Reaction time (residence time)
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Microwave
Advantages of microwave-assisted pyrolysis technology
Microwave-assisted pyrolysis technology has the potential for energy and cost reduction. It has been proven as a powerful tool in waste reduction, material recovery, and converting biomass and bio wastes into value-added products. However, this method has not been industrialized yet, although it is an attractive option for further industrialization. In this section, the advantages of microwave-assisted pyrolysis technology are summarized as an efficient alternative method to conventional
Future directions
Considerable attention has been given to renewable substitutes for fossil fuels due to the twin problems of fossil fuel depletion and environmental degradation, increasing the population, and tremendous amount of wastes. Both thermochemical and biochemical processes can be applied to upgrade the biomass. Pyrolysis is a thermochemical method of energy recovery from biomass resources and offers higher energy production efficiency and less pollution. It allows higher energy recovery from biomass
Conclusions
In conclusion, pyrolysis is one of the most important bioconversion routes to convert biomass virgin resources, biomass residues and wastes (non-conventional sources), and municipal solid wastes and sewage sludge into value-added products. It involves the well-established thermochemical decomposition of biomass (hydrocarbon or organic materials) at elevated temperatures in the absence of oxygen, and can provide a variety of energy-dense products in three different phases: solid, liquid, and
Acknowledgement
The authors appreciate the financial assistance from New Brunswick Soil and Crop Improvement Association, New Brunswick Agricultural Council, Agriculture and Agri-Food Canada.
References (144)
- et al.
A review on prospect of Jatropha curcas for biodiesel in Indonesia
Renewable and Sustainable Energy Reviews
(2011) - et al.
Technical aspects of production and analysis of biodiesel from used cooking oil—a review
Renewable and Sustainable Energy Reviews
(2009) - et al.
A comprehensive review on biodiesel as an alternative energy resource and its characteristics
Renewable and Sustainable Energy Reviews
(2012) - et al.
A review on emissions and mitigation strategies for road transport in Malaysia
Renewable and Sustainable Energy Reviews
(2011) Geothermal energy for the benefit of the people
Renewable and Sustainable Energy Reviews
(2001)- et al.
A review of solar thermal technologies
Renewable and Sustainable Energy Reviews
(2010) - et al.
A review of wind energy technologies
Renewable and Sustainable Energy Reviews
(2007) - et al.
An overview of renewable energy in Spain. The small hydro-power case
Renewable and Sustainable Energy Reviews
(2005) Renewable energy and sustainable development: a crucial review
Renewable and Sustainable Energy Reviews
(2000)- et al.
Role of renewable energy sources in environmental protection: a review
Renewable and Sustainable Energy Reviews
(2011)
Optimization methods applied to renewable and sustainable energy: a review
Renewable and Sustainable Energy Reviews
Promotional policy for renewable energy development in Taiwan
Renewable and Sustainable Energy Reviews
On the physics of power, energy and economics of renewable electric energy sources—Part I
Renewable Energy
Effects of energy policies on industry expansion in renewable energy
Renewable Energy
Opportunities and challenges for renewable energy policy in China
Renewable and Sustainable Energy Reviews
Assessment of renewable energy resources potential for electricity generation in Bangladesh
Renewable and Sustainable Energy Reviews
Distribution, utilization structure and potential of biomass resources in rural China: with special references of crop residues
Renewable and Sustainable Energy Reviews
Renewable energy resources and technologies practice in Bangladesh
Renewable and Sustainable Energy Reviews
Methods and tools to evaluate the availability of renewable energy sources
Renewable and Sustainable Energy Reviews
World geothermal power generation in the period 2001–2005
Geothermics
Overview of Kizildere geothermal power plant in Turkey
Energy Conversion and Management
Geothermal energy potential for power generation in Turkey: a case study in Simav, Kutahya
Renewable and Sustainable Energy Reviews
The Bad Blumau geothermal project: a low temperature, sustainable and environmentally benign power plant
Geothermics
Evaluating the level and nature of sustainable development for a geothermal power plant
Renewable and Sustainable Energy Reviews
Geothermal power production in future electricity markets—a scenario analysis for Germany
Energy Policy
A review on global solar energy policy
Renewable and Sustainable Energy Reviews
On the wind energy in Turkey
Renewable and Sustainable Energy Reviews
Wind energy status in renewable electrical energy production in Turkey
Renewable and Sustainable Energy Reviews
A review on energy scenario and sustainable energy in Indonesia
Renewable and Sustainable Energy Reviews
Renewable energy sources for clean and sustainable energy policies in Turkey
Renewable and Sustainable Energy Reviews
The contribution of biomass in the future global energy supply: a review of 17 studies
Biomass and Bioenergy
Biomass energy in industrialised countries—a view of the future
Forest Ecology and Management
Energy production from biomass pyrolysis: a new coefficient of pyrolytic valorisation
Fuel
Environmental systems analysis of biogas systems-Part I: Fuel-cycle emissions
Biomass and Bioenergy
Biodiesel production by transesterification of duck tallow with methanol on alkali catalysts
Biomass and Bioenergy
Global warming and renewable energy sources for sustainable development: a case study in Turkey
Renewable and Sustainable Energy Reviews
Renewable energy policies and initiatives for a sustainable energy future in Malaysia
Renewable and Sustainable Energy Reviews
Possibilities of application of waste wood biomass as an energy source in Vojvodina
Renewable and Sustainable Energy Reviews
Conventional and microwave induced pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas
Journal of Analytical and Applied Pyrolysis
Fast pyrolysis of rice straw, sugarcane bagasse and coconut shell in an induction-heating reactor
Journal of Analytical and Applied Pyrolysis
Bioenergy and products from thermal pyrolysis of rice straw using plasma torch
Bioresource Technology
Synthetic fuel production from tea waste: characterisation of bio-oil and bio-char
Fuel
Studies on pyrolysis of wheat straw residues from ethanol production by solid-state fermentation
Journal of Analytical and Applied Pyrolysis
Pyrolysis of wheat straw-derived organosolv lignin
Journal of Analytical and Applied Pyrolysis
Pyrolysis of sewage sludge and use of pyrolysis coke
Journal of Analytical and Applied Pyrolysis
Study of the pyrolysis liquids obtained from different sewage sludge
Journal of Analytical and Applied Pyrolysis
Sewage sludge pyrolysis for liquid production: a review
Renewable and Sustainable Energy Reviews
Recycling of auto shredder residue
Journal of Hazardous Materials
Microwave heating processes involving carbon materials
Fuel Processing Technology
A review on microwave-assisted production of biodiesel
Renewable and Sustainable Energy Reviews
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