Biodiesel resources and production technologies – A review

The environmental concern and availability of fuels are greatly affecting the trends of fuels for transportation vehicles. Biodiesel is one of the options as alternative transport fuel. This can be produced from straight vegetable oils (SVOs), oils extracted from various plant species and animal fats. Amongst many resources, availability and cost economy are the major factors affecting the large scale production of the biodiesels. The transesterification is one of the production processes for biodiesel, but incomplete esterification of all fatty acids in the starting material, lengthy purification methods such as water washing, relatively long reaction times, contamination and separation difficulties associated with co-production of glycerol and saponification of the starting material under certain reaction conditions are still being major challenges in the biodiesel production. Technological advancement and enhanced production methods are the demand of present time for large scale and sustainable production of biodiesel. In the present paper, comprehensive review on its production process, feed stock and its applications have been made. From many case studies it was concluded that engine performance with B20 biodiesel blends, and mineral diesel were found comparable.     

Biofuels Bonanza?: Exploring community perceptions of the promises and perils of biofuels production

While the expansion of the biofuels industry has received scholarly attention with respect to environmental and food security concerns, little research has explored the impacts of biofuels industry on local communities where ethanol plants are located. Drawing on sociology of networks and flows theory to situate expansion of the industry globally, this paper uses a community case study approach to examine local community perceptions of benefits and burdens of the ethanol industry. Data from community level surveys, individual and focus group interviews in three case study communities in Iowa and Kansas in the Midwestern region of the United States are utilized to explore community perceptions. Results show that community members believe that ethanol plants have brought modest economic benefits to their community. Increased traffic and water competition were two areas of concern identified by residents with respect to local ethanol plants, but other environmental impacts were not prominently identified by community members. Widespread concerns were expressed about future viability of the ethanol industry and the devastating impacts that future declines in the industry would have on communities. This research highlights the social vulnerabilities that place-bound communities in biofuels regions are experiencing.     

Technical aspects of production and analysis of biodiesel from used cooking oil—A review

The increasing awareness of the depletion of fossil fuel resources and the environmental benefits of biodiesel fuel has made it more attractive in recent times. The cost of biodiesel, however, is the major hurdle to its commercialization in comparison to petroleum-based diesel fuel. The high cost is primarily due to the raw material, mostly neat vegetable oil. Used cooking oil is one of the economical sources for biodiesel production. However, the products formed during frying, can affect the transesterification reaction and the biodiesel properties. This paper attempts to review various technological methods of biodiesel production from used cooking oil. The analytical methods for high quality biodiesel fuel from used cooking oil like GC, TLC, HPLC, GPC and TGA have also been summarized in this paper. In addition, the specifications provided by different countries are presented. The fuel properties of biodiesel fuel from used cooking oil were also reviewed and compared with those of conventional diesel fuel.     

Sustainability of the four generations of biofuels – A review

Biofuel has emerged as an alternative source of energy to reduce the emissions of greenhouse gases in the atmosphere and combat global warming. Biofuels are classified into first, second, third and fourth generations. Each of the biofuel generations aims to meet the global energy demand while minimizing environmental impacts. Sustainability is defined as meeting the needs of the current generations without jeopardizing the needs of future generations. The aim of sustainability is to ensure continuous growth of the economy while protecting the environment and societal needs. Thus, this paper aims to evaluate the sustainability of these four generations of biofuels. The objectives are to compare the production of biofuel, the net greenhouse gases emissions, and energy efficiency. This study is important in providing information for the policymakers and researchers in the decision-making for the future development of green energy. Each of the biofuel generations shows different benefits and drawbacks. From this study, we conclude that the first generation biofuel has the highest biofuel production and energy efficiency, but is less effective in meeting the goal of reducing the greenhouse gases emission. The third generation biofuel shows the lowest net greenhouse gases emissions, allowing the reduction of greenhouse gases in the atmosphere. However, the energy required for the processing of the third generation biofuel is higher and, this makes it less environmentally friendly as fossil fuels are used to generate electricity. The third and fourth generation feedstocks are the potential sustainable source for the future production of biofuel. However, more studies need to be done to find an alternative low cost for biofuel production while increasing energy efficiency.     

A systematic review on green hydrogen for off-grid communities –technologies,advantages, and limitations

Approximately 3.5 billion people worldwide lack reliable and sustainable energy services, mostly in poor off-grid areas of developing countries. Variable renewable energies are options for these communities. However, their high intermittence and complex storage limit their benefits. Green hydrogen research has advanced significantly to the point that some scholars consider it the future's clean energy solution. Multiple applications within the transport, electricity and storage sectors have been envisaged. However, little has been discussed about its potential to provide affordable, dependable, and sustainable energy for the world's poorest. This paper addresses this gap by analyzing the literature on green hydrogen research, its technologies, and its potential implementation in off-grid communities. First, a quantitative bibliometric approach is developed to size and make sense of the green hydrogen research literature. Then, an in-depth review is performed following Dawood et al.'s four-corners framework, categorizing hydrogen research into production, storage, use, and safety. This systematic review unveils green hydrogen's most promising technologies for off-grid applications. It identifies their advantages, limitations, and barriers to widespread dissemination. Thus, this study's primary contributions lie in determining the relationship between published works and identifying gaps in considering green hydrogen as a viable energy alternative for the poor.     

Biofuels,electrofuels, electric or hydrogen?: A review of current and emerging sustainable aviation systems

Climate neutrality is becoming a core long-term competitiveness asset within the aviation industry, as demonstrated by the several innovations and targets set within that sector, prior to and especially after the COVID-19 crisis. Ambitious timelines are set, involving important investment decisions to be taken in a 5-years horizon time. Here, we provide an in-depth review of alternative technologies for sustainable aviation revealed to date, which we classified into four main categories, namely i) biofuels, ii) electrofuels, iii) electric (battery-based), and iv) hydrogen aviation. Nine biofuel and nine electrofuel pathways were reviewed, for which we supply the detailed process flow picturing all input, output, and co-products generated. The market uptake and use of these co-products was also investigated, along with the overall international regulations and targets for future aviation. As most of the inventoried pathways require hydrogen, we further reviewed six existing and emerging carbon-free hydrogen production technologies. Our review also details the five key battery technologies available (lithium-ion, advanced lithium-ion, solid-state battery, lithium-sulfur, lithium-air) for aviation. A semi-quantitative ranking covering environmental-, economic-, and technological performance indicators has been established to guide the selection of promising routes. The possible configuration schemes for electric propulsion systems are documented and classified as: i) battery-based, ii) fuel cell-based and iii) turboelectric configurations. Our review studied these four categories of sustainable aviation systems as modular technologies, yet these still have to be used in a hybridized fashion with conventional fossil-based kerosene. This is among others due to an aromatics content below the standardized requirements for biofuels and electrofuels, to a too low energy storage capacity in the case of batteries, or a sub-optimal gas turbine engine in the case of cryogenic hydrogen. Yet, we found that the latter was the only available option, based on the current and emerging technologies reviewed, for long-range aviation completely decoupled of fossil-based hydrocarbon fuels. The various challenges and opportunities associated with all these technologies are summarized in this study.     

A systematic literature review of societal acceptance and stakeholders’ perception of hydrogen technologies

This paper presents the results of a systematic review that analysed the literature on factors influencing societal acceptance and stakeholders’ perceptions of hydrogen related technologies. This study found that the most influencing factors include prior knowledge, perceived cost/risks, environmental knowledge, higher education and income, personal and distributive benefits, infrastructure availability and close proximity to hydrogen facilities. There was low hydrogen awareness in more than 60% of the countries analysed in the reviewed studies. Although stakeholders had diverse perceptions, there was agreement that infrastructure availability, affordability, local community engagement, regional skill capability development, preservation of biodiversity, and safety and distributive benefits to the community were essential for a successful hydrogen industry. Future research could examine consumer acceptance at different geographical scales, analyse pre-and post-hydrogen project implementation, and social impact of hydrogen infrastructure on local communities. We also recommend diversifying hydrogen research projects and investigating the policy and regulatory arrangements for community-owned hydrogen projects.     

CO2 capture and separation technologies for end-of-pipe applications – A review

Carbon capture from point source emissions has been recognized as one of several strategies necessary for mitigating unfettered release of greenhouse gases (GHGs) into the atmosphere. To keep GHGs at manageable levels, large decreases in CO₂ emissions through capturing and separation will be required. This article reviews the possible CO₂ capture and separation technologies for end-of-pipe applications. The three main CO₂ capture technologies discussed include post-combustion, pre-combustion and oxyfuel combustion techniques. Various separation techniques, such as chemical absorption, physical absorption, physical adsorption, cryogenics, membrane technology, membranes in conjunction with chemical absorption and chemical-looping combustion (CLC) are also thoroughly discussed. Future directions are suggested for application by oil and gas industry. Sequestration methods, such as geological, mineral carbonation techniques, and ocean dump are not covered in this review.     

Technoeconomics of large-scale clean hydrogen production – A review

Hydrogen is widely used in many industries, yet its role in the clean energy transition goes beyond being an element of these industries. Near-term practical large-scale clean hydrogen production can be made available by involving nuclear, solar, and other renewable energy sources in the process of hydrogen production, and coupling their energy systems to sustainable carbon-free hydrogen technologies. This requires further investigation and assessment of the different alternatives to achieve clean hydrogen using these pathways. This paper assesses the technoeconomics of promising hydrogen technologies that can be coupled to nuclear and solar energy systems for large-scale hydrogen production. It also provides an overview of the design, status and advances of these technologies.     

Analytical evaluation of different carbon sources and growth stimulators on the biomass and lipid production of Chlorella vulgaris – Implications for biofuels

The key challenges in lipid production from marine microalgae include the selection of appropriate strain, optimization of the culture conditions and enhancement of biolipid yield. This study is aimed at evaluating the optimal harvest time and effect of chlorella growth factor (CGF) extract, carbon sources and phytohormones on the biomass and lipid production in Chlorella vulgaris. CGF, extracted using hot water from Chlorella has been reported to possess various medicinal properties. However, in the present study, for the first time in C. vulgaris, CGF was found as a best growth stimulator by enhancing the biomass level (1.208 kg m⁻³) significantly on day 5. Gibberellin and citrate augmented the biomass by 0.935 kg m⁻³ and 1.025 kg m⁻³. Combination of CGF and phytohormones were more effective than CGF and carbon sources. Analysis of fatty acid methyl esters indicated that the ratio of saturated to unsaturated fatty acids is higher in cytokinin, abscisic acid and CGF, and are also rich in short chain carbon atoms, ideal criteria for biodiesel. Nitrogen starvation favoured synthesis of more unsaturated fatty acids than saturated. This study shows that CGF enhances the biomass and lipid significantly and thus can be used for large scale biomass production.     

LCA of renewable energy for electricity generation systems—A review

Sustainable development requires methods and tools to measure and compare the environmental impacts of human activities for various products (goods and services). Providing society with goods and services contributes to a wide range of environmental impacts. Environmental impacts include emissions into the environment and the consumption of resources as well as other interventions such as land use, etc. Life cycle assessment (LCA) is a technique for assessing environmental loads of a product or a system. The aim of this paper is to review existing energy and CO₂ life cycle analyses of renewable sources based electricity generation systems.The paper points out that carbon emission from renewable energy (RE) systems are not nil, as is generally assumed while evaluating carbon credits. Further the range of carbon emissions from RE systems have been found out from existing literature and compared with those from fossil fuel based systems, so as to assist in a rational choice of energy supply systems.     

Spinel electrodes for lithium batteries — A review

This paper briefly reviews recent electrochemical data of several transition-metal oxide and sulphide spinel compounds of general formula A[B₂]X₄ that have been employed as cathode materials in both room-temperature and high-temperature (400 °C) lithium cells. Particular attention is given to the performance of the oxide spinels M₃O₄ (M  Fe, Co, Mn) that have like A- and B-type cations, the lithium spinels Li[M₂]O₄ (M  Ti, V, Mn) and LiFe₅O₈, and the thiospinels CuCo₂S₄ and CuTi₂S₄. Reaction processes and the structural characteristics of the reaction products are highlighted.     

Combustion,emission and engine performance characteristics of used cooking oil biodiesel—A review

As the environment degrades at an alarming rate, there have been steady calls by most governments following international energy policies for the use of biofuels. One of the biofuels whose use is rapidly expanding is biodiesel. One of the economical sources for biodiesel production which doubles in the reduction of liquid waste and the subsequent burden of sewage treatment is used cooking oil (UCO). However, the products formed during frying, such as free fatty acid and some polymerized triglycerides, can affect the transesterification reaction and the biodiesel properties. This paper attempts to collect and analyze published works mainly in scientific journals about the engine performance, combustion and emissions characteristics of UCO biodiesel on diesel engine. Overall, the engine performance of the UCO biodiesel and its blends was only marginally poorer compared to diesel. From the standpoint of emissions, NOx emissions were slightly higher while un-burnt hydrocarbon (UBHC) emissions were lower for UCO biodiesel when compares to diesel fuel. There were no noticeable differences between UCO biodiesel and fresh oil biodiesel as their engine performances, combustion and emissions characteristics bear a close resemblance. This is probably more closely related to the oxygenated nature of biodiesel which is almost constant for every biodiesel (biodiesel has some level of oxygen bound to its chemical structure) and also to its higher viscosity and lower calorific value, which have a major bearing on spray formation and initial combustion.     

Multi-scale complexities of solid acid catalysts in the catalytic fast pyrolysis of biomass for bio-oil production – A review

Despite remarkable progress in catalytic fast pyrolysis, bio-oil production is far from commercialization because of multi-scale challenges, and major constraints lie with catalysts. This review aims to introduce major constraints of acid catalysts and simultaneously to find out possible solutions for the production of fuel-grade bio-oil in biomass catalytic fast pyrolysis. The catalytic activities of several materials which act as acid catalysts and the impacts of Bronsted and Lewis acid site on the formation of aromatic hydrocarbons are discussed. Considering the complexity of catalytic fast pyrolysis of biomass with acid catalysts, in-depth understandings of cracking, deoxygenation, carbon-carbon coupling, and aromatization for both in-situ and ex-situ configurations are emphasized. The limitation of diffusion along with coke formation, active site poisoning, thermal/hydrothermal deactivation, sintering, and low aromatics in bio-oil are process complexities with solid acid catalysts. The economic viability of large-scale bio-oil production demands progress in catalyst modification or/and developing new catalysts. The potential of different catalyst modification strategies for an adequate amount of acid sites and pore size confinement is discussed. By critically evaluating the challenges and potential of catalyst modification techniques, multi-functional catalysts may be an effective approach for selective conversion of biomass to bio-oil and chemicals through catalytic fast pyrolysis. This review offers a scientific reference for the research and development of catalytic fast pyrolysis of biomass.     

Safety comparisons of various gas source deposition technologies for large-scale production of III–V solar cells

III–V solar cells offer potential advantages in efficiency and cost for making photovoltaic power systems economic in large-scale utility applications. Relatively safe manufacturing technologies have been developed to fabricate III–V electronic devices but the scale involved in utility power has introduced new safety challengs. Gas source fabrication offers large-scale manufacturing advantages including the ease of gas source materials handling and control. However, the present gas source technologies such as metal-organic chemical vapor deposition (MOCVD) and metal-organic molecular beam epitaxy (MOMBE) involve the potential for significant injury from the toxic materials used. This risk can be greatly reduced by advanced technology vacuum chemical epitaxy (VCE). MOCVD has the problems of low materials utilization with large quantities of toxic effluent, fragile quartz components, cold chamber walls that rapidly build-up residues, no load lock for personnel protection and the potential for hydrogen gas explosions. However MOCVD has been scaled up to medium production levels of III–V solar cells. In contrast MOMBE has the safety advantages of rugged metal chamber walls, load locks and higher utilization of some of the source gases. But MOMBE rapidly builds up toxic residues on cold surfaces and it is not readily scaleable to utility level production volumes. VCE combines many of the best characteristics of MOCVD and MBE. These include higher utilization of all the source materials, hot chamber walls with low residue build-up rates, rugged metal outer chamber walls, load locks and an inherent scalability to large production levels.     

Hydrogen,ethylene and power production from bioethanol: Ready for the renewable market?

The economic sustainability of renewable based sources is a matter of debate and the technology is changing very fast. We here considered three examples of exploitation of bioethanol as renewable source: a) centralised hydrogen prodution; b) heat and power cogeneration (residential scale); c) ethylene production. Bioethanol can be a suitable starting material for the production of H₂, as fuel or chemical, or syngas. After designing the process and the implementation of kinetic expressions based on experimental data collected in our lab or derived from the literature, an economic evaluation and sensitivity analysis allowed to assess the economic sustainability of hydrogen production and purification by the steam reforming of bioethanol. The attention was mainly put on diluted bioethanol solutions, easy to purify and cost effective. The centralised hydrogen production from bioethanol was considered cost effective at least starting from diluted bioethanol from first generation crops. When dowscaling the hydrogen production and purification unit to feed a 5 kW fuel cell, the most undetermined item was the fuel cell cost, since no acclarate market price is still available.Finally, ethylene market is steadily increasing by ca. 4% each year due to economic growth. The demand for renewable ethylene, as well as the increasing oil price experienced in the recent past, suggested the development of alternative routes to ethylene. Based on the increasing availability of ethanol form renewable biomass, bioethanol-to-bioethylene processes have been recently designed, finding economic sustainability, at the moment, in Brazil.     

Information and communication technologies – A new round of household electrification

Information and communication technologies (ICTs) increasingly permeate everyday life in industrialized societies. The aim of this paper is to explore ICT-related transformations of everyday practices and discuss the implications, particularly for residential electricity consumption. The present socio-technical changes are seen in a historical perspective, and it is argued that the integration of ICT into everyday practices can be seen as a new round of household electrification, comparable to earlier rounds that also led to higher electricity consumption. A case study carried out in Denmark in 2007–2008 explores the present changes in everyday life. Based on qualitative interviews, the study focuses on people's ways of integrating ICTs into their everyday practices, on any significant changes in these practices, and on the influence of the changed practices on electricity consumption. The paper concludes with a discussion on the implications for energy policy.     

Environmental evaluation of hydrogen production employing innovative chemical looping technologies – A Romanian case study

A cradle-to-gate life cycle assessment is carried out to evaluate the environmental impact of producing 1 kg of hydrogen implementing innovative chemical looping technologies: chemical looping hydrogen production (CLH), sorption enhanced reforming (SER), and sorption enhanced chemical looping reforming (SECLR). The performance of the looping technologies is compared against conventional hydrogen production without and with CO₂ capture, as well as against green hydrogen production in order to determine the more environmentally-friendly option. Comparing the looping technologies with the reference blue hydrogen production it shows that CLH has a lower environmental burden, presenting smaller values in 9 out of 12 environmental impact indicators. If we confront the looping technologies against each other, CLH shows better performance in 11 out of 12 environmental indicators. As expected, green hydrogen has a much smaller overall environmental impact with the exception of human toxicity, terrestrial ecotoxicity and mineral depletion.     

Renewable biohydrogen production from straw biomass – Recent advances in pretreatment/hydrolysis technologies and future development

Straw is an abundant natural bioresource, especially in developing and agricultural countries. Bio-hydrogen production from this renewable biomass through biological methods is an active research area. Because of its distinctive characteristic of being rich in cellulose, straw has been extensively considered as a promising raw material for clean energy production. In this paper, the recent progress of bio-hydrogen production from straw was reviewed with the emphasis on the advances in pretreatment and hydrolysis technologies. The future development of straw-based biohydrogen production was also analyzed. Based on the physicochemical properties of straw biomass and mechanisms of bio-hydrogen fermentation, various pretreatment procedures have been developed to make the straw substrate more available for hydrogen-producing bacteria to realize large-scale bio-hydrogen production from straw. This review summarized the recent technologies of straw pretreatment and hydrolysis as well as elaborated on the bottlenecks in the field of straw biotransformation in great detail. Furthermore, based on the current technology status and potential, the challenges, prospects and future directions of the production methods were further proposed.     

Application of kinetic models in dark fermentative hydrogen production–A critical review

Kinetic modeling could be viewed as an important step in developing a bioprocess, since models can be used in process control, reducing costs and optimizing processes. In the present study, the application of kinetic models in dark fermentative hydrogen production has been investigated. A wide variety of kinetic models are addressed and compared regarding their accuracy to fit the data. This literature survey indicates that the modified Gompertz was extensively used to describe the production of hydrogen, organic acids and alcohols, substrate degradation, and biomass growth. The development of kinetic models can assist researchers to identify the most important variables, facilitate future research, and maximize hydrogen production.