A comprehensive review on lignocellulosic biomass biorefinery for sustainable biofuel production

The increasingly severe environmental pollution and energy shortage issues have demanded the production of renewable and sustainable biofuels to replace conventional fossil fuels. Lignocellulosic (LC) biomass as an abundant feedstock for second-generation biofuel production can help overcome the shortcomings of first-generation biofuels related to the “food versus fuel” debate and feedstock availability. Embracing the “circular bioeconomy” concept, an integrated biorefinery platform of LC biomass can be performed by employing different conversion technologies to obtain multiple valuable products. This review provides an overview of the principles and applications of thermochemical processes (pyrolysis, torrefaction, hydrothermal liquefaction, and gasification) and biochemical processes (pretreatment technologies, enzyme hydrolysis, biochemical conversion processes) involved in LC biomass biorefinery for potential biofuel applications. The engineering perspective of LC biofuel production on separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP) were also discussed.     

Trends in bioconversion of lignocellulose: Biofuels,platform chemicals & biorefinery concept

Bioconversion of renewable lignocellulosic biomass to biofuel and value added products are globally gaining significant prominence. Market forces demonstrate a drive towards products benign to natural environment increasing the importance of renewable materials. The development of second generation bioethanol from lignocellulosic biomass serves many advantages from both energy and environmental point of views. Biomass an inexpensive feedstock considered sustainable and renewable, is an option with the potential to replace a wide diversity of fossil based products within the energy sector; heat, power, fuels, materials and chemicals. Lignocellulose is a major structural component of woody and non-woody plants and consists of cellulose, hemicellulose and lignin. The effective utilization of all the three components would play a significant role in the economic viability of cellulosic ethanol. Biomass conversion process involves five major steps, choice of suitable biomass, effective pretreatment, production of saccharolytic enzymes-cellulases and hemicellulases, fermentation of hexoses and pentoses and downstream processing. Within the context of production of fuels from biomass, pretreatment has come to denote processes by which cellulosic biomass is made amenable to the action of hydrolytic enzymes. The limited effectiveness of current enzymatic process on lignocellulose is thought to be due to the relative difficulties in pretreating the feedstocks. The present review is a comprehensive state of the art describing the advancement in recent pretreaments, metabolic engineering approaches with special emphasis on the latest developments in consolidated biomass processing, current global scenario of bioethanol pilot plants and biorefinery concept for the production of biofuels and bioproducts.     

Biorefineries: Current activities and future developments

This paper reviews the current refuel valorization facilities as well as the future importance of biorefineries. A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass. Biorefineries combine the necessary technologies of the biorenewable raw materials with those of chemical intermediates and final products. Char production by pyrolysis, bio-oil production by pyrolysis, gaseous fuels from biomass, Fischer–Tropsch liquids from biomass, hydrothermal liquefaction of biomass, supercritical liquefaction, and biochemical processes of biomass are studied and concluded in this review. Upgraded bio-oil from biomass pyrolysis can be used in vehicle engines as fuel.     

Crop residues: applications of lignocellulosic biomass in the context of a biorefinery

Interest in lignocellulosic biomass conversion technologies has increased recently because of their potential to reduce the dependency on non-renewable feedstocks. Residues from a variety of crops are the major source of lignocellulose, which is being produced in increasingly large quantities worldwide. The commercial exploitation of crop residues as feedstocks for biorefineries which could be used to produce a variety of goods such as biofuels, biochemicals, bioplastics, and enzymes is an attractive approach not only for adding value to residues but also for providing renewable products required by the expanding bioeconomy market. Moreover, the implementation of biorefineries in different regions has the potential to add value to the specific crop residues produced in the region. In this review, several aspects of crop residue application in biorefineries are discussed, including the role of crop residues in the bioeconomy and circular economy concepts, the main technical aspects of crop residue conversion in biorefineries, the main crop residues generated in different regions of the world and their availability, the potential value-added bioproducts that can be extracted or produced from each crop residue, and the major advantages and challenges associated with crop residue utilization in biorefineries. Despite their potential, most biomass refining technologies are not sufficiently advanced or financially viable. Several technical obstacles, especially with regard to crop residue collection, handling, and pre-treatment, prevent the implementation of biorefineries on a commercial scale. Further research is needed to resolve these scale-up-related challenges. Increased governmental incentives and bioeconomic strategies are expected to boost the biorefinery market and the cost competitiveness of biorefinery products.     

Integrating social and value dimensions into sustainability assessment of lignocellulosic biofuels

The paper clarifies the social and value dimensions for integrated sustainability assessments of lignocellulosic biofuels. We develop a responsible innovation approach, looking at technology impacts and implementation challenges, assumptions and value conflicts influencing how impacts are identified and assessed, and different visions for future development. We identify three distinct value-based visions. From a techno-economic perspective, lignocellulosic biofuels can contribute to energy security with improved GHG implications and fewer sustainability problems than fossil fuels and first-generation biofuels, especially when biomass is domestically sourced. From socio-economic and cultural-economic perspectives, there are concerns about the capacity to support UK-sourced feedstocks in a global agri-economy, difficulties monitoring large-scale supply chains and their potential for distributing impacts unfairly, and tensions between domestic sourcing and established legacies of farming. To respond to these concerns, we identify the potential for moving away from a one-size-fits-all biofuel/biorefinery model to regionally-tailored bioenergy configurations that might lower large-scale uses of land for meat, reduce monocultures and fossil-energy needs of farming and diversify business models. These configurations could explore ways of reconciling some conflicts between food, fuel and feed (by mixing feed crops with lignocellulosic material for fuel, combining livestock grazing with energy crops, or using crops such as miscanthus to manage land that is no longer arable); different bioenergy applications (with on-farm use of feedstocks for heat and power and for commercial biofuel production); and climate change objectives and pressures on farming. Findings are based on stakeholder interviews, literature synthesis and discussions with an expert advisory group.     

Hydrocarbon plant—New source of energy for future

The development of alternative sources for energy and chemicals, particularly the use of plant biomass as a renewable source for fuel or chemical feedstocks, has received much recent attention. This paper attempts to review the work carried out by many workers on evaluation of some plant materials as source of energy and chemical feedstocks and the possibilities of producing hydrocarbon and related chemical products, directly or indirectly. Also an exploratory work carried out at Regional Research Laboratory, Jorhat is discussed. Some future directions, which need to be considered to promote development of these petrocrops, are suggested.     

Biorefineries from the perspective of sustainability: Feedstocks, products, and processes

Today, sustainability is the buzzword in the developmental parlance. This has brought the issue of availability and utilization of energy into sharp focus. There is an urgent need to find viable alternative to fossils, mainly petroleum. It not only provides the major share of our present energy needs but also feeds the organic chemicals industry with vital raw materials. Among many alternative energy sources being explored biomass is the only one that has the potential for such dual application. Comprehensive yet judicious exploitation of biomass is, therefore crucial. The emerging concept of biorefineries is important in this context which advocates multiprocess and multiproduct biomass based industries. But everything green need not always be clean and sustainable as populism often makes it to be. Needless to say, the choices of feedstocks, processes as well as product mix are many. There is a need to critically examine them. This paper presents a status review of biorefineries from the stand point of feedstocks, products and processes.     

Are plants the new oil? Responsible innovation,biorefining and multipurpose agriculture

Bioenergy is seen as one of the options for industrialised countries to wean themselves off fossil fuels. However bioenergy, transport biofuels in particular, has faced considerable environmental and social controversies. Biorefining has been proposed in the UK and Denmark to address these concerns by using biomass efficiently for multiple purposes (food, feed, fuel, chemicals). Drawing from frameworks on responsible innovation, this paper opens up the implicit assumptions within the biorefinery concept about how biomass should be produced.Stakeholder interviews show that the biorefinery concept is framed within an industrial agricultural paradigm that aims to overcome controversies through large-scale production stimulated by biotechnology innovation. By contrast, an “alternative agriculture” paradigm envisions sustainable multipurpose biomass production in terms of on-farm nutrient and energy cycling and local, smaller scale production. However, there is a potential overlap through the concept of quality industrial biomass production. These three visions provide different perspectives on the bioeconomy in terms of the differences between biomass and fossil fuels; and where biomass should come from. Policy development for bioenergy must reckon with these different visions in innovation pathways for multipurpose biomass.     

Commercialization potential of microalgae for biofuels production

Microalgae feedstocks are gaining interest in the present day energy scenario due to their fast growth potential coupled with relatively high lipid, carbohydrate and nutrients contents. All of these properties render them an excellent source for biofuels such as biodiesel, bioethanol and biomethane; as well as a number of other valuable pharmaceutical and nutraceutical products. The present review is a critical appraisal of the commercialization potential of microalgae biofuels. The available literature on various aspects of microalgae, e.g. its cultivation, life cycle assessment, and conceptualization of an algal biorefinery, has been scanned and a critical analysis has been presented. A critical evaluation of the available information suggests that the economic viability of the process in terms of minimizing the operational and maintenance cost along with maximization of oil-rich microalgae production is the key factor, for successful commercialization of microalgae-based fuels.     

Dual role of microalgae: Phycoremediation of domestic wastewater and biomass production for sustainable biofuels production

Global threats of fuel shortages in the near future and climate change due to green-house gas emissions are posing serious challenges and hence and it is imperative to explore means for sustainable ways of averting the consequences. The dual application of microalgae for phycoremediation and biomass production for sustainable biofuels production is a feasible option. The use of high rate algal ponds (HRAPs) for nutrient removal has been in existence for some decades though the technology has not been fully harnessed for wastewater treatment. Therefore this paper discusses current knowledge regarding wastewater treatment using HRAPs and microalgal biomass production techniques using wastewater streams. The biomass harvesting methods and lipid extraction protocols are discussed in detail. Finally the paper discusses biodiesel production via transesterification of the lipids and other biofuels such as biomethane and bioethanol which are described using the biorefinery approach.     

High temperature production of hydrogen: Assessment of non-renewable resources technologies and emerging trends

Conventional productions of large volume of hydrogen from fossil based resources continue to play a key role in the hydrogen economy. This paper recalls the contribution of these conventional technologies with new technological development and researches. Providing gradual integration of renewable solutions into large-scale production, some emerging developments in the use of the renewable based feedstock and energy resources in reforming processes in order to bridge the gaps from conventional use of fossil feedstock to improve various conversion processes were discussed. This paper focuses on high temperature process technologies for producing hydrogen via non-renewable resources and various industrial technologies and processes (700 °C and above) for the beneficiation of the available carbonaceous feedstocks like natural gas, other hydrocarbons (other fossil based options), coal etc. The paper concludes with the analysis of some development gaps in hydrogen production from various resources, which interplays between the renewable and non-renewable resources as well as likely future trends that should be expected in the hydrogen market in the next decades.     

Crop residues as raw materials for biorefinery systems – A LCA case study

Our strong dependence on fossil fuels results from the intensive use and consumption of petroleum derivatives which, combined with diminishing oil resources, causes environmental and political concerns. The utilization of agricultural residues as raw materials in a biorefinery is a promising alternative to fossil resources for production of energy carriers and chemicals, thus mitigating climate change and enhancing energy security. This paper focuses on a biorefinery concept which produces bioethanol, bioenergy and biochemicals from two types of agricultural residues, corn stover and wheat straw. These biorefinery systems are investigated using a Life Cycle Assessment (LCA) approach, which takes into account all the input and output flows occurring along the production chain. This approach can be applied to almost all the other patterns that convert lignocellulosic residues into bioenergy and biochemicals. The analysis elaborates on land use change aspects, i.e. the effects of crop residue removal (like decrease in grain yields, change in soil N₂O emissions and decrease of soil organic carbon). The biorefinery systems are compared with the respective fossil reference systems producing the same amount of products/services from fossils instead of biomass. Since climate change mitigation and energy security are the two most important driving forces for biorefinery development, the assessment focuses on greenhouse gas (GHG) emissions and cumulative primary energy demand, but other environmental categories are evaluated as well.Results show that the use of crop residues in a biorefinery saves GHG emissions and reduces fossil energy demand. For instance, GHG emissions are reduced by about 50% and more than 80% of non-renewable energy is saved. Land use change effects have a strong influence in the final GHG balance (about 50%), and their uncertainty is discussed in a sensitivity analysis. Concerning the investigation of the other impact categories, biorefinery systems have higher eutrophication potential than fossil reference systems. Based on these results, a residues-based biorefinery concept is able to solve two problems at the same time, namely find a use for the abundant lignocellulosic residues and ensure a mitigation effect for most of the environmental concerns related to the utilization of non-renewable energy resources.Therefore, when agricultural residues are used as feedstocks, best management practices and harvest rates need to be carefully established. In fact, rotation, tillage, fertilization management, soil properties and climate can play an important role in the determination of the amount of crop residue that can be removed minimizing soil carbon losses.     

What drives public acceptance of second-generation biofuels? Evidence from Canada

North American publics are currently much more supportive of second-generation biofuels than of conventional biofuels like corn-based ethanol. But what is the likely future trajectory of consumer acceptance of advanced biofuels? This study considers whether increased awareness of the potential unintended consequences of increasing the production of advanced biofuels could lead to a decline in public support for the technology. Using an experiment embedded in an original survey of Canadian adults, we test for the effect of two anti-biofuels arguments on Canadians' support for policies meant to encourage the production of biofuels. We find that support for biofuels policies was reduced in our experiment when respondents were exposed to an argument about the potential impact of biofuels production on food prices and when they were told that the use of woody biomass as a feedstock for the production of cellulosic biofuels might lead to an increase in commercial logging. In both cases, however, support was reduced only among respondents who did not perceive climate change to pose a significant risk. Overall, our results suggest that public support for advanced biofuels is potentially vulnerable to arguments that focus on the unintended consequences of producing biofuels from non-food feedstocks.     

Energy and economic assessment of soda and organosolv biorefinery processes

Lignocellulosic biomass, particularly agricultural and forestry residues, is becoming a potential renewable energy and products source. Lignocellulosic biomass processing technologies include a primary separation of its main constituents, cellulose, hemicelluloses and lignin, as well as further treatment and processing to obtain different platform chemicals to design consistently structured compounds as chemical building blocks. The economic competitiveness of the obtained products is highly dependent on the separation and purification technologies used and the process energetic efficiency. For this proposal, process simulation tools are very useful to design a competitive and effective biorefinery scheme. In the present work, the energetic and economical efficiencies of two biorefinery processes, soda and organosolv-ethanol systems, were analyzed using the simulation software Aspen Plus^®. The process design consisted of several units (reaction, solid fraction washing, products recovery and liquid fraction processing). Mass and energy balances were established and both systems were compared in terms of yield, solvents/reactants recovery and energy consumption. Aspen HX-Net software was used to analyze the process heat exchange network in order to improve energy consumptions. The development of rigorous simulations allowed to determine the economical feasibility of both biorefinery schemes, and to establish the most appropriate operation conditions for both processes.     

Biofuels in the U.S. – Challenges and Opportunities

Biofuels are of rapidly growing interest for reasons of energy security, diversity, and sustainability – as well as for greenhouse gas mitigation. In recent years, the U.S. has enacted regulations – and adopted aggressive goals – to encourage increased usage of biofuels. Individual States (especially California) have taken even stronger positions with respect to biofuels. Initial efforts have focused mainly on ethanol, produced via fermentation of sugars from grains (especially corn). Today's R&D focus is on “2nd Generation Biofuels” that are produced from a variety of biomass feedstocks utilizing a wide range of conversion technologies. This paper summarizes policy and regulatory drivers for biofuels in the U.S., describes usage trends and projections, and highlights major R&D efforts to promote development and commercialization of 2nd Generation Biofuels. R&D is being conducted in many areas, including biomass resource assessment, development of new biomass feedstocks, improved conversion technologies, and integration of systems. Other important considerations include fuel quality and specifications, as well as requirements for blending, distribution, and storage. Considerable R&D, policy, and regulatory efforts are also focused on the energy and environmental consequences of biofuels. This includes not only direct emissions associated with vehicular uses, but also the fuels' life-cycle impacts with respect to total energy usage, greenhouse gas emissions, and multi-media effects. Due to the wide diversity of biomass feedstocks, conversion technologies, and systems integration approaches, the life-cycle impacts of biofuels can vary widely.     

Opportunity for profitable investments in cellulosic biofuels

Research efforts to allow large-scale conversion of cellulose into biofuels are being undertaken in the US and EU. These efforts are designed to increase logistic and conversion efficiencies, enhancing the economic competitiveness of cellulosic biofuels. However, not enough attention has been paid to the future market conditions for cellulosic biofuels, which will determine whether the necessary private investment will be available to allow a cellulosic biofuels industry to emerge. We examine the future market for cellulosic biofuels, differentiating between cellulosic ethanol and ‘drop-in’ cellulosic biofuels that can be transported with petroleum fuels and have equivalent energy values. We show that emergence of a cellulosic ethanol industry is unlikely without costly government subsidies, in part because of strong competition from conventional ethanol and limits on ethanol blending. If production costs of drop-in cellulosic biofuels fall enough to become competitive, then their expansion will not necessarily cause feedstock prices to rise. As long as local supplies of feedstocks that have no or low-valued alternative uses exist, then expansion will not cause prices to rise significantly. If cellulosic feedstocks come from dedicated biomass crops, then the supply curves will have a steeper slope because of competition for land.     

Biodiesel from oilgae,biofixation of carbon dioxide by microalgae: A solution to pollution problems

Algae containing 30–75% of lipid by dry basis can be called oilgae. All microalgae species produce lipid however some species can contain up to 70% of their dry weight. Microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels. Biodiesel production by using oilgae is an alternative process in contrast to other procedures not only being degradable and non-toxic but also as a solution to global warming via reducing emission gases. Algae-based technologies could provide a key tool for reducing greenhouse gas emissions from coal-fired power plants and other carbon intensive industrial processes. Because algae are rich in oil and can grow in a wide range of conditions, many companies are betting that it can create fuels or other chemicals cheaper than existing feedstocks. The aim of microalgae biofixation of CO₂ is to operate large-scale systems that are able to convert a significant fraction of the CO₂ outputs from a power plant into biofuels.     

An overview of solar decarbonization processes,reacting oxide materials,and thermochemical reactors for hydrogen and syngas production

Solar decarbonization processes are related to the different thermochemical conversion pathways of hydrocarbon feedstocks for solar fuels production using concentrated solar energy as the external source of high-temperature process heat. The main investigated routes aim to convert gaseous and solid feedstocks (methane, coal, biomass …) into hydrogen and syngas via solar cracking/pyrolysis, reforming/gasification, and two-step chemical looping processes using metal oxides as oxygen carriers, further associated with thermochemical H₂O/CO₂ splitting cycles. They can also be combined with metallurgical processes for production of energy-intensive metals via solar carbothermal reduction of metal oxides. Syngas can be further converted to liquid fuels while the produced metals can be used as energy storage media or commodities. Overall, such solar-driven processes allow for improvements of conversion yields, elimination of fossil fuel or partial feedstock combustion as heat source and associated CO₂ emissions, and storage of intermittent solar energy in storable and dispatchable chemical fuels, thereby outperforming the conventional processes. The different solar thermochemical pathways for hydrogen and syngas production from gaseous and solid carbonaceous feedstocks are presented, along with their possible combination with chemical looping or metallurgical processes. The considered routes encompass the cracking/pyrolysis (producing solid carbon and hydrogen) and the reforming/gasification (producing syngas). They are further extended to chemical looping processes involving redox materials as well as metallurgical processes when metal production is targeted. This review provides a broad overview of the solar decarbonization pathways based on solid or gaseous hydrocarbons for their conversion into clean hydrogen, syngas or metals. The involved metal oxides and oxygen carrier materials as well as the solar reactors developed to operate each decarbonization route are further described.     

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.