Category Archives: Advances in Biorefineries
A number of states have implemented subsidy programs to encourage local biofuel production. These programs range from renewable portfolio standards (RPS) to state-wide blending requirements to low — and zero- interest loans for the construction of biorefineries. Blending requirements and RPSs both indirectly affect the economic feasibility of biorefineries by creating demand for their products. Blending requirements mandate the blending of certain volumes of ethanol with gasoline and biodiesel with diesel fuel (usually 5 vol%, although this varies by state) for fuel sold within the state. RPSs mandate that a certain amount of electricity sold within the state come from renewable sources such as a cellulosic ethanol biorefinery.
States have also attempted to attract biorefinery construction by offering low — or zero-interest loans to biofuel companies for their construction within the state. For example, drop-in biofuel company KiOR has received a zero-interest $75 million loan from the state of Mississippi for the construction of a commercial-scale catalytic pyrolysis and upgrading facility within the state (Dolan, 2011). Such loans improve the economic feasibility of recipient biorefineries by eliminating interest payments on initial capital costs. Unlike blending requirements and RPSs, favorable loans are generally directed at individual companies rather than made available for all qualifying producers.
In the future, many consumer products presently derived from fossil fuel resources such as oil, coal and gas, are likely to be derived from renewable and sustainably produced biomass resources. In addition to the production of liquid and gaseous biofuels used for transport, structural composite materials, reinforced plastics using wood fibres, pharmaceuticals, health promoting products and food sweeteners, bio-products from industrial waste gases, innovative packaging and filtration materials, green biodegradable chemicals including polymers and resins, fine chemicals for paints and adhesives, and many other products are being researched and developed using rapidly advancing biotechnologies. It seems highly likely that these products will make a major contribution through both niche and mainstream markets in the bio-economy of tomorrow.
Very small markets are possible for high value specialty biopharmaceuticals up to $100,000 per kg and biochemicals with a market price up to $1,000 per kg, down to relatively low value, bulk, commodity products such as biofuels at around $1 per litre. So the aim of a biorefinery business should be to extract as much value as possible from the biomass feedstocks by achieving the optimum product mix. Focusing on high volume, low value commodities is usually not the most viable strategy, but neither is concentrating on low volume, high value products. The potential process options are being evaluated through international collaborations such as in the IEA Bioenergy’s Task 42, Co-production of Fuels, Chemicals, Fuels and Materials from Biomass (www. ieabioenergy. com/Task. aspx? id=4) that was established in 2007.
The concept of a ‘biorefinery’ varies between a single feedstock converted into a single product (such as sugarcane to ethanol), single feedstock and multi-products (such as oilseed rape to biodiesel, high-protein animal feed, and heat and power generation from the straw), and multi-feedstocks to multi-products. This is analogous to an oil refinery processing a range of petroleum products and base chemicals. During the last century, the number of oil products marketed has grown from a few fuels and lubricants produced by the simple process of distillation to over 2,000 products today using complex thermal and catalytic cracking as well as reforming processes. Many of the lessons learned by process and chemical engineers can be applied to modern biorefineries and hence shorten the experience of learning-by-doing to add value to the bioenergy industry.
But biorefineries are not new. In the 1700s, the forest industry produced pitch, tar and resins, turpentine and rosin used in ship-building and the sailing of them, with some of these still being produced. The modern biorefinery concept has also existed for some decades as exemplified by the Norwegian company Borregaard, which has long used woody biomass from spruce to produce a range of biochemicals, biomaterials and bioethanol. Ethanol is only a minor, relatively low value product of their processing activities, along with the world market domination of some high value, specialist chemicals. The mix of products can be modified as markets dictate.
A strong economic business case can be made for integrating the production of conventional biomass products with new ‘bio-products’. This can provide new employment opportunities, and benefit the local and global environment by the recycling of biomaterials or significantly reducing greenhouse gas emissions to reach a very low carbon footprint. Moving towards a future green bioeconomy that the world requires will enable heat, power, biofuels and materials resulting from the traditional use of biomass feedstocks to be complemented by adding value through the new and emerging bio-product technologies.
Biorefineries can be designed to create intermediate products for processing into end-products in facilities elsewhere, or derive products ready for market directly on-site. Where an available feedstock is seasonal, multi-feedstocks may be needed to keep the biorefinery operating all year round. This can add to the complexity and cost of the front-end of the plant. Minimizing the costs of collection, transport and storage of the feedstock is another challenge that cannot be ignored when determining the optimum scale of processing plant.
The biorefinery concept, even in its simplest form, provides a more complete utilisation of the biomass feedstock than bioenergy alone. This book provides an excellent overview of the numerous opportunities for commercial viability as a result of the science being applied to the engineering concepts of biorefining. New pilot-scale and demonstration plants that produce biofuels and plastic composites from woody biomass have already been established in Finland, Canada and elsewhere, with many others planned using a range of feedstocks. Development of biorefineries usually requires a supportive government policy framework, as well as research and development support in order to overcome the existing technological, social and environmental barriers. For example, recently in
New Zealand, my own country, an international forest paper pulp company has received government support to build a demonstration biorefinery with the aim to utilise plantation forest residues as the main feedstock, and formed a partnership with an oil company and the forest Crown Research organisation.
The biorefinery model enables the agricultural and forest sectors to diversify their traditional markets and products, to become more energy self-sufficient, and to displace fossil fuel-based products with low carbon and renewable alternatives. In a future carbon-constrained global economy, the use of fossil fuels will be constrained and there will be increased demand for renewable and sustainable products arising from biomass resources. Consequently, biorefineries and their bio-products will play an increasingly important economic role. The world-acclaimed editor and authors of this book have helped advance the knowledge needed to achieve that goal and provided a vision for the global green, bioeconomy of the future.
Ralph E. H. Sims, Professor of Sustainable Energy, Massey University, New Zealand
3.2.1 Methods and indicators of sustainable development
Given the broad concept of sustainability outlined above, it is obvious that sustainability assessment does not mean one single method, but that different types of methodologies and assessment procedures may be applied. This calls for the structuring or a typology of approaches, and indeed such typologies can be found in the literature. Before presenting them, at the most simple, three structuring criteria shall be discussed: first, what indicators are used for the assessment, second, how the object of assessment is defined, and third, how the quantitative or qualitative values for the chosen indicators as to the defined object of assessment are generated.
As to the issue of indicators, these can be defined from the three dimensions of sustainability and on different levels; these levels have to be adequate for the object to be assessed. Many indicator systems have been defined at the country level, e. g. the United Nations Commission for Sustainable Development (UNCSD) Theme Indicator Framework (UN, 2001). Some of these indicators may be meaningful also at the company, product or technology level (e. g., the amount of greenhouse gases), but some may be not (e. g., the national debt).
The task to define the object of investigation is not as trivial as it may seem. Every object has a structure — for example, a product has its components, a technology has auxiliary processes and a demand for material and energy — so each object can be seen as a system and the definition of the objects is equal to the definition of the system boundaries. This system can be specified by technological components, but also by geographical or temporal aspects. One idea of a system boundary is specifically prominent in sustainability assessment which is the so-called life cycle of a product. ‘Life cyle thinking’ means looking at the full process chain from extraction of raw materials through production of a product or technology, its use by the consumer and also its end of life, where materials are transferred back to nature.
These two structuring criteria are decisive for the third one, the methodology, with which quantitative or qualitative values for the chosen indicators and the system boundary are generated. Here, usually two types of procedures are encountered: either information is gathered directly via measurement or statistics (or taken from databases which contain respective data), or a model is built in order to generate new data from a set of data fed in. The choice of methodology makes up the tools that are used for assessment.
Typologies found in the literature make use of these criteria in different ways. Singh et al. report on a broad literature overview of sustainability assessment methods, structured by sustainability indicators, classification and evaluation of methodologies. They address guidelines for the construction of indices; in addition, they give a comprehensive survey and description of existing sustainability indices (Singh et al., 2009). Hacking and Guthrie propose a framework and a consistent terminology for approaches to sustainability assessment found in the literature, which uses three axes: ‘the comprehensiveness of the SD coverage; the degree of ‘integration’ of the techniques and themes; and the extent to which a strategic perspective is adopted’ (Hacking and Guthrie, 2008). Ness et al. present a proposal for assessment tools and arrange them into three main categories: indicators/indices, product-related assessment, and integrated assessment tools. There is a ‘parent category’ (monetary valuation tools), which acts in all categories (Ness et al., 2007).
Markevicius et al. use 35 criteria for a so-called Emerging Sustainability Assessment Framework. The majority of indicators focus on environmental issues (12 indicators), while four social indicators and one economic indicator are added (Markevicius et al., 2010). Hueting and Reijnders report on the construction of sustainability indicators. They make the general criticism that so far suggested economic and social elements for inclusion in indicators do not have plausible causal relation to nature conservation, i. e. ‘sustainability defined as a production level that does not threaten the living conditions of future generations’ (Hueting and Reijnders, 2004). Bohringer and Jochem select 11 indices from 500 Sustainable Development Indicators, that are suggested to researchers and policy makers, including the Living Planet Index (LPI), Ecological Footprint (EF), City Development Index (CDI), and Human Development Index (HDI) (Bohringer and Jochem, 2007). Assefa and Frostell discuss an approach for the evaluation of indicators for social sustainability of technical systems (e. g., waste management and energy systems). Three indicators are reviewed: knowledge, perception and fear (Assefa and Frostell, 2007). Finnveden et al. mention the strategic environmental assessment (SEA), the environmental impact assessment (EIA), the environmental risk assessment (ERA), the cost-benefit analysis (CBA), the material flow analysis (MFA), the ecological footprint, and notably life cycle assesment (LCA) as most frequently used methods (Finnveden et al., 2009). Balkema et al. propose a methodology of sustainability assessment structured in three steps following the approach of life cycle assessment: (1) Goal and definition, (2) inventory analysis, and (3) optimization and results. The last step is essential for assessing sustainability (Balkema et al., 2002).
Sustainability assessment also has to be seen as a decision-making process where the interests of many stakeholders have to be taken into account. The various players have their environmental, social and economic criteria and interests for the development of a sustainable system. To support these decision-making processes and take into account different goals and interests, methods such as multi-criteria decision analysis (MCDA), multiobjective decision making (MODM), operations research and management science are proposed. These methods are used to review the assessment of various decisions and political strategies as well as to include the competing interests of various stakeholders and experts (Halog and Manik, 2011). When quantitative sustainability indicators are used, multi-objective optimization can be integrated to identify a group of favorable options for sustainable solutions (Balkema et al., 2002). Such methodology has to be included in a procedural framework of stakeholder participation (see, e. g., Stoll-Kleemann and Welp, 2006).
Waste biomass from the food supply chain (i. e., agricultural residues such as wheat straw, rice husks, waste cooking oil or food manufacturing waste such as tomato peels) are an ideal renewable material as they do not compete with the food and feed industries for land. An FAO report issued in 2011, estimates that ‘one-third of food produced for human consumption is lost or wasted globally, which amounts to about 1.3 billion tons per year’ (Gustavsson et al, 2011). It is important to note the difference between food waste and food loss, the latter being food lost due to the use of poor technological means or diseases affecting crops, for example (Parfitt et al., 2010).
The agro-food supply chain includes a broad variety of manufacturing processes producing consequent cumulative quantities of different wastes, especially organic residues at every step of the supply chain (Gomez et al., 2010; Laufenberg et al., 2003). The increasing demand for chemicals and fuel together with other drivers are encouraging the re-use and valorization of organic waste from the food supply chain for the production of novel added-value bio-derived sustainable products. A description of a food supply chain is given in Fig. 1.6.
Food waste encompasses domestic waste produced by individuals in their homes. This represents a logistical problem as it would be difficult to collect and concentrate in one place, except in large housing complexes. On the other hand, it might be argued that if the waste produced by the agricultural and processing sectors before it reaches the consumer is generated in a more concentrate manner, it would be easier to collect and valorize. The problems associated with these wastes are:
• severe pollution problems due to high associated chemical and biological oxygen demand (COD and BOD) (Kroyer, 1995)
• varying pH (Kroyer, 1995)
• material prone to bacterial contamination (Schieber et al., 2001) (e. g., fruit and vegetable by-products)
• high accumulation rate leading to disposal management problems (Zaror, 1992)
• variations in chemical content due to different varieties and seasonal variations.
Current practices for the management of food waste include:
• incineration (GHG and toxic chemical emissions)
• landfilling (polluting, GHG emissions)
• conversion to cattle feed (uneconomical process, high moisture content)
• anaerobic digestion (loses much of the chemical value and low carbon efficiency).
Composting is a popular re-use practice as it lowers waste management costs, diverts waste from landfill and reduces waste disposal costs (Schaub and Leonard, 1996), but composting is also ‘time consuming, location dependent and subject to contamination’ (Davis, 2008).
While progress is being made in using anaerobic digestion to both treat food waste and provide some energy value, the chemical and material potential of food supply chain waste is such that we should also quickly move to realizing that potential through the use of other green chemical technologies. There are five reasons to develop the valorization of residues and by-products of food waste: they are a rich source of functionalized molecules (i. e., biopolymers, protein, carbohydrates), abundant, readily available, under-utilized and renewable. Many waste streams even contain compounds
such as antioxidants which could be recovered, concentrated and re-used in functional food and lubricant additives (Peschel et al., 2006). Such applications solve both a resource problem and waste management problem as the issues associated with agro-food waste are important. Other than decreasing landfill options, when landfilled, waste is a source of pollution: municipal solid waste for example can produce uncontrolled GHG emissions and contaminate water supplies through leaching of inorganic matter (Cheng and Hu, 2010). Incineration is energy intensive, emits CO2 and toxins and is sensitive to the waste’s moisture content. The scale at which waste from the food supply chain is generated is significant. In the United States, USDA calculated that US$ 50 million could be saved annually if 5% of the waste generated by the processing, retail and service sectors together with consumer food losses were recovered (Laufenberg et al., 2003).
This type of waste represents a valuable and sustainable source of useful products that could be used by other industries, especially the chemical industry, as shown in Fig. 1.7. Novel strategies and technologies for waste valorization can potentially have a global impact on the chemical and biotechnological industries and waste management regulations in the years to come. However, despite the clear benefits, the utilization of food waste represents a challenge. A regular and consistent supply chain is important for the successful realization of a biorefinery. But high cumulative volumes of waste are often generated intermittently, over a period of a couple of months in a year, affecting the year-round availability of chemicals and materials produced from food supply chain by-products and residues. The large volumes of food supply chain by-products available are illustrated in Table 1.4.
Table 1.4 Examples of food supply chain by-products and corresponding volumes available
Nature of the food supply chain Estimated volume/year
Citrus waste produced post-juicing
Used cooking oil
Palm oil residues
Olive mill residue
Wheat straw surplus
5.0. 000 T in Florida, USA 0.7-1 million T in Europe
15.800.0 T in Indonesia
30.0. 000 T in the Mediterranean basin 20 million T in Ivory Coast
110 million T worldwide
194.692.0 T in Brazil 8 million T in Europe 5.7 million T in Europe 4 million T in Europe 15 million T in the USA
7.7 Components of food supply chain waste useful in bio-derived daily consumer products.
Although the availability of some food supply chain by-products is clearly an advantage regarding security of supply, several limitations exist and need to be taken into account as part of the logistics needed to valorize this resource. Food supply chain waste can be/can have:
• a heterogeneous variable composition (lipids, carbohydrates, proteins) (Litchfield, 1987)
• fluctuating in volumes available across the year (Litchfield, 1987)
• a high water content (Laufenberg et al., 2003) and
• a low calorific value (Laufenberg et al., 2003).
At a European level, research is being promoted via the Framework VII KBBE (Knowledge-Based Bio-economy) theme. In the UK, a number of food supply chain waste related research projects are being carried out in collaboration with industry on, for example, the use of supercritical carbon dioxide to extract chemicals from cereal straws and also the use of starch- rich wastes to make adhesives for carpet tiles and other consumer goods. In the Review of Waste Policy issued by DEFRA in June 2011, launching a zero waste economy plan, the UK Government announced it will work with industry to drive innovation in reuse and recycling for materials, such as metals, textiles and all biodegradable waste (DEFRA, 2011). The EU issued new FP7 funding calls for 2012 mentioning that ‘research is needed to develop innovative concepts and practical approaches that would add value to and find markets for food waste of plant and dairy origin’ (CORDIS, 2011).
In France, work on the valorization of oil crop by-products is now being supported by the French government-funded ‘project PIVERT’. In Spain, a research team in Barcelona is studying the use of amino acids derived from food supply chain residues for the synthesis of amino-acid derived surfactants such as ethyl-N-lauroyl-L-arginate HCl or LAE, which have been successfully commercialized (Infante et al., 1992). Waste cooking oil and citrus waste produced from the juicing industry are also being studied in Spain as raw materials for the production of bio-diesel and bio-ethanol/ D-limonene extraction, respectively (Kulkarni and Dalai, 2006; Sunde et al., 2011). In Greece, whey is being explored as feedstock for microbial oil production that could be used for oleochemical synthesis (Vamvakaki et al., 2010).
The topic is gaining increased attention worldwide: the NAMASTE project (EU-India) is directed at the valorization of selected by-products, such as fruit and cereal processing residues, for the global food and drink industry. In the United States, the Center for Crop Utilization Research at Iowa State University is focusing on adding value to Midwest crop (i. e., soy, corn) by-products to increase the value of the food supply chain. Scientists at the American company Cardolite have succeeded in producing thermosetting binder resins for use in the transportation and brake industries from cashew nutshell liquid (highly thermostable, impermeable and durable) (Cardolite, n. d.).
The European Union (EU) has implemented a number of programs incentivizing the production of biorenewable energy, both on a Eurozone scale and a national scale by its member nations. The various programs are broadly split into the categories of biorenewable electricity and biofuels. The EU’s 2009 Renewables Directive (Anon., 2009a) creates two separate binding targets for member nations. First, EU members must derive 10% of their transport energy from renewable sources, including biomass, by 2020. Second, they must also derive 20% of all of their energy from renewable sources, including biomass, by 2020. Member nations are given the flexibility to determine how best to meet these targets. Additionally, the EU has established economic mechanisms to compensate participating facilities within member nations that contribute to reducing greenhouse gas emissions (GHG).
The EU has implemented an Emission Trading Scheme (ETS) to combat anthropogenic climate change resulting from GHG via a cap-and-trade mechanism. Installations located within a member nation that meet a net heat threshold are covered by the ETS. Each member nation receives annually a limited number of GHG emission allowances that are distributed to covered installations, which must in turn purchase additional allowances for any emissions that exceed this allocation.
The ETS affects biorefineries both directly and indirectly. It directly affects biorefineries by allowing them to receive offset credits in the form of emission reduction units (ERU). ERUs are awarded in exchange for activity that results in the avoidance of GHG emissions. Example projects include the production of biogas from landfills for use as fuel, the utilization of waste sawdust as electricity or biofuel feedstock, and the use of sunflower and canola oils as biodiesel fuel feedstocks (Fenhann, 2012). Each ERU represents 1 metric ton (MT) of avoided GHG emissions and can be traded with other parties. In this way, ERUs can directly contribute to the economic feasibility of a qualifying biorefinery by representing an additional value — added product.
The ETS indirectly affects biorefineries by artificially increasing the cost of fossil fuel products relative to renewable fuel products in proportion to their respective carbon footprints. Power plant operators must purchase sufficient carbon allowances to cover the plant’s GHG emissions, the size of which is determined by the feedstock utilized. This increases the value of electricity derived from biorenewables by lowering its cost relative to electricity derived from fossil fuels and thereby increasing demand for it. A similar situation exists for qualifying transportation biofuels. For example, the EU’s decision in 2012 to include airlines operating in Europe within the ETS (Torello et al, 2012) enhanced the value of aviation biofuel, as one method by which covered airlines can avoid GHG emissions (and the need to purchase additional allowances) is by combusting biofuel instead of conventional fossil fuel-based aviation fuel during flights.
The concept of ‘biorefining’ has emerged over many decades, more recently stimulated by the drive for sustainability. The underlying aspiration is that renewable feedstock can be processed to partially replace the non-renewable fossil fuels that currently provide the bulk of our energy and chemicals. Of course, ‘biorefining’ is not new, as the exploitation of biomass for food, fuel and materials precedes the industrial revolution.
In the modern context there have been numerous attempts to define and describe the complex nature of biorefining. The International Energy Agency’s Bioenergy Task 42 has agreed that ‘Biorefinery is the sustainable processing of biomass into a spectrum of marketable products (food, feed, materials and chemicals) and energy (fuels, power and heat)’. Hence, the term ‘biorefinery’ is loosely defined, and can refer to a process, a plant, clusters of facilities, or a concept. Indeed, biorefining can range from the simple modification of biomass for use ‘as is’ in the production of materials, through to the complex extraction of molecular components followed by their bioconversion into higher value chemicals and fuels.
The biorefining industry is beset with many socio-economic and environmental challenges. At the time of writing, biorefining is dominated by the global production of ethanol from grain and sugar. The consequent exploitation of food-grade feedstock has stimulated an on-going debate regarding food vs. fuel. Additional arguments concerning the use of land for producing non-food feedstock are developing around the issue of indirect land use change. A further challenge to successful biorefining is the requirement to operate at scales and efficiencies which are both economically viable and environmentally sustainable. However, whilst biorefining approaches are often sought to produce environmentally beneficial products that replace current fossil-derived materials, they are competing with well — established products which have a number of key economic advantages. Fossil-derived products are relatively cheap, usually commodities, and serve mature global markets that have developed alongside the petrochemical industry over the last century. In contrast, the biorefinery industry is relatively new, undergoing rapid change as it develops, and requires the application and integration of a wide range of highly specialist disciplines, from the biosciences through to advanced chemical and process engineering.
The aim of Advances in biorefineries is to provide a comprehensive and systematic reference on the advanced processes used for biomass recovery and conversion in biorefineries. The volume comprises contributions from internationally recognised experts who have reviewed the latest developments in the area of biorefining, and is divided into two parts:
• Part I, ‘Development and optimisation of biorefining processes’, contains 12 substantial chapters. The first chapter introduces the concept of green chemistry with reference to exploitation of waste streams. This is followed by several chapters considering economic and environmental impacts and sustainability. The remainder of Part I assesses recent developments and optimisation strategies for key unit processes (including biomass pretreatment, catalytic conversion, enzyme development and separation technologies) and a range of biorefinery models.
• Part II, ‘Biofuels and other added value products from biorefineries’ comprises 14 chapters which concentrate on the creation and optimisation of products from biorefineries. Highlighting the diversity of products that can be created from biomass, these chapters provide up-to-date knowledge across a variety of outputs from the improvement of liquid biofuels in internal combustion engines, and the production of platform chemicals, proteins, lipids and carbohydrates through to the creation of high value and specialist products, including adhesives, films and coatings and bio-based nutraceuticals.
The interaction of a technology with its environment is very complex. In general it can be stated that a technology may have impacts on the natural or physical as well as on the economic and sociocultural environment. The ways in which this interaction takes place may be diverse, depending on the kind of technology. However, every technology has a reason for its application, which ultimately is to deliver either a product or a service to society. This function — if it meets the demands of the final consumer — is what makes a new technology enter the market and consequently drives its impact on the environment. This idea of the interaction of technology with its environment through a function that needs to be fulfilled is shown in Fig. 3.1 (Balkema et al, 2002).
Consequently, the impact of a technology is always assessed taking into account its function. This is what makes it possible to compare a novel technology to ‘old’ technologies or to compare different alternatives for shaping a technology to each other. It is even possible to compare different technologies to services provided that the function for the user remains the same. Although the motivation to compare is very important, if not the most widespread one for sustainability assessment, it may also be interesting to assess one technology on its own. This motivation is encountered mostly in cases where the term technology designates not a single device, process or service, but rather a far reaching change in the sense of systems innovation which usually encompasses technology as well as organizational and social
innovation; a well-known example of this is the internet. Here, often the term technology assessment (TA) is used, which covers a wide procedural approach encompassing many methodological tools in order to explore and assess a multitude of possible and maybe interacting consequences on the natural or social environment (van den Ende, 1998; Butschi et al., 2004).
In contrast, the term sustainability assessment of technologies in the literature is rather used for a more focused assessment and comparison of specific technologies and their interaction with their environment. Keeping in mind that the impact of a technology is always connected to its function, one generic approach of assessment has become most popular: the methodology of life cycle assessment (LCA). It mirrors the view of the function as driving force for the use of a technology and as a point of reference for assessment. Most approaches to sustainability assessment of technologies are based on this method, either exclusively or by incorporating it in a wider framework. This notion is also true when looking at the assessment of technologies for energetic or material use of biomass (Dewulf and van Langenhove, 2006). Consequently, in order to reduce the plethora of names and single approaches, this chapter will be restricted to life cycle assessment as the most widespread concept for sustainability assessment of technologies.
The example given in Section 1.3.2 shows how one step change in a process can avoid further fossil resource deletion by recycling waste. But there are smarter ways of using food supply chain waste: this type of co-product is rich in chemical compounds and it is important to take advantage of that resource before using it for energy generation. The food supply chain generates a high amount of waste, even at a pre-consumer stage. Around 89 million tons of food waste is generated every year in the EU-27 (Bio Intelligence Service, 2010). Some 38% is generated by the manufacturing sector, 42% by the household sector (other sectors: 19%). First generation food supply chain waste re-use such as anaerobic digestion, composting, or conversion to animal feed only has marginal economic value compared to the revenue that could be generated from the production of pectin (10-12 £/kg) from citrus peels, for example.
In addition, when using waste, several criteria need to be considered in order to make sure the feedstock chosen is going to be used over the long term. Volumes available, occurrence in several geographical locations, guaranteeing a regular supply throughout the year, chemical functionalities present, extractables recoverable and their value as well as fitting the feedstock with appropriate green chemical technologies are all important parameters to consider when selecting a waste by-product for valorization.
Wheat straw is a major by-product of the agricultural sector. It is estimated that in the UK alone, 6.3 million tonnes of wheat straw was generated in 2007 (NNFCC, 2008), with a net surplus over livestock demand of 5.7 million tonnes in 2007. In the context of the UK Government’s new targets on biomass generated heat and power (5% by 2020) (HM Government, 2009), wheat straw represents a good choice of feedstock for combustion for heat and power generation. However, available valuable chemical functionalities should be recovered before any thermo — or biochemical processes are applied to wheat straw for conversion to energy. Two valorization routes have been demonstrated (see Fig. 1.8): the combustion of wheat straw and subsequent valorization of the slag and fly ash produced and supercritical CO2 extraction of waxes followed by char production from wheat straw by microwave pyrolysis. Both approaches are aiming for the development of a close to zero integrated wheat straw biorefinery. The first one valorizes the by-product of the combustion of wheat straw: the high
1.8 A wheat-straw based biorefinery: comparison between two possible routes.
content of alkalis (chloride, K2O and SiO2) can be extracted by water at room temperature. Up to 30% of the silica present in the ash (wheat straw ash contains 44.25% silica on a dry weight basis) can be extracted at room temperature in the form of a bio-silicate solution by using wheat straw’s own alkali content. Silicates are studied as an alternative to formaldehyde — based adhesives in entirely bio-derived, fire resistant, moisture resistant construction boards and have the potential to improve the cost-effectiveness of energy producing technologies such as combustion and help the direct production of materials from agricultural biomass (Dodson et al, 2011).
The second approach takes advantage of the combination of two green technologies: supercritical CO2 extraction and low temperature microwave pyrolysis, benefiting from the financial return offered by the extraction of phytochemicals prior to the production of char by microwave pyrolysis at 180°C. The first step is the extraction of the wax coating the wheat straw: between 0.9 and 1.1 wt% at 32°C and 100°C, respectively, which is comparable to hexane. The added advantage associated with using supercritical CO2 over hexane is that unwanted components such as pigments, free sugars and polar lipids are less soluble in supercritical CO2 than in hexane. Compounds found in the extracted wax range from 6,10,14-trimethyl 2-pentadecanone used in detergents, to nonacosane, a bio-derived type of paraffin wax, and octadecanal, an aldehyde used as a flavouring additive in foods. The de-waxed wheat straw is then pyrolysed using microwaves as a heating method, producing five fractions. They are described as follows:
1. A char (29 wt%) of a calorific value of 27.2 kJ/g, which can be demineralized to avoid alkali corrosion during combustion due to the formation of alkali ash.
2. Bio-oil (21 wt%) with a reduced water (1%) and acid content (pH 7) compared to oils obtained by fast pyrolysis at temperature above 350°C, requiring less downstream processing to be used in blends with crude oil for chemical and fuel production.
3. An aqueous solution (36 wt% together with the second aqueous fraction) made of formic acid, formaldehyde, acetic acid and acetaldehyde, all of which represent interesting starting materials for further downstream chemistry. Formaldehyde has an existing market as a disinfectant.
4. An aqueous solution of sugars which can be fermented to higher volume chemicals or biofuels.
5. A gaseous fraction (14 wt%) composed of CO and CH4 that could be used to fuel the process and CO2 which could be used for the wax extraction.
It should be noted that both technologies are scalable and are commercially used by the food industry and yield several useful marketable products in the context of a wheat straw biorefinery. Microwave technology is less sensitive to water content than conventional convection heating. The use of biomass with a high water content can prove to be advantageous as water can dissociate at higher temperatures under microwave conditions (Vaks et al., 1994) and can generate an in-situ acidic pseudo catalysis process benefiting the targeted process (extraction, chemical reaction). Furthermore it is portable, tuneable (additive, temperature, pressure, power) and fast, proving to be applicable to a variety of feedstocks, or feedstock agnostic. In terms of energy consumption, the described process only requires 1.8 kJ/g of energy compared to 2.7 kJ/g when using convection heating for the pyrolysis stage (Budarin et al., 2011). Supercritical CO2 may require a very high capital investment, but on a large scale, it has been proven to be more cost-competitive than using hexane (List et al., 1989), as this technique is virtually residue-free, requiring less downstream separation to achieve high purity of the extracted compounds.
Straw represents 50% of the yield of a cereal crop (Clynes, 2009) and with 650,881,002 tonnes of wheat produced in the world in 2010, wheat straw represents an important agricultural by-product occurring on every continent on the planet, with Europe, Asia and North America being the largest wheat producers. In conclusion, by integrating just two green processes, several products can be obtained starting from a unique feedstock available worldwide.
A number of EU member nations have implemented their own programs incentivizing biorenewables as part of the binding targets imposed by the 2009 Renewables Directive. A wide variety of program types are employed, ranging from feed-in tariffs to mandates to tax incentives. The United Kingdom’s (UK) Renewables Obligation establishes a mandate of 20% renewable electricity generation in the country by 2020 (Swinbank, 2009). The UK’s Renewable Transport Fuels Obligation also establishes a mandate for 5 vol% of UK transport fuel consumption to be derived from renewable sources by 2013. Germany initially took a different approach by levying a tax on fossil fuels that was not applied to biofuels before switching to a biofuels mandate in 2007 (Deurwaarder, 2007). The large majority of EU member nations encourage the production of biofuels via tax incentives, blending requirements, or a combination of the two (Pelkmans et al., 2008).
L. A. PFALTZGRAFF and J. H. CLARK, University of York, UK
Abstract: Today fossil resources supply 86% of our energy and 96% of organic chemicals. Future petroleum production is unlikely to meet our society’s growing needs. Green chemistry is an area which is attracting increasing interest as it provides unique opportunities for innovation via use of clean and green technologies, product substitution and the use of renewable feedstocks such as dedicated crops or food supply chain by-products for the production of bio-derived chemicals, materials and fuels. This chapter provides an introduction to the concepts of green chemistry and the biorefinery and, based on examples, discusses second generation re-use of waste and by-products as feedstocks for the biorefinery.
Key words: green chemistry, clean technologies, biorefinery, renewable and sustainable resources, food supply chain waste, resource intelligence.
Through the combination of low environmental impact and safe technologies, the use of biomass can provide a renewable alternative to fossil resources. It can establish a new sustainable supply chain for the production of high value chemicals, including fuels and energy as well as materials.