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Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane Bioenergy systems for the future 3 production of bioalcohol and biomethane
Production of bioalcohol and biomethane K Ghasemzadeh*, E Jalilnejad*, A Basile† *Urmia University of Technology, Urmia, Iran, †Institute on Membrane Technology (ITM-CNR), Rende, Italy Abbreviations AD BOD COD COx DME LHW MF MD MBR NF NOx PSA RO 3.1 anaerobic digestion biochemical oxygen demand chemical oxygen demand carbon oxides dimethyl ether liquid hot water microfiltration membrane distillation membrane bioreactor nanofiltration nitrate oxides pressure swing adsorption reverse osmosis Introduction Energy plays a significant role in the economic growth of any country Based on statistics, global production of oil and gas is approaching its maximum, and the world is now finding one new barrel of oil for every four it consumes (Aditiya et al., 2016; Delfort et al., 2008; Nigam and Singh, 2011) The increasing energy crisis and growing environmental concerns in recent years have driven the development of technologies to allow for the substitution of fossil fuels with renewable energy (Aditiya et al., 2016; Delfort et al., 2008; Nigam and Singh, 2011; Koh and Ghazoul, 2008) Several alternatives are currently being explored, including a range of carbon-free and renewable sources (photovoltaics, wind and nuclear power, and hydrogen) in an attempt to replace natural gas, coal, and oil in the electricity generation sector However, there is no such equivalent in transportation, since fuel cell, electric/hybrid, and natural gas-based cars are still a long way from becoming mainstream vehicles (Murray, 2005) Among the explored alternative energy sources, considerable attentions have been focused on Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00003-X © 2017 Elsevier Ltd All rights reserved 62 Bioenergy Systems for the Future biofuels (bioalcohol and biomethane) because it is widely available from inexhaustible feedstocks that can effectively reduce its production cost Indeed, biofuel can be produced from various kinds of renewable materials such as corn, sorghum, cellulose, and algae biomass However, among all biofuels, bioalcohol such as bioethanol and biomethane is more productable than other types On the basis of the raw material used for its production, bioethanol and biomethane are divided into various types (Aditiya et al., 2016) However, their production involves many processes such as pretreatment, fermentation, recovery, and refining (Thomson, 2008) To the best of our knowledge, the largest energy demand in biofuel production is for the steam and electricity used in the fermentation/distillation process Hence, bioalcohol and biomethane will not be significant without improvements in this process and reduced energy requirements Membrane separation technologies have gained more and more attention due to their reduced energy requirements, lower labor costs, lower floor space requirements, and wide flexibility of operation (Suresh et al., 1999) This technology has been applied in many processes of bioalcohol and biomethane production instead of the traditional process (Stevens et al., 2004; Larson, 2008; Noraini et al., 2014; Bergeron et al., 2012; Galanakis, 2012) Therefore, the main aim of this chapter is to present a state-of-the-art review on the bioalcohol and biomethane production processes and also on the applications of membrane technologies for their production 3.2 Biofuels In general, biofuels are referred to liquid, gas, and solid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, hydrogen, and methane, which are predominantly produced from biomass Renewable and carbon-neutral biofuels are necessary for environmental and economic sustainability Between 1980 and 2005, worldwide production of biofuels increased significantly by an order of magnitude from 4.4 to 50.1 billion liters, with further dramatic increases in the next years (Koh and Ghazoul, 2008; Murray, 2005; Licht, 2008) The economics of each fuel vary with location, feedstock, fermentation technology, and several other factors Political agendas and environmental concerns also play a crucial role in the production and utilization of biofuels The challenging point on use of these fuels is fitting biofuels into the enormous current fuel distribution and vehicle infrastructure (Nexant, Inc, 2006) Major benefits of biofuels are summarized in Table 3.1 With regard to the presented studies (Nigam and Singh, 2011; Alam et al., 2012), biofuels can broadly be classified as primary and secondary biofuels based on their source and type The primary biofuels, also named as natural biofuels, such as vegetables, animal waste, landfill gas, fuelwood, wood chips, and pellets, are used in an unprocessed form, primarily for heating, cooking, or electricity production The secondary biofuels like ethanol, methane, biodiesel, and DME are produced by processing of biomass and can be used in vehicles and various industrial processes The secondary biofuels are modified primary fuels, which are further divided into first-, second-, and third-generation biofuels on the basis of raw material and Production of bioalcohol and biomethane Table 3.1 63 Major benefit of biofuels Economic consequences Sustainability Fuel diversity Increased number of rural manufacturing jobs Increased income taxes Increased investments in plant and equipment Agriculture development International competitiveness Reducing the dependency on imported petroleum Environmental consequences Greenhouse gas reduction Reducing of air pollution Biodegradability Improved land and water use Carbon sequestration Higher combustion efficiency Energy security Domestic targets Supply reliability Reducing use of fossil fuels Ready availability Domestic distribution Renewability technology used for their production They are produced in the form of solids (e.g., charcoal) liquids (e.g., ethanol, biodiesel, pyrolysis oils, and bio-oil), or gases (e.g., biogas (methane), synthesis gas, and hydrogen) and can be used in transport and high-temperature industrial processes (Thomson, 2008; Hoekman, 2009) A tee diagram for classification of biofuel is shown in Fig 3.1 The first-generation liquid biofuels are generally produced from sugars, grains, or seeds like wheat, palm, corn, soybean, sugarcane, rapeseed, oil crops, sugar beet, and maize and require a relatively simple process to produce the finished fuel product Ethanol is the most well-known first-generation biofuel produced by fermenting sugar extracted from crop plants and starch contained in maize kernels or other starchy crops (Nigam and Singh, 2011; Hoekman, 2009; Suresh et al., 1999; Stevens et al., 2004) Due to the increasing growth in production and consumption of biofuels, first-generation fuels are being produced in significant commercial quantity in a number of countries However, the first generation is claimed to be not very successful because of the conflict with food supply and high production cost due to competition with food; thus, it affects food security and global food markets These limitations favor the search of nonedible biomass for the production of biofuels (Larson, 2008; Noraini et al., 2014) Second-generation liquid biofuels are generally produced by two different approaches, that is, biological or thermochemical processing, from agricultural lignocellulosic biomass, which are either nonedible residues of food crop production or 64 Bioenergy Systems for the Future Biofuels Secondary biofuels First generation Source: Seeds, grains, or sugars – Bioethanol or butanol by fermentation of sugars (sugars cane, sugars beet, etc) or starch (wheat, potato, corn, etc) – Biodiesel by transesterification of plant oils (sunflower, palm, soybean, etc) Primary biofuels Second generation Third generation Natural biofuels Source: Lignocellulosic biomass Source: Algae, sea weeds – Bioethanol or butanol by enzymatic hydrolysis – Biodiesel from algae Firewood, wood chips, pellets, animal waste, and landfill gas – Biomethane by anaerobic digestion – Bioethanol from algae and sea weeds – Methanol, DME, etc by thermochemical processes – Hydrogen from green algae and microbes Fig 3.1 Classification of biofuels nonedible whole plant biomass (e.g., grasses or trees specifically grown for production of energy) This generation has more advantages compared with the first generation due to higher production yield and lower land requirement and also using nonedible feedstocks that limits the direct food versus fuel competition associated with firstgeneration biofuels Feedstock involved in the process can be bred specifically for energy purposes, enabling higher production per unit land area, and a greater amount of above-ground plant material can be used to produce biofuels It appears evident from the literature (Bergeron et al., 2012; Galanakis, 2012) that production of second-generation biofuel requires most sophisticated processing production equipment, more investment per unit of production, and larger-scale facilities to confine and curtail capital cost scale economies, which are discussed in future sections To achieve the potential energy and economic outcome of second-generation biofuels, further research, development and application are required on feedstock production and conversion technologies (Prado et al., 2016) As indicated in Fig 3.1, third-generation biofuels use microbes and macro- and microalgae feedstocks as a very promising source for renewable energy production since it can fix the greenhouse gas (CO2) by photosynthesis and does not compete with Production of bioalcohol and biomethane 65 the production of food; hence, it is devoid of the major drawbacks associated with firstand second-generation biofuels On the basis of current scientific knowledge and technology projections, some microorganisms like yeast, fungi, and microalgae can be used as potential sources for biofuel as they can biosynthesize and store large amounts of fatty acids in their biomass (Alam et al., 2012; Noraini et al., 2014) Microalgae can produce lipids, proteins, and carbohydrates in large amounts over short periods of time, and these products can be processed into both biofuels and valuable coproducts (Costa et al., 2012) Fuel production from algae has various advantages such as high growth rate, capability of growing under several conditions including in wastewater, high-efficiency CO2 mitigation, less water demand than land crops, and more cost-effective farming (Noraini et al., 2014) 3.2.1 Bioalcohol production The alcohols are oxygenated fuels in which the alcohol molecule has one or more oxygen that decreases the combustion heat The alcohols used for motor fuels are methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH), but among them, only methanol and bioethanol fuels are technically and economically suitable for internal combustion engines (ICEs) (Demirbas, 2007; Ishola et al., 2013) Bioethanol is a liquid biofuel that can be produced from several different biomass feedstock and conversion technologies It contains 35% oxygen, which reduces particulate and NOx emissions from combustion and also reduced hydrocarbons, carbon monoxide, and particulates in exhaust gases Currently, ethanol is the available commercial biofuel and the most modern biomass-based transportation fuels, which sticks out as the most important liquid biofuel with a global production of 88.7 billion liters in 2011 (Balat, 2011) Bioethanol has been focused as a high potential alternative to substitute liquid fossil fuels due to its eco-friendly characteristics and relatively low production cost when compared with other biobased fuels Bioethanol has a higher octane number (108), low cetane number, broader flammability limits, higher flame speeds, and higher heats of vaporization than gasoline These properties allow for a higher compression ratio, shorter burn time, and leaner burn engine, which lead to theoretical efficiency advantages over gasoline in an ICE (Aditiya et al., 2016; Demirbas, 2007) Adding ethanol to gasoline has a positive effect on the air quality in every polluted urban areas It has been stated that 10% blend of bioethanolS with gasoline would reduce the carbon dioxide emission by 3%–6%, which makes bioethanol a cleaner fuel in addition to being a renewable alternative to petroleum (Demirbas, 2007; Hansen et al., 2005) Bioethanol can be used as a 5% blend with petrol under the EU quality standard EN 228 This blend requires no engine modification and is covered by vehicle warranties With engine modification, it can be used at higher levels, for example, E85 (85% bioethanol) (Balat et al., 2008) Bioethanol is widely used in the United States and in Brazil The United States and Brazil remain the two largest producers of ethanol accounting together for 90% of the global bioethanol production In 2010, the United States generated 49 billion liters, or 57% of global output, and Brazil produced 28 billion liters, or 33% of the total output Corn is the primary feedstock for US ethanol, and sugarcane is 66 Bioenergy Systems for the Future the dominant source of ethanol in Brazil (Balat, 2011; Balat et al., 2008) Table 3.2 shows rate of ethanol production from different agro-waste, at various countries of the world during 2010 3.2.1.1 Production feedstocks Biological feedstocks that contain appreciable amounts of sugar—or materials that can be converted into sugar, such as starch or cellulose—can be fermented to produce bioethanol (Demirbas, 2007) Feedstocks of bioethanol can be conveniently classified into three categories of agricultural raw materials: (i) sucrose-containing feedstocks, (ii) starchy materials, and (iii) lignocellulosic materials Fig 3.2 indicates the feedstock classification for bioethanol production The availability of these materials for bioethanol can vary considerably from season to season and depends on geographic locations For a given production line, the comparison of the feedstocks includes several issues (Balat, 2011): (1) chemical composition of the biomass, (2) cultivation practices, (3) availability of land and land use practices, (4) use of resources, (5) energy balance, (6) emission of greenhouse gases, acidifying gases and ozone depletion gases, (7) absorption of minerals to water and soil, (8) injection of pesticides, (9) soil erosion, (10) contribution to biodiversity and landscape value losses, (11) farm gate price of the biomass, (12) logistic cost (transport and storage of the biomass), (13) direct economic value of the feedstocks taking into account the coproducts, (14) creation or maintenance of employment, and (15) water requirements and water availability Since feedstocks typically account for greater than one-third of the production costs, maximizing bioethanol yield is imperative Table 3.3 illustrates the various feedstocks that can be utilized for bioethanol production and their comparative production potential (Balat, 2009, 2011) Sucrose containing feedstocks Feedstock for bioethanol is essentially composed of sugarcane and sugar beet Two-thirds of world sugar production is from sugarcane and one-third is from sugar beet (Prado et al., 2016; Koc¸ar and Civaş, 2013) Sugarcane as a biofuel crop has much expanded in the last decade, yielding anhydrous bioethanol (gasoline additive) and hydrated bioethanol by fermentation and distillation of sugarcane juice and molasses (Hartemink, 2008) Sugarcane is grown in tropical and subtropical countries, while sugar beet is only grown in temperate-climate countries Brazil is the largest single producer of sugarcane with about 31% of global sugarcane production, average sugarcane yield of about 82.4 tons/ha, and bioethanol yield per hectare of around 6650 L/ha (Koc¸ar and Civaş, 2013; Hartemink, 2008; Gauder et al., 2011) In Asia (India, Thailand, and Philippines), sugarcane is produced on small fields owned by small farmers For example, India has around million small farmers with an average of around 0.25 sugarcane fields (Linoj Kumar et al., 2006) Sugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high concentration of sucrose In 2009, France, the United States, Germany, Russia, Rate of bioethanol production from agro-waste at various countries/continents Countries/ continents Wheat wastes (Tg)/ total bioethanol (GL) Sugarcane waste (Tg)/total bioethanol (GL) Rice wastes (Tg)/ total bioethanol (GL) Barley waste (Tg)/ total bioethanol (GL) Corn waste (Tg)/ total bioethanol (GL) Iran Asia Africa Europe America World 7.5/3 16/50 7/3 140/42 115/20 382/119 4.3/0.63 77/23 13/4 0.01/0.004 181/26 187/55 1.05/0.378 690/202 22/7 4/2 88/12 758/223.5 0.6/0.21 3.5/2 0.5/0.5 47/15.5 19.75/3.5 64.5/22.5 0.5/0.2 45/20 3.5/2.5 31/10 375/45 230/22.5 Production of bioalcohol and biomethane Table 3.2 67 68 Bioenergy Systems for the Future Bioethanol feedstocks Starch Sugar Root crops Stalk crops Root Cereals Cellulose Forest residues Energy crops MSW Agriculture wastes Paper wastes Fig 3.2 Feedstock classification of bioethanol production Table 3.3 Comparison of various bioethanol feedstocks Biomass type Sugarcane Cassava Sweet sorghum Corn Wheat Miscanthus Switchgrass Rice Maize Yield (ton/ ha/ year) Conversion rate to sugar or starch (%) Conversion rate to bioethanol (L/ton) Bioethanol yield (ton/ ha/year) Cost ($/m3) 70 40 35 12.5 25 14 70 150 80 4.9 2.8 160 700 200–300 80 20 30 45 69 66 – – – – 410 390 – – – – 2.05 1.56 1.5 1.5 250–420 380–480 – – – – and Turkey were the world’s five largest sugar beet producers In European countries, beet molasses are the most utilized sucrose-containing feedstock The advantages with sugar beet are a lower cycle of crop production, higher yield, high tolerance of a wide range of climatic variations, and low water and fertilizer requirement Compared with sugarcane, sugar beet requires 35%–40% less water and fertilizer (Demirbas, 2007; Koc¸ar and Civaş, 2013) Sweet sorghum (Sorghum bicolor L.) is one of the most drought-resistant agricultural crops as it has the capability to remain dormant during the driest periods and requires fewer inputs to achieve its maximal production Of the many crops being investigated for energy and industry, sweet sorghum is one of the most promising candidates, particularly for bioethanol production principally in developing countries (Stevens et al., 2004; Whitfield et al., 2012) Production of bioalcohol and biomethane 69 Starchy materials Another type of feedstock used for bioethanol production are starch-based materials Starch is a biopolymer and defined as a homopolymer consisting only one monomer, D-glucose To produce bioethanol from starch, it is necessary to break down the chains of this carbohydrate for obtaining glucose syrup through hydrolysis, which can be converted into bioethanol by yeasts This type of feedstock is the most utilized for bioethanol production in North America and Europe Corn/maize and wheat are mainly employed with these purposes The United States is predominantly a producer of bioethanol derived from corn, and production is concentrated in Midwestern states with abundant corn supplies (Cardona and Sanchez, 2007; Shapouri et al., 2006) Maize is increasingly used as a feedstock for the production of ethanol fuel It is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain The United States produces 40% of the world’s harvest; other top producing countries include China, Brazil, Mexico, Indonesia, India, France, and Argentina Worldwide production was 817 million tons in 2009, more than rice (678 million tons) or wheat (682 million tons) (Koc¸ar and Civaş, 2013; Shapouri et al., 2006) The starch-based bioethanol industry has been commercially viable for about many years; in that time, tremendous improvements have been made in enzyme efficiency, reducing process costs and time and increasing bioethanol yields Lignocellulosic biomass Globally, many lignocellulosic agro-residues such as rice straw, wheat straw, sugarcane bagasse, sugarcane tops, cotton stalk, soft bamboo, and switchgrass have been used to produce bioethanol as abundantly available feedstocks (Ravindranath et al., 2011) Lignocellulosic materials can be classified in four groups based on the type of resource: (1) forest residues, (2) municipal solid waste, (3) waste paper, and (4) crop residue resources These materials could produce up to 442 billion liters per year of bioethanol (Balat, 2011; Gupta and Verma, 2015) The production cost of bioethanol from food crops is very high as the raw materials (maize or sugarcane) constitute about 40%–70% of the production cost As a result, promoting the use of second-generation bioethanol from lignocellulosic biomasses such as nonfood crops, crop residues, and food/crop waste is an alternative way to alleviate the cost and the land use conflict between food needs and fuel needs (Sun and Cheng, 2002) Chemical composition of lignocellulosic materials is a key factor affecting efficiency of biofuel production during conversion processes As the lignocellulosic complex is made up of a matrix of cellulose and lignin bound by hemicelluloses, the main challenge in this case is to reduce the degree of crystallinity of the cellulose and increase the fraction of amorphous cellulose by the process of pretreatment, the most suitable form for the hydrolysis step (Tye et al., 2016) Lignin is one of the drawbacks of using lignocellulosic biomass materials in fermentation, as it makes lignocellulose resistant to chemical and biological degradation Sugars in lignocellulosics are not easily available, due to this tight structure, and require a previous pretreatment to make the hydrocarbon polymers available to 70 Bioenergy Systems for the Future saccharification and fermentation In general, the difficulties of using lignocellulosic materials are their poor porosity, high crystallinity, and lignin contents The cost of bioethanol production from lignocellulosic materials is relatively high when based on current technologies, and the main challenges are the low yield and high cost of the hydrolysis process In spite of this matter, by considering these materials as a cheap and abundant feedstocks, they can be a promising renewable resource for bioethanol production at reasonable costs (Balat, 2011; Sun and Cheng, 2002; Tye et al., 2016) Macro/Microalgea Interest has now been diverted to the third-generation biomass like algae, since the first-generation feedstock (edible crops, sugars, and starches) are under serious controversy considering the competition between food and fuel and the second-generation biomass (lignocellulosic biomass) is limited by the high cost for lignin removal as its incredible resistance to degradation and makes biomass saccharification costly Microalgae and macroalgae are the two groups of algae investigated as potential fuel sources Algal biofuels, also called advanced biofuels, are seen as one of the most promising solutions of global energy crisis and climate change for the years to come (Alam et al., 2012; Noraini et al., 2014) The production of third-generation biofuels has many advantages over the plants used for producing first- and second-generation biofuels due to their faster growth; capability of growing under several conditions, including in saline, brackish, and wastewater; reduced need for water and other resource inputs; the possibility of not occupying arable lands for their cultivation, greenhouse gas fixation ability (net zero emission balance), and high production capacity of lipids (Costa et al., 2012) Cell wall composition of algae differs from those of terrestrial plants The key difference is low content or the absence of lignin in macro- and microalgal feedstocks, which make them less resistant to conversion into simple sugars The biochemical composition of microalgae grown under normal conditions primarily encompasses proteins (30%–50%), carbohydrates (20%–40%), and lipids (8%–15%) The types and quantities of basic monosaccharide components such as mannose, galactose, and arabinose are potentially very suitable for conversion into bioethanol (de Farias Silva and Bertucco, 2016) Ethanol production from microalgae has been reported using the main classes of microalgae, that is, green (Ulva lactuca and U pertusa), red (Kappaphycus alvarezii, Gelidium amansii, G elegans, and Gracilaria salicornia), and brown (Laminaria japonica, L hyperborea, Saccharina latissima, Sargassum fulvellum, Undaria pinnatifida, and Alaria crassifolia) According to the results reported in many researches, the standard strains of Saccharomyces cerevisiae with only a few that have assessed ethanologenic or solventogenic bacterial strains such as Clostridium pasteurianum and recombinant E coli were utilized for optimal utilization and conversion of such diverse carbohydrates to bioethanol (Costa et al., 2012; de Farias Silva and Bertucco, 2016; Doan et al., 2012) 72 Bioenergy Systems for the Future Simultaneous saccharification and fermentation (SSF) Bioethanol Fermentation (Conversion of sugars to bioethanol) Distillation and evaporation Waste management Filter wash Lignin Enzymatic hydrolysis (Convers enzymatic hydrolysis (Conversion of cellulose to sugar) Biomass Pretreatment (Solubilisation of hemicellulose) Recirculation of process streams Residue-to-power production Fig 3.4 Schematic flow sheet for the bioconversion of bioethanol from biomass Bioethanol from lignocellulosic materials Four process steps for ethanol production from lignocellulosic materials are possible, namely, as pretreatment, hydrolysis, fermentation, and product separation/distillation Schematic flow sheet for the bioconversion of biomass to bioethanol is shown in Fig 3.4 The main challenge for this material is to reduce the degree of crystallinity of the cellulose and increase the fraction of amorphous cellulose by the process of pretreatment as the most suitable form for the hydrolysis step After pretreatment, the cellulose undergoes enzymatic hydrolysis in order to obtain glucose that is converted to ethanol by microorganisms (Sun and Cheng, 2002; Tye et al., 2016; Chen and Fu, 2015) Pretreatment process The most important processing challenge in the production of biofuel is pretreatment of the biomass for further chemical or biological treatment Pretreatment methods change the native properties of the substrate by solubilization and separation of one or more of components of biomass and making the remaining solid biomass more accessible to further treatment For instance, starchy substrates can be fermented after breaking starch molecule into simpler glucose molecules, and this can be done by a pretreatment step For lignocellulosic biomass, the pretreatment is done to break the matrix in order to reduce the degree of crystallinity of the cellulose, increase the fraction of amorphous cellulose, and convert it to the most suitable form for enzymatic attack (Balat, 2011; Chen and Fu, 2015) Pretreatment methods can be categorized into physical, chemical, biological, and physicochemical methods, which are discussed in detail below The goals of an effective pretreatment process are (i) to form sugars directly or subsequently by hydrolysis Production of bioalcohol and biomethane 73 (ii) to avoid loss and/or degradation of sugars formed, (iii) to limit formation of inhibitory products, (iv) to reduce energy demands, and (v) to minimize costs (Balat, 2011; Tye et al., 2016) Physical pretreatment The primary steps for ethanol production from agroresidues are combination of methods like mechanical milling, grinding, and chipping that are used to diminish the particle size, increase the surface area, and improve the mass transfer characteristics Also these methods reduce the cellulose crystallinity and improve the efficiency of downstream processing Besides the mechanical combination, the physical pretreatment technology also includes uncatalyzed steam explosion, liquid hot water pretreatment, and high-energy radiation, of which steam explosion loosen the recalcitrant structure of plant cell wall by increasing surface area and removes pentose sugar, but the major drawback of steam treatment during enzymatic hydrolysis is generation of some cellulose inhibitory compounds that hamper the enzymatic hydrolysis of the cellulose substrates (Tye et al., 2016; Chen and Fu, 2015) Chemical and physicochemical pretreatment Chemical pretreatment methods include ozonolysis, acid hydrolysis, and alkali hydrolysis that involve the usage of dilute acid, alkali, ammonia, organic solvent, sulfuric and formic acids, SO2, CO2, or other chemicals The physicochemical pretreatment methods include ammonia fiber explosion and steam pretreatment These methods are easy in operation and have good conversion yields in short span of time But the major impedance of chemical pretreatment is that the utilization of such chemicals affects the total economy of bioconversion of cellulosic biomass Shenoy et al (Balat, 2011) showed that among chemical treatments, the dilute sulfuric acid-based pretreatment is most popular by means of enzymatic hydrolysis using agricultural biomasses Biological pretreatment The biological pretreatment methods mainly involve utilizing different fungal species like brown rot, white rot, and soft rot fungi for degradation of the lignocellulosic complex to liberate cellulose Biological pretreatment renders the degradation of lignin and hemicellulose, and white rot fungi seem to be the most effective microorganism Brown rot attacks cellulose, while white and soft rots attack both cellulose and lignin Celluloseless mutant was developed for selective degradation of lignin and to prevent the loss of cellulose, but in most cases of biological pretreatment, the rate of hydrolysis is very low The advantages of biological pretreatment include low energy requirement and mild environmental conditions (Tye et al., 2016; Mosier et al., 2005) The major effects of pretreatment on lignocellulosic feedstocks are illustrated in Fig 3.5 Hydrolysis process As the pretreatment is finished, the material is prepared for hydrolysis, which means the process of cleavage of a molecule by adding a water molecule as shown below: ðC5 H10 O5 Þn + nH2 O ! nC6 H12 O6 (3.1) Generally, conversion of starchy materials to glucose monomers by saccharification process (above reaction) is catalyzed by acids or enzymes The enzymatic hydrolysis 74 Bioenergy Systems for the Future Major changes – Lignin redistribution – Increased porosity of the lignified cell-wall – Size reduction Major targeted Components – Lignin – Hemicellulose – Cellulose Pretreatment Mechanical and/or Thermo-chemical and/or Biological methods Lignocellulosic feedstock – Increased surface area of cellulose for % of toxic by-products released depends on pretreatment type greater enzymes Energy consumption accessibility – Hydrolysis – Fermentation – Distillation Bioethenol Fig 3.5 Pretreatment upstream process, major effects is a long-timed process with many advantages like very mild conditions (pH 4.8 and temperature 318–323 K) and high yields Its maintenance costs are low compared with alkaline and acid hydrolysis due to no corrosion problems, but the initial cost of enzymes is too high (Prado et al., 2016; Mosier et al., 2005) There are two basic types of acid hydrolysis processes, dilute acid and concentrated acid, each with variations Acids used for chemical hydrolysis include H2SO4, HCl, H2O2, phosphoric acid, and nitric acid Dilute acid hydrolysis processes are conducted under high temperature (473–513 K) and pressure and have reaction times in the range of seconds or minutes In the process, the acid breaks down the matrix structure, and the released polymer sugars, cellulose, and hemicellulose are hydrolyzed into free monomer molecules readily available for fermentation and conversion to bioethanol It is followed by hexose and pentose degradation and formation of high concentrations of toxic compounds including HMF and phenolics detrimental to an effective saccharification (Sun and Cheng, 2002; Chen and Fu, 2015) Concentrated acid hydrolysis, the more prevalent method, has been considered to be the most practical approach Unlike dilute acid hydrolysis, concentrated acid hydrolysis is not followed by high concentrations of inhibitors and produces a high yield of free sugars (90%); however, it requires large quantities of acid and costly acid recycling, which makes it commercially less attractive (Tye et al., 2016; Mosier et al., 2005) Fermentation process Fermentation is one of the oldest processing technologies in the world, and today, the technological advancements have made this process more efficient and valuable Pretreatment and hydrolysis processes are designed to optimize the fermentation process This natural biological pathway requires the presence of microorganisms to ferment sugar into alcohol, lactic acid, or other end products Production of bioalcohol and biomethane 75 depending on the conditions and raw material used Moreover, an optimal fermentative microorganism should be tolerant to a high ethanol concentration and to chemical inhibitors formed during pretreatment and hydrolysis process Microorganisms, termed ethanologens, presently convert an inadequate portion of the sugars from biomass to bioethanol Saccharomyces cerevisiae has also been utilized for corn-based and sugar-based biofuel industries as the primary fermentative strain for bioethanol production (Balat, 2011; Gupta and Verma, 2015; Sun and Cheng, 2002) The fermentation of different substrates for bioethanol production can be achieved by three processes, namely, batch, fed-batch, and continuous fermentation Batch culture can be considered as a closed-loop, discontinuous system that contains an initial, limited amount of nutrient, which is inoculated with microorganisms to allow the fermentation Fed-batch fermentation is a production technique in between batch and continuous fermentation in which one or more feed input, with the right component constitution is required Fed-batch process is a more efficient cultivation strategy than the batch process in which microorganisms work at low substrate concentration with an increasing ethanol concentration This system often provides better yield and productivities than batch cultures by preventing contaminations In continuous fermentation, the substrate is added to the fermenter continuously at a fixed rate This maintains the microorganisms in the logarithmic growth phase, and the fermentation products are taken out continuously The advantage of continuous culture technique is higher percentage of end product in comparison with batch and fed-batch systems Also, the continuous process eliminates much of the unproductive time associated with cleaning, recharging, adjustment of media, and sterilization (Suresh et al., 1999; Balat, 2011; Gupta and Verma, 2015; Chen and Fu, 2015) Separation process Bioethanol obtained from a fermentation conversion requires further separation and purification of ethanol from water through a distillation process Fractional distillation is a process implemented to separate ethanol from water based on their different volatilities Distillation process consumes a great deal of energy for providing heat to change liquid to vapor and condense the vapor back to liquid at the condenser and ethanol distillate recaptured at a concentration of about 95% With rising energy awareness and growing environmental concerns, there is a need to reduce the energy use in industry (Suresh et al., 1999; Larson, 2008) 3.2.2 Biomethane production As mentioned in the previous section, the demand for renewable fuels is increasing with growing concern about climate change, air quality, energy import dependence, and depletion of fossil fuels The biogas is a carbon-neutral source of renewable energy, and it is a competitive alternative in energy production in both its energy efficiency and its environmental impact As biogas replaces fossil fuel, there is an accompanying reduction of greenhouse gas, particles, and nitrogen oxide emissions (Koc¸ar and Civaş, 2013) Biogas production is an efficient way to dispose of organic waste, while extracting energy, fertilizer, and valuable by-products Biogas, a methane-rich 76 Bioenergy Systems for the Future gas produced by anaerobic treatment of any biomass, is a multibenefit, flexible technology that can be applied on household scale, village scale, or industrial scale Biogas production from energy crops is a long-established technology that represents a more thermodynamically efficient option than converting plant matter into liquid fuels Biogas typically contains (v/v) 50%–75% methane, 25%–50% carbon dioxide, 1%–5% water vapor, 0%–5% nitrogen, smaller amounts of hydrogen sulfide (0–5000 ppm), ammonia (0–500 ppm), and trace concentrations of hydrogen and carbon monoxide Biogas is a versatile renewable fuel that can be used for power and heat/cool production, or it can be upgraded to biomethane to be used as vehicle fuel Various technologies, such as water scrubbing, pressure swing adsorption, and membrane technologies, are currently applied to upgrade biogas to biomethane for use as vehicle fuel or to be injected into a natural gas grid (Koh and Ghazoul, 2008; Murray, 2005; Licht, 2008; Nexant, Inc, 2006; Alam et al., 2012; Thomson, 2008; Koc¸ar and Civaş, 2013) The anaerobic conversion of crops into methane is now viable in some countries, and the most spectacular example of this trend is the construction and operation of over 5000 anaerobic digesters in Germany during the past 20 years (Koc¸ar and Civaş, 2013) 3.2.2.1 Production feedstocks Feedstock composition is one of the major factors that affect the production of biogas Methane yields are related to the substrates used as feeding material, ash content, and the level of storage sugars, and also it is linked with the type of interaction between different wastes that interfere with digestibility of wastes in anaerobic digestion (AD) processes A variety of feedstocks can be used for biomethanation; however, the conventional materials for biogas production are agricultural crops, animal wastes, sewage sludge, woody biomass, grass, terrestrial weed, marine biomass, and freshwater biomass The sugar and starch crops are the main energy crops currently used on a commercial scale for the production of biomethane (i.e., 5300–12,390, 6604, and 5400 m3 CH4/ha “methane yield per hectare” for corn, triticale, and sugar beets, respectively) For instance, with wheat or maize, up to three times more net energy yield can be obtained per hectare by making methane instead of biodiesel or bioethanol Although these crops generate high yields of methane, they also have other uses as food and/or feed, which may often compete with biofuel production (Sreekrishnan et al., 2004; G€ ubitz et al., 2010) Germany, Austria, and Denmark produce the largest share of their biogas in agricultural plants using energy crops, agricultural by-products, and manure (Alam et al., 2012) Cellulosic or lignocellulosic crops are represented by different grasses containing small percentage of lignin (hay, clover, and reed canary grass), while other energy crops such as Panicum virgatum, Miscanthus, or switchgrass are containing higher levels of lignin (12%–20%) Switchgrass was chosen as the model lignocellulosic crop by the US Department of Energy in the 1990s and is believed to return 540% more renewable energy than fossil fuel consumption (G€ubitz et al., 2010) Production of bioalcohol and biomethane 77 3.2.2.2 Production methods Methane fermentation technology is considered as the most efficient form of handling and energy generation from biomass in terms of energy input/output ratio In biomethanation insoluble complex compounds like cellulose, proteins and fats are converted to methane by anaerobic microbes But the degradation of lignin is slow and incomplete, and hence, the lignocellulosic materials should be better pretreated to expose other components (Rasi et al., 2011) Methane fermentation is a complex biological process that needs a variety of different microbes at different stages It involves four phases of biomass degradation and conversion-hydrolysis, acidogenesis, cetogenesis, and methanation Enzymes like hydrolases and exoenzymes of facultative or obligatory anaerobic bacteria hydrolyze cellulose, proteins, and fats to simpler monomers During acidogenesis, these monomers are converted to short-chain organic acids, alcohols, hydrogen, and carbon dioxide by different sets of facultative and obligatory anaerobic bacteria Acetogenic microorganisms reduce hydrogen and carbon dioxide to acetic acid During this acetogenic phase, organic acids and alcohols may get converted to acetate These products can serve as substrates for methane-forming bacteria in strict anaerobic conditions The produced methane, being a gas, is separated by itself from the liquid making the product removal easy (Sreekrishnan et al., 2004; G€ ubitz et al., 2010) Methane production in anaerobic fermentation system is not constant but may decrease over time, and the rate depends on the substrate hydrolysis The premixing of feedstock with lignin-degrading enzymes (lignin peroxidase, manganese peroxidase, and soybean peroxidase) or cellulose prior to AD improves the lignocellulosic degradation and enhances methane production The methane production stages are described in detail in the next section (B€orjesson and Mattiasson, 2008) Pretreatment process Cost competitiveness, cost-effectiveness, and ease of downstream processing are the factors to be considered for selecting the most desirable pretreatment method Pretreatments are directed more specifically to enhanced methane production from lignocellulosic biomass since the rate-limiting step in AD of lignocellulosic crops is the hydrolysis of complex polymeric substances and, in particular, the cross-linking of lignin that is nonbiodegradable with the cellulose and hemicellulose Physical, thermochemical, and biochemical (enzymatic) methods have been employed to increase biomass digestibility In physical methods, a large portion of hemicelluloses and lignin can be removed by methods like milling, homogenization, and flow-through In thermochemical methods, various inorganic salts or alkalies (lime, sodium hydroxide, ammonia, sulfuric acid, etc.) can be used, but the use of strong chemicals may have various disadvantages like reactor corrosion, extensive washing requirement for treated solids, and thus production of large volumes of waste streams Also high cost and production of undesirable products like organic acids, furan derivatives, and phenolic compounds make it problematic Therefore, the optimal pretreatment method should require limited capital and operating and maintenance costs and be 78 Bioenergy Systems for the Future Cellulose Pretreatment Hemicellulose Fig 3.6 Schematic representation of pretreatment process on lignocellulosic material sufficiently fast leading to reduced volumes of pretreatment units (Mosier et al., 2005; Sreekrishnan et al., 2004; B€ orjesson and Mattiasson, 2008) Fig 3.6 shows the pretreatment process on lignocellulosic material Main production stages Extraction of biofuels can be carried out by two methods, namely, anaerobic and thermal conversion methods, which are discussed in the following, comprehensively Thermal conversion method involves pyrolysis, partial combustion, and reduction or gasification reactions The whole process is termed as gasification, which converts the available biomass into biofuels like product gas, syngas, and biogas The main constituents present in the product gas are carbon monoxide, hydrogen, carbon dioxide, methane, water vapor, nitrogen oxides, tar (heavy hydrocarbons), sulfur compounds, and particulate matter (Kumar and Shukla, 2016) Thermal conversion method l l Gasification step Gasification technology is basically a process for converting solid or liquid feedstock into a gaseous or liquefied fuel that can be burned to release energy Generally, gasification process is completed in four stages: drying, pyrolysis, partial combustion, and reduction Gasifiers are mainly classified into three types according to the type of feedstock used: fixed bed type, fluidized bed type, and entrained flow type The feedstock is feed from the top of the gasifier through hopper, and the gasifying agent like air, oxygen, or steam is introduced from the sides of the reactor at combustion zone Gasification process involves complex combination of pyrolysis and oxidation where the biomass starts converting gaseous form and releases CO, H2O, CH4, CO2, H2, NOx, and tar (Basu, 2010) Methanation step Methanation is the last stage process in the purification of the product gas The product gas has to be tar-free and has less concentration of CO2 The remaining CO and CO2 left in the gas will undergo catalytic reaction with hydrogen to form methane: Production of bioalcohol and biomethane 79 CO + 3H2 O ! CH4 + H2 O, ΔH ¼ 51:8kcal=mol (3.2) CO2 + 4H2 O ! CH4 + 2H2 O, ΔH ¼ 41:9kcal=mol (3.3) According to the literature, nickel-based catalyst is used at operating temperature of about 300°C, which converts all oxides of carbon to methane and water (Basu, 2010) AD method One such well-known and widely used method for bioconversion of wastes into fuel in the absence of oxygen is AD, which is regarded as the simplest technique due to its very limited environmental impact and high energy recovery potential (G€ ubitz et al., 2010; B€ orjesson and Mattiasson, 2008; Kumar and Shukla, 2016; Basu, 2010; Edelmann et al., 2005) Other advantages of AD include dilution of the toxic substances coming from any of the substrates involved, an improved nutrient balance, synergistic effects on microorganisms, a high digestion rate, and possible detoxification based on the cometabolism process The dilution of toxic substance can reduce GHG emission, thus improving air quality (Edelmann et al., 2005) The metabolic reactions that occur during AD of substrates using microorganisms for methane formation involve four important stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis In addition, the structure of microbial community presented in the system, environmental factors such as temperature and PH play a significant role in determining the performance and fate of the microbial community in anaerobic digesters (Basu, 2010) Researchers have reported that methanogenesis is the rate-limiting step for easily biodegradable substances, whereas hydrolysis is the rate-limiting step for complex organic wastes due to formation of toxic by-products like complex heterocyclic compounds and undesirable volatile fatty acids (Lam and Lee, 2011) Fig 3.7 depicts the main pathways of an AD, and the descriptions for each stage are given in the following section l l l Hydrolysis step Hydrolysis is the first stage of the organic waste decomposition process involving the breakdown of large organic polymer chains into smaller molecules such as simple sugars, amino acids, and fatty acids Other products such as hydrogen and acetate maybe used by methanogens later in the process Saccharolytic and proteolytic microorganisms break down sugars and proteins, respectively This is carried out by several hydrolytic enzymes such as celluloses, cellobiase, xylanase, amylase, lipase, and protease secreted by hydrolytic microbes (Basu, 2010; Demirel and Scherer, 2008) Acidogenesis step The second step is acidogenesis (also referred to as fermentation), in which the hydrolyzed products are degraded further to simpler organic products such as ammonia, acetate, hydrogen, carbon dioxide, and hydrogen sulfide These final products of fermentation will eventually become the precursors of biomethane formation (Demirel and Scherer, 2008) Acetogenesis step During this step, acetogens produce intermediary products such as propionate, butyrate, lactate, ethanol, and energy sources Close cooperation is required between oxidative organisms and methane-producing organisms that are active during methanogenesis This process consumes hydrogen gas, and intermediary products will be converted to simpler organic acid, CO2, and H2 by acetogenic bacteria (Lam and Lee, 2011; Demirel and Scherer, 2008) 80 Bioenergy Systems for the Future Organic polymers Carbohydrates Proteins Lipids Sugars, alcohols Amino acids Fatty acids Hydrolysis Acidogensis Intermediary products acetate, propionate, ethanol, lactate Acetogensis CH4, CO2 H2, CO2 Methanogensis CH4, CO2 Fig 3.7 Diagram of anaerobic digestion process l Methanogenesis step Methanogenesis is the final stage of AD methane production stage, where methanogens produce methane from hydrogen, carbon dioxide, and acetate, and intermediates products from hydrolysis and acidogenesis Methane is produced by two groups of bacteria (methanogens), namely, acetotrophic methanogens and hydrogenotrophic methanogens Acetotrophic methanogens convert acetate to biomethane and CO2, whereas hydrogenotrophic methanogens use H2 as electron donor and CO2 as electron acceptor to produce biomethane (Demirel and Scherer, 2008) 3.3 Membrane processes for biofuels production Nowadays, one of the main challenges to the large-scale industrial production of biofuels is the lack of cost-effective separation methods for the isolation and purification of biobased chemicals and fuels (Wickramasinghe and Grzenia, 2008) Indeed, the separation operations account for 65%–85% of the processing costs of most mature chemical processes (Ragauskas et al., 2006) Hence, membrane separation technologies have gained more attention owing to their reduced energy requirements, lower labor costs, lower floor space requirements, and wide flexibility of operation This Production of bioalcohol and biomethane Table 3.4 81 Membrane technology application in biofuel production Applications Upstream from the fermentation process Clarification or fractionation of feedstock material going to the fermenter Acid and alkali recovery and reuse; separation of lignin from hydrolyzed biomass Protein recovery/removal from hydrolyzed prepared biomass Concentration of sugars to enable product yield enhancement in the fermentation Continuous enzyme reactors retain enzyme and substrate, permitting removal of reaction-inhibiting components Membrane process types UF and/or MF UF and/or NF UF NF UF and/or NF Downstream from the fermentation process Biomass/microbial cell retention that enables continuous recovery of the target product component or removal of fermentation inhibitor molecules Concentration of organic acids with water recovery for reuse Evaporator condensate treatment for water recovery and reuse enabling environmental compliance Amino acid concentration and desalting UF and/or NF RO RO NF promising technology has been applied in many processes of bioethanol production instead of the traditional process (Chapman et al., 2008; Vane, 2005; Qureshi and Manderson, 1995; He et al., 2012; Lipnizki, 2010; Rothman et al., 1983) In general, membrane filtration technologies, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), are proving to be effective procedure to achieve optimum yields and reduce energy costs for biofuels production However, it should be noted that membrane filtration technology shows promise to improve “second-generation” and “third-generation” bioethanol processes As a general point of view, Table 3.4 presents various applications of membrane technologies in biofuel production With regard to literatures (Sadati et al., 2014; Wei and Cheng, 2014; Shah and Sen, 2011), in biofuel production, most applications of membrane technology are devoted to bioethanol production Therefore, an overview of bioethanol production with potential membrane applications is depicted in Fig 3.8 Indeed, the first potential membrane application is the harvesting of microalgae for third-generation bioethanol synthesis By using MF/UF, it is possible to recover microalgae For second- and thirdgeneration bioethanol, pretreatment is a necessary step to make the carbohydrates in the biomass available for conversion The second potential membrane application is the purification and concentration of prehydrolyzates after pretreatment and before fermentation Membrane distillation (MD), NF, and RO can concentrate the sugar solution and remove inhibitors to fermentation process 82 Bioenergy Systems for the Future Starched-based materials Microalgae Cellulosie material MF/UF Membrane process (Harvesting) Pretreatment Scarification MF/UF/MD Membrane process (Concentration of sugar solution) Fermentation-pervaporation (Hybrid process) Ethanol fuel Fig 3.8 Application of membrane process for three generation types of bioethanol production With regard to enzyme and other value-added production recovering, an NF process has been combined with UF process After fermentation, low concentration bioethanol is sent for pervaporation and preconcentration On the other hand, fermentation and pervaporation have been integrated to perform continuous fermentation During the hybrid process, UF and NF process can be applied to remove fermentation inhibitors and yeast However, the various fermentation systems used are batch, continuous, fed-batch and semicontinuous, immobilized systems, and membrane bioreactor (MBR) systems Indeed, the MBR systems, in addition to energy and water savings, can continuously remove ethanol from the fermentation process, thereby accelerating fermentation and increasing product capacity without the installation of additional tank It should be noted that high alcohol-water Production of bioalcohol and biomethane 83 selectivities are critical to the energy efficiency of pervaporation There are some reports in the literature (Chen et al., 2012; Ding et al., 2011; Nomura et al., 2002; Ikegami et al., 1997; Schmidt et al., 1997) discussing about continuous ethanol production by pervaporation using different cultures, membranes, and configurations 3.4 Conclusion and future trends The chapter has discussed about concept of biofuels, different types of biofuels, and various production methods of biofuels Regarding literatures, various types of biofuels could be produced; among them, bioalcohol and biomethane were considered in this work According to studies, biological feedstocks that contain appreciable amounts of sugar or materials that can be converted into sugar, such as starch or cellulose, can be fermented to produce bioethanol, while the conventional feedstocks for biomethane production are agricultural crops, animal wastes, sewage sludge, marine biomass, and freshwater biomass As a general consequence, to improve bioprocesses for biofuel production, lower overall energy costs, and increase valuable product recovery, water removing is necessary Membrane technology in bioprocesses has the potential to greatly reduce operating costs compared with the traditional processes using an evaporator to 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Processing of materials derived from sweet sorghum for biobased products Ind Crop Prod 37, 362–375 Wickramasinghe, S.R., Grzenia, D.L., 2008 Adsorptive membranes and resins for acetic acid removal from biomass hydrolysates Desalination 234, 144–151 Further Reading Ahmed, Y., Yaakob, Z., Akhtar, P., Sopian, K., 2015 Production of biogas and performance evaluation of existing treatment processes in palm oil mill effluent (POME) Renew Sust Energ Rev 42, 1260–1278 ... aim of this chapter is to present a state -of -the- art review on the bioalcohol and biomethane production processes and also on the applications of membrane technologies for their production 3. 2... photosynthesis and does not compete with Production of bioalcohol and biomethane 65 the production of food; hence, it is devoid of the major drawbacks associated with firstand second-generation biofuels... 57% of global output, and Brazil produced 28 billion liters, or 33 % of the total output Corn is the primary feedstock for US ethanol, and sugarcane is 66 Bioenergy Systems for the Future the