**4. Biorefinery systems**

reduced. Human activity cannot be reduced, but this type of activity can be develop on the way of environmental education. In the same way, you can indirectly seek to reduce the

There are two ways to reduce the environmental load. The first of these is to limit the use of resources, which is called dematerialization, which is gradually reducing usage of resources in technological processes. The next step should be the determined counteraction character of the life of a consumer society in developing countries and developed countries. Another way to limit the use of natural resources, including energy ones, is to replace the current raw materials for other unknown resources, by-products, or wastes from other processes, which is

Both of the abovementioned proceedings road are independent, but only their parallel application can provide the most tangible effect of actions to reduce the impact of human activities, including industrial environment. The Earth and its biosphere are thermodynamic systems exchanging with the environment energy only. The components of the biosphere subsystems, however, are open systems, exchanging with their environment both energy and matter. One of the subsystems, so-called man-made technosystem, collects raw materials from the environment and excretes waste. Systematic expansion of the technosystem and its impact not only contributes to an imbalance in the biosphere but also causes a real threat to its future

In the context of this situation arises question about the possibility of avoiding further destruction of the biosphere. Following Johansson, there are two possibilities for remedying

The first one is the complete separation of the technosystem of the biosphere, creating a closed technosystem. This method would involve major technological challenges for the modification of existing technologies for closing circuits of waste, which will entail a significant increase in energy consumption. Note also that technosystem separated from the biosphere would have

The second method proposed by Johansson is the adaptation of the technosystem to the environment in such a way that its action plays the strategy and action, which uses nature. In this solution, however, certainly limitation of many existing technological capabilities would occur, including reduction in the size and density of the local industrial activities, which, at this stage of the development of civilization, have already been exceeded in many cases. Implementation of this strategy would involve fundamental reorganization of the existing technological structure which would entail the search for new technological solutions [7].

Due to the fundamental problem of modern society as of a linear flow of matter from its source as raw materials to the waste stage and the accumulation of products of human activity in this form in order to maintain good environmental status as long as possible, our society must in its actions be inspired by nature, reducing the negative environmental impact to a minimum. A society that wishes to survive must maintain the activity causing disorder within order, possible to achieve by the energy captured from the sun. In addition, waste (degraded material

environmental impact and the burden of every human activity [25, 26, 27].

called transmaterialization [7, 28].

434 Biofuels - Status and Perspective

to thus eliminate human intervention [7].

existence [29, 30].

this problem.

One of the ways to mitigate the negative effects of local ecosystems is the conversion of biomass and organic waste into a different type of chemical substances or biomaterials and energy to fully exploit the value of the biomass, creating the so-called added value and minimizing the quantity of naturally produced substance or waste. This integrated approach reflects the concept of biorefineries and is gaining more and more attention in many parts of the world.

Similarly to the conventional refinery which produces energy and chemical products from petroleum, biorefineries will produce a variety of industrial products from biomass. These products are both LVHV type (low value and large volume), such as transport fuels and highvolume chemicals and other materials, and HVLV type (high value and low volume), as specialized chemicals and cosmetics, for example. In some types of plant, there also can be produced food and animal feed.

Energy sources are the main driving force behind the development of this type of installation, but sometimes when biorefineries will become more advanced and complex systems, the development of other products such as installations also occurs.

Biorefinery systems are nothing more than a kind of open systems, where part of the input streams is biomass, waste, and energy flow. Within the system there is a series of processes resulting in, for example, the energy exchange with the environment in the form of heat and work. An output streams of biorefinery systems constitute a number of products such as fuels, chemicals (both highly valuable, which are obtained in small quantities, and of low value, obtained in large quantities), feed and food products, polymers, and other materials, as well as the energy produced in cogeneration or trigeneration (heat, electricity, and cooling) and processed waste. Please note that these wastes are waste only for the specific biorefining process. For another manufacturing process, these can be a substrate.

Biorefinery systems, imitating in its actions a living organism as open systems, in contrast to conventional petroleum refinery, may therefore constitute one of the elements of sustainable development [33].

### **4.1. The concept of biorefinery**

Repeatedly attempting to define the concept of biorefineries, and as a consequence, a number of incomplete or differing definitions have been established. After attempts to deduce from them the most important elements and characteristics of this new branch of industry, a comprehensive definition of the biorefinery has been established, according to which, it is an integrated "bio-industry," which uses a variety of technologies in order to obtain products such as chemicals, biofuels, food, feed ingredients, biomaterials (including fibers), and heat and energy, focusing on maximizing the added value, taking into account the three pillars of sustainability: environment, economy, and society. According to the definition of the Interna‐ tional Energy Agency (IEA), biorefinery is a way for sustainable biomass processing in a wide range of bio-products of food, feed, chemicals, and biomaterials and bioenergy products such as biofuels, electricity, and heat [34].

By definition, biorefinery is a complex technological system that combines biomass conversion processes and the further processing of products of this conversion to fuels and chemicals – final or intended for further processing. Therefore, biorefinery is equivalent to crude oil processing plants (Figs. 3 and 4), where the substrate is crude oil, natural gas, or other fossil energy resources. These resources are processed in petrorefinery processes on a variety of products, mainly fuel, electricity, heat, chemicals, and various kinds of materials. The subs‐ trated in biorefineries are organic materials such as wood, energy crops, grass, and organic waste, which are processed in biorefinery processes – which are similar to the refinery processes – used in conventional petroleum refineries. Products from biorefinery are also the fuels and cogeneration or trigeneration energy, chemicals, and materials as well as food and animal feed. The basic petrorefinery scheme is shown in Fig. 3; Fig. 4 shows a general schematic diagram of a biorefinery.

As can be seen from a comparison of those two patterns, petrorefinery and biorefinery are related systems, processing a substrate or a plurality of substrates into a product or series of products by means of one or more technological processes which, as mentioned earlier, can be used both in a single and the second type of installation.

As mentioned, it should be noted that both the raw materials and also products of the biorefinery should be a much smaller threat to the environment, mainly emission of green‐ house gases. Hence, industrial biorefineries should constitute the most important element of

Figure 4. Ideological scheme of biorefinery Figure 4. Ideological scheme of biorefinery **Figure 4.** Ideological scheme of biorefinery

diagram of a biorefinery.

diagram of a biorefinery.

work. An output streams of biorefinery systems constitute a number of products such as fuels, chemicals (both highly valuable, which are obtained in small quantities, and of low value, obtained in large quantities), feed and food products, polymers, and other materials, as well as the energy produced in cogeneration or trigeneration (heat, electricity, and cooling) and processed waste. Please note that these wastes are waste only for the specific biorefining

Biorefinery systems, imitating in its actions a living organism as open systems, in contrast to conventional petroleum refinery, may therefore constitute one of the elements of sustainable

Repeatedly attempting to define the concept of biorefineries, and as a consequence, a number of incomplete or differing definitions have been established. After attempts to deduce from them the most important elements and characteristics of this new branch of industry, a comprehensive definition of the biorefinery has been established, according to which, it is an integrated "bio-industry," which uses a variety of technologies in order to obtain products such as chemicals, biofuels, food, feed ingredients, biomaterials (including fibers), and heat and energy, focusing on maximizing the added value, taking into account the three pillars of sustainability: environment, economy, and society. According to the definition of the Interna‐ tional Energy Agency (IEA), biorefinery is a way for sustainable biomass processing in a wide range of bio-products of food, feed, chemicals, and biomaterials and bioenergy products such

By definition, biorefinery is a complex technological system that combines biomass conversion processes and the further processing of products of this conversion to fuels and chemicals – final or intended for further processing. Therefore, biorefinery is equivalent to crude oil processing plants (Figs. 3 and 4), where the substrate is crude oil, natural gas, or other fossil energy resources. These resources are processed in petrorefinery processes on a variety of products, mainly fuel, electricity, heat, chemicals, and various kinds of materials. The subs‐ trated in biorefineries are organic materials such as wood, energy crops, grass, and organic waste, which are processed in biorefinery processes – which are similar to the refinery processes – used in conventional petroleum refineries. Products from biorefinery are also the fuels and cogeneration or trigeneration energy, chemicals, and materials as well as food and animal feed. The basic petrorefinery scheme is shown in Fig. 3; Fig. 4 shows a general schematic

As can be seen from a comparison of those two patterns, petrorefinery and biorefinery are related systems, processing a substrate or a plurality of substrates into a product or series of products by means of one or more technological processes which, as mentioned earlier, can be

As mentioned, it should be noted that both the raw materials and also products of the biorefinery should be a much smaller threat to the environment, mainly emission of green‐ house gases. Hence, industrial biorefineries should constitute the most important element of

process. For another manufacturing process, these can be a substrate.

development [33].

436 Biofuels - Status and Perspective

**4.1. The concept of biorefinery**

as biofuels, electricity, and heat [34].

diagram of a biorefinery.

used both in a single and the second type of installation.

new industrial sectors, based on renewable energy sources (raw materials), offsetting at least part of the progressive deficiency of existing media such as oil, coal, and natural gas [35]. As can be seen from a comparison of those two patterns, petrorefinery and biorefinery are related systems, processing a substrate or a plurality of substrates into a product or series of products by means of one or more technological processes which, as mentioned earlier, can be used both in a single and the second type of installation. As can be seen from a comparison of those two patterns, petrorefinery and biorefinery are related systems, processing a substrate or a plurality of substrates into a product or series of products by means of one or more technological processes which, as mentioned earlier, can be used both in a single and the second type of

Biorefinery can be considered as a tool for the implementation of sustainable development in the processes of energy use and waste of natural resources. According to the concept of sustainable development, this type of installation procuring energy is the most optimal solution that simultaneously takes into account the continuous technological development, production of so-called "clean" energy and other products while reducing greenhouse gases and harmful compounds. This technology is almost "waste-free," which uses the existing potential of biomass waste, which currently is not used at all or is used in an irrational way [35]. As mentioned, it should be noted that both the raw materials and also products of the biorefinery should be a much smaller threat to the environment, mainly emission of greenhouse gases. Hence, industrial biorefineries should constitute the most important element of new industrial sectors, based on renewable energy sources (raw materials), offsetting at least part of the progressive deficiency of existing media such as oil, coal, and natural gas [35]. Biorefinery can be considered as a tool for the implementation of sustainable development in the processes of energy use and waste of natural resources. According to the concept of sustainable development, this type of installation. As mentioned, it should be noted that both the raw materials and also products of the biorefinery should be a much smaller threat to the environment, mainly emission of greenhouse gases. Hence, industrial biorefineries should constitute the most important element of new industrial sectors, based on renewable energy sources (raw materials), offsetting at least part of the progressive deficiency of existing media such as oil, coal, and natural gas [35]. Biorefinery can be considered as a tool for the implementation of sustainable development in the processes of energy use and waste of natural resources. According to the concept of sustainable development, this type of

installation procuring energy is the most optimal solution that simultaneously takes into account the continuous

#### **4.2. Biorefinery processes** technological development, production of so-called "clean" energy and other products while reducing greenhouse gases and harmful compounds. This technology is almost "waste-free," which uses the existing installation procuring energy is the most optimal solution that simultaneously takes into account the continuous technological development, production of so-called "clean" energy and other products while reducing

Depending on the raw material and the desired product, biorefineries use a variety of con‐ version technologies of raw biomass to commercial sources. These processes frequently include fermentation, gasification, and transesterification. New and less traditional methods are still in the research area, especially in the development of synthetic biofuels, such as liquid biofuels from biomass (BtL – biomass to liquid). Other substances, except fuels, produced in biorefinery processes, such as chemicals or other materials, are not as popular as energy biorefinery products and are at a much lower level of development in terms of trade with respect to fuels derived from these plants. potential of biomass waste, which currently is not used at all or is used in an irrational way [35]. 4.2. Biorefinery processes Depending on the raw material and the desired product, biorefineries use a variety of conversion technologies of raw biomass to commercial sources. These processes frequently include fermentation, gasification, and transesterification. New and less traditional methods are still in the research area, especially in the development of synthetic biofuels, such as liquid biofuels from biomass (BtL – biomass to liquid). Other substances, except fuels, produced in biorefinery processes, such as chemicals or other materials, are not as popular as energy biorefinery products and are at a much lower level of development in terms of trade with respect to fuels derived greenhouse gases and harmful compounds. This technology is almost "waste-free," which uses the existing potential of biomass waste, which currently is not used at all or is used in an irrational way [35]. 4.2. Biorefinery processes Depending on the raw material and the desired product, biorefineries use a variety of conversion technologies of raw biomass to commercial sources. These processes frequently include fermentation, gasification, and transesterification. New and less traditional methods are still in the research area, especially in the development of synthetic biofuels, such as liquid biofuels from biomass (BtL – biomass to liquid). Other substances, except fuels, produced in biorefinery processes, such as chemicals or other materials, are not as popular as energy biorefinery products and are at a much lower level of development in terms of trade with respect to fuels derived

The fundamental biorefinery processes used after pretreatment of the biomass material include enzymatic hydrolysis, fermentation, fast pyrolysis, and hydrothermal processing (HTU – *hydrothermal upgrading*), called hydrothermal liquefaction or hydrothermal pyrolysis, with possible further hydrodeoxydation process (HDO – hydrodeoxydation) [36]. from these plants. The fundamental biorefinery processes used after pretreatment of the biomass material include enzymatic hydrolysis, fermentation, fast pyrolysis, and hydrothermal processing (HTU – hydrothermal upgrading), called hydrothermal liquefaction or hydrothermal pyrolysis, with possible further hydrodeoxydation process (HDO – hydrodeoxydation) [36]. from these plants. The fundamental biorefinery processes used after pretreatment of the biomass material include enzymatic hydrolysis, fermentation, fast pyrolysis, and hydrothermal processing (HTU – hydrothermal upgrading), called hydrothermal liquefaction or hydrothermal pyrolysis, with possible further hydrodeoxydation process (HDO –

Regardless of the complexity of the biorefinery processes, the general scheme of the biorefinery can be presented as it is shown in Fig. 5. hydrodeoxydation) [36].

**Figure 5.** General biorefinery diagram [37]

### *4.2.1. Biomass pretreatment*

Pretreatment is required in order to break the crystalline structure of cellulosic biomass, to make it accessible to the enzymes, which may be combined with the cellulose and hydrolyze the carbohydrate polymers into fermentable sugars. The purpose of the pretreatment is a preextraction of hemicellulose, lignin degradation, and release of the cellulose from the plant cell walls. Pretreatment is considered as one of the most costly stages of cellulosic bioethanol production but also has a large potential for its improvement and reduction of costs through continuous research and development.

Many pretreatment technologies have been developed and evaluated for different biomass materials. However, each of these pretreatment methods has its advantages and disadvantag‐ es, and one method is not suitable for all types of raw materials.

The most commonly used methods of pretreatment of biomass in order to apply it in biorefi‐ nery processes are alkaline pretreatment, pretreatment with hot water, and pretreatment with the dilute acid. Alkaline pretreatment process is carried out using dilute sodium hydroxide (NaOH), ammonia, or lime. This process aims to improve the capacity of the fermentation of cellulose. Pretreatment with hot water is a process called autohydrolysis. This process is intended to hydrate the cellulose before the actual processing. The last type of biomass pretreatment process is a dilute acid pretreatment. This process takes place with the partici‐ pation of sulfuric acid of 0.5–1.0 % concentration, and it is designed to effectively remove and recover most of the hemicellulose from the processed biomass.

#### *4.2.2. Enzymatic hydrolysis*

The enzymatic hydrolysis is based on conversion of carbohydrate polymers to monosacchar‐ ides. Although various processes for the conversion of biomass to ethanol were studied, the enzymatic hydrolysis of cellulose provides the ability to improve the technology, so that the ethanol from biomass could be competitive in relation to other fuels in terms of both quality and economically.

Pre-prepared lignocellulosic material is subjected to enzymatic hydrolysis. This process involves the reaction for converting complex sugars to simple compounds – cellulose to glucose and hemicellulose into pentoses (xylose and arabinose) and hexoses (glucose, galac‐ tose, and mannose). Conversion processes of cellulose and hemicellulose are catalyzed by cellulase and hemicellulase. Cellulases play a significant role, because they catalyze the decomposition of cellulose into fermentable sugars. The enzymes involved in the hydrolysis of cellulose include endoglucanases, exoglucanases, and β-glucosidase. Endoglucanase randomly catalyze the decomposition of the internal bonds of the cellulose chain, whereas exoglucanases attack chain ends, releasing cellobiose molecules (disaccharide, which is not present in plants alone, transient degradation product of cellulose).

Enzymatic hydrolysis is a process often before fermentation, so it has to decompose cellulose and hemicellulose into fermentable monosaccharides. A solution of simple sugars can be fermented with microbes. However, some plant sugars, such as sugar beet or sugar cane, can be directly used in the fermentation process, without necessity to undergo the process of enzymatic hydrolysis [38].

### *4.2.3. Fermentation*

**Figure 5.** General biorefinery diagram [37]

continuous research and development.

es, and one method is not suitable for all types of raw materials.

recover most of the hemicellulose from the processed biomass.

Pretreatment is required in order to break the crystalline structure of cellulosic biomass, to make it accessible to the enzymes, which may be combined with the cellulose and hydrolyze the carbohydrate polymers into fermentable sugars. The purpose of the pretreatment is a preextraction of hemicellulose, lignin degradation, and release of the cellulose from the plant cell walls. Pretreatment is considered as one of the most costly stages of cellulosic bioethanol production but also has a large potential for its improvement and reduction of costs through

Many pretreatment technologies have been developed and evaluated for different biomass materials. However, each of these pretreatment methods has its advantages and disadvantag‐

The most commonly used methods of pretreatment of biomass in order to apply it in biorefi‐ nery processes are alkaline pretreatment, pretreatment with hot water, and pretreatment with the dilute acid. Alkaline pretreatment process is carried out using dilute sodium hydroxide (NaOH), ammonia, or lime. This process aims to improve the capacity of the fermentation of cellulose. Pretreatment with hot water is a process called autohydrolysis. This process is intended to hydrate the cellulose before the actual processing. The last type of biomass pretreatment process is a dilute acid pretreatment. This process takes place with the partici‐ pation of sulfuric acid of 0.5–1.0 % concentration, and it is designed to effectively remove and

The enzymatic hydrolysis is based on conversion of carbohydrate polymers to monosacchar‐ ides. Although various processes for the conversion of biomass to ethanol were studied, the enzymatic hydrolysis of cellulose provides the ability to improve the technology, so that the ethanol from biomass could be competitive in relation to other fuels in terms of both quality

Pre-prepared lignocellulosic material is subjected to enzymatic hydrolysis. This process involves the reaction for converting complex sugars to simple compounds – cellulose to glucose and hemicellulose into pentoses (xylose and arabinose) and hexoses (glucose, galac‐

*4.2.1. Biomass pretreatment*

438 Biofuels - Status and Perspective

*4.2.2. Enzymatic hydrolysis*

and economically.

Lignocellulosic biomass subjected to fermentation process requires separation of hemicellu‐ lose and cellulose material from the non-fermentable lignin, which is linked by strong covalent cross bonds. This is done using a pretreatment with an acid, alkali, or steam. Lignin, as waste from the bioethanol production, can be used as fuel and subjected to further processes of combustion or co-firing, in order to obtain energy.

Fermentation of C6 sugars, such as starch or sucrose, requires the use of organisms such as baker's yeast. In contrast, fermentation of C5 sugars – decomposed hemicellulose – requires special organisms, which are capable of fermenting xyloses. Currently, there is a need for more efficient and robust microorganisms that are resistant to higher temperatures and pressures. For example, recent studies carried out to improve the properties of the yeast strain showed that they may contribute to the production of more biofuels from cellulosic plant material by fermentation of all five types of plant sugars: galactose, mannose, glucose, xylose, and arabinose [36].

### *4.2.4. Fast pyrolysis*

Fast pyrolysis is a process of thermal decomposition of biomass to liquid bio-oil, comprising carbohydrates and oxygen content of approx 35–40 %. Through successive hydrogenation and hydrodeoxydation processes or gasification, bio-oil can be converted to a specific hydrocarbon.

The use of fast pyrolysis process, as well as the properties of the thus produced biodiesel, is currently under investigation. However, there is the view that this process can significantly reduce the cost of the gasification process with respect to the direct use of solid biomass in a gas generator.

Fast pyrolysis process requires only one reactor, which involves relatively low costs. The relatively high temperature, - approx. 450–500 °C, the short residence time (approx. one second) of the load at this temperature at atmospheric pressure and resulting high yield of oil, also represents a clear advantage of this process. However, this process is also characterized by a considerable degree of non-selectivity and the formation of many products, including a large amount of soot. The feed used in the fast pyrolysis process must be drained initially, which generates costs and energy consumption and quality of the obtained fuels by the relatively poor [39].

### *4.2.5. Hydrothermal conversion*

Another process of converting biomass in biorefineries is hydrothermal conversion process HTU (*hydrothermal upgrading*), which its diagram is shown in Fig. 6. Originally, this process was used for the conversion of coal to liquid fuels in conventional refining plant. Hydrothermal conversion is the process of biomass depolymerization carried out at high temperature, after which may optionally take place a catalytic hydrodeoxydation process HDO (hydrodeoxyge‐ nation). The temperature of this process is lower than in the fast pyrolysis process (300–400 °C), but the residence time of the feedstock in this temperature is approx. 0.5–1 h while ensuring relatively high operating pressure of approx. 5–20 MPa.

**Figure 6.** Diagram of HTU process [40]

In contrast to the pyrolysis in the HTU process, it is not necessary to pre-dry the biomass, so the process is particularly suitable for processing natural wet biomass.

HTU process takes place in an aqueous environment, where there are complex reaction sequences. The process involved reducing gas and a catalyst, in order to maximize the extraction of oil and its quality. HTU process is characterized by the high quality of the resultant fuel with low water content.

HTU process has a relatively low yield of oil, approx. 20–60 % dry weight of the stock. Also, the need for high pressure works against the financial side of undertaking due to the increasing demand for energy as a feed and the need for appropriate instrumentation [41, 42].

### **4.3. Division of biorefinery installations**

by a considerable degree of non-selectivity and the formation of many products, including a large amount of soot. The feed used in the fast pyrolysis process must be drained initially, which generates costs and energy consumption and quality of the obtained fuels by the

Another process of converting biomass in biorefineries is hydrothermal conversion process HTU (*hydrothermal upgrading*), which its diagram is shown in Fig. 6. Originally, this process was used for the conversion of coal to liquid fuels in conventional refining plant. Hydrothermal conversion is the process of biomass depolymerization carried out at high temperature, after which may optionally take place a catalytic hydrodeoxydation process HDO (hydrodeoxyge‐ nation). The temperature of this process is lower than in the fast pyrolysis process (300–400 °C), but the residence time of the feedstock in this temperature is approx. 0.5–1 h while ensuring

In contrast to the pyrolysis in the HTU process, it is not necessary to pre-dry the biomass, so

HTU process takes place in an aqueous environment, where there are complex reaction sequences. The process involved reducing gas and a catalyst, in order to maximize the extraction of oil and its quality. HTU process is characterized by the high quality of the

the process is particularly suitable for processing natural wet biomass.

relatively poor [39].

440 Biofuels - Status and Perspective

*4.2.5. Hydrothermal conversion*

**Figure 6.** Diagram of HTU process [40]

resultant fuel with low water content.

relatively high operating pressure of approx. 5–20 MPa.

Biorefineries can be divided into three types, based on technological advancement. The first type is analogous installation to existing installations of conventional oil refinery (petrorefi‐ neries). Then in the whole process, one type of raw material which is processed by a single technology is used, thereby providing one primary and main product. Figure 7 shows a schematic diagram of the first type of biorefinery [43].

Figure 7. A schematic diagram of the first type type of biorefinery (type I) **Figure 7.** A schematic diagram of the first type of biorefinery (type I)

Figure 8. A schematic diagram of the second The last type of biorefinery installation processed through multiple technologies of the investment. A schematic diagram

In another type of biorefinery one substrate products, that are equally important from installation is shown in Fig. 8. substrate is processed through a number of processes to from the point of view of investment. A schematic diagram to many "major" diagram of this type of In another type of biorefinery one substrate is processed through a number of processes to many "major" products, that are equally important from the point of view of investment. A schematic diagram of this type of installation is shown in Fig. 8.

Technology process The last type of biorefinery installation is the most advanced system, which uses multiple substrates as input, processed through multiple technologies to a number of main products that are equivalent from the point of view of the investment. A schematic diagram of this type of installation is shown in Fig. 9 [43].

• one substrate Substrates • many technology many technology processes • many main products Products A very important role in the concept of biorefinery installation plays is the possibility of multiple processing of organic waste and more. Biorefinery systems – the first, second, and third type – may use various types of technologies and thus can process various types of biomass. Hence, input substances, regardless of their type, can be processed in the selection of the appropriate installation using appropriate processing technologies. Biomass processed in the so-called "primary" biorefinery systems is often transformed in an incomplete way,

type of biorefinery (type II)

installation is the most advanced system, which uses multiple substrates technologies to a number of main products that are equivalent from the diagram of this type of installation is shown in Fig. 9 [43].

substrates as input, the point of view Figure 7. A schematic diagram of the first type

Substrates

•

products, that are equally important from

installation is shown in Fig. 8.

• one substrate

type of biorefinery (type I)

• one technology process

Technology process

substrate is processed through a number of processes to from the point of view of investment. A schematic diagram

• one main product

Products

to many "major" diagram of this type of

substrates as input,

multiple processing of

installation is the most advanced system, which uses multiple substrates

of biorefinery installation plays is the possibility of multiple

biorefinery cycle, taking into account the carbon cycle in nature.

Figure 8. A schematic diagram of the second type of biorefinery (type II) **Figure 8.** A schematic diagram of the second type of biorefinery (type II)

The last type of biorefinery installation

Figure 9. A schematic diagram of the third type type of biorefinery (type III)

A very important role in the concept of

Figure 10 shows the environmental biorefinery

Figure 10. Biorefinery cycle – natural carbon

which should be understood that there are obtained some parts of the products and also are formed intermediates suitable for further processing. In this case, used are so-called secondary biorefinery installations, in which intermediates are processed by the same or other biorefinery processes. The flow of raw material through a series of biorefinery installations is applied until the total conversion of biomass and waste formation, which is not suitable for further proc‐ essing [44]. organic waste and more. Biorefinery system technologies and thus can process various be processed in the selection of the appropriate processed in the so-called "primary" should be understood that there are obtained suitable for further processing. In this intermediates are processed by the same systems – the first, second, and third type – may use various various types of biomass. Hence, input substances, regardless of appropriate installation using appropriate processing technologies. biorefinery systems is often transformed in an incomplete obtained some parts of the products and also are formed this case, used are so-called secondary biorefinery installations, same or other biorefinery processes. The flow of raw material various types of of their type, can technologies. Biomass incomplete way, which formed intermediates installations, in which material through a series nature.**Figure 9.** A schematic diagram of the third type of biorefinery (type III)

Figure 10 shows the environmental biorefinery cycle, taking into account the carbon cycle in nature. of biorefinery installations is applied until suitable for further processing [44]. until the total conversion of biomass and waste formation, formation, which is not

cycle [45]

**Figure 10.** Biorefinery cycle – natural carbon cycle [45]

which should be understood that there are obtained some parts of the products and also are formed intermediates suitable for further processing. In this case, used are so-called secondary biorefinery installations, in which intermediates are processed by the same or other biorefinery processes. The flow of raw material through a series of biorefinery installations is applied until the total conversion of biomass and waste formation, which is not suitable for further proc‐

nature.**Figure 9.** A schematic diagram of the third type of biorefinery (type III)

type of biorefinery (type III)

• many technology

many technology processes

• many technology

many technology processes

Technology process

type of biorefinery (type II)

Technology process

type of biorefinery (type I)

• one technology process

Technology process

substrate is processed through a number of processes to from the point of view of investment. A schematic diagram

• one main product

• many main products

• many main products

Products

Products

Products

to many "major" diagram of this type of

> substrates as input, the point of view

multiple processing of various types of of their type, can technologies. Biomass incomplete way, which formed intermediates installations, in which material through a series formation, which is not

installation is the most advanced system, which uses multiple substrates technologies to a number of main products that are equivalent from the diagram of this type of installation is shown in Fig. 9 [43].

> of biorefinery installation plays is the possibility of multiple systems – the first, second, and third type – may use various

various types of biomass. Hence, input substances, regardless of appropriate installation using appropriate processing technologies. biorefinery systems is often transformed in an incomplete obtained some parts of the products and also are formed this case, used are so-called secondary biorefinery installations, same or other biorefinery processes. The flow of raw material until the total conversion of biomass and waste formation,

biorefinery cycle, taking into account the carbon cycle in nature.

Figure 10 shows the environmental biorefinery cycle, taking into account the carbon cycle in

cycle [45]

essing [44].

Figure 7. A schematic diagram of the first type

Substrates

Figure 8. A schematic diagram of the second The last type of biorefinery installation processed through multiple technologies of the investment. A schematic diagram

• many substrates

Figure 9. A schematic diagram of the third type A very important role in the concept of organic waste and more. Biorefinery system technologies and thus can process various be processed in the selection of the appropriate

Substrates

processed in the so-called "primary"

should be understood that there are obtained suitable for further processing. In this intermediates are processed by the same of biorefinery installations is applied until suitable for further processing [44].

Figure 10 shows the environmental biorefinery

Figure 10. Biorefinery cycle – natural carbon

**Figure 8.** A schematic diagram of the second type of biorefinery (type II)

Substrates

installation is shown in Fig. 8.

442 Biofuels - Status and Perspective

• one substrate

• one substrate

In another type of biorefinery one substrate products, that are equally important from

•

nature.

Biomass in the form of waste, energy crops, etc., shall be prepared and processed (decomposed) to simple compounds (sugars, proteins, carbohydrates, and fats) for the subsequent processes in the biorefinery. To the biorefinery plant gets adequately prepared feedstock from biomass, which is subjected to thermochemical and fermentation biorefinery processes. As a result of biorefinery processes, there are many products created: heat and electricity in co-generation; bio-products such as specialty chemicals, bio-carbon, and others; and also biofuels such as alcohol fuels, bio-oil (biodiesel), and other liquid fuels.

Considering the emissions from vehicles in the WtW cycle, meaning from the source to the wheels (well to wheel), there is the question of the carbon cycle in nature. According to this, there are undertaken research aimed at maximum reduction of carbon dioxide emissions into the atmosphere and return of carbon to nature through various processes, also the use of the resultant bio-carbon in sequestration processes.

Part of the emitted carbon dioxide throughout the lifecycle is absorbed by plants through photosynthesis process, which enables the development and creation of new plants and, consequently, new biomass for biorefinery processes.

The raw materials used in biorefineries are very diverse renewable raw materials, starting from agricultural products such as corn, wheat, and barley grains, agricultural crops such as oilseeds, waste from the agro-food and forestry industry as agro waste, wood chips and deforestation forest products, as well as special energy crops such as switchgrass or willow. Recently biorefinery raw materials also include organic waste, mainly municipal waste and any waste biomass.

As can be seen in Fig. 10, biorefinery raw materials can be a plant specifically designed for that purpose, by-products of processing of other substances, and products from different indus‐ tries. Biorefinery processes also require power, assuming that the processes need to be exothermic – the energy emitting to the environment. So as biorefinery products is obtained the desired products of all kinds, as well as the energy. A side effect may also be the residual substances (waste). These substances are residues, which in the present state of knowledge cannot be further processed reasonably. It is assumed that the optimal biorefinery should be completely waste-free, because these substances should be used even as internal energy carriers. Therefore, research efforts have led to a comprehensive concept of biorefineries; the diagram is shown in Fig. 11.

**Figure 11.** Comprehensive concept of biorefinery (developed on the basis of [46])

As is apparent from the diagram, the first step of biorefinery processes is biomass fractionation. The result of this process is a fraction of the cellulose, fats, protein, and carbohydrates. For each of the fractions, there are different ways of processing and hence various types of possible products, such as oleochemicals, biofuels, "bio"-plastics, chemicals, and food and feed ingredients.

The biomass can be converted into many useful forms of energy by several processes. There are two basic platforms of biorefining processes: "sugar" and "thermochemical." Both systems can produce chemicals and fuels, including methanol, ethanol, and polymers.

"Sugar" platform is based on the breakdown of biomass to an aqueous sugar solution with the use of chemical and biological agents. Fermenting sugars can be further processed in ethanol (produced by fermentation), aromatic hydrocarbons (through a process of dehydration), or liquid paraffins (by processing the aqueous phase). The residues – mainly lignin – can be used to produce electricity (through co-firing) or can be dedicated to the production of other products (e.g., etherified gasoline).

In the "thermochemical" platform, biomass is converted to synthesis gas via the gasification process to bio-oils by the pyrolysis and hydrothermal conversion (HTC). Bio-oils can be further refined to receive a liquid fuel such as methanol, gasoline and diesel fuel, and other chemical compounds.

The comprehensive biorefinery concept, shown in Fig. 11, assumes the universality and thus the energy cost-effectiveness (economic) of multiple processes. Unfortunately, in today's state of knowledge, those processes are mostly in the research phase (laboratory). Hence, due to the technological possibilities and availability of raw materials, there are four basic biorefinery systems in pre-industrial research phase:

**•** Biorefinery with the feed of the whole plant

As can be seen in Fig. 10, biorefinery raw materials can be a plant specifically designed for that purpose, by-products of processing of other substances, and products from different indus‐ tries. Biorefinery processes also require power, assuming that the processes need to be exothermic – the energy emitting to the environment. So as biorefinery products is obtained the desired products of all kinds, as well as the energy. A side effect may also be the residual substances (waste). These substances are residues, which in the present state of knowledge cannot be further processed reasonably. It is assumed that the optimal biorefinery should be completely waste-free, because these substances should be used even as internal energy carriers. Therefore, research efforts have led to a comprehensive concept of biorefineries; the

diagram is shown in Fig. 11.

444 Biofuels - Status and Perspective

ingredients.

**Figure 11.** Comprehensive concept of biorefinery (developed on the basis of [46])

As is apparent from the diagram, the first step of biorefinery processes is biomass fractionation. The result of this process is a fraction of the cellulose, fats, protein, and carbohydrates. For each of the fractions, there are different ways of processing and hence various types of possible products, such as oleochemicals, biofuels, "bio"-plastics, chemicals, and food and feed

The biomass can be converted into many useful forms of energy by several processes. There are two basic platforms of biorefining processes: "sugar" and "thermochemical." Both systems

can produce chemicals and fuels, including methanol, ethanol, and polymers.


The biomass can be converted into many useful forms of energy by several processes. There are two basic biorefining platforms: "sugar" and "thermochemical". Both systems can obtain chemicals and fuels, including methanol, ethanol, and polymers.

"Sugar" platform is based on the breakdown of biomass to an aqueous sugar solution by using of chemical and biological agents [33].

### *4.3.1. Biorefineries based on feed of the whole plant*

Biorefineries, where crops are feed material are entirely termed "agrorefineries." Common crops so far, mainly their grain, were intended as a basic raw materials for agro-food industry, which is the basis of food security needs of humanity. While in industrialized countries, there is a surplus of food, in third-world countries there is a permanent lack of food. Thus, the earmarking of raw materials for energy purposes (nonfood) is seen as inhumane. For these reasons, the EU began to develop technologies for biofuels and bioliquids from nonfood raw materials, specifying these fuels as second-generation biofuels. Regardless, it was found that first-generation biofuels, which are made from food raw material (ethanol distillers, FAME from rapeseed, sunflower, etc.), do not change the balance of greenhouse gases and in some cases even worsen it.

In turn, further processing of nonfood use plants, and therefore useless in the agri-food industry is very beneficial for social reasons, because of the possibilities of degraded area development for food crops.

The technology assumes the breakdown of the entire crop plants into edible parts and straw. From the edible parts by biotechnology and chemical and also physicochemical methods can be obtained starch derivatives and flour, which can be considered as final products or continue to process them into fuels, chemicals, polymers, and other materials, which are the final products in this process. This process generates heat and power in cogeneration and waste. Straw, which constitutes a second portion of the raw material, is treated by biotechnology and chemical methods into the lignocellulosic material, which is further processed to the final products of the biorefinery process with production of energy in cogeneration and waste.

Figure 12 shows a general illustrative flowchart of biorefinery, where the raw material feed is whole plants.

**Figure 12.** Biorefineries based on the full-load plant (developed on the basis of [46])

#### *4.3.2. Biorefineries with the feed of non-edible parts of plants or entire energy plants*

Another type is "green" biorefinery and therefore that which conventionally uses only the "green" part of the plant as substrates.

The feed is naturally wet biomass, green grass, alfalfa, clover, immature corn. etc. Within the scope of the raw materials also includes redundant or useless for breeding and food industry plants or their parts (silage).

Green biomass (the green parts of the plant) by means of extrusion is converted into liquid and solid substances. Fluids are subjected to biotechnological processes, physical and bio‐ chemical, which leads to the formation of proteins and soluble sugars. By contrast, the solids by the hydrothermal, enzymatic, and thermal methods are converted into cellulose and lignocellulose. The products of these two paths are processed for animal feed, fuels, polymers, chemicals, and other materials. These processes generate energy in cogeneration and waste.

Figure 13 shows a general diagram of a biorefinery platform, where the feed is the green parts of plants.

**Figure 13.** Biorefinery with a load of green plant parts (developed on the basis of [46])

### *4.3.3. Biorefinery with lignocellulosic feedstock (lignorefineries)*

The technology assumes the breakdown of the entire crop plants into edible parts and straw. From the edible parts by biotechnology and chemical and also physicochemical methods can be obtained starch derivatives and flour, which can be considered as final products or continue to process them into fuels, chemicals, polymers, and other materials, which are the final products in this process. This process generates heat and power in cogeneration and waste. Straw, which constitutes a second portion of the raw material, is treated by biotechnology and chemical methods into the lignocellulosic material, which is further processed to the final products of the biorefinery process with production of energy in cogeneration and waste.

Figure 12 shows a general illustrative flowchart of biorefinery, where the raw material feed is

**Figure 12.** Biorefineries based on the full-load plant (developed on the basis of [46])

"green" part of the plant as substrates.

plants or their parts (silage).

*4.3.2. Biorefineries with the feed of non-edible parts of plants or entire energy plants*

Another type is "green" biorefinery and therefore that which conventionally uses only the

The feed is naturally wet biomass, green grass, alfalfa, clover, immature corn. etc. Within the scope of the raw materials also includes redundant or useless for breeding and food industry

Green biomass (the green parts of the plant) by means of extrusion is converted into liquid and solid substances. Fluids are subjected to biotechnological processes, physical and bio‐ chemical, which leads to the formation of proteins and soluble sugars. By contrast, the solids

whole plants.

446 Biofuels - Status and Perspective

Lignorefinery is a plant, which substrates are rich in organic substances of lignocellulose. This type of materials are, for example, naturally dry biomass, wood, straw, redundant or useless fodder maize, and cellulose-containing biomass.

Excellent raw material including this type biorefinery is waste from many industries, such as the forest industry, wood, paper, furniture, etc.

Firstly, lignocellulosic feed is separated into lignin, hemicellulose, and cellulose. In the biorefinery processes in the case of lignorefinery apply various types of auxiliary substances such as enzymes or yeast. Lignin in a chemical way is processed to obtain lignin raw material, and cellulose is converted into sugar raw material by biotechnology and chemical processes. From the products of these two processes and hemicellulose can be obtained fuel, chemicals, polymers, and other materials with energy in cogeneration and waste [47].

A diagram of lignorefinery is shown in Fig. 14.

**Figure 14.** Lignocellulosic biorefinery – lignorefinery (developed on the basis of [46])

### *4.3.4. "Two-platform" biorefineries*

The idea of "two-platform" biorefinery is to obtain a synthesis of gas and sugars and so the parallel production of fuels based on renewable raw materials and other products, in terms of production in two technology platforms.

Raw materials used in this type of biorefinery is widely understood biomass consisting of any substances, mostly waste from various industries, such as agriculture, forestry, marine, food industry, public utilities, etc.

Biomass is divided into two contractual "platforms" – sugar and syngas platform. Sugar raw materials are converted through chemical reactions with the separation of waste, while the synthesis gas is conditioned by thermal and chemical methods. The end products of these processes are fuels, chemicals, polymers, and other materials. In these processes, the energy produced in cogeneration is produced.

Figure 15 shows a flowchart of a "two-platform" biorefinery.

### *4.3.5. Oleorefinery concept*

There is also a variety of agrorefinery called oleorefinery. As the name suggests, it uses oilseeds as raw material such as canola, sunflower, olive trees, and soybeans. Typically, these seeds are used for food production. Therefore, at present, when the first-generation biofuels go into oblivion, oleorefinery may have only use these crops from degraded areas, which cannot be used in food industry. Besides oilseeds as a substrate can also be used animal fats and waste. Oleorefinery products may be biodiesel and oleochemical products such as phytosterols or

**Figure 15.** "Two-platform" biorefinery (developed on the basis of [46])

sphingomyelin. This process also generates energy, which in part can be used as the energy delivered to a subsequent process.

Figure 16 shows a general flowchart of oleorefinery.

**Figure 14.** Lignocellulosic biorefinery – lignorefinery (developed on the basis of [46])

The idea of "two-platform" biorefinery is to obtain a synthesis of gas and sugars and so the parallel production of fuels based on renewable raw materials and other products, in terms of

Raw materials used in this type of biorefinery is widely understood biomass consisting of any substances, mostly waste from various industries, such as agriculture, forestry, marine, food

Biomass is divided into two contractual "platforms" – sugar and syngas platform. Sugar raw materials are converted through chemical reactions with the separation of waste, while the synthesis gas is conditioned by thermal and chemical methods. The end products of these processes are fuels, chemicals, polymers, and other materials. In these processes, the energy

There is also a variety of agrorefinery called oleorefinery. As the name suggests, it uses oilseeds as raw material such as canola, sunflower, olive trees, and soybeans. Typically, these seeds are used for food production. Therefore, at present, when the first-generation biofuels go into oblivion, oleorefinery may have only use these crops from degraded areas, which cannot be used in food industry. Besides oilseeds as a substrate can also be used animal fats and waste. Oleorefinery products may be biodiesel and oleochemical products such as phytosterols or

*4.3.4. "Two-platform" biorefineries*

448 Biofuels - Status and Perspective

industry, public utilities, etc.

*4.3.5. Oleorefinery concept*

production in two technology platforms.

produced in cogeneration is produced.

Figure 15 shows a flowchart of a "two-platform" biorefinery.

**Figure 16.** The general scheme of oleorefinery [37]

### *4.3.6. Prospective biorefinery concept*

There was developed a future-oriented concept of biorefinery based on the raw waste, which the diagram is shown in Fig. 17. That biorefinery practically implements processes in the field of WtL ("wastes to liquid"). Feed for this type of installation can provide all kinds of waste oils: waste used frying oils, animal fats, grease, animal waste, etc. Oil fractions by lipid extraction and refining are converted into crude oil and waste.

The crude oil is converted by transesterification to the methyl ester or glycerol, by hydroge‐ nation into the liquid hydrocarbon (biodiesel), or by chemical and enzymatic modification in all kinds of oleochemical products, such as fatty acids, alcohols, fatty esters, fatty ketones, dimer acids, glycerine, etc. Wastes are converted by gasification into synthesis gas, resulting in a yield of energy and heat in cogeneration. Syngas may be further converted into transport fuels or chemicals by catalytic processes [48].

**Figure 17.** Biorefinery perspective based on the raw waste (developed on the basis of [46])
