Keywords

1 Introduction

Organic matter waste is defined as any residue that decomposes under the action of microorganisms. The terms “compostable or putrescible materials” are reserved for the residential sector. In the industrial, commercial, and institutional (ICI) sector, the term used is “residual organic matter (ROM)” [27].

The main ROM generated by the ICI sector are wood and food processing residues, marine residues, and other commercial residues such as those from food markets and restaurants. The wood residues generated by the construction, renovation, and demolition (CRD) sector come from two main subsectors: infrastructure (e.g., roads) and construction [29]. However, in the industrial sector, the highest quantities of residues are generated by food processing activities. The types and amounts of ROM vary significantly from sector to sector. To date, there are few data available that would allow us to determine in a significant way the amounts of ROM generated by each industrial sector [27].

1.1 Generation of ROM in North America

In 2016, cities generated 2.01 billion tonnes of solid waste worldwide. Waste generation is expected to increase to 3.40 billion tonnes in 2050, an increase of 70.0% from 2016 levels [80]. North America (i.e., Canada, USA, and Mexico) generated around 260 million tonnes of waste in 2012, with an individual contribution of 7.1% for Canada, 77.7% for the USA, and 15.2% for Mexico.

In 2012, 10.18 million tonnes of ROM were generated in Canada, or 299.8 kg/person. The composition of residential waste was food, yard, and paper wastes in a proportion of 28.0%, 38.0%, and 34.0%, respectively. ICI waste generation accounted for a total of 8.3 million tonnes, 242.9 kg/person, with 34.0% of food, 7.0% of yard and wood, and 59.0% of paper waste [9]. The total generation of ROM in Canada in 2012 was 18.4 million tonnes, of which only 24.0% (including both residential and ICI) was diverted from disposal, as shown in Fig. 13.1. This means that close to 14 million tonnes could be valorized.

Fig. 13.1
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Waste management in Canada in 2012 according to CEC [9]

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Canada does not provide a policy framework for solid waste. Instead, each province and territory has its own regulations, guidelines, and policies specifying solid waste treatment and disposal. Municipalities control residential wastes, while the ICI entities manage their wastes by themselves.

In the specific case of the province of Quebec, the Residual Materials Management Policy was recently approved, intended as the foundation of a green economy. The 2.5 million tonnes of the most commonly recycled residual materials recovered in Quebec in 2006 (metal, paper, cardboard, plastic, and glass) were valued at $550 million and generated over 10,000 direct jobs. This policy is meant to address three main challenges:

  • Ending resource waste

  • Promoting the achievement of the goals of the Climate Change Action Plan and of the Quebec Energy Strategy

  • Making all involved stakeholders responsible for residual material management [30]

In 2015, the generation of ROM in the province of Quebec was estimated at 4.4 million tonnes, excluding the agri-food sector. One million tonnes were valorized by composting processes, corresponding to 24.6% of ROM being diverted from disposal [28], as shown in Fig. 13.2.

Fig. 13.2
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Waste management in Quebec in 2015

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Mexico lacks a reliable record of ICI waste generation. In 2012, residential ROM generation was estimated at 27.9 million tonnes, or 238.2 kg/person. The approximate composition was 79.0% of food and yard and 21.0% of paper waste [9]. This indicates a diversion of only 8.9% of generated waste, as shown in Fig. 13.3.

Fig. 13.3
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Residential waste management in Mexico in 2012 according to CEC [9]

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In the USA, the data for 2014 shows that the residential ROM generated represented 222.4 kg/person, for a total of 70.9 million tonnes, the highest total amount in North America. 34.0% of it was food, 32.0% yard, 33.0% paper, and 1.0% wood waste. For ICI, 137.0 million tonnes were generated, 429.8 kg/person. The composition of ICI ROM was 30.0% institutional and commercial food, 25.0% industrial food processing, 6.0% yard, 29.0% paper, and 10.0% wood waste. Figure 13.4 shows the diversion and disposal of ROM in the USA.

Fig. 13.4
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Waste management in the USA in 2014 according to CEC [9]

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Diversion achieved the biggest proportions among the three countries in North America, reaching 31.6% of both residential and ICI waste. Considering the generation of 207.9 million tonnes of ROM, the amount of waste that could be valorized is the largest of the three North American countries, even though the generation in Mexico is underestimated. The potential of ROM valorization in Canada, Mexico, and the USA is shown in Fig. 13.5.

Fig. 13.5
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Valorization potential of waste in North America according to CEC [9]

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In the case of the European Union, in 2014 the management of solid waste was as follows: 28% of the total solid waste generated in the 27 states was recycled, 27% was incinerated, 16% was composted, and 28% was landfilled.

1.2 Socioeconomic Aspect

The byproducts obtained via ROM valorization are varied. They can be used in different industrial processes, contributing to a decrease in the environmental impact of the consumption of fresh raw materials. ROM can be used as feedstock for industrial products such as food supplements, health and beauty products, fertilizers, apparel, and pet food.

In addition, it is important to take into account the socioeconomic benefits that are correlated to these byproducts. For example, renewable natural gas obtained from food waste has a negative life-cycle carbon footprint (−23 g CO2e/Mj). Captured biogas and digestate produced during anaerobic digestion can be used as energy source (in the form of heat and/or electricity) and biofertilizer, respectively [9].

The uses of compost are dictated by its quality. When the compost has harsh foreign matter or a heightened content of trace elements, it may only be used where human contact is less frequent, whereas high-quality compost can be used in agricultural lands, residential gardens, and horticultural operations.

1.3 Environmental Impact: Greenhouse Gases and Climate Change

In small concentrations, greenhouse gases (GHG) are essential for life. They absorb and emit thermal radiation, creating the “greenhouse effect” and making Earth’s atmosphere suitable for life. Since the Industrial Revolution, the consumption of fossil fuels has increased, and in consequence the emissions of carbon dioxide (CO2) and other GHG such as methane (CH4), disrupting the global carbon cycle. The primary source of CO2 is the use of fossil fuel, whereas for CH4, the causes are agricultural activities, waste management, energy use, and biomass burning [35, 71].

Global GHG emissions have been trending up since the beginning of the twenty-first century, due to the increase in CO2 emissions from China and the other emergent economies. In the last decades, climate has changed, anthropogenic activities and the GHG emissions they generate being the main culprit.

Climate change in North America and Europe has had a significant effect over economic activities (i.e., agriculture, energy, and transport) and adverse social impacts (i.e., on ecosystems, as reduction in forest area, wild fauna and flora, or damaged infrastructure) and over population health (i.e., lower of air and water quality and increase in mortality, chronic and new infectious diseases). According to the climate change evidences, the development of measures and policies allows us to anticipate the risks of climate change and be able to ensure the society adapts to the changes across different sectors [38, 42, 73]. In order to achieve that goal, reducing our dependence on fossil fuels and improving forest conservation as greenhouse gas sinks will be considered [15]. Carbon recycling by means of biomass valorization is one of the most viable options for that purpose. For example, one of the most documented applications of densified roasted biomass is as “renewable” fuel in coal-fired power plants. Notably, the use of 1 tonne of biofuel reduces net CO2 emissions by almost 3 tonnes and significantly reduces NOx and SOx emissions from mineral coal [26].

1.4 Management of Residual Organic Materials

There are several technologies commercially available to valorize ROM, other than thermochemical processes. For example, according to CEC [9]:

  • Animal rendering: the cooking and drying processes by which portions of livestock and poultry that are not intended for human consumption are converted into edible and inedible byproducts, thereby providing additional revenue for the meat industry and avoiding costly disposal.

  • Anaerobic processing: the natural process that breaks down organic matter in the absence of oxygen to release a gas known as biogas consisting mainly of CO2 and CH4, leaving an organic residue called digestate.

  • Aerobic processing and treatment: also known as composting, it refers to the transformation of organic materials into humus by aerobic microorganisms.

1.4.1 Thermochemical Technologies

Various technologies can be used for the thermochemical conversion of biomass, including gasification [26, 56], pyrolysis [25, 26, 57, 64, 75], roasting [20, 26, 66], carbonization [26], combustion [26, 57], and hydrothermal processes [88].

Gasification is carried out at high temperatures, from 900 to 2000 °C, which favors gas production.

Pyrolysis is the method used to produce more oil than gas and char [26], consisting of the thermal decomposition of biomass under an inert atmosphere (e.g., nitrogen) [58] or in the presence of a minimal amount of oxygen, at an average temperature from 300 to 900 °C [16].

Roasting is considered a mild pyrolysis process, carried out at a lower temperature [26, 60], between 200 and 350 °C [26, 41, 72]. It produces a high ratio of char [66].

Carbonization is a slow thermochemical process that takes place with an air deficit and a pressure equal to or greater than the atmospheric pressure. Unlike pyrolysis, carbonization is used to produce the maximum amount of char at the expense of oil [26].

The combustion of biomass is defined by a complete oxidation of the material in the presence of air. This technique generates energy that can be used for heating, power generation, or both [26].

Hydrothermal processes can be divided into five categories, based on their temperature range: hot water extraction (HWE) at low temperature (<100 °C), pressurized hot water extraction (PHWE), liquid hot water pretreatment (LHW), hydrothermal carbonization (HTC) at medium temperature (100–250 °C), and hydrothermal liquefaction (HTL) at high temperature (>280 °C) [13].

1.4.2 Trends and Challenges of Thermochemical Valorization

Each byproduct obtained through thermochemical valorization has specific characteristics that limit its industrial exploitation. These limitations must be overcome in order to develop industrial thermochemical mills. To produce heat, the direct combustion of wood seems to be the best solution from the point of view of economy and ease of use. However, the energy produced must be consumed locally. For electricity generation, gasification has almost reached full development. Pyrolysis, which makes it possible to densify the heat capacity of wood in a liquid (bio-oil) that can be transported, stored, and used for transport, encounters the difficulties of using this liquid in standard equipment designed for petroleum products. Carbonization densifies the calories of wood in a solid biochar, which is transportable and storable and can be used as fuel, alone or in mixture with petroleum fuels (e.g., heating oil) in the form of a slurry (particles in suspension) [26].

The choice among thermochemical technologies depends on the energy needs, the availability and quality of the biomass, its proximity, the costs of transformation and distribution, the environmental context, and the availability of technologies to consume the byproducts generated. For example, the oil produced by pyrolysis has very particular properties that do not allow it to be used in diesel engines, turbines, and standard boilers without upgrading [26].

2 Technologies to Produce Pyrolytic Oil and Char

2.1 Thermochemical Conversion Definition and Principles

During thermochemical conversion, the chemical structure of the molecules contained in the biomass, such as cellulose, hemicellulose, and lignin, breaks down, causing the reorganization of molecules and the production of gas, oil, and a solid black material rich in carbon, customarily called “char.” The char, also called “biochar,” differs from mineral “coal” because it is not from fossil origin [16]. In addition, fossil coal contains significant amounts of sulfur and mercury, which makes it highly polluting compared to the char, which is also considered carbon neutral [26].

Three main steps occur during the thermochemical conversion of biomass: (1) loss of moisture in the material; (2) primary production of char, volatiles, and gases; and (3) slow decomposition of char and its chemical rearrangement to form a solid rich in carbon [19].

2.2 Main Technologies to Produce Oil

Pyrolysis is the thermochemical process to produce oil. Depending on the resulting products and operating conditions, pyrolysis can be divided into slow, intermediate, and fast pyrolysis [2].

Slow pyrolysis is a batch process carried out at low temperatures, with slow heating rates and long residence times. The initial sample does not need significant pretreatment. The process is more tolerant regarding the initial conditions of the sample. Although liquid fuel can be produced, this technique is mostly used when the desired product is biochar.

Intermediate pyrolysis is carried out at temperatures of between 300 and 500 °C, vapor residence time of a few seconds, and feedstock residence time between 0.5 and 25 min [2].

Nowadays, fast pyrolysis is an advanced technology that is gaining in importance because of the increasing interest in the production of biofuel from biomass. The aim of this process is to prevent further cracking of the pyrolysis products into non-condensable compounds. The main features of fast pyrolysis process to achieve the maximum amount of bio-oil are the following [83]:

  • Small particle sizes usually less than 5 mm, to improve the heating rates and quick devolatilization

  • Feed moisture content under 10 wt.%

  • High heating rates and high heat transfer rates at the biomass-particle reaction interface because the rate of particle heating is usually the limiting step

  • Controlling the temperature around 500 °C to maximize the liquid yield

  • Short vapor residence time, usually between 0.5 and 15 s, to minimize the secondary reactions

  • Rapid cooling of the pyrolysis vapors to give the bio-oil product

Table 13.1 summarizes the operating conditions of each process and typical product weight yields.

Table 13.1 Operating conditions used for fast, intermediate , and slow pyrolysis and gasification, according to van Swaaij and Palz [83]
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However, there are some drawbacks when the fast pyrolysis process is scaled up. The main one is the ability to reproduce the operating conditions. The high heating rates required are currently only possible at laboratory scale. Industrial pyrolysis does not get bio-oil yields as high as those reported for fast pyrolysis. Moreover, the biomass particle size has to very small, leading to a significant amount of energy required to grind and condition the biomass. The second drawback is related to the inability to isolate each final component desired without modifying the rest, because of the complex internal structure of the biomass used.

Several authors have reported studies focused on the flash pyrolytic conversion of lignocellulosic biomass. Zheng et al. [96] carried out catalytic fast pyrolysis of lignocellulosic biomass to promote the aromatic compounds production. Maliutina et al. [55] carried out a comparative study of the flash pyrolysis characteristics of microalgal and lignocellulosic biomasses, with the lignocellulosic biomass providing higher bio-oil yields. Wang et al. [86] studied the microwave-assisted co-pyrolysis of acid pretreated bamboo sawdust and soapstock in order to achieve the highest production of bio-oil. They got a remarkable improvement in the bio-oil yield with the pretreatment. Lestander et al. [48] characterized the bio-oil properties produced through lignocellulosic biomass pyrolysis at different operating conditions. Adjin-Tetteh et al. [1] carried out a fast pyrolysis of cocoa pod husks for direct production of valuable platform chemicals. Charusiri and Vitidsant [12] analyzed the operating conditions to maximize the biofuel production via the pyrolysis of sugarcane leaves.

2.3 Main Technologies to Produce Char

A variety of thermochemical processes can be used to convert biomass into char, and pretreatments may be necessary to improve the biomass transformation. Fragmentation and drying are frequently required before the biomass can be used in a thermochemical process. Fragmentation consists in the reduction and homogenization of the size of the biomass as raw material by shredding or grinding. This activity provides a material that is easier to handle and dry. The level of dryness of the biomass is the most important property of the raw material; it helps conserve the biomass during storage. In addition, it has a significant impact on fuel energy content and production costs [26].

2.3.1 Available Technologies

The main thermochemical conversion technologies for char production are pyrolysis, roasting, and carbonization. The choice of one technology depends on the energy needs, the availability and the quality of the biomass, the costs of the infrastructures of transformation and distribution, the environmental context, and the market that can consume the products generated [26].

2.3.1.1 Pyrolysis

There are several enterprises specialized in pyrolysis. Some of the ones active in North America and Europe are presented below.

Pyrovac

(Saguenay, QC) has developed a vacuum biomass pyrolysis plant with a capacity of 3.5 t/h of wood bark. The coarsely ground raw material (2–3 cm) enters the reactor after sieving to remove fine particles. A small biomass tank brings the biomass to the upper plateau of the reactor, which is heated with molten salts at temperatures from 500 to 520 °C. At the end of the upper plate, the carbonized raw material falls onto the lower plate, where the char formed fills a vacuum chamber which will supply the pyrolysis reactor under vacuum to produce the pyrolytic oil. Pyrovac’s pyrolysis under vacuum system produces bio-oil (30.7%), an aqueous fraction (19.6%), biochar (29.2%), and gas (20.5%) [26].

Ensyn Technologies Inc.

(Renfrew, ON) produces bio-oil for use as a food supplement and chemical compounds. The system consumes 33,000 tonnes of sawdust annually (100 t/d) using the Rapid Thermal Processing (RTP)™ technology process, developed at the University of Western Ontario. This process transforms wet fragmented biomass at atmospheric pressure and moderate temperature. Part of the energy generated by the flash pyrolysis is diverted to dry the biomass. Currently, seven commercial production plants use this process in the USA and Canada [26].

Dynamotive Energy Systems Corporation

has pilot facilities in Guelph (ON) and a pyrolysis plant in West Lorne (ON), which has the capacity to consume 130 t/d of solid wood flooring factory byproducts and a 2.5 MW turbine which generates electricity [42]. The company is also co-owner of a plant in Guelph with a capacity of 200 t/d of wood residues. Dynamotive is also exploring the possibility of using biochar as amendment for agricultural soils. Dynamotive has also designed a flash pyrolysis process and is developing a Biomass INto GasOil (BINGO) refining process [26].

Biogreen® technology,

developed by ETIA, is an innovative thermochemical conversion process. It includes a roasting-pyrolysis system that creates energy and materials of interest. The French company ETIA also produces another pyrolyzer called Spirajoule® [23].

Mobile pyrolysis technologies are being manufactured by a variety of companies such as Agri Term Inc. (a spin-off of the Institute for Chemicals and Fuels from Alternative Resources (ICFAR) at the University of Western Ontario) and Tech Shelter Inc. (formerly BioRefinery Inc.) [26]. Bioénergie La Tuque (QC) uses the mobile mode to develop and implement all the conditions to the development of the bioenergy sector in the La Tuque territory, including the production of biofuel [85].

Pyrolysis technologies produce more oil than char. The solid fraction of the pyrolysis, the biochar which is considered carbon-neutral and theoretically sulfur-free, is usually burned alone or mixed with liquid fuels. In this case, the mixture becomes an interesting biofuel for boilers, coal-fired power plants, and cement plants, to reduce the emissions of SO2 and CO2 [26]. The char can be densified to form granules or briquettes or to produce heat and even serve as amendment for agricultural soils.

2.3.1.2 Roasting

Roasting is a process that is generally characterized by (1) heat treatment of biomass at temperatures ranging from 200 to 320 °C; (2) atmospheric pressure, with little or no oxygen (http://www.airex-energy.com/en/technology); and (3) residence time of less than 30 min. Roasting creates roasted biomass, while biochar is obtained by carbonization [26].

Roasting technologies are grouped into two main types: technologies that use fragmented biomass (e.g., from chippers, shredders, etc.) and those that use granules (densified biomass). The type of roasting reactor is an important feature distinguishing these technologies. The different types of reactor are rotary kiln (RK), fixed bed (FB), cyclonic bed (CB), toroidal fluidized bed (TFB), column reactor (CR), multi-soleus reactor (MSR), reactor heated screw (RHS), conveyor belt (CB), and microwave reactor (MWR) [26].

Around the world, there are various patent holders of roasting technology for fragmented biomass: AB Torkapparater (Sweden) (RK), Airex Industries Inc. (Quebec) (CB), Alterna Biocarbon (British Columbia) (FB), Agri-Tech Producers LLC (USA) (VC), Andritz AG (Austria) (RK), Bio3D Application (France) (RK), Biolake (the Netherlands) (VC), BTG Biomass Technology Group BV (the Netherlands) (VC), CMI NESA (Belgium) (MSR), Energy Research Center of the Netherlands (ECN) (the Netherlands) (CR), Umea University-ETPC (Sweden) (VC), FoxCoal BV (the Netherlands) (VC), NewEarth Renewable Energy Inc. (USA) (BC), Rotaware Ltd. (UK) (MWR), Stramproy Group (the Netherlands) (CB), Thermya (France) (CR), Topell Energy BV (the Netherlands) (TFB), Torr-Coal Groep (the Netherlands) (RK), and Wyssmont Inc. (USA) (MSR) [3, 26]. There are also a few holders of pellet roasting technologies, including Energex Inc. (Quebec) and the University of Georgia (USA) [26].

2.3.1.3 Carbonization

The carbonization technology is classified according to the heating method: internal, external, and with air recirculation. The internally heated process is the most common system globally. It is a process in which the portion of biomass loaded into the furnace (usually wood) provides the heat necessary to carbonize the rest of the load. The amount of wood consumed depends on the amount of air admitted into the oven through the air intake holes, the wood load, and the enclosure. Ovens are usually made of concrete or brick. Their design is simple and the investment costs are very low. The performance of the Missouri kilns varies from 20% to 30%, depending on the operating conditions and the raw material used. The production cycle, which is a function of the cooling period, varies from 25 to 30 days [26].

The external or indirect heating process (e.g., Van Marion Retort (VMR)) consists of a combustion chamber which is heated by an external energy source (gas or oil). When the pyrolysis begins, the pyro-ligneous vapors are sent to the combustion chamber, where they are burned to generate heat that will be used to heat the second container, placed in the second reactor. At this point, the burner (gas or oil) is stopped. When the carbonization is complete in the first reactor, its container with the char is removed and set to let it cool. Since the VMR process works in an alternating way, the vapors formed in one reactor will serve as a source of heat for the other. The total duration of carbonization of a container varies from 8 to 12 h, and the yield of char, which depends on the raw material used and its moisture content, can reach 30–32%. A 12-reactor unit, operating 24 h a day, has a production capacity of 6000–7000 t/year and requires three shift workers. Several factories use this technology in France, Belgium, and the USA [26].

In the gas recirculation process, the heat transfer is very high. The wood is heated by direct contact with hot inert gases recirculated by fans. Since the gases do not contain oxygen, there is no combustion in the reactor. During cooling, heat can be recovered for use in the system. The Reichert and Lambiotte processes are the main processes that use this principle of carbonization. In the Reichert process reactor, the decomposition vapors flow countercurrent with the raw material, taking out moisture. Incondensable gases pass through the heat exchangers to be heated at the carbonization temperature (450–550 °C). The excess gas is used to pre-dry the raw material. The raw material is introduced into the column with a maximum length of 30 cm and a thickness of 10 cm [26].

A relatively new process called Flash Carbonization™ was developed by the University of Hawaii (UH). This process uses high pressure to produce char from biomass. A commercial-scale demonstration reactor was installed at the UH campus. The fixed carbon yield can reach the thermochemical equilibrium limit in 20–30 min. Not all the carbon found in the raw material is transformed into biochar. There are losses in the form of volatile compounds, CO2, etc. [26].

Hydrothermal carbonization consists in the transformation of slurry into char [6]. To achieve this, an autoclave is required, where the slurry is contained and heated during 2–24 h at temperatures from 150 to 350 °C. Since the slurry is liquid and due to the temperature, vapor is generated, and the pressure rises, leading to a thermochemical transformation of the raw materials contained in the slurry. With this process, gas emissions are reduced and biochar yields improve [68, 81]. This process gives control of the carbonization process and char chemistry as well as particle morphology and size [8].

2.4 Simulation of Pyrolysis and Gasification Process to Produce Oil and Char Using Aspen Plus®

Nowadays, renewable chemical industries have attracted a lot of interest from both the economic and ecological perspectives, as they can reduce the use of fossil sources.

The main barriers for scaling up these technologies have to do with the complexity of the process, the optimization of the operating conditions, and the high investment required. To face this problem, the simulation of processes appears to be a good alternative since it allows performing conceptual designs that can be extrapolated at scale and estimating, through mass and energy balances, thermodynamic models, and chemical equilibriums, the behavior of a process, without having to use an actual pilot plant.

Aspen Plus® software is one of the most widespread commercial simulators of chemical engineering processes. It is a software developed by Aspen Technology Inc. It allows to simulate the whole process and analyze the impact of different operating conditions.

There are few studies focused on the simulation of thermochemical processes using biomass as feedstock. Nilsson et al. [62] simulated a fluidized bed dividing it into three zones according to the type of transformation: pyrolysis of biomass, using homogenous and heterogeneous reactions, each with its corresponding kinetics obtained from literature and experiments. Zhai et al. [95] also proposed a two-stage biomass pyrolysis and gasification scheme for pine sawdust establishing a zero-dimensional thermodynamic equilibrium model. Fernández-López et al. [24] simulated the gasification of animal waste biomass in a dual gasifier where the gasification and the combustion zone were separated. Nur and Syahputra [63] integrated the biomass pyrolysis with organic Rankine cycle for power generation. In this case, the aim is to take advantage of the heat generated during the process to produce power.

On the other hand, Puig-Gamero et al. [67] simulated the pyrolysis and gasification process of pine biomass to produce methanol. In this case, the main steps were gasification process, syngas cleaning, and methanol synthesis (Fig. 13.6). First, the biomass was gasified using steam as the gasifying agent. The gas produced was then fed to a pressure swing adsorption process system (PSA) where it was cleaned and adjusted to achieve a H2/CO ratio close to 2.4–2.5. Finally, the syngas with the optimal ratio was fed to the methanol synthesis unit. In the gasification process, an equilibrium model based on a Gibbs free energy minimization was used to simulate a dual fluidized bed gasifier where the combustion zone was separated from the gasification zone allowing the use of the combustion heat in the rest of the process. In this case, as the desired product was the purified syngas, a catalyst bed of dolomite was used to reduce the amount of tar produced. The PSA system, composed of four units, was then able to capture CO2 and CH4 and simultaneously adjust the stoichiometric ratio of methanol feed. The adsorbent used was the biochar produced in the gasification process. Once the syngas was purified, it was further introduced in the methanol reactor to optimize its operating conditions and achieve the highest methanol yield [67].

Fig. 13.6
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Aspen Plus® flowsheet process

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3 Applications of the Pyrolytic Oils and Chars

3.1 Pyrolytic Oil

The bio-oil contains high amounts of organic compounds such as alkanes, aromatic hydrocarbons, and phenol derivatives and lower amounts of ketones, esters, ethers, sugars, amines, and alcohols with H/C molar ratio higher than 1.5 [36]. It is considered as a potential substitute for petroleum fuel, but its nature is significantly different from petroleum oil because its properties change when stored for long periods. Bio-oil has higher concentrations of oxygenated compounds and is more acidic [2]. The physiochemical properties of the bio-oil depend on several factors such as feed biomass, moisture content in the feed, and the pyrolysis process parameters (vapor residence time, temperature, heating rate, and pressure) [21]. There are advantages to converting lignocellulosic biomass into bio-oil such as easier transportation, higher energy content, and lower impurities (e.g., sulfur) [79].

Many industrially important chemicals can be extracted from bio-oil, such as phenols for the resins industry and hydroxyacetaldehydes and some additives applied in the pharmaceutical industry. Researchers are currently looking for making the best use of the process.

The phenolic compounds present in the bio-oil , such as methylphenols (creosols), methoxyphenols (guaiacol), and methoxypropenylphenol (isoeugenol), have great economic potential in the food, pharmaceutical, cosmetic, and paint industries [21]. Phenols are used as a precursor for the synthesis of bio-plastics, phenol-formaldehyde resins, or epoxy and polyurethane materials [40]. The phenolic compounds have several biological activities such as anti-inflammatory, antimicrobial, antioxidant, antidiabetic, antitumor, and cardioprotective [59].

3.2 Char

Char can be used for various purposes, soil amendment, biofuel, adsorbent, and catalytic support being those with the highest potential for exploitation.

3.2.1 Soil Amendment

Char has the capacity of improving soil quality and releasing nutrients conserving its carbon structure [5, 11, 16, 34, 39, 53, 77, 78, 84, 88]. Char is a highly densified material containing a large proportion of stable carbon that is very resistant to decomposition and can remain in the soil for several hundred years [47, 54]. For this reason, char can be considered as a method to sequester carbon [4, 43, 46].

It is not possible to predict the performance of biochars, and the whole range of useful characteristics has not been determined, limiting the use of biochar in agriculture and other sectors [76]. From an agronomic point of view, it is important to determine if char (1) modifies the properties of the soil at specific application rates, (2) causes toxic effects, (3) improves nutrient availability , and (4) affects the population and density of the soil flora [22].

3.2.2 Biofuel

Regarding bioenergy, biochar was suggested as sustainable source which might be used directly as fuel, serve as substrate or catalyst for gasification processes to product biogases, and replace traditional materials in micro fuel cell (MFC) electrodes and supercapacitor manufacturing (Table 13.2).

Table 13.2 Application of pyrolysis char in bioenergy fields
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As a ready-to-use fuel, biochar is considered a sustainable source of energy in low- and mid-income countries, where the main source of household fuel is still based on limiting fossil coal and wood-derived charcoal. Since lignocellulosic residues (straw, sawdust, fruit shells, phloem, branches, and leaves) from agricultural and forestry activities are abundant, the use of these sources for biochar production would be advantageous for the development of biochar commercialization in these countries. Recent researches suggested that directing production from lignocellulosic waste stream to renewable fuel via pyrolysis might contribute to resolve the laddering demand of energy and pollution issues [37, 52].

In order to produce biochar , lignocellulosic biomass was carbonized through slow pyrolysis under inert atmosphere. After pyrolysis, biochar might be further processed into fuel briquettes that meet commercial product standards [7, 61]. Several properties are required for biochar-based commercial fuel products, including high heating value (HHV), energy density, a fixed carbon content, and ash content [37, 91]. Compared to traditional charcoal, good-quality commercialized biochar should have HHV about 30 MJ/kg with an ash content lower than 5%. Such properties could be improved by using woody-derived biomass [52]. In addition, the competitive price of biochar-derived fuel must be warranted by the low or null cost of the material sources as well as account for the reduced waste management expense. Recent studies suggest that integrating the pyrolysis process into waste management might be a sustainable approach with a reduction of management expenses, an increase in energy efficiency, and lower of biochar production costs [17, 82].

Compared to woody-derived high-carbohydrate content biomass, the biochar generated from pyrolysis of low-carbohydrate-containing biomass (straw, leaves, and municipal waste) has poor yield and thermal properties and is not suitable for commercial fuel application. However, the use of this biochar as feedstock for co-combustion with fossil fuel or other organic wastes was shown to be an interesting solution that might help increase energy efficiency and control polluted air emission [50, 74, 87, 93, 94]. In addition, the biochar can be also used as reserve material for biogas production, via gasification that makes it more convenient to handle and store than raw biomass [89].

Based on its carbon material properties, such as the high electric conductivity and a large pseudo capacitance of char, it can be used as supercapacitor electrodes for energy storage [10].

Another application of biochar in the energy field is its use as a sustainable material for microbial fuel cell electrodes. The biochar-based electrodes were shown to be a promising option to replace the traditional electrodes, which limit the scaling up of microbial fuel cell systems due to their high cost and nonrenewable nature [33, 45].

The porous characteristics of biomass char and the functional groups on its surface make char suitable for use on direct carbon fuel cell (DCFC). It promotes the electrochemical reactions in the low current density region. Graphitized char favors composite conductivity and char can be used as support for electrochemical reactions [10, 69, 90].

3.2.3 Adsorbent

Biochar has been tested as adsorbent to remove pollutants like organic dyes, heavy metals, drugs, and gases. The different functional groups present in biochar, as well as its surface area, structure, and mineral content, are factors that influence the adsorption mechanisms [65]. These variables are affected by the feedstock and production conditions (time and temperature), as well as posttreatment such as functionalization or activation.

Biochar has different surface functional groups, mainly consisting of oxygen-containing groups like carboxylate and hydroxyl. These functional groups strongly interact with several charged molecules through processes such as electrostatic interaction, ion exchange, and surface complexation. These interactions can be analyzed by comparing changes in the functional groups of the biochar before and after the adsorption [65].

3.2.4 Char-Based Catalyst for Chemical Production

Traditional catalysts and catalyst support can be replaced by char, which is a renewable and low-cost material and presents great physical and chemical properties as a catalyst. It is as a promising alternative to conventional expensive and environmentally unfriendly catalyst sources [49, 70, 92]. There are several applications of biochar-based catalysts in the biofuel field, which relates to biodiesel production and syngas and bio-oil upgrading [44]. The main applications of char as catalyst are the following.

3.2.4.1 Catalyst for Biogas Production

Tar Reforming

Biomass pyrolysis or gasification to produce syngas (H2 and CO) creates tar (hydrocarbon mixture). Two main methods are used for tar reforming: thermal cracking and catalytic cracking. Tar reforming by thermal cracking takes place at temperatures higher than 1000 °C and is energy intensive. Catalytic cracking allows tar decomposition at lower temperatures (around 700 °C) using a proper catalyst to improve conversion efficiency. The traditional catalysts are dolomite and olivine and metal-based catalysts (i.e., Ni, alkali, or novel metals). However, a promising alternative is the use of char as catalyst or support for an active metallic phase (K, Ca, Ni, Fe, Cu, Ni-Fe) [31, 51, 69]. As metal support, char reduces metal oxides to metallic state, improving catalytic performance related to surface area and pore size but also to mineral content.

Biogas Reforming

Hydrogen can be generated by CH4 conversion in the presence of CO2 and H2O. Traditional catalysts used for biogas reforming are based on metals (Ni, Co, Pd, Pt, or bimetallic) supported by alumina or ceria. Recent biochar testing shows improved H2 production, especially during biomass pyrolysis or gasification. Biochar compounds (K and Ca) act as catalyst; furthermore, some metals can be supported by biochar in order to improve the catalyst performance [90].

3.2.4.2 Catalyst for Bio-oil Production

Syngas Upgrade

Syngas obtained from pyrolysis or gasification of biomass can be upgraded into fuels. Syngas is used to produce liquid hydrocarbons by Fischer-Tropsch synthesis, using an iron-based catalyst supported on alumina or silica. Char has recently been used to produce carbon-encapsulated iron nanoparticles as catalyst for Fischer-Tropsch synthesis. The conversion of syngas into liquid hydrocarbons showed good efficiency (90% CO conversion and 70% of selectivity to liquid hydrocarbon). Metal-based supported on char presents a great potential as catalyst for syngas upgrading [69, 90].

Esterification/Transesterification

Biodiesel (mixture of methyl ester compounds) is commonly produced by esterification and transesterification reactions of vegetable oil or animal fat using acid catalysts (heterogeneous and homogenous). Biochar can be used as a catalyst for biofuel production directly, or it can be functionalized. Functionalization consists in the chemical activation (i.e., KOH) of char in order to increase the specific surface area and sulfonating with concentrated H2SO4. The tested catalyst presented high efficiencies and high reusability (seven cycles with no significant loss of esterification activity) [10, 69, 90].

3.2.4.3 Catalyst for Pollution Control

Selective Catalytic Reduction (SCR)

Char can be used as catalyst in low-temperature SCR (selective catalytic reduction) used to control NOx emissions. Char is a suitable catalyst for SCR because of the abundance of oxygen functional groups on its surface. Furthermore, char can be activated by impregnation using transition metals, which improve the NOx removal [90].

Photocatalytic Degradation

Functionalized char can be used as a photocatalyst for degradation of organic compounds. For example, char functionalized with TiO2 under ultraviolet irradiation effectively degraded sulfamethoxazole [90].

3.2.5 Activated Carbon

Char can be used as raw material for activated carbon. The process has two main parts: carbonization and activation. Carbonization of raw material to obtain char mainly takes place at temperatures between 600 and 1200 °C under inert atmosphere or limited oxygen atmosphere. Char activation can be chemical (using ZnCl2, KOH, H3PO4, and K2CO3 as agents) or physical (using oxidizing gases such as CO2, steam, or air). Chemical activation can be a one-step process, where carbonization and chemical activation take place simultaneously, or a two-step process if they happen consecutively. Although physical activation is carried out in two steps, it is cleaner and easier to control than a chemical one [69]. Activated char with a large specific surface area and micropore volume as well as specific functional groups on surface could potentially be used for hydrogen or GHG storage or as catalyst support [18, 90].