Lignocellulosic Biomass Conversion into Second- and Third-Generation Biofuels
Introduction
Biofuels are the fuels which are extracted from different sources of biomass which are available around us and fall under the category of renewable material. Also, biomass has high potential for the sustainable and economic growth of industrialized countries (Lee and Lavoie 2013). The biofuels are generally categorized as follows: (1) first-generation biofuels; (2) second-generation biofuels; (3) third-generation biofuels. This chapter mainly focuses on second-generation and third-generation biofuels. Biofuels extracted from a variety of feedstocks, ranging from non-edible lignocellulosic feedstock to municipal solid wastes, are known as second-generation biofuels. The biomass used for the production of second-generation biofuels is classified into three different categories as per Beauchet, Monteil-Rivera, and Lavoie (2012): (1) homogeneous biomass; (2) quasi-homogeneous biomass; (3) heterogeneous biomass.
Wood chips, w'ith a cost ranging from US$100 to nearly US$120/metricton, fall under homogeneous biomass. Agricultural and forest residues, having prices in the range of US$60 to US$80/ton, are considered as quasi-homogeneous biomass. Low- value feedstock like municipal solid waste, priced between US$0 and US$60/metric- ton, are considered to be non-homogenous or heterogeneous biomass. As compared to the prices of vegetable oil, corn, and sugarcane, this biomass has very low prices, so the final yield of biofuel is considered to be cost-effective and profitable in the market. The conversion of biomass to biofuels mainly follows one of two pathways: (1) bio pathways; (2) thermo pathways. As per Brennan and Owende (2010), third- generation biofuels are extracted from algal biomass and have a distinct growth yield in comparison to lignocellulosic biomass.
The biofuel production from algae depends on the lipid content of microorganisms. Mostly, Chlorella species are highly used because of their 60-70% lipid content; for example, the species Chlorella protothecoides has a high yield around 7.4 g/L/d (Ding et al. 2014). There are so many challenges, both technical and geographical, associated w'ith algal biomass. Generally, in ideal growth conditions, algae will yield 1 to 7 g/L/d of biomass (Haykiri-Acma and Yaman 2010). For industrial purposes, large volumes of water are needed, contributing major issues for cold countries like Canada during the large part of the year in which the temperature is below 0°C. Before extracting lipid via ultrafiltration, the water content in the alge needs
FIGURE 9.1 Two different pathways for biomass conversion.
to removed because its creating a huge problem. Lipid extracted from algae is processed through transesterification to produce biodiesel or undergoes hydrogenolysis to produce kerosene-grade alkane, which is suitable for using in drop-in aviation fuels as discussed by Cui et al. (2010). Figure 9.1 shows two different pathways for biomass conversion.
Energy Security and Greenhouse Emission vs Biofuel
Energy is a fundamental need for society that supports human life by improving and developing wealth and the quality of life. Over a century, abundant amounts of conventional power from fossil fuels have played a supporting role for most of the industrialized countries and has brought great improvements in leading a wonderful life. The use of such fossil energy creates significant challenges and problems for the upcoming generation. The continuous use of fossil energy leads to a shortage in stock and also causes ecological destruction including water, air, and soil contamination. The uncertainty of future reserves of fossil fuels, known oil reserves, and the sustainable demand for energy cause a serious energy security problem, and these factors are also contributing highly to climate change globally (Cui et al. 2010).
To avoid vital damages from the anthropogenic point of view in regard to climate change, the level of C02 accumulation needs to stabilize to about 500 ppm. For stabilizing C02 accumulation to this level, emissions should be controlled to the present- day level. But this is one of the big challenges, as the expected CO, emission is going to be double by 2050 as per the current scenario. Some other action is required to control C02 emissions. Emission control is attained through less energy demand, low carbon energy supply, and energy efficiency. Bauen (2006) gives the concept of a series of seven triangular “wedges” which shows stabilization of emissions over the next 50 years. The main categories for achieving the series of seven triangular “wedges” are as follows: (1) energy conservation and efficiency, (2) the decarbonization of fuels and electricity supply, and (3) biological storage in soil and forest.
The improvement in efficiency and reduction in energy supply help a lot to stabilize emissions. They mainly depend on innovative energy supply for stationary and transport end uses. The conservation of energy by making behavioral changes like change of mode in transport, smaller vehicles, and less travel may provide a significant contribution to the stabilization of emissions. For efficient use of resources over a long period of time, energy efficiency and conservation have proven to be a major contributor to emission reduction (Bauen 2006).
In regard to energy supply, energy security is a huge challenge involving the provision of a consistent and acceptable energy supply at an affordable cost. Organisation for Economic Co-operation and Development (OECD) countries’ energy imports are rising; in particular, some European countries’ dependency on energy imports is expected to increase from 50% to 70% by 2030. Like environmental impact, energy insecurities also hinder the growth of society, as energy is a necessary input parameter for every activity happening around modern society. A major drop in the energy supply system can produce severe social and economic complications (Bauen 2006). Energy insecurities are defined as is a situation of elevated risks of a physical, perceived or real, and supply disruption.
The sudden rise in the price of energy causes inflation, which affects the performance of the economic system and thus results in loss of GNP and other effects such as unemployment rates. The abrupt rise in prices of energy supply is a sign of a high level of insecurity. The requirements of public policy, along with the market, may be capable of optimizing the level of energy security for society. To reduce the energy use problems that humans are facing in the present and for future generations, societies are shifting in terms of fossil energy to renewable energy wherever possible (Obeng-Odoom 2013). Out of the various renewable energy sources, biofuel extracted from biomass has high potential to replace fossil energy source to some extent. In both stationary and transport sectors, biofuels may play a crucial role in the upcoming generation’s energy needs (Obeng-Odoom 2013).
Greenhouse gas (GHG) emission is one of the serious problems which is coming into the picture, whether fossil fuel or biofuel energy is being used. The main objective here is to find an energy source with ample ability to handle the greenhouse gas emissions efficiently (Faaij 2006). Let us consider the case of biofuel; if the biofuels are extracted in the right way, then greenhouse gas emission will be highly reduced, but if the method of extraction is wrong, then emission may be even more than that for fossil fuels. Plants utilize CO,, a major greenhouse gas emission, for proper growth and food production (Menten et al. 2013). So, plants have the capacity to reduce the level of carbon dioxide in the environment and consequently reduce global warming. If fuels are obtained from plants, when partial combustion produces C02 then it can be utilized by the plants themselves for their nourishment. So, a continuous cycle having the idea of a one-to-one relationship will be developed. As a result, the gas produced will be taken by the plant and thus there will be zero impact on global warming. But development of such an ideal plant may not be possible (Menten et al. 2013).
For starters, a high amount of energy investment is required for growing the crop in the form of seed planting, ground preparation, and supplying water and nutrients. So, in the end, net negative energy is obtained (Van Eijck et al. 2014). Some companies are focusing on investment of energy in the form of sunlight so as to control the GHG emissions in the production phase. The algae are more suitable for this option where in spite of net energy input, there is no production of GHG (Van Eijck et al. 2014). The other problem coming into the picture is the use of land. The elimination of existing plant life is required for increasing the availability of land for growing biofuels. This is one big disadvantage associated with biofuel: carbon is produced at the cost of plant life. So, again algae are proved to be more beneficial. If somehow the above-mentioned problem is solved, then the impact of biofuels on the environment can be controlled. In such a case, the GHG emission and global warming effect will be lower with biofuels than with fossil fuels (Van Eijck et al. 2014).
Bioenergy around the Globe
Bioenergy contributes around 10% of the total primary energy supply globally by 2005 (47.2 EJ of bioenergy out of 479 EJ), mainly for heating and cooking purposes in the residential sector. Bioenergy contributed 78% of total renewable energy in 2005 (Purohit and Chaturvedi 2018). A total of 97% of biofuel is available in the form of solid biomass, out of which 71% is utilized for residential utilities. Recently, around 85% of bioenergy used as a solid fuel for lighting, cooking, and heating purposes with low efficiency (Guo, Song, and Buhain 2015). In most developing countries, traditional bioenergy dominates bioenergy consumption based on biomass. A variety of biomass sources are utilized for the production of bioenergy in various forms. Some of the biomass applicable for bioenergy production and utilized as electricity generation, heat and CHP (combined heat and power) are following below (Wright 2006).
- 1. Residues obtained during the processing of food, fiber, and wood in the industrial sector.
- 2. Short-rotation crops are grown in the form of energy plantation.
- 3. Agricultural residues from the farm sector.
- 4. Forest residues and agroforest residues.
The traditional forms of biomass like fuelwood, animal dung, and charcoal are crucial sources of bioenergy worldwide. In the past, wood fuels are considered as the most common sources all over the world and gave energy security service to a huge part of society. The purpose of the modern bioenergy system is to develop efficient conversion technology which can utilize the available biomass and convert it into the best form for households, cottage industry, and large-scale industry (Bhutto, Bazmi, and Zahedi 2011). Based on the state of the energy carrier, biofuels are broadly categorized into three different forms, namely, solid fuels (for example wood chips, firewood, pellets, charcoal, briquettes, etc.), liquid fuels (for example bio-oil, biodiesel, and bio-ethanol), and gaseous fuels (for example bio-gas, hydrogen, and synthesis gas) (Speight 2010).
A review of the recent status of bioenergy consumption in G8+5 countries is given in this section. This section mainly focuses on production, consumption, and trading of bioenergy in the different countries of the world. The statistics are given by IEA 2007, which provides detailed, complete, and consistent information on energy matters. The statistical analysis, taken for ten years from 1995 to 2005, shows how supply and consumption trends vary in G8+5 countries (Dam, Junginger, and Faaij 2010).
