Second-generation Biofuels

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. They are made from different feedstocks, including lignocellulosic biomass or woody crops, agricultural waste, as well as dedicated non-food energy crops grown on marginal laud unsuitable for crop production and, therefore, may require different technology to extract usefitl energy from them.

The second-generation biofuels are distinguished from the first-generation biofuels in two aspects: They are obtained from plants that do not have a food function, and they are produced with technological innovations that will allow them to be more ecological and advanced than the current ones. As they are obtained from non-food raw materials, they can be grown on marginal lands that are not used for growing food. Existing biomass industries and relevant conversion technologies must be considered when evaluating the suitability of developing biomass as feedstock for energy. In this sense, they allow greater diversification with new raw materials, new technologies and new final products, thus promoting agricultural, forestry and agroindustry development.

It has been found that biomass from cellulose can be a basic raw material in the production of second-generation biofuels. The cellulose biomass allows the generation of cellulosic bioethanol, so waste from sawmills can be used, and forestry can be reoriented and expanded to diversify the use of forests and protect them from their clearing for agricultural and livestock uses (Balan, 2004). The main resources of second-generation biofuels are:

Energy crops

An energy crop is a plant grown at a low-cost and low-maintenance harvest that is used to make biofuels, such as bioethanol, or combusted for its energy content to generate electricity and/or heat. Energy crops are generally categorized as woody or herbaceous plants; many of the latter are glasses of the family Graminaceae.

Commercial energy crops are typically densely planted, high-yielding crop species which are processed to biofuel and burnt to generate power. Woody crops, such as willow (Mola-Yudego and Arinsson, 2008) or poplar, are widely utilized, as well as temperate glasses, such as Miscanthus and Pennisetum purpureum (both known as elephant grass) (Hodsman et al., 2005). If carbohydrate content is desired for the production of biogas, whole crops such as maize, millet, white sweet clover, and many others can be made into silage and then converted into biogas (Masarovicova et ah, 2009).

Through genetic modification and application of biotechnology, plants can be manipulated in order to obtain greater yields, high energy yields can also be realized with existing crops (Masarovicova et ah, 2009).

Municipal solid waste

Municipal solid waste is formed by a very large range of materials, and total quantities of such waste are increasing. In the United Kingdom, recycling initiatives decrease the proportion of waste going straight for disposal, and the level of recycling is increasing each year. However, there remains significant opportunities to convert this waste to fuel via gasification or pyrolysis (Kretschmer et ah, 2013).

Green waste

Green waste, such as forest residues or garden or park waste (Kretschmer et ah, 2013) may be used to produce biofuel via different routes. For example, biogas captured from biodegradable green waste, and gasification or syngas for further processing to biofuels via catalytic processes. In this case, as with other biomass, problems of scale and variety of residues have yet to be overcome.

Black liquor

Worldwide, the pulp and paper industry currently process about 170 million tons of black liquor (measured as diy solids) per year, with a total energy content of about 2EJ (IEA Bioenergy. 2007), making black liquor a very significant biomass source.

A pulp mill that produces bleached Kraft pulp generates 1.7-1.8 tons of black liquor (measured as diy content) per tonne of pulp. Black liquor, thus, represents a potential energy source of 250-500 MW per mill. As modem Kraft pulp mills have a surplus of energy, they could become key suppliers of renewable fuels in the future energy system (IEA Bioenergy, 2007).

Today, black liquor is the most important source of energy from biomass in countries such as Sweden and Finland with a large pulp and paper industry. It is, thus, of gr eat interest to convert the primary energy in the black liquor to an energy earner of high value. Furthermore, in comparison with other potential biomass sources for chemicals production, black liquor has the gr eat advantage that it is already partially processed and exists in a pumpable. liquid form (IEA Bioenergy, 2007).

“Drop-in ” biofuels

Drop-in biofuels can be defined as “liquid bio-hydrocarbons that are functionally equivalent to petroleum fuels and are frilly compatible with existing petroleum infrastructure” (Karatzoz et al., 2015).

There is considerable interest in developing advanced biofuels that can be readily integrated into the existing petroleum fuel infrastructure—i.e., “dropped-in”—particularly by sectors such as aviation.

where there are no real alternatives to sustainably produced biofuels for low carbon emitting fuel sources. Drop-in biofuels should be fully fungible and compatible with the large existing “petroleum-based” infrastructure.

According to a July 2014 report published by the IEA Bioenergy Task 39. entitled “The Potential and Challenges of Drop-in Biofuels”, there are several ways to produce drop-in biofuels that are functionally equivalent to petroleum-derived transportation fuel blend stocks (IRENA, 2017).

Environmental impact

Greenhouse gas emissions

Lignocellulosic biofuels reduce greenhouse gas emissions by 60-90% when compared with fossil petroleum (Borjesson et al., 2013), which is on par with the best of the current first-generation biofuels, where typical best values are currently 60-80%. In 2010, average savings of biofuels used within Europe was 60% (Laniers et al., 2012). In 2013, 70% of the biofuels used in Sweden reduced emissions by 66% or even higher (Westin and Forsbeng, 2014).

Advantages of second-generation biofuels

The advantages of second-generation biofuels are numerous:

• • By having a greater variety of raw not edible materials, they do not compete with the food function, since they are not alternatives to food, although it may generate growth in the industry that uses vegetable fibers or wood.
• • They can be planted in noil-agricultural or livestock areas, particularly, they can diversify the use of forests and encourage forestry and stop deforestation. In some cases, they may be used to recover eroded land into hillsides or decertified areas and fix CO, through its root system.
• • The water consumed is generated by the forests themselves due to their ecosystem function with the generation of rain.
• • They do not require the massive use of agrochemicals (fertilizers, pesticides, water, land, etc.). The net ratio of energy produced will improve with respect to the current ones.
• • They can use biomass from garbage, from industrial waste or from human consumption.
• • Encourage technological development with diversification effects in the agio-industrial sector.
• • They are highly efficient in reducing emissions of greenhouse gases, particularly CO and CO, from short to medium term.

In the long term, they can lower production costs compared to ctment biofuels.

Disadvantages of second-generation biofuels

One of the disadvantages faced by second generation fuels is the high costs they face because they are now at the marketing threshold due to then relatively high manufacturing cost. This means that second- generation biofuels cannot yet be produced economically on a large scale. Production costs for the pulp and ethanol process (alone) are higher than the prices of gasoline based on mineral oil and conventional bioethanol.

Production costs are uncertain and vary with the feedstock available and conversion process but are currently thought to be above USD 0.80/liter of gasoline equivalent (Sims et al., 2010). Even with oil prices remaining above 80 USD/bbl, second-generation biofuels will probably not become fully commercial nor enter the market for several years without significant additional government support.

Finally, there is no clear candidate for “best technology pathway” between the competing biochemical and thermo-chemical routes. The development and monitoring of several large-scale demonstration projects are essential to provide accurate comparative data (Sims et al., 2010).

Third-generation Biofuels or Algae Fuel

Its elaboration uses production methodologies like those of second generation but using bioenergy crops specially designed or adapted as a raw material to improve the conversion of biomass to biofuels. These improvements or adaptations frequently use molecular biology techniques, such as the development of trees with low lignin percentages, which would reduce costs and improve the production of ethanol, or the modification of com to contain integr ated celluloses.

Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels, using microalgae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly-known biofuel sources, such as com and sugarcane (Scott et al., 2010; Darzins et ah, 2010), since microalgae (unicellular photosynthetic microorganisms, living in saline or freshwater environments that convert to algal biomass) can be converted to bio-oil. bioethanol, bio-hydrogen and biomethaue via thermochemical and biochemical methods. Several companies and government agencies are funding efforts to reduce capital and operating costs and make algae fuel production commercially viable (Oucel, 2013). Like fossil fuel, algae fuel releases CO, when burnt, but unlike fossil fuel, algae fuel and other biofuels only release CO, recently removed from the atmosphere via photosynthesis as the algae or plant grew. The energy crisis and the world food crisis har e ignited interest in fanning algae for making biodiesel and other biofuels using lands unsuitable for agriculture. Among algal fuels, the attractive characteristics are: they can be grown with minimal impact on fresh water resources (Jia et al., 2010), they can be produced using saline and wastewater, they also have a high flash point (Dinli et al., 2009), and are biodegradable and relatively hannless to the environment if spilled (Demirbas, 2011; Demirbas, 2009). Biofuels production costs can vary widely by feedstock, conversion process, scale of production and region. However, algae cost more per unit mass than other second-generation biofuel crops due to high capital and operating costs (Hodsman et al., 2005) but are claimed to yield between 10 and 100 times more fuel per unit area (Greeuwall et al., 2009).