Conventional Biofuels and the Future of Commercial Advanced Biofuels (Part 2)

By Dr. Raj Shah, Dr. Vikram Mittal and Stanley Zhang

In Part 1 of this series we looked at the main types of biofuels, the current role of biofuels in the modern fuel market and recent developments in the production of advanced biofuels. The benefits and drawbacks of different biofuels were also explored. In Part 2, we discuss the potential solutions to enhance the future of alternative transport fuels.

 

Future Developments of Advanced Biofuels

Although the production of biofuels made from edible plant species directly compete with food production, advanced biofuels derived from non-edible plants and agricultural waste are not affected by the same issues. Second-generation biofuels are a category of advanced biofuels produced from sustainable, non-food feedstock sources of biomass, such as lignocellulosic biomass, agricultural residues, organic waste and non-edible crops [16]. The non-edible energy crops chosen for the production of second-generation biofuels are grown on marginal land, thus eliminating competition with conventional food crops.

Lignocellulosic ethanol and biomass-to-liquid (BTL) diesel are the main sources of second-generation biofuels. Lignocellulosic ethanol is produced through the extraction of cellulose from lignocellulosic biomass, which is converted into glucose through enzymatic hydrolysis. The glucose is converted into ethanol by means of fermentation, with the resultant ethanol subjected to distillation and dehydration for purification [17]. Biomass-to-liquid technology is used to produce biodiesel and biokerosene through a thermochemical conversion. Initially, pyrolysis and torrefaction techniques are utilized to prepare biomass to undergo gasification at temperatures in excess of 1000℃ [2]. Synthetic gas (syngas), composed of carbon monoxide and hydrogen, is produced, and subjected to purification to remove sulfur, metals and carbon dioxide. The subsequent step is the Fischer-Tropsch process, which converts the purified syngas into synthetic diesel and kerosene using catalysts [18].

Second-generation biofuels offer better fuel quality and a more favorable GHG balance than first-generation biofuels. Cellulosic ethanol and BTL diesel are estimated to reduce CO₂ emissions by 15% over their first-generation counterparts [19]. Additionally, the cost of biomass used for advanced biofuels is lower than the cost of edible crops used in conventional biofuels. However, the conversion of these biomass sources into adequate fuels is difficult and expensive. Second-generation biofuels are not as commercially available due to high production costs and less long-term policy framework [20]. Because of the relatively recent development of advanced biofuels, large-scale production facilities are scarce, due to requirements in the acquisition of large quantities of available biomass. Considerations must be made regarding maximizing GHG emissions, while minimizing cost, environmental impacts and competition with other agricultural markets [20].

Switchgrass, a grass that commonly grows throughout North America, has been a promising ethanol feedstock over corn. As a potential feedstock for second-generation biofuels, switchgrass is capable of being grown on marginal land due to its deep roots, which allow the plant to acquire nutrients from a variety of soils, and a high tolerance to extreme weather conditions, such as prolonged rainfall or droughts [20]. Recent studies led by Colorado State University have designated switchgrass as a leading candidate for the sustainable production of plant biomass. Analyses of U.S. case studies have shown that the cultivation of switchgrass for cellulosic ethanol production had a per-hectare carbon mitigation potential comparable to reforestation [20]. However, switchgrass-based biofuel production facilities are currently sparse due to switchgrass refinery processes and commercialization still being in its early stages.

Developments have been made toward the use of algae for fuel production, resulting in third-generation biofuels. Algae is capable of much higher yields with lower resource inputs than traditional feedstocks. Algae has been used to produce up to 9,000 gallons of biofuel per acre, which is 10 times the yield of the land-based feedstocks used for second-generation biofuels [22]. Another advantage of algae is their diverse methods of cultivation, as they can be grown in open ponds, closed-looped systems and photobioreactors. Algae cultivation in open ponds has low capital costs but is susceptible to contamination and less efficient. Closed-loop systems are not exposed to the atmosphere and utilize disinfected carbon dioxide, allowing for the potential to be directly linked to a carbon dioxide source that may have previously been released into the atmosphere.

Photobioreactors are advanced closed systems with unrivaled levels of yield and control but are difficult to implement and have high capital costs [20]. In addition, algae can be grown under insensitive conditions like saline, brackish water and coastal seawater, eliminating competition with traditional terrestrial agriculture. However, the largest drawback with algae is the substantial quantities of water, nitrogen and phosphorus required for large-scale cultivation [22]. Although, if developments were made toward the production of cost-effective fertilizers that could adequately sustain large-scale algae agriculture, third-generation biofuels could be the future of transportation fuels.

 

Conclusion

The future success of biofuels largely depends on establishing progressive policies and the commercialization of advanced biofuels. Although the United States, Brazil and the European Union have established frameworks to ensure biofuel sustainability, further support must be given toward implementing policies that incentivize the consumption of biofuels over petroleum products [23].

The adherence to the predominant use of biofuels over traditional mineral fuels is integral to maximize the environmental benefits of alternative fuels. Actions must be taken to encourage the use of flexible-fuel vehicles that utilize high biofuel blends or unblended biofuel, instead of the conventional low percentage biofuel blends that account for the majority of global biofuel consumption. The establishment of legislation that provides economic incentives to produce biofuels, along with stringent requirements for GHG emissions reduction, could facilitate mainstream use of biofuels [25].

Additionally, support policies are necessary for the development of large-scale, advanced biofuel production facilities. Since the investment and production costs of advanced biofuels are currently high, relevant policies that reduce the financial risk of investing in the development of second- and third-generation biofuels are needed [24]. The long-term sustainability of advanced biofuels hinges on the improvement of biomass conversion technologies to drive down costs and increase their economic feasibility. Low production costs and large-scale manufacturing facilities are necessary to the global commercialization of advanced biofuels. The option of utilizing feedstocks with high availability and limited other uses is the key to the success of sustainable, alternative transport fuels.

 

Dr. Raj Shah is a director at Koehler Instrument Company, a leading manufacturer of petroleum testing instruments, and an active ASTM member for the past 25 years. He has held numerous leadership positions within various ASTM committees and is a three-time recipient of the ASTM award of Excellence. Contact him at [email protected].

 

 

Dr. Vikram Mittal is an assistant professor at the United States Military Academy in the Department of Systems Engineering. He earned his doctorate in Mechanical Engineering at the Massachusetts Institute of Technology, where he researched the relevancy of the octane number in modern engines.

 

 

 

Nabill Huq is a chemical engineering student at Stony Brook University, where Dr. Shah is the chair of the advisory board of directors, and Huq is also a part of a thriving internship program at Koehler Instrument Company.

 

 

 

References

[2] “What future for biofuels?” IFPEN. IFP Energies nouvelles.

[16] Naik, S. N, et al. “Production of first and second generation biofuels: A comprehensive review.” Renewable and Sustainable Energy Reviews, vol. 14, no. 2, 2010, pp. 578-597.

[17] Gnansounou, Edgard, and Dauriat, Arnaud. “Chapter 6 – Technoeconomic Analysis of Lignocellulosic Ethanol.” Biofuels, 2011, pp. 123-148.

[18] Swain, Pravat K, et al. “Biomass to liquid: A prospective challenge to research and development in 21st century.” Renewable and Sustainable Energy Reviews, vol. 15, no. 9, 2011, pp. 4917-4933.

[19] Antizar-Ladislao, Blanca, and Turrion-Gomez, Juan L. “Second-generation biofuels and local bioenergy systems.” Biofuels, Bioprod. Bioref., vol. 2, no. 5, 2008, pp. 455-469.

[20] Datta, Arup, et al. “An Overview on Biofuels and Their Advantages and Disadvantages.” Asian Journal of Chemistry, vol. 31, no. 8, 2019, pp. 1851-1858.

[21] Kennedy, Helena T. “Switching to switchgrass – will DOE and USDA funding turn switchgrass into a Rockstar biofuel feedstock?” BiofuelsDigest. 27 Sep. 2020.

[22] “Third Generation Biofuels.” Biofuel UK.

[23] Kotrba, Ron. “State-of-the-Art Algae Photobioreactors.” Biodiesel Magazine. 22 Jul. 2015.

[24] Le Feuvre, Pharoah. “Transport Biofuels.” IEA. Jun. 2020.

[25] Coyle, William T. “The Future of Biofuels: A Global Perspective.” Amber Waves Magazine. 1