Ethanol from Sugarcane and the Brazilian Biomass-Based Energy and Chemicals Sector
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eplacing fossil fuel for bioethanol has a long and successful history in Brazil.1 Ethanol has been used as an additive to gasoline since the 1930s, and after the Proalcool Program in the 1970s, car engines were adapted to run with ethanol only. The total amount of ethanol-fueled vehicles at one point reached 5 million;2however, the cheap price of oil, reduction of subsidies, and shortage in the supply of ethanol, among other issues, decreased the interest in those cars in the 1990s. The market for ethanol biofuel recovered with the development of flex-fuel engine technology in 2003, which allows the use of any mixture of ethanol and Gasoline E27, including 100% ethanol. Currently, most cars produced in Brazil are flex-fuel, and in 2018, ethanol sold more than Gasoline A (derived directly from a refinery) in the Brazilian market, which still contains 25% ethanol.3As sugarcane yield increased due to automatization and new agricultural practices and technologies, potential competition between food and fuel production was reduced, and sugarcane currently occupies less than 10% of the total plantation area.4 Brazil is the second-largest ethanol producer and has further growth potential.5,6 There are research opportunities to increase the yield in first-generation ethanol plants by, for instance, genetically engineering the sugarcane7and fermenta- tion yeasts.8 Modeling published in 2017 showed that expansion of sugarcane in Brazil could displace up to 14% of the oil consumption and decrease carbon emissions signifi- cantly (up to 6%) by 2045 without the use of land dedicated to forest conservation and food production.6 Indeed, a midway strategy has been proposed, in which sugarcane and forests could be used together to preserve and regenerate forests and produce bioenergy at the same time.9
In the bioethanol industry, bagasse accounts for 30%−34%
of the processed sugarcane weight. Most bagasse is currently burned to produce bioelectricity, being responsible for approximately 9% of the electricity produced in Brazil.
However, sugarcane bagasse can be hydrolyzed into enriched solutions of glucose (40−50 wt %) and xylose (20−30 wt %).
Glucose can be directly fermented for the production of second generation (2G) ethanol, but the fermentation of xylose is still challenging and needs technological and scientific improvements.8,10 Nowadays, 2G ethanol is available in the market in Brazil. Two companies (Raizen and Granbio) havé the potential to produce approximately 100 millon liters of 2G ethanol per year. It represents less than 1% of the total ethanol production in Brazil. Still, the situation has improved after more than 10 years of basic science development about the cell wall chemistry and the discovery of new enzymes and their
respective mechanisms of action.11 The scientific knowledge applied to the 2G ethanol production is viable and possibly expandible.6 Alternatively, residual biomass from ethanol production can be converted into meaningful platform molecules for the production of chemicals, plastics, and alternative fuels.12Considering the current market, fermenta- tion of glucose to ethanol appears as the most desirable product; however, as the biorefinery concept is established, other products, such as levulinic acid, 5-hydroxymethylfurfural, andγ-valerolactone, might capture a share of this market. The polysaccharides in the sugarcane cell walls also can be utilized.13 For instance, xylans can be used to produce sweeteners (xylitol) for the food industry. The mixed linkage-β-glucans can be used in cosmetics and also in the pharmaceutical industry as antidiabetics.14 Cellulose and its derivatives can be used in the paper industry and also as food additives.
It is important to highlight that ethanol is also a chemical platform molecule that can be catalytically converted into a wide range of important industrial chemicals, in one-step catalytic processes using multifunctional catalysts.15 The so- called ethanolchemistry was developed in Brazil since the time of the Proalcool Program for the production of drop-in chemicals, such as acetic acid, ethyl chloride, acetic anhydride, cellulose acetate, ethyl ether, acetaldehyde, ethyl acetate, acetone, butanol, ethylene, and propylene.16 Even the production of the rubber monomer 1,3-butadiene from ethanol was a commercial process in Brazil in the past. However, the ethanolchemistry industry did not experience the same investment and technological development as the petrochem- ical industry; it was abandoned in the 1990s and never fully recovered. In 2010, the Brazilian-founded chemical company Braskem became the first and largest producer of biopoly- ethylene from ethanol.17There are real opportunities for the rebirth of the ethanolchemistry industry in Brazil, considering that higher production of ethanol can be still achieved and the undergoing energy transition to electric cars. The most mature technologies in ethanolchemistry are the production of ethylene and acetic acid, but the conversion of ethanol into
Received: March 11, 2021 Published: March 29, 2021
Editorial pubs.acs.org/journal/ascecg
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heavier fuels, such as jet fuel,18 and ethanol steam reforming for the strategic production of H219have large potentials for application. The development of ethanolchemistry processes, and also CO2 capture and conversion processes (CO2 from fermentation and energy cogeneration), near existing sugar- cane distilleries may take maximum advantage of energy surpluses, readily available renewable raw materials, and low transport costs. There is also the opportunity to coproduce a wide range of biobased materials and chemicals from solid residues from ethanol production, such as sugarcane bagasse and lignin. Brazil has the most successful program to replace fossil fuel for bioethanol worldwide and has the potential to become a leader in the development of modern ethanolchem- istry and to transform sugarcane plants into true biorefineries (Scheme 1).
There are still challenges in the field: (i) advances in synthetic biology and plant development, (ii) life-cycle analysis of ethanol and biomass-derived products, (iii) design of multifunctional catalysts for the efficient conversion of ethanol into products, (iv) CO2 conversion into products, such as higher alcohols, (v) biomass conversion into valuable products, (vi) process design, and (vii) computational approaches, which represent types of contributions thatACS Sustainable Chemistry
&Engineeringwould welcome on the topic of bioethanol and
biorefineries. We welcome your feedback and look forward to your manuscript submissions in these areas.
We thank Dr. Lucia G. Appel and Prof. JoséMaria C. Bueno for their contributions and helpful discussions for the preparation of this editorial.
Liane M. Rossi, Associate Editor orcid.org/0000-0001- 7679-0852
Jean Marcel R. Gallo, Early Career Board orcid.org/0000- 0003-2937-2628
Luiz H. C. Mattoso, Editorial Advisory Board orcid.org/
0000-0001-7586-1014
Marcos S. Buckeridge, University of São Paulo Peter Licence, Executive Editor orcid.org/0000-0003- 2992-0153
David T. Allen, Editor-in-Chief orcid.org/0000-0001-6646- 8755
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AUTHOR INFORMATIONComplete contact information is available at:
https://pubs.acs.org/10.1021/acssuschemeng.1c01678
Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
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ACS Sustainable Chemistry & Engineering pubs.acs.org/journal/ascecg Editorial
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