By Elton Alisson | Agência FAPESP – Cellulosic ethanol obtained from sugarcane trash and bagasse, also known as second-generation (2G) ethanol, can be economically viable by 2025 if the current obstacles to its production are surmounted and if the Brazilian sugar and energy industry leaves behind its present stagnation.
This is the opinion of researcher Antonio Bonomi, coordinator of the process intelligence division at the National Bioethanol Science & Technology Laboratory (CTBE), which belongs to the National Energy & Materials Research Center (CNPEM) in Campinas, São Paulo State, and a member of the steering committee for the FAPESP Bioenergy Research Program (BIOEN).
“Currently, it’s clearly more worthwhile from the economic standpoint for firms in the sugar and energy industry to set up a new plant to produce first-generation (1G) ethanol than to build a 2G ethanol plant integrated with a 1G plant, for example, because the return on investment is greater,” Bonomi said.
“However, the tendency is for the cost of producing cellulosic ethanol to equal the cost of producing 1G ethanol in the medium term, by 2025, and for 2G ethanol to become cheaper than 1G ethanol in 2030, as long as the agricultural, industrial and technological obstacles faced today are surmounted and the industry leaves its current stagnation behind.”
2G biofuels are among the subjects being discussed at the 2017 Brazilian BioEnergy Science & Technology Conference (BBEST 2017), which runs through October 19 in Campos do Jordão, Brazil, hosted by BIOEN.
According to Bonomi, principal investigator for a project supported by FAPESP to find ways of valorizing a decentralized biomass supply chain for the production of advanced biofuels, the volume of 2G ethanol currently produced in Brazil is very small.
Only two 2G ethanol plants exist today in Brazil. GranBio in São Miguel dos Campos, Alagoas, in the Northeast, began operating in 2014. Raízen in Piracicaba, São Paulo, began operating at the end of 2014. Their aggregate production capacity is a little over 100 million liters per year, but their actual output is less than half that capacity, according to Bonomi.
“Neither plant produces uninterruptedly,” he said. “They’re still on the learning curve and use equipment that isn’t yet very efficient. Their processes face problems that are being identified and gradually resolved.”
According to estimates made by researchers in July 2014, the production cost of 2G ethanol is about R$1.50 (now about US$0.50) per liter compared with about R$1.15 for 1G ethanol.
However, 2G ethanol may cost only about R$0.75 per liter to produce by 2025 and R$0.52 by 2030, Bonomi said. In partnership with colleagues at CTBE, he conducted a study commissioned by BNDES, the national development bank, that projected the future cost of producing 2G ethanol and the timeframe for the technology to become economically viable in Brazil.
“At a production cost of R$0.52 per liter, 2G ethanol would be competitive even if international oil prices fell as low as US$44 per barrel,” Bonomi said.
To arrive at these numbers, the researchers conducted an initial survey of 22 firms and experts in the fuel ethanol industry and performed computer simulations using Virtual Sugarcane Biorefinery (BVC), a computational tool developed by CTBE to evaluate the integration of new technology with the production chains for sugarcane and other types of biomass in the agricultural, industrial and commercial stages.
The simulations were based on three different scenarios: short-term (2015-20), medium-term (2021-25) and long-term (2026-30).
One of the scenarios represents average production today, especially in the Center-West, Southeast and South, for a 1G ethanol plant with the capacity to process 2 million metric tons of cane during the harvest with basic technology and no energy cogeneration.
The other scenarios assume the processing of at least 4 metric tons with modern technology and assume the production of 1G ethanol alone, 1G+2G, and 2G alone.
The researchers considered two technological routes for the production of 2G ethanol: separate fermentation of five-carbon sugars (xylose) and cofermentation of five- and six-carbon sugars (glucose).
The results of the simulations indicated that in the agricultural stage, one of the obstacles to the economic viability of 2G ethanol is the high cost of biomass.
“The cost of biomass is a hindrance not just to the production of 2G ethanol but also to that of 1G ethanol,” Bonomi said.
Other obstacles are the lack of an agricultural and industrial system designed to make full use of sugarcane, including the leaves of the plant (known among technicians as trash), and the lack of an alternative to cane between harvests, so that a plant can operate 300-330 days per year instead of 200-240 days, on average, at present.
“Energy cane [hybrid varieties obtained by crossing Saccharum officinarum with S. spontaneum with higher fiber content and less sugar than conventional cane] can help in this sense because it has some interesting properties,” Bonomi said.
One of the advantages of energy cane is that these varieties, which have been developed by firms such as GranBio and Vignis, and by research institutions such as the Agronomy Institute (IAC), do not require water stress to accumulate high levels of sugar. Another benefit is that they can also be harvested throughout the rainy season, Bonomi explained.
In the industrial stage, one of the main obstacles to economic viability for 2G ethanol is the high cost of capital goods, i.e., the plant and equipment required to produce it.
“This is a problem that the learning curve will probably solve,” Bonomi said. “The first plant is normally more expensive because there aren’t yet enough manufacturers of the right equipment for production.”
In technology, one of the main problems is pretreatment of biomass to separate lignin from cellulose and hemicellulose in preparation for the process of hydrolysis, which converts cellulose and hemicellulose into fermentable sugars for the production of 2G ethanol.
“This stage, involving preparation of the lignocellulosic materials [cellulose and hemicellulose] so that enzymes can break down the polymers they contain, isn’t fully understood and the equipment required, which is costly, is still being developed,” Bonomi explained.
Another problem is the long time required for hydrolysis, which entails costly tank storage and a risk of contamination.
“For this reason, 2G ethanol plants’ capacity is excessive by design to offset the losses that are likely to occur owing to contamination during the process,” Bonomi said.
A third technological bottleneck, he added, is the fermentation of pentoses, the C5 sugars resulting from hemicellulose hydrolysis.
Hydrolysis of cellulose results in glucose, a C6 sugar that is readily fermentable into ethanol. However, hydrolysis of hemicellulose produces C5 sugars (pentoses), which the microorganisms in today’s yeast fermentation cannot easily metabolize to produce 2G ethanol, resulting in a relatively slow pace of 2G ethanol production from hemicellulose.
“Today, it’s possible to produce 2G ethanol on a large scale from cellulose hydrolysate,” Bonomi said. “Production from hemicellulose hydrolysate is still under development. CTBE has only recently developed a modified yeast capable of producing ethanol from pentoses.
“The progress expected in the agricultural, industrial and technological areas should ultimately make 2G ethanol cheaper than 1G ethanol.”
Each of Brazil’s 2G ethanol plants uses a different technological route. GranBio’s is the standalone route, in that it is dedicated to producing 2G ethanol and not integrated with a 1G ethanol plant.
The plant run by Raízen, a joint venture between multinational Shell and locally owned Cosan, is an integrated facility that produces both 1G and 2G ethanol.
According to Bonomi, an advantage of the technological route chosen by Raízen compared with GranBio’s route is that at least cellulose hydrolysate can be fermented together with cane juice sucrose to make 2G ethanol.
“Whereas GranBio makes ethanol by converting a blend of cellulose hydrolysate and hemicellulose hydrolysate, in which glucose and other C6 sugars from the cellulosic fraction are combined with C5 sugars from the hemicellulosic fraction, Raízen’s technology ferments C6 with sucrose and can ferment C5 sugars separately to produce ethanol,” he said.
Nevertheless, both plants have faced technological challenges to produce 2G ethanol, especially in the raw material pretreatment stage, Bonomi added.
In a press release published in early June by Broadcast, Grupo Estado’s real-time news and market data service, GranBio acknowledged that it had changed its 2G ethanol investment timetable and production targets owing to technological problems relating to pretreatment and also to the economic crisis in Brazil. It added that it expected to produce 2G ethanol as competitively as 1G ethanol by 2019.
Consulted by Agência FAPESP, Raízen replied in a written statement that one of the keys to its successful production of 2G ethanol at its Costa Pinto plant in Piracicaba is 1G-2G integration, which gives rise to significant logistical benefits.
“The company has high hopes for this disruptive technology and believes the technological challenges have been surmounted,” the statement said. “At this time we are pursuing mechanical reliability for our equipment and a satisfactory level of excellence for the plant as a whole.”
The study “De promessa a realidade: como o etanol celulósico pode revolucionar a indústria da cana-de-açúcar: uma avaliação do potencial competitivo e sugestões de política pública” by Bonomi et al. can be retrieved (in Portuguese) from: web.bndes.gov.br/bib/jspui/handle/1408/4283.