Integral use of lignocellulosic residues from different sunflower accessions: Analysis of the production potential for biofuels
Introduction
Current concerns regarding environmental issues and carbon emission footprints have increased interest in the use of biomass as a complementary energy resource, given the great possibilities it offers, including direct and indirect procedures (e.g., combustion and bioconversion, respectively) and procedures of reuse, recovery, and revaluation (Álvarez et al., 2015, Visser et al., 2011).
In this context, a significant proportion of future energy demand is expected to be supplied by bioenergy from agricultural or agro-industrial residues, since these are cheap and available almost everywhere. However, this will require better integrated policies to avoid adverse impacts of rivalry for land, in order to avoid direct competition with food production, for example (Álvarez et al., 2015, Boutesteijn et al., 2017). Of the entire global energy matrix, 18% constitutes renewable energy, the majority of which (78%) originates from bioenergy (organic matter) and the remaining (22%) from other sources of renewable energy. Bioenergy provides 10% of the world’s energy supply, with the possibility of transforming biomass into solid, liquid, or gaseous fuels (World Energy Council, 2016). In Brazil, the electricity matrix is predominantly renewable, with 81.6% of the internal supply of electric energy being from renewable sources (65.4% from generation by water in hydroelectric plants, 8.4% from biomass, 7.6% from wind power, and 0.2% from solar energy) (Brasil, 2017, Ministério de Minas e Energia, 2018). Brazil has great agricultural potential as one of the largest producers of oilseeds in the world (United States Department of Agriculture - Foreign Agricultural Service, 2018). In addition, global production and consumption of oilseeds show a growth forecast for the period 2018–2019, with sunflower seed being one of the oilseeds with predicted continued growth (United States Department of Agriculture - Foreign Agricultural Service, 2018).
The use of biofuels in Brazil has been strongly supported by government policies since 1975, beginning with the National Alcohol Program (Programa Nacional do Álcool – ProÁlcool) (Hall et al., 2009). In 2005, the Brazilian Biodiesel Production and Use Program (Programa Nacional de Produção e Uso do Biodiesel – PNPB) was created (Rathmann et al., 2012), which included among its objectives, the family properties of the semi-arid region of the Brazilian northeast in the biofuel production chain (Porte et al., 2010, Stattman and Mol, 2014). In 2018, the Brazilian government regulated the National Biofuels Policy (Política Nacional de Biocombustíveis – RenovaBio) (Decree 9.308/2018) to stimulate an increase in the production of biofuels. The same year, the biodiesel blending requirement was also increased to 10% for diesel sold in the country, increasing the oilseed demand for biodiesel production by at least 20%. Among the oilseeds grown on family farms for processing in biodiesel, sunflower seed is considered a viable option due to its productivity in Brazilian agro-climatic conditions (Bergmann et al., 2013, Carvalho et al., 2013).
In Sergipe, one of the states in the northeastern region of Brazil, family farmers have grown sunflowers since 2009, and PETROBRAS (a semi-public Brazilian multinational energy corporation) has commercialized the seeds for biodiesel production. Embrapa (Brazilian Agricultural Research Corporation) has been studying sunflower crops in Sergipe since 2007, producing approximately 2000 kg⋅ha−1, which is significantly higher than the national average (1516 kg⋅ha−1) (Carvalho et al., 2017, Conab, 2018).
Sunflower cultivation is considered an alternative energy source due to the use of its biomass (Bonilla et al., 1990). The transformation of sunflower biomass into energy has been studied by several researchers over the last 20 years, for instance, combustion or briquettes (Smith and Lindley, 1988), pyrolysis (Gerçel, 2002, Yorgun et al., 2001), and oil extracted from the seeds (Antolı́n et al., 2002, Reyero et al., 2015). In 2016, sunflowers were grown on 26,205,337 ha worldwide (FAO, 2018), being considered one of the most important oleaginous plants in the world and generating tons of residues (Ziebell et al., 2013). One option for the use of sunflower residues is the production of biofuels (bioethanol) in biorefineries.
However, the chemical characterization of the biomass of sunflower residues has been the subject of few studies. Some recent works have characterized the sunflower stalk (Díaz et al., 2011, Ruiz et al., 2013), but only from one sunflower accession, and do not provide the lignocellulosic fraction yield per hectare (ha) using an estimate of yield, such as 3–7 t⋅ha−1 biomass presented by Marechal and Rigal (1999). Ziebell et al. (2013) studied the chemical differences in the cell wall and the growth patterns of eight Helianthus accessions as an initial step in understanding the potential of sunflowers as a source of lignocellulosic biomass for the production of biofuels. In addition, the authors emphasized the importance of determining the amount of sugars and lignin per hectare.
Knowledge of the lignocellulosic composition of these materials is extremely important for the use of sunflower residues in bioconversion processes, since these compositions will determine the pretreatment of the raw material with a view to improving the release of sugars from both the hemicellulose and cellulose fractions (Ruiz et al., 2006). Moreover, industries are interested in exploring alternative uses for these by-products (Offeman et al., 2014). Offeman et al. (2014) and Ruiz et al. (2013) highlighted that the sugar content of the residues differs among plant varieties, climate, water availability, growing sites, and other conditions that are not well known.
The main objective of the present study was to analyze the potential of the sunflower biomass (seeds, stalk, and capitulum) for use in the production of biodiesel and bioethanol. Four cultivars of sunflower Helianthus annuus L. were planted under controlled conditions to analyze the production of dry biomass and grains. Subsequently, the biomass residue characteristics and their yields per hectare of oil, cellulose, hemicellulose, and lignin were analyzed under the same conditions for each cultivar, which were grown in Sergipe, Northeast Brazil. An economic essay of sunflower cultivation was conducted as a potential raw material for the production of biofuels on an industrial scale, highlighting the costs of the raw material.
Section snippets
Plant material and planting design
Four cultivars of Helianthus annuus L. (Embrapa 122, M734, Hélio 360, and Aguará 4) were sowed, and the produced biomass characterized and evaluated. The experiment adopted the practices used by small farmers in semi-arid Northeast Brazil as a reference. Embrapa provided sunflower seeds and technical support for the crops, and the maintenance of the experiment was carried out by COOPRASE, a settlement cooperative of farmers in Sergipe, Brazil. The adopted methodology was the same as that used
Evaluation of the production potential of dry matter, grains, and oil
The four accessions of Helianthus annuus L., named M734, Aguará 4, Hélio 360, and Embrapa 122, showed similar characteristics with respect to height, circumference, capitulum diameter, grain yield, and seed oil content (Table 1). However, Embrapa 122 had the lowest oil yield, suggesting that, considering only oil production, the cultivars M734, Aguará 4, and Hélio 360 are viable options as raw materials for the production of biodiesel.
The four cultivars showed an average production of
Conclusion
The results of the present study show the characteristic variations in the production of oil and biomass of four cultivars of Helianthus annuus L. The production tests were conducted under controlled conditions that allowed the evaluation of four replicates with respect to plant characteristics and yields of grain, oil, and agricultural residues of sunflowers. The characterization of the lignocellulosic composition of the cell wall separately identified the biomass composition of sunflower
Acknowledgments
This work was supported by the Support to Innovation, Science and Technology Foundation of the State of Sergipe, the National Council for Scientific and Technological Development, the Coordination of Improvement of Higher-Level Personnel, and the Regional Cooperative of Agrarian Reform Settlers of Sergipe’s Semi-Arid and Brazilian Petroleum Biofuel (PETROBRAS Biofuel).
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