Biofuels Tobacco.docx

Tobacco biomass as a source of advanced biofuels Florin G. Barla & Sandeep Kumar To cite this article: Florin G. Barla & Sandeep Kumar (2016): Tobacco biomass as a source of advanced biofuels, Biofuels, DOI: 10.1080/17597269.2016.1242684 To link to this article:

http://dx.doi.org/10.1080/17597269.2016.1242684

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Tobacco biomass as a source of advanced biofuels Florin G. Barla and Sandeep Kumar Department of Civil and Environmental Engineering Old Dominion University, Norfolk, VA 23529, United States ABSTRACT

Tobacco plants can be developed as an energy crop for biofuels production. Tobacco represents a well-established non-food crop with an over 400-year tradition of cultivation in the United States. It is the most popular non-food crop in the world, grown in more than 120 other countries. Energy tobacco as a platform biomass for biofuels, combined with a water-based green-process technology to produce fermentable sugars from tobacco plants or tobacco stalks, was the aim of this study. The composition analysis showed that non-structural sugars in modified or unmodified tobacco leaves are comparable to those of energy crops (switch grass, miscanthus), whereas lignin content in tobacco leaves is significantly lower. Moreover, the elemental analysis of tobacco leaves showed that the carbon content is in the range of 37–39 wt% on a dry basis, and oil content was about 5 wt%. Upon hydrolysis, more than 75 wt% of structural or non-structural sugars in tobacco biomass was available as glucose. The results showed that tobacco cellulose could be effectively converted to hydrolytic products (glucose, cellobiose and oligosaccharides) within a few seconds under hydrothermal liquefaction (HTL) conditions. There are some parameters that are crucial for a successful HTL reaction, such as residence time, temperature, pressure and the particle size of the biomass.

ARTICLE HISTORY

Received 7 January 2016 Accepted 2 September 2016 KEYWORDS

Energy tobacco; hydrothermal liquefaction; biofuels; oil seeds; green coal

Introduction The Energy Independence and Security Act of 2007 set up a mandate to increase the production of biofuels to 36 billion gallons per year (BGY) by 2022 [1,2]. Out of the total 36 BGY of biofuels, 15 BGY would come from corn ethanol and the remaining 21 BGY are needed from lignocellulosic or other second and third non food-based biomass (microalgae, lipid based plants) sources. The development of cellulosic ethanol has been unexpectedly slow due to several technological challenges [1]. As compared to the production of bioethanol from corn, the use of lignocellulosic biomass is more complicated because the polysaccharides are more stable and are not readily available and fermentable by Saccharomyces cerevisiae, whereas the starch from corn can be made available via enzymatic hydrolysis. The concept is to hydrolyze cellulose and hemicelluloses to recover monomeric C 5 and C6 sugars, and then ferment the sugars to bioethanol [3]. The residual lignin which has a relatively higher heating value (24 to 25 MJ/kg) is generally used for generating steam or providing the process heat, and also can be converted to valuable aromatic compounds such as vanillin [4]. Making ethanol from simple sugars (sugarcane juice) is relatively inexpensive. The difficulty level increases when corn is used as a feedstock, where an enzyme is used to hydrolyze starch in corn kernels into the monomeric/fermentable sugar (glucose). Corn to ethanol is a matured technology now and the enzyme (a-amylase and glucoamylase) needed for starch hydrolysis is commercially available. The enzyme is not costly and contributes approximately 3 to 5 cents/gallon of ethanol. The production of ethanol becomes very difficult when lignocellulosic feedstock (switchgrass, pinewood) is used. The sugars are locked in a very complex structure and so require costly enzymes to unlock the sugars. Within the research community this is known as ‘recalcitrance’, and it currently limits brewers to converting just 40% of the energy content available in cellulosic feedstock to ethanol. If monomer sugars are readily available, the fermentation process, by contrast, converts about 90% of the energy in simple sugars to ethanol [5]. Some of the major technological barriers identified in the full-scale commercialization oflignocellulosic biomass to bioethanol feedstock development are lignin utilization and the enzyme cost. There has been a continuous effort in finding and analyzing new renewable sources of energy in the last decade. Among the other nonfood crops targeted,tobacco was recognized as a possible candidate. Since 2006, the US government has encouraged the development of alternative lignocellulosic biomass crops because of the adverse impact first-generation crops can have on food markets. The World Health Organization Framework Convention on Tobacco Control (WHO FCTC ) has addressed, in Article 17, the need to offer economically sustainable livelihood alternatives for

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those affected by an eventual reduction in global tobacco leaf demand. The FCTC has also stressed, in Article 18, the need to protect the environment from the adverse effects of tobacco farming, and the health of persons engaged in tobacco cultivation. Tobacco plants are currently cultivated in at least 124 countries and about 3.8 million hectares of agricultural land is dedicated to tobacco cultivation. Globally tobacco production reached the highest peak in 1997 with over 9 million tonnes and has since declined by almost a quarter, to 7.1 million tones in 2009. Tobacco, if grown for energy production and not in a traditional way for smoking, can produce large amounts of relatively low-cost biomass feedstock, turning tobacco into a very efficient agricultural crop. Tobacco seeds are another feedstock for biofuels that can be collected along with tobacco biomass. Tobacco possesses an effective oil biosynthesis mechanism and can accumulate up to 40– 50% of seed weight in oil. Tobacco cultivation can generate up to 170 tons/ha of biomass when grown for bioenergy. Moreover, tobacco plants can be coppiced to stimulate re-sprouting from the stump after cutting; therefore, multiple harvesting per year would be possible. Tobacco leaves are reported to contain 1.7–4% oil per dry weight [6]. This oil is extractable as fatty acid esters and can be used for biofuel production. However, the oil content of green biomass is much lower quantitatively than that of oil-crop seeds. Many researchers believe that tobacco represents an attractive and promising ‘energy plant’ platform and could also serve as a model for the utilization of other high-biomass plants for biofuel production [6,7].

Tobacco crop Tobacco is a cash crop that active industry intervention has made attractive to farmers, it being the largest non-food crop by monetary value in the world. Most tobacco, about 90%, is cultivated in tropical climate and woodlands areas. Tobacco is a mono-crop, and it is known that this type of culture depletes soil nutrients at a much faster rate than other crops do. When grown for smoking, tobacco leaf must accumulate a higher nicotine content; thus, some agricultural practices such as topping significantly stimulate high uptake of soil nutrients, whereas if grown for energy it is believed that this process is slower. Asian countries account for 64.3% of world tobacco leaf production; North, Central and South America and the Caribbean for 23%; Africa for 7.6%; Europe and the member states of the Commonwealth of Independent States for about 5%; and Oceania for only 0.1% [7]. China alone accounts for 43.9% of world tobacco leaf production, followed by Brazil (14%), India (8%), the United States of America (5%), Argentina (2.4%), Indonesia (2.1%), Turkey (2.1%), Greece (1.9%), Italy (1.8%) and Pakistan (1.7%), as shown in Figure 1. Those 10 main growers produce close to 80% of the global total of tobacco leaves. For countries like China, India, Indonesia and Pakistan, most of the production is used for internal consumption, but for the others a large proportion of the production is exported. Production of Nicotiana rustica for bidis in India is about 200,000 tones per year. A relatively steady increase in global tobacco leaf production can be seen from 1970 to the mid-1990s (an increase of almost 50% between 1970 and 1998), a downward trend until 2003, and then a slow increase until 2011 [7]. This global production tends to outweigh the actual global consumption of tobacco leaves, indicating an oversupply of tobacco leaves in the global market. The cigarette industry is in the unique position of being able to control their supply through tobacco cultivation contracts. Steered overproduction is a method to keep tobacco leaf prices low at the farm gate, to the disadvantage of the tobacco farmers. Growing tobacco also generates considerable amounts of waste in the form of plant stalks that have never been exploited as an energy resource at a large scale. The amount of tobacco waste is abundant but there is no effective way to treat or exploit the materials. The global tobacco industry could be characterized as a highly specialized oligopoly industry that depends exclusively on the cultivation of the tobacco crop (Nicotiana tabacum and, to a much lesser extent, Nicotiana rustica). The value-added production chain of tobacco is composed of three sub-sectors: tobacco farmers, primary processing and the tobacco products industry. Tobacco farmers are producing annually over 7 tonnes of tobacco utilizing a total of 4 million hectares, all around the world. The global crop value is estimated to be US$ 8 billion at the farm gate. Tobacco farmers are involved in the whole processing flow, including the preparation of farms, nursery establishment/greenhouses, planting, farm/crop management, harvesting, curing, sorting and leaf grading, and transportation from their homes to leaf buying centers. At each of the mentioned stages, farmers face challenges that may vary from region to region: challenges related to contracting, extension, and support and marketing/payment systems. The primary processing of the tobacco leaves include a classification of raw tobacco into different quality classes. Specialized companies, also known as ‘first processors’ or ‘leaf companies’, complete this process; however, worldwide only a few companies work in this sector, and usually they have subsidiary companies in the tobacco-growing countries, which act as an interface with the farmers. In some countries, independent national companies also work

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in this sector. Some cigarette manufacturers also possess specialist companies in tobacco-growing countries that act as ‘first processors’. The business model is a vertical integration of the tobacco farmers. The first processors buy readycured tobacco leaves from the farmers under a contractual arrangement, delivering all necessary inputs and providing loans for cropping. By the mechanism of grading the supplied tobacco leaves, the ‘first processors’ fix the price at which each farmer is paid. By the subsequent transformation of the purchased tobacco leaves, the global crop value reaches about US$ 20 billion [7]. The tobacco products industry includes facilities that manufacture cigarettes, cigars, smokeless tobacco (i.e. chewing, plug/twist and snuff tobacco), loose smoking tobacco (i.e. pipe and roll-your-own cigarette tobacco), reconstituted (sheet) tobacco, and other tobacco products such as bidis, and which market them under different brands. It is estimated that in 2007, the global tobacco market reached a volume of about US$ 378 billion. The global cigarette market is predominately shared by five companies that account for 84.2% of global sales. The most important specialized tobacco product is the bidi. India accounts for more than 85% of the world’s bidi production. Bidi tobacco occupied around 30% of the total area under tobacco cultivation and 33% of total tobacco production in the country in 2002. Roughly 4 million people earn their livelihood from bidi rolling. It is important, therefore, to recognize these people as tobacco workers insofar as applicability of the draft policy options and recommendations are concerned. In China, tobacco production and curing is ranked among the most important agro-industries, involving hundreds of millions of farmers and workers and, thus, contributing significantly to the national economy. The tobacco manufacturing process consumes considerable amounts of energy, but with little efficiency. The average energy cost involved in tobacco curing is 2.2–3.2 kg of standard coal for per 1 kg of tobacco, with a process energy efficiency of less than 20%. It has been reported that the production of approximately 5 million tons of dried tobacco yields 1 million tons of tobacco waste [7].

Nicotine: a byproduct As is known, tobacco plant is cultivated mainly for its leaf, which, besides for smoking, sniffing and mastication, is used because of its nicotine content. Nicotine is created in the root of the tobacco plant, mainly from the most common form of nitrogen that is absorbed from the ground, and it is present everywhere in the plant, except in the seed [8]. The distribution of nicotine in tobacco differs from type to type. Pesevski et al. [9] reported that the total nicotine content in Basma, a variety which is rapidly expanding in R. Macedonia, is distributed as follows: 0.417% in root, 0.278% in stem, 1.206% in leaf and 0.513% in flower. According to the same authors, the lower part of the stem contains 0.08%, the middle part 0.13% and the top 0.16% of the total content of nicotine. According to relatively recent estimations, about 300,000 tons of nicotine as waste is globally produced every year [9]. Recently, growing tobacco for energy showed that if some traditional agricultural practices are eliminated, such as topping, the amount of nicotine in the mature plant is considerably lower. On the other hand, the nicotine content in the mature plant could be also controlled by genetic engineering/manipulation. Tobacco waste is a typical agricultural waste material produced during the manufacturing of tobacco. The range of waste products generated from tobacco is diverse, and mainly includes tobacco stems, tobacco dust and tobacco residue. A significant amount of tobacco waste is generated every year, in the smoking tobacco industry, and there is a huge concern related to waste disposal because of its toxic chemical contents, such as nicotine, which could be harmful to both the environment and human health [10]. The conventional method for tobacco waste disposal is burning and/or dumping in landfills, but this could trigger serious environmental pollution, and on the other hand is a wastage of significant and cheap resources [11]. In Thailand, about 500–650 tons of tobacco plant waste is produced annually as a result of various processing stages during post-harvest and manufacturing of tobacco products. There is still no alternative process to utilize such waste in order to minimize the overall costs by extraction of valuable byproducts, and cigarette-making companies are required to pay for its disposal. Most tobacco plant waste is simply burned, a process that has a high cost of operation, most of it related to air pollution problems [12]. However, these large yields of tobacco waste could offer a new fuel resource if treated in an appropriate way. Figure 2 shows a comparison between growing traditional tobacco and tobacco for energy. The values are expressed as wet weight. When tobacco is grown for energy there is virtually no waste; the whole plant is processed and finally contributes to the final biofuel yield.

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Conversion processes The main challenge in biomass conversion to biofuels consists in its high moisture content and variable composition. There are several methods very well described in the literature; however, thermochemical conversion such as pyrolysis and gasification require dried biomass, which increases considerably the overall cost of biofuel production. Basically, three main methods could be used in biomass conversion to biofuels: biochemical (enzymatic hydrolysis), thermochemical and hydrothermal pathways.

Biochemical conversion of biomass There are several methods to pretreat the lignocelluloses where the crystalline structure is opened up and in this way becomes more accessible to the enzymes. During enzymatic treatment of cellulose and hemicellulose, cellobiose, glucose and other sugars are released. In the literature, different strategies are described for enzymatic hydrolysis and fermentation, including: separate enzymatic hydrolysis and fermentation, simultaneous saccharification and fermentation, non-isothermal simultaneous saccharification and fermentation, simultaneous saccharification and cofermentation, and consolidated bioprocessing [13]. Enzymatic hydrolysis is very costly – usually twice as much as for starch – and another challenge is the conversion time, the process being relatively slow [14]. However, process integration and optimization will improve the overall energy consumption, and reducing the price of cellulose will help to improve the economy of the process.

Methane production from tobacco biomass Recently, Gonzalez-Gonzalez and Cuadros [12] proposed two scenarios under which the anaerobic digestion of tobacco biomass could become economically viable. In the first scenario, the biogas generated in the biological process could be used as fuel to produce heat, hence avoiding other fossil fuel consumption. In the second scenario, the electric and thermal power that is generated during anaerobic digestion could be self-consumed or sold to industry. The experiments carried out in semi-continuous mode yielded the highest methane production (53.84 § 15.48 Nm 3 CH4/t fresh tobacco) when the substrate composition was 15% fresh tobacco/85% water during a 16-day degradation period. Methane production rates should be increased up to 90 and 110 Nm 3 CH4/t fresh tobacco (1500 V/ha production costs) in order to achieve 9 years for investment return, according to the scenarios described above [15].

Thermochemical conversion of biomass There are three different processes described in the literature: pyrolysis, gasification and combustion, correlated with the relationship between heat and chemical action generating products and energy. Pyrolysis is the thermal degradation of biomass in the absence of oxygen to produce condensable vapors, gases and charcoal. The main products of pyrolysis are gas, liquid and/or solid material. Generally, dried biomass can be subjected to a pyrolysis process; in flash pyrolysis the biomass is rapidly heated to 400–600 C, and most of the time feedstock organic compounds are converted to liquid products. In this process a catalyst is usually not required and the light decomposed biomass fragments are converted to oily compounds through a homogeneous reaction in the gas phase [16]. Gasification is an alternative option of thermal treatment of biomass, classified as a partial oxidation process. In gasification, thermal decomposition of organic matter primarily produces synthesis gas. Combustion is the simplest method by which the biomass can be used for energy as heat or electricity. Direct combustion can be applied to biomass that has low contents of moisture and ash. Biomass and coal were the major sources of fuels and chemicals until a century ago [16].

Tobacco residue pyrolysis When tobacco residues are subjected to pyrolysis, this leads to three phases (solid, liquid and gaseous) and the yields are directly dependent on the temperature and heating rate [17]. In addition, it is well known that different pyrolysis techniques trigger differences in product quantity and quality. Bio-oils, due to their low contents of nitrogen and sulfur, may possibly be used as fuel in some modified engines and boilers; on the other hand, pyrolysis oils are rich in organic compounds that could be considered to provide additional value. Yang et al. [11] obtained bio-oils via fast pyrolysis with high calorific value which had a similar hydrocarbon distribution to that of standard diesel. Demirbas [18] reported a chemical analysis of tobacco biomass that is shown in Table 1. Putun et al. [17] published a report focused

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on tobacco residue pyrolysis; the tobacco wastes were from Giresun, a place located in the North of Turkey. The samples were dried and ground in a high-speed rotary cutting mill, and screened to give fractions of various particle size (particle diameter, pd): 0.224 mm < pd < 0.425 mm; 0.425 mm < pd < 0.85 mm; 0.85 mm < pd < 1.25 mm; 1.25 mm < pd < 1.8 mm [19]. The fraction having 0.425 mm < pd < 0.85 mm was found to be the average particle size and therefore was used in all experiments. Table 2 lists the properties of the raw material used for these experiments. The results show that the raw material consists of 60.36% holocellulose, 9.2% lignin, 8.43% protein and 16.84% extractives; the elemental composition of the tobacco residue samples was also determined. A comparison of elemental analysis of bio-oils, aliphatic fractions and chars that result during fast and slow pyrolysis is given in Table 3. The maximum oil yield, »27%, was obtained at a pyrolysis temperature of 550 C with a sweeping gas flow rate of 100 cm3 min¡1 by slow pyrolysis. Increasing the heating rate up to 300 C min¡1 caused a 10% increase of liquid yields (»30%). The result of the yields leads to the conclusion that the mass transfer limitations of volatile evolution are much less pronounced for fast pyrolysis. Lower temperatures favor char yields, whereas higher temperatures up to 550 C favor liquid yields. As is known, at high temperatures gasification reactions occur and, under these particular experimental conditions, the maximum gas yield achieved was approximately 35% at a pyrolysis temperature of 700 C with a sweeping gas flow rate of 400 cm3 min¡1.

Hydrothermal conversion of tobacco biomass To hydrolyze carbohydrates from tobacco, hydrothermal liquefaction (HTL) was chosen because of the low energy consumption and environmentally benign process. Fresh-cut tobacco biomass contains 85–95% water on a dry basis and this moisture excess reduces the need for extra water during hydrothermal hydrolysis for carbohydrate recovery. Hydrothermal processes significantly reduce carbon impact and lower the overall cost when paired with suitably productive feedstock. A simplified scheme of the tobacco HTL process is shown in Figure 3; both sugars and oils can be extracted from tobacco biomass via the HTL process [20]. First, the tobacco biomass is wet-ground to a puree that is easily pumped in a continuous hydrothermal reactor (Figure 4). Currently, some varieties of energy tobacco optimized for biomass production can yield approximately 12 dry tons per acre, with 60% sugar and 5–7% oil by dry weight, producing an estimated 1150 gallons of ethanol per acre, and cannot be used for smoking or chewing. Energy tobacco is being processed fresh and not cured in barns. In some areas, tobacco crops could be harvested twice per season, with the first harvest in mid-July, chopping the plants between 6 and 18” to allow regrowth, followed by a second harvest pre-frost. Once harvested, tobacco biomass is squeezed with an industrial press and the juice is removed and further used for extraction of its free sugar contents. The remaining partially dewatered ‘cake’ containing cellulose and hemicellulose can be processed fresh or preserved and stored for year-round processing. The tobacco cake is then processed under a subcritical hydrothermal extractor into sugars, oil and biochar (Figure 5). The difference between the tobacco plant and other lignocellulosic material is that in tobacco the lignin content is considerably lower (one tenth the lignin of switchgrass): about 4–8% dry weight as reported [21]. On the other hand, tobacco juice (obtained by squeezing the plant) has about 2% free sugars, and among these sugars 85% is glucose, followed by galactose, mannose and arabinose as shown in Figure 6 [20]. This juice could be easily fermented into ethanol or other valuable commodities. The nicotine content in juice is about 0.5% in the energy tobacco crop, and it does not represent an inhibitor for the fermentation and yeast growth rate. Genetic engineering offers the possibility to create tobacco varieties that can suppress nicotine accumulation in plants, increasing the sugar production and accumulation. This could drive high-sugar tobacco crops, turning the classic tobacco into energy tobacco. In addition, the tobacco plant has been extensively studied as a source of high-quality proteins, and the results indicate that 1 g of dried tobacco leaf contains 94–146 mg protein. The protein quality is comparable with that of soybean or alfalfa and, given the fact that tobacco could be grown at high density, enables it to yield fourfold more protein per acre compared with soybeans [22,23]. Several reports in the world and in our country confirm that the tobacco plant has uses other than smoking. For example, it can be used in the food industry because of its content (over 10%) of citric acid. The pectines, carotinoides, enzyme pectinase, solanesol (Coenzyme Q10), etc. are separated from tobacco. Recently, via genetically modified

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organism (GMO), tobacco was transformed in order to produce squalene, an adjuvant for vaccine production or an emollient for cosmetics [24,25]. It is interesting to mention that besides lignin, tobacco biomass contains relatively high quantities of cellulose. The highest cellulose content is found in tobacco stems (35–40% of dry matter) [9]. It is reported that the main rib of the leaf of some Bulgarian tobacco varieties contains 10–15% cellulose. Tobacco stems and middle leaf ribs can be used for production of paper and cardboard packaging.

Tobacco seeds Usually tobacco plants yield a relatively modest amount of seeds, only about 600 kg of seeds per acre; however, some authors indicate that this could rise up to 1250 kg/acre or even more [26]. Typically tobacco plant leaves contain 1.7 to 4% of oil per dry weight. Hydrothermal process could successfully extract the oil from either tobacco biomass or seeds, and also could be applied in obtaining green coal process, as described in Figure 7. In Europe, Greece grows approximately 80% of the world’s tobacco, being a major international tobacco producer (one of 11 such countries). As per a 2001 report of the United States Department of Agriculture, global unmanufactured tobacco production for the year 2000 was estimated at 7,722,327 t, while the Greek National Center of Tobacco in year 2000 reported the crop in Greece was estimated at 123,704 t. In Table 4, the oil content in various seeds which are relatively rich in oil/fats, and their moisture contents, are shown [27]. As a particular case, the process flow and the yields of obtaining green coal from rapeseeds is shown in Figure 8, as described previously by Kumar [27]. Tobacco seed is a byproduct of tobacco leaf production. The seeds of the tobacco plant are very tiny, but significant quantities of seeds are produced per plant. They can be preserved for a long time if they are stored in dry conditions, they are resistant to rather high humidity at ordinary temperatures, and they have a strong shell. The oil is accumulated in tobacco seed endosperm that contains thin-walled cells. The oil extracted from tobacco seed is recognized as an nonedible oil; however, some reports indicate that refined tobacco seed oil is used as a salad dressing in some countries and, moreover, the nutritional value of tobacco seed oil is better than that of groundnut or cotton seed oil and comparable to that of safflower oil [28]. Giannelos et al. [29] published a report in which the physical as well as the chemical properties of tobacco oil are discussed. The main fatty acids that were identified in the tobacco oil are listed in Table 5, in the ground seeds and the pre-treated seeds [27]. On 2010, Murthy et al. [30] did some investigations on tobacco seed oil as compared with other species’ seed oil; some of the results are given in Table 6. The crop residue ratio for tobacco is about 1.2, i.e. a crop residue value of 0.833 kg of seeds as residue per each kg of tobacco leaves produced, as reported by [31]. Since the oil of tobacco seeds is recognized as non-edible oil, it is not used as a commercial product in the food industry, and most of the seeds are left unused in the fields [32,33]. Usta [33] proposed an alternative use for tobacco seeds. He prepared and tested a biodiesel fuel produced based on tobacco seed oil; the extraction yield was approximately 38% of the total seed weight. The esterification was done in the presence of methanol in a 6:1 alcohol-to-oil ratio, and NaOH was used as catalyst. The reaction was performed using a rotary evaporator at 55 C for 90 min, with additional mixing for another 90 min, after the heat was turned off. Approximately 86% of the oil was converted to biodiesel. The conversion rate was considered acceptable since the oil used for this experiment was untreated. Further experiments indicated that such biodiesel produced based on tobacco seed oil is suitable to be blended with 25 to 30% fossil diesel. Later, Veljkovic et al. [34] investigated the production of fatty acid methyl ester (FAME) from crude tobacco seed oil presenting high amounts of free fatty acids (acid value higher than 35). The biodiesel production was carried out in a two-step process, an acid-catalyzed esterification step followed by a base-catalyzed transesterification step. The maximum yield of FAME was about 91% in a 30-min reaction in the second step. The tobacco seed oil biodiesel obtained presented fuel properties within the specifications of both American and European standards, with the exception of a somewhat higher acid value than that specified by the European Standard; the results are given in Tables 7 and 8 below [35]. Biodiesel fuel, which consists of the simple alkyl esters of fatty acids, captured great attention as an alternative to fossil diesel fuels made from renewable sources. Furthermore, biodiesel has to meet the engine performance and environmental criteria; and also biodiesel has to compete economically with diesel fuels in order to subsist on the market. Using less-expensive feedstocks that are rich in fatty acids, such as non-edible oils, animal fats and oils, recycled or waste oil and byproducts of refining vegetable oils, might be a viable way to reduce biodiesel production costs. Tobacco (Nicotiana tabacum L.) seed oil, a by-product of tobacco leaf production, has been indicated in several reports to be an appropriate substitute for a diesel fuel [36]. Tobacco seed oil is a non-edible crude oil relatively easy extracted from tobacco seeds. Unlike tobacco leaves, tobacco seeds are not commercial products and are not collected from fields, being considered waste. Giannelos et al. [29] examined tobacco seed oil and pointed out that tobacco

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seed oil may be a good candidate to substitute diesel fuel. Tobacco seed oil methyl ester as a new biodiesel can be partially used in diesel engines without any engine modification and preheating of the blends [29,35]. There is remarkable tobacco seed oil potential for biodiesel production in the world considering the total acres cultivated with tobacco, and also that the tobacco seeds are a kind of waste by-product. In this report, the seed yield was determined to be 617 kg (§142 kg)/ha and the oil extraction yield of tobacco seed was found to be 38% (§2%) on a weight basis with diethyl ether as a solvent. As a result of all of the findings mentioned above, it can be concluded that tobacco seed oil methyl ester can be partially (up to 25–30%) substituted for diesel fuel under most operating conditions in terms of performance parameters and emissions without any engine modification [34]. Tobacco seeds, as a byproduct of tobacco leaf production, can give oil and a subsequent by-product: the cake. Although tobacco cultivars can give a good yield of oil ranging from 33 to 40% of the total seed mass, tobacco seed is not collected from fields and is not considered a commercial product. Tobacco seed oil is free of nicotine and is comparable to other, edible oils. Tobacco cultivars give a good yield of oil, ranging up to 40% of the total seed mass, and the remaining part consists of crude fiber, protein, starch and inorganic material [34]. The main fatty acids of tobacco seed oil are: palmitic, stearic, oleic, linoleic and linolenic acids. Trilinolein and palmitodilinolein are the main triacylglycerols, accounting for about 90% of the composition of the oil. Tobacco cake, a byproduct in the oil extraction, is rich in nitrogen, predominantly in the form of amino acids (15.6%), and could be incorporated into concentrate mixtures for dairy cattle feed, at up to about 25% of the ration. In these ways, tobacco seed oil represents a possible hope for the ‘healthy’ use of tobacco and for the future of tobacco agriculture [34].

Overall biofuel potential from tobacco biomass As we have shown, tobacco has a certain potential to become an energy crop, in which the free sugars and cellulosic sugars (extracted via an HTL process) could be converted into bioethanol. Tobacco seeds, which are currently mostly a waste product of growing tobacco for smoking, could be used as a raw material for oil (38–49 wt% oil in seeds) production and further converted into biodiesel [26,29]. On the other hand, tobacco plants could become an important alternative source of proteins for feed, and also an important source of biochar and activated carbon.

Conclusions Tobacco plant is cultivated worldwide for leaves used as a raw material for making smoking products. Currently, tobacco agricultural practices generate large amounts of vegetable waste material such as stalks and seeds that are usually left in the field or disposed of. The lower lignin content of tobacco biomass, suitable for being grown at a higher density (from 6000 plants/acre up to 20,000 plants/acre) that could generate huge amounts of biomass per acre, and, on the other hand, the decreasing demand for tobacco for smoking, turns the tobacco plant into a valuable candidate for becoming an energy crop. Based on the fact that there is a long history of growing tobacco and agricultural knowledge, repurposing tobacco as an energy crop could become an immediate reality.

Disclosure statement No potential conflict of interest was reported by the authors.

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[26] Usta N, Aydogan B, Con AH, et al. Properties and quality verification of biodiesel produced from tobacco seed oil. Energ Convers Manage. 2011;52(5):2031–2039. [27] Kumar S, Popov S, Majeranowski P, et al. Subcritical water assisted oil extraction and green coal production from oilseeds. Google Patents WO2014066097 A1; 2014. [28] Stanisavljevic IT, Velickovic DT, Teodorovic ZB, et al. Comparison of techniques for the extraction of tobacco seed oil. Eur J Lipid Sci Technol. 2009;111:513–518. [29] Giannelos PN, Zannikos F, Stourmas S, et al. Tobacco seed oil as an alternative diesel fuel: physical and chemical properties. Ind Crop Prod. 2002;16(1):1–9. [30] Murthy YVVS. Performance of tobacco oil-based bio-diesel fuel in a single cylinder direct injection engine. Int J Phys Sci. 2010;5(13):2066–2074. [31] Fujimori S, Matsuoka Y. Development of estimating method of global carbon, nitrogen, and phosphorus flows caused by human activity. Ecol Econ. 2007;62(3–4): 399–418. [32] Usta N. An experimental study on performance and exhaust emissions of a diesel engine fuelled with tobacco seed oil methyl ester. Energ Convers Manage. 2005;46(15–16):2373–2386. [33] Usta N. Use of tobacco seed oil methyl ester in a turbocharged indirect injection diesel engine. Biomass Bioenerg. 2005;28(1):77–86. [34] Veljkovic VB, Lakicevic SH, Stamenkovic OS, et al. Biodiesel production from tobacco (Nicotiana Tabacum L.) seed oil with a high content of free fatty acids. Fuel. 2006;85(17–18):2671–2675. [35] Stanisavljevic I, Lakicevic S, Velickovic D, et al. The extraction of oil from tobacco (Nicotiana Tabacum L.) seeds. Chem Ind Chem Eng Q. 2009;13(1):41–50.

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[36] Oliveira LS, Franca AS. From solid biowastes to liquid biofuels. In: Ashworth GS, Azevedo P, editors. Agricultural wastes. Hauppauge (NY): Nova Science Publishers; 2009.

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Energy Tobacco Transplanting (tobacco plants ~ 50-56 days old) Traditional Tobacco (low density plants/acre) (high density plants/acre) Traditional varieties of Nicotiana Selective breeding/hybrid; GMO

Topping (stalks; seeds) Total biomass (~50-60 days after transplanting)

~9 tones (wet

Harvesting* Whole plant Total biomass (40 tones wet weight)

Harvesting Only leaves weight) (12 tones wet weight) Waste

Processing (fresh leaves (no waste) ~3 tones wet weight) (

Cured leaves

Biomass-sugars / Bioethanol & Biochar

~ 1.3 tones dried)

Seeds-oil / Biodiesel

Figure 2. Comparison diagram showing the differences in growing traditional tobacco and tobacco for energy. In the case of some varieties cultivated in some specific geographic areas, the tobacco plants could be cut 2–3 times/year. Note: GMO, genetically modified organism.

Table 1. Chemical analysis of tobacco biomass (wt% on a dry basis) [18].

Figure 1. World’s 10 largest growers of tobacco leaves. Sample

Hemicellulose Cellulose Lignin

Tobacco stalk

28.2

42.2

27

Tobacco leaf

34.4

36.3

12.1

Ash C

H

O

2.449.3 5.5 42.3 17.2 43

4.5 35.8

N 0.5 0.5

Table 2. Analytical results of tobaccos residue [17]. Elemental analysis

Wt (%) dry basis

C (wt%)

51.65

H (%) N (%) O (%)a Atomic H/C ratio Calorific value (MJ/kg) Proximate analysis Ash (wt%) Moisture (wt%) Volatile compounds (wt%) Fixed carbona

6.20 2.05 40.10 1.43 19.19

Structural analysis Extractive alcohol/benzene

11.16 7.74 67.67 13.43 16.84

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Lignin Hemicellulose Protein Oil Holocellulose aBy difference.

11

9.20 44.25 8.43 2.82 60.36

Table 3. Comparison of elemental analysis of bio-oils, aliphatic fraction and chars obtained by slow and fast pyrolysis [17]. Slow pyrolysis (%)

Bio-oil

C 64.94 H 7.92 N 2.28 O 25.32 H/C 1.47 HHV (MJ/kg) 28.83 Fast pyrolysis (%) C 66.02 H 8.5 N 3.02 O 27.76 H/C 1.53 HHV (MJ/kg) 29.59 Note: HHV, higher heating value.

Aliphatic fraction

Char

86.79 13.21 – – 1.83 48.42

73.93 4.69 2.28 19.10 0.65 28.33

85.84 14.16 – – 1.96 49.47

60.88 3.88 3.21 32.03 0.75 20.42

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F. G. BARLA AND S. KUMAR

Figure 3. Subcritical water reactors for sugar hydrolysis from tobacco puree.

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Figure 4. Puree

prepared from

tobacco biomass via

wet grinding.

Figure 5. Simplified scheme of hydrothermal process on tobacco biomass. Note: DDGs, distiller’s dried grains with solubles.

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F. G. BARLA AND S. KUMAR

Figure 6. (a) Carbohydrate analysis of tobacco stems. Total sugar in this sample is 55.9 wt% on dry weight basis. and (b) sugar profile and ion chromatography of acid hydrolyzed samples (structural sugars) of tobacco biomass [20].

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Figure 7. Diagram for oil and green coal production from tobacco seeds [27]. Table 4. Oil content in some common seeds. – Mustard 7 Sesame 5 Sunflower 5 Safflower 5 25–30 Tobacco 7 35–45

Seeds

Oil/fat (variety)

Cotton Rape

5 9

(wt%)

15 40–45

25–45 25–50 25–50

wt% on dry basis.

Table 5. Fatty acid composition of oils extracted from the ground seeds and pre-treated seeds (210C; wt%).

15

Fatty acid

Ground seeds

Pre-treated seeds

Palmitic acid Stearic acid 19.757.213.27.02.0 16Oleic acid F. G. BARLA AND S. KUMAR §§§§ Linoleic 0.50.50.50.50.5 acid Linolenic acid

57.020.512.77.82.0 §§§§ 0.50.50.50.50.5

§

§

Table 6. Fatty acid distribution in jatropha, rapeseed, soybean and tobacco oils (% by wt) [30].

Fatty acid

Jatropha oil Rapeseed oil Soybean oil Tobacco oil Myristic 0.1 1 0.1 – Palmitic 14.1–15.3 3.5 11.4 15.2 Stearic 3.7–9.8 0.9 3.2 4.8 Arachidic 0.3 0.4–2.4 0.2 – Behenic 0.2 0.6–2.5 0.3–2.4 – Palmitoleic 1.3 0–0.1 0.1–1 – Oleic 34.3–45.8 64.1 21.8 13.2 Linoleic 29–44.2 12.1–22 54.9 66.7 Linolenic 0.3 7.01–9 8.3 1

Table 8. Physical and chemical properties of tobacco seed oil, in various reports [35]. Density (kg/m3) Viscosity (mPas) Index of refraction Iodine value Saponification value Acid value

924 93.3 1.4739 130 193.9 37

920 NA 1.474 137 189.6 NA

917.5 27.7 NA 135 193 NA

923 NA 1.4758 135 197 1.34

Figure 8. Summarization of oil extraction and green coal production from rapeseeds via subcritical water carbonization [27].

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17

NA: not analyzed.

Table 7. The effect of extraction technique, solvent type and temperature on fatty acid of tobacco seed oil composition (%) [35]. Soxhlet Acid Palmitic Stearic Oleic Linoleic Linolenic Others Saturated Unsaturated Mono-unsaturated Poly-unsaturated

25C

BTC

BTC

n-hexane

Petroleum ether

8.5

8.52

8.51

8.5

8.42

8.69

2.77 12.49 71.28 0.93 4.03 11.27 84.7 12.49 72.21

4.72 14.72 69.97 1.06 1.01 13.24 85.75 14.72 71.03

2.8 12.36 70.03 0.98 5.05 11.31 83.64 12.36 71.28

5.055 14.29 69.92 1.03 1.21 13.55 85.24 14.29 70.95

3.78 11.78 72.22 0.84 2.96 12.2 84.84 11.78 73.06

2.9 12.54 72.92 0.89 2.06 11.59 86.35 12.54 73.81

a

Seeds/solvent ratio 1:3 w/v; 20 min. ratio 1:10 w/v; 90 min; BT – boiling temperature.

bSeeds/solvent

25C