Paste yFeedstocks for First Generation bioethanol
Global population growth, which is projected to exceed 9 billion by 2050, will raise the average calorie intake pushing the productivity from already scarce arable land to its limit. The energy demand in developing nations are expected to increase by 84%, and nearly one-third of this additional fuel possibly come from alternative renewable sources such as biofuels (Graham-Rowe, 2011, Dutta et al., 2014).
Figure 1 shows global ethanol production by country or region, from 2007 to 2014. The United States is the world's largest producer of ethanol, having produced over 14 billion gallons in 2014 alone. Together, the U.S. and Brazil produce 83% of the world's ethanol. The vast majority of U.S. ethanol is produced from corn, while Brazil primarily uses sugar (AFDC, 2015).
Figure 1. Global bioethanol production.
Source: Renewable Fuels Association, Ethanol Industry Outlook 2008-2015 reports (AFDC, 2015).
According to Balat et al. (2008), bioethanol feedstocks can be conveniently classified into three types: (i) sucrose-containing feedstocks (e.g., sugar beet, sweet sorghum and sugar cane), (ii) starchy materials (e.g., wheat, corn, and barley), and (iii) lignocellulosic biomass (e.g. wood, straw, and grasses). The availability of feedstocks for bioethanol can vary considerably from season to season and depending up on geographic locations, could also pose difficulty in their availability. The changes in the price of feedstocks can highly affect the production costs of bioethanol (Yoosin and Sorapipatana, 2007). Another point to be analysed is that, the major feedstocks for first generation biofuels are the sources of food, thus may result in a food-fuel competition. It was reported that though only 2% of world's arable land had been used to grow biomass feedstock (OECD/IEA, 2008), for first generation biofuel production, it had significant contribution toward increased commodity prices for food and animal feeds. However, direct or indirect impact of biofuels on food price hike remains inconclusive in literature or media. Till date the largest volume of biofuel is produced in the form of ethanol, 80% of which has come from corn and sugarcane (Dutta et al., 2014).
Technological development can surely help in lowering, both the environmental impact and the prices of the ethanol fuels. Intense research has been carried out for obtaining efficient fermentative organisms, low cost fermentation substrates, and optimal environmental conditions for fermentation to occur (Siqueira et al., 2008).
The world 1G bioethanol production in different countries and the main feedstock used is described in Table 1.
Table 1. World's first generation ethanol production from different feedstocks
Country/Continent Major feedstock sugar and starchy crops Ethanol production per year
(billion liters) Costs
(US$/L)
Asia
China
India
Malaysia
Thailand
Corn, Maize, Sugarcane, Cassava
–
Sugarcane, cassava
–
–
1,0
0,0
0,0
–
0,18
Africa – – –
Europe
Austria
Belgium
Czech Republic
Denmark
EU
Germany
France
Italy
Slovakia
Spain
Sweden
Poland
UK
Wheat
Wheat
Sugar beet
Wheat
Cereal and Sugar beet
Wheat
Sugar beet, Wheat
Cereals
Corn
Barley, Wheat
Wheat
Rye
–
–
0,4
–
–
4,5
0,8
1,0
–
–
0,4
–
0,2
–
–
–
–
–
–
–
0,40-0,45,0,60-0,68
–
–
0,40-0,45
0,55-0,65
–
–
North America
US
Canada
Corn/Maize
Wheat/Cereal
50,3
1,8
0,25-0,40
0,0
South America
Brazil
Argentina
Colombia
Sugarcane
Sugarcane
25,5
0,5
0,16-0,22
–
–
Oceania
Australia
Sugarcane
0,3
–
Source: modified from Gupta and Verma (2015); Haankuku, et al. (2015)
Sugarcane 1G bioethanol
Two-third of world sugar production is from sugarcane and one-third is from sugar beet (Linoj et al., 2006). These two are produced in geographically distinct regions. Sugarcane is grown in tropical and subtropical countries, while sugar beet is only grown in temperate climate countries. Since bioethanol trade is mainly from the South, feedstocks may eventually impact cane sugar trade (Balat et al., 2008). Both of these seem to be the most promising sources for bioethanol production (UNCTAD, 2006).
Brazil is the largest producer of sugarcane with 632 billion tons (Unica, 2015). The centre-south region of Brazil accounts for almost 80% of feedstock production (Zarrilli, 2006). Among its various agro-products such as coffee, soybean, cassava, corn, fruits, sugarcane, etc, the latter has been one of the main products since last several decades. Sugarcane was chosen as the substrate for ethanol production due to a number of reasons, including its great adaptation to the Brazilian soil and weather conditions. As a consequence, agricultural and technological studies were greatly intensified, leading Brazil to a very favorable position in terms of energy security. In central-south Brazil, the average sugar cane yield is reported by Brazilian Sugarcane IndustryAssociation (Unica, 2015 ) to have increased from 48 t cane/ha in 1980 to 70 t cane/ha in 2010 (Unica, 2012). Considering this trend as a linear increase, the sugarcane yields for 2015 and 2020 were estimated to be 79 t cane/ha and 84t cane/ha respectively with an average increase rate of 1.3% per year (Wang et al. 2014).
In the 1970s, Brazil started a program to substitute gasoline by ethanol in order to decrease the dependence from politically and economically variable periods. The National Alcohol Program – ProAlcool, created by the government of Brazil in 1975 resulted less dependency on fossil fuels. (Rosillo-Calle and Cortez, 1998, Soccol et al., 2005). The oil crisis and the low prices of the sugar pushed the country to the beginning of a new strategy to by-pass this situation. The Brazilian government intended to prevent a slow down in energy consumption in order to maintain the economic growth by substituting imported petroleum by domestic sources as fast as possible. In this way, the Brazilian government started its policy to substitute the gasoline with sugarcane alcohol. The program saw the participation of several groups of people involving politicians, military groups, alcohol industry, sugarcane producers, researchers and the media. The government intensified the use of a mixture of ethanol and gasoline (gasohol) to fuel common cars.
The addition of 25% ethanol to gasoline reduced the import of 550 million barrels oil and also reduced the emission CO2 by 110 million tons. Today, around 39,4% of the Brazilian energy matrix is renewable and 157% is derived from sugarcane. Brazil has a land area of 851 million hectares, of which 54% are preserved, including the Amazon forest (350 million hectares). From the land available for agriculture (340 million hectares), only 2.59% is occupied by sugarcane as energy crop, showing a great expansion potential (Udop, 2015). Actually, 10 million hectares of Brazilian lands are cultivated with sugarcane (Unica, 2015).
As one of the worlds' largest ethanol producers, Brazil has used sugarcane as feedstock to produce over 28 billion litres of ethanol in 2014/2015 (Unica, 2015), most of which was destined for use as a fuel. Brazil ethanol production has been commercialized for over 45 years and is entirely based on the fermentation of simple sugars extracted from harvested sugarcane stem either in autonomous distilleries or in annexed plants co-located with sugar mills that co-produce ethanol and crystalline sugar (Seabra et al., 2011, Wang et al., 2014).
Currently, there are 403 bioethanol production units installed in the country (Udop, 2015), of which 392 units are located in the south, southeast and center-west. In the Amazon region, which occupies nearly 50% of Brazilian territory, there are only five units. New units of bioethanol production are expected to be installed in future. However, an expansion of the ethanol production to 104 billion liters in 2025 will necessitate the reduction of production costs to sustain the transportation from more distant areas within Brazil to internal and external markets. In addition, as one add more advanced technology to gain greater productivity per unit of land and provide better environmental performance, the complexity of the production process necessarily increases. This almost always brings with it additional costs. A hectare of sugarcane can produce about 6,000 L of ethanol with production costs ranging from US$0.25 to 0.30/L (Cerqueira Leite et al., 2009). According to IBGE (2008), around 70% of the ethanol production costs are raw material.
The Brazilian car industry became revitalized only with the introduction of flex fuel vehicles (FFVs) in March 2003. FFVs can use various mixtures of alcohol and gas, thus allowing the consumers to react to the different prices signals of the two markets (Hira and Oliveira, 2009). Presently, Brazil has more than 90% of its vehicles are flex fuel (ANFAVEA, 2015).
With the increasing instability in petroleum prices, many countries have decided to direct their energy policy towards the use of biofuels. This imposes an enormous pressure on the production of crops such as maize, sugarbeet and others that can supply bioethanol, always thinking about the conflict with food production.
Sugarbeet 1G bioethanol
Based on the USA Energy Independence and Security Act (EISA) of 2007, sugar beets (Beta vulgaris L.) may be an eligible feedstock for advanced biofuel provided that production and conversion to biofuel meets the 50% greenhouse gas reduction threshold required for advanced biofuel designation (Congress U.S., 2007, NREL, 2014, Haankuku, et al. 2015).
The new energy strategy for Europe from 2011 to 2020 has been discussed in Europea nUnion (EU) institutions (European Commission, 2010; European Parliament, 2010). Thisstrategyhas to beinlinewiththeLisbonTreatytoguidelong-termemission- reduction goals, th eso-called 20'20'20.To achieve energy and climate goals,the potential of bioenergy is a key issue. The main inputs in the production of bioethanol in the EU are sugar beet, wheat, corn or barley (Salazar-Ord''ez et al., 2013).
Wheat and sugar beet are most frequently used in Northwestern Europe at present, while corn is employed in Central Europe and Spain, where barley is also often used. Thirty percent of bioethanol is produced from sugar beets (Agrosynergie, 2011); around 24% of the total production of this crop has been destined to bioethanol in the EU for the last three years (Eurostat, 2011).
Sugar beets are tuber crops composed of about 75% water, 18% sugar (sucrose), and 7% insoluble and soluble materials (which are required to be at low levels). Unlike conventional sugar beets that are bred to produce sucrose for table sugar, biofuel feedstock industrial beets are specialized non-grade varieties bred for total sugar production (Haankuku, et al. 2015).
Some alternative have being studied to reduce bioethanol production from sugar beet costs. Raw material sugar-beets and multieffect evaporation process were proposed as the major factors in the costs change. Although the costs of direct fermentation of sugar-beet juice (adjust the sugar content by adding molasses) is lower than the process using sugarbeet juice concentration, the multi-effect evaporation acquires a high-sugar fermentation and saves distillation and equipment costs (ruan et al., 2001. At the same time, it also reduces the microbial infection of the squeeze juice. Part of impregnated water and diluted water are the waste from the distillation tower. Water can be recycled in the production process and reduce emissions (Zhou et al., 2011). In addition, with this method, separating sugar-beet pulps before fermentation improves the equipment utilization of fermentation and distillation, saves energy consumption and makes the comprehensive utilization of sugar-beet pulps much easier. Enrichment process reserves the sugar, which will be able to extend the production period in ethanol plants.
Corn 1G bioethanol
The U.S. Department of Agriculture (USDA) has an active program devoted to the corn ethanol industry. This program includes economic and policy studies by the Office of Energy Policy and New Uses (OEPNU) and the Economic Research Services (ERS), scientific research programs by the Agricultural Research Service (ARS) and the Cooperative State Research, Education and Extension Services (CSREES). Areas of scientific research address the establishment of new higher-value ethanol co-products, the development of microbes capable of converting various biomass materials into ethanol, improved processes for the enzymatic saccharification of corn fibers into sugars, and various methods of improving corn ethanol process efficiencies (McLoom et al., 2000).
In the 2013/2014 USA's corn production reached nearly 13.8 billion bushels (351.3 million metric tons) of corn and roughly 11 percent of production was exported to more than 100 different countries. More than one-third of USA's corn crop is used to feed livestock. Another 13 percent is exported, much of it to feed livestock as well. Another 40 percent is used to produce ethanol. The remainder goes toward food and beverage production. Previous droughts in the Midwest (most recently in 1988) also resulted in higher food prices, but misguided energy policies are magnifying the effects of the current one. Federal renewable-fuel standards require the blending of 13.2 billion gallons of corn ethanol with gasoline in 2012. This required 4.7 billion bushels of corn, 40 percent of the year's crop (Carter and Miller, 2012, EIA, 2013).
Figure 1. U.S. total corm production and corn fuel ethanol production.
Source: USDA's National Agriculture Statistics Service (2015).
Notes: *2015 values are preliminary.
Fuel ethanol production from corn can be described as a five-stage process: raw material pretreatment, hydrolysis, fermentation, separation and dehydration, and wastewater treatment. The production of bioethanol from starch includes the breakdown of this polysaccharide to obtain an appropriate concentration of fermentable sugars, which are transformed into ethanol by yeasts. After washing, crushing and milling the corn grains (dry milling process), the starchy material is gelatinized in order to suceptilize the amylose and amylopectin for enzymatic attack in the following liquefaction step. This step is considered as a pretreatment process because of the partial hydrolysis of the starch chains using thermostable alpha-amylase. The hydrolyzate obtained has reduced viscosity and contains starch oligomers called dextrins.Then, the fermentation process occurs where sugar is immediately assimilated by the yeast Saccharomyces cerevisiae in the same reactor and converted into ethanol. The culture broth containing 8'11% (w/w) ethanol is recovered in a separation step consisting of two distillation columns. (Quintero et al., 2008).
Cassava 1G bioethanol
Cassava, also known as manioc, yuca or tapioca, is a shrub with tuberous roots. It is the third source of food calories in tropical countries after rice and maize. This Euphorbiaceae was probably produced from pre-Columbian times in Brazil, Guyana and Mexico then brought to Africa by the Portuguese navigators. Cassava is used in both human and animal food, in many industrial sectors, particularly in the form of starch, and more recently to produce ethanol. Cassava is primarily grown for its roots but all of the plant can be used: the wood as a fuel, the leaves and peelings for animal feed and even the stem as dietary salt (UNCTAD. 2015).
World production of cassava is around 250 million tones (Mt) a year. After 15 years of uninterrupted growth and an increase of 13% between 2006 and 2009, it fell to 249 Mt in 2010 following a poor harvest in Thailand due to diseases and drought. Africa contributes to more than half of global supply. Unlike Africa, Asia encourages the development of cassava crops for industrial and energy purposes. This continent contributes to around a third of world production, with 60% produced by Thailand (around 25 Mt) and Indonesia (22 Mt). Vietnam and China are growing in strength and both produce between 8 and 9 million tonnes a year since 2008. India, now the 3rd cassava producer in Asia, is also experiencing continued growth in production with more than a 30% increase between 2006 and 2010. In Latin America and the Caribbean production is relatively stable, around 35 Mt between 2006 and 2009, which represents almost 20% of world supply. Brazil dominates with some 70% of regional production and battles with Thailand, over the years, for second place in world production; the country should increase production following the increase in cultivated land area. Apart from Brazil, the two other important producers are Paraguay (around 5 Mt) and Colombia (1.5-1.7 Mt).
The starch hydrolysis by enzymes is a two-stage process involving liquefaction and saccharification. Liquefaction is a step that starch is degraded by an endo-acting enzyme namely '-amylase, which hydrolyzes only '-1,4 and causes dramatically drop in viscosity reduction of cooked starch. Typically, liquefying enzymes can have an activity at a high temperature (> 85'C) so that the enzyme can help reduce paste viscosity of starch during cooking. The dextrins, i.e. products obtained after liquefaction, is further hydrolzyed ultimately to glucose by glucoamylase enzyme which can hydrolyze both '-1,4 and '-1,6 glycosidic linkage. Glucose is then subsequentially converted to ethanol by yeast. After fermentation, approximately 10%v/v ethanol are obtained, depending on solid loading during fermentation, is subjected to distillation and dehydration to remove water and other impurities, yielding anhydrous ethanol (Sriroth et al, 2012).
Nowadays, the production process of bioethanol from starch feedstock is developed to significantly reduce processing time and energy consumption by conducting saccharification and fermentation in a same step; this process is called 'Simultaneous Saccharification Fermentation', or SSF process (Sriroth et al, 2012). In this SSF process, the liquefied slurry is cooled down to 32', afterward glucoamylase and yeast are added together. While glucoamylase produces glucose, yeast can use glucose to produce ethanol immediately. No glucose is accumulated throughout the fermentation period (Rojanaridpiched et al, 2003).
Cassava is still a small player on the biofuel scenario; its role should increase considering the direction taken by China. In effect, with one tonne of cassava, which has a starch content of 30%, around 280 litres can be produced of 96% pure ethanol (Sriroth et al, 2012). Presently, there are 17 factories operating with the total production capacity of 2.575 million liters/day but most of them have operated under their full production capacity due to oversupply of ethanol.
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