Bioethanol or ethyl alcohol is alcohol made from raw materials that are renewable. Bioethanol is usually produced by fermentation of materials containing glucose or glucose polymers (polysaccharides). Nearly 93% ethanol in the world is bioethanol which is the result of the anaerobic conversion of biomass, ethanol and the rest is chemically synthesized from petroleum derivatives.
Bioethanol can be used as an agent to increase the octane number of gasoline because ethanol is high octane number (135) while the premium octane fuel is sold as 98. The higher the octane number, the more resistant the fuel to not burn yourself so that the stability of the combustion process to obtain a more stable power. Combustion process with a more perfect power would reduce emissions of carbon monoxide gas. 3% bioethanol mix alone, can reduce carbon monoxide emissions to only 1.35% .
Gasoline consumption in Indonesia in 2005 reached 16 jutakilo liter (Sutanto). Fraction of premium generated by the petroleum processing units in Indonesia are not enough to meet the needs of premium Indonesia. To overcome the deficit premium, Indonesia imported premium demand from international markets. Indonesia Premium requirement in 2008 is predicted at 19.6 million kilo liters. With the amount of crude oil processing units are not increased, the production of premium generated Indonesia continues, Indonesia will import premium in larger amounts in future years.
The government has actually been trying to find a solution to reduce oil imports in the future by issuing a Presidential Decree. 5 / 2006 on national energy policy to develop alternative energy sources as a substitute for fuel oil. Based on these regulations is expected in 2025, 17% of Indonesia's energy needs supplied by renewable energy (Yudhoyono, 2005). One source of energy that can be utilized as an energy alternative is ethanol. Although the specific energy density of ethanol is less than the premium (specific energy density of ethanol from 23.4 to 26.8 MJ / kg, specific energy density of the premium from 45 to 48.3 MJ / kg) (Sutanto), but the raw material for ethanol is abundant in Indonesia and ethanol production processes can be developed in Indonesia, the ethanol as an alternative energy source to substitute a premium it is possible to be implemented in Indonesia.
Utilization of ethanol and gasoline-ethanol mixtures as fuel has been carried out since the beginning of the automobile vehicle. Use of pure ethanol as vehicle fuel was first introduced by Henry Ford on the car model assemblies (Husky Energy, 2007), even in April 1933 in Nebraska is 10% bioethanol blend sold at premium (Praj Industries, 2006). Earlier, the stock amount of oil that is not limited and less expensive, the use of ethanol as fuel has not been deemed necessary. But recent decades, rising crude oil prices have prompted the search for alternative energy to overcome energy crisis began to threaten the world. The environmental impact caused by fossil fuel use is also a consideration proper selection of alternative energy and environmentally friendly. The use of ethanol as fuel has several advantages compared with the fuel, namely: a) high oxygen content (35%) so if it burned very clean, b) environmentally friendly due to emission of carbon-mono-oxide is 19-25% lower than the fuel so it does not contribute to the accumulation of carbon dioxide in the atmosphere (Costello and Chun, 1988), and is renewable, while the fuel will be depleted due to fossil raw materials.
Bioethanol produced by fermentation of biomass anaerobic conversion of glucose-containing materials group. The fermentation process generally consists of three stages, namely the manufacture of soluble sugars, fermentation of sugars into ethanol, and the separation and purification of ethanol is usually done by distillation (Badger, 2002).
Bioethanol production technology has been developed and divided into first and second generation technology. The second difference is based on the generation of raw material to produce bioethanol (McCutcheon, 2007). The first generation bioethanol is produced from ingredients that contain sugar or starch, such as molasses, sugar beets, sugar cane, barley, several kinds of wheat, corn, potatoes, cassava, sugar cane.
Starchy material generally contains amylase and amylopectin. Amylase is a linear glucose polymer composed of glucose units linked by al ,4-glycosidic bonds, whereas amylopectin is a branched polymer which in its branches are linked by ties of a-1, 6. Starchy materials used to produce bioethanol is also used as food. Competition raw materials as food and materials to encourage ethanol production business usage of raw materials other than human food chain. Results of development resulted in a second-generation technologies that use materials that contain cellulose or hemicellulose.
Production of ethanol by first-generation technology has been widely applied in the world, including Indonesia. While second-generation technology is still in its early stages of research and development on pilot scale. Although still in its early stages of research, production of ethanol with a second-generation technology has the potential to be developed capable for producing bioethanol with high acquisition without competing with food.
Bioethanol Production with First Generation Technology
Bioethanol production process which has been developed and applied generally involves 2 steps, the process of saccharification and fermentation. Saccharification process aims to break down carbohydrates (like sugar, cellulose and hemicellulose) into sugar monomers.
On the raw material of molasses, sugar beet and sugar cane that had been used widely as material for ethanol production, ethanol-making process is more simple because the raw materials can be directly disakarifikasi by adding glucoamylase (Caylak and Sports, 1998). As for the starchy raw material, before the saccharification process must be done beforehand Liquefaction process, the process with this starchy raw materials has been widely applied especially in Brazil and in the U.S. to produce bioethanol, but in Indonesia are still held at the household scale. Liquefaction Process done because the ethanol fermentation microorganisms are not able to convert starch to ethanol directly, an enzyme needed to convert the starch into maltose oligosaccharides, and go through the process of saccharification is converted into simple sugars are easily fermented.
Saccharification Process
Saccharification process aims to convert the dextrins generated on Liquefaction process so as to produce mono-or in-saccharide (Frings, 2007). Saccharification process was carried out with added glucoamylase. In this process the release of aD-glucose from the non reducing end of sugar 1,4-a-glucan. The reaction took place at pH 4-5 and at a temperature of 50-60 degrees C (Frings, 2006) for 2 h.
Fermentation Process
The fermentation process took place at pH 4-6, at a temperature of 30-35 degrees C (Frings, 2006) and kept anaerobic fermentation conditions. Microbes that help the process of fermentation is Saccharomyces cerevisiae or Zimomonas mobilis. The fermentation process can produce ethanol up to levels above 12% because the levels of microorganisms that help the fermentation process can not work anymore.
Liquefaction Process
At this stage of Liquefaction occurs gelatinasi process to break down starch so that starch dextrin becoming. Liquefaction processes take place at high temperature is 80-90 degrees C and pH 5 (Frings, 2006) for 30 minutes (Anonymous, 2007), starch-solving process is done by adding the enzyme amylase. Amylase is added may consist of two types, namely endo-amylase that will attack the bond of a-1, 4 glycosidic linkages in polymers starch randomly and exo-amylase which will hydrolize glucose or maltose from starch polymer reducing end (Neves, 2006).
Separation and Purification Process
To separate the microbial biomass ethanol broth is done by decantation. Most biomass fermentation padatangki returned again to do further fermentation. To separate the ethanol from the fermentation broth can be done by distillation in stages because the water content in broth was high. Distillates storied able to produce ethanol with a maximum purity of 95.6%, because the purity of the ethanol to form azeotrope with water so as not to be separated again with the usual separation. To obtain fuel ethanol standard, purity 99%, can be done by adding the entrainer, the separation of the membrane by evaporation, or by using molecular sieve (Frings, 2006).
Hydrolysis and Fermentation Process
In the course of the development of bioethanol production processes, hydraulic processes (saccharification) and fermentation can be classified into two different processes, namely process-Separate Hydrolysis-Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF) (Neves, 2006).
Separate process-Fermentation-Hydrolysis
Separate process-Hydrolysis-Fermentation (SHF) is the process of making ethanol in which the stage lasted hydrolysis and fermentation stages separately. Starch-containing raw materials undergo a process of hydrolysis (Liquefaction and saccharification) separately from the fermentation process. After the hydrolysis process is complete, continue the process of fermentation. This is intended to facilitate control of every stage, in order to achieve the desired results. In addition, the interaction between the two stages can be minimized.
SHF process has several weaknesses, including the performance of a-amylase that is not optimal due to the occurrence of the enzyme by the accumulation of sugar inihibisi although the content of a-amylase in the system high. If a-amylase inhibited the Liquefaction process will stop, although not all the available starch is converted into simple sugars (Neves, 2006). Inhibition will eventually affect the ethanol produced.
Simultaneous Saccharification and Fermentation
To overcome the weakness that occurs in the SHF process, it is developing a new process with a process called Simultaneous Saccharification and Fermentation (SSF), as has been patented by the Gulf Oil Company and the University of Arkansas (1979). SSF processes have the same basic SHF process, only phase hydrolysis and fermentation stages take place simultaneously in one tank. Some time after the added a-amylase, glucoamylase is added to the tank to convert the dextrins generated by a-amylase into simple sugars for fermenting into ethanol. Then the tank was also added Saccharomyces cerevisiae to ferment sugar into ethanol, so there is no accumulation of sugar which will cause the inhibition of a-amylase (Neves, 2006).
The presence of yeast / bacteria together with the enzyme in a reaction tank, to reduce the accumulation of sugar in the tank so that the performance of a-amylase to a maximum and can convert all the starch into simple sugars and ethanol produced was higher than the SHF.
SSF process these last few years has been modified to include also the stage cofermentasi than double the sugar substrate. This process is known as Simultaneous Saccharijication and coFermentation (SSCF).
Prior to hydrolysis by the enzyme treatment, the biomass will have initial treatment (pre-treatment) first, in order to condition the biomass to the nature of the enzyme. After having pre-treatment, enzymatic hydrolysis of biomass and then experiencing. The result of this hydrolysis are not all fermented, because some will form a residue. From the results of fermentation was, ethanol can be formed.
Bioethanol Production with Second Generation Technology
Ethanol or gasoline-ethanol mixture as an alternative fuel and has been applied in several countries such as Brazil, USA, and several countries in Europe. Even in America, more than 5 million vehicles already use E85 which is a mixture of 85% bioethanol and 15% premium (Anonymous, 2006). The number of biomass needed to produce ethanol as a biofuel into its own problems due to biomass in the form of simple sugars (such as sugar, sugar cane, corn) are easily degraded into monomeric sugars, also acts as a source of food for both humans and animals. In addition, the reduction of emissions by combustion of bioethanol is not as low as expected.
Both of the above spur development of alternatives as a raw material for bioethanol, which lignocellulosic materials (wood materials, fibers or even the waste can be degraded). Bioethanol with the raw material is referred to as bietanol Second Generation (Second Generation) because it covers the kinds of raw materials more widely.
The advantage of bioethanol is made from lignocellulose, among others (Hagerdal et.al, 2006):
• lignocellulosic raw materials will reduce the likelihood of conflict between land used for food production (and feed) and the land for the production of raw materials pasukanenergi.Harga this type of raw material cheaper than the first generation and can be obtained with the amount of fertilizer, pesticide and energy are relatively more slightly.
• Bioethanol lignocellulose-based greenhouse gas emissions are lower, reducing the environmental impact, especially climate change.
• Bioethanol is likely to open jobs in rural areas
By looking at these benefits, the prospect of starting research towards the development of lignocellulose-based bioethanol. Research on the utilization berselulosa material as raw material for production of ethanol has been started since 1950.
The principle of bioethanol production from berselulosa same material with the production of bioethanol from sugar or starchy material, which consists of two stages. The first stage is the conversion of cellulose into sugar and the second stage is the production of ethanol from sugar conversion results. Conversion of cellulose into sugars through the hydrolysis reaction. Hydrolysis reaction can be carried out chemically or enzymatically. Once a simple sugar obtained from the process of hydrolysis, fermentation to produce ethanol with conventional ethanol production using microbial and reaction conditions previously mentioned.
Chemically by acid hydrolysis
Chemical hydrolysis reaction can be performed using a dilute acid and concentrated acid. The use of dilute acid hydrolysis process carried out at high temperature and pressure with a short reaction time (several minutes). The temperature required is reached 200 degrees C. Dilute acid used is 0.2 to 4% by weight (Nguyen and Tucker, 2002). The use of dilute acid hydrolysis of cellulose ordinary profit could reach up to 50% conversion reaction (Badger, 2002). Low conversion is due to the degradation of sugar that is formed as the result of hydrolysis reaction used in high temperature. The process of hydrolysis using a dilute acid consists of two stages. The first stage is the conversion of materials into simple sugars berselulosa and the second stage is the degradation of simple sugars that are formed into another chemical structure. Degradation of sugar is not only lower the conversion reaction, but also to poison the microorganisms during fermentation reaction on the formation of ethanol.
In addition to dilute acid, the hydrolysis process can also be done using concentrated acid. The use of concentrated acid on cellulose hydrolysis process carried out at temperatures lower than dilute acid. Acid concentration used is 10-30% (Zimbardi et.al). Sources of acid used is sulfuric acid. Reaction temperature is 100 degrees C and requires a reaction time between 2 and 6 hours. A lower temperature to minimize degradation of sugar. The advantage of using concentrated acid is produced by high-sugar conversion, which can reach 90% conversion (Badger, 2002). Lack of this reaction is the reaction time it takes longer and requires a good washing process to achieve the pH of the reaction before adding microbes in the fermentation process of ethanol formation.
By Enzymatic Hydrolysis
Another method used to hydrolyze cellulose is enzymatically. Enzymes are natural proteins that can catalyze a particular reaction. To be able to work, the enzyme should be in direct contact with the substrate to be hydrolyzed. Because cellulose is naturally bound by the lignin that is permeable to water as a carrier of enzymes, then for the enzymatic hydrolysis process requires pretreatmen so that enzymes can be in direct contact with cellulose. Pretreatmen done to break down the crystalline structure of cellulose and lignin that separates the cellulose can be separated. Pretreatmen can be done chemically or physically. Physical methods that can be done is by using high temperature and pressure, milling, radiation, or cooling, all of which require high energy. Meanwhile, the chemically pretreatmen method uses solvents to break down and dissolve the lignin (method deligniflkasi) (Badger, 2002).
The enzymatic hydrolysis of cellulose using enzymes penghidrolisis, namely cellulase or can also directly use the cellulase-producing microbes, for example Trichodermareesei. The advantage is the efficiency of enzymatic hydrolysis are high because the enzyme reaction is selective so that the formation of byproducts can be minimized, the reaction conditions of temperature and pressure is not high, can even be done at room temperature and atmospheric pressure so it does not require special equipment for the reaction. While the lack of the enzymatic hydrolysis process is the reaction time needed for longer, can be reached 72 hours.
China developed a combined chemical and enzymatic hydrolysis of cellulose-based ethanol production in Shanghai
