Bioethanol or ethyl alcohol is alcohol made from raw materials that can be updated. Bioethanol is usually produced by fermentation of material containing glucose or glucose polymers (polysaccharides). Nearly 93% of the world's ethanol is ethanol that is the result of anaerobic conversion of biomass, while the rest is ethanol which is chemically synthesized from petroleum derivatives.
Bioethanol can be used as agents to increase the octane number in gasoline because ethanol is sufficiently high octane number (135) while the premium octane fuel is sold as 98. The higher the octane, the more resistant the fuel to not burn yourself so as to produce stable combustion process to obtain a more stable power. Combustion process with a more perfect power would reduce emissions of carbon monoxide gas. 3% mixture of bioethanol alone, can reduce carbon monoxide emissions to only 1.35% [Anonymous, 2007].
Gasoline consumption in Indonesia in 2005 reached 16 jutakilo liters (Sutanto). Fraction premium generated by petroleum processing units in Indonesia are not sufficient to meet the needs of premium Indonesia. To overcome the deficit premium, Indonesia needs to import premium from international markets. Indonesia needs premium predicted in 2008 of 19.6 million kilo liters. With the amount of crude oil processing unit that has not increased, the production of premium resulting Indonesia remains, then Indonesia will import premium in greater numbers in the coming years.
The government has actually been trying to find a way out to reduce petroleum imports in the future by issuing a Presidential Regulation. 5 of 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 smaller 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 ethanol feedstock is abundant in Indonesia and ethanol production processes can be developed in Indonesia, then the ethanol as an alternative energy source to substitute the premium is very possible to be applied in Indonesia.
Utilization of ethanol and gasoline-ethanol mixtures as fuel has been carried out since the beginning of automobile vehicles. Utilization of pure ethanol as a vehicle fuel was first introduced by Henry Ford on the model of car assemblies thereof (Husky Energy, 2007), even in April 1933 in Nebraska was 10% bioethanol blend sold at premium (Praj Industries, 2006). Earlier, the stock of oil, which was limited and more expensive, the use of ethanol as a fuel has not been deemed necessary. But recent decades, rising oil prices have prompted the search of alternative energy to overcome the energy crisis began to threaten the world. The environmental impact caused by fossil fuel use is also a consideration the right selection of alternative energy and environmentally friendly. The use of ethanol as a fuel has several advantages compared with the fuel, namely: a) a high oxygen content (35%) so if burned very clean, b) environmentally friendly because the carbon-gas emission mono-oxide is 19-25% lower than the fuel thus do not contribute to the accumulation of carbon dioxide in the atmosphere (Costello and Chun, 1988), and is renewable, whereas the fuel will be depleted due to fossil raw materials.
Production of Bioethanol
Bioethanol is produced by anaerobic fermentation of biomass conversion of glucose-containing materials group. The fermentation process generally consists of three stages, namely the manufacture of soluble sugars, fermentation of sugars to ethanol, and the separation and purification of ethanol which is usually conducted in distillate (Badger, 2002).
Bioethanol production technology has been progressing and is divided into first and second generation technologies. The second difference is based on the generation of raw materials to manufacture bioethanol (McCutcheon, 2007). The first generation bioethanol is produced from materials containing sugar or starch, such as molasses, sugar beets, sugar cane, barley, several kinds of wheat, corn, potatoes, cassava, sugar cane.
Starchy materials generally contain 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 branches are connected by bonding a-1, 6. Starchy materials used to produce bioethanol is also utilized as food. Competition raw materials for food and ethanol production materials encourage 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 the 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 a pilot scale. Although still in its early stages of research, production of ethanol with second-generation technology has the potential to be developed capable for producing bioethanol with high gain without competing with food.
Bioethanol Production in First Generation Technology
Bioethanol production process that has been developed and applied in general involves two stages, namely 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 molasses, sugar beet and sugar cane that has been widely used as a feedstock for ethanol, the ethanol-making process is simpler because the raw materials can be directly disakarifikasi by adding glucoamylase (Caylak and Sports, 1998). As for starchy raw materials, before the saccharification process must be done in advance liquefaksi process, a process with a starchy raw material has been applied widely, especially in Brazil and in the U.S. to produce bioethanol, but in Indonesia are still held at the household scale. Liquefaksi done because the process of ethanol fermentation microorganisms are not able to convert starch to ethanol directly, the necessary enzymes to convert starch into maltose oligosaccharides on, then through the process of saccharification converted into simple sugars easily fermented.
Saccharification Process
Saccharification process aims to convert the dextrins produced in liquefaksi process so as to produce mono-or di-saccharides (Frings, 2007). Saccharification process carried out by adding glucoamylase. In this process the release of ad-glucose from the non reducing end sugar 1,4-a-glucan. The reaction takes place at pH 4-5 and at temperatures of 50-60 degrees C (Frings, 2006) for 2 hours (Anonymous, 2007).
Fermentation Process
The fermentation process took place at pH 4-6, at temperatures of 30-35 degrees C (Frings, 2006) and maintained anaerobic fermentation conditions. Microbes that help the process of fermentation is Saccharomyces cerevisiae or Zimomonas mobilis. The fermentation process capable of producing ethanol to levels above 12% because the levels of microorganisms that help the fermentation process can not work anymore.
Process Liquefaksi
At this stage there liquefaksi gelatinasi process to break down starch to form the starch dextrin. Liquefaksi process carried out 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 which will attack the bonding a-1, 4 glycosidic the starch polymer randomly and ekso-amylase which will menghidrolisa glucose or maltose from the reducing end of starch polymers (Neves, 2006).
Separation and Purification Process
To separate the ethanol broth with microbial biomass is done by decantation. Some padatangki fermentation of biomass returned to perform subsequent fermentation. To separate the ethanol from the fermentation broth can be carried out by distillation to rise because the water content in the broth is still high. Capable of producing ethanol distillation storey with a maximum of 95.6% purity, because the purity of the ethanol formed azeotrop with water so it can not be separated again with the usual separation. To get ethanol fuel standard, purity 99%, can be carried out by adding entrainer, with membrane separation in evaporation, or by using a 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 the process of Hydrolysis-Separate-Fermentation (SHF) and the Simultaneous Saccharification and Fermentation (SSF) (Neves, 2006).
Separate process-Hydrolysis-Fermentation
Separate process-Hydrolysis-Fermentation (SHF) is a manufacturing process in which the phase hydrolysis and ethanol fermentation stage takes place separately. Raw materials containing starch hydrolysis process experience (liquefaksi and saccharification) separately from the fermentation process. After the hydrolysis process is complete, continue the process of fermentation. It is intended to facilitate the control of each stage, in order to achieve the desired results. In addition, the interaction between the two stages can be minimized.
SHF process has several drawbacks, including the performance of a-amylase which 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 the a-amylase terinhibisi then the process will halt liquefaksi although not all of the available starch is converted into simple sugars (Neves, 2006). Inhibition will ultimately affect the ethanol produced.
Simultaneous Saccharification and Fermentation
To overcome the weakness that occurs in the SHF, is developing a new process with a process called Simultaneous Saccharification and Fermentation (SSF), as has been patented by Gulf Oil Company and the University of Arkansas (1979). SSF processes have the same basic process of SHF, only phase hydrolysis and fermentation stage takes place simultaneously in one tank. Some time after adding a-amylase, glucoamylase is added to the tank to convert the dextrins produced by a-amylase into simple sugars to ferment into ethanol. Then the tank was also added Saccharomyces cerevisiae to ferment sugars into ethanol, so there is no accumulation of sugar which will cause the a-amylase inhibition (Neves, 2006).
The presence of yeast / bacteria together with the enzyme in a reaction tank, may reduce the accumulation of sugar in the tank so that performance can be a maximum of a-amylase and starch can be converted into simple sugars and all the ethanol produced is higher than the SHF [Neves, 2006].
SSF process these last few years has been modified to include also the stage of substrate cofermentasi double sugar. This process is known as Simultaneous Saccharijication and coFermentation (SSCF).
Prior to hydrolysis by the enzyme treatment, the biomass will experience initial treatment (pre-treatment) in advance, in order to condition the biomass to the nature of the enzyme. After experiencing pre-treatment, enzymatic hydrolysis of biomass and then experiencing. The results of this hydrolysis is not all fermented, because some will form a residue. From the fermentation was, ethanol can be formed.
Bioethanol Production with Second Generation Technology
Ethanol or a mixture of gasoline-ethanol as an alternative fuel has been widely applied in several countries such as Brazil, USA, and several countries in Europe. Even in America, more than 5 million vehicles have been using E85 bioethanol, which is a mixture of 85% and a premium of 15% (Anonymous, 2006). The amount of biomass needed to produce bioethanol as biofuel becomes a separate problem because the biomass in the form of simple sugars (like sugar, sugar cane, corn) is easily degraded into monomeric sugars, also acts as a source of food for both humans and animals. Besides the reduction of emissions by the combustion of bioethanol has not been as low as expected.
Both of the above spur development of alternatives as a bioethanol feedstock, ie lignocellulosic materials (wood products, fiber or even waste that can be degraded). Bioethanol with the raw material is referred to as bietanol Second Generation (Second Generation) because it includes the type of raw material more widely.
The advantage of lignocellulose-based bioethanol, among others (Hagerdal et.al, 2006):
• lignocellulosic raw materials will reduce the likelihood of conflict between land used for food production (and feed) and land for the production of raw materials pasukanenergi.Harga this type is more expensive than first-generation feedstock and can be obtained by the amount of fertilizer, pesticide and energy are relatively more a little.
• Bioethanol made from lignocellulosic produce greenhouse gas emissions are lower, reducing the environmental impact of climate change in particular.
• Bioethanol is likely to open up employment opportunities in rural areas
By looking at these benefits, the prospect of research began heading toward the development of lignocellulose-based bioethanol. Research on berselulosa material utilization as a raw material of ethanol production has been started since 1950.
The principle of production of bioethanol from materials berselulosa equal to 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 hydrolysis reaction. Hydrolysis reaction can be 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.
Acid hydrolysis in Chemistry with
Chemical hydrolysis reaction can be carried out using dilute acid and concentrated acid. The use of dilute acid hydrolysis process carried on 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 hydrolyze cellulose ordinary profit to reach up to 50% reaction conversion (Badger, 2002). Low conversion is due to the degradation of sugars formed by hydrolysis of the reaction temperature used high. Hydrolysis process 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 a simple sugar that is formed into other chemical structures. Degradation of sugar not only lowers the conversion reaction, but also can be toxic to microorganisms at the time of reaction on the formation of ethanol fermentation.
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 much lower than dilute acid. Acid concentration used was 10-30% (Zimbardi et.al). Source of acid used is sulfuric acid. The reaction temperature is 100 degrees C and the reaction takes between 2 and 6 hours. Lower temperatures to minimize degradation of sugars. The advantage of using concentrated acid is produced by a high sugar conversion, which can reach 90% conversion (Badger, 2002). Disadvantages of this reaction is the reaction time required for longer and need a good washing process to achieve the pH of the reaction before adding microbes to the formation of ethanol fermentation process.
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 must be direct contact with the substrate to be hydrolyzed. Since cellulose is naturally bound by lignin, which is permeable to water as a carrier of the enzyme, 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 so that cellulose can be split apart. Pretreatmen can be chemically or physically. Physical methods that can be done is to use high temperature and pressure, milling, radiation, or cooling, all of which require high energy. While 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 cellulases or can also directly use the cellulase-producing microbes, for example Trichodermareesei. The advantage is the efficiency of the enzymatic hydrolysis of high reaction because the enzyme is selective so that the formation of side products 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 required for longer, can be reached 72 hours.
The author is a researcher at the Research Center for Chemistry - LIPI. Written above is taken from the magazine Science News, LIPI
Postingan
Tidak ada komentar:
Posting Komentar