Published on Jul 15, 2018
The effect of ultrasonic on the transesterification reaction of jatropha oil to biodiesel was studied in both homogeneous and heterogeneous catalyst systems. All reactions were operated at 9:1 methanol to oil ratio. In homogeneous catalyst system, the ultrasonic power of 1500 W and frequency of 20 kHz were applied to the mixture of hot oil (100oC) and methanol with 0.5% NaOH.
The ultrasonic transesterification reaction time of 10, 20, and 30 sec were varied. It was found that at the 20 sec reaction time, biodiesel can be produced with high methyl ester content up to 98%. In case of heterogeneous catalyst system, firstly ultrasonic was used to mix together of oil and methanol, then the mixture was passed through the second step for fully transesterification reaction using K/Al2O3 as catalyst. Various parameters such as ultrasonic mixing time, reaction temperature and amount of catalyst were applied to find the optimum condition for the conversion of jatropha oil to biodiesel. It was found that the methyl ester content over 97% can be achieved from all condition. In addition, the contents of mono-, di-, triglycerides in biodiesel were analyzed and compared at different reaction conditions.
The conventional biodiesel production is known as method producing large amount of waste water. Therefore, a new process using heterogeneous catalyst has been developed for environmentfriendly and reduction of production cost. Several different heterogeneous basic catalysts have been proposed for transesterification reaction such as CaO, MgO, ZnO, and Na/γ-Al2O3 etc [3,7]. Normally, the reaction time of biodiesel production from homogeneous transesterification is around 30 min to 1 h depending on reaction temperature, FFA in oil, and amount of catalyst . To shorten the reaction time, ultrasonic wave is one technique providing excellent mixing between the two phases. It will break down the liquid and form the cavitation bubbles resulting in the rising of mass transfer rate and acoustic streaming mixing
The system is equipped with convertor, horn, and reactor. The ultrasonic wave was generated from transducer in the convertor part and transmitted to the horn tip to cause the cavitations in the mixture of oil and methanol. Ultrasonic power and frequency were applied at 1500 W and 20 kHz, respectively into the reaction mixture of 9:1 methanol to oil molar ratio. In this experiment, the neutralized jatropha oil was used and its properties of density, viscosity, acid value, and free fatty acid were measured. For homogeneous transesterification system, a 100 mL of jatropha oil was heated at 100 oC and fed into the ultrasonic reactor to mix with the solution of 0.5 wt% NaOH catalyst in methanol. The ultrasonic reaction time was varied at 10, 20, and 30 sec.
In the heterogeneous transesterification system, ultrasonic was used to enhance the well mixing of jatropha oil and methanol before doing the reaction in the three-neck flask using K/Al2O3 as catalyst. Reaction temperature was controlled at 60oC with time of 0.5, 1, and 3 h. The ultrasonic mixing time was varied at 0, 10, 20, and 30 sec. Furthermore, three different amounts (3.3%, 5%, and 15%) of K/Al2O3 catalyst were used for the reaction. After reaction, glycerol was separated by gravitation and methyl ester was cleaned to remove the access alkali, methanol and water. Consequently, the purified methyl ester or biodiesel was measured for viscosity (Viscometer, Brookfield TC-200) and glyceride content was analyzed using Gas Chromatography . The free fatty acid methyl ester content was analyzed using Gas Chromatography.
In heterogeneous catalyst system, at first oil and methanol were mixed using ultrasound and then K/Al2O3 catalyst was added for the reaction. Table 3 shows the value of viscosity under the change of catalyst amount, ultrasonic mixing time, and reaction time. It was found that catalyst amount is more influential on reaction than ultrasonic mixing time and reaction time. Therefore, the amount of catalyst was fixed for the next study. By using 5% K/Al2O3 catalyst and 3h reaction time, the di- and tri-glyceride contents are remarkably decreased when the ultrasonic mixing time is increased from 5 to 20 sec. The longer ultrasonic mixing time than 20 sec will present less change of glyceride content in biodiesel.
Advantages of the Use of Biodiesel
Some of the advantages of using biodiesel as a replacement for diesel fuel are :
• Renewable fuel, obtained from vegetable oils or animal fats.
• Low toxicity, in comparison with diesel fuel.
• Degrades more rapidly than diesel fuel, minimizing the environmental consequences of biofuel spills.
• Lower emissions of contaminants: carbon monoxide, particulate matter, polycyclic aromatic hydrocarbons, aldehydes.
• Lower health risk, due to reduced emissions of carcinogenic substances.
• No sulfur dioxide (SO2) emissions.
• Higher flash point (100C minimum). S.
• May be blended with diesel fuel at any proportion; both fuels may be mixed during the fuel supply to vehicles.
• Excellent properties as a lubricant.
• It is the only alternative fuel that can be used in a conventional diesel engine, without modifications.
• Used cooking oils and fat residues from meat processing may be used as raw materials.
Disadvantages of the Use of Biodiesel
There are certain disadvantages of using biodiesel as a replacement for diesel fuel that must be taken into consideration:
• Slightly higher fuel consumption due to the lower calorific value of biodiesel.
• Slightly higher nitrous oxide (NOx) emissions than diesel fuel.
• Higher freezing point than diesel fuel. This may be inconvenient in cold climates.
• It is less stable than diesel fuel, and therefore long-term storage (more than six months) of biodiesel is not recommended.
• May degrade plastic and natural rubber gaskets and hoses when used in pure form, in which case replacement with Teflon components is recommended.
• It dissolves the deposits of sediments and other contaminants from diesel fuel in storage tanks and fuel lines, which then are flushed away by the biofuel into the engine, where they can cause problems in the valves and injection systems. In consequence, the cleaning of tanks prior to filling with biodiesel is recommended. It must be noted that these disadvantages are significantly reduced when biodiesel is used in blends with diesel fuel.
Biofuels for transport are commonly addressed according to their current or future availability as first, second or third generation biofuels (OECD/ IEA 2008). Second and third generation biofuels are also called “advanced” biofuels.
First-generation biofuels are commercially produced using conventional technology. The basic feedstocks are seeds, grains, or whole plants from crops such as corn, sugar cane, rapeseed, wheat, sunflower seeds or oil palm. These plants were originally selected as food or fodder and most are still mainly used to feed people. The most common first-generation biofuels are bioethanol (currently over 80% of liquid biofuels production by energy content), followed by biodiesel, vegetable oil, and biogas.
Second-generation biofuels can be produced from a variety of non-food sources. These include waste biomass, the stalks of wheat, corn stover, wood, and special energy or biomass crops (e.g. Miscanthus). Second-generation biofuels use biomass to liquid (BtL) technology, by thermo chemical conversion (mainly to produce biodiesel) or fermentation (e.g. to produce cellulosic ethanol).Many second-generation biofuels are under development such as biohydrogen, biomethanol, DMF, Bio-DME, Fischer-Tropsch diesel, biohydrogen diesel, and mixed alcohols.
Third-generation biofuel: Algae fuel, also called oilgae, is a biofuel from algae and addressed as a third-generation biofuel (OECD/IEA 2008). Algae are feedstocks from aquatic cultivation for production of triglycerides (from algal oil) to produce biodiesel. The processing technology is basically the same as for biodiesel from second-generation feedstocks. Other third -generation biofuels include alcohols like bio-propanol or bio-butanol, which due to lack of production experience are usually not considered to be relevant as fuels on the market before 2050 (OECD/IEA 2008), though increased investment could accelerate their development. The same feedstocks as for first-generation ethanol can be used, but using more sophisticated technology. Propanol can be derived from chemical processing such as dehydration followed by hydrogenation. As a transport fuel, butanol has properties closer to gasoline than bioethanol.
Characteristics of oils or fats affecting their suitability for use as biodiesel
• Calorific Value, Heat of Combustion – Heating Value or Heat of Combustion, is the amount of heating energy released by the combustion of a unit value of fuels.
One of the most important determinants of heating value is moisture content. Air-dried biomass typically has about 15-20% moisture, whereas the moisture content for oven-dried biomass is negligible. Moisture content in coals varies in the range 2-30%. However, the bulk density of most biomass feedstocks is generally low, even after densification – between about 10 and 40% of the bulk density of most fossil fuels. Liquid biofuels however have bulk densities comparable to those for fossil fuels.
• Melt Point or Pour Point -
Melt or pour point refers to the temperature at which the oil in solid form starts to melt or pour. In cases where the temperatures fall below the melt point, the entire fuel system including all fuel lines and fuel tank will need to be heated.
• Cloud Point -
The temperature at which an oil starts to solidify is known as the cloud point. While operating an engine at temperatures below oil’s cloud point, heating will be necessary in order to avoid waxing of the fuel.
• Flash Point -
The flash point temperature of a fuel is the minimum temperature at which the fuel will ignite (flash) on application of an ignition source. Flash point varies inversely with the fuel’s volatility. Minimum flash point temperatures are required for proper safety and handling of diesel fuel.
• Iodine Value -
Iodine Value (IV) is a value of the amount of iodine, measured in grams, absorbed by 100 grams of a given oil.
Iodine value (or Iodine number) is commonly used as a measure of the chemical stability properties of different biodiesel fuels against such oxidation as described above. The Iodine value is determined by measuring the number of double bonds in the mixture of fatty acid chains in the fuel by introducing iodine into 100 grams of the sample under test and 26 measuring how many grams of that iodine are absorbed. Iodine absorption occurs at double bond positions - thus a higher IV number indicates a higher quantity of double bonds in the sample, greater potential to polymerize and hence lesser stability.
• Viscosity –
Viscosity refers to the thickness of the oil, and is determined by measuring the amount of time taken for a given measure of oil to pass through an orifice of a specified size. Viscosity affects injector lubrication and fuel atomization. Fuels with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in leakage or increased wear. Fuel atomization is also affected by fuel viscosity. Diesel fuels with high viscosity tend to form larger droplets on injection which can cause poor combustion, increased exhaust smoke and emissions.
• Cetane Number -
Is a relative measure of the interval between the beginning of injection and auto ignition of the fuel. The higher the cetane number, the shorter the delay interval and the greater its combustibility. Fuels with low Cetane Numbers will result in difficult starting, noise and exhaust smoke. In general, diesel engines will operate better on fuels with Cetane Numbers above 50.
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