Thread Content
Study on the Preparation of Biodiesel from Soybean Oil Footstock and Its Properties. Biodiesel can serve as a substitute for petroleum fuels; it possesses advantages such as being renewable, easily biodegradable, non-toxic, having low sulfur content, and producing fewer harmful substances in exhaust gases, making it one of the most important clean fuels. Currently, research on the production processes of biodiesel focuses on the transesterification reaction. B00c0ck and others investigated the kinetics of the transesterification reaction of soybean oil under uncatalyzed supercritical conditions, while others studied the optimal reaction conditions for this process. This study used soybean oil footstock extract as a raw material to produce biodiesel, investigated the appropriate conditions and kinetics for the transesterification reaction of this soybean oil footstock extract, and evaluated the energy density of the resulting biodiesel. 1 Materials and Methods 1.1 Raw materials Raw material: Soybean oil foot extract (Dongtai Kangda Agriculture, Industry and Commerce Group Company); saponification value of 198.4 mgKOhg, acid value of 1.47 msKOhg, average molecular weight of 897.6, iodine value of 128.5 st/100 g of oil, and density of 925.0 kg/m~ ； The fatty acid composition of the oil extracted from soybean oil residues, as analyzed, is as follows: according to VIP Information http://www.cqvip.com, Volume 31, Issue 4, 2006, China Oils and Fats – arachidonic acid 61.2%, stearic acid 21.5%, elaidic acid 15.0%, arachidic acid 1.7%, palmitic acid 0.3%, oleic acid 0–3% ； All other experimental reagents are of analytical grade. 1.2 Analysis Method The content of fatty acid methyl esters in the product was determined using a 1102 model gas chromatograph. The chromatographic operating parameters and conditions were as follows: hydrogen flame ionization detector, a stainless steel packed column with dimensions of 2 m x 3 mm, OV-17 as the stationary phase, furnace temperature of 250°C, detector temperature of 320°C, injector temperature of 300°C, and an injection volume of 0.1 μL. The content of fatty acid methyl esters was calculated using the internal standard method (with methyl undecanoate as the internal standard). 1.3 Experimental Procedure: In a 500 mL glass reactor equipped with a stirrer, a reflux condenser, a thermometer, and a sampling port, soybean oil footstock extract and methanol were added according to the molar ratio of alcohol to oil. After stirring and heating to the desired reaction temperature, the prepared basic catalyst (Kon+methanol solution) was added. Reaction timing begins. 0.4 mL of the sample is taken at regular intervals; the sample is immediately placed in a weighing vial pre-filled with a 0.5 mE (0.6 mol/L) KH2P04 buffer solution to neutralize the basic catalyst present in the sample and thereby stop the reaction instantly. It is then frozen in ice saline, and for analysis, about 0.15 g of the internal standard methyl undecanoate along with 1.0 mL of benzene as a diluent are added to the sample. 2 Results and Discussion 2.1 Orthogonal experiment on ester exchange reaction Orthogonal experiments were conducted using the molar ratio of methanol to soybean oil leaching oil (A), catalyst dosage (B), reaction temperature (C), and reaction time (D) as factors, in order to determine the optimal process conditions for the transesterification reaction; the factor level values are shown in Table 1. Using the methyl ester content of fatty acids in the product as the evaluation index, the results of the orthogonal experiments and the analysis are shown in Table 2. Table 1 Factor level table. As can be seen from Table 2, the factors affecting the fatty acid methyl ester content are, in order: alcohol to oil molar ratio > catalyst amount > reaction temperature > reaction time. The transesterification reaction between soybean oil footstock extract and methanol is a reversible reaction, and increasing the alcohol-to-oil molar ratio helps drive the reaction in the direction of product formation. When the molar ratio of alcohol to oil is 6:1, the methyl ester content in the product is the highest ； When the molar ratio of alcohol to oil is 7:1, the content of methyl ester in the product decreases. This is because an increase in the amount of alcohol reduces the concentration of oil in the reactants, thereby slowing down the reaction rate; as a result, the transesterification reaction does not reach equilibrium within the reaction time. Excessive amounts of methanol make it difficult to separate glycerol, increasing the costs associated with methanol recovery as well as the losses of methanol during the process. In this experiment, the optimal alcohol-to-oil molar ratio was 6:1. Coating: Results and analysis of orthogonal experiments on the transesterification reaction using soybean oil footstock extract. When the catalyst amount was 1.0%, the content of methyl ester in the product was the highest. Increasing the amount of catalyst actually leads to a decrease in the fatty acid methyl ester content. This is because, as the amount of catalyst increases, saponification occurs during the reaction, resulting in the formation of gel-like substances in the product; this makes it more difficult to separate the biodiesel from the by-product glycerol. The optimal amount of catalyst to use is 1.0%. An increase in reaction temperature and an extension of reaction time are favorable for the formation of fatty acid methyl esters in this reaction. However, as can be seen from the orthogonal analysis, raising the reaction temperature and reaction time from level 2 to level 3 did not result in a significant increase in the content of fatty acid methyl esters. Therefore, the reaction temperature is set at 45°C, and the reaction time is set at 45 minutes. In summary, the appropriate process conditions for the transesterification reaction of soybean oil footstock extract are A2~CaIh. Optimization and verification experiments were carried out under these conditions, resulting in a fatty acid methyl ester content of 96.8% in the product. 2.2 Determination of kinetic parameters The kinetics of the transesterification reaction of soybean oil footstock extract was studied under the conditions of a catalyst dosage of 1% KOH and an alcohol-to-oil molar ratio of 6:1, with the transesterification reaction temperatures set at 25, 35, 45, and 55°C. At each experimental temperature, 15 samples were taken; the experimental results are shown in Figure 1. l00 — 80 80 60 40 convex ∞ 20 o 20 40 60 80 100 time (min) Figure 1 Effect of reaction temperature VIP Information http://www.cqvip.com 70 China Oils and Fats, Vol. 31, No. 4, 2006 Assuming that the transesterification reaction is second-order with respect to the soybean oil residue extract in its initial stage, and assuming that the methanol excess is zero-order, then the rate equation is: …… where: CA = cAo – Cp. Here, cA represents the concentration of the soybean oil residue extract, in mol/L (CAO = 0.755 mol/L) ； j}——reaction rate constant ； cp —— biodiesel concentration, mot/L (Cp = BDF% × 2.265). During the reaction, as shown in Figure 2, the linear regression curve of a second-order reaction is applicable. It can be seen from Figure 2 that, in the initial stage of the reaction, this process can be well described by a second-order reaction; plotting 1/CA against t yields a straight line, and the correlation coefficient is given in Table 3. The slope of the straight-line equation is the reaction rate constant k for the initial stage of the reaction at that temperature. The rate constant k for the second-order reaction in the initial stage of the transesterification reaction at various temperatures is shown in Table 3. As can be seen from Figure 1, as the reaction proceeds, the transesterification reaction becomes first-order; in the later stages it becomes zero-order. In fact, equilibrium is reached in transesterification at the later stage of the reaction. From a kinetic perspective, the entire process is a transition from a second-order reaction to a zero-order reaction. Table 3 shows the reaction rate constant k at the initial stage of the immersion exchange reaction. Based on the data in Table 3, a straight line is obtained by plotting Ink against 1/T; the slope of this line is –1/R = –5,739, the intercept on the vertical axis is Ink0 = 17.91162, and the correlation coefficient is 0.9997. For the transesterification reaction of soybean oil footstock extract, the activation energy Eo = 47.71 kJ/mol, and the frequency factor k0 = 6.01×107 L/(mol·min). The experimental results are the same as those of the kinetic process of cottonseed oil 6 and palm oil transesterification. The activation energy is similar to that of Needl8J, Noured. dini HE9], who believe that the reaction rate constant increases as the amount of catalyst used increases, with an activation energy of 33,837 kJ/mol. 2.3 Evaluation of biodiesel performance Biodiesel prepared from soybean oil meal extract was tested for its performance and compared with diesel fuel; the results are shown in Table 4. Table 4: Properties of biodiesel and comparison with diesel. The main performance indicators of biodiesel are a cold filter plugging point of 2°C and a pour point of 0°C, which are comparable to those of diesel at 2°C and 0°C respectively ； With a flash point of 170°C, ** which is higher than the 72°C of diesel, it is safer to store, transport, and use ； The extremely low sulfur content results in a **reduction in SOx emissions from diesel engine exhaust** ； The aromatic hydrocarbon content is 0; it contains no aromatic hydrocarbons and is therefore not carcinogenic ； The dynamic viscosity of biodiesel is 5.0 cSt at 40°C, which is higher than that of conventional diesel; it meets the diesel standards. Without affecting fuel atomization, it facilitates the formation of an oil film on the inner walls of the cylinders, thereby improving the lubrication of moving parts and reducing wear. Biodiesel has a good color; aside from its high iodine value, all its other key performance parameters meet the standards for Grade 0 diesel (GB 252–1994). Biodiesel has an oxygen content of 11%, which is higher than that of diesel; therefore, it requires less oxygen during combustion, and its combustion and ignition properties are superior to those of diesel. 3 Conclusions (1) The experiments showed that the most suitable reaction conditions for producing biodiesel from soybean oil residue extract are: a reaction temperature of 45°C, an alcohol-to-oil molar ratio of 6:1, a catalyst amount of 1.0% of the oil weight, and a reaction time of 45 minutes ； The biodiesel content can reach 96.8%, and its main performance parameters meet the standards for 0-diesel (G8 252—1994). (2) From a kinetic perspective, the transesterification process of soybean oil footstock extract is a transition from a second-order reaction to a zero-order reaction. At the initial stage of the reaction, it is a second-order reaction, then it becomes a first-order reaction, and eventually it turns into a zero-order reaction. The activation energy for the reaction at the initial stage is 47.71 kJ/mol, while the frequency factor k0 is 6.01×10^7 L/(mol·min).