Biodiesel transesterification reactions

92e7 2 5.77e5 as 5.88el2 14 098el0 5 5.35e3 ag 2.15e4 

The mathematical model for the production of biodiesel in a batch reactor is governed by the following ordinary differential equations 3.63 to 3.68 derived from the mass balance of the batch reactor [31]. 

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In this section, two major research problems have been identified. The first issue is related to the fossil oil depletion and the second relates to how homogeneous catalysts are not suitable to use in biodiesel transesterification reaction. These will be explained in the following subsection. 

The transesterification reactions were conducted in a sealed 250 ml autoclave equipped with a stirrer. The molar ratio of methanol to oil was 12 1, reaction temperature was 200 C-230°C, and the ratio of catalyst to oil was about 2 wt%. Samples were taken out from the reaction mixture and biodiesel portions were separated by centrifuge. 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

G.F. Ghesti, J. Lemos de Macedo, I.S. Resck, J.A. Dias and S.C.L. Dias, ET-Raman spectroscopy quantification of biodiesel in a progressive soybean oil transesterification reaction and its correlation with H NMR spectroscopy methods, Energ. Fuel, 21, 2475-2480 (2007). 

Figure 7 depicts a simplified block flow diagram (BFD) for a typical biodiesel production process using base catalysis. In the first step, methanol and catalyst (NaOH) are mixed with the aim to create the active methoxide ions (Figure 4, step 1(b)). Then, the oil and the methanol-catalyst solution are transferred to the main reactor where the transesterification reaction occurs. Once the reaction has finished, two distinct phases are formed with the less dense (top) phase containing the ester products and unreacted oil as well as some residual methanol, glycerol, and catalyst. The denser (bottom) layer is mainly composed of glycerin and methanol, but ester residues as well as most of the catalyst, water, and soap can also be found in this layer. 

Alkaline earth metal oxides and hydroxides have also been tested in transesterification reactions. Ca(OH)2 did not show significant catalytic activity in the transesterification of rapeseed oil with methanol at conditions normally used to prepare biodiesel.Peterson et al. reported relative alcoholysis activities of a series of supported CaO catalysts under near reflux conditions of methanol-rapeseed oil mixtures at 6 1 molar ratios.Among the catalysts tested, the most active was CaO (9.2 wt% CaO) on MgO. For instance, in a 12 h reaction the total oil conversion using this catalyst was over 95%, similar to... 

Several processes for the production of biodiesel fuel have been developed by acid-, alkali-, and enzyme-catalyzed transesterification reactions (7-10). Transesterification, called alcoholysis, is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis. Transesterification is represented by a number of consecutive and reversible reactions. The reaction step is the conversion of triglycerides to diglycerides, followed by the conversion of diglycerides to monoglycerides and of monoglycerides to glyceride at each step (11,12). 

FAME production of rapeseed oil by alkali-catalyzed transesterification reaction was investigated. To obtain optimum conversion yield, anhydrous methanol and rapeseed oil with a free fatty acid content of <0.5% were used. The optimum conditions for alkali-catalyzed transesterification using KOH were determined as follows an oil to methanol molar ratio of 1 8 to 1 10 KOH, 1.0% (w/w) on the basis of oil weight, as catalyst a reaction temperature of 60°C and reaction time of 30 min. At these conditions, the FAME conversion yield was approx above 98%. From the refined FAME product (biodiesel), the FAME purity was obtained above 99% through posttreatment such as washing and centrifugation. 

The second area of heterogeneous catalysis in biodiesel manufacturing is the transesterification reaction. Here again, the base catalysts exhibit typically much higher activity than the acidic ones, but finding effective catalysts is still an open problem. Some solid metal oxides, such as those of tin, magnesium, and zinc could be used directly, but they actually act by a homogeneous mechanism... 

Shieh et al. (2003) indicated a biodiesel transesterification using soybean oil and methanol and commercial immobilized lipase from R. miehei (Lipozyme IM-77). The response surface analysis showed that the following variables were important reaction time, temperature, enzyme amount, molar ratio of methanol to soybean oil, and added water content on percentage weight conversion to soybean oil methyl ester by transesterification. The optimum yield based on ridge max analysis gave a 92.2% weight conversion. 

The conventional method of preparing biodiesel is an alkaline catalysed transesterification reaction of refined vegetable oils with methanol to produce biodiesel according to E.U. (EN14214) or U.S. (ASTM D6751) standards. 

Colucci, J.A., Borrero, E.E., and Alape, F. 2005. Biodiesel from an alkaline transesterification reaction of soybean oil using ultrasonic mixing. Journal of the American Oil Chemists Society, 82 525-530. 

Biodiesel is made up of the methyl or ethyl esters of fatty acids, and is obtained from the triglycerides found in vegetable oils through the well-known transesterification reaction (Scheme 1). 

The alkali process for biodiesel production can achieve high purity and yield of biodiesel in a short time. However, vegetable oils high in free fatty acids result in the production of soap and the loss of catalyst in the alkali process. To overcome this, the free tatty acids should be removed before the transesterification reaction. Because a homogeneous acid catalyst like sulfuric acid can not be recovered and is toxic, a heterogeneous acid catalyst can be used for the esterification of free fatty acids. Solid catalysts can be easily recovered after the reaction and reused [10-12]. 

The AV of crude tung oil was 9.55mg KOH/g, and its viscosity was 109.4mm /s at 40 °C. Because the fiee fatty acid of oil forms soap with the alkali catalyst and prevents the separation of biodiesel from glycerin, the pretreatment process to convert the free fatty acid to biodiesel is required [3]. Therefore, it is desired that the AV of tung oil decreases to less than Img KOH/g before the transesterification reaction using the alkali catalyst. 

Tung biodiesel was produced by the esterification/transesterification reactions using Amberlyst-15 and KOH from tung oil. Amberlyst-15 showed a good esterification efficiency for the pretreatment of tung oil. The AV of tung oil decreased from 9.55 to... 

CSTR Figure 5.2f). As long as the residence time for diffusion of molecules from the input to the exit is long enough to achieve an acceptable conversion of reactants to products, a standard batch reactor can be turned into a CSTR. As an example, a 4 L flask in a MARS has been used for the preparation of biodiesel via a transesterification reaction with a flow rate of 7.2 L/min (33 s residence time). ... 

Glycerol is a byproduct of the transesterification reaction, and this compound is actually formed in fairly substantial quantities (ca. 10% by mass). This has given rise to research directed toward finding ways to carry out chemical reactions beginning with, or involving, glycerol, such that the cost efficiency of the overall process of biodiesel production might be improved. 

Because of its renewability, biodegradability, and better quality of exhaust gas emission (http //www.netl.doe.gov/tech-nologies/coalpower/ewr/water/pdfs/Water%20Energy%20 Overview 2010.pdf), biodiesel as a source of energy has been receiving great attention [149]. Biodiesel is produced via different techniques such as direct/blends [150], microemulsion [151], pyrolysis [152], and transesterification [153]. Among these methods, transesterification reactions to convert fats and oils into biodiesel fuel are the most adopted technique... 

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