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Ultrasonic Irradiation for Biodiesel Production from Soybean Oil by Novozym 435

Author: WangSong
Tutor: FangXueXun
School: Jilin University
Course: Biochemistry and Molecular Biology
Keywords: Ultrasonic irradiation Vibration Biodiesel Soybean oil Novozym 435
CLC: TE667
Type: Master's thesis
Year: 2010
Downloads: 193
Quote: 1
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Abstract

The need for alternative energy sources that combine environmental friendliness with biodegradability, low toxicity, renewability, and less dependence on petroleum products has never been greater. One such energy source is referred to as biodiesel.Biodiesel (monoalkyl esters of fatty acids) produced from vegetable oils, animal fats and microalgal oils by transesterification or esterification with short chain alcohols has been viewed as promising renewable sources of fuel. Acid and base catalysts were adopted in the conventional method for biodiesel production to form fatty acid alkyl esters. Downstream processing costs and environmental problems associated with biodiesel production and byproducts recovery have led to the search for alternative production methods and alternative substrates. Recently, enzymatic production of biodiesel has attracted considerable interest, since it is more efficient and highly selective, involves less energy consumption, and produces less side products or waste. However, from an economic point of view, the enzyme activity is low in lipase-catalyzed biodiesel production, compared with chemical catalyst; therefore it is necessary to find a proper method to increase the reaction rate to promote the application of enzyme catalytic biodiesel production.Ultrasound has been used to accelerate the rates of numerouschemical reactions. The production of biodiesel with soybean oil and methanol through transesterification by Novozym 435 (Candida antarctica lipase B immobilized on polyacrylic resin) were conducted under two different conditions—ultrasonic irradiation and vibration to compare their overall effects. Effects of reaction conditions, such as ultrasonic power, water content, organic solvents, ratio of solvent/oil, ratio of methanol/oil, enzyme dosage and temperature on the activity of Novozym 435 were investigated under UIV.Compared with vibration, ultrasonic irradiation significantly enhanced the activity of Novozym 435. The reaction rate was further increased under the condition of ultrasonic irradiation with vibration (UIV). The reaction rate was under the influence of mass transfer limitations. The lower rates of the reactions by vibration might due to insufficient liquid circulation currents generated that facilitate uniform mixing at microlevel. While under ultrasonic irradiation, ultrasonic cavitation could destroy the two-tier structure of the interface of methanol and triolein, increase the interfacial area, emulsification speed and activity of the microscopic and macroscopic bubbles, which might increase the reaction rate. It was also possible that compared to vibration,the enzyme behaved more active under ultrasonic irradiation, as the movement increase of the liquid molecules might facilitate the substrate to approach the active site.The increase of ultrasonic power resulted in no obvious difference in enzyme activity, which was inconsistent with the previous studies showing that ultrasonic power had a positive impact on the enzyme activity before a point of diminishing return was reached.The enzyme activities exhibited a bell shaped curve with the changing of water content. When water content was <0.5%, the enzyme activity increased with the increase in water content. Novozym 435 exhibited highest activity when water content was 0.5%. With a further increase of water content, the enzyme activities decreased dramatically.In the present study, the effects of several organic solvents with various log P, dielectric constant, solubility parameter and other parameters were investigated for the transesterification of soybean oil, a comprehensive consideration of all solvent parameters should be taken when choosing an appropriate solvent. Tert-amyl alcohol, instead of widely used tert-butanol, was chosen as the solvent considering the higher enzyme activity in this solvent.The enzyme activity increased greatly with the increase in tert-amyl alcohol/oil volume ratio with a maximum value at a tert-amyl alcohol/oil volume ratio of 1:1. Further increased in tert-amyl alcohol concentration resulted no increment of enzyme activity. The presence of tert-amyl alcohol in the system could improve the solubility of methanol in the reaction mixture, as a result, the inhibition effects of methanol in biodiesel production were eliminated, and lipase maintained high activity even with high amount of methanol presented in the system.The enzymatic activities increased with the increase of substrate ratio from 1:1 to 6:1, and reached the maximum when the substrate ratio was 6:1. As the amount of methanol increases, more cavitation bubbles might be generated because the cavitation events were easier in methanol than in oil, and thus improve the reaction. After this point, with the further increasing of substrate ratio, the enzyme activity decreased gradually. It was probably due to the inhibitory effect of methanol on enzyme become more significant with higher concentrations of methanol.As the loading of Novozym 435 increased, the yield of FAME was also increased. Considering the cost of the enzyme, 6% of Novozym 435 was proved to be the most efficient amount (before this point, the yield of methyl ester witnessed a steep increase, while after the point, the yield increase was much slower).The enzyme activity increased as temperature increased from 30 to 40℃, followed by a decrease at higher temperature.Novozym 435 was not deactivated or denatured under UIV, only a slightly decrease (4%) in enzyme activity was observed after five uses. These results suggested that Novozym 435 was suitable for catalytic usage in UIV conditions.Under the optimum conditions (50% of ultrasonic power, 50 rpm vibration, water content of 0.5%, tert-amyl alcohol/oil volume ratio of 1:1, methanol/oil molar ratio of 6:1, 6% Novozym 435 and 40℃), 96% yield of fatty acid methyl ester (FAME) could be achieved in 4 h. These results indicated that UIV was a fast and efficient method for biodiesel production.

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