Kinetics of ultrasound-assisted enzymatic biodiesel production from Macauba coconut oil

doi:10.1016/j.renene.2014.11.067

Renewable Energy

Volume 76, April 2015, Pages 388-393

https://doi.org/10.1016/j.renene.2014.11.067 Get rights and content

Highlights

•
Enzymatic production of FAEE from Macauba oil solvent-free under the influence of ultrasound irradiation.
•
The use of cheaper raw materials for biodiesel production is a key point towards economic competitiveness of this biofuel.
•
Reaction yields of around 80.1% were obtained.

Abstract

This work reports the production of fatty acid ethyl esters (FAEE) by means of Macauba (Acrocomia aculeata) coconut oil (MCO) solvent-free enzymatic transesterification reactions using a commercial immobilized lipase (Novozym 435) under the influence of ultrasound irradiation. An experimental design was used to evaluate the effects of temperature (40–70 °C), enzyme (5–20 wt%) concentration, oil to ethanol molar ratio (1:3–1:10) and output irradiation power (40–70 % of the maximum supply value) on the reaction yield. Besides, a kinetic study varying the enzyme concentration was also carried out. Results show that ultrasound-assisted lipase-catalyzed transesterification of MCO with ethanol in solvent-free system might be a potential alternative route to conventional alkali-catalyzed and/or traditional enzymatic methods, as reaction yields around 70 wt% were obtained at mild irradiation power supply (∼ 132 W), and temperature (65 °C) in a short reaction time, 30 min. Reutilization of enzyme showed that it may be advantageously employed up to 5 reuse cycles.

Introduction

Macauba (Acrocomia aculeata) is a palm species native of tropical forests and can be found from southern Mexico and the West Indies until Brazil and also in Paraguay, Bolivia and Argentina [1]. The oil produced from Macauba has no tradition as food product and presents several industrial and energetic applications, which demonstrate great potential for biodiesel production [2], [3], [4], [5]. These latter characteristics granted importance to the Macauba coconut oil (MCO) as alternative feedstock to produce biodiesel, especially in a country like Brazil where biodiesel is mainly produced from soybean oil (75–80%). Considering that one-third of soybean production in Brazil is destined to biodiesel production and compared to soybean oil productivity, 400–700 kg of oil per hectare per year, MCO with a productivity of around 6000 kg of oil per hectare per year appears as a very promising alternative source [6], [7].

The use of cheaper raw materials for biodiesel production is a key point towards economic competitiveness of this biofuel. In that sense, the raw vegetable oil should be studied to determine its potential with respect to treated and even refined oils. Raw vegetable oils generally present compounds such as antioxidants, phospholipids, free fatty acid (FFA), pigments, etc., that can affect ester synthesis in some extent and the presence of water, which demands investigation on the use of rectified alcohols. However, there is a clear lack of technical reports in scientific literature involving the use of MCO as feedstock for biodiesel production. The few published works available have studied the production of biodiesel from MCO using basic and acid catalysts [8] and enzymatic catalysis under microwave irradiation [9]. To the best of our knowledge this is the first report on biodiesel production from MCO through enzymatic transesterification under ultrasound irradiation.

Ultrasound is very effective at dispersing material present in solution. The application of ultrasound, therefore, will contribute to a more homogeneous reaction mixture and facilitate dispersion of lipase through substrate media, reducing agglomeration so that the reaction rate does not decrease with the increase of lipase concentration [10]. Moreover, as enzymatic synthesis of biodiesel is much slower than alkali-catalyzed transesterification, ultrasound irradiation appears to be a proper method to increase the reaction rate thus making possible greener biodiesel production through a biological catalyst. Enzyme-catalyzed reactions in solvent-free systems under ultrasound power, in spite of its scientific and industrial relevance, can still be considered a new technology, since just a few studies in this subject can be found in the open literature.

The present work attempts to contribute to build a platform for biodiesel production trough investigation of new transesterifications techniques, especially by exploring non-edible raw materials. Here, the main objective is to investigate the production of Macauba coconut oil esters with ethanol (fatty acid ethyl esters-FAEE) using a commercial lipase under the influence of ultrasound irradiation, in a solvent-free system, evaluating the effects of reaction conditions on the yield of fatty acid esters produced. In this work it was also introduced a new parameter named “convertibility”, which represents the maximum esters conversion that can be achieved from a raw material if every fatty acid available would form an alcoholic ester.

Section snippets

Materials

The MCO was obtained from the processing unit of Macauba in Montes Claros (Minas Gerais, Brazil). Ethanol (Merck 99.9%), n-heptane (Nuclear, 99.5 gg mol⁻¹%), lauric acid (Vetec, 98 gg mol⁻¹%), n-propanol (Synth, 99.5 gg mol⁻¹% of purity), sodium hydroxide (Quimex, 97 gg mol⁻¹%) and acetone (Quimex, analytical grade) were used without further treatment.

Commercial immobilized lipase, Novozym 435, from Candida antarctica (immobilized on a macroporous anionic resin, 1.4 wt% water) was purchased

MCO characterization

The chemical composition of major fatty acids present in the MCO used in this study, determined by gas chromatography analysis, is presented in Table 1 where it can be noticed the predominance of oleic acid (58.0 wt%), which is similar to the fatty acid profile found by Fortes and Baugh [13]. The acid value, water content (wt%) and polymer content of MCO were determined as 88.9 mgKOH/g oil, 0.64 and of 6.1%, respectively. The acid value found in this work is in agreement with those reported by

Conclusions

This work confirms the good efficiency of ultrasound-assisted system to convert Macauba oil into alcoholic esters using a commercial lipase as catalyst, hence pointing the promising use of a low-cost, non-edible oil, with very satisfactory field productivity, towards biodiesel production with an eco-friendly, green technique. The convertibility and the conversion efficiency parameters helped to better specify the extent of the esters conversion reaction in the lipase-catalyzed, ultrasound

Acknowledgments

The authors thank CNPq (process 490061) for the financial support of this work and scholarships.

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Kinetics of ultrasound-assisted enzymatic biodiesel production from Macauba coconut oil

Highlights

Abstract

Introduction

Section snippets

Materials

MCO characterization

Conclusions

Acknowledgments

J Mol Cat B Enzym

Ultrason Sonochem

Ultrason Sonochem

J Anal Appl Pyrolysis

Ultrason Sonochem

Biores Technol

Enzyme Microb Technol

Ultrason Sonochem

Bioresour Technol

Trends Biotechnol

Acrocomia aculeata (jacq) lodd. ex mart – arecaceae: bases para o extrativismo sustentável