Scholarly article on topic 'Biodiesel Production from Waste Cooking Oil by Two-step Catalytic Conversion'

Biodiesel Production from Waste Cooking Oil by Two-step Catalytic Conversion Academic research paper on "Agriculture, forestry, and fisheries"

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{"Waste cooking oil" / "Heterogeneous catalyst" / "Biodiesel production" / "Esterification / Transesterification"}

Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Kao-Chia Ho, Ching-Lung Chen, Ping-Xuan Hsiao, Meng-Shan Wu, Chien-Chang Huang, et al.

Abstract The commercial biodiesel production process is very mature today, but the source of biodiesel is mostly plant oil, which has the drawback of high cost and land competition with food crops. Using waste cooking oil as feedstock for biodiesel production can avoid those problems. However, the transesterification of waste cooking oil involves some challenges. For example, waste cooking oil usually contains a large amount of free fatty acids (FFAs), which could react with base catalyst (such as NaOH) to form soap, resulting in a decrease in biodiesel conversion efficiency. To cope with this, a two-step process, consisting of esterification with acid catalyst and follow-up transesterification with base catalyst was developed. This two-step process could lower the content of FFAs in waste cooking oil in the first step and also improve conversion of transesterification in the second step. Although homogeneous acid catalyst, such as sulfuric acid, could reach a high conversion in a short time, an extra downstream processing is required to remove the acid catalyst (e.g., water rinse). Therefore, we developed a magnetic spinel as acid solid catalyst supporter to replace homogeneous catalyst in order to simplify the overall process. In the first step, esterification of FFAs content in cooking oil was conducted using the self-made solid acid catalyst, which has similar catalytic ability to that of sulfuric acid, and is also much easier for separation. In addition, the residual lipid can be easily transesterified without any pre-treatment. The self-made spinel-supported catalyst could be regenerated by simple calcination.

Academic research paper on topic "Biodiesel Production from Waste Cooking Oil by Two-step Catalytic Conversion"

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Energy Procedia 61 (2014) 1302 - 1305

The 6th International Conference on Applied Energy - ICAE2014

Biodiesel production from waste cooking oil by two-step catalytic conversion

Kao-Chia Hoa, Ching-Lung Chena, Ping-Xuan Hsiaoa, Meng-Shan Wua, Chien-Chang Huangc, Jo-Shu Changa, b*

aDepartment of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan bCenter for Biosciences and Biotechnology, National Cheng Kung University, Tainan, Taiwan _cDepartment of Cosmetic Science, Providence University, Taichung, Taiwan_

Abstract

The commercial biodiesel production process is very mature today, but the source of biodiesel is mostly plant oil, which has the drawback of high cost and land competition with food crops. Using waste cooking oil as feedstock for biodiesel production can avoid those problems. However, the transesterification of waste cooking oil involves some challenges. For example, waste cooking oil usually contains a large amount of free fatty acids (FFAs), which could react with base catalyst (such as NaOH) to form soap, resulting in a decrease in biodiesel conversion efficiency. To cope with this, a two-step process, consisting of esterification with acid catalyst and follow-up transesterification with base catalyst was developed. This two-step process could lower the content of FFAs in waste cooking oil in the first step and also improve conversion of transesterification in the second step. Although homogeneous acid catalyst, such as sulfuric acid, could reach a high conversion in a short time, an extra downstream processing is required to remove the acid catalyst (e.g., water rinse). Therefore, we developed a magnetic spinel as acid solid catalyst supporter to replace homogeneous catalyst in order to simplify the overall process. In the first step, esterification of FFAs content in cooking oil was conducted using the self-made solid acid catalyst, which has similar catalytic ability to that of sulfuric acid, and is also much easier for separation. In addition, the residual lipid can be easily transesterified without any pre-treatment. The self-made spinel-supported catalyst could be regenerated by simple calcination.

© 2014TheAuthors. Published by ElsevierLtd.This is an open access article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of ICAE2014

Keywords: Waste cooking oil, heterogeneous catalyst, biodiesel production, esterification, transesterification

1. Introduction

To find and develop an alternative energy is a major issue to our environment due to the depletion of fossil fuel. Among many kinds of alternative energies, biodiesel can be directly applied to nowadays diesel engines with benefits of low pollutions, high environmental friendliness and sustainability. Thus, biodiesel becomes one of the most promising alternative energy. Waste cooking oil, which is one of the

* Corresponding author. Tel.: +886-275-7575#62651; fax: +886-234-4496. E-mail address: changjs@mail.ncku.edu.tw

1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of ICAE2014

doi: 10.1016/j.egypro.2014.11.1086

best oil sources for biodiesel, will cause problems when conducting transesterification due to its high free fatty acids (FFAs) content. Therefore, a pretreatment of waste cooking oil might be needed to achieve high efficiency biodiesel production from waste cooking oil. For example, an esterification step may be employed to reduce FAAs content and then transesterification is conducted to convert triglyceride into biodiesel. A common homogeneous catalyst, such as sulfuric acid, is excellent for esterification, but the homogeneous catalyst usually remains in the products, causing a negative effect on the subsequent transesterification reaction. As a consequence, more attentions have been paid on the development of heterogeneous catalysts since they have high catalytic activity, can be easier to separate, and possess the potential for repeated uses. The purpose of this research is thus to develop a two-step process to produce biodiesel, combining sequential esterification and transesterification steps, which are catalyzed by self-made magnetic solid acid catalyst and liquid alkaline catalyst, respectively. In the meantime, the best operating conditions for this two-step process was optimized based on the operation cost.

2. Material and Methods

2.1 Synthesis and decoration of magnetic supporter: SrFe2O4

Sr(NO3)2 and Fe(NO3)2.9H2O (Sr/Fe molar ratio = 1/2) were dissolved in DI water first, and then NH4OH was titrated into the solution with vigorous mixing. After that, the precursor obtained by drying the mixture of Sr(OH)2 and Fe(OH)3 was calcinated at 1100oC to obtain SrFe2O4. Following that, SrFe2O4 was mixed with TEOS and NH4OH to synthesize a SrFe2O4/SiO2 core/shell supporter. Finally, SrFe2O4/SiO2 was immersed in a 2M sulfuric acid solution and was then calcinated at 400oC to produce SrFe2O4/SiO2-SO3H. The X-ray diffraction profiles of the resulting spinel carriers are shown in Fig. 1.

2.2 The best temperature conditions for esterification and transesterification

The mixed oil consisting of 20% oleic acid and 80% soybean oil in volume was used to simulate waste cooking oil in the first part of experiments to identify the preferable temperature conditions of the individual reactions. The tests were performed as follows. For esterification, reactants were 10 ml mixed oil and 5 ml MeOH; reaction temperatures were 50, 60, 70, 80, 90, 100, and 110oC for 120 min; catalyst types and doses were SrFe2O4/SiO2-SO3H/mixed oil = 1/10 (w/w) and ^SO^MeOH = 1/100 (w/w). For transesterification, the reactants were 8 ml soybean oil mixed with 5 MeOH; the catalyst was 1.0 wt% NaOH; the temperatures examined were 30, 40, 50, 60, 70, 80, 90, a 100oC; the reaction time was 60 min.

2.3 Examination of the two-step biodiesel production for simulated oil and waste cooking oil

First, 10 ml mixed oil was reacted with 5 ml MeOH using SrFe2O4/SiO2-SO3H or H2SO4 as a catalyst at 100oC for 90 minutes. Following that, the reaction mixture were used for next experiments without any treatment when H2SO4 was used as a catalyst, while for the tests using SrFe2O4/SiO2-SO3H solid catalyst, a magnetic field was applied to remove the solid catalysts from the reaction mixture prior to the next experiments.. In the second step, 5 ml MeOH containing 2 wt% NaOH was added into the reaction mixture resulting from the first step to conduct transesterification at 60oC for 40 min. For comparison, the same procedures were carried out by using waste cooking oil obtained from a fried chicken stallman.

3. Results and Discussion

In this study, four solid acid catalysts based on different spinel, such as CoFe2O4, CuFe2O4, NiFe2O4, and SrFe2O4, were developed. Among them, SrFe2O4/SiO2-SO3H exhibited better catalytic ability on

esterification (Fig. 2). This means that the alkaline earth metal might have positive effect on the sulfonic acid functional groups on the SiO2 shell. Moreover, the recycling test also displays that SrFe2O4/SiO2-SO3H had better stability in catalyzing esterification (Fig. 3). Besides, the XRD profile indicates that the main structure of SrFe2O4 is Sr7Fei0O22 (Fig. 1), and the surface area by BET analysis of SrFe2O4 was 2.3m2/g cat.

To reveal the best operating conditions for esterification and transesterification, a series of experiments were performed. The three-dimensional diagrams given in Figure 4 indicate the effects of the reaction time and temperature on conversions of mixed oil to biodiesel by acid catalysts and soybean oil to biodiesel by NaOH. Consideration both of energy consumption and biodiesel conversion, a reaction temperature of 100oC and a reaction time of 90 min were chosen as the optimal operating condition for esterification. However, for transesterification, the favorable reaction conditions were 60oC for 40 min.

The performance of the two-step biodiesel production of the SrFe2O4/SiO2-SO3H-NaOH and H2SO4-NaOH systems operated under the best operation condition were shown in Fig. 5. The results show that both SrFe2O4/SiO2-SO3H and H2SO4 could completely consume FFAs in the mixed oil and transform them to biodiesel. However, in the following transesterification step, the conversion of triglycerides was different depending on the catalyst used in the first step. The transesterification conversion after esterification by SrFe2O4/SiO2-SO3H was better than that by H2SO4, and the total conversion of the SrFe2O4/SiO2-SO3H-NaOH system was almost 100% but that of H2SO4-NaOH system was just about 90% (Fig. 5). The reason for this could due to the fact that H2SO4 was not removed after esterification, thereby partially consuming NaOH used to catalyze transesterification. This results in an incomplete transesterification because the amount of catalyst (NaOH) was insufficient. On the other hand, SrFe2O4/SiO2-SO3H could be easily removed, so there was no negative effect on the next step.

4. Conclusion

The best operation condition for the two-step biodiesel production catalyzed by SrFe2O4/SiO2-SO3H and NaOH, respectively, was 100oC & 90 min for esterification and 60oC & 40 min for transesterification. The overall conversion of the mixed oil consisting of 20% oleic acid and 80% soybean oil almost achieved 100%. The SrFe2O4/SiO2-SO3H catalyst could be easily separated by applying a magnetic field and be reused many times, thereby having the potential to be commercialized. Moreover, the proposed two-step biodiesel production method is effective in converting FFAs-rich oil (such as waste cooking oil) into biodiesel and can also be applied in practical applications.

5. References

[1] Man Kee Lam, Keat Teong Lee, Abdul Rahman Mohamed, "Homogeneous, heterogeneous and enzymatic SrFe2O4/SiO2-SO3H-NaOH for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: A review," Biotechnology Advances, 28, 19 (2010)

[2]A.S.Silitonga, H.H.Masjuki, et al., "A globalcomparativereviewofbiodieselproductionfrom jatrophacurcas using differenthomogeneousacidandalkalinecatalysts:Studyofphysical and chemicalproperties," RenewableandSustainableEnergyReviews, 24, 20 (2013)

[3]Tianzhong Liu Lin Chen, Wei Zhang, et al., "Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion," Bioresource Technology, 111, 7 (2012)

[4]Yuan-Chung Lin, Po-Ming Yang, et al., "Improving biodiesel yields from waste cooking oil using ionic liquids as catalysts with a microwave heating system," Fuel Processing Technology, 115, 6 (2013)

[5] Zakaria Mana, Yasir A. Elsheikhb, et al., "A Bronsted ammonium ionic liquid-KOH two-stage catalyst for biodiesel synthesis from crude palm oil," Industrial Crops and Products, 41, 6 (2013)

[6] L. Diaz, M. E. Borges, "Low-Quality Vegetable Oils as Feedstock for Biodiesel Production Using K-Pumice as Solid Catalyst. Tolerance of Water and Free Fatty Acids Contents," Agricultural and Food chemistry, 60, 6 (2012)

[7] RaquelDelToro, PetraHernandez, et al., "Synthesis of La0.8Sr0.2FeO3 perovskites nanocrystals by Pechini sol-gelmethod," MaterialsLetters, 107, 4 (2013)

(a) H2SO4 (b) SrFe2O4

Fig. 1 X-ray diffraction profiles of the spinel carrier.

Time (min) Time (min)

Fig. 4 Effect of temperature and operation time on biodiesel conversion (a) H2SO4 was used for the 1st step esterification, (b) SrFe2O4 was used for the 1st step esterification, (c) NaOH was used for the 2nd step transesterification

Fig. 2 Biodiesel conversion using acid catalysts supported on different spinel carriers

Run (times)

Fig. 3 Biodiesel conversion with the solid acid catalyst (SrFe2O4/SiO2-SO3H) after repeated

¿3 40

Fig. 5 Biodiesel conversion of the two-step process using heterogeneous or homogeneous acid catalysts for esterification and NaOH for transesterification. (1) Using H2SO4 as esterification catalyst, (2) using SrFe2O4/SiO2-SO3H as esterification catalyst.