Scholarly article on topic 'Esterification of Free Fatty Acid on Palm Fatty Acid Distillate using Activated Carbon Catalysts Generated from Coconut Shell'

Esterification of Free Fatty Acid on Palm Fatty Acid Distillate using Activated Carbon Catalysts Generated from Coconut Shell Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Procedia Chemistry
OECD Field of science
Keywords
{Biodiesel / "Palm Fatty Acid Distillate" / "biomass waste" / esterification / "coconut shell" / "activated carbon"}

Abstract of research paper on Chemical sciences, author of scientific article — Arif Hidayat, Rochmadi, Karna Wijaya, Arief Budiman

Abstract In the last few years, biodiesel has emerged as one of the most potential renewable energy to replace current petrol-derived diesel. It is a renewable, biodegradable and non-toxic fuel which can be easily produced through esterification of triglycerides (vegetable oils or animal fats) or esterification of free fatty acids (FFAs) with methanol. However, current commercial usage of refined vegetable oils for biodiesel production is impractical and uneconomical due to high feedstock cost and priority as food resources. Low-grade oil, can be a better alternative; however, the high free fatty acids (FFA) content has become the main drawback for this potential feedstock. Solid acid catalysts offer significant advantages of eliminating separation, corrosion, toxicity and environmental problems. Recently, a new strategy of preparing novel carbon-based solid acids has been developed. In this research, the esterification reactions of Palm Fatty Acid Disttillate (PFAD) with methanol, using carbon based solid catalyst from coconut shell activated carbon as catalyst, were studied. The ester preparation involved an esterification reaction, followed by purification. In this study, the activated carbon catalyst catalysts were synthesized by sulfonating the activated carbon using concentrated H2SO4. The physico-characteristics and acid site densities were analyzed by Nitrogen gas adsorption, FT-IR, X-ray fluorescent (XRF), and acid-base back titration methods. The effects of the molar ratio of methanol to oil (6:1 to 12:1), the amount of catalyst (1-10%), and the reaction temperature (40, 50 and 60oC) were studied for the conversion of FFA to optimize the reaction conditions. The optimal conditions were an methanol/PFAD molar ratio of 12:1, the amount of catalyst of 10%wt., and reaction temperature of 60oC.

Academic research paper on topic "Esterification of Free Fatty Acid on Palm Fatty Acid Distillate using Activated Carbon Catalysts Generated from Coconut Shell"

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Procedia Chemistry 16 (2015) 365 - 371

International Symposium on Applied Chemistry 2015 (ISAC 2015)

Esterification of Free Fatty Acid on Palm Fatty Acid Distillate using Activated Carbon

Catalysts Generated from Coconut Shell

Arif Hidayaf, Rochmadib, Kama Wijaya0, Arief Budimanb,d'*

a'hChemical EngineeringDepartment, Indonesia Islamic University, Jalan Kaliurang km 14,5 Ngemplak Sleman Yogyakarta bChemical Engineering Department, Gadjah Mada, Jalan Grafika Bulaksumur Sleman Yogyakarta cChemistry Department, Gadjah Mada, Sekip Utara Bulaksumur Sleman Yogyakarta dCenter for Energy Studies, GadjahMada University, Sekip K1 A, Yogyakarta 55281, Indonesia.

Abstract

In the last few years, biodiesel has emerged as one of the most potential renewable energy to replace current petrol-derived diesel. It is a renewable, biodegradable and non-toxic fuel which can be easily produced through esterification of triglycerides (vegetable oils or animal fats) or esterification of free fatty acids (FFAs) with methanol. However, current commercial usage of refined vegetable oils for biodiesel production is impractical and uneconomical due to high feedstock cost and priority as food resources. Low-grade oil, can be a better alternative; however, the high free fatty acids (FFA) content has become the main drawback for this potential feedstock. Solid acid catalysts offer significant advantages of eliminating separation, corrosion, toxicity and environmental problems. Recently, a new strategy of preparing novel carbon-based solid acids has been developed. In this research, the esterification reactions of Palm Fatty Acid Disttillate (PFAD) with methanol, using carbon based solid catalyst from coconut shell activated carbon as catalyst, were studied. The ester preparation involved an esterification reaction, followed by purification. In this study, the activated carbon catalyst catalysts were synthesized by sulfonating the activated carbon using concentrated H2S04. The physico-characteristics and acid site densities were analyzed by Nitrogen gas adsorption, FT-IR, X-ray fluorescent (XRF), and acid-base back titration methods. The effects of the molar ratio of methanol to oil (6:1 to 12:1), the amount of catalyst (1-10%), and the reaction temperature (40, 50 and 60°C) were studied for the conversion of FFA to optimize the reaction conditions. The optimal conditions were an methanol/PFAD molar ratio of 12:1, the amount of catalyst of 10%wt., and reaction temperature of 60oC.

©2015 The Authors.PublishedbyElsevierB.V. Thisis an open access article under the CC BY-NC-ND license (http://creatiYecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Research Center for Chemistry, Indonesian Institute of Sciences Keywords:BiodiQso[, Palm Fatty Acid Distillate, biomass waste, esterification, coconut shell, activated carbon

* Corresponding author. Tel.: +62-274-902171; fax: +-62-274-902170. E-mail address abudiman@ugm.ac.id

1876-6196 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Research Center for Chemistry, Indonesian Institute of Sciences doi: 10.1016/j .proche.2015.12.065

1. Introduction

Nowadays, the world's total energy output is mainly generated from fossil fuels, however experts have warned about the depletion of this actual source in the near future. Besides, the increasing environmental impact care has imposed restrictions on fuel combustion emissions. These facts have stimulated the alternative sources for fossil fuel development. One of the most promising sources is biodiesel, an alternative diesel fuel derivate from renewable sources [1, 2]. Biodiesel is produced from refined edible oil such as palm oil [3], sunflower [4], soybean [5], and rapeseed [6]. However these feedstocks were not sustainable because of its competition with food thereby increasing both the cost of edible oils and biodiesel. Therefore, low grade feedstocks were studied intensively to replace the edible oil on biodiesel production [7]. The low grade feedstocks have high acid value compared than refined vegetable oil due to presence of high amount of free fatty acids (FFAs). When the amount of FFAs in the feedstocks exceeds 0.5% weight of oils, the use of the alkaline homogeneous technology, which employs sodium hydroxide as catalyst, was not recommended, because a soap making reaction would take place and would consume the catalyst as well as the raw material. Using homogeneous alkaline catalyst also would make more difficult for separation and purification the product of biodiesel process [8]. To overcome this problem, esterification was employed to reduce FFAs on low grade feedstocks. Esterification is one of the most important reactions in biodiesel production where free fatty acids were converted to fatty acid methyl esters (FAME) by using homogeneous acidcatalyst.The traditional homogeneous acid catalysts show a good catalytic activity in biodiesel production. However, the separation of these catalysts from biodiesel requires washing with water which in turn results in loss of FAME, energy consumption, and generates large amounts of waste water. Moreover, these catalysts cause reactor corrosion and are difficult to recover, thus increases the overall biodiesel production cost. The problems associated with the homogeneous acid catalysts can be resolved by using the heterogeneous catalysts in the biodiesel production technology. Heterogeneous acid catalysts simplify the biodiesel production process; where they can be reused repeatedly without any major loss in their catalytic activity, making the process more economical.Recently, biodiesel production using continuous process by reactive distillation column was developed, due to low energy consumption, reduce cost of production and simple process [9-11].

Esterification with solid acid catalyst, including acid zeolites [12], ion-exchange resins [13], sulfonic acid-modified mesostructured silica [14], tungsten oxide zirconia [15], sulfonated polymers (Amberlyst-15) [16], lanthanum (La3+) and HZSM-5 [17] and sulfated zirconia [18] has been carried out. However, most of the catalysts reported so far utilized complex and expensive synthesis routes, demonstrated poor reusability and were non-biodegradable.Carbon-based solid acids are considered good catalysts for many organic reactions due to their chemical inertness, good mechanical strength and thermal stability[19, 20]. Carbon materials are relatively cheap, widely available and can be easily functionalized with -SO3H groups through simple treatment with concentrated sulfuric acid [21].Sulfonated carbons are the most promisingsolid acids and their use have been demonstrated in many acid catalyzed reactions including that of FFAs esterification [22, 23].

The high cost of biodiesel is the key issue for a large scale application of biodiesel as compared to that of conventional petroleum based diesel. In this context, palm fatty acid distillate(PFAD)is considered to be a promising feedstock where the biodiesel production cost could be effectively reduced to 60-70% by using this low cost raw material. During the refining of palm oil, PFAD which has a low value was generated during the fatty acid stripping and deodorization stages. PFAD is potentially a valuable, lowgrade feedstock for the production of biodiesel.The production of biodiesel from PFAD will not only avoid the competition of the same oil resources for food and fuel but will also solve the problems associated with PFAD disposal.

In this paper, the development of activated carbon catalyst as the heterogeneous acid catalyst for esterification of FFAs on PFAD was studied. The results of this research will promote the environmentally friendly biodiesel production process.The activated carbon (AC) catalysts have been characterized bythe nitrogen adsorption, Fourier Transform Infra-RedSpectroscopy (FT-IR), elemental analysis using X-Ray Fluorosence (XRF)and back titration to determine acid densities. The performance of this catalyst will be evaluated in terms of methanol to PFAD molar ratio, catalyst amountand reaction temperature. The reusability of the catalyst also would be studied.

2. Methodology

2.1. Catalyst synthesis

The AC catalyst samples were prepared via concentrated sulfuric acid. The activated carbon weresulfonated according to the method of Toda et al. [19]. 100 mL of concentrated sulfuric acid was added to 10 g of activated carbon in a 500 mL round bottom flask. The mixture was heated to 150oC for 12 hours. After heating, the slurry was placed in cool distilled water and filtered. The activated carbon catalyst was washed with 80oC distilled water until the wash water was neutral and free from sulfate ions. Following filtration, the activated carbon was dried in an oven at 70°C for approximately 1 h.

2.2. Characterization of the AC catalyst

The surface area and pore size of the AC catalyst were analyzed by gas sorption analyzer. The acid densities of the carbons were determined by titration method as follows: 0.04 g of a carbon sample was added into anaqueous solution of sodium hydroxide (0.01 mol.L-1, 20 mL). Then,the suspension was dispersed by stirring with a magnetic stirrer for4 h uniformly, at room temperature. After centrifugal separation,the supernatant solution was titrated by an aqueous solution ofhydrochloric acid (0.01 mol.L-1) using phenolphthalein as an indicator. The -SO3H densities of sulfonated carbons were estimatedusing acid-base back titration methods by assuming that all sulfur present in thecarbon samples was due to -S03H groups.

2.3. The performance test

Esterification of PFAD using the AC catalysts was performed in batch runs on a hot plate with a magnetic stirrer at different process conditions. The samples were analyzed by titration procedure for the evaluation of free residual acidity. Once the sample was taken from the reactor, it was washed with water in order to stop the reaction and separates the catalyst and the alcohol from the oil phase. To improve the separation of the phases, the sample was centrifuged for 20 min. A weighted amount of the sample was dissolved in ethanol and diethyl ether in order to be able to make the titration analyses, and some drops of phenolphthalein as indicator were added to the system to be able to measure the conversion. The titration was done with a 0.02 N alkaline solution of KOH. The acid value of the samples can be calculated using the following equation:

V. 1000.MW.C

wherea is the acid value of the mixture, V is volumeof solution employed for titration,MW is molecular weight of the

solution,C is concentration measured by titration andrnis weight of sample.

And using this definition, the conversion of free fatty acid was calculated using this equation:

wherea, is the initial acidity ofthe mixture and at is the acidity at "i" time.

3.Results and Discussion

3.1. Characterization ofcatalyst

The specific surface area and pore size diameter of activated carbon and AC catalyst were reported in Table 1. The specific surface area of activated carbon was 355m2/g while for the AC catalyst was andl63 m2/g. After sulfonation the specific surface areas decreased in respect to activated carbon, which indicates the successful linking of sulfonic groups on surface. In the other hand, pore size diameter of activated carbon was smaller compared than the AC catalyst. Sulfonation clearly increased the acid density as measured by base titration and the sulfur content of

the carbon (Table 1). The acid density that measured by back titration method, was significantly larger than that indicated by the sulfur content, suggesting that sulfonation using H2S04 not only created sulfonic acid groups, but created additional weak acid groups (e.g., COOH). According to Table 1, the ratio of O and S against C are high in the catalyst suggested that the catalyst consist of carbon sheets that are high in SO3H, COOH, and OH functional groups.

Table l.Surface area and acid properties of the samples.

Sample Surface area (m2/g) Average pore size radius (nm) Elemental composition (wt%) Acid density (mmol/g)

C O S Total S03H

Activated carbon 355 2.39 54.26 44.97 - 0.12 -

AC catalyst 163 2.87 73.91 21.12 4.45 2.24 1.93

FTIR spectra of activated carbon and AC catalyst were shown in Fig. 1. The vibration band at 1040 cm"1 is attributed to S=0 symmetric stretching vibration. This band is not visible in the FT-IR spectrum of the activated carbon and it is proof of the presence of SO3H groups in the sulfonated samples. The band at 1719 cm"1 was assigned to C=0 stretching vibration band; the broad hide the band centered at 3440 cm"1 assigned to the O-H stretching modes of the -COOH and phenolic OH groups. The band at 1610 cm"1 was assigned to the aromatic like C=C stretching modes in polyaromatic material.

4000 3500 3000 2500 2000 1500 1000 500 Wavelength (an'1)

Fig. l.The FT-IR spectra of activated carbon and AC catalysts.

3.2. Effect of molar ratio

The esterification reaction between PFAD and methanol followsa reversible path. Higher equilibrium conversion can only beobtained if the backward reaction is minimized. One waysto reduce the rate of backward reactionwas to use one of the reactants in excess. In this study, the using excess methanolhas been employed to shift the reaction towards theformation of FAME. In order to study the influence of the molarratio of methanol to PFAD on the conversion of FFA,experiments using the AC catalyst had conducted. In this study the molar ratio of methanol to PFAD was varied from 6:1 to 12:1. Fig.2shows the effect of the molar ratio on the conversion of the FFA content of PFAD. It has been seen that yield of the process increases with increase in molar ratioof methanol to PFAD. The conversion of FFA was 70% for a molar ratio of methanol to PFADof 6:1. The conversion of FFA gradually increased to 76and 88% when the molar ratio of methanol to PFAD was8:l and 10:1, respectively. With further increase in molar ratio the conversion efficiency more or less remains the same. The highest conversion of FFA was achieved at 91% on the molar ratio of methanol to PFAD of 12:1.

6:1 8:1 10 : 1 12 : 1 molar ratio methanol to PAFD

Fig.2. Effect of molar ratio on conversion of FFA. 3.3. Effect ofthe amount ofcatalyst

Esterification reactions usually have low equilibrium constantsand require the addition of a catalyst in order to obtain high conversion.To study the effect ofthe amount ofcatalyst loading on FFA conversion, the reaction was carried out at four different amountof catalyst (1, 2.5, 5, and 10%wt. of PFAD) used while the reaction conditions were kept constant. The results are shown in Fig.3.It can observed that there is a significant increase in FFA conversion as the amountof catalystincreased from 1 to 10% under identical conditions. The conversion of FFA was 72% atthe amountof catalystl%wt. of PFAD, and this gradually increased to 77% whenthe amountof catalyst was increased to 2.5%. With a further increase in theamountof catalystto 5%wt. of PFAD, the conversion of FFA was 84%.The highest conversion of FFA was achieved at91% when the amountof catalystlO%wt. of PFAD. The increase in the reaction rate wasdue to the increase in the total number of acid sites available forthe reaction with increasing catalyst amount. Therefore, the 10%weight ofthe amount of PFAD was considered optimum for this study.

•35 80

1% 2.5 5% 10 Catalyst amount (%wt. of PFAD)

Fig.3.Effect ofthe amount ofcatalyst on conversion of FFA.

3.4. Effect ofreation temperature

Temperature is one of the most important variables affectingthe conversion of FFA. In order to optimize the reactionconditions, the effect of different reaction temperature on theesterification, three reaction temperatures such as 40, 50 and 60oC have been selected to investigate the influence of reaction temperatures on the esterification

of PFAD with methanol and theresults were shown in Fig. 4.This figure shows that the FFA conversion increases from 64to 82% as the temperature increases from 40 to 60oC. This was because increase intemperature caused higher molecule motion speed and masstransfer rate. A high temperature could greatly accelerate thereaction rate and improve the mass transfer limitation betweenreactant and catalyst.

40 50 60

Reaction temperature (°C)

Fig.4.Effect of reaction temperatures on conversion of FFA.

3.5. Catalyst reusability

The reusability and stability of heterogeneous catalyst are the most important criteria in the selection of appropriate catalyst for industrial application. In heterogeneouscatalyst application for biodiesel preparation, it is important to ensurethat the active species are not leached from the solid support of thecatalyst during the process. In this study, the reusability of AC catalyst was determined by carrying out three esterificationreaction cycles. The following reaction conditions were applied:reaction time of 2 h, methanol to PFAD molar ratio was 1:12, catalystamount of 10% weight of PFAD, reaction temperature of 60°C, andstirring speed was at 500 rpm.For fresh catalyst the maximum conversion was 91% as shown in Fig. 5. For subsequent reaction, the biodiesel yield was decreased to 74%, and for the third cycle the yield of biodiesel was just only 51%. The decrease of biodiesel yield occurred because some of the active species in AC catalyst were leached or deactivated during esterification reaction of FFA in PFAD with methanol.

•S3 80

1% 2.5 5% 10 Catalyst amount (%wt. of PFAD)

Fig.5.Reusability of the AC catalyst.

Conclusion

The effects of the molar ratio of methanol to PFAD (6:1 to 12:1), the amount of catalyst (1, 2.5, 5, and 10%wt. of

PFAD)and the reaction temperature (40, 50 and 60°C) were studied for the conversion of PFAD to optimize the

reaction conditions. The optimal conditions were an methanol/PFAD molar ratio of 12:1, the amount of catalyst of

10%wt, and reaction temperature of 60°C.

References

[1] Borges ME, Diaz L. Recent developments on heterogeneous catalysts for biodiesel production by oil esterification and transesterification reactions: A review. RenewSustainEnergRev2012;16:2839-49.

[2] Fatimah I, Hidayat A, Setiawan KH. Preparation of aluminium pillared clay from Indonesian montmorillonite and its catalytic activity in bio-oil cracking^s/a« J. Chem. 2010;22(5):3793-801.

[3] Chen GY, Shan R, Shi JF, Yan BB.Transesterification of palm oil to biodiesel using rice husk ash-based catalysts.FuelProcessTechnol 2015;133: 8-13.

[4] Lopez AJ, Morales IJ, Gonzalez JS, Torres PM. Biodiesel production from sunflower oil by tungsten oxide supported on zirconium dopedMCM-41 silica. JMolCatal A: Chem 2011;335:205-9.

[5] Nasreen S, Liu H, Skala D, Waseem A, Wan L. Preparation of biodiesel from soybean oil using La/Mn oxide catalyst. Fuel ProcessTechnol 2015; 131:290-6

[6] Wang B, Li S, Tian S, Feng R, Meng Y. A new solid base catalyst for the transesterification of rapeseed oil to biodiesel with methanol ..Fwe/ 2013;104:698-703.

[7] Kawentar, WA, Budiman A. Synthesis ofbiodiesel from second-used cooking oil. EnergyProc20!3;32:l90-9.

[8] Marchetti JM, Miguel VU, Errazu AF. Heterogeneous esterification of oil with high amount of free fatty acids. Fwe/2007;86:906-10.

[9] Budiman A, Ishida M. Relationship between distillation column and distribution of exergy losses and driving forces, JChem Eng Japan 1997, 30(5), 966-9.

[10] Budiman A, Sutijan, Sawitri DR. Graphical exergy analysis of retrofitted distillation column. IntJExergy, 2011;8(4):477-93.

[11] Kusumaningtyas RD, Rochmadi, Purwono S, Budiman A. Graphical exergy analysis of reactive distillation column for biodiesel production. IntJExergy 2014;l(4):447-67.

[12] Ozbay N, Oktar N, Tapan NA. Esterification of free fatty acids in waste cooking oils (WCO): Role of ionexchange resins.Fwe/2008; 87:10-11:1789-98.

[13] Melero JA, Bautista LF, Morales G, Iglesias J, Vazquez RS. Biodiesel production from crude palm oil using sulfonic acid-modified mesostructured catalysts. ChemEngJ2010;161:323-31.

[14] Park YM, Lee JY, Chung SH, Park IS, Lee SY, Kim DK. Esterification of used vegetable oils using the heterogeneous W03/Zr02 catalyst for production ofbiodiesel. BioresourTechnol20l0;l0l:59-6l.

[15] TalukderMMR,Wu JC, Lau SK, Cui LC, Shimin G, Lim A. Comparison ofNovozym 435 and Amberlyst 15 as heterogeneous catalyst for production ofbiodiesel from palm fatty acid distillate. EnergyFuels2009;23>:\:\-4.

[16] Vieira SS, Magriotis ZM, Santos NAV, AA Saczk, Hori CE, Arroyo PA. Biodiesel production by free fatty acid esterification using lanthanum (La3+) and HZSM-5 based catalysts. BioresourTechnol2013;33:24$-55.

[17] Li Y, Zhang XD, Sun L, Zhang J, Xu HP. Fatty acid methyl ester synthesis catalyzed by solid superacid catalyst S02"4 /Zr02-Ti02/La3+. ApplEnerg 2010;87:156-9

[18] Lou WY, Zong MH, Duan ZQ. Efficient production ofbiodiesel from high free fatty acid-containing waste oils using various carbohydrate-derived solid acid catalysts. BioresourTechnol2QQ%;99:%152-'&.

[19] Toda M, Takagaki A, Okamura M, Kondo JN, Hayashi S, Domen K, Green chemistry - biodiesel made with sugar catalyst. Nature 2005;438:178.

[20] Hidayat A, Rochmadi, Wijaya K, Hinode H, Budiman A, Comparison of activated carbon prepared from Indonesian forest and agricultural residues.Asian /C^em2013:25:3:1569-79.

[21] Zong MH, Duan ZQ, Lou WY, Smith TJ, Wu H. Preparation of a sugar catalyst and its use for highly efficient production of biodiesel. Green Chem 2007;9:434-7.

[22] Guo F, Xiu Z, Liang Z. Synthesis of biodiesel from acidified soybean soapstock using a lignin-derived carbonaceous catalyst. ApplEnerg 2012;98:47-52.