Biodiesel Production from Palm Fatty Acids by Esterification using Solid Acid Catalysts

Transcription

1 Biodiesel Production from Palm Fatty Acids by Esterification using Solid Acid Catalysts Tanapon Tanapitak 1,3, Nawin Viriya-empikul 2,* and Navadol Laosiripojana 1,3 1 The Joint Graduate School of Energy and Environment, King Mongkut s University of Technology Thonburi, Bangkok 2 National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), 111 Thailand Science Park, Phahonyothin Road, Pathumthani Center for Energy Technology and Environment, Ministry of Education, Thailand * Corresponding author: Tel.: ext 6570, Fax: , address: nawin@nanotec.or.th Abstract: The esterification of palm fatty acid distillate (PFAD), a by-product from palm oil industry, in the presence of solid acid catalyst was studied in the present work. A suitable catalyst that is active with good selective and high stablility was determined under the mild conditions. Various solid acids (ion-exchange resins, zeolites, tungsten oxide zirconia, and mixed metal oxides) were selected as catalysts in the esterification of palm fatty acid distillate with methanol. It was found that among all solid acid catalyst, the reaction in the present of Amberlyst 15 (ion-exchange resins) at 120 C, 120 min, 1:55 (oil:methanol), 500 rpm and 1.5% wt of catalyst shown the highest fatty acid methyl ester (FAME) yield 97.8%. Furthermore, it required shorter time, lower temperature and less amount of alcohol compared to the reactions without catalyst. Keywords: Esterification, Ion-exchange resin, Zeolite, Tungsten oxide zirconia, Metal oxide and Palm fatty acid distillate 1. INTRODUCTION Biodiesel is the one of an alternative fuel for petroleum-based fuel substitution, which can be produced from the tranesterification of vegetable oil or animal fat with short chain alcohols. Currently, palm oil is the major feedstock for biodiesel production in Thailand due to its availability and good conversion efficiency. Typically, crude palm oil (CPO) contains high amount of free fatty acids (FFAs) more than 0.5% of free fatty acid (FFA), which easily converts to soap by sponification during the transesterification reaction and consequently reduces the overall yield of biodiesel [1]. And they will make more difficult separation and purification of the biodiesel. To avoid the soap formation, most of FFAs in CPO must be firstly treated or removed (as called palm fatty acid distilled or PFAD). Recently, some researchers have suggested that the conversion of PFAD to fatty acid methyl ester (FAME) by esterification reaction (1) is a good procedure to reduce the production cost of biodiesel and making biodiesel enable to compete economically with petroleum-based fuel. Typically, the esterification reaction is an acid-catalyzed process such as sulfuric acid and hydrochloric acid. But the main drawback of the acid homogenous catalyst are high corrosion in system and difficulty for separation of biodiesel; hence, extensive washing is usually required to remove all acid compounds from the biodiesel product and making large amount of the overall production cost. In order to solve these problems, heterogeneous catalyst has widely been used in the production due to its easily regenerated and have a less corrosive nature, leading to safer, cheaper and more environment-friendly operations [2]. Free fatty acids (FFAs) + methanol Fatty acid methyl esters (FAMEs) + water (1) In the present work, we aimed to study the esterification of PFAD in the presence of solid acid catalyst i.e. ionexchange resin, zeolites, tungsten oxide zirconia, and mixed metal oxides. The highest yield of biodiesel composition among all catalyst was studied under the limited temperature and the FAME composition was tested by Gas chromatography (GC) with Flame ionization detector (FID). Then the optimization condition of the selected catalyst on the esterification reaction in term of temperature, time, oil per alcohol ratio, agitation and amount of catalyst were investigated in this research and the low cost of the production was determined. 2. METHODS 2.1 Chemical PFAD sample used in this study was provided by Patum Vegetable Oil Co. Ltd, Thailand. It consists of 93.5 wt.% free fatty acid (FFA)(44.8% palmitic, 35.6% oleic, 7.9% linoleic, 3.0% stearic, 1.2% myristic, 0.5% tetracosenoic, 0.2% linolenic, 0.1% ecosanoic, 0.1% ecosenoic, and 0.1% palmitoleic acid) and the rest elements are triglycerides, diglycerides (DG), monoglycerides (MG) and traces of impurities.methyl ester standard (methyl palmitate, methyl stearate and methyl oleate) were obtained from Wako Chemicals, USA. Commercial grade methanol (95%) and analytical grade hexane (99.9%) ware purchased from Fisher scientific, UK. And palmatic acid (98%) was obtained from Sigma (Steinheim,Germany). 95

2 2.2 Catalyst preparation The ion exchange resin (e.g. Amberlyst 15 and Amberlyst 16) was purchased from Sigma (Steinheim, Germany). Mesoporous material RH-MCM-41 Was modified from [3]. Tungsten oxide zirconia was synthesized by two methods. First, WO 3 -ZrO 2 was prepared by wet impregnation method using ZrO 2 (Aldrich, 99%) as the support and ammonium (para) tungstate hydrate solution as tungsten precursor. ZrO 2 powder was added and the mixture was stirred for 8-10 h. The excess of water was evaporated to dryness and the obtained product was dried at 95 C and calcined at 700 C at the rate of 10 C/min in static air for 3 h. Second, WO 3 -ZrO 2 was prepared by co-precipitation method. The ammonium (para) tungstate hydrate solution was placed into a 0.5-L container, and the other two solutions (zirconium chloride octahydrate and ammonium hydroxide) were added slowly to the former one. A constant and vigorous agitation was maintained during the precipitation procedure. The catalyst was washed and dried at 95 C and calcined at 700 C at the rate of 10 C/min in static air for 3 h. Mixed MgO-ZrO 2 was synthesized using the sol-gel technique described by Aramendia et al (2004). The catalyst with Mg/Zr atomic ratio of 3.3 was prepared by adding Mg(NO 3 ) 2 6H 2 O and ZrOCl 2 8H 2 O to H 2 O. Then, the mixture was stirred and NaOH solution was added until ph = 10. The magnesiazirconia gel was aged, vacuum-filtrated, oven dried (110 C) and calcined in air at 600 C for 3 h. The solid was used to carry out aldol-condensation reactions. 2.3 Catalyst characterizations Measurements of BET surface area, cumulative pore volume and average pore diameter were performed by N 2 physisorption technique using Micromeritics ASAP 2020 surface area and porosity analyzer. NH 3 - and CO 2 -TPD were used to determine the acid-base properties of catalysts. The amount of acid-base sites on the catalyst surface was calculated from the desorption amount of NH 3 and CO 2. It was determined by measuring the areas of the desorption profiles obtained from the Chemisorption System analyzer. 2.4 Study of esterification reaction The study of biodiesel production by esterification process was consisted of 2 parts. In the first part, the esterification was tested at the same operation condition in the presence of different types of solid acid catalyst (e.g. Amberlyst 15, Amberlyst 16, RH-MCM-41, Tungsten oxide zieconia and Mixed MgO-ZrO 2 ) with an aim to determine the suitable catalyst that making the highest yield of FAME production for further study. From the second part, the esterification was studied by selected catalyst to find the effect of operating condition with 5 important parameters (e.g. temperature, acid per oil ratio, mount of catalyst, time and agitation). A batch type reactor was applied to study the esterification reaction in the present work. The first step, palmatic acid (98%) was use instead of PFAD because of palmatic acid is a major component in PFAD. Palmatic acid was firstly melted at 65 C and mixed with methanol (45:1-60:1 methanol per acid ratio), The mixture was charged into the vessel and the catalyst was added to the mixture ( wt.%). The reaction was then taken place under specified reaction times ( min) with a constant stirring ( rpm) and temperatures ( C). After reaction, the product was cooled down and separated into three phases. The upper phase was water and methanol, the middle phase was methyl ester, and the lower phase was solid catalyst. The solid acid catalyst was taken out of the sample by filtration. Lastly water and methanol was removed from the product by heating at 100 C for 3 hrs. Then, the methyl ester was analyzed. 2.5 Analysis Methyl ester content in the products was measured by GC analysis according to the EN test method. At first, standard (STD) solution was prepared as 10 mg/ml of methyl heptadecanoate (C17:0) with heptane solution. The sample (250 mg) was added in the standard solution (5 ml). The mixed sample with STD solution was analyzed by GC. The methyl ester content was determined by the equation (2). Methyl ester content (%) = A A s x C s V s x 100 (2) A s m where A = summation of peak areas of methyl esters (C14:0 C24:1), A s = peak area of methyl heptadecanoate (STD material), C s = concentration of STD solution (10 mg/ml), V s = volume of STD solution (5 ml), and m = amount of sample (250 mg). 3. RESULT AND DISCUSSION 3.1 Catalytic reactivity on esterification of palmatic acid by difference types of catalyst. All solid acid catalysts (e.g. Amberlyst 15, Amberlyst 16, RH-MCM-41, Tungsten oxide zirconia and Mixed MgO- ZrO 2 ) was tested on esterification process by using the same condition (e.g. 120 C, 1:50 acid per oil ratio, 1.5% wt of catalyst, 120 min and 500 rpm) to find the suitable catalyst for the reaction. Table 1 shows the reaction reactivity in term of FAME yield. It can be seen among all catalyst Amberyst 15 provides the highest yield of 96%, which is 96

3 relatively higher than Amberlyst 16 (87.6% of yield). In addition to that the esterification by using RH-MCM-41, tungsten oxide zirconia, and mixed MgO-ZrO 2 as catalysts shows no reaction. Table 1 The FAME production yield from the esterification of PFAD using different solid acid catalysts. Type of catalyst % FAME Amberlyst Amberlyst MCM 41 WOxZrO2 (impregnation) WOxZrO2 (co-precipitation) Mixed MgO-ZrO Catalyst characterization The specific surface area (m 2 /g), porosity (%), and acid content (mmol H + /gcat) of Amberlyst 15 and Amberlyst 16 are summarized in Tables 2 and 3. Table 2 Physical properties of amberlyst 15 (dry) Shape beed Surface (m 2 /g) 55 Average pore diameter (Aº) 300 acid content(mmol H + /gcat) 4.7 Table 3 The physical properties of amberlyst 16 (wet) Shape beed Surface (m 2 /g) 30 Average pore diameter (Aº) 250 acid content(mmol H + /gcat) Effect of operating conditions on the esterification of palmatic acid Based on the above results, it can be seen that Amberlyst 15 was highly active among all catalysts tested. Therefore, Amberlyst 15 was selected for optimizing the operating conditions to maximize the yield of FAME production. Firstly, the effect of methanol per oil was studied by varying the ratio from 45:1-60:1. As seen in Fig. 1, the yield of FAME production increases with increasing the methanol per acid ratio from 45:1 to 55:1. Theoretically the esterification reaction requires one mole of alcohol and fatty acid to produce one mole of fatty acid ester and water. Nevertheless after increasing amount of alcohol, the equilibrium was been shifted from left-hand side to right-hand side and making more yield of FAME production. But after increasing alcohol per acid ratio to 60:1 the FAME composition slightly decrease to 88.2% because the large excess of methanol will cause flooding of the active sites and making the complexation of the fatty acid protonated at the active sites. However, the use of too high amount of alcohol could also increase the cost of biodiesel production; hence the optimization of required alcohol must be intensively considered. In Fig. 2, it can be seen that the yield of FAME production increases considerably with increasing the catalyst (Amberlyst 15) to PFAD mass ratio from 0.0 wt% to 1.5 wt%. The optimum catalyst loading for this reaction was 1.5 wt.%. This result can be explained as follows: the reaction will be enhanced by increasing catalyst loading to increase the proton concentration in the interface, and making more FAME formation. As for the effect of reaction time, the results in Fig. 3 indicate that the reaction rate increase with increasing reaction time from min and giving the yield of FAME production of 96% for 120 min. Regarding to the effect of the reaction temperature, it can be seen in Fig. 4 that the higher temperature produces higher yield of FAME production. Nevertheless, it should be noted that the temperature of the reaction is limited at 160 C because Amberlyst 15 could been collapsed above this temperature [4]. Lastly, Fig 5 presents the effect of agitation on the yield of FAME production; it was observed that the optimum agitation for the reaction occurred with 500 rpm which contain the yield of biodiesel product of 96%. At higher agitation (e.g. 700 rpm and 900 rpm), the yield of FAME production decreases to 86% and 87.2% respectively. It can be explained that the yield of FAME product reduce with increasing mixing speed from 500 rpm to 700 rpm and 900 rpm because inside reactor maybe occurred the dead-end at the edge after higher mixing speed. 97

4 Fig. 1 Effect of methanol to acid molar ratio on the yield of FAME production from esterification of palmatic acid at 120 C, 1.5 % wt of Amberlyst 15, 120 min and 500 rpm. Fig. 2 Effect of catalyst loading on the yield of FAME production from esterification of palmatic acid at 120 C, 50:1 methanol per oil ratio, 120 min and 500 rpm. Fig. 3 Effect of reaction time on the yield of FAME production from esterification of palmatic acid at 120 C, 50:1 methanol per oil ratio, 1.5% wt of Amberlyst 15 and 500 rpm. 98

5 Fig. 4 Effect of reaction temperature on the yield of FAME production from esterification of palmatic acid at 120 min, 60:1 methanol per oil ratio, 1.5% wt of Amberlyst 15 and 500 rpm. Fig. 5 Effect of agitation on the yield of FAME production from esterification of palmatic acid at 120 min, 50:1 methanol per oil ratio, 1.5% wt of Amberlyst 15 and 120 C. 4. CONCLUSION FAME could be efficiently produced from the esterification of palmatic acid in the presence of solid acid catalyst. Among all solid acid catalysts (e.g. Amberlyst 15, Amberlyst 16, RH-MCM-41, Mixed Mg/Zr and Si/Al), Amberlyst 15 shows the highest yield of biodiesel product. The optimum conditions for esterification reaction by using Amberlyst 15 was found at the reaction temperature of 120 C, reaction time of 120 min, methanol per oil ratio of 55:1, catalyst concentration of 1.5% wt and agitation of 500 rpm, from which provides the FAME yield of 97.8%. It should also be noted that higher amount of FAME can be produced when larger portion of alcohol was used. 5. REFERENCES [1] Ma, F., Clements, L.D. and Hanna, M.A. (2009) The effect of mixing on transesterification of beef tallow, Bioresource Technology, 69, pp [2] Cardoso, A.L., Neves, S.C.G. and da Silva, M.J. (2003) Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl 2 : A Kinetic Investigation, Energies, 1, pp [3] Chumee, J., Grisdanurak, N., Neramittagapong, A. and Wittayakun, J. (2007) Characterization of platinum iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation, Sci. Technol. Adv. Mater,