Biodiesel production from waste frying oils and animal fat over heterogeneous basic catalysis

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1 Biodiesel production from waste frying oils and animal fat over heterogeneous basic catalysis Mónica Catarino Instituto Superior Técnico, Lisboa, Portugal February 2017 Abstract Biodiesel, free fatty acids methyl esters, was produced from pork lard and waste frying oils in order to improve its sustainability. The transesterification was carried out using Ca based catalysts obtained from calcium rich alimentary wastes. Mollusk and crustaceous shells were grounded, and calcined for 3h at 800 C. The obtained white materials were reduced to a fine powder using an agate mortar. The XRD pattern of fresh catalyst revealed a mixture of nanno crystalized lime (19 nm) and calcite (31 nm). The methanolysis tests were carried out for 150 min using 5% (W/W) catalyst (fat basis) at methanol reflux temperature. IPA was used as a co-solvent in order to reduce the immiscibility between phases. The obtained data showed that co-processing lard/soybean oil mixtures reduces the negative effect of acidity on the performance of calcium catalyst. IPA as a co-solvent has a positive effect on catalyst activity for high methanol/ipa ratios. Keywords: Biodiesel, pork lard, soybean oil, CaO catalysts, co-solvents, deactivation 1. Introduction Modern society energetic consumption growth, global warming and socio-economic issues related to the instability of oil and derivates market prompt the search for fossil fuel renewable substitutes. Biodiesel, a mixture of fatty acid methyl esters obtained by the methanolysis of triglycerides in the presence of a catalyst, is referred as a eco-friendly, viable substitute for fossil diesel [1]. Life cycle analysis of biodiesel showed that its usage allows the reduction of CO 2 emissions by 78%, being this one major greenhouse gas [2,3]. Nonetheless, NOx emissions grows by 5% when compared with fossil diesel [4]. This disadvantage can be overcome by small modifications in diesel motors [5]. Nowadays, biodiesel is produced through a homogeneous basic catalyzed batch process [6] and use as main feedstock vegetable oils, usually edible ones. This raw materials prices, accouting between 60% and 70% of biodiesel production costs, together with process complexity make this fuel more expensive than fossil fuel [7, 8]. In fact, biodiesel production is only viable when Brent price rises to US$70 or US$80 (Figure 1, which data was obtained from [9]) [10]. The increase in world population will tend to make feedstock issue worse because more arable lands will be need [11]. Additionally, vegetable oils are limited by seasonal availability [12]. Furthermore, biodiesel production growth (Figure 2, which data was obtained from [13]) will also increase the use of arable lands to oilseeds cultivation. All this will lead to a biodiesel versus food competition which could result in the loss of biodiversity, not only because deforestation but also due to usage of ecologically relevant areas. In this scenerio biodiesel will have a negative impact in ecosystems [8]. In order to overcome this problem, waste frying oil (WFO) and animal fat, low grade fats, can be used to produced cheaper and more sustainable biodiesel [14]. Recently the use of animal fats as biodiesel feedstocks was intensified. Besides, despite the high FAME yield, homogeneous catalysts are not truly suitable for biodiesel production since their easy separation and reuse cannot be achieved. In addition, the biodiesel purification steps, with this kind of process, is complex, expensive, and generates a huge amount of wastewater [8, 15]. Concerning to the solution of the above stated, heterogeneous catalysts are seen as a viable option due to their easy separation of the reaction mixture, which allows their reuse and thus the reduction of biodiesel production cost [8, 16]. In addition, heterogeneous catalysts prevent process steps related with neutralization of the biodiesel and glycerine 1

2 Figure 1: Brent FOB price in European market, between January, and August, Data from [9, 10]. phases, reducing the wastewater, and avoid contamination of reaction products. In fact, the glycerol phase of heterogeneous processes has 98 % purity, in contrast to a homogeneous one that can not exceed 80 % [16 18]. Other advantages of heterogeneous catalysts are their non-corrosive and non-toxicity, both problems associated to homogeneous catalysis [19]. Although their great advantages, heterogeneous basic catalysts promote soap formation during the methanolysis of low grade fats since these feedstocks have more free fatty acids (FFA) than semi-refined vegetable oils [20 22]. The acid value of the raw material is related to the FFA content, and for more than 1 mgkoh/g fat the efficiency of the reaction is affected. For low grade fats this value is relaxed to 2 mgkoh/g fat and may even reach 10 mgkoh/g fat [23, 24]. The acid value for different biodiesel feedstocks are presented in Table 1. Heterogeneous Ca-based catalysts, prepared from shells of molluscs and crustaceans by calcination, are referred to be promising catalysts for alcoholysis of fats [7, 25] since they are cheap, environmentally harmless and their catalytic performance can be improved by a small amount of water, therefore becoming suitable for the methanolysis of low grade fats [16, 26]. Using WFO, animal fat and Ca-based catalysts from food wastes sources could help solving both the higher price of biodiesel production and the disposal of food wastes, which is also a problem for modern society [27]. Figure 2: Consumption of biodiesel in the transport sector for the Europe of 27, according to the national action plan of each country. Data from [13]. Table 1: Acid values for different biodiesel feedstocks. Adapted from [17, 22]. Feedstock Acid value (mgkoh/g fat ) Refined vegetable oil <0,1 Crude vegetable oil 0,6-1,4 WFO 4-14 Animal fat The use of heterogeneous catalysts add a third 2

3 phase to the system, which hinder mass transfer, slowing down the reaction, hence reducing FAME yield [28]. An increase in the reaction temperature would improve the miscibility of the different phases. However, a 10 C increase only improve miscibility by 2 % or 3 %. The energy consumption of this approach would overcome the benefits [29, 30]. The addition of a co-solvent to the reaction mixture would be able to promote reaction components miscibility [29]. The main concern associated with this solution is the increased complexity of the phase purification system and recovery of the co-solvent. In order to overcome these drawbacks, the choice of the co-solvent should lie in a compound whose boiling point is close to that of the alcohol used in transesterification [2]. Several researchers used dimethyl sulfoxide (DMSO), ethanol, methyl tert-butyl ether (MTBE), and recently, n- hexane and acetone as co-solvents [2,14,30 33]. For methanolysis reactions, THF is usually chosen [29]. Additional concerns regarding the hazard level of the most commonly used co-solvents are frequently raised [2, 34]. Notwithstanding, for THF, recent studies indicate that it does not pose a hazard to humans or the environment. The use of isopropyl alcohol (IPA) is not often mentioned, with the exception of Lee et al. (1995) [35] whom studied oils and fats transesterification using branched-chain alcohols. More recently, Roschat et al. [32] studied the effect of several co-solvents on FAME yield, concluding that the use of IPA allows an increase in FAME yield. The present work focuses on sustainable biodiesel production using low grade fats (lard and WFO) over heteroregenous basic catalysts from Ca rich food wastes. 2. Experimental 2.1. Preparation and Characterization of the Catalysts Calcium based catalysts were prepared using food wastes, such as shrimp, crustaceans and eggs shells, and cuttlebone. The collected shells were washed, dried, crushed and finally calcined at 800 C for 3h in a muffle. After calcination the white powder was carefully grounded in an agate mortar to obtain a fine granulometry. The powdered raw materials were characterized by X-ray diffraction and thermogravimetry under air. The thermal degradation profiles were used to choose the calcination temperature. The fresh catalysts were characterized by XRD and infrared spectroscopy using a reflectance mode (ATR-FTIR). The post reaction catalysts were also characterized by XRD, ATR-FTIR and thermogravimetry. Details on the catalyst characterization are given elsewhere [1]. The diffractograms were recorded with a Rigaku Geigerflex diffractometer with Cu Kα radiation at 40 kv and 40 ma (2/min). The thermograms were acquired (30 C/min) for mg of powder samples in alumina crucibles using a Netzsch TG-DTA- DSC thermobalance. ATR-FTIR spectra were obtain with a Perkin Elmer, Spectrum Two IR spectrometer, using a 4 cm 1 resolution and 4 scans. To all ATR-FTIR data was applied the Kubelka-Munk model to minimize the measure noise Methanolysis Reaction Tests The methanolysis of alimentary grade soybean oil was used to select the most suitable catalyst. Pork lard and pork lard/soybean oil mixtures were used to produce biodiesel over Ca based catalyst. Additionally, different amounts of IPA were used as co-solvent to improve the miscibility of the reaction components, which is poor for lower level of fat conversion [36, 37]. The methanolysis reactions, at methanol reflux temperature, were carried out using 5 % (W/W) of catalysts (fat basis) and a methanol/oil = 12 molar ratio. For each reaction batch, the catalyst was previously contacted with methanol for 1 h (65 C) and then the pre-heated oil (100 g, 100 C) was added to the reaction flask. After the reaction period (150 min), the slurry, containing the catalyst, the unreacted oil, the methyl esters and the glycerin, was cooled down and the catalyst was removed by filtration. The collected liquid was transferred into a decantation funnel for gravity separation of the glycerin from the oily phase containing the biodiesel and the unreacted oil. The FAME content of the oily phase was evaluated by ATR-FTIR, through characteristic biodiesel band at 1436 cm 1 [38]. The post reaction catalysts were dried overnight at 105 C before characterization and eventual reutilization. The catalysts stability was studied by reusing the same catalyst sample in consecutive reaction batches without intermediate reactivation procedure. More details on the reaction procedure are given elsewhere [39]. As generally accepted, the FAME content of the oily phase was used as measure of the catalytic activity [40] and feedstocks acid value was determined by colorimetric titration. 3. Results 3.1. Methanolysis test The different used feedstocks were analyzed by thermogravimetry and is worth noting that all the triglycerides sources showed the same behavior during the thermal degradation, as can be observed in Figure 3. There was no significant water loss neither to WFO or to lard, contrary to what was expected since low grade fats are known to have high water contents. Feedstocks acid value was evaluated by colorimet- 3

4 Figure 3: Thermograms (TG ( ) and DTG ( )) of used feedstocks under air flow and 25 C/min. ric titration obtaining the values presented in Table 2. Pure lard acid value is lowest than animal fats acidity usually reported, however, in this study it was used commercial lard, being this already processed. mixtures. Table 2: Acid value for used feedstocks Feedstock Acid value (mgkoh/g fat ) Semi-refined soybean oil 0,6 Lard 1,4 WFO 2,2 The use of catalysts from different Ca rich food waste sources showed that their catalytic activity is almost the same, varying between 99.2 % and 79.9 %. The lowest value belongs to cuttlebone methanolysis and can be attributable to the before calcination catalyst composition, being mainly aragonite whereas all the other were calcite. The chosen catalyst for the remaining tests was the one derived from scallop shells. Co-processing of lard/soybean oil mixtures showed, as expected, a decrease in FAME yield with the increase of lard. The obtained FAME yields are between 74.8 % and 92.2 %, with the lowest value belonging to the methanolysis of pure lard. Besides, with lard increase more soap was formed with consumption of catalyst, thus helping explaining the reducing of catalyst activity. The FAME yields for the different co-processed mixtures can be consulted in Figure 4. Figure 5 shows the ATR-FTIR spectra, in the interest range [41], for the lard/soybean oil Figure 4: FAME yields for different lard/soybean oil mixtures methanolysis. The methyl ester rich phase analyzed was not submitted to any purification treatment. The study of IPA as a co-solvent began by choosing the optimum reaction time. The methanolysis was performed during 150 min, 210 min, 270 min and 360 min, concluding that 210 min was the optimum time since it allows the completion of the methanolysis reaction without promoting the reduction of FAME yield, which was observed for the higher times. FAME yield decreasing for higher reaction times can be due to the inverse reaction or 4

5 Figure 5: ATR-FTIR spectra of the methyl ester rich phase for the different lard/soybean oil mixtures. Biodiesel spectrum for comparison. Figure 6: ATR-FTIR spectra of the methyl ester rich phase for the different IPA quantities. Biodiesel and IPA spectra for comparison. 5

6 to the esters hydrolysis, particularly relevant for low grade fats. Different IPA quantities were tested, permitting to conclude that high cosolvent quantities do not allow phases separation at reaction end, being necessary to dry the reaction mixture. On the other hand, higher FAME yield was achieved when using small quantities of IPA, as 84.9 % for 56:1 methanol to IPA volumetric ratio and 80.8 % for 28:1. These yields are higher than the one obtained without IPA showing that it is a good co-solvent for the methanolysis of lard. The ATR-FTIR spectra in Figure 6 shows IPA influence in the methyl ester rich phase. As can be seen, to wavelengths between 1480 cm 1 and 1410 cm 1, used to FAME yield determination, the first band is affected by IPA presence. FAME yields obtained for all tested IPA quantities are presented in Figure 7. To 5.6:1 and 1.5:1 volumetric ratios there is a significant IPA influence and the yields determined to those tests were completely out of the evidenced tendency. All the methanolysis reaction using IPA as co-solvent were performed using pure lard as feedstock Catalysts characterization The XRD patterns of raw Ca materials showed, as reported before [1, 7], lines mainly attributable to calcite (majority of the samples) and aragonite, slightly contaminated with lime, with different degrees of crystallinity. Thus, the used temperature and/or calcination time were not enough to achieved total decomposition of CaCO 3 into CaO. The catalyst prepared from cuttlebone was the only one that presented XRD lines belonging to calcium hydroxide nanocrystalized. This result can be related with the fact that cuttlebone raw material mainly showed XRD lines belonging to aragonite whereas the other materials were mainly calcite. Samples with higher content of organic matter presented lower crystallinity. The calcination of shell and cuttlebone at 800 C allowed the total degradation of organic matter since the samples, after calcination, presented chalky-white shades. Brownish to gray shades indicate the presence of partially degraded organic matter. The post reaction catalysts, after drying overnight, were also characterized by XRD (Figure 8). Figure 7: FAME yields for different IPA quantities tested. The methyl ester rich phase analyzed was not submitted to any purification treatment. Since the methanolysis of 56:1 and 28:1 were performed to 150 min, it is interesting to note that modifications in IPA quantities can lead to a alteration in optimum reaction time. It was also studied the methyl ester rich phase to each feedstock, namely soybean oil, WFO and lard. The obtained FAME yield were 88.4 %, 76.3 % and 74.8 %, respectively. As expected, the semi-refined soybean oil achieved the higher yield, however the results obtained are similar, agreeing with the idea that WFO and lard are good raw materials for the production of biodiesel. Figure 8: XRD patterns of scallop catalyst, fresh and post first and second reaction using soybean oil (JCPDS files standards are displayed for crystalline phases identification). Contrarily to the reported by Dias et al. [1] for lime catalysts, who reported the formation of Ca(OH) 2 after the first reaction batch, the scallop derived catalysts during the first reaction (batch#1) was converted into a mixture of calcium methoxide, calcium diglyceroxide showing, however, low intensity XRD lines of CaO. This apparent disagreement can be due to the fact that fresh catalyst was mainly calcite instead of lime. After the second reaction (batch#2) the features belonging to lime were vanished. The post reaction catalyst samples, after coprocessing lard/soybean oil mixtures, showed different patterns depending on the lard/soybean oil 6

7 used (Figure 9). It seems that water formed during saponification of FFA promotes the calcium methoxide and diglyceroxide leaching. The catalyst after co-processing the mixture containing 50 % of each fat showed Ca(OH) 2 pattern. For other mixtures the XRD patterns retains the lines belonging to calcite of the fresh catalyst with minor lines of calcium methoxide and diglyceroxide. Figure 10: XRD patterns of scallop catalyst after reaction with lard using IPA as co-solcent (JCPDS files standards are displayed for crystalline phases identification). Figure 9: XRD patterns of scallop catalyst after reaction with lard/soybean oil mixtures (JCPDS files standards are displayed for crystalline phases identification). The use of IPA as a co-solvent seems to avoid the formation of calcium methoxide and diglyceroxide, as can be seen in Figure 10, eventually due to the improvement of miscibility of the reaction medium components, thus allowing fast removal of the formed glycerin from the vicinity of catalyst surface, avoiding the formation of calcium diglyceroxide. The faster methanolysis reaction when the co-solvent was used also reduces the formation of calcium methoxide since surface methoxide species are fat combined with triglycerides to form esters. 4. Conclusions Nowadays, first generation biodiesel production faces serious socio-economic issues which make it unsustainable. The methanolysis of soybean oil, lard and WFO, in standard conditions, showed good FAME yields, however far beyond what is legally required. Lard/soybean oil co-processing appears as a valid strategy to minimize the acidity of low grade feedstocks, achieving FAME yields higher than 90 % for 10 % to 50 % of lard. As expected, for Lard methanolysis tests, soap formation was verified. IPA usage as a co-solvent proven to reduce the adsorption of oily species in catalyst surface. IPA can also be used to wash the catalyst between tests since it allows the removal of triglycerides adsopted in catalyst surface. Acknowledgements The author would like to thank to FCT Fundao para a Cincia e Tecnologia, Lisboa, Portugal, for funding project PTDC/EMS-ENE/4865/2014. References [1] Ana Paula Soares Dias, Jaime Puna, João Gomes, Maria Joana Neiva Correia, and João Bordado. Biodiesel production over lime. catalytic contributions of bulk phases and surface ca species formed during reaction. Renewable Energy, 99: , [2] Jon Van Gerpen. Biodiesel processing and production. Fuel processing technology, 86(10): , [3] Overview of greenhouse gases. overview-greenhouse-gases. Acedido a [4] María D Cárdenas, Octavio Armas, Carmen Mata, and Felipe Soto. Performance and pollutant emissions from transient operation of a common rail diesel engine fueled with different biodiesel fuels. Fuel, 185: , [5] Rajat Chakraborty, Abhishek K Gupta, and Ratul Chowdhury. Conversion of slaughterhouse and poultry farm animal fats and wastes to biodiesel: Parametric sensitivity and fuel quality assessment. Renewable and Sustainable Energy Reviews, 29: , [6] Jaime F Puna, João F Gomes, João C Bordado, M Joana Neiva Correia, and Ana 7

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