BIODIESEL PRODUCTION FROM NON-FOODSTUFF: CHEMISTRY, CATALYSIS AND ENGINEERING

1. Introduction Biodiesel (BD) is a liquid biofuel that is defined as a fatty acid methyl ester fulfilling standards such as the ones set by European (EN 14214) and the American (ASTM 6751) regulations. BD is obtained by the transesterification (Scheme 1.1) or alcoholysis of natural triglycerides contained in vegetable oils, animal fats, waste fats and greases, waste cooking oils (WCO) or side-stream products of refined edible oil production with short-chain alcohols, usually methanol or ethanol and using an alkaline homogeneous catalyst (Perego and Ricci, 2012). Scheme 1.1. Transesterification reaction. BD presents several advantages over petroleum-based diesel such as: biodegradability, lower particulate and common air pollutants (CO, SOx emissions, unburned hydrocarbons) emissions, absence of aromatics and a closed CO2 cycle. Refined, low acidity oilseeds (e.g. those derived from sunflower, soy, rapeseed, etc.) may be easily converted into BD, but their exploitation significantly raises the production costs, resulting in a biofuel that is uncompetitive with the petroleum-based diesel (Santori et al., 2012; Lotero et al., 2005). Moreover, the use of the aforementioned oils generated a hot debate about a possible food vs. fuel conflict, i.e. about the risk of diverting farmland or crops at the expense of food supply. It is so highly desirable to produce BD from crops specifically selected for their high productivity and low water requirements (Bianchi et al., 2011; Pirola et al., 2011), or from low-cost feedstock such as used frying oils (Boffito et al., 2012a) and animal fats (Bianchi et al., 2010). The value of these second generation biofuels, i.e. produced from crop and forest residues and from non-food energy crops, is acknowledged by the European Community, which states in its RED directive (European Union, RED Directive 2009/28/EC): \u2018\u2018For the purposes of demonstrating compliance with national renewable energy obligations [\u2026], the contribution made by biofuels produced from wastes, residues, non-food cellulosic material, and ligno-cellulosic material shall be considered to be twice that made by other biofuels\u2019\u2019. However, the presence of free fatty acids in the feedstock, occurring in particular in the case of not refined oils, causes the formation of soaps as a consequence of the reaction with the alkaline catalyst. This hinders the contact between reagents and the catalyst and makes difficult the products separation. Many methods have been proposed to eliminate FFA during or prior to transesterification (Pirola et al., 2011; Santori et al., 2012). Among these the FFA pre-esterification method is a very interesting approach to lower the acidity since it allows to lower the acid value as well as to obtain methyl esters already in this preliminary step (Boffito et al., 2012a, 2012b; 2012c Bianchi et al., 2010, 2011; Pirola et al., 2010, 2011). Aims of the work The aims of this work are framed in the context of the entire biodiesel production chain, ranging from the choice of the raw material, through its standardization to the actual biodiesel production. The objectives can be therefore summarized as follows: Assessing the potential of some vegetable or waste oils for biodiesel production by their characterization, deacidification and final transformation into biodiesel; To test different ion exchange resins and sulphated inorganic systems as catalysts in the FFA esterification; To assess the use of ultrasound to assist the sol-gel synthesis of inorganic sulphated oxides to be used as catalysts in the FFA esterification reaction; To assess the use of sonochemical techniques such as ultrasound and microwave to promote both the FFA esterification and transesterification reaction. 2. Experimental details 2.1 Catalysts In this work, three kinds of acid ion exchange resins were used as catalysts for the FFA esterification: Amberlyst\uae15 (A15), Amberlyst\uae46 (A46) (Dow Chemical) and Purolite\uaeD5081 (D5081). Their characteristic features are given in Tab. 2.1. Various sulphated inorganic catalysts, namely sulphated zirconia, sulphated zirconia+titania and sulphated tin oxide were synthesized using different techniques. Further details will be given as the results inherent to these catalysts will be presented. Catalyst A15 A46 D5081 Physical form opaque beads Type Macroreticular Matrix Styrene-DVB Cross-linking degree medium medium high Functional group -SO3H Functionalization internal external external external Form dry wet wet Surface area (m2 g-1) 53 75 514a Ave. Dp (\u1fa) 300 235 37a Total Vp (ccg-1) 0.40 0.15 0.47 Declared Acidity (meq H+g-1) 4.7 0.43 0.90-1.1 Measured acidity (meq H+g-1) 4.2 0.60 1.0 Moisture content (%wt) 1.6 26-36 55-59 Shipping weight (g l-1) 610 600 1310a Max. operating temp (K) 393 393 403 Tab. 2.1. Features of the ion exchange resins used as catalysts. The acidity of all the catalysts was determined by ion exchange followed by pH determination as described elsewhere (L\uf3pez et al., 2007; Boffito et al., 2012a; 2012b). Specific surface areas were determined by BET (Brunauer, Emmett and Teller, 1938) and pores sizes distribution with BJH method (Barrett, Joyner and Halenda, 1951). XRD, XPS SEM-EDX and HR-TEM analyses were performed in the case of catalysts obtained with the use of ultrasound (Boffito et al. 2012a). Qualitative analyses of Lewis and Br\uf8nsted acid sites by absorption of a basic probe followed by FTIR analyses was also carried out for this class of catalysts (Boffito et al, 2012a). 2.2 Characterization of the oils Oils were characterized for what concerns acidity (by acid-base titrations) as reported by Boffito et al. (2012a, 2012b; 2012c), iodine value (Hannus method (EN 14111:2003)), saponification value (ASTM D5558), peroxide value and composition by GC analyses of the methyl ester yielded by the esterification and transesterification. Cetane number and theoretical values of the same properties were determined using equations already reported elsewhere (Winayanuwattikun et al., 2008). 2.3 Esterification and transesterification reactions In Tab. 2.2, the conditions adopted in both the conventional and sonochemically-assisted esterification are reported. For all these experiments a temperature of 336 K was adopted. Vials were used to test the sulphated inorganic oxides, while Carberry reactor (confined catalyst) (Boffito et al., 201c) was used just for the FFA esterification of cooking oil. Rector oil (+ FFA) (g) MeOH (g) catalyst amount vial 21 3.4 5%wt/gFFA sulphated inorganic catalysts slurry 100 16 - 10 g ion exchange resins - 5%wt/gF FA sulphated inorganic catalysts Carberry 300 48 10 g (5 g in each basket) Tab. 2.2. Free fatty acids esterification reaction conditions for conventional and sonochemically-assisted experiments. All the sonochemically-assisted experiments were performed in a slurry reactor. FFA conversions were determined by acid-base titrations of oil samples withdrawn from the reactors at pre-established times and calculated as follows: "FFA conversion (%)=" (\u3016"FFA" \u3017_"t=0" "-" \u3016"FFA" \u3017_"t" )/\u3016"FFA" \u3017_"t=0" " x 100" In Tab. 2.3, the conditions of both the conventional and ultrasound (US)-assisted transesterification are reported. KOH and CH3ONa were used for conventional experiments, while just KOH for the US-assisted experiments. The BD yield was determined by GC (FID) analysis of the methyl esters. Method Reactor Step gMeOH/100 goil gKOH/100 goil Temp. (K) Time (min) traditional batch step 1 20 1.0 333 90 step 2 5.0 0.50 60 US-assisted batch step 1 20 1.0 313, 333 30 US-assisted continuos step 1 20 1.0 338 30 Tab. 2.3. Transesterification reaction conditions. 3. Results and Discussion 3.1 Characterization and deacidification of different oils by ion exchange resins: assessment of the potential for biodiesel production In Tab. 3.1 the results of the characterization of the oils utilized in this work are displayed. The value in parentheses indicate the theoretical value of the properties, calculated basing on the acidic composition. The acidity of all the oils exceeds 0.5%wt (~0.5 mgKOH/g), i.e. the acidity limit recommended by both the European normative (EN 14214) and American standard ASTM 6751 on biodiesel (BD). The iodine value (IV) is regulated by the EN 14214, which poses an upper limit of 120 gI2/100 g. The number of saturated fatty chains in the fuel determines its behaviour at low temperatures, influencing parameters such as the cloud point, the CFPP (cold filter plugging point) and the freezing point (Winayanuwattikun et al., 2008). The IV are in most of the cases similar to the ones calculated theoretically. When the experimental IV differs from the theoretical one, it is in most of the cases underestimated. This can be explained considering the peroxide numbers (PN), which indicates the concentration of O2 bound to the fatty alkyl chains and is therefore an index of the conservation state of oil. Oils with high IV usually have a high concentration of peroxides, whereas fats with low IV have a relatively low concentration of peroxides at the start of rancidity (King et al., 1933). Moreover, although PN is not specified in the current BD fuel standards, it may affect cetane number (CN), a parameter that is regulated by the standards concerning BD fuel. Increasing PN increases CN, altering the ignition delay time. Saponification number (SN) is an index of the number of the fatty alkyl chains that can be saponified. The long chain fatty acids have a low SN because they have a relatively fewer number of carboxylic functional groups per mass unit of fat compared to short chain fatty acids. In most of the cases the experimental SN are lower than the ones calculated theoretically. This can be explained always considering the PN, indicating a high concentration of oxygen bound to the fatty alkyl chains. Oil Acidity (%wt) IV1 (gI2/ 100 g) PN2 (meqO2 /kg) SN3 (mg KOH/g) CN4 Fatty acids composition (%wt) animal fat (lard)* 5.87 51 2.3 199 62.3 n.d. soybean* 5.24 138 3.8 201 42.4 n.d. tobacco1 1.68 143 (149) 21.9 199 (202) 41.6 (39.8) C14:0 (2.0) C16:0 (8.3) C18:0 (1.5) C18:1 (12.0) C18:2 (75.3) C18:3 (0.6) C20:0 (0.1) C22:0 (0.2) sunflower* 3.79 126 3.7 199 45.4 n.d. WSO5 0.50 118 (129) 71.3 187 (200) 48.9 (44.6) C16:0 (6.9) C18:0 (0.9) C18:1 (40.1) C18:2 (50.9) C18:3 (0,3) C20:0 (0.1) C20:1 (0.4) C22:0 (0.4) palm 2.71 54.0 (53.0) 12.3 201 (208) 61.3 (60.6) 16:0 (43.9) 18:0 (5.6) 18:1 (40.5) 18:2 (8.6) WCO6 2.10 53.9 (50.7) 11.0 212 (196) 59.9 (62.7) C16:0 (38.8) C18:0 (4.1) C18:1 (47.9) C18:2 (4.2) WCO:CRO =3:1 2.12 69.0 (75.5) 30.1 200 (212) 58.1 (55.1) C16:0 (30.1) C18:0 (3.1) C18:1 (51.9) C18:2 (12.0) C18:3 (2.%) C20:0 (0.2) C22:0 (0.1) WCO:CRO =1:1 2.19 76.8 (90.7) 51.3 188 (203) 58.1 (52.8) C16:0 (21.5) C18:0 (2.1) C18:1 (55.8) C18:2 (14.7) C18:3 (5.1) C20:0 (0.8) C22:0 (0.1) WCO:CRO =1:3 2.24 84.5 (104) 62.4 177 (202) 58.1 (49.9) 14:0 (0.1) 16:0 (14.7) 16:1 (0.7) 18:0 (6.85) 18:1 (40.0) 18:2 (37.0) 18:3 (0.25) 20:0 (0.25) 22:0 (0.15) rapeseed (CRO7) 2.20 118 (123) 71.6 165 (200) 52.8 (45.9) C16:0 (4.1) C18:0 (0.1) C18:1 (63.7) C18:2 (20.2) C18:3 (10.2) C20:0 (1.5) C22:0 (0.2) rapeseed* 4.17-5.12 108 (107) 3.5 203 (200) 48.9 (49.5) C16:0 (7.6) C18:0 (1.3) C18:1 (64.5) C18:2 (23.7) C18:3 (2.4) C20:0 (0.5) Brassica juncea 0.74 109 (110) 178 (185) 52.4 (51.1) C16:0 (2.4) C18:0 (1.1) C18:1 (19.9) C18:2 (19.2) C18:3 (10.9) C20:0 (7.2) C20:1 (1.7) C22:0 (0.9) C22:1 (34.8) 24:0 (1.9) safflower 1.75 139 48.9 170 47.1 n.d. WCO: tobacco2 =1:1 4.34 119 (112) 56.0 191 (203) 48.1 (48.0) C16:0 (22.5) C18:0 (3.2) C18:1 (32.0) C18:2 (42.1) C18:3 (0.2) tobacco2 6.17 141 (151) 33.4 183 (201) 44.4 (39.5) C16:0 (8.7) C18:0 (1.6) C18:1 (12.8) C18:2 (76.0) C18:3 (0.7) C20:0 (0.1) C22:0 (0.1) 1Iodine value; 2Peroxide number; 3Saponification number; 4Cetane number; 5Winterized sunflower oil, 6Waste cooking oil; 7Crude rapeseed oil; * refined, commercial oils acidified with pure oleic acid up to the indicated value. Tab. 3.1. Results of the characterization of the oils. The results of the FFA esterification performed on the different oils are given in Fig. 3.1. Fig. 3.1. Results of the FFA esterification reaction on different oils. The dotted line represents a FFA concentration equal to 0.5%wt, i.e. the limit required by both the European and American directives on BD fuel and to perform the transesterification reaction avoiding excessive soaps formation. The FFA esterification method is able to lower the acidity of most of the oils using the ion exchange resins A46 and D5081 as catalysts in the adopted reaction conditions. High conversion was obtained with A15 at the first use of the catalyst, but then its catalytic activity drastically drops after each cycle. The total loss of activity was estimated to be around 30% within the 5 cycles (results not shown for the sake of brevity). A possible explanation concerning this loss of activity may be related to the adsorption of the H2O yielded by the esterification on the internal active sites, which makes them unavailable for catalysis. When H2O molecules are formed inside the pores, they are unable to give internal retro-diffusion due to their strong interaction with H+ sites and form an aqueous phase inside the pores. The formation of this phase prevents FFA from reaching internal active sites due to repulsive effects. What appears to influence the FFA conversion is the refinement degree of the oil. WCO is in fact harder to process in comparison to refined oils (Bianchi et al., 2010; Boffito et al., 2012c), probably due to its higher viscosity which results in limitations to the mass transfer of the reagents towards the catalyst. Indeed, the required acidity limit is not achieved within 6 hours of reaction. A FFA concentration lower than 0.5%wt is not achieved also in the case of WCO mixture 3:1 with CRO and 1:1 with tobacco oil and in the case of the second stock of tobacco oil (tobacco2). This is attributable to the very low quality of these feedstocks due to the waste nature of the oil itself, in the case of WCO, or to the poor conservation conditions in the case of tobacco oilseed. In this latter case, the low FFA conversion was also ascribed to the presence of phospholipids, responsible for the deactivation of the catalyst. BD yields ranging from 90.0 to 95.0 and from 95.0 to 99.9% were obtained from deacidified raw oils using KOH and NaOCH3 as a catalyst, respectively. In Fig. 3.2, the comparison between A46 and D5081 at different temperatures and in absence of drying pretreatment (wet catalyst) is displayed. As expected, D5081 performs better than A46 in all the adopted conditions. Nevertheless, the maximum conversion within a reaction time of 6 hours is not achieved by any of the catalysts both operating at 318 K and in the absence of drying pretreatment. A more detailed study on the FFA esterification of WCO and its blends with rapeseed oil and gasoline was carried out. In Tab. 3.2 a list of all the experiments performed with WCO is reported together with the FFA conversion achieved in each case, while in Fig. 3.3 the influence of the viscosity of the blends of WCO is shown. Fig. 3.2. Comparison between the catalysts. D5081 and A46 at a) different catalysts amounts and b) temperatures and treatments. The results show that Carberry reactor is unsuitable for FFA esterification since a good contact between reagents and catalyst is not achieved due to its confinement. A15 deactivated very rapidly, while A46 and D5081 maintained their excellent performance during all the cycles of use due to the reasons already highlighted previously. The blends of WCO and CRO show an increase of the reaction rate proportional to the content of the CRO, that is attributable to the decreases viscosity (Fig. 3.3), being all the blend characterized by the same initial acidity. Also the use of diesel as a solvent resulted in a beneficial effect for the FFA esterification reaction, contributing to the higher reaction rate. Feedstock %wtFFAt=0 Reactor Cat. gcat/100 goil gcat/100 g feedstock Number of cat. re-uses FFA conv. (%), 1st use, 6 hr 1 WCO 2.10 Carberry A15 3.3 3.3 6 15.4 2 WCO 2.10 slurry A15 10 10 6 71.7 3 WCO 2.10 Carberry A46 3.3 3.3 6 7.7 4 WCO 2.10 slurry A46 10 10 6 62.0 5 WCO 2.10 slurry D5081 10 10 6 63.7 6 CRO 2.20 slurry A46 10 10 10 95.9 7 CRO 2.20 slurry D5081 10 10 10 93.7 8 WCO 2.10 slurry A46 10 10 0 62.0 9 WCO 75 CRO 25 2.12 7.5 71.3 10 WCO 50 CRO 50 2.19 5.0 79.9 11 WCO 25 CRO 75 2.24 2.5 86.1 12 CRO 2.20 10 95.9 13 WCO 75 DIESEL 25 1.74 7.5 76.8 14 WCO 50 DIESEL 50 1.17 5.0 58.7 15 WCO 25 DIESEL 75 0.65 2.5 40.4 16 WCO 25 DIESEL 75 (higher FFA input) 2.44 2.5 63.5 Tab. 3.2. Experiments performed with waste cooking oil. . Fig. 3.3. FFA conversions and viscosities of the blend of WCO with rapeseed oil. 3.2. Sulphated inorganic oxides as catalysts for the free fatty acid esterification: conventional and ultrasound assisted synthesis Conventional syntheses In Tab. 3.3, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Catalyst Composition Prep. method precursors T calc. SSA (m2g-1) Vp (cm3g-1) meq H+g-1 1 SZ1 SO42-/ZrO2 one-pot sol-gel ZTNP1, (NH4)2SO4 893 K O2 107 0.09 0.90 2a SZ2a SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 893 K 102 0.10 0.11 2b SZ2b SO42-/ZrO2 two-pots sol-gel ZTNP, H2SO4 653 K 110 0.10 0.12 3 SZ3 SO42-/ZrO2 Physical mixing ZrOCl2.8H2O (NH4)2SO4 873 K 81 0.11 1.3 4 SZ4 Zr(SO4)2/SiO2 Impregnation Zr(SO4)2.4H2O SiO2 873 K 331 0.08 1.4 5 SZ5 Zr(SO4)2/Al2O3 Impregnation Zr(SO4)2.4H2O Al2O3 873 K 151 0.09 0.67 6 ZS Zr(SO4)2.4H2O (commercial) - - - 13 0.12 9.6 7 STTO_0 SO42-/SnO2 Physical mixing + impregnation SnO2 TiO2 P25 H2SO4 773 K 16.8 0.10 3.15 8 STTO_5 SO42-/95%SnO2-5%TiO2 773 K 15.9 0.11 3.43 9 STTO_10 SO42-/ 90%SnO2-10%TiO2 773 K 16.5 0.09 5.07 10 STTO_15 SO42-/ 85%SnO2-15%TiO2 773 K 14.9 0.11 7.13 11 STTO_20 SO42-/ 80%SnO2-20%TiO2 773 K 16.9 0.09 7.33 Tab. 3.3. Sulphated inorganic catalysts synthesized with conventional techniques. The FFA conversions of the sulphated Zr-based systems are provided in Fig. 3.4a and show that Zr-based sulphated systems do not provide a satisfactory performance in the FFA esterification, probably due to their low acid sites concentration related to their high SSA. Even if catalysts such as SZ3 and SZ4 exhibit higher acidity compared to other catalysts, it is essential that this acidity is located mainly on the catalyst surface to be effectively reached by the FFA molecules, as in the case of ZS. In Figure 3.4b, the results of the FFA esterification tests of the sulphated Sn-Ti systems are shown. Other conditions being equal, these catalysts perform better than the sulphated Zr-based systems just described. This is more likely due to the higher acidity along with a lower surface area. With increasing the TiO2 content, the acidity increases as well. This might be ascribable to the charge imbalance resulting from the heteroatoms linkage for the generation of acid centres, (Kataota and Dumesic, 1988). As a consequence, the activity increases with the TiO2 content along with the acidity of the samples. For the sake of clarity, in Fig. 3.4c the FFA esterification conversion is represented as a function of the number of active sites per unit of surface area of the samples. Ultrasound- assisted synthesis In Tab. 3.4, the list of all the catalyst synthesized with conventional techniques is reported together with the results of the characterization. Samples SZ and SZT refer to catalysts obtained with traditional sol-gel method, while samples termed USZT refer to US-obtained sulphated 80%ZrO2-20%TiO2. The name is followed by the US power, by the length of US pulses and by the molar ratio of water over precursors. For example, USZT_40_0.1_30 indicates a sample obtained with 40% of the maximum US power, on for 0.1 seconds (pulse length) and off for 0.9 seconds, using a water/ZTNP+TTIP molar ratio equal to 30. SZT was also calcined at 773 K for 6 hours, employing the same heating rate. This sample is reported as SZT_773_6h in entry 2a. Further details about the preparation can be found in a recent study (Boffito et al., 2012b). Entry Catalyst Acid capacity (meq H+/g) SSA (m2g-1) Vp (cm3g-1) Ave. BJH Dp (nm) Zr:Ti weight ratio S/(Zr+Ti) atomic ratio 1 SZ 0.30 107 0.20 6.0 100 0.090 2 SZT 0.79 152 0.19 5.0 79:21 0.085 2a SZT_773_6h 0.21 131 0.20 5.0 n.d.1 n.d 3 USZT_20_1_30 0.92 41.7 0.12 12.5 80:20 0.095 4 USZT_40_0.1_30 1.03 47.9 0.11 9.5 81:19 0.067 5 USZT_40_0.3_30 1.99 232 0.27 4.5 81:19 0.11 6 USZT_40_0.5_7.5 1.70 210 0.20 5.0 78:22 0.086 7 USZT_40_0.5_15 2.02 220 0.20 5.0 80:20 0.13 8 USZT_40_0.5_30 2.17 153 0.20 5.0 78:22 0.12 9 USZT_40_0.5_60 0.36 28.1 0.10 10 79:21 0.092 10 USZT_40_0.7_30 1.86 151 0.16 5.0 78:22 0.11 11 USZT_40_1_15 3.06 211 0.09 7.0 80:20 0.15 12 USZT_40_1_30 1.56 44.1 0.09 7.0 80:20 0.17 Tab. 3.4. Sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel technique. Some of the results of the characterizations are displayed in Tab. 3.4. The results of the catalytic tests are shown in Fig. 3.5 a, b and c. In Fig. 3.5a and 3.5b the FFA conversions are reported for the samples synthesized using the same or different H2O/precursors ratio, respectively. Fig. 3.5. FFA conversions of sulphated inorganic Zr-Ti systems synthesized with ultrasound-assisted sol-gel for a) the same amount of H2O, b) different amount of H2O used in the sol-gel synthesis, c) in function of the meq of H+/g of catalyst Both the addition of TiO2 and the

The Sonophotocatalytic Degradation of Pharmaceuticals in Water by MnOx-TiO2 Systems with Tuned Band-Gaps

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Ultrasound-enhanced photodegradation of Diclofenac Na

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An ultrasound-assisted photocatalytic treatment to remove an herbicidal pollutant from wastewaters

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Ultrasound-assisted impregnation for high temperature Fischer-Tropsch catalysts

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Eco-friendly synthesis from industrial wastewater of Fe and Cu nanoparticles over NaX zeolite and activity in 4-nitrophenol reduction

We deposited Fe and Cu over zeolite NaX (Fe/NaX and Cu/NaX) by adsorption from effluent industrial wastewater. We synthesized the zeolite NaX by the hydrothermal method. 5g of NaX completely adsorbed 350 and 380mg of Fe and Cu from the industrial wastewater, respectively, in 6h. The distribution of Fe and Cu over the NaX was uniform and amounted at 14 and 18mass%, respectively. Fe and Cu modify the morphology of the NaX zeolite: the particle size increased from 9\uce\ubcm to 10\uce\ubcm for the former and decreased to 3\uce\ubcm for the latter. Fe/NaX and Cu/NaX are less crystalline than NaX. BET analysis showed that the specific surface area decreased by 30% and 50% compared to NaX for Fe/NaX and Cu/NaX, but the ratio between meso- and micropores increased by 7 and 13 times, respectively. Fe/NaX and Cu/NaX synthesized by adsorption from industrial wastewater reduced +99% of 4-p-nitrophenol to 4-aminophenol in less than 100s, which is comparable to noble metal

Sustainable biodiesel production from alternative oils

Introduction Biodiesel, besides bioethanol, is the only renewable energy source in liquid form that can be actually produced on a large scale at the moment. The main barriers still limiting the widespread use of this fuel are twofold: the ethical issues posed by the competition of the raw materials used for its production with the food requirements and the relatively high manufacturing costs of biodiesel production, making it not competitive with normal diesel. Waste oils or oils extracted from specifically selected vegetable cultures represent potential substitutes to edible oils. The main drawback of these raw materials is their high content of free fatty acids (FFA), which cause saponification problems during the transesterification [1,2]. Moreover, FFA concentrations lower than 0.5% per weight are required by the European standard for biodiesel EN 14214. In the present work the deacidification of different kinds of alternative oils is investigated. The proposed method consists in the esterification of FFA with methanol and in presence of an acid catalyst so to obtain methyl esters already at this stage, as represented in the following scheme: RCOOH + MeOH bc0 cc6 RCOOMe + H2O. Acid ion exchange resin Amberlyst\uae46 (A46, Dow Advanced Materials) was selected by the authors after some preliminary studies carried out to assess its performance and durability in the reaction environment [3]. The use of oils extracted from Brassica juncea, Cartamus tinctorius, i.e. crops not addressed to the food market, and waste cooking oil (WCO), is studied. In the case of WCO a study on the lifetime of the catalyst was also carried out recycling it through multiple runs. The potential of the adopted feedstock was investigated taking into account EN 14214 standard. Experimental The performed deacidification experiments are listed in Table 1. All the esterification tests have been carried out in slurry modality adopting A46 as catalyst. A46 is a sulphonic ion exchange acid resin which has the peculiarity of being sulphonated only on its surface [3]. Table 1: Esterification experiments. Oil (common name) Initial acidity (FFA wt %) Experiment(s) Conditions biphasic 65 \ub0C MeOH:oil=16:100 B. juncea (indian mustard) 0.74 monophasic 80 \ub0C MeOH:oil=5:100 Biphasic 65 \ub0C MeOH:oil=16:100 C. tinctorius (safflower) 1.75 monophasic 80 \ub0C MeOH:oil=5:100 Waste Cooking Oil (WCO) 2.30 biphasic, recycle of the catalyst 65 \ub0C MeOH:oil=16:100 WCO:rapeseed oil 1:1 2.20 Biphasic 65 \ub0C MeOH:oil=16:100 WCO:rapeseed oil 3:1 2.20 Biphasic 65 \ub0C MeOH:oil=16:100 The experiments in monophasic conditions were arranged by mixing the oil with the necessary amount of methanol to obtain a single liquid phase at 80\ub0C. The purpose of these tests was to investigate if a maximized contact between methanol and FFA could be beneficial. Each test has been carried out for six hour, withdrawing samples from the reactor at pre-established times to analyze their acidity content through acid-base titrations [4]. Biodiesel was produced from the oilseeds following the well known procedure described in literature [5]. Product composition was analyzed through gaschromatography. Iodine value (gI2/100 g oil), density, viscosity of the tested oils were measured by standard methods in order to verify the compliance with the EN 14214 requirements. Results and Discussion The main characteristics of the tested oils, as per EN 14214 standard, are listed in Table 2. Table 2: Values of some properties of the selected oils Oil (common name) Iodine value (gI2/100g oil) Viscosity (mm2/s 40 \ub0C) Density (kg/m3 15\ub0 C) B. juncea 111 32.6 914 C. tinctorius 109 n.d. n.d. WCO 54 82.2 918 WCO:rapeseed oil 1:1 85 52.8 914 WCO:rapeseed oil 3:1 100 40.5 926 Rapeseed 115 n.d. n.d. Biodiesel standard EN 14214 <120 3.5-5 860-900 All the tested samples are characterized by an iodine value satisfying the required limit. Iodine values exceeding the imposed limit may in fact be responsible of fuel\u2019s instability to the oxidation, making it unsuitable for diesel engines. On the other hand, oils with too low iodine values and high viscosities, such as WCO, cannot be used as well, as they may plug equipment filters [7]. Regarding viscosity it has to be however considered that the original value will be reduced of 1/10-1/15 after the transesterification process [6]. It is possible to adjust properties like iodine value and viscosity, so as the fall within the required limits, by blending the feedstock with oils characterized by opposite properties. This is shown in Table 2 by the values obtained in the case of the mixtures of WCO and rapeseed oil. The results of the deacidification tests performed on the selected feedstock are shown in Figure 1. 0.230.520.880.520.370.741.752.302.202.2000.511.522.5B. junceaC. tinctoriusWCOWCO: Rapeseed 1:1WCO: Rapeseed 1:3FFA (% wt.)Residual AcidityAcidity removed by esterification-69%-70%-76%-62%-83% Figure 1: Deacidification of different oils with A46, slurry reactor, wt ratio catalyst: oil=10: 100, wt ratio MeOH: oil=16:100, 65\ub0 C, 6 hours. As can be seen the use of the catalyst A46 allows, in most of cases, to lower acidity below 0.5% within 6 hours . In the case of WCO the acidity removed by esterification is not enough to enable a potential application on a larger scale. This is probably due to the high viscosity of this medium which prevents an optimal contact between the reagents and the catalyst. A possible solution might be to blend the feedstock with other raw oils characterized by lower viscosity, so as to reach the required acidity limit within 6 hours of reaction. The effectiveness of this approach is evidenced in the graph by the residual acidities obtained when WCO is mixed with rapeseed oil, achieving the plateau of conversion within the six hours of reaction. Experiments at 80 \ub0C, using the methanol amount vs. oil required at this temperature to obtain a single liquid phase, were also carried out in the case of B. juncea and C. tinctorius oilseeds. The outcome of this study evidenced how the quantity of methanol adversely affects FFA conversion within 6 hours, notwithstanding the higher operating temperatures and the better contact between reagents. Therefore, when operating in slurry modality, biphasic esterification is to be preferred to the process in monophasic conditions. In the case of WCO, the same batch of the catalyst A46 was recycled for 5 runs, showing no significant decrease in its catalytic activity. Biodiesel of 98.5% of purity was obtained from B. juncea oilseed. Conclusions The esterification reaction of FFA contained in raw oils with the use of Amberlyst\uae46 as a catalyst is an effective and efficient method of deacidification. Brassica juncea and Cartamus tinctorius represent two valuable choices for what concerns the selection of the substrates to be used for biodiesel production. However, it is possible to improve the properties of the raw materials by mixing different oils, as demonstrated by the blends of waste cooking oil (characterized by low iodine value and high viscosity) with rapeseed oil. References 1. M. Di Serio, R. Tesser, M. Dimiccoli, F. Cammarota, M. Nastasi, E. Santacesaria, J. Molec. Catal. 239 (2005) 111. 2. M. Canakci, H. Sanli, J. Ind. Microbiol. Biotechnol., 35 (2008) 431. 3. Pirola, C.L. Bianchi, D.C. Boffito, g. Carvoli, V. Ragaini, Ind. Eng. Chem. Res. 49 (2010) 4601. 4. C.L. Bianchi, D. Boffito, C. Pirola, V. Ragaini, Catal. Lett. 134 (2009) 179. 5. R. Pena, R. Romero, M.S. Luz, M.J. Ramos, A. Martinez, R. Natividad, Ind. Eng. Chem. Res. 48 (2009) 1186. 6. K. Krisnangkura, T. Yimsuwan, R. Pairintra, Fuel 85 (2006) 107. 7. M.B. Dantas, A.R. Albuquerque, A.K. Barros, M.G. Rodrigues, N.R.Antoniosi, S.M. Sinfronio, R. Rosenhaim, L.E.B. Soledade, I.M.G. Snatos, A.G. Souza, Fuel 90 (2011) 773 8. J.M. Encinar, J.F. Gonz\ue1lez, A. Pardal, G. Mart\uednez, Fuel. Proc. Technol. 91 (2010) 1530

High loading Fe-based catalysts for Fischer Tropsch Synthesis : optimization of synthesis procedure

Fischer-Tropsch synthesis (FT) is one of the great processes of the industrial chemistry. Starting from syngas (CO + H2), it is possible to produce a wide range of hydrocarbons, from 1 to 100 carbon atoms, using mainly cobalt or iron-based (promoted by potassium and copper) catalysts. Iron-based catalysts are widely investigated for FT due to their low costs and their good performance. Iron-based catalysts are industrially used without any support. Notwithstanding the major inconveniences, related to the employment of massive catalysts, are their fast physical degradation and their low superficial area. Instead several advantages derive from the use of supported iron catalysts, such as improved catalytic stability and lower deactivation rate, catalysts containing a support usually display a lower activity than the unsupported ones. In this work supported iron catalysts on silica for FT with high amount of metal have been prepared, characterized and tested. The iron loading has been changed between 10 and 50%wt in the presence or non-presence of promoters K and Cu. The quantity of promoters has been changed too in order to optimize the catalysts performance. An optimized catalysts, containing 30% of Fe, 2% of K and 3.75% of Cu has been identified and then prepared using different preparation methods, i.e. traditional impregnation or using ultrasound (US) and microwave (MW) in different conditions. To correlate the modification of the catalysts features (caused by the preparation method) with their performances in reaction, characterizations by BET, SEM, TEM, TPR, XRD and micro-Raman techniques have been also performed. Aim of this work is to assist the traditional impregnation method using ultrasound (US) or microwave (MW) to optimize the iron deposition. The main advantages of catalysts prepared by US derived from acoustic cavitation: bubbles formed by ultrasonic waves tend to collapse preferentially near the solid surfaces (i.e. silica surface) and collapsing bubbles generate localized hot spot. The effect of acoustic cavitation is favoured by the presence of noble gases dissolved like argon. Microwave treatment is a promising technique for catalyst preparation because of its dielectric heating characteristic, due to the possibility to generate an electric field able to polarize charges in a material. This effect is enhanced if the irradiated material presents a strong dipolar nature, as SiO2, an oxide with many surface polar OH groups. FT synthesis were carried out in a fixed bed reactor under reaction condition of 210-310 \ub0C, 20 bar and H2/CO ratio of 0.5, 1, 2, 3 for 60 h. The catalysts performance is strictly correlated with their activation, depending both by the gas and by the temperature of this step, and the treatment in syngas at T= 350\ub0C at P=3 bar for t=4 h gives the best results. A complete characterization of catalysts after different activation procedures has been performed

Ultrasonic free fatty acids esterification in tobacco and canola oil

Ultrasound accelerates the free fatty acids esterification rate by reducing the mass transfer resistance between methanol in the liquid phase and absorbed organic species on Amberlyst\uae46 catalyst. The reaction rates of canola oil is three times greater than for tobacco seed oil but half the reaction rate of pure oleic acid as measured in a batch reactor. The beneficial effects of ultrasound vs. the conventional approach are more pronounced at lower temperatures (20 \ub0C and 40 \ub0C vs. 63 \ub0C): at 20 \ub0C, the free fatty acids conversion reaches 68% vs. 23% with conventional mechanical stirring. The increased conversion is attributed to acoustic cavitation that increases mass transfer in the vicinity of the active sites. The Eley-Rideal kinetic model in which the concentration of the reacting species is expressed taking into account the mass transfer between the phases is in excellent agreement with the experimental data. Ultrasound increases the mass transfer coefficient in the tobacco oil 6 and 4.1 fold at 20 \ub0C and 40 \ub0C, respectively