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Heterogeneous catalysis for free fatty acids esterification reaction as a first step towards biodiesel production
No full textDifferent non-food-grade oils characterized by a high
content of free fatty acids have been successfully
deacidified with the use of commercial resins Amberlyst®46
(A46), Purolite®D5081and zirconium sulphate. Not refined
or waste oils have been selected in order to reduce the
biodiesel production costs, mostly depending on the raw
material’s high price. Five sulphated, Zr-based, catalysts
have been synthesized through different methods based
on sol-gel or impregnation techniques and tested in the
same reaction. The role played by the different catalysts’
features in affecting their catalytic activity in the studied
reaction is discussed. The economic sustainability of the
whole process is also assessed
BIODIESEL PRODUCTION FROM NON-FOODSTUFF: CHEMISTRY, CATALYSIS AND ENGINEERING
Full text link1. 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):
‘‘For the purposes of demonstrating compliance with national renewable energy obligations [...], 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’’.
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®15 (A15), Amberlyst®46 (A46) (Dow Chemical) and Purolite®D5081 (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 (Ǻ) 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 (López 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 Brønsted 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 (%)=" (〖"FFA" 〗_"t=0" "-" 〖"FFA" 〗_"t" )/〖"FFA" 〗_"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
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FT synthesis were carried out in a fixed bed reactor under reaction condition of 210-310 °C, 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°C at P=3 bar for t=4 h gives the best results. A complete characterization of catalysts after different activation procedures has been performed
Sonochemical techniques to increase the efficiency of methyl esters production from non-food oils
No full textIndustrially practiced transesterification for biodiesel production can accept a restricted range of feedstocks, with free fatty acids (FFA) concentration and moisture content lower than 0.5 and 0.2%wt, respectively. Refined oils usually match this requirement but their use increases biodiesel production costs, besides being in competition with food production. Non-food raw oils may require several pretreatment steps before proceeding with the transesterification. The search for high efficiency transformation methods is therefore a key issue. In this work, FFA esterification, catalysed by ion exchange resins, and the homogeneously catalysed transesterification to produce fatty acids methyl esters are studied using single and combined sonochemical techniques such as ultrasound and microwaves. The results show that microwaves are able to enhance FFA esterification activity, allowing to achieve 90% of conversion in 2 hours rather than 4 hours, required by the traditional method. US increases tremendously transesterification conversions, yielding methyl esters above 96.5%wt within 30 minutes, while more than 2 hours are usually required with the traditional method. Moreover, much lower reagents and catalyst amount are requires when ultrasound are applied. The positive effect of microwaves is attributable to the re-orientation of the methanol dipole leading to the formation of a methanol-oil/emulsion with very high exchange area between the phases. The benefits brought by the use of ultrasound may be ascribed to both chemical and physical effects generated by acoustic cavitation
Feasibility study for the production of biofuel from Brassicaceae spp. and Nicotiana tabacum oilseeds and from by-products or waste materials
No full textBiodiesel is a non-toxic, biodegradable, environmentally
friendly alternative diesel fuel, produced from food-grade vegetable
oils through a transesterification reaction with methanol and
an alkaline catalyst. Using not refined or waste oils as a feedstock
represents a convenient way to lower biodiesel production costs.
The main problem using this type of low-cost feedstock lies in its
high content of FFA (Free Fatty Acids), leading to the formation of
soaps during the transesterification reaction.
The use of Brassicaceae spp. (B. carinata, B. juncea) and Nicotiana
tabacum for biodiesel production is investigated. Using a LCA
(Life Cycle Analysis) we assess the sustainability of biodiesel production
from these two innovative cultivations in crop rotation.
B. carinata has high yield both in adverse conditions and under
low cropping system. The aim is to exploit Brassiacaceae spp. better
agronomic performances in areas characterized by unfavorable
environmental conditions for other cultivations. Moreover Brassicaceae
spp. tissues contain high concentrations of glucosinolates
that can be hydrolyzed to isothiocyanate by the plant enzyme under
conditions of physical injury. Biofumigation effect of isothiocyanate
release from soil-incorporated Brassicaceae spp. tissues is known to
reduce soil plant pathogens and it could be an alternative method to
chemical plant disease control measure. This is useful for Nicotiana
tabacum, susceptible to nematode infection, being an interesting
alternative oil seed cultivation due to its high yield patent selections
(Fogher et al.). Tacking advantage of all these Brassicaceae spp.
and Nicotiana tabacum characteristics it could be possible not only
to produce high yield of oil seeds but also to reclaim nematode
infected fields.
Vegetables oils produced from new kinds of oil seeds were
selected and de-acidified by the direct esterification reaction of
their FFA in presence of pure methanol and using solid acid resins
as heterogeneous catalysts in mild working conditions (T = 338 K)
Free fatty acids esterification of waste cooking oil and its mixtures with rapeseed oil and diesel
No full textThe choice of waste cooking oil (WCO) as a raw material for biodiesel production is recognized to be an attractive and economic alternative to the use of vegetable oils. However, the presence of free fatty acids, impurities and high viscosity of WCO may require several pretreatments before the transesterification. In this study WCO deacidification by esterification is investigated: the results show how both Amberlyst®46 and Purolite®D5081 catalysts maintain their performance in a Carberry reactor (where catalyst is confined to minimize mechanical stress) and a slurry reactor after several recycles. A46 was tested in the free fatty acids esterification of blends of WCO with different ratios of crude rapeseed oil and diesel as a solvent. The results show how both the use of the blends with another oil with lower viscosity and diesel are both beneficial to the reaction rate and to the properties of the finished biodiesel
Ultrasound assisted catalysis for biodiesel production
Full text linkThe EU directive 2009/28/EC has set the targets of
achieving in each member State, by 2020, a minimum
share of 10% of energy consumption in transport sector
from renewable sources. In this context special consideration
is paid to the production of biofuels. The most
recent challenges concerning biodiesel production (BD)
deal with the use of non food-grade oilseeds and their
standardization to make them suitable to be transformed
into methyl esters (BD) through transesterification [1,
2]. In fact raw oils contain high acidities which, besides
giving saponification problems during the BD production
are also regulated by the European normative on
BD (EN14214) [3].The aim of the present work is to
conceive an efficient method able to perform both the
standardization and the transformation into BD of raw
oils. In this work heterogeneously acid-catalyzed esterification
of free fatty acids (FFA) and homogeneously
basic-catalysed transesterification are investigated in
raw tobacco and rapeseed oils along with the use of
ultrasound (US). The most outstanding result of this
study concerns how US are able to increase reactions
yields because of the occurrence of the acoustic cavitation
in the liquid reaction medium as well as the occurrence
of the surface cavitation which generates mechanical
effects on the catalyst’s surface
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