Biodiesel Production from Leather Industry Wastes Luís Ramos, Rui Fernandes, António Crispim Ribeiro, Elisa Ramalho*, Nídia S. Caetano, Paula Silva CIETI-Centro de Inovação em Engenharia e Tecnologia Industrial, Instituto Superior de Engenharia do Porto, R. Dr. António Bernardino de Almeida, 431, 4200 Porto, Portugal Keywords: Biodiesel, Fleshings, Transesterification, Methyl esters, Beef tallow Topic: Multi-scale and/or multi-disciplinary approach to process-product innovation
Abstract Animal fat was extracted from fleshings, a residue from the leather industry, by a two step procedure. First the fleshings are mixed with water (60 ºC) and then the fat rich phase obtained is treated with n-hexane to extract the fat and leave the proteic residue. This fat presents a high acid value and therefore the direct transesterification to biodiesel with an alkaline catalyst was not possible. A pre-treatment step was performed, consisting of an esterification reaction with methanol in the presence of sulfuric acid, and acid values were lowered below 3 mg KOH/g. The transesterification with methanol was carried out with KOH as catalyst at 65ºC in two stages using 80% of the methanol/KOH solution in the first step and the remaining in the second step. The methyl ester product was characterized and the parameters are, in most cases, within the specifications. The exception is the methyl ester content (94,2%) indicating that further adjustments are needed in the production process in order to improve the quality of the final product. 1 Introduction Sustainable energy management is a main world concern, considering the fact that fossil fuels supplies are limited and energy demand continues to rise. Search for alternative renewable fuels has therefore gained fundamental importance. Among biofuels, biodiesel has very good utilization and environmental properties, and became a widely used alternative to fossil fuels, with ten years long commercial use in Europe and a rapidly growing world market. Biodiesel cost is mainly determined by feedstock prices. Presently, the cost of the cereals that are used to produce biodiesel is increasing due to the growing market demand. Also, this huge demand introduces a sustainability problem for the next coming years. Significant research effort is being dedicated to the search for alternative feedstocks. Among these, animal fats from different sources, leather industry, butcher’s and slaughterhouses, are potentially interesting. Furthermore, the re-use of these wastes is an environmental friendly disposal option. Animal fats present usually a high acid value and its fatty acid composition shows a more saturated character than vegetable oils, as can be seen in table 1.
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Table 1.Typical fatty acid compositions of vegetable oils and animal fats (Scrimgeour, 2005). Fatty acid (wt %)
Myristic (14:0)
Palmitic (16:0)
Palmitoleic (16:1)
Stearic (18:0)
Oleic (18:1)
Linoleic (18:2)
Linolenic (18:3)
Soybean oil
0.1
11
0.1
4
23.4
53.2
7.8
Beef tallow
2,7-4,8
20,9-28,9
2,3-9,1
7,0-26,5
30,4-48,0
0,6-1,8
0,3-0,7
Biodiesel is a mixture of fatty acid esters, obtained by the transesterification of vegetable oils or animal fats with a low molecular weight alcohol, with glycerol as a byproduct, as shown in fig. 1. O CH2
O
O
C
R1
CH3
O CH
O
O
C
R2 + 3 CH3OH
CH3
O
O
OH
R2 +
CH
OH
R3
CH2
OH
C
O CH2
CH2
O
(catalyst)
C
R1
O
C
R3
CH2
Triglyceride
Methanol
O
C
Mixture of methyl esters
Glycerol
Figure 1. Transesterification reaction of vegetable oils or fats. Almost all biodiesel production processes are based on the transesterification of triglycerides with methanol using an alkaline homogenous catalyst (NaOH or KOH), in batch or continuous plants. This process requires feed stocks with low free fatty acid (FFA) and water contents. Typical animal fats contain from 5% to 30% FFAs (Gerpen, 2005), and soap formation (fig. 2) occurs in considerable amounts, making product separation very difficult.
O HO
C
O R
Fatty acid
+ NaOH Sodium hydroxide
Na+ -O
C
R
+
Sodium soap
H2O Water
Figure 2. Saponification reaction of free fatty acids. To avoid this problem, a pretreatment step is required to convert FFAs to methyl esters, thereby reducing the FFA level. This treatment consists of an esterification with methanol and sulfuric acid as catalyst, as shown in fig. 3. After this reaction, the treated fat can be transesterified with an alkali catalyst to convert the triglycerides to methyl esters.
O HO
C
O
(H2SO4)
R
Fatty acid
+ CH3OH Methanol
CH3
O
C
R +
Methyl ester
H2O Water
Figure 3. Esterification reaction of free fatty acids. The purpose of this work is to investigate the possibility of using fleshings (bovine) from the leather industry in biodiesel production. These leather industry wastes contain 40 to 60 wt % of fat (dry basis). Beef tallow is also tested for comparison purposes, because it is a similar residue and previous works showed the feasibility of this feedstock for biodiesel production (Lebedevas, 2006). 2 Materials and methods Analytical methods Acid value was determined according to EN 14104 Standard and iodine value was determined according to EN 14111 Standard. Viscosity was determined according to EN ISO 3104 Standard and density was determined using a picnometer method. Methyl ester content was determined by a GC method, according to EN 14103 Standard. Fat extraction To obtain the fat from beef tallow, the solid is melted at 140 ºC and the product is filtered to remove any solid particles that may be present. To obtain fat from fleshings two steps are needed: first, the solids are mixed with water and heated in order to break the bonds between the fat and protein material. The optimal conditions for this step are solid:water mass ratio of 1:0.75, for 2h at 70 ºC. Three different phases are obtained, a fat rich phase, a water rich phase and a protein rich phase. In the second step, the fat rich phase is treated with n-hexane to extract the fat and leave the proteic residue. The operating conditions for extraction are: rich fat phase:solvent mass ratio of 1:10, ambient temperature and 1h. The product is filtered to remove the proteins and nhexane is separated from the fat by distillation. Biodiesel production All these animal fats present high acid values depending on the source, and thus a pretreatment step is needed. This pre-treatment consists of an esterification of the free fatty acids with methanol and sulfuric acid as catalyst at 70ºC. After the phases are separated, the fat phase is transesterified with methanol using potassium hydroxide as catalyst. Initial experiments with a single step transesterification of the fleshings (fat:methanol:KOH mass ratio of 1:0.238:0.01 at 65ºC and 3h) resulted in a product with a low ester content (70%). Therefore a two-stage operation procedure was performed (Baptista, 2008). The first step consisted of a transesterification using 80% of the total volume of the methanol/KOH solution at 65 ºC. The glycerol phase was then removed and the ester rich phase was reacted again with the remaining methanol/KOH solution. After the separation of the glycerol phase, the ester phase was washed with water and dried. The acid value, iodine number, ester content, density and viscosity of the product were determined.
3 Results and discussion Concerning fat extraction, the first step yield (mass of fat rich phase/mass of dryed fleshings) ranged from 81 to 89%. For the hexane extraction step, yields of 58-70% were obtained (mass of fat /mass of fat rich phase). Acid esterification reaction times were studied and the results are shown in figure 4. As can be seen, one hour is sufficient to reduce the acid number to acceptable values for the transesterification step.
Figure 4. Acid value of the fat as a function of the esterification time.
The results of two step transesterification preliminary studies (3h+2h) presented in table 2, show that the methyl ester products from both raw-materials are similar. This behaviour was expected, as fat from bovine fleshings should have the same composition as beef tallow. Further studies allowed to reduce characterization is presented in table 3.
reaction
times
to
1h+1h,
and
product
Table 2. Characterization and yield of methyl ester product (reaction times 3+2h). Fat source
Acid value (mg KOH/g)
Ester content (%)
Density, 15ºC (g/cm3)
Viscosity, 40ºC (mm2/s)
Yield (%)
Beef tallow
0.17
94.2
0.87
4.8
65
Fleshings
0.18
94.1
0.87
4.8
57
Table 3. Methyl ester characterization (reaction times 1+1h). Parameter
Result
EN 14214 reference values
Methyl esters (wt%) Density, 15ºC (g/dm3)
94,2 872
≥ 96.5 860-900
Viscosity, 40ºC (mm2/s) Acid value (mg KOH/g)
4,8 0,172
3,5-5,0 < 0,5
Iodine value (g I2 /100g)
48,5
< 120
The values obtained are, except for methyl ester content, within the specifications for biodiesel (EN 14214 standard). The product presents methyl ester contents close to the standard value, so further optimization of operating and purifying conditions is needed. 4 Conclusions This study shows the feasibility of using the fleshings from the leather industry to produce biodiesel, but further adjustments are needed in the production process in order to improve the quality of the final product. Biodiesel produced from this kind of raw material, will present a high CFPP and will need to be blended (with biodiesel produced from vegetable sources or petroleum diesel) prior to final utilization.
Acknowledgements Authors are thankful to Agência de Inovação (AdI) for financial support (Project VEGORADI/2007/U 4.1/ 0061). References Baptista, P., Felizardo, P., Menezes, J.C., Correia, M.J.N., (2008). Multivariate near infrared spectroscopy models for predicting the methyl esters content in biodiesel. Analytica Chemica Acta, 607, 153-159 Gerpen, J.V., (2005). Biodiesel processing and production, Fuel Processing Technology, 86, 1097-1107 Lebedevas, S., Vaicekauskas, A., Lebedeva, G., Makareviciene, V., Janulis, P., Kazancev, K., (2006). Use of waste fats of animal and vegetable origin for the production of biodiesel fuel: quality, motor properties and emissions of harmful components. Energy and Fuel, 20, 2274-2280 Scrimgeour, C., (2005). Chemistry of fatty acids, in Bailey’s Industrial Oil and Fat Products, Volume 6, Wiley, New York.
