Ind. Eng. Chem. Res. 2008, 47, 7997–8004
7997
Biodiesel from Low-Grade Animal Fat: Production Process Assessment and Biodiesel Properties Characterization Laureano Canoira,*,† Miguel Rodrı´guez-Gamero,† Enrique Querol,† Ramo´n Alca´ntara,† Magı´n Lapuerta,‡ and Fermı´n Oliva‡ Department of Chemical Engineering & Fuels, ETS Ingenieros de Minas, UniVersidad Polite´cnica de Madrid, Rı´os Rosas 21, 28003-Madrid, Spain, and Ma´quinas y Motores Te´rmicos, ETS Ingenieros Industriales, UniVersidad de Castilla La Mancha, AVenida Camilo Jose´ Cela s/n, 13071-Ciudad Real, Spain
Biodiesel from different mixtures of animal fat and soybean oil has been synthesized, and its properties have been evaluated and related to its composition. A mixture of 50 vol % of both raw materials has been selected as a suitable feedstock for industrial biodiesel production, and a computer simulation of the production process using Aspen Plus software has been carried out to evaluate the industrial feasibility of this scheme using this cheaper feedstock. The results obtained suggest that the process proposed and described produces a biodiesel with the selected feedstock acceptable by the standards with a lower final cost. The feedstocks employed are cheaper and consist of a waste fat without any other use, thus increasing the environmental benefits of the biodiesel and reducing dependency on conventional agricultural raw materials. Introduction Biodiesel is defined as “a fuel comprised of monoalkyl esters of long chain fatty acids derived from vegetable oils or animal fats”.1 Transesterification (also called alcoholysis) of triglycerides for biodiesel manufacture has been extensively studied in the past few years in our research group2–4 and by others.5–10 The European Union has issued Directive 2003/30/EC, which mandates the use of biofuels in a percentage ranging from 2% in 2005 to 5.75% in 2010 (calculated on the basis of energy content) for all transportation fuels marketed within the member states, and it is expected that a significant portion of this amount will be biodiesel due to the growing “dieselization” of the fuel markets in some European countries. Biodiesel can be synthesized from a variety of feedstocks, including vegetable oils, animal fats, and used cooking oils. Usually, refined vegetable oils are the main feedstock for biodiesel production. However, in the past few years, the prices of these refined vegetable oils (soybean, rapeseed, palm, and others) have been increasing steadly,11 making biodiesel production from these feedstocks unprofitable in many locations. Waste greases such as used cooking oil and animal fats can also be used as feedstock because of their availability and low cost.12–20 Animal fats have also been used without transformation to improve the rheological properties of fuel oil.21 The use of these waste greases to produce biodiesel opens a route to recycle this waste that otherwise would finish in the drain or could only be sold as feedstock for the soap industry. Moreover, animal fats are considered lowquality feedstock compared to refined vegetable oils because of their free fatty acids (FFA) content that may increase up to 15 wt % by contrast with refined soybean oil, which typically contains less than 0.5 wt % FFA. The price of this yellow animal fat is around 419 euros/ton11 in contrast to the 2007 price of soybean oil of 780 euros/ton11 and probably increasing in the near future. Because of this price difference, the use of waste animal fat feedstock for biodiesel production could be a reasonable way to lower the overall biodiesel production costs. * To whom correspondence should be addressed. Tel.: 34 91 336 6949. Fax: 34 91 336 6948. E-mail:
[email protected]. † Universidad Polite´cnica de Madrid. ‡ Universidad de Castilla La Mancha.
Moreover, the quality, engine performance, and emissions of harmful compounds derived from biodiesel from animal fats have already been evaluated,22,23 and also the safety of a biodiesel production process using prion-contaminated animal fat as a feedstock has been checked.24,25 In this paper, we have studied different mixtures of waste animal fat and soybean oil as feedstock for biodiesel production, since the biodiesel obtained exclusively from animal fat could hardly meet the EN 14214 or ASTM D6751 standards specifications, and we have analyzed some parameters of the biodiesel obtained with each one of these mixtures as feedstock. We have carried out also a computer simulation17 of a possible industrial process based on our laboratory and pilot plant experiments using this less expensive feedstock. Results and Discussion Pretreatments. The high FFA acid content of the waste animal fat (Table 1) renders it inadequate for the most traditional direct one-step base-catalyzed transesterification process to biodiesel due to soap formation. However, an indirect multistep process allows the use of these feedstocks with high FFA concentrations by first carrying out an acid-catalyzed esterification of the FFA before the base-catalyzed triglyceride transesterification.26–29 Moreover, the low quality of the animal fat used as feedstock in this study poses other problems that need to be addressed in the production process. The higher nitrogen and sulfur contents of the animal fat (Table 1) indicate that still some protein and phosphoglycerides (usually called gums) remain in the feedstock; the phosphoglycerides are essential constituents of the animal cell membranes and they concentrate in the lipids fraction. For this reason, a degumming process to eliminate the phosphoglycerides has been proposed as the first step of this multistep process. The degumming method with 60 wt % orthophosphoric acid has been taken from the literature among the existing ones,30–39 and it produces between 3 and 5 wt % gums, which are separated by centrifugation, depending on the quality of the fat. The esterification of the FFA was carried out at 60 °C with stirring (600 rpm) using a molar ratio of 6:1 methanol/oil-fat with acid catalysis. Among the acids of choice to catalyze this
10.1021/ie8002045 CCC: $40.75 2008 American Chemical Society Published on Web 06/25/2008
7998 Ind. Eng. Chem. Res., Vol. 47, No. 21, 2008 Table 1. Characteristics of the Feedstock Acidity Index of the Feedstock Before and After Esterification animal fat/ soybean oil, vol %
acidity index initial (EN ISO 660/2000)
100/0 80/20 60/40 50/50 40/60 0/100
13.6 10.4 6.8 7.2 4.8 0.5
acidity index after esterification (EN ISO 660/2000) 1.7 0.5 0.6 0.6 0.3
Elemental Analysis of the Feedstocka feedstock
%C
%H
%N
S, mg/kg
animal fat soybean oil
76.51 77.56
12.36 11.96
0.26 0.18
380.9
