Valorization of Waste Frying Oils and Animal Fats for Biodiesel Production

Teresa M. Mata, Antonio A. Martins, and Nidia S. Caetano

Abstract The increased demand for biodiesel and the difficulties in obtaining enough quantities of raw materials for its production are stimulating the search for alternative feedstocks. Among the various possibilities, the utilization of residual fatty materials, in particular waste frying oils and animal fat residues from the meat and fish processing industries, are increasingly seen as viable options for biodiesel production. This work reviews the state of the art regarding the utilization of waste oils and animal fats as feedstocks for biodiesel production, which are characterized by the presence of high levels of impurities such as high acidity and moisture con­tent. The relative advantages and disadvantages of the different routes for biodiesel production are presented and discussed in this chapter, focusing on their chemical and technological aspects. Also discussed are the questions related to the viability and potential economic advantages of using this type of feedstocks in biodiesel production for road transportation.

T. M. Mata(H)

Laboratory for Process, Environmental and Energy Engineering (LEPAE), Faculty of Engineering, University of Porto (FEUP), R. Dr. Roberto Frias, s/n, 4200-465, Porto, Portugal e-mail: tmata@fe. up. pt

A. A. Martins

Center for Transport Phenomena Studies (CEFT), Faculty of Engineering, University of Porto (FEUP), R. Dr. Roberto Frias, s/n, 4200-465, Porto, Portugal

N. S. Caetano

Laboratory for Process, Environmental and Energy Engineering (LEPAE), Faculty of Engineering, University of Porto (FEUP),

R. Dr. Roberto Frias, s/n, 4200-465, Porto, Portugal

Department of Chemical Engineering, School of Engineering (ISEP), Polytechnic Institute of Porto (IPP), R. Dr. Antonio Bernardino de Almeida, s/n, 4200-072, Porto, Portugal

J. W. Lee (ed.), Advanced Biofuels and Bioproducts, DOI 10.1007/978-1-4614-3348-4_28, 671

© Springer Science+Business Media New York 2013

1 Introduction

As energy demands increase and the fossil fuel reserves are limited or are becoming harder and harder to explore, research is being directed towards the development of renewable fuels. This aspect is particularly relevant in the transportation sector, where the dependence on fossil fuels is even more evident and any possible alternative (e. g. fuel cells and hydrogen) is harder to develop and implement in practice. In the short term, especially in Europe, biodiesel (mono-alkyl esters of long-chain fatty acids) derived from renewable biological sources such as vegetable oils or animal fats are attracting a lot of attention. Among its main key features one can point out its renewability, biodegradability, improved viscosity, better quality of exhaust gases, and also the possibility of being used, as a petroleum diesel substitute or combined with diesel fuels, in conventional combustion ignition engines without significant modifications.

Biodiesel promises to supplement and even replace at a local/regional level fossil diesel while contributing to rural development and reducing the dependence on fos­sil fuels. However, under current production technology, its use in transportation even blended with diesel has some pros and cons. First, biodiesel production costs are higher than those of petroleum diesel, mainly due to its production from expen­sive edible vegetable oils that account for 88% of the total estimated cost for biod­iesel production [90]. This is one of the major hurdles in biodiesel commercialization, making it difficult to compete in price with fossil diesel and requiring in many cases subsidies or fixed prices policies to be competitive with current fossil fuels or to fulfil specific national or international targets for the incorporation of bio-based fuels. Second, the continued development, market growth, and market share of biodiesel, with the corresponding need of raw materials for its production, has risks of their own and is causing more harm than good. For example, some of the most relevant feedstocks, such as soybean oil and palm oil, are placing additional pres­sure on food supplies during a period of great demand increase in developing coun­tries and diverting valuable resources away from food production. Until new technologies and/or feedstocks unconnected with the human food supply chain are developed, the use of edible vegetable oils to produce biodiesel might further strain the already tight supplies of arable land and water all over the world, potentially pushing food prices up even further. Furthermore, biodiesel feedstocks are impacted by previous and current land use practices, and cultures are adapted to specific cli­mate and soil conditions available in restricted regions of the world. Thus, moving a culture from one region of the world to another will surely influence the crop yield potential. For example, requiring the utilization of more fertilizers, having an impact on the local biodiversity as some of the species can be invasive and displace native species, or bringing pests with them, with potential direct consequences to local ecosystems. Also, a more intense agriculture normally increases the soil erosion due to carbon loss and nitrate and phosphorous loss [82] .

To circumvent the problems referred above, new feedstocks are needed what is currently an extensive area of research. An example includes microalgae that have the ability to grow under harsher conditions, in areas unsuitable for agricultural purposes, and with reduced needs for nutrients. This way, the competition with other crops for arable soil, in particular for human consumption, is greatly reduced. Also, microalgae are easy to cultivate and can grow at low cost with little attention, using water unsuitable for human consumption. However, very high energy requirement for drying the algal biomass is a barrier to its commercialization at present [66] . Another example is Jatropha curcas L, currently at a very early stage of development for biodiesel production. Since the markets of the different products from this plant have not yet been properly explored or quantified, the optimum economic benefit of its production has not been achieved [57].

From the currently available alternative feedstocks for biodiesel production, some attention is being given to residual oil and fat, such as waste frying oils from restaurants or food industry, and animal fats resulting from the meat or fish process­ing industries, which otherwise need to be disposed off with care and represents an operational cost. Even though the residual oil or fat are of lesser quality than virgin vegetable oils and more difficult to process due to the presence of impurities or to their high acidity, they may be a good option for biodiesel production, allowing one to use a waste and treating it appropriately in the production of a product (biodiesel) with value that can be used internally by the company or sold out. Moreover, these fatty materials are available at a lower cost (in many cases even for free) and can be used as feedstock for biodiesel production. Araujo et al. [8] evaluated the biodiesel production from waste frying oil concluding that it can be economically feasible provided that logistics are well configured.

The most common animal fats that can be processed into biodiesel are beef tallow, pork lard, and poultry fat. Fish oils are also possible to be converted into biodiesel, although research in this area is not so advanced as for the animal fats. In most of these cases, the oil or fat are not readily available for use in biodiesel production, but need to be firstly extracted from the fatty residues. It is estimated that about 38% of the bovine, 20% of the pork, and 9% of the poultry are fatty material for rendering (e. g. bones, fat, head, other non edible materials, etc.) from which can be obtained about 12-15% of tallow, lard, or poultry fat that can be used for biodiesel production [25, 36].

The lipid content in fish varies a lot depending on the type of fish and by-product. For example, Gunasekera et al. [45] reported the lipid content of 17% in carp offal, 13% in carp roe, 57% in trout offal, 31% in fish frames, and 13% in “surimi” pro­cessing waste and fish meal. Oliveira and Bechtel [74] reported 11.5% of lipids in pink salmon heads and 4% in salmon viscera. Kotzamanis et al. [55] reported 12% of lipids in trout heads.

In the European Union, about one million tonnes of tallow is rendered each year

[69] . The United States generates in average about 4 kg/person of yellow grease per year, and based on this statistic, Canada should produce about 120,000 tonne/year of waste fats of various origins [100]. Brazil generates about 1,382,472 tonne/year of beef tallow and 194,876 tonne/year of lard from slaughterhouses, which is nor­mally used for producing meal and oil for animal feed [25] . The world fi sh capture and aquaculture production was in 2004 about 140 million tonnes of fish, from which about 25% was for non-food uses, in particular for the manufacture of fish oil and animal meal [ 34]. The amount of waste frying oil generated annually in several countries is also huge, accounting for more than 15 million tonnes, varying according to the amount of edible oil consumed. For example, the United States generates around 10 million tonnes of waste frying oils, followed by China with 4.5 million tonnes and by the European Union with a potential amount ranging from

0. 7 to 1.0 million tonnes [44]. However, the worldwide amount of waste oils generated should be much larger than that and it is expected to increase in the near future.

Some studies available in the open literature show some potential for these feed­stocks. For example, Chua et al. [30] performed a LCA to study the environmental performance of biodiesel derived from waste frying oils in comparison with low sul­phur diesel and concluded that biodiesel is superior in terms of global warming poten­tial, life cycle energy efficiency, and fossil energy ratio. Godiganur et al. [41] tested biodiesel from fish oil in compression ignition engines, showing overall good com­bustion properties and environmental benefits. In particular, there are no major devia­tions in diesel engine’s combustion and no significant changes in the engine performance. Moreover, there is a reduction of the main noxious emissions in com­parison with fossil diesel, with the exception on the nitrogen oxide (NOx) emissions. Wyatt et al. [97] produced biodiesel from lard, beef tallow, and chicken fat by alkali — catalyzed transesterification. The biofuel obtained from these animal fats were tested and the NOx emissions determined and compared with soybean biodiesel as 20% volume blends (B20) in petroleum diesel. Results show that the three animal fat-based B20 fuels have lower NOx emission levels (3.2-6.2%) than the soy-based B20 fuel.

Animal fats and vegetable oils differ on their physical and chemical properties. While vegetable oils have a large amount of unsaturated fatty acids, animal fats have in their composition a large amount of saturated fatty acids [20] . Animal fats such as tallow or lard are solid at room temperature. An exception is the poultry fat which is liquid at room temperature and has in its composition a low percentage of satu­rated triglycerides, comparable to soybean oil. Fish oils contain a wide range of fatty acids, some of them with more than 18 atoms in their carbon chain and even some with an odd number of carbons [37]. Chiou et al. [28] analysed and compared the methyl esters derived from salmon oil extracted from fish processing by-prod­ucts with methyl esters derived from corn oil, concluding that, although there are some differences in the fatty acid composition, salmon and corn oil methyl esters have similar physical properties.

The physical and chemical properties of waste frying oil and the corresponding fresh edible oil are almost identical, but differ from source to source depending on the oil source. Waste oils have normally higher moisture and free fatty acids (FFA) contents than fresh edible oil, particles of different composition, and also polymer­ized triglycerides are formed during frying due to the thermolytic, oxidative, and hydrolytic reactions that may occur [ 44] . Additionally, during frying, the oil is heated at temperatures of 160-200°C in the presence of air and light for a relatively long period of time, what contributes to increase its viscosity, specific heat, and darkens its colour.

For processing these fatty waste materials and to improve the quality of biodiesel produced, different solutions can be employed. For example, Guru et al. [46] stud­ied biodiesel production from waste animal fats in a two-step catalytic process and adding organic-based nickel and magnesium compounds as additives in order to achieve a reduction in the biodiesel pour point. Canoira et al. [22] evaluated biodiesel obtained from different mixtures of animal fat and soybean oil using a process simu­lation software (Aspen Plus™), concluding that a mix of 50% (v/v) of both raw materials is the most suitable to obtain a final product with a quality according to the standards and with the minimum costs. This is relevant to optimize the production processes and ensure that the costs of disposal should be higher than the costs of making biodiesel corrected by the potential economical gains, for example reducing the consumption of fossil fuels.

As most of the biodiesel feedstocks have similar characteristics, any improvement in the way how the pre-processing, reaction, and final processing are done, in particu­lar related to the reaction time and final product quality, will have a profound impact in the production capacity and in the overall process. As two phases are formed and the diverse reactants are presented in different phases, the effects of mixing are significant to the process. The interfacial area between phases increases with high mixing intensity, facilitating the mass transfer between phases and naturally increas­ing the reaction rates [10]. Noureddini and Zhu [73] confirm these conclusions and have shown that, depending on the reaction stage, both the mass transport and the reaction kinetics are dominant aspects controlling the process performance.

In this work, the various steps for biodiesel production are described, depending on the characteristics of the waste oil or animal fat, having in mind the process improvement.

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