ARTICLE IN PRESS

Bioresource Technology xxx (2005) xxx–xxx

The potential of restaurant waste lipids as biodiesel feedstocks Mustafa Canakci

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Department of Mechanical Education, Kocaeli University, 41380 Umuttepe-Izmit, Turkey Received 16 March 2005; received in revised form 25 April 2005; accepted 23 November 2005

Abstract Biodiesel is usually produced from food-grade vegetable oils that are more expensive than diesel fuel. Therefore, biodiesel produced from food-grade vegetable oil is currently not economically feasible. Waste cooking oils, restaurant grease and animal fats are potential feedstocks for biodiesel. These inexpensive feedstocks represent one-third of the US total fats and oil production, but are currently devoted mostly to industrial uses and animal feed. The characteristics of feedstock are very important during the initial research and production stage. Free fatty acids and moisture reduce the eYciency of transesteriWcation in converting these feedstocks into biodiesel. Hence, this study was conducted to determine the level of these contaminants in feedstock samples from a rendering plant. Levels of free fatty acids varied from 0.7% to 41.8%, and moisture from 0.01% to 55.38%. These wide ranges indicate that an eYcient process for converting waste grease and animal fats must tolerate a wide range of feedstock properties.  2005 Elsevier Ltd. All rights reserved. Keywords: Alternative fuel; Biodiesel; Animal fat; Restaurant waste oil

1. Introduction Rudolph Diesel, a German engineer, introduced the diesel engine over a century ago (Nitske and Wilson, 1965). Since then a great deal of research and development has taken place, not only in the design area but also in Wnding an appropriate fuel. For many years, the ready availability of inexpensive middle-distillate petroleum fuels provided little incentive for experimenting with alternative, renewable fuels for diesel engines. However, since the oil crisis of the 1970s, research interest has expanded in the area of alternative fuels. Many proposals have been made regarding the availability and practicality of an environmentally sound fuel that could be domestically sourced. Methanol, ethanol, compressed natural gas (CNG), liqueWed petroleum gas (LPG), liqueWed natural gas (LNG), vegetable oils, reformulated gasoline and reformulated diesel fuel have all been considered as alternative fuels. Of these alternative fuels, only ethanol and vegetable oils are non-fossil fuels. *

Tel.: +90 262 303 2285; fax: +90 262 303 2203. E-mail address: [email protected]

0960-8524/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.11.022

Many researchers have concluded that vegetable oils and their derivatives hold promise as alternative fuels for diesel engines rather than spark-ignited engines due to their low volatility and high cetane number (Wagner et al., 1984; Scholl and Sorenson, 1993; Bagby et al., 1987; Goering et al., 1982). However, using raw vegetable oils for diesel engines can cause numerous engine-related problems (Korus et al., 1982; Perkins and Peterson, 1991). The increased viscosity and low volatility of vegetable oils lead to severe engine deposits, injector coking, and piston ring sticking (Perkins and Peterson, 1991; Pestes and Stanislao, 1984; Clark et al., 1984; Vellguth, 1983). However, these eVects can be reduced or eliminated through transesteriWcation of the vegetable oil to form an alkyl ester (Perkins and Peterson, 1991; Zhang et al., 1988). The process of transesteriWcation removes glycerin from the triglycerides and replaces it with the alcohol used for the conversion process (Kusy, 1982; Van Gerpen et al., 1997). This process decreases the viscosity but maintains the cetane number and the heating value. The alkyl monoesters of fatty acids from vegetable oils and animal fats, known as biodiesel, are receiving increasing attention as an alternative, non-toxic, biodegradable and

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M. Canakci / Bioresource Technology xxx (2005) xxx–xxx

Table 1 Fatty acid distribution of some vegetable oils and animal fats Product

Rapeseed oil SunXower oil SunXower oil Lard Tallow Soybean oil Yellow grease Brown grease a

Fatty acid distribution (% by weight) C14:0

C16:0

C16:1

C18:0

C18:1

C18:2

C18:3

– – – 1–2 3–6 – 2.43 1.66

3.49 6.08 8.60 28–30 24–32 10.58 23.24 22.83

– – – – – – 3.79 3.13

0.85 3.26 1.93 12–18 20–25 4.76 12.96 12.54

64.40 16.93 11.58 40–50 37–43 22.52 44.32 42.36

22.30 73.73 77.89 7–13 2–3 52.34 6.97 12.09

8.23 – – – – 8.19 0.67 0.82

Saturation level (%)

References

4.34 9.34 10.53 41–50 47–63 15.34 38.63 37.03

Goering et al. (1982) Goering et al. (1982) Goering et al. (1982) Linstromberg (1970) Linstromberg (1970) a a a

Measured by Woodson-Tenent Laboratories, Inc., Des Moines, IA.

renewable diesel fuel. Many studies have shown that the properties of biodiesel are very close to diesel fuel (Mittelbach et al., 1992; Peterson et al., 1992, 1994). Therefore, biodiesel fuel can be used in diesel engines with little or no modiWcation. Biodiesel has a higher cetane number than diesel fuel, no aromatics, no sulfur, and contains 10–11% oxygen by weight. These characteristics of biodiesel reduce the emissions of carbon monoxide (CO), hydrocarbon (HC) and particulate matter (PM) in the exhaust gas compared to diesel fuel (Vellguth, 1983; Chang et al., 1996). One drawback of biodiesel is that there is a tradeoV between biodiesel’s level of saturation and its cold Xow properties. Table 1 shows the fatty acid distribution of some common vegetable oils and animal fats. Saturated compounds (C14:0, myristic acid; C16:0, palmitic acid; C18:0, stearic acid) have higher cetane numbers and are less prone to oxidation than unsaturated compounds but they tend to crystallize at unacceptably high temperatures. Biodiesel from soybean oil is highly unsaturated so its cold Xow properties are acceptable; however, it is more prone to oxidation. Since the 1980s, considerable research has been conducted to investigate the properties of biodiesel and its performance in engines, as well as to provide the supporting data needed to satisfy the Environmental Protection Agency’s Fuels and Fuel Additives Registration program (Chang and Van Gerpen, 1997; Schumacher and Van Gerpen, 1996; Schmidt and Van Gerpen, 1996; Zhang and Van Gerpen, 1996; Chang et al., 1996). Virtually all of this work is based on the methyl ester of soybean oil. Soybean oil was chosen because, in the United States, soybean oil is the only oil that is available in suYcient quantity to supply a national market as shown in Table 2. However, the cost of food-grade soybean oil limits its use in diesel engines. Therefore, biodiesel is currently not economically feasible. Reducing the cost of the feedstock is necessary for biodiesel to be commercially viable. As can be seen in Table 2, there are large amounts of low-cost feedstocks, such as greases and rendered animal fat, which can be used in biodiesel production. The primary objective of this paper is to present the amount and properties of these low-cost, high free fatty acid feedstocks to produce commercially viable biodiesel.

Table 2 US production of fats and oils (billion pounds) Vegetable oil

Animal fat

Soybean Corn Peanuts SunXower Cottonseed Others

18.340 2.420 0.220 1.000 1.010 0.669

Total

23.659

Edible tallow Inedible tallow Lard and grease Yellow grease Poultry fat

1.625 3.859 1.306 2.633 2.215 11.638

Source: National Renderers Association (USDA averages, 1995–2000).

2. TransesteriWcation of vegetable oil One approach for reducing the viscosity of vegetable oils is transesteriWcation. TransesteriWcation is a chemical process of reacting vegetable oils with alcohol in the presence of a catalyst as shown in Fig. 1. TransesteriWcation signiWcantly reduces the viscosity of vegetable oils without aVecting the heating value of the original fuel. Therefore, fuel atomization, combustion, and emission characteristics will display better results than pure vegetable oil if the esters of vegetable oils are used in engines. Alcohols such as ethanol, methanol, or butanol can be used in the transesteriWcation and the monoesters are named methyl esters, ethyl esters or butyl esters, respectively. The catalysts used in transesteriWcation are generally classiWed in two categories, acidic and alkaline. The most commonly preferred acid catalysts are sulfuric, sulphonic and hydrochloric acids. Sodium hydroxide, sodium meth-

CH2

CH

CH2

O

O

O

O || C O || C O || C

Triglyceride

R1

CH3

O

Catalyst R2 + 3CH3OH

R3

CH3 O

CH3 Methanol

O || C O || C

O || O C

R1

CH2 OH

R2 + CH

R3

Methyl Esters

CH2

OH

OH

Glycerin

Fig. 1. TransesteriWcation of triglyceride using methanol and catalyst.

ARTICLE IN PRESS M. Canakci / Bioresource Technology xxx (2005) xxx–xxx Table 3 Standard speciWcation for biodiesel fuel (B100) blend stock for distillate fuels (ASTM D 6751-02) Property

ASTM method

Limits

Units

Flash point (closed cup) Water and sediment Kinematic viscosity, 40 °C Sulfated ash Sulfur Copper strip corrosion Cetane number Cloud point Carbon residue, 100% sample Acid number Free glycerin Total glycerin Phosphorus content Distillation temperature, atmospheric equivalent temperature, 90% recovered

D 93 D 2709 D 445 D 874 D 5453 D 130 D 613 D 2500 D 4530 D 664 D 6584 D 6584 D 4951 D 1160

130.0 min. 0.050 max. 1.9–6.0 0.020 max. 0.05 max. No. 3 max. 47 min. Report 0.050 max. 0.80 max. 0.020 max. 0.240 max. 0.001 max. 360 max.

°C vol% mm2/s mass% mass% – – °C mass% mg KOH/g mass% mass% mass% °C

oxide and potassium hydroxide are preferred as alkaline catalysts. In the transesteriWcation of vegetable oil with alkaline catalysts, other researchers (Romano, 1982; Freedman et al., 1984) have emphasized that the vegetable oil and alcohol should not contain water and free fatty acids (FFA) since they slow the reaction. Romano (1982) and Canakci and Van Gerpen (1999) found that even a small amount of water, such as 0.1%, in the transesteriWcation reaction will decrease the amount of ester formed signiWcantly. The properties of biodiesel vary somewhat depending on the oil feedstock and alcohol used but are always very close to diesel fuel (Mittelbach et al., 1992; Peterson et al., 1992, 1994). Biodiesel must meet American Society of Testing and Materials (ASTM) speciWcations designated in ASTM D-6751. Standard SpeciWcation for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels is shown in Table 3. The objective of this standard is to have biodiesel meet the performance requirements of engines without specifying the actual composition of the fuel. This will allow biodiesel to be made from any feedstock as long as the standard can be met. 3. Waste vegetable oils and animal fats In general, all greases and oils are classiWed as lipids. Chemically, greases and oils are classiWed as triglycerides. However, oils are generally considered to be liquids at room temperature, while greases and fats are solid at room temperature. Many animal fats and hydrogenated vegetable oils tend to be solid at room temperature. Both hydrogenated and non-hydrogenated vegetable oils are used in commercial food frying operations. Recycled grease products are referred to as waste grease. Greases are generally classiWed in two categories, yellow grease and brown grease. The main sources of animal fats are primarily meat animal processing facilities. Another source of animal fats is

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the collection and processing of animal mortalities by rendering companies. Yellow grease is produced from vegetable oil or animal fat that has been heated and used for cooking a wide variety of meat, Wsh or vegetable products. Renderers Wlter out the solids and heat the spent cooking oil to drive out moisture until it meets industry speciWcations for yellow grease. Yellow grease is required to have a free fatty acid (FFA) level of less than 15%. If the FFA level exceeds 15%, it is called brown grease, sometimes referred to as trap grease, and it may be sold at a discount, or blended with low FFA material to meet the yellow grease speciWcations. Trap grease is material that is collected in special traps in restaurants to prevent the grease from entering the sanitary sewer system where it could cause blockages. Many rendering plants will not process trap grease because it is usually contaminated with cleaning agents. These cleaning agents may not themselves be hazardous but they make detection of harmful substances more diYcult. Approximately 2.5 billion pounds of waste restaurant fats are collected annually from restaurants and fast-food establishments in the US (Haumann, 1990). The US Department of Energy’s National Renewable Energy Laboratory (NREL) sponsored a study on urban waste grease resources in 30 randomly selected metropolitan areas in the United States (Wiltsee, 1998). This study showed that an average of 9 pounds/year person of yellow grease and 13 pounds/year person of trap grease were produced in 1998. Table 4 shows quantitative data for yellow grease and trap grease from 30 metropolitan areas in the United States. The cities ranged in population size from 83,831 (Bismarck, ND) to 3,923,574 (Washington, DC). These data also showed that the cities had an average of 1.4 restaurants per 1000 people. Although the range of the data was fairly wide, the NREL study also concluded that the volume of the waste restaurant grease produced correlated to general population as well as to the number of restaurants. Waste vegetable oils and fats are generally low in cost and are currently collected from large food processing and service facilities. They are then rendered and used almost exclusively in animal feed. The prices of rendering plant products are shown in Table 5. The price of yellow grease varies widely from $0.09 to $0.20/lb. Brown grease is usually discounted $0.01–$0.03 below this (Simenson, 2000). Brown grease is often cited as a potential feedstock for biodiesel because it currently has very low value. However waste vegetable oil from restaurants and rendered animal fats are inexpensive compared with food-grade vegetable oil. According to the US Department of Agriculture, a combination of greases and animal fats represents one-third of the US total fats and oils production, as seen in Table 2, but soybean oil alone represents more than half of US production. However, biodiesel production from grease can be expected to beneWt from a raw material cost advantage and it will help to reduce overall biodiesel cost. One pound of most fats and oils can be converted to a pound of biodiesel.

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M. Canakci / Bioresource Technology xxx (2005) xxx–xxx

Table 4 Urban waste grease resources in 30 metropolitan areas (Wiltsee, 1998) No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Metro area

Sacramento Olympia Provo Denver Lincoln Bismarck Bloomington Battle Creek MansWeld Elmira Boston Harrisburg Altoona Hagerstown Washington Richmond Danville Fayetteville Florence Greenville Lexington Memphis Decatur Macon Lakeland Bradenton Baton Rouge Shreveport Beaumont Bryan

State

CA WA UT CO NE ND IL MI OH NY MA PA PA MD DC VA VA NC SC SC KY TN AL GA FL FL LA LA TX TX

Population

1,481,102 161,238 263,590 1,848,319 213,641 83,831 129,180 135,982 126,137 95,195 1,950,855 587,986 130,542 121,393 3,923,574 865,640 108,711 274,566 114,344 640,861 348,428 981,747 131,556 281,103 405,382 211,707 528,264 334,341 361,226 121,862

Urban waste grease resources (pounds/year)

Urban waste grease resources (pounds/year person)

Number of restaurants

Yellow grease

Trap grease

Total grease

Restaurant /1000 P

Yellow grease

Trap grease

2200 240 400 2670 350 133 200 211 244 140 3000 900 143 170 5000 1480 157 384 185 1017 562 1128 245 348 445 360 657 442 383 198

4,500,000 1,080,000 4,380,000 17,000,000 4,500,000 430,000 500,000 1,500,000 650,000 950,000 10,400,000 6,000,000 1,300,000 1,200,000 39,000,000 8,700,000 1100,000 2,700,000 1,100,000 6,400,000 3,500,000 9,800,000 1,300,000 2,800,000 4,100,000 2,100,000 5,300,000 3,300,000 3,600,000 1,200,000

16,600,000 1,200,000 7,000,000 15,900,000 2,600,000 400,000 2,300,000 1,500,000 190,000 1,500,000 33,600,000 10,800,000 1,000,000 1,000,000 50,000,000 17,300,000 1,900,000 2,100,000 900,000 4,600,000 3,600,000 18,500,000 2,400,000 5,900,000 4,600,000 3,000,000 5,800,000 4,700,000 3,900,000 2,000,000

21,100,000 2,280,000 11,380,000 32,900,000 21,600,000a 830,000 2,800,000 3,000,000 840,000 2,450,000 44,000,000 16,800,000 2,300,000 2,200,000 89,000,000 26,000,000 3,000,000 4,800,000 2,000,000 11,000,000 7,100,000 28,300,000 3,700,000 8,700,000 8,700,000 5,100,000 11,100,000 8,000,000 7,500,000 3,200,000

1.49 1.49 1.52 1.44 1.64 1.59 1.55 1.55 1.93 1.47 1.54 1.53 1.10 1.40 1.27 1.71 1.44 1.40 1.62 1.59 1.61 1.15 1.86 1.24 1.10 1.70 1.24 1.32 1.06 1.62

3.04 6.70 16.62 9.20 21.06 5.13 3.87 11.03 5.15 9.98 5.33 10.20 9.96 9.89 9.94 10.05 10.12 9.83 9.62 9.99 10.05 9.98 9.88 9.96 10.11 9.92 10.03 9.87 9.97 9.85

11.21 7.44 26.56 8.60 12.17 4.77 17.80 11.03 1.51 15.76 17.22 18.37 7.66 8.24 12.74 19.99 17.48 7.65 7.87 7.18 10.33 18.84 18.24 20.99 11.35 14.17 10.98 14.06 10.80 16.41

14.25 14.14 43.17 17.80 101.10b 9.90 21.68 22.06 6.66 25.74 22.55 28.57 17.62 18.12 22.68 30.04 27.60 17.48 17.49 17.16 20.38 28.83 28.12 30.95 21.46 24.09 21.01 23.93 20.76 26.26

1.41

8.87

13.37

23.09

Weighted average a b

Total grease

Lincoln total includes 14,500,000 pounds/year of food plant waste grease. Lincoln total includes 67.87 pounds/year person of food plant waste grease.

Table 5 Prices of rendering plant products (Rudbeck, 2000) Bulk Animal/livestock feed Tallow Grease Blood Hydrolyzed feather meal

Price range (per pound) $0.09–$0.14 $0.10–$0.20 $0.07–$0.20 $0.20 $0.125

Average price $0.12 $0.17 $0.16 $0.20 $0.125

If all of the 11.638 billion pound/year of greases and animal fats were converted to biodiesel, it would replace about 1.5 million gallons of diesel fuel. 4. Properties of waste restaurant oil and animal fat In food frying, vegetable oils are used at very high temperatures. This process causes various chemical reactions such as hydrolysis, polymerization and oxidation. Therefore, the physical and chemical properties of the oil change during frying. A great deal of research has been conducted to characterize these physical and chemical

changes (Al-Kahtani, 1991; Chu and Luo, 1994; Tyagi and Vasishtha, 1996; Ovesen et al., 1998). The percentage of FFAs has been found to increase due to the hydrolysis of triglycerides in the presence of food moisture and oxidation. As an example, the FFA level of fresh soybean oil changed from 0.04% to 1.51% after 70 h of frying at 190 °C (Tyagi and Vasishtha, 1996). Increases in viscosity were also reported due to polymerization, which resulted in the formation of higher molecular weight compounds. Other observations were that the acid value, speciWc gravity and saponiWcation value of the frying oil increased, but the iodine value decreased. The peroxide value increased to a maximum and than started to decrease (Mittelbach et al., 1992). Very few data are available in the literature for the actual composition of the feedstocks at rendering plants. As part of this study, samples of rendering plant feedstocks and Wnal products were collected and analyzed to deWne the range of properties that should be expected for biodiesel production. Table 6 shows the detailed chemical analysis of samples of rendering plant feedstocks and Wnal products

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Table 6 Chemical analysis results of restaurant grease and animal fat samples (Canakci, 2001) Test/sample

Soy oil 1 Soy oil 2 SIM-01 SIM-02 SIM-03 SIM-04 SIM-05 SIM-07 SIM-08 SIM-09 SIM-10 SIM-11 SIM-24

MIU (%) 0.44 Moisture and volatiles 0.01 by hot plate Insoluble impurities (%)