Waste edible oil

BDF is eco-friendly fuel because of its non-toxicity, biodegradability, low concentration of small particulate matter and SOx in exhaust gas, and because it does not add to the amount of carbon in the total environment. In addition, conversion of waste edible oil to BDF contributes to the reduction and recycle of the waste material. These advantages have attracted attention all over the world European demand for BDF was 3.2 million tons in 2005, and estimated to double in 2006. In United States, which firstly proposed BDF, the demand was 260 thousand tons in 2005. In Japan, meanwhile, several local governments including Kyoto city produce BDF from waste edible oil to use as a fuel for public transportation, but the total demand in 2005 was only several thousand tons because of difficulty of collecting used frying oils from households. 

BDF is produced currently by a chemical process with an alkaline catalyst, which has some drawbacks, such as the energy-intensive nature of the process, the interference of the reaction by free fatty acids (FFAs) and water, the need for removal of alkaline catalyst from the product, the difficulty in recovering glycerol, and the treatment of alkaline wastewater. To overcome these problems, the processes using ion-exchange resins (Shibasaki-Kitakawa et al., 2007), supercritical MeOH (Kusdiana and Saka, 2004), MeOH vapor (Ishikawa et al, 2005), and immobilized lipases (Mittelbach, 1990 Nelson et al, 1996 Selmi and Thomas, 1998) have been proposed. In this paper, enzyme processes for production of BDF from waste edible oil, waste FFAs, and acid oil recovered from soapstock are described. In addition, applications of the element reactions to the oil and fat industry are introduced. 

The increase of velocity in methanolysis of the waste edible oil can be explained as follows. Water in the oil is attracted to the glycerol layer generated by methanolysis. Because the water goes out of the field of enzymatic methanolysis (oil layer), the reaction velocity gradually increased. Actually, the content of water in the acylglycerols/FAMEs layer (oil layer) decreased from 0.2 to 0.05 wt% and that of the glycerol layer was 4.1 wt% after five cycles (Watanabe et al, 2001). 

To study the stability of immobilized C. antarctica lipase in methanolysis of waste edible oil, the three-step methanolysis was repeated by transferring the enzyme to a fresh substrate mixture. The conversion was maintained during 50 cycles (100 days) (Watanabe et al., 2001), showing that contaminants in waste oil do not affect the stability of the lipase preparation. In a chemical alcoholysis with an alkaline catalyst, FFAs in a waste edible oil convert to alkaline soap the water present disturbs an efficient reaction. Hence, FFAs and water should be removed before the reaction, and a small amount of alkaline soap generated must be removed by washing with water after the reaction. But the enzymatic process does not need the pretreatment and downstream purification. 

It is not feasible to use virgin vegetable oil as material for BDF in Japan because the country must import much of it. However, it might be possible to utilize waste edible oil as material for BDF. 

In Japan, about 2,500,000 tons of edible oil is consumed in a year, and about 450,000 tons of waste edible oil is discarded from food factories, and as household garbage. About 200,000 tons is collected and utilized mainly as materials for soap and animal feed. Some of the collected waste edible oil is converted into FAME and used as BDF. 

Someya-shoten, a collection trader company in Tokyo, produces about 1500 L of FAME from waste edible oil each day through an alkaline catalyst method, and sells it at a price of 80 yen/L (about 67 cents/L). This company has been collecting 20-30 tons of waste edible oil daily and selling it as animal feed. By selling a part of the waste edible oil as BDF, the company could increase its profit by one-million yen per month (almost 10 thousand U.S. dollars/month). 

When waste edible oil is converted into FAME by use of an alkaline catalyst, free fatty acid has to be removed prior to the reaction to maintain the activity of the catalyst. This however reduces the yield of the process. 

The current state of research on the conversion of vegetable oil, especially waste edible oil, into BDF has been introduced. In Japan, about 46 million kL of diesel fuel is consumed in a year. The waste edible oil can support only about 1% of that total consumption, even if all the waste edible oil in Japan is utilized as materials for BDF. However, the technologies introduced in this paper can be applied for wide range of botanical resources such as waste effluent, or by-products from oil refining factories in the Southeast Asia which do not compete with resources for edible use. 

Improving Enzymatic Transformation of Waste Edible Oil to Biodiesel by Adding Organic Base... 

The transesterification of waste edible oil and methyl acetate to biodiesel catalyzed by the immobilized lipase Novozym 435 was explored. Novo m 435 could catalyze the transesterification of waste oil with high fi e fatty acid (FFA) content (up to 27.8%) and methyl acetate, and methyl ester (ME) yield reached 77.5% after a reaction time of 24 h, which was much lower than that with refined com oil being the raw material (86.2%). FFA was demonstrated to be the major influential factor on the reaction, ME yield dropped sharply with increasing FFA concentration. Acetic acid, the by-product formed in the transesterification of FFA with methyl acetate, was found to be responsible for the decrease of ME yield. Addition of organic base trihydroxymethyl aminomethane and triediylamine at the concentration of 5% based on oil weight to the reaction system could not only speed up the reaction, but improve ME yield. 

Wastes edible oil, originated from restaurants and household disposals, is creating serious problems of environmental control and food safety. Production of biodiesel with waste edible oil as feedstock not only could reduce disposal problems, but, more importantly, would decrease the cost of biodiesel. 

Presently industrial production of biodiesel from waste edible oil is performed by chemical alkaline catalysts, but it has been found that high content of free fatty acid (FFA) in waste edible oil (FFA>2%) would decrease the yield sharply due to soaps formed in the process (7). Several studies showed that enzymatic methanolysis with waste edible oil was a promising alternative owing to its mild reaction condition and free of chemical waste (2, 5). However, this conventional protocol was associated with many drawbacks such as deactivation of lipase caused by methanol and absorption of glycerol to lipase surface, thus resulting in serious negative effect on the reaction (4,5). 

Du et al. (6) have recently reported that methyl acetate was an effective acyl acceptor for biodiesel production. To the best of our knowledge, the biodiesel production from waste edible oil with methyl acetate as the acyl acceptor has not yet been reported. Therefore, the transesterification of different kinds of waste edible oil to biodiesel with methyl acetate in a solvent free system was explored in this paper and the major influential factor on the reaction was further investigated. 

One waste edible oil (WDO-1) was collected from fast food restaurant, the other (WDO-2) was obtained from local restaurant waste oil pool and pretreated with activated clay. The refined com oil (RCO) was purchased from local supermarket. Novozym 435 (lipase B from Candida antarctica, 164 U/g, lunit corresponds to the amount of enzyme that produces 1 pmol methyl oleate from triolein per minute at 35 °C) was kindly donated by Novo Nordisk Co. (Denmark). Methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate and methyl heptadecanoate (as an internal standard) were purchased from Sigma (USA). All other chemicals were also obtained commercially and of analytical grade. 

The reaction was carried out at 40 °C and 150 rpm. The reaction mixture contained 5 g waste edible oil, 6.93 g methyl acetate with the molar ratio of... 

Table I. Main parameters of waste edible oil and refined oil...

Sudesh K, Abe H, Doi Y (2000) Synthesis, structure and properties of polyhydroxyalkanoates biological polyesters. Prog Polym Sci 25(10) 1503-1555 Sudesh K, Iwata T (2008) Sustainability of biobased and biodegradable plastics. Clean 36 433-442 Taniguchi I, Kagotani K, Kimura Y (2003) Microbial production of poly(hydroxyalkanoate)s from waste edible oils. Green Chem 5 545-548... 

Tsai, J.H., Chen, S.J., et al., 2015. Characteristics of exhaust emissions of a diesel generator fueled with water-containing butanol and waste-edible-oil-biodiesel blends. Aerosol and Air Quality Research 15 (5), 2129—2139. 

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