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NEDO High-efficiency Bioenergy Conversion Project

- R & D for Biodiesel Fuel (BDF) by Two-step Supercritical Methanol Method -

Shiro Saka, Eiji Minami and Dadan Kusdiana

Graduate School of Energy Science, Kyoto University

Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501

saka@energy.kyoto-u.ac.jp

Biodiesel fuel (BDF) is one of the most promising bioenergies, which can be produced from oils/fats

through transesterification. A current commercial process for BDF production involves the use of alkali

catalyst, followed by the removal of the catalyst and saponified products from free fatty acids (FFA). Inaddition, water-containing waste oils/fats depress the catalyst activity. These cannot allow the low-quality

feedstocks, such as waste cooking oil and waste industrial oil, available for their efficient utilization.

For solving these problems, our research group has been working to develop non-catalytic biodiesel

production by supercritical methanol treatment (>239oC, >8.09MPa) since 1998. Variables affecting the

reaction were investigated followed by proposing the optimum conditions to be 350oC, 20MPa and 9 min.

Compared with the alkali-catalyzed method, the supercritical methanol method has superiorities in terms of

reaction time and purification step. In addition, the yield of BDF is higher than that of alkali-catalyzed

method due to a simultaneous conversion of FFA to its methyl esters through esterification. These findings

indicate that the supercritical methanol treatment has a great availability to perform transesterification of

triglycerides (TG) and methyl esterification of FFA, and that would provide a clue as to establishment of

the efficient biodiesel production process.

Although the catalyst-free supercritical methanol method (Saka process) has been proven to produce

BDF in high yield, it requires a restrictive reaction condition compared to the conventional alkali- and

acid-catalyzed methods. Therefore, further effort was made to develop an alternative method through the

two-step preparation; hydrolysis of TG in subcritical water and subsequent methyl esterification of the fatty

acids in supercritical methanol as shown in Figure 1. In this two-step method (Saka-Dadan process),

therefore, esterification is the main reaction for BDF production, while in the conventional supercritical

method, transesterification is the most major one. The proposed reaction conditions were 270oC, 7MPa and

20 min for hydrolysis and methyl esterification, respectively. For such conditions, the common stainless

steel can be applicable and resist enough for reaction vessel. Furthermore, the BDF product was found to be

low in total glycerol content which satisfies the biodiesel specification standards in EU, US and Kyoto City.

Fortunately, this research project has been selected as one of the NEDO High-efficiency Bioenergy

Conversion Projects in FY2003 for coming 3 years with a budget of about 840 million. Figure 2 shows

the framework of this industry-university joint research team. In this project, Asahi KASEI Corp. is

responsible for establishment of the commercial process to produce high quality BDF (total glycerol

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content < 0.24wt% through a high energy efficiency, > 80%), while Kyoto University is for fundamental

study on the reactions and BDF evaluation, Asahi Engineering Co., Ltd. is for development of the

pre-/post-treatment and automatic control systems, Asahi Research Center Co., Ltd. is for establishment of

the business model on BDF and Toyota Tsusyo Corp. is for market research on the oil/fat feedstocks and

BDF, respectively.

In FY2003, two flow-type systems have been designed and developed based on scientific and

technical knowledge at Kyoto University; one is the laboratory-scale equipment for the fundamental study

on the reactions, while the other is the bench-scale plant in Fuji City, as shown in Figure 3, which is used to

discuss a mass production technology. In addition, pre- and post-treatment steps for oil/fat feedstocks and

waste water were, respectively, examined to establish the total process of the system. On the other hand, a

trend survey on BDF including its production, utilization and policy was made in Japan as well as foreign

countries. A market research on oil/fat feedstocks was also carried out to assure the feedstock suppliers.

Oils/fats

Water

Subc ritic al Wate r

(270oC/7MPa)

Glycerol

MeOH

Biodiesel fuel

BDF

Wate r phase

Oil pha se

Supercritica l MeO H

(270oC/7MPa)

Waste wa ter

MeOH reco very

Purification

Figure 1. Scheme of the two-step supercritical methanol method (Saka-Dadan Process)

NEDO

Consignation

Asahi Engine ering Co ., Ltd .

Kyoto University

Asahi Research Cen ter Co ., Ltd.

Toy ota Tsusho Co rp.

Asahi KASEI Corp.

Re-consignation

Ta rgets

1. Estab lishment of c omm ercialprocess

2. Esta blishme nt o f b usiness mod el

3. Tota l glyce rol con tent < 0.24wt%4. Energy efficiency > 80%

Figure 2. Framework of the NEDO project Figure 3. Bench-scale plant in Fuji City for the

two-step supercritical methanol method