High Quality Biodiesel Fuel Production From Crude Jatropha Oil without Upstream and Downstream Processing

1.      Introduction

Jatropha curcas oil has been received much attention as a renewable source of biodiesel fuel with no competing food uses.  Crude Jatropha oil has high contents of free fatty acid (FFA) and water.  FFA and water in the raw oil significantly decrease the yield and quality of the product biodiesel in the industrial production process using the homogeneous alkali catalyst.  Thus, the present production process is usually accompanied by a refining process to remove FFA in the raw oil to less than 0.5 wt% and a dewatering process of the raw oil.  In addition, the downstream purification process to remove the by-products, such as soap and glycerin, from the biodiesel is required to satisfy the fuel's quality requirements.  These upstream and downstream processes raise the production cost of the biodiesel fuel.

In this study, the bench-scale production system connected the expanded-bed reactor packed with the cation-exchange resin and that packed with an anion-exchange resin in series was constructed.  The cation-exchange resin has a catalytic ability to convert FFA to biodiesel by esterification reaction without inhibition by water¹.   The anion-exchange resin has a catalytic ability to convert glycerides to biodiesel by transesterification reaction without soap formation² as well as an absorbent ability to remove the impurities such as glycerin, water and pigment contained in the product³.   Thus, high quality biodiesel fuel would be produced from the crude Jatropha oil without any pretreatment of the raw oil and the purification of the products.

2. Experimental methods

A water-jacketed column packed with the cation-exchange resin, Diaion PK208LH, and two columns packed with the anion-exchange resin, Diaion PA306S, were connected in series in the bench-scale production system (Fig.1).  The temperature of each column was kept constant at 50 °C using a hot-water recirculating system.  The mixed-solution of the crude Jatropha oil (FFA content of 2 wt%, water content of 3300 mg/kg) and methanol at the stoichiometric molar ratio of methanol to the total fatty acid residue in the oils was supplied to the bottom of the first column at the constant flow rate.  The effluent solutions from the top of the columns were collected, and the concentrations of the reactants and products in the solution were determined.

3. Results and discussion

Figure 2 shows the HPLC chromatograms of the feed (a) and the effluents from the first column (b), the second column (c), and the third column (d).  Several peaks of the FFA, diglyceride (DG), and triglyceride (TG) were observed in the feed.  In the effluent from the first column, the peaks of the FFA completely disappeared and the peaks of the fatty acid methyl ester (FAME) appeared.  The peaks of diglyceride and triglyceride became smaller in the effluent from the second column and completely disappeared in the effluent from the third column.   Thus, the FFA and glycerides in the crude Jatropha oil were completely converted to FAME.

Table 1 shows the analytical results of the product biodiesel compared with standards of USA (ASTM D6751) and Europe (EN14214).  The acid value and the contents of free glycerin and total glycerin in the product fully satisfied with both standards without downstream processing.  In addition, the contents of remaining reactants (monoglyceride, diglyceride, triglyceride), water and FAME also satisfied with the standards of Europe.  The glycerin and water as well as FFA and pigment were confirmed to be removed by the adsorption on the resin.  Therefore, the proposed system permitted the production of high quality biodiesel fuel without upstream and downstream processing.

4. Reference

1) N.Shibasaki-Kitakawa et al., Energy Fuels, 24, 3634 (2010)

2) N.Shibasaki-Kitakawa et al., Bioresour. Technol., 98, 416 (2007)

3) T.Tsuji et al., Energy Fuels, 23, 6163 (2009)

Fig. 1 Photograph of bench-scale production system with cation- and anion-exchange resins

Fig. 2  HPLC chromatograms of feed and effluents from each column

Table 1 Comparison of product properties with standards of biodiesel fuel

property	units	product	standards
			ASTM D6751	EN14214
acid value (FFA)	[mg-KOH/g]	0.03	≤0.8	≤0.5
free glycerin	[wt%]	0.01	≤0.02	≤0.02
total glycerin	[wt%]	0.03	≤0.24	≤0.25
monoglyceride	[wt%]	0.06	-	≤0.80
diglyceride	[wt%]	0.01	-	≤0.20
triglyceride	[wt%]	0.10	-	≤0.20
water	[mg/kg]	148	-	≤500
FAME	[wt%]	99.1	-	≥96.5