Fossil Diesel Substitution Potential of Biodiesel Produced from Rubber

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Fossil Diesel Substitution Potential of Biodiesel Produced from Rubber Seed Oil as a Byproduct of Rubber Wood Plantation Takashi Yanagida,*,†,‡ Yukihiko Matsumura,‡ Bashir Abubakar Abdulkadir,§ Siti Shafrina bt. Mohd Afandi,§ Noridah Osman,§ and Yoshimitsu Uemura§ ‡

Division of Energy and Environment, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan Center of Biofuel and Biochemical Research, Universiti Teknologi Petronas, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia

§

ABSTRACT: Rubber seed oil (RSO) is a well-known non-edible oil currently not commercially used because no major application has been identified. Recently, studies of biodiesel produced from RSO have been reported. However, RSO biodiesel production potential and fossil diesel substitution potential have not been clarified. We report here estimates of the biodiesel production potential from rubber seed in natural-rubber-producing countries, with a combination of statistical data and original experimental data. The result shows that Indonesia has a RSO production potential of 889 098 tons/year as the highest country. In Nigeria, 15.1% of current fossil diesel consumption can potentially be replaced by biodiesel produced from an annual output of RSO locally. The usage of RSO for producing biodiesel is one option of reducing the biodiesel production dependency upon edible oil in these countries. The development of biodiesel production using RSO could play an important role in the naturalrubber-producing countries, such as Nigeria, Indonesia, Thailand, Malaysia, Myanmar, and Ivory Coast.

1. INTRODUCTION Biodiesel has attracted much attention as an alternative to diesel fuel produced from fossil resources. Worldwide biodiesel production has increased rapidly in the past decade, as shown in Figure 1.1

the world. In particular, emerging economics, such as China and India, which are leading importers of edible oils, will be affected by changes to the market. On the basis of the actual biofuel investment plans of many countries, international prices for oil seeds will increase by 18% by 2020.12 One possible solution to circumvent this problem is to use non-edible oils. Rubber seed oil (RSO) is a well-known non-edible oil currently not commercially used because no major application has been identified. Several researchers have demonstrated biodiesel production using RSO.13−15 Biodiesel production using RSO would require no land use change because the seeds are harvested from the rubber tree (Hevea brasiliensis) currently grown on plantations to produce natural rubber. The potential for biodiesel production from RSO is likely significant, although no estimates have been reported to date. Recently, the rubber seed yield through in situ counting of seeds from the rubber trees has been reported.16 According this report, this is one of the first studies to clearly investigate and report on the average rubber seed yield of rubber trees, of different ages, as well as rubber plantations. They also estimated the biodiesel potential production from the RSO. However, they did not mention the diesel substitution potential, which shows the impact for reduction of the dependence upon fossil fuel. Furthermore, several assumptions for the biodiesel conversion process, such as transesterification of RSO, were used for the potential estimation. Many of the past studies for the biodiesel production have not be considered mass balance in a series of processes from oil extraction to transesterification of its oil. For the calculation of the biodiesel production potential

Figure 1. World biodiesel production, 1991−2011.

Biodiesel can be produced from various seed oils or animal fat by chemically reacting the oil with alcohols.2−9 Currently, more than 95% of the biodiesel produced globally is from edible oils, such as rapeseed, sunflower, palm, and soybean.10 Global demand for edible oils has increased rapidly in the past decade.11 There are two major markets for these oils: food (80%) and industry (20%), which includes biodiesel. The demand for edible oils for food use continues to grow as well as the demand from the biodiesel sector. Therefore, biodiesel is actually competing with the food industry for the same oil crop, providing both substantial challenges and opportunities. For example, the continuous and large-scale production of biodiesel from edible oil without proper planning may negatively impact © 2016 American Chemical Society

Special Issue: In Honor of Michael J. Antal Received: May 10, 2016 Revised: August 31, 2016 Published: September 15, 2016 8031

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were determined by a standard titration procedure based on EN 14104. In the second step, 3 g of RSOE was transesterified with 0.8 g of methanol (molar ratio to oil = 7) and 0.03 g of potassium hydroxide (1.0 wt % oil) as the catalyst, using the approach described for the first step. After reaction, the RSOE transesterification product, i.e., free fatty acid methyl ester (FAME), was separated and weighed. The biodiesel yield from RSO (YBD) was calculated from eq 3

amount, to use the data of mass balance based on a series of experimentations in the conversion process of extraction oil from rubber seeds and the transesterification of its oil is expected. The objective of this study is to clarify the diesel substitution potential of biodiesel produced from RSO based on the combined statistical data for the harvested rubber wood plantation area and mass yield data obtained from the experiment of the biodiesel conversion process.

YBD = WRSOE/WRSO‐SWFAME/WRSOE‐S

where WRSOE is the weight of RSOE produced from RSO (g), WRSO‑S is the weight of the RSO sample for the first esterification step (g), WFAME is the weight of FAME produced from RSOE (g), and WRSOE‑S is the weight of the RSOE sample for the second esterification step (g). 2.2.4. Verification for Esterification of RSO. The conversion ratio from RSO to RSOE was monitored by a high-performance liquid chromatography (HPLC) system (HPLC Shimadzu system, Shimadzu Co., Japan). A sample of 100 μL was dissolved in HPLC-grade hexane of 3.0 mL before being injected into HPLC. The column was adopted a silica gel type (Shim-pack CLC-SIL, Shimadzu Co., Japan). The solution of the mobile phase was selected as n-haxane/2-propanol (99.5:0.5, v/v). The flow rate was 1.0 mL/min, and the injection volume was 20 μL. The oven temperature was set at 40 °C. The refractive index (RI) detector was used. FAME composition in the RSOE was determined by a gas chromatography (GC) system (Shimadzu GC2010, Shimadzu Co., Japan), which was equipped with a flame ionization detector (FID). The GC separation was accomplished on a BPX70 column (30 m × 0.25 mm inner diameter, 0.25 μm film thickness, Shimadzu GLC, Ltd., Japan). The sample of 50 mg was dissolved in 1.0 mL of 0.625 mg/mL methylheptadecane solution in heptane before being injected into GC. The sample solution was injected in the split mode (1:100), using helium as the carrier gas at a column flow velocity of 1.0 mL/min. The oven temperature was held at 120 °C. The temperature was raised to 180 °C with a heating rate of 5 °C/min, and then the temperature was raised once again to 240 °C with a heating rate of 10 °C/min and held for 7 min. Meanwhile, the injector and detector temperatures were at constants of 240 and 250 °C, respectively. 2.2.5. Potential Estimation. The potential estimation was performed using Crystal Ball (Oracle Corporation). The Monte Carlo simulation was conducted at 10 000 trials with a combination of β distribution for experimental data and uniform distribution for the seed yield from the rubber plantation.

2. METHODOLOGY 2.1. Calculations for Biodiesel Production Potential Using RSO. The potential amount of biodiesel was calculated using eq 1

PRBD = ARPYRSYRSOYBD

(1)

where PRBD is the potential amount of biodiesel from rubber seed, ARP is the area of rubber plantations, YRS is the rubber seed yield from rubber plantations, YRSO is the RSO yield from rubber seed, and YBD is the biodiesel yield from RSO. 2.2. Materials and Experiments. 2.2.1. Materials. Oil recovery experiments from rubber seeds were conducted. The rubber seed samples were collected from rubber plantations in Kampumg Bali, Tronoh, Perak, Malaysia, during the harvest in September 2013. A photograph of a rubber seed, kernel, and shell is shown in Figure 2.

Figure 2. Photograph of a rubber seed, kernel, and shell. The seeds were dried in an oven at 50 °C for 12 h and weighed. In this process, a low temperature was adopted to avoid an oil alteration. The seeds were then shelled to obtain the kernels. The kernels were dried again under the same conditions and weighed, and then the dried kernels were milled in preparation for the oil extraction process. 2.2.2. Oil Extraction. Oil extraction was conducted using a Soxhlet extractor. A total of 10 g of milled kernels was placed in a Soxhlet apparatus and extracted with 50 g of n-hexane for 5 h, and then nhexane was removed using a vacuum evaporator. The extracted RSO was weighed. The RSO yield from rubber seed (YRSO) was calculated from eq 2

YRSO = WRSK /WRS‐SWRSO/WRSK‐S

(3)

3. RESULTS AND DISCUSSION 3.1. Area Cultivated for Rubber Plantations. Data for the area cultivated for rubber plantations were obtained from Food and Agriculture Organization of the United Nations (FAO) statistics.17 The trend for the global cultivated area over 50 years is shown in Figure 3 and shows an average rate of increase of 1.9% per year. Therefore, there should be large and increasing amounts of rubber seed available in the coming years. The area devoted to rubber plantations in 2012 is shown in Table 1.17 Indonesia has the largest area, approximately 3.5 million hectares (ha), which is 35.3% of the global rubber plantation area. Thailand and Malaysia rank second and third, with 20.8 and 12.2%, respectively, followed by China, Vietnam, India, Nigeria, Myanmar, Philippines, Brazil, Ivory Coast, and Sri Lanka. In all countries, little of the rubber seed produced is used. 3.2. Rubber Seed Yield from Rubber Plantations. Little attention has been given to the rubber seed yield as a result of the lack of rubber seed application. Few studies have investigated the rubber seed yield. In India, the rubber seed yield averages 160 kg ha−1 year−1 of the rubber plantation,18

(2)

where WRSK is the weight of the rubber seed kernels (g), WRS‑S is the weight of rubber seed sample (g), WRSO is the weight of RSO extracted from milled kernel (g), and WRSK‑S is the weight of the milled kernel sample (g). 2.2.3. Esterification of RSO. The esterification process consists of two steps: acid esterification and alkaline transesterification. In the first step, 10 g of RSO was placed in a three-necked roundbottom flask equipped with a vertical condenser and stirrer magnet and placed in a water bath on a heater/magnetic stirrer plate. The temperature was raised and maintained at 50 °C, and then a mixture of 5.75 g of methanol (molar ratio to oil = 15) and 0.3 g of sulfuric acid (3.0 wt % oil) as the catalyst was added. Heating was stopped after 1 h, and 10 g of hot water (50 °C) was added. The reaction solution was separated into two layers. The top layer contained the RSO esterification product (RSOE) and was separated using a separation funnel and weighed. Free fatty acid (FFA) contents of RSO and RSOE 8032

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Table 2. Experimental Results for the Oil Yield from Rubber Seed WRSK (g) WRS‑S (g) WRSO (g) WRSK‑S (g)

892.21 1631.19 23.91 50.00

weight weight weight weight

of of of of

the rubber seed kernels the rubber seed sample RSO extracted from the milled kernel the milled kernel sample

YRSO = WRSK /WRS‐SWRSO/WRSK‐S = 892.21/1631.19 × 23.91/50.00 = 0.262

The average oil content in rubber seeds from different countries is 40%,20,21 which is higher than our experimental result of 26%. However, the proximate composition of rubber seed kernel is similar to rubber seed grown in Nigeria. Our experimental results show that the rubber seed kernel contains 47.8% oil, 2.9% ash, and 2.7% moisture contents, whereas the percentages for oil, ash, and moisture contents in rubber seed from Nigeria are 45.63, 2.71, and 3.71%, respectively.13 3.4. Biodiesel Yield from RSO. For biodiesel production, the yield from the esterification process decreases considerably if the FFA content is greater than 2%.14 Previously, an attempt was made to investigate the effect of the FFA level on the ester conversion with an alkaline catalyst (potassium hydroxide), but the addition of 5% palmitic acid produced a solid soap mixture that prevented separation of glycerin from methyl ester.22 Therefore, alkaline-catalyzed transesterification is not suited for the production of ester from high FFA content oil. The FFA content of RSO used in this research was 12.03%, in line with many reports of RSO containing a high content of FFA.13−15,18,23 Acid esterification is commonly used to produce biodiesel from high FFA content oil.22 Ramadhas et al.14 proposed a two-step esterification process to convert RSO into its monoesters. In the first step, acid-catalyzed esterification reduces the FFA content of the oil to less than 2%. In the second step, alkaline-catalyzed transesterification converts the products of the first step to monoesters and glycerol. Here, RSO was esterified using the two-step esterification process. The first step decreased the FFA content to 0.23%. Our experimental results for the biodiesel yield from RSO are shown in Table 3. According to eq 3, the biodiesel yield from RSO (YBD) was 0.986.

Figure 3. Global area cultivated for rubber plantations.

Table 1. Area Devoted to Rubber Plantations in 201217 country

ARP (ha)

percentage (%)

Indonesia Thailand Malaysia China, mainland Vietnam India Nigeria Myanmar Philippines Brazil Ivory Coast Sri Lanka others world

3484100 2050000 1200000 600000 505805 442000 345000 200000 176244 137814 135000 128700 459391 9864054

35.3 20.8 12.2 6.1 5.1 4.5 3.5 2.0 1.8 1.4 1.4 1.3 4.7 100.0

(4)

and in Malaysia, the rubber seed yield averages approximately 150 kg ha−1 year−1.21 The rubber seed yield from rubber plantations varies from 100 to 160 kg ha−1 year−1 depending upon conditions such as soil fertility, crop density, type of rubber tree, and weather.19 The latest report from China shows that the average yield is 1554 kg ha−1 year−1.16 This value is far greater than many other studies on the rubber seed yield. According to their explanation,16 one of the reasons for this yield value gap between the report by China and other past studies is that many of the past studies have based yield values on government reports or sales figures from farmers rather than directly investigating the number of fruit on trees. In this study, therefore, the minimum and maximum yields of rubber seeds from a rubber plantation (YRS) are 100 and 1554 kg/ha, respectively. 3.3. Oil Yield from Rubber Seed. The experimental results for the oil yield from rubber seed are shown in Table 2. The weight of the rubber seed sample (WRS‑S) was 1631.19 g. After shelling, the weight of the rubber seed kernels (WRSK) was 892.21 g, indicating that the kernel constitutes approximately 55% of the seed by weight. A total of 50 g of milled kernel provided 23.91 g of RSO by the Soxhlet extraction method. Using eq 2, the RSO yield from rubber seed (YRSO) was calculated to be 0.262.

YBD = WRSOE/WRSO‐SWFAME/WRSOE‐S = 10.08/10.02 × 2.94/3.00 = 0.986

(5)

Table 3. Experimental Results for the Biodiesel Yield from RSO WRSOE (g) WRSO‑S (g)

10.08 10.02

WFAME (g) WRSOE‑S (g)

2.94 3.00

weight of RSOE produced from RSO weight of the RSO sample for the first esterification step weight of FAME produced from RSOE weight of the RSOE sample for the second esterification step

3.5. FAME Composition and Heating Value of RSO Biodiesel. The gas chromatogram of RSO biodiesel is shown in Figure 4. The most abundant FAMEs in RSO biodiesel are methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, and methyl linolenate. The percentage of FAME composition is shown in Table 4. Among the FAMEs, methyl linoleate is predominant with 40.70%. On the basis of this 8033

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Figure 4. Gas chromatogram of RSO biodiesel.

Table 4. FAME Composition of RSO Biodiesel FAME

formula

molecular weight (g/mol)

composition (%)

methyl palmitate methyl stearate methyl oleate methyl linoleate methyl linolenate unknown total

C17H34O2 C19H38O2 C19H36O2 C19H34O2 C19H32O2

270.45 298.51 296.49 294.26 292.46

7.32 8.77 19.44 40.70 19.64 4.13c 100.0

fH°

(kJ/mol)a

−1441.8 (l) −945.6 (s) −731.7 (l) −617.01 (l) −492.75 (l)

cH°

(kJ/mol)b

−10107 −11961.9 −11889.9 −11718.8 −11557.2

HHV (MJ/kg) 37.4 40.1 40.1 39.8 39.5 39.4d 39.6e

From the NIST Chemistry WebBook.24 bcH°CxHyOz = xfH°CO2(g) + y/2fH°H2O(l) − fH°CxHyOz, where fH°CO2(g) = −393.51 kJ/mol and fH°H2O(l) = −285.83 kJ/mol. cTotal of unknown peaks in the gas chromatogram, as shown in Figure 4. dHHV of the unknown FAME is assumed to be 39.4 MJ/ kg as the average value of FAMEs. eThe value is calculated by a weighted mean method. a

FAME composition, the higher heating value (HHV) of the RSO biodiesel can be estimated. The standard enthalpy change of combustion (cH°)24 was estimated on the basis of the standard enthalpy change of formation (fH°). Thus, the HHV of RSO biodiesel is 39.6 MJ/kg, which is less than that of fossil fuel diesel of 44.8 MJ/kg.25 3.6. Biodiesel Production Potential from RSO. The potential amount of RSO biodiesel (PRBD) was calculated using eq 1. The result of predicted PRBD in Indonesia by Monte Carlo simulation is shown in Figure 5. The minimum and maximum amounts are defined by the lower and upper limits of the 95% confidence interval, respectively. Indonesian RSO biodiesel production potential ranges from 140 344 to 1 889 510 tons/ year, and the average is 889 098 tons/year. The range is very wide. The sensitivity analysis gave the result as approximately 90% affected according to the value of the rubber seed yield from rubber plantations (YRS). The Monte Carlo simulation were conducted for all countries, and the results are shown in Table 5. The world PRBD is in the range from 397 338 to 5 349 510 tons/year. The world diesel consumption in 2012 was 1 180 141 000 tons/year,26 as shown in Table 5. The diesel substitution potential is calculated as eq 6.

Figure 5. Prediction value of RSO biodiesel production by Monte Carlo simulation.

current world biodiesel production rate against world diesel consumption, the HHV of the biodiesel is assumed to be 39.6 MJ/kg. The current world biodiesel production, mainly from edible oils, is 18.2 million tons,1 and the world diesel consumption is 1180 million tons.26 The current world biodiesel production rate is calculate to be 1.4%. Thus, the world potential biodiesel production from RSO is smaller than the current biodiesel production rate. However, one of the

diesel substitution potential (%) = PRBD(HHV of RSO biodiesel/HHV of fossil diesel) /fossil diesel consumption × 100

(6)

The world minimum and maximum diesel substitution potential is 0.03 and 0.40%, respectively. To evaluate the 8034

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Energy & Fuels Table 5. Potential Amount of Biodiesel (PRBD) from RSO, Diesel Consumption, and Biodiesel Production Amount PRBD (tons/year)a country

minimum (lower limit of confidence interval)

average

maximum (upper limit of confidence interval)

diesel consumptionb (1000 tons/year)

biodiesel production (tons/year)c

Indonesia Thailand Malaysia China Vietnam India Nigeria Myanmar Philippines Brazil Ivory Coast Sri Lanka world

140344 82577 48338 24169 20375 17804 13897 8056 7099 5551 5438 5184 397338

889098 523134 306225 153112 129075 112793 88040 51037 44975 35168 34450 32843 2517182

1889510 1111764 650788 325394 274310 239707 187102 108465 95581 74740 73214 69797 5349510

23785 17662 8629 164993 7847 63061 517 1112 5906 42264 789 1541 1180141

1292000d 535500e 106250d

18184205f

a Results of the Monte Carlo simulation (see Figure 5). bData for 2012 from ref 26. cThe density of biodiesel is assumed as 0.85 kg/L. dData for 2011 from ref 27. eData for 2011 from ref 28. fData for 2011 from ref 1.

biodiesel production using RSO could play an important role in the production of biofuel in these countries.

benefits of RSO biodiesel is not competing with edible oil. In terms of energy security, an improvement of the energy selfsufficiency rate of the individual country is important. The national policy for biofuels of most developing countries is focused on reducing imported fossil fuels. Figure 6 shows the

4. CONCLUSION The fossil diesel substitution potential of producing biodiesel from RSO was estimated on the basis of statistical data for the harvested rubber wood plantation area and mass yield experimental data of the RSO biodiesel conversion process. The world fossil diesel substitution potential of RSO biodiesel is quite small. The world substitution potential is only 0.03− 0.40% of the current world fossil diesel consumption. However, in Nigeria, if the RSO is converted to biodiesel locally, 15.1% (32.3% at a maximum) can potentially be replaced on the basis of the current domestic diesel consumption. In terms of improvement of the energy self-sufficient rate on individual rubber-producing countries, to evaluate fossil diesel substitution potential is important. The development of biodiesel production using RSO could play an important role in the production of biofuel in natural-rubber-producing countries, such as Nigeria, Indonesia, Thailand, Malaysia, Myanmar, and Ivory Coast.

Figure 6. Fossil diesel substitution potential of biodiesel produced from RSO.

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fossil diesel substitution potential with RSO biodiesel in the individual natural-rubber-producing countries. The substitution potential for Nigeria is much higher than that for the other countries. The diesel consumption of Nigeria can potentially be substituted approximately 15.1% (from a minimum of 2.4% to a maximum of 32.3%) by biodiesel from RSO produced locally. When viewed in comparison to the world current biodiesel production rate of 1.4%, the average substitution potential of RSO biodiesel in Indonesia, Thailand, Malaysia, Myanmar, and Ivory Coast exceeds 1.4%. In Indonesia, Thailand, and Malaysia, current biodiesel production is reliant on edible oil feedstock, mainly palm oil. These countries are looking at opportunities for using non-edible feedstock oil. Biodiesel production in Indonesia has increased considerably, from 65 million L in 2006 to 1520 million L in 2011.27 The biodiesel production amounts in Thailand and Malaysia were 630 million L28 and 125 million L27 in 2011, respectively. Clearly, the use of RSO for producing biodiesel is one option for reducing the dependency upon edible oil. Therefore, the development of

AUTHOR INFORMATION

Corresponding Author

*Telephone: +81-29-829-8305. Fax: +81-29-874-3720. E-mail: tyanagida@ffpri.affrc.go.jp. Present Address †

Takashi Yanagida: Department of Wood Properties and Processing, Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was performed at the Center for Biofuel and Biochemical Research (CBBR), Universiti Teknologi Petronas. The authors are very grateful and express their gratitude to laboratory members at CBBR for their technical support in this research. 8035

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