Computers and Chemical Engineering 33 (2009) 1091–1096
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Production of biodiesel from Jatropha curcas L. oil夽 Houfang Lu, Yingying Liu, Hui Zhou, Ying Yang, Mingyan Chen, Bin Liang ∗ College of Chemical Engineering, Sichuan University, Chengdu 610065, PR China
a r t i c l e
i n f o
Article history: Received 11 February 2008 Received in revised form 5 August 2008 Accepted 25 September 2008 Available online 7 October 2008 Keywords: Jatropha curcas L. oil Biodiesel Pre-esterification Transesterification
a b s t r a c t A two-step process consisting of pre-esterification and transesterification was developed to produce biodiesel from crude Jatropha curcas L. oil. The free fatty acids (FFAs) in the oil were converted to methyl esters in the pre-esterification step using sulfuric acid or solid acid prepared by calcining metatitanic acid as catalysts. The acid value of oil was reduced from the initial 14 mg-KOH/g-oil to below 1.0 mg-KOH/g-oil in 2 h under the conditions of 12 wt% methanol, 1 wt% H2 SO4 in oil at 70 ◦ C. The conversion of FFAs was higher than 97% at 90 ◦ C in 2 h using 4 wt% solid acid and a molar ratio of methanol to FFAs of 20:1. Phospholipid compounds were eliminated during pre-esterification and a separate degumming operation was unnecessary. The yield of biodiesel by transesterification was higher than 98% in 20 min using 1.3% KOH as catalyst and a molar ratio of methanol to oil 6:1 at 64 ◦ C. © 2008 Elsevier Ltd. All rights reserved.
1. Introduction Biodiesel is an alternative fuel produced from renewable vegetable oils, animal fats or recycled cooking oils by transesterification reaction. Biodiesel has drawn significant attention due to increasing environmental concern and diminishing petroleum reserves (Ma & Hanna, 1999). Presently, biodiesel is produced commercially in Europe and USA to reduce air pollution and the net emission of greenhouse gas. Surplus edible oils, such as rapeseed oil and soybean oil, are used as raw materials for biodiesel (Körbltz, 1999; Wood, 2005). However, using edible oils to produce biodiesel is not encouraged in China because China imports more than 400 million tons of edible oils annually to satisfy its consumption needs. Some Chinese biodiesel producers use recycled waste oils to produce biodiesel, but the scale is limited. Although the use of waste oils can lower the feedstock cost significantly, complicated procedures are needed to remove the impurities, resulting in high operating costs (Al-Widyan & Al-Shyoukh, 2002; van Kasteren & Nisworo, 2007; Zhang, Dubé, McLean, & Kates, 2003a; Zhang, Dubé, McLean, & Kates, 2003b). Non-edible oils like Jatropha curcas L. oil are attractive (Foidl, Foidl, Sanchez, Mittelbach, & Hackel, 1996; Mohibbe Azam, Waris, & Nahar, 2005; Sarin, Sharma, Sinharay, & Malhotra, 2007; Tiwari, Kumar, & Raheman, 2007; Wood, 2005).
夽 Supported by the Key Grant Project of Chinese Ministry of Education (No. 307023). ∗ Corresponding author at: College of Chemical Engineering, Sichuan University, 24 South Section 1, Yihuan Road, Chengdu 610065, PR China. Tel.: +86 28 85460556; fax: +86 28 85460557. E-mail address:
[email protected] (B. Liang). 0098-1354/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compchemeng.2008.09.012
J. curcas L. trees can grow in arid, semiarid and wastelands. It has a high-seed yield and high oil content (Wood, 2005). In China, its plantation area is being expanded quickly along the Yangzi River as promoted by an environment protection act. In conventional processes, biodiesel is manufactured by the transesterification of oils with methanol in the presence of catalysts, such as alkalis (KOH, NaOH) or their corresponding alkoxides (Freedman, Pryde, & Mounts, 1984; Holser & Harry-O’Kuru, 2006; Ikwuagwu, Ononogbu, & Njoku, 2000; Jitputti et al., 2006; Leung & Guo, 2006; Ma & Hanna, 1999; Siler-Marinkovic & Tomasevic, 1998): triglycerides + methanol → biodiesel + glycerol The process design and operation parameters vary with the properties of the feedstock oils and the desired biodiesel quality. Commercial biodiesel processes using rapeseed oil (in Europe) and soybean oil (in the USA) have been well researched, and thereby the properties of their biodiesel products have also been comprehensively investigated. However, J. curcas L. oil with high content of free fatty acids (FFAs) cannot be directly used in an alkali catalyzed transesterification process because FFAs react with alkali catalyst to form soaps, resulting in serious emulsification and separation problems. Pre-esterification catalyzed by homogeneous acids, such as sulfuric acid, phosphorous acid, or sulfonic acid, is a conventional and useful method to reduce the content of FFAs, which can turn the raw oils transesterificable by an alkali catalyst and convert FFAs to valuable fatty acid methyl esters (FAME) (Ghadge & Raheman, 2005; Tiwari et al., 2007). Compared with conventional liquid acid catalysts, solid acid catalyst is more environmentally friendly (López,
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Suwannakarn, Bruce, & Goodwin, 2007; Mbaraka & Shanks, 2005; Narasimharao et al., 2007). The effect of methanol to oil ratios on FFA conversion at the reaction temperature of 50 ◦ C, a reaction time of 1 h, and a H2 SO4 to oil ratio of 1% (w/w) has been investigated (Berchmans & Hirata, 2008). The optimum methanol to oil ratio was found to be 60% (w/w) for an FFA concentration less than 1%, and an acid value (AV) of 2 mg-KOH/g-oil. We propose a two-step method to convert raw J. curcas L. oil into biodiesel. A pre-esterification operation was applied to eliminate FFAs by reacting the oil with methanol in the presence of an acid catalyst. The process can be simply described as pre-esterificatin → purification → transesterification → phase separation Raw oil was firstly reacted with methanol, followed by phase separation to remove acidic water and gum impurities. The purified oil was further reacted with methanol in Section 2.4 in the presence of an alkali catalyst. Finally, the biodiesel product was separated from the glycerol by-product by phase separation. In this work, factors influencing the pre-esterification and transesterification were systematically investigated, and the solid acid catalyst SO4 2− /TiO2 prepared by calcining metatitanic acid was tested and characterized. The properties of the biodiesel were measured. 2. Experimental 2.1. Materials The J. curcas L. seeds were collected from the Panzhihua area, Sichuan Province, southwest China. Jatropha oil was obtained by grinding the seeds. The oil was filtrated to remove solid impurities. In order to investigate the effects of FFAs, water and phospholipids on the reaction kinetics, we used simulated oils obtained by mixing refined oil with different impurities. The refined oil was prepared by processing the crude Jatropha oil with NaOH solution and active earth to remove FFA and moisture. The refined Jatropha oil contained FFAs < 0.2 mg-KOH/g-oil, water < 0.1% and phospholipids < 0.04%. Oil samples with different FFAs, water and phospholipids contents were prepared by adding oleic acid, deionized water and soluble phospholipids into the refined Jatorpha curcas L. oil in order to quantitatively investigate the effects of these factors on the pre-esterification step. The solid acid catalyst used in the pre-esterification reaction was prepared by calcining metatitanic acid. The metatitanic acid (the molar ratio of S/Ti is 0.1) was obtained from a commercial TiO2 pigment process of the Titanium Industry Company, Panzhihua Iron and Steel Groups. Phospholipids were purchased from Beijing Huaqing Meiheng Co. Ltd. (China), in which the content of acetone insoluble material > 98%. Other chemical reagents were of analytical grade without further purification. 2.2. Pre-esterification process catalyzed by sulfuric acid Pre-esterification was conducted in a 250 ml three-neck flask. The flask was equipped with a mechanical agitator and a reflux condenser, and heated with a water bath to control the reaction temperature. In the experiments, flasks loaded with Jatropha oil samples were firstly heated to the designated temperature. This was followed by the addition of the methanol and sulfuric acid mixture before turning on the agitator, marking the start of the esterification reaction. The esterification products were separated in a tap funnel to obtain the upper oil layer, which was then washed
with water several times until the pH of washing water was close to 7.0. The resultant pre-esterified oil was dried by anhydrous magnesium sulfate before subsequent transesterification. 2.3. Preparation of solid acid catalyst and its application in pre-esterification process The metatitanic acid was a semifinished product collected from the hydrolysis section of the commercial TiO2 pigment process. It was a hydrolysis product containing adsorbed sulfuric acid and titanium sulfates without further purification. The metatitanic acid sample was dried at 110 ◦ C in air for 5 h, and then crushed and sieved. The particles with a size under 125 m were further calcined to prepare the solid acid catalyst. In order to investigate the effect of calcination on the catalytic properties, different calcination temperatures and times were tested. Pre-esterification using the solid acid catalyst took place inside an autoclave. Both the reactants and the catalyst were added at the beginning, and the reactor was rapidly heated at 7 ◦ C/min under a mechanical agitation of 1500 rpm. After the completing the reaction, the reactor was quenched to stop the reaction. The slurry was filtered under vacuum and the liquid phases were allowed to settle in a tap funnel to separate the acidic water and oil phase. The acidic water and methanol are the components in the upper layer. The oil phase was obtained at the lower layer and was kept at 110 ◦ C for 90 min in an oven to evaporate the residual moisture and methanol. The treated oil was then used as the feedstock for transesterification. 2.4. Transesterification Transesterification experiments were carried out under atmospheric pressure using KOH as the catalyst. The reactor and the process were similar to those at pre-esterification. The products were FAME and glycerol. FAME was washed with water to remove soap and catalyst before drying. 2.5. Analytical method The moisture, acid value, glycerol content and saponification value were determined following the National Standards of PRC: GB/T 5528-1995, GB/T 5530-1998, GB/T 13216.6-91 and GB9104.288, respectively. The content of phospholipids was determined by molybdenum blue colorimetry. The specific surface area of catalyst was determined by the BET method. The sulfur content was measured by elemental sulfur analysis. The acid concentration was determined by titration. The composition of fatty acid was analyzed by a Shimadzu GCMS-QP2010 after methylation. The qualities of biodiesel including density, kinematic viscosity, flash point and cold filter plug point (CFPP) were measured following the Standards of PRC: GB/T 2540, GB/T 265, GB/T 261 and SH/T 0248, respectively. 3. Results and discussion 3.1. Homogeneous pre-esterification reaction In the presence of an acid catalyst, FFAs react with methanol to form FAME. The reaction can be represented as FFAs + methanol = FAME + water Under conditions favorable to esterification, the reaction rate of triglycerides with methanol was much slower compared to that of FFAs. The conversion of the pre-esterification reaction was measured by comparison of the acid values before and after the reaction.
H. Lu et al. / Computers and Chemical Engineering 33 (2009) 1091–1096
Fig. 1. Effect of temperature on conversion for a 2 h reaction time with 4.8 wt% methanol in oil and 1.0 wt% sulfuric acid (98%).
Fig. 2. Effect of reaction time on conversion at 70 ◦ C with 4.8 wt% methanol in oil and 1.0 wt% sulfuric acid (98%).
The raw J. curcas L. oil with an initial AV of 14.0 mg-KOH/g-oil was tested in the pre-esterification reaction. The amount of catalyst used was 1.0 g sulfuric acid per 100 g oil. The results are shown in Figs. 1–3. One can infer from Figs. 1–3 that the pre-esterification could easily reduce the AV of the raw oil. For example, using 12 wt% methanol in oil at 70 ◦ C, the AV of oil was reduced from 14.0 mg-KOH/g-oil to below 1.0 mg-KOH/g-oil in 2 h. The treated oil could be used as the feedstock of transesterification. From Figs. 1–3, one can observe that the conversion increased with increasing methanol concentration and temperature. How-
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Fig. 4. Effect of water content on the pre-esterification. Reaction conditions: Initial acid value = 19.9; temperature, 70 ◦ C, reaction time, 2 h; the amount of methanol, 12 wt% in oil; the amount of sulfuric acid (98%), 1.0 wt% in oil.
ever, the temperature should be controlled below the boiling point of methanol. For vegetable oils, the acid value of the raw oil may change with different oil sources. If the AV is higher than 20, the preesterification process can be enhanced by adding more methanol and/or by removing water. Esterification is a reversible reaction. The product water influences both the conversion and reaction rate. The effect of moisture was measured by adding water into the refined oil (as described in Section 2.1). The results are shown in Fig. 4. One can observe that the conversion dropped from 95.6% to 52.5% when the water content increased from 0% to 1.5%. The dramatic drop of conversion with moisture content was caused by kinetic influence rather than the equilibrium influence. The water might greatly reduce the acid catalyst concentration in oil. Crude vegetable oil contains many gums, such as phospholipids. Freedman et al. (1984) found that phospholipids can possibly deactivate the alkaline catalyst in biodiesel production. Gerpen (2005) reported that 50 ppm phosphorus in oil reduced the yield of methyl esters by 3–5%. Higher phosphorus content also causes higher sulfate ash of biodiesel, and thus leads to higher particulate emissions, which in turn may influence the performance of the catalytic converters (Mittelbach, 1996). Therefore, conventional biodiesel processes often have a degumming operation to remove phospholipids. The effect of phospholipids on the pre-esterification of J. curcas L. oil was investigated by adding phospholipids into the refined oil. It was found that phospholipids did not show much influence on the final FFA conversion during pre-esterification (see Table 1). Furthermore, we measured the change of phospholipid content after the pre-esterification operation. The phospholipid content was significantly reduced after the pre-esterification operation. In fact, the separation operation behind the pre-esterification is more or less similar to the degumming operation. Phospholipids are hydrophilic and tend to aggregate when moisture is present, especially in the presence of acidic water. The sedimentation and washing may remove most of the phospholipids and the phospholipid content decreased from the original 0.33% to the final 0.04%. Table 1 Effect of phospholipids on pre-esterification.
Fig. 3. Effect of methanol on conversion at 70 ◦ C for 1 h with 1.0 wt% sulfuric acid (98%).
Phospholipid content before pre-esterification (%) Phospholipid content after pre-esterification (%) The removal of phospholipids (%) Initial AV of oil (mg-KOH/g) AV after pre-esterification (mg-KOH/g-oil) Pre-esterification conversion (%)
0.33 0.04 87.9 20.5 1.18 94.2
1.03 0.05 95.1 20.9 1.34 93.6
1.62 0.12 92.6 20.6 2.04 90.1
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H. Lu et al. / Computers and Chemical Engineering 33 (2009) 1091–1096 Table 4 Effect of reaction time on conversion. Reaction time (h)
Conversion (%)
1 2 3 4 5
89.9 95.9 97.5 94.8 93.0
Condition: Methanol/FFA, 20:1; catalyst concentration, 4 wt% in oil; temperature, 90 ◦ C. Table 5 Effect of temperature on conversion.
Fig. 5. Effect of calcinations temperature on activity. The conversion was measured for 3 h pre-esterification at 120 ◦ C; time: 3 h with 4 wt% ST in oil; a molar ratio of methanol to oleic acid of 20:1 and an agitation rate of 1500 rpm.
Thus, a separate degumming operation was unnecessary if the preesterification operation was applied in the biodiesel process using crude J. curcas L. oil as feedstock.
Temperature (◦ C)
Conversion (%)
70 80 90 100 110 120 130 140
89.9 95.9 97.5 94.8 93.0 92.5 93.0 91.5
Condition: Methanol/FFA, 20:1; catalyst concentration, 4 wt% in oil; and reaction time, 3 h.
3.2. SO4 2− /TiO2 solid acid catalyst for pre-esterification The surface acid site measurements showed that the esterification activity is associated with the surface acidic strength and acidic center density (see Table 3). Sample obtained by calcining at 500 ◦ C possessed more acidic sites of −12.70 to −8.2 and the strongest acidic centers to catalyze the esterification. At higher calcination temperature, such as 700 ◦ C, the strong acidic centers disappeared with the decomposition of surface sulfate (Yang, Lu, & Liang, 2007). The effects of the methanol/oleic acid molar ratio, reaction time, temperature and catalyst amount on the conversion of the preesterification reaction were investigated. The results are shown in Tables 4 and 5 and Figs. 6 and 7. The conversion increased with the reaction time during the initial period (Table 4). Because esterification is an exothermal reversible reaction, a reaction time longer than 3 h did not change the conversion any more. Higher conversion was obtained at 90 ◦ C (Table 5). The conversion increased from 70 to 90 ◦ C due to dynamic reasons and the improvement of mutual solubility. Above 90 ◦ C the conversion decreased because of thermodynamic reasons. The higher molar ratio of methanol/oleic acid resulted in greater conversion. Although the stoichiometric ratio for
We screened different solid acid catalysts for pre-esterification, including resin D72, molecular sieves HM, SAPO-11, HZSM-5, H and the prepared ST-serials solid catalysts. The SO4 2− /TiO2 solid catalysts (ST-serials catalysts) showed higher activities in the esterification of oleic acid with methanol. The ST-serials catalysts were prepared by calcining the metatitanic acid. The XRD measurements of the ST catalysts showed that the amorphous TiO2 converted to the anatase form during hightemperature calcination. The IR measurements revealed that the adsorbed SO4 2− converted to the S2 O7 2− form during the calcining process, which made the surface acid centers stronger. Therefore, the calcination temperature has a strong influence on the activity of the solid catalyst (see Fig. 5). The results of the activation measurements showed that the calcination temperature should not exceed 500 ◦ C, because a higher calcination temperature would lead to a reduction of activity. From the TG experiments, we observed that the sulfur loss started at 500 ◦ C. Table 2 shows that the drop of activation was caused by both the reduction of BET surface and the surface density of S at high temperature. Table 2 Characterization of ST(500) and ST(600). Solid acid
BET surface area (m2 /g)
Pore volume (cm3 /g)
Average pore size (nm)
SO4 2− content (wt%)a
SO4 2− density (SO4 2− /nm2 )
Surface coverage (%)
ST(500) ST(600)
88.80 55.14
0.3361 0.2516
15.14 18.25
4.92 2.58
3.48 2.94
87.0 73.5
a
SO4 2− contents were calculated from the measured S contents. ST(500) and ST(600) represent catalysts obtained by calcining at 500 and 600 ◦ C, respectively.
Table 3 The variation of acid site concentration with acid strength of ST solid acid (mmol/g). Solid acid
ST(300) ST(400) ST(500) ST(600) ST(700) ST(800) ST(900) ST(1000)
3.3 ≤ H0 ≤ 4.6
0.8 ≤ H0 ≤ 3.3
−8.2 ≤ H0 ≤ 0.8
−12.70 ≤ H0 ≤ −8.2
−13.60 ≤ H0 ≤ −12.70
0.279 0.127 0.071 0.120 0.092 0.034 0.026 0.013
0.513 0.088 0.200 0.036 0.000 0.000 0.000 0.000
0.223 0.742 0.208 0.111 0.000 0.000 0.000 0.000
0.000 0.000 0.068 0.049 0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
H. Lu et al. / Computers and Chemical Engineering 33 (2009) 1091–1096
Fig. 6. Effect of the ratio of methanol to FFA on conversion at 90 ◦ C for 3 h with 4 wt% catalyst in oil.
the esterification is 1:1, the excessive methanol could increase the rate and promote the completion of the reaction (Fig. 6). When the amount of catalyst was lower than 2%, the conversion increased with the amount of catalyst. When the amount was over 4%, the conversion did not increase further (Fig. 7). The optimal conditions of the pre-esterification reaction for the J. curcas L. oil are: 20:1 molar ratio of methanol/FFA, 4% solid catalyst, 90 ◦ C and 2 h. The conversion of FFAs reached 97%. 3.3. Transesterification process In pre-esterification, FFA was converted to methyl ester, while triglyceride was further converted to methyl ester in the following transesterification in the presence of KOH. The reaction during the transesterification can be represented as triglyceride (oil) + methanol = FAME + glycerol The inter-solubility of FAME–methanol–glycerol, J. curcas L. oil–FAME–methanol, J. curcas L. oil–glycerol–methanol, and J. curcas L. oil–FAME–glycerol between 298.15 and 333.15 K has been measured by Zhou, Lu, & Liang (2006a). Methanol is completely soluble in both FAME and glycerol, but insoluble in oil. With increasing mass fraction of FAME, the solubility of methanol in oil-FAME phase increases. As a result, the transesterification reaction shows an induction period because the reaction is carried out in the methanol phase. When the content of FAME increases to 70%, the oil–methanol–FAME mixture becomes a homogeneous phase. Glycerol has a low solubility in both oil and FAME and is thus easily separated from the final product biodiesel. The yield of methyl ester and glycerol can be used to represent the progress of the transesterification reaction. For the high FFA
Fig. 7. Effect of the amount of catalyst on conversion at 90 ◦ C for 3 h with a methanol/FFA ratio of 20:1.
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Fig. 8. Relationship between the yield of products and acid value of raw oil for a reaction time of 1 h at 64 ◦ C with a methanol to oil molar ratio of 6:1.
content oil, such as the crude J. curcas L. oil, we found that the yield of methyl ester is often lower than the yield of glycerol (Fig. 8) (Liu, Lu, Liang, & Chen, 2007). The loss of methyl ester is due to the product loss during the separation process and the washing operation. The presence of FFAs results in emulsification that makes the separation of ester difficult. Therefore, it is important to lower the AV below 1.5 mg-KOH/g-oil during the pre-esterification. Higher molar ratios of methanol to oil lead to greater conversion for a given reaction time. Many researchers indicated that a molar ratio of 6:1 was the best for numerous oils (Freedman et al., 1984; Holser & Harry-O’Kuru, 2006; Leung & Guo, 2006). Reaction between J. curcas L. oil and methanol was found to be similar. KOH was a possible catalyst for this system. Temperature influenced the reaction rate and higher yield was obtained at a higher temperature between 35 and 65 ◦ C. The conversion increased with reaction time. The first 15 min is the fastest period of the reaction, in which a conversion of 90% is possible. The optimal conditions were: 64 ◦ C with 1.3% KOH as catalyst and a molar ratio of methanol to oil at 6:1 (Zhou, Lu, Tang, & Liang, 2006b). Furthermore, the kinetics of the transesterification reaction of J. curcas L. oil and methanol was investigated. The rate constant for the transesterification of J. curcas L. oil is 0.6628, 0.8045 and 0.9474 L/(min mol) at 32, 41 and 51 ◦ C, respectively. These results showed that the reaction follows a pseudo-second-order mechanism, while the reaction system can be described as pseudohomogeneous. The activation energy Ea was 15. 46 kJ/mol (Zhou et al., 2006b). 3.4. Quality of biodiesel from J. curcas L. oil The properties of crude J. curcas L. oils vary with their origins. Fatty acid contents in the crude J. curcas L. oil affect the biodiesel production process and the biodiesel fuel properties. Table 6 lists the fatty acid compositions of two J. curcas L. oil samples. They were prepared in the two-step process under the optimized conditions described above. The results indicated that the two-step process could convert the J. curcas L. oils to diesel. After esterification and transesterification, the AV and kinematic viscosity decreased significantly and the flash point was much higher than those of the petro-diesel (Table 7). The AV, density, viscosity, free glycerin, and flash point meet the biodiesel standards of ASTM D6751. AV for biodiesel is primarily an indicator of FFA and AV higher than 0.8 mgKOH/g have been associated with fuel system deposits causing reduced life of fuel pumps and filters. Higher viscosity fuels can cause poor fuel combustion that leads to deposit formation. The FAME’s flash point is much higher than that of petro-diesel which can result in improved fire safety. The free glycerin number measures the amount of by-product glycerin presenting in the biodiesel.
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Table 6 Fatty acid content in the refined oil. Composition
Sample 1 (wt%) Sample 2 (wt%)
C14:0
C16:1
C16:0
C18:2
C18:1
C18:0
C20:0
C22:0
C26:0
Content of unsaturated
0.13 0.04
1.18 0.79
18.97 13.98
38.36 38.38
35.28 40.16
5.60 6.45
0.13 0.17
– 0.03
0.37 –
74.82 79.33
Table 7 Quality of biodiesel from Jatropha curcas L. oil. Property
AV (mg-KOH/g-oil) (20 ◦ C)
Density (g/ml)
Kinematic viscosity (mm2 /s) (40 ◦ C)
Content of glycerol (%)
Flash point (◦ C)
CFPP (◦ C)
Sample 1, oil Sample 1, FAMA Sample 2, oil Sample 2, FAMA ASTM D6751
10.1 0.29 2.80 0.18
