17.6. Biodiesel Production
Fig. 17.4 shows an example of a small-scale laboratory biodiesel production reactor. The reactor consists of 1 L jacketed glass batch reactor, reflux condenser to recover methanol, a sampling device, overhead mechanical stirrer, refrigerator, and a circulating water bath to control the reaction temperature [1]. Ref. [65] can also show another good example of schematic layout of biodiesel production setup.
Alkaline-catalyzed transesterification is the most widely used process for biodiesel production because it is very fast and yields large amount of biodiesel (Fig. 17.5).
The excess methanol is later recovered and reused. In transesterification process, the triglyceride molecule was taken after neutralizing the free fatty oils (free fatty acid, FFA), releasing the glycerin, and creating an alcohol methyl ester when methanol is used as catalyst. This is accomplished by mixing methanol with sodium hydroxide to make sodium methoxide. This liquid is then mixed into vegetable oil. The entire mixture then settles. The methyl esters or biodiesel will be on top while glycerin will be left at the bottom. The produced glycerin can be used in soap manufacture and the methyl esters are washed and filtered.
However, to use alkaline catalysts, the FFA level should be below a desired limit (ranging from less than 0.5% to less than 3%). Most of the nonedible oils have high FFA values. Therefore, transesterification with alkali-based catalyst yield a considerable amount of soap which are emulsifiers that make the separation of glycerol and ester phases very difficult. Acid-catalyzed esterification was found to be a good solution to this problem. However, the reaction rate was considerably less, requiring lengthy reaction periods. Therefore, the best approach to produce biodiesel from nonedible oils with high FFA values is the acid-catalyzed esterification process followed by Alkaline-catalyzed transesterification process.
Therefore, production of biodiesel can be conducted as follows [1]:
1. pretreatment process,
2. esterification process,
3. transesterification process,
4. posttreatment process.
17.6.1. Pretreatment Process
In this process, crude oil is entered into a rotary evaporator and heated to remove moisture for 1 h at 95°C under vacuum.
Table 17.2
Physicochemical Properties of the Produced Biodiesel [1,17,47,48,50,63,64]
| No | Property | CIME | JCME | SME | CME | SFME | PME | COME | MOME | CMME | PEME | MME | ASTM D6751 Limit |
| 1 | Kinematic viscosity at 40°C (mm2/s) | 5.5377 | 4.9476 | 4.3745 | 4.5281 | 6.3717 | 4.6889 | 3.1435 | 5.0735 | 4.0707 | 5.2296 | 8.3425 | 1.9–6.0. |
| 2 | Dynamic viscosity at 40°C (mPa s) | 4.8599 | 4.2758 | 3.8014 | 3.9212 | 5.5916 | 4.0284 | 2.705 | 4.3618 | 3.453 | 4.5551 | 7.4067 | – |
| 3 | Density at 40°C (kg/cm³) | 0.8776 | 0.8642 | 0.869 | 0.866 | 0.8776 | 0.8591 | 0.8605 | 0.8597 | 0.8704 | 0.8710 | 0.8878 | – |
| 4 | Oxidation stability (h at 110°C) | 6.12 | 4.84 | 4.08 | 7.08 | 1.46 | 23.56 | 8.01 | 12.64 | 0.71 | 0.57 | 0.52 | 3 h min |
| 5 | CFPP (°C) | 11 | 10 | −3 | −10 | 2 | 12 | −1 | 18 | −4 | −8 | 5 | – |
| 6 | Cloud point (°C) | 12 | 10 | 1 | −3 | 1 | 13 | 1 | 21 | −3 | −6 | 1 | Report |
| 7 | Pour point (°C) | 13 | 10 | 1 | −9 | 2 | 15 | −4 | 19 | −2 | −4 | 3 | – |
| 8 | Flash point (°C) | 162.5 | 186.5 | 202.5 | 186.5 | 130.5 | 214.5 | 118.5 | 176 | 164 | N/D | N/D | 130 min |
| 9 | Copper strip corrosion (3 h at 50°C) | 1a | 1a | 1a | 1a | 1a | 1a | 1a | 1a | 1a | 1a | 1a | No.3 max |
| 10 | Caloric value (kJ/kg) | 39,513 | 39,738 | 39,976 | 40,195 | 40,001 | 40,009 | 38,300 | 40,115 | 39,786 | 39,625 | 39,070 | – |
| 11 | CCR (m/m%) | 0.4069 | 0.0440 | 0.0204 | 0.0291 | 0.2911 | 0.0118 | 0.0114 | 0.022 | 0.028 | N/D | N/D | 0.050% mass max |
| 12 | Saponification value | 201.3 | 201.5 | 201.2 | 199.25 | N/D | 206.7 | 272.5 | 196.5 | 200.4 | 200.8 | 201.7 | – |
| 13 | Iodine value | 87 | 105.7 | 137 | 122.1 | N/D | 59.9 | 7.8 | 71.224 | 152 | 119.2 | 149.2 | – |
| 14 | Cetane number | 53.8 | 49.6 | 42.6 | 46.2 | N/D | 59.2 | 64.6 | 90.1 | 39.3 | 46.7 | 39.8 | 47 min |
| 15 | Total sulfur (ppm) | 4.11 | 3.84 | 0.86 | 0.83 | 7.02 | 1.81 | 0.94 | N/D | N/D | N/D | N/D | 15 max (S15) 500 max (S500) |
| 16 | Absorbance (abs) at WL 656.1 | 0.057 | 0.045 | 0.037 | 0.041 | 0.057 | 0.05 | 0.035 | 0.046 | 0.041 | 0.160 | 0.146 | – |
| 17 | Transmission (%) at WL 656.1 | 87.7 | 90.3 | 92 | 91.1 | 87.9 | 89.1 | 92.3 | 90 | 91.1 | 69.2 | 71.5 | – |
| 18 | Refractive index (RI) at 25°C | 1.4574 | 1.4513 | 1.4553 | 1.4544 | 1.4557 | 1.4468 | 1.4357 | 1.4494 | 1.4569 | 1.4551 | 1.4698 | – |
| 19 | Viscosity index | 183.2 | 194.6 | 257.8 | 236.9 | 174.4 | 203.6 | 230.8 | 206.7 | 276.3 | 211.8 | 176 | – |
| 20 | Viscosity at 100°C (mm2/s) | 1.998 | 1.8557 | 1.764 | 1.7864 | 2.1954 | 1.7921 | 1.3116 | 1.9108 | 1.6781 | 1.9651 | 2.6683 | – |
| No | Property | FOME | APME | ASTM D6751 Limit |
| 1 | Kinematic viscosity at 40°C (mm2/s) | 4.77 | 4.7177 | 1.9–6.0. |
| 2 | Dynamic viscosity at 40°C (mPa s) | N/D | 4.1210 | – |
| 3 | Density at 40°C (kg/cm³) | 0.8776 | 0.8735 | – |
| 4 | Oxidation stability (h at 110°C) | N/D | 0.16 | 3 h min |
| 5 | CFPP (°C) | 11 | 5 | – |
| 6 | Cloud point (°C) | N/D | 8 | Report |
| 7 | Pour point (°C) | N/D | 8 | – |
| 8 | Flash point (°C) | 174.8 | 188.5 | 130 min |
| 9 | Copper strip corrosion (3 h at 50°C) | 1a | N/D | No.3 max |
| 10 | Caloric value (kJ/kg) | 39,954 | 39,960 | – |
| 11 | CCR (m/m%) | 0.0206 | N/D | 0.050% mass max |
| 12 | Saponification value | 201.3 | 201.5 | – |
| 13 | Iodine value | 61 | 105.7 | – |
| 14 | Cetane number | N/D | 49.6 | 47 min |
| 15 | Total sulfur (ppm) | 4.11 | 3.84 | 15 max (S15) 500 max (S500) |
| 16 | Absorbance (abs) at WL 656.1 | N/D | 0.045 | – |
| 17 | Transmission (%) at WL 656.1 | N/D | 90.3 | – |
| 18 | Refractive index (RI) at 25°C | N/D | 1.4513 | – |
| 19 | Viscosity index | N/D | 220.7 | – |
| 20 | Viscosity at 100°C (mm2/s) | N/D | 1.8239 | – |
Table 17.3
A Comparison of Some Physicochemical Properties of Edible and Nonedible Biodiesel Relative to Palm Oil Biodiesel (PME) [1]
| No | Property | CIME | JCME | SFME | MOME | CMME | PEME | PME | SME | CME | CoME | MME |
| NE1 (%) | NE2 (%) | NE3 (%) | NE4 (%) | NE5 (%) | NE7 (%) | E1 (Ref) (%) | E2 (%) | E3 (%) | E4 (%) | E5 (%) | ||
| 1 | Kinematic viscosity at 40°C (mm2/s) | +18.1 | +5.5 | +35.9 | +8.2 | −13.2 | +11.5 | 0.0 | −6.7 | −3.4 | −33.0 | +77.9 |
| 2 | Dynamic viscosity at 40°C (mPa s) | +20.6 | +6.1 | +38.8 | +8.3 | −14.3 | +13.1 | 0.0 | −5.6 | −2.7 | −32.9 | +83.9 |
| 3 | Density at 40°C (kg/cm³) | +2.2 | +0.6 | +2.2 | +0.1 | +1.3 | +1.4 | 0.0 | +1.2 | +0.8 | +0.2 | +3.3 |
| 4 | Oxidation stability (h at 110°C) | −74.0 | −79.5 | −93.8 | −46.3 | −97.0 | −97.6 | 0.0 | −82.7 | −69.9 | −66.0 | −97.8 |
| 5 | CFPP (°C) | −8.3 | −16.7 | −83.3 | +50.0 | −133.3 | −166.7 | 0.0 | −125.0 | −183.3 | −108.3 | −58.3 |
| 6 | Cloud point (°C) | −7.7 | −23.1 | −92.3 | +61.5 | −123.1 | −146.2 | 0.0 | −92.3 | −123.1 | −92.3 | −92.3 |
| 7 | Pour point (°C) | −13.3 | −33.3 | −86.7 | +26.7 | −113.3 | −126.7 | 0.0 | −93.3 | −160.0 | −126.7 | −80.0 |
| 8 | Flash point (°C) | −24.2 | −13.1 | −39.2 | −17.9 | −23.5 | N/D | 0.0 | −5.6 | −13.1 | −44.8 | N/D |
| 9 | Caloric value (kJ/kg) | −1.2 | −0.7 | +0.0 | +0.3 | −0.6% | −1.0 | 0.0% | −0.1% | +0.5% | −4.3% | −2.3 |
| 10 | Absorbance (abs) at WL 656.1 | +14.0% | −10.0% | +14.0% | −8.0% | −18.0% | +220.0 | 0.0% | −26.0% | −18.0% | −30.0% | +192.0 |
| 11 | Transmission (%) at WL 656.1 | −1.6% | +1.3% | −1.3% | +1.0% | +2.2% | −22.3 | 0.0% | +3.3% | +2.2% | +3.6% | −19.8 |
| 12 | Refractive index (RI) at 25°C | +0.7 | +0.3 | +0.6 | +0.2 | +0.7 | +0.6 | 0.0 | +0.6 | +0.5 | −0.8 | +1.6 |
| 13 | Viscosity index | −10.0 | −4.4 | −14.3 | +1.5 | +35.7 | +4.0 | 0.0 | +26.6 | +16.4 | +13.4 | −13.6 |
| 14 | Viscosity at 100°C (mm2/s) | +11.5 | +3.5 | +22.5 | +6.6 | −6.4 | +9.7 | 0.0 | −1.6 | −0.3 | −26.8 | +48.9 |
Figure 17.4 Experimental setup used to perform biodiesel production: (1) reflux condenser, (2) overhead mechanical stirrer, (3) circulating water bath, (4) jacketed glass batch tank reactor (1 L), (5) hoses, and (6) refrigerator [1].
Figure 17.5 Schematic representation of transesterification process [66].
17.6.2. Esterification Process
In this process, the molar ratio of methanol to crude oils with high acid values was maintained at 12:1 (50% v/v); 1% (v/v) of sulfuric acid (H2SO4) was added to the preheated oils at 60°C for 3 h and 400 rpm stirring speed in a glass reactor. On completion of this reaction, the products were poured into a separating funnel to separate the excess alcohol, sulfuric acid, and impurities presented in the upper layer. The lower layer was separated and entered into a rotary evaporator and heated at 95°C under vacuum conditions for 1 h to remove methanol and water from the esterified oil.
Due to the high acid value of some crude oils, the amount of methanol can be increased to reduce the acid value to less than 4 mg KOH/g oil.
17.6.3. Transesterification Process
In this process, crude oils with low acid values and esterified oils were reacted with 25% (v/v) of methanol and 1% (m/m) of potassium hydroxide (KOH) and maintained at 60°C for 2 h and 400 rpm stirring speed. After completion of the reaction, the produced biodiesel was deposited in a separation funnel for 12 h to separate glycerol from biodiesel. The lower layer that contained impurities and glycerol was drawn off.
17.6.4. Posttreatment Process
Methyl ester formed in the upper layer from the previous process was washed to remove the entrained impurities and glycerol. In this process, 50% (v/v) of distilled water at 60°C was sprayed over the surface of the ester and stirred gently. This process was repeated several times until the pH of the distilled water became neutral. The lower layer was discarded and upper layer was entered into a flask and dried using Na2SO4 and then further dried using rotary evaporator to make sure that biodiesel is free from methanol and water.
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