Handbook of plant based biofuels - Chapter 20 (end) ppt

A two-step esterifica-tion process, that is, acid esterificaesterifica-tion followed by alkaline transesterificaesterifica-tion was developed to convert the unrefined rubber seed oil to

from Rubber Seed Oil

Arumugam Sakunthalai Ramadhas, Simon Jayaraj, and Chandrashekaran Muraleedharan

AbstrAct

Rubber seed oil is a high free fatty acid content, nonedible vegetable oil The acid value of unrefined rubber seed oil is about 34 Neither alkaline-catalyzed transes-terification nor acid-catalysed estranses-terification alone is suitable A two-step esterifica-tion process, that is, acid esterificaesterifica-tion followed by alkaline transesterificaesterifica-tion was developed to convert the unrefined rubber seed oil to its methyl esters and glycerol The process parameters, such as quantity of catalyst and methanol used, reaction temperature, and reaction duration, are analysed The properties of methyl esters

of rubber seed oil are comparable to that of diesel The performance and emission characteristics of biodiesel-diesel blends provide evidence that methyl esters of rub-ber seed oil are a suitable alternative fuel to diesel

contents

Abstract 281

20.1 Introduction 282

20.2 Potential of Rubber Seed Oil as an Alternative Fuel 282

20.2.1 Transesterification 283

20.2.1.1 Acid Esterification 284

20.2.1.2 Alkaline Transesterification 285

20.3 Properties of Methyl Esters of Rubber Seed Oil 287

20.4 Engine Tests with Biodiesel 287

20.4.1 Brake Thermal Efficiency 287

20.4.2 Specific Fuel Consumption 288

20.4.3 Carbon Monoxide Emission 288

20.4.4 Carbon Dioxide Emission 289

20.4.5 Smoke Density 289

20.4.6 Exhaust Gas Temperature 290

20.5 Conclusions 290

References 291

20.1 IntroductIon

Recent concerns over the environment, increasing fuel prices, and scarcity of supply have promoted interest in the development of alternative sources to petroleum fuels The vegetable oils are a promising alternative fuel to diesel as their fuel properties approximate those of diesel The sources of the vegetable oils, seeds, grow renew-ably in oil-yielding crops Diesel fuel consists of saturated, nonbranched hydrocar-bon molecules, with carhydrocar-bon ranging between 12 and 18, whereas the vegetable oil molecules are of triglycerides, generally nonbranched chains of different lengths and different degrees of saturation Important properties such as energy density, cetane number, heat of vaporization, and stoichiometric air-fuel ratio of vegetable oil are comparable to those of diesel (Montague 1996) Currently biodiesel is produced mainly from field crop oils, such as rapeseed, sunflower, and soybean oil (Zhang 1996; Zeiejerdki and Pratt 1986) The prices of the edible oils are several-fold higher than nonedible oils Nonedible oils also have potential for the production of biodie-sel, including jatropha oil, karanji oil, rubber seed oil, etc Biodiesel production from the nonedible oils would reduce the overall biodiesel cost This chapter describes the biodiesel production method from unrefined rubber seed oil, its physiochemical properties, cost analysis, and evaluation of engine performance and emission char-acteristics with biodiesel-diesel blends

20.2 potentIAl of rubber seed oIl As An AlternAtIVe fuel

The rubber tree (Hevea brasiliensis) is indigenous to the Amazon in Brazil It grows

quickly and is a fairly sturdy perennial tree of 25 to 30 m in height The young plant shows its characteristic growth pattern of alternating periods of rapid elongation and consolidated development The leaves are trifoliate with long stalks The rubber tree may live for a hundred years or even more However, its economic life period on plantations, is generally about 32 years, that is, seven years of immature phase and

25 years of productive phase It flowers during the months of February and March The fruits mature in the months between July and September, and have ellipsoidal capsules with three carpels, each containing a seed These open up during the sun-shine and the seeds fall on the ground and are normally hand picked The rubber seeds resemble castor seeds but are slightly larger in size and each weighs 2 to 4 g The seeds, which fall on the ground, deteriorate very rapidly due to moisture and infection These lead to rapid increase in the free fatty acid (FFA) content of the oil Therefore, it is essential to collect the seeds as quickly as possible and dry them, so

as to reduce the moisture to a value less than 5% in order to arrest increase in the FFA The rubber seed oil is normally obtained by expelling of the seeds Depending

on the pre-extraction history of the kernels, the color of the oil ranges from water white to pale yellow for low FFA content (about 5%) to dark color for high FFA content (about 10 to 40%) The fatty acid composition of rubber seed oil is given

in Table 20.1 (Aigbodion and Pillai 2000; Aigbodion et al 2003) The molecular formula of rubber seed oil is C18H32O2 and its molecular weight is 278 The impor-tant physiochemical properties of rubber seed oil and diesel are shown in Table 20.2 (Ramadhas, Jayaraj, and Muraleedharan 2005a) The specific gravity of rubber seed

oil is higher than that of diesel; hence it has almost the same calorific value as diesel

on a volumetric basis The flash point of rubber seed oil is much higher than that of diesel and hence, from a storage point view, it is much safer than diesel One of the undesirable properties of the oil is its viscosity, which is several times higher than that of the diesel The calorific value of rubber seed oil is about 12% lower than that

of the diesel However, the lower calorific value of oil is compensated for by the enhanced lubrication

20.2.1 t ranSeSterification

For alkaline transesterification, triglycerides should have lower acid value and all reactants should be substantially anhydrous The difficulty with processing noned-ible oils and fats is that these often contain large amounts of FFA that cannot be converted to biodiesel using the alkaline catalysis method The addition of excess sodium hydroxide catalyst with oil can compensate the higher acidity but the result-ing soap would increase its viscosity or formation of the gels that interfere with

tAble 20.1

fatty Acid composition of rubber seed oil

fatty Acid formula structure composition (%)

Palmitic c C16H32O2O2 16:0:0 10.2.2

Stearic C18H36O2O2 18:0:0 8.7.7

Oleic C18H34O2O2 18:1:1 24.6.6

Linoleic C18H32O2O 2 18:2:2 39.6.6

Linolenic C18H30O2O2 18:3:3 13.2.2

(Reprinted from Aigbodion, A l., Pillai, C K S [2000] Preparation, analysis and applications of

rubber seed oil and its derivatives as surface coating material, Progress in Organic Coatings, 38,

187–192, Elsevier Publications, with permission.)

tAble 20.2

properties of rubber seed oil in comparison with diesel

property test method rubber seed oil diesel

Specific gravity ASTM D4052 0.91 0.835 Viscosity (mm2/s) at 40(C°) ASTM D445 66 4.5

Flash point (ºC) ASTM D93 198 48

Fire point (ºC) ASTM D93 210 55

Calorific value (MJ/kg) ASTM D240 37.5 42.5

Saponification value ASTM D94 206

-Acid value ASTM D664 34.0 0.062 (Reprinted from Ramadhas, A S., Jayaraj, S., Muraleedharan, C [2005], Chacterization and effect of

using rubber seed oil as fuel in the compression ignition engines, International Journal of Renewable

Energy 30 (5), 795–803, Elsevier Publications, with permission.)

the forward reaction as well as with separation of the glycerol The yield of the transesterification process would decrease considerably with increase in FFA The acid value of unrefined rubber seed oil is 34 mg KOH/g, that is 17% FFA content

It is known that alkaline-catalyzed transesterification does not occur if FFA content

in the oil is more than 3% (Canakci and Van Gerpen 2001, 1999) Nevertheless, the refining process reduces the acid value of the oils but it increases the overall biodiesel production cost The acid esterification process can be used to produce biodiesel from oils having FFA content higher than 3% But this reaction is much slower than that of alkaline transesterification A two-step esterification process is developed to produce biodiesel from unrefined rubber seed oil The first step, acid esterification, converts FFA to esters and reduces the acid value of the oil to about 4 The second step is the alkaline-catalyzed transesterification process

20.2.1.1 Acid esterification

A measured quantity of the rubber seed oil is stirred and heated in the reactor to about 60˚C The calculated quantity of the methanol is mixed with the preheated rubber seed oil and the mixture is stirred vigorously for a few minutes and allowed

to run at medium speed Then a precise quantity of the concentrated sulfuric acid is added in the mixture The heating and stirring are continued for 20 min and then the products are poured into the separating funnel The excess alcohol with the sulfuric acid and impurities, if any, move to the upper layer and the lower layer is separated for the second step

20.2.1.1.1 Effect of the Amount of Acid Catalyst

The quantity of the acid catalyst used in the process is an important parameter that affects the yield and quality of the biodiesel The methanol is used in excess with varying amounts of concentrated sulfuric acid (0.25 to 2%) It was found that 0.5% concentrated sulfuric acid (v/v) gave the maximum yield (Figure 20.1) An excess amount of sulfuric acid does not increase the yield but darkens the color of the prod-uct and adds to the cost However, an insufficient amount of the sulfuric acid lowers the yield

20.2.1.1.2 Effect of the Amount of Methanol

The quantity of the methanol used is an important factor that affects the yield of the process and the production cost of the biodiesel The molar ratio is defined as the ratio of number of moles of alcohol to number of moles of triglycerides Theoreti-cally, 3 mol of alcohol is required for the conversion of 1 mol of triglyceride to 3 mol of the ester and 1 mol of the glycerol However, in practice, an excess methanol

is required to drive the reaction towards completion Experiments carried out with the optimal catalyst quantity (0.5% v/v) revealed the maximum yield with 20 ml of methanol for 100 ml of the rubber seed oil (Figure 20.2) With further increase in the amount of methanol, there was only little improvement in the yield However, reduction in viscosity of the mixture was observed with increase in the quantity of methanol Excess methanol in the biodiesel would reduce the flash point of the fuel

20.2.1.1.3 Effect of Reaction Temperature

The reaction temperature strongly influences the reaction rate and the yield of the

process The yield of biodiesel from the rubber seed oil was very low (about 10%) when the reaction was carried out at room temperature The optimum temperature was in the range of 45 ± 5°C The boiling point of the methanol is 60°C and hence higher temperature results in loss of the methanol and darkens the color of the prod-uct Furthermore, higher reaction temperature consumes more energy and thus increases the overall production cost of the biodiesel

20.2.1.2 Alkaline transesterification

The product of the first step, that is, the oil-ester mixture (the lower layer in the separating funnel) was heated to the reaction temperature The catalyst (anhydrous sodium hydroxide pellet) was dissolved in the methanol and added to the preheated mixture Heating and stirring were continued for 30 min at the required tempera-ture The reaction produced two liquid phases: ester in the upper layer and crude glycerol in the lower layer The phase separation was observed within 10 to 15 min after stirring was stopped but the complete separation required a longer time (2 to

10 h) The catalyst-glycerol mixture, settled at the bottom, was drained for further processing The ester layer was washed with water (about 25% volume of the oil) by

0 0.4 0.5 1 1.5 2 20

40 60 80 100 120

Sulphuric Acid (% v/v)

fIgure 20.1 Effect of amount of acid catalyst on yield.

0

20

40

60

80

100

120

10 15 20 30 40

Methanol (% v/v)

fIgure 20.2 Effect of methanol quantity on yield of first step.

gentle agitation several times until the washed water was clear, that is, the pH value was neutral

20.2.1.2.1 Effect of the Amount of Alkaline Catalyst

In order to study the effect of the amount of alkaline catalyst on the production of biodiesel from rubber seed oil, sodium hydroxide pellets in the range of 0.3 to 1%

by weight (weight of NaOH/weight of oil) were dissolved in the excess methanol The yield of the process with respect to amount of catalyst is shown in Figure 20.3 The maximum yield was achieved with the use of 0.5% NaOH Excess amounts of catalyst increased the viscosity of the mixture and led to the formation of soap Also, insufficient amounts of catalyst did not initiate the reaction

20.2.1.2.2 Effect of the Amount of Methanol

Figure 20.4 shows the yield of biodiesel with respect to the quantity of methanol used in the process The maximum ester yield was obtained with 30% methanol

by volume With further increase in the molar ratio or methanol quantity, the yield remained almost the same On settling of the mixture, excess methanol moved over the ester layer

0 20 40 60 80 100

0.3 0.4 0.45 0.5 0.55 0.6 0.7 0.8

Sodium Hydroxide (% w/w)

fIgure 20.3 Effect of alkaline catalyst on yield.

0

20

40

60

80

100

10 20 30 40 50

Methanol (% v/v)

fIgure 20.4 Effect of methanol amount on yield of second step.

20.3 propertIes of methyl esters of rubber seed oIl

The physiochemical properties of the biodiesel in comparison with the ASTM biod-iesel standards, ASTM D 6751, are given in Table 20.3 The properties of the methyl esters are comparable to those of diesel and match the ASTM biodiesel standard C,

H, and O compositions of the rubber seed oil methyl esters were 76.85%, 11.82%, and 11.32%, respectively The fuel analysis showed that the transesterification pro-cess improved the fuel properties of the oil, particularly the viscosity and flash point The viscosity of the methyl esters of rubber seed oil was found to be closer to that of diesel, and hence, no hardware modifications are required for storage and handling

of biodiesel

The engine tests were conducted with the blends of biodiesel and diesel as fuel at the rated speed of 1500 rpm Here, B20 represents a blend that contains 20% biod-iesel and 80% dbiod-iesel The engine performance and emission characteristics obtained using biodiesel-diesel blends as fuel are described below (Ramadhas, Jayaraj, and Muraleedharan 2005b)

20.4.1 B raKe t Hermal e fficiency

Figure 20.5 shows the variation in the brake thermal efficiency of the engine with respect to its brake mean effective pressure (BMEP) operating with various blends

of biodiesel and diesel Increase in brake thermal efficiency of the engine with load was observed due to reduction in heat loss and increase in power The brake thermal efficiency of 28% was achieved with B10 as compared to 25% with diesel The lower percentage concentration of biodiesel in the blends improved the brake thermal effi-ciency of the engine The additional lubricity provided by the biodiesel that reduced frictional power and the presence of the oxygen makes complete combustion But, at the higher blends, the brake thermal efficiency of the engine decreased because of its lower calorific value

tAble 20.3

properties of methyl esters of rubber seed oil in comparison with diesel

property

test procedure

biodiesel standard Astm d6751-0202

rubber seed oil methyl ester diesel

Specific gravity ASTM D4052 0.87–0.90 0.874 0.835 Calorific value (MJ/kg) ASTM D240 – 36.50 42.5 Viscosity (mm2/s) at 40°C ASTM D445 1.9-6.0 5.81 3.8 Flash point (°C) ASTM D93 >110 130 48 Cloud point (°C) ASTM D2500 -3–12 4 -1 Pour point (°C) ASTM D97 -15–10 -8 -16

20.4.2 S Pecific f uel c onSumPtion

The variation of specific fuel consumption with respect to the BMEP for the dif-ferent fuels tested is depicted in Figure 20.6 The specific fuel consumption of the engine fueled with the lower concentration of biodiesel in the blend was lower than that of diesel at all the loads The specific fuel consumption of B50 to B100 was found to be higher as compared to diesel because of their lower calorific values About 12% increase in fuel consumption with neat biodiesel was observed as com-pared to neat diesel

20.4.3 c arBon m onoxide e miSSion

CO emission was found to be lower at lighter load conditions and increased with load for all the fuels tested CO emission increased as the air-fuel ratio became lower than that of the stoichiometric air-fuel ratio (Figure 20.7) CO emission was found

to be negligibly small at the stoichiometric air-fuel ratio or on the lean side of the stoichiometric The diesel-fueled engine emitted more CO as compared to that of the biodiesel blends under all the loading conditions

0.2 0.25

0.3 0.35

0.4 0.45

0.5 0.55

0.6

0 100 200 300 400 500 600 700 800

Brake Mean Effective Pressure (kPa)

uel Consumption (kg/k

Diesel B5 B10 B20 B100

fIgure 20.6 Comparison of specific fuel consumption of the engine at various BMEP values.

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600 700 800

Brake Mean Effective Pressure (kPa)

Diesel B5 B10 B20 B100

fIgure 20.5 Comparison of brake thermal efficiency of the engine at various brake mean

effective pressure (BMEP) values.

20.4.4 c arBon d ioxide e miSSion

CO2 emission increased with the increase in the load, as expected The lower per-centage of biodiesel in the blends emit very low amounts of CO2 in comparison with that of the diesel (Figure 20.8) It was observed that neat biodiesel operation emit-ted slightly higher amounts of the carbon dioxide as compared to that of the diesel operation This indicated the complete combustion of the fuel and hence higher com-bustion chamber temperature

20.4.5 S moKe d enSity

The variation of the smoke density for different fuels tested in the engine is depicted

in Figure 20.9 The smoke density of the biodiesel blends was found to be lower than that of the diesel These results support the better combustion of biodiesel blends as compared to diesel

0

2

4

6

8

10

12

14

Diesel B5 B10 B20 B100

Fuel

0 kPa 200 kPa 350 kPa

500 kPa 575 kPa 700 kPa

fIgure 20.8 Comparison of CO2 emission of the engine at various BMEP values.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Diesel B5 B10 B20 B100

Fuel

0 kPa 200 kPa

350 kPa 500 kPa

575 kPa 700 kPa

fIgure 20.7 Comparison of CO emission of the engine at various BMEP values.

20.4.6 e xHauSt G aS t emPerature

The variation of the exhaust gas temperature with respect to BMEP of the engine for different fuels tested is shown in Figure 20.10 The exhaust gas temperature increased with increase in the load for all the fuels tested It was observed that with increase in the concentration of biodiesel in the blend, the exhaust gas tempera-ture increased marginally The nitrogen oxides emission was directly related to the engine combustion chamber temperatures, which in turn indicated the prevailing exhaust gas temperature

Low-cost, high-FFA feedstocks for the production of biodiesel were investigated High-FFA vegetable oils such as rubber seed oil could not be transesterified with the alkaline-catalyzed transesterification process A two-step transesterfication process was developed to convert the high-FFA vegetable oil to its methyl esters The first step, acid-catalyzed esterification, followed by the second step, alkaline-catalyzed transesterification, converts vegetable oils into mono-esters and glycerol This

two-0

100

200

300

400

500

600

700

800

Diesel B5 B10 B20 B100

Fuel

C 0 kPa 200 kPa 350 kPa 500 kPa 575 kPa 700 kPa

fIgure 20.10 Comparison of exhaust gas temperature of the engine at various BMEP values.

0

5

10

15

20

25

30

35

40

45

50

Diesel B5 B10 B20 B100

Fuel

0 kPa 200 kPa

350 kPa 500 kPa

575 kPa 700 kPa

fIgure 20.9 Comparison of smoke density of the engine at various BMEP values.