**3.2.1 Experimental details**

12 Biodiesel – Feedstocks and Processing Technologies

evidences that with the dilution with rapeseed oil it is possible to decrease the viscosity of WCO but increasing the number of IV. Nevertheless also in the case of most diluited sample

WCO 54 82.2 918

It has to be taken into account that after the transesterification process the IV of the feedstock remain unchanged, the viscosity is reduced from 10 to 15 times, whereas density has been found to remain almost the same or to be reduced in some cases (Zheng & Hanna,

As already mentioned in the introduction paragraph, the use of raw, non edible oils poses the problem of standardization before the transesterification process, especially with regard to acidity decrease. In fact oils, besides triglycerides contain also free fatty acids (FFA). These lasts are able to react with the alkaline catalyst used for the transesterification reaction yielding soaps which prevent the contact between the reagents. A FFA content lower than

Among the different deacidification methods listed in the introduction, the authors have recently paid attention to the pre-esterification process (Loreto et al., 2005; Pirola et al., 2010; Bianchi et al., 2010). This method is particularly convenient as it is not only able to lower the acidity content of the oils but also provides methyl esters already at this stage, so increasing the final yield in biodiesel. A scheme of the FFA esterification reaction is given in Fig.2.

> RCOOH CH3OH RCOOCH3 H2O acid catalysis

The use of heterogeneous catalysts (Sharma & Singh, 2011) is usually preferred to the use of homogeneous ones (Alsalme et al., 2008) as it prevents neutralization and separation costs, besides being not corrosive, so avoiding the use of expensive construction materials. Another important advantage is that the recovered catalysts can be potentially used for a

In the recent years the authors have deepened the study of the pre-esterification process investigating the effect of the use of different kinds of oils, different types of reactors and catalysts and different operating conditions (Pirola et al., 2010; Bianchi et al., 2010; Pirola et

In the following paragraphs, the most relevant aspects of the experimental work and the results obtained by the authors for what concerns the pre-esterification process are reported.

WCO:rapeseed oil 1:1 85 52.8 914 WCO:rapeseed oil 3:1 100 40.5 926 Rapeseed 115 n.d. n.d.

**Viscosity (mm2/s 40 °C)** 

**Density (kg/m3 15° C)** 

**(gI2/100g oil)** 

Table 5. IV, viscosities and densities of some potential raw materials for biodiesel

the IV value is lower than those of rapeseed oil.

production.

1996).

al. 2011)

**Oil Iodine value** 

**3.2 Oil standardization: Free fatty acids esterification reaction** 

Fig. 2. Scheme of the Free Fatty Acid Esterification Reaction.

0.5% wt is also required by the EN 14214.

long time and/or multiple reaction cycles.

A remarkable aspect of the proposed process is represented by the mild operative conditions, i.e. low temperature (between 303 and 338 K) and atmospheric pressure. Moreover, the adopted working temperature is the same of the following transesterification reaction and of the methanol recovery by distillation. Each single reaction has been carried out for six hours withdrawing samples from the reactor at pre-established times and analysing them through titration with KOH 0.1 M. The percentage of FFA content per weight was calculated as otherwise reported (Marchetti & Errazu, 2007, Pirola et al. 2010).

All the esterification experiments have been conducted using a slurry reactor as the one already described elsewhere (Bianchi et al., 2010). A slurry reactor is the simplest type of catalytic reactor, in which the catalyst is suspended in the mass of the regents thanks to the agitation.

Much attention has been paid by the authors to the use of acid ion exchange resins. Amberlyst ®46 (named A46 in this chapter), i.e. a commercial product by Dow Advanced Materials, and D5081, a catalyst at the laboratory development stage by Purolite® have been successfully applied in this reaction. The main features of the employed catalysts are reported in Tab. 6.


Table 6. Main features of the ion exchange resins adopted as catalysts in the FFA esterification reaction.

The acid capacity of the catalysts, corresponding to the number of the active sites per gram of catalyst was also experimentally determined by the authors by ion exchange with a NaClsaturated solution and successive titration with NaOH (López et al., 2007). The values were found to be in agreement with the ones provided by technical sheets.

A distinguishing feature of A46 and D5081 is represented by the location of the active acid sites: these catalysts are in fact sulphonated only on their surface and not inside the pores. Consequently, A46 and D5081 are characterized by a smaller number of acid sites per gram if compared to other Amberlysts®, which are also internally sulphonated (Bianchi et al., 2010).

#### **3.2.2 Deacidification results**

In Fig. 3 the results from the esterification reaction performed on different raw oils are shown.

From the graph it can be noticed that in almost all the cases it is possible to obtain a FFA concentration lower than 0.5% wt after 6 hours of reaction. The differences in the acidic composition seem not to affect the final yield of the reaction. What seems to influence the FFA conversion is the refinement degree of the oil. Waste cooking oil (WCO) is in fact more hardly processable with the esterification in comparison to refined oils, probably due to its higher viscosity which results in limitations to the mass transfer of the reagents towards catalysts. Indeed, the required acidity limit is not achieved within 6 hours of reaction. Adding rapeseed oil, less viscous, to the WCO in different ratios it is possible to increase the

Non Edible Oils: Raw Materials for Sustainable Biodiesel 15

run 1 run 2 run 3 run 4 run 5

WCO:rapeseed=1:1 WCO:rapeseed=1:3

0 120 240 360

reaction time (min)

The lifetime of the catalyst is a very important issue from an industrial standpoint. The authors have already performed a deep study on the ion exchange resins endurance in the FFA esterification reaction (Pirola et al., 2010). The most important outcome of this study is that resins like A46 (Dow Advanced Materials) and D5081 (Purolite), which are functionalized only on their surface are very stable in the reaction conditions and can

0 60 120 180 240 300 360 420

D5081 10% D5081 8% D5081 6% A46 10% A46 8% A46 6%

weight % catalyst/oil Catalyst's loading: mcat/moil

time (mins)

Fig. 5. FFA conversion (%) vs reaction time for different amounts of catalysts A46 and D5081, rapeseed oil with initial acidity=5%, slurry reactor, weight ratio

methanol/oil= 16:100, T=338K. Dots are experimentally obtained.

Fig. 4. FFA conversion (%) vs reaction time of waste cooking oil (WCO) and its blends with rapeseed oils: slurry reactor, T=338K, catalyst: Amberlyst® 46 weight ratio

methanol /oil= 16:100, weight ratio catalyst/oil=1:10.

guarantee long operating times without being replaced. A comparison between these two resins is displayed in Fig. 5.

Continue lines are simulated (see paragraph 3.2.3)

FFA conversion (%)

FFA conversion (%)

final FFA conversion and reaching a FFA content lower than 0.5% wt. The blend of a raw oil characterized by high viscosity with a less viscous one is also effective in shortening the time to reach the plateau of conversion, as displayed in Fig. 4.

Fig. 3. Acidity removed by esterification (6 hr) and residual acidity of different oils used as raw material: slurry reactor, T=338K, catalyst: Amberlyst® 46 weight ratio methanol/oil= 16:100, weight ratio catalyst/oil=1:10; \*commercial, refined oils with the addition of pure oleic acid.

In Fig. 4 the conversion curves concerning the recycles of the use of the catalyst A46 in the case of WCO are also shown. The catalyst does not show a drastic drop in its activity notwithstanding the used substrate is not refined. This decrease in the catalytic performance might be ascribable to the catalyst's settling in the reaction environment (Pirola et al., 2011) or to the presence of cations inside the oil. This aspect is still under investigation.

It is convenient to use an excess of methanol respect the stoichiometric amount in order to shift the equilibrium towards the product. Nevertheless, when adding methanol a double phase system is formed (the maximum solubility of methanol in oil is in the interval 6- 8%) and therefore it is not convenient to increase further this parameter.

final FFA conversion and reaching a FFA content lower than 0.5% wt. The blend of a raw oil characterized by high viscosity with a less viscous one is also effective in shortening the time

4.14


0.52 0.23 0.48 0.27 0.35 0.25


Rapeseed

Fig. 3. Acidity removed by esterification (6 hr) and residual acidity of different oils used as raw material: slurry reactor, T=338K, catalyst: Amberlyst® 46 weight ratio methanol/oil= 16:100, weight ratio catalyst/oil=1:10; \*commercial, refined oils with the addition of pure

In Fig. 4 the conversion curves concerning the recycles of the use of the catalyst A46 in the case of WCO are also shown. The catalyst does not show a drastic drop in its activity notwithstanding the used substrate is not refined. This decrease in the catalytic performance might be ascribable to the catalyst's settling in the reaction environment (Pirola et al., 2011) or to the presence of cations inside the oil. This aspect is still under

It is convenient to use an excess of methanol respect the stoichiometric amount in order to shift the equilibrium towards the product. Nevertheless, when adding methanol a double phase system is formed (the maximum solubility of methanol in oil is in the interval 6- 8%)

Sunflower\*

Palm

2.22

1.68

Tobacco

and therefore it is not convenient to increase further this parameter.

0.88

Waste cooking oil

Waste cooking oil:

Rapeseed 1:1

Waste cooking oil:

Rapeseed 1:3

2.96 2.30


Residual Acidity

Acidity removed by esterification

0.52 0.37


2.20 2.20


to reach the plateau of conversion, as displayed in Fig. 4.

0.74


Indian mustard

0

oleic acid.

investigation.

Soybean\*

1

2

3

FFA (% wt)

4

5

6

5.76


Fig. 4. FFA conversion (%) vs reaction time of waste cooking oil (WCO) and its blends with rapeseed oils: slurry reactor, T=338K, catalyst: Amberlyst® 46 weight ratio methanol /oil= 16:100, weight ratio catalyst/oil=1:10.

The lifetime of the catalyst is a very important issue from an industrial standpoint. The authors have already performed a deep study on the ion exchange resins endurance in the FFA esterification reaction (Pirola et al., 2010). The most important outcome of this study is that resins like A46 (Dow Advanced Materials) and D5081 (Purolite), which are functionalized only on their surface are very stable in the reaction conditions and can guarantee long operating times without being replaced.

A comparison between these two resins is displayed in Fig. 5.

Fig. 5. FFA conversion (%) vs reaction time for different amounts of catalysts A46 and D5081, rapeseed oil with initial acidity=5%, slurry reactor, weight ratio methanol/oil= 16:100, T=338K. Dots are experimentally obtained. Continue lines are simulated (see paragraph 3.2.3)

Non Edible Oils: Raw Materials for Sustainable Biodiesel 17

The transesterification reaction has been performed by the authors on the rapeseed and *B.juncea* (Indian mustard) oilseeds deacidified with the esterification process described in

Sodium Methoxide (MeONa) was employed as catalyst. MeONa is known to be the most active catalyst for triglycerides transesterification reaction, but it requires the total absence of water (Schuchardt, 1996). For this reason, the unreacted methanol and the reaction water were evaporated from the deacidified oils before processing them with the

The employed experimental setup was the same employed for the slurry esterification. Being the transesterification an equilibrium reaction, it was performed in two steps, removing the formed glycerine after the first step. The adopted conditions were the

 1st step: weight ratio methanol/oil=20:100, weight ratio MeONa/oil=1:100, 233 K, 1,5 h; 2nd step: weight ratio methanol/oil=5:100, weight ratio MeONa/oil=0.5:100, 233 K, 1 h. The total ester content is a measure of the completeness of the transesterification reaction. Many are the factors affecting ester yield in the transesterification reaction: molar ratios of glycerides to alcohol, type of catalyst(s) used, reaction conditions, water content, FFA

The European prEN14214 biodiesel standard sets a minimum limit for ester content of >96.5% mass, whereas the US ASTM D 6751 biodiesel standard does not set a specification

Mono- and di-glycerides as well as tri-glycerides can remain in the final product in small quantities. Most are generally reacted or concentrated in the glycerine phase and separated

Both in the case of rapeseed oil and *B.juncea* oilseed, the final yield in methylester was

The analyses of methyl esters and unreacted mono-, di- and triglycerides are accomplished

The detailed requirements for biodiesel according to both EN 14214 and US ASTM D 6751

In the US a standard for biodiesel (ASTM D 6751 – Standard Specification for Biodiesel Fuel (B100) does not include the same number of parameters as prEN 14214 but the parameters that coincide have similar limits. The US specification covers sulfur biodiesel (B100) content much higher if compared to the one of European Standard. For use as a blend component with diesel fuel oils defined by ASTM D 975 Grades 1-D, 2-D, and low sulfur 1-D and 2-D.

The use of the oilseed deriving from alternative crops or waste oils as a feedstock for biodiesel production represents a very convenient way in order to lower the production

From the agronomic point of view the authors verified that the green manure of *B.juncea* resulted in nematode infestation drastically decreased and improved soil quality, reflected in higher yield of crops in agronomic succession. In the first year of experimentation *B. juncea* was preferred to *B.carinata* because of its suitability to spring planting (starting period

**3.3 Oil transformation: The transesterification reaction** 

the previous paragraph.

transesterification reaction.

following:

concentration, etc.

for ester content.

from the ester.

higher than 98%.

**4. Conclusion** 

costs of this biofuel.

through gas chromatography.

(Environment Australia, 2003).

are listed in paragraph 1.

As can be seen from the graph, catalyst D5081 shows better results than A46 at lower catalyst's loading. This can be easily explained by the higher number of acid sites located on its surface. In particular, the use of a ratio of 10 %wt of catalyst D5081 vs. oil allows reaching the maximum conversion in 2 hours. From the graph can be seen how the curves for 6% of D5081 and 10% wt catalyst/oil of A46 perfectly overlap. This outcome suggested that a fixed amount of acid active sites per gram of FFA was required to reach the maximum of conversion in 4 hours. Based on the experimental data obtained, this amount was found to be equal to 1.2 meq of H+.

#### **3.2.3 Simulation of the catalytic results**

The considered reaction system turns out to be an highly non-ideal system, being formed by a mixture of oil, methylester, methanol, FFA and water. Indeed, activity coefficients instead of concentrations are used not only for the phase and chemical equilibria calculations, but also for the kinetic expressions. Modified UNIFAC model was used adopting the parameters available in literature and published by Gmehling et al., 2002 (Pirola et al., 2011).

A pseudohomogeneous model was used for describing the kinetic behavior of the reaction (Pöpken et al., 2000). The adopted model is displayed in the following equation:

$$\mathbf{r} = \frac{1}{\mathbf{m}\_{\rm cat}} \frac{1}{\mathbf{p}\_{\rm i}} \frac{\mathbf{dn}\_{\rm i}}{\mathbf{dt}} = \mathbf{k}\_1 \mathbf{a}\_{\rm FFA} \mathbf{a}\_{\rm methanol} - \mathbf{k}\_{-1} \mathbf{a}\_{\rm methylester} \mathbf{a}\_{\rm water}$$

where:

r= reaction rate mcat= dry mass of catalyst, gr υi= stoichiometric coefficients of component i n1= moles of component i t = reaction time k1= kinetic constant of direct reaction k-1= kinetic constant of indirect reaction ai= activity of component i The temperature dependence of the rate constant is expressed by the Arrhenius law:

$$\mathbf{k}\_{\mathrm{i}} = \mathbf{k}\_{\mathrm{i}} \, ^{0} \exp\left(\frac{\cdot \mathbf{E}\_{\mathrm{A},\mathrm{i}}}{\mathrm{RT}}\right).$$

where ki 0 and EA,i are the pre-exponential factor and the activation energy of the reaction i, respectively (i=1 for the direct reaction, i=-1 for the indirect reaction), T is the absolute temperature and R the Universal Gas Constant. The adopted parameters set is the same reported by Steinigeweg (Steinigeweg & Gmehling, 2003).

All the simulations were carried using Batch Reactor of PRO II by Simsci – Esscor. The model turned out to be able to reproduce qualitatively the behavior of different systems, characterized by different catalyst type and content.

In the previous Figure 5, continue lines represent simulated behaviors using the same parameters, but considering a different catalyst mass due to different catalyst acidity and concentration.

As can be seen from the graph, catalyst D5081 shows better results than A46 at lower catalyst's loading. This can be easily explained by the higher number of acid sites located on its surface. In particular, the use of a ratio of 10 %wt of catalyst D5081 vs. oil allows reaching the maximum conversion in 2 hours. From the graph can be seen how the curves for 6% of D5081 and 10% wt catalyst/oil of A46 perfectly overlap. This outcome suggested that a fixed amount of acid active sites per gram of FFA was required to reach the maximum of conversion in 4 hours. Based on the experimental data obtained, this amount was found to

The considered reaction system turns out to be an highly non-ideal system, being formed by a mixture of oil, methylester, methanol, FFA and water. Indeed, activity coefficients instead of concentrations are used not only for the phase and chemical equilibria calculations, but also for the kinetic expressions. Modified UNIFAC model was used adopting the parameters available in literature and published by Gmehling et al., 2002

A pseudohomogeneous model was used for describing the kinetic behavior of the reaction

FFA1 methanol <sup>1</sup> methylester water <sup>i</sup>

aakaak

 0 A,i

0 and EA,i are the pre-exponential factor and the activation energy of the reaction i,


(Pöpken et al., 2000). The adopted model is displayed in the following equation:

The temperature dependence of the rate constant is expressed by the Arrhenius law:

i i

k =k exp RT

respectively (i=1 for the direct reaction, i=-1 for the indirect reaction), T is the absolute temperature and R the Universal Gas Constant. The adopted parameters set is the same

All the simulations were carried using Batch Reactor of PRO II by Simsci – Esscor. The model turned out to be able to reproduce qualitatively the behavior of different systems,

In the previous Figure 5, continue lines represent simulated behaviors using the same parameters, but considering a different catalyst mass due to different catalyst acidity and

r

icat

m 1

υi= stoichiometric coefficients of component i

k1= kinetic constant of direct reaction k-1= kinetic constant of indirect reaction

υ 1

reported by Steinigeweg (Steinigeweg & Gmehling, 2003).

characterized by different catalyst type and content.

dt dn

be equal to 1.2 meq of H+.

(Pirola et al., 2011).

where:

where ki

concentration.

r= reaction rate

t = reaction time

mcat= dry mass of catalyst, gr

n1= moles of component i

ai= activity of component i

**3.2.3 Simulation of the catalytic results** 
