**3. New trends in biodiesel technologies**

The new developments in biodiesel production technologies are focused on simplification of the existing technologies by using co-solvents (Guan et al., 2009b), supercritical solvents (Geuens et al., 2008), new catalysts (including heterogeneous and biocatalysts) (Fu and Vasudevan, 2009; Soriano et al., 2009; Leung et al., 2010) and the efforts are directed on founding new blends and raw materials (including the waste glycerol (Guerrero-Perez, et. al., 2009)) to increase the amount of biofuel produced on a given agricultural area. Some of the improved methods are discussed below.

#### **3.1 Trans-esterification with phase mixing materials**

Base catalyzed trans-esterification of the vegetable oils with methanol is a slow process in the two-phase system due to the mass transfer limitation. The butanolysis is much faster because it takes place in homogeneous phase. Therefore, the possibilities to create a homogeneous mixture by using an appropriate co-solvent which homogenizes the vegetable oil and methanol has extensively been studied (Guan et al., 2009a; 2009b; Leung et al., 2010; Meng et al., 2009; Soiano et al., 2009). The best solvents are the ether-type compounds like THF, methyl tertiary butyl ether, Me2O or diethers. Phase diagrams of different vegetable oils - ethereal solvents (1,4-dioxane, THF, Et2O, diisopropyl ether and MTBE)-methanol have been studied (Boocok et al., 1996a) and THF was found to be the preferred solvent on the basis of the volume required by the miscibility and boiling point considerations. Initially the reactions are very fast , but they slow down drastically due to the polarity changes in the mixed phase containing esters and decreasing amount of alcohol [Boocock et al., 1998). The decreasing polarity of the intermediate mixture could be avoided only by using large excess of methanol (methanol/oil molar ratio 27) when the methyl ester production exceed 94.4 % in 7 min even at room temperature. The separation of the glycerol phase in the presence of THF was much more rapid as in the case of two-phase trans-esterification reaction mixtures (Boocock et al., 1996a). The use of cyclic THF or 1,4-dioxane provides a possibility to decrease the amount of the co-solvent and perform the trans-esterification at higher oil : cosolvent ratios. The THF and the dioxane are miscible with vegetable oils and methanol in any proportion and they have hydrogen bonding ability (Boocock et al., 1996b). In spite of that 5 % dioxane ensures almost complete reaction within 30 min at room temperature at a 6:1 methanol : oil molar ratio, the 1,4-dioxane ring opens up during the trans-esterification reaction at the presence of 1 % KOH catalyst, thus it cannot be recycled at all.

Dimethyl ether can be separated easily with depressurizing the reaction system and Me2O as a polar compound ensures a sufficiently high trans-esterification reaction rate at room temperature. The effects of the reaction conditions on the reaction time indicated that under the usual conditions, such as 1 % of KOH and 2-fold molar excess of methanol (6:1 methanol : oil molar ratio), the reactions can be performed within 5-10 min which would provide a good technological base for the continuous production of biodiesels (Guan et al, 2009a and 2009b). The gaseous state of form of the Me2O requires pressurized reactors and the risk of explosion is very high.

Recently a new technology has been developed (Kótai et al., 2008) for the phase-mixing of methanol (or other alcohols) and vegetable oils in trans-esterification reactions with alkoxyalkanol phase transfer agents. These are hemi-ethers of glycols. They are polar endgroup, but they have oil-soluble alkyl chain as well. The best candidate is the butylglycol (2 butoxy-ethanol), which can act at even 1 % concentration, and at the 6:1 MeOH : rapeseed

The new developments in biodiesel production technologies are focused on simplification of the existing technologies by using co-solvents (Guan et al., 2009b), supercritical solvents (Geuens et al., 2008), new catalysts (including heterogeneous and biocatalysts) (Fu and Vasudevan, 2009; Soriano et al., 2009; Leung et al., 2010) and the efforts are directed on founding new blends and raw materials (including the waste glycerol (Guerrero-Perez, et. al., 2009)) to increase the amount of biofuel produced on a given agricultural area. Some of

Base catalyzed trans-esterification of the vegetable oils with methanol is a slow process in the two-phase system due to the mass transfer limitation. The butanolysis is much faster because it takes place in homogeneous phase. Therefore, the possibilities to create a homogeneous mixture by using an appropriate co-solvent which homogenizes the vegetable oil and methanol has extensively been studied (Guan et al., 2009a; 2009b; Leung et al., 2010; Meng et al., 2009; Soiano et al., 2009). The best solvents are the ether-type compounds like THF, methyl tertiary butyl ether, Me2O or diethers. Phase diagrams of different vegetable oils - ethereal solvents (1,4-dioxane, THF, Et2O, diisopropyl ether and MTBE)-methanol have been studied (Boocok et al., 1996a) and THF was found to be the preferred solvent on the basis of the volume required by the miscibility and boiling point considerations. Initially the reactions are very fast , but they slow down drastically due to the polarity changes in the mixed phase containing esters and decreasing amount of alcohol [Boocock et al., 1998). The decreasing polarity of the intermediate mixture could be avoided only by using large excess of methanol (methanol/oil molar ratio 27) when the methyl ester production exceed 94.4 % in 7 min even at room temperature. The separation of the glycerol phase in the presence of THF was much more rapid as in the case of two-phase trans-esterification reaction mixtures (Boocock et al., 1996a). The use of cyclic THF or 1,4-dioxane provides a possibility to decrease the amount of the co-solvent and perform the trans-esterification at higher oil : cosolvent ratios. The THF and the dioxane are miscible with vegetable oils and methanol in any proportion and they have hydrogen bonding ability (Boocock et al., 1996b). In spite of that 5 % dioxane ensures almost complete reaction within 30 min at room temperature at a 6:1 methanol : oil molar ratio, the 1,4-dioxane ring opens up during the trans-esterification

reaction at the presence of 1 % KOH catalyst, thus it cannot be recycled at all.

Dimethyl ether can be separated easily with depressurizing the reaction system and Me2O as a polar compound ensures a sufficiently high trans-esterification reaction rate at room temperature. The effects of the reaction conditions on the reaction time indicated that under the usual conditions, such as 1 % of KOH and 2-fold molar excess of methanol (6:1 methanol : oil molar ratio), the reactions can be performed within 5-10 min which would provide a good technological base for the continuous production of biodiesels (Guan et al, 2009a and 2009b). The gaseous state of form of the Me2O requires pressurized reactors and the risk of

Recently a new technology has been developed (Kótai et al., 2008) for the phase-mixing of methanol (or other alcohols) and vegetable oils in trans-esterification reactions with alkoxyalkanol phase transfer agents. These are hemi-ethers of glycols. They are polar endgroup, but they have oil-soluble alkyl chain as well. The best candidate is the butylglycol (2 butoxy-ethanol), which can act at even 1 % concentration, and at the 6:1 MeOH : rapeseed

**3. New trends in biodiesel technologies** 

the improved methods are discussed below.

explosion is very high.

**3.1 Trans-esterification with phase mixing materials** 

oil molar ratio with 1 % KOH a catalyst. The reaction is almost completed within 30 min even at room temperature. By using 5 % of butylglycol, the reaction time is 5-10 min. Since the butyl glycol acts also as an alcohol ( not only as an ether), thus not only methyl esters but 2-butoxyethyl esters – R-C(O)-O-C2H4-OC4H9 - are also formed. These esters are formed in an amount of 2-3 %w/w and act as fuel components. In this way, the phase mixing agents built into the ester phase and they contribute to the mass of the biodiesel and do not need to recover it which simplifies the production technology. The catalyst solution prepared from KOH, butylglycol and methanol was used in our plant scale experiment performed in Hungary in 2009, when a continuous trans-esterification process with continuous separator was put into operation. The method could be combined with the ion exchange type removal and recycling of the neutralization agent (KHSO4, chapter 3. 2), because the reaction takes place at room temperature and the amount of soaps formed and appeared in the ester phase was very small. The catalyst distribution between the ester and glycerol phase is around 2:98. The ester phase has been neutralized with KHSO4, when the potassium content is decreased with the continuous operation mode below 50 ppm without any further washing. The further purification steps, washing with water and removing the residual MeOH in vacuum, are the same as in the classical biodiesel technologies, however, the amount of the dissolved MeOH, due to the lack of soaps and residual catalyst is much lower than in the usual technologies. The flow-sheet of the technology is shown in Fig 2.

In order to decrease the length of the tube reactor and the residence time of the mixture in the apparatus, a two-stage trans-esterification seems to be the most reliable, when after decreasing the rate of the reaction, after the first separator a further amount of methanol and catalyst are added, when the reaction rate is suddenly increases: it is attributed to the extra methanol ensuring a large excess for the residual triglyceride, thus the conversion reaches 98 % in 20-30 min reaction time. We have used 50 m3 tanks for the esterification with intensive stirring. Separators for removing the glycerol phase, and the same volume of the separator was used to separate the neutralization agent and the ester phase which was mixed in a tube after exit of the first separator and before entering into the second one.

#### **3.2 Removal of the residual catalyst from the biodiesel (decontamination)**

In spite of the efforts to produce solid phase non-soluble alkaline catalysts or highly active acidic (super-acidic) catalysts (Di Serio et al, 2008; Leung et al., 2010; Soriano et al., 2009), the homogeneous catalytic (KOH or NaOMe catalyzed) trans-esterification of vegetable oils have been the most commonly used method in the biodiesel industry (Huber et al., 2006). However, soap formation during the alkaline-catalyzed trans-esterification is the most problematic by-reaction. In case of low water and carboxylic acid containing vegetable oils the main source of the soap formation is the hydrolysis of the formed methyl esters during washing, which is a strongly pH dependent process. Thus the neutralization preceding the washing is an essential step to minimize the saponification by-reactions. The amount and type of the formed soap is strongly affected by the separation characteristics of the glycerol and the ester phase. The acid treatment is generally needed to start or quicken the phase separation process producing aqueous glycerol solution. It is well known that the distribution of the catalyst between the glycerol and the methyl ester phase is strongly depends on the temperature, type of the catalyst, excess of methanol and the composition of the two separated phases [Chiu et al., 2005; Di Felice et al., 2008; Zhou and Boocock, 2006). Table 2 shows the distribution of 1 % KOH and 0.5 % of H2SO4 distribution at different temperatures depending on the amount of methanol at biodiesel : glycerol molar ratio of 1:3.

An Integrated Waste-Free Biomass Utilization

Fig. 2. Flow-sheet of biodiesel synthesis

shown in Fig. 2.

(Scherer, 2001).

(Kótai et al., 2008a).

System for an Increased Productivity of Biofuel and Bioenergy 207

K-ions are bound by the resin phase). The dilute sulfuric acid is combined with the other stream of the K2SO4, when KHSO4 forms which can be recycled without further treatment

 K2SO4 + H2SO4 = 2KHSO4 (2) The exhausted ion exchanger can be regenerated with the 20 % sulfuric acid solution consumed also for the formal neutralization. The potassium sulfate solution obtained during the regeneration process of the ion exchanger resin can be used as a fertilizer component.

However, the recycling of the KHSO4 solutions is recommended only 2-20 times due to the accumulation of glycerol and methanol in the aqueous KHSO4 solutions. The process flow is

The completely neutralized KHSO4 solution turns into K2SO4, therefore it can be used as a fertilizer component together with the K2SO4 originated from the ion exchange regeneration cycle. Similarly, the potassium hydroxide content of the glycerol phase may be utilized in the same way after processing its glycerol and methanol content with H2SO4 catalyst into fuel (see in Chapter 4.2). In this way, the starting potassium based catalyst (KOH) is used not only as a catalyst but as a fertilizer source in an advantageous sulfate form, which helps to avoid the chloride accumulation in the soil and supplies the sulfur deficiency of the soil, especially in the case of rape plant cultures of high sulfur demand

Production of biodiesels from non-food quality vegetable oils with high fatty acid content is an important area of the biodiesel developments. The common alkaline catalysts cannot be used economically, because they reacts with the fatty acids and form soaps causing high catalyst consumption and a decrease in the catalyst activity. The alkali soaps are the cause of

**3.3 Trans-esterification of high acid containing vegetable oils** 

The ion exchanger can be regenerated and used again several thousand times.


Table 2. Distribution of the KOH catalyst between the ester and glycerol phase in the function of temperature and MeOH excess (K= Cglycerol /Cester phase)

It can be seen that increasing temperature increases the amount of the catalyst in the ester phase. The amount of dissolved methanol also increases the amount of dissolved catalyst. The K values of the distribution of methanol, however, 10.9 and 7.5 at 3 and 8.5 and 4.8 at 6 moles of methanol towards 3 mol of biodiesel and 1 moles of glycerol at 25 and 75 °C, respectively. In the presence of 1 % KOH, these values changed to 2.29, 1.64, 1.90 and 1.48, respectively.

Due to the room-temperature reaction, there is low catalyst and low methanol concentration in the ester phase, thus the amount of the required neutralization agent is also low. Considering the use of a continuous separator, the relative volumes of the separated phases should be adjusted between 10-1:1, so it is possible to use dilute (2 %) KHSO4 solution. The neutralization acts as the first washing step, when the potassium content in the biodiesel phase was proved to be up to 8 ppm without further aqueous washing. Instead of mineral acids we used an acidic salt as hydrogen ion sources, namely, potassium hydrogen sulfate (KHSO4). Potassium hydrogen sulfate has as strong acidic function as the pure sulfuric acid without the disadvantages of the sulfuric acid, e.g. it is a solid crystalline mass can be stored without risk and can be dissolved in water without extreme heat generation, and no acidic vapors as in the case of hydrochloric acid can be felt. Due to the low amount of soaps in the ester phase, the dissolved methanol content of the ester phase is lower than in case of the classical biodiesel technologies. Potassium hydrogen sulfate as a strong "acid" reacts with KOH catalyst and soaps easily and spontaneously as

$$\text{KOR} + \text{KHSO4} = \text{K}\_2\text{SO4} + \text{HOR} \tag{1}$$

where R = alkylcarbonyl radical (potassium soaps) or H (KOH). The aqeous KHSO4 solution decomposes soaps immediately without emulsion formation. The formed potassium sulfate is neutral, soluble in water, insoluble in the ester phase and has no phase transfer property at all. The concentration of the formed potassium sulfate is low (~2-3 %), since dilute KHSO4 solutions is used for neutralization of the potassium compounds in the ester phase. The aqueous phase will contain potassium sulfate, glycerol, methanol, and other water soluble components. The dilute solution can easily be ion-exchanged with strong acidic cationic exchangers as Varion KSM resin. The glycerol and the methanol containing aqueous phase is a strong polar solution, thus regeneration and recycling of the KHSO4 should be taken place. However, stopping and controlling the operation of the ion exchanger at the stage of the hydrogen sulfate formation is difficult. Therefore, the K2SO4 containing material stream is divided into two equal parts. One part of the K2SO4 is ion-exchanged in a common way with the formation of H2SO4 solution (the

H2SO4

25 3 95 25 3 53 25 6 77 25 6 46 75 0 47 75 0 31 75 3 45 75 3 28 75 6 35 75 6 24

25 0 60

**Catalyst T, °C MeOH, mol K Catalyst T, °C MeOH, mol K** 

Table 2. Distribution of the KOH catalyst between the ester and glycerol phase in the

It can be seen that increasing temperature increases the amount of the catalyst in the ester phase. The amount of dissolved methanol also increases the amount of dissolved catalyst. The K values of the distribution of methanol, however, 10.9 and 7.5 at 3 and 8.5 and 4.8 at 6 moles of methanol towards 3 mol of biodiesel and 1 moles of glycerol at 25 and 75 °C, respectively. In the presence of 1 % KOH, these values changed to 2.29, 1.64, 1.90 and 1.48,

Due to the room-temperature reaction, there is low catalyst and low methanol concentration in the ester phase, thus the amount of the required neutralization agent is also low. Considering the use of a continuous separator, the relative volumes of the separated phases should be adjusted between 10-1:1, so it is possible to use dilute (2 %) KHSO4 solution. The neutralization acts as the first washing step, when the potassium content in the biodiesel phase was proved to be up to 8 ppm without further aqueous washing. Instead of mineral acids we used an acidic salt as hydrogen ion sources, namely, potassium hydrogen sulfate (KHSO4). Potassium hydrogen sulfate has as strong acidic function as the pure sulfuric acid without the disadvantages of the sulfuric acid, e.g. it is a solid crystalline mass can be stored without risk and can be dissolved in water without extreme heat generation, and no acidic vapors as in the case of hydrochloric acid can be felt. Due to the low amount of soaps in the ester phase, the dissolved methanol content of the ester phase is lower than in case of the classical biodiesel technologies. Potassium hydrogen sulfate as a strong "acid" reacts with

where R = alkylcarbonyl radical (potassium soaps) or H (KOH). The aqeous KHSO4 solution decomposes soaps immediately without emulsion formation. The formed potassium sulfate is neutral, soluble in water, insoluble in the ester phase and has no phase transfer property at all. The concentration of the formed potassium sulfate is low (~2-3 %), since dilute KHSO4 solutions is used for neutralization of the potassium compounds in the ester phase. The aqueous phase will contain potassium sulfate, glycerol, methanol, and other water soluble components. The dilute solution can easily be ion-exchanged with strong acidic cationic exchangers as Varion KSM resin. The glycerol and the methanol containing aqueous phase is a strong polar solution, thus regeneration and recycling of the KHSO4 should be taken place. However, stopping and controlling the operation of the ion exchanger at the stage of the hydrogen sulfate formation is difficult. Therefore, the K2SO4 containing material stream is divided into two equal parts. One part of the K2SO4 is ion-exchanged in a common way with the formation of H2SO4 solution (the

KOR + KHSO4 = K2SO4 + HOR (1)

25 0 98

function of temperature and MeOH excess (K= Cglycerol /Cester phase)

KOH catalyst and soaps easily and spontaneously as

KOH

respectively.

K-ions are bound by the resin phase). The dilute sulfuric acid is combined with the other stream of the K2SO4, when KHSO4 forms which can be recycled without further treatment (Kótai et al., 2008a).

$$\mathrm{K\_2SO\_4 + H\_2SO\_4 = 2KHSO\_4} \tag{2}$$

The exhausted ion exchanger can be regenerated with the 20 % sulfuric acid solution consumed also for the formal neutralization. The potassium sulfate solution obtained during the regeneration process of the ion exchanger resin can be used as a fertilizer component. The ion exchanger can be regenerated and used again several thousand times.

Fig. 2. Flow-sheet of biodiesel synthesis

However, the recycling of the KHSO4 solutions is recommended only 2-20 times due to the accumulation of glycerol and methanol in the aqueous KHSO4 solutions. The process flow is shown in Fig. 2.

The completely neutralized KHSO4 solution turns into K2SO4, therefore it can be used as a fertilizer component together with the K2SO4 originated from the ion exchange regeneration cycle. Similarly, the potassium hydroxide content of the glycerol phase may be utilized in the same way after processing its glycerol and methanol content with H2SO4 catalyst into fuel (see in Chapter 4.2). In this way, the starting potassium based catalyst (KOH) is used not only as a catalyst but as a fertilizer source in an advantageous sulfate form, which helps to avoid the chloride accumulation in the soil and supplies the sulfur deficiency of the soil, especially in the case of rape plant cultures of high sulfur demand (Scherer, 2001).

#### **3.3 Trans-esterification of high acid containing vegetable oils**

Production of biodiesels from non-food quality vegetable oils with high fatty acid content is an important area of the biodiesel developments. The common alkaline catalysts cannot be used economically, because they reacts with the fatty acids and form soaps causing high catalyst consumption and a decrease in the catalyst activity. The alkali soaps are the cause of

An Integrated Waste-Free Biomass Utilization

biodiesel production system.

**4. Butanol as raw material in biodiesel production** 

1,3-dioxane- or dioxolane type fuel additives (Silva et al., 2010)

**4.1 Butanol as blending or reactive component in biodiesel production** 

System for an Increased Productivity of Biofuel and Bioenergy 209

By using of butanol as blending material for gasoline and diesel fuels has many advantages towards fuel ethanol (Andersen et al., 2010; Bruno et al., 2009, Duck and Bruce, 1945, Workman et al., 1983), additionally, it can also be used as reactive component in biodiesel production. Butanol can substitute methanol as an alcohol for esterification (Wahlen et al., 2008; Nimcevic et al., 2000, Stoldt and Dave, 1998), it can be an acetal forming compounds for transforming of acetone or other ketones into acetals, or can easily be converted to butyraldehyde for the conversion of glycerol formed during trans-esterification of oils into

The butanol or the butanol - acetone - ethanol mixture produced in the ABE fermentation have been tested already during the World War II as a blending components for gasoline powered engines (Duck and Bruce, 1945). The engines can be powered with gasoline containing butanol up to 40 % without any technical modification of the engine. The characteristics of pure butanol and ABE solvent mixtures as gasoline or diesel fuel additives have been tested in detail. Generally, the blended mixtures produce almost the same power and thermal efficiency as the gasoline (Schrock and Clark, 1983). The same time the blending has a positive effect via substantially decreasing the NOx content of the exhaust gases. Since the modern mobile agricultural equipment used in the production of biomass is mostly diesel powered, both ethanol and butanol have been tested for using them as blending components of diesel fuels. By the addition of butanol or ABE blends to diesel fuel the thermal efficiency could be increased, the exhaust gas temperatures are lowered and the soot formation is decreased. The operational parameters of the engine have been studied in detail (Workman et al., 1983). Butanol proved to be an alternative diesel fuel blend. By using butanol as a reactive component in vegetable oil butyl ester preparation or preparation of butanol based acetals, the residual butanol content does not has to be removed from the reaction mixture because it can act as blending component. A special case of the extraction of butanol from aqueous solutions during ABE fermentation is when the extractant is vegatable oil (Welsh and Williams, 1989). The butanol to be extracted can be reacted easily with the extractant. Since the vegetable oil alkyl esters are also extractants of the butanol (Crabbe et al., 2001, Ishizaki et al., 1999), this method can easily be integrated into a catalyst free supercritical trans-esterification technology, when the partially trans-esterified vegetable oil is recycled into the extraction process until its complete transformation into butylester. Since the butanol content extracted in the last step does not need to be separated from the butyl ester product, the method is advantageously integrated into the waste free

The use of butanol as a reactive component in biodiesel production has a lot of advantage. First of all, the convenient base catalyzed reaction takes place in homogeneous phase, thus the reaction is faster, the separation of the glycerol is better and the temperature of the reaction can be lowered. The excess of the butanol does not need to be removed from the ester phase. The viscosity of the butylester mixture prepared from soya oil was found to be 4.50 mm2/s at 40 °C, the cetane index was 69. The cloud point of butyl-biodiesel is -3 °C. The flash point and pour point were found to be 44 and –13 °C, respectively (Wahlen et al., 2008). Since butanol reacts with free acids faster than methanol, the high acid containing vegetable oils (free fatty acid content of vegetable oils varies from 7 to 40 %), the waste

problems in the phase separation and the decreasing in the yield of esters. The calcium soaps do not dissolve in water and not surface active agents, do not cause problems in the phase separation and using calcium methanolate as catalyst in the trans-esterification of the vegetable oils is a well-known process (Lindquist, 1991). Due to the insolubility of CaO and Ca(OH)2 in methanol, the CaO and the Ca(OH)2 are known as less active or inactive compounds for the vegetable oil trans-esterification (Di Serio, et al., 2008), but the activation of calcium oxide to act as a catalysts in this reaction leads to good results (Kótai et al., 2006, 2008b). The free acid content of the vegetable oils and CaO were immediately reacted with formation of calcium soaps, and the Ca(OH)2 formed from the excess of CaO played role in the trans-esterification. The best results (quantitative conversion of triglycerides into methyl esters) was obtained by using calcium hydroxide (5.6 %) prepared in situ by slaking of CaO at a 3:1 CaO to H2O mass ratio and at a 10:4 oil: methanol ratio for 1 h under reflux. Excess of CaO is essential in this reaction. Using half amount of catalyst and methanol, the conversion was 90 % only, and 9% triglyceride and 1 % diglyceride could be detected in the ester phase. In case of high fatty acid containing starting vegetable oils the calcium soaps formed is partially soluble in the methanol containing ester phase, thus after separation of the soap containing glycerol the ester phase was treated with a slight excess of concentrated sulfuric acid. The sulfuric acid has multiple roles in the system,


Since the optimal trans-esterification can be performed at 2-4 fold excess of methanol, the residual methanol content means a very high (30-60 fold) excess toward the liberated fatty acids taking part in the acid catalyzed trans-esterification (Khelevina 1968). The anhydrous CaSO4 formed in the neutralization step promotes the esterification reaction of the liberated fatty acids due to binding of the water formed in the equilibrium esterification reactions:

$$\text{R-COOH} + \text{MeOH} \rightleftharpoons \text{RCOOMe} + \text{H}\_2\text{O} \tag{3}$$

$$\text{CaSO}\_4 + 0.5\text{H}\_2\text{O} = \text{CaSO}\_4\\0.5\text{H}\_2\text{O} \tag{4}$$

Although the calcium sulfate has di-hydrate, in this system only the hemihydrate has formed (Kótai et al., 2008b). The solid CaSO4.0.5H2O can be used as sulfur fertilizer and improve the properties of unbound (sandy like) soils due to its binding properties with water (plaster of paris). During the removal of the polyunsaturated (Benjumea et al., 2011) labile compounds by sulfuric acid various compounds having acidic character form. The acid number of the ester phase is around 3.2 mg KOH/g oil. It is essential to remove these acids from the ester phase. It has been tried with filtering this ester phase through calcium or iron carbonate containing mineral granulates. This method, however, have not been effective, and in case of calcium carbonate some oil soluble products were also formed which increased the ash content of the ester. By using Varion ADA type resin (alkylammonium type ion exchanger in OH form) the acidic constituent could easily be removed. The acid number was found to be 1.25 mg KOH/g oil, practically the same as was found for this oil after complete vacuum distillation (1.24 mg KOH/g oil) (Kótai et al., 2008b).

problems in the phase separation and the decreasing in the yield of esters. The calcium soaps do not dissolve in water and not surface active agents, do not cause problems in the phase separation and using calcium methanolate as catalyst in the trans-esterification of the vegetable oils is a well-known process (Lindquist, 1991). Due to the insolubility of CaO and Ca(OH)2 in methanol, the CaO and the Ca(OH)2 are known as less active or inactive compounds for the vegetable oil trans-esterification (Di Serio, et al., 2008), but the activation of calcium oxide to act as a catalysts in this reaction leads to good results (Kótai et al., 2006, 2008b). The free acid content of the vegetable oils and CaO were immediately reacted with formation of calcium soaps, and the Ca(OH)2 formed from the excess of CaO played role in the trans-esterification. The best results (quantitative conversion of triglycerides into methyl esters) was obtained by using calcium hydroxide (5.6 %) prepared in situ by slaking of CaO at a 3:1 CaO to H2O mass ratio and at a 10:4 oil: methanol ratio for 1 h under reflux. Excess of CaO is essential in this reaction. Using half amount of catalyst and methanol, the conversion was 90 % only, and 9% triglyceride and 1 % diglyceride could be detected in the ester phase. In case of high fatty acid containing starting vegetable oils the calcium soaps formed is partially soluble in the methanol containing ester phase, thus after separation of the soap containing glycerol the ester phase was treated with a slight excess of concentrated

2. catalyzes the reaction of the liberated fatty acids and the methanol excess used in the

3. destroys the instable polyunsaturated compounds which could cause deposition in the

Since the optimal trans-esterification can be performed at 2-4 fold excess of methanol, the residual methanol content means a very high (30-60 fold) excess toward the liberated fatty acids taking part in the acid catalyzed trans-esterification (Khelevina 1968). The anhydrous CaSO4 formed in the neutralization step promotes the esterification reaction of the liberated fatty acids due to binding of the water formed in the equilibrium esterification reactions:

 CaSO4 + 0.5H2O = CaSO4.0.5H2O (4) Although the calcium sulfate has di-hydrate, in this system only the hemihydrate has formed (Kótai et al., 2008b). The solid CaSO4.0.5H2O can be used as sulfur fertilizer and improve the properties of unbound (sandy like) soils due to its binding properties with water (plaster of paris). During the removal of the polyunsaturated (Benjumea et al., 2011) labile compounds by sulfuric acid various compounds having acidic character form. The acid number of the ester phase is around 3.2 mg KOH/g oil. It is essential to remove these acids from the ester phase. It has been tried with filtering this ester phase through calcium or iron carbonate containing mineral granulates. This method, however, have not been effective, and in case of calcium carbonate some oil soluble products were also formed which increased the ash content of the ester. By using Varion ADA type resin (alkylammonium type ion exchanger in OH form) the acidic constituent could easily be removed. The acid number was found to be 1.25 mg KOH/g oil, practically the same as was found for this oil after complete vacuum distillation (1.24 mg KOH/g oil) (Kótai et

R-COOH + MeOH = RCOOMe + H2O (3)

sulfuric acid. The sulfuric acid has multiple roles in the system, 1. it forms calcium sulfate and releases the bound fatty acids

4. decreases the iodine number and the ash content in the ester phase

trans-esterification

engines

al., 2008b).
