Feasibility of modified bentonite as acidic ...

Journal of Molecular Liquids 254 (2018) 260–266

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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

Feasibility of modified bentonite as acidic heterogeneous catalyst in low temperature catalytic cracking process of biofuel production from nonedible vegetable oils Abdelrahman M. Rabie, Eslam A. Mohammed, Nabel A. Negm ⁎ Egyptian Petroleum Research Institute, 1-Ahmed El Zommer Street, Nasr city, Cairo, Egypt

a r t i c l e

i n f o

Article history: Received 25 December 2017 Received in revised form 14 January 2018 Accepted 19 January 2018

Keywords: Heterogeneous catalyst Catalytic cracking Biofuel Oil

a b s t r a c t Acidic bentonite clay was obtained through surface modification of bentonite clay using hydrochloric acid as acidic precursor to increase the acidity of the bentonite. The modified catalyst was examined via X-ray fluorescence (XRF), XRD analysis, Brunauer Emmett and Teller surface area (BET), FTIR analysis and temperatureprogrammed desorption (TPD) analysis. XRF analysis showed that the acid modification of bentonite clay results in an increase in the silica content and lower abundance of metal oxides, due to the dissolve of Fe2O3, MnO, CaO, Na2O. Ca2+, Na+ cations from the interlayer and octahedral sheets. FTIR spectroscopy showed that the acid activation decreased the intensity of the absorption bands at 915, 875 and 836 cm−1 which arise from the binding modes of OH groups. NH3-TPD analysis showed a considerable increase in the moderate and strong Bronosted acid cites on the modified bentonite compared to the native clay. The modified bentonite was evaluated as economic and efficient heterogeneous catalyst in catalytic cracking process of two nonedible vegetable oils to obtain the corresponding biofuels at moderate processing temperature of 250–280 °C. It was observed that the catalytic conversion was preceded under mild temperature and obtained efficient biofuels with approved physical and fuel properties according to ASTM specifications. The role of the catalyst ratio was considerable on the yield percent and the properties of the obtained biofuels. The catalytic activity-reaction mechanism was discussed based on NH3-TPD analysis. © 2018 Elsevier B.V. All rights reserved.

1. Introduction The demand for crude oil was raised rapidly due to the increase of industrialization activities around the world. The economic development led to huge demand of energy, where its major part is derived from fossil fuel, i.e., petroleum, coal and natural gas. However, the limited reserve of fossil fuel has drawn the attention of several research trends to find alternative renewable energy resources which can be used to produce energy [1]. Biofuel researches are of growing interest recently and have been strongly recommended according to the environmental regulations as alternative for petroleum fuel. Biofuels including biodiesel and biogasoline are generally blended by petroleum fuel due to their similar fuel properties with less hazardous effect on the environment [2]. Biofuels are mainly produced from renewable and sustainable sources such as edible and nonedible vegetable oils and fats. There are four primary methods to produce biofuels: catalytic hydrogenation, microemulsion, pyrolysis (thermal or catalytic) and transesterification. In catalytic hydrogenation process, unsaturated oils are converted into saturated hydrocarbons throughout consumption a large amounts of ⁎ Corresponding author. E-mail address: [email protected] (N.A. Negm).

https://doi.org/10.1016/j.molliq.2018.01.110 0167-7322/© 2018 Elsevier B.V. All rights reserved.

hydrogen [3,4]. The beneficial characteristic of catalytic transesterification process is the reduction of the corrosiveness of biofuels occurred due to the contaminated free fatty acids in the raw materials, but it accompanied by the depression of the energetic values of the produced biofuels [5,6]. Pyrolysis includes treatment of oils and fats under influence of heat either from thermal agitation or microwave treatment [7–9]. Microwave heating offers a promising approach for the conversion of biomass into biofuel products with improved properties [10,11]. Comparable to these techniques, the flow catalytic cracking process consumes zero hydrogen and has the potential of converting biomass into biofuels compatible with existing petroleum products [12,13]. Flow catalytic cracking is a key process in biofuel production, which use the fossil fuels as the feedstock and breaks low economic molecules (higher molecular weights and refineries residuals) into smaller ones with high economic value [14–17]. The approved environmental regulations aim to reduce CO2 emission according utilization of renewable energy sources and biofuels. The proportion of fuel obtained from renewable sources in the total gasoline pool and diesel pool in the European Union is supposed to be at least 10% by 2020 [18]. Thus, it is a challenge to substitute JCO for fossil fuels in the future. Catalyst is the key technology of flow catalytic cracking process; it is a target to design a suitable and effective catalyst towards high gasoline/diesel yield, high

A.M. Rabie et al. / Journal of Molecular Liquids 254 (2018) 260–266

octane number of gasoline and low coke formation (i.e. low CO2 emission). The ideal catalyst is expected to include mesoporus and microporus systems. Mesoporus system enhances the accessibility of active sites when the large molecules are involved in the reaction; while microporus system enhances the selectivity of the process and aliphatic chains carbon distribution [19,20]. In this study, bentonite clay was chemically modified via reaction by hydrochloric acid to enhance its activity and produce more acidic heterogeneous catalyst. The prepared catalyst was characterized using FTIR, XRF, XRD, NH3-TPD and N2-adsorption desorption measurements. The prepared catalyst was evaluated as heterogeneous catalyst in catalytic cracking of two nonedible oils at moderate temperature of 250–280 °C. The catalyst activity was determined and the properties of the obtained biofuels were measured and compared to the ASTM standard specifications.

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were centrifuged to remove any solid contaminants and water, and used without further purification or treatment. 2.2.2. Oils characterization The oils were characterized for their fatty acids profile and their physical properties. The fatty acids profile of the obtained Jatropha oil and castor oil were determined using GC-Chromatographic analysis using GC-7890A instrument equipped with DB-23 column, 60 mm × 0.25 mm, i.d. of 0.25 μm. The physical properties of the different oils were determined including the following properties: viscosity, density, specific gravity, sulfur content, pour point, cloud point, acid value, fatty acid composition, iodine value, saponification value, and oxidation stability. 2.3. Preparation of biofuels using the modified catalysts

2. Materials and methods 2.1. Catalysts Acidic bentonite was used in this study as catalysts for cracking of castor oil and jatropha oil to obtain the corresponding biofuels. 2.1.1. Preparation of modified bentonite Modification of bentonite was performed by adding 50 g of bentonite clay to 1 M HCl (500 mL) and the medium was refluxed at 110 °C for 4 h under atmospheric pressure in a round-bottom flask equipped with a reflux condenser. The resulting clay suspension was rapidly quenched by adding 500 mL ice-cold water. The reaction matrix was then filtered, repeatedly washed with distilled water until chloride ions disappeared (using AgNO3 as indicator) [21]. The modified bentonite then dried in an oven at 100 °C, calcined at 550 °C for 4 h and finally ground in a mortar pastel to powder form. 2.1.2. Characterization of catalysts XRD analysis of pure bentonite sample as well as acid treated samples were carried out using a Philips PW-1050-25 diffractometer fitted with PW-1965-40 and PW-2100-00 using goniometers employing Nifiltered Cu. Ka radiation at 500 KV and 30 mA, in order to confirm the crystal structure. The scans were taken at 2θ = 4–80°. X-ray fluorescence (XRF) was recorded using a Bruker (S4 EXPLORER) operated at 20 mA and 50 kV. The Brunauer, Emmett, and Teller (BET) surface area of the catalysts was measured using Quanta chrome AS1Win, Quanta chrome Instrument v2.01. Prior to such measurements, all samples were perfectly degassed at 200 °C for 6 h before experiments. The specific surface area (ABET) was determined from the linear part of the adsorption curve. The pore diameter distribution was calculated from the desorption branch using BJH formula. FTIR analysis was performed using Nicolet IS-10 FTIR over the wave number 4000–400 cm−1. Temperature-programmed desorption (TPD) studies were obtained using an adsorption unit Micromeritics, (Chemisorb-2705) equipped with TCD detector. 500.0 mg catalyst sample was pretreated under helium flow at 500 °C for 30 min and allowed it to cool up to 100 °C, and at this temperature the gas was switched to 5% NH3 in helium with a flow rate of 20 mL/min for 30 min and subsequently purged with helium gas at 100 °C for 1 h to remove the physically adsorbed NH3. NH3-TPD curves were obtained at temperature range of 100–800 °C with a ramping rate of 10 °C/min and hold at 800 °C for 30 min. Thermogravimetric analysis (TGA) was performed using thermogravimetric analyzer (TG-DSC TAQ600). 2.2. Oils 2.2.1. Extraction of oils Native castor and jatropha oils were obtained by cold hydraulic pressing of dried Jatropha and castor seeds. After pressing, the oils

2.3.1. Catalytic cracking process Catalytic cracking procedures were performed as follows [22]: 150 mL of the different oils were charged in 500 mL two necked flask equipped by mechanical stirrer and distillation tail connected to a glass reservoir. Modified bentonite was added in different ratios of 0.2, 0.4, 0.6, 0.8 and 1% by weight relative to the used oil. The mixture was mixed and allowed to thermal agitation for 4 h at 280 °C. The reaction setup was connected to nitrogen flow (5 mL/min) and stirring rate at 150 rpm. The reaction products were collected and their volumes were determined. The obtained biofuels were settled in a separating funnel to separate the produced water and then centrifuged to remove any contaminated or dispersed water. The obtained vapors during the reactions were also collected to determine the efficiency of the reaction conversion. 2.3.2. Biofuel specification The obtained biofuels from the catalytic cracking reactions of the different oils using different ratios of the modified bentonite as catalyst were characterized by determining the following properties: viscosity, density, specific gravity, carbon residue, ash content, sulfate content, pour point, flash point, and fire point according to the following specifications: ASTM D-4052 [23], ASTM D-445 [24], ASTM D-4530 [25], ASTM D-482 [26], ASTM D-4294-16 [27], ASTM D-97 [28], and ASTM D-93 [29]. 2.4. Reusability of catalysts The reusability of the used catalyst was determined by repeating the catalytic cracking reaction of the oils using one portion of the catalysts for several rounds and the properties of the obtained biofuel were determined after each round [30]. Before each experiment, the catalyst was washed by benzene and dried to remove the formed contaminations on its surface and the loss in weight was compensated. The reactions were stopped after drawback the properties of the obtained biofuels. 3. Results and discussion 3.1. Characterization of bentonite and modified bentonite For effective examination of the impacts of acid activation by mineral acids on the crystalline structure and acidity of the bentonite clay (Montmorillonite), the following characterizations were done. 3.1.1. XRF analysis XRF analysis of the natural bentonite and acid-activated bentonite powders are given in Table 1. It is clear that SiO2 and Al2O3 are the main constituents of the bentonite, with trace amounts of other metal oxides. As it is evident from the changes in chemical composition represented in Table 1, acid activation modifies the bentonite chemistry. HCl

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Table 1 XRF analysis of bentonite and modified bentonite. Component (%)

Bentonite

Modified bentonite

SiO2 TiO2 Al2O3 Fe2O3 MnO CaO MgO Na2O K2O P2O5 Cl− SO− 3 L.O.I

48.9 0.71 17.2 5.35 0.04 2.02 3.57 1.85 0.39 0.29 0.21 0.22 19.1

59.5 0.79 17.8 4.85 0.02 0.67 3.49 0.86 0.40 0.27 0.24 0.06 10.9

activation results in an increase in the silica content and lower abundance of metal oxides especially Fe2O3, MnO, CaO, Na2O, Ca2+, Na+ cations correspond to the inter-layer exchangeable cations, which dissolve readily by mild acid treatment. However, Al3+, Fe3+, Mg2+ cations belong to the octahedral sheet in the bentonite structure, which is much resistant to acid attack. The increase in the relative content of the insoluble Si4+ cations occurs as a result of a decrease of the other cations from the interlayer and octahedral sheets [31–33]. As a result, the hydronium cations intercalate into the interlayer spacing of the clay keeping the layer structure. It was reported that H2SO4 activation leads to a considerable increase in SO− 3 and L.O·I content and also a decrease in silica and alumina content. This occurred initially by replacing the interlayer cations with H+ ions of the acid with subsequent dissolution of structural cations (Si4+, Al3+), consequently the clay specific surface area is increased as a result of the dealumination of the clay structure [34]. The literature reported also that H3PO4 activation leads to increase in SiO2 content as a result of a decrease of the other cations from the interlayer and octahedral sheets [31], and high content of P2O5 was observed. 3.1.2. XRD analysis XRD spectra of the unmodified and the acid modified bentonite clays are given in Fig. 1. The natural bentonite cations such as sodium rich montmorillonite (NaM), with the d (001) value of 1–25 nm as the common mineral in clay, appear to be well crystallized. The first peak appeared at 2θ = 7.94° shows width increasing and intensity reduction [35]. The intensity of this peak determines the degree of laminar structure retained by the clay. Whereas, the intensity of the Montmorillonite

Fig. 1. XRD spectra of bentonite and acid modified bentonite.

Fig. 2. FTIR spectra of bentonite and acidic modified bentonite.

peak in case of the HCl-activated bentonite is approximately similar to that of the unmodified bentonite, indicating a structural preservation of bentonite after acidic modification. 3.1.3. FTIR spectroscopy FTIR spectra of the bentonite and acid modified bentonite are shown in Fig. 2. The intensity of the absorption bands at 875, 915, and 836 cm−1 of bentonite originated from the bending modes of the hydroxyl groups of AlFeOH, AlAlOH, and AlMgOH respectively [36,37] were decreased after its acid modification. This observation suggests the partial dissolution of Al, Mg and Fe cations from the bentonite structure. Same trend was observed for the bands at 3423 and 1639 cm−1 of bentonite, which assigned for the stretching and bending vibrations of the OH groups for the water molecules absorbed on the bentonite surface. This is because of the removal of octahedral cations, causing the loss of water and hydroxyl groups coordinated to the clay framework [33]. The formation of three–dimensional networks of amorphous Si-O-Si units after the acid modification of bentonite was confirmed by the increase of the band intensity at 1090 cm−1 [38]. 3.1.4. Surface texture analysis The results of the N2-adsorption-desorption analysis and the variation in pore volumes of the bentonite and the acid activated bentonite catalyst are shown in Figs. 3–4. The bentonite clay and the acid modified

Fig. 3. Adsorption-desorption isotherm of bentonite and acid modified bentonite.


Fig. 4. Variation of pore volume of bentonite clay after acid modification.

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Fig. 5. NH3-TPD profiles of bentonite before and after acid modification.

3.2. Oil characterization bentonite exhibit type (IV) isotherm. A sharp inflection appeared at relative pressures (P/Po) ranging from 0.8 to 1.0 (Table 2) indicates that the bentonite sample has a wide pore size distribution [31]. Calculation of the total pore volume and average pore diameters from Fig. 4 (data listed in Table 2) revealed that acid modification of bentonite increased these to parameters considerably compared to the native bentonite clay.

3.1.5. NH3-TPD analysis The NH3-TPD profiles of the bentonite and the acid modified bentonite are represented in Fig. 5. Table 3 listed the weak, medium and strong acid sites of the two clays in equivalent to mmol/g. The results in Table 3 indicated that both acid intensity and number of acid sites were improved in acid modified bentonite compared to bentonite itself. The peak below 200 °C in bentonite and acid modified bentonite occured due to desorption of ammonia from Lewis acid sites because week coordinate bonds break at low temperature. The peak around 400–450 °C is due to moderate Bronosted acid sites. However, that occurs at 600–650 °C in the case of acid modified bentonite is due to the strong Bronosted acid sites (strong ionic bonds) [39,40]. The results revealed that surface acidity and textural properties including surface area and pore volume are largely dependent on the structural modifications resulting during acid treatment. Also, acid treatment of bentonite enlarges the edges of the platelets, which is responsible for surface area and pore diameter increase [41]. Bentonite itself is a weak acidic catalyst due to the presence of some acidic compounds including TiO2, Al2O3, Fe2O3 and P2O5. The low catalytic activity of bentonite in biofuel production was reported [42]. The data in Table 1 represents that the acidic compounds which responsible for the acidity of bentonite were not changed significantly after the treatment. So that, the activity of the bentonite after the treatment is due to the acid treatment which increased the acidic cites on the framework of the bentonite. The catalyst showed acceptable activity for 4 rounds with a yield of 87% after the fourth reaction round.

Table 2 Specific surface area, pore volume and pore diameter of bentonite and acid activated bentonite. Catalyst

SBET (m2/g)

Pore volume (cm3/g)

Pore diameter (nm)

Bentonite Modified bentonite

69.39 87.55

0.12 0.18

6.95 8.53

The fatty acid content (FAC) and the physical properties of the used castor oil and jatropha oil are listed in Table 4. The castor oil showed the following fatty acids: palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), and recinoleic acid (C18:1:OH). While, jatropha oil showed the following fatty acids: palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and arachidic acid (20:0). Recinoleic acid (C18:1:OH) was the predominant fatty acid in castor oil by a ratio of 89%; while palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2) were the predominant fatty acids in jatropha oil by a total ratio of 92%. Ramos et al. [43] suggested that the ideal vegetable oil composition for biofuel includes a high percentage of monounsaturated fatty acids, in addition to low proportions of polyunsaturated acids and a minimum content of saturated fatty acids. Based on this principle, the castor oil and jatropha oil can be considered as ideal feedstock for biofuel production. The other properties identified for the used castor oil were: photometric color, saponification value, iodine value, acid value, refraction index, and water content.

3.3. Physical and fuel properties of the obtained biofuels The obtained biofuels from the catalytic cracking reaction of castor oil and jatropha oil using modified bentonite were characterized for their fuel properties including the following properties: density, viscosity at 40 °C, flash point, cloud point, pour point, water content, sulfur content, copper corrosion, ash content, carbon residue, Table 5. These properties were compared to ASTM standard specifications. The amounts of water obtained after the catalytic cracking of jatropha oil and castor oil were in the average of 5–6% and 9–10%, respectively. The higher amount of water obtained from catalytic cracking of castor oil can be attributed to the high percentage of recinoleic acid in its chemical structure. Recinoleic acid contains hydroxyl groups, which produces higher amount of water.

Table 3 Acidity of bentonite and acid activated bentonite measured by NH3-TPD. Catalyst

Weak Lewis site

Moderate Acid site

Strong Bronosted site

Total acid sites (mmol/g)

Bentonite Acid modified bentonite

0.155 0.119

0.178 0.493

Absence 0.588

0.333 1.2

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Table 4 Fatty acid profile of the used castor oil and jatropha oil. Fatty acid

Castor oil

Jatropha oil

Palmitic acid (16:0) Palmitoleic acid (16:1) Stearic acid (18:0) Oleic acid (18:1) Linoleic acid (18:2) Linolenic acid (18:3) Arachidic acid (20:0) Recinoleic acid (18:1, OH) Acid value, (mg KOH/g) Viscosity at 40 °C, (mm2/s) Density, (kg/m3) at 15 °C Cloud point, (°C) Pour point, (°C) Oxidation stability, (h) Iodine value, g I2/100 g oil Sulfur content

1.0 – – 3.0 5.0 1.0 – 89.0 2.8 43.0 0.959 8 3 5.5 80.5 0.005

15.0 0.7 6.8 44.0 32.0 – 0.20 – 3.70 37.0 0.910 8 3 2.6 104.5 0.005

3.3.1. Density The density of the fuel represents the weight of 1 g of it. The density is an important factor during the fuel processing and ignition, because the fuel represents an extra weight on the vesicle. Consequently, higher density of fuel will consume larger amount of fuel during the automotive work. The obtained densities of Jatropha oil and castor oil cracking using modified bentonite as a catalyst at 0.2% ratio were 0.8988 and 0.9210 g/cm3, respectively. These values are located within the range of ASTM D-4052 specification of biodiesel. It is clear from Table 5 that the gradual increase in the amount of catalyst used in the catalytic cracking reaction of both castor oil and jatropha oil is gradually decrease the densities of the obtained biofuel. The minimum densities of the obtained biofuels from the catalytic cracking reaction were 0.8812 and 0.0.8891 g/cm3, respectively obtained by using 1% of the catalyst. It was reported that most of biofuels densities obtained from nonedible oils such as rapeseed oil, and linseed oil [44] are high due to the presence of high unsaturation and oxygen contents in their chemical structures, which is overcame by the mixing with short chain aliphatic alcohols such as ethanol or propanol to decrease their density. Castor oil and Jatropha oil are characterized by predominant presence of oleic and recinoleic acids, in addition to relatively high amounts of aliphatic fatty acids such as palmitic acid and stearic acid and low content of polyunsaturated fatty acids. As a result, the densities of the obtained biofuels are comparatively low.

3.3.2. Viscosity The viscosity of the fuel represents the degree of fluidity of the fuel in the tubes and in the circulating system of the engine. It is an important characteristic due to high viscous fuel requires strong pumping into the ignition or compression chambers of the various engines. The viscosity of the obtained biofuels after the catalytic cracking using the prepared

catalyst (0.2%–1%) (Table 5) were in the range of 3.25–3.20 cSt for castor oil biofuel and 6.12–6.06 cSt for jatropha oil biofuel. The obtained values were within the ASTM D-445 limit of 1.6 to 7.0 cSt. Increasing the amount of the catalysts used from 0.2% to 1% has a decreasing effect on the viscosities of the obtained biofuels. That can be attributed to the catalytic cracking effect of the modified bentonite on castor oil and Jatropha oil. Increasing the catalyst amount from 0.2% to 1% increases the fragmentation extent of the different fatty acid chains of the oils and consequently decreases the produced carbon chain length, which decreases the biofuels viscosities [45]. 3.3.3. Pour point and cloud point The pour point of the fuel represents the temperature at which the fuel becomes solid before it and liquid after it. Pour point is important characteristic during the transportation of the fuel at elevated low temperatures. In cold climate countries of low temperatures, high pour point fuels freeze. The pour points of the obtained biofuel (Table 5) were ranged between −3 and −6 °C in case of jatropha oil and −3 and −5 °C in case of jatropha oil, which are within the specific ASTM standard limit of −5 to 15 °C. Low pour points of the different biofuels at the various ratios of the used catalyst indicate that the oils are decomposed to relatively short chain hydrocarbons [46]. The cloud point of the fuel represents the temperature at which the regular crystal of the hydrocarbons starts to form. Low cloud points of the biofuels are important property due to the formation of regular clusters of the hydrocarbons lowers the fluidity of the biofuel which decreases its transportation through pipes and tubes. The approved cloud point values of ASTM D-97 are in the range of −3 to 15 °C, and the obtained values for the produced biofuels were in the range of 3 to 7 and 3 to 6 °C for jatropha oil biofuel and castor oil biofuel, respectively. These values are considered as acceptable values for the biofuel at all catalysts ratios [47]. Increasing the ratio of the used catalysts decreases the cloud point of the produced biofuel, and the lowest cloud points were 3 °C at 1% catalyst ratio. 3.3.4. Flash and fire points The flash point of the fuel represents the temperature at which the fuel starts to ignite. The obtained biofuels from catalytic cracking of Jatropha oil and castor oil using acidified bentonite (0.2% and 1%) as a catalytic cracking catalysts have flash points ranged between 42 and 46 °C and 44 to 47 °C by using jatropha oil and castor oil, Table 5. These values are comparable to the limits of ASTM D-93 specification [2]. Flash and fire points of the fuels determine for large extent their applications as biodiesel, bio-gasoline or bio-Jet. The flash points of the obtained biofuels are lower than those of the biodiesel, but in the range of the bio-gasoline. The lower flash points of the obtained biofuels can be attributed to the low hydrocarbon chains produced by the cracking reaction. The use of highly active catalyst or high ratio of this catalyst causes a strong destructive reaction on the fatty acids of the oils, and

Table 5 Physical and fuel properties of the obtained biofuels from catalytic cracking of jatropha oil and castor oil using different amounts of acid modified bentonite. Biofuel type

Jatropha oil biofuel

Castor oil biofuel

Catalyst ratio Yield, % Density/15 °C, gm/cm3 Flash point, °C Pour point, °C Cloud point, °C Kinematic viscosity, cSt Water and Sediment, wt% Total Sulfur, wt% Copper corrosion strip (50 °C) Carbon Residue, wt% Ash content, wt%

0.2% 65 0.901 54 −6 6 6.11 Nil 0.005 2A

0.4% 75 0.895 54 −5 5 6.11 Nil 0.005 1A

0.6% 82 0.842 51 −5 4 6.10 Nil 0.004 1A

0.8% 87 0.832 50 −4 3 6.07 Nil 0.002 1A

1% 90 0.831 49 −3 3 6.04 Nil 0.002 1A

0.2% 72 0.912 53 −5 7 3.25 Nil 0.005 2A

0.4% 81 0.899 53 −5 6 3.24 Nil 0.005 2A

0.6% 85 0.854 52 −4 6 3.22 Nil 0.004 1A

0.8% 88 0.831 50 −3 4 3.22 Nil 0.002 1A

0.07 Nil

0.06 Nil

0.06 Nil

0.05 Nil

0.04 Nil

0.03 Nil

0.03 Nil

0.02 Nil

0.01 Nil

Petroleum diesel

Specification limits

ASTM specification

1% 92 0.931 50 −3 3 3.20 Nil 0.002 1A

– – 0.8394 52 −9 3 2.96 Nil 0.012 1A

– – Reported 52 (min.) 15 (max.) Reported 1.6–7 0.1 (max.) 0.1 (max.) 1A (max.)

– – ASTM D-4052 ASTM D-93 ASTM D-97 ASTM D-2500 ASTM D-445 ASTM D-2709 ASTM D-4294 ASTM D-130

0.006 Nil

0.07 Nil

0.1 (max.) 0.01 (max.)

ASTM D-4530 ASTM D-482


consequently produces comparatively short chain hydrocarbons with low flash and fire points. 3.3.5. Sulfur content, ash content and carbon residue Petroleum fuel generally contains comparative high amount of sulfur in the form of free sulfur, thiols, di-sulfides and mercaptans due to the origin of the petroleum oil and its formation conditions [48]. Ignition of petroleum fuel produces large amounts of sulfur dioxide gas, which is highly toxic and corrosive when combined with water and in respiratory system, skin and eye of human (Eq. (1)). RSH þ O2 →CO2 þ SO2 þ Heat

ð1Þ

Biofuels contain less amounts of sulfur compared to petroleum fuels, as the biological sulfur in the non-edible oils is low. Hence, it is expected to obtain low sulfur content in the ignition products of biofuels compared to those obtained from ignition of petroleum fuel. The sulfur contents of the used Jatropha oil and castor oil were 0.005% by weight. The sulfur contents of the obtained biofuels were lower than the virgin oils in the range of 0.004 to 0.001 wt%. It is clear from Table 5 that the sulfur contents of both jatropha oil and castor oil biofuels are decreased by increasing the ratio of the catalyst used. On the other hand, the carbon and ash residue as a result of the fuel ignition play an important factor on the life time of the engine components and also on the environment. Solid particulates are considered as polluting threats for the environment. Decreasing the produced solid particulates from the fuel ignition is one of the important aims of using biofuels. The approved limits of the carbon and ash residue after biofuel ignition are not more than 0.01 wt% according to ASTM D-4530 and ASTM D-482, respectively. The obtained carbon and ash residues of the produced biofuels were ranged between 0.01 and 0.006%. These values are comparatively lower than those obtained in case of petroleum fuel. 3.4. Catalytic cracking mechanism and catalyst reactivity The thermal cracking of organic compounds including petroleum hydrocarbons and vegetable oils or fats involves chemical decomposition of long organic molecules under the action of heat to produce shorter hydrocarbon molecules. Thermal cracking of vegetable oils produces large hydrocarbon fractions with high unsaturation content. That is due to the thermal cracking of the oils occurred via decarboxylation of the triglyceride fatty acid chains [49,50]. The reaction occurred at the terminal of the chains and continued at the branching centers of these chains. While, catalytic cracking of the vegetable oils and fats occurred through two main reactions. The first is the decarboxylation reaction in which the hydrocarbon chains lose carbon dioxide and carbon monoxide to produce a mixture of saturated and unsaturated hydrocarbons. The second is the hydrodeoxygenation of the hydrocarbon products [51]. The hydrodeoxygenation reaction involves production of saturated hydrocarbons [51]. Due to the hydrogenation reaction occurs under mild conditions (i.e., at temperature around 250–300 °C), it was proposed in this study that the catalytic cracking of jatropha oil and castor oil proceeds firstly through hydrogenation reaction, as the temperature is kept around 250–300 °C. Then the hydrogenated products undergo decarboxylation reaction. In the decarboxylation reaction, carbon dioxide and water are produced. The amount of the produced water is increased in case of increasing the amount of oxygenated fatty acids in the triglycerides used. It was observed that in case of catalytic cracking of castor oil, the amount of the produced water during the reaction is comparatively higher than that produced in case of jatropha oil. That is due to recinoleic acid (C18:1/OH) is the dominant fatty acid in its composition. The measured physical properties of the biofuels obtained from jatropha oil and castor oil indicated the higher saturated hydrocarbons in their chemical composition. That can be appeared from the low viscosity, density, flash point, pour point and cloud point values, Table 5. Comparing between the physical properties of the biofuels obtained

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from catalytic cracking of jatropha oil and castor oil revealed that the processing of jatropha oil as feedstock for biofuel production produces more preferable physical properties than that obtained when castor oil is used. That can be attributed to two reasons. The first is the higher oxygenated fatty acid content in castor oil decreases the yield % of the biofuel, Table 5. The second is the higher percent of saturated fatty acid content in jatropha oil and the absence of oxygenated fatty acids, which increases the yield % of the obtained biofuels. The reactivity of the prepared catalyst was determined by determining the variation of the total acidic sites in the bentonite and the acid modified bentonite, Table 3. It is clear from Table 3 that bentonite has large number of weak and moderate acid sites (0.155, 0.178) and no strong Bronosted acid sites were recorded. The total acid sites number of bentonite were equivalent to 0.333 mmol/g. Due to the weak acidity of native bentonite, the catalytic reaction of both jatropha oil and castor oil shows no product at the applied temperature of the process (250–280 °C). Modification of bentonite decreased the weak Lewis acid sites to 0.119 and increased the moderate acid sites to 0.493, while the strong Bronosted acid sites were considerably increased to 0.588 to reach the total acid sites of the modified bentonite equivalent to 1.2 mmol/g. The higher total acid sites of the modified bentonite catalyst are responsible for its high reactivity. The catalytic mechanism of the acid modified bentonite is performed through adsorption of the partially charged carbonyl groups along the triglyceride molecules to form a complex structure. The complex structure is decomposed under the effect of process temperature to produce carbon dioxide and water. The hydroxyl groups in the castor oil triglyceride molecules are readily eliminated to produce water molecules. The decomposition of the carboxyl groups and the hydroxyl groups were determined by the yield average of each process. The increasing of the reaction conversion of the two oils into the corresponding biofuels and the improvement of the physical properties of the obtained biofuel were revealed to the increase of the catalyst ratio. The increase of catalyst ratio in the catalytic cracking reaction showed decrease in the physical properties related to the molecular weights of the produced hydrocarbons, such as viscosity, density, flash point, and cloud points. The decrease in the molecular weights of the obtained hydrocarbon was attributed to the high catalytic effect of the catalyst and this activity was increased by increasing its amount. The variation of the physical properties of the obtained hydrocarbons by changing the amounts of the used catalyst indicates that the type of each biofuel product can be used as different type of biofuel. At higher catalyst ratio (0.8% and 1%) the obtained physical properties qualified the obtained biofuel in biogasoline applications, while decreasing the catalyst ratio (0.9–0.2%) produces a biodiesel like biofuel. The type of obtained biofuel in the study depends on the amount of catalyst used and also on the used oil. In case of using castor oil, the properties of the obtained fuel were in the range of gasoline, hence it is biogasoline. But, using lower ratio of catalyst 0.2–0.8% produced biofuel with comparative properties to diesel, so it is biodiesel. The reaction parameters can determine the type of the obtained biofuel. Also, castor oil produces lighter fractions than Jatropha oil based on the fact that castor oil has several weak points during the catalytic cracking, which produces more short fractions with smaller carbon chains than Jatropha oil do. The two fractions, either biodiesel or biogasoline can be separated from the process output by simple distillation. Comparing the physical and fuel properties of the different biofuel obtained from the catalyzed process of oils cracking by those of regular gasoline and regular diesel revealed that the prepared catalysts can be used as efficient and economic catalyst in catalyzed cracking of vegetable oils to produce biofuels with comparable properties to petroleum fuels. 4. Conclusions ⁎ Acid modification of bentonite was performed. ⁎ The variation of bentonite chemistry was determined.

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