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ZSM-5 composite catalysts
Applied Catalysis A: General 433–434 (2012) 170–178
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Liquid hydrocarbon fuels from jatropha oil through catalytic cracking technology using AlMCM-41/ZSM-5 composite catalysts G. Ramya, R. Sudhakar, J. Amala Infant Joice, R. Ramakrishnan, T. Sivakumar ∗ Catalysis Laboratory, Department of Chemical Engineering, A.C. Tech, Anna University, Chennai 600025, India
a r t i c l e
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Article history: Received 26 December 2011 Received in revised form 2 May 2012 Accepted 12 May 2012 Available online 18 May 2012 Keywords: Composite catalyst Green gasoline Vegetable oil Cracking Bioliquid fuels, Porous materials
a b s t r a c t Biofuels, the hydrocarbons less than C18 , produced by catalytic cracking of nonedible vegetable oils are the potential source to battle energy demand and pollution. Among the non edible oils, jatropha is the apt candidate for the production of biofuel. Jatropha oil can be cracked catalytically over solid acid catalysts to yield liquid fuels with superior characteristics. We present here the hydrothermal syntheses of a microporous solid acid catalyst (HZSM-5 with Si/Al = 14), mesoporous materials (AlMCM-41) with varying Si/Al ratios (Si/Al = 18, 41, 72 and 95) and composite catalyst comprising HZSM-5 (as core) and varying coating percentages (5, 10 and 20%) of AlMCM-41 (as shell). All the synthesized catalysts were characterized by using XRD, BET N2 sorption studies, ICP, TPD and SEM techniques. Herein we report the catalytic activities of all the synthesized catalysts towards the cracking of jatropha oil obtained at the optimized conditions of temperature – 400 ◦ C, WHSV – 4.6 h−1 and reaction time – 1 h. Of all the mesoporous catalysts with varying Si/Al ratios, AlMCM-41 (Si/Al = 18) was found to be the most active catalyst as it converted 65% of jatropha oil yielding 39% of bioliquid fuel with 47% and 36% selectivities towards green diesel and green gasoline respectively. In the core–shell architecture of the composite catalyst, different % coatings of the best active mesoporous material (AlMCM-41, Si/Al = 18) over the best active microporous material (ZSM-5, Si/Al = 14) were done. AlMCM-41/ZSM-5 (25, 15, 10) showed remarkable performance in the conversion of jatropha oil (99%) yielding 70% of bioliquid fuel with very high selectivity (61%) towards green gasoline. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The extensive use of fossil fuels to satisfy the majority of our energy needs has a negative impact on the environment. The levels of toxic gases such as NOX and SOX , photochemical oxidants, lead, particulate matter, etc., in the atmosphere are very high and alarming [1–3]. Finite nature of fossil fuels stimulates the interest among the researchers to look out for alternative fuels [4]. Hence a good alternative fuel should be in correlation with sustainable development, energy conservation, efficiency and more importantly environmental preservation [5–7]. Vegetable oils are the best alternative sources from which an environmentally benign fuel can be derived [8]. Although the research on alternative fuels emerged in 1900 itself by Rudolf Diesel’s test on his engine with peanut oil it was not successful due to engine related problems [9]. There have been several methods reported for the production of biofuel through transesterification (biodiesel), pyrolysis (lower
∗ Corresponding author. Tel.: +91 44 22359193; fax: +91 44 22352642. E-mail addresses: [email protected], [email protected] (T. Sivakumar). 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2012.05.011
hydrocarbons) and catalytic cracking (engine friendly hydrocarbons) [10–13]. The biodiesel, mono-alkyl esters of long chain fatty acid produced from transesterification of vegetable oils needs high reaction time and requires higher molar ratio of methanol to oil and hence it is not cost effective. Moreover biodiesel can be used in diesel engine only. In addition, biodiesel has to blended with fossil fuels and cannot be used as such [14–16]. Biodiesel is not economically attractive because it requires blending with petrol or diesel and it also does not burn cleanly as it forms gums on engines. Pyrolysis, which is a direct thermal decomposition method, operates at a very high temperature (700–1000 ◦ C) and yields mostly gaseous products containing straight chain hydrocarbon fuels [12]. Among various biofuels that can be obtained by different methods, biofuels obtained through catalytic cracking from nonedible vegetable oils outshine other biofuels due to their (i) ease to use in engines as such, (ii) sustainable and non-polluting nature (no sulphur and nitrogen containing compounds) and (iii) low cost of production. Catalytic cracking of vegetable oils also has an edge over other processes as it requires lower operating temperature (<450 ◦ C) and low catalyst to oil ratio. The biofuel obtained through catalytic cracking also shows very high selectivity towards gasoline fraction and burns cleanly.
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Among the nonedible plants, Jatropha curcas, a drought resistant plant has the potential to satisfy the needs of an alternative fuel from its oil [17]. This plant is widely cultivated in arid, semiarid, alkaline soils and tropical regions of world and it is a drought resistant perennial plant that grows over fifty years [18]. It requires minimum rainfall of 250 mm. The oil content of jatropha varies from 30 to 50% by weight from seed and 45 to 60% from kernel [19]. Micro and mesoporous materials are known for their ability to crack various compounds of high molecular weight [20–22]. Microporous zeolites such as HY, H and HZSM-5 have been used for cracking of various compounds since many decades for their attributes such as high acidity and good thermal stability [23,24]. However, their small pore openings make it difficult for the entry of bulky molecules such as triglycerides. This has led to the development of mesoporous catalysts with large pore opening that facilitates the entry of bigger molecules but they suffer from their low acidic nature and poor hydrothermal stability [25]. We have reported the catalytic activities of microporous materials such as HY, H, HMor and HZSM-5 in the cracking of jatropha oil [26,27]. Among the microporous catalysts, HZSM-5 was found to be the most active in terms of conversion of jatropha oil (65%), yield of BLP (29%) and selectivity towards green gasoline (50%). In order to improve the % yield of BLP and the selectivity towards green gasoline, modification has to be done on the catalytic system. The combination of these micro and mesoporous materials in these composite catalysts with core–shell arrangement has the advantages of both micro and mesoporous catalysts. This kind of restructuring mesoporous walls into zeolite matrix has been reported for variety of reactions such as hydrocracking, cracking and alkylation reactions [28–31]. In the present study composite catalyst is architected as core–shell model and synthesized by overgrowing different amounts of AlMCM-41 over HZSM-5, characterized by using different instrumental techniques and its catalytic activities towards the cracking of jatropha oil were compared with those of micro and mesoporous materials.
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Fig. 1. Flowchart showing the synthesis of composite catalyst [AlMCM-41/ZSM-5 (25, 14, 10)].
nitrate, filtered, dried and converted into H-form by calcining at 550 ◦ C.
2. Experimental methods
2.2. Synthesis of catalysts
2.2.2. Synthesis of AlMCM-41 Sodium meta silicate and aluminium sulphate were used as the sources for silicon and aluminium respectively. Cetyl trimethyl ammonium bromide (CTAB) was used as structure directing agent. Sodium meta silicate (42 g) dissolved in 160 ml of water and aluminium sulphate (different amounts) in 10 ml of water were stirred separately. Aluminium sulphate solution was added to sodium meta silicate solution dropwise with constant stirring for 1 h. The pH of the mixture was decreased to 11.6 using 4 N H2 SO4 . The gel obtained was stirred for 1.5 h. CTAB (14.58 g) dissolved in 48 ml of water was added to the obtained gel dropwise while stirring. The resulting mixture was stirred for another 2 h. The gel was autoclaved at 160 ◦ C for 17 h in an air oven. The product obtained was washed, filtered, dried and calcined at 550 ◦ C for 1 h in the flow of N2 and 5 h in the flow of air [33,34].
2.2.1. Synthesis of HZSM-5 ZSM-5 with Si/Al = 14 was synthesized by hydrothermal method according to the molar composition of Al2 O3 :20 Na2 O:30 SiO2 :3 TPABr:943 H2 O using sodium silicate, aluminium sulphate as raw materials and TPABr as surfactant [32]. The gel was autoclaved at 170 ◦ C for 7 days. The white mass obtained after 7 days was washed with distilled water, dried at 100 ◦ C over night and calcined at 550 ◦ C for 5 h. The Na-form of HZSM-5 was converted into the NH4 -form by ion exchange using 1 M solution of ammonium
2.2.3. Synthesis of composite materials Composite catalysts were synthesized by taking 10 g of ZSM-5 (Si/Al = 14) and overgrowing different amounts of AlMCM-41 so as to have 5%, 10% and 20% of AlMCM-41 over HZSM-5. The flowchart of synthesis of 10% coating of AlMCM-41 (Si/Al = 25) over HZSM5 is shown in Fig. 1. The different catalysts obtained are coded as AlMCM-41/ZSM-5 (A, B, C) where A refers to Si/Al ratio of AlMCM41, B refers to Si/Al ratio of HZSM-5 and C refers to the % coating of AlMCM-41 over HZSM-5. Since the composite material is derived
2.1. Materials The precursors such as sodium meta silicate, sodium aluminate and aluminium sulphate required for the synthesis of various solid acid catalysts such as HZSM-5, AlMCM-41 and AlMCM-41/ZSM-5 (25, 14, 10) were obtained from CDH, India. SRL, India, supplied tetra propyl ammonium bromide (TPABr) and cetyl trimethyl ammonium bromide (CTAB). Sulphuric acid was purchased from Merck. The jatropha oil was kindly supplied by DIBER (Defence Institute of Bio-Energy Research, Nainital, India). The supplied jatropha oil was filtered to remove the solid particles present in it.
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Fig. 2. Reactor setup for the cracking reactions.
from two different porous materials, it is difficult to determine the correct Si/Al ratio for this material.
2.3. Catalyst characterization Silicon and aluminium contents of micro and mesoporous materials were determined using an inductively coupled plasma (ICP) spectrometer (Perkin Elmer, IOC OES 5300 Dual View). XRD patterns were recorded using X-ray diffractometer (Seifert X-ray Diffractometer JSO 2002) using nickel filtered Cu K␣ radiation ˚ at 2 values of 0.6–40◦ for mesoporous and compos( = 1.514 A) ite materials and 10–70◦ for HZSM-5 with a step of 0.04◦ /2.4 s. The BET surface area of the materials was measured by using BET surface area analyser (Micromeritics Pulse Chemisorb 2700) at liquid N2 temperature by using 30:70 ratio (N2 :He). Before sorption analysis the samples were degassed under flow of N2 at 200 ◦ C for 2 h (Micromeritics Desorb 2300A). Temperature programmed desorption (TPD) study was carried out for acidity determination (Micromeritics, USA) with software ChemiSoft TPx 2750 V1.02. In a typical TPD analysis, 120 mg of catalyst was first pretreated at 600 ◦ C for 1 h in He atmosphere (20 ml/min) and cooled to room temperature. Then doses of ammonia were introduced with the help of microlitre syringe until the sample no longer uptook ammonia. The physisorbed ammonia was driven out by increasing the temperature to 70 ◦ C and the ammonia adsorbed over the catalysts was then desorbed by increasing the temperature from 30 ◦ C to 700 ◦ C at 10 ◦ C/min in the TPD setup attached to a thermal conductivity detector. The morphology of catalysts was studied by scanning electron microscope (FEI Quanta 200 ESEM FEG, USA).
2.4. Catalytic activity Cracking of jatropha oil was carried out using a fixed bed quartz catalytic reactor (2 cm width, 40 cm height) as shown in Fig. 2. The reaction was performed over 0.5 g of catalyst packed in between the quartz wool at a reaction temperature of 400 ◦ C with WHSV of 4.6 h−1 . The reactor was electrically heated and the temperature was controlled by a digital temperature controller. Flow rate of the oil was controlled by using an infusion pump (Miclins, India). The products were allowed to pass through a Leibig condenser with flow of ice cold water and collected in a receiver kept in NaCl–ice mixture. Based on our earlier experiments the conversion and selectivity were found to be maximum at 1 h [27]. The condensed liquid products were collected in a receiver and uncondensed gaseous products were measured using manometer.
2.5. Analysis of products Gas chromatograph (Shimadzu GC 17A) fitted with a flame ionization detector (FID) and Apeizon L column (2 m length, 1/8 in. diameter) was used for the analysis of the liquid fuels, whereas the gaseous products were analysed by using the thermal conductivity detector (TCD) and a Poropak Q column (2 m length, 1/8 in. diameter). An injector port with an oil trap was fabricated and connected to one end of column of the gas chromatograph. The temperature of the oil trap was kept at 250 ◦ C (less than the boiling point of the oil) so that the unreacted oil with higher boiling point was retained in the oil trap and the hydrocarbons with boiling point less than 250 ◦ C vapourize and reach the GC column. Both the BLF
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Fig. 3. XRD patterns of micro, mesoporous and composite catalysts: (a) HZSM-5 (Si/Al = 14), (b) AlMCM-41 of different Si/Al ratios and (c) AlMCM-41/ZSM-5 with different percentage coatings.
and gaseous products were analysed using N2 as carrier gas. Retention time of the authentic hydrocarbons was compared with those of the hydrocarbons present in the sample. The retention times for each fraction were defined by injecting corresponding commercial samples of gasoline, kerosene and diesel in gas chromatograph. The BLF obtained is classified into three fractions according to their boiling ranges; GG fraction (60–120 ◦ C), GK fraction (120–180 ◦ C) and GD fraction (180–250 ◦ C) [35]. The following equations were used for the calculation of % conversion, % yield of BLF and % selectivities towards various fractions: Conversion (%) =
BLF (g) + gas (g) + coke (g) + water (g) feed mass of oil (g) (1)
Yield of BLF or gaseous products (%) =
mass of BLF (g) or mass of gaseous products (g) feed mass of oil (g)
(2)
Selectivity of GG, GK and GD (%) =
mass of hydrocarbon present in GG, GK and GD (g) mass of BLF (g)
(3)
3. Results and discussion 3.1. Characterization XRD patterns of HZSM-5, AlMCM-41 with different Si/Al ratios (18, 41, 72 and 95) and composite catalyst [AlMCM-41/ZSM-5 (25, 14, 10)] are given in Fig. 3. The d-spacing values were calculated by using the formula n = 2d1 0 0 sin and the unit cell √ constants were calculated based on the equation a0 = 2d1 0 0 / 3. The XRD peak of HZSM-5 observed at 2 between 22◦ and 25◦ indicates the phase formation (Fig. 3a) [36]. The three peaks for the corresponding 1 0 0, 1 1 0 and 2 0 0 planes were observed at 2 values less than 5◦ which confirm the formation of MCM-41 (Fig. 3b) [37]. These peaks are characteristics of mesoporous nature of the synthesized catalyst. On increasing the aluminium content the intensity of the peak decreased and shifted towards higher 2 values. This is due to the decrease in the d1 0 0 spacing value due to the incorporation of aluminium [22]. Fig. 3c shows the XRD pattern of composite catalyst AlMCM-41/ZSM-5 (25, 14, 10). The peaks at 2 below 5◦ and between 22◦ and 25◦ reveal the presence of both microporosity and mesoporosity of the composite catalyst. The inset of Fig. 3c confirms the presence of microporous ZSM-5 in the composite material. Generally mesoporous materials exhibit peak at 2 = 2.2◦ but in the composite material it was observed at 1.98◦ . This shows that there is a slight structural deformation of MCM-41 occurring when it is
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Table 1 Physico-chemical properties of the different solid acid catalysts. Catalysts
Si/Al ratioa
d1 0 0 (nm)
Unit cell (a0 ) (nm)
BET surface area (m2 /g)
Pore volume (cm3 /g)
Average pore size (nm)
Wall thickness (nm)
Total acidity (ml/g)
HZSM-5 AlMCM-41 AlMCM-41 AlMCM-41 AlMCM-41 C1 C2 C3
14.2 18.2 41.0 72.0 95.4 – – –
3.85 3.58 4.09 4.20 4.20 4.50 4.47 4.46
– 4.13 4.72 4.84 4.84 5.19 5.16 5.15
483 951 977 1018 1023 490 510 529
– 0.94 0.95 0.95 0.96 0.44 0.67 0.78
– 2.50 2.53 2.63 2.64 1.90 1.85 1.75
– 1.08 1.56 1.57 1.56 2.60 2.62 2.71
4.67 3.80 3.75 3.70 3.68 3.85 3.80 3.50
a Experimental values of Si/Al ratio as obtained by ICP analysis. C1, C2, C3 refer to composite materials AlMCM-41/ZSM-5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20).
coated over HZSM-5 [38]. Silicon and aluminium contents analysed by ICP, unit cell parameter a0 obtained through XRD analysis, BET surface area, pore size and pore volume values obtained by N2 sorption studies and acidity values of all the synthesized catalysts by TPD technique are given in Table 1. Experimental Si/Al values found by ICP analysis were found to be close to those of theoretical values. With increase in Si/Al ratio of AlMCM-41, d1 0 0 value increased from 3.58 nm to 4.20 nm. Since the 2 value decreased with increase in Si/Al ratio it is obvious that d1 0 0 value increased. The unit cell parameter a0 also increased from 4.13 nm to 4.84 nm on increasing the Si/Al ratio of the mesoporous material. Since increase in aluminium content decreases the crystallinity of the mesoporous material a0 value also decreased [39]. For composite material the a0 value and crystallinity decreased with increase in coating of AlMCM41 over HZSM-5. BET surface area, pore volume and pore size of AlMCM-41 were found to increase with increase in Si/Al ratio. This trend was found to be consistent with the literature already reported [40]. Since the higher surface area (AlMCM-41) mesoporous material is coated over HZSM-5, its increase in % resulted in increase in the surface area. Figs. 4 and 5 show the BET isotherms of mesoporous and composite materials respectively. A steep increase in the adsorption–desorption isotherm at P/P0 = 0.3–0.4 was observed for mesoporous materials which clearly indicated the presence of ≈3 nm mesoporous sieves [41,42]. BET isotherms of composite material indicate that there are more number of meso and micropores but with narrow openings. Meso and micropores gets successively filled up gradually with increase in P/P0 during adsorption. However on desorption, N2 comes out from both the pores simultaneously resulting in larger hysteresis. Increase in % coating of AlMCM-41 over ZSM-5 increased the uptake of N2 [43].
NH3 -TPD signals obtained for micro, meso and composite materials are shown in Fig. 6. All the catalysts showed a peak centred around 200 ◦ C. However, the number of peaks, intensities and pattern of the TPD spectrum are different from each other. Both meso and microporous catalysts exhibited an additional peak at around 500 ◦ C. This showed that type of acidity present in these two samples is different from HZSM-5. Areas of these peaks were measured to determine the total acidity of representative samples of micro, meso and composite catalysts and are given in Table 1. Among all the catalysts, HZSM-5 possessed the highest acidity (4.67 ml of NH3 /g). Both meso and composite materials possessed comparable acidities however on decreasing the aluminium content in the mesoporous material the total acidity decreased. Acidity levels of the composite materials were found to be less than those of HZSM5. The observation was justifiable because less acidic mesoporous is coated over more acidic HZSM-5. Since the acidic sites of HZSM-5 in the composite material are not exposed to the probe molecule acidity values were found to be low. SEM pictures of microporous, mesoporous and composite catalysts are shown in Fig. 7. Discrete spherical and rod shaped micron sized particles are seen in the SEM photograph of HZSM-5 (Fig. 7a). Aggregation of these particles was found and the particle size of HZSM-5 as measured by SEM was in the range of 600–900 nm. Fibrous cauliflower-like morphology of AlMCM-41 (Si/Al = 18) particles was found in their SEM photograph (Fig. 7b). Since all the particles appear alike, formation of AlMCM-41 is homogeneous. This homogeneous nature is an indication of the incorporation of all the aluminium into the lattice [44]. As expected, composite material adopted core–shell architecture where ZSM-5 occupied the core and AlMCM-41 (Si/Al = 25) occupied the shell positions
Fig. 4. Nitrogen adsorption–desorption isotherms of AlMCM-41 of various Si/Al ratios.
Fig. 5. Nitrogen adsorption–desorption isotherms of composite materials with various % coatings.
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Fig. 6. TPD signals of microporous, mesoporous and composite catalysts: (a) HZSM-5 (Si/Al = 15), (b) AlMCM-41 (Si/Al = 18) and (c) AlMCM-41/ZSM-5 (25, 14, 10%).
(Fig. 7c). The fibrous nature of the mesoporous AlMCM-41 is clearly seen in the SEM photograph of composite material. This SEM photograph also shows that almost all the ZSM-5 particles are completely covered by the fibrous AlMCM-41. Spherical shape of core–shell type particles again confirms the presence of microporous material inside these particles. 3.2. Catalytic activities of the catalysts in the cracking of jatropha oil Reaction parameters (temperature – 400◦ C, WHSV – 4.6 h−1 and reaction time – 1 h) were optimized and reported by us for the cracking of jatropha oil using H [27]. Our earlier cracking of jatropha oil under these optimized conditions with different microporous catalysts showed that HZSM-5 was the best catalyst in terms of conversion (62%) and selectivity towards GG (50%) [26]. However the % yield of BLF was found to be only 29%. In order to improve the bioliquid fuel (BLF) content in the product it was planned to synthesize the composite materials comprising both micro and mesopores. Hence attempts were made to fabricate a new composite material comprising the best identified microporous material (HZSM-5) and the most active mesoporous material (AlMCM-41). Conversion and product distribution obtained in the catalytic cracking of jatropha oil over different solid acid catalysts are given in Table 2. The mixture of liquid hydrocarbons which can be termed as bioliquid fuel (BLF), CO, CO2 , gaseous hydrocarbons, water and coke were the different products obtained in the vapour phase catalytic cracking of jatropha oil. All the catalysts were effective in converting jatropha oil into products of different compositions.
The conversion levels were found to be almost the same over both microporous and mesoporous materials however these catalysts convert jatropha oil to a lesser extent when compared to composite materials. On increasing the % coating of mesophase to 10% the conversion increased but with further increase in the % of mesophase to 20%, the conversion decreased. Among the mesoporous materials, the conversion levels decreased on increasing the Si/Al ratio due to decrease in acidity. Like % conversion, % yield of BLF also followed the same trend and it was maximum (70%) over AlMCM-41/ZSM-5 (25, 14, 10) and decreased to 28% on increasing the % coating further to 20%. Percentage yield of gaseous products was found to be same over all the catalysts except AlMCM-41 (72) and AlMCM-41 (95) catalysts. Low yield of gaseous products obtained over AlMCM-41 (72) and AlMCM-41 (95) is due to low aluminium content in it which leads to lower acidity. Selectivities towards GG, GK and GD obtained for different catalysts in the cracking of jatropha oil is shown in Fig. 8. With increase in the Si/Al ratio of the mesoporous materials the selectivity towards GD increased and reached a maximum of 70%. This shows that the lower acidity favours the formation of longer hydrocarbons. It is desirable to get maximum conversion with high % yield of BLF and maximum selectivity towards GG. It is remarkable that AlMCM-41/ZSM-5 (25, 14, 10) converted jatropha oil to maximum extent into various products. In the composite catalyst, the mesoporous material provides suitable pore size and very high surface area but it lacks acidity so synergism takes place when both micro and meso catalysts are combined which results in high conversion
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Fig. 7. SEM micrographs of microporous, mesoporous and composite catalysts: (a) HZSM-5, (b) AlMCM-41 (Si/Al = 18) and (c) AlMCM-41/ZSM-5 (25, 14, 10).
and maximum selectivity towards GG. This newly architected composite material [AlMCM-41/ZSM-5 (25, 15, 10)] yielded the desired result viz., the increase in the conversion and yield of BLF to 99% and 70% respectively. This new composite material not only increased conversion and yield of BLF but also significantly increased the selectivity towards GG. The selectivities towards GG over the composite materials were found to be 60% irrespective of % coating of mesoporous material in them.
Direct comparison of catalytic activities of composite catalyst cannot be made as cracking of jatropha oil is being reported for the first time by us. However cracking of other oils over composite catalysts can be compared. Chew and Bhatia [45] have performed catalytic cracking of fresh and used palm oils over REY, HZSM-5, H and SBA-15 catalysts using a transport riser reactor at the reaction temperature of 450 ◦ C with very high catalyst to oil ratio of 5 g g−1 . The conversion levels
Table 2 Conversion and product distribution in the catalytic conversion of jatropha oil. Catalysts
Conversion (%)
Yield of BLF (%)
Yield of gas (%)
Yield of coke (%)
Yield of water (%)
HZSM-5 (14) AlMCM-41 (18) AlMCM-41 (41) AlMCM-41 (72) AlMCM-41 (95) C1 (25, 14, 5) C2 (25, 14, 10) C3 (25, 14, 20)
62 65 63 60 55 94 99 56
29 39 40 35 32 66 70 28
23 18 17 14 13 17 19 22
1 5 2 7 5 8 7 5
9 3 4 4 5 3 3 1
C refers to composite material (AlMCM-41/ZSM-5). Reaction conditions: temperature – 400 ◦ C, WHSV – 4.6 h−1 and reaction time – 1 h.
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similar levels of selectivities towards gasoline fraction but the bioliquid product (BLF) obtained over MCM-41 contained hydrocarbon with low octane number and the BLF obtained over micro and composite catalysts contained hydrocarbon with high octane number [43]. For the same cracking, Ooi et al. [49] showed increase in selectivity towards gasoline fraction over another composite catalyst (MCM-41/HZSM-5). The importance of thinner coating of mesoporous material over microporous material, aluminium content in the mesophase and shape selective property of HZSM-5 in the catalytic conversion of palm oil were well explained by Twaiq et al. [43]. 3.3. Possible mechanism for cracking of vegetable oils Fig. 8. Selectivity of catalysts towards various fractions of BLF obtained in the cracking of jatropha oil [C1, C2, C3 refer to composite materials AlMCM-41/ZSM-5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20)].
were found to be in the range of 71–84% and the selectivity towards gasoline fraction was in the range of 33–38%. Twaiq et al. [46] used a microreactor to crack palm oil over HZSM-5 with various Si/Al ratios at 450 ◦ C and obtained 94–96% conversion with selectivity of 45–49% towards gasoline. Commercial rapeseed oil cracked by using equilibrium FCC catalyst at 480–585 ◦ C by Dupain et al. [47] produced the conversion of 57% and selectivity of 34% gasoline. Twaiq et al. [43] cracked palm oil to the level of 88–90% using mesoporous aluminosilicate materials synthesized by different methods and obtained very high selectivity towards liquid hydrocarbons. Comparison of selectivities obtained over micro (H) and meso (MCM-41) porous materials by Ooi et al. [48] in the catalytic cracking of palm oil showed that although the conversion levels were in the same range, selectivity towards gasoline fraction was found to be very high (73%) over MCM-41 when compared to H (39%). Significant enhancement in the selectivity towards gasoline fraction (75%) was reported for composite catalysts when compared to H (39%) in the cracking of palm oil [43]. Comparison of selectivity made for MCM-41 and composite material indicated
The reaction mechanism of vapour phase catalytic cracking of triglyceride molecule over composite catalyst is shown in Fig. 9. The formation of non-condensable (CO and CO2 ), condensable hydrocarbons and aromatics is explained through this possible cracking mechanism of composite catalysts. The bigger shaded circles and dark small circles correspond to mesoporous and microporous materials respectively. The composite catalyst depicted in this figure comprises less acidic mesoporous catalyst as shell coated over higher acidic microporous material. The high reaction temperature of about 400 ◦ C volatilizes the vegetable oil and at first the vapours access the shell. When the bulky triglyceride molecule enters into the mesoporous (shell) layer, it may crack into three fractions namely A, B and C as indicated by dotted brackets on the triglyceride. Part ‘A’ of the triglyceride may cleave as propane or propene and part ‘B’ may crack to yield CO and CO2 in the mesophase. ‘C’ may crack in any fashion depending on Si/Al ratio of mesophase. Since the acidity level of mesoporous material is kept at very low level, it is expected that long chain hydrocarbons are formed in the shell. These fragmented molecules further enter into the microporous material where the secondary cracking of oil takes place. The higher acidic nature of catalyst facilitates the extensive cracking of oil into shorter fragment. ‘A’ gets cracked further into ‘X’ (C1 –C3 hydrocarbons), these hydrocarbons may or may not take part in the
Fig. 9. Possible cracking mechanism of triglyceride over composite catalyst. A- Propane or propene, B- CO or CO2 , C- long chain hydrocarbons, X- C1 – C3 hydrocarbons, Y – both straight chain and branched hydrocarbons (Cn H2n+2 ) and aromatics.
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oligomerization and aromatization. Fragment ‘B’ does not undergo any reactions further and exist as ‘B’ itself. The shape selective property of microporous ZSM-5 tailors the ‘C’ fragment and the cracked fragments isomerize to form ‘Y’ which is branched hydrocarbon named as BLF. The hydrocarbons present in BLF comprise hydrocarbons present in commercially available gasoline, kerosene and diesel. 4. Conclusions Microporous (HZSM-5, Si/Al = 14), mesoporous (AlMCM-41, Si/Al = 18, 41, 72 and 95) and composite materials [AlMCM-41/ZSM5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20)] were synthesized by hydrothermal method. All the catalysts were characterized by using physico-chemical techniques. The presence of mesoporous and microporous materials in the composite catalyst was confirmed by the XRD peak at 1.98◦ and 22–25◦ respectively. The growth of mesoporous AlMCM-41 over microporous ZSM-5 was clearly seen in its SEM micrograph of composite material. The fixed bed catalytic cracking of jatropha oil was done over these catalysts and among the synthesized microporous [HZSM-5 (14)], mesoporous [AlMCM-41 (18, 41, 72 and 95)] and composite catalysts [AlMCM-41/ZSM-5 (25, 14, 5/10/20), AlMCM41/ZSM-5 (25, 14, 10)] was found to be the most active catalyst for the cracking of jatropha oil as it showed 99% conversion with 70% BLF content and 61% selectivity towards GG. Acknowledgement
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Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata
Liquid hydrocarbon fuels from jatropha oil through catalytic cracking technology using AlMCM-41/ZSM-5 composite catalysts G. Ramya, R. Sudhakar, J. Amala Infant Joice, R. Ramakrishnan, T. Sivakumar ∗ Catalysis Laboratory, Department of Chemical Engineering, A.C. Tech, Anna University, Chennai 600025, India
a r t i c l e
i n f o
Article history: Received 26 December 2011 Received in revised form 2 May 2012 Accepted 12 May 2012 Available online 18 May 2012 Keywords: Composite catalyst Green gasoline Vegetable oil Cracking Bioliquid fuels, Porous materials
a b s t r a c t Biofuels, the hydrocarbons less than C18 , produced by catalytic cracking of nonedible vegetable oils are the potential source to battle energy demand and pollution. Among the non edible oils, jatropha is the apt candidate for the production of biofuel. Jatropha oil can be cracked catalytically over solid acid catalysts to yield liquid fuels with superior characteristics. We present here the hydrothermal syntheses of a microporous solid acid catalyst (HZSM-5 with Si/Al = 14), mesoporous materials (AlMCM-41) with varying Si/Al ratios (Si/Al = 18, 41, 72 and 95) and composite catalyst comprising HZSM-5 (as core) and varying coating percentages (5, 10 and 20%) of AlMCM-41 (as shell). All the synthesized catalysts were characterized by using XRD, BET N2 sorption studies, ICP, TPD and SEM techniques. Herein we report the catalytic activities of all the synthesized catalysts towards the cracking of jatropha oil obtained at the optimized conditions of temperature – 400 ◦ C, WHSV – 4.6 h−1 and reaction time – 1 h. Of all the mesoporous catalysts with varying Si/Al ratios, AlMCM-41 (Si/Al = 18) was found to be the most active catalyst as it converted 65% of jatropha oil yielding 39% of bioliquid fuel with 47% and 36% selectivities towards green diesel and green gasoline respectively. In the core–shell architecture of the composite catalyst, different % coatings of the best active mesoporous material (AlMCM-41, Si/Al = 18) over the best active microporous material (ZSM-5, Si/Al = 14) were done. AlMCM-41/ZSM-5 (25, 15, 10) showed remarkable performance in the conversion of jatropha oil (99%) yielding 70% of bioliquid fuel with very high selectivity (61%) towards green gasoline. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The extensive use of fossil fuels to satisfy the majority of our energy needs has a negative impact on the environment. The levels of toxic gases such as NOX and SOX , photochemical oxidants, lead, particulate matter, etc., in the atmosphere are very high and alarming [1–3]. Finite nature of fossil fuels stimulates the interest among the researchers to look out for alternative fuels [4]. Hence a good alternative fuel should be in correlation with sustainable development, energy conservation, efficiency and more importantly environmental preservation [5–7]. Vegetable oils are the best alternative sources from which an environmentally benign fuel can be derived [8]. Although the research on alternative fuels emerged in 1900 itself by Rudolf Diesel’s test on his engine with peanut oil it was not successful due to engine related problems [9]. There have been several methods reported for the production of biofuel through transesterification (biodiesel), pyrolysis (lower
∗ Corresponding author. Tel.: +91 44 22359193; fax: +91 44 22352642. E-mail addresses: [email protected], [email protected] (T. Sivakumar). 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2012.05.011
hydrocarbons) and catalytic cracking (engine friendly hydrocarbons) [10–13]. The biodiesel, mono-alkyl esters of long chain fatty acid produced from transesterification of vegetable oils needs high reaction time and requires higher molar ratio of methanol to oil and hence it is not cost effective. Moreover biodiesel can be used in diesel engine only. In addition, biodiesel has to blended with fossil fuels and cannot be used as such [14–16]. Biodiesel is not economically attractive because it requires blending with petrol or diesel and it also does not burn cleanly as it forms gums on engines. Pyrolysis, which is a direct thermal decomposition method, operates at a very high temperature (700–1000 ◦ C) and yields mostly gaseous products containing straight chain hydrocarbon fuels [12]. Among various biofuels that can be obtained by different methods, biofuels obtained through catalytic cracking from nonedible vegetable oils outshine other biofuels due to their (i) ease to use in engines as such, (ii) sustainable and non-polluting nature (no sulphur and nitrogen containing compounds) and (iii) low cost of production. Catalytic cracking of vegetable oils also has an edge over other processes as it requires lower operating temperature (<450 ◦ C) and low catalyst to oil ratio. The biofuel obtained through catalytic cracking also shows very high selectivity towards gasoline fraction and burns cleanly.
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Among the nonedible plants, Jatropha curcas, a drought resistant plant has the potential to satisfy the needs of an alternative fuel from its oil [17]. This plant is widely cultivated in arid, semiarid, alkaline soils and tropical regions of world and it is a drought resistant perennial plant that grows over fifty years [18]. It requires minimum rainfall of 250 mm. The oil content of jatropha varies from 30 to 50% by weight from seed and 45 to 60% from kernel [19]. Micro and mesoporous materials are known for their ability to crack various compounds of high molecular weight [20–22]. Microporous zeolites such as HY, H and HZSM-5 have been used for cracking of various compounds since many decades for their attributes such as high acidity and good thermal stability [23,24]. However, their small pore openings make it difficult for the entry of bulky molecules such as triglycerides. This has led to the development of mesoporous catalysts with large pore opening that facilitates the entry of bigger molecules but they suffer from their low acidic nature and poor hydrothermal stability [25]. We have reported the catalytic activities of microporous materials such as HY, H, HMor and HZSM-5 in the cracking of jatropha oil [26,27]. Among the microporous catalysts, HZSM-5 was found to be the most active in terms of conversion of jatropha oil (65%), yield of BLP (29%) and selectivity towards green gasoline (50%). In order to improve the % yield of BLP and the selectivity towards green gasoline, modification has to be done on the catalytic system. The combination of these micro and mesoporous materials in these composite catalysts with core–shell arrangement has the advantages of both micro and mesoporous catalysts. This kind of restructuring mesoporous walls into zeolite matrix has been reported for variety of reactions such as hydrocracking, cracking and alkylation reactions [28–31]. In the present study composite catalyst is architected as core–shell model and synthesized by overgrowing different amounts of AlMCM-41 over HZSM-5, characterized by using different instrumental techniques and its catalytic activities towards the cracking of jatropha oil were compared with those of micro and mesoporous materials.
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Fig. 1. Flowchart showing the synthesis of composite catalyst [AlMCM-41/ZSM-5 (25, 14, 10)].
nitrate, filtered, dried and converted into H-form by calcining at 550 ◦ C.
2. Experimental methods
2.2. Synthesis of catalysts
2.2.2. Synthesis of AlMCM-41 Sodium meta silicate and aluminium sulphate were used as the sources for silicon and aluminium respectively. Cetyl trimethyl ammonium bromide (CTAB) was used as structure directing agent. Sodium meta silicate (42 g) dissolved in 160 ml of water and aluminium sulphate (different amounts) in 10 ml of water were stirred separately. Aluminium sulphate solution was added to sodium meta silicate solution dropwise with constant stirring for 1 h. The pH of the mixture was decreased to 11.6 using 4 N H2 SO4 . The gel obtained was stirred for 1.5 h. CTAB (14.58 g) dissolved in 48 ml of water was added to the obtained gel dropwise while stirring. The resulting mixture was stirred for another 2 h. The gel was autoclaved at 160 ◦ C for 17 h in an air oven. The product obtained was washed, filtered, dried and calcined at 550 ◦ C for 1 h in the flow of N2 and 5 h in the flow of air [33,34].
2.2.1. Synthesis of HZSM-5 ZSM-5 with Si/Al = 14 was synthesized by hydrothermal method according to the molar composition of Al2 O3 :20 Na2 O:30 SiO2 :3 TPABr:943 H2 O using sodium silicate, aluminium sulphate as raw materials and TPABr as surfactant [32]. The gel was autoclaved at 170 ◦ C for 7 days. The white mass obtained after 7 days was washed with distilled water, dried at 100 ◦ C over night and calcined at 550 ◦ C for 5 h. The Na-form of HZSM-5 was converted into the NH4 -form by ion exchange using 1 M solution of ammonium
2.2.3. Synthesis of composite materials Composite catalysts were synthesized by taking 10 g of ZSM-5 (Si/Al = 14) and overgrowing different amounts of AlMCM-41 so as to have 5%, 10% and 20% of AlMCM-41 over HZSM-5. The flowchart of synthesis of 10% coating of AlMCM-41 (Si/Al = 25) over HZSM5 is shown in Fig. 1. The different catalysts obtained are coded as AlMCM-41/ZSM-5 (A, B, C) where A refers to Si/Al ratio of AlMCM41, B refers to Si/Al ratio of HZSM-5 and C refers to the % coating of AlMCM-41 over HZSM-5. Since the composite material is derived
2.1. Materials The precursors such as sodium meta silicate, sodium aluminate and aluminium sulphate required for the synthesis of various solid acid catalysts such as HZSM-5, AlMCM-41 and AlMCM-41/ZSM-5 (25, 14, 10) were obtained from CDH, India. SRL, India, supplied tetra propyl ammonium bromide (TPABr) and cetyl trimethyl ammonium bromide (CTAB). Sulphuric acid was purchased from Merck. The jatropha oil was kindly supplied by DIBER (Defence Institute of Bio-Energy Research, Nainital, India). The supplied jatropha oil was filtered to remove the solid particles present in it.
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Fig. 2. Reactor setup for the cracking reactions.
from two different porous materials, it is difficult to determine the correct Si/Al ratio for this material.
2.3. Catalyst characterization Silicon and aluminium contents of micro and mesoporous materials were determined using an inductively coupled plasma (ICP) spectrometer (Perkin Elmer, IOC OES 5300 Dual View). XRD patterns were recorded using X-ray diffractometer (Seifert X-ray Diffractometer JSO 2002) using nickel filtered Cu K␣ radiation ˚ at 2 values of 0.6–40◦ for mesoporous and compos( = 1.514 A) ite materials and 10–70◦ for HZSM-5 with a step of 0.04◦ /2.4 s. The BET surface area of the materials was measured by using BET surface area analyser (Micromeritics Pulse Chemisorb 2700) at liquid N2 temperature by using 30:70 ratio (N2 :He). Before sorption analysis the samples were degassed under flow of N2 at 200 ◦ C for 2 h (Micromeritics Desorb 2300A). Temperature programmed desorption (TPD) study was carried out for acidity determination (Micromeritics, USA) with software ChemiSoft TPx 2750 V1.02. In a typical TPD analysis, 120 mg of catalyst was first pretreated at 600 ◦ C for 1 h in He atmosphere (20 ml/min) and cooled to room temperature. Then doses of ammonia were introduced with the help of microlitre syringe until the sample no longer uptook ammonia. The physisorbed ammonia was driven out by increasing the temperature to 70 ◦ C and the ammonia adsorbed over the catalysts was then desorbed by increasing the temperature from 30 ◦ C to 700 ◦ C at 10 ◦ C/min in the TPD setup attached to a thermal conductivity detector. The morphology of catalysts was studied by scanning electron microscope (FEI Quanta 200 ESEM FEG, USA).
2.4. Catalytic activity Cracking of jatropha oil was carried out using a fixed bed quartz catalytic reactor (2 cm width, 40 cm height) as shown in Fig. 2. The reaction was performed over 0.5 g of catalyst packed in between the quartz wool at a reaction temperature of 400 ◦ C with WHSV of 4.6 h−1 . The reactor was electrically heated and the temperature was controlled by a digital temperature controller. Flow rate of the oil was controlled by using an infusion pump (Miclins, India). The products were allowed to pass through a Leibig condenser with flow of ice cold water and collected in a receiver kept in NaCl–ice mixture. Based on our earlier experiments the conversion and selectivity were found to be maximum at 1 h [27]. The condensed liquid products were collected in a receiver and uncondensed gaseous products were measured using manometer.
2.5. Analysis of products Gas chromatograph (Shimadzu GC 17A) fitted with a flame ionization detector (FID) and Apeizon L column (2 m length, 1/8 in. diameter) was used for the analysis of the liquid fuels, whereas the gaseous products were analysed by using the thermal conductivity detector (TCD) and a Poropak Q column (2 m length, 1/8 in. diameter). An injector port with an oil trap was fabricated and connected to one end of column of the gas chromatograph. The temperature of the oil trap was kept at 250 ◦ C (less than the boiling point of the oil) so that the unreacted oil with higher boiling point was retained in the oil trap and the hydrocarbons with boiling point less than 250 ◦ C vapourize and reach the GC column. Both the BLF
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Fig. 3. XRD patterns of micro, mesoporous and composite catalysts: (a) HZSM-5 (Si/Al = 14), (b) AlMCM-41 of different Si/Al ratios and (c) AlMCM-41/ZSM-5 with different percentage coatings.
and gaseous products were analysed using N2 as carrier gas. Retention time of the authentic hydrocarbons was compared with those of the hydrocarbons present in the sample. The retention times for each fraction were defined by injecting corresponding commercial samples of gasoline, kerosene and diesel in gas chromatograph. The BLF obtained is classified into three fractions according to their boiling ranges; GG fraction (60–120 ◦ C), GK fraction (120–180 ◦ C) and GD fraction (180–250 ◦ C) [35]. The following equations were used for the calculation of % conversion, % yield of BLF and % selectivities towards various fractions: Conversion (%) =
BLF (g) + gas (g) + coke (g) + water (g) feed mass of oil (g) (1)
Yield of BLF or gaseous products (%) =
mass of BLF (g) or mass of gaseous products (g) feed mass of oil (g)
(2)
Selectivity of GG, GK and GD (%) =
mass of hydrocarbon present in GG, GK and GD (g) mass of BLF (g)
(3)
3. Results and discussion 3.1. Characterization XRD patterns of HZSM-5, AlMCM-41 with different Si/Al ratios (18, 41, 72 and 95) and composite catalyst [AlMCM-41/ZSM-5 (25, 14, 10)] are given in Fig. 3. The d-spacing values were calculated by using the formula n = 2d1 0 0 sin and the unit cell √ constants were calculated based on the equation a0 = 2d1 0 0 / 3. The XRD peak of HZSM-5 observed at 2 between 22◦ and 25◦ indicates the phase formation (Fig. 3a) [36]. The three peaks for the corresponding 1 0 0, 1 1 0 and 2 0 0 planes were observed at 2 values less than 5◦ which confirm the formation of MCM-41 (Fig. 3b) [37]. These peaks are characteristics of mesoporous nature of the synthesized catalyst. On increasing the aluminium content the intensity of the peak decreased and shifted towards higher 2 values. This is due to the decrease in the d1 0 0 spacing value due to the incorporation of aluminium [22]. Fig. 3c shows the XRD pattern of composite catalyst AlMCM-41/ZSM-5 (25, 14, 10). The peaks at 2 below 5◦ and between 22◦ and 25◦ reveal the presence of both microporosity and mesoporosity of the composite catalyst. The inset of Fig. 3c confirms the presence of microporous ZSM-5 in the composite material. Generally mesoporous materials exhibit peak at 2 = 2.2◦ but in the composite material it was observed at 1.98◦ . This shows that there is a slight structural deformation of MCM-41 occurring when it is
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Table 1 Physico-chemical properties of the different solid acid catalysts. Catalysts
Si/Al ratioa
d1 0 0 (nm)
Unit cell (a0 ) (nm)
BET surface area (m2 /g)
Pore volume (cm3 /g)
Average pore size (nm)
Wall thickness (nm)
Total acidity (ml/g)
HZSM-5 AlMCM-41 AlMCM-41 AlMCM-41 AlMCM-41 C1 C2 C3
14.2 18.2 41.0 72.0 95.4 – – –
3.85 3.58 4.09 4.20 4.20 4.50 4.47 4.46
– 4.13 4.72 4.84 4.84 5.19 5.16 5.15
483 951 977 1018 1023 490 510 529
– 0.94 0.95 0.95 0.96 0.44 0.67 0.78
– 2.50 2.53 2.63 2.64 1.90 1.85 1.75
– 1.08 1.56 1.57 1.56 2.60 2.62 2.71
4.67 3.80 3.75 3.70 3.68 3.85 3.80 3.50
a Experimental values of Si/Al ratio as obtained by ICP analysis. C1, C2, C3 refer to composite materials AlMCM-41/ZSM-5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20).
coated over HZSM-5 [38]. Silicon and aluminium contents analysed by ICP, unit cell parameter a0 obtained through XRD analysis, BET surface area, pore size and pore volume values obtained by N2 sorption studies and acidity values of all the synthesized catalysts by TPD technique are given in Table 1. Experimental Si/Al values found by ICP analysis were found to be close to those of theoretical values. With increase in Si/Al ratio of AlMCM-41, d1 0 0 value increased from 3.58 nm to 4.20 nm. Since the 2 value decreased with increase in Si/Al ratio it is obvious that d1 0 0 value increased. The unit cell parameter a0 also increased from 4.13 nm to 4.84 nm on increasing the Si/Al ratio of the mesoporous material. Since increase in aluminium content decreases the crystallinity of the mesoporous material a0 value also decreased [39]. For composite material the a0 value and crystallinity decreased with increase in coating of AlMCM41 over HZSM-5. BET surface area, pore volume and pore size of AlMCM-41 were found to increase with increase in Si/Al ratio. This trend was found to be consistent with the literature already reported [40]. Since the higher surface area (AlMCM-41) mesoporous material is coated over HZSM-5, its increase in % resulted in increase in the surface area. Figs. 4 and 5 show the BET isotherms of mesoporous and composite materials respectively. A steep increase in the adsorption–desorption isotherm at P/P0 = 0.3–0.4 was observed for mesoporous materials which clearly indicated the presence of ≈3 nm mesoporous sieves [41,42]. BET isotherms of composite material indicate that there are more number of meso and micropores but with narrow openings. Meso and micropores gets successively filled up gradually with increase in P/P0 during adsorption. However on desorption, N2 comes out from both the pores simultaneously resulting in larger hysteresis. Increase in % coating of AlMCM-41 over ZSM-5 increased the uptake of N2 [43].
NH3 -TPD signals obtained for micro, meso and composite materials are shown in Fig. 6. All the catalysts showed a peak centred around 200 ◦ C. However, the number of peaks, intensities and pattern of the TPD spectrum are different from each other. Both meso and microporous catalysts exhibited an additional peak at around 500 ◦ C. This showed that type of acidity present in these two samples is different from HZSM-5. Areas of these peaks were measured to determine the total acidity of representative samples of micro, meso and composite catalysts and are given in Table 1. Among all the catalysts, HZSM-5 possessed the highest acidity (4.67 ml of NH3 /g). Both meso and composite materials possessed comparable acidities however on decreasing the aluminium content in the mesoporous material the total acidity decreased. Acidity levels of the composite materials were found to be less than those of HZSM5. The observation was justifiable because less acidic mesoporous is coated over more acidic HZSM-5. Since the acidic sites of HZSM-5 in the composite material are not exposed to the probe molecule acidity values were found to be low. SEM pictures of microporous, mesoporous and composite catalysts are shown in Fig. 7. Discrete spherical and rod shaped micron sized particles are seen in the SEM photograph of HZSM-5 (Fig. 7a). Aggregation of these particles was found and the particle size of HZSM-5 as measured by SEM was in the range of 600–900 nm. Fibrous cauliflower-like morphology of AlMCM-41 (Si/Al = 18) particles was found in their SEM photograph (Fig. 7b). Since all the particles appear alike, formation of AlMCM-41 is homogeneous. This homogeneous nature is an indication of the incorporation of all the aluminium into the lattice [44]. As expected, composite material adopted core–shell architecture where ZSM-5 occupied the core and AlMCM-41 (Si/Al = 25) occupied the shell positions
Fig. 4. Nitrogen adsorption–desorption isotherms of AlMCM-41 of various Si/Al ratios.
Fig. 5. Nitrogen adsorption–desorption isotherms of composite materials with various % coatings.
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Fig. 6. TPD signals of microporous, mesoporous and composite catalysts: (a) HZSM-5 (Si/Al = 15), (b) AlMCM-41 (Si/Al = 18) and (c) AlMCM-41/ZSM-5 (25, 14, 10%).
(Fig. 7c). The fibrous nature of the mesoporous AlMCM-41 is clearly seen in the SEM photograph of composite material. This SEM photograph also shows that almost all the ZSM-5 particles are completely covered by the fibrous AlMCM-41. Spherical shape of core–shell type particles again confirms the presence of microporous material inside these particles. 3.2. Catalytic activities of the catalysts in the cracking of jatropha oil Reaction parameters (temperature – 400◦ C, WHSV – 4.6 h−1 and reaction time – 1 h) were optimized and reported by us for the cracking of jatropha oil using H [27]. Our earlier cracking of jatropha oil under these optimized conditions with different microporous catalysts showed that HZSM-5 was the best catalyst in terms of conversion (62%) and selectivity towards GG (50%) [26]. However the % yield of BLF was found to be only 29%. In order to improve the bioliquid fuel (BLF) content in the product it was planned to synthesize the composite materials comprising both micro and mesopores. Hence attempts were made to fabricate a new composite material comprising the best identified microporous material (HZSM-5) and the most active mesoporous material (AlMCM-41). Conversion and product distribution obtained in the catalytic cracking of jatropha oil over different solid acid catalysts are given in Table 2. The mixture of liquid hydrocarbons which can be termed as bioliquid fuel (BLF), CO, CO2 , gaseous hydrocarbons, water and coke were the different products obtained in the vapour phase catalytic cracking of jatropha oil. All the catalysts were effective in converting jatropha oil into products of different compositions.
The conversion levels were found to be almost the same over both microporous and mesoporous materials however these catalysts convert jatropha oil to a lesser extent when compared to composite materials. On increasing the % coating of mesophase to 10% the conversion increased but with further increase in the % of mesophase to 20%, the conversion decreased. Among the mesoporous materials, the conversion levels decreased on increasing the Si/Al ratio due to decrease in acidity. Like % conversion, % yield of BLF also followed the same trend and it was maximum (70%) over AlMCM-41/ZSM-5 (25, 14, 10) and decreased to 28% on increasing the % coating further to 20%. Percentage yield of gaseous products was found to be same over all the catalysts except AlMCM-41 (72) and AlMCM-41 (95) catalysts. Low yield of gaseous products obtained over AlMCM-41 (72) and AlMCM-41 (95) is due to low aluminium content in it which leads to lower acidity. Selectivities towards GG, GK and GD obtained for different catalysts in the cracking of jatropha oil is shown in Fig. 8. With increase in the Si/Al ratio of the mesoporous materials the selectivity towards GD increased and reached a maximum of 70%. This shows that the lower acidity favours the formation of longer hydrocarbons. It is desirable to get maximum conversion with high % yield of BLF and maximum selectivity towards GG. It is remarkable that AlMCM-41/ZSM-5 (25, 14, 10) converted jatropha oil to maximum extent into various products. In the composite catalyst, the mesoporous material provides suitable pore size and very high surface area but it lacks acidity so synergism takes place when both micro and meso catalysts are combined which results in high conversion
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Fig. 7. SEM micrographs of microporous, mesoporous and composite catalysts: (a) HZSM-5, (b) AlMCM-41 (Si/Al = 18) and (c) AlMCM-41/ZSM-5 (25, 14, 10).
and maximum selectivity towards GG. This newly architected composite material [AlMCM-41/ZSM-5 (25, 15, 10)] yielded the desired result viz., the increase in the conversion and yield of BLF to 99% and 70% respectively. This new composite material not only increased conversion and yield of BLF but also significantly increased the selectivity towards GG. The selectivities towards GG over the composite materials were found to be 60% irrespective of % coating of mesoporous material in them.
Direct comparison of catalytic activities of composite catalyst cannot be made as cracking of jatropha oil is being reported for the first time by us. However cracking of other oils over composite catalysts can be compared. Chew and Bhatia [45] have performed catalytic cracking of fresh and used palm oils over REY, HZSM-5, H and SBA-15 catalysts using a transport riser reactor at the reaction temperature of 450 ◦ C with very high catalyst to oil ratio of 5 g g−1 . The conversion levels
Table 2 Conversion and product distribution in the catalytic conversion of jatropha oil. Catalysts
Conversion (%)
Yield of BLF (%)
Yield of gas (%)
Yield of coke (%)
Yield of water (%)
HZSM-5 (14) AlMCM-41 (18) AlMCM-41 (41) AlMCM-41 (72) AlMCM-41 (95) C1 (25, 14, 5) C2 (25, 14, 10) C3 (25, 14, 20)
62 65 63 60 55 94 99 56
29 39 40 35 32 66 70 28
23 18 17 14 13 17 19 22
1 5 2 7 5 8 7 5
9 3 4 4 5 3 3 1
C refers to composite material (AlMCM-41/ZSM-5). Reaction conditions: temperature – 400 ◦ C, WHSV – 4.6 h−1 and reaction time – 1 h.
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similar levels of selectivities towards gasoline fraction but the bioliquid product (BLF) obtained over MCM-41 contained hydrocarbon with low octane number and the BLF obtained over micro and composite catalysts contained hydrocarbon with high octane number [43]. For the same cracking, Ooi et al. [49] showed increase in selectivity towards gasoline fraction over another composite catalyst (MCM-41/HZSM-5). The importance of thinner coating of mesoporous material over microporous material, aluminium content in the mesophase and shape selective property of HZSM-5 in the catalytic conversion of palm oil were well explained by Twaiq et al. [43]. 3.3. Possible mechanism for cracking of vegetable oils Fig. 8. Selectivity of catalysts towards various fractions of BLF obtained in the cracking of jatropha oil [C1, C2, C3 refer to composite materials AlMCM-41/ZSM-5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20)].
were found to be in the range of 71–84% and the selectivity towards gasoline fraction was in the range of 33–38%. Twaiq et al. [46] used a microreactor to crack palm oil over HZSM-5 with various Si/Al ratios at 450 ◦ C and obtained 94–96% conversion with selectivity of 45–49% towards gasoline. Commercial rapeseed oil cracked by using equilibrium FCC catalyst at 480–585 ◦ C by Dupain et al. [47] produced the conversion of 57% and selectivity of 34% gasoline. Twaiq et al. [43] cracked palm oil to the level of 88–90% using mesoporous aluminosilicate materials synthesized by different methods and obtained very high selectivity towards liquid hydrocarbons. Comparison of selectivities obtained over micro (H) and meso (MCM-41) porous materials by Ooi et al. [48] in the catalytic cracking of palm oil showed that although the conversion levels were in the same range, selectivity towards gasoline fraction was found to be very high (73%) over MCM-41 when compared to H (39%). Significant enhancement in the selectivity towards gasoline fraction (75%) was reported for composite catalysts when compared to H (39%) in the cracking of palm oil [43]. Comparison of selectivity made for MCM-41 and composite material indicated
The reaction mechanism of vapour phase catalytic cracking of triglyceride molecule over composite catalyst is shown in Fig. 9. The formation of non-condensable (CO and CO2 ), condensable hydrocarbons and aromatics is explained through this possible cracking mechanism of composite catalysts. The bigger shaded circles and dark small circles correspond to mesoporous and microporous materials respectively. The composite catalyst depicted in this figure comprises less acidic mesoporous catalyst as shell coated over higher acidic microporous material. The high reaction temperature of about 400 ◦ C volatilizes the vegetable oil and at first the vapours access the shell. When the bulky triglyceride molecule enters into the mesoporous (shell) layer, it may crack into three fractions namely A, B and C as indicated by dotted brackets on the triglyceride. Part ‘A’ of the triglyceride may cleave as propane or propene and part ‘B’ may crack to yield CO and CO2 in the mesophase. ‘C’ may crack in any fashion depending on Si/Al ratio of mesophase. Since the acidity level of mesoporous material is kept at very low level, it is expected that long chain hydrocarbons are formed in the shell. These fragmented molecules further enter into the microporous material where the secondary cracking of oil takes place. The higher acidic nature of catalyst facilitates the extensive cracking of oil into shorter fragment. ‘A’ gets cracked further into ‘X’ (C1 –C3 hydrocarbons), these hydrocarbons may or may not take part in the
Fig. 9. Possible cracking mechanism of triglyceride over composite catalyst. A- Propane or propene, B- CO or CO2 , C- long chain hydrocarbons, X- C1 – C3 hydrocarbons, Y – both straight chain and branched hydrocarbons (Cn H2n+2 ) and aromatics.
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oligomerization and aromatization. Fragment ‘B’ does not undergo any reactions further and exist as ‘B’ itself. The shape selective property of microporous ZSM-5 tailors the ‘C’ fragment and the cracked fragments isomerize to form ‘Y’ which is branched hydrocarbon named as BLF. The hydrocarbons present in BLF comprise hydrocarbons present in commercially available gasoline, kerosene and diesel. 4. Conclusions Microporous (HZSM-5, Si/Al = 14), mesoporous (AlMCM-41, Si/Al = 18, 41, 72 and 95) and composite materials [AlMCM-41/ZSM5 (25, 14, 5), AlMCM-41/ZSM-5 (25, 14, 10) and AlMCM-41/ZSM-5 (25, 14, 20)] were synthesized by hydrothermal method. All the catalysts were characterized by using physico-chemical techniques. The presence of mesoporous and microporous materials in the composite catalyst was confirmed by the XRD peak at 1.98◦ and 22–25◦ respectively. The growth of mesoporous AlMCM-41 over microporous ZSM-5 was clearly seen in its SEM micrograph of composite material. The fixed bed catalytic cracking of jatropha oil was done over these catalysts and among the synthesized microporous [HZSM-5 (14)], mesoporous [AlMCM-41 (18, 41, 72 and 95)] and composite catalysts [AlMCM-41/ZSM-5 (25, 14, 5/10/20), AlMCM41/ZSM-5 (25, 14, 10)] was found to be the most active catalyst for the cracking of jatropha oil as it showed 99% conversion with 70% BLF content and 61% selectivity towards GG. Acknowledgement
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