CHAPTER 2 LITERATURE REVIEW AND THE SCOPE OF THE PRESENT STUDY

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1 23 CHAPTER 2 LITERATURE REVIEW AND THE SCOPE OF THE PRESENT STUDY 2.1 LITERATURE REVIEW The use of vegetable for diesel fuel production was first expressed by Rudolph Diesel, the inventor of the diesel engine, who described the use of peanut as a fuel to power compression ignition engines (Knothe et al 2009). In the earlier years of the diesel engine, vegetable was directly used as fuel. Despite the early success of vegetable, it became clear that it was not a suitable fuel for diesel engines. Several issues encountered are high viscosity, poor cold flow properties and low volatility, injector tips cooking, carbon deposition in combustion chamber, piston ring sticking, polymerization, and oxidations (Ma and Hanna 1999, Canakci and Sanli 2008, Singh and Singh 2010). By 1920, the rapid development of the petroleum industry soon made petro diesel a cheaper and quality alternative to vegetable (Manzanera et al 2008). One solution to the poor fuel properties of vegetable was to convert it into mono alkyl esters of fatty acids by the process of transesterification and esterification. Traditionally, biodiesel is produced through homogenous alkali catalysis. However, this process suffers from several shortcomings among which are the expensive downstream separation and the high cost of edible refined vegetable. These shortcomings are translated into high manufacturing cost that hinders biodiesel economic viability. In recent years,

2 24 the research frontier for biodiesel has shifted to the identification of suitable heterogenous catalysts that could achieve high yields while reducing production cost. Alkyl fatty acid esters can be prepared from any fatty acid sources as such biodiesel has been prepared from various feed stocks. The most popular type of feedstock for biodiesel production is edible refined vegetable s such as soybean, rapeseed, sunflower, palm, coconut and linseed (Singh and Singh 2010). As the demand for vegetable s for food has increased tremendously in recent years, it is impossible to justify the use of these s. Hence, the contribution of non-edible s is significant for biodiesel production. Several non edible s were utilized for biodiesel production such as Honge (Pongamia pinnata), Jatropha (Jatropha curcas) and Mahua (Madhuca indica) etc., (Meher et al 2006). In this study Azadirachta Indica and Calophyllum inophyllum have been selected for biodiesel production. Azadirachta Indica (neem) grows almost in all type of ss. It thrives well in arid and semiarid climate with maximum shade temperature as high as 49 C, bearing rainfalls as low as 250 mm/year. Nabi et al (2008) have produced biodiesel from neem by using 20% methyl alcohol and 0.6% anhydrous NaOH catalyst at the temperature 60 C. There has not been much research done so far with this and there is no literature available with heterogenous catalyst. The tree Calophyllum inophyllum (pinnai) thrives in xerophytic habitat. It grows best in deep s or exposed sea sands. The rainfall requirement is just mm/year. Pinnai contains 24.96% saturated and 72.65% unsaturated fatty acids. Sahoo et al (2009) obtained comparatively higher flash point than petroleum diesel fuel from pinnai, indicating better safety condition for storage. Very few literature is available

3 25 on pinnai and it is found that even in those cases only conventional catalysts have been employed. The difference between transesterification and esterification becomes very important, when choosing feedstock and catalyst to avoid problems. Transesterification is catalyzed by base or acid catalysts. Esterification, however, is only catalyzed by acid catalysts. In the presence of a base catalyst, the undesirable saponification reaction could take place if the feedstock contains free fatty acids, contributing to the hard down stream process in the removal of soaps. Lotero et al (2005) recommends a feedstock containing less than 0.5 wt% free fatty acid when using base catalyst to avoid soap formation. Therefore, the composition of the feedstock controls the predominant chemical pathway and dictates the catalyst to be used for the biodiesel production. Feed stocks containing substantial amounts of free fatty acid should be subjected to acid, enzyme catalysis or supercritical transesterification as the methods which could tolerate the FFA Heterogenous acid catalyst Tungsten oxide zirconia, sulphated zirconia and amberlyst were examined for better esterification of crude sunflower and tungsten oxide zirconia has been chosen as a promising heterogenous catalyst because of the higher conversion up to 93% and also no leaching of WO 3 in the reaction products (Park et al 2010). Lu et al (2008) screened different solid acid catalysts for pre-esterification, including resin D72, molecular sieves, HM, SAPQ-11, HZSM-5, H with prepared ST- solid catalyst (Synthesized meta titanic acid). The SO 2-4 / TiO 2 showed higher activities in the esterification of oleic acid with methanol (Lu et al 2008). But they reported high catalyst amount for esterification reaction. Sulphonated ordered mesoporous carbons were tested for the esterification of oleic acid by Liu and his co-workers (2008), but the conversion was only 73%. The catalytic activity of

4 26 Al-MCM-41 for the esterification of palmitic acid with methanol, ethanol and isopropanol was determined from the acidity index of the final product by Carmo et al (2009). They reported Al-MCM-41 is active for the low Si/ Al ratios. Jacobson et al (2008) synthesized zinc stearate immobilized on silica gel and evaluated for the esterification of free fatty acids present in waste cooking and also the transesterification of triglycerides. The only draw back in their study is the high temperature requirement for esterification. Lin et al (2010) have chosen FDU-15 mesoporous polymer and modified via sulfonation and showed nearly 99% conversion of fatty acid. But they used 5% catalyst for effective esterification which seems to be high when compared to other catalysts. Caetano et al (2008) studied the esterification of palmitic acid using tungstophosphoric acid, molibdophoshoric acid and tungstosilicic acid immobilized by sol-gel technique on silica and observed that tungstophosphoric acid-silica shows high activity. Though the conversion efficiency is 100% the time required for complete requirement is 30 h. Mesoporous polyoxometalate - tantalum pentoxide composite catalyst was reported by Xu et al (2008), for the esterification of lauric acids. Some inorganic salt have also tried as solid acid catalysts by several researchers. Wan Omar et al (2009) used ferric sulphate to esterify the free fatty acids present in waste cooking, and achieved about 81.3% yield. Buasri et al (2009) reduced the acid value of crude palm to less than 1mg KOH/ g of by using Fe 2 (SO 4 ) 3 as catalyst. Cordeiro et al (2008) synthesized zinc hydroxide nitrate and evaluated its activity towards the esterification of lauric acid with methanol and the reusability was also tested. Three different cation - exchange resins were selected by a group of researchers and their reactivity was examined for the biodiesel production via esterification of acidified (Feng et al 2010). They concluded that the

5 27 highest conversion was obtained by NKC-9 and it showed excellent reusability. They explained that, NKC-9 with lowest water content can absorb the water produced in esterification; hence it could decrease the concentration of water in the reaction system and promote the esterification. But in all the above said findings in which polymeric resins were used as solid acid catalysts, the main drawback is the swelling property of resins. Due to the drawbacks posed by other catalysts, zeolites came in to lime light. Zeolites are among the strongest and most synthesized solid acid catalyst, so it is not surprising that they were used to catalyze esterification. This group of catalyst dragged particular interest as it could be engineered for various pore sizes, proton exchange ability and acid strength. However, as pointed out by Lotero et al (2005) and later established by Rothenberg et al (2005) mass transfer is a limiting factor because of the micro porous nature of zeolites and the large molecular size of triglycerides and free fatty acids. This limited diffusion slows down the catalytic activity. Rothenberg et al (2005) showed that zeolites only showed a minor increase in yield (1-4%) compared to the uncatalyzed reaction. As mentioned by the authors, a lower ratio of SiO 2 :Al 2 O 3 increases the acidity of the catalyst and its hydrophilicity. Silica molecular sieves, doped with aluminum, zirconium, titanium or tin to enhance acidic strength, were thought to be strong acid catalysts. In reality, they behaved more like a weak acid. Two commercial catalysts CBV 780 (zeolite type SDUSY-ZEOLYST TM) and niobic acid (CBMM) and two synthesized catalysts, SAPO-34 (molecular sieve type alumino- silicate phosphate) and niobia were tested for the esterification of palmitic acid by group of researchers (Souza et al 2009).In our study two zeolites Mordenite and -zeolite were chosen and modified with phosphoric acid and used for esterification of FFA present in neem and pinnai.

6 Table 2.1 Recently reported literature on Solid acid catalyzed esterification Initial free fatty acid amount Name of catalyst Catalyst loading Time Methanol to ratio Temperature Conversion Reference 0.94 mgkoh/g Acidic resin A-15 2 wt% 40 min 20 % vol C 45.7% (Ozbay et al 2008) mgkoh/g 1.25 mgkoh/g 279 mgkoh/g Dowex monosphere 550 A 2.26 wt% 2 h 6.128:1 45 C - (Marchetti et al 2007) Mordenite 1 g 3 h 30:1 60 C 80.9% (Chung et al 2008) H 3 PW 12 O 40 / 50 mg 3 h 9:1 80 C 84.9% (Xu et al 2008) Ta 2 O mgkoh/g Cation exchange resins NKC- 9,001 7 and D mgkoh / g of 20 wt% 4 h 6:1 66 C 90% (Feng et al 2010 WO 3 /ZrO 2 29 wt% 2 h 9:1 75 C 93% (Park et al 2010b) 190 mgkoh/g of Al-MCM wt% 2 h 60:1 130 C 79% (Carmo Jr et al 2009) 190 mg KOH/g of Hetero poly acids immobilized on silica 0.2 g 30 h 30 ml 60 C 100% (Caetano et al 2008) 14 mg KOH/g of Metatitanic acid 4 wt% 2 h 20:1 90 C 97% (Lu et al 2008) mg KOH /g of 33.4 mg KOH/g of Fe 2 (SO 4 ) g 3 h 7:1 60 C 81.3% (Wan omar et al 2009) Fe 2 (SO 4 ) 3 2 wt% 2 h 10:1 95 C 80% (Buasri et al 2009) 28

7 Table 2.1 (Continued) Initial free fatty acid amount Name of catalyst 15 mg KOH/ g of Zinc stearate immobilized on silica gel 279 mg KOH/ g of Catalyst loading Time Methanol to ratio Temperature Conversion Reference 3 wt% 10 h 18:1 200 C 98% (Jacobson et al 2008) Amberlyst wt% 2 h 6:1 80 C >90% (Park et al 2010a) Waste cooking Cation-exchange resin - 3 h % (Kouzu et al 2008) 279 mg KOH/ g of 279 mg KOH/ g of 279 mg KOH/ g of 204 mg KOH/ g of SO 4 2- / TiO 2 12 wt% 2 h 20:1 70 C 97% (Lu et al 2008) Sulphonated ordered mesoporous carbons 50 mg 10 h 10:1 80 C 73.9% (Liu et al 2008) Zn 5 (OH) 8 -(NO 3 ) 2.2H 2 O 4 wt% - 6:1 140 C 97.4% (Cordeiro et al 2008) FDU-15-SO 3 H 5 wt% 6:1 70 C 99% (Lin et al 2010) 8.7 mg KOH/ g of Amberlyst wt% 2 h 7.5:1 80 C 91% (Park et al 2008) 6 mg KOH/ g of Ionac NM (w/v) min 5: C 100% (Jeong et al 2007) 204 mg KOH/ g of Zeolite CBV wt% 2.5 h 2:1 100 C 30% (Souza et al 2009) 29

8 Table 2.2 Recently reported literature on solid base catalyzed transesterification Methanol to Substrate Catalyst loading Time Temperature Conversion Reference ratio Soybean CaO 8 wt% 12:1 1.5 h 65 C 95% (Liu et al 2008) Rapeseed Alkali doped metal 4 g 9:1 3 h 60 C 90% (Mac Leod et al 2008) oxide Soybean Calcined layered 1 wt% 15:1 2 h 60 C 77.6% (Shumaker et al 2008) double hydroxide Soybean SrO 1 wt% 12:1 30 min 70 C 95% (Liu et al 2007) Canola MgCoAl-LDH 2 wt% 16:1 5 h 200 C 96% (Li et al 2008) Soybean CaO 4 wt% - 2 h - >99% (Kouzu et al 2008) Ethyl butyrate MgO/CaO 62 g 4:1 3 h 60 C 80% (Albuquerque et al 2008) Soybean Mg-Al hydrotalcite 7.5 wt% 15:1 9 h 60 C 67% (Xie et al 2006) Soybean Metal oxide 2 wt% 3:1 15 min 215 C 85% (Singh et al 2007) Soybean NaX zeolites loaded 10 wt% 10:1 8 h 65 C 85.6% (Xie et al 2007) with KOH Sunflower ZrO 2 supported La 3 O 3 5 wt% 30:1-200 C 84.9% (Sun et al 2010) Sunflower Mg-Al layerd double 6 wt% 24:1 6 h 120 C 90% (Brito et al 2009) hydroxide Rape seed K 2 CO 3 -Al 2 O 3 4 wt% 15:1 3 h 50 C 98% (Liu et al 2010) Cotton seed KF/-Al 2 O 3 4 wt% 12:1 3 h 65 C <90% (Lingfeng et al 2007) Soybean Calcium ethoxide 3 wt% 12:1 1.5 h 65 C 95% (Liu et al 2008) 30

9 Table 2.2 (Continued) Substrate Catalyst loading Methanol to ratio Time Temperature Conversion Reference Sunflower (Al 2 O 3 ) X (SnO) Y (ZnO) Z - 10:1 4 h 60 80% (Macedo et al 2006) Soybean Al 2 O 3-12:1 3 h 65 99% (Teng et al 2009) Soybean PbO 2 2 g 7:1 2 h % (Singh et al 2008) Canola KOH loaded MgO 3 wt% 6:1 9 h 60 95% (Ilgen et al 2009) Soybean SiO 2 /ZrO 2-10:1 3 h 50 96% (Faria et al 2009) Chicken fat Crab and cockle shells 4.9 wt% 0.55:1 3 h 65 98% (Boey et al 2010) palm HF/Hydrotalcite 3 wt% 12:1 5 h 65 92% (Gao et al 2008) Palm Al 2 O 3 -supported metal oxide 10 wt% - 3 h 60 94% (Benjapornkulaphong et al 2008) 31

10 Heterogenous Base Catalyst Solid base catalysts are typically synthesized by inorganic wet chemistry techniques such as precipitation, co-precipitation, sol-gel process, hydrothermal synthesis or impregnation (Livage 1998). Catalyst preparation has been carried out through any of the conventional catalyst synthesis route but wet impregnation is the dominant method perhaps due to its simplicity and its ability to produce very active catalysts. Briefly, wet impregnation is the deposition of desired catalytic species on a catalyst support, often a metal oxide. The catalyst support must meet certain criteria such as tolerance to synthesis and reaction solvents, high surface area and good catalytic properties. Widely used catalysts for transesterification of triglycerides are metal oxides and mixed metal oxides. Kouzu et al (2008) investigated the catalyst activity of CaO, Ca (OH) 2 and CaCO 3 towards the transesterification of triglycerides of soybean and reported that CaO shows better activity. Transesterification of soybean was tested with series of metal oxide catalysts like MgO, CaO, PbO, PbO 2, Pb 3 O 4, Tl 2 O 3 and ZnO with different BET (Brunauer, Emmett and Teller) surface area, acidity/basicity and acid/base site strength by Singh et al (2008). Albuquerque et al (2008) synthesized MgO, CaO and tested for transesterification of ethyl butyrate. Various mixed Mg-Al oxides synthesized from Mg-Al hydrotalcites by Xie et al (2006) were tested for the methanolysis of soybean. ZrO 2 supported La 2 O 3 catalyst was prepared by impregnation method and it was examined in the transesterification reaction of sunflower with methanol to produce biodiesel. A study made on the double hydroxide catalyst by Brito et al (2009), which says that Mg-Al hydrotalcite catalyzed transesterification reaction shows more than 90% yield. Macedo et al (2006) synthesized three different solid base catalysts like (Al 2 O 3 ) 4 (SnO), (Al 2 O 3 ) 4 (ZnO) and Al 2 O 3

11 33 and analyzed their activity in transesterification in presence of short chain alcohols. But the work done with metal oxides and mixed metal oxides reported either high methanol to ratio, high temperature or high catalyst amount for transesterification reaction. Zeolites and mesoporous materials and their modified forms were also used as solid base catalysts. NaX zeolite modified with KOH was tested for transesterification of soybean by Xie and his coworkers (2007). -zeolites modified with La 3+ has been employed for the synthesis of biodiesel from soybean (Shu et al 2007). A study of transesterification of sunflower over zeolite using different metal loading was done by Ramos et al (2008). Very few studies have been carried out so far using modified silica based material. Lukic et al (2009) used SiO 2 /Al 2 O 3 supported K 2 CO 3 as a catalyst for biodiesel synthesis from sunflower. In this study modified silica gel has been chosen for transesterification of triglycerides Kinetics Understanding the reaction mechanism is important in the selection and design of an industrial reactor for a specific reaction. An accurate kinetic model will enable further insight for modeling of biodiesel reactor system. The kinetics of sunflower methanolysis was investigated by Veljkovi et al (2009) and Stamentovi et al (2010) on CaO and Ca(OH) 2 respectively. Both studies assumed that the methanol adsorption on the surface and product desorption were not rate determining steps to begin and that the rate determining step was the reaction between methanol adsorbed on the surface and triacylglycerols in the bulk fluid for both CaO and Ca(OH) 2. Hattori et al (2001) and later Dossin et al (2006) proposed the reaction mechanisms for ethyl acetate transesterification over basic heterogenous catalysts. Dossin et al (2006) modeled the transesterification of ethyl acetate

12 34 on MgO and investigated fifteen models based on Eley-Rideal (ER) and Langmuir-Hinshelwood kinetics Kinetics of esterification Several authors have reported the kinetics of free fatty acid esterification in homogenous systems. Berrios et al (2007) reported the kinetic study of free fatty acids in sunflower with sulfuric acid as the homogenous catalyst and modeled the reaction with pseudo homogenous first order for the forward reaction and second order for the reverse reaction. Similarly, Tesser et al (2009) described the esterification of oleic acid over an ion-exchange sulfonic resin by a pseudo-second order kinetic model. Ni and coworkers (2007) investigated the esterification of palmitic acid in sunflower over a silica-supported Nafion resin and compared its activity with sulfated zirconium oxide. SnCl 2 was successfully used for the esterification of oleic acid in soybean using ethanol and the catalyst was found to yield comparable result with homogenous H 2 SO 4 catalyzed reactions (Cardoso et al 2008) Kinetics of Transesterification The early work on the kinetics of transesterification dealt with homogenous catalyst, in particular homogenous base catalyst. The kinetics of homogenous base catalyzed transesterification of edible and non-edible s has been investigated by several authors (Freedman et al 1986, Veljkovic et al 2009, Stamenkovic et al 2010). Freedman et al (1986) studied the transesterification of soybean by sodium butoxide and concluded that the forward reaction was a pseudo first order when the to alcohol ratio was larger (1:30) or second order for lower ratio (1:6). They also observed that the reverse reaction was second order. Nourreddini et al (1997) studied the

13 35 kinetics of soybean transesterification by sodium hydroxide and reported activation energy values consistent with the findings of the previous authors. The kinetics of heterogenously catalyzed vegetable transesterification has also generated interest in recent years. Singh et al (2007) studied the kinetics of soybean transesterification by MgO, CaO, BaO, PbO and MnO2 in a high pressure reactor to determine the overall rate constant and the reaction order. The reaction order was first order for all catalysts except for BaO which had a third order. 2.2 SCOPE OF THE PRESENT STUDY Biodiesel which is gaining importance as an alternate to fossil fuels is produced via a two step process. It involves esterification catalyzed by solid acid catalyst followed by transesterification catalyzed by solid base catalyst. Two different zeolites are chosen and modified with phoshphoric acid and used as a catalyst for esterification. Two silica gels with different mesh sizes were chosen for amine functionalization and used for transesterification. The scope of the present study is To modify the H forms of both mordenite and zeolite with phosphoric acid. To characterize the modified and unmodified zeolites by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Thermo Gravimetric Analysis (TGA) and NH 3 Temperature Programmed Desorption (NH 3 - TPD) analysis. To modify the two silica gels having different mesh sizes with the help of a modifying agent 3-aminopropyltriethoxysilane. To characterize the modified and unmodified silica gels by FTIR, XRD, SEM, TGA and NH 3 -TPD analysis.

14 36 To find out the percentage reduction of FFAs present in neem and pinnai and study the catalytic activity of phosphoric acid modified zeolites towards the esterification reaction. To optimize the esterification reaction parameters such as temperature, methanol to ratio and catalyst amount and study the esterification kinetics based on pseudo first order kinetic model. To find out the percentage conversion of triglycerides present in neem and pinnai by Nuclear Magnetic resonance (H 1 -NMR) spectra and study the catalytic activity of amine functionalized silica gel towards the transesterification reaction. To optimize the transesterification reaction parameters such as temperature, methanol to ratio and catalyst amount and study the transesterification kinetics based on pseudo first order kinetic model. To study the recovery and reusability of the phosphoric acid modified zeolites and silane functionalized silica gels to facilitate their efficacy towards biodiesel production. To study the fuel properties of the biodiesel obtained.