STUDIES ON THE STABILITY OF BIODIESEL FROM JATROPHA CURCAS OIL

Abstract

The increasing urbanization and industrialization has led to the steep rise in the consumption of petroleum fuels all over the world. The growing economy of India requires huge energy resources and hence, the energy demand is increasing at a rate of 6.5% per annum while the indigenous production is much less as evidenced by the fact that more than 80% of crude oil is imported to meet the demand in the country. The huge gap between the demand and supply has put the energy security and sustainability at stake apart from paying huge foreign exchange for oil imports. The situation has forced the developing counties to look for alternatives for liquid fuels. Since huge diesel is consumed to fuel the diesel engines for varied applications, the possibility of its substitution by biodiesel from oils and animal fats based feedstocks has necessaciated the development of biodiesel processes for its production in the country. Biodiesel, an ecofriendly and renewable substitute of diesel, has been getting serious attention of researchers/scientists of all over the world including India. Under the National Biodiesel Mission of Government of India, Jatropha curcas oil (JCO) — A non-edible oil, is being given the top priority for conversion to biodiesel and its utilization in IC engines. The biodiesel quality is governed by its fatty acid profile which is reported as the major factor impacting the biodiesel quality over time. The presence of unsaturation (double bonds) in fatty acids is of serious concern when the biodiesel is stored over longer period of time, as the fuel starts deteriorating with passage of time due to exposure to air and/or light, temperature, presence of metals (of containers) etc resulting in the sediments and gum formation and finally fuel darkening. This degraded fuel quality poses serious operational problems like fuel filter plugging, injector fouling, deposit formation in engine combustion chamber and other components of the fuel system, which badly affect the engine performance. To meet these challenges, the biodiesel stability is required to be improved in terms of oxidation, thermal and storage stability of biodiesel and its blends with diesel. Oxidation stability studies are carried out to develop the relationship between Induction Period (IP) and other fuel quality parameters, the storage stability is based on m studying the effect of storage conditions on the stability of biodiesel while the thermal stability needs to study the effect of temperature and addition of natural and synthetic antioxidants on fuel quality. Improvement in biodiesel stability is actually its resistance to oxidation during long-term storage. Several approaches are available on enhancing the relative resistance to oxidation of fatty acid derivatives. Literature reveals significant work on oxidation, thermal and storage stability of biodiesel from edible oils but very little work on the stability of biodiesel from non-edible oil resources like Jatropha curcas, Pongamia pinnata, etc. The biodiesel was prepared from JCO employing the methodologies already developed by the authors. The stability studies are limited to Jatropha curcas biodiesel (JCB) only in view of its possibility as substitute of petro-diesel in future in India. Neat JCB (l3i ) showed an IP of 3.27 hrs which meets the limit of 3 hrs IP in accordance with recent ASTM D-6751 standard but did not achieve the minimum limit of 6 hrs IP as required by EN-14112/IS- 15607. Thermal stability of JCB is also found very poor as indicated by ASTM D6468. Therefore, the present thesis is devoted to study the oxidation, thermal and storage stability of JCB. The following are the objectives of the thesis: (i) Synthesis and purification of biodiesel from JCO. (ii) Modification of the Karl Fischer (KF) coulometer apparatus for the measurement of oxidation stability as alternative to Rancimat apparatus. (iii) Analysis and determination of fuel properties of fresh JCB to create baseline data. (iv) Study the oxidation, storage and thermal stability of JCB. (v) Study the effects of metal contaminants and antioxidants on the above stabilities. (vi) Develop relationships between fuel stabilities with metal contaminants, antioxidant concentrations and storage time. (vii) Optimization of antioxidant concentration for attaining maximum fuel stability conforming to standards. (viii) Study the effect of stabilized JCB on engine performance and exhaust emissions. Different antioxidants in concentration ranging from 100 to 600 ppm were added to JCB to study the 'effectiveness of antioxidants. Pyrogallol (PY) was found as the most effective antioxidant to increase the oxidation and thermal stability of JCB. Therefore, further studies, only PY has been selected as most effective antioxidant and mixed in different concentrations in JCB to study its effect on oxidation, thermal and storage stability. Different metal contaminants with concentration from 0.5 to 3 ppm were also added to JCB and it is found that when metal concentration is increased beyond 2 ppm, the effect of metal contamination on oxidation stability become constant and therefore, a maximum concentration of 2 ppm has been selected for adding different metals in JCB. Range of metal concentration is varied from 0 to 2 ppm for the oxidation, thermal and storage stability, while the range of antioxidant concentration is varied from 0 to 600 ppm for oxidation and thermal stability, however for storage stability, antioxidant concentration is varied from 0 to 800 ppm. To study the storage stability biodiesel samples were stored for a period of 6 months. Samples were prepared using the above range of parameters for experiments and their effect on different stabilities. Design of experiments based on Response Surface Methodology (RSM) approach has been used to optimize the antioxidants concentration for optimum oxidation, thermal and storage stability. Oxidation stability is an important parameter in the characterization of oils and fats. According to EN-14112/IS 15607, oxidation stability is usually measured by Rancimat apparatus which is very costly and not commonly available in laboratories and therefore, an attempt was made to develop alternative apparatus. For this purpose KF coulometer apparatus available in the laboratory was modified to conduct the Rancimat test. The results of modified KF coulometer apparatus were compared with the Rancimat apparatus and both are found to have comparable sensitivity, repeatability and reproducibility indicating that the modified KF coulometer apparatus can be used in place of Rancimat apparatus which is not only cheaper but also affordable by common laboratories for the measurement of oxidation stability of fats and oils. Development of modified KF coulometer apparatus is the first study of its kind carried by the authors to offer an alternative to conventional Rancimat apparatus. A PY concentration of 82.86 ppm is found optimum to achieve specified IP of 6 hrs without metallic contaminants, i.e., with storage of JCB in non-metallic containers. On the other hand, when JCB is stored in metallic containers, higher PY concentration as additive is required to achieve the same stability. Optimization using.RSM has found the need to B add a maximum of 326.96, 361.64, 386.15, 471.24 and 600 ppm PY to achieve an IP of 6 hrs for Fe; Ni, Mn,. Co, Cu contaminated JCB respectively. Based on these results, it may be recommended to store JCB in non- metallic containers made of plastic/ PVC or other materials but looking at their life and long time ease of handling when JCB is stored in metallic container made up of different metal alloys, the use. of PY additive is required to be added in optimum concentrations as referred to above. The results on the effect of blending of JCB with petro-diesel has shown that less than 20% blending of JCB with diesel does not require any antioxidant but require large storage capacity. When the proportion of JCB is further increased in the blend, the antioxidant in smaller amount is required than neat JCB. These findings reveal that more antioxidant is required as the proportion of JCB in the blend is increased as evidenced by the observation that for B100, 82.86 ppm and for B30, 50 ppm PY is required to be added to meet the international specification of oxidation stability for pure biodiesel and its blends respectively. In the present work, Thermo Gravimetric Analysis (TGA) and ASTM D6468 method are employed to study the thermal stability of JCB with respect to activation energy and insoluble formation respectively. Activation energy is found to increase and insoluble formation to decrease with increase in PY concentration in JCB. The effect of mixing of Fe, Ni, Mn, Co, and Cu in JCB in different concentration has shown an increase in insoluble formation and decrease in activation energy of JCB with increase in metal concentration. These metals are found to enhance the oxidation process and reduction in activation energy due to the acceleration of free-radical oxidation and reduction in thermal degradation temperature due to metal mediated initiation reaction, which, in turn, increases the insoluble formation. As International/ national standards do not provide any limit for biodiesel thermal stability and therefore, the studies are carried out related to thermal stability of biodiesel to achieve minimum insoluble and maximum activation energy. A minimum insoluble of 0.417, 0.451, 0.468, 0.538 and 0.493 mg/100ml and a maximum activation energy of 59.32, 60.36, 58.30, 55.03 and 50.55 KJ/mol is found in Fe, Ni, Mn, Co, Cu contaminated JCB samples respectively dosed with 600 ppm PY. V Further, the correlations developed between oxidation and thermal stability of JCB are found very useful for the prediction of thermal stability in terms of insoluble formation and activation energy based on the oxidation stability in terms of IP of JCB. These correlations developed, will be very useful to measure the oxidation stability of JCB. The AV, PV and viscosity of JCB is found to increase from 0.15 to 0.45 mg KOH/gm, 4.16 to 38.26 mg/kg and 4.38 to 5.63 cSt over a period of 6 months respectively without metal contaminants. But when metals are added in JCB, the viscosity increases due to acceleration in the oxidation process due to increase in peroxide formation. Owing to the above reasons, the stability of metal contaminated JCB deteriorates drastically. Fe is found to have the least effect and Cu, the strongest effect on storage stability of JCB. These observations support the earlier findings that JCB should be stored in non-metallic containers. Alternatively, metallic storage made up of Fe dominated alloy is preferable than Cu dominated alloy containers. Further, the fresh JCB with and without metal contaminants is found to have same percentage of oleic, linoleic and linolenic acid in all samples but with the passage of time (storage time), the relative percentage of oleic, linoleic and linolenic acid in JCB is found to vary from 39.1 - 47.37%, 36 - 20.99% and 0.20 - 0.026% respectively without metal additives. When the metals are mixed in JCB, the relative percentage of oleic acid is found as 47.48, 47.67, 47.78, 47.87 and 47.99 %, the relative percentage of linoleic acid as 20.78, 20.35, 20.13, 19.92 and 19.70 and the relative percentage of linolenic acid as 0.024, 0.22, 0.021, 0.019 and 0.018 % for Fe, Ni, Mn, Co and Cu respectively after 6 months of storage. These observations indicate that increase in relative percentage of oleic acid and -decrease in relative percentage of linoleic and linolenic acid is indicative of the accelerated oxidation process after the addition of metal contaminants. It may, therefore, be concluded that as the oxidation deterioration advances, linolenic and linoleic acids methyl ester contents decreases while oleic acid methyl ester becomes relatively higher. When PY is added to JCB, the rate of increase of AV with time decreases due to retardation in the oxidation process as evidenced by the lowering of peroxide formation with storage time. These findings reveal that increase in the antioxidant concentration results in the retardation of oxidation process yielding low peroxides, a parameter indicating the improvement in the storage stability. The improvement in the storage vi stability of JCB for longer period of time is further supported by decrease in relative percentage of oleic acid and increase in relative percentage of linoleic and linolenic acid. RSM based optimization has indicated that for JCB without metal, 200 ppm PY is enough to maintain the JCB stability for 6 months, while when metal (Fe) concentration of 2 ppm or more is added, 800 ppm PY is found sufficient to make biodiesel stable for 5.5 months. The storage time for Ni, Mn, Co and Cu contaminated JCB is found as 3.62, 3.24, 2.76 and 2.07 months respectively to maintain the IP of 6 hrs as per IS 15607/ EN 14112. The engine performance and exhaust emissions were analyzed using stabilized JCB samples and compared with unstabilized one. It is found that brake specific fuel consumption (BSFC) of engine decreases and brake thermal efficiency (BTE) increases when stabilized JCB is used compared to unstabilized one. When JCB is stored for longer period. (6 months), BSFC is found to increase and BTE to decrease while CO, HC and NO emissions are found to reduce due to decrease in Total Position Equivalent (TPE) due to advancement of oxidation reaction. As such, no significant negative impact of antioxidants on engine performance and emissions is observed. In view of the above findings, it is recommended to store JCB in a non metal container like glass, plastic, etc to maintain its stability. However, looking at the long life of metal container, the optimum concentration of PY may be added/ mixed in JCB to get the desired stability. Based upon the above findings, there is a need to study the effect of mixing/ adding saturated fatty acids in JCB and its effect on fuel stability and its impact on engine performance and exhaust emissions. A detailed investigation is required to study the effect of thermal behavior of fatty acids on thermal stability of biodiesel. Also, there is need to prepare synthetic biodiesel using varying proportions of pure methyl esters of different fatty acids and to develop a monogram for knowing the stability of a given biodiesel based on fatty acid compositions.