Second Generation Feedstock: Biodiesel from Jatropha

IJBSTR REVIEW PAPER VOL-1[ISSUE 5] MAY 2013

ISSN- 2320-6020

Second Generation Feedstock: Biodiesel from Jatropha Apoorvaa Singh and R. P. Singh* ABSTRACT: Depleting finite oil reserves and the ever increasing demand for the fuel is driving forces to search alternatives fuels from renewable resources with smaller environmental impact. One of the most promising alternatives to the petroleum based fuels is the Biodiesel, which is of the plant origin. Biodiesel is defined by the American Society for Testing and Materials (ASTM) as the mono- alkyl ester of long chain fatty acids derived from a renewable lipid feedstock. The major oil seed crops used for the production of biodiesel include sunflower, soybean, rapeseeds, linseed, cottonseed, canola etc. Majority of which are edible in nature. Use of edible oils for biodiesel production is unaffordable and illogical due to the high cost of the edible feedstock, an increasing demand for food worldwide and concerns about using virgin forests and arable land for large scale biodiesel production have thrown considerable attention on non- edible oils such as, JATROPHA, as attractive alternative feedstock. Crude Jatropha oil has FFA content up to 15%, which is beyond the acceptable limit for the processing using a conventional base- catalyzed process. Using a conventional homogeneous- catalyzed process to produce biodiesel from the crude Jatropha is technically, economically, and environmentally more challenging than using the same process to make biodiesel from edible oils. It requires multi-step processing, oil pre-treatment, neutralization of the waste homogenous catalyst, water washing of the crude biodiesel and glycerol, and treatment of the waste generated. All these processes are complex and are too inefficient to be considered for industrial scale production of biodiesel. The Problems associated with using a homogeneous catalyzed process to make biodiesel from feedstock with high FFA content have been addressed by using the heterogeneous catalyzed process for the production of biodiesel from the oil containing FFA. This review paper will cover the 2and Generation heterogeneous catalyzed process technology, which is a single step integrated process with a high quality of biodiesel from the crude JATROPHA oil.

KEY WORDS: Jatropha, FFA, feedstock, heterogeneous catalyzed process, trans-esterification, and lipids.

Introduction The ever increasing energy demand of industrial world for industry, transport, agriculture etc., the extra dependency on fossil fuels and consequent pollution problem, day to day depleting oil reserves are major driving force to search for alternative fuel from renewable sources with smaller environmental impact [1]. Biofuels are considered in part, a solution to such issues as sustainable development, energy security and a reduction of greenhouse gas emissions biodiesel, an environmental friendly. Diesel fuel similar to petro-diesel in combustion properties, has received considerable attention in the recent past worldwide [2].

Biodiesel is a biodegradable and non-toxic renewable alternative to diesel fuel that is composed of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats. Biodiesel is increasing in importance because of its benign impact on the environment.

Corresponding Author- Apoorvaa Singh Harcourt Butler Technological Institute, Kanpur 208002 India E-mail: asworthit@gmail.com *Professor Dr. R. P. Singh Oil Technology Oil & Paint Technology Department Harcourt Butler Technological Institute, Kanpur 208002 India *E-mail: rpshbti@rediffmail.com

Biodiesel is produced mainly through the trans-esterification of vegetable oils using short-chain alcohols, typically methanol or ethanol, because these are cheap and readily available from syngas, in which methanol is usually preferred.

Globally the availability of feedstock’s for biodiesel production varies considerably according to the location and climate.

The important factors to be considered in the selection of biodiesel feedstocks are chemical composition of fats and oils, its cost and availability, transport and pre-treatment. Out of the three chemical compositions is important to determine the amount of free fatty acids (FFAs) in oil. In the first generation feedstock various edible oil seeds such as soybean, rapeseed oil, sunflower oil, palm oil, and canola oil have been used for the production of biodiesel. But in today’s generation the high cost of edible feedstocks, an increasing demand for food worldwide and concern about using virgin forest and arable land for large scale biodiesel production have thrown considerable attention on non-edible oils. The use of nonedible oils such as grease, waste oil, JATROPHA oil[3], animal fats, used cooking oil comprises the second generation feedstocks. Among the non-edible oils Jatropha is considered as one of the most advantageous feedstock in terms of economical, sociological and environmental implications.

Jatropha is considered as the main source of biodiesel in the future. Apart from its high content of oil up to 40% it has other numerous advantage as well, such as fast growth, easy propagation, non-competitive to other crops, ability to grow in arid and semi-arid region also its high yield per hector per year. More over jatropha oil has properties similar to that of petroleum diesel. Traditionally transesterification process is used to convert the vegetable oil into biodiesel.

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IJBSTR REVIEW PAPER VOL-1[ISSUE 5] MAY 2013 The transesterification of jatropha oil with methanol, also known as methanolysis, is typically carried out in presence of homogeneous acid or base catalyst. Homogeneous basic catalyst including sodium hydroxide, potassium hydroxide, and sodium and potassium alkoxide have more catalytic activity compared to the acid catalyst. Since acid catalysts are more corrosive than basic catalyst, base catalysts are usually preferred for commercial purposes. Crude jatropha oil can have an FFA contain of up to 15%, which is beyond the acceptable limit for the processing using a conventional base catalysed process [4]. This limitation can be overcome by using the two steps processes involving an acid-catalysed esterification followed by a base catalysed transesterification.

How-ever this two-step process increases the system complexity and raises the cost of producing the biodiesel from Jatropha oil. Using a conventional homogeneous catalysed process to produce biodiesel from crude jatropha oil is technically, economically, and environmentally more challenging than using the same process to make biodiesel from edible oils.

It requires multistep processing, oil-pre-treatment, neutralization of the waste homogenous catalyst, water washing of crude biodiesel and glycerol, and treatment of waste generated- all of which make the purification of the biodiesel to meet the biodiesel quality standards more difficult. The problem associated with using a homogeneous catalysed process to make biodiesel from feedstock with high FFA content have been addressed by using a heterogeneous catalysed process for the production of biodiesel from jatropha oil. Recently heterogeneous catalysts used to catalyse the transesterification reaction to prepare fatty acid methyl esters (FAME) have attracted the considerable attention. There are various heterogeneous catalyst that are being used in the transesterification process which can be divided in to broad categories namely solid acid catalyst and solid base catalyst.

Solid acid catalysts are replacement of the liquid acids and also eliminating the corrosion problem and environmental hazard. Studies have shown that no correlations yet have been established between the acid strength and the catalytic activity.

Few of the examples of the solid acid catalyst are tungsten oxide, sulphonated zirconia and artificial acidic zeolite. Solid basic catalysts have been used a lot as the heterogeneous catalyst with a great success. Various basic catalysts are under study and their catalytic effect on the jatropha oil biodiesel production via transesterification. Various solid basic catalyst studied in this review work are basic zeolite, Nano-sized hydrotalcite particles MgO (magnesium oxide), calcium oxide, and various catalyst supported over alumina. Their initial stage of the use and the modification made to enhance the yield and conversions have also been taken into account. The review suggests that the interest in the heterogeneous catalyst for biodiesel production have been growing since last few years.

Though the use of heterogeneous catalyst have open up a new path way for the biodiesel production, but to sustain the ongoing momentum and advancement at the commercial level more research are need.

ISSN- 2320-6020 1. Second generation feedstock-jatropha oil First generation feedstock contain various edible oil seeds such as soybean, rapeseed oil, sunflower oil etc. using such crops for the biodiesel production could lead to various problems. The high cost of edible feedstocks, an increasing demand of food worldwide and the concern about using the virgin forest and arable land for the large scale biodiesel production have thrown considerable attention on the nonedible oils. Using non-edible oils for the commercialised production of biodiesel have eliminated all the conditions for the fuel verses food as these non-edible oils can nowhere be used for the human or animal consumption. The non-edible oils such as grease, jatropha oil, waste vegetable oil etc. comprises the second generation feedstock, which don’t require special attention for their production. Among various available options as the second generation feedstock we choose Jatropha oil as the key centre of our studies. The highlighting factors of our choice are mainly based on its yield per hector per year (it’s around 5-10 ton per hector per year), its productivity for forty long years and also importantly its high oil content that is around 40-60% of the total oil seed content. Moreover the chemical composition of the jatropha oil [4] is more or less similar to that of other edible oils, which is one of the important factor to be considered which selecting an oil species for the commercialized biodiesel production.

Apart from these major advantages the Jatropha plant can virtually grow anywhere. It does not particularly require fertile land. They are inexpensive as well as abundant in nature.

Adding to these it is an easily grown and propagating with medicinal importance.

Transesterification reaction The vegetable oil can’t be directly used in CI engines because it requires engine modification and is not feasible due to its higher viscosity and low volatility. So the Jatropha oil has to be converted into Jatrodiesel before it could be used for other commercial purposes. Reducing the viscosity of jatropha oil to use it in CI engines there are four common methods: blending them with petro-diesel, pyrolysis, transesterification and emulsification. With pyrolysis and emulsification the engine requires a modification as these process produces heavy carbon deposits and undesirable side products such as alkane, alkene etc. moreover it leads to incomplete combustion. To produce biodiesel, the easiest way is transesterification of the triglycerides using alcohol in the presence of acid/base catalyst. In transesterification reaction the ester group from the triglyceride is detached to form three alkyl esters. This process comprises of three sequential reversible reactions, wherein triglyceride reacts to form diglycerides, monoglycerides and glycerol.

Triglycerides + ROH ↔ diglycerides+

FAME

Diglycerides + ROH ↔ monoglycerides+ FAME Monoglycerides+ ROH ↔ glycerol+ FAME

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IJBSTR REVIEW PAPER VOL-1[ISSUE 5] MAY 2013 The Biodiesel production consist of esterification (or its variation such as glycerolysis, enzymatic or temporary solid catalyst) and transesterification. Traditional esterification method uses methanol with a homogenous acid catalyst such as sulphuric acid to convert FFA into esters. And transesterification uses homogenous base catalyst such as sodium methylate or potassium methylate along methanol to convert to the triglycerides into biodiesel and glycerine. With high % of FFA homogenous catalyst start offering various problems.

Catalyst Catalyst is a chemical that help speed up the chemical process without actually participating in the reaction. There are two type of catalyst typical to any bio diesel production Homogenous and heterogeneous Homogenous catalysts function in the same phase (liquid, gaseous, etc.) as the reactants. Typically homogenous catalysts are dissolved in a solvent with the substrate. Heterogeneous catalysts occur in the different phase than that of the reactants. Most of the heterogeneous are mainly solid that act on a substrate in a liquid or gaseous reaction mixture. The diverse mechanisms for the reaction on the surface are known and it depends on how the adsorption takes place. Total surface area of the solid has an important effect on the reaction rate for the heterogeneous catalyst Homogenous catalysts for biodiesel production have been used for quite a sometime but the uses for the heterogeneous catalysts have been fairly new development.

The process Biodiesel processing involving high FFA content of the oil is comprised of two steps, esterification and transesterification.

During the esterification, a predetermined quantity of the sulphuric acid based on the FFA content of the oil being processed, is added to the oil along with methanol. The reaction temperature is around 65-70 degree Celsius under atmospheric pressure. The important by-product of the esterification process is water which dilutes the conventional homogeneous catalyst thereby hindering the esterification process. Higher yield can be obtained if the water is removed.

The addition of the material such as XYLOL to form azeotropic mixture with water or application of the mild vacuum to the reaction vessel is useful aid in removing the water of the reaction. Transesterification reaction also occurs at the time of the esterification only after esterification has reached its equilibrium. After reducing the FFA of the oil through esterification process to less than 1% the oil goes to the transesterification phase. Direct transesterification –more usages of the catalyst. Higher process cost due to the acid no. issue that has to be fixed so that fuel produced can meet the ASTM D6751 specification. During the transesterification of the oil with high free fatty acids, when the triglycerides are converted to the di-/mono- glycerides, the FFA is converted into soaps. Higher FFA, higher soap production, which goes into the glycerine phase in the settling process or centrifuging.

There is also some residual homogenous catalyst left over

ISSN- 2320-6020 from bio-diesel process that has to be removed. This increases the cost of biodiesel. Thus using homogeneous catalysed process to produce biodiesel from crude jatropha oil is technically, economically and environmentally more challenging.

Heterogeneous catalyst Knowing that catalyst is an important part of a chemical reaction (transesterification here) and having learnt the disadvantages of the conventional homogeneous catalyst, the need for a search for second generation catalyst leads us to heterogeneous catalyst. Comparing heterogeneous catalyst to homogeneous catalyst, heterogeneous catalyst [5] offers a moderate rate of conversion in a continuous process. These are neither water sensitive nor to FFA. They offer a possibility of reuse and are cheaper. Heterogeneous catalyst can be broadly categorized into two categories: solid acid catalyst and solid base catalyst [6]. Solid acid catalyst is substitute of corrosive hazardous conventional liquid acid catalyst. But these catalysts did not an industrial application due to the following major reasons as these catalyst offer slow reaction rate/activity, and adverse side reactions. Adding to its solid acid catalyst must have pores that should be interconnected and available on entire surface. The surface should be hydrophobic to poromote preferential adsorption of oily hydrophobic species on the catalyst surface. The catalyst is deactivated by the strong adsorption of the polar by products [7,8]. The thermal stability of the solid acid catalyst becomes issue at higher temperature (in order to achieve the higher reaction rate). Moreover the correlation between the acidic character and the activity has not been studied yet. The various acid catalysts are: tungsten oxide, sulphonated zirconia, sulphonated saccharides, acid zeolites (artificial) etc.

Solid base catalyst They are comparatively more active even at lower temperature. The various examples of solid base catalyst includes basic zeolites, Nano sized hydrotalcite particle, CaO, MgO. (1) Basic zeolites • The activity of such catalyst depend upon basic site in cation • Basic strength of alkali ion exchanged zeolite increases on increasing positive nature of exchanged cations.

• Exchange can affect the water tolerant behaviour.

• Li containing zeolites have been used for transesterification.

(2) Oxides as catalyst MgO, CaO are extensively used owing to their easy availability, low cost and non-corrosive nature.MgO initially gave low conversion(rate of 18%) due to low surface area but presently 92% conversion was obtained using 12:1 molar ratio, 5% catalyst.Its activity can be further enhanced by loading it on mesoporoussilicas which can be done better in

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IJBSTR REVIEW PAPER VOL-1[ISSUE 5] MAY 2013 suite or via impregnation. Magnesium concentration found to be more dominant over physical properties [9]. KOH loaded over MgO gave high conversion (99.36%). KOH/MgO after calcination was resistant to water and at as heterogeneous catalyst thus displayed better results. K2CO3 and Ca combination have also been used and a high yield was obtained (98%) but it was found to be water sensitive. The catalyst can be reused ^ times, but only after calcination.

Various nano-sized catalyst have been prepared from gammaAl2O3 spheres and Mg(NO3)2.6H2O by urea hydrolysis method. Mg and Al doubled layered hydroxide are formed which on heating gave magnesia rich magnesium aluminate spinel frame work (MgO.MgAl2O4) which was an aggregate of nano sized particle. Comparing the yield of calcined and uncalcined double oxide the yield of MgO.MgAl2O4 was found to be better. The possible reason for this could be high basic strength, high surface area, large pore size and volume and better diffusion of reactant and products over its surface.

Like MgO, CaO can also be effectively used for the biodiesel production after treating it with ammonium carbonate solution followed by calcination at 900 degree celcius. For Jatropha oil it gave a high yield of 93% at optimum temperature and pressure conditions [10]. This catalyst can be used three times with 92% conversion [11]. Various compounds like lithium nitrate, potassium nitrate, sodium nitrate were doped on MgO and CaO and a correlation between the basic strength and the activity have been established [12]. Leaching of catalyst is a major drawback in the case of calcium oxide.

(3) Mixed oxides as catalyst The mixed oxide of Zn and Al offer a high conversion rate of 98.2% but high temperature and pressure condition are required [9]. ZnO loaded on Sr(NO3)2 and Ba(NO3)2 gave unsatisfactory results while the other way round gave up to 99% conversion. The yield can be increased using the THF as a co-solvent. Ca-Zn mixed oxide formed by the coprecipitation has been used as catalyst for the transesterification. It contains Cao and ZnO nano clusters.

They are smaller in size, high surface area. The amount of Zinc in the mixture reduces the size. The catalyst could be used three times.

ISSN- 2320-6020 i.e. calcination at high temperature also makes the process energy intensive. Calcination leads to transformation of the origination compound to a new compound that possesses catalytic-active species. Calcination also enhances the basicity, pore size, and pore volume of the catalyst. This is evidenced from MgO as catalyst which initially did not showed catalytic activity, but after its modification (calcination, etc.), a high yield and conversion was obtained.

Alumina loaded with various compound have been tried as Catalyst and have shown varying results. Alumina loaded with KNO3 and Eu2O3 have shown conversion less than 90%, whereas alumina loaded KF and KOH has shown high yield of 90–91%. On contrary KI/Al2O3 has shown a high conversion of 96% and is near to the specification of EN 96.5%). Zeolites have shown conversion ranging from 85% to 95% and have taken longer reaction time for completion of reaction and thus will need further modification for a higher yield and conversion to meet the international specifications. The energy efficiency and cost aspect of biodiesel is a very important aspect and has to be dealt exhaustively for a catalyst. This has been dealt to some extent in the review paper by examining the calcination temperature and time, reaction conditions (molar ratio, time, temperature, and the type and amount to catalyst used). This is a general assumption and does not necessarily be used for comparison of catalyst to be suitable in industrial point of view. A technique that utilizes supercritical conditions has gained attention for the synthesis of biodiesel where the catalyst is generally not added. A high temperature, pressure, and alcohol volume is needed which makes the process costly. However, the process is tolerant to high FFA and water contents in the feedstock and the reaction gets completed in comparatively shorter time duration.

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CONCLUSION The review indicates a growing interest in the development of heterogeneous catalyst. The emphasis laid on the application of heterogeneous catalyst is mainly to overcome the limitation incurred by homogeneous one. These limitations were mainly: separation of catalyst from reaction mixture, large amount of water generated during washing stage. However, most of the catalysts listed in the review require comparatively longer time duration while some of them need higher temperature conditions. Modification of the catalyst by an additional step,

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