Upgraded Biofuel Diesel Production by Thermal Cracking of Castor

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Upgraded biofuel diesel production by thermal cracking of Castor biodiesel Roghaieh Parvizsedghy, Seyed Mojtaba Sadrameli, and Jafar Towfighi Darian Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01879 • Publication Date (Web): 03 Nov 2015 Downloaded from http://pubs.acs.org on December 4, 2015

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Upgraded biofuel diesel production by thermal cracking of Castor biodiesel Roghaieh Parvizsedghy, Seyed Mojtaba Sadrameli1, Jafar Towfighi Darian Chemical Engineering Department, Tarbiat Modares University, Tehran, Iran

Abstract The continual growth in commercial diesel fuel and more strict environmental legislations have led to immense interest in developing green diesel fuels from renewable biomass. Thermal cracking of vegetable oil, as a method to produce green fuel, is gaining worldwide attention and significance as it is a low-costing process. This study was performed to evaluate the use of transesterified vegetable oil (famous to biodiesel) as feedstock in thermal cracking to overcome limitations of crude vegetable oil thermal cracking, namely low biofuel production yield with high amount of water content. Central composite method was used to design the experiments with reaction temperature and feed flowrate as parameters. Experiments were conducted in a continuous cracking reactor system using castor methyl ester as feedstock. Pre-transesterification improved thermal cracking of vegetable oil by increasing the yield of desirable liquid cracking product (up to 94%) and decreasing water content into a negligible amount. Diesel fraction separated from primary liquid crackate, as the main product of this study, contained very low high-MW FAMEs compared with original feedstock which contained nearly 100% FAME. Thus, diesel fraction produced by this method showed similar distillation curve with typical petrol diesel, unlike biodiesel feedstock. Properties of diesel product, including heating value, kinematic viscosity, cetane index, and cloud point and pour point, were compatible with standard diesel No.2 according to ASTM D975. Thermal cracking may lead to an attractive process to

1

Email: [email protected] Postal Address: Chemical Engineering Department, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran. Phone:0098 21 82884902, Fax: 0098 21 82883381

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produce bio-based diesel. Moreover, thermal cracking could be used to upgrade biodiesel by improving heating value, viscosity and cold properties.

Keywords Thermal Cracking, Biodiesel, Biofuel Diesel, Castor Oil, Fuel Properties 1. Introduction Diesel, as an important product of petroleum refineries, is produced by fractional distillation of C8–C25 liquid cuts from petroleum and it is a common fuel for diesel engines and home heating systems in all around the world [1]. Despite this extensive consumption, renewable fuel sources are being signified as alternative for petrol fuel (e.g. diesel) because of the world’s decreasing petroleum reservoirs and environmental issues [2]. Transesterification of vegetable oil is an alternative technology which leads to biodiesel (fatty acid methyl ester or FAME) production. Biodiesel blended with petrol diesel is applied in engine motors. Some problems associated with biodiesel are its inherent higher price, slightly increased NOx exhaust emissions, low oxidative stability, and high cold flow properties [3]. Moreover, pyrolysis or thermal cracking of vegetable oil represents another technology to produce renewable bio-based products [4-6] with the advantage of low processing costs and compatibility with engines and fuel standards [7]. Despite all the advantages, this method has a low yield of liquid pyrolytic oil with remarkable water content [8-10] and large quantities of long chain fatty acids [5, 7]. Besides, production of very toxic compound of acrolein normally occurs in vegetable oil cracking processes [5]. Therefore, further studies are required to improve this technology and its products. Previous studies on vegetable oil pyrolysis have been typically performed in batch reactor mediums at atmospheric pressure and temperatures ranging 300–500 °C [7, 9, 11, 12] with a narrow property analysis of pyrolytic oil. Vegetable oils are composed of triglycerides, derived from glycerol and three fatty acids. The process of cracking triglycerides occurs in two stages. In the first stage, known as primary cracking, acid species are generated through the decomposition of triglyceride molecules because of the C–O bonds break between the glyceride part and fatty acid chain. In the second stage, known as secondary cracking, degradation of the fatty acids produced in the first stage occurs leading to the formation of hydrocarbons with properties similar to those of petroleum products [5]. In this research, transesterification of vegetable oil is used instead of the primary cracking to separate the glycerin from the backbone of triglycerides. FAME biodiesel decomposition starts at 270 °C and shorter chain length and more saturated molecules have higher thermal stability and tend to decompose later [13, 14]. The most important thermal decomposition reactions occurring with FAMEs at high temperatures are summarized in Scheme 1. These reactions include production of alkanes, alkenes and methyl esters of unsaturated fatty acids (Scheme 1, reaction 1) with low amounts of aromatics at high temperature pyrolysis and short residence time [15]. However, decarboxylation reaction (Scheme 1, reactions 2,3,4) occurs at lower temperature pyrolysis and longer residence time with a


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catalyst [15]. Unlike vegetable oils, FAMEs do not yield significant amounts of fatty acids (Scheme 1, reaction 2) during thermal cracking process [16]. Three later reactions in Figure 1 belong to the pyrolysis of ricin oleate as the main fatty ester in castor biodiesel. Methyl ricin oleate thermal cracking within alkaline medium causes molecules split into heptaldehyde and undecylenate, while caustic oxidation cleaves the double bound leading to octanol-2 and sebacic acid production [17] (Scheme 1, reaction 8). High temperatures heating of castor oil causes a bond between hydroxyl group on the molecule of ricin oleic acid and carboxyl group of another ricin oleic acid leading to lactone like estolides (Scheme 1, Reaction 10). Moreover, polymerization (through Diels–Alder reaction) and formation of diesters (Scheme 1, Reaction 1) leads to the formation of high-MW hydrocarbons. Such heavy molecules formation is not desired in this research and it can be controlled by adjusting reaction conditions. Few biodiesel thermal cracking studies were published in the literature namely thermal cracking of methyl ester of soybean oil and canola oil in a batch reactor with a maximum yield of 88% for the pyrolytic oil in which pyrolytic oil cold properties were analyzed showing improvement compared to biodiesel [16]. This study was aimed at finding optimal (suitable) conditions for a thermal cracking process to improve the yield of bio based diesel at minimum energy and capital investment (e.g., low cracking temperature and no catalysts). Another goal was to determine how this cracking upgrade influences the fuel properties of FAME biodiesel, including density, viscosity, cold properties, flash point, heating value and cetane index. In this survey, castor biodiesel was used for thermal cracking followed by a multistage distillation step to separate three different bio based cuts named as green gasoline, green diesel and heavy cut. 2. Experimental Methods 2.1. Material Refined castor oil was purchased from an oil supply store (Tehran, Iran) with typical compositional analyses given in Table 1. For oil transesterification, methanol (99%) and sodium methoxide (95%) were purchased from Dr. Mojalali company (Tehran, Iran) and Fluka company (St. Gallen, Switzerland) sequentially. Table 1: Composition profiles of castor oil and biodiesel Component Pentadecanoic Acid Palmitic Acid Stearic Acid Oleic Acid Linoleic Acid Linolenic Acid Ricin oleic Acid Gondoic Acid Nervonic Acid

C15 C16:0 C18:0 C18:1 C18:2 C18:3 C18:1-OH C20:1 C24:1


Wt. % 7.38 3.51 3.67 1.38 12.15 1.03 60.81 0.61 9.46

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1. Decomposition of FAME

2. Demethylation of FAME

3. Decarboxylation of Fatty Acid

4. Decomposition and reduction of Ketone

5. Decomposition of Olefins to Diolefins 6. Cyclization of Olefin and Diolefin in Diels-Alder reaction RR’-

-R”’ -R”

7. Aromatization of paraffin, Olefin and Diolefin 8. Decomposition of ricin oleate

9. Dehydration of ricin oleate

10. Formation of Estolide

Scheme 1. Thermal decomposition reactions of castor biodiesel [7, 17, 18]


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2.2. Experimental Setup and Procedures Fatty acid methyl ester was produced through transesterification reaction in a batch reactor. Fatty acid methyl ester was then thermally cracked through a continuous process as shown in Figure 1. The thermal cracking reactor was a cylinder made of quartz with a volume of 0.21 liter. An electrical cylindered furnace externally heated the reactor up to the desired temperature and then the biodiesel was fed by a peristaltic pump to the reactor from top. One dispenser distributed the feed through the reactor uniformly. The tubular reactor was filled with inert pellets with 40% porosity to increase the surface area for the thermal cracking reactions. Gaseous products left the reactor into a collecting container with a jacket of ice around that acted as a flash tank. Thus, non-condensable gas was separated from the condensable fraction and passed out through a flare system followed by a combustion gas relief. Liquid product (bio-oil) was accumulated in the mentioned container. Reactor was purged using nitrogen gas to remove the trapped oxygen and hydrocarbons inside the reactor at the beginning and at the end of each experimental test with a flowrate of 1 lit/min for 10 minutes. Decoking was done by means of airflow (at 1 liter/min rate for 180 minutes) while the reactor remained isothermally at 500 °C. Residence time was found regarding reactor temperature, feed mass flowrate, reactor volume and porosity (shown in Table. 2).

Figure 1. Continuous Thermal Cracking System


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Bio-oil was distilled according to the ASTM D86 standard method [19] with the purpose of fractionating into three cuts as below: - IBP-160 °C named as green gasoline - 160-350 °C named as green diesel - More than 350 °C named as heavy bio-oil Coke was produced during the first pretests but the amount was very low so it was neglected in the mass balance. Therefore, feed was converted into gasous and liquid products. Process at each experiment continued for 8 hours to produce enough products for property analysis. In order to carry out a comprehensive analysis of the thermal cracking process, 3 main dependent responses were considered which were; Bio-oil Yield, Green Diesel Yield, and Green Gasoline Yield. The deviation of bio-oil yield from 100% shows the yield of gaseous products. Yields of the products were defined as: Y ield (wt .%) =

Desired Pr oduct ( g ) *100 Feed ( g )

2.3. Experimental Design According to the literature, the important factors in a thermal continuous cracking system were found to be reactor temperature, pressure and feed residence time which could be replaced and measured by feed flowrate. According to the setup which was operating at atmospheric pressure, temperature and feed flowrate were chosen as independent factors. Some initial experiments were done as pre-tests to narrow the range of the factors for producing a reasonable yield of green diesel which was the aim of this study. Then, a series of experimental tests were conducted to evaluate two reaction parameters using castor oil biodiesel. In this study, multiple responses, including products yield and biodiesel properties were used to determine the effects of selected parameters. A 13 run Central Composite Design was applied to plan the experiments. Central Composite Design can be used to model or optimize any response that is affected by the levels of one or more quantitative factors. Central Composite Design consists of factorial points, central points, and axial points [20]. The experimental tests were also performed in a random order to avoid any “order” bias for the experiments. According to the primary tests, the levels of the reaction parameters were chosen in the range of 450-500 °C and 20-40 g/h. 2.4. Property Analysis Bio-oil was analyzed with Karl-Fischer method to investigate the water content. Green diesel fuel properties including density, kinematic viscosity, cold flow properties, cetane index, heating value and flash point were analyzed based on the ASTM standard methods provided in Table 5. Green diesel was also analyzed using ASTM method D86, a batch distillation process. The sample was continuously boiled and its vapor was condensed and weighed continuously, while monitoring the boiling point with a thermometer.


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The detailed composition of biodiesel and green diesel were characterized by GC-MS analysis using a GC with mass spectrometric detectors (Varian Cp-3800, Saturn 2200). NIST Ms Spectral search program (version 2.0) was used as library to identify the species. The instrumentation for GC analysis used Helium as carrier gas with a flow rate of 1 ml/min. The column oven was programed to be heated with a ramp of 5ºC/min. The mass spectrometric detectors used Ion trapIonization for mass analysis which scanned ranging 10-500 m/z. A VARIAN Capillary Column (VF-5 MS) was used with 30 m length and 0.25 mm inside diameter. The temperature program started at 40 °C for 2 min, followed by a gradient of 5 °C/min to the final temperature of 250 °C and was then held for 20 min. The product identification was performed by matching the retention times with those of standards. 3. Results and Discussion 3.1. Process Conditions Screening The experimental conditions used in the experimental tests and the resulting yields of products are shown in Table 2. Bio-oil yield was in range of 80-93.6% showing a considerable progress compared to using vegetable oil in thermal cracking to produce biofuel. The deviation of the bio-oil yield from 100% shows that non-condensable products were produced. Bio-oil included less than 1% (wt/wt) water which is considerable comparing with high water production during vegetable oil cracking. Higher bio-oil production yield with less water content is superiority of this method. Green diesel yield, as the main product, was in range of 42.5-53.1% and green gasoline yield, as a by-product, was in range of 23-32 %. Green gasoline production as a light cut proves that biodiesel thermal cracking occurs at temperatures in range of 450-500 °C. This can be verified by Wayne Seames et.al experimental data showed that light fraction could be produced only at temperatures ranging from 400 °C to mixture boiling point. In addition to target product, noncondensable gases and a dark viscous heavy cut consisting of heavy-MW hydrocarbons and polymers (Figure 1, Reactions 1, 2, 6, 10) were produced. The statistical significance of each effect was judged with a 95% confidence level. Statistical studies showed a significant difference among green diesel yield values in different experiments. According to these studies, reaction temperature and feed flowrate were two important factors with meaningful impact on products yield. However, the combination of these two factors had no impact on the mentioned results. The average results of the center point, which were repeated 5 times, are reported. Table 2. Yields of the products in the designed experiments Reaction Run No. Temperature, °C 1 457 2 493 3 457 4 493 5 450 6 500 7 475 8 475 Center 475

Feed Flow, g/h 23 23 37 37 30 30 20 40 30

Residence time, sec 63.5 60.5 39.5 37.6 49.2 46 71.3 35.6 47.5

Bio-oil Yield, wt. % 89.1 80 93.6 86.5 92.3 82 87 92.9 88.9


Green Diesel Yield, wt. % 48.7 42.5 53.1 47.6 51.4 44.3 46.6 51.1 48.5

Green Gasoline Yield, wt. % 26.3 30.9 23.1 27.5 23 28.9 29.2 25.3 32

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point

It could be concluded that, the bio-oil yield consistently decreased with increasing temperature, reflecting increasing generation of non-condensable products. In addition, green diesel fraction yield decreased with temperature suggesting more pronounced cracking. Cracking reaction residence time was also studied (reverse relation with feedstock flow rate) as this is another key operating variable affecting both product yield and quality. Increasing the residence time (decreasing the feed flowrate) decreased the yield of bio-oil and green diesel fraction for more non-condensable and lighter molecules generation. 3.2. Properties of the Green diesel Green diesel fuel properties were analyzed to investigate the produced fuel efficiency. The produced green diesel samples obtained from the thermal cracking/distillation units were characterized by their density, kinematic viscosity, cold flow properties and cetane index (Table 3) to study the changes of these properties over the reaction parameters. Statistical studies indicated that produced green diesel in several conditions show significantly different properties. Moreover, both reaction parameters had significant influence on the purified green diesels properties while their binary interactions had minor effect. These properties are dependent on the molecular structure of fuel and differ by changing the experimental factors. Important factors in molecular structure are chain length, degree of saturation, configuration of double bonds, branching, and aromatic content. Increasing reaction temperature and/or residence time means severe cracking and subsequently more cleavage of bonds and more shortening of the chain length. Therefore, by increasing reaction and/or residence time lighter molecules are expected. Impact of the thermal cracking parameters on saturation degree is not found in the literature, however comparison between feed and products imply that increasing the temperature of the reaction and/or residence time could increase the saturation degree of the products [16]. Table 3. Properties of green diesel samples Cloud Pour Run Densitya, Viscosityb, kg/m3 cst Point, °C Point, °C No. 1 866.8 2.1 -33 -36 2 862 1.82 -42 -45 3 872 2.19 -18 -30 4 867 1.93 -33 -36 5 869.2 2.48 -27 -33 6 865 2.03 -36 -39 7 866 1.95 -39 -39 8 870.2 2.73 -21 -30 Center 868.4 2.41 -33 -36 point a Density was measured at 20 °C. b Kinematic viscosity was measured at 40 °C.


Cetane Index 42.32 39.72 42.03 41.32 42.49 40.19 40.89 41.82 41.06

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Hydrocarbon density increases with chain length (number of carbon atoms) which happens by increasing the cracking temperature and/or residence time. According to the response surface, green diesel density decreased with increasing the temperature and/or residence time. Hydrocarbon viscosity increases with chain length (number of carbon atoms) and degree of saturation. Moreover, some factors such as double bond configuration affect viscosity (cis double bond configuration giving a lower viscosity than trans) whereas double bond position has insignificant effect on viscosity [21]. According to the response surface, kinematic viscosity of the green diesel decreased with increasing the temperature and/or residence time for generation of shorter chain molecules. Moreover, viscosity variation in the lower residence time (near to 40 g/h) is negligible. Biodiesel performance at cold weather is an important quality criterion. The key parameters for low temperature fuel applicability are cloud point and pour points. Diesel standards do not include minimum values for cold behavior as it relates to the weather of the area in which the fuel is used but the values should be reported (Table 5). Lower cloud point and pour point result better cold flow properties, which could be also applied in cold weather. Cloud point refers to the temperature below which wax in diesel or bio-wax in biodiesel forms a cloudy appearance. Pour point refers to the temperature at which the fuel becomes semi solid and loses its flow characteristics. One of the major issues for biodiesel usage is poor cold properties, indicated by relatively high cloud points and pour points. Unsaturated fatty compounds have significantly lower melting points than saturated fatty compounds. Thus, biodiesel fuels derived from fats or oils with minor amounts of unsaturated fatty compounds display higher CPs and PPs [22]. Also, cloud point decreases with branching and lower chain length [23]. Green diesel cold flow properties decreased with increasing the temperature and/or residence time as shrinkage of chain and branching increased. Cetane number is a measure of the ignition delay of a diesel fuel. A high cetane number helps to ensure short interval between fuel injection and its burning. Cetane number is mostly significant in low temperature starting and even combustion [24]. The Cetane Index is useful for estimating cetane number when a test engine is not accessible for determining this property directly. Cetane number relates to the structure of the molecules and it increases with increasing the chain length, increasing saturation, and decreasing branching. Aromatic compounds have low CNs [22]. Therefore, CN is expected to decrease by increasing the temperature and/or residence time of cracking. As expected and according to the response surface, CI of green diesel decreased with increasing the temperature and/or residence time as the shrinkage of chain chanced more and chain length decreased. Indeed, at high temperature and/or high residence time, more aromatic was expected to produce which led to lower CN. 3.3. Chemical Composition of green diesel Sample chromatograms of the original castor biodiesel feedstock and green diesel are provided in Figure 3; showing the occurrence of alcohols, ketones, aldehydes, FAMEs and alkenes in green diesel. The major fraction of green biodiesel was cyclic compounds. This means that cyclization played an important role in the thermal cracking of castor biodiesel. Most probably, it is because of diolefins production through dehydration of ricin oleate (Figure 1, Reaction 9) which enhances Diels-Alder reaction to produce cyclic hydrocarbons. Besides, the predominance


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of alcohols and ketones among the composition of green diesel indicated that deoxygenation reactions [decarboxylation/decarbonylation/deketenization reactions (Scheme 1, Reactions 3,4)] were more common. A remarkable fraction of green diesel relates to FAMEs. This means the ester bond in FAMEs appeared to survive cracking. However, most of the existing FAMEs were higher molecules indicating that a high fraction of castor biodiesel do not participate in the decomposition reactions and just go through isomerization and dehydrogenation. The new high-MW FAMEs were unsaturated with two double bonds suggesting the liberation of a significant quantity of H2 upon dehydrogenation. The produced hydrogen might enhance dehydration of ricin oleate or hydrogenation of other hydrocarbons. Low fraction of aromatic compounds in the composition of green diesel showed that aromatization occurred as minor process path through thermal cracking of castor biodiesel. Hydroxy fatty acids were not appeared in the composition of green diesel meaning the decomposition of ricin oleate through C-C bong cleavage. This product distribution (of GC-identified products), enriched by cyclic alcohols, ketones and aldehydes is unique compared to previously known cracking routes. Details of the identified compounds were shown in Table 4.

Table 4. Composition profile of green diesel Compound FAME C8-C16 FAME C16-C21 Total FAME Olefin Ketone and Aldehyde Alcohol Aromatic Unidentified Total Saturated Total Unsataturated Total cyclic

% Area 8.1 17.4 25.5 4.5 13.8 35.5 1.7 18.9 6.5 64 48.5


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Figure 3. Sample chromatograms of green diesel and original castor biodiesel feedstock

3.4. Characterization of green diesel Additional property analysis was done to investigate green diesel produced in the optimized conditions (Table 5). Heating value (investigated by ASTM D4868) of fuel indicates the


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economic efficiency of diesel fuel. A drawback of biodiesel is its low heating value in comparison with petrol diesel. High heating value of green diesel (44.240 Mj/Kg) showed a significant change comparing with the high heating value of castor biodiesel (37.9 Mj/Kg). The presence of oxygen lowers the heat content as exposed by the heating values of biodiesels, which are 9%-13% lower than those of conventional diesel fuels on a mass basis [7]. Therefore, deoxygenation of FAMEs that happens during the thermal cracking of castor biodiesel led to compounds with higher heating value. Thus, heating value of biodiesel was improved noticeably during the thermal cracking and green diesel was compatible with diesel engine. In addition, high cold flow properties are the other drawback of biodiesel meaning that this fuel is not proper for cold weather conditions. Cloud point and pour point of biodiesel are mostly above zero [22].The presence of unsaturated and/or branched compounds lower the cold properties of fuel. Winterization of FAMEs as a method to improve cold behavior of biodiesel leaves a mixture with higher content of unsaturated fatty esters and thus lowers CP and PP. The use of branched esters such as iso-propyl instead of the methyl esters is another approach for improving the low-temperature properties of biodiesel [22]. Production of unsaturated FAMEs and branched compounds during thermal cracking of castor biodiesel lowered the cloud point and pour point. Thus green diesel exposed highly improved cold flow properties. Unlike its worthy cold flow properties, castor biodiesel shows very poor kinematic viscosity. Kinematic viscosity is not a downside of biodiesel for most of the oils it is produced. Viscosity increases with chain length and degree of saturation [22]. This process decreased the high kinematic viscosity of the castor biodiesel by shortening the size of molecules so that they could easily slide past one another. In addition, unsaturation of FAMEs helped lowering kinematic viscosity. Kinematic viscosity of the castor green diesel is still approved by the criteria of ASTM D975. High flash point means burning issues of the fuel and very low flash point means less safety of fuel storage. In this process, flash point was decreased near to the borderline of standard amount. High cetane number is one of the advantages of biodiesel, which is higher than that of refinery diesel. Cetane number decreases with increasing unsaturation and decreasing chain length [22]. Besides, cyclic compounds expose lower CN [25]. Cetane number of castor biodiesel decreased during thermal cracking as cyclic compounds with unsaturated FAMEs and alkenes were produced. Thus, green diesel showed lower cetane index but it was still compatible with standard value. A major issue with biodiesel is low oxidation stability, which refers to the ability of the fuel to resist chemical changes during long-term storage. The reason for autoxidation is the presence of double bonds in the chains of fatty compounds which lead to hydroperoxides formation. Intermolecular cleavages change hydroperoxides to aldehydes, acids, and other oxygenates. However, the double bonds may also be prone to polymerization-type reactions. Therefore Acid value and viscosity of biodiesel increase during oxidation [3]. Castor biodiesel contained of 85.4% (Table 1) unsaturated high-MW FAMEs which decreased to 17% (Table 4) through thermal cracking. Moreover, presence of low-MW deoxygenated compounds in green diesel seems to increase fuel stability.


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Table 5. Properties of castor biodiesel and green diesel D93

Green Diesel 55

Castor Biodiesel 190

360, max

D1160

330

390

D445

1.9-6.0

D445

2.2

14

D976 ------D2500 D97

------47min Report Report

-----D613 D2500 D97

42 -------29 -45

------50 -14 -30

Property

ASTM D975-08a

Flash Point, °C Distillation Temperature, °C (90% vol. Recovered) Kinematic Viscosity, mm2/s Cetane Index Cetane Number Cloud Point, °C Pour Point, °C

52, min

D93

93, min

282-338

D86

1.9-4.1 40 min ------Report Report

ASTM D6751-12

The boiling range distribution of green diesel provides an insight into the composition of product related to the thermal cracking process. The distillation curve (ASTM D86) of the green diesel produced in the optimized reaction conditions and a typical petrol diesel (Figure 4) were very similar. This indicated that thermal cracking of castor biodiesel produced lighter molecules with less boiling points and the achieved product was very similar to the petrol diesel from the distillation perspective. Actually, the main reason of proximity between the properties of diesel and green diesel (as shown in Table 5) is the similarity of their distillation curve, which means similar distribution of molecular weight. FAME biodiesel could not be distilled in the atmospheric conditions as the heavy molecules crack before their boiling point. The fatty acid chains in biodiesel are mainly comprised of straight chain hydrocarbons with 16 to 18 carbons that have similar boiling temperatures. So, biodiesel exhibits a narrow boiling range. Distillation curve of biodiesel was created in reduced pressure (as standard method of ASTM D1160) and is shown in Figure 4. Biodiesel is composed of much heavier molecules in comparison to the diesel as it is almost methyl ester of fatty acids, which have high boiling points so FAME biodiesel and petrol diesel differ significantly from distillation perspective which lead to differences in the properties of these products.

450 400 350 Temperature (°C)

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Green Diesel (D1160)

300 250 200

Typical Diesel No.2[24]

150

Castor Biodiesel

100 50 0 0

20 40 60 80 Distillation Volume Fraction (%)

100

Figure 4. Distillation Curves of castor oil biodiesel, petrol based diesel and green diesel


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Analyzed properties of the produced green diesel showed that thermal cracking of the biodiesel was a viable process as these properties were approved by the criteria of ASTM D975. Moreover, most of the examined properties of the produced green diesel show improvement, in comparison with biodiesel, through this process. 4. Conclusion Thermal cracking was applied to castor oil methyl ester for feasibility investigation of this method to produce bio-based fuel. Cracking temperature and feed flowrate were studied as two main process parameters, which had significant impact on the yields and properties of the products. Replacing vegetable oil with its methyl ester was recognized as an enhanced process yielding more bio-oil. Moreover, fractionated diesel cut exposed properties fell in the limits specified of standard diesel No.2 by ASTM D975. Diesel produced by biodiesel thermal cracking showed improved properties compared to feedstock. Therefore, biodiesel upgrading could be achieved with this method. Despite the advantages of biodiesel thermal cracking, additional studies are required for economical investigation of this technology because of material loss by heavy compound production in liquid bio-oil. Acknowledgement Authors are greatly appreciating the support extended to this study by Dr. Hamid Seifi who responded promptly to the requests and brought improvement by his suggestions. Financial support from Tarbiat Modares University is also acknowledged. References 1.

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Upgraded Biofuel Diesel Production by Thermal Cracking of Castor

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