thermophysical characterization of the seeds of invasive chinese tallow tree: importance for biofuel...

Thermophysical Characterization of the Seeds of Invasive ChineseTallow Tree: Importance for Biofuel ProductionLaura Picou and Doran Boldor*

Department of Biological and Agricultural Engineering, Louisiana State University Agricultural Center, 149 EB Doran Building BatonRouge, Louisiana 70803, United States

*S Supporting Information

ABSTRACT: The limited supply of traditional fossil based fuels, andincreased concern about their environmental impact has driven theinterest in the utilization of biomass based energy sources, includingthose that are underutilized or otherwise nuisance species such asChinese tallow trees (Triadica sebifera [L.]). This species is a prolificseeds producer, and this paper shows that they contain more than 50%lipids by mass that are suitable for conversion into biodiesel. Wepresent here, for the first time, the seeds’ thermophysical propertiesimportant for biofuel production. The seeds were characterized usingthermogravimetric analysis (TGA), differential scanning calorimetry(DSC), and ultimate analysis; their thermal conductivity, thermaldiffusivity, and specific heat were determined. The characterizationresults were correlated to fatty acid composition and lipid content for whole seeds and individual layers, as well as to the protein,hemicellulose, cellulose, and lignin content. The TGA analysis indicated the presence, in addition to lipids, of hemicellulose,cellulose, lignin, and proteins, depending on the layer analyzed. Thermal conductivity and specific heat were, respectively 0.14 ±0.007 W/mK and 3843.5 ± 171.16 J/kgK for wax, 0.20 ± 0.002 W/mK and 2018.7 ± 5.18 J/kgK for shells, 0.13 ± 0.0 W/mKand 1237 ± 3.15 J/kgK for internal kernel, and 0.13 ± 0.000 W/mK and 2833.9 ± 104.11 J/kgK for whole seeds. Theseproperties and characterization method can be further used in engineering analysis used to determine the most optimumprocessing method for production of biofuels from this feedstock.

■ INTRODUCTION

In 2005, the Energy Policy Act was signed into law, whichmandates that by 2022 the United States should produce 15billion gallons of biofuels, 4 billion gallons of noncorn ethanolbiofuels, 1 billion gallons of biomass-based biodiesel, and 16billion gallons of cellulosic biofuels produced from wood,grasses, or nonedible plant matter.1 Such interest in theproduction of biofuels stems from increasing environmentalconcerns as well as the depletion of current supplies of fossilfuels. Rising oil prices due to high energy demands andincreased efficiency in the production of these biofuels has ledto bioenergy becoming more competitive with traditional fuelsources.2

While there are many sources for alternative energyproduction, biomass based sources are the only type that isdirectly convertible into a refined liquid fuel (mainly as ethanoland biodiesel) for use in unmodified vehicles,3 with reducedemission profiles.4 However, a major concern exists relative tothe use of agricultural resources for the production of biofuels.5

Consequently, for an alternative fuel to be considered viable, itmust be environmentally sustainable as well as have minimalimpact on world food supply and agricultural land. Materialssuited to this ideal include lignocellulosic based crops suitablefor conversion into bioethanol, biomethanol, and bio-oil such assweet sorghum, energy cane, woody biomass; whereas high oil

content nonfood seeds (Jatropha curcas, etc.) or algae aresuitable for conversion into biodiesel.One of the most interesting potential materials, that does

neither compete with the food market nor requires primeagricultural land, are the seeds of the Chinese tallow tree(CTT). The CTT seeds are of particular importance as they arenot a food crop and can be grown on fields not currently usedfor agricultural production.1,6 Potentially, the branches andtwigs leftover after harvesting could also be used as analternative wood fuel source.The Chinese tallow tree (Triadica sebifera [L.]) was

introduced to the United States by Benjamin Franklin due toits physical appearance, pest resistance, and colorful fall leaves.7

However, this plant has become a subtropical invader in theSoutheastern U.S. due to its ability to naturalize a variety ofhabitats.6c Due to its success as an invasive species and itsresistance to many known elimination methods, alternativeusage of the species has been suggested, including oil forvarnishes and paints as well as soap and biofuels.6a,7 CTT is oneof nature’s most prolific producers of renewable hydrocarbons,

Received: June 11, 2012Revised: August 20, 2012Accepted: September 26, 2012Published: September 26, 2012

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estimated to yield the equivalent of 500 gallons of fats and oilsper acre per year, far exceeding the yields of traditional oil seedcrops.6b,8 CTT seeds are unusual in that they contain both ahighly saturated fat and a highly unsaturated oil,6a with totallipids content exceeding 40%.9 The lipid content is distributedalmost equally between the external vegetable tallow coatingand the seed’s kernel, and both fractions were deemed suitablefor conversion into biodiesel,8 however, a detailed analysis ofthe fatty acid composition was not provided. Two recentstudies were published in the literature estimating the lipidcontent of these seeds10 and their storage stability,11 but noinformation was available in the published literature estimatingthe lipid contents and fatty acid composition of each fraction,their corresponding elemental composition, and thermalproperties important for processing operations. These missingthermal properties include not only thermal conductivity,diffusivity, and specific heat, but also information pertaining totheir behavior during thermal decomposition and thermal stresscycling via thermogravimetric analysis (TGA) and differentialscanning calorimetry (DSC), respectively. These properties arecritical to identify the thermal stability and behavior, as well asmaterial composition.TGA allows investigations of pyrolysis and combustion

behavior of fuels12 by measuring the amount and rate of changein the weight of a material as a function of temperature or timeunder a controlled atmosphere.13 The application of processingtechnologies using biomass feedstocks for energy purposesrequires knowledge of the thermal behavior of these fuels andreliable kinetic data describing their thermal decompositionbehavior.14 For lignocellulosic materials, like the internal shellof CTT seeds, the thermal degradation characteristics arestrongly influenced by their chemical composition: cellulose,hemicelluloses, and lignin.14,15 DSC is the most popularthermal analysis technique,16 designed to measure endothermicand exothermic transitions as a function of temperatureincluding a range of thermal events including melting,crystallization, glass transitions, curing reactions, and decom-position reactions. As with TGA, the DSC thermolytic behaviorof biomass materials is dependent on its chemical compositionand structure.17 While a large number of studies have beenperformed on the thermal characterization of flours andstarches, none have been on the thermal properties of CTTseeds.Specific heat capacity,18 thermal conductivity (the ability to

conduct heat), and thermal diffusivity (the ability of a materialto conduct thermal energy relative to its ability to store thermalenergy) are also important properties required for processdesign calculations. Thermal conductivity and specific heatvalues of agricultural materials including a range of grains and

seeds do exist literature,19 but no data exists with respect toCTT seeds.The study presented here was designed specifically to fill in

these knowledge gaps about the thermo-physical properties ofCTT seeds, a feedstock that has the potential to not onlycontribute significantly to the emerging US bioeconomy, but inthe same time, alleviate an important environmental concernrelated to the invasiveness of this particular species. As tallowtrees are extremely prolific seed producers, and the majorinvasive pathway is via seed dispersal, seed collection andutilization in biofuel production would significantly reducepropagule pressure and mitigate ecosystem damages in thesoutheastern U.S. In this respect CTT seeds were analyzed viaTGA, DSC, ultimate analysis of each layer, gas chromatographyof the oils, and a thermal conductivity probe, in order todetermine material composition and heating characteristics.

■ MATERIALS AND METHODS

CTT seed samples were harvested by hand from trees local tothe Baton Rouge area during the months of October andNovember 2010 and placed in 2 gallon plastic storage bags.Seeds’ moisture content was homogenized by thorough mixingprior to storage. Seeds were kept at −20 °C until testing, atwhich time they were allowed to return to room temperatureand then separated by hand into their component layers(Figure 1). The percentage mass weight of each layer wasmeasured in triplicate. For TGA and DSC analysis, each layerwas ground with a mortar and pestle. For thermal conductivityanalysis, a fine grade food mill was utilized to grind the shell,kernel, and whole seed to aid in compression of the materials.The external wax of the seed was sufficiently broken up duringremoval such that grinding was not necessary prior to thermalanalysis.Each layer, as well as the ground whole seed samples, was

process through a Soxhlet apparatus with hexane as solvent for10 h in duplicate to establish maximum oil content. Therecovered oils (Figure 1) were analyzed for fatty acidcomposition. Thermal analysis of the CTT seeds, both beforeand after oil extraction, was performed using a Thermogravi-metric Analyzer 2950 (TA Instruments, New Castle, DE).Sample holder used was the bottom of an aluminum hermeticpan. Equipment setup and calibration was performed accordingto manufacturer’s instruction. Analysis was performed in thepresence of nitrogen gas, with a temperature ramp of 10 °C permin up to a final temperature of 600 °C. TGA and differentialthermogravimetric curves obtained during pyrolysis were usedto determine combustion behavior and some characteristicstemperatures such as initial decomposition temperature (Tin),

Figure 1. Left: Component layers of CTT seeds. A. External wax, B. Shell, C. Internal kernel. D. Whole Seed, E. Cross-section. Right: Oil samplesfollowing extraction (from left: whole seeds, kernel, shell, wax).

Environmental Science & Technology Article

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peak temperature (Tmax), and total weight loss up to 600 °C. Atheoretical TGA curve was developed20 using a weighted masspercent average for each layer.21

DSC analysis of the seeds, both before and after oilextraction, was performed using a differential scanningcalorimeter 2920 (TA Instruments, New Castle, DE).Calibration was performed using a sapphire disk for hermeticpans (part no. 915079.902, TA Instruments, New Castle, DE).Purge gas used was nitrogen, while cooling was performedusing liquid nitrogen. Three heating/cooling cycles (10 °C/min) were performed over a temperature range of 0−200 °Cunder an inert nitrogen atmosphere. Tests were performed on awhole seed sample, the kernel, the wood shell, and on the outerwax. A theoretical DSC curve for the whole seed was created20

based on weighted mass percentage of each layer.21

Ultimate analysis was performed to determine total nitrogen,carbon, hydrogen, phosphorus, and sulfur. Total nitrogen andcarbon were quantified with a CHN elemental analyzer(Elementar, Vario EL III) in triplicate. Phosphorus and sulfurwere analyzed using microwave digestion coupled with ICP-

OES with axially viewed plasma. For full procedural detailsplease see the Supporting Information. Oxygen content wascalculated from the mass balance as residue. Results areexpressed as a percentage of the total composition. Analysis ofthe fatty acid methyl esters using GC-MS was performed induplicate in order to characterize the lipids present in eachcomponent layer of the CTT seeds. Experimental conditionswere as described in literature.22 Full procedure is described inthe Supporting Information. A KD2 Pro thermal propertiesanalyzer (Decagon Devices, Pullman, WA) was used tomeasure the thermal conductivity, specific heat capacity,thermal diffusivity, and thermal resistivity of selected materialsin triplicate. Full procedural details are provided elsewhere.20 Avariety of other materials were tested for comparison with theCTT seeds. Statistical analysis was performed using MicrosoftExcel 2007 with Analysis ToolPak add-in using two-sample ttests assuming equal variance and single-factor ANOVA.

Figure 2. TGA (dotted lines) and DTG (solid lines) thermal curves of CTT seed component layers before (top) and after (bottom) lipid extraction.S, W, and K refer to peaks in shell, wax, and kernel layers, respectively . P1 is indicative of a group of residual solvent peaks after lipid extraction. Theprime (′) sign is indicative of peaks after extraction.



■ RESULTS AND DISCUSSIONThermogravimetric Analysis. Pyrolysis is important in

the thermal conversion process for combustion and gas-ification.23 The TGA thermal curve (weight loss) and derivativethermogravimetry (DTG) curve are shown in Figure 2, withmain points summarized in Table 1, where Tin is pyrolysis

onset, Tmax is main decomposition temperature, d%m/dtmax ismaximum rate of decomposition, and total weight loss ispercentage of original sample that has decomposed. Massbalance and percentage of lipids and waxes in each layer is alsodescribed (Table 1). The kernel was found to form the largestpercentage of the seed on a mass basis. For TGA analysis, notenough repetitive scans were performed to determine thedeviation associated with the procedure as all scan repetitionsyielded identical results to those first obtained.Three main weight loss steps appear in the DTG profiles

(Figure 2). The first weight loss step within the 100−150 °C(peak S1) temperature range accounts for moisture release forabsorbed and bound water, while the second and third weightloss steps within 200−500 °C correspond to volatile matterrelease (see W1, S2, S3, W2, K1).12b,24 Total weight loss asdescribed in Table 1 is the total percentage of volatiles presentin the materials. The shell had the highest level of materialremaining following pyrolysis. This material present afterpyrolysis is ash and residual lignin and is indicative of theshell having fewer volatile components and more fixed carbon.The wax (term used due to appearance only) had the highest

rate of decomposition (d%m/dt)max and the greatest weightloss of the materials studied. Its TGA curve is very similar tothat indicated by other hydrocarbon waxes such as paraffin wax,carnauba wax, and beeswax.25 Pyrolysis of the wax starts ataround 195 °C (W1 in Figure 2) and continues with itsmaximum rate and corresponding derivative peak around 400°C (W2) (Table 1). The kernel, on the other hand, startsdevolatilizing at slightly higher temperatures (235 °C) and hasa peak at 416 °C (K1). In the shell DTG profile, the first peak(S1) is due to the release of water. The second peak around275 °C (S2) most likely represents the decomposition ofhemicelluloses with the peak around 350 °C (S3) correspond-ing to the decomposition of cellulose.12b The flat trailingsection corresponds to the decomposition of lignin. Compar-ison between the profiles shows that wax begins to devolatilizeat lower temperatures than the shell and kernel, indicatingweaker bonds between its macromolecular constituents.12b Thesharp peak in the wax around 400 °C (W2) is most similar tothe DTG curve of pure cellulose,26 but in this case it indicatesthe additional presence of diglycerides and triglycerides thathave the same decomposition peak at 400 °C.27 The singlepeak present in the curve for the CTT kernel (K1) is at ahigher temperature than (W2) because it has a lot of proteins

containing stronger S and P-bonds, making it more stable thanthe fatty acids present in the wax layer. Other importantcontributions to peak K1 come from starches,24 while the slightbump present prior to the sharp peak in the DTG curve for theCTT wax (W1) is likely due to the presence of somehemicelluloses.28 Reports indicate that hemicelluloses areknown to decompose at 225−325 °C and cellulose at 325−400 °C.29 The peaks in the DTG curve for the CTT shellfollow this trend precisely. As lignin decomposes gradually overa temperature range of 250−500 °C, without specificcomposition data, it is difficult to determine if lignin acts as amajor component in the pyrolysis of CTT seeds.30 Volatiliza-tion of other minor constituents is also likely occurringsimultaneously.To confirm the impact of lipids on initial TGA analysis, a

second analysis was performed following oil extraction (Figure2 bottom). Although the peaks occur at lower temperaturesthan in the initial test (due to greater separation of componentswithin the samples allowing for lower pyrolysis temperatures)they may be correlated with those that occur in Figure 2 (top).Peak (P1) in all three layers (up to 150 °C) is attributable toboth water and residual hexane from the extraction step. Forthe DTG curve of wax following extraction, the peak value(W2′) is much lower than the peak for the original DTG curve(W2) and shifted toward lower temperatures corresponding tocellulose decomposition. This confirms that the peak (W2) inFigure 2 (top) is the result of a combined effect of both lipidsand cellulose.As the shell still contains 2 main peaks (S2′) and (S3′), the

peaks (S2) and (S3) may be considered entirely due to thepresence of hemicellulose and cellulose with minor contribu-tions resulting from the 11% lipids present in the shell layer(S2/S2′ and S3/S3′ peaks occur at the same temperature). Asthe kernel still contains one peak primarily (K1′) shifted tolower temperatures, the original peak (K1) is confirmed asbeing primarily due to the presence of starch, protein, and lipidswithin the kernel layer. The wax peak is much lower than thatof the kernel, indicating that, percent-wise, the wax had morelipids than the kernel, lipids that disappeared after theextraction step. Compositional analysis (hemicellulose, cellu-lose, and lignin) for each layer may be of interest in futurestudies. Overall, TGA following oil extraction allows us to moreclearly see the effects of hemicelluloses, cellulose, and lignin onthe thermal properties of CTT seeds.The overlap between the experimentally found TGA and

DTG curves for the whole CTT seed and the theoretical TGAand DTG curves found by the additive rule of the threecomponents of the seeds (based on composition % in Table 1)indicates a synergy between the component layers duringpyrolysis (Supporting Information Figure S1 a and b). Biomassis a multicomponent material so its decomposition occurssimultaneously, which complicates determination of individualcomponents from the whole seed TGA (SupportingInformation Figure S2). Theoretical and experimental profilesof the whole seed virtually overlap with only slight deviationsthat may be due to differences in percentage of eachcomponent layer present. Linear statistical analysis oftheoretically derived values versus the experimentally measuredvalues indicate a very high correlation (r2 = 0.999); similarresults may be obtained for their derivatives (r2 = 0.983),confirming the validity of the addition rule. Experimentally andtheoretical DTG curves for whole seeds (SupportingInformation Figure S2), peak 1 and 2 are due to hemi-

Table 1. Pyrolysis Characteristics and Percent Compositionof Each Layer As Well As Percentage of Each Layer That IsLipids of CTT Samples

Tin (°C)Tmax(°C)

(d%m/dt)max

total weightloss (%) upto 600 °C)

percentmass of

whole seed(%)

lipidsandwaxes(%)

kernel 235.33 416.21 0.85 90.54 37.13 61.82wax 195.35 408.12 1.88 95.93 30.89 87.56shell 259.43 346.97 0.59 59.50 31.98 11.28



celluloses31 and cellulose, respectively, while peak 3 is due tolipids, proteins and starch. It is notable that the peaks are not assharp as for individual components, which is to be expected dueto the varying compositions in the different layers.Lipid Composition and Ultimate Analysis. As material

composition plays an important role in the thermal effects

observed in thermal analysis curves, the ultimate analysis ofeach component layer as well as a lipid compositional analysiswould allow further correlations with the thermal behavior ofeach layer. Other analyses concerning the fatty acidcomposition of the oil extracted from the whole seed may befound in literature for a variety of extraction methods,10,11,32

Table 2. Fatty Acid Methyl Esters of CTT Seed Oil for Each Component Layer and Elemental Composition As Percentagesa

compound name wax (87.56%) kernel (61.82%) shell (11.28%) whole seed (56.55%)

lauric acid (C12:0) 0.00 0.00 0.16 0.00palmitic acid (C16:0) 62.57 9.84 19.81 31.08heptadecenoic acid (C17:1) 2.15 5.90 9.98 5.27stearic acid (C18:0) 0.54 0.00 0.00 0.75oleic (C18:1) 18.01 16.98 5.48 11.79linoleic acid (C18:2) 0.64 18.65 0.82 2.78linolenic acid (C18:3) 0.00 0.00 0.51 0.43gamma-linolenic acid (C18:3) 0.00 10.93 0.00 4.62arachidic acid (C20:0) 1.35 3.72 6.92 3.01erucic acid (C22:1) 14.21 30.40 53.62 36.95docosadienoic acid (C22:2) 0.50 1.86 1.43 1.01nervonic acid (C24:1) 0.00 1.55 0.58 2.22tetracosanoic acid (C24:0) 0.03 0.00 0.00 0.03docosahexaenoic (C22:6) 0.00 0.16 0.68 0.06Elemental Components (95% Confidence Intervals Shown for C, H, N, and O)carbon (C) 68.9 ± 0.51 64.2 ± 2.39 43.0 ± 1.28 57.9 ± 2.66hydrogen (H) 10.9 ± 0.09 9.1 ± 0.05 6.3 ± 0.55 8.5 ± 0.38nitrogen (N) 0.2 ± 0.02 4.4 ± 0.26 0.3 ± 0.09 1.4 ± 0.18oxygen (O) 19.8 ± 0.58 21.4 ± 2.53 50.4 ± 1.08 31.8 ± 2.84phosphorus (P*) 0.19 0.89 0.01 0.32sulfur (S*) 0.01 0.02 0.00 0.01

*Note: Single point measurements. aLipid mass percentage in each layer is in parentheses in column heads.

Figure 3. DSC melting and crystallization curve for CTT seed wax, shell, kernel, and whole seed samples. Top inset: wax after lipid extraction.Bottom inset: glass transition region.



but no published studies were found concerning thecomposition of each layer of the seeds (shown here in Table2). As some elements are relatively minor constituents, theymay not necessarily show up during analysis of the whole seed.Palmitic acid, which is solid at room temperature, was presentin all layers, but forms a major component of the wax andwhole seed with a decreased percentage in the shell and kernellayer, respectively. Oleic, linoleic, and γ-linolenic acids, whichare unsaturated fatty acids and liquid at room temperature, arethe main components of the kernel layer (Figure 1 and Table2). Erucic acid is present in large quantities in all layers, havinga majority partition in the shell lipids, and almost a third of thekernel lipids layer. This particular fatty acid renders the lipids inCTT seeds unsuitable for human consumption, and is alsopresent in rapeseeds in large quantities. Other fatty acids arealso present in lesser quantities in each component layer. Bydetermining the fatty acid profile for each layer, for futureprocessing, we may determine which layer is of the highestvalue and perform oil extractions on that layer specifically,which could possibly alter current processing methods.An ultimate analysis of the samples prior to lipid extraction

was also performed for each of the sample layers. Ultimateanalysis was performed to determine the percentages of carbon,hydrogen, nitrogen, phosphorus, sulfur, and (by taking thedifference from 100%) oxygen (Table 2). This analysis revealedthat each of the sample layers is primarily composed of carbonand oxygen. Nitrogen is almost entirely represented in thekernel layer in the form of proteins and amino acids. The valuesseen in the whole seed sample are approximately the average ofeach of the component layers, based on the almost equaldistribution of each layer in the whole seed sample. Thephosphorus and sulfur components form trace constituents ofthe CTT seeds. From this table, the empirical formula for CTTseeds was extrapolated by dividing the percent composition ofeach element in the seeds by its atomic weight, and was foundto be C4.82H8.47N0.10O1.99S0.00P0.01. This analysis may shed lighton future studies for determining the fuel quality of CTT seeds.Differential Scanning Calorimetry. In the DSC scans

shown in Figure 3 (for all four kind of samples), exothermicpeaks (upward) and endothermic peaks (downward) indicatefirst order transitions such as melting and crystallization,whereas second-order transitions such as glass transitions showsas a stepwise change.13 The samples’ thermal history was“removed” by cycling the heating/cooling (Figure 3 depicts thesecond heating cycle).The wax DSC curve shows characteristics similar to those

found in DSC curves of hardened oils and fats that start to meltat higher temperatures (i.e., solid at room temperature) thanoils that are liquid at room temperature such as linseed oil, andare completely melted by 50 °C (peak (c) Figure 3). In oils and

fats, the melting characteristics are caused by the mixture offatty acids present in the mixture as well as proportions ofwater.33 The known lipid composition (Table 2) allowsidentification of specific moieties responsible for melting andcrystallization characteristics identified in the thermogram.For wax, three peaks are present during the heating phase

and two peaks during the cooling phase. Peaks “a” (13.95 °C),“b” (24.52 °C), and “c” (51.50 °C) are representative ofmelting (endothermic transition), as heat breaks the material’scrystalline structure. Peaks “d” (9.27 °C) and “e” (25.31 °C)are typical for crystallization during cooling, and have slightlylower temperatures than their corresponding melting curvesdue to a supercooling effect prior to nucleation. The enthalpyof melting (determined by calculating the area above themelting peaks), and of crystallinization (area under the peaks)are similar (68.70 J/g for peaks “a”, “b”, and, “c”, respectively66.92 J/g for peaks “d” and “e”), leading to the conclusion thatmass and energy are being conserved in the system. The threedifferent melting transitions occur due to specific fatty acidcomposition of the wax which is a good predictor of lipidcrystallization behavior.34 Unsaturated fatty acids, such aslinoleic acid (C18:2), oleic acid (C18:1), and erucic acid(C22:1) will have lower melting temperatures that thesaturated fatty acids present such as palmitic (C16:0) orarachidic acid (C20:0) all of which are present in CTT seed(Table 2). Oleic acid, which has a melting temperature of 13−14 °C may be directly correlated to peak (a). Peak (b) (presentin both shell and wax layers) is likely the result of erucic acid,which is present in large quantities in both the shell and waxlayers. Peak (c) is likely the combined result of several saturatedfatty acids, such as palmitic and arachidic, and some unsaturatedfatty acids, such as heptadecenoic acid, which have a range ofmelting temperatures that causes the slight double peak presentat (c).These particular fatty acids are also immiscible with water,

which affects their melting characteristics. As they arehydrophobic, they are not likely to form close bonds with thehydrophilic cellulose and as such, their melting temperaturesare likely to be lower than if they were more closely associatedwith the cellulose in the sample structure. The proportions inwhich these fatty acids are present will affect the DSC curve andwill influence the peaks’ morphology. The thermal behavior ofCTT wax during decomposition, characterized by a change ofenergy release from the first to the third endotherm (peaks “a”,“b”, “c”), has been reported previously for agricultural materials,such as grasses used for biofuels and rice husks.35 Cellulose andhemicellulose cannot be identified using this DSC analysis, asthese components have much higher reaction temperatures.36

The DSC thermogram for wax after the lipid extraction (Figure3, top inset) confirms that the original peaks in wax are a direct

Table 3. Average Thermal Values from Thermal Analysis with 95% Confidence Intervalsa

density specific heat thermal conductivity thermal diffusivity thermal resistivity

material kg/m3 J/(kg·K) W/(m·K) mm2/s °C·cm/W

CTT shell (granular) 716.6 2018.7 ± 5.18b 0.20 ± 0.002 0.14 ± 0.001 500.8 ± 5.02CTT kernel (granular) 922.7 1237.0 ± 3.15 0.13 ± 0.000e 0.12 ± 0.001 748.0 ± 3.06soy flour 638.5 2340.9 ± 25.01a 0.11 ± 0.000 0.10 ± 0.000 951.9 ± 3.57CTT wax (granular) 394.1 3843.5 ± 171.16c 0.14 ± 0.007def 0.09 ± 0.001g 732.1 ± 33.77peanut butter 1000.2 2001.7 ± 12.48b 0.24 ± 0.000 0.10 ± 0.001 417.9 ± 1.12CTT whole (granular) 728.9 2833.9 ± 104.11 0.13 ± 0.000df 0.13 ± 0.001 773.2 ± 5.57candle wax (solid) 775.4 3731.7 ± 109.67c 0.26 ± 0.008d 0.09 ± 0.000g 385.5 ± 10.67

aSamples with the same letter superscripted are not statistically different. Bold text emphasizes CTT and its layers.



result of lipids and fatty acids present, and not of cellulose andhemicellulose. Other materials discussed in literature, such asgrain sorghum wax, do not necessarily exhibit the samebehavior. The sorghum wax DSC analysis indicated higherthermal transition peaks than do the component layers of theCTT seeds, which may be attributed to differing composi-tions.37

The glass transitions (separating the glassy and rubberbehavior 13) show up as a step transition rather than as a peak(Figure 3, bottom inset). The whole seed sample did notexhibit an apparent glass transition, probably due tocancellation of the glass transition of individual layers. If asample is heated to glass transition temperature (Tg) and thencooled, it will become brittle, if heated, it will become soft. Thistransition is reversible and can be an important characteristic inheat processing. In this case, wax has a Tg of 166.2 °C, the shell165.4 °C, and the kernel 167.0 °C.20 As cellulose, hemi-celluloses, and lignin are known to have glass transitions in thistemperature range (depending on sample preparation andtechnique used),38 it is likely that this glass transition is acombined effect of these components.Thermal Properties. Engineering thermal properties (i.e.,

specific heat, thermal conductivity, thermal diffusivity, andthermal resistivity, Table 3) provides information by whichother material characteristics, such as heating characteristics anddecomposition, may be predicted, and are used in engineeringanalysis. Values for soy flour, measured to ensure accurate dataand for calibration purposes, were found to be in the rangeindicated in literature.39

For specific heat, significant differences were found amongsome of the sample materials, but not always. For the detailedstatistical analysis (F-values and p-values) see ref 20. The CTTwax had the highest specific heat value, while the CTT kernelhad the lowest. This difference can significantly affect theheating characteristics of seeds during processing. As watercontent plays a large role in determining specific heat, variationsin water content among the different samples may have resultedin larger statistical differences. Regardless, these values arewithin the range of normal for flours, grains, and oils/fats.40

Among the CTT seed samples only, there was also asignificant difference in specific heat among the threecomponent layers (Table 3). Using the percent compositionof each component layer, a theoretical value for the whole seedwas calculated based on the additive rule and found to be2360.82 J/kgK, but this value was significantly different thanthe measured value (Table 3). While the moisture content wasapproximately the same for CTT samples, the explanationprobably lies in the effects from grinding whole seeds versusindividual layers, affecting packing density and subsequentmeasurements.41

The thermal conductivity values as measured fall below thoseof materials with higher moisture contents, but in the samerange as other agricultural materials, such as wheat, barley, oats,and soybeans, that have more similar moisture contents.19,42

Millet grains (at 0.119−0.223 Wm1−K−1)43 have values similarto those found here. Statistically, significant differences werefound for thermal conductivity among the sample materials(see Picou, 2012). Values for common fruits and vegetables aretypically much higher than those of CTT seeds, but that ismostly due to their higher moisture content.44 Thermaldiffusivity showed significant differences among the samples,20

with the exception between CTT wax and candle wax (thelowest diffusivity values among all materials investigated here).

These materials will also melt at a higher temperature, at whichpoint their thermal diffusivity will change drastically. Whencompared to literature values for corn (0.086−0.1011 mm2/s)and potato (0.171 mm2/s), measured values of thermaldiffusivity appear to be within the expected range.45 Thermalresistivity analysis yielded similar results with thermal diffusivityin term of significant differences among the different samples.20

The low variances in the measurements indicate a highdegree of precision and a low rate of error within measure-ments. Values obtained here may be applied to temperaturedata from processing operations to estimate a theoreticalinternal seed temperature. For processing purposes, thesevalues are important as even if the thermal conductivity valuesare similar, the heating process is affected by the specific heat,which are quite different between each of the component CTTseed layers.

■ ASSOCIATED CONTENT*S Supporting InformationAdditional information as noted in the text. This material isavailable free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*Corresponding author.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe acknowledge the assistance received from Robert Coyle,Pedro Robles, Dr. Sundar Balasubramanian, James Allen, SeonA. Lee, Pranjali Muley, Cong Chen, and Casey McMann, andBrianna Bourgeois for their assistance with seed collection andseparation. Special thanks go to Dr. Raphael Cueto for hisassistance with TGA and DSC analysis. This project was fundedin part by the LA Board of Regent Fellowship Fund, LSUBiological and Agricultural Engineering Department, and LSUAgCenter. Published with the approval of the Director of theLouisiana Agricultural Experiment Station as manuscript no.2012-232-7354.

■ REFERENCES(1) Bennett, D. Biofuel advocates: Proposed legislation, new studyboth flawed. Southwest Farm Press 2011.(2) Roos, A.; Graham, R. L.; Hektor, B.; Rakos, C. Critical factors tobioenergy implementation. Biomass Bioenergy 1999, 17, 113−126.(3) Gui, M. M.; Lee, K. T. Bhatia, Feasibility of edible oil vs. non-edible oil vs. waste edible oil as biodiesel feedstock. Energy 2008, 33,1646−1653.(4) Meher, L. C.; Sagar, D. V.; Naik, S. N. Technical aspects ofbiodiesel production by transesterification - a review. Renewable andsustainable energy reviews 2006, 10 (3), 248−268.(5) (a) Perlack, R. D.; Wright, L. L.; Turhollow, A.; Graham, R. L.;Stokes, B.; Erbach, D. C. Biomass As Feedstock for Bioenergy andBioproducts Industry: The Technical Feasibility of a Billion-Ton AnnualSupply; Oak Ridge National Laboratory: Oak Ridge, TN, 2005;(b) Huber, G. W.; Iborra, S.; Corma, A. Synthesis of transportationfuels from biomass: Chemistry, catalysts, and engineering. Chem. Rev.2006, 106, 4044−4098.(6) (a) Bolley, D.; McCormack, R. Utilization of the seed of theChinese tallow tree. J. Am. Oil Chem. Soc. 1950, 27 (3), 84−87.(b) Scheld, H. W. The Chinese tallow tree as a specialty oilseed crop.J. Am. Oil Chem. Soc. 1984, 61 (4), 670−671. (c) Urbatsch, L. Plant



http://pubs.acs.org

Guide: Chinese Tallow Tree; United States Department of Agriculture:Baton Rouge, 2000.(7) Jubinsky, G.; Anderson, L. C. The invasive potential of ChineseTallow-tree (Sapium sebiferum Roxb.) in the Southeast. Castanea 1996,61 (3), 226−231.(8) Shupe, T. F. Hydrothermal processing of Chinese Tallow tree(Triadica sebifera syn. Sapium Sebiferum) biomass. Wood Fiber Sci.2006, 38 (1), 55−63.(9) Duke, J. A., Handbook of Energy Crops; Purdue University, 1997.(10) Boldor, D.; Kanitkar, A.; Terigar, B. G.; Leonardi, C.; Lima, M.;Breitenbeck, G. A. Microwave assisted extraction of biodiesel feedstockfrom the seeds of invasive Chinese Tallow tree. Environ. Sci. Technol.2010, 44, 4019−4025.(11) Terigar, B. G.; Balasubramanian, S.; Boldor, D. Effect of storageconditions on the oil quality of Chinese Tallow tree seeds. J. Am. OilChem. Soc. 2010, 87, 573−582.(12) Gil, M. V.; Casal, D.; Pevida, C.; Pis, J. J.; Ruberia, F. Thermalbehavior and kinetics of coal/biomass blends during co-combustion.Bioresour. Technol. 2010, 101, 5601−5608. (b) Yuzbasi, N. S.; Selcuk,N. Air and ocy-fuel combustion characteristics of biomass/ligniteblends in TGA-FTIR. Fuel Process. Technol. 2011, 92, 1101−1108.(13) Zhang, S.; Li, L.; Kumar, A. Materials CharacterizationTechniques; CRC Press: Boca Raton, FL, 2009.(14) Skreiberg, A.; Skreiberg, O.; Sandquist, J.; Sorum, L. TGA andmacro-TGA characterisation of biomass fuels and fuel mixtures. Fuel2011, 90, 2182−2197.(15) Mansaray, K. G.; Ghaly, A. E. Determination of kineticparameters of rice husks in oxygen using thermogravimetric analysis.Biomass Bioenergy 1999, 17, 19−31.(16) Gabbott, P. Principles and Applications of Thermal Analysis;Blackwell Publishing: Oxford, UK, 2008.(17) Fischer, G.; Schrattenholzer, L. Global bioenergy potentialsthrough 2050. Biomass Bioenergy 2001, 20 (3), 151−159.(18) Louaer, W.; Maeniai, A.-H.; Grolier, J.-P. E. Thermal analysis ofthe influence of water content on glass transitions: Heat capacities ofstarches from different origins. J. Therm. Anal. Calorim. 2008, 93 (2),605−610.(19) Jirickova, M.; Pavlik, Z.; Cerny, R. In Thermal Properties ofBiological Agricultural Materials, Thermophysics; Bratislava, Slavakia,2006; p 68.(20) Picou, L. A. Rapid Microwave Drying of Non-Food AgriculturalFeedstock for Improved Biofuel Production; Louisiana State University:Baton Rouge, 2012.(21) Vamvuka, D.; Kakara, E.; Kastanaki, E.; Grammelis, P. Pyrolysischaracteristics and kinetics of biomass residuals mixtures with lignite.Fuel 2003, 82, 1949−1960.(22) David, F.; Sandra, P.; WylieP. L. Improving the Analysis of FattyAcid Methyl Esters Using Retention Time Locked Methods and RetentionTime Databases; Agilent Technologies: Santa Clara, CA, 2003(23) Bridgwater, A. V. Renewable fuels and chemicals by thermalprocessing of biomass. Chem. Eng. J. 2003, 91 (2−3), 87−102.(24) Barreto, P. L. M.; Pires, A. T. N.; Soldi, V. Thermal degradationof edible films based on milk proteins and gelatin in inert atmosphere.Polym. Degrad. Stab. 2003, 79 (1), 147−152.(25) Craig, R. G.; Powers, J. M.; Peyton, F. A. Thermogravimetricanalysis of waxes. J. Dent. Res. 1971, 50 (2), 450−454.(26) Raveendran, K.; Ganesh, A.; Khilar, K. C. Pyrolysis character-istics of biomass and biomass components. Fuel 1996, 75 (8), 987−998.(27) Cayli, G.; Kusefoglu, S. Increased yields in biodiesel productionfrom used cooking oils by a two step process: Comparison with onestep process using TGA. Fuel Process. Technol. 2008, 89 (2), 118−122.(28) Yang, H.; Yan, R.; Chen, H.; Zheng, C.; Lee, D. H.; Liang, D. T.In-dept investigation of biomass pyrolysis based on three majorcomponents: Hemicellulose, cellulose, and lignin. Energy Fuels 2006,20, 388−393.(29) Varhegyi, G.; Czegeny, Z.; Jakab, E.; Mcadam, K.; Lui, C.Tobacco, pyrolysis: Kinetic evaluation of thermogravimetric-massspectrometric experiments. J. Anal. Appl. Pyrol. 2009, 86, 310−322.

(30) Vassilev, S. V.; Baxter, D.; Anderson, L. K.; Vassileva, C. G. Anoverview of the chemical composition of biomass. Fuel 2010, 89, 913−933.(31) Singh, K.; Risse, M.; Das, K. C.; Worley, J. In Determination ofComposition of Cellulose and Lignin Mixtures Using ThermogravimetricAnalysis (TGA), 15th North American Waste to Energy Conference,Miami, FL, American Society of Mechanical Engineers: Miami, FL,2007; pp 219−226.(32) Christie, W. W. The glyceride structure of sapium sebiferumseed oil. Biochim. Biophys. Acta, Lipids Lipid Metab. 1969, 187 (1), 1−5.(33) Kaisersberger, E. DSC investigations of the thermal character-ization of edible fats and oils. Thermochim. Acta 1989, 151, 83−90.(34) Couvreur, S.; Hurtaud, C.; Lopez, C.; Delaby, L.; Peyraud, J. L.The linear relationship between the proportion of fresh grass in thecow diet, milk fatty acid composition, and butter properties. J. DairySci. 2006, 89 (6), 1956−1969.(35) (a) Ranalli, G.; Bottura, G.; Taddei, P.; Garavani, M.; Marchetti,R.; Sorlini, C. Composting of solid and sludge residues fromagricultural and food industries: Bioindicators of monitoring andcompost maturity. J. Environ. Sci. Health 2001, A36 (4), 415−436.(b) Leifeld, J. Calorimetric characterization of grass during itsdecomposition. J. Therm. Anal. Calorim. 2008, 93 (2), 651−655.(36) Yang, H.; Yan, R.; Chen, H.; Lee, D. H.; Zheng, C.Characteristics of hemicellulose, cellulose, and lignin pyrolysis. Fuel2007, 86, 1781−1788.(37) Hwang, K. T.; Weller, C. L.; Cuppett, S. L.; Hanna, M. Changesin composition and thermal transition temperatures of grain sorghumwax during storage. Ind. Crops Prod. 2004, 19 (2), 125−132.(38) L, S. Temperature and Water Induced Softening Behaviour of WoodFiber Based Materials, Department of Paper Technology; The RoyalInstitute of Technology: Stockholm, Sweden, 1982.(39) Wallapapan, K.; Sweat, V. E. Thermal conductivity of defattedsoy flour. Trans. ASABE 1982, 25 (5), 1440−1444.(40) Sweat, V. E., Thermal properties of foods. In EngineeringProperties of Foods, 2nd ed.; Rao, M. A., Rizvi, S. S. H., Eds.; MarcelDekker: New York, 1995; pp 99−137.(41) Mohsenin, N. N. Physical Properties of Food and AgriculturalMaterials; Routledge: London, 1989.(42) Jasansky, A.; Bilanski, W. K. Thermal conductivity of whole andground soybeans. Transa. ASAE 1973, 16 (1), 100−103.(43) Subramanian, S.; Viswanathan, R. Thermal properties of minormillet grains and flours. Biosyst. Eng. 2003, 84 (3), 289−296.(44) Buhri, A. B.; Singh, R. P. Measurement of food thermalconductivity using differential scanning calorimetry. J. Food Sci. 1993,58 (5), 1145−1147.(45) Chen, D. A new method for HTST sterilization of particulatefoods; Purdue University: West Lafayette, IN, 1990.



thermophysical characterization of the seeds of invasive chinese tallow tree: importance for biofuel...

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