journal of analytical and applied pyrolysis
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Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230
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Journal of Analytical and Applied Pyrolysis
journa l h om epage: ww w.elsev ier .com/ locate / jaap
haracterization of high acid value waste cottonseed oil byemperature programmed pyrolysis in a batch reactor
zong-Rong Linga,∗, Jyh-Shyong Changb, Yuh-Jing Chioub, Jia-Ming Chernb,se-Chuan Chouc
Department of Chemical Engineering, I-Shou University, Ta-Hsu Hsiang, Kaohsiung 84008, Taiwan, ROCDepartment of Chemical Engineering, Tatung University, 40 Chungshan North Road, Third Section, Taipei, Taiwan, ROCDepartment of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
r t i c l e i n f o
rticle history:eceived 29 December 2015eceived in revised form 13 May 2016ccepted 13 May 2016vailable online 21 May 2016
eywords:emperature-programmed pyrolysisottenseed oilhermogravimetric analysis
a b s t r a c t
Temperature programmed pyrolysis of high acid value waste cottonseed oil (WCO) was carried out in abatch type reactor. A thermogravimetric analysis (TGA) method, which did not require a carrier gas, wasused to study the properties of oil products. Weight loss data were obtained at heating rates (from 5 to15 ◦C min−1) and used to estimate the pyrolysis activation energy. A systematic study of the molecularweight distribution was made for the pyrolysis of WCO and virgin cottonseed oil at different heatingrates. The yields of the products including: gases, liquids (collected pyrolytic oil), and solids (residualchar) were quantified in this work. The production of pyrolysis gas was estimated during heating. Theweight loss results indicated that the optimum pyrolysis rate occurred between 400 and 450 ◦C at aheating rate of 10 ◦C min−1 from room temperature to 600 ◦C. Our work indicated that high acid value
WCO yields comparatively greater volumes of gases and masses of residual products when comparedto virgin cottonseed oil. After the temperature programmed pyrolysis of WCO (acid value 8.66 mg KOHg−1), at a heating rate of 10 ◦C min−1, the average boiling point of the pyrolytic oil was ∼349 ◦C, which issignificantly lower than that of the unprocessed WCO (456 ◦C). The pyrolytic oil produced in this processetha
after esterification with m. Introduction
Biodiesel production from various edible vegetable oils e.g. soy-ean, corn and cottonseed has been explored as a possible routeowards a commercially viable diesel substitute [1,2]. However, theommercialization of biodiesel production from edible vegetableils remains problematic, due to high production costs and theemands placed on such crops for human and animal consump-ion; thus, reducing feedstock costs will be necessary to ensureiodiesel’s long-term commercial success. A possible ‘green’ routeo reducing the raw material cost is to use cheaper feedstocks,.g. waste cooking oils from commercial catering establishmentsnd possibly non-edible vegetable oils that have lower associatedarvesting costs [3]. Without reclamation facilities waste cookingils and fats can give rise to significant disposal problems and in
oing so create odor and pollution. Addressing this waste disposalroblem to create a fuel substitute potentially offers both eco-omical and environmental benefits. Many developed countries∗ Corresponding author.E-mail address: [email protected] (T.-R. Ling).
ttp://dx.doi.org/10.1016/j.jaap.2016.05.009165-2370/© 2016 Elsevier B.V. All rights reserved.
nol, was found to comply with biofuel specification requirements.© 2016 Elsevier B.V. All rights reserved.
have outlawed the disposal of waste cooking oil in the domesticdrainage system [4]. The Energy Information Administration (EIA)has estimated that about 9 Lbs of waste cooking oil are generatedper person per year in the United States (USA) [5]. The estimatedamount of waste cooking oil collected in Europe is approximately0.49–0.7 million gallons/day [6].
Waste cooking oil, as an alternative feedstock for biodiesel, hasbeen studied with the intention of optimizing key process anddesign variables, using methods such as supercritical methanol(SCM) transesterification [7–9]. The pyrolysis of vegetable oils hastypically been carried out at atmospheric pressure in batch reac-tors at temperatures between 300 and 500 ◦C [10]. The productstypically include gaseous liquid hydrocarbons, carboxylic acids, CO,CO2, H2, and water [11]. The yield of gasoline and related productsfrom the catalytic pyrolysis of vegetable oil, or used vegetable oil,depends to a large extent on variables such as the: initial compo-sition of the oil [12], reaction temperature [13], residence/reactiontime [14] as well as the type of catalyst used [10,15]. The catalytic
pyrolysis of vegetable oils to produce liquid fuels has been exten-sively researched [10,13] in conjunction with pilot-scale reactors[12]. However, the use of waste edible vegetable oils (used oil)as a feedstock for catalytic pyrolysis is relatively new compared
T.-R. Ling et al. / Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230 223
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ig. 1. Schematic diagram of temperature programmed pyrolysis combined with grE) signal transducer, (F) computer, (G) electronic scale accurate to third decimal plollector.
o established transesterification based processes. A number oftudies have been carried out with used sunflower oil [16–18] toroduce ‘gasoline range’ oil products. Similar to virgin oil pyroly-is, the type of oil, temperature, catalyst and reactor configurationffect the product yield and chemical distribution from used oilransesterification processes [16,19].
The application of thermal analysis techniques to study theehavior and kinetics of fossil fuels under heating is now attract-
ng significant interest, due to its industrial significance and forider economic/environmental considerations. One of the majorifficulties in processing crude oils is that their thermal behaviorsre not well understood. There have been many studies dealingith the characterization of crude oils using various thermal anal-
sis techniques. Thermogravimetric analysis (TGA) is a techniqueommonly applied to fossil fuels undergoing combustion or pyrol-sis. The TGA instrument records the temperature and weightssociated with valorization or conversion, to give quantitativend qualitative data related to heating behavior [20–22]. Pyroly-is experiments are typically carried out by progressively heating
sample, while monitoring its weight loss and the liberation ofolatized products. Understanding pyrolysis is vital for character-ng materials, e.g. coal, petroleum, plastics, and biomass, for theirtability and as potential fuel sources. The final pyrolysis reactionroducts are gases, volatile tars and oils, and char.
Cottonseed oil is significantly less expensive than olive oil oranola oil. With annual production averaging more than 1 billionounds, cottonseed oil ranks third in volume behind soybean andorn oil, representing about 5–6% of the total domestic fat and oilupply in the US. Most cottonseed oil is used for animal feed, biofuel,extiles or other industrial uses and not directly for food. Of theood uses, most genetically modified (GM) food reaches grocerytore shelves in the form of processed products. However, despitets widespread use by a variety of industries there are few reportselated to the fate of waste cottonseed oil [23].
In general, waste cooking oils have high viscosities and high acidalues. Although such properties may reasonably be expected to
nfluence the results of both thermal cracking and pyrolysis therere few studies that report the relation between the propertiesf waste cooking oils and their pyrolytic products, which include:ases, recovered oil, and tar residues.tric analysis: (A) glass tube 20 mL, (B) thermocouple, (C) cover, (D) graphite gaskets,) side tube, (I) heat insulation, (J) heater, (K) temperature controller, and (L) liquid
In the present work, the pyrolysis of waste cottonseed oil(WCO) using a temperature program technique was studied in abatch type reactor. The gas production rate and the generationof tar residue from thermal cracking were monitored. The result-ing pyrolytic oils were characterized by TGA, gas chromatographicanalysis (GC) and matrix-assisted laser desorption ionization/time-of-flight-mass spectrometry (MALDI/TOF-MS). A comparison studywas made to investigate the relationship between WCO, with dif-ferent acid values, and the yields of pyrolysis products including:gases, liquids (collected pyrolytic oil), and solids (residual char). Forbiofuel production, it is necessary to find a suitable methodologythat predominantly gives pyrolytic oils with low viscosities and lowboiling points. To decrease the acid value of the pyrolytic oil, i.e. tolower its carboxylic acid content, it was esterified with methanoland deacidified with alkali.
2. Experimental
2.1. Materials
Pure (100%) cottonseed oil (Sigma-Aldrich) was used as thestarting material. Other chemicals and solvents, purchased fromSigma-Aldrich and Fisher Chemicals, were of Analytical reagentgrade. WCO from food processing companies is plentiful; however,it is not suitable for this study as there is likely to be significantvariation between batches, and there will have been little or nocontrol over the thermal cycles and cooking conditions to which ithas been subjected. For this reason, ‘simulated’ WCO was preparedin a controlled laboratory environment by taking virgin cottonseedoil and subjecting it to well-defined thermal cycling. Cottonseed oil(100 mL) was placed in a 200 mL beaker, which was in turn placedin a heating mantle with digital temperature controller fitted witha thermocouple to determine the oil’s temperature (set at 250 ◦Cand held for 10, 30 or 50 h).
2.2. Temperature programmed pyrolysis apparatus
Temperature programmed pyrolysis was carried out, without acarrier gas, using a glass tube enclosed with a steel jacket in a tem-perature programmed furnace (electric heating) as shown in Fig. 1.
224 T.-R. Ling et al. / Journal of Analytical and A
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ig. 2. (A) TG curves and (B) DTG curves for different compounds: (a) water (b)lycerol (c) cottonseed oil at a constant heating rate of 10 ◦C min−1.
he temperature of the oil sample in the glass tube was monitoredy a thermocouple. Both the glass tube and electric heater werelaced on an electronic scale (accurate to 0.001 g), thus enabling theemperature increase (at a constant rate e.g. 5, 10, 15, 20 ◦C min−1)nd the weight loss to be measured simultaneously during the heat-ng process. A multichannel transducer connected to a computer
as used to record and analyze data. The TGA instrumentationas calibrated using pure water and glycerol, see Fig. 2(A): the liq-id weights, decreased at their boiling points, during heating, theertical lines for the pure compounds (water and glycerol) respec-ively show that their boiling points are close to their referencealues (i.e. 100 ◦C and 292 ◦C respectively). At normal atmosphereressure, the smoke point of cottonseed oil is 216 ◦C. At this temper-ture, volatile compounds, such as free fatty acids, and short-chainegradation oxidation products appear and subsequently degrade
n air to form soot. For the multi-compound virgin cottonseed oil,he average boiling point was approximately 420 ◦C, see Fig. 2(B).heoretically, vaporization and pyrolysis of the oil should occurimultaneously at its boiling point temperature. In this work, pyrol-sis combined with gravimetric analysis was used to characterizehe oil’s properties in order to distinguish differences between WCOnd virgin oil.
.3. Product analysis
Preliminary GC/MS analysis was undertaken using either a SHI-
ADZU QP2010, or a GC (Techcomp Shanghai Ltd. Co.) GC7900,quipped with the same capillary column i.e. DB-5 (J&M Scientificatalog 122-5062; l, 60 m; i.d, 0.25 mm; thickness, 0.25 �m), oper-ting with an oven temperature programmed from 50 to 250 ◦C
pplied Pyrolysis 120 (2016) 222–230
(heating rate 10 ◦C min−1), or at 250 ◦C for 20 min, injected liq-uid volume (0.2 �L.). Confirmatory analysis with respect to themolecular weight distribution of the pyrolytic oils was confirmedusing MALDI/TOF-MS, Autoflex III, Bruker Daltonics GmbH, Leipzig,Germany. The acid values were determined by auto-titration(Metrohm 877 Titrino Plus).
2.4. Pyrolytic kinetics
Theoretically, the reaction rate, of a thermal pyrolysis reaction,depends on conversion (�), temperature (T) and time (t). Thesemethods make use of the isoconversional principle which statesthat at a constant extent of conversion, the reaction rate is a func-tion only of the temperature, so that:[
d ln(d˛/dt)dT−1
]= 1
z
d ln ˇ
d(1/T)= −Ea
R(1)
In Eq. (1), Ea is the Arrhenius parameter (apparent activationenergy), R is the gas constant, T is the temperature, t is the time,z is a constant ∼1, and�is the extent of conversion, which can bedetermined from TGA analysis as a fractional mass loss [20]. Themodel-free kinetics program is based on the Vyazovkin theory ofdecomposition during complex reactions. This approach follows allpoints of conversion from multiple experiments, instead of thosederived from a single investigation. The chemical reaction rate ismeasured, as a minimum, with at least three different heating rates(�) [21].
2.5. Deacidification process
The production of pyrolytic oils with high acid values was effec-tively reduced by esterification with methanol. In this work, theesterification reaction was carried out at 80 ◦C for 5 h based onan initial weight ratio of MeOH: pyrolitic oil = 1:4, using NaHSO4as a catalyst (10 wt%). According to the literature [24], deacidifica-tion can also be carried out by using a 15% excess volume of NaOH(0.5N) at 60 ◦C for 40 min to give a deacidified product with an acidvalue below 0.5 mg KOH g, see European biodiesel standards(pr EN14104) .
3. Results and discussion
3.1. Temperature programmed pyrolysis for TG and DTG
The thermal pyrolysis of cottonseed oil and WCO were carriedout at different constant heating rates (5, 10, 15 ◦C min−1). As shownin Figs. 3 and 4, weight loss was clearly apparent at 400–450 ◦C,depending on the heating rate. For cottonseed oil pyrolysis, theweight loss peaks, i.e. 389 ◦C, 418 ◦C and 449 ◦C, correspond torespective heating rates of 5 ◦C min−1, 10 ◦C min−1 and 15 ◦C min−1,as shown in Fig. 3(B). For WCO pyrolysis, similar respective weightloss peaks are located at 425 ◦C, 445 ◦C, and 464 ◦C as shown inFig. 4(B). Interestingly, the pyrolysis of cottonseed oil appears toproceed more rapidly than that of WCO.
The activation energy, which is a function of the extent of con-version in the isoconversional method, is related to the rate ofheating [25]. Using Eq. (1), the activation energies of WCO andvirgin cottonseed oil can be determined with the different con-version extents (�). Fig. 5 of (Ea vs. �) is plotted according to thedata in Figs. 3 and 4. In this work, the pyrolysis activation energy isestimated based on the weight loss of the liquid oil. The pyrolysis
reaction simuteneously involves the volatilization of liquid oil inthe batch type reactor. The extent of conversion is directly relatedto the pyrolysis and volatilization processes. The activation energyof WCO (b) is higher than that of virgin cottonseed oil(a) in Fig. 5.
T.-R. Ling et al. / Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230 225
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Fig. 4. (A) TG curves and (B) DTG curves for the pyrolysis of WCO with acid valuesof: 8.66 mg KOH g−1 at constant heating rates of (a) 5 ◦C min−1, (b) 10 ◦C min−1, (c)15 ◦C min−1.
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ig. 3. (A) TG curves and (B) DTG curves for pyrolysis of virgin cotton seed oilith acid value of 0.24 mg KOH g−1 at constant heating rates of: (a) 5 ◦C min−1,
b) 10 ◦C min−1, (c) 15 ◦C min−1.
he conversion (�) was between 0.3 and 0.7 with the heating rateange examined (5, 10, 15 ◦C min−1). It is reasonable to concludehat high viscosity WCO has a higher activation energy for pyrolysisnd volatilization than virgin oil.
Similar studies, based on TG experiments, for oil shales [25],unflower oil and their biodiesel products have been reported26]. The model-free kinetic approach applied in the research hasroven to be reliable for studying the pyrolysis of the oils. Inhis study, the activation energy values for the pyrolysis WCOere apparently higher than those of virgin cottonseed oil. These
alues are consistent with the idea that the pyrolysis or volatiliza-ion of compounds with higher molecular weights and viscositiesequires more energy. It was also observed that virgin cottonseedil requires a lower temperature to achieve the same degree ofyrolysis conversion compared to WCO.
.2. Comparison of WCO and virgin cottonseed oil
TGA was used to characterize the average boiling points of WCOith a high acid value [8.6 mg KOH g −1 (from a heating treatmentrocess)] and virgin cottonseed oil with acid value of 0.24 mg KOH−1, see Fig. 6 (a). The cottonseed oil exhibited a sharp profile at
he average boiling point i.e. 418 ◦C. The differential gravimetricDTG) Fig. 6(b) shows that WCO has a broader profile than virginil. The long-term aging process might change the oil’s propertiesuch as acidification, due to oxidation by air, or it may ‘crack’ into
Fig. 5. Activation energy as a function of conversion for pyrolysis of: (a) virgin cot-tonseed oil with acid value of 0.24 mg KOH g−1 and (b)WCO with acid value of8.66 mg KOH g−1 using the model-free kinetics.
226 T.-R. Ling et al. / Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230
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Fig. 7. GC analysis of oils obtained by temperature programmed pyrolysis of: (A)WCO with an acid value of 8.66 mg KOH g−1 and (B) virgin cottonseed oil with an acidvalue of 0.24 mg KOH g−1 at different heating rates. The temperature programmed
ig. 6. (A) TG curves and (B) DTG curves for pyrolysis of: (a) virgin cottonseed oilith acid value of 0.24 mg KOH g−1 and (b)WCO with acid value of 8.66 mg KOH g−1
t a constant heating rate of 10 ◦C min−1.
maller molecules as a result of thermal processes. WCO with someow boiling point compounds lost its weight at lower tempera-ures during TGA, see Fig. 6 (note: virgin cottonseed oil deterioratedt a moderate temperature, i.e. 250 ◦C over 50 h). Obviously, theong-term application of such a temperature still provides suffi-ient energy to slowly change the oil’s molecular structure andomposition.
.3. GC analysis
For the analysis of pyrolytic oils, GC was used to observe theireak profile evolution with time. Cottonseed oil predominantlyomprises three fatty acids, namely palmitic acid, oleic acid, andinoleic acid. [27] Some low boiling point compounds are formedn WCO at moderate temperatures over relatively short durationsi.e. 250 ◦C for 50 h) as evidenced by the GC–MS analysis Fig. 7(A).
CO cracking produced a variety of degradation products e.g.ntadecane, 9-octandecene, n-heptadecane, n-hexadecanoic acid,-hexadecenal, 7-tetradecenal, et al. as shown at a0 in Fig. 7(A).he virgin cottonseed oil deteriorated, producing small amounts ofoth low boiling point compounds (a0 in Figs. 7(A)) and high boilingoint compounds (a0 in Figs. 8(A)).
For WCO and virgin cottonseed oil, various peaks elutedetween 5 and 30 mins as shown in (a0, b0) Figs. 7(A) and 7(B).uring pyrolysis, at different heating rates, i.e. 3, 5, 10, 15 ◦C min−1
rom room temperature (RT) to 600 ◦C, several peaks [designated
pyrolysis was carried out using different heating rates: (a0,b0): initial WCO andvirgin cottonseed oils: (a1,b1): 3 ◦C min−1 (a2,b2): 5 ◦C min−1, (a3,b3): 10 ◦C min−1,(a4,b4): 15 ◦C min−1.
(a1,b1), (a2,b2), (a3,b3), (a4,b4) in Figs. 7(A) and 7(B)] appeared atlower temperatures before 15 min with two peaks appearing laterat approximately 30 min. The GC results indicate that compoundswith a range of molecular weights were simultaneously generatedduring pyrolysis. The GC profile shown in Fig. 7(A), reveals that thepeak profiles of the pyrolytic oils, derived from WCO at differentheating rates, were similar and thus independent of the heatingrate. However, for the pyrolysis of virgin cottonseed oil, greaterquantities of the light compounds were found when using low heat-ing rates (3, 5 ◦C min−1). This indicates that the pyrolysis of virgincottonseed oil at a slow heating rate can yield high amounts of lowmolecular weight products, due to the longer pyrolysis time. Theseresults show that virgin cottonseed oil is comparatively easier topyrolyse than WCO.
3.4. MALDI/TOF-MS analysis
To characterize the pyrolysis products, MALDI/TOF-MS was
used to examine the molecular weight distribution of the pyrol-ysis products of virgin cottonseed oil and WCO as some largeroil molecules that could not be easily analyzed by GC. Shownin Fig. 8 are the molecular weight distribution profiles of the
T.-R. Ling et al. / Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230 227
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Fig. 8. Molecular weight distribution of MALDI/TOF-mass spectrometry for: (A)WCO with an acid value of 8.66 mg KOH g−1 and (B) virgin cottonseed oil withan acid value of 0.24 mg KOH g−1 obtained by temperature programmed pyrolysisa3
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Fig. 9. Gas production from temperature programmed pyrolysis of WCO with dif-ferent acid values (A) –�–: 8.66,(B) –�—: 6.57,(C) –©–: 4.13 and (D) –�–:0.24, mg
t different heating rates: (a0,b0): initial WCO and virgin cottonseed oils: (a1,b1):◦C min−1 (a2,b2): 5 ◦C min−1, (a3,b3): 10 ◦C min−1, (a4,b4): 15 ◦C min−1.
yrolysis products obtained at different heating rates (3, 5, 10,5 ◦C min−1). WCO with a high acid value [8.66 mg KOH g−1 (from
heating treatment process)] has a significantly higher moleculareight (∼400–550 m/z) than virgin cottonseed oil (∼300–450 m/z).s shown in Fig. 8(A), a similar distribution of pyrolytic oils
average mass 360 m/z), was produced at different heating rates.nterestingly, the WCO pyrolytic oil molecular weight distributionomponent profile did not significantly change with different heat-ng rates. This may indicate that within the range of heating ratesmployed (3–15 ◦C min−1) the larger and relatively more stableCO molecules can only be cracked into similar and more uni-
ormly sized molecules. However, the situation is not the sameor the pyrolysis of virgin cottonseed oil (acid value 0.24 mg KOH−1), where the generation of lower molecular weight pyrolyticils (average masses 310 and 320 m/z) was found to occur usinglow heating rates, i.e. 3 and 5 ◦C min−1 respectively. This suggestshat the slower heating rate may result in the pyrolysis reactionroceeding more slowly and also that the virgin cottonseed oil isore easily cracked into smaller molecules during thermal pyroly-
is. When taken together the MALDI/TOF-MS results are seen to beimilar to the GC analysis, see Fig. 6.
.5. Gas production from the pyrolysis of WCO with different acidalues
Gas production, was measured by water displacement duringyrolysis. The pyrolysis gases were collected in a glass bottle andheir volumes were quantified. Four kinds of WCO with different
KOH g−1. The gas accumulation volume was measured by water displacement forgas collection at the heating rate of 10 ◦C min−1 from RT to 600 ◦C. The pyrolysis isbased on 10 g oil for each run.
acid values (0.17, 4.13, 6.57, and 8.66) were used to study gasproduction. As shown in Fig. 9, no gas was collected at pyrolysistemperatures below 150 ◦C. At programmed temperatures greaterthan 300 ◦C, the evolution of gas was apparent with the volumeof gas being produced increasing as the pyrolysis temperatureapproached 400 ◦C and decreasing thereafter, with only a smallamount gas being produced at temperatures greater than 500 ◦C.The volume of gas produced from WCO was greater than from virgincottonseed oil as shown in Table 1. Each WCO pyrolysis run (usingdifferent acid value starting materials) was repeated three times.The relative errors were less than 3% for pyrolytic oil and less than18% for the tar residue. As a whole, the data trend was acceptable.To keep the data reproducible and minimize the relative errors, theside tube and cover of the apparatus was cleaned carefully prior toeach run. The higher acid value WCO yielded a larger amount of gasand tar residue products based on initial weight; however, it alsogave a lower oil recovery after pyrolysis. It is also possible that thegas produced is related to the pyrolysis of acid compounds derivedfrom WCO. In general, the gaseous compounds typically includeCO2, CO, H2, water, alkanes and short chain alkenes.
3.6. Production yields analysis between virgin cottonseed oil andWCO
The production yields of pyrolytic oil, residual char and gas werequantified during experimentation with various pyrolysis heatingrates for virgin cottonseed oil and WCO, i.e. from RT to 600 ◦C, asshown in Tables 2 and 3. As a whole, the slower heating rate pro-duced higher yields of gas and residual char, but with a lower yieldof pyrolytic oil. Meanwhile, a higher pyrolytic oil acid value wasfound with the slower heating rate for both virgin cottonseed oiland WCO. Our results also indicated that the slower heating rate canprovide longer retention times for the pyrolysis of virgin cottonseedoil and WCO molecules in the batch system. Thus, a suitable heatingrate can be used to characterize the oil’s properties and estimatethe pyrolytic ‘production yield’.
3.7. Properties analysis
The properties of WCO and its pyrolytic oils (obtained at varioustemperatures) are shown in Table 4. Higher acid value WCOs wereprepared by protracted thermal treatment and found to have higher
228 T.-R. Ling et al. / Journal of Analytical and Applied Pyrolysis 120 (2016) 222–230
Table 1Product yields of temperature programmed pyrolysis of WCO with different acid values.
Various oils (AV) (mg KOH g−1) Product Yield (wt.%)
Pyrolytic oil (WL/Wo) (AV) (mg KOH g−1) Residue char (WS/Wo) Gasa (WG/Wo)
Cottonseed oil (0.24) 89.49 ± 0.74 (144.05 ± 6.57) 1.75 ± 0.31 8.76 ± 0.62WCO1 (4.13) 86.94 ± 0.62 (153.38 ± 2.78) 3.38 ± 0.49 9.68 ± 0.40WCO2 (6.57) 84.92 ± 1.24 (157.92 ± 1.49) 4.30 ± 0.47 10.78 ± 0.78WCO3 (8.66) 83.50 ± 0.73 (163.52 ± 5.39) 4.65 ± 0.55 11.85 ± 0.62
The pyrolysis reaction were carried out at the heating rate of 10 ◦C min−1 from RT to 600 ◦C.Each run for WCO pyrolysis was carried out for three times and initial weight (WO) of WCO was based on 5 g.Pyrolytic oil (WL) was cooled from the side tube in air and into the liquid collector.Residue char (WS) can be obtained by calculating the final weight.WCO1,WCO2,WCO3 with different acid values: (4.13, 6.57, 8.66 mg KOH g−1) were, respectively, prepared from cottonseed oil heated at 250 ◦C for 10, 30, and 50 h.
a Gas production yield (WG/WO), WG = WO − WL − WS.
Table 2Product yields with temperature programmed pyrolysis of virgin cottonseed oil (acid value 0.24 mg KOH g−1) at heating rates of 5, 10, 15 and 20 ◦ min−1.
Heating rate min−1)(◦C min−1) Product Yield (wt.%)
Pyrolytic oil (WL/Wo) (AV) (mg KOH g−1) Residue char (WS/Wo) Gas (WG/Wo)
5 87.01 ± 0.62 (152.91 ± 3.57) 2.71 ± 0.36 10.28 ± 0.7210 89.49 ± 0.74 (144.04 ± 6.57) 1.75 ± 0.31 8.76 ± 0.6215 89.83 ± 0.73 (138.71 ± 1.00) 1.48 ± 0.21 8.68 ± 0.5520 90.87 ± 0.50 (133.87 ± 1.36) 1.05 ± 0.09 8.07 ± 0.51
The pyrolysis reaction were carried out respectively at different heating rates of 5, 10, 15 and 20 ◦C min−1 from RT to 600 ◦C. Each reaction run, based on 5 g virgin cottonseedoil, was carried out at heating rates specified three times.
Table 3Product yields using temperature programmed pyrolysis of WCO (acid value 8.66 mg KOH g−1) at heating rates of 5, 10, 15 and 20 ◦C min−1.
Heating rate (◦C min−1) Product Yield (wt.%)
Pyrolytic oil (WL/Wo) (AV) (mg KOH g−1) Residue char (WS/Wo) Gas* (WG/Wo)
5 81.56 ± 1.04 (166.26 ± 3.50) 6.34 ± 0.76 12.08 ± 1.6510 83.50 ± 0.73 (163.52 ± 5.39) 4.65 ± 0.55 11.85 ± 0.6215 85.78 ± 0.48 (155.54 ± 2.02) 3.86 ± 0.33 10.35 ± 0.7720 86.69 ± 0.66 (147.98 ± 1.32) 3.04 ± 0.23 10.26 ± 0.90
The pyrolysis reaction were carried out respectively at different heating rates of 5, 10, 15 and 20 ◦C min−1 from RT to 600 ◦C. Each reaction run, based on 5 g of WCO, wascarried out at heating rate specified three times.
Table 4Properties of WCO and the pyrolytic oil.
Property Cottonseed oil WCO1 WCO2 WCO3 Pyrolytic oil Etherified pyrolytic oil Biodiesel (B100) Requirements in USA
kinematic Viscosity(mm2 s−1)at 40 ◦C+ 17.43 23.73 47.33 64.32 3.73 3.61 1.9–6.0Specific gravity 0.92 0.94 0.97 1.02 0.87 0.87 0.86–0.9Acid value, mg KOH g−1 0.24 4.13 6.57 8.66 159.24 0.46 0.5maxAverage boiling point ◦C# 418 425 441 456 349 330 360max
+W respec
vtnpa(ia4tcws
3
G
: test method D445; #: estimated based on TGA in this work.CO1,WCO2,WCO3 with different acid values: (4.13, 6.57, 8.66 mg KOH g−1) were,
iscosities, densities and average boiling points. Obviously, thehermal treatment process promotes partial oxidation, and combi-ation or bonding among the oil molecules. After the temperaturerogrammed pyrolysis of WCO at 10 ◦C min−1, the pyrolytic oil has
significantly lower viscosity (3.73 mm2 s−1) than the initial WCO64.32 mm2 s−1). But, the acidity of the pyrolytic oil significantlyncreases, i.e. from 8.66 to 159.24 mg KOH g−1. Nevertheless, thecidity of the pyrolytic oil was able to be significantly reduced to.35 mg KOH g−1 by esterification with methanol − thus enabling ito be compared favorably with existing biofuels. After further pro-essing (deacidification), the esterified oil, gave a resulting productith an acid value of 0.46 mg KOH g−1, which is within the US
pecification (0.5max mg KOH g−1).
.8. Comparison of esterified pyrolytic oil with diesel
The final product was compared with commercial diesel usingC and DTG methods, as shown in Fig. 10 and analyzed by GC–MS
tively, prepared from cottonseed oil heated at 250 ◦Cfor 10, 30, and 50hr.
using a capillary column (DB-5). Serveral peaks appear in Fig. 10(A)in part (a) for the esterified pyrolytic oil. The main peaks, mostof which are methyl esters, are as follows: 1: hexanoic acid,methyl ester (C7H14O2); 2: heptanoate (C8H16O2); 3: octanic acidmethyl ester (C9H18O2); 4: nonanoic methyl ester (C10H20O2); 5:decanoic acid methyl ester (C11H22O2); 6: 3-tetradecene (C14H28);7: dodecane (C12H26); 8: 9-octadecenal (C18H34O); 9: palmitic acid,acid methyl ester (C17H34O2); 10: octadecenoic acid methyl ester(C19H36O2). mass spectrometer (GC/MS). The data acquisition isbased on NIST libraries/databases. All of the peaks examined in thisstudy (mainly methyl esters) show that the compounds found, andtheir reference compounds, are well-correlated with highly similarindices (SI) > 90.
In Fig. 10(A) in part (b) for diesel. The diesel compounds
are listed as follows: 1: nonane (C9H20); 2: decane(C10H22); 3:undecane (C11H24); 4: dodecane (C12H26); 5: tridecane(C13H28);6: tetradecane (C14H30); 7: pentadecane (C15H32); 8: Hexade-cane (C16H34); 9: heptadecane (C17H36); 10: octadecane (C18H38);
T.-R. Ling et al. / Journal of Analytical and A
5 10 15 20 25 30 35 40
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0.020(B)
(a)
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ivat
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eigh
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s -d
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Temperature (oC)
(b)
Fig. 10. (A) Gas chromatogram of: (a) esterified pyrolytic oil (b) commercial diesela2t
1(d(tntcr
gi(aoraFtafv
nalyzed at the heating rate of 10 ◦C min−1 from 50 to 250 ◦C, kept at 250 ◦C for0 min and (B) DTG curves of (a) and (b) at the heating rate of 10 ◦C min−1 from 50o 600 ◦C.
1:nonadecane (C19H40); 12: Eicosane (C20H42); 13: heneicosaneC21H44); 14: methyl ester octadecanoic acid (C19H38O2); 15: 1-ocosene (C22H44); 16:9-Tricosene, (C23H46); 17: 9-HexacoseneC26H52). The peak’s SI is greater than 90 for all of compounds inhe database. From the GC analysis, some high boiling point compo-ents appear in the final product. From DTG as shown in Fig. 10(B),he average boiling point of the final product is higher than that ofommercial diesel; however, both methods show broadly similaresults.
Esterification is a commonly used method to stabilize oil thatives rise to many oxygenated compounds. The oxidation stabil-ty of the esterified oil was tested using the Rancimat methodEN14112). The induction period for the esterified oil, measureds 3.5 h, was obviously longer than that for the original pyrolyticil (1.2 h). In the biodiesel standard specification, the minimumequirement for the induction period (an indication of the oxidationnd storage stability of middle distillate fuels) is 3 h [ASTM D6751.or the carbon residue analysis, the amounts of carbon residue in
3
he esterified oils prepared from virgin cottonseed oil and WCOt heating rates of 3 ◦C min−1 and holding at 430 ◦C for 1 h wereound to be 0.0425 and 0.1270%, respectively. The former of thesealues (obtained for virgin cottonseed oil) is below the commercialpplied Pyrolysis 120 (2016) 222–230 229
biodiesel standard (0.05% max) for US. The oil’s original propertiestogether with the slower heating rate, or the more suitable pyroly-sis temperature and the better cooling system for vapor reflux, maybe responsible for the lower carbon residue in the final pyrolyticoil: this is a matter of ongoing investigation. Under high tempera-ture conditions it is possible to produce toxic compounds (such asacrolein from glycerol burning) during the pyrolysis of vegetableoils [10], however acrolein concentrations have not been found tobe significant in pyrolytic cottonseed oil.
Batch type reactors provide a simple way to characterize oils’properties and produce pyrolytic oils. Additionally, the pyroly-sis reaction in an inert gas environment, or with an appropriatecatalyst, might improve cracking, while decreasing the level offormation of acidic and oxygenated compounds [28–30]. The com-bination of these approaches and attributes should be a usefulapproach for a variety of diversified applications.
4. Conclusions
The temperature programmed pyrolysis of WCO was investi-gated in a batch type reactor on a mini-laboratory scale: relativeerrors with respect to the amounts of the main products werelow and acceptable for thermal cracking in each run (<3% forpyrolytic oil and <18% for the tar residue). Using the isoconver-sional method, the estimated activation energies for the pyrolysisWCO were apparently higher than those of virgin cottonseed oil.Operating without a carrier gas, TGA was used to analyze the pyrol-ysis process in conjunction with the weight loss data. An optimumpyrolysis rate for WCO, determined from the weight loss data, wasfound to be at temperatures between 400 and 450 ◦C, this beingsimilar to the data showing the optimization of gas production inrelation to the pyrolysis temperature. Quantification and analysis ofthe pyrolytic products including gases, liquids, and solids can pro-vide information enabling us optimize the heating program, whilelow molecular weight pyrolytic oils can be obtained at suitableheating rates (<3 ◦C min−1) to meet biodiesel requirements.
Overall this research, focused on the characterization of wasteoil and the production of pyrolytic oil, should serve as a basis fordeveloping environmentally friendly waste oil recovery methodswith multiple applications in the food and oil processing industries.
Acknowledgement
Funding provided for this research by the National ScienceCouncil and Ministry of Science and Technology of Republic of China(Grant No. NSC 102-2622-E-036-001-CC1, MOST 103-3113-E-036-001) and CTCI Corporation is gratefully acknowledged.
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