ethylene glycol

Fuel Processing Technology 161 (2017) 162–168

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Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc

Research article

The miscibility of hydrogenated bio-oil with diesel and its applicability test in diesel engine: A surrogate (ethylene glycol) study Shiliang Wu, Hongwei Yang, Jun Hu, Dekui Shen, Huiyan Zhang, Rui Xiao ⁎ Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing 210096, China

a r t i c l e

i n f o

Article history: Received 19 September 2016 Received in revised form 8 March 2017 Accepted 18 March 2017 Available online xxxx Keywords: Hydrogenated bio-oil Ethylene glycol Miscibility Engine performance Emissions

a b s t r a c t In this work, the miscibility of hydrogenated biomass-pyrolysis-oil with diesel and its applicability in diesel engine has been tested by using its surrogate-ethylene glycol. The miscibility of ethylene glycol and 1,3-propylene glycol with diesel has been tested, finding that only 10% vol ethylene glycol could be mixed with diesel and 1,3-propylene glycol is immiscible with diesel. In order to make a direct comparison, 10% ethanol-90% diesel, 10% ethylene-90% diesel, and 10% ethyl acetate-90% diesel blends have been tested in a diesel engine under the same operation conditions. The engine performance of ethylene glycol is comparable to ethanol and ethyl acetate. There is no significant difference in brake specific fuel consumption and exhaust gas temperature for blends. The three oxygenated compounds all have lower CO emissions than diesel. Besides, ethylene glycol and ethyl acetate could reduce the NOx emission. All the three fuels have reported the reduction of soot emission. This work offers the possibility that ethylene glycol (hydrogenated bio-oil) could be used as a useful additive (up to 10% vol) in diesel. © 2017 Published by Elsevier B.V.

1. Introduction With the depletion of fossil fuels, applications of bio-fuels in internal combustion engines are receiving increasing attention [1]. The firstgeneration bio-fuels, biodiesel and bioethanol lead to the problem of food versus fuel [2]. Under this condition, researches and applications on the second-generation bio-fuels, which are made from lignocellulosic biomass, woody crops, and agricultural residues, flourished after 2000 [3–5]. Bio-oils from fast pyrolysis of lignocellulosic biomass show different characteristics from conventional fossil oils, like high water content, high density, acidic, and low heating value. What's more, bio-oils are highly polar and contain a large amount of oxygen (about 35–40 wt% in dry basis), resulting that bio-oils are not soluble in fossil fuels [6]. However, considering their potential to replace or partly replace fossil fuels, the applications of bio-oil from fast pyrolysis of biomass are the focus of intense studies [7]. Normally, bio-oils are injected into engines with diesel by dualinjection system or blended and emulsified with diesel before injection. Though some researchers have reported the applicability of raw bio-oil in internal combustion engine, severe problems also appeared when running raw bio-oil, such as its poor ignition characteristics [8–10], and causing severe corrosions and blockages on injectors [11–13]. In order to deal with these problems, catalytic hydrogenation ⁎ Corresponding author. E-mail address: [email protected] (R. Xiao).

http://dx.doi.org/10.1016/j.fuproc.2017.03.022 0378-3820/© 2017 Published by Elsevier B.V.

and esterification have been used to upgrade raw biomass pyrolysis oil. Though there are some reports on the catalytic hydrogenation and esterification process of pyrolysis oil [14], few of them covered the application of upgraded biomass pyrolysis oil in internal combustion engines. Pelaez-Samaniego et al. prepared bio-oil rich in esters form sugarcane trash pyrolysis oil, suggesting that it was technically feasible to use blends of carboxylic acids esters derived from the biomass bio-oil with gasoline in conventional Otto engines [15]. Bert Van de Beld et al. treated pine wood pyrolysis oil with mild hydrogenation and reactive distillation (with butanol) to get bio-oil, after 40 h fueling with upgraded pyrolysis oil in diesel engine, they reported that no notable effect on flue gas emissions and fuel consumption [16]. Wildschut et al. hydrotreated beech wood pyrolysis oil in a autoclave with catalysts and tested the received bio-oil in a 5 kW engine, finding that smooth engine operation was successful when hydrotreated pyrolysis oil was used, while engine operation was not successful when crude pyrolysis oil was used [17]. Bio-oil catalytic hydrogenation has been regarded as a potential routes for production of second generation bio-fuels in the future [14]. Table 1 lists the main product distribution of catalytic hydrogenated aqueous biomass pyrolysis oil referred from Vispute et al.'s work [18]. From Table 1, it could be concluded that the main products after hydrogenation were polyols(ethylene glycol and propylene glycol), and the distribution of ethylene glycol and propylene glycol took up more than 50% after high temperature hydrogenation process. Compared with surrogates for other popular bio-fuels, such as ethanol for bio-ethanol, and ethyl acetate for bio-diesel, few studies have

S. Wu et al. / Fuel Processing Technology 161 (2017) 162–168 Table 1 Product distribution of catalytic hydrogenated aqueous biomass pyrolysis oil.

Acetic acid Levoglucosan Methanol Ethanol 1-Propanol Ethylene glycol Propylene glycol Cyclohexanol 1,2-Butanediol 1,4-Butanediol butyrolactone Glycerol 1,2-cyclohexanediol Sorbitol

Low temperature hydrogenationa

High temperature hydrogenationb

mmol carbon L-1

Percentage (%)

(mmol carbon L-1)

Percentage (%)

203.2 341.8 49.1 19.7 9.7 498 236.1 124.6 32.1 54.2 103 0 106.9 386.9

9.38 15.79 2.27 0.91 0.45 23.00 10.90 5.75 1.48 2.50 4.76 0.00 4.94 17.87

104.9 0 56.8 47.9 42.5 465.1 400.8 51.3 137.4 68.6 110.6 48.8 107.7 21.8

6.30 0.00 3.41 2.88 2.55 27.95 24.08 3.08 8.26 4.12 6.65 2.93 6.47 1.31

a

Low temperature hydrogenation, 5% wt Ru/C catalyst, temperature 398 K (125 °C). High temperature hydrogenation, after low temperature hydrogenation, continue using 5% wt Pt/C catalyst, 523 K(250 °C). b

been reported about the combustion and emission characteristics of glycols. In this article, ethylene glycol, ethanol, and ethyl acetate were chose as the surrogates for a direct comparison on performance and emission characteristics in a diesel engine. Brake specific fuel consumption, exhaust gas temperature, CO, NO, NO2, soot (smoke opacity) emissions were compared based on fuel types and operating conditions. 2. Experimental procedure and specifications Ethanol, ethylene glycol, and ethyl acetate used in this study were purchased from Sigma Chemical Co. and used directly without any further treatment. The commercial 0# diesel was purchased from PetroChina (Nanjing). The properties of diesel, ethanol, ethylene glycol, ethyl acetate and the blends were listed in Table 2. Compared to ethanol and ethyl acetate, ethylene glycol has a lower LHV (lower heating value) but a higher density. Besides, boiling point and viscosity of ethylene glycol are much higher than ethanol and ethyl acetate. For the blends, there is no big difference observed for low heating value and density. The high boiling point lead to a higher T10 for 90% diesel/10% ethylene glycol blend. Adding 10% of blends to diesel will decrease the cetane number of diesel a bit, changing from 56 to around 50. To study the miscibility of polyols in diesel, diesel, ethanol/ethylene glycol/1,3-propylene glycol, ethyl acetate were mixed into a homogeneous mixture by a magnetic stirrer at room temperature 25 °C (As ethyl acetate is miscible with diesel and ethanol, it was used to improve the miscibility of polyols with diesel). Each component (ethanol/

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ethylene glycol/1,3-propylene glycol) was varied from 0% to 100% by volume with 10% increment. After agitation, all of the blends were kept motionless for 24 h at 25 °C to observe the physical stabilities. Finally, phase grams were used to depict the results of three-component systems [19,20]. Standard 0# diesel, ethanol (10% vol)-diesel (90% vol), ethylene glycol (10% vol)-diesel (90% vol), ethyl acetate (10% vol)-diesel (90% vol) blends were prepared for engine testing. A one-cylinder, 4-cycle, direct injected, water-cooled Changchai R170 diesel engine was used in this study. Specifications of the engine were shown in Table 3. Loads were applied by using a hydraulic dynamometer provided by Xiangyi Co., Changsha, China. A MRU VARIO PLUS gas analyzer was used to measure the exhaust temperature (type K thermocouple) and exhaust gas emissions of CO, NO, and NO2 (electrochemical sensors). A NANHUA NHT-6 opacimeter was used to measure the exhaust gas opacity. The analyzers were calibrated routinely by fresh air before every run of experiments. The diesel engine was controlled by an engine control system provided by Xiangyi Co., Changsha, China. A simplified representation of the experimental setup was illustrated as Fig. 1. The engine ran between no load and 90% load conditions. 2.7 kW (rated output) which corresponded to 90% of maximum output of the engine was achieved as the maximum engine load. All the tests had been repeated to check the reproducibility of the experiments and the average values had been used for following analysis. 3. Results and discussions 3.1. The miscibility of polyols in diesel The miscibility of bio-oil with diesel is a big problem to the use of bio-oil [6]. Therefore, emulsification for bio-oil/diesel mixture is necessary [21]. In order to remove the influence of emulsifiers/additives, and to make a direct comparison between ethanol, polyols, and ethyl acetate, direct blends of these fuels with diesel were used. Under this condition, the miscibility of polyols should be checked firstly. Seen from Table 1, ethylene glycol and propylene glycol take up the main fraction in hydrogenated bio-oil, so the miscibility of ethylene glycol, and 1,3propylene glycol has been tested here. Fig. 2 showed the miscibility of ethylene glycol with diesel at room temperature (25 °C). Seen from Fig. 2, only 10% vol ethylene glycol could be mixed with diesel, and 90% vol ethylene glycol could be mixed with 10% vol ethyl acetate. What's more, adding ethyl acetate didn't improve the miscibility of ethylene glycol with diesel. This made a big difference to the miscibility of ethanol [20]. For ethanol at the same room temperature, 10% vol and above 80% vol ethanol could be mixed with diesel, and ethanol was miscible with ethyl acetate, with the help of ethyl acetate, ethanol, ethyl acetate, and diesel could be mixed with any ratio (Fig. 3).

Table 2 Properties of diesel, ethanol, ethylene glycol, ethyl acetate and the blends. 0# diesel Low heating valueb/MJ kg−1 44.1 0.8341 Densityc (20 °C)/g cm−3 T10 = 223 Boiling pointd/°C T50 = 266 T90 = 311 Flash point/°C 63 e 2 −1 4.462 Viscosity (40 °C)/mm s 56.1 Cetane numberf Oxygen content (% mass) – a b c d e f

Ethanola Ethylene glycola Ethyl acetatea 90% diesel/10% ethanol 90% diesel/10% ethylene glycol 90% diesel/10% ethyl acetate 28.6 0.790 78

17.47 1.1132 197

23.90 0.902 77

13 1.1 6 34.78

115 10.2 – 51.61

7.2 0.45 – 36.36

The properties of ethanol, ethylene glycol and ethyl acetate are from Wikipedia. The low heating value of 0# diesel and the blends are measured by GB 384-1981. The density of 0# diesel and the blends are measured by SH/T 0604-2000. The boiling point of 0# diesel and the blends are measured by GB/T 6536-2010. The viscosity of 0# diesel and the blends are measured by GB/T 265-1988 (2004). The cetane number of 0# diesel and the blends are measured by GB/T 0694-2000.

43.63 0.8293 T10 = 172 T50 = 269.5 T90 = 323 – 4.414 51.1 –

43.23 0.8415 T10 = 231 T50 = 270 T90 = 327 – 6.387 50.8 –

43.31 0.8333 T10 = 119.5 T50 = 268.5 T90 = 334 – 3.112 48.1 –

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S. Wu et al. / Fuel Processing Technology 161 (2017) 162–168

3.2. Engine performance and emissions

Table 3 Specifications for R170 diesel engine. Model Type Combustion chamber Cylinder bore Piston stroke 12 h-rated power 1 h-rated power Rated speed Cooling method Injection pressure Compression ratio

Changchai R170 Horizontal, single-cylinder, 4-stroke Direct injection 70 mm 60 mm 2.72 kW 3 kW 2600 rpm Water cooling 13.24 Mpa 21:1

Fig. 4 showed the miscibility of 1,3-propylene glycol with diesel at 25 °C. The miscibility of 1,3-propylene glycol was worse than ethylene glycol. The results found that 1,3-propylene glycol was immiscible with diesel, even with the help of ethyl acetate. In order to explain the miscibility of ethylene glycol and 1,3-propylene glycol, the structures and dipole moments of ethanol, ethylene glycol, and 1,3-propylene glycol were illustrated as Fig. 5. The structures of these compounds were referred from NIST chemistry webbook, and the structures have already been optimized to their minimum energy [22], while the dipole moments were calculated by Gaussian 03 package [23]. Diesel is normally regarded as a non-polar solvent, according to “like dissolves like” expression, non-polar molecules are more easily to be solved in diesel. The polarity of molecule could be decided by its dipole moment, a larger dipole moment means a higher polarity of the molecule. For ethylene glycol, as it has a symmetric chemical formula HOCH2CH2OH, the dipole moment of ethylene glycol is zero and it should be a non-polar molecule. However, seeing from Fig. 5, the structure of ethylene glycol with minimum energy is “boat type”, not a symmetric structure, and this asymmetric structure result in 2.7466 Debye dipole moment of ethylene glycol, larger than that of ethanol, explaining that the miscibility of ethylene glycol is worse than that of ethanol. Besides, 1,3-propylene glycol has the highest dipole moment, this leads to the worst miscibility of 1,3-propylene glycol among the three compounds. According to the miscibility of the tested molecules, as 1,3-propylene glycol can't be mixed with diesel, and only 10% vol ethylene glycol could be mixed with diesel, so in order to make a direct comparison of the tested compounds and avoid influence caused by emulsification, 10% vol ethanol, ethylene glycol, and ethyl acetate have been blended directly with diesel in the following engine test.

10% ethanol-90% diesel, 10% ethylene glycol-90% diesel, and 10% ethyl acetate-90% diesel direct blends have been tested in R170 diesel engine in 0–90% load range, brake specific fuel consumption (BSFC), exhaust gas temperature, CO emission, NO emission, NO2 emission, and soot (smoke opacity) have been checked to make a direct comparison between ethanol, ethylene glycol, and ethyl acetate. 3.2.1. Brake-specific fuel consumption Fig. 6 showed the brake specific fuel consumption of the tested blends. Consistent with their heating value (Table 2), diesel had the lowest BSFC, while ethylene glycol/diesel blend had the highest BSFC. However, as only 10% vol of tested compounds have been added to diesel, the difference of BSFC between them was not so significantly, especially when the load increased to above 30% load. This was consistent with Rakopoulos et al.'s work, adding 5% and 10% vol ethanol only caused a little increase of BSFC [24]. At low load conditions, ethylene glycol and ethyl acetate consumed more fuel per energy than diesel and ethanol, this may cause by insufficient vaporization of ethylene glycol and ethyl acetate. So according to Nadir Yilmaz's opinion, this problem could be mitigated if preheated intake air was used [25]. 3.2.2. Exhaust gas temperature Fig. 7 described the exhaust gas temperature of tested blends. It was clear that as the load increased, the exhaust temperature increased for all the tested blends. After 10% vol ethanol, ethylene glycol, and ethyl acetate added, the decrease extent of exhaust gas temperature was consistent with their influence on BSFC, indicating that lower calorific value of added oxygenated compounds could reduce the exhaust gas temperature [26]. Besides, since these tested compounds have oxygenated functional groups and lower cetane number (Table 2), which caused a lower burning temperature and shorter combustion duration, finally leading to the decrease of exhaust gas temperature [26,27]. 3.2.3. CO emissions CO emissions for tested blends have been illustrated in Fig. 8. The blended oxygenated compounds all led to the mitigation of CO emission. This was consistent with previous works running with ethanol/diesel blends [24,28,29]. Adding oxygenated compounds could influence CO emissions in two ways: 1) the improved oxygen content of the blends resulted in better combustion and lower CO emissions; 2) the reduced gas temperature (this was caused by the cooling effect of blended oxygenated compounds as they have much lower heating value than diesel) led to

1. R170 diesel engine 2. Dynamometer 3. FC2000 Engine Control System 4. Exhaust gas analysis system 5. Fuel gauge component 6. Fuel tank 7. Monitor Fig. 1. Schematic diagram of the experimental setup. 1. R170 diesel engine 2. Dynamometer 3. FC2000 Engine Control System 4. Exhaust gas analysis system 5. Fuel gauge component 6. Fuel tank 7. Monitor.


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Clear liquid 1 phase

Ethyl acetate 100

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Fig. 2. The miscibility of ethylene glycol with diesel at room temperature (25 °C).

higher CO emissions. In this study, only a small amount of oxygenated compounds have been added to diesel, so the first way evolved as the main influence factor and caused the decrease of CO emissions. All the tested blends showed the same trend with the increase of load, this was consistent with Kwanchareon et al.'s work [19]. The decrease extent of CO emission was consistent with the oxygen content of the oxygenated compounds (Table 2). Ethylene glycol had the maximum oxygen content and largest CO mitigation among the three, indicating that ethylene glycol could be treated as a useful additive in diesel to alleviate CO emission.

3.2.4. NO and NO2 emissions The NO and NO2 emissions had been depicted as Figs. 9 and 10, respectively. For NO emissions, ethanol/diesel blends emitted more NO than diesel, in line with Can et al.'s experiment [28]. While ethylene glycol/diesel and ethyl acetate/diesel all reported lower NO emission under most conditions, but at 90% load, all the three tested blends emitted higher NO than diesel. For NO2 emissions, the blends all had higher NO2 emissions than diesel, and ethanol had the highest NO2 emission. Meantime, the NO2 emissions were much lower than NO emissions. Combined with Figs. 9 and 10, it could be found that ethylene glycol

Ethyl acetate


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Fig. 4. The miscibility of 1,3-propylene glycol with diesel at room temperature (25 °C).

Fig. 5. The structures and dipole moments of ethanol, ethylene glycol, and 1,3-propylene glycol.

4000 Diesel 10% Ethanol-90% Diesel 10% Ethylene glycol-90% Diesel 10% Ethyl acetate-90% Diesel

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Fig. 7. Exhaust gas temperature for tested diesel engine running on diesel, 10% ethanol-90 diesel, 10% ethylene glycol glycol-90% diesel, and 10% ethyl acetate-90% diesel.

could usefully lightened the NOx emission at most conditions but not 90% load. There are two ways could be used to explain the generation of NOx for oxygenated/diesel blends. The first one is the low cetane number of oxygenated fuels, which will increase ignition delay and cause greater pressure rise rates, resulting in higher peak cylinder pressure and higher peak combustion temperatures. The higher peak temperature will increase NOx formation. The second one is that the high heat of vaporization and low heating value of oxygenated compounds will decrease the flame temperature, leading to lower NOx emissions. Therefore, the NOx emissions depended on the type of blended fuel, the ratio of the blended fuel, the operation conditions, and the diesel engine techniques [28]. 3.2.5. Soot emissions (smoke opacity) Fig. 11 showed the smoke opacity of the tested three blends. Smoke opacity is an indicator of dry soot emissions which is the main components of particulate matter. It was clear to see that blended oxygenated compounds, namely ethanol, ethylene glycol, and ethyl acetate, were contribute to the reduction of soot. The extent of reduction followed this order: ethanol b ethylene glycol b ethyl acetate. Besides, with the increase of load, the reduction extent also increased. The decrease of smoke opacity could be explained by that the presence of fuel oxygen reduced the formation of rich zones (high local fuel-air ratio) and

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promoted the oxidation of soot nuclei during fuel combustion in the engine [29,30]. To sum up, ethylene glycol presents a lower heating value, higher boiling point, higher oxygen content, and lower miscibility with diesel comparing with ethanol and ethyl acetate, therefore, ethylene glycol can't be used directly in diesel engine and can't be blended directly with diesel at a high ratio. This also indicates that hydrogenated biooil can't be used in these ways. However, the engine tests of ethylene glycol showed that the engine performance of ethylene glycol is comparable to ethanol and ethyl acetate. In some aspects, such as CO mitigation, its performance is even better than ethanol and ethyl acetate, suggesting that ethylene glycol (and hydrogenated bio-oil) could be regarded as a useful additive (up to 10% vol) in diesel for CO and NOx mitigation and soot reduction. 4. Conclusions In this work, the miscibility of ethylene glycol and 1,3-propylene glycol has been tested firstly, finding that 10% vol ethylene glycol could be mixed with diesel and 1,3-propylene glycol is immiscible with diesel. So ethylene glycol and hydrogenated bio-oil can't be used in diesel engine in a large amount, and emulsification is needed when more than 10% vol of ethylene glycol and hydrogenated bio-oil are blended with diesel. Diesel 10% Ethanol-90% Diesel 10% Ethylene glycol-90% Diesel 10% Ethyl acetate-90% Diesel

80


900

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Fig. 9. NO emissions for tested diesel engine running on diesel, 10% ethanol-90 diesel, 10% ethylene glycol glycol-90% diesel, and 10% ethyl acetate-90% diesel.

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Fig. 10. NO2 emissions for tested diesel engine running on diesel, 10% ethanol-90 diesel, 10% ethylene glycol glycol-90% diesel, and 10% ethyl acetate-90% diesel.

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Load (%) Fig. 11. Smoke opacity for tested diesel engine running on diesel, 10% ethanol-90 diesel, 10% ethylene glycol glycol-90% diesel, and 10% ethyl acetate-90% diesel.

To make a direct comparison, 10% ethanol-90% diesel, 10% ethylene90% diesel, and 10% ethyl acetate-90% diesel blends have been tested in a diesel engine under the same operation conditions and compared to a baseline diesel fuel. There is no significant difference in brake specific fuel consumption and exhaust gas temperature for blends. The three oxygenated compounds all have lower CO emissions than diesel and ethylene glycol has the lowest CO emission. Ethylene glycol and ethyl acetate could reduce the NOx emission while ethanol improve the NOx emission. And all the three fuels have reported the reduction of soot emission. Overall speaking, the engine performance of ethylene glycol is totally comparable to ethanol and ethyl acetate. This work suggest that ethylene glycol (hydrogenated bio-oil) could be used as a useful additive (up to 10% vol) in diesel, and the application of hydrogenated bio-oil in engine needs more attention and research. Acknowledgements The authors greatly acknowledge the funding from the projects supported by National Natural Science Foundation of China (51525601, 51476035 and 51476034), the Scientific Research Foundation of Graduate School of Southeast University (YBJJ1504), the Fundamental Research Funds for the Central Universities and the scientific innovation research program of college graduate in Jiangsu province (KYLX_0118). References [1] E. Sadeghinezhad, S. Kazi, F. Sadeghinejad, A. Badarudin, M. Mehrali, R. Sadri, M.R. Safaei, A comprehensive literature review of bio-fuel performance in internal combustion engine and relevant costs involvement, Renew. Sust. Energ. Rev. 30 (2014) 29–44. [2] A. Gupta, J.P. Verma, Sustainable bio-ethanol production from agro-residues: a review, Renew. Sust. Energ. Rev. 41 (2015) 550–567. [3] F.J. Gómez-de la Cruz, F. Cruz-Peragón, P.J. Casanova-Peláez, J.M. Palomar-Carnicero, A vital stage in the large-scale production of biofuels from spent coffee grounds: the drying kinetics, Fuel Process. Technol. 130 (2015) 188–196. [4] J.S.J. Alonso, C. Romero-Ávila, L.S.J. Hernández, A.-K. Awf, Characterising biofuels and selecting the most appropriate burner for their combustion, Fuel Process. Technol. 103 (2012) 39–44.

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