Physical and Chemical Characteristics of Particulate Matter from

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Energy Fuels 2010, 24, 3195–3198 Published on Web 04/27/2010

: DOI:10.1021/ef901388c

Physical and Chemical Characteristics of Particulate Matter from Biodiesel Exhaust Emission using Non-thermal Plasma Technology Pan Wang,*,† Yi-xi Cai,† Lefu Zhang,† and Clemens Tolksdorf‡ † School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China, and Faculty for Environmental Engineering, Hochschule Amberg-Weiden (HAW), 92224 Amberg, Germany

‡

Received November 17, 2009. Revised Manuscript Received April 17, 2010

This research report is about the effect of non-thermal plasma (NTP) on particulate matter (PM) and on the physical and chemical characteristics of rice bran biodiesel (RBD) fuel engines. First, the RBD fuel was successfully prepared by the transesterification method. The main components of the RBD fuel were detected by gas chromatography-mass spectrometry. Other properties, such as the density, the water content, and the calorific value of the fuel, were examined. Second, the bench test was carried out with NTP technology, and the results showed a marked decrease in smoke conversion after NTP treatment. In the third step, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) were used to detect the physical and chemical characteristics of the PM sample. The amount of carbon atoms in the PM sample was significantly reduced, while other metal components were almost the same after NTP treatment.

In recent years, many researchers have made progress in the research of NTP technology used for reducing PM emissions from a diesel engine. It is shown that NTP has the oxidation effect of PM in diesel exhaust at low temperatures.8-10 However, the effects on the physical and chemical characteristics of PM by NTP need to be further examined. NTP generated a great number of high-energy particles with an excited state of atoms.7,11 Particle collision would lead to a series of complicated physical and chemical reactions, which would have a big impact on the generation of PM emissions as well as on the physical and chemical characteristics of PM (e.g., particle size, morphology, chemical composition, etc.). Therefore, it is necessary to study the effects of NTP technology on the physical and chemical characteristics of PM from diesel engines. In this paper, the exhausts from the diesel engine fueled with rice bran biodiesel (RBD) were examined. JSM-7001F thermal field emission scanning electron microscopy (SEM) and Inca Energy 350 energy-dispersive X-ray spectrometry (EDS) were used to detect the surface of PM samples for physical and chemical analyses. The relations between the physical and chemical characteristics of PM and the active radicals from NTP were measured and discussed. Some comparisons to the change of PM elements from a RBD engine before and after NTP treatment were studied.

1. Introduction The global concern over the exhaust emissions of diesel engines has triggered awareness focused on the development of diesel exhaust after-treatment technology. In comparison to the gasoline engine, the diesel engine has the advantages of high thermal efficiency, power range, as well as lower HC and CO emissions. However, diesel engines emit roughly 30-100 times more particulate matter (PM) than gasoline engines. PM emissions from the diesel engine are mainly composed of porous carbon with a size of 0.1-10 μm, which have a very large surface area and a strong adsorption capacity and would adsorb carcinogenic substances, such as benzo(a)pyrene, benzo(a)anthracene, and other organic matter. Particularly, the PM with a size of 0.1-0.5 μm can lead to a variety of chronic diseases, such as emphysema, skin diseases, and morbid disease, when they are directly inhaled into the human body.1-3 Therefore, it is an important research topic to control PM emissions of diesel engines. With regard to the advantages of the high conversion rate of gas, the wide temperature range of treating pollutants without secondary pollution, and plasma chemical processing, which can be simply operated at room temperature, non-thermal plasma (NTP) technology has been investigated as a promising way to reduce harmful emissions for diesel engines.4-7

2. Experimental Section 2.1. RBD Fuel. RBD fuel was made from crude rice bran oil by a transesterification method. The process of transesterification is very complex. Rice bran oil was poured into a flask that was kept in a water bath and maintained at 50 °C. The fatty acids were converted to esters in a pretreatment process with an acid catalyst. The molar ratio of methanol/rice bran oil was 6:1,

*To whom correspondence should be addressed. E-mail: wangpan176@ 163.com. (1) Wei, Y. J.; Han, I. K.; Shao, M.; Hu, M.; Zhang, J. F.; Tang, X. Y. Environ. Sci. Technol. 2009, 43, 4757–4762. (2) Neeft, J. P. A.; Makkee, M.; Moulijn, J. A. Fuel Process. Technol. 1996, 47, 1–69. (3) Lee, M. W.; Chen, M. L.; Lung, S. C. C.; Tsai, C. J.; Yin, X. J.; Lin, C. Y.; Wang, K. H. Energy Fuels 2004, 18, 477–484. (4) Wen, B.; Yeom, Y. H.; Weitz, E.; Sachtler, W. M. H. Appl. Catal., B 2004, 48, 125–131. (5) Tonkyn, R. G.; Barlow, S. E.; Hoard, J. W. Appl. Catal., B 2003, 40, 207–217. (6) Fushimi, C.; Madokoro, K.; Yao, S. L.; Fujioka, Y.; Yamada, K. Plasma Chem. Plasma Process. 2008, 28, 511–522. (7) Yao, S. L. Recent Pat. Chem. Eng. 2009, 2, 67–75. r 2010 American Chemical Society

(8) Jeon, S. G.; Kim, K. H.; Shin, D. H.; Nho, N. S.; Lee, K. H. Korean J. Chem. Eng. 2007, 24, 522–526. (9) Okubo, M.; Arita, N.; Kuroki, T.; Yamamoto, T. Thin Solid Films 2007, 515, 4289–4295. (10) Chae, J. O. J. Electrost. 2003, 57, 251–262. (11) Durme, J. V.; Dewulf, J.; Leys, C.; Langenhove, H. V. Appl. Catal., B 2008, 78, 324–333.

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pubs.acs.org/EF

Energy Fuels 2010, 24, 3195–3198

: DOI:10.1021/ef901388c

Wang et al.

Figure 1. Process flow schematic of RBD fuel production.

Figure 2. Gas chromatogram of fatty acid composition of RBD.

and the amount of the KOH catalyst in methanol was 0.9%. Transesterification of rice bran oil with the catalyst, 0.9% (w/w) potassium hydroxide, gave the best yields of the esters. With a further increase in catalyst quantity, there was a little decrease in the conversion efficiency. The sulfuric acid methanol solution was added to the preheated rice bran oil and stirred for some minutes at the same rate. After that, the product was poured into a separating funnel to separate the excess methanol. The schematic diagram of the preparation process is illustrated in Figure 1. The components of RBD fuel were determined by gas chromatography, and the fatty acid composition of RDB is shown in Figure 2. The main fatty acid compositions of RBD were hexadecanoic acid methyl ester (ME) (16%), 9-octadecenoic acid ME (41%), and 9,12-octadecadienoic acid ME (38%), while other contents of fatty acid were very low. 2.2. NTP Reactor. The NTP reactor was designed on the basis of the dielectric barrier discharge theory, which consisted of three cylindrical quartz glass tubes (the outer and inner diameters of each tube were 13 and 10 mm, respectively). A 2 mm diameter stainless-steel rod was put inside the tube as the positive electrode, and a brass plate outside the tube was the negative electrode. The length of the effective discharge region was 15 cm. The discharge voltage was measured using a voltage probe to obtain its analog signal that could be digitized using an oscilloscope (Tektronix TDS 2024B), and the discharge power measurement using the Q-V Lissajous method was carried out by measuring voltage changes of a capacitor inserted in the discharge circuit. A high-frequency, high-voltage, alternating current (AC) power supply can be adjusted in the range of 0-25 kV and 8-20 kHz. The discharge frequency was 13 kHz. 2.3. Experimental Setup. The experiment was carried out with the measurement and control system of the internal combustion engine. A Horiba exhaust gas analyzer (MEXA-7200D) and AVL exhaust particle analyzer were used to measure the concentration of exhaust emissions. The schematic diagram of the bench test is shown in Figure 3. A stationary, direct-injection (DI) diesel engine (rated power is 6.5 kW; rated speed is 3600 revolutions/min; and displacement volume is 0.406 L) was used for the investigation of the exhaust properties with NTP. The experimental conditions varied from 15 to 90% of the full load

Figure 3. Schematic diagram of the test bench.

at rated speed and 2800 revolutions/min speed. The particles before and after NTP treatment were collected with the use of the AVL SPC472 smart sampler, and those particle samples from the RBD engine and the regular diesel engine were analyzed with JSM-7001F SEM and Inca Energy 350 EDS, to observe and analyze the physical and chemical change of PM with the NTP technology. A smoke opacity was measured by a smoke meter (AVL 439). The conversion rate of smoke before and after NTP treatment was calculated according to the formula given below η - η2 η ¼ 1 η1 where η is the conversion rate, η1 is the value of smoke opacity before NTP, and η2 is the value of smoke opacity after NTP.

3. Results and Discussion 3.1. RBD Fuel Characteristics. The characteristics of RBD fuel were analyzed, and the results are shown in Table 1. Table 1 shows that most parameters of the RBD fuel comply with the limits prescribed in the American Society for Testing and Materials (ASTM) D6751-02 and Deutsche IndustrieNorm (DIN) V51606 standards for biodiesel, indicating that RBD fuel can be directly used in diesel engine without modifying the structure of the engine. 3196

Energy Fuels 2010, 24, 3195–3198

: DOI:10.1021/ef901388c

Wang et al.

Table 1. Fuel Properties of RBD biodiesel standards property density (at 15 °C) (kg/m3) viscosity (at 40 °C) (mm2/s) flash point (°C) cold filter plugging point (°C) mass fraction of sulfur (%) cetane index water content (%) ash content (%) copper corrosion (3 h, at 50 °C) iodine value (g of iodine/100 g) calorific value (MJ/kg)

RBD

ASTM D6751-02

884

DIN V51606

regular diesel

875-900

830

4.12

1.9-6.0

3.5-5.0

2.4

205 -2

>130

>120 0

55

0.01