- Email: [email protected]
Catalytic upgrading of oil fractions separated from food waste leachate
Bioresource Technology 102 (2011) 3952–3957
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Catalytic upgrading of oil fractions separated from food waste leachate Hyeon Su Heo a, Sang Guk Kim b, Kwang-Eun Jeong c, Jong-Ki Jeon d, Sung Hoon Park e, Ji Man Kim f, Seung-Soo Kim g, Young-Kwon Park a,h,⇑ a
Graduate School of Energy and Environmental System Engineering, University of Seoul, Seoul 130-743, Republic of Korea Korea Institute of Energy Research, Daejeon 303-343, Republic of Korea c Green Chemistry Research Division, Korea Research Institute of Chemical Technology, Daejeon 305-600, Republic of Korea d Department of Chemical Engineering, Kongju National University, Cheonan 330-717, Republic of Korea e Department of Environmental Engineering, Sunchon National University, Suncheon 540-742, Republic of Korea f Department of Chemistry, BK21 School of Materials Science and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea g Department of Chemical Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea h School of Environmental Engineering, University of Seoul, Seoul 130-743, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 6 September 2010 Received in revised form 21 November 2010 Accepted 22 November 2010 Available online 28 November 2010 Keywords: Food waste oil fractions Catalytic pyrolysis HZSM-5 Gallium Aromatics
a b s t r a c t In this work, catalytic cracking of biomass waste oil fractions separated from food waste leachate was performed using microporous catalysts, such as HY, HZSM-5 and mesoporous Al-MCM-48. The experiments were carried out using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) to allow the direct analysis of the pyrolytic products. Most acidic components, especially oleic acid, contained in the food waste oil fractions were converted to valuable products, such as oxygenates, hydrocarbons and aromatics. High yields of hydrocarbons within the gasoline-range were obtained when microporous catalysts were used; whereas, the use of Al-MCM-48, which exhibits relatively weak acidity, resulted in high yields of oxygenated and diesel-range hydrocarbons. The HZSM-5 catalyst produced a higher amount of valuable mono aromatics due to its strong acidity and shape selectivity. Especially, the addition of gallium (Ga) to HZSM-5 significantly increased the aromatics content. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The generation of organic waste continues to increase. The abandoning, landfilling and ocean disposal of organic waste, such as food waste, livestock excretion, wastewater sludge and butchery waste, has caused severe environmental pollution. Thus, the direct landfilling of organic waste has been banned in a number of countries. Methods for the appropriate treatment of organic waste are being considered in South Korea to limit the ocean disposal of organic waste. In 2006, 13,300 ton/day of food waste was generated in South Korea, resulting in an annual economic loss of about $15 billion (Lee et al., 2009). Food waste can be treated using various processes, including composting, feedstuff production, anaerobic digestion for energy production and pulverization for the production of fuel. While the detailed procedures of these processes vary depending on the purpose of the treatment, dehydration, usually by press rolling, and the removal of impurities are common pre-treatment steps. Water and particulate matter are separated as leachate during ⇑ Corresponding author at: Graduate School of Energy and Environmental System Engineering, University of Seoul, Seoul 130-743, Republic of Korea. Tel.: +82 2 2210 5623; fax: +82 2 2244 2245. E-mail address: [email protected] (Y.-K. Park). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.11.099
the press rolling dehydration stage, with the dehydrated cake sent to a dryer. The leachate is a sludge that contains water, solid particulate matter and oil fractions. Existing food waste leachate treatment processes, without oil separation, result in blocking of the gate screens within water treatment plants with clotted oil. Moreover, there is a build-up of oil layers on the water surface of the aeration tank, hindering the air supply for microorganism breeding. The danger of fire has been a serious problem in the drying process of the sludge separated from food waste leachate due to the oil layer accumulating on the wall of the discharge duct. Therefore, a process to separate oil from food waste leachate has been developed (Kim, 2010). Usually, one liter of leachate contains 5 g of oil fractions, which are mainly composed of animal and vegetable derived oils (Kim, 2010). The oil fractions separated from the leachate can be used as an energy source. At the same time, the oil fractions can be converted to a more useful product, biofuel, which is also an alternative energy source. Animal and vegetable oils can generally be converted to biodiesel via transesterification, and can also be converted to bio-oils via pyrolysis. The bio-oils produced via biomass pyrolysis can be used as heating fuel, but the fuel quality is low (Park et al., 2010a). Therefore, numerous efforts have been made to produce reformed oils, with improved quality, via catalytic reactions of the lowquality bio-oils (Lee et al., 2008; Park et al., 2010b,c). Investigations
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
have recently been conducted to produce bio-fuels from vegetable oils via catalytic pyrolysis (Ngo et al., 2010; Ong and Bhatia, 2010; Prado and Filho, 2009). To the best of our knowledge, catalytic pyrolysis has never been applied to the production of valuable oils via the reforming of food waste oil. Also, Al-MCM-48, a mesoporous material with cubic symmetry, has not been applied to the catalytic pyrolysis of biomass, despite its higher catalytic ability than Al-MCM-41 (Park et al., 2008). One objective of this study was to investigate the performance of microporous and mesoporous catalysts, such as HY, HZSM-5 and Al-MCM-48, for the catalytic cracking of oil fractions separated from food waste leachate. Another objective was to increase the fractions of valuable aromatic compounds in bio-oil using HZSM-5 with the addition of Ga. The experiments were carried out using the Py-GC/MS instrument to allow the direct analysis of the pyrolytic products. Several Py-GC/MS studies have been carried out before using different catalysts (Adam et al., 2005; Lu et al., 2009, 2010; Pattiya et al., 2008). The product distribution after the catalytic reaction was compared to reveal the catalytic effects of different catalysts.
3953
vacuum for 5 h at 250 °C, using nitrogen as the adsorption gas at the temperature of liquid nitrogen. The nitrogen adsorption– desorption isotherms and BET surface area were then obtained. The surface acidities of the catalysts were measured using temperature programmed desorption of ammonia (NH3-TPD), employing a BEL-CAT TPD analyzer with a TCD detector (Park et al., 2010d). 2.4. Py-GC/MS analyses
The oil fractions separated from food waste leachate were obtained from the KIER using the normal hexane extractive chemical test. For more details on the procedure for the normal hexane extractive chemical test, one can refer to the literature (Kim, 2010). Pyrolysis tests were performed using a TGA analyzer (PerkinElmer, Pyris 1 TGA). A typical sample mass of 20 mg was heated at 10 K/min, with nitrogen purging, to a final temperature of 873 K.
A double-shot pyrolyzer (Frontier-Lab Co., Py-2020iD), coupled directly to GC/MS, was used for identification of the catalytic cracking products. For the sample preparation, the food waste oil fraction (1 ll) and catalyst (1 mg) were placed in a sample cup, which was then placed into a 500 °C furnace under a He atmosphere. The gaseous species generated during the catalytic cracking were directly introduced into a GC inlet port (split ratio of 1/ 100) and onto a metal capillary column (Ultra ALLOY-5MS/HT; 5% diphenyl and 95% dimethylpolysiloxane, length 30 m, i.d. 0.25 mm, film thickness 0.5 lm; Frontier Laboratories Ltd., Japan). To prevent condensation of the products, the interface and inlet temperatures were both maintained at 300 °C. The column temperature was programmed to ramp from 40 (5 min) to 320 °C (10 min), at a heating rate of 5 °C/min. The temperature of the GC/MS interface was 280 °C, with the MS operated in the EI mode at 70 eV. The program was run in the scanning range from 29 to 400 amu, at a rate of 2 scans/s. The identification of peaks was performed using the NISTMS library. The experiments were conducted at least three times for each catalyst to confirm the reproducibility of the reported procedures. The average values of the peak area and peak area% as received were calculated for each identified product.
2.2. Preparation of catalyst
3. Results and discussion
Microporous catalysts, such as HY (Si/Al = 2.6) and HZSM-5 (Si/ Al = 15, 40), were purchased from Zeolyst. 1 wt.% Ga was impregnated into HZSM-5 using Ga(NO3)3 by incipient wetness method. The impregnated Ga/HZSM-5 catalyst was dried overnight at 110 °C and calcined in air at 550 °C for 5 h, reduced in a hydrogen stream at 500 °C for 4 h, and finally calcined in air at 550 °C for 5 h. The MCM-48 was prepared using the following procedure. First, to prepare pure MCM-48, 10.0 g of CTABr, 1.5 g of Brij-30 and 190.5 g of distilled water were mixed. When the mixture became transparent, 46.13 g of sodium silicate solution (Na/Si = 0.5) was slowly added, drop wise, with stirring. The prepared solution was placed in an oven at 100 °C for 48 h for the reaction to take place. After 48 h, the solution was cooled and its pH adjusted to 10 using 50 wt.% acetic acid. The solution was then placed in the oven at 100 °C for the reaction to take place for a further 48 h. The pH adjusting process was repeated three times. The solution was then washed with distilled water, filtered and dried in the oven for 24 h, which was followed by another washing with ethanol, filtering, drying for 24 h and baking at 550 °C for 4 h. Aluminum incorporation into MCM-48 was performed using the post-synthetic grafting method (Park et al., 2008). Before baking, the prepared mesoporous material was introduced into a solution prepared by dissolving AlCl3 in 100 mL of ethanol, according to the desired Si/Al ratio. The solution was stirred for 24 h, washed with ethanol, filtered, dried for 24 h and calcined for 4 h at 550 °C.
3.1. Characteristics of oil derived from food waste leachate
2. Experimental 2.1. Oil fractions separated from food waste leachate
2.3. Catalyst characterization The BET surface area of the catalyst was measured using an ASAP 2010 apparatus (Micrometrics). The catalyst sample was dried, with 0.3 g of the dried sample taken, and outgassing under
The elemental composition of the oil derived from food waste leachate was C 75.45 wt.%, H 13.85 wt.%, N 0.53 wt.%, S 0.01 wt.% and O 10.16 wt.% (by difference). The HHV was calculated following the formula suggested in the literature (Demibras, 1997). As the HHV of the oil (39.52 MJ/kg) was slightly lower than that of soybean oil (40.09 MJ/kg) (Ngo et al., 2010), the oil can be classified as a promising fuel. However, the oil cannot be applied directly to industry due to its high viscosity and high fatty acid content; therefore, an additional process, such as catalytic pyrolysis, will be required for its conversion into a valuable fuel. To investigate the pyrolytic behavior of food waste leachate, TGA and DTG analyses were carried out (data not shown). When 20 mg of leachate was analyzed using TGA, DTG peaks were observed at 110, 280 and 450 °C, which appeared to be the results of reductions of water, low-molecular-weight hydrocarbons and high-molecular-weight acids, respectively, in the leachate due to pyrolysis. Also, a considerable mass reduction was achieved below 500 °C. Based on this result, the catalytic pyrolysis reactions in this study were conducted at 500 °C. 3.2. Characterization of catalysts Table 1 shows the physical properties of the catalysts used in this study. HZSM-5 had the smallest surface area, while the surface area of Al-MCM-48 was largest. Zeolite catalysts were shown to have sub-nanometer pores (0.7 nm for HY and 0.5 nm for HZSM5); whereas, Al-MCM-48 had nano-pores (2.97 nm). Fig. 1 shows the TPD results. The number of acid sites on the Al-MCM-48 catalyst was smaller than those of the other catalysts, and Al-MCM-48
3954
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Table 1 Physical properties of catalysts. Catalyst
BET surface area (m2/g)
Average pore diameter (nm)
Si/Al ratio
HY HZSM-5 (15) HZSM-5 (40) Al-MCM-48
730 400 425 1380
0.74 0.74 [1 1 1]a 0.51 0.55 [1 0 0]a 0.53 0.56 [0 1 0]a 0.51 0.55 [1 0 0]a 0.53 0.56 [0 1 0]a 2.97
2.6 15 40 20
Channel diameter viewed along [hkl] direction.
50
Distribution (area%)
a
60
40
400oC 500oC 600oC 700oC
30
20
HY HZSM5 (15) Ga/HZSM5 (15) HZSM5 (40) Al-MCM48
10
0
Intensity (a.u)
s se Ga
es at en g y Ox
s id Ac
ns bo ar c o dr Hy
ics at om r A
Fig. 2. Product distribution of noncatalytic pyrolysis of oil fractions separated from food waste leachate. 100
0
100
200
300
400
500
600
700
Temperature ( oC) Fig. 1. NH3 TPD of catalysts.
had weak acid sites that exhibited a maximum peak at about 250 °C. Conversely, the HY catalyst had the largest number of acid sites: weak acid sites with a peak at about 220 °C and medium acid sites with a shoulder peak at about 330 °C. HZSM-5 had weak acid sites and strong Brönsted acid sites, with peaks at about 220 and 400 °C, respectively. The order of the numbers of acid sites was HY > HZSM-5 (15) > Al-MCM-48; whereas, the order of the strengths of acid sites was HZSM-5 > HY > Al-MCM-48. When the Si/Al ratio of HZSM-5 was increased from 15 to 40, the number of acid sites decreased. The addition of Ga to HZSM-5 decreased the number of acid sites of HZSM-5. 3.3. Noncatalytic pyrolysis The oil fraction of the food waste leachate was pyrolyzed using Py-GC/MS. One of the drawbacks of Py-GC/MS is that it does not allow product collection, thus, the exact bio-oil yield cannot be determined. Moreover, the GC/MS technique cannot provide quantitative analyses of the volatile products. However, the chromatographic peak area of a compound was considered to be linear with respect to its quantity, and the peak area% with its content. During each experiment, the masses of the oil and catalyst were the same. Therefore, the corresponding chromatographic peak area% can be compared to show the change in the relative content of the pyrolysis vapors (Adam et al., 2005; Lu et al., 2010; Heo et al., 2010a,b; Pattiya et al., 2008; Wang et al., 2010). Supplementary data, Table S1 shows the results of the decomposition of the food waste leachate oil fraction at different temperatures between 400 and 700 °C. The product species accounting for the largest area% at every temperature tested was oleic acid, the main component of olive oil. Fatty acid esters, such as octadecanoic acid ethyl ester, hexadecanoic acid ethyl ester and linoleic acid ethyl ester, were also contained in the products. These species stem from the animal and vegetable oils that comprise the food waste leachate. As the pyrolysis products were a mixture of a num-
Distribution (area%)
80
400oC 500oC 600oC 700oC
60
40
20
0
1 to 4
5 to 9
10 to 17
over 17
Carbon number Fig. 3. Carbon number distribution of noncatalytic pyrolysis of oil fractions separated from food waste leachate.
ber of species, these species were roughly grouped into five categories: gases (CO, CO2, and hydrocarbons up to C4), oxygenates, acids, hydrocarbons (aliphatic alkanes and alkenes) and aromatics. Fig. 2 shows that with increasing temperature, the fatty acids were decomposed into low-molecular-weight hydrocarbons, aromatics and gases. In particular, the amount of oleic acid, which accounted for the largest amount of the product, was shown to decrease dramatically with increasing pyrolysis temperature (Table S1). Fig. 3 illustrates the results of the product grouping based on the number of carbon atoms in the molecules. With increasing pyrolysis temperature, the fractions of low-molecular-weight species increased; C5–C9 species accounted for the largest fraction at 700 °C. This result suggests that the food waste oil fraction can be converted to high-quality fuels by pyrolysis at high temperature. However, a high-temperature decomposition reaction requires a lot of energy. Therefore, it would be better to make the same reaction take place at a lower temperature using catalysts. 3.4. Catalytic pyrolysis Supplementary data, Table S2 shows the list of the products obtained from the decomposition of the food waste leachate oil fraction, with the aid of various catalysts, at 500 °C. It can be seen that
3955
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Distribution (area%)
40
Non-catalytic Al-MCM48 HY HZSM5 (40) HZSM5 (15)
30
20
10
0 s se Ga
e at en yg x O
s
ns ics at bo m ar ro oc A r d Hy
id Ac
Hs PA
n ow kn Un
Fig. 4. Product distribution of catalytic pyrolysis of oil fractions separated from food waste leachate.
the use of catalysts led to the decomposition of high-molecularweight species into those with low-molecular-weights. In particular, most of the oleic acid was decomposed when catalysts were used. In order to illustrate the trend in the fractions of different species in the reaction products according to the catalysts used, as shown in Fig. 4, the product species were grouped into seven categories: gases, oxygenates, acids, hydrocarbons, aromatics (monocyclic aromatic hydrocarbons), polycyclic aromatic hydrocarbons (PAHs) and unknowns. A considerable amount of fatty acids produced under the non-catalytic conditions were decomposed further with the use of catalysts. The product distribution was, to a large extent, dependent on the catalyst used. When the Al-MCM-48 catalyst, with a large pore size, was used, the amounts of oxygenates, hydrocarbons and monocyclic aromatics (benzene, toluene and alkylated derivatives) were higher than in the case of non-catalytic pyrolysis. When the HY zeolite catalyst was used, most oxygenates and fatty acids were converted into gases, hydrocarbons and monocyclic aromatics. HZSM-5 showed a similar effect to that of HY zeolite: oxygenates and fatty acids were converted into gases, hydrocarbons and monocyclic aromatics. In particular, when HZSM-5 was used, the amounts of monocyclic aromatics and gases were very high compared to the cases where the other catalysts were used. It is well known that hydrocarbons and aromatics are regarded as valuable products due to their contribution to the calorific value of the bio-oil. However, HY and HZSM-5 also produced PAHs, which are well known to be toxic and mutagenic compounds. Fatty acids are decomposed on the acid sites of the catalysts. Mesoporous catalysts, such as Al-MCM-48, are advantageous for the decomposition of high-molecular-weight species due to their large pore size. Nevertheless, the number and strength of their acid sites are lower than those of HY zeolite and HZSM-5 (Fig. 1), leading to a relatively lower decomposition efficiency. Therefore, when Al-MCM-48 was used, the fatty acids contained within the food waste leachate were mainly decomposed into oxygenates and hydrocarbons, with slight conversion to aromatic compounds. Lukyanov et al. (1994, 1995) reported that the presence of strong Brönsted acid sites in a catalyst, such as HZSM-5, enhanced the production of aromatics. HZSM-5 could accelerate the oligomerization of ethylene and propylene to form C4–C10 olefins, which then undergo dehydrogenation to form diolefins (or dienes). The subsequent cyclization and further dehydrogenation resulted in the formation of aromatic hydrocarbons. In this study, more aromatic
compounds were generated when HY or HZSM-5, which have a greater number of Brönsted acid sites, was used compared to the case where a mesoporous catalyst with fewer Brönsted acid sites was used. In particular, with the use of HZSM-5, which has greater acid site strength than the HY catalyst, considerable amounts of hydrocarbons were converted into aromatics. It can be suggested that some higher-molecular-weight compounds in the oil separated from food waste would react on the surface of the HZSM-5 catalyst and generate many low-molecular-weight hydrocarbons, such as ethylene and propylene. These low-molecular-weight hydrocarbons then subsequently enter the three-dimensional pore system of the HZSM-5 catalyst and undergo further polymerization and aromatization to form aromatic hydrocarbons. Ooi et al. (2004, 2005) obtained similar results from their fatty acids mixture cracking experiments conducted using various catalysts: paraffinic hydrocarbons were the main products when Al-SBA-15 and AlMCM-41 were used; whereas, the use of HZSM-5 resulted in high yields of aromatic compounds. Additional experiments were carried out to investigate the effect of the acidity of the catalysts. Fig. 4 also shows the results obtained by using different Si/Al ratios for the HZSM-5 catalyst. As shown in this figure, the HZSM-5 catalyst with a Si/Al ratio of 40 led to the production of more hydrocarbons and less aromatics than that with a Si/Al ratio of 15. This result indicated that a significant amount of hydrocarbons was converted into aromatics when the catalyst with a Si/Al ratio of 15 was used. The use of the catalyst with a Si/Al ratio of 15 also resulted in the production of higher amounts of gases. The results of these experiments indicated that the catalyst with a Si/Al ratio of 15, which has a greater number of Brönsted acid sites, effectively enhanced the catalytic cracking and aromatization, implying that Brönsted acid sites play an important role in the production of aromatics. The shape selectivity of HZSM-5 also affects the selectivity for aromatics production (Adjaye et al., 1996). The pores of HZSM-5, with intersecting channels, are ideal for producing aromatic compounds. The newly formed aromatic compounds can then either diffuse from the catalyst or remain inside the pores to form coke. Williams and Horne (1994) reported that the unique pore structure of HZSM-5 led to a high yield of aromatics in bio-oil. Pan et al. (2010) also reported the importance of the three-dimensional pore system of HZSM-5 catalyst in the production of aromatic hydrocarbons. Fig. 5 shows the product distribution according to the number of carbon atoms in the molecules. The use of catalysts was shown to facilitate the conversion of high-molecular-weight species into 80
60
Distribution (area%)
50
Non-catalytic Al-MCM48 HY HZSM5(40) HZSM5(15)
40
20
0 1 to 4
5 to 9
10 to 17
over 17
Carbon number Fig. 5. Carbon number distribution of catalytic pyrolysis of oil fractions separated from food waste leachate.
3956
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Table 2 Effect of Ga addition on product distribution in terms of area%.
Gas Oxygenates Acid Hydrocarbon Monocyclic aromatics PAHs
HZSM-5 (15) (area%)
Ga/HZSM-5 (15) (area%)
17.83 10.45 0.87 18.13 42.41 6.57
15.43 9.26 0.85 10.39 58.07 5.94
Brönsted acid sites led to a significantly enhanced production of aromatic compounds.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.biortech.2010.11.099. References
those with low-molecular-weights. Mesoporous Al-MCM-48 led to the largest production of diesel-range compounds, with the number of carbon atoms ranging from 10 to 17. It is believed that the large pore size of Al-MCM-48 would be favorable for the production of high-molecular-weight species; whereas, its weak acidity would suppress excessive decomposition. When HY zeolite and HZSM-5 were used, the dominant products were gasoline-range compounds, with the number of carbon atoms ranging from 5 to 9, which can be attributed to their small pore sizes and strong Brönsted acid sites. In particular, when HZSM-5, which has the strongest Brönsted acidity, was used, the production of low-molecular-weight gases was the highest. The use of HY, which had weaker acid strength and a larger pore size than HZSM-5, resulted in higher fractions of C10–C17 compounds and PAHs, but a lower fraction of gases than HZSM-5. In another set of experiments, Ga was added to HZSM-5. As shown in Table 2 the addition of Ga resulted in the decreased production of hydrocarbons, but increased aromatics. In particular, the fraction of monocyclic aromatics, with high economic values, e.g., benzene, toluene and xylene, were significantly increased from 42.41% to 58.07%, and the fraction of hydrocarbons decreased as much, while the other species were affected much less by the addition of Ga. The addition of Ga to HZSM-5 is known to result in an interaction between the Brönsted and Lewis acid sites, which promotes the conversion of hydrocarbons and bio-oil components into aromatics. Kwak and Sachtler (1994) reported that Brönsted acid sites catalyze oligomerization and ring closure, but Ga, with respect to protons, acts as a dehydrogenating site. Park et al. (2007, 2010d) also suggested that the incorporation of Ga cations into a MFI type zeolite increased the initial dehydrogenation rates of alkanes, as well as the subsequent dehydrogenation rates required to more rapidly transform alkenes to aromatics, leading to considerably larger aromatics production than obtained by the parent MFI type zeolite. It is believed that Ga played a similar role in this study: a considerable amount of hydrocarbons may have been converted into aromatics at the Ga and Brönsted acid sites. When Ga was added, the carbon number distribution of the product was similar to that obtained without the addition of Ga, but the production of gases was slightly decreased while the C5–C9 and C10–C17 hydrocarbon fractions were slightly increased (data not shown). This result was attributed to the loss of some strong acid sites from HZSM-5 due to the addition of Ga, resulting in partial suppression of the decomposition reactions (Park et al., 2007, 2010d). 4. Conclusions The pyrolysis of the food waste leachate oil fraction was conducted using Py-GC/MS. The use of catalysts resulted in a significant improvement in the production of bio-oil. Al-MCM-48 suppressed excessive decomposition and converted the oil fraction mainly into diesel-range compounds. Conversely, HY and HZSM-5 showed high selectivity to gasoline-range compounds. In particular, HZSM-5 provided a high aromatics yield, which can be attributed to its strong Brönsted acid sites and shape selectivity. When Ga was added to HZSM-5, the interaction between the Ga and
Adam, J., Blazso, M., Meszaros, E., Stocker, M., Nilsen, M.H., Bouzga, A., Hustad, J.E., Gronli, M., Oye, G., 2005. Pyrolysis of biomass in the presence of Al-MCM-41 type catalysts. Fuel 84, 1494–1502. Adjaye, J.D., Katikaneni, S.P.R., Bakhshi, N.N., 1996. Catalytic conversion of a biofuel to hydrocarbons: effect of mixtures of HZSM-5 and silica–alumina catalysts on product distribution. Fuel Process. Technol. 48, 115–143. Demibras, A., 1997. Calculation of higher heating values of biomass fuels. Fuel 76, 431–434. Heo, H.S., Park, H.J., Park, Y.K., Ryu, C., Suh, D.J., Suh, Y.W., Yim, J.H., Kim, S.S., 2010a. Bio-oil production from fast pyrolysis of waste furniture sawdust in a fluidized bed. Bioresour. Technol. 101, S91–S96. Heo, H.S., Park, H.J., Park, S.H., Kim, S., Suh, D.J., Suh, Y.W., Kim, S.S., Park, Y.K., 2010b. Fast pyrolysis of rice husks under different reaction conditions. J. Ind. Eng. Chem. 16, 27–31. Kim, S.G. System for separation of oil and sludge from food waste leachate. Korea Patent 10-2010-0053719. Kwak, B.S., Sachtler, W.M.H., 1994. Effect of Ga/Proton balance in Ga/HZSM-5 catalysts on C3 conversion to aromatics. J. Catal. 145, 456–463. Lee, H.I., Park, H.J., Park, Y.K., Hur, J.Y., Jeon, J.K., Kim, J.M., 2008. Synthesis of highly stable mesoporous aluminosilicates from commercially available zeolites and their application to the pyrolysis of woody biomass. Catal. Today 132, 68–74. Lee, S.W., Shin, T.S., Yang, J., Kim, K.Y., Cho, B.R., Yeon, I.J., 2009. Fermentation of food waste mixed with additives by indigenous bacteria at room temperature and utilization of fermented feed for animal. J. Kor. Waste Manage. 26, 243–251. Lu, Q., Xiong, W.M., Li, W.Z., Guo, Q.X., Zhu, X.F., 2009. Catalytic pyrolysis of cellulose with sulfated metal oxides: a promising method for obtaining high yield of light furan compounds. Bioresour. Technol. 100, 4871–4876. Lu, Q., Zhang, Y., Tang, Z., Li, W.Z., Zhu, X.F., 2010. Catalytic upgrading of biomass fast pyrolysis vapors with titania and zirconia/titania based catalysts. Fuel 89, 2096–2103. Lukyanov, D.B., Gnep, N.S., Guisnet, M.R., 1994. Kinetic modeling of ethane and propene aromatization over HZSM-5 and GaHZSM-5. Ind. Eng. Chem. Res. 33, 223–234. Lukyanov, D.B., Gnep, N.S., Guisnet, M.R., 1995. Kinetic modeling of propane aromatization reaction over HZSM-5 and GaHZSM-5. Ind. Eng. Chem. Res. 34, 516–523. Ngo, T.A., Kim, J., Kim, S.K., Kim, S.S., 2010. Pyrolysis of soybean oil with H-ZSM-5 (proton-exchange of zeolite socony mobil #5) and MCM41 (mobil composition of matter no. 41) catalysts in a fixed-bed reactor.. Energy 35, 2723–2728. Ong, Y.K., Bhatia, S., 2010. The current status and perspectives of biofuel production via catalytic cracking of edible and non-edible oils. Energy 35, 111–119. Ooi, Y.S., Zakaria, R., Mohamed, A.R., Bhatia, S., 2004. Catalytic conversion of palm oil-based fatty acid mixture to liquid fuel. Biomass Bioenergy 27, 477–484. Ooi, Y.S., Zakaria, R., Mohamed, A.R., Bhatia, S., 2005. Catalytic conversion of fatty acids mixture to liquid fuel and chemicals over composite microporous/ mesoporous catalysts. Energy Fuel 19, 736–743. Pan, P., Hu, C., Yang, W., Li, Y., Dong, L., Zhu, L., Tong, D., Qing, R., Fan, Y., 2010. The direct pyrolysis and catalytic pyrolysis of Nannochloropsis sp. residue for renewable bio-oils.. Bioresour. Technol. 101, 4593–4599. Park, H.J., Dong, J.I., Jeon, J.K., Yoo, K.S., Yim, J.H., Sohn, J.M., Park, Y.K., 2007. Conversion of the pyrolytic vapor of radiata pine over zeolite. J. Ind. Eng. Chem. 13, 182–189. Park, H.J., Yim, J.H., Jeon, J.K., Kim, J.M., Yoo, K.S., Park, Y.K., 2008. Pyrolysis of polypropylene over mesoporous MCM-48 material. J. Phys. Chem. Solids, 1125– 1128. Park, H.J., Heo, H.S., Park, Y.K., Yim, J.H., Jeon, J.K., Park, J., Ryu, C., Kim, S.S., 2010a. Clean bio-oil production from fast pyrolysis of sewage sludge: effects of reaction conditions and metal oxide catalysts. Bioresour. Technol. 101, S83–S85. Park, H.J., Heo, H.S., Yim, J.H., Jeon, J.K., Ko, Y.S., Kim, S.S., Park, Y.K., 2010b. Catalytic pyrolysis of Japanese larch using spent HZSM-5. Korean J. Chem. Eng. 27, 73–75. Park, K.H., Park, H.J., Kim, J., Ryu, R., Jeon, J.K., Park, J., Park, Y.K., 2010c. Application of hierarchical MFI zeolite for the catalytic pyrolysis of Japanese larch. J. Nanosci. Nanotechnol. 10, 355–359. Park, H.J., Heo, H.S., Jeon, J.K., Kim, J., Ryoo, R., Jeong, K.E., Park, Y.K., 2010d. Highly valuable chemicals production from catalytic upgrading of radiata pine sawdust-derived pyrolytic vapors over mesoporous MFI zeolites. Appl. Catal. B: Environ. 95, 365–373. Pattiya, A., Titiloye, J.O., Bridgwater, A.V., 2008. Fast pyrolysis of cassava rhizome in the presence of catalysts. J. Anal. Appl. Pyrolysis 81, 72–79. Prado, C.M.R., Filho, N.R.A., 2009. Production and characterization of the biofuels obtained by thermal cracking and thermal catalytic cracking of vegetable oils. J. Anal. Appl. Pyrol. 86, 338–347.
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957 Wang, P., Zhan, S., Yu, H., Xue, X., Hong, N., 2010. The effects of temperature and catalysts on the pyrolysis of industrial wastes (herb residue). Bioresour. Technol. 101, 3236–3241.
3957
Williams, P.T., Horne, P.A., 1994. Characterisation of oils from the fluidized bed pyrolysis of biomass with zeolite catalyst upgrading. Biomass Bioenergy 7, 223– 236.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Catalytic upgrading of oil fractions separated from food waste leachate Hyeon Su Heo a, Sang Guk Kim b, Kwang-Eun Jeong c, Jong-Ki Jeon d, Sung Hoon Park e, Ji Man Kim f, Seung-Soo Kim g, Young-Kwon Park a,h,⇑ a
Graduate School of Energy and Environmental System Engineering, University of Seoul, Seoul 130-743, Republic of Korea Korea Institute of Energy Research, Daejeon 303-343, Republic of Korea c Green Chemistry Research Division, Korea Research Institute of Chemical Technology, Daejeon 305-600, Republic of Korea d Department of Chemical Engineering, Kongju National University, Cheonan 330-717, Republic of Korea e Department of Environmental Engineering, Sunchon National University, Suncheon 540-742, Republic of Korea f Department of Chemistry, BK21 School of Materials Science and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea g Department of Chemical Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea h School of Environmental Engineering, University of Seoul, Seoul 130-743, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 6 September 2010 Received in revised form 21 November 2010 Accepted 22 November 2010 Available online 28 November 2010 Keywords: Food waste oil fractions Catalytic pyrolysis HZSM-5 Gallium Aromatics
a b s t r a c t In this work, catalytic cracking of biomass waste oil fractions separated from food waste leachate was performed using microporous catalysts, such as HY, HZSM-5 and mesoporous Al-MCM-48. The experiments were carried out using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) to allow the direct analysis of the pyrolytic products. Most acidic components, especially oleic acid, contained in the food waste oil fractions were converted to valuable products, such as oxygenates, hydrocarbons and aromatics. High yields of hydrocarbons within the gasoline-range were obtained when microporous catalysts were used; whereas, the use of Al-MCM-48, which exhibits relatively weak acidity, resulted in high yields of oxygenated and diesel-range hydrocarbons. The HZSM-5 catalyst produced a higher amount of valuable mono aromatics due to its strong acidity and shape selectivity. Especially, the addition of gallium (Ga) to HZSM-5 significantly increased the aromatics content. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The generation of organic waste continues to increase. The abandoning, landfilling and ocean disposal of organic waste, such as food waste, livestock excretion, wastewater sludge and butchery waste, has caused severe environmental pollution. Thus, the direct landfilling of organic waste has been banned in a number of countries. Methods for the appropriate treatment of organic waste are being considered in South Korea to limit the ocean disposal of organic waste. In 2006, 13,300 ton/day of food waste was generated in South Korea, resulting in an annual economic loss of about $15 billion (Lee et al., 2009). Food waste can be treated using various processes, including composting, feedstuff production, anaerobic digestion for energy production and pulverization for the production of fuel. While the detailed procedures of these processes vary depending on the purpose of the treatment, dehydration, usually by press rolling, and the removal of impurities are common pre-treatment steps. Water and particulate matter are separated as leachate during ⇑ Corresponding author at: Graduate School of Energy and Environmental System Engineering, University of Seoul, Seoul 130-743, Republic of Korea. Tel.: +82 2 2210 5623; fax: +82 2 2244 2245. E-mail address: [email protected] (Y.-K. Park). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.11.099
the press rolling dehydration stage, with the dehydrated cake sent to a dryer. The leachate is a sludge that contains water, solid particulate matter and oil fractions. Existing food waste leachate treatment processes, without oil separation, result in blocking of the gate screens within water treatment plants with clotted oil. Moreover, there is a build-up of oil layers on the water surface of the aeration tank, hindering the air supply for microorganism breeding. The danger of fire has been a serious problem in the drying process of the sludge separated from food waste leachate due to the oil layer accumulating on the wall of the discharge duct. Therefore, a process to separate oil from food waste leachate has been developed (Kim, 2010). Usually, one liter of leachate contains 5 g of oil fractions, which are mainly composed of animal and vegetable derived oils (Kim, 2010). The oil fractions separated from the leachate can be used as an energy source. At the same time, the oil fractions can be converted to a more useful product, biofuel, which is also an alternative energy source. Animal and vegetable oils can generally be converted to biodiesel via transesterification, and can also be converted to bio-oils via pyrolysis. The bio-oils produced via biomass pyrolysis can be used as heating fuel, but the fuel quality is low (Park et al., 2010a). Therefore, numerous efforts have been made to produce reformed oils, with improved quality, via catalytic reactions of the lowquality bio-oils (Lee et al., 2008; Park et al., 2010b,c). Investigations
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
have recently been conducted to produce bio-fuels from vegetable oils via catalytic pyrolysis (Ngo et al., 2010; Ong and Bhatia, 2010; Prado and Filho, 2009). To the best of our knowledge, catalytic pyrolysis has never been applied to the production of valuable oils via the reforming of food waste oil. Also, Al-MCM-48, a mesoporous material with cubic symmetry, has not been applied to the catalytic pyrolysis of biomass, despite its higher catalytic ability than Al-MCM-41 (Park et al., 2008). One objective of this study was to investigate the performance of microporous and mesoporous catalysts, such as HY, HZSM-5 and Al-MCM-48, for the catalytic cracking of oil fractions separated from food waste leachate. Another objective was to increase the fractions of valuable aromatic compounds in bio-oil using HZSM-5 with the addition of Ga. The experiments were carried out using the Py-GC/MS instrument to allow the direct analysis of the pyrolytic products. Several Py-GC/MS studies have been carried out before using different catalysts (Adam et al., 2005; Lu et al., 2009, 2010; Pattiya et al., 2008). The product distribution after the catalytic reaction was compared to reveal the catalytic effects of different catalysts.
3953
vacuum for 5 h at 250 °C, using nitrogen as the adsorption gas at the temperature of liquid nitrogen. The nitrogen adsorption– desorption isotherms and BET surface area were then obtained. The surface acidities of the catalysts were measured using temperature programmed desorption of ammonia (NH3-TPD), employing a BEL-CAT TPD analyzer with a TCD detector (Park et al., 2010d). 2.4. Py-GC/MS analyses
The oil fractions separated from food waste leachate were obtained from the KIER using the normal hexane extractive chemical test. For more details on the procedure for the normal hexane extractive chemical test, one can refer to the literature (Kim, 2010). Pyrolysis tests were performed using a TGA analyzer (PerkinElmer, Pyris 1 TGA). A typical sample mass of 20 mg was heated at 10 K/min, with nitrogen purging, to a final temperature of 873 K.
A double-shot pyrolyzer (Frontier-Lab Co., Py-2020iD), coupled directly to GC/MS, was used for identification of the catalytic cracking products. For the sample preparation, the food waste oil fraction (1 ll) and catalyst (1 mg) were placed in a sample cup, which was then placed into a 500 °C furnace under a He atmosphere. The gaseous species generated during the catalytic cracking were directly introduced into a GC inlet port (split ratio of 1/ 100) and onto a metal capillary column (Ultra ALLOY-5MS/HT; 5% diphenyl and 95% dimethylpolysiloxane, length 30 m, i.d. 0.25 mm, film thickness 0.5 lm; Frontier Laboratories Ltd., Japan). To prevent condensation of the products, the interface and inlet temperatures were both maintained at 300 °C. The column temperature was programmed to ramp from 40 (5 min) to 320 °C (10 min), at a heating rate of 5 °C/min. The temperature of the GC/MS interface was 280 °C, with the MS operated in the EI mode at 70 eV. The program was run in the scanning range from 29 to 400 amu, at a rate of 2 scans/s. The identification of peaks was performed using the NISTMS library. The experiments were conducted at least three times for each catalyst to confirm the reproducibility of the reported procedures. The average values of the peak area and peak area% as received were calculated for each identified product.
2.2. Preparation of catalyst
3. Results and discussion
Microporous catalysts, such as HY (Si/Al = 2.6) and HZSM-5 (Si/ Al = 15, 40), were purchased from Zeolyst. 1 wt.% Ga was impregnated into HZSM-5 using Ga(NO3)3 by incipient wetness method. The impregnated Ga/HZSM-5 catalyst was dried overnight at 110 °C and calcined in air at 550 °C for 5 h, reduced in a hydrogen stream at 500 °C for 4 h, and finally calcined in air at 550 °C for 5 h. The MCM-48 was prepared using the following procedure. First, to prepare pure MCM-48, 10.0 g of CTABr, 1.5 g of Brij-30 and 190.5 g of distilled water were mixed. When the mixture became transparent, 46.13 g of sodium silicate solution (Na/Si = 0.5) was slowly added, drop wise, with stirring. The prepared solution was placed in an oven at 100 °C for 48 h for the reaction to take place. After 48 h, the solution was cooled and its pH adjusted to 10 using 50 wt.% acetic acid. The solution was then placed in the oven at 100 °C for the reaction to take place for a further 48 h. The pH adjusting process was repeated three times. The solution was then washed with distilled water, filtered and dried in the oven for 24 h, which was followed by another washing with ethanol, filtering, drying for 24 h and baking at 550 °C for 4 h. Aluminum incorporation into MCM-48 was performed using the post-synthetic grafting method (Park et al., 2008). Before baking, the prepared mesoporous material was introduced into a solution prepared by dissolving AlCl3 in 100 mL of ethanol, according to the desired Si/Al ratio. The solution was stirred for 24 h, washed with ethanol, filtered, dried for 24 h and calcined for 4 h at 550 °C.
3.1. Characteristics of oil derived from food waste leachate
2. Experimental 2.1. Oil fractions separated from food waste leachate
2.3. Catalyst characterization The BET surface area of the catalyst was measured using an ASAP 2010 apparatus (Micrometrics). The catalyst sample was dried, with 0.3 g of the dried sample taken, and outgassing under
The elemental composition of the oil derived from food waste leachate was C 75.45 wt.%, H 13.85 wt.%, N 0.53 wt.%, S 0.01 wt.% and O 10.16 wt.% (by difference). The HHV was calculated following the formula suggested in the literature (Demibras, 1997). As the HHV of the oil (39.52 MJ/kg) was slightly lower than that of soybean oil (40.09 MJ/kg) (Ngo et al., 2010), the oil can be classified as a promising fuel. However, the oil cannot be applied directly to industry due to its high viscosity and high fatty acid content; therefore, an additional process, such as catalytic pyrolysis, will be required for its conversion into a valuable fuel. To investigate the pyrolytic behavior of food waste leachate, TGA and DTG analyses were carried out (data not shown). When 20 mg of leachate was analyzed using TGA, DTG peaks were observed at 110, 280 and 450 °C, which appeared to be the results of reductions of water, low-molecular-weight hydrocarbons and high-molecular-weight acids, respectively, in the leachate due to pyrolysis. Also, a considerable mass reduction was achieved below 500 °C. Based on this result, the catalytic pyrolysis reactions in this study were conducted at 500 °C. 3.2. Characterization of catalysts Table 1 shows the physical properties of the catalysts used in this study. HZSM-5 had the smallest surface area, while the surface area of Al-MCM-48 was largest. Zeolite catalysts were shown to have sub-nanometer pores (0.7 nm for HY and 0.5 nm for HZSM5); whereas, Al-MCM-48 had nano-pores (2.97 nm). Fig. 1 shows the TPD results. The number of acid sites on the Al-MCM-48 catalyst was smaller than those of the other catalysts, and Al-MCM-48
3954
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Table 1 Physical properties of catalysts. Catalyst
BET surface area (m2/g)
Average pore diameter (nm)
Si/Al ratio
HY HZSM-5 (15) HZSM-5 (40) Al-MCM-48
730 400 425 1380
0.74 0.74 [1 1 1]a 0.51 0.55 [1 0 0]a 0.53 0.56 [0 1 0]a 0.51 0.55 [1 0 0]a 0.53 0.56 [0 1 0]a 2.97
2.6 15 40 20
Channel diameter viewed along [hkl] direction.
50
Distribution (area%)
a
60
40
400oC 500oC 600oC 700oC
30
20
HY HZSM5 (15) Ga/HZSM5 (15) HZSM5 (40) Al-MCM48
10
0
Intensity (a.u)
s se Ga
es at en g y Ox
s id Ac
ns bo ar c o dr Hy
ics at om r A
Fig. 2. Product distribution of noncatalytic pyrolysis of oil fractions separated from food waste leachate. 100
0
100
200
300
400
500
600
700
Temperature ( oC) Fig. 1. NH3 TPD of catalysts.
had weak acid sites that exhibited a maximum peak at about 250 °C. Conversely, the HY catalyst had the largest number of acid sites: weak acid sites with a peak at about 220 °C and medium acid sites with a shoulder peak at about 330 °C. HZSM-5 had weak acid sites and strong Brönsted acid sites, with peaks at about 220 and 400 °C, respectively. The order of the numbers of acid sites was HY > HZSM-5 (15) > Al-MCM-48; whereas, the order of the strengths of acid sites was HZSM-5 > HY > Al-MCM-48. When the Si/Al ratio of HZSM-5 was increased from 15 to 40, the number of acid sites decreased. The addition of Ga to HZSM-5 decreased the number of acid sites of HZSM-5. 3.3. Noncatalytic pyrolysis The oil fraction of the food waste leachate was pyrolyzed using Py-GC/MS. One of the drawbacks of Py-GC/MS is that it does not allow product collection, thus, the exact bio-oil yield cannot be determined. Moreover, the GC/MS technique cannot provide quantitative analyses of the volatile products. However, the chromatographic peak area of a compound was considered to be linear with respect to its quantity, and the peak area% with its content. During each experiment, the masses of the oil and catalyst were the same. Therefore, the corresponding chromatographic peak area% can be compared to show the change in the relative content of the pyrolysis vapors (Adam et al., 2005; Lu et al., 2010; Heo et al., 2010a,b; Pattiya et al., 2008; Wang et al., 2010). Supplementary data, Table S1 shows the results of the decomposition of the food waste leachate oil fraction at different temperatures between 400 and 700 °C. The product species accounting for the largest area% at every temperature tested was oleic acid, the main component of olive oil. Fatty acid esters, such as octadecanoic acid ethyl ester, hexadecanoic acid ethyl ester and linoleic acid ethyl ester, were also contained in the products. These species stem from the animal and vegetable oils that comprise the food waste leachate. As the pyrolysis products were a mixture of a num-
Distribution (area%)
80
400oC 500oC 600oC 700oC
60
40
20
0
1 to 4
5 to 9
10 to 17
over 17
Carbon number Fig. 3. Carbon number distribution of noncatalytic pyrolysis of oil fractions separated from food waste leachate.
ber of species, these species were roughly grouped into five categories: gases (CO, CO2, and hydrocarbons up to C4), oxygenates, acids, hydrocarbons (aliphatic alkanes and alkenes) and aromatics. Fig. 2 shows that with increasing temperature, the fatty acids were decomposed into low-molecular-weight hydrocarbons, aromatics and gases. In particular, the amount of oleic acid, which accounted for the largest amount of the product, was shown to decrease dramatically with increasing pyrolysis temperature (Table S1). Fig. 3 illustrates the results of the product grouping based on the number of carbon atoms in the molecules. With increasing pyrolysis temperature, the fractions of low-molecular-weight species increased; C5–C9 species accounted for the largest fraction at 700 °C. This result suggests that the food waste oil fraction can be converted to high-quality fuels by pyrolysis at high temperature. However, a high-temperature decomposition reaction requires a lot of energy. Therefore, it would be better to make the same reaction take place at a lower temperature using catalysts. 3.4. Catalytic pyrolysis Supplementary data, Table S2 shows the list of the products obtained from the decomposition of the food waste leachate oil fraction, with the aid of various catalysts, at 500 °C. It can be seen that
3955
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Distribution (area%)
40
Non-catalytic Al-MCM48 HY HZSM5 (40) HZSM5 (15)
30
20
10
0 s se Ga
e at en yg x O
s
ns ics at bo m ar ro oc A r d Hy
id Ac
Hs PA
n ow kn Un
Fig. 4. Product distribution of catalytic pyrolysis of oil fractions separated from food waste leachate.
the use of catalysts led to the decomposition of high-molecularweight species into those with low-molecular-weights. In particular, most of the oleic acid was decomposed when catalysts were used. In order to illustrate the trend in the fractions of different species in the reaction products according to the catalysts used, as shown in Fig. 4, the product species were grouped into seven categories: gases, oxygenates, acids, hydrocarbons, aromatics (monocyclic aromatic hydrocarbons), polycyclic aromatic hydrocarbons (PAHs) and unknowns. A considerable amount of fatty acids produced under the non-catalytic conditions were decomposed further with the use of catalysts. The product distribution was, to a large extent, dependent on the catalyst used. When the Al-MCM-48 catalyst, with a large pore size, was used, the amounts of oxygenates, hydrocarbons and monocyclic aromatics (benzene, toluene and alkylated derivatives) were higher than in the case of non-catalytic pyrolysis. When the HY zeolite catalyst was used, most oxygenates and fatty acids were converted into gases, hydrocarbons and monocyclic aromatics. HZSM-5 showed a similar effect to that of HY zeolite: oxygenates and fatty acids were converted into gases, hydrocarbons and monocyclic aromatics. In particular, when HZSM-5 was used, the amounts of monocyclic aromatics and gases were very high compared to the cases where the other catalysts were used. It is well known that hydrocarbons and aromatics are regarded as valuable products due to their contribution to the calorific value of the bio-oil. However, HY and HZSM-5 also produced PAHs, which are well known to be toxic and mutagenic compounds. Fatty acids are decomposed on the acid sites of the catalysts. Mesoporous catalysts, such as Al-MCM-48, are advantageous for the decomposition of high-molecular-weight species due to their large pore size. Nevertheless, the number and strength of their acid sites are lower than those of HY zeolite and HZSM-5 (Fig. 1), leading to a relatively lower decomposition efficiency. Therefore, when Al-MCM-48 was used, the fatty acids contained within the food waste leachate were mainly decomposed into oxygenates and hydrocarbons, with slight conversion to aromatic compounds. Lukyanov et al. (1994, 1995) reported that the presence of strong Brönsted acid sites in a catalyst, such as HZSM-5, enhanced the production of aromatics. HZSM-5 could accelerate the oligomerization of ethylene and propylene to form C4–C10 olefins, which then undergo dehydrogenation to form diolefins (or dienes). The subsequent cyclization and further dehydrogenation resulted in the formation of aromatic hydrocarbons. In this study, more aromatic
compounds were generated when HY or HZSM-5, which have a greater number of Brönsted acid sites, was used compared to the case where a mesoporous catalyst with fewer Brönsted acid sites was used. In particular, with the use of HZSM-5, which has greater acid site strength than the HY catalyst, considerable amounts of hydrocarbons were converted into aromatics. It can be suggested that some higher-molecular-weight compounds in the oil separated from food waste would react on the surface of the HZSM-5 catalyst and generate many low-molecular-weight hydrocarbons, such as ethylene and propylene. These low-molecular-weight hydrocarbons then subsequently enter the three-dimensional pore system of the HZSM-5 catalyst and undergo further polymerization and aromatization to form aromatic hydrocarbons. Ooi et al. (2004, 2005) obtained similar results from their fatty acids mixture cracking experiments conducted using various catalysts: paraffinic hydrocarbons were the main products when Al-SBA-15 and AlMCM-41 were used; whereas, the use of HZSM-5 resulted in high yields of aromatic compounds. Additional experiments were carried out to investigate the effect of the acidity of the catalysts. Fig. 4 also shows the results obtained by using different Si/Al ratios for the HZSM-5 catalyst. As shown in this figure, the HZSM-5 catalyst with a Si/Al ratio of 40 led to the production of more hydrocarbons and less aromatics than that with a Si/Al ratio of 15. This result indicated that a significant amount of hydrocarbons was converted into aromatics when the catalyst with a Si/Al ratio of 15 was used. The use of the catalyst with a Si/Al ratio of 15 also resulted in the production of higher amounts of gases. The results of these experiments indicated that the catalyst with a Si/Al ratio of 15, which has a greater number of Brönsted acid sites, effectively enhanced the catalytic cracking and aromatization, implying that Brönsted acid sites play an important role in the production of aromatics. The shape selectivity of HZSM-5 also affects the selectivity for aromatics production (Adjaye et al., 1996). The pores of HZSM-5, with intersecting channels, are ideal for producing aromatic compounds. The newly formed aromatic compounds can then either diffuse from the catalyst or remain inside the pores to form coke. Williams and Horne (1994) reported that the unique pore structure of HZSM-5 led to a high yield of aromatics in bio-oil. Pan et al. (2010) also reported the importance of the three-dimensional pore system of HZSM-5 catalyst in the production of aromatic hydrocarbons. Fig. 5 shows the product distribution according to the number of carbon atoms in the molecules. The use of catalysts was shown to facilitate the conversion of high-molecular-weight species into 80
60
Distribution (area%)
50
Non-catalytic Al-MCM48 HY HZSM5(40) HZSM5(15)
40
20
0 1 to 4
5 to 9
10 to 17
over 17
Carbon number Fig. 5. Carbon number distribution of catalytic pyrolysis of oil fractions separated from food waste leachate.
3956
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957
Table 2 Effect of Ga addition on product distribution in terms of area%.
Gas Oxygenates Acid Hydrocarbon Monocyclic aromatics PAHs
HZSM-5 (15) (area%)
Ga/HZSM-5 (15) (area%)
17.83 10.45 0.87 18.13 42.41 6.57
15.43 9.26 0.85 10.39 58.07 5.94
Brönsted acid sites led to a significantly enhanced production of aromatic compounds.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.biortech.2010.11.099. References
those with low-molecular-weights. Mesoporous Al-MCM-48 led to the largest production of diesel-range compounds, with the number of carbon atoms ranging from 10 to 17. It is believed that the large pore size of Al-MCM-48 would be favorable for the production of high-molecular-weight species; whereas, its weak acidity would suppress excessive decomposition. When HY zeolite and HZSM-5 were used, the dominant products were gasoline-range compounds, with the number of carbon atoms ranging from 5 to 9, which can be attributed to their small pore sizes and strong Brönsted acid sites. In particular, when HZSM-5, which has the strongest Brönsted acidity, was used, the production of low-molecular-weight gases was the highest. The use of HY, which had weaker acid strength and a larger pore size than HZSM-5, resulted in higher fractions of C10–C17 compounds and PAHs, but a lower fraction of gases than HZSM-5. In another set of experiments, Ga was added to HZSM-5. As shown in Table 2 the addition of Ga resulted in the decreased production of hydrocarbons, but increased aromatics. In particular, the fraction of monocyclic aromatics, with high economic values, e.g., benzene, toluene and xylene, were significantly increased from 42.41% to 58.07%, and the fraction of hydrocarbons decreased as much, while the other species were affected much less by the addition of Ga. The addition of Ga to HZSM-5 is known to result in an interaction between the Brönsted and Lewis acid sites, which promotes the conversion of hydrocarbons and bio-oil components into aromatics. Kwak and Sachtler (1994) reported that Brönsted acid sites catalyze oligomerization and ring closure, but Ga, with respect to protons, acts as a dehydrogenating site. Park et al. (2007, 2010d) also suggested that the incorporation of Ga cations into a MFI type zeolite increased the initial dehydrogenation rates of alkanes, as well as the subsequent dehydrogenation rates required to more rapidly transform alkenes to aromatics, leading to considerably larger aromatics production than obtained by the parent MFI type zeolite. It is believed that Ga played a similar role in this study: a considerable amount of hydrocarbons may have been converted into aromatics at the Ga and Brönsted acid sites. When Ga was added, the carbon number distribution of the product was similar to that obtained without the addition of Ga, but the production of gases was slightly decreased while the C5–C9 and C10–C17 hydrocarbon fractions were slightly increased (data not shown). This result was attributed to the loss of some strong acid sites from HZSM-5 due to the addition of Ga, resulting in partial suppression of the decomposition reactions (Park et al., 2007, 2010d). 4. Conclusions The pyrolysis of the food waste leachate oil fraction was conducted using Py-GC/MS. The use of catalysts resulted in a significant improvement in the production of bio-oil. Al-MCM-48 suppressed excessive decomposition and converted the oil fraction mainly into diesel-range compounds. Conversely, HY and HZSM-5 showed high selectivity to gasoline-range compounds. In particular, HZSM-5 provided a high aromatics yield, which can be attributed to its strong Brönsted acid sites and shape selectivity. When Ga was added to HZSM-5, the interaction between the Ga and
Adam, J., Blazso, M., Meszaros, E., Stocker, M., Nilsen, M.H., Bouzga, A., Hustad, J.E., Gronli, M., Oye, G., 2005. Pyrolysis of biomass in the presence of Al-MCM-41 type catalysts. Fuel 84, 1494–1502. Adjaye, J.D., Katikaneni, S.P.R., Bakhshi, N.N., 1996. Catalytic conversion of a biofuel to hydrocarbons: effect of mixtures of HZSM-5 and silica–alumina catalysts on product distribution. Fuel Process. Technol. 48, 115–143. Demibras, A., 1997. Calculation of higher heating values of biomass fuels. Fuel 76, 431–434. Heo, H.S., Park, H.J., Park, Y.K., Ryu, C., Suh, D.J., Suh, Y.W., Yim, J.H., Kim, S.S., 2010a. Bio-oil production from fast pyrolysis of waste furniture sawdust in a fluidized bed. Bioresour. Technol. 101, S91–S96. Heo, H.S., Park, H.J., Park, S.H., Kim, S., Suh, D.J., Suh, Y.W., Kim, S.S., Park, Y.K., 2010b. Fast pyrolysis of rice husks under different reaction conditions. J. Ind. Eng. Chem. 16, 27–31. Kim, S.G. System for separation of oil and sludge from food waste leachate. Korea Patent 10-2010-0053719. Kwak, B.S., Sachtler, W.M.H., 1994. Effect of Ga/Proton balance in Ga/HZSM-5 catalysts on C3 conversion to aromatics. J. Catal. 145, 456–463. Lee, H.I., Park, H.J., Park, Y.K., Hur, J.Y., Jeon, J.K., Kim, J.M., 2008. Synthesis of highly stable mesoporous aluminosilicates from commercially available zeolites and their application to the pyrolysis of woody biomass. Catal. Today 132, 68–74. Lee, S.W., Shin, T.S., Yang, J., Kim, K.Y., Cho, B.R., Yeon, I.J., 2009. Fermentation of food waste mixed with additives by indigenous bacteria at room temperature and utilization of fermented feed for animal. J. Kor. Waste Manage. 26, 243–251. Lu, Q., Xiong, W.M., Li, W.Z., Guo, Q.X., Zhu, X.F., 2009. Catalytic pyrolysis of cellulose with sulfated metal oxides: a promising method for obtaining high yield of light furan compounds. Bioresour. Technol. 100, 4871–4876. Lu, Q., Zhang, Y., Tang, Z., Li, W.Z., Zhu, X.F., 2010. Catalytic upgrading of biomass fast pyrolysis vapors with titania and zirconia/titania based catalysts. Fuel 89, 2096–2103. Lukyanov, D.B., Gnep, N.S., Guisnet, M.R., 1994. Kinetic modeling of ethane and propene aromatization over HZSM-5 and GaHZSM-5. Ind. Eng. Chem. Res. 33, 223–234. Lukyanov, D.B., Gnep, N.S., Guisnet, M.R., 1995. Kinetic modeling of propane aromatization reaction over HZSM-5 and GaHZSM-5. Ind. Eng. Chem. Res. 34, 516–523. Ngo, T.A., Kim, J., Kim, S.K., Kim, S.S., 2010. Pyrolysis of soybean oil with H-ZSM-5 (proton-exchange of zeolite socony mobil #5) and MCM41 (mobil composition of matter no. 41) catalysts in a fixed-bed reactor.. Energy 35, 2723–2728. Ong, Y.K., Bhatia, S., 2010. The current status and perspectives of biofuel production via catalytic cracking of edible and non-edible oils. Energy 35, 111–119. Ooi, Y.S., Zakaria, R., Mohamed, A.R., Bhatia, S., 2004. Catalytic conversion of palm oil-based fatty acid mixture to liquid fuel. Biomass Bioenergy 27, 477–484. Ooi, Y.S., Zakaria, R., Mohamed, A.R., Bhatia, S., 2005. Catalytic conversion of fatty acids mixture to liquid fuel and chemicals over composite microporous/ mesoporous catalysts. Energy Fuel 19, 736–743. Pan, P., Hu, C., Yang, W., Li, Y., Dong, L., Zhu, L., Tong, D., Qing, R., Fan, Y., 2010. The direct pyrolysis and catalytic pyrolysis of Nannochloropsis sp. residue for renewable bio-oils.. Bioresour. Technol. 101, 4593–4599. Park, H.J., Dong, J.I., Jeon, J.K., Yoo, K.S., Yim, J.H., Sohn, J.M., Park, Y.K., 2007. Conversion of the pyrolytic vapor of radiata pine over zeolite. J. Ind. Eng. Chem. 13, 182–189. Park, H.J., Yim, J.H., Jeon, J.K., Kim, J.M., Yoo, K.S., Park, Y.K., 2008. Pyrolysis of polypropylene over mesoporous MCM-48 material. J. Phys. Chem. Solids, 1125– 1128. Park, H.J., Heo, H.S., Park, Y.K., Yim, J.H., Jeon, J.K., Park, J., Ryu, C., Kim, S.S., 2010a. Clean bio-oil production from fast pyrolysis of sewage sludge: effects of reaction conditions and metal oxide catalysts. Bioresour. Technol. 101, S83–S85. Park, H.J., Heo, H.S., Yim, J.H., Jeon, J.K., Ko, Y.S., Kim, S.S., Park, Y.K., 2010b. Catalytic pyrolysis of Japanese larch using spent HZSM-5. Korean J. Chem. Eng. 27, 73–75. Park, K.H., Park, H.J., Kim, J., Ryu, R., Jeon, J.K., Park, J., Park, Y.K., 2010c. Application of hierarchical MFI zeolite for the catalytic pyrolysis of Japanese larch. J. Nanosci. Nanotechnol. 10, 355–359. Park, H.J., Heo, H.S., Jeon, J.K., Kim, J., Ryoo, R., Jeong, K.E., Park, Y.K., 2010d. Highly valuable chemicals production from catalytic upgrading of radiata pine sawdust-derived pyrolytic vapors over mesoporous MFI zeolites. Appl. Catal. B: Environ. 95, 365–373. Pattiya, A., Titiloye, J.O., Bridgwater, A.V., 2008. Fast pyrolysis of cassava rhizome in the presence of catalysts. J. Anal. Appl. Pyrolysis 81, 72–79. Prado, C.M.R., Filho, N.R.A., 2009. Production and characterization of the biofuels obtained by thermal cracking and thermal catalytic cracking of vegetable oils. J. Anal. Appl. Pyrol. 86, 338–347.
H.S. Heo et al. / Bioresource Technology 102 (2011) 3952–3957 Wang, P., Zhan, S., Yu, H., Xue, X., Hong, N., 2010. The effects of temperature and catalysts on the pyrolysis of industrial wastes (herb residue). Bioresour. Technol. 101, 3236–3241.
3957
Williams, P.T., Horne, P.A., 1994. Characterisation of oils from the fluidized bed pyrolysis of biomass with zeolite catalyst upgrading. Biomass Bioenergy 7, 223– 236.