Biodiesel Production from Sewage Sludge: New Paradigm for Mining

Aug 20, 2012 - This work demonstrates that the production of biodiesel using the lipids extracted from sewage sludge (SS) could be economically feasib...
0 downloads 11 Views 3MB Size
Download PDF
Article pubs.acs.org/est

Biodiesel Production from Sewage Sludge: New Paradigm for Mining Energy from Municipal Hazardous Material Eilhann E. Kwon,† Sungpyo Kim,‡ Young Jae Jeon,† and Haakrho Yi†,* †

Bio-Energy Research Team, Research Institute of Industrial Science and Technology (RIST), 813-1 Keumho-Dong, Kwang-Yang-City Cholla-Nam-Do, South Korea, 545-090 ‡ Department of Environment Systems Engineering, Korea University, Chung-Nam, South Korea S Supporting Information *

ABSTRACT: This work demonstrates that the production of biodiesel using the lipids extracted from sewage sludge (SS) could be economically feasible because of the remarkably high yield of oil and low cost of this feedstock, as compared to conventional biodiesel feedstocks. The yield of oil from SS, 980 000 L ha−1 year−1, is superior to those from microalgal and soybean oils, 446 and 2200 L ha−1 year−1, respectively. According to the case study of South Korea, the price of the lipids extracted from SS was approximately $0.03 L−1 (USD), which is lower than those of all current biodiesel feedstocks. This work also highlights the insight of a novel methodology for transforming lipids containing high amounts of free fatty acids (FFAs) to biodiesel using a thermochemical process under ambient pressure in a continuous flow system. This allowed the combination of esterification of FFAs and transesterification of triglycerides into a single noncatalytic process, which led to a 98.5% ± 0.5% conversion efficiency to FAME (fatty acid methyl ester) within 1 min in a temperature range of 350−500 °C. The new process for converting the lipids extracted from SS shows high potential to achieve a major breakthrough in minimizing the cost of biodiesel production owing to its simplicity and technical advantages, as well as environmental benefits.

1. INTRODUCTION Fossil-fuel-derived energy resources, including petroleum, coal, and natural gas, are currently responsible for about 75% of world’s primary energy consumption.1 The alternatives to these energy resources, such as nuclear power (5%), hydropower (6%), and biomass (13%) currently make up only 25%.1−3 In this regard, it is imperative that our society should develop more effective technology using more abundant and renewable resources for the production of energy and chemicals. The production of biofuels has been drawing much attention in recent years because of their environmental benefits.4 Among the renewable and sustainable biofuels, biodiesel produced from vegetal oils has been considered a key technology because of its advantages in being able to use existing distribution networks and current engine technology as well as to provide energy security for our society.5 For these reasons, biodiesel, or FAME (fatty acid methyl ester), production has increased dramatically in the past decade, although it has become evident that its production competes with food production by engrossing agricultural cropland.6,7 Thus, energy production roadmaps for this alternative liquid fuel have been revised, and a second generation using inedible oil feedstocks and/or a third generation using microalgal oil feedstocks have been proposed.7−10 Despite the bright prospect of biodiesel production, efforts to commercialize it have been very limited. One of the major obstacles has been the high price associated with refined oil © 2012 American Chemical Society

feedstock, which makes up nearly 70−75% of the total production costs.5,9−11 Hence, in order to reduce the cost of biodiesel production, using cheaper feedstocks such as waste oil or low-quality oil has been proposed. Sewage sludge (SS), a relatively inexpensive feedstock, is a promising raw material for such a purpose.12 However, its use has been challenging as a result of impurities such as water and large amounts of free fatty acids (FFAs), which are common in most waste materials. Thus, economically viable biodiesel conversion technology must be developed and implemented. Biodiesel is mainly being produced in the industry via the transesterification reaction using triglycerides (which are made up of an ester derived from glycerol and three fatty acids and are the main form of fat) and methanol (MeOH) in the presence of homogeneous base catalysts.13,14 Although these catalysts are relatively cheap, they are very sensitive to FFAs and the water content in oils, since the side reactions of saponification and hydrolysis, respectively, can occur.15 It is well-known that the conventional catalytic processes used for biodiesel production cannot efficiently handle such inexpensive lipid feedstocks without additional pretreatment steps, which add extra processing costs.15,16 Received: Revised: Accepted: Published: 10222

May 16, 2012 July 8, 2012 August 20, 2012 August 20, 2012 dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

were weighed and analyzed using a gas chromatograph-mass spectrometer (GC/MS; HP-790A/5975C MSC) and a GC/ flame ionization detector (FID; HP-7890A) calibrated with a Supelco mixture (lot no. LB-80557). The DB wax (J&W 1277012) and HP-5MS (19091S-413E) GC columns were used for the GC/MS analysis. The EN-14103 method was used for the FAME conversion. 2.3. Understanding the Microbial Community Involved in SS Formation Using 16S rDNA Sequence Analysis. Genomic DNA from each sample was extracted using a PowerSoil DNA isolation kit (MO BIO Laboratories, Inc., CA). The quantity and quality of the extracted DNA were estimated using gel electrophoresis and UV spectrophotometry. After performing PCR for 16S rDNA amplification, the PCR product was purified using a PCR Purification Kit (Quiagen) and cloned using a pGEM-T vector cloning system (Promega). The 16S rDNA clone sequences were clustered into OTUs (operational taxonomic units) at a cutoff of 97% by the MOTHUR program. Genealogical information about the 16S rDNA clones and related microbes was obtained from the GenBank database using a BLAST (Basic Local Alignment Search Tool) search on EZ-Taxon. Sequence alignment was conducted with the Clustal-X software.

Alternative methods, including biodiesel production via transesterification with a heterogeneous catalyst under subcritical conditions and noncatalytic synthesis under supercritical conditions, have been examined to address these issues in conventional biodiesel production methods.17−20 One method that has been getting a lot of attention lately is the application of supercritical methanol technology. However, this promising technology also has an obvious disadvantage: its high operating temperature and pressure, which result in high production costs for biodiesel.21−23 Therefore, the main objective of the present work was to develop and mechanistically validate the simplest noncatalytic transesterification process for the conversion of the lipids extracted from SS into biodiesel in a continuous system under ambient pressure. This work also proved that efficient noncatalytic biodiesel conversion could be achieved by using only activated alumina (Al2O3) in the presence of carbon dioxide (CO2). Moreover, this study showed the economic feasibility of biodiesel production from SS.

2. MATERIALS AND METHODS 2.1. Instruments and Materials for the Characterization of Sewage Sludge (SS). SS collected from several WWTPs (wastewater treatment plants) was used for our experimental work. The lipids in SS were extracted using nhexane (Sigma-Aldrich, St. Louis, MO). The KS H ISO 1242 method was used to determine the acid value of the lipids extracted from SS. The enthalpy of combustion of SS was determined by using an oxygen bomb calorimeter (PARR 6500) pressurized with excess pure oxygen. The C, H, N, and S contents in SS were determined by using an Elemental Determinator (LECO Corp., CHN-2000 and S-144DR). 2.2. Experimental Setup for Noncatalytic Biodiesel Production. A tubular reactor (TR) made of 1-in. outer diameter (OD) quartz tubing (Chemglass CGQ-0800T-13) and a 1 in. Stainless Ultra-Torr Vacuum Fitting (Swagelok SS4-UT-6-400) was used to maintain airtight conditions. Activated alumina purchased from Dae-Jung Chemicals (Incheon, South Korea) was packed into the reactor. The activated alumina was characterized in terms of surface area (297.350 m2 g−1) and pore distribution (average pore diameter: 5.4113nm) using a BELSORP-mini II (BEL Japan Co., Ltd.). As shown in Supporting Information Figure SI-1, the experimental temperature in the range 250−500 °C was achieved using a split-hinged furnace (AsOne, Japan); the temperature was simultaneously monitored by an S-type thermocouple to ensure that the target temperature had been met. An insulation collar (high-temperature Duraboard insulation) at the end of the furnace was used to block heat transfer during operation and to protect the quartz tubing. The lipids extracted from SS and MeOH were continuously fed into the tubular reactor using a gear pump (micro annular gear pump MZR-2905, Germany) and a high-performance liquid chromatography (HPLC) pump (Lab Alliance ON#F40SFX01). All gases used in the experiments were of ultrahigh purity and obtained from AirTech Korea. All gas flow rates were set using Brooks mass flow controllers (Brooks SLA5800A Series). A computer-aided control system with LabVIEW (National Instrument) was used. After the reaction, the mixture was allowed to settle for 2 h before the glycerin layer and the top layer including the biodiesel fraction were separated and subsequently removed into separate bottles. The samples collected from each layer

3. RESULTS AND DISCUSSION 3.1. Economic Feasibility of Biodiesel Production from Sewage Sludge (SS) in Korea. It has been reported that all WWTPs in Korea capable of treating ∼24 000 000 m3 day−1 (i.e., covering ∼92% of the total generation of wastewater) annually generated 4 million tons of SS as an inevitable byproduct. As shown in Figure 1(a), SS disposal in Korea has been heavily dependent on ocean dumping (61.6% of the total SS generated), which was planned to be prohibited after 2011 by the London Convention 97 protocol. Unfortunately, enforcement of this rule has been delayed. Establishing environmentally and ecologically benign practices for SS treatment is urgently imperative. The conventional uses of SS include industrial utilization, incineration, and composting for utilization as a fertilizer in farmland. However, the use of SS as an energy source (i.e., refuse-derived fuel: RDF) would only be a suitable option after these raw materials were dried and solidified, because of their high moisture content (∼80%). Unfortunately, the current policy of the Korean government does not allow combustion of only these raw materials because of air pollution control issues. Moreover, cofiring of SS with coal for power generation is stringently regulated according to the minimum heating value of the cofiring feedstocks (i.e., 3000 kcal kg−1). As a result, most SS used as cofiring feedstock must be thermally treated to reduce the moisture content (to less than 10%), which increases the heating value of these raw materials. The WWTP in Suwon-City has recently demonstrated that WWTPs can recover energy from SS in Korea. As depicted in Figure 1(b), 78% of the SS generated from the WWTP in Suwon-City was converted into RDF. This RDF has been cofired in the coal power plant since 2010. Instead of direct cofiring, the RDF can also be utilized as a biodiesel feedstock because of its high lipid content, which is approximately equivalent to that of soybeans (i.e., 18−20% lipid content, dry basis). Based on the annual generation of SS in Korea, 40% of the current biodiesel consumption (BD2 renewable standard portfolio base in Korea) can be further supported by SS. The residual RDF after extracting the lipids has a heating value of 10223

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

feedstock) and biodiesel conversion, respectively.9,10,24−26 As a result, the economic feasibility of biodiesel is highly contingent on the biodiesel feedstock. In addition, an inexpensive and reliable biodiesel conversion process would also be a key factor. As evidenced in Figure 1(c), the oil yield from SS (i.e., 980 000 L ha−1 year−1) is superior to those of microalgae and soybeans by factors of ∼82 and ∼2200, respectively. Considering all factors in Table 1, the price of oil derived from SS (i.e., $0.03 L−1) would be lower than those of all other biodiesel feedstocks. All assumption used in Table 1 was obtained from the overall process level of current facilities operated in Korea. For example, the disposal cost of 1 ton of wet SS paid by the Korean government is 58.3 USD and drying cost of 1 ton of wet SS is 57.17 USD. Dried SS is usually sent to the coal power plant and cement manufacturer and its cost (i.e., 1 ton of dried SS) is 10 USD. Thus, biodiesel production from the lipids extracted from SS would be the most economical. This economic feasibility would be synergetic with an inexpensive and reliable biodiesel conversion process. The authors propose that this can be achieved by noncatalytic biodiesel conversion under ambient pressure in a continuous flow system.27,28 3.2. Basic Properties of SS and Related Information. The characterization of SS from the WWTP in Suwon-City, including proximate analysis, ultimate analysis, and determination of the enthalpy of combustion, was carried out. The moisture content was approximately 80% (i.e., dewatered sewage sludge). Compared to cellulosic biomass, SS has an exceptionally high ash content (i.e., ∼40%). Thus, SS has relatively low fixed carbon content and ash content. However, the enthalpy of combustion of SS is roughly similar to that of lignocellulosic biomass. This can be explained by the amount of volatile matter, such as triglycerides and FFAs, in SS. The acid value of the lipids extracted from SS is 29.39. The fatty acid profile of SS will be explained later. In order to understand the bacterial community involved in the degradation of the organic content in the sewage waste, the bacterial diversity was determined using 16S rDNA extracted from SS. The results are shown in Figure 2, which indicates that the SS contained quite divergent bacterial communities. The analysis classified 26 different bacterial genera that potentially filled ecological roles. These bacterial communities are potential lipid sources for biodiesel production from cell membranes using major C16−18 FFAs. Furthermore, these bacterial genera could potentially be used as oleaginous cell factories for biodiesel production as glycerol, and thus an inevitable byproduct from biodiesel production could be further utilized. 3.3. Noncatalytic Biodiesel Conversion of the Lipids Extracted From SS. 3.3.1. Noncatalytic Biodiesel Conversion Mechanism. The viability of noncatalytic biodiesel conversion in a continuous flow system is highly contingent on instant biodiesel conversion. In order to achieve this, the authors postulated that temperature could be the main driving force for the transesterification reaction: the activation energy can be reached by providing thermal energy.27,28 For example, the activation energy of the transesterification reaction (11.2 kJ mol−1)30,31is lower than those of other catalytic applications, such as methane reforming (209.2 kJ mol−1).32 In general, triglycerides, the main constituents of lipids, start to evaporate at ∼400 °C, and thermal cracking is observed at ∼550 °C. Thus, the noncatalytic biodiesel conversion should be carried out at temperatures lower than 550 °C. In addition, a way to increase the contact time for the triglycerides and MeOH is needed. In order to achieve this, various porous

Figure 1. (a) SS generation and its disposal in Korea, (b) disposal of SS by the WWTP in Suwon-City, (c) oil yields of various lipid feedstocks for biodiesel and cost analysis of first-generation biodiesel, and (d) prices of various oil feedstocks for biodiesel (Figure 1 (c) and (d) share the same x-axis).

approximately 3080 kcal kg−1, which meets the minimum heating value for cofiring feedstocks in coal power plants. Thus, the economic feasibility of biodiesel production from SS was considered herein. All assumptions accounting for the oil yield and oil prices are summarized in Table 1. The cost analysis of biodiesel in Figure 1(c) indicates that 75% and 12% of the total cost of biodiesel are raw materials (oil 10224

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

Table 1. All Assumptions Used for Economic Feasibility Analysis 1. oil yield estimation biomass sewage sludge microalgae palm rapeseed jatropha sunflower soybean

oil content (dry basis)

oil purification cost

reference

−1

18−20% 1290 g m day 20−30% 20 g m−2 day−1 36% 3.9 g m−2 day−1 42% 0.65 g m−2 day−1 28% 0.67 g m−2 day−1 40% 0.47 g m−2 day−1 18−20% 0.59 g m−2 day−1 2. estimation of the price of oil extracted from sewage sludge cost (USD)

sludge disposal cost (paid by the government) Sludge Drying Cost (f uel: LNG) oil extraction costb

oil yield (dry basis) −2

a

−$58.3 1 ton of wet SS $57.17 1 ton of wet SS $23.86 1 ton of dry SS $17.64 1 ton of oil

unit oil price (USD)

experimental data Yusuf Chisti10 Chisti et al.9,24 Lin et al.25 G. Pahl29 You et al.26 AO-Algae innovation Summit

reference

−$1.4907 L−1 $1.3843 L−1

POSCO E&C (www.poscoenc.com) POSCO E&E (www.prosoene.com), POSCO POWER (www.poscopower.com) Korean EPA JC food (www.cj.net)

$0.1219 L−1

Samyang Well Food (www.wellfood.com) Cargill Korea (http://www.cargillfeed.co.kr)

$0.015 L−1

JC Chemical (www.jcchemical.co.kr) SK energy (www.SK.com)

Total: $0.0305 a b

Total area of WWTP in Suwon-City: 38 ha. Real area of WWTP in Suwon-City: 3.8 ha. Average wastewater treatment capacity: 530 000 m3 day−1. Extraction method: solvent extraction with n-hexane (18% oil content in dry SS).

Table 2. Proximate and Ultimate Analysis of SS RDF proximate analysis [wt.%] SS RDF from the WWTP in Suwon

ultimate analysis [wt.%]

H2O

VM

Ash

FC

C

H

N

S

heat of combustion [kcal kg−1]

5.94

65.15

22.5

6.41

44.1

6.58

5.18

0.91

4480

materials were used, because porous material intrinsically provides tortuosity and adsorption capability. The overall reaction mechanism is illustrated in Figure 3. For example, a porous material, such as activated alumina, can trap

Figure 2. Microorganism diversity index from 16S rDNA extracted from sewage sludge.

Figure 3. Illustration of noncatalytic biodiesel conversion. 10225

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

observed as a result of the relatively high experimental temperatures, but the amounts of cracked chemical species are negligible. Some aromatic compounds were also identified. Among them, the most abundant aromatic compound was toluene. Compared with those of other aliphatic hydrocarbons, the amount of toluene was negligible. These aliphatic and aromatic compounds are common in petroleum-derived diesel; thus, these chemical species should not be problematic. One interesting feature of this biodiesel conversion technology is that it can convert lipid feedstocks with high amounts of FFAs into biodiesel. For example, the acid value of the lipid extracted from SS was 29.39. Thus, this biodiesel conversion was independent of the FFA content in the lipid feedstock. This observation allows us to combine the esterification of FFAs and transesterification of triglycerides into a single process. The impact of temperature on FAME conversion was also investigated in the temperature range from 250 to 500 °C. As shown in Figure 5 (a), the FAME conversion efficiencies of

triglycerides and MeOH in its pores by means of absorption/ adsorption. The gas phase of MeOH (boiling point of ∼65 °C) behaves like a mobile phase, and the liquid phase of triglycerides acts like a stationary phase. Thus, the porous material can potentially provide space for the transesterification reaction. The heterogeneous transesterification reaction mainly occurs in the pores, and the reaction rate is enhanced by the thermal energy. Then, the converted biodiesel and byproduct (glycerin) are eluted from the pores as a result of their relatively lower boiling points compared to that of the triglycerides. Considering the average molecular size of triglycerides (i.e., 2 nm), a porous material having meso- and macropores would be suitable for the noncatalytic transesterification reaction. In addition, this biodiesel conversion was free from saponification, since no basic catalyst such as KOH or NaOH was used. This observation allowed us to combine the esterification of FFAs and transesterification of triglycerides into a single process.27,28 The noncatalytic biodiesel conversion can be enhanced by the presence of carbon dioxide (CO2). This idea arose from the enhancement of the thermochemical (pyrolysis and gasification) processes obtained by means of using CO2 as the reaction medium.33 For example, the impact of a CO2 cofeed on the thermochemical processes involving biomass and municipal solid waste (MSW) is substantial;34 the use of a CO2 cofeed can enhance the thermal cracking of volatile compounds, which directly leads to a reduction in the formation of condensable hydrocarbons (tar) and an increase in the generation of CO. However, no such effect was discernible in the temperature regime below 550 °C. On the other hand, utilizing CO2 indeed expedited the rate of the transesterification reaction without leading to the thermal cracking of the oil feedstock and provided favorable conditions for the transesterification reaction by means of impeding the reversible transesterification reaction. 3.3.2. Biodiesel Conversion of the Lipids Extracted from SS. The activated alumina was packed into a tubular reactor with a total reaction volume of 80 mL. The lipids (acid value of 29.39) extracted from SS and MeOH were continuously fed into the tubular reactor using a gear pump and an HPLC pump, respectively. The initial volumetric feeding ratio of oil feedstock to MeOH was 8:1. The feed rates of oil feedstock and MeOH were 8 mL min−1 and 1 mL min −1 , respectively. A representative chromatogram of the biodiesel from the lipids extracted from SS at 380 °C is shown in Figure 4. As shown in Figure 4, the C16−18 range of biodiesel is most abundant. The thermal cracking of biodiesel was indeed

Figure 5. Biodiesel conversion at various temperatures (a) and various volumetric ratios of MeOH to oil at 380 °C (b).

various oil feedstocks are roughly identical (85−99% ± 0.5%) and independent of their FFA contents. This observation enables the use of a much broader variety of oil feedstocks, including all edible/inedible oils. In addition, Figure 5(a) shows that the conversion of biodiesel is enhanced in the presence of CO2, which is consistent with the previous discussion. The maximum biodiesel conversion was achieved at 360 °C; however, the rate of biodiesel conversion was highly dependent on the experimental temperature. Various ratios of the volumetric flow of MeOH to oil were investigated at 380 °C in order to optimize the operational

Figure 4. Representative chromatogram of biodiesel from the lipids extracted from SS. 10226

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

(9) Yusuf, C. Biodiesel from microalgae beats bioethanol. Trends Biotechnol. 2008, 26 (3), 126−131. (10) Yusuf, C. Biodiesel from microalgae. Biotechnol. Adv. 2007, 25 (3), 294−306. (11) Song, D.; Fu, J.; Shi, D. Exploitation of oil-bearing microalgae for biodiesel. Chin. J. Biotechnol. 2008, 24 (3), 341−348. (12) Mondala, A.; Liang, K.; Toghiani, H.; Hernandez, R.; French, T. Biodiesel production by in situ transesterification of municipal primary and secondary sludges. Bioresour. Technol. 2009, 100 (3), 1203−1210. (13) Zullaikah, S.; Lai, C.-C.; Vali, S. R.; Ju, Y.-H. A two-step acidcatalyzed process for the production of biodiesel from rice bran oil. Bioresour. Technol. 2005, 96 (17), 1889−1896. (14) Ghadge, S. V.; Raheman, H. Process optimization for biodiesel production from mahua (Madhuca indica) oil using response surface methodology. Bioresour. Technol. 2006, 97 (3), 379−384. (15) Kwiecien, J.; H?ek, M.; Skopal, F. The effect of the acidity of rapeseed oil on its transesterification. Bioresour. Technol. 2009, 100 (23), 5555−5559. (16) Liang, X.; Gao, S.; Yang, J.; He, M. Highly efficient procedure for the transesterification of vegetable oil. Renewable Energy 2009, 34 (10), 2215−2217. (17) Benjapornkulaphong, S.; Ngamcharussrivichai, C.; Bunyakiat, K. Al2O3-supported alkali and alkali earth metal oxides for transesterification of palm kernel oil and coconut oil. Chem. Eng. J. 2009, 145 (3), 468−474. (18) Shu, Q.; Zhang, Q.; Xu, G.; Wang, J. Preparation of biodiesel using s-MWCNT catalysts and the coupling of reaction and separation. Food Bioproducts Process. 2009, 87 (3), 164−170. (19) Demirbas, A. Production of biodiesel fuels from linseed oil using methanol and ethanol in non-catalytic SCF conditions. Biomass Bioenergy 2009, 33 (1), 113−118. (20) Saka, S.; Isayama, Y. A new process for catalyst-free production of biodiesel using supercritical methyl acetate. Fuel 2009, 88 (7), 1307−1313. (21) Wen, D.; Jiang, H.; Zhang, K. Supercritical fluids technology for clean biofuel production. Prog. Nat. Sci. 2009, 19 (3), 273−284. (22) Marchetti, J. M.; Miguel, V. U.; Errazu, A. F. Possible methods for biodiesel production. Renewable Sustain. Energy Rev. 2007, 11 (6), 1300−1311. (23) Demirbas, A. Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods. Prog. Energy Combust. Sci. 2005, 31 (5−6), 466−487. (24) Yusuf, N. N. A. N.; Kamarudin, S. K.; Yaakub, Z. Overview on the current trends in biodiesel production. Energy Convers. Manage. 2011, 52 (7), 2741−2751. (25) Lin, L.; Cunshan, Z.; Vittayapadung, S.; Xiangqian, S.; Mingdong, D. Opportunities and challenges for biodiesel fuel. Appl. Energy 2011, 88 (4), 1020−1031. (26) You, Y.-D.; Shie, J.-L.; Chang, C.-Y.; Huang, S.-H.; Pai, C.-Y.; Yu, Y.-H.; Chang, C. H. Economic cost analysis of biodiesel production: Case in soybean Oil. Energy Fuels 2007, 22 (1), 182−189. (27) Kwon, E. E.; Seo, J.; Yi, H., Transforming animal fats into biodiesel using charcoal and CO2. Green Chemistry 2012. (28) Kwon, E. E.; Yi, H.; Park, J.; Seo, J. Non-catalytic heterogeneous biodiesel production via a continuous flow system. Bioresour. Technol. 2012, 114 (0), 370−374. (29) Pahl, G., Biodiesel: Growing a New Energy Economy; Chelsea Green Publishing Company: White River Junction, VT, 2005; p 281. (30) Granjo, J. F. O.; Duarte, B. P. D.; Oliveira, N. M. C.; Rita Maria de Brito Alves, C. A. O. d. N.; E. C. Biscaia, Jr., Kinetic models for the homogeneous alkaline and acid catalysis in biodiesel production. In Computer Aided Chemical Engineering; Elsevier, 2009; Vol. 27, pp 483488. (31) Pessoa, F. L. P.; Magalhães, S. P.; Falc, P. W. C.; Rita Maria de Brito Alves, C. A. O. d. N.; E. C. Biscaia, Jr., Kinetic study of biodiesel production by enzymatic transesterification of vegetable oils. In Computer Aided Chemical Engineering; Elsevier, 2009; Vol. 27, pp 18091814.

conditions for biodiesel conversion. As shown in Figure 5(b), biodiesel conversion under ratios of volumetric flows of MeOH to oil of 1:10 and 2:10 reached approximately 89% and 98%, respectively. This volumetric flow ratio is lower than those reported in previous work done by other authors. This would be one of advantage of our biodiesel conversion technology, even though it is possible to recover MeOH. In summary, this work validated that SS would be the most economical feedstock for producing biodiesel among the various feedstocks considered. The oil yield of SS was superior to those of microalgal and soybean oil by factors of ∼88 and 2200, respectively. In addition, this work showed that utilizing a porous material, such as activated alumina, enabled the lipid extracted from SS to be converted into biodiesel without a catalyst under ambient pressure. Noncatalytic conversion of biodiesel can be enhanced by the presence of CO2.

■

ASSOCIATED CONTENT

S Supporting Information *

Figure SI-1. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Phone: 82-61-799-2707 Fax: 82-61-792-0768 E-mail: [email protected] Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully acknowledge Dr. Hyun-Han Kwon for his support and advice in this work. In addition,we would like to name this new process “Kwon’s process.”

■

REFERENCES

(1) Biermann, U.; Bornscheuer, U.; Meier, M. A. R.; Metzger, J. O.; Schäfer, H. J. Oils and fats as renewable raw materials in chemistry. Angew. Chem. Int. Edi. 2011, 50 (17), 3854−3871. (2) Kerschbaum, S.; Rinke, G.; Schubert, K. Winterization of biodiesel by micro process engineering. Fuel 2008, 87 (12), 2590− 2597. (3) Huber, G. W.; Cortright, R. D.; Dumesic, J. A. Renewable Alkanes by aqueous-phase reforming of biomass-derived oxygenates. Angew. Chem. Int. Ed. 2004, 43 (12), 1549−1551. (4) Sarantopoulos, I.; Che, F.; Tsoutsos, T.; Bakirtzoglou, V.; Azangue, W.; Bienvenue, D.; Ndipen, F. M. An evaluation of a smallscale biodiesel production technology: Case study of Mango’o village, Center province, Cameroon. Phys. Chem. Earth, A/B/C 2009, 34 (1− 2), 55−58. (5) Lardon, L.; Helias, A.; Sialve, B.; Steyer, J.-P.; Bernard, O. Lifecycle assessment of biodiesel production from microalgae. Environ. Sci. Technol. 2009, 43 (17), 6475−6481. (6) de Oliveira, J. S.; Leite, P. M.; de Souza, L. B.; Mello, V. i. M.; Silva, E. C.; Rubim, J. C.; Meneghetti, S. M. P.; Suarez, P. A. Z. Characteristics and composition of Jatropha gossypiifoliaand Jatropha curcas L. oils and application for biodiesel production. Biomass Bioenergy 2009, 33 (3), 449−453. (7) Puhan, S.; Vedaraman, N.; Ram, B. V. B.; Sankarnarayanan, G.; Jeychandran, K. Mahua oil (Madhuca indica seed oil) methyl ester as biodiesel-preparation and emission characterstics. Biomass Bioenergy 2005, 28 (1), 87−93. (8) Pleanjai, S.; Gheewala, S. H. Full chain energy analysis of biodiesel production from palm oil in Thailand. Appl. Energy 2009, 86 (Supplement 1), S209−S214. 10227

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228

Environmental Science & Technology

Article

(32) Hou, K.; Hughes, R. The kinetics of methane steam reforming over a Ni/alpha-Al2O catalyst. Chem. Eng. J. 2001, 82, 311−328. (33) Butterman, H. C.; Castaldi, M. J. Syngas production via CO2 enhanced gasification of biomass fuels. Environ. Eng. Sci. 2009, 26 (4), 703−713. (34) Kwon, E.; Westby, K. J.; Castaldi, M. J., An investigation into the syngas production from municipal solid waste (MSW) Gasification under various pressures and CO2 concentration atmospheres. In ASME Conference Proceedings, 2009; Vol. 48807, 231−236.

10228

dx.doi.org/10.1021/es3019435 | Environ. Sci. Technol. 2012, 46, 10222−10228