ARTICLE pubs.acs.org/IECR
Toward Hydrotreating of Waste Cooking Oil for Biodiesel Production. Effect of Pressure, H2/Oil Ratio, and Liquid Hourly Space Velocity Stella Bezergianni,*,† Athanasios Dimitriadis,† Aggeliki Kalogianni,† and Kim G. Knudsen‡ † ‡
Center for Research & Technology Hellas, Chemical Process Engineering Research Institute, Thermi-Thessaloniki, Greece Haldor Topsoe R&D, Refinery and Environmental Catalyst and Technology, Lyngby, Denmark ABSTRACT: This work focuses on the use of waste cooking oil (WCO) as the main feedstock for hydrotreatment to produce biodiesel. In this study three parameters are considered for evaluating the effectiveness of this technology, pressure, hydrogen-to-oil (H2/oil) ratio and liquid hourly space velocity (LHSV). For all experiments the same commercial hydrotreating catalyst was utilized. Hydrotreatment pressure, as a key parameter of hydrotreatment reactions, was initially studied via three experiments covering a range between 8.27 and 9.65 MPa. The H2/oil ratio was examined via three experiments between 543 and 890 N m3/m3 in order to evaluate its effect on biodiesel yield. Finally three different LHSVs (0.5, 1.0, and 1.5 h-1) were explored in order to study both hydrotreating catalyst effectiveness and catalyst life expectancy.
1. INTRODUCTION Since the petroleum crises in the 1970s, the rapidly increasing prices and uncertainties regarding petroleum availability as well as the growing concern for the environment and the greenhouse gas emissions effect during the last decades have revived more and more the interest in the use of biofuels as a substitute for fossil fuels. In Europe, as the diesel demand is continuously growing, diesel alternatives gained more interest, such as FAME biodiesel, that is, biodiesel derived from the fatty acid methyl esters of vegetable oil.1-3 Even though FAME biodiesel has shown a potential of reducing the net carbon dioxide emissions,4 its high production cost as compared to petroleum-based diesel limits its large scale commercialization. Studies show that most of its production cost (70-95%) arises from the cost of raw material; that is, the cultivation cost of energy crops.5,6 For this reason other alternative routes are being explored which have the potential to lower the overall production cost. Such a route is hydrotreating (HDT) the triglyceride-containing feedstocks.7,8 Hydrotreating is used in the petroleum refinery industry to remove S, N, and metals from petroleum-derived feedstocks including heavy gas-oil or vacuum gas-oil.9 The advantages of hydrotreating are that the former is compatible with the current infrastructure, the process leads to a deoxygenated and stable product that is fully compatible with petroleumderived diesel fuels and that the product exhibits high cetane number and low sulfur content.10,11 Sebos et al. (2009)12 studied the conversion of esters included in refined cottonseed oil into hydrocarbon molecules. Murata K. et al. (2010)13 studied the production of synthetic diesel by hydrotreatment of jatropha oils using Pt-Re/H-ZSM-5 catalysts and found that Pt/H-ZSM5 catalysts were active for hydrotreating of triglycerides such as vegetable oil and jatropha oil to form C15-C18 hydrocarbons directly. Simacek et al. (2010)14 studied the fuel properties of hydroprocessed rapeseed oil and found that the composition and physiochemical properties of hydroprocessed rapeseed oil predetermine this product as a high cetane diesel fuel, but its poor low-temperature properties (pour point higher than þ20 °C) prevent its utilization in the pure form. r 2011 American Chemical Society
Alternatively the use of waste cooking oil (WCO) as a feedstock for biodiesel production could greatly reduce the production cost as it is available at a significantly low price. Hydrocracking of WCO was the first hydroprocessing route explored as a potential for biofuels production15 offering mainly biodiesel but also biogasoline products. In a recent study hydrotreating of WCO appeared as an effective technology for biodiesel production,16,17 offering high yields (∼90%) of a biodiesel consisting of normal and iso-paraffins within C8-C25 range. The effect of temperature as the most dominant parameter of hydrotreatment was explored in the authors' previous work.16,17 Hydrotreating of WCO for biodiesel production is further studied in this paper through experimental investigation of three other operating parameters, that is, pressure, liquid hourly space velocity (LHSV), and H2/oil ratio. Reaction pressure is a very important parameter as it affects the hydrogenation and cracking reactions. In this analysis three hydrotreating pressures within the typical operating range of 8.27-9.65 MPa was examined via three experiments. The H2/oil ratio also affects the hydrogenation reactions. In this paper three typical ratios are examined, 543, 712, and 890 N m3/m3. The hydrotreatment extent can also be observed via the feed flow (mL/h) to catalyst volume (m3) or LHSV. The LHSV is a key parameter for regulating both catalyst effectiveness and catalyst life expectancy. In this study three typical LHSVs, 0.5, 1.0, and 1.5 h-1, were tested. It should be noted that for all experiments the same commercial hydrotreating catalyst was utilized.
2. METHODOLOGY The innovative part of this work is the feedstock employed which comprises 100% of waste cooking oil (WCO). The WCO is mainly collected from local restaurants as well as households, after being used for frying.15 Before introducing it into the Received: February 3, 2011 Accepted: February 24, 2011 Revised: February 19, 2011 Published: March 04, 2011 3874
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Figure 1. Schematic diagram of pilot-plant hydroprocessing unit and its operating range.
experimental unit, WCO is filtered via a regular sieve to remove any food particles remaining in the oil after frying. The study was conducted via a series of hydrotreating experiments which were carried out in a small-scale pilot plant unit of CPERI/CERTH which was described in more detailed in the authors' previous work.18 It is a continuous flow hydroprocessing unit consisting of a feed system, a reactor system, and a product separation system, as shown in Figure 1. A commercial hydrotreating NiMo-type catalyst is used in this study, which is presulfided according to the catalyst provider’s recommended procedure. Furthermore to maintain catalyst activity, dimethyl disulfide (DMDS ) and tetrabutylamine (TBA) were added to achieve a specific sulfur and nitrogen concentration in each feedstock. It should be noted that the sulfur level and the nitrogen level in the feed without DMDS and TBA were 50 wppm each. The various operating parameters were studied via different experiments (conditions). Each condition lasted a time period where it reached steady state, usually after 5-6 days on stream. This is verified by monitoring the product density and sulfur content of the liquid product daily. Once these properties are stabilized, the individual effects of each experiment are considered stable, and the study of that condition is complete. As it was described in the authors’ previous work,15 at the end of each condition the product collected is analyzed (including simulated distillation, density, sulfur and nitrogen, carbon and hydrogen), as it represents that particular condition. To analyze the effectiveness of hydrotreating reactions, the measures of conversion and selectivity are utilized. The total liquid product is collected and several analyses can take place in the analytical laboratory of CPERI. The simulated distillation curve is determined via an Agilent 6890N-GC according to the ASTM D-7213 procedure, which is in agreement with the TBP curve.19 The density of the total liquid product is measured via an Anton-Paar density/concentration meter DMA 4500 according to ASTM D-1052. The concentration of sulfur and nitrogen is measured via an Antek 5000 system, according to ASTM D5453-93 and ASTM D4629 procedures, respectively. Total carbon concentration is measured via a CHN LECO 800 analyzer. Finally, hydrogen is measured via an Oxford Instruments NMR MQA 7020. Once total carbon, hydrogen, sulfur, and nitrogen wt % are determined, the oxygen concentration is indirectly determined assuming it is the only significant element contained in the product. The assumption that no other element besides C, H, S, N, and O is verified by research of trace elements found on vegetable oils.20 This study by Llorent-Martínez et al. (2011) showed that the concentration of trace elements in basic edible oils was of the order of ppb. In particular, this study on virgin olive, olive, pomace-olive, sunflower, soybean, and corn oil showed that they contain trace elements (Ag, As, Ba, Be, Cd, Co,
Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Ti, Tl, V) in negligible concentrations, which add up to 8-120, 17-200, 3.5-200, 3800, 3.5-336, 5-342 ng 3 g-1, respectively. Thus, as the metals in edible vegetable oils are of such low concentration, the aforementioned oxygen determination methodology is valid for such applications. The aforementioned stoichiometric analyses are also performed for the feedstocks. The reaction gases are analyzed offline via a Hewlett-Packard 5890 Series II-GC equipped with two detectors, a thermal conductivity detector (TCD) and a flame ionization detector (FID). The TCD is used for the analysis of H2, CO, CO2, O2, N2, and H2S while the FID is used for CH4 and C2-C6 hydrocarbons. Catalyst life is an important issue for hydrotreating. Normally hydrotreating catalysts have a life expectancy between 6 and 18 months. However catalyst life is shortened during experimental studies in pilot plant units as the catalyst severity is perturbed by reactor temperature, LHSV, and other operating parameters. This was shown in the previous work were the catalyst life of a hydrocracking catalyst was evaluated.18 Catalyst life is affected by reaction parameters, such as temperature, LHSV, H2 partial pressure, etc. which cannot be covered in this paper.
3. RESULTS As it was previously mentioned three different parameters are studied in this work, that is, pressure, H2/oil ratio and LHSV. For the pressure, a range of 8.27-9.65 MPa was studied. In the case of H2/oil, three ratios in the range of 543-890 N m3/m3 were investigated, while three LHSVs of 0.5, 1.0, and 1.5 h-1 were explored. It should be noted that quantitative analysis as well as qualitative analysis for the feed and product were performed in the authors’ previous work.17 3.1. Effect of Pressure. The hydrotreatment pressure is a very important parameter of hydrotreatment reactions as it has a strong effect on the hydrogenation, isomerization, and cracking reactions. For this study three experiments were conducted at pressures 8.27, 8.96, and 9,65 MPa. The product yields are determined by the simulation distillation data of the total liquid product at each hydrotreatment pressure, which are given in Table 1. From this data it is evident that WCO hydrotreatment results in two main biofuel products, one which includes molecules that spread within the gasoline range to be called biogasoline and one which includes molecules spread within the diesel range to be called biodiesel. The biodiesel yield is estimated as the vol % of the total liquid product that has a boiling range between 453.15 and 633.15 K, while the biogasoline yield is the vol % of the total liquid product with a boiling range between 313.15 and 473.15 K. Regarding the gasoline and diesel cutpoints, it should be noted that they refer to the ones employed in practice during fractionation of the total 3875
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Table 1. Quality Comparison of Hydrotreatment Products at Different Pressuresa
Table 2. Quality Comparison of Hydrotreatment Products at Different H2/Oil Ratios (Nm3/m3)a feed
543 Nm3/m3
712 Nm3/m3
890 Nm3/m3
density (kgr/m3)
899.7
781.9
779.6
781.1
82 0
S (wppm) N (wppm)
21870 544.71
109.80 0.00
126.50 0.00
166.70 0.00
14.60
14.64
H (wt %)
11.32
14.45
14.47
14.53
84.49
84.64
C (wt %)
74.08
84.8
84.72
85.69
0.89
0.7
O (wt %)
12.34
0.73
0.79
-0.24
feed
8.27 MPa
8.96 MPa
9.65 MPa
density (kg/m3)
898.4
773.5
777.0
776.1
S (wppm) N (wppm)
21960 543.91
87.3 0.9
53 0
H (wt %)
11.42
14.56
C (wt %)
74.08
84.19
O (wt %)
12.24
1.24
IBP (°C)
286.6
94.2
127.2
117.8
IBP (°C)
286.6
148.2
124.6
124.6
5% (°C)
519.8
196.8
216.6
220.4
5% (°C)
519.8
232.8
215.4
212.4
10% (°C)
543.0
270.6
271.8
271.2
10% (°C)
543.0
271.6
255.2
254.8
20% (°C) 30% (°C)
596.8 601.0
287.8 300.2
288.8 302.2
288.2 302.0
20% (°C) 30% (°C)
596.8 601.0
293.2 303.4
268.6 290.2
268.4 289.6
40% (°C)
603.6
304.2
305.2
304.8
40% (°C)
603.6
305.6
292.4
291.6
50% (°C)
607.4
310.6
314.6
315.4
50% (°C)
607.4
313.4
305.2
305.4
60% (°C)
609.2
318.2
319.6
319.0
60% (°C)
609.2
319.4
311.2
310.0
70% (°C)
610.4
333.6
339.4
341.2
70% (°C)
610.4
343.2
351.8
357.0
80% (°C)
611.4
394.0
398.4
402.8
80% (°C)
611.4
405.6
414.2
418.6
90% (°C)
612.8
458.8
459.4
460.8
90% (°C)
612.8
460.8
464.2
466.0
95% (°C) FBP (°C)
622.2 739.8
479.0 695.8
476.6 570.4
477.2 572.8
95% (°C) FBP (°C)
622.2 739.8
479.0 572.8
482.0 568.8
489.2 589.0
All experiments were performed at T = 643 K, LHSV = 1.0 h-1, and H2/oil = 712 N m3/m3. a
liquid product in order to separate the two fractions, and they can overlap as they are set to collect the molecules that might be drawn away due to the momentum of the fractionation column. In the analysis of gasoline and diesel yields, two actual cutpoints are considered which are used to evaluate the potential of gasoline and diesel production yields. Lighter products (with boiling point < 313.15) are gaseous molecules and are not considered as liquid biofuels. The distillation data indicate that biodiesel production is dominant at all reactor pressures. Particularly in the highest hydrotreating pressure (9.65 MPa) biodiesel exhibits the highest yield of 71.36% of the total liquid product (Table 1). However, biogasoline yield decreases with pressure. As the hydrotreating pressure increases, the biogasoline yield reduces from 5.16% at 8.27 MPa to 4.03% at 9.65 MPa. It should be noted that biodiesel appears as the main biofuel produced from WCO hydrotreatment, and for that reason all further analysis will focus on biodiesel production. The effectiveness of hydrotreating reactions is also shown via the reduction of heteroatom concentration (mainly sulfur, nitrogen, and oxygen). Even though sulfur and nitrogen are not present in WCO, they are artificially added to the feedstock in significant amounts to regulate catalyst activity. Nevertheless the produced biodiesel contains only traces of these two elements (Table 1). Oxygen is naturally present in WCO and in significant concentration (>12%) as shown in Table 1. Nevertheless, the produced biodiesel has over 90% decrease of oxygen concentration. The extent of heteroatom removal is expressed as the percentage of the sulfur, nitrogen, and oxygen contained in the feed which has been removed during hydrotreatment reactions. Among the three heteroatoms, nitrogen is most effectively removed reaching 100% at 8.96 and 9.65 MPa. Sulfur is also effectively removed by over 99.60% for all cases. Furthermore, the most difficult element to remove is oxygen. In the lowest
a
All experiments were performed at P = 8.27 MPa, T = 643 K, and LHSV = 1.0 h-1.
Figure 2. Biogasoline and biodiesel product yields (wt %) at different hydrotreatment H2/oil ratios (Nm3/m3). All experiments were performed at P = 8.27 MPa, LHSV = 1.0 h-1, and T = 643 K.
pressure (8.27 MPa) the oxygen removal is also the lowest (89.86%). However, by increasing the pressure, the oxygen removal gradually reaches over 94.25% (9.65 MPa). From Table 1 it is evident that higher pressures favor all heteroatom removal from the final products. 3.2. Effect of H2/Oil. Another important operating parameter for hydrotreating processes is the hydrogen (gas feed) to oil (liquid feed) ratio or H2/oil ratio which is deemed to have a main impact on hydrogenation and cracking reactions efficiency. In this case the H2/oil ratio represents the ratio of hydrogen feed over the WCO. For this study, three H2/oil ratios ranging between 543 and 890 N m3/m3 were examined via three different experiments. Table 2 shows the simulation distillation data of the total liquid product at each hydrotreatment H2/oil ratio as well as the product quality (density, heteroatom concentration, etc.). According to the simulated distillation data (Table 2), the biofuel products are mainly biodiesel while a small percentage of biogasoline was also present (Figure 2). For this reason the 3876
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Industrial & Engineering Chemistry Research primary product is considered the biodiesel. Conversion and biodiesel selectivity are calculated from the simulated distillation data of the total liquid product of each hydrotreatment H2/oil ratio (Bezergianni et al. 2009a) . The maximum WCO conversion observed is 72.90% and obtained at the lowest hydrotreatment H2/oil ratio (543 N m3/m3) as shown in Figure 3. Results revealed that WCO conversion efficiency decreases with H2/oil ratio, which is expected as increasing H2/oil ratio favors the undesirable cracking and hydrogenation reactions competing with the desirable hydrotreatment reactions. Similarly to conversion, biodiesel selectivity is also not favored by H2/oil ratio, as shown in Figure 3 as cracking reactions increase for increasing H2/oil ratio. These hydrocracking reactions convert heavier molecules including even some biodiesel molecules into lighter biogasoline molecules. At the lowest H2/ oil ratio, biodiesel selectivity is at its peak reaching 96.80%. As the H2/oil ratio increases, biodiesel selectivity drops to 95.10% at 890 N m3/m3, which is however still significantly large. It is important to note that the high biodiesel selectivity values indicate that more than 90% of WCO is converted into biodiesel at all H2/oil ratios. The heteroatom removal at the three different H2/oil ratios is compared in Figure 4 as percent of its concentration in the feed. Among the three heteroatoms, nitrogen is most effectively removed by over 99% for all cases, while sulfur is also effectively removed as shown in Figure 4. The most difficult element to remove is oxygen as discussed in an earlier section. Oxygen level is indirectly calculated after C, H, S and N concentrations are determined in the product, and not via a direct analytical measurement. Therefore the oxygen concentration value depends on the measurement validity of C, H, S, and N. On that basis, the O concentration may be negative or O removal rate may exceed 100%, as observed in Figure 4. Thus, in the highest H2/oil ratio studied (890 N m3/m3) oxygen removal percentage
Figure 3. Effect of H2/oil ratio (Nm3/m3) on hydrotreatment biodiesel conversion (black) and selectivity (gray). All experiments were performed at P = 8.27 MPa, LHSV = 1.0 h-1, and T = 643 K.
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is the highest (101%), indicating that the optimal H2/oil ratio is different for each heteroatom to be removed. 3.3. Effect of LHSV. The liquid hourly space velocity (LHSV) is an important operating parameter for regulating catalyst effectiveness and also catalyst life expectancy, as it determines the time that the reacting feed (hydrogen þ WCO) remains within the reactor. This study on product quality and yields was performed on hydrotreating of WCO at three different LHSVs (0.5, 1.0, and 1.5 h-1). The quality comparison of hydrotreatment products at different LHSV (h-1) is depicted in Table 3. It should be noted that two more LHSVs were studied (2 and 2.5 h-1) but were too large, and the experiments failed as the catalyst was poisoned in the first couple of days. The conversion as well as the biodiesel selectivity is given in Figure 5. An overall increasing trend for both conversion and selectivity is observed with increasing LHSV. Conversion reaches a maximum of 83.08% (1 h-1), while biodiesel selectivity rises Table 3. Quality Comparison of Hydrotreatment Products at Different LHSVs (h-1)a feed
0.5 h-1
1 h-1
1.5 h-1
density (kg/m3)
899.5
770.9
767.9
767.6
S (wppm)
16760
25.80
71.80
34.90
N (wppm)
431.13
0.00
0.59
0.00
H (wt %)
11.60
14.71
14.78
14.74
C (wt %)
74.66
84.34
85.04
83.34
O (wt %)
12.01
0.94
0.16
1.91
IBP (°C)
69.8
93.4
49.2
81.6
5% (°C) 10% (°C)
534.2 591.8
196.0 270.6
212.6 271.0
239.4 271.4
20% (°C)
599.4
287.4
287.8
294.0
30% (°C)
600.8
301.6
302.2
302.8
40% (°C)
604.6
303.6
304.0
304.0
50% (°C)
607.0
305.8
304.8
304.8
60% (°C)
608.0
316.8
316.0
316.4
70% (°C)
608.8
318.6
318.2
318.0
80% (°C) 90% (°C)
609.4 610.0
356.8 432.0
338.2 418.6
340.8 436.0
95% (°C)
610.4
468.6
462.4
465.4
FBP (°C)
627.2
556.4
536.0
546.0
H/C
0.1398
0.1745
0.1739
0.1769
Br index
41300
171.9
130.0
170.8
a
All experiments were performed at P = 8.27 MPa, T = 643 K and H2/oil = 543 N m3/m3.
Figure 4. Heteroatom (sulfur, nitrogen, and oxygen) removal at different hydrotreatment H2/oil ratios (Nm3/m3). All experiments were performed at P = 8.27 MPa, LHSV = 1.0 h-1, and T = 643 K. 3877
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production of biodiesel from WCO, that is, pressure, H2/oil, and LHSV. In the case of pressure, lower values favor biodiesel production as higher pressures promote cracking reactions which reduce the biodiesel selectivity. Similarly WCO conversion efficiency decreases with H2/oil ratio and cracking reactions are triggered, lowering biodiesel production yields. Regarding LHSV, higher values are preferable as they promote biodiesel production. In all cases studied, heteroatom removal effectiveness was also assessed, showing excellent results in all cases. In particular sulfur and nitrogen removal exceeded 99% in all experiments, while oxygen removal performance was also significant (>90%). Figure 5. Effect of LHSV (h-1) on hydrotreatment biodiesel conversion (black) and selectivity (gray). All experiments were performed at P = 8.27 MPa, H2/oil = 543 N m3/m3 and T = 643 K.
Figure 6. Heteroatom (sulfur, nitrogen, and oxygen) removal at different hydrotreatment LHSVs (h-1). All experiments were performed at P = 8.27 MPa, H2/oil = 543 N m3/m3 and T = 643 K.
from 96.4% (0.5 h-1) to 97.46% (1 h-1). Increasing LHSV (therefore decreasing reaction time) causes less cracking and therefore a smaller production of the lighter products. So, higher LHSVs promote biodiesel production. Regarding heteroatom removal, sulfur and nitrogen are easily removed by over 99.7% for all cases as depicted in Figure 6. On the other hand, oxygen is also effectively removed but at a slightly smaller percentage. In particular at low LHSVs, oxygen removal is less effective. As the LHSV rises from 0.5 to 1 h-1 the oxygen removal increases from 76.1% to its peak of 95.8%. To conclude, the highest heteroatom removal for all the three elements together is observed at the highest LHSV (1 h-1). Saturation of double bonds is another parameter indicating hydrotreating effectiveness, as it enables both heteroatom removal and cracking reactions, and has been included in the study of the effect of LHSV. WCO contains a large amount of double bonds, indirectly indicated by bromine index and carbon-tohydrogen ratio (Table 3). From Table 3 it is clear that the H/C ratio remains relatively constant for all LHSVs (∼0.1752 ( 0.017), indicating that saturation of double bonds is not influenced significantly by LHSV. Similarly the bromine index is significantly decreased after hydrotreatment achieving over 99.5% decrease for all LHSVs. Therefore, saturation definitely occurs during hydrotreatment and is slightly favored for increasing LHSVs.
4. CONCLUSIONS Three main hydrotreatment operating parameters were studied in terms of their effect on product yields and quality for the
’ AUTHOR INFORMATION Corresponding Author
*Tel.: þ30-2310-498315. Fax: þ30-2310-498380. E-mail:
[email protected]. Address: Chemical Process Engineering Research Institute—CPERI, Centre for Research & Technology Hellas—CERTH, 6th km Harilaou-Thermi Road, ThermiThessaloniki 57001, Greece.
’ ACKNOWLEDGMENT The authors wish to express their appreciation for the financial support provided by the program LIFEþ of the European Commission, which funded 50% the Environmental Policy and Governance project LIFE08 ENV/GR/000569. The authors would also like to thank Carborundum Universal Limited for providing one of the main materials for conducting the experiments. ’ REFERENCES (1) Knothe, G.; Van Gerpen, J. H.; Krahl, J. The Biodiesel Handbook; AOCS Press: Champaign, IL, 2005. (2) Pahl, G. Biodiesel: Growing a New Energy Economy. Chelsea Green Publishers: White River Junction VT, 2005. (3) Van Gerpen, J. H. Biodiesel processing and production. Fuel Process. Technol. 2005, 86, 1097–107. (4) Biodiesel Handling and Use Guidelines; NREL: Golden, CO, 2001; p 22; http://www.angelfire.com/ks3/go_diesel/files042803/biodiesel_ handling.pdf. (5) Krawczyk, T. Biodiesel. Inform 1996, 7 (8), 801–22. (6) Connemann, J.; Fischer, J. Biodiesel in Europe, Biodiesel Processing Technologies. Proceedings of the International Liquid Biofuels Congress, July, 19-22, 1998, Brazil; Oelmuhle Leer Connemann GmbH & Co.: Germany, 1998. (7) Rocha Filho, G. N.; Brodzki, D.; Djega-Mariadassou, G. Formation of alkanes, alkylcycloalkanes, and alkylbenzenes during the catalytic hydrocracking of vegetable oils. Fuel 1993, 72, 543–9. (8) Gusmao, J.; Brodzki, D.; Djega-Mariadassou, G.; Frety, R. Utilization of vegetable oils as an alternative source for diesel-type fuel: Hydrocracking on reduced Ni/SiO2 and sulphided Ni-Mo/c-Al2O3. Catal. Today 1989, 5, 533–44. (9) Farrauto, R. J.; Bartholomew, C. Introduction to Industrial Catalytic Processes; London: Chapman & Hall, 1997. (10) Stumborg, M.; Wong, A.; Hogan, E. Hydroprocessed vegetable oils for diesel fuel improvement. Bioresour. Technol. 1996, 56, 13–8. (11) Snare, M.; Kubic, K. I.; Maki-Arvela, P.; Chichova, D.; Eranen, K.; Murzin, D. Catalytic deoxygenation of unsaturated renewable feedstocks for production of diesel fuel hydrocarbons. Fuel 2008, 87, 933–45. (12) Sebos, A.; Matsoukas, V.; Apostolopoulos, N.; Papayannakos, N. Catalytic hydroprocessing of cottonseed oil in petroleum diesel mixtures for production of renewable diesel. Fuel 2009, 88, 145–9. 3878
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