Coprocessing of Conventional FCC Feed and Rapeseed Oil for Clean Transportation Fuels
Drs. Siauw Ng1*, Fuchen Ding2, Mustafa Al-Sabawi1, Yu Shi1 (1) Research Scientist, Canmet Energy Upgrading Program, Natural Resources Canada, Devon, AB, Canada, (2) Professor, Beijing Institute of Petrochemical Technology, Beijing, China
1. Introduction
Biofuels refer to a wide range of fuels derived from biological sources, especially biomass. Owing to considerations such as price escalation, energy security, and environmental concerns, biofuels, being a source of renewable energy, are gaining increased industrial and scientific interest. In 2008, biofuels provided 1.8% of the world’s transportation fuels.1 The European Union set targets for biofuel usage of 2% in 2005 and 5.75% in 2010.2
Canola is a cultivated variety of rapeseed, and canola oilseeds are rich in oil content (40–43%). The name “canola” was derived from “Canadian Oilseed, Low-Acid” (referring to the erucic acid content). The canola plant produces seed-filled pods. The seeds are crushed to produce canola oil in addition to canola meal for animal feed.
Through transesterification, canola oil can be converted to biodiesel, which is known to produce fewer emissions and provide better lubrication than low-sulfur diesel from petroleum sources. The option to produce biogasoline from canola oil through thermal or catalytic cracking has been investigated by researchers in North America and Europe.3–7. Most of these studies dealt with cracking of canola oil using inert materials or pure zeolites in fixed-bed reactors at relatively low temperatures (<500°C) and low weight hourly space velocities (WHSV, <3.6 h-1). In this study, a canola oil, a refinery FCC feed, and a 50/50 blend of the two were catalytically cracked over an equilibrium catalyst in a fluid-bed batch reactor at commercially relevant conditions.
2. Experimental
Edible-grade canola oil was obtained from a supermarket. This oil is similar in analysis to the bulk canola oil available from commercial suppliers except for the color (pale yellow versus green). The conventional FCC feed and equilibrium catalyst were supplied by a US refinery. Properties of the feeds and catalyst are given in Tables 1 and 2, respectively. The feeds were cracked in a fluid-bed microactivity test (MAT) unit at 540°C and 10–25 h-1 WHSV, with a constant oil injection time of 30 s. Details of the experiment have been reported elsewhere.8
Table 1. Feed Properties
1 Analysis Unit FCC Feed Canola Oil 50/50 Blend Density g/mL 0.8928 0.9169 0.9072 Carbon wt% 86.46 77.63 81.52 Hydrogen wt% 13.20 11.92 12.51 Sulfur wppm 687 <0.55 335 Nitrogen wppm 370 0.71 190 Oxygen wt% 0.31 11.58 6.52 Saturates wt% 65.8 0.0 29.6 Aromatics wt% 32.1 0.6 16.3 Polars wt% 2.1 99.4 54.0 Asphaltenes wt% 0.0 0.0 0.0
Table 2. Properties of Equilibrium Catalyst
Catalyst Equilibrium Catalyst
Al2O3, wt % 35.9 SiO2, wt % 51.0 Re2O3, wt % 0.28 TiO2, wt % 1.27 Na2O, wt % 0.52 Fe2O3, wt % 0.40
3. Results and Discussion
3.1. Conversion
Conversion is defined as the portion of the feed converted to 221°C– products, including gas and coke. Figure 1 shows that conversion increased with catalyst/oil (C/O) ratio. At a given ratio, canola oil gave the highest conversion, followed by the 50/50 blend and the conventional FCC feed. All curves tended to converge to the same conversion level at very high C/O ratio. At C/O ratio of 10, canola oil exhibited conversion ~5.5wt% higher than that of the FCC feed. It is important to determine whether the high conversion was due to high-value products such as gasoline and liquefied petroleum gas or low-value constituents such as dry gas and coke.
2 86
84 0v% Canola 82
% 80 t w
,
N 78 O I
S 50v% Canola R
E 76 V N O
C 74
72 100v% Canola 70
68 4 5 6 7 8 9 10 11 C/O RATIO, g/g Figure 1. Relationship between Conversion and C/O Ratio
3.2. Dry Gas
Dry gas is composed of H2, H2S, CO, CO2, and C1–C2 hydrocarbons. Figure 2 shows that dry gas yield increased exponentially with conversion. At a given conversion, canola oil and the blend gave higher dry gas yields than the FCC feed. The increase of dry gas yield with conversion was particularly strong for canola oil. Both CO and CO2 were detected during cracking of the feeds containing canola oil, with CO yields at ~0.95 and ~2.55wt% and CO2 yields at 1.3–1.8wt% and 1.3–2.2wt%, for the blend and pure canola oil, respectively.
9
8 0v% Canola
7 % t w
6 , S
A 50v% Canola G
Y 5 R D
4
100v% Canola 3
2 68 70 72 74 76 78 80 82 84 86 CONVERSION, wt% Figure 2. Relationship between Dry Gas Yield and Conversion
3.3. Liquefied Petroleum Gas
Liquefied petroleum gas (LPG) consists of C3 and C4 gaseous hydrocarbons.
3 LPG is considered a valuable product since its components can be used as alkylation and petrochemical feedstocks. Figure 3 shows that, in contrast to the dry gas yields, the blend and canola oil exhibit lower LPG yields at a given conversion than the FCC feed.
24
23 0v% Canola
22
21 % t w
, 20 50v% Canola G P L 19
18
100v% Canola 17
16 68 70 72 74 76 78 80 82 84 86 CONVERSION, wt% Figure 3. Variation of LPG Yield with Conversion
3.4 Gasoline
Gasoline (C5–221°C boiling point) is the major and the most desirable product in FCC operation. Perhaps the most striking feature in cracking the canola-containing feeds was the significant drop in gasoline yield relative to that of the FCC feed. Figure 4 shows that, at 80wt% conversion, the blend lowered the gasoline yield by ~4.3wt% compared to the FCC feed whereas canola oil further reduced the yield by ~2.0wt% compared to the blend. It was believed that the loss of gasoline was mostly due to the formation of water, CO, and CO2 from the canola component in the feeds. The water yield varied from 5.4 to 6.0wt% and from 10.2 to 11.0wt% for the blend and canola oil, respectively. Overcracking was observed for canola oil at 78–82wt% conversion.
4 50
48 0v% Canola
46 % t w
, E N
I 44 50v% Canola L O S A G 42
40 100v% Canola
38 68 70 72 74 76 78 80 82 84 86 CONVERSION, wt%
Figure 4. Relationship between Gasoline Yield and Conversion
3.5 Coke
In FCC operation, coke is necessary to supply heat for feed preheating and cracking. However, too much coke can seriously poison the catalyst and overload the air blower during catalyst regeneration, causing excessively high temperatures in the regenerator. Figure 5 shows that coke yield increased with conversion. The blend had a similar coke profile to that of the FCC feed but canola oil showed a sharp increase in coke yield at conversions higher than 80wt%.
6.5
6.0 0v% Canola 5.5
5.0 % t 4.5 w
, 50v% Canola E K
O 4.0 C
3.5
3.0 100v% Canola 2.5
2.0 68 70 72 74 76 78 80 82 84 86 CONVERSION, wt% Figure 5. Relationship between Coke Yield and Conversion
3.5 Oxygen Balance
Table 3 gives the oxygen distribution in the gaseous and liquid products. It can
5 be seen that, after cracking, most of the oxygen in the canola oil appears as H2O (79.7– 88.7 and 78.6–84.1wt% for the blend and canola oil, respectively), with the rest forming CO (8.5–9.3 and 12.2–12.8wt% for the blend and canola oil, respectively), or be retained in the TLP as phenols (about 2wt% for both feeds).
Table 3. Oxygen Balance in Cracking 50/50 Blend and Canola Oil
Run Number 3114D 3115D 3116D 3117D 3120D 3121D 3122D 3124D Feed 50/50 Blend Canola Oil Catalyst/Oil Ratio g/g 4.761 6.234 7.931 10.828 4.675 6.058 7.699 10.271 WHSV g/h/g 25.20 19.25 15.13 11.08 25.67 19.81 15.59 11.68 CO Yield wt% 0.92 0.97 0.98 0.89 2.47 2.54 2.57 2.60 H2O Yield wt% 5.41 5.71 5.85 6.02 10.24 10.61 10.96 10.97 Conversion wt% 76.41 80.50 82.77 85.25 79.17 82.11 84.60 84.99 O2 conc in TLP wt% 0.26 0.28 0.25 0.26 0.35 0.38 0.423 0.43 O2 balance (relative wt% to feed oxygen)
O2 as CO 8.7 9.2 9.3 8.5 12.2 12.5 12.7 12.8 O2 as H2O 79.7 84.1 86.1 88.7 78.6 81.4 84.0 84.1 O2 in TLP 2.4 2.4 2.0 1.9 1.8 1.8 1.9 1.9 Tot O2 90.9 95.8 97.4 99.1 92.6 95.7 98.6 98.8
4. Conclusions
Catalytic cracking of feeds containing canola oil results in the formation of water, carbon monoxide, and carbon dioxide at the expense of gasoline production. Conversions of all feeds increase with C/O ratio. When the proportion of canola oil in the feed is higher, the conversion at a constant C/O ratio increases. For a given feed, as conversion increases, yields of unconverted products (i.e., diesel and heavy fuel oil) decrease while yields of other products increase, except for gasoline of which the increase may show a parabolic variation. At a given conversion, as the content of canola oil in the feed increases, yields of dry gas, diesel, coke, and water increase, while yields of LPG, gasoline, and heavy fuel oil decrease.
After cracking, most of the oxygen in canola oil appears as H2O, with the rest forming CO, CO2, and oxygenates, such as phenols, in the TLP.
Acknowledgments
The authors wish to thank the analytical laboratory of CanmetENERGY.
References.
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