(15h) Catalytic Cracking of a Rapeseed Oil for Production of Transportation Fuels and Chemicals: Yield Structure

1. Introduction

         Biofuels are a wide range of fuels derived from biological resource, especially from biomass. Being a source of renewable energy and driven by factors such as oil price hikes, increased energy security, and environmental concerns, biofuels are gaining increased industrial and scientific attention and interests. In 2008, biofuels provided 1.8% of the world's transportation fuels.¹ The European Union has set directives for the biofuels at 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 low erucic acid content). The canola plant produces seed-filled pods. After crushing, the seeds generate canola oil in additional to canola meal for animals.

Through transesterification, canola oil can be converted to biodiesel which is known to produce fewer emissions, and provides better lubrication than low-sulfur diesel from petroleum source. The option to produce biogasoline from canola oil through thermal or catalytic cracking has been investigated by researchers in the 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 rather low temperatures (<500°C) and low weight hourly space velocity (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 benchmark conditions which were able to produce yield data close to commercial values.

2. Experimental

         Edible-grade canola oil was obtained from a supermarket. This oil is similar in analysis compared with the commercial bulk canola oil from the supplier except for the color (light yellow versus green). The conventional FCC feed and equilibrium catalyst were supplied by a US refinery. Properties of feeds and catalyst were given in Tables 1 and 2, respectively. Feeds were cracked in a fluid-bed microactivity test (MAT) unit at 540°C, 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

         Table 2. Properties of Equilibrium Catalysts

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 a conversion which was ~5.5 wt% higher than that of the FCC feed. It is important to examine if the high conversion was contributed by the high-value products such as gasoline and liquefied petroleum gas or the low-value counterparts such as dry gas and coke.

         Figure 1. Relationship between Conversion and Catalyst/Oil Ratio

3.2. Dry Gas

              Dry gas is composed of H₂, H₂S, CO, CO₂, and C₁?C₂ hydrocarbons. Figure 2 depicts 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 degree of increase with conversion was particularly intense for canola oil. Both CO and CO₂ were detected during cracking of the canola-containing feeds, with CO yields at ~0.95 and ~2.55wt%, and CO₂ yields at 1.3?1.8 wt% and 1.3?2.2 wt%, for the blend and canola oil, respectively.

         Figure 2. Correlation of Dry Gas Yield with Conversion

3.3. Liquefied Petroleum Gas

         Liquefied Petroleum Gas (LPG) consists of C₃ and C₄ gaseous hydrocarbons. LPG is considered a valuable product since its components can be used as alkylation and petrochemical feedstocks. In contrast to the increases in dry gas yield, the blend and canola oil in Figure 3 exhibit decreases in LPG yield at a given conversion, compared with the FCC feed.

         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 drops 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 with the FCC feed whereas canola oil further reduced the yield by ~2.0wt% compared with 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.

         Figure 4. Relationship between Gasoline Yield and Conversion

3.5 Coke

         In FCC operation, coke is necessary to supply heat for feed pre-heat and cracking. However, too much coke can seriously poison the catalyst and overload the air blower during catalyst regeneration, causing excessively high temperature in the regenerator. Figure 5 demonstrates that coke yield increased with conversion. The blend had similar coke profile to that of the FCC feed but canola oil showed a sharp increase in coke yield at conversions higher than 80wt%.

         Figure 5. Correlation of Coke Yield with Conversion

3.5 Oxygen Balance

              In this study, the oxygen distribution in the gaseous and liquid products is shown in Table 3.

              Table 3. Oxygen Balance in Cracking 50/50 Blend and Canola Oil

4. Conclusions

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• Catalytic cracking of canola-containing feeds resulted in the formation of water, carbon monoxide, and carbon dioxide at the expense of gasoline production;

  ·       

• Conversions of all feeds increased with C/O ratio. When the proportion of canola oil in the feed was higher, the conversion at a constant C/O ratio increased;

  ·       

• For a given feed, as conversion increased, yields of unconverted products (i.e., diesel and heavy fuel oil) decreased while yields of other products increased, except for gasoline which might show a parabolic variation;

  ·       

• At a given conversion, yields of dry gas, diesel, coke, and water increased, while yields of LPG, gasoline, and heavy fuel oil decreased;

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• After cracking, most of the oxygen in canola oil appeared 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.

[1]         ?Towards Sustainable Production and Use of Resources: Assessing Biofuels?. United Nations Environment  Programme 2009-10-16.

[2]         Selçuk, S., Kaygusuz, K., Sari, A., Energ. Sour. 2004, 26 1119-1129.

[3]         Idem, R.O., Katikaneni, S.P.R., Bakhshi, N.N. ?Thermal Cracking of Canola Oil: Reaction Products in the Presence and Absence of Steam?, Energy Fuels 1996, 10 1150?1162.

[4]         Katikaneni, S.P.R., Adjaye, J.D., Idem, R.O., Bakhshi, N.N. ?Performance Studies of Various Cracking Catalysts in the Conversion of Canola Oil to Fuels and Chemicals in a Fluidized-Bed Reactor?, JAOCS 1998, 75(3) 381?391.

[5]         Sadrameli, S.M., Green, A.E.S. ?Systematics of Renewable Olefins from Thermal Cracking of Canola Oil?, Journal of Analytical and Applied Pyrolysis 2007, 78(2) 445-451.

[6]         Katikaneni, S. P.R., Adjaye, J.D., Bakhshi, N.N. ?Catalytic Conversion of Canola Oil to Fuels and Chemicals over Various Cracking Catalysts?,  CJChE 2009, 73(4) 484 ? 497.

[7]         Dupain, X., Costa, D., Schaverien, C.J., Makkee M., Moulijn, J. ?Cracking of a Rapeseed Vegetable Oil under Realistic FCC Conditions?, Applied Catalysis B: Environment 2007 72 44?61.

[8]         Ng, S. H., Zhu, Y., Humphries, A., Zheng, L., Ding, F., Gentzis, T., Charland, J. P., Yui, S., Energy Fuels  2002, 16, 1196-1208.

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