A Critical Review of Biodiesel as a Transportation Fuel in Canada

2. BIODIESEL PRODUCTION AND ECONOMICS

Vegetable oils offer good ignition characteristics and have been used as fuels in diesel engines at the time of fuel shortages. However, some of the properties of vegetable oils, especially their viscosity and quick oxidation tendency, make them undesirable for use in modern diesel engines. The viscosity of vegetable oils, when used as fuel, can be reduced in at least four different ways: dilution, pyrolysis, microemulsion, and transesterification. Out of these options, transesterification is the current method of choice, by which vegetable oils can be converted to the products called "Biodiesel", with properties very similar to diesel fuel. Biodiesel can be used in its neat form or as a blend in conventional diesel fuel. Various types of animal fats, used oils and fats, and microalgal oils can also be converted to biodiesel type products. Two technologies exist for conversion of vegetable or biomass derived oils and animal fats to biodiesel.

2.1 Biodiesel by Esterification Process

The traditional technology to produce biodiesel is through "transesterification'1, a process that combines vegetable oils, animal fats, and/or microalgal oils with alcohol (ethanol or methanol) in the presence of a catalyst (sodium or potassium hydroxide) to form fatty esters (ethyl or methyl ester). Converting triglyceride oils to methyl or ethyl esters through a transesterification process reduces the molecular weight to one-third that of the oil, reduces the viscosity by a factor of eight, and increases the volatility. The most important variables that influence the transesterification reaction time and conversion efficiency are temperature, catalyst type and its concentration, alcohol to ester ratio, and stirring rate. Purity of reactants, for example, presence of water, free fatty acids, and other contaminants found in unrefined oils (or other feedstocks) is also very important. Figure 1 shows the flow diagram for the transesterification process."

Figure 1: Flow diagram for manufacturing methyl esters via transesterification

A stoichiometric material balance yields the following simplified equation:

Oil or Fat (1000kg) + Methanol (107.5 kg) = Methyl ester (1004.5 kg) + Glycerol (103 kg)

After the reaction, the products are separated into two phases1 which facilitates easy removal of glycerol, a valuable industrial byproduct, in the first phase. The remaining alcohol/ester mixture is then separated and the excess alcohol is recycled. The esters are sent to the cleanup or purification process, which consists of water washing, distillation, vacuum drying, and filtration. The biodiesel produced from this process is commonly referred to as "vegetable ester". The basic properties of methyl esters produced from different types of vegetable oils are shown in Table 1.

Table 1. Property Data for Methyl Ester Biodiesel Fuels

Source Oil	Density: 9/cc @ 15.50C	Viscosity: cSt @ 400C	Cetane No.	Heating Value (MJ/kg)	Cloud Point (0C)
Palm (Pischinger et al., 1982)	0.880	5.7	62	37.8	+13
Soybean (Schwab et al., 1987)	0.884	4.08	46.2	39.8	+2
Sunflower (Pischinger et al., 1982)	0.880	4.6	49	38.1	+1
Tallow (Ali et al., 1985)	0.887	4.1	58	39.9	+12
Canola (Reaney, 1997)	0.880	4.4	49.6	40.1	-1*

* Pour Point instead of Cloud Point

The cost of producing biodiesel in North America is currently much higher than the price of conventional diesel fuel. For example. the current cost of biodiesel in the U.S. is about $0.66 per liter compared to the pump price of diesel at about $0.30 per liter. At roughly two to three times the cost of diesel fuel, biodiesel simply cannot compete head-to-head economically. In many parts of Europe, tax incentives for biodiesel allow rapeseed oil methyl ester to sell at the pump for about the same price as diesel fuel. In Canada and the U.S. no such tax allowance is currently available. Without that aid, biodiesel has to compete not only with diesel fuel but with other alternative fuels as well.

Roughly 75 to 90 per cent of the cost of biodiesel is the raw materials. In Canada, biodiesel can be made from food-grade canola seed, but that would result in high cost. Lower quality canola oil - from over-heated canola seed, frost-damaged seed, and small fines from the screening process - could also be used, which can be one4ourth the cost of food-grade canola seed. The oil from lower quality feedstock has a pungent odor, and dark brown color, but it does not have any adverse effect on the quality of ester product (Reaney, 1997).

Although oils destined for conversion to biodiesel need not meet the rigorous standards of the edible oil industry, they may still require processing. Depending on the biodiesel fuel standard, which is still being developed, some processing steps may be necessary to reduce sulfur and phosphorus content of oils from off-quality seed.

Another option in reducing the cost of biodiesel is to look to other fats and oils sources that have less competition, where biodiesel could reign as the primary consumer. For example, the use of waste frying oils can substantially reduce the cost of raw materials but may increase the processing cost. Waste frying oil is often hydrogenated oil with a higher pour point, which may present a problem in biodiesel. There can also be problems with the relatively high free fatty acid content in waste oils, which make it more difficult to properly separate the glycerol and esters obtained from the transesterification process. Therefore, in selecting a feedstock, the cost of raw materials, as well as the processing cost and its effect on the quality of biodiesel and other byproducts, need careful assessment.

An important factor in biodiesel economics is the market value of the glycerol produced. Glycerol markets are limited; any major increase in biodiesel production may cause glycerol sales prices to decline, meaning that the biodiesel price would have to cover an increasing share of total costs.

Improvements in the transesterification technology would also lower the cost of production. Currently, biodiesel is produced in small quantities using a batch process. The use of a continuous process would be more efficient and could offer the economies of scale benefits to the production cost of biodiesel.

Based on data for the last two decades the average price of diesel and soybean oil, ignoring peaks, has been around US $200 and US $600 per tonne respectively (krawczyk, 1996). In producing biodiesel from vegetable oil the return on investment and processing cost are essentially compensated by the byproduct credits, making the price of biodiesel approximately the same as the price of vegetable oil. Prediction of future price ratios becomes difficult because vegetable oil prices are set by the global market, whereas the final sale price of diesel is subject to taxes, which vary from country to country. In Europe, the taxes on diesel fuel have averaged about US $400 per tonne, which brings the pump price of diesel to the same level as the biodiesel price without any tax. However in Canada and the U.S., due to the lack of tax incentives for biodiesel and lower taxes on conventional diesel, biodiesel is currently about three times more costly.

According to a recent market analysis conducted in the U.S., the cost of biodiesel produced in a small-scale operation using soybeans is approximately $0.66 I liter. Large scale production using current technology could reduce biodiesel cost to 0.40 to $0.45 I liter. Additional research advances using existing feedstocks or innovative feedstocks such as microalgae could further reduce the costs. The goal of the US Department of Energy and the National Renewable Energy Laboratory (DOEINREL) program is to reduce the cost of biodiesel production by 50-65% i.e. production at $0.26 I liter.

2.2 Biodiesel by Hydrogenation Process

The second process, which involves simultaneous catalytic hydrogenation and cracking of vegetable and tree oils, was developed at the Saskatchewan Research Council under the sponsorship of the Canada Center for Mineral and Energy Technology (CANMET). This process has been used to produce biodiesel type material from "Tall Oil", a byproduct from the Kraft pulping process. The principal constituents of tall oil are unsaturated C18 fatty acids, resin acids and unsaponifiable hydrocarbons such as di-terpenic alcohols/aldehydes. The biodiesel produced from this process has been given the name "SuperCetane", due to its high Cetane number close to 60.

The CANMET technology has been licensed to Arbokem of Vancouver, Canada, to market the process worldwide. The world production of tall oil is estimated at about 1.2 million tonnes/year. Well over 60% of that comes from the U.S. BC Chemicals is a leading producer of tall oil in Canada.

In its traditional use, the crude tall oil (CTO) is first depitched and then upgraded by distillation to produce more valuable products such as tall oil fatty acids ~OFA) and tall oil rosin (TOR). The CANMET process, aimed to convert tall oil into higher value products, involves simultaneous catalytic hydrogenation and cracking of the depitched tall oil (DPTO). Two continuous trickle bed reactor systems were used in this program. The first unit, a once through semi-pilot plant with a 750 ml reactor was used for the initial work. The second system, a process development unit (PDU) with a 10 liter reactor which fully simulates the features of the process in commercial units, was used to produce sufficient quantities of Supercetane for engine testing.

In the production process of SuperCetane, shown in Figure 2, the DPTO feed is pumped into the high pressure system where it combines with hydrogen and the gas-liquid phase passes through a series of electric pre-heaters before entering the catalytic trickle bed reactor. The product is collected in two flash columns, decanted to remove the water1 and then distilled in a batch unit to obtain the desired cut. The process gas is recycled after removing the impurities in a series of scrubbers. Long duration pilot-plant runs were successfully carried out at CANMET's Energy Research Laboratories in Ottawa, to convert tall oil into SuperCetane, and the process is now ready for scale-up.

The boiling point distributions of DPTO and the liquid hydrocarbon product separated in three distinct fractions, naphtha (IBP-1600C), Supercetane (1600C-3250C, diesel fuel cut), and heavy gas oil (3250C +) are shown in Figure 3. Properties of Supercetane and DPTO feed1 along with the specifications for No.1 diesel fuel (D-1) for comparison, are given in Table 2.

Figure 2: Schematic of CANMET Supercetane Process

Figure 3: True boiling point distribution of DPTO and a sample of liquid hydrocarbon products

Figure 4: Chromatogram of SuperCetane Product

Table 2. Properties of Feed, Supercetane (SC) and Specification of Diesel No.1 (D-1)

Property	DPTO	SC	D-1
Density, g/ml	0.9616	0.8297	0.850
API, 60/60 ºF	15.7	39.0	-
C, wt%	79.1	86.4	-
H, wt%	11.0	13.5	-
O, wt%	9.5	0.02	-
N, ppm	58	1.3	-
S, ppm	993	18.6	500
Mercaptan S, ppm	-	50
Acid Number, g KOH/g	152.2	<0.05	0.1
Distillation
10% Recovered, ºC	345	225	215
90% Recovered, ºC	404	322	288
End Point, ºC	573	344	316
Cetane Number	-	64	40

The GC-MS analysis indicates that the predominant components of SuperCetane are normal alkanes which range from n-C9 to n-C24. The n-C17 and n-Cl 8 alkane components account for approximately 72% of total alkanes in the product (Feng, Wong and Monnier, 1993). The chromatogram of the product shown in Figure 4 clearly depicts two intense peaks associated with n-C17 and n-C18 alkanes. The chromatogram for conventional diesel fuel, shown in Figure 5, indicates the presence of alkanes from n-Cl 0 to n-C22. The Cetane Number of the product was greater than 55. The GC-MS analysis further revealed that the sulfur content in SuperCetane is extremely low, while the cyclic hydrocarbon and aromatic contents are much lower than in diesel fuel.

Figure 5. Chromatogram of Conventional Diesel Fuel

The production cost for 8upe~etane. including the capital and operating costs in a large scale plant is estimated at 10 to 12 cents per liter (Monnier, 1997). The cost of the tall oil as raw material could vary from 8 to 20 cents per liter of SuperCetane. Thus the total cost of this product could range between 18 to 32 cents per liter, which makes it economically more attractive than vegetable esters currently costing about 66 cents per liter.

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