1. Introduction
The diminishing supply of fossil fuel reserves and increasing environmental problems associated with the burning of fossil fuel have made renewable energies very promising as future alternative energy sources [
1,
2,
3]. Among the renewable energies, biodiesel has been touted as one of the most important renewable energy sources, especially in the context of Malaysia [
4,
5]. Biodiesel is defined as mono-alkyl esters derived from long chain fatty acids contained in animal fats and vegetable oils, and processed using alcohol and a catalyst. It is environmentally friendly, non-toxic, and of course, abundant in nature [
6,
7,
8].
Reference [
9] focuses on the engine performance of biodiesel when used in diesel engines. The research reveals that fuels from biodiesel, made through transesterification of waste vegetable oil, may be used without significant impacts on the performance of direct injection (DI) and indirect injection (IDI) diesel engines. In reference [
10], the authors conducted experiments to investigate the benefits of mixing biodiesels with petrol diesel fuel, with one-cylinder diesel engines using a wide range of biodiesel blends from linseed oil and conclusive results were obtained showing that a mixture of B20 (Biodiesel 20%) produces the optimum thermal efficiency and emissions for the engine. In other studies, it has been shown that 10% biodiesel blends of non-edible oils;
Jatropha curcas,
Ceiba pentandra, and
Calophyllum inophyllum, provides the best engine performance in terms of thermal efficiency, engine power, engine torque, and fuel consumption of a Compression Ignition (CI) engine [
11]. These studies serve to demonstrate the huge potential of biodiesel to supplement or even replace fossil diesel fuel, without requiring engine modifications and without experiencing deterioration in engine performance. Furthermore, the use of biodiesel can extend the life of the diesel engine; due to its better lubricating properties as compared to petrol diesel [
12].
There are different types of feedstocks; from animal fats, vegetable oils, and algae, that may be used to produce environmentally friendly biodiesel. First generation feedstocks, produced directly from food crops and edible vegetable oils, such as rapeseed and soybean oils are the most commonly used raw materials for the production of biodiesel. However, the use of first generation feedstock has somehow been given negative publicity recently and has attracted the attention of researchers due to the issue of “food versus fuel”. As first generation feedstocks are essentially food crops, its use for the production of biodiesel has driven away a large chunk of food crops from the global food consumption market; causing an inevitable increase in its price.
Hence, a number of researchers have turned their attention to second generation feedstocks. These second generation feedstocks are generally produced from non-edible food crops or non-edible vegetable oils such as wood, waste, etc., in order to avoid the conflict associated with the first generation feedstocks. Included in the second generation feedstocks is waste or used cooking oil [
13,
14,
15]. Numerous works have reported the potential of non-edible vegetable oils due to its physicochemical properties, its environmentally friendliness, and availability; allowing the production of biodiesel in a sustainable manner.
In addition, recent studies also present third generation feedstocks, taking advantage of specifically engineered energy crops such as microalgae for biodiesel production. References [
16,
17,
18] have reported the economic advantages of using microalgae as feedstocks, in terms of the minimal land required as well as higher oil extraction capability of microalgae as compared to other feedstocks. Microalgae can also be grown on land and water unsuitable for food agriculture; reducing the strain on fertile lands and our already-depleted water sources. Because of these, third generation feedstocks have huge potential to be the future source of feedstocks for the production of biodiesel.
The production of biodiesel from feedstocks may be achieved using different techniques such as direct/blends [
19,
20], micro-emulsion [
21], pyrolysis [
22,
23], and transesterification [
24,
25]; with the transesterification reaction with a catalytic process being the most commonly adopted technique for production [
26]. Commonly, homogeneous catalysts such as Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH) are used. Recently, the use of new heterogeneous catalysts in transesterification processes has become an interesting option for researchers. References [
27,
28,
29,
30,
31,
32,
33] address the use of different heterogeneous catalysts for the production of biodiesel using different feedstocks. The authors in reference [
30] investigated biodiesel production from Jatropha oil using nanometer magnetic base catalysts and have shown that a 95–99% biodiesel yield is achievable under optimal conditions. These studies have demonstrated that the use of heterogeneous catalysts has reduced the effects of using low quality feedstocks, whilst providing high biodiesel yields under optimal conditions. Another interesting technique for biodiesel production is through catalyst-free techniques as demonstrated in references [
34,
35]; with a maximum biodiesel yield of 99.6% obtained in reference [
35] for biodiesel production from Jatropha oil. Despite all these advancements, the determining factor in the choice of catalysts to be used in biodiesel production still hinges on the economic viability of the resulting biodiesel fuel; and hence, the current popularity of NaOH and KOH due to its relatively cheap price.
It is believed that the production of biodiesel should not rely on one source of feedstocks and the use of a single catalyst only. By taking lessons from our past dependency on fossil fuels, the over reliance on a single feedstock or catalyst will result in the fundamental economic problem of resource scarcity, especially in the long term. As such, the research communities continue to explore new possible source of feedstocks and catalysts for biodiesel production; the more varieties of feedstocks that are available and tested, the more assured is biodiesel in terms of sustainability and feasibility. Several examples of research efforts on crops for the production of biodiesel are
calophyllum inophyllum [
36],
pongamia glabra (koroch seed) [
37],
jatropha curcas [
38,
39],
eruca sativa. L [
40],
Hevea brasiliensis and Ricinus communis [
41]
pongamia pinnata (karanja) [
42,
43],
sterculia foetida [
44],
azadirachta indica (neem) [
45],
madhuca indica (mahua) [
46],
soap nut [
47,
48],
milkweed (Calotropis gigantean) [
49],
guizotia abyssinica [
50],
tung [
51],
pistacia chinensis [
52], and
algae [
18].
This paper attempts to expand the body of knowledge on possible feedstocks for the production of biodiesel. It is noted that there is very little information available in the literature on the production of biodiesel from
Reutealis trisperma [
53]; despite its abundance in the Southeast Asian region. Therefore, the objective of the present paper is to examine the opportunity of biodiesel production from
Reutealis trisperma oil as a potential source of future energy supply and to explore its implementation aspects. These are important in the context of Southeast Asia as feedstocks for biodiesel usually depends on the availability of that feedstock in its geographical region [
54].
3. Results and Discussion
In this study, laboratory experiments were conducted to find the physicochemical properties of Reutealis trisperma methyl ester (RTME) biodiesel. To achieve optimal conditions for esterification and transesterification processes for Reutealis trisperma oil, an ultrasonic bath stirrer method with the maximum total power of 40 KHz was used. The esterification process was performed using 2% (v/v) sulfuric acid (H2SO4), with a Methanol-to-oil molar ratio of 60% at a temperature of 55 °C for 1 hour at 1000 rpm stirring speed. For the transesterification process, a catalyst of 0.5 wt % Potassium hydroxide (KOH) was used with a Methanol-to-oil molar ratio of 60% at a temperature of 60 °C for 1.5 hours at a stirrer speed of 1000 rpm.
The results of the laboratory experiments are tabulated in
Table 1. Also tabulated are the physicochemical properties of other selected biodiesel sources;
Sterculia foetida methyl ester (SFME) [
44],
Calophyllum inophyllum methyl ester (CIME) [
61], and
Ceiba pentandra methyl ester (CPME) [
62], for comparison purposes. Furthermore, ASTM D6751 and EN 14214 biodiesel standard limits are also tabulated; to ensure compliance with these standards.
It is clearly demonstrated in the table that the properties of Reutealis trisperma are in agreement with the two biodiesel standard limits and hence, it can be concluded that Reutealis trisperma is a potential feedstock to be used for the production of biodiesel.
3.1. Economic Indicator
Table 2 shows the summary of the economic data indicators used in this study for a typical 50 kt biodiesel plant in Malaysia. The lifetime of the project has been set to 20 years, which includes the first year for the construction and startup of the plant. It is assumed that the plant shall operate at 100% capacity throughout the duration of the project. Capital costs for the project are assumed to be paid through private investment and no loans are taken for the project; to make our calculations simpler, as no repayment on the loans need to be considered. The capital costs for the plant are calculated based on the required land area, equipment and instrumentations, as well as the cost for building construction. The feedstock under consideration in this paper is
Reutealis trisperma oil which shall be used for the production of biodiesel oil. To operate at maximum capacity, approximately 57 kt of crude
Reutealis trisperma oil is required to produce 50 kt of biodiesel, assuming a biodiesel conversion efficiency (
CE) of 98%. The selling price of biodiesel is taken to be
$0.47/L for the first ten years and
$2.00/L for the rest of the project lifetime.
3.2. Life Cycle Cost Analysis and Payback Period
The data from
Table 2 above are used to calculate the life cycle cost and payback period for biodiesel plant using
Reutealis trisperma oil in Malaysia. Results of the calculations are shown in
Table 3 and
Figure 3. Results from the analysis indicate that the total life cycle cost of the project is approximately
$710 million, giving a unit cost of the biodiesel fuel of
$0.696/L of biodiesel. The unit price of
$0.696/L of biodiesel is lower than the
$0.78/L price calculated in reference [
65] for biodiesel from
jatropha curcas, however, it is higher than
$0.64/L price calculated in reference [
63] for biodiesel from palm oil. It is also higher than the retail price of
$0.58/L for fossil diesel in Malaysia. The feedstock costs from crude
Reutealis trisperma oil are the biggest contributors to the life cycle cost of the project; with a percentage of around 83% of the total life cycle cost or
$0.5896 for every liter of biodiesel produced. This is followed by its operating costs; with a percentage of around 17% of the total life cycle cost or
$0.13 for every liter of biodiesel produced during the 20 years project lifetime, the sale of glycerol, by-product of the plant, contributing
$16,927,840. This is equivalent to the plant clawing back
$0.0169 for every liter of biodiesel produced. The time for the project to recoup its initial capital investment of
$11,882,425 or its payback period is 4.34 years and thus, the payback period is less than one fourth of the lifetime of the project. These results indicate the economic feasibility of the project.
3.3. Potential Fuel Saving
The sum of diesel fuel substitution is a function of the yearly diesel fuel consumption with a substitution ratio with biodiesel. The total biodiesel required for replacing the diesel fuel is estimated by the diesel fuel substitution multiplied by the biodiesel to diesel fuel substitution ratio. Since biodiesel and diesel fuels have some dissimilarity in heating value or calorific value, there are different amounts of biofuel required to replace fossil diesel fuel. The fossil diesel consumption and potential diesel replacement are tabulated in
Table 4.
3.4. Sensitivity Analysis
Sensitivity analysis is performed to investigate the effect of variations on some input parameters on the life cycle cost of the project. Five (5) input variables of the model are chosen for the analysis; feedstock unit price (
FP), operating rate (
OR), initial capital cost (
CC), interest rate/discount rate (
r), and biodiesel conversion efficiency or oil conversion yield (
CE). The feedstock cost (
FC), operating cost (
OC), and initial capital cost (
CC) are three of the dominant costs associated with the
LCC as identified in Equation (1) and are demonstrated in
Table 3 and
Figure 3; with feedstock cost and operating cost determined by the feedstock unit price (
FP) and operating rate (
OR), respectively. As present value calculations are employed, the interest rate value (
r) also influences the
LCC of the project; a higher interest rate is expected to reduce the
LCC of the project and vice versa. Finally, since the plant is assumed to produce at its maximum capacity of 50 kt of biodiesel, the biodiesel conversion efficiency (
CE) dictates the amount of feedstock that should be fed into the plant to produce the required output.
Figure 4 below demonstrates the effect of varying the five (5) input variables on the
LCC of the biodiesel project. The left side of the figure shows the possible values of the variables; “favorable”, “assumed”, and “unfavorable” values on the order of appearance. For instance, the “assumed” value of the feedstock price (
$980/t) is the value used in the
LCC calculations, giving a
LCC value indicated by the mid-line on the figure. A reduction in the feedstock price to the “favorable” value (
$680/t) lowers the
LCC value to less than approximately
$530 million and its increase to “unfavorable” value (
$1280/t), increases the
LCC value to approximately
$890 million.
It can be seen from the figure that variations in feedstock prices have the most impact on the life cycle cost of the project; expected as the feedstock price was previously identified as the most dominant cost associated with the
LCC. From the figure, a reduction in the price of
Reutealis trisperma oil from
$980/t to
$680/t reduces the total life cycle cost from approximately
$710 million to
$529 million whilst an increase in price to
$1280/t gives a total life cycle cost of
$890 million. This is followed by the interest rate/discount rate used in the calculation of
LCC. An increase of the interest rate to 10% per annum results in a 13% reduction in total life cycle cost whilst a decrease to 6% per annum results in a 17.5% increase in the total life cycle cost. For the operating rate; defined as the operating cost per ton of biodiesel produced, decreasing the rate to
$175/t reduces the total life cycle cost to
$673 million or a reduction of 5% from the original
LCC. Increasing the operating rate to
$325/t increases the total life cycle cost to
$746 million, corresponding to a 5% increase. From the figure, the
LCC value is least sensitive to variation in the Initial Capital Cost (
CC) and is then followed by the biodiesel conversion efficiency (
CE); from the five input variables considered in this study. The relationship between the market price of crude
Reutealis trisperma oil prices and FBC is warranted and is given in
Figure 5. It can be seen that the final biodiesel unit cost (
FBC) has a linear correlation with the price of the feedstock; an increase in the price of
Reutealis trisperma oil by
$0.1/kg results in an increase in the final biodiesel unit cost by
$0.05/L.
3.5. Biodiesel Taxation and Subsidy Scenarios
Taxation and subsidy levels play important roles in encouraging the adoption of biodiesel as a replacement for fossil diesel, especially as biodiesel is less attractive economically when compared to fossil diesel. Imposing a high tax rate has the effect of increasing its selling price whilst giving a subsidy that helps biodiesel to be more competitive in the market.
Table 5 provides a comparison on the effect of different taxation and subsidy policies on the competitiveness of the biodiesel, obtained from
Reutealis trisperma. The scenarios with total tax exemption, a tax rate of 15%, and subsidy amounts of
$0.10/L and
$0.18/L on the biodiesel are analysed and compared with the price of fossil diesel; currently at
$0.58/L, the retail price of diesel fuel in Malaysia. It is noted that subsidy amounts of
$0.10/L and
$0.18/L are current subsidies given by the Malaysian government for petrol fuel and fossil diesel, respectively. The biodiesel to fossil diesel substitution ratio is taken to be 1.07. This allows for a like-for-like comparison of biodiesel and fossil diesel on the basis of energy production, instead of on the basis of volume. At a subsidy cost of
$0.18/L, the current subsidy for fossil diesel, the price of the biodiesel is actually lower than the fossil diesel. In fact, the subsidy cost at anything above
$0.12/L makes biodiesel have a lower price than fossil diesel and hence, is more competitive. Of course, this is based on the assumptions previously made on the different costs associated with the production of biodiesel from
Reutealis trisperma oil; importantly the feedstock cost of
$980/t, subsidy cost for fossil diesel at
$0.18/L, as well as the retail price of fossil diesel at
$0.58/L.
Naturally, the market prices of crude petroleum oil and
Reutealis trisperma oil are important factors in determining whether biodiesel from
Reutealis trisperma oil can actually compete with fossil diesel and if subsidies are required to encourage the use of biodiesel.
Figure 6 presents the breakeven price of
Reutealis trisperma oil used in the production of biodiesel at different prices of crude petroleum oil. For a given price of crude petroleum oil,
Reutealis trisperma oil’s prices above the line indicates that the subsidy is required for biodiesel to compete with fossil diesel whilst any prices below, indicates that no subsidy is required and savings may be expected by substituting fossil diesel with biodiesel. As an example, for the price of crude petroleum oil at
$100/barrel, any price above
$1585/t (on the line) for the
Reutealis trisperma oil would require a biodiesel subsidy so that biodiesel would be able to compete with fossil diesel. Any price below
$1585/t would make biodiesel naturally attractive and savings may be expected by using biodiesel. The opposite is also true. For a given price of crude
Reutealis trisperma oil (CRTO), the CRTO price to the left of the line indicates that the subsidy for biodiesel is required to encourage the use of biodiesel over fossil diesel. Whilst the CRTO price to the right indicates that savings can potentially be obtained by substituting from fossil diesel to biodiesel.
Figure 7 plots the Final Biodiesel unit Cost (FBC) as a function of feedstock price (
FP), with the fixed retail price of fossil diesel at
$0.58/L and fossil diesel subsidy of
$0.18/L. It can be seen that at feedstock prices below
$0.8/kg, biodiesel can compete with fossil diesel, provided that biodiesel is tax exempted. At biodiesel subsidy levels of
$0.10/L and
$0.18/L, biodiesel remains competitive against fossil diesel provided that the feedstock prices do not exceed
$1/kg and
$1.19/kg, respectively. Feedstock prices over these values would see the price of biodiesel be higher than fossil diesel.
3.6. Potential Environmental Impact
Analysis on the potential environmental impact of adopting biodiesel includes potential emission reductions studies that may be achieved from substituting fossil diesel with biodiesel. This may simply be represented as the total energy saved (
) from foregoing fossil diesel as well as the potential reduction in carbon emission (
) from the substitution. Also, the estimates of the cropland required for the feedstocks (
) is important. The results from the analysis for different replacement rates
, for a fixed assumption on fossil diesel, are given in
Table 6 below. An increase in the fossil diesel replacement rate increases the amount of biodiesel required to facilitate the biodiesel to fossil diesel substitution. This increase in the requirement for biodiesel necessitates more cropland to supply the increasing feedstock. Diesel replacement rates of 1%, 20% and 50% require 31 kHa, 626 kHa and 1564 kHa respectively. Substituting fossil diesel with biodiesel, obviously reduces fossil diesel consumption which translates into total energy saving from fossil diesel. Furthermore, as biodiesel is more environmentally friendly than fossil diesel, in terms of carbon emission, the substitutions also translates into total carbon savings.
Figure 8 illustrates the total carbon emission from fossil diesel and biodiesel for different years having different diesel replacement rates. Although total carbon emissions from both fossil diesel and biodiesel increase with an increase in the diesel replacement rate, total carbon emissions from fossil diesel is clearly higher due to its higher carbon emission factor. The difference between the carbon emissions from fossil diesel and carbon emissions from biodiesel, gives the total carbon saving (
TCS) due to the diesel substitutions; from a more polluting fossil diesel onto a more efficient biodiesel. From the table, the diesel replacement rate of 1% results in total energy savings from diesel (
TGS) of 3,573,785 MJ and total carbon saving (
TCS) of 127,169 kg, and at the diesel replacement rate of
20%, total energy savings from diesel (
TGS) and total carbon saving (
TCS) are 71,575,710 MJ and 2,543,381 kg, respectively. Increasing the displacement replacement rate further has been shown to further increase the
TGS and
TCS values. Meanwhile, the ecosystem carbon payback period may be estimated by dividing the difference between the carbon stock from converting the natural land into biodiesel feedstock cropland with the yearly carbon savings by utilizing biodiesel fuel, as given in Equation (27). A carbon payback period (
CPP) value of 25 years is obtained.