*3.7. Sensitivity Analysis*

The effects of changes in the price of the most expensive raw materials (Figure 5), i.e., seed, castor plant residues, methanol, and NaOH, on bioethanol and biodiesel price are presented in Figure 9. The results indicate that seed oil and methanol prices significantly affect the manufacturing price of biodiesel. For example, 13% and 23% increases in the biodiesel manufacturing cost for scenarios 1 and 2 are observable after a 50% increase in seed oil price, respectively. The next effective parameter is the methanol price. Increasing the methanol price by 50% leads to a 5% increase in the manufacturing cost of biodiesel in scenario 2.

▲ ♦ ● **Figure 9.** The effect of NaOH price on bioethanol price in scenario 1 (•) (**A**), effect of the price of plant residuals on the bioethanol manufacturing cost in scenarios 1 (N) and 2 () (**B**), and effect of methanol price on biodiesel price in scenario 2 () (**C**). The empty sign represents the base case values of the profitability index.

**Commented [JL3]:** Please define the legend for 4 subfigures, refer to Figure 11 caption: (▲), (♦)…

**Commented [K4R3]:** Thanks, it was very messy and difficult to understand; thus, we omit one of the unnessary one and add the symbols in the legend. The legend is also

modified.

The price of plant residuals and NaOH had a direct effect on the bioethanol cost. As shown in Figure 9A,B by increasing the price of plant residuals and NaOH, the bioethanol manufacturing cost is increased and has a secure margin compared with the ethanol in the Iranian market. In both scenarios, bioethanol is the main byproduct. The biodiesel price is calculated by dividing the net yearly production expenses into the annual biodiesel production rate. The net yearly production expenses are calculated by subtraction of ethanol revenues from total production costs of the plant. Thus, the biodiesel manufacturing cost is decreased by increasing the ethanol production price.

The effects of bioethanol and heat prices, the main byproducts, on the biodiesel manufacturing cost are presented in Figure 10. The results indicate that there is no revenue from the byproduct by 50% increase in the byproduct price in the base cases. The price and amount of glycerol, CO2, and salts have minimal effects and do not significantly affect the process economy. Moreover, the effects of

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Bioethanol price (\$/L)

**B D** 

0 0.02 0.04 0.06 0.08

Plant residuals price (\$/kg)

bioethanol and heat price on biodiesel price are also investigated. For both scenarios, the credit from bioethanol significantly affected the manufacturing cost of biodiesel.

0.25 0.28 0.31 0.34 0.37 0.4 0.43

Biodesel price (\$/L)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Methanol price (\$/kg)

**Figure 10.** The effects of bioethanol and heat prices on the biodiesel manufacturing cost.

The effects of the primary feedstock (castor seeds) price on the profitability index of each scenario are investigated (Figure 11). Increasing the seed oil price leads to decreasing the profitability index. By changing the price of seed oil in the range of 0–400%, the profitability index is larger than one for both scenarios, indicating a wide safe margin for PI.

▲ ♦ **Figure 11.** The effects of seed oil cost on the profitability index in scenarios 1 (N) and 2 (). The empty sign represents the base case values of the profitability index.
