*3.1. Material and Energy Balance*

The amounts of feedstocks, products, and utilities are calculated and shown in Table 3. The primary raw materials used in the two scenarios (i.e., NaOH, nutrients, pH control agents, and enzymes) are equal. However, in the biodiesel production unit of scenario 2, based on experimental data, KOH consumption is more than scenario 1, and therefore, the amount of H2SO<sup>4</sup> that is used for catalyst neutralization in scenario 2 is more than that in scenario 1. In scenario 1, a part of ethanol produced

from the residues is used in the transesterification unit. Based on the experimental data, the conversion of this reaction in scenario 1 is 85.0%, while it is 88.2% in scenario 2. In scenario 1, 15% of raw oil is unreacted and recycled to the transesterification reactor, resulting in higher biodiesel production than that in scenario 2. Moreover, the biodiesel composition in each scenario is different. It is in the form of fatty acid ethyl ester in scenario 1, while it is fatty acid methyl ester in scenario 2. Consequently, the energy content of biodiesel in each scenario is different from another.


**Table 3.** Energy and material balances for each scenario based on simulation results.

<sup>1</sup> The purity of NaOH is 60% weight per volume and used KOH is solid. <sup>2</sup> The nutrients are a mixture of 60% (*w*/*w*) of super triple phosphate and 40% (*w*/*w*) of urea. <sup>3</sup> The pH controls with Na2CO3. <sup>4</sup> m<sup>3</sup> per year. <sup>5</sup> Megawatt per year.

The main difference in the scenarios is the production of net ethanol. In scenario 1, about 40% of produced ethanol is used for biodiesel production, resulting in a much lower net ethanol production yield than that in scenario 2.

The prices of all components are shown in Table 3. Based on the price and amount of each component, seeds and solid residuals are the primary feeds of biorefinery. The price of NaOH (due to high consumption) and nutrients, which are expensive, is in the next position.

The distribution of raw material cost and product sales is shown in Figure 5. In scenario 1, the highest income is from biodiesel sale; in scenario 2, the transesterification reaction is conducted with methanol, and the highest revenue is from bioethanol sale.

The type and amount of utilities are shown in Table 3 for the two scenarios. The water is mainly used as makeup in the cooling system, in the pretreatment unit for washing the solid material, and to regulate NaOH concentration and in the fermentation step for adjusting the total solid in the fermenters. High pressure steam is used in distillation towers and also for heating. Low pressure steam is used to regulate the temperature and preheat the feeds. Fuel and hot oil are used for heating the oil streams in the biodiesel production unit in each scenario [33].

Sc1

Sc2

**Figure 5.** The distribution of raw material cost and product sales.

The breakdown of energy consumption in different units of each scenario is shown in Figure 6. Distillation towers in ethanol purification and energy consumption in biodiesel production are the most energy demanding units. Pretreatment of lignocellulosic materials at 100 ◦C and the anaerobic digestion at 55 ◦C, as well as the filtration system in the wastewater treatment unit, also need considerable amounts of energy.

**Figure 6.** Breakdown of energy consumption in units of each scenario. Dark and light green represent scenarios 1 and 2, respectively.
