Exergy and energy analyses of two biodiesel production processes that integrate solar energy as the main energy source were developed to determine the process with the higher efficiency from an energy and exergy approach. The biodiesel production processes were simulated in ASPEN PLUS^®, and the solar energy supply was studied in TRNSYS^®, using EXCEL^® simultaneously for the exergetic analysis. The solar thermal energy collection system can supply 81% of the energy required by the alkali process in the Flash separation equipment. For the supercritical process, solar thermal energy can supply 74.5% of the energy in the preheating and separation stages. The energy efficiency of the supercritical process is higher; nevertheless, the exergetic efficiency of the alkaline process is higher than the supercritical one. Solar collection systems contribute from 85% to 93% of the exergy destroyed by the global process for both cases. The alkaline biodiesel production process has the highest advantages when using solar energy as the main source of energy, compared to a process in supercritical conditions that presents greater irreversibilities and requires more infrastructure to collect the solar resource. However, using solar energy as the foremost energy source offers an alternative to fossil fuels, and it provides an environmental benefit concurrently with the use of biodiesel.

Bioethanol is a promising alternative to fossil fuels. This study evaluated bioethanol production from orange peel (OP) and brewer’s spent grain (BSG) through acid hydrolysis, followed by fermentation with Saccharomyces cerevisiae. A factorial design was applied to assess the influence of temperature, acid concentration, and time on sugar release. Hydrolysis of OP at 125 °C with 0.5% H₂SO₄ yielded 52.14 g/L of glucose and 15.70 g/L of xylose. For BSG, the best results were obtained with 2.5% H₂SO₄ at 160 °C, producing 27.10 g/L of glucose and 14.22 g/L of xylose. Fermentation at 30 °C achieved 5.25% v/v bioethanol in OP and 1.5% v/v in BSG, representing 41.4 g/L and 11.8 g/L of bioethanol, respectively. The kinetic models showed high predictive accuracy (R² > 0.98). These findings demonstrate the potential of OP and BSG as viable substrates for bioethanol production under mild processing conditions.

The orange juice industry generates large amounts of waste, leading to significant environmental impacts. Within the framework of a citrus biorefinery, this study evaluates an integrated pilot-scale scheme combining essential oil extraction with hydrolysis of orange waste. A self-designed modular system was used, characterized by ease of operation and maintenance, consisting of a 20 L sealed reactor and a condenser with water recirculation. Essential oil extraction was carried out by hydrodistillation, producing 35 mL of essential oil per run and a yield of 2.57 mL per 100 g of orange peel. Hydrolysis was investigated using a 2³ factorial design considering time (30 and 60 min), waste type (with and without pulp), and H₂SO₄ concentration (0 and 0.25% v/v). ANOVA results showed that the waste type was the dominant factor, while the acid concentration had no significant effect. The optimal hydrolysis condition was waste with pulp, 0% acid, and 30 min, achieving 108.5 g/L of glucose and 30.4 g/L of xylose. Under these conditions, the kinetics of glucose and xylose release were determined. The energy consumption was 45.96 MJ, equivalent to 70.61 kJ/g of glucose and 236.59 kJ/g of xylose, with corresponding costs of 0.0017 and 0.0057 USD/g, respectively. Orange waste containing pulp, obtained directly from juice-processing facilities, exhibits greater valorization potential than orange waste without pulp to produce essential oil, glucose, and xylose within a biorefinery scheme.