Olivera S. Stamenković

Biomass combustion waste ash, such as wood ash, represents a promising low-cost raw material for the biodiesel industry, as it predominantly consists of alkali and alkaline earth metal oxides. In this study, biodiesel production from sunflower oil via methanolysis was investigated using waste wood ash as a catalyst. This is the first study to integrate detailed physicochemical characterization, catalytic performance evaluation, and a preliminary economic assessment for the valorization of waste wood ash as a catalyst in sunflower oil methanolysis. The catalyst was comprehensively characterized to determine its thermal behavior, chemical and phase composition, textural properties, morphology, and base strength. The catalyst composition indicated Ca (43 wt.%) and K (18 wt.%) as the major elements, consistent with the XRD results, which identified their oxides as dominant phases. The catalytic performance of wood ash was evaluated under atmospheric pressure in batch mode. The influence of catalyst loading (5-15 wt.%, based on the oil mass) and methanol-to-oil molar ratio (9:1-15:1) on the fatty acid methyl esters (FAMEs) content was investigated at a reaction temperature of 60 °C. The rapid conversion of triacylglycerol (TAG) into FAME was observed, indicating negligible TAG mass transfer limitations. Increasing catalyst loading significantly enhanced FAME formation with 15 wt.% as the optimal value within the investigated range. While the methanol-to-oil molar ratio had a slight positive effect on the final FAME content, higher ratios reduced the reaction time required to achieve FAME contents above 95% from 40 to 20 min at the highest catalyst loading. Despite the high feedstock cost indicated by preliminary cost analysis, the results demonstrated that waste wood ash is an effective low-cost catalyst for biodiesel production, although its catalytic activity is limited to a single reaction cycle.

Hemp (Cannabis sativa L.) is a versatile crop used across multiple industries, and its seed oil has potential application as a renewable raw material for biodiesel production. This study investigates the kinetics of biodiesel production via quicklime-catalyzed methanolysis of hemp seed oil (HSO). Owing to the moderately high concentration of free fatty acids, HSO was first subjected to esterification. The methanolysis of the esterified HSO was performed at methanol-to-HSO molar ratios of 6:1, 9:1, and 12:1, with quicklime amounts of 3%, 5%, and 7% of HSO mass, at 60 oC under atmospheric pressure. The kinetics of the methanolysis reaction was evaluated using two different kinetic models: a pseudo-first order model and a model involving a changing reaction mechanism coupled with triacylglycerol (TAG) mass transfer limitations. The pseudo-first order model effectively described the reaction kinetics within two distinct regimes, initially controlled by TAG mass transfer, followed by a chemical reaction-controlled regime. The second model provided a continuous description of the reaction kinetics over the whole reaction course. The volumetric TAG mass transfer coefficient and the parameter defining the affinity of TAG to the active sites of the catalyst were found to be independent of methanol concentration but increased with catalyst amount. Both models yielded the same apparent reaction rate constant (0.155 min-1) and demonstrated very good agreement with experimental TAG conversion degree data (MRPD = ±10.8%, 81 data points). Despite comparable accuracy, the model involving the changing reaction mechanism and TAG mass transfer limitations is recommended due to its computational simplicity and consistent applicability.

This study focuses on the development of a sustainable biodiesel production process using non-edible hemp seed oil (HSO) and an environmentally friendly, lowcost quicklime catalyst. HSO was recovered via cold-pressing, with major fatty acids identified as linoleic acid (55.70%), linolenic acid (15.59%) and oleic acid (13.72%). Due to the slightly elevated free fatty acids (FFAs) content in HSO, a two-stage process was employed: esterification of FFAs in HSO catalyzed by sulfuric acid, followed by methanolysis of the esterified HSO using quicklime as a catalyst. The methanolysis reaction was optimized using a 33 factorial design with three central points, combined with response surface methodology (RSM). The optimal reaction conditions for achieving maximum fatty acid methyl esters (FAME) content were determined to be: methanol-to-HSO molar ratio of 6:1, catalyst concentration of 6.8%, and reaction time of 45 min. Additionally, the produced biodiesel meets the EN 14214 biodiesel quality standard specifications, with the exception of the iodine value. Overall, the methanolysis of non-edible HSO using low-cost quicklime presents a promising, sustainable approach for biodiesel production.

Possibilities of using waste plum stones in biodiesel production were investigated. The plum kernels were used as a source to obtain oil by the Soxhlet extraction method, while the whole plum stones, the plum stone shells that remained after the crashing, and the plum kernel cake that remained after the oil extraction, were burned off to obtain ashes. The collected ashes were characterized by elemental composition, porosity, and base strength and tested for catalytic activity in transesterification of esterified plum kernel oil. Dominant elements were potassium, calcium, and magnesium at different contents in the three obtained ashes. The most active catalyst was the plum stone shell ash, so the effect of temperature (40, 50, and 60?C) on the reaction rate was investigated. The reaction rate constant increased with the reaction temperature with the activation energy value of 58.8 kJ mol-1. In addition, the plum stone shell ash can be reused as a catalyst after recalcination.

Apple pomace is a solid waste derived from the apple processing industry. To foster sustainability, the apple processing industry must implement the circular economy model of biorefinery and treat apple pomace as a valuable source of apple seed oil. For the first time, this study dealt with the design, economic, and potential environmental impact assessment of biodiesel production from apple seed oil obtained from apple pomace. An Aspen Plus? and WAR? software were used to evaluate the designed biodiesel production. The main production steps were the supercritical CO2 extraction, the methanolysis of apple seed oil, the methanol recovery, and the biodiesel separation. The production facility was assumed to process 24 tons of apple seeds daily. The total capital and production costs were 1.26 US$ million and 2.82 US$ million, respectively. If revenues from selling apple seed meal as cattle feed were included, a biodiesel price could be 0.39 US$/kg. The process was environmentally friendly when apple seed meal was not treated as waste.

Camelina sativa (L.) Crantz is an oilseed crop with favorable potentials for biodiesel production, such as the high plant yield, high oil content in the seed, high net energy ratio, and low oil production cost. This review paper deals with the present state and perspectives of biodiesel production from camelina oil. First, important issues of camelina seed pretreatment and biodiesel production are reviewed. Emphasis is given to different biodiesel technologies that have been used so far worldwide, the economic assessment of the camelina oil biodiesel (COB) production, the camelina‐based biorefineries for the integrated biodiesel production, the COB life cycle analysis, and impact human health and ecosystem. Finally, the perspectives of COB production from the techno‐economic and especially genetic engineering points of view are discussed.