Widely used catalysts in biodiesel production: a review

Utilization of iron fillings solid waste for optimum biodiesel production

This study explores the innovative application of iron filings solid waste, a byproduct from mechanical workshops, as a heterogeneous catalyst in the production of biodiesel from waste cooking oil. Focusing on sustainability and waste valorization, the research presents a dual-benefit approach: addressing the environmental issue of solid waste disposal while contributing to the renewable energy sector. Particle size distribution analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Thermal analysis (TG-DTA), and FTIR analysis were used to characterize the iron filings. The response surface methodology (RSM) was used to guide a series of experiments that were conducted to identify the optimum transesterification settings. Important factors that greatly affect the production of biodiesel are identified by the study, including catalyst loading, reaction time, methanol-to-oil ratio, reaction temperature, and stirring rate. The catalyst proved to be successful as evidenced by the 96.4% biodiesel conversion efficiency attained under ideal conditions. The iron filings catalyst's reusability was evaluated, demonstrating its potential for numerous applications without noticeably decreasing activity. This work offers a road towards more environmentally friendly and sustainable chemical processes in energy production by making a strong argument for using industrial solid waste as a catalyst in the biodiesel manufacturing process.

Advancements in enzyme immobilization on magnetic nanomaterials: toward sustainable industrial applications

Enzymes are widely used in biofuels, food, and pharmaceuticals. The immobilization of enzymes on solid supports, particularly magnetic nanomaterials, enhances their stability and catalytic activity. Magnetic nanomaterials are chosen for their versatility, large surface area, and superparamagnetic properties, which allow for easy separation and reuse in industrial processes. Researchers focus on the synthesis of appropriate nanomaterials tailored for specific purposes. Immobilization protocols are predefined and adapted to both enzymes and support requirements for optimal efficiency. This review provides a detailed exploration of the application of magnetic nanomaterials in enzyme immobilization protocols. It covers methods, challenges, advantages, and future perspectives, starting with general aspects of magnetic nanomaterials, their synthesis, and applications as matrices for solid enzyme stabilization. The discussion then delves into existing enzymatic immobilization methods on magnetic nanomaterials, highlighting advantages, challenges, and potential applications. Further sections explore the industrial use of various enzymes immobilized on these materials, the development of enzyme-based bioreactors, and prospects for these biocatalysts. In summary, this review provides a concise comparison of the use of magnetic nanomaterials for enzyme stabilization, highlighting potential industrial applications and contributing to manufacturing optimization.

Biodiesel production and characteristics from waste frying oils: sources, challenges, and circular economic perspective

Biodiesel serves as a viable alternative to traditional diesel due to its non-toxicity, biodegradability, and lower environmental footprint. Among the diverse edible and inedible feedstocks, waste frying oil emerges as a promising and affordable feedstock for biodiesel production. Commonly waste frying oils include those derived from palm, corn, sunflower, soybean, rapeseed, and canola. The primary challenge related to biodiesel production technologies is the high production cost, which poses a significant barrier to its widespread adoption. Thus, refining the production techniques is essential to enhance yield, reduce capital expenditure, and curtail raw material expenses. An examination of the research focusing on feedstock availability, production, hurdles, operational expenditures, and future potential is pivotal for identifying the most economically and technically viable solutions. This paper critically reviews such research by exploring feedstock availability, production techniques, challenges, and costs intrinsic to biodiesel synthesis. It also underscores the economic feasibility of biodiesel production, shedding light on the pivotal factors that influence profitability, especially when leveraging waste frying oils. Through an in-depth understanding of these considerations, optimal production and feedstock choices for biodiesel production can be identified. Addressing cost and production bottlenecks could potentially enhance the economic viability of waste frying oil-based biodiesel, thus fostering both environmental sustainability and more extensive adoption of biodiesel as an environmental-friendly fuel in the future.

Calcined Biowaste Durian Peel as a Heterogeneous Catalyst for Room-Temperature Biodiesel Production Using a Homogenizer Device

Calcined biowaste durian peel (BDP) contains 86% potassium element as the main compound and has successfully catalyzed the transesterification of palm oil to biodiesel at room temperature. The effect of catalyst weight, molar ratio of palm oil to methanol, reaction time, and rotational speed of the homogenizer device was investigated on biodiesel conversion and yield. The highest biodiesel conversion of 97.4 ± 0.3% was achieved using the following reaction conditions: a catalyst weight of 5 wt %, a molar ratio of palm oil to methanol of 1:15, a reaction time of 10 min, and a rotational speed of 6000 rpm. Unfortunately, calcined BDP could not hold its catalytic activity in the reusability study. The biodiesel conversion was decreased in the second cycle due to the decrease of both catalyst weight and concentration of potassium ions after the first cycle. However, the calcined BDP paired with a homogenizer device could produce biodiesel in a short reaction time and at room temperature.

A systematic review on utilization of biodiesel-derived crude glycerol in sustainable polymers preparation

With the rapid development of biodiesel, biodiesel-derived glycerol has become a promising renewable bioresource. The key to utilizing this bioresource lies in the value-added conversion of crude glycerol. While purifying crude glycerol into a pure form allows for diverse applications, the intricate nature of this process renders it costly and environmentally stressful. Consequently, technology facilitating the direct utilization of unpurified crude glycerol holds significant importance. It has been reported that crude glycerol can be bio-transformed or chemically converted into high-value polymers. These technologies provide cost-effective alternatives for polymer production while contributing to a more sustainable biodiesel industry. This review article describes the global production and quality characteristics of biodiesel-derived glycerol and investigates the influencing factors and treatment of the composition of crude glycerol including water, methanol, soap, matter organic non-glycerol, and ash. Additionally, this review also focused on the advantages and challenges of various technologies for converting crude glycerol into polymers, considering factors such as the compatibility of crude glycerol and the control of unfavorable factors. Lastly, the application prospect and value of crude glycerol conversion were discussed from the aspects of economy and environmental protection. The development of new technologies for the increased use of crude glycerol as a renewable feedstock for polymer production will be facilitated by the findings of this review, while promoting mass market applications.

Comparative life cycle cost analysis of bio-valorized magnetite nanocatalyst for biodiesel production: Modeling, optimization, kinetics and thermodynamic study

An active, high surface area, recyclable, magnetic, basic, iron oxide-based nanocatalyst was developed from banana leaves waste and used for microwave-assisted transesterification of soybean oil to biodiesel. According to the Hammett indicator, the catalyst has a high total basicity of 15 < H < 18.4. After optimization through the response surface methodology, the reaction allows 96.5 % biodiesel yield in the presence of 24:1 methanol to soybean oil molar ratio, 6 wt% BLW@Fe3O4, 0.5 h at 65 °C. The magnetic nature of the catalyst improves reusability for up to 6 cycles. Thermodynamic analyses showed that transesterification of soybean oil to biodiesel is an endothermic reaction. Moreover, the catalyst has the potential to reduce biodiesel production costs by utilizing abundant biomass waste materials. The calculated cost for 1 kg of catalyst is $1.14, while the biodiesel's cost per kg produced in this work is merely $1.05, showing high commercial viability.

An ICP-MS study on metal content in biodiesel and bioglycerol produced from heated and unheated canola oils

This study addresses the challenges of biodiesel production costs and waste oil disposal by investigating the use of low-cost waste oil as a feedstock. The impact of heating temperature on biodiesel yield and trace metal levels is examined using response surface methodology (RSM). Optimal conditions for high biodiesel yields (95-98%) from canola oil are determined with a methanol/oil ratio of 12:1, 1 wt% catalyst, and 60-min reaction time. For crude bioglycerol, the optimal conditions involve a methanol/oil ratio of 4.25:1, 2.93 wt% catalyst, and 119.15-min reaction time. Elemental analysis reveals the presence of high-concentration metals like Cu and Zn and low-concentration ones such as Pb, As, Se, and Zr in both oil feedstocks and their respective biodiesel and bioglycerol products. The study demonstrates that thermal stress on canola oil significantly impacts biodiesel and bioglycerol yields and trace metal levels during the transesterification process. The findings contribute to enhancing cost-effectiveness and environmental sustainability in biodiesel production.

Efficient Expression of Candida antarctica Lipase B in Pichia pastoris and Its Application in Biodiesel Production

Lipase B from Candida antarctica (CALB) is an important biocatalyst with many potential applications. However, original CALB is usually with lower enzyme activity and also costly to produce from Candida antarctica; hence, it is often necessary to prepare recombinant CALB through gene heterologous expression. In this research, seven promoters and five signal peptides were compared respectively for expressing codon-optimized CALB in Pichia pastoris, and then recombinant P. pastoris containing 3 copies of calb gene were obtained by screening with high concentrations of antibiotics under the condition of the optimal combination. In a 1.3-L bioreactor, the maximum CALB activity and total protein content reached 444.46 ± 18.81 U/mL and 5.41 ± 0.1 g/L, respectively, after about 9 days of incubation in FM22 medium, which were 34 times and 20 times higher than the initial strains, respectively. In addition, the obtained CALB was used to catalyze the transesterification of acidified gutter oil with methanol, suggesting a promising pathway to convert waste or low quality of bio-oil feedstocks with high amount of free fatty acids into biodiesel by using recombinant CALB as catalyst. The results can provide with a good reference for efficient expression of CALB and enhancing lipase production in P. pastoris. It is supposed to bring with new possibility for the bio-production of other valuable proteins.

Sodium phosphate solid base catalysts for production of novel biodiesel by transesterification reaction

The efficient sodium phosphate (Na3PO4) solid base catalysts were prepared and applied in the production of novel biodiesel: ethylene glycol monomethyl ether monolaurate (EGMEML) by transesterification. The calcined sodium phosphate catalysts (NaP-T) were characterized using thermogravimetry analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) and so on. The effects of calcination temperature of Na3PO4 and main reaction parameters such as molar ratio of ethylene glycol monomethyl ether (EGME) to methyl laurate (ML), dosage of catalyst, reaction time and temperature on the yield of EGMEML were examined. The results showed that the maximum yield of EGMEML could reach 90% under 120 °C within 4 h and 5 wt% of Na3PO4 calcined at 400°, and the catalysts displayed good stability and recovery. In addition, the kinetics of transesterification reaction was explored and the results showed that the transesterification reaction followed 1st order kinetics when a large excess of EGME was used, the activation energy (Ea) was found to be 40.2 kJ mol-1.

Biosynthesis, characterization and anthelmintic activity of silver nanoparticles of Clerodendrum infortunatum isolate

Over the past few decades, the green synthesis of nanoparticles has gained importance for their therapeutic efficacy and eco-friendly nature. Integrating green chemistry principles into multidisciplinary nanoscience research has paved the way for developing environmentally benign and sustainable methods for synthesizing gold and silver nanoparticles. In the present study, the flowers obtained from Clerodendrum infortunatum (L.), belonging to the family Verbenaceae, have been used for biosynthesizing silver nanoparticles (AgNPs) to evaluate the anthelmintic potential. UV-Vis spectroscopy, XRD, FTIR, SEM and TEM analyses were performed to ascertain the formation of AgNPs. Clerodendrum-derived AgNP (CLE-AgNP) has significantly affected the normal physiological functions of the poultry parasite Raillietina spp., a menace to the livestock industry. Our study manifests that CLE-AgNPs cause considerable distortion of the surface tegument of this cestode parasite leading to changes in the host-parasite interface. The histochemical localization studies of the tegument-associated enzymes viz. AcPase, AlkPase, ATPase and 5'-Nu, exposed to the drug, showed a substantial activity decline, thus establishing the anthelmintic potential of the CLE-AgNPs.

Utilization of vanillin to prepare sulfated Calix[4]resorcinarene as efficient organocatalyst for biodiesel production based on methylation of palmitic acid and oleic acid

Recently, biodiesel production from palm oils has been thoroughly investigated to substitute crude oil due to its scarcity. However, the biodiesel production process is time-consuming due to its slow kinetics; thus, concentrated sulfuric acid has been used to fasten the reaction process in some industries. Unfortunately, sulfuric acid is a toxic, corrosive, and non-environmentally friendly catalyst. In this study, we prepared sulfated Calix[4]resorcinarene derived from vanillin as an efficient organocatalyst to replace sulfuric acid. The catalytic activity of sulfated Calix[4]resorcinarenes was evaluated through the methylation of palmitic acid and oleic acid as model compounds due to their abundant amounts in palm oil. The Calix[4]resorcinarene and sulfated Calix[4]resorcinarenes have been obtained through a one-pot reaction in 71.8-98.3% yield. Their chemical structures were confirmed by using FTIR, NMR and HRMS spectrometry analyses. The results showed that the sulfated Calix[4]resorcinarene exhibited high catalytic activity for methyl palmitate and methyl oleate productions in 94.8 ± 1.8 and 97.3 ± 2.1% yield, respectively, which was comparable to sulfuric acid (96.3 ± 1.8 and 95.9 ± 2.5%). The optimum condition was achieved by using 0.020 wt equivalent of organocatalyst for 6 h reaction process at 338 K. The methylation of palmitic acid and oleic acid fits well with the first-order kinetic model (R² = 0.9940-0.9999) with a reaction rate constant of 0.6055 and 1.1403 h^-1, respectively. Further investigation reveals that the hydroxyl group of vanillin plays a pivotal role in the organocatalytic activity of sulfated Calix[4]resorcinarene.

Optimization and characterization of biodiesel from waste cooking oil using modified CaO catalyst derived from snail shell

Currently, research has diverted toward generating renewable fuels due to the unreliable supply and rising cost of conventional fuels. Biodiesel is renewable fuel commonly obtainable via a simple process. Biodiesel was produced via the transterification of waste cooking oil (WCO) using heterogeneous catalysts. The aim of this study was to synthesis a ZnO and TiO₂-supported CaO catalyst from a snail shell for the transterification of waste cooking palm oil to produce biodiesel. Sol-gel and wet-impregnated methods were adopted to synthesize ZnO and catalyst, respectively. The physicochemical properties of waste cooking oil and biodiesel were characterized in accordance to AOAC and ASTMD standard methods. The FTIR and XRD analyses were carried out to characterize the biodiesel and the prepared catalysts. The result of this study revealed that CaO catalyst derived from snail shall, resulted to a WCO-derived biodiesel yield of 80%. The CaO catalyst modified with ZnO and TiO₂, further led to an increased biodiesel of 90% and 95%, respectively. The result of this study showed that the optimum conditions associated with highest biodiesel yield over the synthesized catalysts were at 3% catalyst weight, 65 °C, a 6:1 methanol-to-oil ratio and 3-h reaction time. The FTIR spectra also proved successful formation of biodiesel. Biodiesel was successfully synthesized from WCO, and the CaO catalyst synthesized from snail shells and modified with ZnO and TiO₂, showed potential to substitute for costly catalysts derived from chemical reagents for biodiesel production.

Catalytic performance of Ni-Co/HZSM-5 catalysts for aromatic compound promotion in simulated bio-oil upgrading

Bio-oil can be used as a substitute for fossil fuels after it is upgraded. Bimetal-modified HZSM-5 catalysts with various Ni-to-Co ratios were prepared to address catalysis problems, including deactivation of the catalysts and low hydrocarbon yields. The catalytic performance of Ni-Co/HZSM-5 in upgrading the simulated bio-oil was investigated with a fixed-bed reactor, and the influence of the loaded duplex metal ratio was also discussed. The new moderately strong/strong acid sites of Ni-Co/HZSM-5 changed according to the Ni/Co loading ratios, which substantially affected the acidity, catalytic activity and selectivity of the Ni-Co/HZSM-5. However, incorporating Co and Ni into the zeolite did not alter the structure of the HZSM-5. The interactions of the loaded bimetallic oxides reached equilibrium in 6Ni-4Co/HZSM-5, in which moderately strong acid sites and strong acid sites were formed after loading with Co₃O₄ and NiO. With a suitable acid site ratio, 6Ni-4Co/HZSM-5 exhibited excellent performance, with a lower coke deposition of 3.29 wt% and stable catalytic activity, and the conversion remained at 83-73% during 360 min of uninterrupted catalysis. Periodic changes in the acid sites and interfacial protons were the critical factors that improved the properties of the 6Ni-4Co/HZSM-5 and enhanced its selectivity for aromatic compounds.

Utilization of waste banana peels as heterogeneous catalysts in room-temperature biodiesel production using a homogenizer

Banana peels as agro-waste residues contain potassium oxide as the main component after calcination. The calcined waste banana peels (WBPs) successfully transesterified palm oil to biodiesel at room temperature using a homogenizer. The catalyst was characterized by TGA, SEM, XRD and XRF. The catalytic activity of calcined WBPs was determined using parameters of the molar ratio of palm oil to methanol, catalyst weight, reaction time and rotational speed of the homogenizer. The highest biodiesel conversion of 97.7 ± 0.6% was achieved with a molar ratio of 1 : 15, catalyst weight of 7 wt%, reaction time of 30 min and rotational speed of 6000 rpm. Unfortunately, the calcined WBP cannot be reused unless some fresh catalyst is added to defend its catalytic activity, as the concentration of K₂O decreases after the reaction. However, the catalyst showed better performance as the transesterification reaction could be carried out at room temperature in a short reaction time using a homogenizer compared with other methods.

Microwave-assisted biodiesel production using bio-waste catalyst and process optimization using response surface methodology and kinetic study

Providing sufficient energy supply and reducing the effects of global warming are serious challenges in the present decades. In recent years, biodiesel has been viewed as an alternative to exhaustible fossil fuels and can potentially reduce global warming. Here we report for the first time the production of biodiesel from oleic acid (OA) as a test substrate using porous sulfonic acid functionalized banana peel waste as a heterogeneous catalyst under microwave irradiation. The morphology and chemical composition of the catalyst was investigated using Powder X-ray diffraction (PXRD) analysis, Fourier transform infrared (FTIR) spectroscopy, Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM), and Scanning electron microscopy- Energy dispersive X-ray spectroscopy (SEM-EDX). The SEM-EDX analysis of the catalyst revealed the presence of sulfur in 4.62 wt% amounting to 1.4437 mmol g^-1 sulfonic acids, which is accorded to the high acidity of the reported catalyst. Using response surface methodology (RSM), through a central composite design (CCD) approach, 97.9 ± 0.7% biodiesel yield was observed under the optimized reaction conditions (methanol to OA molar ratio of 20:1, the temperature of 80 °C, catalyst loading of 8 wt% for 55 min). The catalyst showed excellent stability on repeated reuse and can be recycled at least 5 times without much activity loss.

Black soldier fly (Hermetia illucens) larvae as potential feedstock for the biodiesel production: Recent advances and challenges

Black soldier fly larvae (BSFL) Hermetia illucens is fastest growing and most promising insect species especially recommended to bring high-fat content as 5th generation bioenergy. The fat content can be fully optimized during the life-cycle of the BSFL through various organic dietary supplements and environmental conditions. Enriched fat can be obtained during the larval stages of the BSF. The presence of high saturated and unsaturated fatty acids in their body helps to produce 70 % of extractable oil which can be converted into biodiesel through transesterification. The first-generation biodiesel process mainly depends on catalytic transesterification, however, BSFL had 94 % of biodiesel production through non-catalytic transesterification. This increases the sustainability of producing biodiesel with less energy input in the process line. Other carbon emitting factors involved in the rearing of BSFL are less than the other biodiesel feedstocks including microalgae, cooking oil, and non-edible oil. Therefore, this review is focused on evaluating the optimum dietary source to produce fatty acid rich larvae and larval growth to accumulate C16-18 fatty acids in larger amounts from agro food waste. The process of optimization and biorefining of lipids using novel techniques have been discussed herein. The sustainability impact was evaluated from the cultivation to biodiesel conversion with greenhouse gas emissions scores in the entire life-cycle of process flow. The state-of-the-art in connecting circular bioeconomy loop in the search for bioenergy was meticulously covered.

Fatty acid wax from epoxidation and hydrolysis treatments of waste cooking oil: synthesis and properties

To provide low-cost wax and a new methodology for utilizing waste cooking oil (WCO), fatty acid wax based on WCO was synthesized by using epoxidation and hydrolysis treatments, whose properties included melting point, color, hardness, combustion properties, aldehyde content, and microscopic morphology were tested and analyzed. The obtained WCO-based wax contained mixed fatty acids, including palmitic acid and 9,10-dihydroxystearic acid as main constituents, which could form a 3D stable crossing network constructed by large long-rod crystals. The WCO-based wax with high fatty acid content (96.41 wt%) has a high melting point (44-53 °C), light color (Lovibond color code Y = 11.9, R = 2.3), good hardness (needle penetration index = 2.66 mm), long candle burning time (293 min), and low aldehyde content (7.98 × 10^-2 μg g^-1), which could be a lower-cost alternative of commercial soybean wax (SW) for producing various wax products including candles, crayons, waxworks, etc.

Metal-Organic Frameworks as bio- and heterogeneous catalyst supports for biodiesel production

As biodiesel (BD)/Fatty Acid Alkyl Esters (FAAE) is derived from vegetable oils and animal fats, it is a cost-effective alternative fuel that could complement diesel. The BD is processed from different catalytic routes of esterification and transesterification through homogeneous (alkaline and acid), heterogeneous and enzymatic catalysis. However, heterogeneous catalysts and biocatalysts play an essential role towards a sustainable alternative to homogeneous catalysts applied in biodiesel production. The main drawback is the supporting material. To overcome this, currently, Metal-Organic Frameworks (MOFs) have gained significant interest as supports for catalysts due to their extremely high surface area and numerous binding sites. This review focuses on the advantages of using various MOFs structures as supports for heterogeneous catalysts and biocatalysts for the eco-friendly biodiesel production process. The characteristics of these materials and their fabrication synthesis are briefly discussed. Moreover, we address in a general way basic items ranging from biodiesel synthesis to applied catalysts, giving great importance to the enzymatic part, mainly to the catalytic mechanism in esterification/transesterification reactions. We provide a summary with recommendations based on the limiting factors.

Prospects of Catalysis for Process Sustainability of Eco-Green Biodiesel Synthesis via Transesterification: A State-Of-The-Art Review

Environmental pollution caused by conventional petro-diesel initiates at time of crude oil extraction and continues until its consumption. The resulting emission of poisonous gases during the combustion of petroleum-based fuel has worsened the greenhouse effect and global warming. Moreover, exhaustion of finite fossil fuels due to extensive exploitation has made the search for renewable resources indispensable. In light of this, biodiesel is a best possible substitute for the regular petro-diesel as it is eco-friendly, renewable, and economically viable. For effective biodiesel synthesis, the selection of potential feedstock and choice of efficient catalyst is the most important criteria. The main objective of this bibliographical review is to highlight vital role of different catalytic systems acting on variable feedstock and diverse methods for catalysis of biodiesel synthesis reactions. This paper further explores the effects of optimized reaction parameters, modification in chemical compositions, reaction operating parameters, mechanism and methodologies for catalysts preparation, stability enhancement, recovery, and reusability with the maximum optimum activity of catalysts. In future, the development of well-planned incentive structures is necessary for systematic progression of biodiesel process. Besides this, the selection of accessible and amended approaches for synthesis and utilization of specific potential catalysts will ensure the sustainability of eco-green biodiesel.

Recent Advances in the Valorization of Biodiesel By-Product Glycerol to Solketal

The exponential rise of the biodiesel production has resulted in a considerable amount of glycerol as a by-product, which must be valorized to ensure the sector’s long-term viability. As a result, cost-effective glycerol conversions for significant value-added chemicals are essential for the biodiesel production in the long run. Solketal, a glycerol by-product, is obtained as a potential fuel additive in the biodiesel industry. Recently, several heterogeneous acid-catalysts stand out as a promising catalyst for solketal production where biomass-based catalyst gained attraction owing to their biodegradability, eco-friendly, and abundant availability. Furthermore, magnetic nanoparticles-derived catalysts along with sulfonated functionalized catalyzed, zeolites, resins, enzymatic, etc. have proved their efficiency in solketal production. In this review, a wider study on the recent advances of the catalysts has been discussed along with their preparation, various reaction parameters, its application, and efficiency for biodiesel industry. This study opens up incredible prospects for us to use renewable energy sources, which will benefit the industry, the environment, and the economy.

Towards a sustainable waste-to-energy pathway to pequi biomass residues: Biochar, syngas, and biodiesel analysis

The waste-to-energy (WTE) valorization pathway of Caryocar brasiliense (pequi) seeds was investigated via pyrolysis, gasification, and transesterification to understand its potential as biochar, syngas, and biodiesel. First, the pyrolysis (300-700 °C) was conducted in N₂ atmosphere for pequi seeds (PS) and pequi seeds without its extractives (PSWE), characterizing its biochar properties. The PSWE was then gasified at 1000 °C under O₂/N₂, O₂/CO₂/N₂ and O₂/H₂O/N₂ atmospheres to evaluate the characteristics of the producer gas. The PS extractives were then transesterified and characterized for biodiesel production. Finally, a multiple-criteria decision analysis assessed the PS products' potential within the thermochemical routes. The results evidenced better biochar (up to 22.29% HHV enhancement, higher mass and energy yield, up to 75.9 and 85.5% reduction of O/C and H/C, respectively, and enriched N content) via PSWE pyrolysis than PS considering biofuel application and optimistic perceptions for soil amendment. This indicates that the preceding extraction of vegetal fat from PS strengthens the WTE by including further processing of extracted oil. The produced syngas under O₂/H₂O/N₂ gasification atmosphere showed better applicability as a biofuel (16.37 MJ·kg^-1 lower heating value, 107.33% cold gas efficiency, and 113.55% carbon conversion efficiency) with up to 24% higher success rate. The transesterification of the extractives revealed its potential (98% conversion rate) for use as feedstock for in situ power generation, or blended for biodiesel production. The results provide insights into the circular economy in agro-extractivist communities that may support Brazil's small and medium agro-food industries with their energy demands.

Waste Passion Fruit Peel as a Heterogeneous Catalyst for Room-Temperature Biodiesel Production

A low-cost, green, and highly active catalyst which could transesterify oil under ambient conditions is required to reduce the biodiesel production cost. A novel heterogeneous catalyst derived from the waste agroproduct has been developed from passion fruit peel. The catalytic activity of calcined waste passion fruit peel (WPFP) which mainly contains potassium in the form of chloride and carbonate has been evaluated using factorial design to determine the interaction of molar ratio of oil to methanol, catalyst weight, and reaction time with three different reaction conditions such as 65, 45 °C, and room temperature. The transesterification of palm oil to biodiesel achieved a conversion of >90% for all variables determined at a reaction temperature of 45 and 65 °C, respectively, while a maximum biodiesel conversion of 95.4 ± 2.8% was obtained at room temperature and a reaction time of 30 min. The addition of certain amounts of the catalyst is required to reuse the catalyst as the leaching study showed the reduction of 22% of catalyst weight. The ability of calcined WPFP to catalyze transesterification at room temperature opens up the possibility to reduce biodiesel production cost.

Utilization of agricultural lignocellulosic wastes for biofuels and green diesel production

The ever-growing human population has resulted in the expansion of agricultural activity; evident by the deforestation of rainfoamrests as a means of acquiring fertile land for crops. The crops and fruits produced by such means should be utilized completely; however, there are still losses and under-exploitation of these produces which has resulted in wastes being mounted in landfills. These underutilized agricultural wastes including vegetables and fruits can serve as a potential source for biofuels and green diesel. This paper discusses the main routes (e.g., biological and thermochemical) for producing biofuels such as bioethanol, biodiesel, biogas, bio-oil and green diesel from underutilized crops by emphasizing recent technological innovations for improving biofuels and green diesel yields. The future prospects of a successful production of biofuels and green diesel by this source are also explained. Underutilized lignocelluloses including fruits and vegetables serve as a prospective biofuel and green diesel generation source for the future prosperity of the biofuel industry.

Parts-Per-Million (Salen)Fe(III) Homogeneous Catalysts for the Production of Biodiesel from Waste Cooking Oils

This work describes the application of a library of iron(III)-salen catalysts in the production of biodiesel from vegetable oils. The conversion of neutral soybean oil is complete within two hours at 160–180 °C with low catalyst loading (0.10 mol%). A comparative screening reveals that the catalysts containing acetate as a fifth ligand are the most performing, and these have been conveniently used to convert acidic and waste cooking oils (WCO). WCOs were used as received without further purification to produce biodiesel in high yield (85–90%) under optimized conditions (2 h at 180 °C, catalyst loading 0.1 mol%, oil to alcohol molar ratio 1:20). The iron content in the lipophilic and hydrophilic phases of the crude mixture was investigated and the residual concentration in biodiesel was found to be in the order of 10–14 ppm, comparable to that contained in biodiesels from other sources.

Graphical Abstract

Synthesis and properties of wax based on waste cooking oil

In this work, a cost-effective wax was synthesized from waste cooking oil (WCO), and its properties including melting point, color, hardness, combustion performance and micro-morphology were tested and analyzed. The obtained results showed that the epoxy waste cooking oil had lighter color, higher melting point and hardness than that of original WCO, which could be used as wax. Moreover, introducing stearic acid further improved the performances of WCO-based wax. The WCO-based wax made of epoxy waste cooking oil and stearic acid (containing ≥50 wt% stearic acid) displayed a relatively high melting point (≥46 °C), light color (Lovibond color code Y ≤ 16.1, R ≤ 2.3), good hardness (needle penetration index ≤2.95 mm) and long combustion time (≥227 min), and could achieve the required national standard and be used as a substitute for the commercially available soybean wax. Together with many additional benefits such as low synthesis cost, mild reaction conditions, convenient synthesis route, and no secondary pollution, producing wax based on WCO could provide a new path for WCO recycling in economically trailing regions.

Low-cost wax based on waste cooking oil (WCO) was synthesized and could be a substitute for commercial soybean wax.

Facile Synthesis of Silane-Modified Mixed Metal Oxide as Catalyst in Transesterification Processes

The fast depletion of fossil fuels has attracted researchers worldwide to explore alternative biofuels, such as biodiesel. In general, the production of biodiesel is carried out via transesterification processes of vegetable oil with the presence of a suitable catalyst. A mixed metal oxide has shown to be a very attractive heterogeneous catalyst with a high performance. Most of the mixed metal oxide is made by using the general wetness impregnation method. A simple route to synthesize silane-modified mixed metal oxide (CaO-CuO/C6) catalysts has been successfully developed. A fluorocarbon surfactant and triblock copolymers (EO)106(PO)70(EO)106 were used to prevent the crystal agglomeration of carbonate salts (CaCO3-CuCO3) as the precursor to form CaO-CuO with a definite size and morphology. The materials show high potency as a catalyst in the transesterification process to produce biodiesel. The calcined co-precipitation product has a high crystallinity form, as confirmed by the XRD analysis. The synthesized catalyst was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). The mechanism of surface modification and the effects of the catalytic activity were also discussed. The biodiesel purity of the final product was analyzed by gas chromatography. The optimum biodiesel yield was 90.17% using the modified mixed metal oxide CaO-CuO/C6.

Optimization of biodiesel synthesis from Jatropha curcas oil using kaolin derived zeolite Na–X as a catalyst

Biodiesel is an alternative renewable green fuel obtainable from the reaction of plant or animal oil with a low molecular weight alcohol in the presence of a catalyst. However, the cost of its production remains high due to costly feedstock, the majority of which is competitively also used as food, and the use of homogeneous catalysts, which pose difficulties in product purification and resulting environmental pollution. The aim of this study was to explore the production of biodiesel through transesterification of non-edible and cheap Jatropha curcas (JC) oil using a zeolite Na–X catalyst obtained from naturally occurring kaolin clay. The transesterification parameters, namely reaction temperature, reaction time, catalyst loading and methanol to oil molar ratio were optimized using the L₁₆(4⁴) Taguchi orthogonal array approach. The catalyst loading was found to be the most influential parameter at 93.79%. The optimum conditions for the conversion of JC oil, with a biodiesel yield of up to 93.94%, were found to be a methanol to oil molar ratio of 10 : 1, catalyst loading of 8%, reaction temperature of 70 °C and reaction time of 5 h. Fuel characterization parameters were within the European Norm (EN) 14214:2019 biodiesel specifications. Our findings offer insights into the ideal parametric conditions for the cost-effective synthesis of biodiesel from JC oil via zeolite-catalyzed esterification.

Zeolite Na–X derived from inexpensive kaolin clay is an effective catalyst (up to 94% yield) for Jatropha curcas oil conversion to biodiesel; Taguchi optimization shows methanol/oil ratio of 10, with 8% catalyst loading at 70 °C for 5 h as optimum.

Obtention of biodiesel through an enzymatic two-step process. Study of its performance and characteristic emissions

We describe the enzymatic synthesis of biodiesel from waste cooking oil (WCO) in a two-step production process: hydrolysis of WCO, followed by acid-catalyzed esterification of free fatty acids (FFAs). Among the three commercial enzymes evaluated, the inexpensive lipase Lipex® 100L supported on Lewatit® VP OC 1600 produced the best overall biodiesel yield (96.3%). Finally, we assessed the combustion efficiency of the obtained biodiesel and its blends. All blends tested presented lower emissions of CO and HC compared to diesel. The NOx emissions were higher due to biodiesel's high volatility and viscosity. The cost of biodiesel production was calculated using the process described.

The inexpensive lipase Lipex® 100L produced biodiesel from waste cooking oil in a two-step process, with an overall yield of 96.3%.

Recent advances in biodiesel production: Challenges and solutions

Mono alkyl fatty acid ester or methyl ethyl esters (biodiesel) are the promising alternative for fossil fuel or petroleum derived diesel with similar properties and could reduce the carbon foot print and the greenhouse gas emissions. Biodiesel can be produced from renewable and sustainable feedstocks like plant derived oils, and it is biodegradable and non-toxic to the ecosystem. The process for the biodiesel production is either through traditional chemical catalysts (Acid or Alkali Transesterification) or enzyme mediated transesterification, but as enzymes are natural catalysts with environmentally friendly working conditions, the process with enzymes are proposed to overcome the drawbacks of chemical synthesis. At present 95% of the biodiesel production is contributed by edible oils worldwide whereas recycled oils and animal fats contribute 10% and 6% respectively. Although every process has its own limitations, the enzyme efficiency, resistance to alcohols, and recovery rate are the crucial factors to be addressed. Without any benefit of doubt, production of biodiesel using renewable feedstocks and enzymes as the catalysts could be recommended for the commercial purpose, but further research on improving the efficiency could be an advantage.

Recirculating used cooking oil and Nagkesar seed shells in dual-stage catalytic biodiesel synthesis with C1-C3 alcohols

The presented study discusses biodiesel synthesis by utilizing two wastes: Mesua ferrea Linn (MFL) seed shells (inert support for developing catalysts) and used cooking oil (feedstock). The MFL shells were used for heterogeneous acid and base catalyst development through carbonization, steam activation and subsequent doping of H₂SO₄ or KOH, which upon instrumental examination showed effective doping of functional groups on the MFL char. The conversion approach uses methanol with sulfonated char (SC) for esterification, while the second stage utilizes 2-propanol for transesterification with KOH-doped char (KC) as a catalyst. Both stages optimize 5 controlling parameters such as mixing intensity, duration of reaction, catalyst load, alcohol concentration and reaction temperature in an L16 Taguchi experimental matrix. Thus, the obtained biodiesel has an ester content of 99.16%, while 97.35% of the free fatty acids (FFA) were converted, resulting in the product showing improved physico-chemical properties as assessed through fuel characterization tests. Reusability tests for the catalysts showed 4 reuses for acid catalyst compared to 9 reuses for base catalyst. Catalyst development costs were only $1.27/kg for activated char, while due to reuse, the prepared catalysts cost only $0.53/kg of biodiesel. Hence, the catalytic process holds great potential for commercialization if scaled up appropriately.

Current State and Perspectives on Transesterification of Triglycerides for Biodiesel Production

Triglycerides are the main constituents of lipids, which are the fatty acids of glycerol. Natural organic triglycerides (viz. virgin vegetable oils, recycled cooking oils, and animal fats) are the main sources for biodiesel production. Biodiesel (mono alkyl esters) is the most attractive alternative fuel to diesel, with numerous environmental advantages over petroleum-based fuel. The most practicable method for converting triglycerides to biodiesel with viscosities comparable to diesel fuel is transesterification. Previous research has proven that biodiesel–diesel blends can operate the compression ignition engine without the need for significant modifications. However, the commercialization of biodiesel is still limited due to the high cost of production. In this sense, the transesterification route is a crucial factor in determining the total cost of biodiesel production. Homogenous base-catalyzed transesterification, industrially, is the conventional method to produce biodiesel. However, this method suffers from limitations both environmentally and economically. Although there are review articles on transesterification, most of them focus on a specific type of transesterification process and hence do not provide a comprehensive picture. This paper reviews the latest progress in research on all facets of transesterification technology from reports published by highly-rated scientific journals in the last two decades. The review focuses on the suggested modifications to the conventional method and the most promising innovative technologies. The potentiality of each technology to produce biodiesel from low-quality feedstock is also discussed.

Catalyst and Elemental Analysis Involving Biodiesel from Various Feedstocks

The world is currently faced with the depletion of fossil fuel energy sources and their use is associated with environmental pollution. This has triggered the need to seek alternative energy sources that are renewable, sustainable and environmentally benign. Biodiesel, an alternative fuel of interest, is obtainable from biomass feedstocks. In existing biodiesel fuel, there are concerns that it is a contaminant due to its elemental contents, which over time also affect its quality. This study aimed to investigate the influence of a bifunctional catalyst on the conversion of free fatty acids and the elemental composition of biodiesel obtained from waste oils of sunflower and palm feedstocks. The synthesised catalyst was characterised using BET, XRD, FTIR and SEM while ICP-OES and Rancimat were used for elemental contents and oxidation in feedstocks and biodiesels. The effect of Cu, Zn and Fe metals on the stability of synthesised biodiesel was further studied. The catalyst showed characteristics of bifunctionality with improved textural properties necessary for the conversion of high free fatty acids feedstocks to biodiesel, despite increasing Ca content within the produced biodiesel. Sunflower biodiesel showed superior fuel quality, although palm biodiesel had more oxidation stability. An increase in the concentration of metals decreased the induction period, with Cu and Fe being more effective than Zn metal.

Copper molybdate synthesized by sonochemistry route at room temperature as an efficient solid catalyst for esterification of oleic acid

Copper molybdate nanoplates were synthesized by a sonochemical process at room temperature, which we report as a simple and cost-effective route. Structural analysis of the material by the Rietveld method of X-ray diffraction (XRD) data revealed lindgrenite Cu3(MoO4)2(OH)2 in a single-phase structure. All the vibrational modes characteristic of the space group were identified by Raman vibrational and near-infrared (NIR) spectroscopies. The profile obtained for N2 adsorption/desorption was type III hysteresis, characteristic of mesoporous materials, with a surface area of 70.77(1) m2 g-1. The micrographs of the material obtained by scanning electron microscopy showed nanoplates with nanometric sizes and an anisotropic growth aspect. The catalytic activity of lindgrenite was evaluated by esterifying oleic acid with methanol, showing high conversion rate to methyl oleate and good catalyst stability after seven recycling cycles. Above all, the best catalytic performance was reached when we optimized parameters such as oleic acid:methanol molar ratio of 1:5, 5% of catalyst dosage, and reaction time of 5 h, resulting in 98.38% of conversion at 413 K. Therefore, sonochemically synthesized lindgrenite proved to be a high potential material for biofuel production by oleic acid esterification.

Progress on Modified Calcium Oxide Derived Waste-Shell Catalysts for Biodiesel Production

The dwindling of global petroleum deposits and worsening environmental issues have triggered researchers to find an alternative energy such as biodiesel. Biodiesel can be produced via transesterification of vegetable oil or animal fat with alcohol in the presence of a catalyst. A heterogeneous catalyst at an economical price has been studied widely for biodiesel production. It was noted that various types of natural waste shell are a potential calcium resource for generation of bio-based CaO, with comparable chemical characteristics, that greatly enhance the transesterification activity. However, CaO catalyzed transesterification is limited in its stability and studies have shown deterioration of catalytic reactivity when the catalyst is reused for several cycles. For this reason, different approaches are reviewed in the present study, which focuses on modification of waste-shell derived CaO based catalyst with the aim of better transesterification reactivity and high reusability of the catalyst for biodiesel production. The catalyst stability and leaching profile of the modified waste shell derived CaO is discussed. In addition, a critical discussion of the structure, composition of the waste shell, mechanism of CaO catalyzed reaction, recent progress in biodiesel reactor systems and challenges in the industrial sector are also included in this review.

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.