Biodiesel Production Using Homogeneous, Heterogeneous, and Enzyme Catalysts via Transesterification and Esterification Reactions: a Critical Review

The covalent immobilization of β-galactosidase from Aspergillus oryzae and alkaline protease from Bacillus licheniformis on amino-functionalized multi-walled carbon nanotubes in milk

This study aimed was to covalently immobilize β-galactosidase from Aspergillus oryzae and protease from Bacillus licheniformis on amino-functionalized multi-walled carbon nanotubes. In this study, a two-level factorial design was employed to investigate the impact of seven continuous variables (activation pH, glutaraldehyde molarity, activation time (0-8 h), buffer solution pH (8-0), buffer solution molarity, MWCNT-NH 2 -glutaraldehyde quantity, and stabilization time (0-180 h)) on the immobilization efficiency and enzymatic activity of protease and β-galactosidase. Furthermore, the effect of time on the percentage of enzymatic activity was examined during specific intervals (24, 48, 72, 96, and 120 h) of the immobilization process. The analysis of variance results for protease enzymatic activity revealed a notable influence of the seven variables on immobilization efficiency and enzymatic activity. Additionally, the findings indicate that activation time, buffer pH, MWCNT-NH 2 -glutaraldehyde quantity, and stabilization time significantly affect the activity of the protease enzyme. The interplay between buffer pH and stabilization time is also significant. Indeed, both activation time and the quantity of MWCNT-NH 2 -glutaraldehyde exert a reducing effect on enzyme activity. Notably, the influence of MWCNT-NH 2 -glutaraldehyde quantity is more significant (p < 0.05). In terms of beta-galactosidase enzymatic activity, the study results highlight that among the seven variables considered, only the glutaraldehyde molarity, activation time, and the interplay of activation time and the quantity of MWCNT-NH 2 -glutaraldehyde can exert a statistically significant positive impact on the enzyme's activity (p < 0.05). The combination of activation time and buffer solution molarity, as well as the interactive effect of buffer pH and MWCNT-NH2-glutaraldehyde, can lead to a significant improvement in the stabilization efficiency of the protease of carbon nanotubes. The analysis of variance results demonstrated that the efficiency of covalently immobilizing β-galactosidase from Aspergillus oryzae on amino-functionalized multi-walled carbon nanotubes is influenced by the molarity of glutaraldehyde, buffer pH, stabilization time, and the interplay of activation time + buffer pH, buffer pH + activation time, activation time + buffer molarity, and glutaraldehyde molarity + MWCNT-NH 2 -glutaraldehyde (p < 0.05). Through the optimization and selection of optimal formulations, the obtained results indicate enzyme activities and stabilization efficiencies of 64.09 % ± 72.63 % and 65.96 % ± 71.77 % for protease and beta-galactosidase, respectively. Moreover, increasing the enzyme stabilization time resulted in a reduction of enzyme activity. Furthermore, an increase in pH, temperature, and the duration of milk storage passing through the enzyme-immobilized carbon nanotubes led to a decrease in enzyme stabilization efficiency, and lactose hydrolysis declined progressively over 8-h. Hence, the covalent immobilization of β-galactosidase from Aspergillus oryzae and protease from Bacillus licheniformis onto amino-functionalized multi-walled carbon nanotubes is anticipated to be achievable for milk applications.

Catalyst-Enhancing Hydrothermal Carbonization of Biomass for Hydrochar and Liquid Fuel Production-A Review

The research impact of catalysts on the hydrothermal carbonization (HTC) process remains an ongoing debate, especially regarding the quest to enhance biomass conversion into fuels and chemicals, which requires diverse catalysts to optimize bio-oil utilization. Comprehensive insights and standardized analytical methodologies are crucial for understanding HTC's potential benefits in terms of biomass conversion stages. This review seeks to understand how catalysts enhance the HTC of biomass for liquid fuel and hydrochar production, drawing from the following key sections: (a) catalyst types applied in HTC processes; (b) biochar functionality as a potential catalyst; (c) catalysts increasing the success of HTC process; and (d) catalyst's effect on the morphological and textural character of hydrochar. The performance of activated carbon would greatly increase via catalyst action, which would progress the degree of carbonization and surface modification, alongside key heteroatoms. As catalytic HTC technology advances, producing carbon materials for thermochemical activities will become more cost-effective, considering the ever-growing demands for high-performance thermochemical technologies.

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.

Algal carbohydrate polymers: Catalytic innovations for sustainable development

Algal polysaccharides, harnessed for their catalytic potential, embody a compelling narrative in sustainable chemistry. This review explores the complex domains of algal carbohydrate-based catalysis, revealing its diverse trajectory. Starting with algal polysaccharide synthesis and characterization methods as catalysts, the investigation includes sophisticated techniques like NMR spectroscopy that provide deep insights into the structural variety of these materials. Algal polysaccharides undergo various preparation and modification techniques to enhance their catalytic activity such as immobilization. Homogeneous catalysis, revealing its significance in practical applications like crafting organic compounds and facilitating chemical transformations. Recent studies showcase how algal-derived catalysts prove to be remarkably versatile, showcasing their ability to customise reactions for specific substances. Heterogeneous catalysis, it highlights the significance of immobilization techniques, playing a central role in ensuring stability and the ability to reuse catalysts. The practical applications of heterogeneous algal catalysts in converting biomass and breaking down contaminants, supported by real-life case studies, emphasize their effectiveness. In sustainable chemistry, algal polysaccharides emerge as compelling catalysts, offering a unique intersection of eco-friendliness, structural diversity, and versatile catalytic properties. Tackling challenges such as dealing with complex structural variations, ensuring the stability of the catalyst, and addressing economic considerations calls for out-of-the-box and inventive solutions. Embracing the circular economy mindset not only assures sustainable catalyst design but also promotes efficient recycling practices. The use of algal carbohydrates in catalysis stands out as a source of optimism, paving the way for a future where chemistry aligns seamlessly with nature, guiding us toward a sustainable, eco-friendly, and thriving tomorrow. This review encapsulates-structural insights, catalytic applications, challenges, and future perspectives-invoking a call for collective commitment to catalyze a sustainable scientific revolution.

A scientometric analysis and recent advances of emerging chitosan-based biomaterials as potential catalyst for biodiesel production: A review

Chitosan is a widely available polymer with a reasonably high abundance, as well as a sustainable, biodegradable, and biocompatible material with different functional groups that are used in a wide range of operations. Chitosan is frequently employed in widespread applications such as environmental remediation, adsorption, catalysts, and drug formulation. The goal of this review is to discuss the potential applications of chitosan and its chemically modified solids as a catalyst in biodiesel production. The existing manuscripts are integrated based on the nature of materials used as chitosan and its modifications. A short overview of chitosan's structural characteristics, properties, and some ideal methods to be considered in catalysis activities are addressed. This article includes an analysis of a chitosan-based scientometric conducted between 1975 and 2023 using VOS viewer 1.6.19. To identify developments and technological advances in chitosan research, the significant scientometric features of yearly publication results, documents country network, co-authorship network, documents funding sponsor, documents institution network, and documents category in domain analysis were examined. This review covers a variety of organic transformations and their effects, including chitosan reactions against acids, bases, metals, metal oxides, organic compounds, lipases, and Knoevenagel condensation. The catalytic capabilities of chitosan and its modified structures for producing biodiesel through transesterification reactions are explored in depth.

Recent advances in transesterification for sustainable biodiesel production, challenges, and prospects: a comprehensive review

Biodiesel, a renewable and sustainable alternative to fossil fuels, has garnered significant attention as a potential solution to the growing energy crisis and environmental concerns. The review commences with a thorough examination of feedstock selection and preparation, emphasizing the critical role of feedstock quality in ensuring optimal biodiesel production efficiency and quality. Next, it delves into the advancements in biodiesel applications, highlighting its versatility and potential to reduce greenhouse gas emissions and dependence on fossil fuels. The heart of the review focuses on transesterification, the key process in biodiesel production. It provides an in-depth analysis of various catalysts, including homogeneous, heterogeneous, enzyme-based, and nanomaterial catalysts, exploring their distinct characteristics and behavior during transesterification. The review also sheds light on the transesterification reaction mechanism and kinetics, emphasizing the importance of kinetic modeling in process optimization. Recent developments in biodiesel production, including feedstock selection, process optimization, and sustainability, are discussed, along with the challenges related to engine performance, emissions, and compatibility that hinder wider biodiesel adoption. The review concludes by emphasizing the need for ongoing research, development, and collaboration among academia, industry, and policymakers to address the challenges and pursue further research in biodiesel production. It outlines specific recommendations for future research, paving the way for the widespread adoption of biodiesel as a renewable energy source and fostering a cleaner and more sustainable future.

OH-Impregnated Household Bleach-Making Sediments for the Catalysis of Waste Cooking Oil Transesterification: Parameter Optimization

Industrial and academic societies have been bothered with the generation and subsequent management of residues settled out from household bleach, due to its corrosive properties. Therefore, the aim of this research was to introduce a NaOH-impregnated calcium-based solid catalyst from the aforementioned sediments for waste cooking oil transesterification. To prepare the catalyst (RC-ITB), the wet impregnation technique was followed and successfully characterized via X-ray diffraction (XRD), X-ray fluorescence(XRF), differential scanning calorimetry (DSC), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) methods. The study findings suggested that RC-ITB has a BET surface area of 9.312 m2 g-1 and is largely made up of calcium with its compound forms such as carbonates, hydroxides, and oxides. The evaluation of pH values verified that RC-ITB is more alkaline (i.e., pH = 12.65) relative to its precursor RC (pH = 10.66), largely attributable to OH impregnation. To study the catalytic performance, three numeric factors with three levels of treatment were used, and their influences were analyzed through a response surface approach. Accordingly, the optimal yield of biodiesel was found to be 80.04% at a reaction temperature of 61 ± 2 °C, catalyst weight of 6.33 wt %, and a molar ratio of 23.94. Moreover, FTIR analysis verified that the glycerol part of triglycerides had been replaced with a methoxyl unit. Also, the fuel quality parameters of the FAME product were examined, including density, kinematic viscosity, acid value, density, cetane number, cloud point, saponification value, and pour point; all of these values fall within the ASTM D6751-accepted limits. Thus, the findings showed that the sediments of household bleach production could be a candidate source to explore heterogeneous basic catalysts.

Room temperature esterification of high-free fatty acid feedstock into biodiesel

The esterification of a high-free fatty acid feedstock to biodiesel is often performed in high-temperature conditions using either homogeneous or heterogeneous acid catalysts. Thus, this study attempts to esterify oleic acid to biodiesel in room temperature conditions using sulphuric acid as a catalyst and a homogenizer device. The influences of process parameters including the molar ratio of oleic acid to methanol, catalyst concentration and rotational speed on biodiesel conversion were determined in different reaction times. The maximum conversion of 96.1 ± 0.4% was obtained in the presence of a molar ratio of 1 : 12, catalyst concentration of 0.7 mol L-1, a rotational speed of 4000 rpm and a reaction time of 30 minutes. The catalytic reusability test showed that the addition of fresh methanol is required to maintain the catalytic activity. However, the homogenizer-intensify esterification of oleic acid to biodiesel showed better performance than other methods as the reaction could conducted at room temperature and at a short reaction time. The predicted biodiesel properties meet the international standard except for oxidative stability. However, the flow properties revealed that the biodiesel can be used in winter season.

Valorization of calcium hypochlorite precipitate as a new source of heterogeneous catalyst development for biodiesel production: A preliminary experiment

One of the main problem related with liquid bleach production from calcium hypochlorite is the amount of precipitates generated and its consequent management. As a result, academic and industrial communities have been challenged with searching of a means for its valorization. Therefore, this research explores the application of the precipitate as a viable source of Ca-based heterogeneous catalyst development for the production of waste cooking oil methyl esters for the first-time. The catalyst was prepared by dividing the precipitates into three forms, viz. raw untreated (RC), heat treated (RC-TB), and NaOH impregnated plus thermally activated (RC-ITB). The prepared catalysts were efficiently characterized by XRF, XRD, FTIR, SEM, and BET techniques. The characterization results indicated that the catalysts are mainly composed of calcium metal in the form of oxides (CaO), calcite (CaCO3) and Portlandite (Ca(OH)2), which are the promising constituents of basic catalysts. The BET inspection of RC, RC-TB, and RC-ITB revealed the specific surface area of 8.509, 9.089, and 9.312 m2/g, respectively. At the same reaction conditions, the maximum biodiesel yield of 76.05 % was achieved by RC-ITB compared to RC-TB (62.57 %) and RC (19.74 %), because it's larger specific surface area and highest basic nature (pH = 12.65 at 1:5 w/v) improves the reaction catalysis through better catalyst-substrates interactions. The lower biodiesel yield was attained through the RC catalyst due to its untreated surface, lower specific area, and weak alkaline nature (pH value = 10.66 at 1:5 w/v). Furthermore, regardless of the amount of yield, almost similar fuel properties and functional groups of the products over the coded catalysts were observed. Generally, the possibility of calcium hypochlorite precipitate as a precursor of Ca-based heterogeneous catalyst has been effectively proven in this research, which could be very important for environmental safety and industrial resource integration.

Biocatalytic production of biolubricants: Strategies, problems and future trends

The increasing worries by the inadequate use of energy and the preservation of nature are promoting an increasing interest in the production of biolubricants. After discussing the necessity of producing biolubricants, this review focuses on the production of these interesting molecules through the use of lipases, discussing the different possibilities (esterification of free fatty acids, hydroesterification or transesterification of oils and fats, transesterification of biodiesel with more adequate alcohols, estolides production, modification of fatty acids). The utilization of discarded substrates has special interest due to the double positive ecological impact (e.g., oil distillated, overused oils). Pros and cons of all these possibilities, together with general considerations to optimize the different processes will be outlined. Some possibilities to overcome some of the problems detected in the production of these interesting compounds will be also discussed.

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.

Microwave-Assisted Enzymatic Esterification Production of Emollient Esters

Currently, esterification production of isopropyl myristate (IPM) or isopropyl palmitate (IPP) uses a homogeneous or heterogeneous acid substance as a catalyst and is conducted at high temperatures and pressures. Utilization of this type of catalyst requires an additional postproduction process (neutralization and purification), which burdens the production cost. Microwave enzymatic esterification is a simple and fast method. The results showed that reaction time, ratio molar of fatty acids to isopropyl alcohol, catalyst weight, and microwave power have a significant effect on the IPM or IPP conversion. Further, the energy consumption of this process is less than other enzymatic esterification and is certainly more energy efficient, which could save 99 and 29% of processing time.

Biodiesel Production Using Palm Oil with a MOF-Lipase B Biocatalyst from Candida Antarctica: A Kinetic and Thermodynamic Study

This research presents the results of the immobilization of Candida Antarctica Lipase B (CALB) on MOF-199 and ZIF-8 and its use in the production of biodiesel through the transesterification reaction using African Palm Oil (APO). The results show that the highest adsorption capacity, the 26.9 mg·g^-1 Lipase, was achieved using ZIF-8 at 45 °C and an initial protein concentration of 1.20 mg·mL^-1. The results obtained for the adsorption equilibrium studies allow us to infer that CALB was physically adsorbed on ZIF-8 while chemically adsorbed with MOF-199. It was determined that the adsorption between Lipase and the MOFs under study better fit the Sips isotherm model. The results of the kinetic studies show that adsorption kinetics follow the Elovich model for the two synthesized biocatalysts. This research shows that under the experimental conditions in which the studies were carried out, the adsorption processes are a function of the intraparticle and film diffusion models. According to the results, the prepared biocatalysts showed a high efficiency in the transesterification reaction to produce biodiesel, with methanol as a co-solvent medium. In this work, the catalytic studies for the imidazolate, ZIF-8, presented more catalytic activity when used with CALB. This system presented 95% biodiesel conversion, while the biocatalyst formed by MOF-199 and CALB generated a catalytic conversion percentage of 90%. Although both percentages are high, it should be noted that CALB-MOF-199 presented better reusability, which is due to chemical interactions.

Biocatalysis of triglycerides transesterification using fungal biomass: a biorefinery approach

BACKGROUND

The use of microbial biomasses, such as fungal biomass, to catalyze the transesterification of triglycerides (TG) for biodiesel production provides a sustainable, economical alternative while still having the main advantages of expensive immobilized enzymes.

RESULTS

Biomasses of Aspergillus flavus and Rhizopus stolonifera were used to catalyze the transesterification of TG in waste frying oil (WFO). Isopropanol as an acyl-acceptor reduced the catalytic capability of the biomasses, while methanol was the most potent acyl-acceptor with a final fatty acid methyl ester (FAME) concentration of 85.5 and 89.7%, w/w, for R. stolonifer and A. flavus, respectively. Different mixtures of the fungal biomasses were tested, and higher proportions of A. flavus biomass improved the mixture's catalytic capability. C. sorokiniana cultivated in synthetic wastewater was used as feedstock to cultivate A. flavus. The biomass produced had the same catalytic capability as the biomass produced in the control culture medium. Response surface methodology (RSM) was adopted using central composite design (CCD) to optimize the A. flavus biomass catalytic transesterification reaction, where temperature, methanol concentration, and biomass concentration were selected for optimization. The significance of the model was verified, and the suggested optimum reaction conditions were 25.5 °C, 250 RPM agitation with 14%, w/w, biomass, 3 mol/L methanol, and a reaction duration of 24 h. The suggested optimum conditions were tested to validate the model and a final FAME concentration of 95.53%. w/w was detected.

CONCLUSION

Biomasses cocktails might be a legitimate possibility to provide a cheaper technical solution for industrial applications than immobilized enzymes. The use of fungal biomass cultivated on the microalgae recovered from wastewater treatment for the catalysis of transesterification reaction provides an additional piece of the puzzle of biorefinery. Optimizing the transesterification reaction led to a valid prediction model with a final FAME concentration of 95.53%, w/w.

Experimental and theoretical assessment of phenomena linked with separation and purification of biodiesel from Ricinus communis seed oil

This study investigated the phenomena associated with the separation and purification of biodiesel produced from Ricinus communis oil seeds using experimental and theoretical approaches. The alkaline transesterification technique was used to produce the biodiesel from the Ricinus communis oil seeds which were later compared with standards based on EN and ASTM. Experimental investigation of the components in the mixture for separation and purification was conducted using the standard turbidimetric method for binodal solubility and tie-line compositions. The gas chromatographic technique was used to determine the composition of the homogeneous mixture. Novel components separation and purification of the Ricinus communis seed oil biodiesel was achieved using ternary diagrams highlighting the constituent components of the biodiesel at different temperatures for enhanced separation and purification. At the coexisting extract and raffinate phases, the orientation angle of the component compositions increases as the methanol concentration increases and temperature increases. The analysis of seed oil in terms of its physicochemical properties showed density, refractive index, acid value, and free fatty acid values of 905 kg/m³, 1.486, 0.79 mg KOH/g, and 0.390 mg KOH/g respectively. The fatty acid composition of the seed oil and biodiesel revealed that the major characteristics of the oil and biodiesel were defined by the presence of linoleic acid (C_18:2) and a ricinoleic acid hydroxyl group (C_18:1, OH) with compositions of approximately 30% and 20% respectively. Fourier Transform Infra-Red (FTIR) spectrometry analysis of the oil and biodiesel showed that the absorption spectrum in terms of the wave number (cm^-1) ranged from 1000 to 4000 cm^-1 with esters as the main functional group providing the main structural backbone. The presence of different fatty acids leads to lateral homogeneity of the biodiesel molecules which can serve to organize the molecules into discrete domains with different properties for enhanced separation and purification at the investigated temperatures. Optimal separation and purification were achieved at the different temperatures showing the castor oil biodiesel, glycerol, and methanol components system at the prevailing composition, time, and temperatures from the tie-lines and binodal solubility compositions. This approach provides a means for the design of a more efficient separation process for optimal biodiesel purification after production with knowledge of how the components are distributed in the ternary mixture after the transesterification reaction. This, leads to greater efficiency of the process, reducing material and operational costs and eliminating environmental issues linked with the biodiesel production process as the volume of wastewater generated would be hugely eradicated. The findings of this study will be useful in the setting up of a small-to-medium-size biodiesel production facility with improvement in the efficiency of product separation and purification.

Effects of Synthesis Variables on SAPO-34 Crystallization Templated Using Pyridinium Supramolecule and Its Catalytic Activity in Microwave Esterification Synthesis of Propyl Levulinate

A detailed investigation of the hydrothermal crystallization of SAPO-34 in the presence of the novel 1-propylpyridinium hydroxide ([PrPy]OH) organic structural directing agent is presented. The synthesis conditions are systematically tuned to investigate the effects of various parameters (viz. concentrations of each reactant, crystallization time, and temperature) on the nucleation and crystallization of SAPO-34. The results show that a careful variation in each of the synthesis parameters results in the formation of competing phases such as SAPO-5, SAPO-35, and SAPO-36. Pure and fully crystalline SAPO-34 can be crystallized using a precursor hydrogel of a molar ratio of 2.0 Al: 4.7 P: 0.9 Si: 6.7 [PrPy]OH: 148 H2O at 200 °C for only 19 h, which is a shorter time than that found in previous studies. The prepared SAPO-34 is also very active in the esterification of levulinic acid and 1-propanol. By using microwave heating, 91.5% conversion with 100% selectivity toward propyl levulinate is achieved within 20 min at 190 °C. Hence, the present study may open a new insight into the optimum synthesis study of other zeolites using novel pyridinium organic moieties and the opportunity of replacing conventional harmful and non-recyclable homogeneous catalysts in levulinate biofuel synthesis.

Opportunities and Challenges for Lignin Valorization in Food Packaging, Antimicrobial, and Agricultural Applications

The exploration of renewable resources is essential to help transition toward a more sustainable materials economy. The valorization of lignin can be a key component of this transition. Lignin is an aromatic polymer that constitutes approximately one-third of the total lignocellulosic biomass and is isolated in huge quantities as a waste material of biofuel and paper production. About 98% of the 100 million tons of lignin produced each year is simply burned as low-value fuel, so this renewable polymer is widely available at very low cost. Lignin has valuable properties that make it a promising material for numerous applications, but it is far from being fully exploited. The aim of this Perspective is to highlight opportunities and challenges for the use of lignin-based materials in food packaging, antimicrobial, and agricultural applications. In the first part, the ongoing research and the possible future developments for the use of lignin as an additive to improve mechanical, gas and UV barrier, and antioxidant properties of food packaging items will be treated. Second, the application of lignin as an antimicrobial agent will be discussed to elaborate on the activity of lignin against bacteria, fungi, and viruses. Finally, the use of lignin in agriculture will be presented by focusing on the application of lignin as fertilizer.

Kinetic studies on the extraction of oil from a new feedstock (Chukrasia tabularis L. seed) for biodiesel production using a heterogeneous catalyst

This study has identified a new feedstock Chukrasia tabularis L. (C. tabularis) seed for the production of biodiesel. Oil was extracted from the seeds with and without autoclave-assisted ultrasonic homogenization (AUH) pretreatment using different solvents. The solvent n-hexane with AUH pretreatment yielded a maximum oil yield of 32 wt%. The kinetics and thermodynamics of the extraction process were studied in a batch. The data showed that extraction followed first-order kinetics with a rate constant of 1.4 × 10^-4 min^-1, activation energy of 63.604 kJ mol^-1 and pre-exponential factors of 66.66 × 10⁴ s^-1. The physiochemical properties of the oil were determined from which it was identified that C. tabularis oil has high free fatty acid (FFA) content, requiring a single-step esterification cum transesterification reaction to produce biodiesel economically. The modified aryl diazonium salt reduction process was used to synthesize a heterogeneous acid catalyst (HAC) from activated carbon precursor and was used to catalyze biodiesel reaction. Furthermore, HAC was characterized by different analytical techniques and it was found that it had an acid site density of 1.02 mmol g^-1 and a specific surface area of 602 m² g^-1. The parameters affecting the biodiesel process were studied to obtain a maximum biodiesel conversion of 98.5% at 6 wt% catalyst loading, 15:1 methanol to oil molar ratio, 120 min reaction time, 70 ºC reaction temperature, and 500 rpm stirring rate. Reusability studies were performed which showed that HAC can be recycled up to five cycles with a conversion above 90% in the fifth cycle. Moreover, the fuel properties of biodiesel were determined using standard methods and were compared with ASTM D6751 and EN14241 standards.

Lipozyme® TL IM Biocatalyst for Castor Oil FAME and Triacetin Production by Interesterification: Activity, Stability, and Kinetics

Global climate change and present geopolitical tensions call for novel, renewable, and, ideally, sustainable resources and processes that, in the end, will be integrated in the natural cycles of carbon and water, progressively replacing non-renewable feedstocks. In this context, the production of biofuels and, in consequence, of biodiesel plays a notable role. This work is focused on the production of fatty acid methyl esters (FAME) from castor oil, an abundant non-edible oil, using a sustainable technology approach based on industrial lipases and methyl acetate as a methylating reagent to reduce biocatalyst inactivation. We have selected a stable industrial enzyme preparation to determine its suitability for FAME production: Lipozyme® TL IM (an inexpensive lipase from Thermomyces lanuginosus immobilized by agglomeration in silica gel). Several operational variables affecting the enzyme activity have been studied: methanol excess (6:1 to 13:1), temperature (from 40 to 60 °C), and enzyme concentration (10 and 30% w/w). At all temperatures and reagent ratios, we have also tested the enzyme stability for six cycles, showing its low to negligible inactivation under operational conditions. Finally, a novel multivariable kinetic model has been proposed and fitted to experimental data obtained in a wide experimental range for the first time, showing that direct and reverse in-series reactions are present. We have estimated the values of the kinetic constants and their standard errors, and goodness-of-fit parameters, observing that the kinetic model fitted very reasonably to all retrieved experimental data at the same time.

KNO3-Loaded Coffee Husk Ash as a Heterogeneous Alkali Catalyst for Waste Frying Oil Valorization into Biodiesel

In this study, a heterogeneous basic catalyst was synthesized from a catalyst composite material (CCM) of coffee husk ash and char mixture (A/C) impregnated with KNO₃ and employed to transesterify crude waste frying oil (WFO). The effect of CCM calcination temperature (CCMCT) (500-700 °C) on the catalyst physicochemical properties was investigated. A differential scanning calorimeter was used to examine potential phase changes during the calcination of A/C and CCM. The catalysts from each CCMCT were characterized by X-ray diffraction (XRD), Brunauer-Emmet-Teller surface area analyzer, scanning electron microscopy (SEM), SEM with energy-dispersive X-ray diffractometer, colorimeter, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometer. The methoxy functional group FTIR peak integral value and the dynamic viscosity of the biodiesel synthesized by each catalyst were used to determine the qualitative WFO conversion. Furthermore, the quantitative WFO conversion was determined using nuclear magnetic resonance (¹H NMR) analysis. Crystallinity, elemental composition, basicity, and morphology of catalysts were highly dependent on the CCMCT. Without transesterification condition optimization (reaction temperature of 45 ± 2.5 °C, catalyst loading of 3 wt %, methanol to oil molar ratio of 12:1, and reaction time of 1 h), a higher catalytic performance (72.04% WFO conversion) was reached using a catalyst from the CCMCT of 600 °C. When using a coffee husk ash catalyst without KNO₃ impregnation (C-00-600), the WFO conversion was only 52.92%. When comparing the C-25-600 and C-00-600 catalysts, it was observed that KNO₃ impregnation had a substantial impact on the catalyst crystallinity, basicity, and morphology.

Synthesis of Ibuprofen Monoglyceride Using Novozym®435: Biocatalyst Activation and Stabilization in Multiphasic Systems

This work was focused on the enzymatic esterification of glycerol and ibuprofen at high concentrations in two triphasic systems composed of toluene+ibuprofene (apolar) and glycerol or glycerol–water (polar) liquid phases, and a solid phase with the industrial immobilized lipase B from Candida antarctica named Novozym®435 (N435) acting as the biocatalyst. Based on a preliminary study, the concentration of the enzyme was set at 30 g·L−1 and the stirring speed at 720 r.p.m to reduce external mass transfer limitations. To obtain more information on the reaction system, it was conducted at a wide range of temperatures (50 to 80 °C) and initial concentrations of ibuprofen (20–100 g·L−1, that is, 97 to 483 mM). Under these experimental conditions, the external mass transfer, according to the Mears criterion (Me = 1.47–3.33·10−4 << 0.15), was fast, presenting no limitation to the system productivity, regardless of the presence of water and from 50 to 80 °C. Considering that the enzyme is immobilized in a porous ion-exchange resin, limitations due to internal mass transfer can exist, depending on the values of the effectiveness factor (η). It varied from 0.14 to 0.23 at 50 to 80 °C and 0.32–1 mm particle diameter range in the absence of water, and in the same ranges, from 0.40 to 0.66 in the presence of 7.4% w/w water in the glycerol phase. Thus, it is evident that some limitation occurs due to mass transfer inside the pores, while the presence of water in the polar phase increases the productivity 3–4 fold. During the kinetic study, several kinetic models were proposed for both triphasic reacting systems, with and without first-order biocatalyst deactivation, and their fit to all relevant experimental data led to the observation that the best kinetic model was a reversible hyperbolic model with first-order deactivation in the anhydrous reaction system and a similar model, but without deactivation, for the system with added water at zero time. This fact is in sharp contrast to the use of N435 in a water-glycerol monophasic system, where progressive dissolution of ibuprofen in the reacting media, together with a notable enzyme deactivation, is observed.

Heterogeneous Catalyzed Biodiesel Production Using Cosolvent: A Mini Review

Biodiesel is gaining recognition as a good replacement for typical diesel owing to its renewability, sustainability, and eco-friendly nature. Transesterification is the leading route for biodiesel generation, which occurs during homogeneous/heterogeneous/enzymatic catalysis. Besides this, the usage of heterogeneous catalysts is considered more advantageous over homogeneous catalysts due to the easy catalyst recovery. Consequently, numerous heterogeneous catalysts have been synthesized from multiple sources with the intention of making the manufacturing process more efficient and cost-effective. Alongside this, numerous researchers have attempted to improve the biodiesel yield using heterogeneous catalysts by introducing cosolvents, such that phase limitation between oil and alcohol can be minimized. This short review is aimed at examining the investigations performed to date on heterogeneously catalyzed biodiesel generation in the presence of different cosolvents. It encompasses the techniques for heterogeneous catalyst synthesis, reported in the literature available for heterogeneous catalyzed biodiesel generation using cosolvents and their effects. It also suggests that the application of cosolvent in heterogeneously catalyzed three-phase systems substantially reduces the mass transfer limitation between alcohol and oil phases, which leads to enhancements in biodiesel yield along with reductions in values of optimized parameters, with catalyst weight ranges from 1 to 15 wt. %, and alcohol/oil ratio ranges from 5.5 to 20. The reaction time for getting the maximum conversion ranges from 10 to 600 min in the presence of different cosolvents. Alongside this, most of the time, the biodiesel yield remained above 90% in the presence of cosolvents.

Use of heterogeneous catalysis in sustainable biofuel production

Biofuel is a sustainable energy source that may use to replace fossil-based carbon dioxide and mitigate the adverse effects of exhaust emissions. Nowadays, we need to replace petroleum fuels with alternatives from environmentally sustainable sources of increasing importance. Biofuels derived from biomass have gained considerable attention, and thus most of the traditional methods that harm the environment and humans have retreated. Developing an active and stable heterogeneous catalyst is a step of utmost importance in the renewable liquid fuel technology. Thus, there is a great interest in developing methods for producing liquid fuels from non-edible sources. It may also be from dry plant tissues such as agricultural waste. Lignocellulosic biomass can be a sustainable source for producing renewable fuels and chemicals, as well as the replacement of petroleum products. Hence, the researchers aspired to synthesize new catalysts using a cheap technology developed to hydrolyze cellulose and then produce bioethanol without needing expensive enzymes, which may ultimately lead to a lower fuel price. In this paper, we will focus on the recent technologies used to produce sustainable biofuels through inexpensive incentives and innocuous to the environment.

Conversion of Plastic Waste into Supports for Nanostructured Heterogeneous Catalysts: Application in Environmental Remediation

Plastics are ubiquitous in our society and are used in many industries, such as packaging, electronics, the automotive industry, and medical and health sectors, and plastic waste is among the types of waste of higher environmental concern. The increase in the amount of plastic waste produced daily has increased environmental problems, such as pollution by micro-plastics, contamination of the food chain, biodiversity degradation and economic losses. The selective and efficient conversion of plastic waste for applications in environmental remediation, such as by obtaining composites, is a strategy of the scientific community for the recovery of plastic waste. The development of polymeric supports for efficient, sustainable, and low-cost heterogeneous catalysts for the treatment of organic/inorganic contaminants is highly desirable yet still a great challenge; this will be the main focus of this work. Common commercial polymers, like polystyrene, polypropylene, polyethylene therephthalate, polyethylene and polyvinyl chloride, are addressed herein, as are their main physicochemical properties, such as molecular mass, degree of crystallinity and others. Additionally, we discuss the environmental and health risks of plastic debris and the main recycling technologies as well as their issues and environmental impact. The use of nanomaterials raises concerns about toxicity and reinforces the need to apply supports; this means that the recycling of plastics in this way may tackle two issues. Finally, we dissert about the advances in turning plastic waste into support for nanocatalysts for environmental remediation, mainly metal and metal oxide nanoparticles.