Heteropoly acids as supported solid acid catalysts for sustainable biodiesel production using vegetable oils: A Review

Sustainable Production of Biofuels from Biomass Feedstocks Using Modified Montmorillonite Catalysts

The rampant exploitation of fossil fuels has led to the significant energy scarcity and environmental disruption, affecting the sound momentum of development and progress of human civilization. To build a closed-loop anthropogenic carbon cycle, development of biofuels employing sustainable biomass feedstocks stands at the forefront of advancing carbon neutrality, yet its widespread adoption is mainly hampered by the high production costs. Montmorillonite, however, has garnered considerable attention serving as an efficient heterogeneous catalyst of ideal economic feasibility for biofuel production, primarily due to its affordability, accessibility, stability, and excellent plasticity. Up to now, nevertheless, it has merely received finite concerns and interests in production of various biofuels using montmorillonite-based catalysts. There is no timely and comprehensive review that addresses this latest relevant progress. This review fills the gap by providing a systematically review and summary in controllable synthesis, performance enhancement, and applications related to different kinds of biofuels including biodiesel, biohydrogenated diesel, levulinate, γ-valerolactone, 5-ethoxymethylfurfural, gaseous biofuels (CO, H2), and cycloalkane, by using montmorillonite catalysts and its modified forms. Particularly, this review critically depicts the design strategies for montmorillonite, illustrates the relevant reaction mechanisms, and assesses their economic viability, realizing sustainable biofuels production via efficient biomass valorization. Overall, this may offer valuable insights into cost-effective biofuel production and proposes strategic recommendations for advancement of montmorillonite applications and future biofuel development.

Enhanced electrolytic production of hypochlorous acid using phosphorus-modified carbon felt electrodes: A study in disinfectant synthesis

In this study, we fabricated phosphorus-modified carbon felt electrode anodes for chloride oxidation in saline solutions to produce HClO via electrocatalysis, forming a compound fungicide saline applicable for debridement and disinfection. A low-cost phosphorus-modified carbon felt electrode (P@CF) with high chlorine evolution reaction activity was synthesized to address the reduced efficiency of CER and the solution's pH increase. Heteroatoms P and O were introduced into the carbon felt by phosphoric acid activation followed by heat treatment. The maximum active chlorine concentration on the P@CF electrode could reach 616.8 mg/L in 60 min under the optimal synthesis conditions of a phosphoric acid mass fraction of 30%, a phosphoric acid impregnation time of 3 h, and a heat treatment temperature of 300 °C. The active chlorine concentration was 1.8 times higher on the P@CF electrode compared to the original carbon felt electrode. The optimal reaction conditions for the generation of active chlorine were as follows: salt concentration of 9 g/L, voltage of 7 V, and electrode spacing of 2 cm as verified by response surfaces. This electrolysis reaction follows one-stage reaction kinetics. Subsequently, the disinfection efficacy of the produced disinfectants was examined. The prepared disinfectant was also compared to a commercially available hypochlorite disinfectant, showing similar disinfection effects on E. coli for both.

Biomass as an alternative feedstock to oleochemicals

The huge demands for petrochemicals have led to a rapid increase in the production of these fossil-based derivatives. Biomass represents a promising feedstock for addressing the challenges related to petrochemicals in terms of the necessity to apply renewable sources and the need to decrease carbon emissions. Among the natural biomass products, most studies have attempted to upgrade natural oils owing to their promising advantages of worldwide availability, low-cost processing, and built-in functionality. This paper discusses the upgradation of natural oils to the most beneficial oleochemicals, including fatty acids, fatty alcohols, and fatty acid methyl esters. This review also covers the utility, physico-chemical properties, and the production processes for such materials. The interconnected reaction routes to produce oleochemicals and the affecting parameters (catalyst design, temperature, and pressure) are also elucidated. Furthermore, this article discusses the future perspective of oleochemicals based on their development in recent years.

Biodiesel production from sewage sludge using supported heteropolyacid as heterogeneous acid catalyst

Phosphotungstic acid (HPW) and silicotungstic acid (HSiW) were tested as homogeneous and as heterogeneous catalysts (after immobilized on different supports as high surface area graphite -HSAG500-, montmorillonite -MMT- and alumina -Al2O3-) for the in situ transesterification of sewage sludge lipids. Both catalysts exhibited similar performance in homogeneous phase, with slightly higher biodiesel yield for HPW. When the different supports were tested with HPW, the maximum yield obtained follow the trend: MMT > HSAG500 > Al2O3, but a greater leaching of the heteropolyacid (HPA) was observed with MMT. Therefore, HSAG500 showed the best results with a good FAMEs profile. The percentage of active phase was optimized from 1 to 40%, reaching the optimum at 10%. A more heterogeneous surface is obtained with larger quantities, also favouring the HPA leaching. The reaction temperature and the use of sonication as pre-treatment were also optimized. The best results were obtained after sonication with HPW-HSAG500 (10%) as catalyst, catalyst/sludge ratio 1:2, MeOH/sludge ratio 33:1, 120 °C and 21 h of reaction time with a maximum biodiesel yield of 31.1 % (FAMEs/lipids). In view of the results obtained HPW supports on HSAG500 offers a novel alternative as heterogeneous acid catalyst for in situ transesterification using sewage sludge as raw material.

RSM and ANN methodologies in modeling the enhanced biodiesel production using novel protic ionic liquid anchored on g-C3N4@Fe3O4 nanohybrid

Herin, a new nanohybrid acid catalyst was fabricated for the efficient biodiesel production. At the first, magnetic porous nanosheets of graphitic carbon nitride (g-C3N4@Fe3O4) was prepared and then functionalized with sulfonic acid. Next, the preparation of the catalyst was completed by mixing this surface modified support with n-methyl imidazolium butyl sulfonate zwitterion to achieve non-covalent immobilized acidic ionic liquid on g-C3N4@Fe3O4 support. The catalyst underwent characterization through various techniques such as 1H and 13C NMR, FTIR, SEM, TEM, TGA, EDX and BET which revealing that the magnetic support loaded acidic ionic liquids via a robust charge interaction effect enabling the one-pot production of biodiesel from low-quality oils. Furthermore, the catalyst could be simply recovered using a permanent magnet and reused multiple times without a significant decline in catalytic activity. Consequently, the solid catalyst based on ionic liquids holds promise for the sustainable and eco-friendly production of biodiesel from low-quality oils. Furthermore, Response Surface Methodology (RSM) and Artificial Neural Networks (ANN) were used to model the yield and various process parameters. The findings underscore the enhanced predictive capabilities of ANN in comparison to RSM.

Recent Progress on Functionalized Nanoporous Heteropoly Acids: From Synthesis to Applications

Functionalized nanoporous heteropoly acids (HPAs) have garnered significant attention in recent years due to their enhanced surface area and porosity, as well as their potential for low-cost regeneration compared to bulk materials. This review aims to provide an overview of the recent advancements in the synthesis and applications of functionalized HPAs. We begin by introducing the fundamental properties of HPAs and their unique structure, followed by a comprehensive overview of the various approaches employed for the synthesis of functionalized HPAs, including salts, anchoring onto supports, and implementing mesoporous silica sieves. The potential applications of functionalized HPAs in various fields are also discussed, highlighting their boosted performance in a wide range of applications. Finally, we address the current challenges and present future prospects in the development of functionalized HPAs, particularly in the context of mesoporous HPAs. This review aims to provide a comprehensive summary of the recent progress in the field, highlighting the significant advancements made in the synthesis and applications of functionalized HPAs.

Dual Regulation of Charge Separation and the Oxygen Reduction Pathway by Encapsulating Phosphotungstic Acid into the Cationic Covalent Organic Framework for Efficient Photocatalytic Hydrogen Peroxide Production

Previous research on covalent organic framework (COF)-based photocatalytic H2O2 synthesis from oxygen reduction focuses more on charge carrier separation but less on the electron utilization efficiency of O2. Herein, we put forward a facile approach to simultaneously promote charge separation and tailor the oxygen reduction pathway by introducing phosphotungstic acid (PTA) into the cationic COF skeleton. Experiments verified that PTA, as an electron transport medium, establishes a fast electron transfer channel from the COF semiconductor conductor band to the substrate O2; meanwhile, the reaction path is optimized by its catalytic cycle for preferable dioxygen capture and reduction in oxygen reduction reaction (ORR) kinetics. The existence of PTA promotes the rate and tendency of converting O2 into •O2- intermediates, which is conducive to boosting the photocatalytic activity and selectivity toward the sequential two-step single-electron ORR. As expected, compared to the pristine TTB-EB, the optimal PTA0.5@TTB-EB achieves a 2.2-fold improvement of visible-light-driven photocatalytic performance with a H2O2 production rate of 897.94 μmol·L-1·h-1 in pure water without using any sacrificial agents. In addition, owing to the robust electrostatic interaction and the confinement effect of porous TTB-EB channels, the PTA@TTB-EB composite possessed favorable stability.

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.

Insights into Preparation Methods and Functions of Carbon-Based Solid Acids

With the growing emphasis on green chemistry and the ecological environment, researchers are increasingly paying attention to greening materials through the use of carbon-based solid acids. The diverse characteristics of carbon-based solid acids can be produced through different preparation conditions and modification methods. This paper presents a comprehensive summary of the current research progress on carbon-based solid acids, encompassing common carbonization methods, such as one-step, two-step, hydrothermal, and template methods. The composition of carbon source material may be the main factor affecting its carbonization method and carbonization temperature. Additionally, acidification types including sulfonating agent, phosphoric acid, heteropoly acid, and nitric acid are explored. Furthermore, the functions of carbon-based solid acids in esterification, hydrolysis, condensation, and alkylation are thoroughly analyzed. This study concludes by addressing the existing drawbacks and outlining potential future development prospects for carbon-based solid acids in the context of their important role in sustainable chemistry and environmental preservation.

Low-cost diatomite supported binary transition metal sulfates: an efficient reusable solid catalyst for biodiesel synthesis

Using a simple method of impregnation and then calcination, diatomite supported binary transition metal sulfates (Fe and Zr, designated as Fe2(SO4)3&Zr(SO4)2@diatomite) were prepared and used as a catalyst in the preparation of renewable biofuels. The synthesised Fe2(SO4)3&Zr(SO4)2@diatomite catalyst (Fe2(SO4)3 : Zr(SO4)2 : diatomite = 1 : 2 : 6, mass ratio) was thoroughly characterised using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, microbeam X-ray fluorescence (μ-XRF) spectroscopy and thermogravimetric analysis (TG). The results demonstrated that the sulfate was successfully loaded onto the diatomite with a uniform distribution. The N2 adsorption/desorption analysis indicated that the catalyst's specific surface area was 1.54 m2 g-1. The catalyst exhibited outstanding performance in the preparation of renewable biofuel (biodiesel) from waste fatty acids and the optimal parameters were methanol-to-oil 1.25 : 1, reaction temperature 70 °C, catalyst concentration 10 wt%, reaction time 4 h. The conversion was found to reach 98.90% under optimal parameters, which is better than that of Fe2(SO4)3·xH2O, Zr(SO4)2·4H2O, Fe2(SO4)3@diatomite and Zr(SO4)2@diatomite. Moreover, the catalyst can be recycled by simple filtration and reused for three cycles after regeneration without noticeable reduction in catalytic activity.

Application of Tubular Reactor Technologies for the Acceleration of Biodiesel Production

The need to arrest the continued environmental contamination and degradation associated with the consumption of fossil-based fuels has continued to serve as an impetus for the increased utilization of renewable fuels. The demand for biodiesel has continued to escalate in the past few decades due to urbanization, industrialization, and stringent government policies in favor of renewable fuels for diverse applications. One of the strategies for ensuring the intensification, commercialization, and increased utilization of biodiesel is the adaptation of reactor technologies, especially tubular reactors. The current study reviewed the deployment of different types and configurations of tubular reactors for the acceleration of biodiesel production. The feedstocks, catalysts, conversion techniques, and modes of biodiesel conversion by reactor technologies are highlighted. The peculiarities, applications, merits, drawbacks, and instances of biodiesel synthesis through a packed bed, fluidized bed, trickle bed, oscillatory flow, and micro-channel tubular reactor technologies are discussed to facilitate a better comprehension of the mechanisms behind the technology. Indeed, the deployment of the transesterification technique in tubular reactor technologies will ensure the ecofriendly, low-cost, and large-scale production of biodiesel, a high product yield, and will generate high-quality biodiesel. The outcome of this study will enrich scholarship and stimulate a renewed interest in the application of tubular reactors for large-scale biodiesel production among biodiesel refiners and other stakeholders. Going forward, the use of innovative technologies such as robotics, machine learning, smart metering, artificial intelligent, and other modeling tools should be deployed to monitor reactor technologies for biodiesel production.

Preparation of Activated Carbon-Based Solid Sulfonic Acid and Its Catalytic Performance in Biodiesel Preparation

With activated carbon as raw material, AC-Ph-SO₃H was prepared after oxidation with nitric acid, modification with halogenated benzene and sulfonation with concentrated sulfuric acid. After modified by 10% bromobenzene with toluene as a solvent for 5 h, followed sulfonation with concentrated sulfuric acid at 150°C, the -SO₃H content of prepared AC-Ph-SO₃H was 0.64 mmol/g. Acid content test, infrared spectroscopy and Raman spectroscopy detection proved that the surface of AC-Ph-SO₃H was successfully grafted with -SO₃H group. When used as a catalyst for the methylation of palmitate acid, the catalytic performance of AC-Ph-SO₃H was explored. When the reaction time was 6 h, the amount of catalyst acid accounted for 2.5 wt% of palmitic acid, and the molar ratio of methanol/palmitic acid was 40, the esterification rate of palmitic acid was 95.2% and the yield of methyl palmitate was 94.2%, which was much better than those of its precursors AC, AC-O, and AC-Ph (both about 4.5%). AC-Ph-SO₃H exhibited certain stability in the esterification reaction system and the conversion rate of palmitic acid was still above 80% after three reuses.

Comparative Catalytic Performance Study of 12-Tungstophosphoric Heteropoly Acid Supported on Mesoporous Supports for Biodiesel Production from Unrefined Green Seed Canola Oil

In this study, three solid acid catalysts, namely mesoporous aluminophosphate-supported 12-tungstophosphoric heteropoly acid (HPW/MAP), mesoporous aluminosilicate-supported 12-tungstophosphoric heteropoly acid (HPW/MAS), and gamma alumina-supported 12-tungstophosphoric heteropoly acid (HPW/γ-Al2O3) were prepared and characterized. Mesoporous aluminophosphate (MAP) and mesoporous aluminosilicate (MAS) were synthesized via sol-gel and hydrothermal methods, respectively, and 25 wt.% of 12-tungstophosphoric heteropoly acid (HPW) was immobilized on the support materials using the wet impregnation method. The features of the fabricated catalysts were comprehensively investigated using various techniques such as BET, XRD, NH3-TPD, TGA, and TEM. The surface area of the supported catalysts decreased after HPW impregnation according to BET results, which indicates that HPW loaded on the supports and inside of their pores successfully. The density and strengths of the acid sites of the support materials and the catalysts before reaction and after regeneration were determined by the NH3-TPD technique. Accordingly, an increase in acidity was observed after HPW immobilization on all the support materials. The catalytic performance of the catalysts was studied through alcoholysis reaction using unrefined green seed canola oil as the feedstock. The maximum biodiesel yield of 82.3% was obtained using 3 wt.% of HPW/MAS, with a methanol to oil molar ratio of 20:1, at 200 °C and 4 MPa over 7 h. The reusability study of HPW/MAS showed that it can maintain 80% of its initial activity after five runs.

Biodiesel production from candlenut oil using a non-catalytic supercritical methanol transesterification process: optimization, kinetics, and thermodynamic studies

The present study was conducted to determine the feasibility of biodiesel production from candlenut oil using supercritical methanol (scMeOH) as a non-catalytic transesterification process. The influence of the scMeOH transesterification process was determined with varying pressure (85-145 bar), temperature (260-300 °C), methanol to oil (M : O) ratio (15 : 1-35 : 1), and reaction time (15-25 min). The experimental conditions of the scMeOH transesterification process were designed using central composite design (CCD) of experiments, and the process was optimized using response surface methodology (RSM). It was found that scMeOH temperature, pressure, M : O ratio, and reaction time substantially influenced the transesterification process. The maximum biodiesel yield of 96.35% was obtained at an optimized scMeOH transesterification process at the pressure of 115 bar, the temperature of 285 °C, M : O ratio of 30 : 1, and reaction time of 22 min. A second-order kinetics model and Eyring equations were utilized to determine the kinetics and thermodynamics of biodiesel production from candlenut oil. The activation energy value was determined to be 28.35 KJ mol-1. Analyses of the thermodynamic properties of biodiesel revealed that the transesterification process was non-spontaneous and endothermic. The physicochemical properties of produced candlenut biodiesel via scMeOH complied with most of the biodiesel properties as per ASTM D6751 and EN14214, thereby referring to good quality biodiesel production. The findings of the present study reveal that the scMeOH is an effective non-catalytic transesterification process for biodiesel production from candlenut oil.