Cyclic acetals as next-generation oxygenated diesel additives from lignocellulosic biomass and plastic waste

1 Introduction

Climate change is one of the most pressing global challenges, affecting both developed and developing countries and intensifying at an unprecedented rate. The transportation sector is a major contributor to global emissions, accounting for approximately 26% of total greenhouse gas (GHG) emissions in 2018, while remaining highly dependent on petroleum-based fuels (IEA)(Kumar R. et al., 2024). This sector remains heavily dependent on fossil fuels, being almost entirely petroleum-based (Manfroni et al., 2021). The combustion of fuels such as gasoline and diesel releases large quantities of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), significantly contributing to global warming (Raheem et al., 2025). In addition, fossil fuel combustion leads to environmental problems such as smog formation and acid rain, which degrade air quality and negatively impact aquatic ecosystems, wildlife, and vegetation (Perera, 2017). These trends are reflected in atmospheric CO₂ concentrations, now exceeding 50% above pre-industrial levels. Global CO₂ emissions have continued their upward trajectory, reaching a new record of 36.3 Gt in 2024 (+0.9% compared to 2023), underscoring the urgent need for effective mitigation strategies (Deng et al., 2025; Rosen et al., 2025).

Among the potential solutions, biofuels compatible with existing fuel systems are expected to play an important role in reducing emissions in transportation sectors that are difficult to electrify, such as heavy-duty road transport, marine shipping, and aviation (Rosales Calderon et al., 2024). In this context, “renewable diesel” has attracted significant attention in recent years. Renewable diesel refers to diesel-range hydrocarbons produced from renewable feedstocks such as vegetable oils and animal fats. Unlike conventional biodiesel, which consists of fatty acid methyl esters (FAME) containing oxygenated functional groups, renewable diesel is composed of fully deoxygenated hydrocarbons that are chemically similar to petroleum-derived diesel. As a result, it can be used as a drop-in fuel in existing diesel engines and infrastructure without blending limitations (Estevez et al., 2024).

Beyond simply replacing fossil-derived feedstocks with renewable resources, current research increasingly focuses on designing synthetic fuels with tailored molecular structures to improve combustion efficiency and reduce pollutant emissions. Oxygenated fuels are particularly attractive because the presence of oxygen atoms in their molecular structure enhances oxygen availability during combustion, leading to more complete oxidation of fuel molecules. This effect helps reduce soot formation and allows higher exhaust gas recirculation (EGR) rates, which can effectively lower nitrogen oxide (NO_x) emissions without increasing particulate matter. However, many oxygenated fuel candidates—such as oxymethylene ether (OME₁), which has a boiling point of only 42 °C—exhibit high vapor pressures and low boiling points, limiting their practical application primarily to blending with conventional fossil fuels (Deutz et al., 2018).

Recent research has therefore explored alternative oxygenated molecules with improved physicochemical properties. One promising approach involves the development of bio-hybrid fuels that integrate carbon from multiple sustainable sources, including biomass, captured CO₂, and recycled carbon streams (Chen et al., 2025). By combining CO₂ utilization with biomass-derived intermediates and green hydrogen produced from renewable electricity, it is possible to generate synthetic fuels with significantly reduced lifecycle carbon emissions. This concept highlights the potential role of bio-hybrid fuels alongside conventional biofuels, renewable electricity and electrofuel (e-fuel) in the future sustainable energy landscape (Figure 1). In this context, cyclic acetals have emerged as promising oxygenated fuel candidates due to their favorable fuel properties, molecular stability, and compatibility with existing fuel infrastructure (Shen et al., 2023).

Recent review articles have summarized the acetalization strategy in biomass valorization, focusing primarily on catalytic systems, reaction mechanisms, and the role of acetalization in improving product selectivity (He et al., 2024). However, these studies mainly emphasize reaction chemistry, while a systematic integration of synthesis strategies with the structural features of cyclic acetals and their potential as transportation fuels remains limited. In particular, the relationship between molecular structure and fuel-related performance has not been comprehensively discussed.

Therefore, this review aims to bridge this gap by providing a comprehensive and integrated perspective on cyclic acetals, linking their synthesis, structure, and potential application as next-generation low-carbon fuels.

2 Production of cyclic acetals

Owing to their unique physicochemical properties, cyclic acetals have found applications across several industrial sectors. Traditionally, they have been widely used as protecting groups in organic synthesis, solvents and additives in fine chemicals, fragrance and flavor intermediates, and stabilizers in polymer processing (Falco et al., 2008; Iovinella et al., 2023; Mazahar et al., 2023). More recently, cyclic acetals have attracted increasing attention as oxygenated fuel components and fuel additives because of their favorable combustion characteristics, including relatively high cetane numbers, excellent cold-flow properties, and the ability to promote cleaner combustion (Zahid et al., 2020; Xu et al., 2022). These attributes make cyclic acetals promising candidates for next-generation sustainable fuels compatible with existing diesel and aviation fuel infrastructure.

Cyclic acetals are typically synthesized through the acid-catalyzed condensation of carbonyl compounds (aldehydes or ketones) with diols, forming stable five- or six-membered ring structures known as 1,3-dioxolanes (typically kinetically favoured) and 1,3-dioxanes (thermodynamically more stable) (Vazhenin et al., 2025). The reaction proceeds via nucleophilic addition of the diol to the carbonyl group, followed by intramolecular cyclization and the removal of water. This transformation can be catalyzed by homogeneous acids, such as sulfuric acid or p-toluenesulfonic acid, as well as heterogeneous solid acids, including ion-exchange resins, zeolites, and metal oxides (Qiu et al., 2014; Beydoun and Klankermayer, 2019; Yamada et al., 2020). In recent years, alternative synthetic routes have been explored to enhance sustainability and scalability. These include the use of biomass-derived intermediates such as glycerol or furfural, catalytic conversion of CO₂ with hydrogen, and C₁ building blocks derived from chemical recycling of plastic waste (Zhang X. et al., 2025). The acetalization of glycerol with furfural highlights several key factors governing cyclic acetal formation. In particular, the synergistic combination of Brønsted and Lewis acid sites plays a crucial role in activating the carbonyl group and promoting dehydration and cyclization steps. Moreover, catalyst structural properties, especially mesoporosity (∼10 nm), significantly influence product selectivity (∼82%) by facilitating the formation of bulkier six-membered cyclic acetals (Kumar S. et al., 2024). Such developments support the integration of cyclic acetal production into emerging bio-hybrid and circular carbon utilization strategies. In addition to conventional liquid-phase acetalization, recent studies have demonstrated the feasibility of integrating lignocellulosic biomass and biodiesel byproducts into circular synthesis routes. For example, lignin-derived solid acid catalysts have been employed to convert benzaldehyde and glycerol into cyclic acetals, enabling a waste-to-chemicals approach that improves carbon atom economy (Zhang C. et al., 2025).

The main synthesis pathways differ primarily in the C₁ source used for cyclic acetal formation (Figure 2). The conventional industrial route (Route 1) employs formaldehyde in the presence of sulfuric acid as a catalyst (Li et al., 2024). However, the use of formaldehyde presents significant health and safety concerns. A more sustainable alternative (Route 2) utilizes CO₂ in combination with green hydrogen. Finally, Route 3 employs polyoxymethylene (POM) plastic waste as the C₁ feedstock, using Bi(OTf)₃ as a Lewis acid catalyst (Beydoun et al., 2020). Mechanistically, Bi(OTf)₃ coordinates to the oxygen of POM, promoting Lewis acid-catalyzed depolymerization to release formaldehyde equivalents via sequential unzipping. These formaldehyde monomers then undergo nucleophilic attack by the diol (e.g., 1,3-propanediol), forming a hemiacetal intermediate, followed by intramolecular cyclization and dehydration to yield the 1,3-dioxane product. This pathway provides chemical recycling of plastic waste into value-added cyclic acetals.

The main synthesis pathways differ primarily in the C₁ source used for cyclic acetal formation (Figure 2). The conventional industrial route (Route 1) employs formaldehyde in the presence of sulfuric acid as a catalyst (Li et al., 2019). However, the use of formaldehyde presents significant health and safety concerns because it is a volatile and flammable compound that can cause irritation to the skin, eyes, and respiratory tract and is classified as a human carcinogen. Consequently, strict safety measures, including adequate ventilation and appropriate personal protective equipment, are required during handling (Machireddy and He, 2024). A more sustainable alternative (Route 2) utilizes CO₂ in combination with green hydrogen, typically requiring hydrogenation catalysts, such as [Ru (triphos)(tmm)] or Co(BF₄)₂/triphos, together with a Lewis acid co-catalyst. This approach represents a promising carbon capture and utilization (CCU) strategy. Finally, Route 3 employs polyoxymethylene (POM) plastic waste as the C₁ feedstock, using Bi(OTf)₃ as a Lewis acid catalyst, thereby providing a pathway for the chemical recycling of plastic waste into value-added cyclic acetals. Collectively, these routes demonstrate the versatility of C₁ sources—from conventional formaldehyde to CO₂ and recycled plastics—for the sustainable production of cyclic acetals (Beydoun et al., 2020).

Building on the foundation of conventional and CO₂-based acetalization processes, recent developments have increasingly focused on the use of renewable feedstocks, particularly lignocellulosic biomass, for the production of key intermediates (Delidovich et al., 2016). By replacing petrochemical-derived formaldehyde with bio-based aldehydes or other renewable intermediates, more sustainable pathways for cyclic acetal synthesis can be established. Such strategies reduce dependence on fossil-derived chemicals while enabling the integration of biomass valorization into advanced fuel and chemical production systems. In addition, the use of renewable carbon sources aligns closely with the principles of green chemistry by promoting the efficient synthesis of high-value chemicals and fuels while minimizing hazardous reagents, toxic byproducts, and overall carbon emissions. Consequently, the incorporation of lignocellulosic biomass-derived intermediates represents a promising direction for developing environmentally friendly and scalable production routes for cyclic acetals.

2.1 Using lignocellulose biomass as a substrate

A wide range of lignocellulosic biomass resources—including agricultural residues such as oat hulls, corn cobs, sugarcane bagasse, and cereal or rice straw—have been extensively investigated as renewable feedstocks for the production of furfural, an important platform chemical (Edumujeze et al., 2025). These biomass sources are particularly attractive due to their abundance, low cost, and underutilization, offering opportunities to convert agricultural waste streams into value-added chemicals. Furfural is typically produced through the selective dehydration of pentose sugars derived from the hemicellulose fraction of lignocellulosic biomass under acidic conditions. Once generated, furfural can undergo further chemical transformations, most notably acetalization reactions with diols such as ethylene glycol to form cyclic acetals. When both furfural and the diol are derived from renewable biomass resources, the resulting acetalization pathway represents a fully bio-based and carbon-conscious synthetic route (He et al., 2024).

Conventional acetalization reactions generally require acid catalysts, which may lead to equipment corrosion and environmental concerns. To address these limitations, recent studies have explored catalyst-free approaches for cyclic acetal synthesis. In one example, the catalyst-free acetalization of furfural with ethylene glycol (Figure 3) was systematically investigated as a simple and efficient method for producing oxygenated acetal fuel additives (Bai et al., 2023a). Under optimized conditions—a furfural-to-ethylene glycol molar ratio of 1:15 in cyclohexane at 160 °C for 2 h—a high molar yield of 78.6% of 2-(furan-2-yl)-1,3-dioxolane (FD), a cyclic acetal, based on furfural, was obtained. Kinetic analysis revealed a relatively low activation energy (15.8 kJ mol^-1), indicating favorable reaction kinetics (Bai et al., 2023a). Thermodynamic analysis further suggested that the reaction is endothermic and endergonic under the studied conditions. A plausible mechanism involving two parallel pathways was proposed, in which water generated during the acetalization step may facilitate the reaction by promoting hydrolysis of ethylene glycol intermediates. Importantly, this protocol was also effective for a variety of biobased aldehydes and alcohols, enabling the synthesis of diverse oxygenated fuel additives. Furthermore, the reaction was successfully scaled up, producing FD with a molar yield of 60.2%, thereby demonstrating its potential for larger-scale applications (Bai et al., 2023a). The preferential formation of 1,3-dioxolane derivatives in this system can be attributed to the favorable kinetics and lower ring strain associated with five-membered ring structures, which often results in higher selectivity compared to six-membered dioxanes. In addition, the reversible nature of acetalization highlights the critical role of water management in driving the reaction toward product formation.

A versatile range of diesel fuel additives can be produced via the acid-catalyzed condensation of furfural, derived from lignocellulose biomass, with various diols, followed by hydrogenation (Patil et al., 2019; Bai et al., 2023b). This approach allows selective extraction of acetal intermediates and enables post-hydrogenation modifications, such as etherification or acetylation, to obtain different chemical structures (Figure 4). By varying the diol substrate, a broad spectrum of renewable fuel additives can be obtained, demonstrating the flexibility of this pathway for generating multiple high-value products from biomass-derived intermediates (Patil et al., 2019). This variation in product structure arises from differences in diol chain length and functionality, which influence ring size, steric effects, and ultimately the physicochemical and fuel properties of the resulting acetals.

In addition to lignocellulosic biomass, starch represents another promising renewable feedstock for biorefinery applications. Starch-derived carbohydrates can be converted into cyclic acetals through a sequential pathway involving glucose formation, dehydration to 5-hydroxymethylfurfural (HMF), and subsequent acetalization with diols. As a biodegradable polysaccharide composed of glucose units, starch is the second most abundant component of plant biomass after cellulose, making it an inexpensive and widely available carbon resource (Heo et al., 2019; Läufer, 2019). Structurally, starch consists of two main components: linear amylose and highly branched amylopectin. The relative proportions of these two fractions vary depending on the botanical source and strongly influence the physicochemical properties of starch, including granule structure, solubility, and chemical reactivity (Roy Goswami et al., 2015). Through appropriate processing, starch can be depolymerized into glucose using mild acidic conditions, elevated temperatures, or ionic-liquid-based systems, thereby providing a flexible feedstock for integrated catalytic and chemical conversion processes. The glucose obtained from starch hydrolysis can undergo several transformation pathways to produce valuable platform chemicals. For instance, glucose dehydration yields HMF, an important intermediate for the synthesis of furan-based chemicals and fuels (Zhang et al., 2022). Alternatively, catalytic hydrogenation converts glucose into sorbitol, a polyol widely used in food, pharmaceutical, and chemical industries. Under stronger acidic conditions, glucose can also be transformed into levulinic acid, which serves as a versatile precursor for fuels, solvents, and other value-added chemicals (Signoretto et al., 2019; Tian et al., 2021). These conversion routes highlight the chemical versatility of starch and its compatibility with modern catalytic technologies. By integrating starch-derived intermediates into hybrid production pathways, biorefineries can convert this renewable resource into a range of platform chemicals—including HMF, sorbitol, and levulinic acid—thereby supporting sustainable and scalable carbon utilization (Sriariyanun et al., 2023). Owing to its abundance, chemical versatility, and compatibility with catalytic upgrading technologies, starch continues to play a key role as a renewable raw material for the production of bio-based fuels, chemicals, and materials, contributing to the advancement of a circular bioeconomy while reducing dependence on fossil resources (Marques et al., 2018).

2.2 Biohybrid approach for cyclic acetal production

The bio-hybrid approach has emerged as a promising paradigm in sustainable chemistry, integrating biomass-derived feedstocks or intermediates obtained from plastic recycling with CO₂ as a recycled carbon source and renewable hydrogen to produce low-carbon fuels, chemicals, and solvents (Junge and Beller, 2020). In this concept, CO₂ is no longer regarded merely as a waste product but rather as a valuable carbon building block that can be combined with biobased platform molecules to construct more complex and functional molecular structures. By coupling carbon capture and utilization strategies with biomass valorization, the bio-hybrid framework enables the efficient integration of multiple non-fossil and recycled carbon streams. Recent advances in non-fossil energy technologies, particularly the production of green hydrogen from renewable electricity, further enhance the feasibility of these integrated systems. As a result, the bio-hybrid strategy closely aligns with the principles of green chemistry, emphasizing resource efficiency, waste minimization, and the use of renewable feedstocks (Anita et al., 2017). This approach provides a unified pathway for the simultaneous valorization of biomass and CO₂, supporting the development of sustainable chemical production systems and contributing to the transition toward a low-carbon circular economy (Beydoun and Klankermayer, 2019) (Figure 5).

The bio-hybrid strategy provides an integrated pathway for converting biomass-derived carbohydrates into valuable platform chemicals through a combination of biotechnological and catalytic processes. In this approach, glucose obtained from biomass is first converted into acetaldehyde using genetically engineered Saccharomyces cerevisiae (Madhavan et al., 2012). To avoid cytotoxic effects caused by acetaldehyde accumulation, the product is continuously removed during fermentation, enabling glucose conversion efficiencies of up to 37% with recovery yields of approximately 75%. The resulting acetaldehyde can then be further transformed into 3,4-butanediol through a multi-enzyme catalytic cascade carried out in a micro-aqueous reaction medium. This system enhances enzyme stability while reducing the overall water content, thereby simplifying downstream separation and improving process efficiency (Mengers et al., 2022). Similar strategies can also be applied to other aldehyde intermediates, enabling the synthesis of a broader range of higher diols as versatile chemical building blocks (Zeng and Sabra, 2011; Niaz et al., 2025). In the final stage, these diols undergo chemo-catalytic conversion with captured CO₂ and renewable hydrogen to form cyclic acetals. This transformation is typically catalyzed by a homogeneous system based on [Ru (triphos)(tmm)] in combination with a Lewis acid, which promotes the formation of cyclic dioxolane derivatives (Maeda et al., 2014; vom Stein et al., 2014). Overall, this multistep process demonstrates how biomass-derived substrates, carbon capture technologies, and green hydrogen can be integrated within a single production framework. Such a bio-hybrid route highlights the potential for transforming simple sugars into oxygenated cyclic acetals that can serve as valuable components for fuels, solvents, and other high-value chemical applications.

Recent studies have expanded the conventional acetalization chemistry of diols with formaldehyde by developing transition-metal-catalyzed systems capable of producing both cyclic and linear acetals from multiple renewable carbon sources (Beydoun and Klankermayer, 2019). In these emerging approaches, CO₂ captured from industrial emissions or the atmosphere is utilized together with molecular hydrogen generated from renewable energy and biomass-derived diols (Gu et al., 2021). This integrated strategy enables the synthesis of value-added acetal compounds in a more sustainable manner. Through careful optimization of catalyst design, reaction parameters, and the use of appropriate co-catalysts, such as a ruthenium-based catalyst, the selectivity of the reaction can be directed toward either cyclic or linear acetal products, depending on the desired application (Figure 6). Importantly, this methodology reduces dependence on fossil-derived formaldehyde while simultaneously incorporating carbon capture and renewable hydrogen into the synthetic pathway. As a result, it offers a promising framework for linking CO₂ utilization with biomass valorization in a single catalytic system. The development of such catalytic processes represents an important step toward more sustainable and scalable chemical manufacturing. In particular, these strategies provide new opportunities for producing bio-hybrid fuels, solvents, and chemical intermediates with reduced carbon footprints. Furthermore, the modular nature of the catalytic systems allows them to accommodate a wide range of diol feedstocks, including those derived from lignocellulosic sugars or industrial by-products, thereby expanding the potential scope of cyclic and linear acetal production within sustainable chemical technologies.

Beydoun and Klankermayer proposed a mechanistic pathway for the formation of 1,3-dioxane from CO₂, as illustrated in Figure 7. In the initial step, CO₂ is hydrogenated in the presence of a ruthenium catalyst to generate formic acid, which acts as a reactive C₁ intermediate. This species subsequently undergoes acid-catalyzed condensation with 1,3-propanediol to form 3-hydroxypropyl formate, thereby linking the carbonyl functionality of formic acid with the hydroxyl group of the diol. In the following step, the resulting intermediate is subjected to hydrogenative reduction, also catalyzed by the ruthenium complex, leading to the formation of a hemiacetal intermediate containing both hydroxyl and ether functionalities within the same molecule. Finally, this hemiacetal undergoes intramolecular acetalization in the presence of an acidic co-catalyst, yielding the cyclic acetal product. The resulting 1,3-dioxane derivative is a stable oxygenated compound that can serve as a potential fuel additive or as an intermediate for further chemical synthesis (Beydoun and Klankermayer, 2019).

In addition to biomass, plastic waste has recently attracted attention as an alternative carbon resource for the production of platform chemicals. Converting plastics into chemical intermediates offers a dual advantage: it generates valuable building blocks for fuels, solvents, and advanced materials while simultaneously addressing the growing global plastic waste problem by redirecting discarded plastics away from landfills and natural environments into productive chemical processes (Al-Salem et al., 2009). Among various plastic types, poly (ethylene terephthalate) (PET) represents one of the most abundant single-use polymer waste streams worldwide. Global PET consumption increased dramatically from approximately 13 million tons in 1997 to about 26 million tons in 2007, reflecting its widespread use in packaging, particularly in beverage bottles (Karayannidis and Achilias, 2007). However, PET’s high chemical stability and resistance to natural degradation make its accumulation in municipal solid waste a significant environmental concern.

Chemical recycling has therefore emerged as a promising strategy to establish a more sustainable and circular lifecycle for PET (Table 1). Through controlled depolymerization processes such as hydrolysis or glycolysis, post-consumer PET can be converted back into its original monomers—terephthalic acid (TPA) and ethylene glycol (EG)—or into value-added oligomeric intermediates (Figure 8) (Pang et al., 2016; Saad et al., 2025). Among these products, EG is particularly valuable because it functions as a diol component in acetalization reactions. After recovery and purification, EG can react with suitable carbonyl compounds—such as aldehydes derived from biomass (e.g., furfural) or C₁ intermediates generated from CO₂ hydrogenation—to form cyclic acetals, typically five-membered 1,3-dioxolane derivatives (Pan et al., 2020). This transformation generally occurs through an acid-catalyzed condensation mechanism in which the diol reacts with the carbonyl compound, followed by intramolecular cyclization and removal of water. By integrating PET depolymerization with acetalization chemistry, plastic waste can therefore be converted into value-added oxygenated molecules that are useful as fuel additives, solvents, or chemical intermediates (Cao et al., 2022). These recovered compounds can subsequently be repolymerized to produce virgin-quality PET or further upgraded into high-value materials, including unsaturated polyester resins and UV-curable methacrylated oligomers (Karayannidis et al., 2007; George and Kurian, 2014). In addition to reducing plastic waste, chemical recycling can significantly lower the environmental footprint of PET production. Life-cycle assessments indicate that such processes may reduce greenhouse gas emissions by up to 50% compared with conventional production from virgin feedstocks, and in some cases achieve reductions approaching 80%, moving toward a carbon-neutral material cycle (Babaei et al., 2024).

TABLE 1. Comparative bio-hybrid cyclic acetal synthesis routes.

3 Cyclic acetals as the missing link for carbon-neutral liquid fuels

The hydrogenated acetal products were evaluated for several key fuel properties, including miscibility with commercial diesel, cloud point, and flash point. Experimental results showed that several of these compounds exhibit excellent compatibility with diesel, even at relatively high blending ratios, highlighting their strong potential as fuel additives (Patil et al., 2019; Peng et al., 2021). In addition, certain derivatives were found to improve the cloud point of diesel, indicating that hydrogenated acetals derived from furfural and diols can function as versatile bio-based blending components for diesel fuels (Patil et al., 2019). The measured and predicted octane numbers further demonstrate the promising performance of these compounds. All furfural derivatives, such as ethyl furfuryl ether, propyl furfuryl ether, and furfural diethyl acetal, evaluated exhibit octane numbers above 100, with an average value of approximately 107 and a mean absolute deviation of 7 (Tarazanov et al., 2018). These results suggest that furfural-derived mono- and di-ethers are highly effective oxygenated additives for improving fuel octane performance.

From a process perspective, however, the use of furfural acetals presents additional advantages compared with ether-based compounds. In particular, acetal synthesis can avoid the additional hydrogenation step required for ether formation, thereby simplifying the production pathway and reducing energy consumption and operational complexity. Consequently, the one-step synthesis route to furfural-derived cyclic acetals, such as furfural dipropyl acetal (FDPA), offers a more practical and economically attractive alternative for large-scale production (Tarazanov et al., 2018). Furthermore, cyclic acetals have recently been recognized as a potential missing link in the development of carbon-neutral liquid fuels. Their molecular structure combines the benefits of oxygenated functionality with physicochemical properties that remain compatible with existing diesel and aviation fuel infrastructure. Moreover, cyclic acetals can be synthesized from multiple renewable and recycled carbon sources, including biomass-derived aldehydes, captured CO₂, and recycled plastics, enabling the integration of diverse carbon streams within a unified fuel production framework. This unique versatility positions cyclic acetals as promising intermediates that bridge bio-based feedstocks, carbon capture technologies, and sustainable fuel design, contributing to the development of scalable low-carbon fuel systems for the transportation sector.

Cyclic acetals exhibit several advantageous properties that make them attractive candidates for diesel fuel applications. Their relatively high oxygen content can promote cleaner combustion and contribute to reduced soot formation, while their good miscibility with conventional diesel allows blending without phase separation (Smirnov et al., 2018; He et al., 2024). The cleaner combustion behavior of cyclic acetals can be attributed to several synergistic effects related to their molecular structure. The presence of fuel-bound oxygen shifts reaction pathways toward the formation of CO rather than soot precursors such as acetylene (C₂H₂), thereby suppressing soot nucleation. At the same time, oxygenated functionalities promote the formation of reactive species such as OH radicals, which enhance the oxidation of any soot formed during combustion. In addition, the absence or reduced presence of C–C bonds in certain acetal structures limits the growth of hydrocarbon chains necessary for soot formation. Furthermore, their favorable volatility and physicochemical properties improve fuel–air mixing, increasing the fraction of premixed combustion and reducing locally fuel-rich zones where soot typically forms (Härtl et al., 2015). In addition, the presence of polar functional groups may enhance fuel lubricity, an important property for ultra-low-sulfur diesel fuels that typically suffer from reduced natural lubricating capacity (Sudarsanam et al., 2013; Sisodiya et al., 2026). From a production perspective, cyclic acetals can also offer process advantages, as their synthesis may avoid additional hydrogenation steps required in some alternative oxygenated fuel pathways, potentially simplifying production and reducing associated costs. Furthermore, their favorable thermal stability contributes to reliable storage performance and compatibility with existing diesel fuel systems. Beyond their potential as bio-hybrid fuel components, cyclic acetals also possess significant structural versatility, enabling a broader range of applications. Recent studies have explored their use as environmentally friendly bio-based solvents (Moity et al., 2015), as well as monomeric building blocks for ring-opening polymerization processes that can lead to the development of new polymeric materials (Mousa et al., 2023). These emerging applications further highlight the potential of cyclic acetals as multifunctional platform molecules within sustainable chemical and materials development.

4 Challenges in the production of cyclic acetals and technology translation

Cyclic acetals are increasingly recognized as versatile platform molecules with broad applications across fuels, chemicals, and materials, while also offering significant potential for reducing environmental impacts through circular carbon utilization. Their unique molecular structure, combining oxygenated functionality with physicochemical stability, enables their integration into multiple industrial sectors.

One of the most prominent applications of cyclic acetals is in the energy sector, where they serve as oxygenated fuel components and additives. Their relatively high oxygen content promotes cleaner combustion by suppressing soot formation and reducing particulate emissions. In addition, cyclic acetals exhibit excellent miscibility with conventional diesel fuels, favorable cold-flow properties, and adequate thermal stability, making them suitable for blending without requiring modifications to existing fuel infrastructure. These properties position cyclic acetals as promising candidates for low-carbon diesel and aviation fuels, particularly in sectors where electrification remains challenging.

Beyond fuel applications, cyclic acetals have long been utilized in the chemical industry as solvents, intermediates, and protecting groups in organic synthesis. Their tunable polarity, relatively low toxicity, and potential biodegradability make them attractive alternatives to conventional petroleum-derived solvents in applications such as coatings, extraction processes, and pharmaceutical formulations. Furthermore, their role as intermediates in fragrance, flavor, and fine chemical synthesis highlights their industrial versatility.

Recent advances have also expanded the use of cyclic acetals into polymer and materials science. As monomeric building blocks, cyclic acetals can undergo ring-opening polymerization to produce biodegradable and chemically recyclable polymers. These materials are of growing interest for sustainable packaging, coatings, and biomedical applications, where environmental compatibility and end-of-life recyclability are critical considerations.

From an environmental perspective, cyclic acetals offer a unique advantage due to their compatibility with multiple renewable and recycled carbon sources. They can be synthesized from lignocellulosic biomass-derived intermediates, CO₂ through catalytic hydrogenation, and depolymerized plastic waste, thereby enabling the integration of diverse carbon streams within a circular economy framework. This flexibility supports the development of low-carbon and potentially carbon-neutral production pathways.

However, the environmental performance of cyclic acetal production systems depends strongly on process design and operational conditions. Chemical recycling of plastics provides a valuable route for generating diol intermediates, but it is often associated with high energy demand and the use of organic solvents and catalysts, which has led to critical scrutiny (Scown et al., 2021; Gaffey et al., 2024). Life cycle assessment (LCA) has therefore become an essential tool for evaluating the environmental performance of chemical recycling technologies, including their potential to reduce greenhouse gas emissions and fossil resource consumption compared with alternative end-of-life management options (Scown et al., 2021; Gaffey et al., 2024). Because most chemical recycling processes are still at the pilot or demonstration stage, current LCAs primarily estimate their environmental performance under modeled or idealized conditions (Sanabria Garcia et al., 2025). Additional experimental data and industrial-scale studies are required to validate these assessments and better understand the real-world environmental impacts of such processes. In particular, infrastructure limitations and the need for stronger international collaboration remain major barriers to the large-scale deployment of recycling technologies (Babaei et al., 2024).

Although the fundamental chemistry of cyclic acetal synthesis is well established and offers clear opportunities for integrating renewable carbon sources, the industrial implementation of fully integrated bio-hybrid production systems remains limited. Significant knowledge gaps persist, particularly in the long-term operation of continuous or semicontinuous reactors using real biomass-derived feedstocks containing impurities, as most existing studies focus on purified model compounds. In addition, process intensification strategies such as reactive extraction and reactive distillation have not been fully optimized in line with recent advances in multiphase computational fluid dynamics (CFD) and process simulation tools. For example, in the synthesis of cyclic acetals such as 1,3-dioxolane, yields of up to 0.995 can be achieved in reactive distillation systems, with product purities reaching 99.9 wt% through subsequent pressure-swing distillation (Li et al., 2019), demonstrating the potential of integrated reaction–separation processes.

Market projections indicate a growing demand for cyclic acetals and related compounds. The global market for 1,3-dioxane was valued at approximately US$250 million in 2024 and is expected to reach nearly US$400 million by 2033, corresponding to a compound annual growth rate (CAGR) of about 5.5% (IndustryArc, 2026). Demand is driven primarily by applications in pharmaceutical synthesis, electronics manufacturing, and specialty polymer production. However, conventional production routes based on formaldehyde and fossil-derived feedstocks face increasing sustainability concerns. Consequently, greener production strategies—such as the use of bio-based diols, recyclable heterogeneous catalysts, and continuous-flow reactor technologies—are gaining importance for meeting future demand while minimizing environmental impacts.

To fully realize the potential of cyclic acetals across these applications, future research should focus on integrating biomass conversion, CO₂ utilization, and catalytic upgrading into unified process frameworks. Such approaches would enable more efficient use of renewable carbon resources while reducing greenhouse gas emissions. In addition, systematic life-cycle assessment methodologies and pilot-scale validation will be essential for accurately evaluating environmental performance and supporting industrial implementation. Parallel efforts should also address engine compatibility and infrastructure requirements to ensure the successful deployment of cyclic acetals as sustainable fuel components.

Overall, cyclic acetals represent a promising class of multifunctional molecules that bridge renewable feedstocks with advanced applications in fuels, chemicals, and materials. Their ability to integrate biomass, CO₂, and recycled carbon into a single value chain highlights their potential role in advancing circular carbon strategies and reducing the environmental footprint of modern chemical industries.

5 Conclusion

Cyclic acetals have emerged as promising bio-derived oxygenated compounds with significant potential for the development of carbon-neutral diesel and other low-carbon liquid fuels. Their stable cyclic structures, containing multiple oxygen atoms, promote cleaner combustion, reduce soot formation, and improve fuel lubricity. In addition, cyclic acetals exhibit excellent miscibility with conventional diesel, allowing blending levels of approximately 10%–15% without phase separation or storage instability. These characteristics make them attractive oxygenated fuel additives compatible with existing diesel infrastructure. Cyclic acetals can be produced through bio-hybrid pathways that integrate multiple renewable carbon sources, including biomass-derived diols, carbon dioxide captured and converted using renewable hydrogen, and C₁ intermediates derived from plastic waste. Recent advances in catalytic systems and process intensification strategies—such as reactive extraction and reactive distillation—have enabled more efficient synthesis and purification while overcoming earlier thermodynamic and phase-separation limitations. Promising production routes include furfural-based acetalization, synthesis without added catalyst, and transition-metal-catalyzed CO₂ utilization. Despite these advances, further research is required to support industrial deployment. Key priorities include pilot-scale demonstrations, evaluation of catalyst stability and impurity tolerance, and comprehensive techno-economic and life-cycle assessments. Addressing these challenges will be essential for translating laboratory-scale innovations into scalable, economically viable technologies capable of supporting the transition toward low-carbon transportation fuels and circular carbon utilization.

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Footnotes

Edited by: Balamurugan Srinivasan, SRM Institute of Science and Technology, India

Reviewed by: Yeddula Nikhileshwar Reddy, SRM Institute of Science and Technology (Deemed to be University) Research Kattankulathur, India

Seyed Emad Hashemnezhad, Aston University, United Kingdom