FDCA Production Research Articles

Base-free atmospheric O2-mediated oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic acid triggered by Mg-bearing MTW zeolite supported Au nanoparticles

Mg-bearing MTW silicalite zeolite, MgSi-ZSM-12, was straightforwardly synthesized by involving an unusual acidic pre-gelation system and engaged as the task-specific support for loading the Au nanoparticles (NPs). The resulting Au/MgSi-ZSM-12 catalyst showed stably excellent activity for the oxidation of HMF into FDCA in the presence of atmospheric dioxygen (O2) without externally adding any liquid base, affording a yield of 87 % and turnover number (TON) of 331 based on the surface Au sites. Superior basicity was evidenced by embedding Mg species into the all-silica zeolitic skeleton, which enables strong, weak, and near-zero affinity towards aldehyde, alcohol, and carboxyl groups, respectively, thus, allows rapid and high-uptake adsorption of HMF, but negligible adsorption of FDCA. This unique feature of the Mg-bearing all-silica zeolite support together with its synergy with the active sites of Au NPs is revealed to accelerate the production of FDCA under the base-free mild condition.

From sugars to FDCA: a techno-economic assessment using a design concept based on solvent selection and carbon dioxide emissions

Process simulations allow the evaluation of the emissions and selling price for the production of the key monomer FDCA based on different feedstocks and solvent systems, alongside considerations of safety and current process development.

Early-stage sustainability assessment of enzyme production in the framework of lignocellulosic biorefinery

The use and integration of enzymatic processes for the biotransformation of biomass within the biorefinery framework creates the need to confirm whether these novel production systems are in the route to environmental sustainability. In this study, the environmental profiles of the production of two oxidative enzymes, hydroxymethylfurfural oxidase (HMFO) from Methylovorus and unspecific peroxygenase (UPO) from Chaetomium globosum (CglUPO) for the enzymatic production of FDCA as precursor of bioplastics were analyzed. Laboratory-scale experiments allowed the identification of the consumption of energy, with over 80% share in every impact category for HMFO and chemicals and energy in CglUPO as primary hotspots of the systems. The results are transposed for HMFO when laboratory inventories were extrapolated to full scale processing, showing that impacts are attributed not only to energy demand but also to the use of chemicals required for the formulation of the culture medium. In terms of process units, the fermenter, where enzyme production takes place, corresponds to the stage that contributes the most to the environmental impacts, with a 57% share, followed by the downstream separation scheme (37%). Extrapolation of laboratory data to full-scale also represented a change in the relative difference of the impact per functional unit of 45% for CgIUPO. The endpoint damage categories showed a significant reduction in their full-scale impacts to about half the burden. The analysis of the outcomes of the uncertainty analysis showed that the resource depletion category had the least dispersion of data, while the level of uncertainty is more relevant for human health, as it takes into account the combined effect of a larger number of impact categories and the processes involved. This study shows that, although being bio-based catalysts, the production of enzymes involves several steps which may incur in environmental impact. Thus, it is recommended that enzymes are carefully included within the system boundaries for their evaluation, since they could be the major hotspot in the biorefinery value chain. De-fossilization of the plastic industry will be possible with thoroughly optimized bio-transformations, with carbon-based media from residual resources, minimized use of chemicals and the implementation of energy integration measures.

Homogeneous Base‐Free Oxidation of 5‐Hydroxymethyfufural to 2, 5‐Furandicarboxylic Acid over Au/Mg(OH)2 Catalysts

Abstract2, 5‐Furandicarboxylic acid (FDCA) obtained from selective 5‐hydroxymethyfufural (HMF) oxidation is an important biodegradable polyester monomer and its production strongly depends on homogeneous base additives. The production of FDCA over solid base catalyst is green and environment‐friendly. Herein, Au/Mg(OH)2 as the metal‐solid base catalyst, was prepared by a simple colloidal method and applied to the oxidation of HMF. Detailed characterizations (XRD, TEM, XPS, TGA, CO2‐TPD, etc.) were performed to uncover the structure‐activity relationship of the catalyst. 92.6 % yield of FDCA was achieved under the optimal reaction condition. Moreover, a plausible mechanism for HMF oxidation over the metal‐solid base catalyst was proposed by combining the surface properties of catalyst with the oxidation reaction results.

Process synthesis and analysis of green plastic monomer production from cellulose

As a renewable building block, 2,5-furandicarboxylic acid (FDCA) is a potentially viable alternative to petro-based terephthalic acid (TPA). For the commercialization of FDCA production, economically feasible process development is crucial. In this study, we design a new catalytic conversion process for the production of the green plastic monomer (FDCA) and evaluate the economic feasibility of the process. In the proposed process, the FDCA is produced from cellulose using a bio-based green solvent composed of gamma-valerolactone (GVL) and H2O via three-step conversion involving cellulose hydrolysis, glucose dehydration and 5-hydroxymethylfurfural (HMF) oxidation subsequently. For the efficient recovery of solvents and products, the separation subsystem is designed and integrated with the conversion process. Moreover, to improve energy efficiency, a heat exchanger network combined with a heat pump is designed. The new process increases the FDCA productivity by 17% and reduces the total capital investment by 52.6% after optimization. Furthermore, this proposed process leads to the minimum selling price (MSP) of $1366/t for FDCA, which suggests that the proposed process for bio-based FDCA production is a promising approach to substitute petro-based TPA ($1445/t). The sensitivity analysis identifies that the main cost drivers are a feedstock price, steam price and discount rate, which should be investigated for the further improvement of the economics of the process.

Screening and Evaluation of New Hydroxymethylfurfural Oxidases for Furandicarboxylic Acid Production.

The enzymatic production of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF) has gained interest in recent years, as FDCA is a renewable precursor of poly(ethylene-2,5-furandicarboxylate) (PEF). 5-Hydroxymethylfurfural oxidases (HMFOs) form a flavoenzyme family with genes annotated in a dozen bacterial species but only one enzyme purified and characterized to date (after heterologous expression of a Methylovorus sp. HMFO gene). This oxidase acts on both furfuryl alcohols and aldehydes and, therefore, is able to catalyze the conversion of HMF into FDCA through 2,5-diformylfuran (DFF) and 2,5-formylfurancarboxylic acid (FFCA), with only the need of oxygen as a cosubstrate. To enlarge the repertoire of HMFO enzymes available, genetic databases were screened for putative HMFO genes, followed by heterologous expression in Escherichia coli After unsuccessful trials with other bacterial HMFO genes, HMFOs from two Pseudomonas species were produced as active soluble enzymes, purified, and characterized. The Methylovorus sp. enzyme was also produced and purified in parallel for comparison. Enzyme stability against temperature, pH, and hydrogen peroxide, three key aspects for application, were evaluated (together with optimal conditions for activity), revealing differences between the three HMFOs. Also, the kinetic parameters for HMF, DFF, and FFCA oxidation were determined, the new HMFOs having higher efficiencies for the oxidation of FFCA, which constitutes the bottleneck in the enzymatic route for FDCA production. These results were used to set up the best conditions for FDCA production by each enzyme, attaining a compromise between optimal activity and half-life under different conditions of operation.IMPORTANCE HMFO is the only enzyme described to date that can catalyze by itself the three consecutive oxidation steps to produce FDCA from HMF. Unfortunately, only one HMFO enzyme is currently available for biotechnological application. This availability is enlarged here by the identification, heterologous production, purification, and characterization of two new HMFOs, one from Pseudomonas nitroreducens and one from an unidentified Pseudomonas species. Compared to the previously known Methylovorus HMFO, the new enzyme from P. nitroreducens exhibits better performance for FDCA production in wider pH and temperature ranges, with higher tolerance for the hydrogen peroxide formed, longer half-life during oxidation, and higher yield and total turnover numbers in long-term conversions under optimized conditions. All these features are relevant properties for the industrial production of FDCA. In summary, gene screening and heterologous expression can facilitate the selection and improvement of HMFO enzymes as biocatalysts for the enzymatic synthesis of renewable building blocks in the production of bioplastics.

Heterogeneous Catalytic Conversion of Sugars Into 2,5-Furandicarboxylic Acid.

Achieving the goal of living in a sustainable and greener society, will need the chemical industry to move away from petroleum-based refineries to bio-refineries. This aim can be achieved by using biomass as the feedstock to produce platform chemicals. A platform chemical, 2,5-furandicarboxylic acid (FDCA) has gained much attention in recent years because of its chemical attributes as it can be used to produce green polymers such polyethylene 2,5-furandicarboxylate (PEF) that is an alternative to polyethylene terephthalate (PET) produced from fossil fuel. Typically, 5-(hydroxymethyl)furfural (HMF), an intermediate product of the acid dehydration of sugars, can be used as a precursor for the production of FDCA, and this transformation reaction has been extensively studied using both homogeneous and heterogeneous catalysts in different reaction media such as basic, neutral, and acidic media. In addition to the use of catalysts, conversion of HMF to FDCA occurs in the presence of oxidants such as air, O2, H2O2, and t-BuOOH. Among them, O2 has been the preferred oxidant due to its low cost and availability. However, due to the low stability of HMF and high processing cost to convert HMF to FDCA, researchers are studying the direct conversion of carbohydrates and biomass using both a single- and multi-phase approach for FDCA production. As there are issues arising from FDCA purification, much attention is now being paid to produce FDCA derivatives such as 2, 5-furandicarboxylic acid dimethyl ester (FDCDM) to circumvent these problems. Despite these technical barriers, what is pivotal to achieve in a cost-effective manner high yields of FDCA and derivatives, is the design of highly efficient, stable, and selective multi-functional catalysts. In this review, we summarize in detail the advances in the reaction chemistry, catalysts, and operating conditions for FDCA production from sugars and carbohydrates.

Toward an Intensified Process of Biomass-Derived Monomers: The Influence of 5-(Hydroxymethyl)furfural Byproducts on the Gold-Catalyzed Synthesis of 2,5-Furandicarboxylic Acid

The utilization of biomass and development of intensified processes are essential to establish a sustainable production of chemicals in the future. Herein, we report on a strategy that allows one to directly convert the biomass-derived platform molecule 5-(hydroxymethyl)furfural (HMF) over Au/ZrO2 in aqueous medium to 2,5-furandicarboxylic acid (FDCA), a renewable building block for biobased polymers like polyethylene furanoate. The focus lies on identifying the influence of 5-(hydroxymethyl)furfural synthesis byproducts, like unconverted sugars, levulinic acid, and formic acid as well as the remaining inorganics, on the synthesis of 2,5-furandicarboxylic acid to save the intermediate step of HMF purification. These components were added to the reaction mixture individually and in combination to study their effect. Although most of these substances lowered the FDCA yield, the reaction conditions could be optimized to produce FDCA quantitatively. Only the addition of levulinic acid led to a severe deterioration of the production of FDCA, which was attributed to poisoning of the catalyst. In a realistic technical scenario, the direct oxidation of impure HMF from unconcentrated sugar syrup in high FDCA yield (74%) was demonstrated. Catalyst stability was investigated in the presence of sugars. On the basis of these studies, highly needed recommendations for the HMF synthesis were developed to establish a more sustainable, technically feasible, and intensified process for direct FDCA production from sugars at industrial scales.

2,5-Furandicarboxylic acid production via catalytic oxidation of 5-hydroxymethylfurfural: Catalysts, processes and reaction mechanism

Catalytic oxidation is a promising manner to produce 2,5-furandicarboxylic acid (FDCA) from 5-Hydroxymethylfurfural (HMF). This review summarizes the progress in the thermocatalysis, electrocatalysis, and photocatalysis for FDCA production, including catalyst screening, synthesis processes, and reaction mechanism. Biomass conversion to value-added chemicals has received tremendous attention for solving global warming issues and fossil fuel depletion. 5-Hydroxymethylfurfural (HMF) is a key bio-based platform molecule to produce many useful organic chemicals by oxidation, hydrogenation, polymerization, and ring-opening reactions. Among all derivatives, the oxidation product 2,5-furandicarboxylic acid (FDCA) is a promising alternative to petroleum-based terephthalic acid for the synthesis of biodegradable plastics. This review analytically discusses the recent progress in the thermocatalytic, electrocatalytic, and photocatalytic oxidation of HMF into FDCA, including catalyst screening, synthesis processes, and reaction mechanism. Rapid fundamental advances may be possible in non-precious metal and metal-free catalysts that are highly efficient under the base-free conditions, and external field-assisted processes like electrochemical or photoelectrochemical cells.

Improved biosynthesis of 2,5-Furandicarboxylic acid through coupling of heterologous pathways in Escherichia coli and native pathways in Pseudomonas putida

2,5-Furandicarboxylic acid (FDCA) is one of the most important platform chemicals especially as a promising alternative to terephthalic acid. In this study, a new and prospective tandem whole-cell cascade composed of recombinant Escherichia coli and wild Pseudomonas putida KT2440 was constructed for FDCA production from 5-hydroxymethylfurfural (HMF) based on their respective alcohol and aldehyde oxidation activities. In particular, P. putida proved superior biocatalytic ability to furanic aldehydes. In the stepwise reaction, HMF (up to 100 mM) was fully oxidized to FDCA, with bioconversion rate much faster than other reported biocatalysts either as single enzyme or as combinations. Besides, this study is the first time to construct a whole-cell cascade system achieving FDCA production with quantitative yield.

Liquid-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Co/Mn/Br Catalyst

2,5-Furandicarboxylic acid (FDCA), mainly synthesized by the selective oxidation of 5-hydroxymethylfurfural (HMF), is a biobased monomer for high-performance polymers. In this work, we have a comprehensive investigation on the rapid and highly selective oxidation process of HMF to FDCA in acetic acid (HAc) with Co/Mn/Br catalyst and air as the oxidant. It was found that both aldehyde and hydroxymethyl functional groups of HMF could be first oxidized in the sequential oxidation of HMF to FDCA, but 2,5-diformylfuran (DFF) was the main oxidation intermediate. Apart from the side reaction of HMF overoxidation to COx (CO and CO2) and HMF condensation to polymers, a small part of HMF will be further oxidized to maleic acid (MA) and fumaric acid (FA) via the ring-opening reactions under severe conditions because of the instability of furan ring. To reduce the side reactions and maximize the FDCA yield, the effects of temperature, pressure, substrate solvent ratio, catalyst composition and concentration, and water concentration on the main reactions and side reactions of the HMF oxidation were systematically evaluated. Under the optimum conditions, the selectivity of FDCA reached 92% with the total conversion of HMF in less than 20 min at a high mass ratio of substrate and solvent (1/9), and the purity of FDCA exceeded 99.8%. The experimental results provide a great reference and inspiration for the optimization of the HMF oxidation process and the large-scale production of FDCA.

Bioconversion of 5-Hydroxymethylfurfural (HMF) to 2,5-Furandicarboxylic Acid (FDCA) by a Native Obligate Aerobic Bacterium, Acinetobacter calcoaceticus NL14.

2,5-Furandicarboxylic acid (FDCA), one of the top biomass-based platform chemical, is highly promising for resins and polymers, and it can be prepared from the bio-oxidation of hydroxymethyl furfural (HMF), which can be obtained mainly from lignocellulosic glucose that has a high production potential from not edible biomass.A native strain, Acinetobacter calcoaceticus NL14, that could convert HMF into FDCA is used for combining degradation and fermentation by consolidated bioprocessing (CBP). In this study, it was observed that the initial HMF concentration and pH neutralizer played important roles in the bioconversion of HMF, 5g/L of HMF could be converted by 100% within 48h with 0.5g/L sodium carbonate (Na2CO3) with the production of 0.31g/L FDCA. Extra glucose and hydrogen peroxide (H2O2) addition could further promote the production of FDCA to 0.54g/L with 100% HMF conversion and a higher conversion rate. This report could provide a potential native bacterium for furan chemicals bioconversion and bioelimination, especially for FDCA bioproduction.

Engineering Stable Pseudomonas putida S12 by CRISPR for 2,5-Furandicarboxylic Acid (FDCA) Production

FDCA (2,5-furandicarboxylic acid) can be enzymatically converted from HMF (5-hydroxymethylfurfural). Pseudomonas putida S12 is promising for FDCA production, but generating stable P.putida S12 is difficult due to its polyploidy and lack of genome engineering tools. Here we showed that coupling CRISPR and λ-Red recombineering enabled one-step gene integration with high efficiency and frequency, and simultaneously replaced endogenous genes in all chromosomes. Using this approach, we generated two stable P.putida S12 strains expressing HMF/furfural oxidoreductase (HMFH) and HMF oxidase (HMFO), both being able to convert 50 mM HMF to ≈42-43 mM FDCA in 24 h. Cosupplementation of MnO2 and CaCO3 to the medium drastically improved the cell tolerance to HMF and enhanced FDCA production. Cointegrating HMFH and HMFT1 (HMF transporter) genes further improved FDCA production, enabling the cells to convert 250 mM HMF to 196 mM (30.6 g/L) FDCA in 24 h. This study implicates the potentials of CRISPR for generating stable P.putida S12 strains for FDCA production.

Enzymatic conversion reactions of 5-hydroxymethylfurfural (HMF) to bio-based 2,5-diformylfuran (DFF) and 2,5-furandicarboxylic acid (FDCA) with air: mechanisms, pathways and synthesis selectivity

Background2,5-Furandicarboxylic acid (FDCA) is one of the top biomass-derived value-added chemicals. It can be produced from fructose and other C6 sugars via formation of 5-hydroxymethilfurfural (HMF) intermediate. Most of the chemical methods for FDCA production require harsh conditions, thus as an environmentally friendly alternative, an enzymatic conversion process can be applied.ResultsCommercially available horseradish peroxidase (HRP) and lignin peroxidase (LPO), alcohol (AO) and galactose oxidase (GO), catalase (CAT) and laccase (LAC) were tested against HMF, 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furoic acid (HMFA) and 5-formyl-2-furoic acid (FFA). Enzyme concentrations were determined based on the number of available active sites and reactions performed at atmospheric oxygen pressure. AO, GO, HRP and LPO were active against HMF, where LPO and HRP produced 0.6 and 0.7% of HMFA, and GO and AO produced 25.5 and 5.1% DFF, respectively. Most of the enzymes had only mild (3.2% yield or less) or no activity against DFF, HMFA and FFA, with only AO having a slightly higher activity against FFA with an FDCA yield of 11.6%. An effect of substrate concentration was measured only for AO, where 20 mM HMF resulted in 19.5% DFF and 5 mM HMF in 39.9% DFF, with a Km value of 14 mM. Some multi-enzyme reactions were also tested and the combination of AO and CAT proved most effective in converting over 97% HMF to DFF in 72 h.ConclusionsOur study aimed at understanding the mechanism of conversion of bio-based HMF to FDCA by different selected enzymes. By understanding the reaction pathway, as well as substrate specificity and the effect of substrate concentration, we would be able to better optimize this process and obtain the best product yields in the future.

Green conversion of 5-hydroxymethylfurfural to furan-2,5-dicarboxylic acid by heterogeneous expression of 5-hydroxymethylfurfural oxidase in Pseudomonas putida S12.

SummaryTransforming petrochemical processes into bioprocesses has become an important goal of sustainable development. The chemical synthesis of 2,5‐furandicarboxylic acid (FDCA) from 5‐hydroxymethylfurfural (HMF) is expensive and environmentally unfavourable. The study aims to investigate a whole‐cell biocatalyst for efficient biotransformation of HMF to FDCA. For the first time, a genetically engineered Pseudomonas putida S12 strain expressing 5‐hydroxymethylfurfural oxidase (HMFO) was developed for the biocatalytic conversion of HMF to FDCA. This whole‐cell biocatalyst produced 35.7 mM FDCA from 50 mM HMF in 24 h without notable inhibition. However, when the initial HMF concentration was elevated to 100 mM, remarkable inhibition on FDCA production was observed, resulting in a reduction of FDCA yield to 42%. We solve this substrate inhibition difficulty by increasing the inoculum density. Subsequently, we used a fed‐batch strategy by maintaining low HMF concentration in the culture to maximize the final FDCA titre. Using this approach, 545 mM of FDCA was accumulatively produced after 72 hs, which is the highest production rate per unit mass of cells to the best of our knowledge.

Biotransformation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid by a Syntrophic Consortium of Engineered Synechococcus elongatus and Pseudomonas putida.

2,5-furandicarboxylic acid (FDCA) is one of the top platform chemicals that can be produced from biomass feedstock. To make the cost of industrial FDCA production compatible with plastics made from fossils, the price of substrates and process complexity should be reduced. The aim of this research is to create a CO2 -driven syntrophic consortium for the catalytic conversion of renewable biomass-derived 5-hydroxymethylfurfural (HMF) to FDCA. Sucrose produced from carbon fixation by the engineered Synechococcus elongatus serves as the sole carbon source for the engineered Pseudomonas putida to catalyze the reaction of HMF to FDCA. The yield of FDCA by the consortium reaches around 70% while the conversion of HMF is close to 100%. With further surface engineering to clump the two strains, the FDCA yield is elevated to almost 100% via the specific association between an Src homology 3 (SH3) domain and its ligand. The syntrophic consortium successfully demonstrates its green and cost-effective characteristics for the conversion of CO2 and biomass into platform chemicals.

Interfacial Engineering of MoO2‐FeP Heterojunction for Highly Efficient Hydrogen Evolution Coupled with Biomass Electrooxidation

Simultaneous highly efficient production of hydrogen and conversion of biomass into value-added products is meaningful but challenging. Herein, a porous nanospindle composed of carbon-encapsulated MoO2 -FeP heterojunction (MoO2 -FeP@C) is proposed as a robust bifunctional electrocatalyst for hydrogen evolution reaction (HER) and biomass electrooxidation reaction (BEOR). X-ray photoelectron spectroscopy analysis and theoretical calculations confirm the electron transfer from MoO2 to FeP at the interfaces, where electron accumulation on FeP favors the optimization of H2 O and H* absorption energies for HER, whereas hole accumulation on MoO2 is responsible for improving the BEOR activity. Thanks to its interfacial electronic structure, MoO2 -FeP@C exhibits excellent HER activity with an overpotential of 103 mV at 10 mA cm-2 and a Tafel slope of 48 mV dec-1 . Meanwhile, when 5-hydroxymethylfurfural is chosen as the biomass for BEOR, the conversion is almost 100%, and 2,5-furandicarboxylic acid (FDCA) is obtained with the selectivity of 98.6%. The electrolyzer employing MoO2 -FeP@C for cathodic H2 and anodic FDCA production requires only a low voltage of 1.486 V at 10 mA cm-2 and can be powered by a solar cell (output voltage: 1.45 V). Additionally, other BEORs coupled with HER catalyzed by MoO2 -FeP@C also have excellent catalytic performance, implying their good versatility.

Influence of Support Properties and Particle Size on the Gold‐Catalyzed Base‐Free Aerobic Oxidation of 5‐Hydroxymethylfurfural

AbstractSelective oxidation of biomass platform molecule 5‐hydroxymethylfurfural (HMF) into valuable bio‐monomer 2,5‐furandicarboxylic acid (FDCA) is an important biorefinery process. In our work, the structure‐activity relationship of Au nanoparticles supported on the composite of hydrotalcite and activated carbon (HT‐AC) toward selective oxidation of HMF to FDCA without a base was studied with a focus on the influence of support property and Au particles size. The initial conversion rate of substrates and the intrinsic selectivity of products were investigated. Various physicochemical techniques including XRD, Raman, XPS, CO2‐TPD and TEM were used to characterize the HT‐AC supports and the Au/HT‐AC catalysts. Synergistic support effect was observed when HT and AC were combined to show the features of both basic sites and oxygen‐containing functional groups attached to the catalyst surface, which eventually promoted the adsorption of HMF and the formation of FDCA. The Au NPs were found in metallic state and highly dispersed with a mean size of 2.5 nm, which was favored to efficiently convert HMF to FDCA. It was disclosed that both the support effect and Au size effect could promote FDCA production through accelerating the conversion rate of HMF and HMFCA, and the rate‐determining step was determined in HMFCA transformation.

Recent Developments in Metal-Based Catalysts for the Catalytic Aerobic Oxidation of 5-Hydroxymethyl-Furfural to 2,5-Furandicarboxylic Acid

Biomass can be used as an alternative feedstock for the production of fuels and valuable chemicals, which can alleviate the current global dependence on fossil resources. One of the biomass-derived molecules, 2,5-furandicarboxylic acid (FDCA), has attracted great interest due to its broad applications in various fields. In particular, it is considered a potential substitute of petrochemical-derived terephthalic acid (PTA), and can be used for the preparation of valuable bio-based polyesters such as polyethylene furanoate (PEF). Therefore, significant attempts have been made for efficient production of FDCA and the catalytic chemical approach for FDCA production, typically from a biomass-derived platform molecule, 5-hydroxymethylfurfural (HMF), over metal catalysts is the focus of great research attention. In this review, we provide a systematic critical overview of recent progress in the use of different metal-based catalysts for the catalytic aerobic oxidation of HMF to FDCA. Catalytic performance and reaction mechanisms are described and discussed to understand the details of this reaction. Special emphasis is also placed on the base-free system, which is a more green process considering the environmental aspect. Finally, conclusions are given and perspectives related to further development of the catalysts are also provided, for the potential production of FDCA on a large scale in an economical and environmentally friendly manner.

Immobilization of the engineered Raoultella ornithinolytica BF60 for biocatalytic synthesis of 2, 5-furandicarboxylic acid.

As a bio-based platform chemical, 2, 5-furandicarboxylic acid (FDCA) is a promising substitute of terephthalic acid to synthesize poly (ethylene furanoate) used for bio-substitute of polyethylene terephthalate (PET). In previous work, we engineered a Raoultella ornithinolytica BF60 strain and achieved the effective biocatalytic synthesis of FDCA from 5-hydroxymethylfurfural (HMF). Herein, to improve the reusability of the engineered R. ornithinolytica BF60 cells, we used two materials PVA1799-boric acid and sodium alginate-Ca2+ to immobilize the cells. The sodium alginate-Ca2+ was more suitable for FDCA production, and 22 mmol/L FDCA was obtained with Ca(H2PO4)2 as the cross-linker. In addition, the immobilization conditions were optimized and FDCA production was further increased to 74.8 mmol/L. Here the developed immobilization strategy for R. ornithinolytica BF60 cells may be helpful for the economical production of FDCA in the future.